A Comprehensive Review on the Phytochemical Constituents and Pharmacological Activities of Pogostemon cablin Benth.: An Aromatic Medicinal Plant of Industrial Importance

Pogostemon cablin Benth. (patchouli) is an important herb which possesses many therapeutic properties and is widely used in the fragrance industries. In traditional medicinal practices, it is used to treat colds, headaches, fever, nausea, vomiting, diarrhea, abdominal pain, insect and snake bites. In aromatherapy, patchouli oil is used to relieve depression, stress, calm nerves, control appetite and to improve sexual interest. Till now more than 140 compounds, including terpenoids, phytosterols, flavonoids, organic acids, lignins, alkaloids, glycosides, alcohols, aldehydes have been isolated and identified from patchouli. The main phytochemical compounds are patchouli alcohol, α-patchoulene, β-patchoulene, α-bulnesene, seychellene, norpatchoulenol, pogostone, eugenol and pogostol. Modern studies have revealed several biological activities such as antioxidant, analgesic, anti-inflammatory, antiplatelet, antithrombotic, aphrodisiac, antidepressant, antimutagenic, antiemetic, fibrinolytic and cytotoxic activities. However, some of the traditional uses need to be verified and may require standardizing and authenticating the bioactivity of purified compounds through scientific methods. The aim of the present review is to provide comprehensive knowledge on the phytochemistry and pharmacological activities of essential oil and different plant extracts of patchouli based on the available scientific literature. This information will provide a potential guide in exploring the use of main active compounds of patchouli in various medical fields.

A major constituent obtained from the leaves of P. cablin is the essential oil (patchouli oil) which possesses many pharmacological properties. The curative action of patchouli oil is directly related to its qualitative as well as quantitative chemical constituents. The known volatile chemical components of patchouli oil are presented in Table 1, while the structures of some major and important compounds are depicted in Figure 1. Generally, steam or fractional distillation is used to obtain patchouli oil [23,24], although these processes cause the thermal degradation of a few of the chemical constituents present in the oil. Therefore, Donelian et al. [25] established the supercritical carbon dioxide extraction method to obtain the maximum yield of patchouli oil with better extraction quality. Molecular distillation has also been reported by Hu et al. and Chen et al. [26,27]. However, microwave assisted extraction using ethanol as solvent improves oil extraction compared to other conventional methods as it employs a precise computer controlled high temperature in a closed vessel equipped with a magnetic stirrer [28].
Patchouli oil is rich in sesquiterpenes, mainly the patchouli alcohol (patchoulol), a tricyclic sesquiterpene which is widely used in perfumery products, soaps and other cosmetic goods [29]. Patchoulenes, guaiene, seychellene are few other sesquiterpene hydrocarbons also characterize the aroma of patchouli oil. According to many researchers, patchoulol and α-patchoulene are the major constituents which regulate and control patchouli oil quality [25,29,30]. Several other minor sesquiterpenes, caryophyllene, pogostol, α-, β-, γ-and δ-patchoulene, seychellene, cycloseychellene, α-and β-bulnesene, α-and β-guaiene and norpatchoulenol are also reported in patchouli oil [31,32]. The biological activities of patchouli oil are strongly associated with the chemical constituents such as pogostone, patchoulol, α-and β-patchoulene. Previous studies have stated that pogostone as one of the major chemical constituent of patchouli oil largely responsible for the intense aromatic odor and more recently this compound has been demonstrated to exert many pharmaceutical activities [33][34][35]. Later on, the chemical structure of pogostone present in the patchouli oil was revealed by Zheng et al. [36].
The chemical composition of patchouli oil varies among samples collected from different geographic locations. Li et al. [52] revealed the significant effect of different habitats, collection periods, and processing methods on the volatile oil yield and its main constituents. Similarly, the oil yield is also influenced by different collection times. It is reported that contents of volatile oil obtained from leaves harvested from June to August and cultivated in Hainan, China were 0.8%, 0.7% and 0.6%, respectively, while the patchouli alcohol content was highest in the month of June [53]. Gas chromatography (GC), Gas chromatography/mass spectroscopy (GC/MS) and nuclear magnetic resonance (NMR) were used for studying the chemical composition of patchouli oil from Vietnam. The major compounds identified were α-, β-and δ-patchoulene, β-elemene, β-caryophyllene, α-and δ-guaiene, seychellene, α-bulnesene, δ-cardinene, pogostol and patchouli alcohol. The presence of 32%-37% patchouli alcohol content was found to be more odor intensive component of the essential oil [41]. However, in the Philippines, it was predicted that a distinct aroma is due to the occurrence of germacrene-B, a new sesquiterpene identified as the major component of the patchouli oil [11]. Later, Rakotonirainy et al. [42] used 1-and 2-dimensional NMR and GC/MS to derive the structural formulae of the compounds, including α-patchoulene, α-bulnesene, α-guaiene, and seychellene.

