Pistacia lentiscus: from phytopharmacology to scientific expla- nations on its anti-inflammatory and antimicrobial capacity

There is an increasing interest in revisiting plants for drug discovery proving scientifically their role as remedies. Pistacia lentiscus (PL) is a wild-growing shrub rich in terpenoids, which are pharmacological appealing. The more recurrent components in the oil are represented by α-pinene, terpinene, caryophyllene, limonene, and myrcene. High concentration of polyphenols enriches the extracts. PL-extracts showed in vitro and in animal model strong anti-inflammatory and anti-oxidative activities. The anti-inflammatory activity mainly occurs due to inhibition of NF-kB pathway or directly toward the proinflammatory cytokines, or arachidonic acid cascade against COX-2 and LOX. The antimicrobial activity of PL essential oil and extracts includes among others Staphylococcus aureus, Escherichia coli, periodontal bacteria and Candida sp.. In conclusion, the biological properties, and particularly the anti-inflammatory and anti-microbial capacity, propose PL as a new safe pharmaceutical agent.


Introduction
The undesirable side effects of antibiotics in addition to increasing microbial resistance have created a demand for new alternative molecules [1]. Also, non-steroidal antiinflammatory drugs (NSAIDs) or even steroids, often inducing toxic side-effects [2][3] have gained further interest in safe molecules presenting anti-inflammatory character [4].
On these bases, there is an increasing attention in revisiting plants for drug discovery proving scientifically their role as popular remedy to diseases.
The capacity of essential oils (EO) from plants is related to the presence of different chemical classes among which terpenoids, also called terpen or terpenes, are promising agents in prevention and treatments of diseases [5]. Terpenoids are pharmacologically versatile: they are lipophilic, interact with cell membranes, neuronal and muscle ion channels, neurotransmitter receptors, G-protein coupled receptors, second messenger systems and enzymes [6]. Terpenoid values, eventually potentiated by using nanotechnology [7][8], are attracting researchers to further explore them with the intent to improve human health.
In this contest, Pistacia lentiscus (PL) is a wild-growing shrub rich in terpenoids [9]. PL includes numerous wild and cultivated species, distributed in the Mediterranean and Middle Eastern areas. PL has been utilized for centuries by communities for social, culinary, and ritual purposes as well as for medicinal intent.
Despite the fact that many researches deeply documented the pharmaceutical properties of the resin (better known as mastic or mastix) derived from PL var. chia Desf. [10][11], scientific data regarding PL oil or extracts of leaves, fruits, and woods have been not summarized yet. Today, the scientific interest in these compounds is widespreading as some studies underlined the potential benefit in inflammation, infections, and human health in general [12][13][14][15].
Given the above considerations, the purpose of this review was to screen the biological properties of PL EO and extracts of leaves, fruits, and woods, which are widely applied in the Mediterranean ethnopharmacology. Further, we revised the chemistry of PL growing in the different geographical areas and the scientific discovering, emphasizing the anti-inflammatory and antimicrobial abilities.

Botany and taxonomy
PL belongs to the genus Pistacia and the Anacardiaceae family, order Sapindales. Different classifications have been proposed regarding Pistacia genus. One of the most known is that of Zohary [16], who classified such genus into four main groups according to the characteristics of the leaf and nut morphology (Table 1). Table 1 Taxonomy description of Pistacia genus (Zohary 1952) an important source to increase milk quality and dairy products from ruminants browsing Mediterranean maquis. [25].

Ethno-pharmacology
The ethnopharmacological survey on the medicinal use of PL is reported in Table 2. As previously referred, there are few written indications on the medicinal use of the oil as crude compound, or of the extracts as well. Drinking water extracts and topical application of the extracts or even whole parts of the plant (woods or leaves) have been the most common means in antagonizing gastrointestinal, hepatic, urinary, pulmonary and neurological diseases. In fact, the medicinal value of PL in popular medicine covers a wide range of diseases manly including inflammatory processes, and infections.
