Journal of Advances in Medical and Pharmaceutical Sciences

Aims: Currently there is enormous demand for skin-lightening agents, creating a quest for identification of new substances. Tyrosinase has become the main drug target for reducing skin pigmentation. The objective of this study was to detect tyrosinase inhibitory effects of eight medicinal plants that are used to treat skin conditions.

Study Design:  In vitro assay.

Place and Duration of Study: Department of Biochemistry, Faculty of Medicine, University of Peradeniya, Sri Lanka, from June 2016 to December 2017.

Methodology: Tyrosinase inhibitory effects of methanol extracts of eight plant species that are used to treat various skin conditions were measured using 3,4-Dihydroxy-L-phenylalanine (L-DOPA) as the substrate. Kojic acid was used as the positive control. IC₅₀ values of extracts with high activity were measured using a range of concentrations. Statistical significance of the differences between the inhibitory effects was calculated using ANOVA.

Results: Thespesia populnea bark showed the highest inhibition among the tested, with an IC₅₀ of 190 µg/mL. Phyllanthus emblica fruit also showed higher inhibitory effect with IC₅₀ value of 251 µg/mL. IC₅₀ value of kojic acid (3.4 µg/mL) against tyrosinase was significantly lower than that of P. emblica and T. populnea. Even though Santalum album bark and Vernonia cinerea plant showed 36.3 and 32.8% inhibitions respectively at 0.5 mg/mL, these effects did not show a dose-dependent increase. Extracts of Coscinium fenestratum, Persea Americana, Vigna radiata and Vigna unguiculata demonstrated only lower inhibitory effects on tyrosinase.

Conclusion: Current study reveals higher antityrosinase activities in methanol extracts of P. emblica fruit and T. populnea bark.