Dual effects of silibinin treatment on autophagy-regulated dermal apoptosis retardation and epidermal apoptosis up-regulation in UVB-induced skin inflammation.

Skin inflammation induced by ultraviolet B (UVB) radiation is characterized by migration and chemotaxis of inflammatory cells, epidermic thickening and erythema. Apoptosis and autophagy of epidermal and dermal cells are involved in its development through the adjustment of balance between cell survival and death. In this study, the role of balance between cell survival and apoptosis in dermis and epidermis in UVB-induced skin inflammation and the effect of autophagy on the balance were elucidated, and the protective mechanism of silibinin was investigated through the examination of the influence of autophagy activation or inhibition on erythema, migration, and chemotaxis of inflammatory cells as well as apoptosis adjustments. In UVB-irradiated controls, dermal apoptosis was retarded and the survival of inflammatory cells was promoted through the up-regulation of dermal autophagic level; epidermal apoptosis was increased through the down-regulation of epidermal autophagic level, causing migration and chemotaxis of neutrophils and mast cells as well as skin erythema. In silibinin-treated group (50 mg/kg/day for 4 days), dermal apoptosis was increased through inhibiting dermal autophagy; improper adjustment of epidermal apoptosis was attenuated through promoting epidermal autophagy, presenting dual effects on the balance between autophagy and apoptosis of epidermal and dermal cells and the protection.