Review of phytomedicine, phytochemistry, ethnopharmacology, toxicology, and pharmacological activities of Cymbopogon genus

The Cymbopogon genus belongs to the Andropoganeae family of the family Poaceae, which is famous for its high essential oil concentration. Cymbopogon possesses a diverse set of characteristics that supports its applications in cosmetic, pharmaceuticals and phytotherapy. The purpose of this review is to summarize and connect the evidence supporting the use of phytotherapy, phytomedicine, phytochemistry, ethnopharmacology, toxicology, pharmacological activities, and quality control of the Cymbopogon species and their extracts. To ensure the successful completion of this review, data and studies relating to this review were strategically searched and obtained from scientific databases like PubMed, Google Scholar, ResearchGate, ScienceDirect, and Elsevier. Approximately 120 acceptable reviews, original research articles, and other observational studies were included and incorporated for further analysis. Studies showed that the genus Cymbopogon mainly contained flavonoids and phenolic compounds, which were the pivotal pharmacological active ingredients. When combined with the complex β-cyclodextrin, phytochemicals such as citronellal have been shown to have their own mechanism of action in inhibiting the descending pain pathway. Another mechanism of action described in this review is that of geraniol and citral phytochemicals, which have rose and lemon-like scents and can be exploited in soaps, detergents, mouthwash, cosmetics, and other products. Many other pharmacological effects, such as anti-protozoal, anti-bacterial, anti-inflammatory and anti-cancer have been discussed sequentially, along with how and which phytochemicals are responsible for the observed effect. Cymbopogon species have proven to be extremely valuable, with many applications. Its phytotherapy is proven to be due to its rich phytochemicals, obtained from different parts of the plant like leaves, roots, aerial parts, rhizomes, and even its essential oils. For herbs of Cymbopogon genus as a characteristic plant therapy, significant research is required to ensure their efficacy and safety for a variety of ailments.

distribution of Cymbopogon species from different countries across the world is shown in Figure 1.
The ethnopharmacology of Cymbopogon species has been shown to possess a diverse set of characteristics that supports their traditionally applications in cosmetic, pharmaceuticals, insect repellants, insecticides, and perfumery, mainly due to their high level of essential oils (Khanuja et al., 2005;Aibinu et al., 2007). Several findings have confirmed the nutritional value of Cymbopogon species as well as their therapeutic and pharmacological properties. Many countries in the world use this species as an herbal remedy on urinary tract infection, detoxication effects on the kidney and liver, bone diseases, hypertension, hypercholesteremia, stomach ulcers, weight loss and indigestion (Takaisi-Kikuni et al., 2000;Jirovetz et al., 2007;Francisco et al., 2011;Kpoviessi et al., 2014;Karami et al., 2021). When it comes to dosage, in countries like Tanzania, it is believed that patients with stomach ulcers can have a cup of tea of this herb half an hour before eating in the morning, afternoon, and evening. In diabetic patients, you boil the lemongrass leaves and add ginger powder and take them before dinner. The doses and how it is consumed vary in other countries, as some consume it as tea or decoction with different dosages. C. citratus is one of the most extensively employed species in the world, with pharmacological effects such as anti-inflammatory, antitrypanosomal, and stomach discomfort treatments (Francisco et al., 2011;Kpoviessi et al., 2014). Other species with antimicrobial effects include C. giganteus (Jirovetz et al., 2007), C. pendulus and C. winterianus as antifungals (Pandey et al., 1996;Oliveira-Verbel et al., 2011), C. flexuosus as a chemo preventive (Sharma et al., 2009), C. densiflorus Stapf as an antibacterial (Takaisi-Kikuni et al., 2000).

