Cymbopogon essential oils

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International Journal of Essential Oil Therapeutics (2009) 3, 56-65

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International Journal of

Essential Oil Therapeutics

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www.ijeot.com

Cymbopogon essential oils: Chemical compositions and bioactivities D. Ganjewala Plant Biotechnology Division, School of Biosciences and Technology, Vellore Institute of Technology (VIT) University, Vellore-632 014,Tamil Nadu, India Abstract The genus Cymbopogon (Poaceae) is most important from the point of view of their essential oils. Essential oils from these species are widely used in flavours, fragrances, cosmetics, soaps, detergents and perfumery owing to their typical lemon and rose-like aroma. Cymbopogon essential oils and constituents present therein e.g. citral, geraniol, citronellol, citronellal and piperitone, have been known to possess impressive antibacterial, antifungal, antiyeast, insecticidal and insect repellent activities for a long time. However, the biological and pharmacological significance of these essential oils has been rapidly expanded in the past ten years; anti-inflammatory, anticancer, allelopathic, free radical scavanging and other useful biological activities have now been demonstrated. Cymbopogon essential oils and constituents offer outstanding biological activities and therefore may be used in the treatment of several diseases, including cancers, and in applications of industrial importance particularly food packaging. The present review discusses the chemical compositions and biological activities essential oils from Cymbopogon species and emphasizing mechanisms of action. These details were gathered from reports on the bioactivities of essential oils of Cymbopogon species published during 1999-2009. Keywords: allelopathic, anticancer, anti-inflammatory, antioxidant, Cymbopogon species, essential oil, isointermedeol Introduction The genus Cymbopogon (Poaceae) is renowned for their essential oils of immense commercial significance in flavours, fragrances, cosmetics, perfumery, soaps, detergents and pharmaceuticals [1]. The genus comprises of about 140 species of which most are aromatic and yield an essential oil upon the steam distillation of their aerial parts [2]. Some most important species of this genus are: • Cymbopogon flexuosus Stapf. (East Indian lemongrass) • Cymbopogon citratus DC Stapf. (West Indian lemongrass) • Cymbopogon nardus (L) • Cymbopogon winterianus Jowitt (citronella) • Cymbopogon martinii Roxb. (palmarosa) • C. nardus x C. jwarancusa (jamarosa hybrid ) [3]. Essential oils from Cymbopogon species of diverse origin * Corresponding author. E-mail address: [email protected] © Essential Oil Resource Consultants. All rights reserved.

have been studied extensively, both previously and currently [1-9]. The essential oils of Cymbopogon species mainly consist of the monoterpene fractions. Several reports published earlier have revealed the presence of citral (a mixture of geranial and neral), geraniol, citronellol, citronellal, linalool, elemol, 1,8-cineole, limonene, geraniol, β-caryophyllene, methyl heptenone, geranyl acetate and geranyl formate in the essential oils of different species with marked variations have been reported. Also, the essential oil components are greatly influenced by genetic, environmental and geographical conditions [1-3]. The essential oils in Cymbopogon species are biosynthesized in the rapidly growing leaves and stored in specific oil cells in the parenchymal tissues [10,11]. For many years lemongrass (C. flexuosus) has been used as a culinary flavouring in Asia. The leaves are cooked with foods, especially curries, and the peeled stems are available in local markets. Fresh leaves crushed in water are used as hair wash and toilet water in India. Beside their traditional uses, studies aimed to evaluate the biological activities of the essential oils and constituents of Cymbopogon species


