Poster presentation, P29

Official XXIst International Pigment Cell Conference website - 21-24 Sept 2011, Bordeaux - France | updated: September 04 2011

UVA radiation induces melanogenesis through modulation of phase II antioxidant enzymes: The protective effect of gallic acid

Ultraviolet A (UVA) has been recognized as a major factor for skin hyperpigmentation through increased melanogenesis. While melanin exhibits photoprotective properties, its overproduction could cause genotoxicity probably leading to melanomagenesis, especially in lightly pigmented skin. UVA-induced oxidative stress may play a role in melanogenesis and thus improving antioxidant defenses may be useful in inhibition of abnormal melanin synthesis. Phase II antioxidant enzymes including γ-glutamate cysteine ligase (γ-GCL), the rate-limiting enzyme for GSH synthesis, and glutathione S-transferase (GST) are essential for the skin in protecting against photooxidative stress. Therefore, attempts have been made to study the roles of antioxidants including gallic acid, a phenolic present in various botanicals, in protecting against UVR-induced melanogenesis in order to develop effective depigmenting agents. This study aimed to investigate antimelanogenic effects of gallic acid (up to 60 microM) on lightly pigmented human melanoma (G361) cells irradiated with UVA with respect to modulation of γ-GCL and GST activity and mRNA. Melanin synthesis, tyrosinase activity, GSH content and GST activity were determined using spectrofluorophotometric methods as well as γ-GCL and GST mRNA levels were assessed using real-time RTPCR. Gallic acid was capable of inhibiting UVA-induced melanin production and tyrosinase activity in relation to restoration of GSH levels and GST activity as well as upregulation of γ-GCL and GST mRNA in G361 cells. However, UVA radiation exhibited time-dependent effect on γ-GCL and GST mRNA expression as downregulation of γ-GCL and GST mRNA levels was observed at 2-h post-irradiation but recovery of the mRNA levels was achieved by 4 h. In conclusion, upregulation of phase II enzymes including γ-GCL and GST could be a possible mechanism by which gallic acid provides protection against UVA-mediated melanogenesis. This work was supported by Faculty of Medicine Siriraj Hospital, Mahidol University, Thailand.

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