Ethnopharmacology and traditional significance
Cymbopogon species has diverse uses in different countries, contributing to the discovery of traditional medicines and commercial applications. On continents like Asia, South America, and Africa, the Cymbopogon leaves have been traditionally utilized as tea or decoction. Different parts of the Cymbopogon plant embrace key bioactive chemicals which determine the anti-inflammatory, antiseptic, anti-dyspeptic, and anti-fever actions, antispasmodic, analgesic, antipyretic, tranquilizer, anti-hermetic, and diuretic characteristics of the plant (Ademuyiwa et al., 2015;Bayala et al., 2018). In Tanzania, lemongrass tea is utilized as an anti-fever to reduce fever and is used by women to ease dysmenorrhea. The tea is also believed to clean the fallopian tubes, which facilitates easier blood flow. In Singapore, C. citratus is employed to alleviate paronychia, cold and flu symptoms, bug bites, sore and itchy throats, flatulence, indigestion, and cancer prevention (Siew et al., 2014). Interestingly, several countries also choose C. citratus as an insect repellent against mosquitos, house flies, and fleas (Boaduo et al., 2014). In India, C. flexuosus is generally accepted to treat fever, rheumatism, and cancers (Sureshkumar et al., 2017). It has been argued that the aerial parts of Cymbopogon jwarancusa (Jones ex Roxb.) Schult (C. in body rejuvenation. It can also be found in a variety of items, including perfumes, local soaps, and candles (Dutta et al., 2016). In several Asian and African countries, the leaf has been shown to have some snake and reptile repellent functions. Figure 3 summarizes some of the ethnopharmacology observed in Cymbopogon species.

Tannins
C. citratus is a Cymbopogon specie whose tannin content is heavily exploited. The species from Portugal and fractionated extracts contained about 10 mg of hydrolysable tannins (prothocyanidins) (Figueirinha et al., 2008), whereas C. citratus from Nigeria embraced about 0.6 percent tannins. Some studies have also proven the content of condensed tannins in C. nardus (Gebashe et al., 2020).

Phenol
In a particular study, total soluble phenolic content was obtained in methanolic root extracts of C. nardus, wherein it was shown that its content ranged from 4.2 to 30.9 mg GAE/g DW (milligrams of gallic acid equivalents per g). p-coumaric, ferulic, and chlorogenic acids are some of the phenolic acids isolated from the roots of C. nardus (Gebashe et al., 2020).

Mineral contents
In a study performed on Cymbopogon citratus, some of the reported essential mineral constituents were potassium (K), sodium (Na), calcium (Ca), magnesium (Mg), manganese (Mn), iron (Fe), zinc (Zn), phytate and phosphorus (P) (Boukhatem et al., 2014). Other minerals that can be found in C. citratus include chromium (Cr), nickel (Ni), copper (Cu), arsenic (As), cadmium (Cd), and lead (Pb) (Anal 2014). Essential minerals found in Cymbopogon schonenanthus include Ca, P, K, Mg, Cu, Zn, Mn and cobalt (Co.) (Alameen 2020). The percentage of mineral content was calculated at a concentration of (mg/100 g) while in other reports the content was converted from (parts per million) ppm to percentage (as shown in Table 5).

Pharmacology
Most of the pharmacological investigations have been conducted based on the components present. These components have led to the discovery of different pharmacological effects, which are proved by the mechanism of action discovered. Figure 6 highlights some of the mechanisms of action observed in Cymbopogon species.

Antiprotozoal effect
Citral is the major component of C. citratus and C. flexuosus essential oils. According to some findings, myrcene and citral have been discovered to have an antileishmanial effect on different species like Leishmania infantum, Leishmania tropica, and Leishmania major (Ganjewala et al., 2012). Citral, on the other hand, has been shown to exert anti-trypanosoma cruzi activity (Cardoso and Soares 2010) and to inhibit the anatomic and ultrastructural changes of Leishmania amazonensis without cytotoxicity (Santin et al., 2009). In other studies, Entamoeba histolytica was shown to be active in broth culture from cymbopogon essential oil (Dutta et al., 2016).

