Planta Med 2007; 73 - P_464
DOI: 10.1055/s-2007-987244

Anti-tyrosinase activity of South African plant extracts

N Lall 1, MB Mapunya 2, RV Nikolova 2, PJ Houghton 3
  • 1University of Pretoria, Department of Botany, 0002, South Africa
  • 2University of Limpopo, School of Molecular and Life Sciences, Turfloop campus, Private Bag X1106, Sovenga, 0727, South Africa
  • 3Pharmaceutical Sciences Division, Kings College London, 150 Stamford Street, London SE1 9NH, UK

Tyrosinase is known to be the key enzyme in melanin biosynthesis. Melanin is the pigment that is responsible for the colour of eyes, hair and skin in humans. Over-activity of this enzyme leads to dermatological disorders such as age spots, melasoma and site of actinic damage [1].

Ten plants belonging to four families (Asphodelaceae, Anacardiaceae, Olaceae and Rutaceae) were investigated on their effect on tyrosinase using both L-tyrosine and L-DOPA as substrates [1]. Ethanol leaf extracts of Aloe aculeate, Aloe pretoriensis and Aloe sessiliflora showed 31%, 17% and 13% inhibition of tyrosinase activity respectively at

0.5mg/ml when L-tyrosine was used as a substrate. Extracts of leaves and bark of Harpephyllum caffrum showed inhibition of 90% and 92% respectively at 0.25mg/ml. H. caffrum (leaves) at a concentration of 0.5mg/ml had an inhibitory effect of 70% on tyrosinase when L-DOPA was used as a substrate.

Following the results obtained from the tyrosinase assay, extracts from H. caffrum were selected for further testing on their effect on melanin production and their cytotoxicity on melanocytes in vitro. Fifty percent inhibitory (IC50) concentration of both extracts was found to be 1.5×10-3 mg/ml for melanocyte cells. Bark and leaf extracts of H. caffrum showed 26% and 20% reduction respectively in melanin content of melanocyte cells at a concentration of 6×10-3 mg/ml. Therefore, both extracts of H. caffrum could be considered as anti-tyrosinase agents for dermatological disorders such as age spots, melasoma and pigmentation disorders.

Acknowledgements: National Research Foundation, University of Pretoria, University of Limpopo.

Reference: 1. Nerya, O. et al. (2003)J. Agric. Food Chem, 51: 1201–1207.