Age- and sun exposure-dependent differences in 8-hydroxy-2'-deoxyguanosine and Nε-(carboxymethyl)lysine in human epidermis

Aging and exposure to sunlight are two major factors in the deterioration of skin function. In this study, thirty-six fixed human skin samples from sun-exposed and unexposed areas from young and old individuals were used to evaluate the localization of oxidative stress according to levels and distribution of 8-hydroxy-2'-deoxyguanosine and Ne-(carboxymethyl)lysine in samples using immunohistochemistry. In the epidermis of the young, negligible amounts of 8-hydroxy-2'-deoxyguanosine and Ne-(carboxymethyl)lysine were detected in unexposed areas, whereas nuclear 8-hydroxy-2'-deoxyguanosine and cytoplasmic Ne-(carboxymethyl)lysine were increased in the lower epidermis in sun-exposed areas. In contrast, the aged presented prominent nuclear 8-hydroxy-2'-deoxyguanosine and nuclear Ne-(carboxymethyl)lysine in the epidermis of unexposed areas, concomitant with dermal increase in Ne-(carboxymethyl)lysine. However, the immunostaining of 8-hydroxy-2'-deoxyguanosine and Ne-(carboxymethyl)lysine revealed a decrease in the epidermis of sun-exposed areas in the aged. These results suggest an age-dependent difference in the adaptation and protective mechanisms of the epidermis against sunlight-associated oxidative stress, thus necessitating distinct standards for evaluation in each age group. Further investigation is warranted to elucidate underlying molecular mechanisms.