have revealed their usefulness. Perhaps their significance has been best realized in the past ten years. Studies have revealed many useful biological activities of the essential oils and essential oil constituents of Cymbopogon species in recent years such as anti-inflammatory, anticancer and allelopathic activities [12-16]. There are few reports available describing other bioactivities of agricultural and ecological significance such as food packaging and insect repellent of essential oils of Cymbopogon species [17-20]. For example, C. martinii (palmarosa) essential oil is used as fumigation to control beetles like Callosobruchus chenesis and Tribolium castaneum, which grow in stored grain [18]. Similarly, the insect repellent properties of C. winterianus (citronella) are used to protect cartons containing muesli and wheat germ from beetles [19]. It is also reported that the essential oils of Cymbopogon flexuosus, C. citratus, C. martinii, C. winterianus, C. nardus, C. khasianus, C. nervatus, C. schoenanthus, C. giganteus and C. densiflorus possess several useful bioactivities. In addition, individual chemical constituents such as citral, geraniol, citronellol, citronellal, linalool, limonene, piperitone, borneol, bisabolol and isointermedeol have demonstrated remarkable bioactivities, including anticancer activity [14]. The easy availability, pleasant olfactory properties and insignificant toxicity of the Cymbopogon essential oils make them most promising candidates for the treatment of chronic diseases [14]. In addition, their semio-chemical properties are useful as an alternative to synthetic chemical pesticides in an integrated pest management programme [18]. Certainly, essential oils of the Cymbopogon species are occupying increasingly and vastly varied significance in pharmaceuticals and medicine owing to their potential bioactivities. This trend, however, has been increased progressively in the past ten years. Despite the fact that the numbers of reports are increasing on the bioactivities of Cymbopogon essential oils, these reports have not been analyzed or reviewed at one place. In this review article, I have discussed chemical compositions and various bioactivities of the essential oils of Cymbopogon species from the collation of reports published in the past ten years. Also, the biosynthesis and accumulation of the essential oils has been briefly mentioned. Essential oil extraction from Cymbopogon species Essential oils from members of the genus Cymbopogon are usually extracted by steam or hydrodistillation of the aerial parts, such as leaves and inflorescences in mini Clevenger apparatus (Figure 1). They yield an essential oil with a characteristic aroma due to the presence of the significant monoterpene fractions. Cymbopogon flexuosus (East Indian lemongrass) oil is yellow to reddish-brown in colour and the odour is powerful lemon like, while that of C. martinii (palmarosa) and C. flexuosus mutant cv. GRL-1 essential oil has a rose-like aroma due to the higher proportion of geraniol. Chemical compositions of the essential oils Essential oils of a number of Cymbopogon species have been

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extensively studied for their chemical composition by gas chromatography, GC-MS and NMR spectroscopy [1-9]. In recent years C. flexuosus, C. citratus, C. martinii, C. winterianus, C. nardus, C. giganteus, C. schoenanthus and C. parkeri have been investigated for their chemical compositions as well as evaluated for biological activities The studies have revealed that their essential oils mainly consist of monoterpenes (acyclic and acyclic), whilst those of C. flexuosus and C. parkeri also consist of bicyclic monoterpenes, piperitone and sesquiterpenes such as isointermedeol [14, 21]. Isointermedeol is a major component in the essential oil of C. flexuosus that has anticancer properties [18].

Figure 1. Mini Clevenger apparatus for extraction of essential oil. Figure 1. Mini Clevenger apparatus for essential oil extraction.

Gas chromatographic analyses of essential oils of C. flexuosus cultivars OD-19 and GRL-1 has revealed the presence of several monoterpenes viz., citral (a and b), geraniol, borneol, isopulegol and 6-methyl hept-5-en-2one, geranyl acetate, γ-terpinene, α-thujene, α-pinene, sabinene, n-decanol, α-terpenyl acetate, β-caryophyllene, α-humulene, germacrene D, β-bisabolene and γ-cadinene [1-9]. Structures of some of these monoterpenes are presented in Figure 2. Our earlier study of essential oil compositions in eight cultivars of C. flexuosus revealed that essential oils of the seven cultivars consisted mainly of citral (75-85%), except that of cultivar GRL-1, which is mainly composed of geraniol (90%) [1]. Citral is an isomeric mixture of geranial (citral a) and neral (citral b) and are major components in the essential oils of several species of Cymbopogon [10]. Both citral and geraniol have immense commercial significance due to their characteristic lemon and roselike smell in the flavour, fragrance, cosmetics, perfumery and pharmaceutical industries [1,22]. A study of essential oil composition and phylogenetic relationship in 19 Cymbopogon taxa by Khanuja et al. 2005 [2] revealed marked variation in the essential oil content and compositions of these taxa. Essential oils from C. confortiflorus and C. nardus var. confortiflorus were rich in geraniol with observed values of 68% and 46%, respectively, whereas essential oils from C. nardus var. nardus and C. winterianus had very little amount of geraniol. Essential oil extracted from C. pendulus, C. flexuosus and C. citratus mainly consisted of

