Research Article Melanogenesis and Antityrosinase Activity of Selected South African Plants

Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Melanin is the pigment that is responsible for the colour of eyes, hair, and skin in humans. Tyrosinase is known to be the key enzyme in melanin biosynthesis. Overactivity of this enzyme leads to dermatological disorders such as age spots, melanoma and sites of actinic damage. Ten plants belonging to four families (Asphodelaceae, Anacardiaceae, Oleaceae, and Rutaceae) were investigated for their effect on tyrosinase using both L-tyrosine and L-DOPA as substrates. Ethanol leaf extracts (500 µg/mL) of Aloe ferox, Aloe aculeata, Aloe pretoriensis, and Aloe sessiliflora showed 60%, 31%, 17%, and 13 % inhibition of tyrosinase activity respectively, when L-tyrosine was used as a substrate. Harpephyllum caffrum (leaves) at a concentration of 500 µg/mL had an inhibitory effect of 70 % on tyrosinase when L-DOPA was used as a substrate. The IC50 of Harpephyllum caffrum (leaves and bark) were found to be 51±0.002 and 40±0.035µg/mL, respectively. Following the results obtained from the tyrosinase assay, extracts fromHarpephyllum caffrum were selected for further testing on their effect on melanin production and their cytotoxicity on melanocytes in vitro. The IC50 of both extracts was found to be 6.25 µg/mL for melanocyte cells. Bark extract of Harpephyllum caffrum showed 26% reduction in melanin content of melanocyte cells at a concentration of 6.25 µg/mL. The leaf extract of this plant showed some toxicity on melanocyte cells. Therefore, the bark extract of Harpephyllum caffrum could be considered as an antityrosinase agen