The stimulating effect of extracts of South African plants on melanin production and their antibacterial activity against Cutibacterium acnes

Abstract

Pigmentary disorders are a global problem. Although most hypopigmented diseases are not harmful and do not result in physical pain, the emotional and psychological effects of these conditions can be devastating to the affected patient. Progressive macular hypomelanosis (PMH) is a skin disorder which results in reduced amount of pigment and the PMH-lesion areas contain a high-density of Cutibacterium acnes. The current treatments include the use of ultra-violet radiation in combination with antibiotics, however side effects from antibiotic include severe rashes, blistering and dryness, whereas excessive UV radiation leads to premature ageing and susceptibility to skin cancer development. Hence in the present study, eleven medicinal plants, prepared into thirty-three extracts using water, ethanol and dichloromethane were investigated for their antibacterial activity against C. acnes and their stimulatory activity towards tyrosinase and melanin production as possible treatments for PMH. Of the eleven plants, two showed significant results, the ethanolic Sideroxylon inerme extract had a minimum inhibitory concentration (MIC) of 125 μg/mL against C. acnes (ATCC 6919) and when combined with tetracycline, had an additive effect. The ethanolic Bulbine frutescens extract increased the monophenolase activity of tyrosinase and increased melanin production by 31.44 ± 1.41% and 8.55 ± 1.66%, respectively, at 200 μg/mL. The α-melanocyte stimulating hormone increased melanin production by 13.39 ± 1.44% at 100 μM. Both ethanolic Sideroxylon inerme and Bulbine frutescens showed to have no antiproliferative activity towards the human melanoma (UCT-Mel-1) and human keratinocyte (HaCaT) cell lines at 400 μg/mL. The ethanolic leaf and stem extracts of Sideroxylon inerme and Bulbine frutescens could potentially be used as an alternative treatment for PMH dur to their antibacterial and melanin production activity. Further investigation into the cosmetic safety of the extracts as a topical treatment by evaluating the irritancy potential of the extracts and conducting in vivo hypopigmentation trials to determine their efficacy.