Dietary effect of green tea extract on epidermal levels of skin pH related factors, lactate dehydrogenase protein expression and activity in UV-irradiated hairless mice

Purpose: Skin pH, an indicator of skin health, is maintained by various organic factors, which include lactate, free amino acid (FAA), and free fatty acid (FFA). As skin ages or with illness, skin pH becomes less acidic, and functional food has been developed to maintain the acidic pH of skin. In this study, we determined the dietary effect of green tea extract (GTE) on skin pH of photo-aged mice, as measured by epidermal levels of lactate, FAA, and FFA. The protein expression and activity of lactate dehydrogenase (LDH), an enzyme of pyruvate reduction for lactate generation, was further determined. Methods: Albino hairless mice were fed a control diet (group UV+) or a diet with 1% GTE (group GTE) in parallel with UV irradiation for 10 weeks. A normal control group was fed a control diet without UV irradiation for 10 weeks (group UV-). Results: Skin pH was higher (less acidic) in group UV+ than in group UV-. In parallel, epidermal levels of lactate and FFA, as well as of LDH protein expression and activity, were reduced in group UV+. Dietary supplementation of GTE (group GTE) reduced skin pH to similar to the level of group UV-, and inversely increased epidermal levels of lactate, LDH protein expression and activity, but not of FFA. Although epidermal levels of FAA were similar in groups UV- and UV+, it was increased in group GTE to a level higher than in group UV-. In further analysis of major FFA, epidermal levels of palmitic acid [16:0], oleic acid [18:1(n-9)], and linoleic acid [18:2(n-6), but not of stearic acid [18:0] in group GTE were similar to or lower than those in group UV+. Conclusion: Dietary GTE normalized skin pH with increased levels of lactate and FAA, as well as with increased protein expression and activity of LDH in the epidermis of UVB irradiated hairless mice.