Antimicrobial and wound-healing activity of crude extracts of medicinal plants used in parts of the Free State region, South Africa

Abstract

A wound develops when the tissue’s integrity is damaged, which results in the loss of its protective capabilities. Wound healing is a progressive, overlapping, and complicated process. Microbial infections and excessive free radicals inhibit the advancement of the wound-healing process. Furthermore, available treatments for wounds are accompanied by growing resistance, and because of this there is a continuing search for novel therapeutic options. Malva parviflora, Elephantorrhiza elephantina, Pentanisia prunelloides, and Dicoma anomala are some of the medicinal plants that have been used for the treatment of wounds. This research aimed to evaluate the antimicrobial and wound-healing properties of M. parviflora, E. elephantina, P. prunelloides, and D. anomala. METHODOLOGY: The phytochemical screening of M. parviflora, E. elephantina, P. prunelloides, and D. anomala was qualitatively and quantitatively conducted using a colorimetric assay. Disc diffusion, nitric oxide (NO) scavenging, and lipoxygenase assays were used to investigate the antimicrobial, antioxidant, and anti-inflammatory properties of crude extracts of M. parviflora, E. elephantina, P. prunelloides, and D. anomala. The 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) test was used to assess the cellular proliferation of the four selected plants on human epidermal keratinocytes (HaCaT) cells and their ability to promote cell proliferation, which contributes to wound healing. The tube formation assay was utilised to evaluate the ability of the extract to promote angiogenesis. RESULTS: The phytochemical screening revealed the presence of flavonoids, saponins, tannins, terpenoids, steroids, and phenols from the methanol and aqueous extracts of D. anomala, with the absence of alkaloids, glycosides, and anthraquinones. E. elephantina had a strong presence of anthraquinones, saponins, flavonoids, tannins, steroids, terpenoids, and phenols, while alkaloids were not detected. Screened phytochemicals of interest were present from the aqueous and methanol extracts of P. prunelloides and M. parviflora; however, there was a lack of phenols from P. prunelloides and terpenoids from M. parviflora. The quantitative estimation of total flavonoids and phenol content showed the M. parviflora aqueous extracts to possess most flavonoids, with E. elephantina aqueous extracts having more phenols than the other extracts analysed. All methanol extracts of all the tested plants at low (50 μg/mL) and high concentrations (200 μg/mL) were cytotoxic to the treated HaCaT cells, while the aqueous extracts were not cytotoxic. However, D. anomala demonstrated cytotoxicity at low concentrations of 50 μg/mL for the methanol and aqueous extracts; thus excluding it from further investigation for its ability to promote cell proliferation. The antimicrobial activity assay showed that the aqueous extract of P. prunelloides (minimum inhibition concentration [MIC] = 100 μg/mL) and E. elephantina (MIC = 50 μg/mL) inhibited the growth of Candida albicans, while M. parviflora and D. anomala showed no antifungal activity against C. albicans. The antibacterial results showed the aqueous extracts of M. parviflora, D. anomala, P. prunelloides, and E. elephantina to possess antibacterial activity against Staphylococcus aureus, S. epidermidis, and Pseudomonas aeruginosa. The M. parviflora extract (MIC = 50 μg/mL and 100 μg/mL) was the most promising extract as it was effective against P. aeruginosa (inhibition zone of 28 mm at a concentration of 50 μg/mL), S. epidermidis (inhibition zone of 25 mm), and S. aureus (inhibition zone of 27 mm) at concentrations of 100 μg/mL. Antioxidant plant extracts can protect wounds from oxidative damage. The M. parviflora leaf extract and whole plant extract had the same antioxidant activities as catechin, which was used as the standard. E. elephantina showed good anti-inflammatory activity at a concentration of 200 μg/mL by inhibiting the lipopolysaccharide-induced production of NO. However, the E. elephantina and D. anomala extracts had cytotoxic effects on the HaCaT cells. P. prunelloides also indicated promising anti-inflammatory activity by showing low NO production across the concentration of 200 μg/mL, with less cytotoxic effects on HaCaT cells. When analysing the cell viability over the period of 24 hours, both the M. parviflora leaf and whole plant extracts displayed no cytotoxic activity on the HaCaT cells, but rather promoted the cell growth. The results obtained from the tube formation assay demonstrated that the angiogenic factors secreted by the E. elephantina extract are capable of inducing tube formation over time after three days. The extract is also able to facilitate the migration and growth of endothelial cells to the wound site to promote wound healing. CONCLUSION: The findings of this study proved that the investigated medicinal plants – E. elephantina, M. parviflora, and P. prunelloides – can be of medicinal value to humans; however, because of its high cytotoxicity results, D. anomala was excluded from the study and not investigated further for wound healing. All extracts, especially the E. elephantina extracts, showed promising results due to their antimicrobial and anti-inflammatory activity, as well as their ability to promote the proliferation of cells. The plant also displayed novel findings on the angiogenesis assay by promoting vascular tube formation. This plant can therefore be considered a good candidate for further investigation as a potential source of new active antimicrobial activity compounds for the treatment of microbial infections in wounds and for the promotion of the wound-healing process.