321 Lowering the intracellular antioxidant system triggers impaired barrier function

Abstract

Dryness is a typical feature of aged skin due to reduced levels of ceramide. It is also known that lowering the intracellular antioxidant system is one causative factor for skin aging. However, the relationship between oxidative stress initiated by lowering the intracellular antioxidant system and skin dryness has not been precisely identified. Therefore, clarifying the mechanism underlying the relationship between lowering the antioxidant system and skin dryness is important to propose treatments for skin dryness. This study was conducted to clarify the possibility that increased intracellular oxidative stress caused by lowering the antioxidant system triggers skin dryness due to influencing the expression of proteins or lipids that contribute to skin hydration. In this study, reduction of the intracellular antioxidant system was induced with buthionine sulfoximine (BSO), which is an inhibitor of glutathione (GSH) synthesis. Transepidermal water loss (TEWL) in BSO-treated reconstructed human epidermal equivalents (RHEEs) showed higher values compared to untreated RHEEs and was restored by treatment with GSH. Those results indicated that intracellular oxidative stress triggered the induction of impaired barrier function. To identify the mechanism involved, the mRNA expression levels of barrier function-related proteins in BSO-treated normal human epidermal keratinocytes (NHEKs) were then examined using real time PCR. NHEKs treated with BSO showed a significant decrease in mRNA expression levels of keratin 10, transglutaminase 1, ceramide synthases 3 and 4, and HMG-CoA reductase. Further, those changes in mRNA expression levels in BSO-treated NHEKs were restored in the presence of GSH. The sum of these results shows that increased intracellular oxidation conditions induced by lowering the intracellular antioxidant system triggers impaired barrier function through the down-regulated expression of barrier function-related genes. Thus, to improve/prevent skin dryness such as occurs in aged skin, we propose the application of antioxidants with humectants.