Antibacterial Activities
In traditional medicine, patchouli plants are used for treating common cold and fungal infections [67]. Among 10 essential oils studied for antibacterial and antifungal activity, patchouli oil was found to be more effective in inhibiting 20 bacterial strains and all 12 fungi [68]. The essential oils of P. cablin from three different geographic regions (China, India and Indonesia) were assessed in vitro against 17 pathogenic fungi and 16 commensal bacteria (from the skin, mucous membrane, nail, foot and armpit). The results revealed a clear antifungal and antibacterial activity of patchouli oil [69]. The essential oil of patchouli was effective in inhibiting Acenitobacter baumanii, Aeromonas veronii, Candida albicans, Enterococcus faecalis, Escherichia coli, Klebsiella pneumonia, Pseudomonas aeruginosa, Salmonella enteric and Staphyllococcus aureus [70]. Patchouli oil, tea tree oil, geranium oil, lavender oils and Citricidal TM (seed extract of grapefruit) were used against bacteria. They also used patchouli oil for treating epidemic methicillin-resistant S. aureus infection and when compared to a blend of β-sitosterol and stigmasterol and 7,3ʹ,4-tri-O-methyleriodictyol, patchoulol and hexane extract of dried patchouli leaves evidenced higher antibacterial activity against Staphylococcus aureus and Bacillus subtilis [60,71]. The antimicrobial activity of patchouli oil was studied by using molecular docking technology and in vitro antimicrobial assay [72]. The study confirmed the strong antimicrobial effects. Mainly the constituents, pogostone and (−)-patchoulol had broader therapeutic prospects in bacterial infection. The aqueous and organic extracts of patchouli and geranium leaves showed significant antimicrobial properties against E. coli, B. subtilis, S. aureus and E. aerogenes [73]. Patchouli oil was effective in preventing biofilm formation by food borne pathogens, Staphylococcus aureus [74]. In recent times, green synthesis of nanoparticles was performed by using the essential oils of vanilla, patchouli and ylang-ylang. These nanobiosystems were very effective against adherence and biofilm formation by clinical strains of Staphylococcus aureus and Klebsiella pneumonia [75]. Patchouli oil also exhibited antimicrobial activity against the isolated enteric bacteria from common house lizard faecal droppings [76]. Selective antibacterial activity against Helicobacter pylori was exhibited by patchoulol without affecting the normal flora of the gastrointestinal tract. Patchoulol also possessed urease inhibitory potential and thus it can be used as a promising biomolecule to cure H. pylori infections [77]. The gram-positive bacteria such as Staphylococcus, Bacillus, and Streptococcus species were successfully inhibited by using patchouli oil [78].

Antifungal Activities
The medium having 100 µg/mL of an oil mixture (lemongrass, thyme, patchouli and cedarwood oils inhibited mycelial growth of C. albicans [79]. Patchouli alcohol (44.52%) of the plant essential oil showed antifungal activity against a population of Aspergillus species [80]. The potential of pogostone, a natural product from P. cablin effective in treatment of Candida infections, particularly for vulvovaginal candidiasis, was evidenced by Li et al. [34]. Similarly, patchouli oil effectively inhibited C. albicans [81]. Further, pogostone and its synthesized analogues showed effective activities against Gram-positive, Gram-negative bacteria and C. albicans. Based on molecular docking studies, it was suggestd that a promising antifungal agent can be obtained by appropriate structural modifications of pogostone analogues [33].

