Natural and Synthetic Sources as Antioxidant and Inhibitors of Tyrosinase

Melanogenesis is a physiological pathway for the formation of melanin, a pigment which plays an important role in the protection against UV damage and represents an important defense system of the skin against harmful factors. Overproduction and accumulation of melanin occur in several skin disorders including solar melanosis, ephelides, melasma, senile lentigos and postinflammatory hyperpigmentation. Since tyrosinase is the limiting step enzyme in melanogenesis, its inhibitors have become increasingly important as depigmenting agents in hyperpigmentation disorders. Since (or considering that) many known whitening agents have been proven to be toxic, there has been increasing impetus to identify alternative tyrosinase inhibitors, especially from natural sources. In this thesis has been investigated the inhibitory activity on tyrosinase of different natural extracts (Asphodelus. microcarpus, Sarcopoterium spinosum, Phytolacca dioica and several honeys) and of synthetic heteroarylcoumarins. It has been also evaluated the antioxidant activity and the citotoxicity of several compounds and extracts. The results showed that all extracts have a direct inhibitory anti-tyrosinase activity with flowers ethanol extract of Asphodelus microcarpus and ethylacetate extract of Phytolacca dioica exhibiting the stronger effect. The same extracts showed the highest antioxidant activity and an elevated levels of total phenolics and flavonoid content. As for the neo-synthesized compounds, two of them have shown inhibitory activity on tyrosinase even on B16F10 cells. These results encourage the the further deepening of research both on synthetic compounds derived from coumarins and on the extracts, that could be a good source of bioactive compounds useful as depigmenting agents in skin disorders.