Next Article in Journal / Special Issue
Development and Validation of an HPLC-PDA Method for Biologically Active Quinonemethide Triterpenoids Isolated from Maytenus chiapensis
Previous Article in Journal
Kampo Therapies and the Use of Herbal Medicines in the Dentistry in Japan
Previous Article in Special Issue
New Approaches to Detect Biosynthetic Gene Clusters in the Environment
 
 
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:
Background:
Review

Mitragyna speciosa: Clinical, Toxicological Aspects and Analysis in Biological and Non-Biological Samples

1
Centro de Investigação em Ciências da Saúde, Faculdade de Ciências da Saúde da Universidade da Beira Interior (CICS-UBI), 6200-506 Covilhã, Portugal
2
Serviço de Química e Toxicologia Forenses, Instituto de Medicina Legal e Ciências Forenses—Delegação do Sul, 1169-201 Lisboa, Portugal
3
Universidad de Buenos Aires, Facultad de Farmacia y Bioquímica, Cátedra de Toxicología y Química Legal, Laboratorio de Asesoramiento Toxicológico Analítico (CENATOXA). Junín 956 7mo piso. Ciudad Autónoma de Buenos Aires (CABA), Buenos Aires C1113AAD, Argentina
*
Author to whom correspondence should be addressed.
Medicines 2019, 6(1), 35; https://doi.org/10.3390/medicines6010035
Submission received: 31 January 2019 / Revised: 24 February 2019 / Accepted: 27 February 2019 / Published: 4 March 2019
(This article belongs to the Special Issue Biological Potential and Medical Use of Secondary Metabolites)

Abstract

:
The abuse of psychotropic substances is a well-known phenomenon, and many of them are usually associated with ancestral traditions and home remedies. This is the case of Mitragyna speciosa (kratom), a tropical tree used to improve work performance and to withstand great heat. According to several published studies, the main reasons for kratom consumption involve improving sexual performance and endurance, but also social and recreational uses for the feeling of happiness and euphoria; it is also used for medical purposes as a pain reliever, and in the treatment of diarrhea, fever, diabetes, and hypertension. However, this plant has gained more popularity amongst young people over the last years. Since it is available on the internet for purchase, its use is now widely as a drug of abuse, namely as a new psychoactive substance, being a cheaper alternative to opioids that does not require medical prescription in most countries. According to internet surveys by the European Monitoring Centre for Drugs and Drug Addiction in 2008 and 2011, kratom was one of the most widely supplied new psychoactive substances. The composition of kratom is complex; in fact, more than 40 different alkaloids have been identified in Mitragyna speciosa so far, the major constituent being mitragynine, which is exclusive to this plant. Besides mitragynine, alkaloids such as corynantheidine and 7-hydroxamitragynine also present pharmacological effects, a feature that may be attributed to the remaining constituents as well. The main goal of this review is not only to understand the origin, chemistry, consumption, and analytical methodologies for analysis and mechanism of action, but also the use of secondary metabolites of kratom as therapeutic drugs and the assessment of potential risks associated with its consumption, in order to aid health professionals, toxicologists, and police authorities in cases where this plant is present.

Graphical Abstract

1. Introduction

Several botanical products can be used for recreational purposes, and the effects include changes in mood, perception, behavior, and even in physiological parameters [1]. Although consumers usually have the wrong idea that they are completely safe and consumption does not involve any social or health risks, it is important to note that evidence of toxicity of such products has already been reported [2,3]. Commonly, the consumption of certain plants is associated with specific locations where people use them for what it seems to be the “natural effects” of the plant compounds. Regardless, a recurrent problem is the purification of the natural compounds in order to achieve stronger effects. This justifies the importance of early studies on addiction potential and classification of newly emerging psychoactive compounds.
Globally, the figures concerning consumption of new psychoactive substances (NPS) of natural origin are not clear. According to the European Monitoring Centre for Drugs and Drug Addiction (EMCDDA), the proportion of seizures in the category of other NPS (including those of natural origin) was of 12% in 2013 [4].
Mitragyna speciosa, belonging to the Rubiaceae family, found in both Asia and Africa, is a good example of such a NPS of natural origin. It is known as kratom, kakuam, kraton, ketum, ithang, or thom in Thailand and biak-biak in Malaysia or krypton when combined with O-demethyltramadol [5,6,7,8,9].
In Thailand, kratom’s tree can mostly be found in the south of the country, and it is easily obtained from teashops, being used as a substitute for alcohol and opium.
Two types of kratom can be identified based on the color of the leaf vein, which can be either green or red. Locals usually prefer the red vein, characterized for its bitterness and longer effects [5]. Fresh leaves, at a dosage of normally 10 to 30 fresh leaves per day, are mostly used chewed swallowed as a powder, but they can also be dried for smoking or used to make tea [10].
In 1943, kratom was put under regulatory control by the Kratom Act in Thailand which was believed to be an economic move rather than a decision based on the concern for public health. During that time, taxes were involved with the opium trade and, because it was so expensive, people started to use kratom as a substitute, and this had consequences for the Thai government’s income. Later in 1979, kratom was classified in Category V of a narcotics classification by the Thai government in the Narcotics Act, the same as cannabis, opium, and hallucinogenic mushrooms (the least restrictive and punitive level) [10,11,12].
Kratom was originally used mainly for its medicinal value in treating mild medical problems, namely fever, diarrhea, diabetes, pain, as a wound poultice, and to reduce the strain and fatigue of physical labor; however, it became also known and used to suppress opiate withdrawal symptoms given its affordability and availability [11,12,13,14]. In recent years, young consumers started to use kratom tea as a base for a cocktail known as “4 × 100”, consisting of kratom tea, cough syrup, Coca-Cola, and ice cubes. This eventually became a concern since these consumers were using additives such as benzodiazepines to enhance the effects [10].
Vicknasingam et al. [13] studied the major reasons for kratom consumption and also the socio-demographic characteristics of its users. The study was conducted on 136 active users, of which 76.5% had a previous history of drug use. The presented reasons for kratom’s consumption were reduction in addiction to other drugs, improvement of opiate addiction withdrawal symptoms, and its affordability relatively to heroin. A lot of short and long-term users claimed to have felt an increase in their capability for hard work, activeness, and heightened sexual desire [13,15]. An anonymous cross-sectional online survey was conducted in the USA in 2006, where 8049 users were studied through available social media and online resources from the American Kratom Association [16]. This study concluded that kratom is primarily used by middle-aged (31–50 years) and middle-income ($35,000 and above) individuals, the main purposes being to treat pain (68%) and emotional or mental conditions (66%).
Mitragyna speciosa can still be easily found on the internet for purchase, being a rather cheap alternative for opioids that does not require medical prescription [17,18]. In Europe, products labeled as Mitragyna speciosa (‘kratom acetate’ or ‘mitragynine acetate’) have been available since the early 2000s [19]. In recent years, products containing kratom are sold as ‘incense’ for their psychoactive effects, but concentrations of these active components vary depending on the variety of kratom used, circumstances, and harvesting time. The United Nations Office on Drugs and Crime questionnaire on NPS also revealed that kratom was one of the top three plant-based substances, along with khat and Salvia divinorum. Because kratom was not often under surveillance in national drug abuse surveys, information on its prevalence has been limited. Kratom and its active alkaloids are not listed under the 1961 and 1971 Conventions, but several countries have made policies for its control, also including mitragynine and 7-hydroxymitragynine (7-HMG) [20]. According to the internet surveys by EMCDDA in 2008 and 2011, kratom was one of the most widely supplied NPS [21]. Currently, Mitragyna speciosa is not illegal in most European countries or in the USA. In many EU countries, such as Denmark, Latvia, Lithuania, Poland, Romania, and Sweden, Mitragyna speciosa and/or mitragynine and 7-HMG are controlled drugs due to their high misuse potential. In other countries they are under control by the narcotic laws, including Australia, Malaysia, Myanmar, and Thailand (which has legalized the use of kratom and cannabis plants for medicinal use on December 2018). In New Zealand, Mitragyna speciosa and mitragynine are controlled under the Medicines Amendment Regulations [21].
Different formulations are available, including raw leaves, capsules, tablets, powder, and concentrated extracts. So far, more than 40 alkaloids have been identified in Mitragyna speciosa, the major constituent being mitragynine, which is exclusive to this plant [5,22,23,24]. Their relative amount varies monthly and according to the geographic origin of the plant [25,26]. Other constituents are paynantheine (PAY)–9%, speciogynine (SG)–7%, 7-HMG–2%, and speciociliatine (SC)–1% [25,27]. 7-HMG is a 7-hydroxyindolenine derivative of mitragynine (Figure 1) [28].
These are indole alkaloids of the corynanthe-type with a monoterpene (iridoid) moiety. Other compounds include raubasine and a few yohimbe alkaloids [26,29]. In general, kratom contains at least one alkaloid that can block calcium channels and reduces N-methyl-D-aspartate (NMDA)-induced currents [30]. Other compounds, such as flavonoids, terpenoid saponins, polyphenols, and various glycosides are also present [25]. Veeramohan et al. [31] performed a metabolomics study using the mature leaves of the green variety of Mitragyna speciosa in order to obtain a more complete profile of kratom’s secondary metabolites.
The alkaloids known to have a pharmacological effect are mitragynine, corynantheidine, and 7-HMG, but the remaining constituents might also provide this effect [25].

2. Research Methodology

The search for this review was conducted online on Pubmed, Google Scholar, and European Monitoring Centre for Drugs and Drug Addiction websites. Research papers, bibliographic reviews and case reports were included, the research done in Portuguese and in English. The search strings used were: “Mitragyna speciosa” and “consumption” and “toxicology” and “pharmacokinetics” and “case reports” and “pharmacological effects”. The search was performed between December of 2018 and January of 2019. No publishing date restrictions were used. In order to assess their relevance, all papers fulfilling the search strings were screened independently by four of the authors. Only those that were selected by at least two authors were subjected to review and were included in the manuscript.