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Figure 2. Chemical structures of Cymbopogon essential oil constituents 1, citral a; 2, citral, b; 3, citronellol; 4, citronellal; 5, geraniol; 6, geranyl acetate; 7, limonene; 8, linalool; 9, nerol; 10, cisocimene; 11, piperitone; 12, α-terpineol, 13, thujane; 14, α-bisabolol, 15, isointermedeol; 16, borneol; 17, α-pinene; 18, β-pinene. citral that accounted for 80-84% [2]. The essential oil obtained from the roots of C. citratus consisted of ten components including longifolene-(V4) that accounted for 56.67% of the essential oil; also present as a major constituent was selina-6-en-4-ol (20.03%) [16]. The chemical composition of the essential oil from the shoots of C. citratus was completely different to that of the root essential oil, with the former consisting of 12 components with citral (88%) as the major constituent [16]. Cymbopogon giganteus essential oil has shown a very distinct composition, which is mainly characterised by

the presence of cis- and trans-p-1(7),8-menthadien-2-ol (19.9% and 22.3%), cis- and trans-p-2,8-menthadien-1-ol (10.1% and 14.3%) [13]. Like C. giganteus, the essential oil of C. schoenanthus L. Spreng from Tunisia also had a very distinguished chemical composition, but characterised by different types of monoterpenes such as limonene (10.5–27.3%), β-phellandrene (8.2–16.3%), δ-terpinene (4.3–21.2%) and α-terpineol (6.8–11.0%) [23]. So far, these essential oil compositions are unique. The essential oil of the C. martinii studied by GC-FTIR indicated the presence of geraniol (65%) and geranyl


acetate (20%) as major components [24]. Similar composition of the leaf and flower essential oils of C. martinii with geraniol as dominating component (53.41% in leaf and 69.63% in flower oil) is reported [25]. In addition to geraniol, piperitone (6.0%) in flower and nerol (24.76%) and α-pinene (4.32%) in leaf essential oils have also been identified [25]. Phytochemical analysis of the essential oil of C. winterianus Jowitt (java citronella) showed presence of geraniol (40.06%), citronellal (27.44%) and citronellol (10.45%) as major components [26]. The essential oil of C. winterianus consisted of 23 compounds as revealed by gas chromatographic analyses; major constituents identified were citronellal (27%), trans-geraniol (23%), and citronellol (10%) [27]. Earlier studies have shown similar essential oil composition of C. winterianus with citronellol, citronellal, limonene and linalool as major components [28]. The essential oil composition of C. nardus is almost identical to that of C. winterianus, characterised by the presence of geraniol, citronellal, and citronellol. However, α-terpineol, cis-sabinene and carvone were identified as major constituents besides citronellal and geraniol in the essential oil of C. nardus harvested from India [29]. The essential oil of C. parkeri Stapf. from Iran has piperitone (81%) as major component with some other minor constituents including germacrene-D (5%), santolinyl acetate (2.1%) and α-eudesmol (2.1%) [21]. The study of the essential oil composition of various Cymbopogon species presented here led to the conclusion that the monoterpene compositions of the essential oils markedly varied among the species. Invariably, essential oil content and compositions are greatly influenced by climate, season and diurnal effects. Additionally, developmental and ontogenic variations in the essential oil composition in Cymbopogon species have been reported [1,3]. Essential oil biosynthesis and accumulation Essential oils are complex mixture of acyclic and/ or

