Possible role of cutaneous metallothionein in protection against photo-oxidative stress--epidermal localization and scavenging activity for superoxide and hydroxyl radicals.

It is reported that increasing metallothionein (MT) synthesis suppressed sunburn cell formation in the mouse skin after ultraviolet B (UVB) irradiation, implying a photo-protective effect of the cysteine-rich protein. To understand the mechanism of the defense by cutaneous MT against UVB injury, an immunohistological localization of MT in human normal skin was studied following examination of lesional skin. MT in the skin was localized in granular layer with diffuse staining pattern in normal skin, defect in psoriatic lesions, positive but thin in granular cells in the lesions of lichen planus. MT treatment showed a significant decrease in chemiluminescence induced by superoxide radicals and depressed signal intensity of hydroxyl radicals derived from the Fenton reaction system. From the viewpoint of characteristic localization and probable role in scavenging activity for reactive oxygen species, MT in the epidermis may contribute to the protection against phototoxic injury in association with enzymatic and non-enzymatic antioxidants. These findings may support the previous results of UV defense by cadmium-induced MT in the skin.