Palmarosa Cymbopogon martinii is a tall herbaceous plant that belongs to the Poaceae family. It is originally from India and Nepal. It is sometimes called Indian geranium because of its plume flowers resembling those of geranium. The smell of its leaves and flowers is reminiscent of a scent close to that of a rose.
Palmarosa has been used in traditional Indian medicine for thousands of years for its tonic, antiseptic and healing properties.
It contains various chemical compounds including monoterpene alcohols (70-85% geraniol), esters such as geranyl acetate (7-9%), monoterpenes and sesquiterpenes. Its essential oil has many beneficial effects.
Palmarosa essential oil exhibits an inhibitory effect on many Gram-negative and Gram-positive bacteria, including Staphylococcus aureus, Staphylococcus epidermidis, Enterococcus faecalis, Salmonella Enteritidis and Escherichia coli. Geraniol is responsible for this broad spectrum antibacterial effect (MURBACH TELES ANDRADE & al., 2016).
Geraniol isolated from palmarosa also exhibits an inhibitory effect on enterotoxigenic strains of Escherichia coli (DUBREUIL, 2013).
In addition, palmarosa essential oil and geraniol exhibit antimicrobial activity against Propionibacterium acnes without modulating the immune response of T helper (Th) 1 and Th17 cells stimulated by this bacterium. This is interesting because this microorganism also called Cutibacterium acnes is associated with the pathogenesis of acne (ANDRADE & al., 2016).
In addition, they induce a modification of the bacterial proteome, affecting the protein content necessary for bacterial survival and growth. In addition, they exhibit an anti-inflammatory effect in keratinocytes by stimulating the production of interleukin-10 (MURBACH TELES ANDRADE & al., 2018).
Palmarosa essential oil has an antiparasitic effect in vitro against trichostrongylids from naturally infected sheep (95 % Haemonchus contortus and 5 % Trichostrogylus spp.). It has an inhibitory effect on these parasites demonstrated in various tests including egg hatching, larval development, feeding inhibition and larval sheath migration (KATIKI & al., 2011). They show an antiparasitic effect in vitro against the nematode Caenorhabditis elegans (KUMARAN & al., 2003).
Palmarosa essential oil exhibits a broad spectrum antifungal effect in vitro. In particular, it inhibits the growth of Tricophyton (T) rubrum and Microsporum (M) gypseum with minimum inhibitory concentrations lower than those of griseofulvin, ketoconazole and fluconazole. In addition, it exhibits an antifungal effect against Aspergillus (A) flavus, A. niger, A. fumigatus, Microspoum audouni, M. nanum, Tricophyton mentagrophytes, T. verrucosum and T. violaceum (DELESPAUL & al., 2000 ; PRASAD & al., 2010). It reduces the activities of the elastase and keratinase enzymes of Aspergillus fumigatus and Trichophyton rubrum. This is interesting because it is known that the production of elastases and keratinases is involved in the pathogenesis of Aspergillus and Tricophyton infections (KHAN & AHMAD, 2011).
It shows an antifungal effect in vitro on different strains of Candida albicans, with a greater effect than fluconazole and amphotericin B on resistant strains (KHAN & al., 2012). Furthermore, eugenol exhibits antibiofilm activity against Candida albicans. This efficacy is greater than that of amphotericin B and fluconazole (KHAN & AHMAD, 2012).
In addition, it exhibits in vivo efficacy against superficial fungal lesions induced in guinea pigs. It reduces skin redness, the severity of lesions and the appearance of dermatophytes when applied to the skin (PRASAD & al., 2010).
Geraniol exhibits anti-cancer effects in vitro and in vivo on different types of cancer.
It decreases the development of colon cancer induced by dimethylhydrazine in vivo in rats. It reduces the number of total aberrant crypt foci and increases the level of apoptosis in the colon (VIEIRA & al., 2011).
Geraniol also inhibits tumor growth of lung cancer cells in vitro, simultaneously with induction of apoptosis in vivo (GALLE & al., 2014).
In addition, geraniol possesses antiproliferative properties in vitro in hepatocellular carcinoma lines (GALLE & al., 2020). Its anti-cancer effects are partly linked to its anti-angiogenic activity in tumors (WITTIG & al., 2015).
Palmarosa essential oil and geraniol exert anti-inflammatory and immunomodulatory action by increasing the production of interleukin-10 in human monocytes cultured in vitro (MURBACH TELES ANDRADE & al., 2014).
Geraniol exhibits an anti-inflammatory effect in macrophages activated with lipopolysaccharide (LPS) in vitro by inhibiting many pro-inflammatory mediators: it inhibits the production of nitrogen oxide and prostaglandin E2 in a dose-dependent manner, it decreases the levels of gene and protein expression of cyclooxygenase-2 induced by LPS, and reduces the activation of the nuclear factor κB (SU & al., 2010).
In addition, geraniol decreases the activation of human neutrophils measured by the adhesion reaction induced by tumor necrosis factor alpha (TNF-a) in vitro (ABE & al., 2003).