Anti-bacterial and antifungal effect
C. citratus has been used to isolate, characterize, and analyze essential oils like citral (geranial) and citral (neral), which have been shown to be antibacterial chemicals that are active against both gram-positive and gram-negative microorganisms (Soares et al., 2013). Bacterial infections like meningitis, pneumonia, impetigo, cellulitis, folliculitis and food poisoning have been treated traditionally by this herb (Ntulume et al., 2019). C. jwarancusa oil can distinctly inhibit the growth of various bacteria like Klebsiella pneumoniae, Citrobacter, Proteus mirabilis, Salmonella enteric sertyphi, and Shigella flexneri species (Prasad et al., 2014). Marvelously, myrcene has been shown to have low antibacterial activity but is very active when combined with other essential oils (Orafidiya 1993;Wannissorn et al., 2005). While the essential oil of C. martinii is reported to possess magnificent antibacterial activity against Staphylococcus aureus, S. pyagens, E. coli, and Corynebacterium ovis (Chouhan et al., 2017).
Cymbopogon oil has been affirmed to be one of the most effective anti-dermatophytes medications. Examples of dermatophytes treated by this herb include Trichophyton mentagrophytes, T. rubrum, Epidermophyton floccosum, and Microsporum gypseum (Wannissorn et al., 1996). Cymbopogon essential oils have also been corroborated to possess prominent resistance to pathogenic fungal stimulus that cause problems with mycotoxins released during grain storage and restrain filamentous fungus development by yeast cells, which has been reported to have antagonistic and synergistic effects on food storage (Nguefack et al., 2012;Kpoviessi et al., 2014). Coincidently, C. jwarancusa is proven to be extremely efficient against Fusarium oxyporium sp-lini (Dutta, Munda et al., 2016). Conformably, C. citratus can suppress fungal infections like athlete's foot, ringworm, jock itch, yeast infections, and keratinophilic fungi (Abe et al., 2003).

Anti-cancer effect
In different studies, the essential oils of C. densiflorus and C. flexuosus were analyzed to see if they had antitumor effects. Evidence suggested that C. flexuosus oil triggered apoptosis in human leukemia cell lines (HL-60 cells) in vitro and a murine sarcoma inoculated with S-180 tumor cells in vivo. Amazedly, the greatest effect was seen on the human cancer lines of colon, liver, cervix, and neuroblastoma. The oil treatment of C. densiflorus is suggested to have antitumor effects on TP53 wild-type and mutated bladder cancer cells. These results indicate that C. flexuosus and C. densiflorus oils could be a reasonable Tricin and flavone C-glycosides Tea, drinks, food flavoring, antioxidant and skin conditioner Sharp and Simon (2002) C. caesius (Hook and Arn.) Stapf Carvone, limonene, perillyl alcohol, citronellol and citronellal Treating morning sickness in pregnant women and mosquito repellent Russell et al. (1991); Leistner (2000) Cymbopogon citratus (DC.) Stapf Camphene, limonene, nonan-4-ol, citronellal, citronellol, neral, geraniol and citral Antidiarrheal, antibacterial, antifilarial, antifungal, antiinflammatory, antimalarial, hypoglycemic and hypolipidemic effects, and culinary purposes Adeneye and Agbaje (2007) Anti-inflammatory, cough, common cold, asthma, chronic bronchitis, antibacterial and antifungal effects Zhang et al. (2011) Frontiers in Pharmacology frontiersin.org 11 alternative for novel antineoplastic drugs (Sharma et al., 2009;Pereira et al., 2021).

Anti-inflammatory effect
Chronic inflammation is a major worldwide health problem that has been associated with life-threatening conditions like cancer (Colotta et al., 2009). Cymbopogon's ethnopharmacological studies have confirmed citral to have anti-inflammatory properties. The essential oil of C. flexuosus, which has high citral content, has been announced to substantially reduce numerous inflammatory biomarkers in human skin cells and conspicuously subdue chemical agentsinduced skin inflammation both topically and orally in a mouse model (Han and Parker 2017). Currently, it has been widely used as an ingredient in lotions and ointments to treat topical inflammation (de Cassis da Silveira e Sa et al., 2013;Boukhatem et al., 2014).

Antimalarial and antitrypanosomal effect
The essential oils of C. giganteus, C. citratus, C. nardus, and C. schoenanthus have been shown to have an effect against Trypanosoma brucei brucei and Plasmodium falciparum. Some secondary metabolites like citral (3, 7-dimethyl-2, 6-octadienal), myrcene, and citronellal were referred to as antimalarial compounds when compared to chloroquine, as they were found to decrease Plasmodium's growth by 86.6 percent (Melariri 2010;Arrey Tarkang et al., 2014;Kpoviessi et al., 2014). While, elemicin was declared to be present in 53.7 percent of C. pendulus essential oil. This compound is an essential starting material for the synthesis of the antimalarial drug trimethoxy prim. In another study, the ethanol extracts of C. citratus essential oil were shown to ameliorate the antioxidant state of oxidative stress-related malaria effects (Tchoumbougnang et al., 2005;Akono Ntonga et al., 2014).