PL has been one of most used plants in Israeli and neighbouring countries traditional pharmacology [26]. In Jordan, it was commonly used to antagonize jaundice [27,28]. In Algeria, it is known as antimicrobial, antioxidant, hypotensive and hypoglycaemic agent [29,30]. In Morocco and Tunisia [31,32], PL has been largely used as a remedy against gastrointestinal, kidney and hepatic disorders, in addition to treat hypertension, diabetes, cardiac diseases, coughs, sore throats, and eczema. Similar applications are reported in Turkey [33] and in Iran [34,35]. While, in Tunisia, Spain, and in the centre of Italy, it has emerged as an agent against hypertension and heart diseases [31][32][33][34][35][36].
Sardinian population has always found the medicinal properties of PL really appealing. A large number of publications report PL oil and water extracts as useful means against a wide variety of inflammatory diseases, infections, allergies [9,22,[37][38][39][40], ulcerations [41], gastrointestinal disorders [42], and as wound healing [38,43,44]. It is further interesting to note that Sardinian population administrated PL as a smoke obtained by burning or boiling the soft wood and leaves, particularly in the cases of osteoarthritis, bronchitis and allergies [22].
In addition, PL is still used as a remedy toward toothache and gingival inflammation by administering extracts from the leaves as oral mouthwash, beverages or by directly chewing the soft stems and leaves [22]. Similar beneficial effects have been reported by using the plants growing in the Southern (Campania) [23] and in the centre of Italy (Abruzzo, Marche and Toscana), in Tunisia [45] and in Spain [46].
The reports suggest PL molecules spread the anti-inflammatory and then, the regenerative properties, via epidermis or mucosal epithelium by rapid metabolism and redistribution. These properties have been attributed to the high account of monoterpenoids [47][48][49][50][51]. In this contest, the lipophilicity and lower molecular weight of these molecules [52], are important parameters to make them effective also at the Central Nervous System (CNS). Lipophilicity, molecular size, and protein complex formation make terpenoids capable to the passage to the CNS, where they were not only able to antagonize the inflammatory process [13,53,54] but also demonstrated relevant anticancer properties in neuroblastoma cell lines [14,55].
Regarding the veterinary use, in Sardinia, domestic animals are still treated by PL wood to combat gastrointestinal disorders, and by swab bark in wound healing procedures and skin diseases [56]. While, in Spain, the leaves are mentioned to treat specifically canine distemper [57].
All these reports highlight the important biological activities of the terpens fingerprint of PL [58]. However, variability in the concentration of monoterpens, possible related to the growing area of the plant, might explain the better ability of some chemical profile of PL oil or extracts in treating a disorder in comparison to another.

Phytochemical constituents
PL is constituted by a mixture of terpenoids, mainly monoterpenes and sesquiterpenes, which are also responsible for the characteristic smelling and flavouring of the plant. Terpens family, also known as terpenoids or isoprenoids, comprises the most chemically and structurally heterogenous family of natural products, including more than 80.000 members among which steroids and carotenoids [59].