Antiviral Activities
Traditional medicines from herbs, including patchouli were screened for ant-influenza viral activity. It was shown that about 10 μg/mL concentration of methanol extract of patchouli leaves could inhibit influenza virus A/PR/8/34 (H1N1) up to 99.8% and the IC50 values was estimated to be 2.6 μM [82]. Similarly, the results presented by Wu et al. [83] suggested anti-influenza A (H2N2) viral activities of patchoulol with an IC50 of 4.0 μM and thus making it a potent anti-influenza viral agent to be used by pharma industries. The in vivo anti-influenza virus effect of patchouli alcohol was studied using mouse as a model and the study confirmed that oral administration of patchouli alcohol (20 mg/kg to 80 mg/kg) augmented protection against influenza virus infection by improving the immune response and attenuating systemic as well as pulmonary inflammatory responses [84]. More recently, Wu et al. [85] observed anti-influenza viral properties using patchoulol (10 μg/mL) under in vitro condition and found that patchoulol enhanced the ability of innate immune recognition and response, and restrained the expression of IFN-α inflammatory factor to attenuate the inflammatory responses.

Treatment of HIV/AIDS and Opportunistic Infections
In French hospitals, essential oils were used as suitable antimicrobial agents to treat specific opportunistic infections caused by Candida albicans, Cryptococcus neoformans, methicillin-resistant Staphylococcus aureus and Herpes simplex type I and II found in Acquired Immunodeficiency Syndrome patients [86].

Gastrointestinal Protective Activity
Water extract of P. cablin was shown to protect and maintain the membrane fluidity of intestinal epithelial cells by regulating the levels of nitric oxide and tumor necrosis factor in serum. This study provides an experimental basis for gastrointestinal protection against trauma or surgical operation [87].

Defaecation and Constipation
Mikuriya et al. [89] carried out an experiment to study the influence of patchouli oil on defecation and constipation using two mouse models; one having flaccid constipation and other with constipation because of lower fibrous food intake. It was found that in both models the number of faeces and its dry weight increased after smelling the patchouli oil aroma. Also, it was proved that olfactory neurotransmission systems responsible for overcoming constipation in mice.

Blood Coagulation and Fibrinolytic Activities
Blood coagulation and fibrinolytic activity of various essential oils including patchouli was studied using in vitro enzymatic reactions such as fibrin formation from fibrinogen by thrombin and fibrin resolution by urokinase. The study revealed that both coagulation and fibrinolytic activities were demonstrated by chamomile, eucalyptus and neroli oils while an efficient hyperfibrinolysis was revealed by the oils of citrus, pine, patchouli and frankincense [90].

Antithrombotic Activities
Park et al. [91] have examined in vitro, ex vitro and in vivo use of the herbal medicine Sunghyangjunggisan and its ingredients (P. cablin, Perilla frutescens, Arisaema amurensa, Aucklandia lappa, Atractylodes macrocephala, Citrus unshiu, and Ziziphus jujuba) as a novel antithrombotic agent. In vitro adenosine 5ʹ-diphosphate (ADP) and collagen induced rat platelet aggregations were not inhibited by Sunghyangjunggisan. However, Sunghyangjunggisan significantly inhibited ex vitro rat platelet aggregation. It also showed significant protection from death due to pulmonary thrombosis in mice.

Antioxidant Activities
Patchouli oil showed an efficient free radical scavenging activity and inhibited the oxidation of hexanal to hexanoic acid [92]. Reactive oxygen species induced brain cell injury can be treated by using patchouli herb [93]. P. cablin protected from cell death due to necrosis and apoptosis induced by hydrogen peroxide in human neuroglioma cell line A172, thus suggesting its use for treating many neurodegenerative disorders. Patchouli oil prevented photoaging by exhibiting antioxidative property and maintained skin structural integrity caused by UV irradiation [94]. Similarly, the use of patchoulol increased the revitalization of UV-induced skin lesions through antioxidant and anti-inflammatory actions together with down-regulating the expression of matrix metalloproteinases (MMP-1 and MMP-3) [95]. Lipopolysaccharides present on the outer membrane of Gram-negative bacteria are responsible for causing mastitis and the study conducted by Li et al. [96] showed that patchouli alcohol was efficient in inhibiting TNF-α, IL-6, and IL-1β productions. It was also observed that patchouli alcohol attenuated mammary histopathologic changes, therefore patchouli alcohol can be used as a potent therapeutic reagent for preventing mastitis.

