Kinetic Behaviour of Skin Pigmentation Inhibitory Activity of some Selected Nigerian Medicinal Plants and Other Related Antioxidant Properties

Background: Over exposure to Ultra Violet (UV) radiation is one of the most significant external stress-inducing factors resulting into occurrence of skin pigmentation among others in human body. The biological implication of such disorders is not only limited to premature skin aging and cancer, but also resulted into economic loss of perishable agricultural products. Methods: Methanol extracts of ten (10) medicinal plants with skin health traditional history were selected for this study. The biological profile of the extracts was assessed in an in-vitro system using colorimetric assays: tyrosinase inhibition, Ferric-ion Reducing Antioxidant Power (FRAP), Trolox Equivalent Absorbance Capacity (TEAC) and Fe II-induced microsomal lipid peroxidation. Results: Representative of asteraceae such as Laggera pterodonta (S3); Ageratum conyzoides (S4) and Chromolaena odorata (S5), while Euphorbia convoluloides (S8) were found to possess good anti- tyrosinase activity (IC50 = 177.50; 125.08; 167.58; 161.92) μg/ml respectively, in which the rate of formation of dopachrome proceeded via pseudo second order kinetic using the Largergren model. Other notable inhibition of oxidative stress displayed by the methanol extracts includes S7 (FRAP = 1905.12 ± 2.85 μM AAE/g); S1 & S6 (TEAC = 2163.48 ± 2.80; 1044.35 ± 28.99) μM TE/g, while S7 & S9 showed highest inhibitory activities on Fe II-induced microsomal lipid peroxidation (IC50 = 33.625; 35.125) μg/ml, respectively in competitive manner to that of the commercial anti-oxidant EGCG (IC50 = 36.250 μg/ml). Conclusion: The outcome of the biological properties of the selected plant extracts in this study suggested the existence of relationship between the traditional claims and the scientific data therein.