It has been reported that terpenes in PL are more genetically than environmentally related [60]. Nevertheless, environment of growing, seasonability of harvesting and kind of material (edible or not edible parts of the plant) have to be considered when explaining differences in chemistry of the oils and extracts [9] (Table 3).  α-pinene, α-thujene, camphene, sabinene, β-pinene, myrcene, α-phellandrene, α-terpinene, para-cymene, βphellandrene, trans-ocemene, γ-terpene, terpinolene, 2nonanone, linalool, isopentyl isovalerate, terpin-4-ol, αterpiniol, and others In Table 3, it is reported that hydro-distillation using Clevenger-type devices, and ethanol extraction have been the more common methods to obtain the oil from the leaves, fruits and from the exudate of the trunk (mastic). However, the oil obtained by hydrodistillation and the extracts by solvents can have different organoleptic profiles and chemical compositions. These differences in turn will affect some properties, among which the antimicrobial capacity that is reported higher in a material solvent extracted in comparison to the hydro-distilled [61]. Additionally, the gas chromatography-mass spectroscopy (GC/MS) and the high-performance liquid chromatography (HPLC) have been the most useful means to quantify phytochemically the oils and extracts respectively [62]. Up to 64 chemical constituents have been reported in PL EO fingerprint, in addition to other fractions that cannot be quantified by the assays [15]. Interestingly, some of these terpenoids are constituent fractions of Cannabis sativa [51], and called "non-cannabinoids terpenoids". In PL oil, non-cannabinoid terpenoids are more likely represented by αpinene, myrcene, limonene, (E)-β-caryophyllene and γ-terpinene (Table 3). They are also included in the list of "terpene super classes" [51]. Furthermore, it is appealing to report that when non-cannabinoid terpenoids reach a concentration equal or higher 0.05% in an oil, they can confer pharmacological properties to such an oil, which can be classified as pharmaceutical active [6].
In view of the prevalent fractions of monoterpenes and oxygenated sesquiterpenes, the EO can be grouped in different chemotypes [17]. In this regard, the recurrent higher amount of α-pinene (16.89-19.5%) and terpinen-4-ol (7.7-16.49%) in comparison to the other compounds, allowed to classify the oil from the leaves of PL growing in Sardinia as α-pinene/terpinen-4-ol chemotype [9,15]. Similarly, the Greek oil from PL leaves is αpinene/terpinen-4-ol chemotype [63]. Nevertheless, the simultaneous existence of different chemotypes in a place can be justified by dissimilar geographical sites of harvesting in that country. An example is represented by the Corsican chemotype, which is expressed by three main phenotypes: the first is α-pinene/terpinen-4-ol; the second is terpinen-4-ol/limonene; and the third is myrcene-rich (88%) [9]. Very characteristic is the high content of δ-3-carene (65%) in the Egyptian oil [64], while the monoterpen terpinen-4-ol, together with α-pinene and the sesquiterpene myrcene are among the higher represented fractions in the chemistry of PL EO from Spain, Morocco and Turkey [65][66][67]. Conversely, α-pinene (65 -86%) and β-myrcene (3%) are the major fractions to characterize the oils of mastic from plants growing in Spain [65]. And, the bioactive triterpenes are the most important compounds in such a resin with high role against the oxidative stress [68].
Further comprehensive studies have been conducted analysing methanol and alcohol extracts of PL leaves, at the same time investigating on the chemical profile and efficacy of the polyphenol content. In this regard, an interesting analysis was recently carried out by Romani and co-workers [69]. Using ethyl acetate and methanol fractions of PL leaves and semi-preparative HPLC, HPLC-photodiode array detection and HPLC-MS analysis, together with NMR analysis, the authors identified high polyphenol content in the extracts, which represented 7.5% of the leaf dry-weight. Further, three major classes of secondary metabolites were identified (i) gallic acid and galloyl derivatives of both glucose and quinic acid; (ii) flavonol glycosides, i.e. myricetin and quercetin glycosides; and (iii) anthocyanins, namely delphinidin 3-O-glucoside and cyanidin 3-O-glucoside. These findings suggest PL extracts as an important source of bio-molecules of relevant biological properties. Particularly, the high content of galloyl derivates, equal to 5.3% of the leaf dry-weight, was indicated for the high activity of PL to inhibit the HIV-1 lifecycle by targeting key HIV enzymes [70,71] and in cancer therapy [72]. Myricetin derivatives, which in the extracts were 1.5% on a dry weight basis, exhibited relevant pharmacological activities in regard to the generation of apoptosis in cancer cells [73,74]. Additionally, the HPLC with diode array coupled to an electrospray ionization mass spectrometry and the use of a negative ionization mode, recognized 46 different compounds in the methanol extracts of PL leaves from plants growing in Algeria [75]. Among the new 20 compounds characterized for the first time, there have been included important antioxidant agents in preventing diabetic complications, managing intestinal inflammatory response, cholesterol absorption and lipid metabolism. This further attests the precious value of PL as a nutraceutical in human health.
