Low molecular weight antioxidants released from the skin's epidermal layers: an age dependent phenomenon in the rat

Skin is one of the tissues most exposed to oxidative stress both from endogenous and exogenous sources. Therefore, it can be speculated that skin possesses an extremely efficient antioxidant defense mechanism, particularly in its epidermal layers. The present study shows that human and rat skins possess different and unique reducing antioxidant profiles. These reducing antioxidants can be washed out into the surrounding environment. Non-invasive measurements indicated that skin releases low molecular weight antioxidants (LMWA) from its epidermal layers. Cyclic voltammetry measurements have shown that rat skin releases three major groups of reducing antioxidants at peak potentials of 476 and 889 and 1044 mV while human skin releases two major groups at peak potentials of 779 and 1068 mV. In rat, the overall concentrations of the LMWA secreted decreased significantly with age. The major components of the LMWA composing the first anodic wave in rats were identified as uric acid and ascorbic acid. Uric acid and other as yet uncharacterized LMWA, but not ascorbic acid, were released in human skin. Differences in the ability to release high levels of uric acid among species were well correlated with their metabolic rates. It is suggested that in rat the released LMWA may serve as a possible marker for aging of the skin.