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cyclic terpenoids. Monoterpenes are colourless, lipophilic, volatile substances responsible for the characteristic odours of essential oils and scents of many plants [3]. The monoterpenes are mainly derived from geranyl diphosphate (GPP) through interconversions such as, stereo specific isomerization, acetylation, deacetyaltion, cyclisation and dehydrogenation [31,31]. Geranyl diphosphate (GPP) is believed to be biosynthesised by condensation of the isopentenyl diphosphate (IPP) with dimethylallyl diphosphate (DMAPP) in a head to tail fashion. Isopentenyl pyrophosphate is the universal precursor of all isoprenoids including monoterpenes and sesquiterpenes and is thought to be derived either from the cytoplasmic acetate-MVA pathway or the newly discovered methylerythritol-4-phosphate (MEP) pathway (Figure 3) [22, 3234]. Incorporation studies in C. flexuosus (lemongrass) and C. martinii (palmarosa) using radiolabel substrates [2-14C]acetate, 14CO2, [14C]-sucrose favoured acetate-MVA origin of the essential oil [22,35,36]. The essential biosynthesis and accumulation is subjected to developmental regulation in Cymbopogons [1]. Previous incorporation studies in lemongrass and palmarosa revealed only young and rapidly growing leaves and inflorescences are most active in biogenesis as well as accumulation of essential oil [22, 36,37]. Histochemical methods using Schiff’s reagent have shown that Cymbopogon flexuosus cv. OD-19 and C. citratus accumulate essential oils in oil cells located in the adaxial side of the leaf mesophyll, commonly adjacent to non photosynthetic tissue and between vascular bundles [10,11]. Bioactivities of Cymbopogon essential oils The bioactive potential of Cymbopogon essential oils and their constituents have been rapidly recognised in the past ten years (Table 1), although the conventional bioactive properties against microbes have been known for much

Figure 3. Monoterpene biosynthesis via cytosolic acetate-MVA and plastidic MEP pathway. DMAPP, dimethylallyl diphosphate; G-3-P, glyceraldehyde-3-phosphate; GPP, geranyl diphosphate; IPP, isopentenyl diphosphate. Secondary transformations of GPP produce diverse monoterpenes structures.

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longer. Essential oils of Cymbopogon species are easily available, have a pleasant aroma, are non-toxic and safe; the active principles are therefore becoming increasingly popular in pharmaceuticals and medicines. Also, semiochemical properties of the Cymbopogon essential oils has been promising in integrated pest management programme since this property may lead to development of alternatives to synthetic chemical pesticides [18]. While several research groups have investigated the bioactive potential of essential oils and their constituents using animal models and cell systems, others have elucidated and proposed mechanisms underlying their actions. A number of reports published in recent years have described several novel bioactivities viz., allelopathic, anthelmintic, anti-inflammatory, anticancer, antioxidant and insect and mosquito repellency of some Cymbopogon essential oils and the mechanisms of action. Among the various species, C. citratus has been recognised most promising since the essential oil of this species has exhibited a variety of fundamental and novel bioactivities (Table 1). Cymbopogon martinii and C. winterianus were other species that showed outstanding bioactivities, particularly insect repellent and anthelmintic. In contrast, C. schoenanthus essential oil demonstrated antioxidant activity. The bioactive potential of other species of Cymbopogon have not yet been fully exploited. Like essential oils, monoterpene constituent of the essential oil have displayed useful bioactivities [12-16]. For instance, citral, a major constituent in essential oils of many Cymbopogon species has shown strong antimicrobial properties against plant and human pathogens and insecticidal properties [38-41]. Similarly, limonene and borneol present in the essential oil of C. flexuosus have immunostimulatory, analgesic and anaesthetic properties, respectively [42, 43]. Some other constituents such as geraniol, geranyl acetate, α-bisabolol and isointermedeol have also been correlated with different types of bioactivities. Isointermedeol, a major component in C. flexuosus essential oil, possesses anticancer properties [14]. The number of reports describing the bioactivities of Cymbopogon essential oils is growing. Most of the bioactivities shown by Cymbopogon essential oils are discussed in the following sections. Antimicrobial activities Rapidly developing resistance of pathogenic microorganisms against currently available drugs/ treatment is a major concern in recent years. Essential oils of Cymbopogon species have strong antimicrobial properties and thus could produce alternative therapeutics to current antibiotic drugs. The antimicrobial properties of C. flexuosus, C. citratus, C. martinii, C. winterianus, C. nardus, and C. parkeri have been well documented (Table 1). Most of the studies have determined the antimicrobial activity of the essential oil and its constituents in terms of minimum inhibitory concentration (MIC), which is required for 50% inhibition of the growth of microorganisms. From these studies it has become clear that essential oils of Cymbopogon species have outstanding antifungal activities and significant antibacterial activities. Cymbopogon nervatus inflorescence essential oil