In respect to PL leaves oil, the fruits oil changes significantly its chemistry: limonene, sabinene, and myrcene have been dosed as the main representative fractions in addition to α-pinene [76]. Also, the oil from the berries is rich in anthocyanins, which confer high antioxidant ability to the material and induce autophagy, a self-degradative process that plays an important role in cell survival and maintenance [77].

Anti-inflammatory activity
As mentioned above among the ethnopharmaceutical indications, the anti-inflammatory effect of PL is of high importance. On this matter, many studies demonstrated the mechanisms by which PL modulates the immune-inflammatory cascade. With this purpose, the anti-inflammatory properties of the oil and extracts were tested toward the activity of pro-inflammatory cytokines, i.e. interleukin (IL)-1β, IL-6, and tumour necrosis factor-α (TNF-α). Also, the inhibitory capacity against the arachidonic acid cascade, particularly against cyclooxygenase (COXs) and lipoxygenase (LOXs) enzymes, by which derive accumulation of prostaglandins and leukotrienes, has been investigated. Furthermore, the protective effect of PL against reactive oxygen species (ROS) molecules has been largely proved. These evaluations have been conducted by means of in vitro and in vivo analysis both using the whole compounds or selective chemical fractions of PL EO or extract (Table 4).

Inhibitory activity against proinflammatory cytokines
Remila and co-workers [78] examined the anti-inflammatory activity of leaves and fruits extract by measuring the secretion of IL-1β by macrophages exposed to adenosin triphosphate (ATP) or H2O2. The authors found PL leaves extract significantly reduced the production of IL-1β from ATP or H2O2 activated cells. The inhibitory capacity of the leaves extract was higher in comparison to that of the fruits and of quercetin and gallic acid (tested as isolated fractions of the polyphenol mixture). The data was explained in the higher content of the total phenols and flavonoids in the leaves compared to the fruits and by synergy between the pharmacological terpenes of PL extract.
The anti-inflammatory efficacy was confirmed in rats model using the carrageenan induced paw edema and cotton pellet induced granuloma [41]. Particularly, it was evidenced that when applied topically, PL EO from leaves significantly inhibited the development of granuloma and the serum level of TNF-α and IL-6 in replay to the irritants. The result was mainly related to the activity of α-pinene, β-pinene, αphellandrene, and sabinene that were highly represented in the chemistry of that hydrodistilled oil.

Inhibitory activity against arachidonic acid cascade
Only one study has investigated the inhibitory activity of PL oil from leaves against COXs and LOXs [15]. The IC50 values was 10.3 ±4.4 μg/mL and 6.1 ±2.5 μg/mL PL EO for COX-1 and COX-2 respectively, with higher inhibitory activity toward COX-2 in comparison to that produced to COX-1. Also, COX-2 inhibition by the EO was similar to that recorded using Ibuprofen as a positive control. The activity of the oil against LOX did not reach the IC50 value, as PL EO lowered LOX activity by 30% compared to the control. Although the low LOX inhibition, the study strengthens the oil as a dual inhibitory potential compound, which was intensively researched in pharmacology to antagonize a great number of inflammatory processes where these enzymes sustain and amplify the disease [79,80]. The data obtained in that investigation were addressed to the mixture of terpenoids composing the oil with particular regard to α-pinene and terpinen-4-ol (33.38%), enriched by the non-cannabinoid terpenoid limonene (3.89%), β-myrcene (0.87%), (Z)caryophyllene (1.39%) and (E)-β-caryophyllene (0.07%). The mixture allowed to classify the oil as pharmacologically active [6].