3. Toxicokinetics and Pharmacodynamics

Kratom’s pharmacokinetics in humans has not been well studied so far, and several factors such as metabolic half-life, protein binding properties, elimination rates, and metabolism are not yet known [26,32]. Studies in rats showed that the absorption of Mitragyna speciosa after oral administration presents a much smaller AUC compared to intravenous administration, despite the oral dose being higher. The low oral bioavailability may be related to poor aqueous solubility of Mitragyna speciosa, which results in a smaller fraction for absorption [33]. Mitragynine is also believed to be a basic drug, becoming highly solubilized and ionized in the stomach, which reduces its absorption and therefore bioavailability [34]. Furthermore, using Caco-2 cells to predict intestinal absorption, mitragynine showed better permeability than 7-HMG [35].
In terms of elimination/half-life, mitragynine demonstrated biphasic elimination from plasma, suggesting distribution into inner tissue compartments. However, given the short half-life (mean half-life of 2.9 ± 2.1 h after injection), it is rapidly eliminated. Still, there are some contradictory reports on this matter, stating a higher half-life for mitragynine [35,36]. A case report of a young kratom user showed that approximately 10–14 days after consumption has stopped kratom metabolites could still be detected in urine. Saturation of enzymatic pathways or high plasma protein binding could account for this situation, but none was proven to be right [35].
Concerning distribution, according to a case report, after conducting high-throughput molecular screening of mitragynine activity at central nervous system receptors, it was shown that it is a mu- and kappa-opioid agonist [37]. Mitragynine and 7-HMG are transported by passive diffusion, presenting reflux ratios of 1 and 1.2 respectively [35]. Also, a complementary pharmacokinetics study was performed, in which the effects of a single intravenous dose of mitragynine (5 mg/kg, mitragynine hydrochloride) were compared to those of either a single oral dose (20 mg/kg, mitragynine hydrochloride), lyophilized kratom tea, or the organic fraction of the lyophilized kratom tea at an equivalent mitragynine dose of 20 mg/kg in rats. After intravenous administration, mitragynine exhibited a decrease in the concentration–time profile, indicating its fast distribution from the systemic circulation or central compartment to peripheral compartments [38]. Another study was performed by Yusof et al. [39], who have evaluated for the first time the rate and the extent of mitragynine and 7-HMG transport across the blood–brain barrier.
Kratom metabolism is mainly hepatic and there is some evidence that it can affect the metabolism and efficiency of other drugs via induction of drug-metabolizing enzymes such as CYP450s and UDP-glucuronosyl transferase (UGT) [40].
An assay evaluated the effect of Mitragyna speciosa alkaloid extract on CYP, and has found that kratom was responsible for CYP3A4, CYP2D6, and CYP2C9 inhibition [41], but unfortunately there are no studies that can help finding which particular kratom alkaloid is responsible for this inhibition. Kamble et al. [42] verified that CYP3A4 was mainly responsible for the metabolism, with minor contributions of CYP2D6 and CYP2C9. The same authors have described that mitragynine was extensively metabolized in liver microsomes primarily to O-demethylated and mono-oxidated metabolites. Due to these cytochrome-related genetic variations in humans, these enzymes will partly account for inter-individual differences in drug metabolism and toxicity [43].
Additionally, Philipp et al. [44] observed that isomeric compounds found in the kratom users’ urine were SG and its metabolites, which can be also used as markers for Mitragyna speciosa presence.
Renal excretion of mitragynine is not considered significant, and mitragynine is not expected to be prone to substantial postmortem redistribution [36,45].
There are several studies that evaluate the effects of Mitragyna speciosa on human recombinant CYP450 enzyme activities [41]. This leads to implications, especially when mitragynine is co-administered together with herbal or modern drugs which follow the same metabolic pathway, contributing to herb–drug interactions [46].
According to Hanapi et al. [46], mitragynine might inhibit cytochrome P450 enzyme activities, specifically CYP2D6, and the strongest inhibitory effect was observed on CYP2D6, with a half-maximal inhibitory concentration (IC50) value of 0.45 ± 0.33 mM, followed by CYP2C9 and CYP3A4 with IC50 values of 9.70 ± 4.80 and 41.32 ± 6.74 μM respectively. Similar results are presented by Kong et al. [41], with apparent IC50 values of 0.78 µg/mL and 0.636 µg/mL for CYP3A4 and CYP2D6, respectively. Cinosi et al. [47] corroborate the possibility of a drug interaction if mitragynine and 7-hydroxymitragynine are administered together with drugs that are P-glycoprotein substrates. The authors mention, however, that Mitragyna speciosa is unlikely to have any significant clinical effects on CYP3A4 activity, but on the other hand might inhibit CYP2D6. Moreover, Lim et al. [48] performed an in vitro evaluation of cytochrome P450 induction and of the inhibition potential of mitragynine, and found that this alkaloid induces mRNA and protein expression of CYP1A2 consistent with the increased CYP1A2 enzymatic activity. Nevertheless, this alkaloid appears as a weak CYP3A4 inducer at the transcriptional level and a weak CYP3A4 enzyme inhibitor, leading to the same conclusion of Cinosi et al. [47], that it is unlikely to cause any significant clinical effects on CYP3A4 activity.
In this sense, the overall opinion is that the concomitantly administered drugs that may modulate these CYP isoenzymes activities will lead to clinically significant drug–drug interactions. Such interactions may result in serious adverse drug reactions, especially regarding drugs with short therapeutic windows such as carbamazepine, theophylline, digoxin warfarin, and phenytoin [49].
According to a review made by Ulbricht et al. [50], Mitragyna speciosa is likely to be unsafe if used by patients with neurologic disorders or that are taking either neurologic agents, such as alcohol, sedatives, benzodiazepines, opioids, or opium-containing products, or stimulant substances, such as caffeine, caffeine-containing products, cocaine, yohimbine, or related compounds. Also, the co-administration with monoamine oxidase inhibitors (MAOIs) is not advised. Recently, a case report of a fatality in a 27-year-old man was described by Hughes [51], who found a toxic blood concentration of quetiapine in conjunction with mitragynine.
Concerning the interactions of Mitragyna speciosa herb and food, there are some reports on this matter. According to a previous systematic review [50], the concomitant use of MAOIs, ayahuasca (Banisteriopsis caapi), syrian rue (Peganum harmala), or passion flower (Passiflora incarnata) with Mitragyna speciosa may potentially cause serious reactions. Moreover, yohimbe (Pausinystalia yohimbe) combined with Mitragyna speciosa may cause overstimulation and increased blood pressure, as it also occurs with the concomitant use of caffeine [50].
There have been reports on the concomitant use of opioids with Mitragyna speciosa causing oversedation or potential respiratory depression [52,53]. Mitragyna speciosa has reportedly been used for centuries for its psychoactive properties, opium-like effects, and ability to treat opioid addiction and opioid withdrawal. Reports starting in the mid-1800s give an account of Mitragyna speciosa being used as an opium substitute [54].

4. Clinical Effects/Pharmacology

Kratom has been found to have addiction potential in animal models when mitragynine and 7-HMG were given orally for five days [55].

4.1. Analgesic Properties

Mitragynine has a high affinity to mu-opioid receptors [56,57,58]. These receptors mediate analgesia, respiratory depression, and euphoria. It has been shown that its antinociceptive activity is mostly mediated by the supraspinal mu- and delta-opioid receptor subtypes, therefore making it the alkaloid responsible for the analgesic activity of kratom [57,58,59]. This also corroborates the claim that kratom can be used as an opium substitute or to diminish opium addiction, reducing the pain from withdrawal symptoms. Its affinity for kappa-receptors is considerably lower [58]. However, Stolt et al. [60] concluded that it exhibits analgesic effects via kappa-receptors and showed as well depressant effects on locomotor activity via presynaptic dopamine effects. The reinforcing effects of 7-HMG are mediated in part by mu- and delta-opiate receptors [61].
It is possible to use kratom as an anesthetic, and Vermaire et al. [62] reported the first case of this application by a patient using kratom for chronic pain.
Stimulation of post-synaptic alpha-2 adrenergic receptors, and/or blockage stimulation of 5-HT2 receptors by Mitragyna speciosa is also suggested. It is theorized that the effectiveness of the methanolic extract on alleviating positive and negative symptoms of psychosis may be due to inhibition of D2 and 5-HT2 receptors [63,64].
7-HMG also demonstrated high opioid receptor potency. In terms of analgesic activity, both mitragynine and 7-HMG were found to be more potent than morphine (mitragynine is about 13 times more effective, while 7-HMG is four times more effective) [13,55]. However, in a more recent study, kratom powder was found to have less affinity for the mu-opioid receptor than morphine [65].
At a cellular level, mitragynine can inhibit neurotransmitter release by reversibly blocking neuronal Ca2+ channels. It is proposed by the authors that the decrease in neurotransmitters leads to inhibition of pain transduction [66]. Mitragynine also inhibited adenylyl cyclase in NG108-15 cells through opioid receptors.
Cardiotoxicity was observed by induction of potentially fatal ventricular tachyarrhythmia (Torsade de Pointes). Blockage of the human Ether-a-go-go-Related Gene (hERG) channel in the heart constitutes a major risk of cardiotoxicity, and it is believed that Mitragyna speciosa suppresses hERG-mediated K+ currents and prolongs action duration [67].
Opioid agonistic activities were studied with twitch contraction in guinea pig ileum induced by electrical stimulation. The crude extract inhibited the twitch contraction, which was reversed by naloxone. Also, each extracted alkaloid (7-HMG, mitragynine, SC, PAY, and SG) inhibited the electrically-induced twitch contraction in a concentration-dependent fashion [68].
Both methanolic and the alkaloid extract of Mitragyna speciosa leaves were found to prolong the latency of nociceptive response on heat-induced pain in the hot plate test in mice, but not in the tail-flick test [69]. However, when Sabetghadam et al. [70] performed a study comparing the antinociceptive effects of alkaloid (20 mg/kg), methanolic (200 mg/kg), and aqueous extracts (100–400 mg/kg), they concluded that they all prolonged the latency of nociceptive responses in both tests. These analgesic effects were blocked by naloxone, which suggests partial mediation by opioid-receptors, similar to what occurs with morphine. Returning to the tail-flick and hot-plate tests, 7-HMG was again demonstrated to have a more potent antinociceptive activity than morphine. Its higher lipophilicity apparently makes it easier to penetrate the blood–brain barrier [71].

4.2. Anti-Inflammatory Properties

The anti-inflammatory effects of Mitragyna speciosa have also been studied [56,72,73]. The cyclooxygenase isoforms, COX-1 and COX-2, are involved in the inflammatory pathway that catalyzes prostaglandin PGE2 formation, which is one of the strongest inflammatory mediators. Mitragynine is capable of inhibiting COX-2 mRNA and protein expression, and therefore inhibits PGE2 formation. At lower concentrations it did not affect COX-1 mRNA and protein expression, but caution is advised at higher doses [72]. Overall, authors suggest that the anti-inflammatory properties of Mitragyna speciosa may result from a combination of inhibition of pro-inflammatory mediator release and vascular permeability in addition to enhanced immunity, stimulation of tissue repair, and healing processes [73].

4.3. Gastrointestinal Effects

Kratom also seems to have gastrointestinal effects [56]. The in vivo effect of the methanolic extract of kratom leaves in the gastrointestinal tract of rats reduced defecation frequency and fecal weight in castor oil-induced diarrhea. A single dose of the extract resulted in intestinal transit reduction; however, further decreases were not observed with prolonged intake. Since pre-treatment with naloxone had no impact on defecation frequency, it is believed that kratom may affect other pathways besides opioid-receptors [74].
Centrally injected mitragynine into the fourth ventricle of anesthetized rats resulted in a dose-dependent inhibition of 2-deoxy-d-glucose-stimulated gastric acid secretion; however, this effect was reversed by naloxone, which indicates the involvement of opioid receptors [75]. Mitragynine injected into the lateral cerebroventricle had no influence in acid secretion. Its effects of anorexia and weight loss may be related to the direct inhibition of neurons in the lateral hypothalamus. As for 7-HMG, a subcutaneous injection on mice resulted in gastrointestinal transit inhibition [71].
Mitragyna speciosa both acute and chronic effects include reduction of food and water consumption, and the additionally gained weight had a tendency to be reduced [76].
A study on the modulation of the glucose transport system of L8 muscle cells demonstrated that kratom can increase the rate of glucose uptake as well as protein levels of glucose transport, corroborating anti-diabetic effects [77].