has demonstrated antibacterial activities against Shigella dysenteriae and Klebsiella pneumoniae [44], whilst that of C. densiflorus has a wide spectrum of antibacterial activity against Gram positive and Gram negative bacteria [45]. De Billerbeck et al. [46] have studied the effect of the essential oil of C. nardus on the growth of Aspergillus niger. The study revealed that the essential oil (800 mg/ ml) had strong inhibitory action causing cytological modifications on growth of the mycelium. It was suggested that the essential oil damaged the plasma membrane and mitochondrial structural organization. Subsequently, Helal et al. [47] described a very similar antifungal property of C. citratus essential oil with negative effects on the growth, lipid content and morphogenesis in A. niger ML2-strain.The MIC of the essential oil was 1.5-2.0 μ/ml. Observation of A. niger hyphae treated with essential oils under the light, scanning electron and transmission microscope demonstrated the ultra structural alterations in the hyphae, which might be developed during treatment with essential oil. Fumigation with essential oil also caused great loss in Ca2+, K+ and Mg2+ ions from the mycelium. Moreover, C. citratus essential oil is reported to block aflatoxin B production in A. niger [48, 49].The essential oil of C. martinii displayed remarkable antiyeast activity against Saccharomyces cerevisiae at a concentration as low as 0.1% [24]. Geraniol, which accounts for 90% of palmarosa essential oil, was found to be responsible for this activity. Two mechanisms of antiyeast activity have been suggested. Geraniol arrests the growth of yeast cells causing excessive K+ ion leakage from yeast cells and essential oil treatment induces alterations in the S. cerevisiae cell membrane composition by increasing the proportion of saturated fatty acid and decreasing that of unsaturated fatty acid, resulting in growth inhibition. Besides the effects of palmarosa on S. cerevisiae, the oil has shown inhibitory effects on the growth of dermatophytes and filamentous fungi [50]. This was studied by applying essential oil ointments against induced ringworm in a guinea pig model; hair samples were collected after 7-21 days of the treatment and examined for fungal growth [50]. The essential oil from C. citratus has been found to be useful in treatment of oral and vaginal candidiasis [51], with citral exhibiting powerful inhibitory effects on growth of the yeast [51]. Other yeasts significantly affected include Candida oleophila, Hansenula anomala, Saccharomyces cerevisiae, S. uvarum, Schizosaccharomyces pombe and Metschnikowia fructicola. Cymbopogon citratus essential oil has also shown significant inhibitory activities against a number of filamentous fungi, namely Alternaria alternata, Aspergillus niger, Fusarium oxysporum and Penicillium roquefortii [52]. The essential oil and powder of C. citratus is used to control storage deterioration and aflatoxin contamination of melon seeds caused by Aspergillus flavus, A. niger, A. tamarii and Penicillium citrinum [53]. The advantages of this treatment are that the essential oil does not affect the biochemical composition of the seeds and has strong effects comparable to that of a commercial fungicide iprodione. Thus it is a better and safe natural control. Unlike essential oils of other Cymbopogon species, C. parkeri essential oil has shown substantial activity against

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Table 1. Bioactivities of Cymbopogon essential oils, constituents and extracts. Cymbopogon species Cymbopogon citratus Stapf. Cymbopogon citratus

essential oil Essential oil Essential oil and components Essential oil Essential oil Essential oil, citral Essential oil Essential oil and powder Lemon grass extract Citral

MIC/IC50 value 126.5 and 15.5 μg/ml N.D.

