Potential medicinal plants for progressive macular hypomelanosis

Progressive macular hypomelanosis (PMH) is a hypopigmentation disorder caused by the bacterium identified as Propionibacterium acnes. The current treatments for PMH are antibiotics together with ultra violet radiation; however, UV radiation is not a recommended method to increase melanin production. Currently, there are no known plants used traditionally or medicinally for PMH. The objective of this study was to find plants that could stimulate tyrosinase activity induce melanin production and inhibit P. acnes' growth. Seventeen ethanol plant extracts, used traditionally in Africa for skin diseases, were screened for their antibacterial activity against P. acnes, their effect on monophenolase activity of tyrosinase and their cytotoxicity and stimulation of melanin production on mouse melanocytes (B16-F10). Hypericum revolutum Vahl subsp. revolutum (Hypericaceae) and Withania somnifera L. Dunal (Solanaceae) (twigs and leaves), combined with the known drug tetracycline, exhibited significant antibacterial activity against P. acnes, with the minimum inhibitory concentration ranging from 5.47 μg/ml to 14.06 μg/ml. The combination of a known drug with other antibacterial compounds not only decreases the concentration needed to inhibit bacterial growth, but also decreases the chances of bacterial resistance. W. somnifera was the only plant extracts that resulted in an increase in the monophenolase activity of tyrosinase. Four compounds typically present in plant extracts, namely coumarin, quercetin, withaferin and winthanone, were docked into the active site of tyrosinase enzyme to determine the interaction with active site residues. Mouse melanocytes (B16F10) treated with H. revolutum, W. somnifera (leaves) and Terminalia prunoides showed an increase in total melanin content as compared to untreated cells at 12 μg/ml, 12 μg/ml and 150 μg/ml respectively. Considering both the antibacterial activity and the stimulatory effect of the treatment on melanin production, H. revolutum and W. somnifera (leaves) could be considered as potential plants for further studies for PMH.