4.4. Anti-Depressant Activity

Furthermore, kratom has also shown anti-depressant activity [78]. The overproduction of corticosterone reflects a hyperactivity of the hypothalamic–pituitary–adrenal axis, which provides a depression indicator. By significantly reducing corticosterone concentration in mice exposed to the forced swim test and tail suspension tests, mitragynine seems to possess anti-depressant effects [79].
Ismail et al. [80] also discovered an impairment between spatial learning and memory processing during chronic administration of kratom, observing learning deficits similar to those induced by chronic morphine or Δ-9-tetrahydrocannabinol treatment. However, an investigation on the acute effects of Mitragyna speciosa extract and mitragynine on short-term memory and motor coordination in mice showed that neither of them had a significant effect [81]. In 2018, a study conducted in humans [82] corroborated precisely these results, and apparently high intakes of kratom juice (>3 glasses daily) did not impair motor, memory, attention, nor executive function of regular kratom users.

4.5. Antioxidant and Anti-Bacterial Properties

As for antioxidant and anti-bacterial properties, Mitragyna speciosa proved to have both [83]. Nevertheless, there is no sufficient evidence that supports the use of Mitragyna speciosa for clinical indications and this becomes even clearer due to the contradictory information existing on this matter.

5. Toxicology

The pharmacologic effects of kratom leaves and their constituents are dose-dependent. Low to moderate dosages (1 to 5 g) can offer light stimulant effects to help workers against fatigue, while moderate to high dosages (5 to 15 g) may have opioid-like effects [13]. However, kratom also presents stimulant effects at high dosages (>15 g) [25,84]. Anxiety, irritability, and enhanced aggression are described, and long-term high dose consumption has been related to several atypical effects [13]. Hyperpigmentation of the cheeks, tremor, anorexia, weight loss, and psychosis have been noted in individuals with long-term addiction [84]. Although the use of kratom in opioid withdrawal situations is discussed in the scientific literature, some authors [85,86,87,88] have examined the consequences of withdrawal from kratom. Withdrawal is highly uncomfortable for some users, and as such maintaining abstinence becomes difficult. In fact, clinicians need to be aware of withdrawal symptoms and implement a similar approach as for opioid withdrawal scenarios, with long-term maintenance to prevent relapse. Trakulsrichai et al. [36] performed a study on the pharmacokinetics of mitragynine in 10 male subjects using kratom tea, and no serious adverse effects were found. All subjects have reported developing tongue numbness after drinking the tea and an increase in blood pressure and heart rate. These last symptoms had a delayed onset of 8 hours after tea consumption, which was even later than Tmax (0.83 ± 0.35 h), and as such further studies are required.
A recent study reported the death of rats after treatment with 200 mg/kg total alkaloid extract [89]. Other assays showed greater toxicity of the alkaloid extract when compared to the methanolic extract, with LD50 values of 173.20 mg/kg and 4.90 g/kg, respectively, in mice. In a 14-day period to evaluate acute toxicity, 100, 500, and 1000 mg/kg doses of standardized methanolic extract were administered to rats and did not affect spontaneous behavior, food and water consumption, absolute and relative organ weight, nor hematological parameters. It did however significantly increase blood pressure one hour after administration, and the highest dose of extract also induced acute severe hepatotoxicity and mild nephrotoxicity after single dose administration [90]. Sub-chronic high doses of Mitragyna speciosa have also been found to damage the kidneys and lungs, as emphysema, over-inflation of the alveoli, and an increase in serum creatinine and blood urea were observed [91]. Furthermore, both the plant extract and mitragynine showed cytotoxicity to human neuronal cells, but no genotoxicity in the mouse lymphoma gene mutation assay (Saidin). Also, no mutagenic effects were observed in a study performed using the Ames test [92]. The results concerning the benefits and toxicity of kratom are inconclusive; for instance, Fluyau et al. [93] have not determined if the biochemical benefits of the plant outweigh its toxicity and risks. On the contrary, it seems that the potential side effects outweigh the benefits, and severe and real health hazards can, insidiously, lead to death.
Cases involving multiple toxicity and fatal outcomes after mitragynine or kratom use have been reported, but the underlying causes remain unclear. Recently, in 2019, Rusli et al. [94] attempted to correlate the effects of mitragynine with glycoprotein-P, a multidrug transporter which modulates xenobiotic pharmacokinetics and plays a key role in the mediation of drug–drug interactions. Using biomolecular techniques, these authors concluded that mitragynine interacted with important residues at the nucleotide binding domain site of glycoprotein-P’s structure, but not with the residues from the substrate binding site. Therefore, mitragynine is likely to be a glycoprotein-P inhibitor in vitro but it is not a substrate. Hence, concurrent administration of mitragynine-containing kratom products with psychoactive drugs which are glycoprotein-P substrates may lead to toxicity, and this can be clinically significant.

6. Case Reports

Some case reports have also been published. In the following section the main case reports found in literature will be discussed, in order to better understand the toxic effects of this plant. A 64-year-old male, who regularly used kratom to self-medicate his chronic pain, was found by his wife unconscious and seizing. A urine concentration of mitragynine of 167 ± 15 ng/mL was detected [95].
Nine unintentional deaths were reported due to consumption of krypton. Both mitragynine (0.02 to 0.18 μg/g) and O-desmethyltramadol (0.4 to 4.3 μg/g) concentrations were determined in postmortem blood samples [96].
A 44-year-old subject with chronic abdominal pain started taking kratom after reading about it on the internet. The increase of dose intake and subsequent attempts to reduce failed due to experiencing withdrawal symptoms. The patient gained 60 pounds, became lethargic and developed myxedematous face. A severe primary hypothyroidism was diagnosed, and the authors have related it to Mitragyna speciosa due to the reduction of the thyroid gland response to thyroid-stimulating hormone [97].
Another case report of a 25-year-old man suggested that kratom had induced intrahepatic cholestasis, which was confirmed by liver biopsy. Mitragynine was detected in both urine and serum samples [98].
Furthermore, a 44-year-old man with a history of depression, alcohol dependence, and other substance misuse was admitted for kratom detoxification. Prior to his admission, the patient was consuming approximately 40 g of kratom divided into 4 doses over 24 h. The patient also experienced withdrawal symptoms, even though he was regularly consuming kratom, which suggests the short half-lives of the active substances in kratom and a dependence syndrome primarily via agonist activity at the opioid receptors [99].
Domingo et al. [100] also reported a 22-year-old male with a history of drug addiction who used to mix an unknown amount of herbal substances. Prior to his death he fell from a window before going to bed but did not attend the hospital. A very high blood concentration of mitragynine was detected; however, the cause of death was determined to be aspiration of chyme. It is believed that, although kratom was not the direct cause of death, it had an important role in it. High doses produce sedative effects, and postmortem examination confirmed a humerus fracture of the left arm. It seems that the pain was alleviated by mitragynine, explaining the lack of urgency of the subject to seek medical attention [100].
Kratom’s consumption in Southeast Asia is changing. A recent study performed by Singh et al. [101,102] based on self-reported information suggested that prolonged kratom use does not result in serious health risks nor impairs social functioning. Two recent trends have also emerged: the first involves the reported use of kratom to ease withdrawal from opioid dependence in rural settings, while the second is related to adulterated kratom cocktails being consumed by young people to induce euphoria in urban areas.
The presented evidences corroborate the fact that kratom is not only toxic but can also be lethal. The Food and Drug Administration [103] reported 44 deaths associated to kratom use, one of them involving mitragynine alone. These findings have prompted the institution to issue warning letters to numerous businesses that were illegally selling kratom. Nevertheless, it is not always clear which substances may be responsible for the effects, because in many situations kratom is not the only product being consumed, hence further studies are required on this matter.