Inhibiting activity against ROS molecules
The antioxidant potency of PL EO and extracts has been closely related to the richness in polyphenols, including tannins and flavonoids, sterols and monoterpenes [81,82]. Also, the high content in fatty acids, such as oleic acid and linoleic acid, increases the scavenging activity [12]. The protective effects of polyphenols have been connected to the capacity to transfer electrons to free radicals and chelate metal catalysts [83], to activate antioxidant enzymes [84], to reduce α -tocopherol radicals [85] and to inhibit known free radical producing enzymes, such as myeloperoxidase and NADPH oxidase [86], and xanthine oxidase [87]. Furthermore, flavonoids have demonstrated the capacity to inhibit LDL peroxidation with important cardioprotective effects [88]. Many studies focused to demonstrate these capacities.
Remila and co-workers [78] proved the high antioxidant capacity of PL leave extract using the oxygen radical absorbance capacity in macrophages, melanoma and mammary mouse cell lines. Furthermore, due to activation of apoptosis mechanisms, the extracts significantly inhibited the growth of melanoma cells. The data was related to the richness in phenolics, flavonoids and tannins in the extracts. Similar conclusions were obtained by Atmani [89], who examined hexane, and chloroform aqueous extracts of PL leaves by the highly concentrated flavonoids. In relation to the peak of hydroxyl groups, the aqueous formulations strongly inhibited lipid peroxidation. The mechanism was explained in the scavenging of peroxyl radicals by the extracts. Radicals play a role in development of cardiovascular disease and cancer. In this regard, it is particularly attractive the scavenger activity of gallic acid and galloylquinic derivatives, isolated from PL leaves. Notable, a progressive increase of the anti-radical activity associated with the number of galloyl groups in quinic acid was found [90]. Furthermore, all the tested metabolites strongly reduced the oxidation of low-density lipoproteins, thus strengthening the protection of PL against the lipid peroxidation.
Although having preventive capacity, a potential ability to halt or reverse oxidative stressrelated diseases has been endorsed to PL. In fact, the ability in fighting aggressive tumours, i.e. glioblastoma and neuro-blastoma [55], and other important tumour cell lines have been proved by in vitro studies [91][92][93].
Animal testing further explored the anti-ROS efficacy of PL derivates. Khedir and coworkers [94] determined the scavenger and anti-inflammatory activity of the fruits oil using the carrageenan-induced paw edema in rat model. In that study, PL oil demonstrated significant better anti-inflammatory activity with edema inhibition, in comparison to those produced by the control NADPH. Moreover, PL oil was able to increase the expression of superoxide dismutase, catalase, and glutathione peroxidase, which are released as a response to the oxidative stress in the inflamed tissue. The effects were interpreted as a consequence of the content of humulene, caryophyllene, and polyunsaturated fatty acid in the oil. Humulene and caryophyllene have been shown to inhibit the nuclear factor kappa B (NF-kB) pathway, responsible for the transcription of several proinflammatory cytokines, i.e. TNF-α, IL-1β, IL-6, and iNOS and COX-2 enzymes [95]. The polyunsaturated fatty acid in the oil might have partially replaced the arachidonic acid in the inflamed cell membranes [96], consequently lowering COX-2 production, the local inflammation and ROS generation.
Other in vivo studies demonstrated the administration of PL oil before the induction of the Bilateral Common Carotid Artery Occlusion followed by Reperfusion (BCCAO/R) is able to prevent the oxidative stress challenge in the nervous tissue due to the ischemic insult [13,97]. In the cerebral tissue, PL oil restored the membrane phospholipid DHA and decreased the activity of COX-2 enzyme. Also, PL oil increased the concentration of the anti-inflammatory endocannabinoid congeners palmitoylethanolamide (PEA) and oleoylethanolamide (OEA) [13]. The outcomes were related to the high presence of the phytocannabinoid (E)-β-caryophyllene, which worked synergistically with the other compounds in the oil expanding the levels of cannabinoid receptor type 2 (CB2) and PPAR-alpha receptors. Further researches attest the role of β-caryophyllene as CB2 agonists demonstrating its capacity to antagonize the release of cytokines from LPSstimulated monocytes (TNF-α and IL-1 β) [98,99].

