ENTADA AFRICANA GUILL. & PERR. (MIMOSACEAE) AS A SOURCE OF SKIN WHITENING AGENTS

Entada africa Guill. & Perr. (Mimosaceae) is a small tree mainly growing in tropical areas. In Mali, it is found in the southern region of the country, known with the popular name of “Samanèrè”. It is used in Traditional Medicine for various type of illness and leaves, stem bark and root are employed. Based on primary ethnobotanical field research with healers, various uses were attributed to this species for the treatment of many diseases such as malaria fever, hepatitis, respiratory tract complaints and wound healing (1). Previous biological studies have shown anti-inflammatory, hepatoprotective, antibacterial and anti-proliferative activities (2). As a part of our investigations on plant extracts as sources of skin whitening agents (3), in this work we evaluated the inhibitory effects of E. africana root extracts on the activity of tyrosinase, the key enzyme for melanin biosynthesis in plants and animals. Among known melanogenesis inhibitors derived from plants, flavonoids are playing a prominent role and a previous study reported that flavonoids represent the major phytocostituents of E. africana root (4). For the study, air-dried and powdered roots were firstly defatted with n-hexane and then sequentially extracted with CHCl3, CHCl3/MeOH (9:1) and MeOH by exhaustive maceration to give, after removing the solvent under reduced pressure, the respective residues. Thus, all the extracts were screened for the inhibition of tyrosinase activity. Results showed that CHCl3/CH3OH extract (CHME) evidenced the highest inhibitory effects on tyrosinase (51% at 200 μg/ml). The average total flavonoid content of CHME was also determined as 6%. Additionally, CHME showed a strong Fe2+-chelating ability (66.94% at 500 μg/ml). It is reported that many flavonoids interfere with the activity of tyrosinase through chelation of copper ions in its active site. Therefore, the tyrosinase-inhibitory activity of CHME may be correlated to the presence of flavonoid compounds acting as chelating agents and E. africana root may be proposed as a potential source of new therapeutic whitening agents for the reduction of hyperpigmentation in cosmetic and pharmaceutical products, as well for the prevention of enzymatic browning in the food industry.