7. Analytical Methodologies

To date, there are some techniques that have been suggested for the determination of Mitragyna speciosa, with special focus on mitragynine [104]. These techniques are imperative, not only for identification and quantification of plant components, but also for metabolic studies, and forensic and clinical toxicology. Therefore, it is important to achieve easy, inexpensive, and efficient ways to identify this plant or its components in biological specimens [104]. An increased focus must be given when kratom is present with other products or when there is adulteration of its chemical composition. Chromatographic methods seem to be the most commonly used, with high-performance liquid chromatography (HPLC) being the most popular [105]. Other methods include gas chromatography and liquid chromatography coupled to mass spectrometry (MS). Genetic methods have inclusively been used to identify the plant [9]. Some of the methods are reviewed in Table 1 (biological samples) and Table 2 (plant material).
Kowalczuk et al. [106] proposed a comprehensive authentication procedure that involves botanical analysis of leaf material and mitragynine identification by thin layer chromatography (TLC) and HPLC. Although microscopic analysis cannot be used by itself for kratom identification due to fragmentation of material and similarities between species, it can help in gathering information on the characteristic elements of the powdered material, especially because of the difficulty of dried plant material analysis due to incomplete removal of chlorophyll.
Lesiak et al. [32] proposed the identification of unique biomarkers for Mitragyna speciosa recurring to high resolution (HR)-DART-MS, a robust and fast way for data acquisition, without the need for sample pre-preparation steps. Fresh leaves and leaf extract analysis allowed the identification of Mitragyna speciosa following the detection of mitragynine isomers and 7-HMG. However, there was a significant difference in the amount of information provided by each different specimen, with a drop of 56% of the obtained information when the leaf extract was used. The possibility of identifying Mitragyna speciosa by comparison of the mass spectral data with those of unknown plant leaves was also approached with the help of linear discriminant analysis (LDA), being successful [32].
Parthasarathy et al. [107] reported a method with HPLC-diode array detection (DAD). DAD may be used for Mitragyna speciosa analysis because it stands as a fast and simple method, although it is not specific enough and seems to lack clear definition [105]. Comparison of extracts showed a higher mitragynine concentration in methanol and alkaloid-rich extracts when compared to the water extract. This is explained by the poor mitragynine solubility in water. Acid–base extraction technique also increased mitragynine concentration by converting the compound (and also other alkaloids) into its salt form, which is water soluble, and then back extracting the compound into the organic layer after neutralization, resulting in more concentrated extracts [107].
Ion mobility spectrometry (IMS) has also been used for the detection of mitragynine in 15 commercial samples. Its high sensitivity, at the ng level, and portability makes it attractive for screening. Fuenffinger et al. [108] used IMS and later compared the results with those obtained using liquid chromatography–tandem mass spectrometry (LC–MS/MS). LC–MS/MS detected mitragynine in one additional sample, whose concentration was below the IMS detection limit.
Furthermore, a monoclonal antibody (MAb) against mitragynine was produced and its ability to provide detection in leaf samples was also studied. The immunogens were prepared by means of the glutaraldehyde and carbodiimide methods. Immunogenicity was confirmed by determining the hapten numbers using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS). This method provided a rapid and sensitive way of mitragynine quantification [109].
Gas chromatography (GC) systems are viable and readily accessible due to their high selectivity and relative low maintenance costs. Their coupling to MS provides good determination capabilities for compounds. Still, there are some issues that cannot be ignored. The high temperature required for alkaloid elution combined with the upper temperature limit of the polymeric GC stationary phases impairs the parametric adjustment of resolution of alkaloid mixtures, and derivatization is often deemed necessary [105]. In addition, these systems are not capable of adequately resolving a number of diastereomers, such as mitragynine’s. This stands as an even bigger issue given the importance of mitragynine in Mitragyna speciosa analysis [105]. A study using GC–MS for urine samples could only detect mitragynine metabolites and some SC, SG, and PAY metabolites, with detection limits of 100 ng/mL for all diastereomers and PAY [110].
A comparison between GC and MS, supercritical fluid chromatography (SFC) and DAD, and UHPLC and MS and DAD for the analysis of mitragynine and other indole and oxindole alkaloids reported the GC method as less satisfactory. It proved to be unable to resolve mitragynine and SC. These diastereomers are only differentiated by the orientation of a single inner hydrogen atom, which makes the separation very hard by GC with a liquid stationary phase. In addition, the use of standard capillary columns may also have contributed to the inadequate resolution of the compounds.
SFC methods stood as a better choice given that they are faster, simpler and do not require as much organic liquids as the HPLC techniques [105]. Both were able to analyze mitragynine and other indole and oxindole alkaloids, but they differ in their effectiveness to identify mitragynine when its stereoisomers SG and SC are also present; indeed, and although mitragynine is the main compound of Mitragyna speciosa, it is important to find methods capable of identifying possible interferences from other diastereomers, which highlights the need for chromatographic separation [105].
The extraction technique can influence the yield in raw extracts and the relative alkaloid content of Mitragyna speciosa leaves, also highlighting the importance of extraction optimization. Mudge et al. [111] used the HPLC–UV technique to determine mitragynine and 7-HMG, and compared extraction solvents reporting methanol as the best choice; furthermore, they observed better extraction efficiency of mitragynine with 70% methanol with 0.5 M acetic acid. Other factors, such as the extraction method (shaking versus sonicating), solvent volume (10 versus 20 mL), and time (30 versus 60 min) were evaluated. Although results were inconclusive, shaking seemed to improve precision [111]. Other assays [112] compared ultrasound assisted extraction (UAE), microwave-assisted extraction (MAE), and supercritical carbon dioxide extraction (SFE-CO2) (using methanol, ethanol, water, and binary mixtures). Using LC/ESI–MS analysis, MAE (methanol:water, 1:1) gave the highest alkaloid fraction amount, while UAE showed the best yield for mitragynine. The authors concluded that UAE (methanol:water) seemed to be the most effective method to obtain a large quantity of the alkaloid [112].
Scientific literature concerning the determination of the main active compounds of Mitragyna speciosa in biological fluids is very scarce, mostly focusing on urine specimens. In these cases, hydrolysis is usually performed with β-glucuronidase and/or arylsulfatase because metabolites are majorly excreted in the conjugate form [110,113,114,115,116]. Regarding extraction procedures, some authors use liquid–liquid extraction with methyl tert-butyl ether [113,117], ethyl tert-butyl ether [115], or n-butyl chloride [116].
However, solid phase extraction (SPE) seems promising. It yields clean chromatograms due to its capability of removing interferences from the matrix, leading to increased sensitivity, precision, and accuracy; it also presents short total analysis time and requires smaller sample volumes [33,114,118]. In fact, Mcintyre et al. [45] describe a fatal case report where peripheral blood, central blood, liver, vitreous, gastric content, and urine were used to screen for mitragynine by SPE (C18) followed by GC–MS. Using this approach the authors achieved limits of detection and limits of quantitation of 0.03 and 0.05 mg/L, respectively. Holler et al. [116] report the first publication of a death involving propylhexedrine and mitragynine. The authors determined mitragynine presence in urine and blood, after previous hydrolysis with β-glucuronidase and sulfatase. The extraction was performed with 3 mL of n-butyl chloride and the analysis was performed using a LC–MS/MS system. The authors achieved limits of detection and quantitation of 0.25 and 1 ng/mL respectively, and successfully applied the extraction technique to other specimens (liver, vitreous humor, kidney, heart, spleen, lung, and bile) in order to detect mitragynine. Heart was the only specimen in which the compound was not detected.
Bar adsorptive microextraction, using a modified N-vinylpyrrolidone polymer sorbent phase, combined with liquid desorption followed by HPLC–DAD, was used in human urine matrices (BAμE–LD/HPLC–DAD). This technique provided high selectivity for mitragynine, good performance, and it is easy to work-up and environmentally friendly [119].
Although most of these methods proved to be reliable for mitragynine analysis, they require complex sample preparations. They can also be too laborious, expensive, and not so easily accessible; therefore, further studies are required on this matter. One should keep in mind that so far kratom constituents are not detected by conventional drug screening tests (e.g., immunoassay tests).
Table 1 and Table 2 review the available literature (PubMed) about the analytical techniques (from 2010 to present) studied in human biological matrices and plant material.

8. Conclusions and Future Perspective

It is still very compelling for people to use substances that can enhance their abilities. Several NPS or so-called ‘designer drugs’ are usually used in non-medical scenarios as synthetic alternatives for illicit drugs of abuse. Kratom is an example of these new trended drugs. Its consumption is traditional in southern Thailand, and it was formerly consumed for the purposes of withstanding great heat and fatigue. Nowadays there are a wide amount of other reasons for consumption, such as opium substitution, to diminish opium addiction, or reduce pain from withdrawal symptoms. Unfortunately, kratom itself seems to cause dependence, therefore leading to withdrawal symptoms whenever people stop using it. It has also been reported to cause an increase in blood pressure, hepatotoxicity, nephrotoxicity, emphysema, over-inflation of the alveoli, and cytotoxicity to human neuronal cells and there are even several reports regarding fatalities after kratom consumption. This alone is a pretty good reason to pay more attention to this plant. It is important to develop simple, inexpensive, and effective methods for Mitragyna speciosa analysis so that more information about toxicity, interactions with other drugs, metabolic actions, and pharmacology can be understood. This becomes even clearer due to the ease of acquisition on the internet. The lack of a convenient test for mitragynine detection makes it a lot harder for authorities to detect kratom users, and therefore harder to provide health care for them. A small plant that was originally used traditionally in a particular region in Asia is now used worldwide with no need for medical prescription or supervision and for which a dependence treatment is yet to be known.
Mitragyna speciosa also seems to present interesting effects, namely antinociceptive, anti-inflammatory, gastrointestinal, anti-depressant, antioxidant, and anti-bacterial. Still, there is no sufficient evidence that supports its use for clinical purposes, and therefore further studies are required.

Author Contributions

V.M. was responsible for the article search and writing of the manuscript sections concerning secondary metabolites. T.R. was responsible for the article search and writing of the manuscript sections concerning analytical methodologies. M.B. was responsible for designing the study, writing the section about legal aspects and toxicology, and revising the manuscript. S.S. was responsible for the article search and writing of the manuscript sections concerning toxicology. J.G. was responsible for the article search and writing of the manuscript sections concerning the case reports. Â.L. was responsible for the article search and writing of the manuscript sections concerning clinical effects and pharmacology. D.C. participated in the article search about analytical methods for the identification and/or quantification of Mitragyna speciosa in leaves and plant material and in writing of the manuscript. A.Y.S. participated in the article search about analytical methods for the identification and/or quantification of Mitragyna speciosa in biological samples and writing of the manuscript. N.F. was responsible for the article search and writing of the manuscript sections concerning pharmacokinetics and pharmacodynamics. A.P.D. was responsible for designing the study and revising the manuscript. E.G. was responsible for designing the study, organization, and revising the manuscript.

Funding

This reseach was funded by FEDER funds through the POCI —COMPETE 2020—Operational Programme Competitiveness and Internationalization in Axis I—Strengthening research, technological development, and innovation (Project POCI-01-0145-FEDER-007491) and National Funds by FCT—Fundação para a Ciência e a Tecnologia (Project UID/Multi /00709/2013). S. Soares and J. Gonçalves acknowledge Program Santander–Totta Universidades in the form of a fellowship (Bolsa BID/UBI–Santander Universidades/2018). Â. Luís acknowledges the contract in the scientific area of microbiology (Scientific Employment) financed by FCT.

Conflicts of Interest

The authors declare that they have no conflict of interest or financial involvement regarding this submission.