biological activity Anti-proliferative Allelopathic

ref. 12 16

1.0 - 1.5 μl/ml 1.0- 3.0 μl/ml 100 μg/ml 1.0 - 1.5 μl/ml 1-10 g/100 g seeds and 0.1 to 1.0 ml/100 g seeds 100 mg/kg body weight 22.25 μM

Antifungal Antiyeast Antifungal Antifungal Antifungal

47 48 51 49 53 55 56

Methanol, water infusion & decoction Essential oil Essential oil Essential oil Fresh leaf aqueous extract Citral Lemongrass infusion

50-100 μg/ml

Essential oil

4.2 to 79 μg/ml

Anticancer Inducer of caspase-3 in tumor cell lines Free radical scavenging and antioxidant Antinociceptive effect Anxiolytic Neurobehavioral effect Hypoglycemic and hypolipidemic Anti-clastogenic In the treatment of oral thrush in HIV/AIDS Anticancer

30 and 20 μg/ml

Anticancer

14

Cymbopogon martini Roxb. Cymbopogon martini Cymbopogon martini Cymbopogon martini

Essential oil, isointermedeol Essential oil Essential oil, geraniol Oil extract Essential oils

0.1% 66.7 μg/ml N.D. 150 and 500 ppm

24 60 18 50

Cymbopogon martini

Essential oil

150 and 500 ppm

Cymbopogon martini Cymbopogan martini var. sofia Cymbopogon schoenanthus (L.) Spreng. Cymbopogon schoenanthus

Essential oil Essential oil Essential oil

N.D. 1 ml 0.47 mg/ml

Essential oil, piperitone Essential oil Essential oil Essential oil Essential oil Citronella extract Citronellal Essential oil Essential oil Essential oil

1.6 μl/l and 2.7 μl/l

Antimicrobial Anthelmintic Insecticidal Antifungal activity dermatophytes Antifungal activity dermatophytes Anthelmintic activity Repellent Antioxidant Antiacetylcholineesterase Insecticidal

33.3 μl/l 100- 400 mg/kg N.D. 1-10 μl/ml 0.2 g/m2 of carton board 2.5 mM 800 mg/l N.D. N.D.

Insecticidal Anticonvulsant Insecticidal/ repellent Antimicrobial Insect repellent Phytotoxicity Antifungal Antibacterial activity Antibacterial

58 26 60 27 19 17 46 45 44

Cymbopogon citratus Cymbopogon citratus Cymbopogon citratus Cymbopogon citratus Cymbopogon citratus Cymbopogon citratus Cymbopogon citratus Cymbopogon citratus Cymbopogon citratus Cymbopogon citratus Cymbopogon citratus Cymbopogon citratus Cymbopogon citratus Cymbopogon citratus Cymbopogon flexuosus (Nees ex Steud) Wats Cymbopogon flexuosus

Cymbopogon schoenanthus Cymbopogon winterianus Jowitt Cymbopogon winterianus Cymbopogon winterianus Cymbopogon winterianus Cymbopogon winterianus Cymbopogon nardus Cymbopogon densiflorus Steud. Cymbopogon nervatus Stapf. N.D. = not detected

50-200 mg/kg N.D. 0.5 - 1.0 g/kg 125-500 mg/kg 60 mg/kg body weight N.D.