Antimicrobial activity
Several studies reported about the antimicrobial activity of PL terpenes. Commonly studied pathogens comprise bacteria known for antibiotic resistance (Staphylococcus aureus incl. methicillin-resistant strains (MRSA), Escherichia coli, Pseudomonas aeruginosa), bacteria associated with oral diseases as well as yeasts with particular regard to Candida albicans (Table 5).  Although α-pinene together with the monoterpenes terpinene and myrcene are among the most represented fractions in the Mediterranean antimicrobial oils, (Table 5), it is of general interest if higher antimicrobial activity could be related to specific PL chemotypes [100]. In this contest, as just reported regarding the anti-inflammatory capacity, synergy between chemical fractions are proposed to explain PL antimicrobial activities.
Synergy was recently claimed to discuss the inhibitory activity of the EO against Porphyromonas gingivalis, Tannerella forsythia as laboratory as clinical isolate sp. and Fusobacterium nucleatum [15] (Milia et al 2020). In particular, the MIC of such PL EO against P. gingivalis, and T. forsythia was 3.13 mg/mL. The result was related to the pharmacological interplay of the terpenes characterizing the oil chemotype from North Sardinia, which was α-pinene-terpinen-4-ol, further augmented by the non-cannabinoid terpenoids limonene and β-myrcene, the sesquiterpenes (Z)-caryophyllene and (E)-βcaryophyllene. Interestingly, using the MTT assay, that study also documented an increase in viability of fibroblasts in the presence of the EO, together with good biocompatibility to oral fibroblasts and keratinocytes. All these reports remark the extraordinary biological character of PL EO.
Synergy between the polyphenols composing the extracts is also claimed explaining their antimicrobial potency [24,29,30,101]. This is the case of the ethanol extract of fruits, which showed the higher inhibition potential against P. gingivalis in comparison to other 20 extracts of pharmaceutical plants [101]. Furthermore, the potency of the fruits extract resulted higher than that of the leaves and woody parts, with MIC values against P. gingivalis of 8 μg/mL. Additionally, the selective index (SI) of cytotoxicity to human gingival cells was >256, meaning that all the agents have therapeutic benefit with no toxicity.
Recently, Mandrone and co-workers [102] related the antimicrobial activity of aqueous MeOH extracts of fruits and leaves to the concentration of phenolic components. That research further attests the high potential of the extracts against multi-resistant bacteria among which MRSA, and carbapenemase-producing Klebsiella pneumoniae.
Concerning Candida sp., the activity of PL derivates is reported very controversial (Table  5). Low or any sensitivity of the yeast to the leaves and or aerial parts, or to the fruits oil was often found. Despite this, PL leaves oil from Sardinian biodiversity produced low MIC values against the yeasts, ranging from 6.25 mg/mL for C. glabrata to 12.5 mg/mL for C. albicans [15]. The results were explained in a consequence of the recurrence of pharmacological concentrations of six terpenes, which were above 0.05% in the fingerprint. Also, the EO documented the ability to inhibit COX-2 and LOX, which are very important proteins to the development of Candida virulence.
Further high inhibition of C. albicans was reported using PL extracts. The activity of water or ethanol extracts has been attributed to the flavonoid contents. Noteworthy, the phenolic compound tannic acid was reported as more active against the yeast than the antifungals nystatin and amphotericin [101].

Summary and conclusion
In this review, we summarized the existing knowledge about PL phytochemistry and some of its biological activities mainly focusing to its anti-inflammatory and antimicrobial capacity.