References

  1. Dennehy, C.E.; Tsourounis, C.; Miller, A.E. Evaluation of Herbal Dietary Supplements Marketed on the Internet for Recreational Use. Complement. Altern. Med. 2014, 39, 1634–1639. [Google Scholar] [CrossRef] [PubMed]
  2. Singh, D.; Müller, C.P.; Vicknasingam, B.K. Kratom (Mitragyna speciosa) dependence, withdrawal symptoms and craving in regular users. Drug Alcohol Depend. 2014, 139, 132–137. [Google Scholar] [CrossRef] [PubMed]
  3. Singh, D.; Müller, C.P.; Vicknasingam, B.K.; Mansor, S.M. Social Functioning of Kratom (Mitragyna speciosa) Users in Malaysia. J. Psychoact. Drugs 2015, 47, 125–131. [Google Scholar] [CrossRef] [PubMed]
  4. European Monitoring Centre for Drugs and Drug Adiction. New Psychoactive Substances in Europe. Available online: http://www.emcdda.europa.eu/system/files/publications/65/TD0415135ENN.pdf (accessed on 12 January 2019).
  5. Adkins, J.E.; Boyer, E.W.; Mccurdy, C.R. Mitragyna speciosa, A Psychoactive Tree from Southeast Asia with Opioid Activity. Curr. Top. Med. Chem. 2011, 11, 1165–1175. [Google Scholar] [CrossRef] [PubMed]
  6. Takayama, H. Chemistry and Pharmacology of Analgesic Indole Alkaloids from the Rubiaceous Plant, Mitragyna speciosa. Chem. Pharm. Bull. 2004, 52, 916–928. [Google Scholar] [CrossRef] [PubMed]
  7. Gong, F.; Gu, H.; Xu, Q.; Kang, W. Genus Mitragyna: Ethnomedicinal uses and pharmacological studies. Phytopharmacology 2012, 3, 263–272. [Google Scholar]
  8. Davis, G.G. Drug abuse: Newly-Emerging drugs and trends. Clin. Lab. Med. 2012, 32, 407–417. [Google Scholar] [CrossRef] [PubMed]
  9. Maruyama, T.; Kawamura, M.; Kikura-Hanajiri, R.; Takayama, H.; Goda, Y. The botanical origin of kratom (Mitragyna speciosa; Rubiaceae) available as abused drugs in the Japanese markets. J. Nat. Med. 2009, 63, 340–344. [Google Scholar] [CrossRef] [PubMed]
  10. Tanguay, P. Kratom in Thailand. Transl. Inst. Legis. Reform Drug Policies 2011, 13, 1–16. [Google Scholar] [CrossRef]
  11. Saingam, D.; Assanangkornchai, S.; Geater, A.F.; Balthip, Q. Pattern and consequences of krathom (Mitragyna speciosa Korth.) use among male villagers in southern Thailand: A qualitative study. Int. J. Drug Policy 2018, 24, 351–358. [Google Scholar] [CrossRef] [PubMed]
  12. Singh, D.; Narayanan, S.; Vicknasingam, B. Traditional and non-traditional uses of Mitragynine (Kratom): A survey of the literature. Brain Res. Bull. 2016, 126, 41–46. [Google Scholar] [CrossRef] [PubMed]
  13. Vicknasingam, B.; Narayanan, S.; Beng, G.T.; Mansor, S.M. The informal use of ketum (Mitragyna speciosa) for opioid withdrawal in the northern states of peninsular Malaysia and implications for drug substitution therapy. Int. J. Drug Policy 2010, 21, 283–288. [Google Scholar] [CrossRef] [PubMed]
  14. Swogger, M.T.; Hart, E.; Erowid, F.; Erowid, E.; Trabold, N.; Yee, K.; Parkhurst, K.A.; Priddy, B.M.; Walsh, Z. Experiences of Kratom Users: A Qualitative Analysis. J. Psychoact. Drugs 2015, 47, 360–367. [Google Scholar] [CrossRef] [PubMed]
  15. Assanangkornchai, S.; Muekthong, A. The Use of Mitragynine speciosa (“Krathom”), an Addictive Plant, in Thailand. Subst. Use Misuse 2006, 6084, 2145–2157. [Google Scholar]
  16. Grundmann, O. Patterns of Kratom use and health impact in the US—Results from an online survey. Drug Alcohol Depend. 2017, 176, 63–70. [Google Scholar] [CrossRef] [PubMed]
  17. Schmidt, M.M.; Sharma, A.; Schifano, F.; Feinmann, C. “Legal highs” on the net-Evaluation of UK-based Websites, products and product information. Forensic Sci. Int. 2011, 206, 92–97. [Google Scholar] [CrossRef] [PubMed]
  18. Hillebrand, J.; Olszewski, D.; Sedefov, R. Legal Highs on the Internet. Subst. Use Misuse 2010, 45, 330–340. [Google Scholar] [CrossRef] [PubMed]
  19. European Monitoring Centre for Drugs and Drug Adiction. Khat Drug Profile. Available online: http://www.emcdda.europa.eu/publications/drug-profiles/khat (accessed on 11 January 2019).
  20. United Nations Office on Drugs and Crime (UNODC). UNODC Early Warning Advisory (EWA) on New Psychoactive Substances (NPS). Available online: https://www.unodc.org/LSS/Home/NPS (accessed on 16 January 2019).
  21. Kratom (Mitragyna speciosa) Drug Profile. Available online: http://www.emcdda.europa.eu/publications/drug-profiles/kratom (accessed on 11 January 2019).
  22. Ahmad, K.; Aziz, Z. Mitragyna speciosa use in the northern states of Malaysia: A cross-sectional study. J. Ethnopharmacol. 2012, 141, 446–450. [Google Scholar] [CrossRef] [PubMed]
  23. Jansen, K.; Prast, C. Ethnopharmacology of kratom and mitragyna alkaloids. J. Ethnopharmacol. 1988, 23, 115–119. [Google Scholar] [CrossRef]
  24. Shellard, E.J. Ethnopharmacology of kratom and the Mitragyna alkaloids. J. Ethnopharmacol. 1989, 25, 123–124. [Google Scholar] [CrossRef]
  25. Feng, L.-Y.; Battulga, A.; Han, E.; Chung, H.; Li, J.-H. New psychoactive substances of natural origin: A brief review. J. Food Drug Anal. 2017, 25, 461–471. [Google Scholar] [CrossRef] [PubMed]
  26. Raffa, R.B. Kratom and Other Mitragynines: The Chemistry and Pharmacology of Opioids from a Non-Opium Source, 1st ed.; Raffa, R.B., Ed.; CRC Press: Boca Raton, FL, USA, 2014. [Google Scholar]
  27. Schro, S.; Stu, B.; Arndt, T.; Claussen, U.; Gu, B.; Werle, A.; Wolf, G. Kratom alkaloids and O-desmethyltramadol in urine of a “Krypton” herbal mixture consumer. Forensic Sci. Int. 2011, 208, 47–52. [Google Scholar]
  28. Ponglux, D.; Wongseripipatana, S.; Takayama, H.; Kilcuchi, M.; Kurihara, M. A New Indole Alkaloid, 7a-Hydroxy-7H-mitragynine, from Mitragyna speciosa in Thailand. Planta Med. 1994, 60, 581–582. [Google Scholar] [CrossRef] [PubMed]
  29. Prozialeck, W.C.; Jivan, J.K.; Andurkar, S.V. Pharmacology of Kratom: An Emerging Botanical Agent with Stimulant, Analgesic and Opioid-Like Effects. J. Am. Osteopath. Assoc. 2012, 112, 792–799. [Google Scholar] [PubMed]
  30. Hendrickson, J.B.; Sims, J.J. Mitragyna alkaloids: The structure of stipulatine. Tetrahedron Lett. 1963, 4, 929–935. [Google Scholar] [CrossRef]
  31. Veeramohan, R.; Azizan, K.A.; Aizat, W.M.; Goh, H.-H.; Mansor, S.M.; Yusof, N.S.M.; Baharum, S.N.; Ng, C.L. Metabolomics data of Mitragyna speciosa leaf using LC-ESI-TOF-MS. Data Br. 2018, 18, 1212–1216. [Google Scholar] [CrossRef] [PubMed]
  32. Lesiak, A.D.; Cody, R.B.; Dane, A.J.; Musah, R.A. Rapid detection by direct analysis in real time-mass spectrometry (DART-MS) of psychoactive plant drugs of abuse: The case of Mitragyna speciosa aka “Kratom”. Forensic Sci. Int. 2014, 242, 210–218. [Google Scholar] [CrossRef] [PubMed]
  33. Parthasarathy, S.; Ramanathan, S.; Ismail, S.; Adenan, M.I.; Mansor, S.M.; Murugaiyah, V. Determination of mitragynine in plasma with solid-phase extraction and rapid HPLC-UV analysis, and its application to a pharmacokinetic study in rat. Anal. Bioanal. Chem. 2010, 397, 2023–2030. [Google Scholar] [CrossRef] [PubMed]
  34. Ramanathan, S.; Parthasarathy, S.; Murugaiyah, V.; Magosso, E.; Tan, S.C.; Mansor, S.M. Understanding the physicochemical properties of mitragynine, a principal alkaloid of Mitragyna speciosa, for preclinical evaluation. Molecules 2015, 20, 4915–4927. [Google Scholar] [CrossRef] [PubMed]
  35. Manda, V.K.; Avula, B.; Ali, Z.; Khan, I.A.; Walker, L.A.; Khan, S.I. Evaluation of in vitro absorption, distribution, metabolism, and excretion (ADME) properties of mitragynine, 7-hydroxymitragynine, and mitraphylline. Planta Med. 2014, 80, 568–576. [Google Scholar] [CrossRef] [PubMed]
  36. Trakulsrichai, S.; Sathirakul, K.; Auparakkitanon, S.; Krongvorakul, J.; Sueajai, J.; Noumjad, N.; Sukasem, C.; Wananukul, W. Pharmacokinetics of mitragynine in man. Drug Des. Dev. Ther. 2015, 9, 2421–2429. [Google Scholar]
  37. Boyer, E.; Babu, K.; Adkins, J.; McCurdy, C.; Harpern, J. Self-treatment of opioid withdrawal using kratom (Mitragynia speciosa Korth). Addiction 2013, 103, 1048–1050. [Google Scholar] [CrossRef] [PubMed]
  38. Avery, B.A.; Boddu, S.P.; Sharma, A.; Furr, E.B.; Leon, F.; Cutler, S.J.; McCurdy, C.R. Comparative Pharmacokinetics of Mitragynine after Oral Administration of Mitragyna speciosa (Kratom) Leaf Extracts in Rats. Planta Med. 2018, in press. [Google Scholar] [CrossRef] [PubMed]
  39. Yusof, S.R.; Mohd Uzid, M.; Teh, E.-H.; Hanapi, N.A.; Mohideen, M.; Mohamad Arshad, A.S.; Mordi, M.N.; Loryan, I.; Hammarlund-Udenaes, M. Rate and extent of mitragynine and 7-hydroxymitragynine blood–brain barrier transport and their intra-brain distribution: The missing link in pharmacodynamic studies. Addict. Biol. 2018, in press. [Google Scholar] [CrossRef] [PubMed]
  40. Azizi, J.; Ismail, S.; Mansor, S.M. Mitragyna speciosa Korth leaves extracts induced the CYP450 catalyzed aminopyrine-N-demethylase (APND) and UDP-glucuronosyl transferase (UGT) activities in male Sprague-Dawley rat livers. Drug Metab. Drug Interact. 2013, 28, 95–105. [Google Scholar] [CrossRef] [PubMed]
  41. Kong, W.M.; Chik, Z.; Ramachandra, M.; Subramaniam, U.; Raja Aziddin, R.E.; Mohamed, Z. Evaluation of the effects of Mitragyna speciosa alkaloid extract on cytochrome P450 enzymes using a high throughput assay. Molecules 2011, 16, 7344–7356. [Google Scholar] [CrossRef] [PubMed]
  42. Kamble, S.H.; Sharma, A.; King, T.I.; León, F.; McCurdy, C.R.; Avery, B.A. Metabolite profiling and identification of enzymes responsible for the metabolism of mitragynine, the major alkaloid of Mitragyna speciosa (kratom). Xenobiotica 2018, 14, 1–31. [Google Scholar] [CrossRef] [PubMed]
  43. Uno, Y.; Uehara, S.; Murayama, N.; Yamazaki, H. Cytochrome P450 1A1, 2C9, 2C19, and 3A4 Polymorphisms Account for Interindividual Variability of Toxicological Drug Metabolism in Cynomolgus Macaques. Chem. Res. Toxicol. 2018, 31, 1373–1381. [Google Scholar] [CrossRef] [PubMed]
  44. Philipp, A.A.; Wissenbach, D.K.; Weber, A.A.; Zapp, J.; Maurer, H.H. Metabolism studies of the Kratom alkaloid speciociliatine, a diastereomer of the main alkaloid mitragynine, in rat and human urine using liquid chromatography-linear ion trap mass spectrometry. Anal. Bioanal. Chem. 2011, 399, 2747–2753. [Google Scholar] [CrossRef] [PubMed]
  45. Mcintyre, I.M.; Trochta, A.; Stolberg, S.; Campman, S.C. Mitragynine ‘Kratom’ Related Fatality: A Case Report with Postmortem Concentrations. J. Anal. Toxicol. 2014, 39, 152–155. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  46. Hanapi, N.A.; Ismail, S.; Mansor, S.M. Inhibitory effect of mitragynine on human cytochrome P450 enzyme activities. Pharmacogn. Res. 2013, 5, 241–246. [Google Scholar]
  47. Cinosi, E.; Martinotti, G.; Simonato, P.; Singh, D.; Demetrovics, Z.; Roman-Urrestarazu, A.; Bersani, F.S.; Vicknasingam, B.; Piazzon, G.; Li, J.H.; et al. Following “the Roots” of Kratom (Mitragyna speciosa): The Evolution of an Enhancer from a Traditional Use to Increase Work and Productivity in Southeast Asia to a Recreational Psychoactive Drug in Western Countries. Biomed. Res. Int. 2015, 2015, 1–11. [Google Scholar] [CrossRef] [PubMed]
  48. Koe, X.F.; Jamil, M.F.A.; Adenan, M.I.; Tan, M.L.; Lim, E.L.; Seah, T.C.; Majid, M.I.A.; Wahab, H.A. In vitro evaluation of cytochrome P450 induction and the inhibition potential of mitragynine, a stimulant alkaloid. Toxicol. In Vitr. 2012, 27, 812–824. [Google Scholar]
  49. Showande, S.J.; Fakeye, T.O.; Kajula, M.; Hokkanen, J.; Tolonen, A. Potential inhibition of major human cytochrome P450 isoenzymes by selected tropical medicinal herbs—Implication for herb–drug interactions. Food Sci. Nutr. 2019, 7, 44–55. [Google Scholar] [CrossRef] [PubMed]
  50. Ulbricht, C.; Costa, D.; Dao, J.; Isaac, R.; Leblanc, Y.C.; Rhoades, J.; Windsor, R.C. An evidence-based systematic review of kratom (Mitragyna speciosa) by the natural standard research collaboration. J. Diet. Suppl. 2013, 10, 152–170. [Google Scholar] [CrossRef] [PubMed]
  51. Hughes, R.L. Fatal combination of mitragynine and quetiapine—A case report with discussion of a potential herb-drug interaction. Forensic Sci. Med. Pathol. 2018, 15, 110–113. [Google Scholar] [CrossRef] [PubMed]