57 62 63 64 65 66 67 15

25 25 20 23 59

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phytopathogenic fungi, namely Rhizoctonia solani, Pyricularia orizea and Fusarium oxysporum [54] Anticancer activity Until recently, relatively little was known about the anticancer properties of Cymbopogon essential oils and their mechanism of actions; only few reports are available. The first report on anticancer activity was the effects of lemongrass on hepatocarcinogenesis in male Fischer 344 rats administered with diethylnitrosamine [55]. Consequently, the anticancer activity of citral has been reported. Citral functions as a new inducer of caspase-3 in tumour cell lines, with the mechanism of action involving DNA fragmentation and enhancement of caspase-3 catalytic activity, eventually inducing apoptosis in several hematopoietic cell lines [56]. However, apoptotic effects were dependent on a- and b- unsaturated aldehyde groups. The most defined work on anticancer activity of Cymbopogon essential oil has been recently carried out [14,15]. The two reports provided deeper insight in to anticancer principle of the essential oil and its mechanisms of action. Kumar et al. [14] have investigated the anticancer activity of C. flexuosus (CFO) essential oil and its major constituent, isointermedeol (ISO) in human leukaemia HL-60 cells. This study revealed that C. flexuosus essential oil and isointermedeol (ISO) induce apoptosis in human leukaemia HL-60 cells and anticancer activity of these materials was correlated with down regulation of NF-κB expression and caspase activation. The caspase activation was through apical receptors and mitochondrial signaling pathways. As a part of the mechanism of action it was suggested that significantly increased levels of cytochrome c in mitochondria after essential oil treatment, played a role in triggering apoptosis. Sharma et al. [15] have studied the anticancer activity of C. flexuosus essential oil in human cancer cell lines HL-60, murine Ehrlich and Sarcoma-180 tumors in combination with electron microscopy. This indicated some morphological changes favouring induction of apoptosis in cancer cells lines that were most probably triggered by the essential oil. Chromatin condensation and induced apoptosis and fragmentation of the nuclei and apoptosis were apparent morphological changes in HL-60 and sarcoma-180 cell lines, respectively [15]. Antiproliferative, anti-inflammatory and antioxidant activities The antiproliferative effect of C. citratus essential oil against Trypanosoma cruzi was demonstrated to be due to citral. Citral also showed significant trypanocidal activity against the parasite [12]. Cymbopogon giganteus is widely used in traditional medicine against several diseases. The chemical constituents of this essential oil showed inhibitory effects in vitro on 5-lipoxygenase. The 1,1-diphenyl-2-picrylhydrazyl (DPPH) method was used for determination of the antiradical scavenging activity of the essential oil [13]. Antioxidants are substances with the ability to scavenge free radicals and the essential oils of Cymbopogon species have shown this ability and are thus considered as antioxidants. However, the antioxidant properties of Cymbopogon species have not yet been sufficiently evaluated. The essential

oil of C. schoenanthus L. (Spreng.) has shown the ability of scavenging of free radicals and also anti-acetylcholine esterase activity, hence believed to be a strong antioxidant [23]. Cymbopogon schoenanthus is consumed in salads and used to prepare traditional meat recipes in Tunisia. With C. citratus, instead of essential oil, the methanol, methanolwater extract, infusion and decoction of leaves exhibited powerful antioxidant properties. The antioxidant activity of the essential oils of the above species were determined using the DPPH assay [23,57]. Allelopathic, repellent and anthelmint activities It is reported that Cymbopogon essential oils and their major constituents function as allelochemicals. Allelochemicals affect insect biology and behaviour and hence are used in biocontrol. Cymbopogon schoenanthus essential oil functions as an allelochemical and is used to control Callosobruchus maculates development in cowpea stock [58, 59]. Piperitone, a major chemical constituent, was more toxic than the essential oil to neonatal larvae. The essential oil of C. citratus exhibited alleopathic activity and affects seed germination and seedling growth of corn and barnyard grass [16]. Very likely, C. winterianus essential oil has allelo-chemical property that affects the growth of Spodoptera frugiperda larvae [60]. An extract of citronella also has repellent activity [19] and it is for this reason that citronella extract is used to prevent cartoons containing muesli and wheat germ from beetles [19]. Similarly, C. martinii var. sofia essential oil exhibited repellent action against Anopheles sundaicus [20]. Palmarosa oil is safe for human use and is thus recommended for protection from malaria due to its potent repellent action against mosquitoes. Beside mosquito repellent activity, palmarosa essential oil also showed strong pesticidal activity against insect infestation and is used to protect stored wheat and grain from the beetles Callosobruchus chenesis and Tribolium castaneum [18]. Palmarosa essential oil demonstrated significant anthelmintic activity against the nematode Caenorhabditis elegans [61]. and this was mainly due to geraniol (a major chemical constituent). Palmarosa oil has also showed anthelmintic activity against the Indian earthworm Pheretima posthuma [25]where it causes paralysis and death in a short time. Other biological activities Essential oils of Cymbopogon species have some other less studied bioactivities. Cymbopogon citratus is reported to possess additional properties such as antinociceptive, anxiolytic-type, and neurobehavioral activity [53, 6265]. Aqueous extracts of C. citratus leaves have shown hypoglycaemic and hypolipidaemic effects in rats suggesting its possible therapeutic role in Type 2 diabetic mellitus [65]. Administration of aqueous extracts of leaves (125-500 mg/ kg body weight) in normal male Wistar rates for 42 days resulted in a significant decline in fasting plasma glucose, increase in plasma HDL-c level and no change in plasma triglycerides level [65]. The essential oil of C. winterianus is used in Brazilian folk