Analgesic and Anti-Inflammatory Activities
The methanol extract of patchouli plants was demonstrated to have analgesic and anti-inflammatory activity in mice. This validates the good acceptance of the patchouli herb in traditional medicinal practices [97]. Results of an analgesic study indicated that acetic acid induced writhing responses were decreased by using methanol extracts of patchouli (1.0 g/kg). The extracts of Chrysanthemum indicum, P. cablin and Curcuma wenyujin herbs, the components of the traditional medication recipe CPZ used in China, exhibited a strong anti-inflammatory response by regulating interleukin-1β (IL-1β) and prostaglandin E(2). Likewise, patchoulol effectively regulated the expression of TNF-α, IL-1β, IL-6, iNOS and COX-2 mRNAs in RAW264.7 cells due lipopolysaccharide induced inflammation [98]. Similarly, patchouli oil and ethanol extract of its root and rhizome exhibited strong in vivo anti-inflammatory properties [99,100]. The mechanism involved in anti-inflammatory property of patchoulol was investigated in mouse macrophage and human colorectal cancer cells [101]. More recently, Li et al. [35] revealed that pogostone possessed anti-inflammatory effect and suggested its use for development of a pharmaceutical drug to treat septic shock. Water extracts of patchouli herb suppressed colon inflammation through suppressing the expression of pro-inflammatory cytokines [102].

Effects on Tumors/Cancer Cells and the Immune System
The compounds 5,7-dihydroxy-3ʹ,4ʹ-dimethoxyflavanone, ombuin and licochalcone A were shown to exhibit cytotoxicity. The compound, licochalcone A showed PI-PLC gamma 1 inhibition activity. When licochalcone A was applied to promyelocyti leukaemia cells (HL-60), terminal differentiation along with the production of monocytes was observed [56]. However, patchoulol inhibited HeLa cell proliferation, suppressed cell differentiation and enhanced apoptosis in human colorectal cancer cell lines, HCT116 and SW480 [104,105]. According to these authors, patchouli alcohol inhibited histone deacetylase 2 expressions and histone deacetylase enzyme activity, down regulating c-myc and activating NF-κB pathway. A patchouli sesquiterpenoid, α-bulnesene was effective in inhibiting platelet-activating factor [106]. Anti-platelet activity was due to induction of intracellular signal transduction by α-bulnesene which interferes with activities of cyclooxygenase resulting in decreased thromboxane production. Now α-bulnesene is considered as a potent anti-platelet aggregation agent. The investigation on immunomodulatory potential of patchouli alcohol in Kumming mice revealed that patchouli alcohol activates the mononuclear phagocytic system and improves humoral immune response by suppressing the cellular immune response [107]. Xinxiang granule (XXG) is prepared from Biond magnolia flowers (Magnolia biondii), patchouli herb and small centipeda herb (Centipeda minima) and is used to treat allergic rhinitis and passive skin irritability [108]. Recently, the potential uses of patchouli oil for its antinociceptive and anti-allergic activities were confirmed in mouse models [109].

Effects against Skin Diseases
The essential oils, including patchouli oil at 12% concentration, effectively controlled skin infections and odor in patients suffering ulcers, torn skin, skin abrasions and pressure sores. The healing duration was considerably reduced by the use of essential oils [110]. The structural integrity of UV irradiated skin was maintained by the application of patchouli essential oil and prevented photoaging and increased revival of skin lesions [97,98].

Pharmacokintetic Activities
A simple and sensitive liquid chromatography tandem mass spectroscopy (LC-MS) method was developed to analyze pogostone in the plasma of rat after intravenous and oral administration [111]. This method is useful in pharmacokinetic studies of preclinical investigations. Lately, Li et al. [112] investigated the metabolic profile of pogostone in vitro and in vivo using LC-MS. Patchouli oil exhibited significant gastroprotective effects against gastric ulceration. According to them, the possible mechanism of anti-ulcerogenic potential of patchouli oil might be due to stimulation of COX-mediated PGE2, improvement of antioxidant and anti-inflammatory status, preservation of GBF and NP-SH, as well as boost of gastric mucus production [113].