  52. Chan, K.B.; Pakiam, C.; Rahim, R.A. Psychoactive plant abuse: The identification of mitragynine in ketum and in ketum preparations. Bull. Narc. 2007, 249, 249–256. [Google Scholar]
  53. Roche, K.M.; Hart, K.; Sangalli, B.; Lefberg, J.; Bayer, M. Kratom: A Case of a Legal High. Clin. Toxicol. 2008, 46, 598. [Google Scholar]
  54. Ward, J.; Rosenbaum, C.; Hernon, C.; McCurdy, C.R.; Boyer, E.W. Herbal Medicines for the Management of Opioid Addiction. CNS Drugs 2011, 25, 999–1007. [Google Scholar] [CrossRef] [PubMed]
  55. Matsumoto, K.; Horie, S.; Takayama, H.; Ishikawa, H.; Aimi, N.; Ponglux, D.; Murayama, T.; Watanabe, K. Antinociception, tolerance and withdrawal symptoms induced by 7-hydroxymitragynine, an alkaloid from the Thai medicinal herb Mitragyna speciosa. Life Sci. 2005, 78, 2–7. [Google Scholar] [CrossRef] [PubMed]
  56. Hassan, Z.; Muzaimi, M.; Navaratnam, V.; Yusoff, N.H.M.; Suhaimi, F.W.; Vadivelu, R.; Vicknasingam, B.K.; Amato, D.; von Hörsten, S.; Ismail, N.I.W.; et al. From Kratom to mitragynine and its derivatives: Physiological and behavioural effects related to use, abuse, and addiction. Neurosci. Biobehav. Rev. 2013, 37, 138–151. [Google Scholar] [CrossRef] [PubMed]
  57. Thongpradichote, S.; Matsumoto, K.; Tohda, M.; Takayama, H.; Aimi, N.; Sakai, S.I.; Watanabe, H. Identification of opioid receptor subtypes in antinociceptive actions of supraspinally-administered mitragynine in mice. Life Sci. 1998, 62, 1371–1378. [Google Scholar] [CrossRef]
  58. Yamamoto, L.T.; Horie, S.; Takayama, H.; Aimi, N.; Sakai, S.I.; Yano, S.; Shan, J.; Pang, P.K.T.; Ponglux, D.; Watanabe, K. Opioid receptor agonistic characteristics of mitragynine pseudoindoxyl in comparison with mitragynine derived from Thai medicinal plant Mitragyna speciosa. Gen. Pharmacol. 1999, 33, 73–81. [Google Scholar] [CrossRef]
  59. White, C.M. Pharmacologic and clinical assessment of kratom. Bull. Am. Soc. Hosp. Pharm. 2018, 75, 261–267. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  60. Stolt, A.-C.; Schröder, H.; Neurath, H.; Grecksch, G.; Höllt, V.; Meyer, M.R.; Maurer, H.H.; Ziebolz, N.; Havemann-Reinecke, U.; Becker, A. Behavioral and neurochemical characterization of kratom (Mitragyna speciosa) extract. Psychopharmacology 2014, 231, 13–25. [Google Scholar] [CrossRef] [PubMed]
  61. Hemby, S.E.; McIntosh, S.; Leon, F.; Cutler, S.J.; McCurdy, C.R. Abuse liability and therapeutic potential of the Mitragyna speciosa (kratom) alkaloids mitragynine and 7-hydroxymitragynine. Addict. Biol. 2018, in press. [Google Scholar] [CrossRef] [PubMed]
  62. Vermaire, D.J.; Skaer, D.; Tippets, W. Kratom and General Anesthesia: A Case Report and Review of the Literature. A A Pract. 2019, 12, 103–105. [Google Scholar] [CrossRef] [PubMed]
  63. Vijeepallam, K.; Pandy, V.; Kunasegaran, T.; Murugan, D.D.; Naidu, M. Mitragyna speciosa leaf extract exhibits antipsychotic-like effect with the potential to alleviate positive and negative symptoms of psychosis in mice. Front. Pharmacol. 2016, 7, 464. [Google Scholar] [CrossRef] [PubMed]
  64. Watanabe, K.; Yano, S.; Horie, S.; Yamamoto, L. Inhibitory effect of mitragynine, an alkaloid with analgesic effect from Thai medicinal plant Mitragyna speciosa, on electrically stimulated contraction of isolated guinea-pig ileum through the opioid receptor. Life Sci. 1997, 60, 933–942. [Google Scholar] [CrossRef]
  65. Havemann-Reinecke, U. P01-50-Kratom and alcohol dependence: Clinical symptoms, withdrawal treatment and pharmacological mechanisms—A case report. Eur. Psychiatry 2011, 26, 50. [Google Scholar] [CrossRef]
  66. Matsumoto, K.; Yamamoto, L.T.; Watanabe, K.; Yano, S.; Shan, J.; Pang, P.K.T.; Ponglux, D.; Takayama, H.; Horie, S. Inhibitory effect of mitragynine, an analgesic alkaloid from Thai herbal medicine, on neurogenic contraction of the vas deferens. Life Sci. 2005, 78, 187–194. [Google Scholar] [CrossRef] [PubMed]
  67. Lu, J.; Wei, H.; Wu, J.; Fadzly, M.; Jamil, A. Evaluation of the Cardiotoxicity of Mitragynine and Its Analogues Using Human Induced Pluripotent Stem Cell- Derived Cardiomyocytes. PLoS ONE 2014, 9, e115648. [Google Scholar] [CrossRef] [PubMed]
  68. Horie, S.; Koyama, F.; Takayama, H.; Ishikawa, H.; Aimi, N.; Ponglux, D.; Matsumoto, K.; Murayama, T. Indole alkaloids of a Thai medicinal herb, Mitragyna speciosa, that has opioid agonistic effect in guinea-pig ileum. Planta Med. 2005, 71, 231–236. [Google Scholar] [CrossRef] [PubMed]
  69. Reanmongkol, W.; Keawpradub, N.; Sawangjaroen, K. Effects of the extracts from Mitragyna speciosa Korth. leaves on analgesic and behavioral activities in experimental animals. Songklanakarin J. Sci. Technol. 2017, 29, 39–48. [Google Scholar]
  70. Sabetghadam, A.; Ramanathan, S.; Mahsufi Mansor, S. The evaluation of antinociceptive activity of alkaloid, methanolic, and aqueous extracts of Malaysian Mitragyna speciosa Korth leaves in rats. Pharmacogn. Res. 2010, 2, 181–185. [Google Scholar]
  71. Matsumoto, K.; Hatori, Y.; Murayama, T. Involvement of μ-opioid receptors in antinociception and inhibition of gastrointestinal transit induced by 7-hydroxymitragynine, isolated from Thai herbal medicine Mitragyna speciosa. Eur. J. Pharmacol. 2006, 549, 63–70. [Google Scholar] [CrossRef] [PubMed]
  72. Utar, Z.; Majid, M.I.A.; Adenan, M.I.; Jamil, M.F.A.; Lan, T.M. Mitragynine inhibits the COX-2 mRNA expression and prostaglandin E2 production induced by lipopolysaccharide in RAW264.7 macrophage cells. J. Ethnopharmacol. 2011, 136, 75–82. [Google Scholar] [CrossRef] [PubMed]
  73. Mossadeq, W.M.S.; Sulaiman, M.R.; Mohamad, T.A.T.; Chiong, H.S.; Zakaria, Z.A.; Jabit, M.L.; Baharuldin, M.T.H.; Israf, D.A. Anti-Inflammatory and Antinociceptive Effects of Mitragyna speciosa Korth. Med. Princ. Pract. 2009, 18, 378–384. [Google Scholar] [CrossRef] [PubMed]
  74. Chittrakarn, S.; Sawangjaroen, K.; Prasettho, S.; Janchawee, B.; Keawpradub, N. Inhibitory effects of kratom leaf extract (Mitragyna speciosa Korth.) on the rat gastrointestinal tract. J. Ethnopharmacol. 2008, 116, 173–178. [Google Scholar] [CrossRef] [PubMed]
  75. Tsuchiya, S.; Miyashita, S.; Yamamoto, M.; Horie, S.; Sakai, S. Effect of mitragynine, derived from Thai folk medicine, on gastric acid secretion through opioid receptor in anesthetized rats. Eur. J. Pharmacol. 2002, 443, 185–188. [Google Scholar] [CrossRef]
  76. Sabetghadam, A.; Ramanathan, S.; Sasidharan, S.; Mansor, S.M. Subchronic exposure to mitragynine, the principal alkaloid of Mitragyna speciosa, in rats. J. Ethnopharmacol. 2013, 146, 815–823. [Google Scholar] [CrossRef] [PubMed]
  77. Purintrapiban, J.; Keawpradub, N. Study on glucose transport in muscle cells by extracts from Mitragyna speciosa (Korth) and mitragynine. Nat. Prod. Res. 2011, 25, 1379–1387. [Google Scholar] [CrossRef] [PubMed]
  78. Kumarnsit, E.; Keawpradub, N.; Nuankaew, W. Effect of Mitragyna speciosa aqueous extract on ethanol withdrawal symptoms in mice. Fitoterapia 2007, 78, 182–185. [Google Scholar] [CrossRef] [PubMed]
  79. Farah Idayu, N.; Taufik Hidayat, M.; Moklas, M.A.M.; Sharida, F.; Nurul Raudzah, A.R.; Shamima, A.R.; Apryani, E. Antidepressant-like effect of mitragynine isolated from Mitragyna speciosa Korth in mice model of depression. Phytomedicine 2011, 18, 402–407. [Google Scholar] [CrossRef] [PubMed]
  80. Ismail, N.I.W.; Jayabalan, N.; Mansor, S.M.; Müller, C.P.; Muzaimi, M. Chronic mitragynine (kratom) enhances punishment resistance in natural reward seeking and impairs place learning in mice. Addict. Biol. 2017, 22, 967–976. [Google Scholar] [CrossRef] [PubMed]
  81. Hazim, A.I.; Mustapha, M.; Mansor, S.M. The effects on motor behaviour and short-term memory tasks in mice following an acute administration of Mitragyna speciosa alkaloid extract and mitragynine. J. Med. Plants 2011, 5, 5810–5817. [Google Scholar]
  82. Singh, D.; Narayanan, S.; Müller, C.P.; Vicknasingam, B.; Yücel, M.; Ho, E.T.W.; Hassan, Z.; Mahsufi Mansor, S. Long-Term Cognitive Effects of Kratom (Mitragyna speciosa Korth.) Use. J. Psychoact. Drugs 2018, 51, 19–27. [Google Scholar] [CrossRef] [PubMed]
  83. Parthasarathy, S.; Bin Azizi, J.; Ramanathan, S.; Ismail, S.; Sasidharan, S.; Mohd, M.I.; Mansor, S.M. Evaluation of antioxidant and antibacterial activities of aqueous, methanolic and alkaloid extracts from Mitragyna speciosa (rubiaceae family) leaves. Molecules 2009, 14, 3964–3974. [Google Scholar] [CrossRef] [PubMed]
  84. Suwanlert, S. A study of kratom eaters in Thailand. Bull. Narc. 1975, 27, 21–27. [Google Scholar] [PubMed]
  85. Stanciu, C.N.; Gnanasegaram, S.A.; Ahmed, S.; Penders, T. Kratom Withdrawal: A Systematic Review with Case Series. J. Psychoact. Drugs 2019, 51, 12–18. [Google Scholar] [CrossRef] [PubMed]
  86. Smid, M.C.; Charles, J.E.; Gordon, A.J.; Wright, T.E. Use of Kratom, an Opioid-like Traditional Herb, in Pregnancy. Obstet. Gynecol. 2018, 132, 926–928. [Google Scholar] [CrossRef] [PubMed]
  87. Davidson, L.; Rawat, M.; Stojanovski, S.; Chandrasekharan, P. Natural Drugs, Not So Natural Effects: Neonatal Abstinence Syndrome Secondary to ‘Kratom’. J. Neonatal-Perinat. Med. 2018, 1–4. [Google Scholar] [CrossRef] [PubMed]
  88. Swogger, M.T.; Walsh, Z. Kratom use and mental health: A systematic review. Drug Alcohol Depend. 2018, 183, 134–140. [Google Scholar] [CrossRef] [PubMed]
  89. Azizi, J.; Ismail, S.; Mordi, M.N.; Ramanathan, S.; Said, M.I.M.; Mansor, S.M. In vitro and in vivo effects of three different Mitragyna speciosa korth leaf extracts on phase II drug metabolizing enzymes-glutathione transferases (GSTs). Molecules 2010, 15, 432–441. [Google Scholar] [CrossRef] [PubMed]
  90. Harizal, S.N.; Mansor, S.M.; Hasnan, J.; Tharakan, J.K.J.; Abdullah, J. Acute toxicity study of the standardized methanolic extract of Mitragyna speciosa Korth in Rodent. J. Ethnopharmacol. 2010, 131, 404–409. [Google Scholar] [CrossRef] [PubMed]
  91. Ilmie, M.U.; Jaafar, H.; Mansor, S.M.; Abdullah, J.M. Subchronic toxicity study of standardized methanolic extract of Mitragyna speciosa Korth in Sprague-Dawley Rats. Front. Neurosci. 2015, 9, 1–6. [Google Scholar] [CrossRef] [PubMed]
  92. Saidin, N.A.; Randall, T.; Takayama, H.; Holmes, E.; Gooderham, N. Malaysian Kratom, a phyto-pharmaceutical of abuse: Studies on the mechanism of its cytotoxicity. Toxicology 2008, 253, 19–20. [Google Scholar] [CrossRef]
  93. Fluyau, D.; Revadigar, N. Biochemical benefits, diagnosis, and clinical risks evaluation of kratom. Front. Psychiatry 2017, 8, 62. [Google Scholar] [CrossRef] [PubMed]
  94. Rusli, N.; Amanah, A.; Kaur, G.; Adenan, M.I.; Sulaiman, S.F.; Wahab, H.A.; Tan, M.L. The inhibitory effects of mitragynine on P-glycoprotein in vitro. Naunyn-Schmiedebergs Arch. Pharmacol. 2019, 1–16. Available online: https://link.springer.com/article/10.1007%2Fs00210-018-01605-y (accessed on 3 March 2019).
  95. Nelsen, J.L.; Lapoint, J.; Hodgman, M.J.; Aldous, K.M. Seizure and Coma Following Kratom (Mitragynina speciosa Korth) Exposure. J. Med. Toxicol. 2010, 6, 424–426. [Google Scholar] [CrossRef] [PubMed]
  96. Kronstrand, R.; Roman, M.; Thelander, G.; Eriksson, A. Unintentional Fatal Intoxications with Mitragynine and O-Desmethyltramadol from the Herbal Blend Krypton. J. Anal. Toxicol. 2011, 35, 242–247. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  97. Hypothyroidism, S.P.; Sheleg, S.V.; Collins, G.B. A Coincidence of Addiction to “kratom” and Severe Primary Hypothyroidism. Am. Soc. Addict. Med. 2011, 5, 300–301. [Google Scholar]
  98. Kapp, F.G.; Maurer, H.H.; Auwärter, V.; Winkelmann, M. Hermanns-Clausen, M. Intrahepatic Cholestasis Following Abuse of Powdered Kratom (Mitragyna speciosa). J. Med. Toxicol. 2011, 7, 227–231. [Google Scholar] [CrossRef] [PubMed]
  99. McWhirter, L.; Morris, S. A case report of inpatient detoxification after kratom (Mitragyna speciosa) dependence. Eur. Addict. Res. 2010, 16, 229–231. [Google Scholar] [CrossRef] [PubMed]
  100. Domingo, O.; Roider, G.; Stöver, A.; Graw, M.; Musshoff, F.; Sachs, H.; Bicker, W. Mitragynine concentrations in two fatalities. Forensic Sci. Int. 2017, 271, e1–e7. [Google Scholar] [CrossRef] [PubMed]