The chemistry shows that PL EO is composed of up to 64 molecules, while till 46 constituents are present in the extracts. Further minor fractions have been indicated in the reports even if they could not be quantified. The more recurrent chemical components in the plants growing in the Mediterranean area are represented by α-pinene, terpinenes, caryophyllene, limonene, and myrcene. Important properties in antagonizing immunemediated and autoimmunity, neuroinflammatory, neurological, and neurodegenerative diseases, in addition to infections and cancer are attributed to these molecules. Nevertheless, the biological character of PL cannot be addressed to only one of the main concentrated molecules. The abilities should be referred to the mixture of the whole terpenes working in synergy or in addition independently by their concentration in the agent. It is remarkable to note that concentrations of non-cannabinoid terpenoids equal or above 0.05% increase the pharmacological potency of PL oil. Regarding the extract, the high polyphenol content is attracting in prevention, and in therapy of chronic illness and infections.
Regarding the anti-inflammatory capacity, PL EO and extracts are able to inhibit the proinflammatory cytokines IL-1β, IL-6, and TNF-α. Also, it was highlighted the capacity to adverse the arachidonic acid cascade particularly antagonizing COX-2, enzyme and then the first phase of the active inflammation by the inhibition of prostaglandins. The potential LOX inhibitory capacity could propose PL as a COX-2-LOX dual inhibitory natural compound, which might have potential against inflammation and the consequent tissue damage.
Among the non-cannabinoid terpenoid fractions, (E)-β-caryophyllene has been endorsed to the anti-inflammatory activity of the oil. Interestingly, the molecule has strong affinity to CB2, where it inhibits the release of cytokines from LPS-stimulated monocytes, such as TNF-α and IL-1 β expression. Furthermore, studies in experimental animals have proved the important role of (E)-β-caryophyllene in preventing ischemic/reperfusion oxidative injury when the oil was administered as a dietary assumption. In this contest, studies strengthened the adjuvant capacity of α-pinene merging in addition to caryophyllene, in PL oils by the high anti-inflammatory properties. Conversely, in addition the noncannabinoid myrcene, caryophyllene contributed to inhibit nitric oxide production, IL-1βinduced iNOS mRNA, NF-kB and other catabolic and inflammatory mediators being of importance in rheumatoid arthritis.
The high anti-oxidant property of the extracts is impressive in the studies. Animal testing further supports the in vitro anti-ROS potency of PL with a higher efficacy in comparison to NADPHs. The ability is attributed to the richness in polyphenols, including tannins and flavonoids, sterols and monoterpenes. Notable, the aqueous formulations showed greater capacity in inhibiting lipid peroxidation compared to other extracts. The mechanism is explained in scavenging of peroxyl radicals, which suggests PL to be preventive of cardiovascular disease and cancer. In this matter, the non-cannabinoid limonene may play a relevant role in oxidative stress-related diseases by inhibiting proinflammatory mediator, leukocyte migration, and vascular permeability.
In regard to the antimicrobial activity, the capacity of the oil and extracts against periodontal bacteria has been documented. This evidence can justify the popular use of PL in the case of gingival bleeding and tooth ache. This ability, further ameliorated by the anti-inflammatory potency, is attractive to a possible use of the EO to antagonize gingivitis, as a primary strategy to prevent periodontitis, and a secondary preventive strategy to recurrent periodontitis after periodontal surgery. The possibility to formulate PL as a potential oral health care product or therapeutic in periodontal disease is also based on the documented biocompatibility to oral fibroblasts and keratinocytes.
Other important considerations concern the activity of PL against Candida infections. PL inhibits the growth of C. albicans and C. glabrata with low MICs. In addition, the prevention of arachidonic acid oxidation by COX-2 and LOX antagonism by PL oil is of interest as this may inhibit the development of biofilm and disseminations. Following, PL could act directly against the yeast and indirectly against its virulence, with no oral cytotoxicity.
All the above considerations can propose PL as nutraceutical and therapeutic agent by the high capacity against a wide range of diseases based on inflammation and infections.
Conflicts of Interest: The authors declare no conflict of interest.