Antibacterial and anti-inflammatory activity of extracts and major constituents derived from Stachytarpheta indica Linn. leaves and their potential implications for wound healing

Abstract

Wounds of various types continue to have a severe socioeconomic impact on the cost of health care. Globally, there has been increased interest surrounding the identification of bioactive compounds that promote or modulate the wound healing process. Stachytarpheta indica Linn. is traditionally used to heal wounds and relieve inflammation, however, the theorised pharmacological properties have not yet been scientifically validated. In this study, dried and ground plant leaves were extracted with water and methanol, which were then subjected to various analyses. Antimicrobial activity of the plant extracts and isolated compounds was determined using well diffusion assays, while the minimum inhibitory concentrations were determined with a colorimetric assay. Morphological changes of human keratinocytes in response to plant extracts were observed with differential interference contrast microscope imaging. Cell viability, proliferation and migratory effects post-treatment with the plant extracts were also evaluated via colorimetric cytotoxicity assays and a real-time cell analyser protocol. Anti-inflammatory effects of plant extracts and isolated compounds were evaluated by flow cytometry and cyclooxygenase and lipoxygenase enzyme inhibition assays. Three active compounds i.e. ipolamiide, verbascoside and iso-verbascoside, were isolated from S. indica leaves. Verbascoside demonstrated broad-range antibacterial activity and imposed strong inhibition at 9.77 μg/mL against Staphylococci spp. S. indica extracts (0.1-0.2 mg/mL) were shown to improve human keratinocyte proliferation up to 60 % and induce morphological changes by producing cytoplasmic projections at concentrations higher than 0.4 mg/mL. Plant extracts (6.25-100 μg/mL) and individual compounds (3.125-50 μg/mL) elicited strong anti-inflammatory effects by suppressing the expression of interleukin-8 and inhibiting cyclooxygenase-1 and 5-lipoxygenase enzymes. Collectively, these results indicate that plant extracts and isolated compounds derived from S. indica have the potential to inhibit bacterial growth, promote tissue regeneration and reduce inflammation, hence, potentially providing the basis for a novel therapeutic for the treatment of wounds.