Chemical characterization, enantiomeric distribution, and bioactivity analysis of essential oil from the selected lamiaceae plants of Nepal and their application in topical formulation

Abstract

Essential oils (EOs) are complex mixtures of biologically active volatile compounds that have been utilized for a long time as flavoring agents, preservatives, and natural ingredients in many commercial products. In recent years, they have drawn great attention due to their increasing demand for food, cosmetics, and pharmaceuticals. Since many studies have revealed the good antimicrobial, antioxidant, and cytotoxic activities of essential oils, it is very important to characterize them based on their chemical profiles. In the present study, some selective plants from the Lamiaceae family of Nepal were collected to determine the chemical composition, enantiomeric distribution, and biological activities. The hydro-distilled essential oils were characterized for volatile compounds by Gas Chromatography and Mass Spectrometry (GC-MS), GC-Flame Ionization Detection (GC-FID), and enantiomeric composition by Chiral GC-MS. The chemometric analysis was applied to identify the chemotaxonomic relationship among Lamiaceae essential oils. The antimicrobial property was evaluated by the microbroth dilution method using some ATCC bacterial and fungal strains. The antioxidant activity was determined by DPPH and ABTS radical-scavenging assays. The in vitro cytotoxicity was evaluated in human breast cancer (MCF-7) and fibroblast (NIH-3T3) cell lines by using the Cell Counting Kit-8 kit assay. The antioxidant-rich essential oils were blended into the cream formulation. The results revealed the variation in the yield of essential oils with harvesting seasons. The species showed higher essential oil yield in the summer season and tropical regions than others. Ocimum tenuiflorum L. had the highest concentration (1.68±0.13%), and Leucosceptrum canum Sm. had the lowest yield among the samples (0.15±0.05%). The average essential oil yield obtained from the Lamiaceae plant species in Nepal was about 0.76%. Oxygenated monoterpenes were the dominant class of terpenoids present in most of the essential oil samples, with concentrations above 49%. Mentha pulegium L. showed the highest proportion of oxygenated monoterpenes (91.63%), followed by Mentha spicata L. (85.3%) and Perilla frutescens (L.) (83.05%). The lowest yield of oxygenated monoterpenes was found in Colebrookea oppositifolia Sm. at 0.89%. The single compound, carvone, was detected in the highest concentration for Mentha spicata L. oil (68.51%). The seasonal variations in the chemical composition of essential oils were also detected among the Lamiaceae samples. Origanum majorana L. comprises linalool and terpinen-4-ol as major compounds, with 13.8% and 32.1% in spring, and 15.37% and 33.35% in summer. Similarly, the carvone of M. spicata L. was not much influenced by seasonal variation, with 51.96% in winter and 68.51% in summer. Major constituents of O. tenuiflorum L., eugenol (32.15 to 34.95%), and trans-β-elemene (29.08 to 32.85%) were not much influenced by seasonal variation except minor ones. The same result was also detected in O. basilicum L., where methyl chavicol (62.16–64.42%) and linalool (26.92–27.09%) were not variable during the winter and summer seasons. A minor seasonal variation in the major compounds was observed for M. pulegium L. In contrast, the major constituents of L. canum Sm. were highly influenced by seasonal variations. The leading compound, β-pinene, of L. canum Sm. was found at 29.07% in winter, which decreased to 15.21% during summer. Similarly, another leading compound, β-caryophyllene, of L. canum Sm. was found at 13.29% in winter, which increased to 33.51% during summer, thereby indicating the seasonal variation in the chemical composition of Lamiaceae essential oils. In the chemometric analysis, agglomerative hierarchical cluster analysis for Lamiaceae essential oil showed two main groups of volatile classes: the first dominated by oxygenated monoterpenes and the second by sesquiterpene hydrocarbons. Both principal component analysis and clustered heatmaps confirmed the two distinct groups of volatile components as assigned by HCA. The chiral GC-MS revealed several chiral compounds in the essential oil samples. The α-thujene, αpinene, sabinene,β-pinene,camphene,limonene,1-octen-3-ol,linalool,α-terpineol,cis-sabinene hydrate, menthone, β-caryophyllene, terpinen-4-ol, germacrene D, borneol, β-bisabolene, δcadinene,(E)-β-ionone, and (E)-nerolodol were common chiral compounds in the EO,dominating in the levorotatory form (62.4%). In the DPPH assay, O. tenuiflorum L. exhibited relatively good antioxidant activity (IC50 69.2382.99µg/mL),when compared to the standards (ascorbicacid,IC50 6.37 µg/mL and BHT, IC5012.46 µg/mL), and in the ABTS aasay, this essential oil exhibited the strongest activity (IC505.88-17.69 µg/mL), when compared to the standards (ascorbic acid, IC50 1.98 µg/mL and quercetin, IC50 7.79 µg/mL). The least activity was noted in M. pulegium L. from Nuwakotduring the summer with an IC50 value of 646.58 µg/mL in the DPPH assay and with an IC50 valueof 145.35 µg/mL in the ABTS assay. The antioxidant activity M. spicata L., P. frutescens (L.), L.canum Sm., and O. majorana L. The essential oils obtained in the summer was higher as compared to the essential oils collected during the winter. In contrast, O. ameicanum L., O. basilicum L., and O. tenuiflorum L. The essential oils collected during winter exhibited higherantioxidant activity than those from the summer. The present study also revealed that the seasons and environmental conditions may influence the phytochemistry of plants, thereby affecting their antioxidant properties. Samples from tropical zones had better antioxidant activities than the other parts. The effect of these essential oil samples on the viability of human breast cancer (MCF-7) and fibroblast NIH-3T3 cell lines was also found to be significant. Among the Lamiaceae essentialoils, P. frutescens (L.) (IC50 7.41 and 8.14 µg/mL), C. umbrosum (M. Bieb.) C. Koch (IC50 21.70and 12.53 µg/mL), M. longifolia L.(IC50 23.76 and 12.12 µg/mL), and O. tenuiflorum L. (23.43µg/mL) samples were highly cytotoxic as compared to other species against both cell lines.While M. pulegium L., M. spicta L., P. glabar Benth., and O. basilicum L. essential oils displayed the least toxicity, with the IC50 values varying from 99.64 to 90.56 µg/mL. Among the essential oil studied against fungal strains, O. majorana L., M. pulegium L., and O. tenuiflorum L. were more effective against Candida albicans and Aspergillus niger (MIC, 78.1 µg/mL). O. majorana L. essential oil exhibited a broad spectrum of antimicrobial activity, with a MIC value of at least 156.3 to 312.5 µg/mL for all tested organisms. For anti-bacterial activity, only slight inhibition of these oils was found against all the tested bacterial strains. Similarly, the essential oils of O. majorana L., O. tenuiflorum L., and O. basilicum L. were utilized for the formulation of cream, which showed the retention of their best efficacy after extensive investigation of several pharmacological parameters. Hence, the present study concluded that the chemotaxonomic profiles of many essential oil samples from the Lamiaceae family of Nepal were prepared. They also exhibited excellent and varied biological efficacies, which can be useful in bioprospecting for the benefit of human health. Keywords: Lamiaceae, Essential Oil, GC-MS, Chemical Composition, Enantiomer, Antioxidant, Antimicrobial, Cytotoxicity, Formulation.