A Mode of Action for Butylated Hydroxytoluene-Mediated Photoprotection

Abstract

Dietarily administered butylated hydroxytoluene (BHT) has previously been shown to inhibit UV radiation induction of carcinogenesis, erythema, and ornithine decarboxylase (ODC) activity. Butylated hydroxytoluene feeding also resulted in significant increases in epidermal absorption and it was suggested that BHT's photoprotective properties might be attributable to a diminution of UV radiation dose reaching respective target sites. To explore this possibility, the contribution of stratum corneum to BHT's photoprotective action was examined. SKH-Hr-1 hairless mice were fed diets containing 0.5% (w/w) BHT for 2 weeks prior to experimentation. Control animals received the unsupplemented ration. Stratum corneum from both groups was isolated and spectral transmission recorded. Transmission, between 280-320 nm, was approximately 65% greater through stratum corneum obtained from control animals compared with that of BHT-treated animals. Further evidence of the biologic significance of this BHT effect upon stratum corneum absorption was obtained when stratum corneum was first removed by tape-stripping, the animals irradiated with 0.45 J/cm2 of UVB, and epidermal ODC activity determined. BHT provided the usual inhibition of ODC activity induction in nonstripped animals, but ODC activity induction in BHT-treated, tape-stripped animals was restored to levels that did not significantly differ from controls. The protective effect exhibited by the stratum corneum could not be attributed to BHT-induced alteration of physical dimension, as neither the thickness of stratum corneum nor the number of stratum corneum layers, as determined from measurement of NaOH-distended frozen sections, differed from controls. Although the mechanism remains obscure, these data support the contention that systemically administered BHT results in diminished levels of UV radiation reaching potential epidermal target sites and delimits a large component of the photoprotective effect to the stratum corneum.