  101. Singh, D.; Narayanan, S.; Vicknasingam, B.; Corazza, O.; Santacroce, R.; Roman-Urrestarazu, A. Changing trends in the use of kratom (Mitragyna speciosa) in Southeast Asia. Hum. Psychopharmacol. Clin. Exp. 2017, 32, e2582. [Google Scholar] [CrossRef] [PubMed]
  102. Singh, D.; Narayanan, S.; Müller, C.P.; Swogger, M.T.; Chear, N.J.Y.; Bin Dzulkapli, E.; Yusoff, N.S.M.; Ramachandram, D.S.; León, F.; McCurdy, C.R.; et al. Motives for using Kratom (Mitragyna speciosa Korth.) among regular users in Malaysia. J. Ethnopharmacol. 2019, 233, 34–40. [Google Scholar] [CrossRef] [PubMed]
  103. Food and Drug Administration Statement from FDA Commissioner Scott Gottlieb, M.D., on the Agency’s Scientific Evidence on the Presence of Opioid Compounds in Kratom, Underscoring Its Potential for Abuse. Available online: https://www.fda.gov/newsevents/newsroom/pressannouncements/ucm595622.htm (accessed on 18 January 2019).
  104. Kikura-Hanajiri, R. Detection of mitragyne and its analogs. In Kratom and Other Mitragynines: The Chemistry and Pharmacology of Opioids from a Non-Opium Source; Raffa, R.B., Ed.; CRC Press: Boca Raton, FL, USA, 2014; pp. 153–166. [Google Scholar]
  105. Wang, M.; Carrell, E.J.; Ali, Z.; Avula, B.; Avonto, C.; Parcher, J.F.; Khan, I.A. Comparison of three chromatographic techniques for the detection of mitragynine and other indole and oxindole alkaloids in Mitragyna speciosa (kratom) plants. J. Sep. Sci. 2014, 37, 1411–1418. [Google Scholar] [CrossRef] [PubMed]
  106. Kowalczuk, A.; Losak, A.; Zjawiony, A.L. Comprehensive methodology for identification of Kratom in police laboratories. Forensic Sci. Int. 2013, 233, 238–243. [Google Scholar] [CrossRef] [PubMed]
  107. Parthasarathy, S.; Ramanathan, S.; Murugaiyah, V. A simple HPLC-DAD method for the detection and quantification of psychotropic mitragynine in Mitragyna speciosa (ketum) and its products for the application in forensic investigation. Forensic Sci. Int. 2013, 226, 183–187. [Google Scholar] [CrossRef] [PubMed]
  108. Fuenffinger, N.; Ritchie, M.; Ruth, A.; Gryniewicz-ruzicka, C. Evaluation of ion mobility spectrometry for the detection of mitragynine in kratom products. J. Pharm. Biomed. Anal. 2017, 134, 282–286. [Google Scholar] [CrossRef] [PubMed]
  109. Limsuwanchote, S.; Wungsintaweekul, J.; Keawpradub, N.; Putalun, W.; Morimoto, S.; Tanaka, H. Development of indirect competitive ELISA for quantification of mitragynine in Kratom (Mitragyna speciosa (Roxb.) Korth.). Forensic Sci. Int. 2015, 244, 70–77. [Google Scholar] [CrossRef] [PubMed]
  110. Philipp, A.A.; Meyer, M.R.; Wissenbach, D.K.; Weber, A.A.; Zoerntlein, S.W.; Zweipfenning, P.G.M.; Maurer, H.H. Monitoring of kratom or Krypton intake in urine using GC-MS in clinical and forensic toxicology. Anal. Bioanal. Chem. 2011, 400, 127–135. [Google Scholar] [CrossRef] [PubMed]
  111. Mudge, E.M.; Brown, P.N. Determination of mitragynine in Mitragyna speciosa raw materials and finished products by liquid chromatography with UV detection: Single-laboratory validation. J. AOAC Int. 2017, 100, 18–24. [Google Scholar] [CrossRef] [PubMed]
  112. Orio, L.; Alexandru, L.; Cravotto, G.; Mantegna, S.; Barge, A. UAE, MAE, SFE-CO2 and classical methods for the extraction of Mitragyna speciosa leaves. Ultrason. Sonochem. 2012, 19, 591–595. [Google Scholar] [CrossRef] [PubMed]
  113. Le, D.; Goggin, M.M.; Janis, G.C. Analysis of Mitragynine and Metabolites in Human Urine for Detecting the Use of the Psychoactive Plant Kratom. J. Anal. Toxicol. 2012, 36, 616–625. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  114. Philipp, A.A.; Wissenbach, D.K.; Zoerntlein, S.W.; Klein, O.N.; Kanogsunthornrat, J.; Maurer, H.H. Studies on the metabolism of mitragynine, the main alkaloid of the herbal drug Kratom, in rat and human urine using liquid chromatography-linear ion trap mass spectrometry. J. Mass Spectrom. 2009, 44, 1249–1261. [Google Scholar] [CrossRef] [PubMed]
  115. Guddat, S.; Görgens, C.; Steinhart, V.; Schänzer, W.; Thevis, M. Mitragynine (Kratom)—Monitoring in sports drug testing. Drug Test. Anal. 2016, 8, 1114–1118. [Google Scholar] [CrossRef] [PubMed]
  116. Holler, J.M.; Vorce, S.P.; McDonough-Bender, P.C.; Magluilo, J.; Solomon, C.J.; Levine, B. A drug toxicity death involving propylhexedrine and mitragynine. J. Anal. Toxicol. 2011, 35, 54–59. [Google Scholar] [CrossRef] [PubMed]
  117. Lu, S.; Tran, B.N.; Nelsen, J.L.; Aldous, K.M. Quantitative analysis of mitragynine in human urine by high performance liquid chromatography-tandem mass spectrometry. J. Chromatogr. B Anal. Technol. Biomed. Life Sci. 2009, 877, 2499–2505. [Google Scholar] [CrossRef] [PubMed]
  118. Prutipanlai, S.; Botpiboon, O.; Janchawee, B.; Theanchaiwattana, S. Solid phase extraction method for determination of mitragynine in urine and its application to mitragynine excretion study in rats receiving caffeine. Trop. J. Pharm. Res. 2017, 16, 1675. [Google Scholar] [CrossRef] [Green Version]
  119. Neng, N.R.; Ahmad, S.M.; Gaspar, H.; Nogueira, J.M.F. Determination of mitragynine in urine matrices by bar adsorptive microextraction and HPLC analysis. Talanta 2015, 144, 105–109. [Google Scholar] [CrossRef] [PubMed]
  120. Basiliere, S.; Bryand, K.; Kerrigan, S. Identification of five Mitragyna alkaloids in urine using liquid chromatography-quadrupole/time of flight mass spectrometry. J. Chromatogr. B 2018, 1080, 11–19. [Google Scholar] [CrossRef] [PubMed]
  121. Janchawee, B.; Keawpradub, N.; Chittrakarn, S.; Prasettho, S.; Wararatananurak, P.; Sawangjareon, K. A high-performance liquid chromatographic method for determination of mitragynine in serum and its application to a pharmacokinetic study in rats. Biomed. Chromatogr. 2007, 183, 176–183. [Google Scholar] [CrossRef] [PubMed]
  122. Chittrakarn, S.; Penjamras, P.; Keawpradub, N. Quantitative analysis of mitragynine, codeine, caffeine, chlorpheniramine and phenylephrine in a kratom (Mitragyna speciosa Korth.) cocktail using high-performance liquid chromatography. Forensic Sci. Int. 2012, 217, 81–86. [Google Scholar] [CrossRef] [PubMed]
Figure 1. Structures of secondary metabolites: (A) mitragynine, (B) 7-hydroxymitragynine (7-HMG), (C) paynantheine (PAY), (D) speciogynine (SG) and (E) speciociliatine (SC).
Figure 1. Structures of secondary metabolites: (A) mitragynine, (B) 7-hydroxymitragynine (7-HMG), (C) paynantheine (PAY), (D) speciogynine (SG) and (E) speciociliatine (SC).
Medicines 06 00035 g001
Table 1. Analytical methods for the identification and/or quantification of Mitragyna speciosa in biological samples.
Table 1. Analytical methods for the identification and/or quantification of Mitragyna speciosa in biological samples.
CompoundsBiological Sample (amount)Analytical TechniqueInternal StandardExtraction ProcessLinear Range
(ng/mL)
LOD
(ng/mL)
LOQ
(ng/mL)
Recovery
(%)
Reference
Mitragynine,
7-hydroxymitraginine, speciogynine, speciocilliatine, and paynantheine
Urine
(1 mL)
LC–ESI–MS–QTOFmitragynine-d3
7-hydroxymitraginine-d3
Solid-phase extraction
(PolyChrom ClinII cartridges)
2–5000.25–10.5–196–63[120]
Mitragynine,
5-desmethylmitragynine and 17-desmethyldihydro-Mitragynine, and
7-hidroxymitragynine
Urine
(0.2 mL)
UHPLC–ESI/MS–MS
and LC–ESI/MS–MS
MitraphyllineEnzymatic hydrolysis and liquid-liquid extraction (methyl tert-butyl ether)1–500-1.0078–94[113]
MitragynineUrine
(1 mL)
HPLC–DAD-BAµE (N-vinylpyrrolidone polymer) and back-extraction with methanol/acetonitrile (1:1, v/v) under sonication0.6–240.10.33103[119]
MitragynineUrine
(1 mL)
LC–ESI–MS
(QTRAP)
methyltestosteroneEnzymatic hydrolysis and liquid-liquid extraction
(ethyl tert-butyl ether)
0.25–1.50.20.2583[115]
MitragyninePeripheral blood, central blood, liver, vitreous, gastric content, and urine
(1 mL)
GC–MS
(EI)
mitragynine-d3Solid-phase extraction
(Trace-J cartridges)
50–10003050-[45]
Mitragynine, paynantheine, speciogynine, speciociliatine, 16-carboxy-mitragynine, 9-O-demethyl-mitragynine, and 9-O-demethyl-16-carboxy-mitragynineUrine
(3 mL)
GC–MS
(EI)
-Enzymatic hydrolysis and solid-phase extraction
(HCX cartridge)
-100--[110]
MitragynineUrine
(2 mL)
LC–ESI/MS–MSAjmalicineLiquid extraction;
liquid-liquid extraction
(Methyl tert-butyl ether)
0.01–50.020.181[117]
MitragynineBlood and urine (1 mL), tissues (liver, kidney, heart, spleen, lung −1g), bile, and vitreous humorLC–ESI/MS–MSProadifenEnzymatic hydrolysis and liquid-liquid extraction
(n-butyl chloride)
1–100.251103[116]
MitragynineRat serum
(0.1 mL)
HPLC–UV
LC–ESI–MS
AcenaptheneLiquid–liquid extraction
(diethyl ether)
100–10,0003010085–84[121]
MitragynineRat plasma
(0.1 mL)
HPLC–UVMefloquineSolid-phase extraction
(MCX Oasis cartridges)
50–1000255096–98[33]
MitragynineRat and human urine
(1 mL)
HPLC–DAD-Solid-phase extraction
(Oasis® HLB cartridge)
100–10,000-10093–101[118]
Mitragynine and metabolitesRat and human urine
(1 mL)
LC–ESI.LIT and
LC–ESI.Orbitrap MS
-Enzymatic hydrolysis and solid-phase extraction
(Isolute Confirm HCX and Isolute Confirm C18 cartridges)
----[114]
BAµE: Bar adsorptive microextraction; DAD: Diode-array detection; EI: Electron ionization mode; ESI: Electrospray ionization; GC: Gas chromatography; HPLC: High-performance liquid chromatography; HPLC–UV: High-pressure liquid chromatography with ultraviolet detector; LC: Liquid chromatography; LD: Liquid desorption; LIT: Linear ion trap; MS: Mass spectrometry; LOQ: Limit of detection; LOQ: Limit of quantitation; MS/MS: Tandem mass spectrometry; MTBE: Methyl t-butyl ether; RP–HPLC: Reverse-phase high performance liquid chromatography; SIM: Selective ion mode; TBME: t-Butyl methyl ether; TOF: Time of flight; UHPLC: Ultra-high-performance liquid chromatography.
Table 2. Analytical methods for the identification and/or quantification of Mitragyna speciosa in leaves and plant material.
Table 2. Analytical methods for the identification and/or quantification of Mitragyna speciosa in leaves and plant material.
CompoundsSample (Amount)Analytical TechniqueExtractionLODLOQRecovery (%)Reference
Several secondary metabolitesMature leaves (100 mg)LC–ESI–TOF–MSIce cold methanol---[31]
MitragynineDried leaves (1.13 kg)icELISA and HPLC–DADMethanol maceration, acid-base extraction, and silica gel column chromatography32.47 μg/mL--[109]
MitragynineLeaves (5 kg)HPLC–DADMethanol maceration and liquid extraction (chloroform)0.25 μg/mL0.5 μg/mL95–101[107]
Ketum drink (1 mL)Direct injection
Mitragynine
7-OH mitragynine
Raw materials and powdered extracts (100 mg) and capsulesHPLC–UVFor dry test materials (0.5 M acetic acid in 70% methanol)
For beverages (dilution with methanol)
0.002% (w/w)0.006% (w/w)94–95[111]
Liquid finished products and/or beverages0.2 μg/mL0.6 μg/mL
7-hidroxymitragynineRaw materials, powdered extracts, and capsules0.004% (w/w)0.011% (w/w)96–99
Liquid finished products and/or beverages0.4 μg/mL1.1 μg/mL
MitragynineKetum cocktailHPLC–DADFreeze drying and reconstitution with methanol:water (80:20, v/v)1.000 μg/mL3.000 μg/mL95[122]
MitragynineDried plant material (2 g)TLC and HPLC–UVEthanol1 μg /mL--[106]
MitragynineKratom (powder or ground leaves material (100 mg); ¼ tea-spoon, liquid: 250 μL, capsule: 1)IMS and LC–MS/MSMethanol and ultrasonic bath sonication0.5 ng/μL--[108]
2000 μg/mL6000 μg/mL
Mitragynine,
7-hydroxymitragynine, and mitraphylline
(stereoisomers, mitraciliatine, speciogynine, speciociliatine)
Plant material as fresh leaves (1.0 cm × 0.5 cm)HR–DART–MSEthanol---[32]
DAD: Diode-array detection; DART: Direct analysis in real time; HPLC: High-performance liquid chromatography; HPLC–UV: High-pressure liquid chromatography with ultraviolet detector; HR: High resolution; icELISA: Indirect competitive enzyme-linked immunosorbent assay; IMS: Ion mobility spectrometry; LC: Liquid chromatography; LDA: Linear discriminant analysis; LOQ: Limit of detection; LOQ: Limit of quantitation; MS: Mass spectrometry; MS/MS: Tandem mass spectrometry; TLC: Thin layer chromatography; TOF: Time of flight.

