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The oral administration of hyaluronans (HAs) (molecular weight, 300k and less than 10k) to photoaged hairless mice increased the moisture content of the stratum corneum and decreased the epidermal thickness, respectively. Furthermore, orally administered HAs suppressed the low-molecular weight of HA content of the skin. This study indicates oral administered HAs may ameliorate the skin condition resulting from photoaging.

Collagen hydrolysate (CH) was orally administered to UVB-irradiated hairless mice at doses of 20, 200-2000 mg/kg BW/day. The low dose of CH increased the skin hydration and reduced the transepidermal water loss on damaged skin. These results suggested the optimal dose of collagen to improve the UV-damaged skin condition.

We examined the effect of the daily ingestion of herb extract from Eucommia ulmoides leaves and Korean ginseng on skin damage induced by repeated UV irradiation of hairless mice. The herb extract was orally administered to mice at a dose of 1000 mg/kg/day. The hydration of mice dorsal skin decreased significantly with repeated UV irradiation, but did not decrease when the herb extract was administered for seven weeks. Transepidermal water loss (TEWL) increased with UV irradiation, but decreased with the administration of dietary herb extract. These effects were more pronounced when combined with the administration of collagen hydrolysate. Geniposidic acid from E. ulmoides leaves and ginsenoside Rg1 from Korean ginseng reduced TEWL and increased the skin moisture content of UV-damaged skin on hairless mice, respectively. We concluded that this dietary herb extract reduced the skin damage caused by UV-induced aging, with geniposidic acid and ginsenoside Rg1 detected in the blood.

Dietary glucosylceramide increased the expression of claudin-1 in UVB-irradiated mouse epidermis. Sphingosine and phytosphingosine, metabolites of glucosylceramide, increased trans-epithelial electrical resistance, and phytosphingosine increased claudin-1 mRNA expression in cultured keratinocytes. Our results indicate that the skin barrier improvement induced by dietary glucosylceramide might be due to enhancement of tight junction function, mediated by increased expression of claudin-1 induced by sphingoid metabolites.