FIGURE 4
Major phytoconstituents extracted from Cymbopogon species.
Frontiers in Pharmacology frontiersin.org 12  Frontiers in Pharmacology frontiersin.org potency of C. citratus at dosage rates of 400 and 800 mg, by decreasing the levels of insulin (p < 0.001), glucose (p < 0.001) and triglycerides (p < 0.001) (Bharti et al., 2013). Another report on the effect of lemongrass tea (mainly containing phenolics and terpenes) in a type 2 diabetes rat model suggested that the inhibition of glucokinase activity attributed to its antidiabetic  effect, which resulted in enhancement of hyperglycemia, glucose tolerance ability, insulin sensitivity, T-cell functions, and dyslipidemia (Garba et al., 2020).

Anti-obesity and antihypertensive effect
Cymbopogon leaves have been commonly consumed as tea to manage glucose, lipid, and fat levels in the blood serum, which may help to prevent obesity and hypertension (Shah et al., 2011). An experiment conducted with an aqueous extract of C. citratus showed a decrease in fasting plasma, glucose, total cholesterol, triglycerides, low-density lipoproteins, and very low-density lipoprotein while raising the plasma high-density lipoprotein level of rats with no effect on the plasma triglyceride levels (Adeneye and Agbaje 2007). Similarly, C. nardus could also console obesity by downregulating adipogenic and lipogenic genes (Ruangaram and Kato 2022). The evidence also suggested that Cymbopogon could reduce blood pressure and maintain blood glucose by secreting insulin (hyperinsulinemia) (Shimono et al., 2010).

Antinociceptive effect
Cymbopogon has long been used as a traditional medicine to relieve pain and anxiety in living beings (Ademuyiwa et al., 2015). Citronellal, a monoterpene observed in several Cymbopogon species, demonstrated the inhibition of descending pain pathways with anti-hyperalgesic actions that lasted longer when forming a βcyclodextrin complex (Santos et al., 2016). While the essential leaf oil of C. winterianus exhibits antinociceptive effects through the inhibition of prostaglandin synthesis (Leite et al., 2010).

Insecticidal activity
Pathogens and insects have been controlled using essential oils from different Cymbopogon species, for example, piperitone from C. schoenanthus is proven to be a strong repellant against Crematogaster spp (Bowers et al., 1993) and Callosobruchus maculatus (Ketoh et al., 2006). The essential oils of C. citratus, C. nardus, and C. martini are reported to be extremely efficient against anopheline mosquitos, Anopheles culicifacies, Anopheles The involved mechanisms of action observed in Cymbopogon species for disease management.

Anti-HIV effect
In HIV/AIDS patients, citronella oil extracted from C. citratus leaves was reported to heal oral thrush caused by Candida albicans in 1-5 days (Wright et al., 2009).

Perfumery
Most Cymbopogon species could produce a lot of essential oils that are aromatic, hence their extensive use in perfumery and the fragrance industry. Known as natural fragrance, Java citronella oil is used for the extraction of aromatic isolates, which has been added to several products due to their basic aromas. In East Indian perfumery, lemongrass oil from C. pendulus is the primary source. For C. winterianus oil, it provides scent and good odor to low-cost items such as sprays, disinfectants, and polishes. Palmarosa oil from C. martinii is extensively used in soaps more than any other oil due to its rose-like prominent and lasting odor, which can also be found in some mouth fresheners (Guenther and Althausen, 1948;Opdyke 1975). Other oils that can be used in perfuming soaps and scenting cosmetics include the essential oil of C. caesius, ginger grass oil, Palmarosa oil, C. winterianus oil, Java citronella oil, etc.