Share and Cite

MDPI and ACS Style

Meireles, V.; Rosado, T.; Barroso, M.; Soares, S.; Gonçalves, J.; Luís, Â.; Caramelo, D.; Simão, A.Y.; Fernández, N.; Duarte, A.P.; et al. Mitragyna speciosa: Clinical, Toxicological Aspects and Analysis in Biological and Non-Biological Samples. Medicines 2019, 6, 35. https://doi.org/10.3390/medicines6010035

AMA Style

Meireles V, Rosado T, Barroso M, Soares S, Gonçalves J, Luís Â, Caramelo D, Simão AY, Fernández N, Duarte AP, et al. Mitragyna speciosa: Clinical, Toxicological Aspects and Analysis in Biological and Non-Biological Samples. Medicines. 2019; 6(1):35. https://doi.org/10.3390/medicines6010035

Chicago/Turabian Style

Meireles, Vânia, Tiago Rosado, Mário Barroso, Sofia Soares, Joana Gonçalves, Ângelo Luís, Débora Caramelo, Ana Y. Simão, Nicolás Fernández, Ana Paula Duarte, and et al. 2019. "Mitragyna speciosa: Clinical, Toxicological Aspects and Analysis in Biological and Non-Biological Samples" Medicines 6, no. 1: 35. https://doi.org/10.3390/medicines6010035

Note that from the first issue of 2016, this journal uses article numbers instead of page numbers. See further details here.

Article Metrics

Back to TopTop