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Abstract
f -Tocopherol is a lipophilic vitamin that exhibits an antioxidative activity. The purpose of this study was to clarify the roles of f -tocopherol in the regulation of intracellular glutathione (GSH) levels in HaCaT keratinocytes. When HaCaT keratinocytes were cultivated with f -tocopherol for 24 h, the intracellular GSH was increased at every concentration of f -tocopherol tested. Furthermore, the HaCaT keratinocytes cultured with f -tocopherol at 50 w M for 24 h exhibited resistance against H 2 O 2 . However, a short exposure of HaCaT keratinocytes to f -tocopherol for 1 h did not influence either the GSH level or the resistance to H 2 O 2 . These findings suggest that GSH, which is inductively synthesized by f -tocopherol, effectively reduces exogenous oxidative stress. To evaluate the effect of f -tocopherol on the GSH level, BSO, which is a typical inhibitor of n -glutamylcysteine synthetase ( n -GCS), was used. When BSO was added to HaCaT keratinocytes, no action of f -tocopherol on the GSH level was observed. On the other hand, f -tocopherol resulted in the up-regulation of n -GCS-HS (heavy subunit) mRNA. In addition, water soluble f -tocopherol derivatives ( f -tocopherol phosphate and trolox) caused no changes in GSH level. From these results, it was concluded that f -tocopherol increases the intracellular GSH level of HaCaT keratinocytes through the up-regulation of n -GCS-HS mRNA.