Toxicology
Generally, Cymbopogon is safe when consumed orally, topically, or used as aromatherapy. However, there are some factors, like heavy metal contamination from the soil, interaction of Cymbopogon with some drugs, and wrong consumption that can cause an undesirable effect (Ekpenyong et al., 2015a). According to some studies, citronella oil derived from the species C. afronardus, C. nardus, C. validus, and C. winterianus, is one of the ingredients in insect repellents and is applied topically to prevent mosquito bites. However, some adverse effects have aroused public concern. This includes skin reactions or irritation in some people, lung damage prior to its inhalation, and some reports of child poisoning after ingesting citronella oil-contained insect repellent (RxList 2021a, November 6). Other negative effects documented prior to the use of lemon grass include skin allergies when used directly on the skin, toxic alveolitis when inhaled, an elevation in amylase, and bilirubin (RxList 2021b, February 9). Relevant findings suggest that toxicological biomarkers and genotoxicity of C. citratus essential oil have a low toxicity level but are suitable and safe in long-term treatment at doses up to 100 mg/kg (Bidinotto et al., 2011). Although the United States has classified lemongrass as relatively safe., it is not recommended for use during pregnancy and breast-feeding, considering its stimulation to uterine and menstrual flow (Nimenibo-Uadia and Nwosu, 2020).

Quality control
Quality control is important for medicinal herbs as it helps in identifying the herb, discovering the active and minimal components, and becoming acquainted with the extraction, separation, or isolation process of the herb (Wang et al., 2019). Figure 7 summarizes this process of Cymbopogon genus. This was conducive to assure the safety of the herb, its ethnopharmacology, and its pharmacological effects.

Plant collection
Fresh plant leaves are obtained and then washed rigorously with either distilled water or normal saline. The leaves are then ground into fine powder with the aid of an electric blender and then stored at room temperature.

Extraction process
Via the maceration technique, several grams of powdered plant leaves are extracted with a litre of methanol in a stopped bottle overnight while being stirred periodically. And the sample is sieved and then filtered using filter paper. After that, several grams of plant leaves are simmered in a conical flask with 500 ml of double-distilled water for 1 h. The decoction is cooled for 3 h and then filtered using a piece of clean, sterile, white cotton cloth. The extract/filtrate is then concentrated to interesting concentrations using a rotary evaporator at a specific temperature, and stored in an airtight container and kept in the freezer until further use. The concentrate can then be used to prepare different concentrations (mg/ml) of the extract using distilled water (Adeneye and Agbaje, 2007;Elekofehinti et al., 2020).

Isolation process
Isolation of essential oils is done via hydrodistillation, where several grams of plant leaves are steam distilled for 3 h in a modified Clevenger-type apparatus. The essential oils are stored in a sealed vial at a specific temperature and the yields are calculated referring to the following formula: Yield (%) = (Oil (ml))/(Plant (g)) × 100 (Kpoviessi et al., 2014;Tavares et al., 2015;Mendes Hacke et al., 2020). The yields are based on the volume of water, the size of the leaves, and the extraction time (Thakker et al., 2016).

Physicochemical and spectroscopic techniques
The basic physical and chemical properties of a substance are known as physicochemical properties. This includes color, boiling temperature, refraction index, density, volatility, water solubility, and flammability. According to the research done on Cymbopogon citratus, an Atago ND R5000 refractometer (Osaka, Japan) was used to measure the refractive index of oil, according to the 921.08 AOAC (2000) method. The density was evaluated according to the 985.19 AOAC (2000) method using a 2 ml pycnometer. The density and refractive index are in the range (ρ = 0.848-0.949 g/ml; IR = 1.332-1.482). A yellow hue was detected using a Color Guard 05 colorimeter in transmittance mode when measuring the color parameters (Paviani et al., 2006;Essien et al., 2008;Tovar et al., 2011;del Carmen Vázquez-Briones et al., 2015). Spectroscopic techniques are precise analytical methods used to discover the structures of atoms, molecules, and unknown chemical compositions in Cymbopogon genus. Some of the techniques used to discover Cymbopogon essential oils and constituents include gas chromatography-mass spectrometry, fourier transform infrared spectrometry, nuclear magnetic resonance, differential scanning calorimetry, and scanning electron microscopy (Fortuna et al., 2011;del Carmen Vázquez-Briones et al., 2015;da Silva Martins et al., 2021).

