Medicinal properties of Hermannia Depressa N.E.Br.

Abstract

Microbial infections, inflammation, and oxidative stress constitute a pathological triad that is challenging to manage effectively, resulting in millions of mortalities and morbidities while burdening healthcare systems and declining economic growth globally. This research aimed to investigate the medicinal properties of Hermannia depressa leaves and stems and to validate their use in ethnomedicine to treat various ailments. Acetone, methanol, and hot water extracts of H. depressa were used in the study. The broth microdilution method was used to determine antimicrobial activity against bacterial and fungal pathogens. Scanning and Transmission electron microscopy (SEM and TEM) were used to observe ultrastructural changes in microbial cells following extract treatment. Anti-inflammatory activity was evaluated through nitric oxide inhibition assay in lipopolysaccharide (LPS)-stimulated RAW 264.7 macrophages. The 2,2-diphenyl-1-picrylhydrazyl (DPPH) free radical scavenging assay and the ferric reducing antioxidant power (FRAP) assay were used to measure the antioxidant potential of the extracts. Cytotoxicity was assessed using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay on Vero and RAW 264.7 cells. Phytochemical characterisation was conducted through gas chromatography-mass spectrometry (GC–MS), with compound identification based on the Wiley and National Institute of Standards and Technology (NIST) spectral databases. After maceration, the methanol extract showed the highest extraction yield (29%), followed by the acetone extract (26%) and the aqueous extract (6.28%). Antimicrobial evaluation revealed potent activity against certain pathogenic strains, particularly against Candida albicans and Staphylococcus aureus, for both acetone (MIC = 0.31 mg/mL) and methanol (MIC = 0.63 mg/mL) extracts. The aqueous extract inhibited S. aureus (MIC = 2.5 mg/mL) and Streptococcus pyogenes (MIC = 2.5 mg/mL), showing weaker activity. The aqueous extract demonstrated the highest selectivity (SI = 37.2) for Vero and RAW 264.7 cells against S. aureus and S. pyogenes. Acetone extracts also showed selective activity (SI = 2.1 against C. albicans and SI = 1.0 against S. aureus), while methanol extracts exhibited moderate selectivity (SI = 2.2) against C. albicans and SI = 1.1 against S. aureus). Scanning and transmission electron microscopy studies of the effects of acetone extracts of H. depressa on C. albicans cells confirmed morphological changes, including microbial damage to cellular structures such as the cell membranes and cell wall, as well as possible disruption of reproductive processes. The anti-inflammatory assessment revealed potent dose-dependent inhibition of nitric oxide (NO) production (89% at 250 μg/mL) by the acetone extract, whereas the aqueous and methanol extracts showed insignificant NO inhibition. The anti-inflammatory specificity was promising for the acetone extracts (SI >1), suggesting that the anti-inflammatory activity was likely due to specific NO inhibition rather than cytotoxicity. H. depressa extracts showed weak FRAP antioxidant results (Trolox equivalents <1) but potent DPPH activity (78% - 100% DPPH free radical scavenging across all extracts), indicating pathway-dependent antioxidant effects. The aqueous and methanol extracts showed no significant toxicity against Vero and RAW 264.7 cell lines, while the acetone extracts exhibited notable cytotoxicity against RAW 264.7 cells and no significant toxicity against Vero cells. The acetone and methanol extracts contained a diverse array of bioactive compounds after GC-MS analysis, including terpenoids (neophytadiene, phytol, trans-β-ionone), phenolic compounds (scopoletin, 2,4-di-tert-butylphenol), and other pharmacologically active compounds, such as benzothiazole and Vitamin E, and these phytochemicals are likely responsible for the biological activities observed in H. depressa. The results of this study demonstrate the therapeutic potential of H. depressa in managing diseases associated with microbial infections, chronic inflammation, and oxidative stress. The cytotoxicity results highlight the suitability of using aerial parts of H. depressa over roots in the preparation of traditional remedies, a practice that would likely enhance safety in the medicinal use of the plant. Furthermore, the aerial parts of H. depressa contain valuable bioactive compounds with significant antimicrobial, anti-inflammatory, and antioxidant properties, which can provide essential leads to the discovery of novel therapeutic agents. Therefore, rigorous scientific research involving the isolation and elucidation of pure compounds, in vivo biosafety studies, and standardised product development are recommended.