Mushroom tyrosinase activity of phenolic compounds isolated from Greyia flanaganii (bolus)

Pigmentation has become an important phenotypical characteristic in the pharmaceutical, medicinal as well as in the cosmetic field. Plants are inexpensive resource that can be utilized to inhibit tyrosinase activity as well as melanin production [1]. Ethanolic leaf extract of Greyia flanaganii (Bolus) showed significant (p<0.05) anti-tyrosinase activity when L-tyrosine was used as a substrate exhibiting the 50% inhibitory concentration (IC₅₀) of 32.62µg/ml. The extract exhibited significant (p<0.05) 9.89% reduction of melanin content at 6.25µg/ml and no toxicity on melanocyte cells was observed at the highest concentration (400µg/ml) tested. Seven phenolic compounds; 2',4',6'-trihydroxydihydrochalcone (C1), 2',6',4-trihydroxy-4'- methoxydihydrochalcone (asebogenin/lyonogenin) (C2), 2',6'-dihydroxy-4'-methoxydihydrochalcone (C3), 5,7-dihydroxyflavanone [(2S)-pinocembrin] (C4), 2',6'-dihydroxy-4',4-dimethoxydihydrochalcone (C5), (2R,3R)-3,.5,7-trihydroxy-3-O-acetylflavanone (pinobanksin-3-acetate/dihydrogalangin-3-acetate) (C6) and a possible novel compound (C7) were isolated from the ethanolic leaf extract of Greyia flanaganii. The isolated compounds were tested for their antioxidant, cytotoxicity and tyrosinase activities. C1 resulted in significant (p<0.01) antityrosinase activity exhibiting an IC₅₀ value of 17.86µg/ml as compared to the other compounds and the positive control Kojic acid. C1 also showed low toxicity effect on melanocytes cells (IC₅₀ of 95.56µg/ml) and caused 10% reduction of melanin content at 1.5µg/ml. C1, C2, C3 and C4 showed good antioxidant activity (IC₅₀ values ranged from 0.895±0.04, to 19.5±0.11µg/ml). The leaf extract, C1, C7 and C2 exhibited a minimum inhibitory concentration of 250, 250, 500 and 12.5µg/ml against Propionibacterium acnes. The leaf extract of Greyia flanaganii can be considered as effective tyrosinae inhibitors and can be used for treating dermatological disorders such as age spot, melasma, actinic damage etc.

Reference: [1] Momtaz, S. et al. (2008)J. Ethnopharmacol. 119:507–512.