Insecticidal Activity
Cymbopogon nardus and P. cablin leaf ashes at 1% (w/w) each caused pest mortality and were found to be effective repellents against Stegobium paniceum with 78% and a 64% repellency, respectively [114]. High fumigation insecticidal activity against four museum insect pests (Lasioderma serricorne, Sitophilus zeamais, Tribolium confusum and Falsogastrallus sauteri) by geranium oil, spikenard oil, muskmelon oil and patchouli oil was reported by Chun et al. [115]. Both patchouli oil and its main constituent, patchoulol showed toxicity and repellency towards Formosan subterranean termites (Coptotermes formosanus Shiraki). Topical application of patchoulol to the dorsum portion showed unusual tissue damage inside the exoskeleton of the termite [116]. Similarly, insecticidal activity against Trypanosoma cruzi was exhibited by the sesquiterpene hydroperoxides such as 10 α-hydroperoxyguaia-1,11-diene, 1α-hydroperoxyguaia-10(15),11-diene and 15α-hydroperoxyguaia-1(10),11-diene [65]. Thirty eight essential oils were screened against the mosquito under laboratory conditions using human subjects. From the report it was noticed that the use of undiluted Patchouli oil was effective in providing two hours of complete mosquito repellency [117].
An eco-friendly, biodegradable insecticidal agent, consisting of petroleum ether extracts of C. cassia, P. cablin and E. caryophyllata can be used to control the house dust mite (Dermatophagoides farina) [118]. Patchouli oil showed strong repellency to three species of urban ants and possessed strong bio-insecticidal activity and particularly, patchouli alcohol had the most effective repellent activity against Ades aegypti, Anopheles stephensi and Culex quinquefasciatus mosquito bites [119,120]. Likewise, Phal et al. [121] evaluated herbal mosquito coils against Aedes aegypti mosquito and found a combination of patchouli and valamus (75:25) exhibiting significant knockdown activity at 7.5% concentration with all the coils (rice husk, corn cob and sawdust-based coils). In recent times, strong larvicidal activity, antifeedant activity, pupicidal activity and growth inhibition property were exhibited by progostone against Spodoptera litura and Spodoptera exigua thus making it a promising candidate to control various insects which destroy agricultural plants [122].

Aromatherapy
In aromatherapy, patchouli oil is used to help reduce tension, insomnia and anxiety. It's wine-like intoxicating aroma functions as an aphrodisiac and helps to sharpen intelligence, improve concentration, and provide insight. Spiritually, it is used in incense sticks as it helps to create a calming atmosphere. In normal adult subjects, the fragrance inhalation effects on sympathetic activities was studied by measuring the amount of catecholamine content in the serum and monitoring fluctuations in blood pressure. There was a decreased sympathetic activity after inhalation of fragrance in normal subjects [123]. Aqueous cream containing lavender oil, sweet marjoram oil, patchouli oil and vetiver oil was applied five times a day onto the bodies and limbs of care facility residents and the results indicated a decreased frequency of dementia-associated behavior. Mental alertness and awareness in participants was improved by the use oils. The problems related to stress due to exhaustion and anxiety can be addressed by using essential oils as they stimulate adrenal hormone secretion [124]. The anti-inflammatory and cooling oils such as P. cablin and Citrus limonum were used for treating symptoms of menopause such as hot flashes and sweating. An aromatherapy oil blend of patchouli, with jasmine, ylang-ylang, sandalwood, rose and vetiver can definitely inspire clarity and a harmonious flow of energy that interacts with thyroid glands and balances hormonal secretion [125]. Various psychiatric disorders can be treated by aromatherapy. Patchouli oil influences cerebral functions including calming, sedative and uplifting [126]. The vaporized mixtures of essential oils (patchouli, orange, ylang ylang, rosemary, basil, peppermint, geranium, bergamot, rosewood, chamomile and jasmine) reduced disturbed behavior among 10 patients with dementia [127]. The physiological responses such as blood pressure, pulse rate, stress index and brain waves were reduced after sniffing patchouli oil odor. This suggests that patchouli oil odor improves mood and possess curative effects when its fragrance is inhaled by humans. The influence of odor was due to its main compound, patchouli alcohol [128]. Aromatherapy (inhalation, compresses, baths and massages) can help to manage stress and reduce perceptions of chronic pain [86].

Conclusions and Recommendations
P. cablin is being explored globally to obtain key chemical compounds for making new drug molecules with great therapeutic potential as well as in the fragrance industry. This review summarizes the updated research studies on the phytochemisty and pharmacological effects of P. cablin. The present information helps in bridging the gap between modern scientific studies and available traditional medical reports on this plant. As chemical constituents of P. cablin vary depending on the origin and plant parts, a protocol needs to be standardized to isolate and obtain pure compounds.
Though various chemical compounds have been isolated, purified and characterized, many compounds are yet to be studied in detail. Till now, limited efforts are made in the pharmacokinetics investigations related to the mechanism of action of the individual isolated compounds under in vivo conditions. Also, research should be emphasized on the toxicity and safety aspects of P. cablin compounds using animal models. Further, therapeutic prospects of many new chemical compounds from P. cablin under in vitro and in vivo conditions should be explored in detail.