medicine as an analgesic and anxiolytic [15]. A recent study has revealed anticonvulsant and depressant activity of C. winterianus essential oil on central nervous system (CNS) of rodents [26]. Citronella essential oil exhibited significant inhibitory effects on the growth of several weed species like Ageratum conyzoides, Chenopodium album, Parthenium hyterophorus, Malvastrum coromendelianum, Cassia accidentalis and Phalaris minor [17]. It is suggested that a major component, citronellal, exerts multiple effects on the biochemistry and physiology of the weeds and inhibits their emergence. Citronellal mainly impairs the photosynthetic and respiratory metabolism, disrupts cuticular wax, clogs stomata, shrinks epidermal cells and causes rapid electrolyte leakage. Post-emergence application of citronella has been equally effective and cause chlorosis, necrosis, wilting and finally death of the weeds [17]. Citral possesses many useful bioactivities and one of these is an anti-clastogenic effect in nickel chloridetreated mouse micronucleus system [66]. The citral caused inhibition of micronuclei formation and enhanced the superoxide scavenging activity. Elevated superoxide scavenging activity was thought to be responsible for the anti-clastogenic effects of the citral [66]. Recently, Wright et al. [67] have reported that lemon juice and C. citratus infusion is safe in and highly effective in the treatment of oral thrush in HIV/AIDS patients in comparison to group using gentian violet aqueous solution (0.5%). This randomised controlled trial validated the efficacy of lemon juice and lemongrass for the treatment of oral candidiasis in an HIV population in South Africa. Conclusion Essential oils of Cymbopogon species that are diverse in chemical composition possess many important and potential bioactivities of great pharmaceutical and medicinal significance. Some of the novel bioactivities of Cymbopogon essential oils and constituents include anti-inflammatory, anticancer, antioxidant and insect repellency. In addition, they have a number of other activities of ecological and industrial significance. At present, the focus of several research laboratories is to investigate plausible mechanism/s of action underlying the newer bioactivities of Cymbopogon essential oils. Despite the fact that Cymbopogon essential oils have offered immense biological, ecological and pharmaceutical properties, little efforts have been made to harvest the maximum bioactive potential of these species. Only C. citratus has been extensively investigated and it possesses a range of outstanding bioactivities. One of the major concerns with regard to bioactivity screening is subsequent adequate clinical trials in human subjects, which are often lacking in many cases.The absence of clinical trails severely impedes the development of the bioactive component identified as an alternative medicine or therapeutic agent. Thus the studies of Cymbopogon essential oils also need to be substantiated by clinical trials in human subjects. It is true that our interest in Cymbopogon essential oils has

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rapidly increased, shifting from their aromatic potential to bioactive potential. It is very timely to investigate bioactive potential of this genus when the demand for natural remedies from the public is escalating because of their safe use with no side effects. Also, the growing resistance of pathogenic microbes against current antibiotics has prompted the search for plant-based new or alternative drugs. Acknowledgement The author is grateful to the Chancellor, Vellore Institute of Technology (VIT) University, Vellore, India for providing necessary support and facilities. This work is done under the project “Metabolic fingerprinting of the monoterpenes in the genus Cymbopogon” financially supported by the Department of Science and Technology (DST), New Delhi, government of India. References 1.

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