Discussion
The use of traditional medicines is widespread and dates back a long time before the increase in technology and knowledge that we have now (Wang et al., 2019(Wang et al., and, 2022. Cymbopogon species can also be termed as medicinal plants due to their many reported medical benefits, which mostly ascribe to their essential oils and the whole parts of the plant in general. Most Cymbopogon species are declared relatively safe to consume, except for some like C. winterianus, C. schoenanthus, C. pendulus, and obtectus, whose edible uses are unknown but are known to be used for medicinal purposes, perfumery products, cosmetics and household insecticides. Traditionally, the use of these species varies from simply being consumed as tea, drinks, or food flavoring. Medically, they have been argued to exhibit: a) anti-inflammatory, antiseptic, anti-dyspeptic, and anti-fever actions; b) antispasmodic, analgesic, antipyretic, tranquilizer, anti-hermetic, and diuretic anti-fever; c) ease dysmenorrhea; d) detoxication effects on the kidney and liver. The dosage used traditionally is not standard nor scientifically approved. However, it is believed in most countries that one tea cup of lemongrass daily can strengthen individual's immunity. Clinically, citral, the main component in lemongrass, together with its other components, is thought to have anticancer ability and reduce the risk of various developing cancers by attacking the cancer cells or by boosting the immunity system. On the other hand, some cancer patients are given lemongrass tea after going through rounds of chemotherapy or radiation for relief. A study manifested that C. citratus tea can help get rid of gastric ulcers or even reduce the risk of gastric ulcers obtained from synthetic drugs like aspirin (Fernandes et al., 2012). Evidence also documented that drinking lemon grass tea every day for a month boosted the red blood cell count by increasing the amount of hemoglobin concentration, which was attributed to its superior antioxidant properties (Ekpenyong et al., 2015b).
Frontiers in Pharmacology frontiersin.org Furthermore, many investigations have been dedicated to exploring the phytochemistry, phytotherapy and pharmacology of Cymbopogon species. In one of the studies, it has been reported that a dichloromethane extract of C. ambiguous was demonstrated to have antiplatelet activity, which is believed to be highly because of its eugenol content (Uddin et al., 2011). Another study substantiated that the methanolic extract of C. citratus can achieve a dose-dependent relaxant activity through endothelial vasoconstriction via the nitric oxide pathway (Pereira et al., 2013). As to adverse effects, it is generally safe to consume some of the Cymbopogon species, but several adverse effects have been reported by oral or topical administration. Adverse effects observed orally include fatigue, dry mouth, excessive urination, and vertigo. Noteworthily, lemongrass essential oil might harm the mucous membranes in the stomach and liver when excessive and unrestrained use. When applied topically, skin reactions or irritation can be observed. It is also advisable to avoid taking it with drugs that are glutathione-S-transferase substrates and cytochrome p450 substrates to prevent any risk of increased side effects of these drugs. Moreover, pregnant and breastfeeding mothers can also avoid consuming lemongrass tea, citronella oil and its related products, so as to prevent its effects on infant development (Memorial Sloan Kettering Cancer Center 2020, February 14).

Conclusion and future prospects
Cymbopogon species are very fascinating, diverse, and rich in every sense, from their simple traditional uses like culinary and tea. Of which some of the species like C. nardus are not edible due to their unpleasant nature, while some remain unknown as to whether they are edible or not. To their medicinal uses, the robust pharmacological activity is mainly attributed to their richness in essential oils, such as monoterpenes, monoterpenoids, sesquiterpenes, sesquiterpenoids, and certain fatty alcohols. This genus is widespread throughout the world, with species like C. giganteus and C. densiflorus found in tropical Africa, C. nardus in eastern Africa, C. caesius in southern and eastern Africa, C. martinii, C. flexuosus, C. distans, and C. coloratus in eastern Asia, among others, all of which have unique medicinal and commercial benefits. Lastly, more research is needed to improve the ones that are known and to reveal those with little knowledge. Researchers can come up with more essential products that can be made using natural ingredients to replace those manufactured with harsh chemicals, which cause a lot of side effects and negative health factors. In addition, the drug dosage and mode of drugs traditionally given to people should be effectively tested, and this will aid in the increase of certified medicinal drugs and enhanced pharmacological effects in the future. Meanwhile, the exact clinical efficacy and potential organ toxicity of some species or active ingredients also need to be further elucidated.

Author contributions
QZ and XW designed this review and revised the final manuscript. JT and QY collected the data, sorted out the figures and tables, and wrote the manuscript. The final version of the manuscript was read and approved by all authors.

Funding
This work was supported by the National Natural Science Foundation of China (82160816, 81660700 and 82104533), the Ningxia National Natural Science Foundation (2020AAC02017), the China Postdoctoral Science Foundation (2020M683273) and the Science & Technology Department of Sichuan Province (2021YJ0175).