Phytochemical profiling of antimicrobial and potential antioxidant plant: Nepeta cataria

Abstract

Traditional and phytochemical studies have confirmed the richness and diversity of medicinal plants such as Nepeta cataria (N. cataria), but more studies are needed to complete its metabolite profiling. The objective of this research was to enhance the metabolomic picture and bioactivity of N. cataria for better evaluation. Phytochemical analysis was performed by bio-guided protocols and gas chromatography-mass spectrometry (GC/MS). For this, solvents such as methanol, ethanol, water, acetone, and hexane were used to extract a wide number of chemicals. Antibacterial analysis was performed using the 96-well plate test, Kirby Bauer's disk diffusion method, and the resazurin microdilution test. Antioxidant activity was determined by the DPPH assay and radical scavenging capacity was evaluated by the oxygen radical absorbance capacity (ORAC) assay. GC/MS analysis revealed a total of 247 identified and 127 novel metabolites from all extracts of N. cataria. Water and acetone extracts had the highest identified metabolites (n = 79), whereas methanol extract was the highest in unidentified metabolites (n = 48). The most abundant phytochemicals in methanol extract were 1-isopropylcyclohex-1-ene (concentration = 27.376) and bicyclo [2.2.1] heptan-2-one (concentration = 20.437), whereas in ethanol extract, it was 9,12,15-octadecatrienoic acid (concentration = 27.308) and 1-isopropylcyclohex-1-ene (concentration = 25.854). An abundance of 2 methyl indoles, conhydrin, and coumarin was found in water extracts; a good concentration of eucalyptol was found in acetone extract; and 7,9-di-tert-butyl-1-oxaspiro is the most abundant phytochemicals in hexane extracts. The highest concentration of flavonoids and phenols were identified in hexane and methanol extracts, respectively. The highest antioxidant potential (DPPH assay) was observed in acetone extract. The ethanolic extract exhibited a two-fold higher ORAC than the methanol extract. This examination demonstrated the inhibitory effect against a set of microbes and the presence of polar and non-polar constituents of N. cataria. The results of this study provide a safe resource for the development of food, agriculture, pharmaceutical, and other industrial products upon further research validation.

Keywords: Nepeta cataria; antibacterial susceptibility testing (AST); antioxidants; gas chromatograph/mass spectrometry (GC/MS); phytochemicals.

Figure 1

Qualitative analysis of phytochemicals in polar and non-polar extracts of Nepeta cataria. List of phytochemicals from (i) to (xi) were identified in various polar and non-polar extracts. The 2-D structure of phytochemicals are supported via PubChem.

Figure 2

Quantitative analysis of phytochemicals (A) DPPH mediated antioxidant activity, (B) flavonoids concentration, (C) phenols concentration, (D) oxygen radical absorbance capacity values.

Figure 3

Percentage growth inhibition of bacterial strains by Nepeta cataria plant extracts in different solvents at different dose levels (96 well method).

Figure 4

(A,B) Percentage inhibition of bacterial growth determined in comparison with the growth inhibition by chloramphenicol (resazurin method).

Figure 5

(A) GC/MS chromatogram of set of extracts of Nepeta cataria showing peaks of metabolites in each extract. (B) The 2-D structures of important phytochemicals are retrieved via PubChem. i. Betulin was most abundant phytochemical in methanol and ethanol (ME), ii. Uvol in ethanol, iii. 2-methyl Indole in water, iv. Eucalyptol in acetone and methanol (AM) and v. 7,9-Di-ter-butyl-1-oxaspiro is most abundant phytochemical in hexane extract.