UV-B-induced photooxidation of vitamin E in mouse skin

Topically applied alpha-tocopherol (alpha-TH, vitamin E) inhibits UV-B (290 -320 nm) photocarcinogenesis, yet alpha-TH undergoes rapid photooxidation b y UV-B in vitro. To examine the effect of W-B on alpha-TH in vivo, we studi ed the fate of alpha-TH in UV-B-irradiated mouse skin. [C-14]-alpha-TH was applied to mouse skin at various times prior to W-B irradiation, UV-B irrad iation for 1 h at a dose rate of 2.6-2.9 J m(-2) s(-1) resulted in consumpt ion of 40-60% of the applied dose and formation of oxidation products. The major product fraction formed in UV-B-irradiated mice treated topically wit h alpha-TH contained an alpha-TH dihydroxy dimer and its two-electron oxida tion product, a spirodimer. Products previously identified as being derived from photochemical or peroxyl radical scavenging reactions of alpha-TH wer e also observed, including alpha-tocopherolquinone (alpha-TQ), alpha-tocoph erolquinone 2,3-epoxide (alpha-TQE 1), alpha-tocopherolquinone 5,6-epoxide (alpha-TQE 2), and 8a-(hydroperoxy)epoxytocopherones. These results indicat e that topically applied alpha-TH is extensively oxidized in skin and sugge st that alpha-TH photoproducts may be involved in the observed effects of t opically applied vitamin E in W-B-irradiated skin.