EFFECT OF UVB ON HYDROLYSIS OF ALPHA-TOCOPHEROL ACETATE TO ALPHA-TOCOPHEROL IN MOUSE SKIN

We have assessed the hydrolysis of alpha-tocopherol acetate (alpha-TAc ) to the active antioxidant alpha-tocopherol (alpha-TH) in mouse epide rmis and in supernatant from epidermal homogenates. Topically administ ered alpha-TH prevents UVB photocarcinogenesis in C3H mice, whereas al pha-TAc does not. Hydrolysis in skin was monitored in mice treated top ically with deuterium labeled alpha-TAc (d(3)-alpha-TAc). Epidermal sa mples were isolated from mice and analyzed for endogenous (d(0)-alpha- TAc) and d(3)-alpha-TH by gas chromatography-mass spectrometry, Within 24 h, the levels of d(3)-alpha-TH increased up to 10-fold over endoge nous d(0)-alpha-TH levels; however, in mice irradiated with UVB prior to the application of d(3)-alpha-TAc, levels of d(3)-alpha-TH increase d up to 30-40-fold over endogenous d(0)-alpha-TH. This enhancement of alpha-TAc hydrolysis increased with increasing UVB dose. Prior UVB exp osure may increase hydrolysis of alpha-TAc by increasing epidermal est erase activity. Nonspecific esterase activity was measured in the 2000 X g supernatant from epidermis of unirradiated and irradiated mice. a lpha-Napthyl acetate, a nonspecific esterase substrate, was converted to alpha-napthol in supernatants from unirradiated mice. Hydrolysis to alpha-napthol increased approximate to 3-fold in supernatants from ir radiated mice. Hydrolysis of alpha-TAc to alpha-TH also occurred in su pernatant from unirradiated mice, and this hydrolysis increased approx imate to 3-fold in supernatant from irradiated animals. These data ind icate that nonspecific esterase activity was increased by UVB in the s kin, that alpha-TAc is converted to alpha-TH in the homogenate fractio n containing nonspecific esterase, and that UVB exposure modulates the metabolism of alpha-TAc to alpha-TH in vivo.