Cutaneous Metabolism

According to the literature, the metabolism of other organs than the liver such the skin seems much less studied. Indeed, skin represents the major protective barrier of the body to the environment and chemicals exposure but is not really yet considered as an organ involved in xenobiotic metabolism. It appears to be a tissue of weak catalytic activity generating less diverse metabolites and less funny reaction mechanisms. However, this assertion could be due to the lack of specific tools to study skin metabolism such as particular sample preparation protocols or analytical methods which are accurate and sensitive enough.

Thus, as skin is the largest organ of the human body, even if weak enzymatic activities are observed, they can become consequent when considering its total surface area. Consequently, research on skin metabolism would require a real scientific effort and dynamism to characterize skin metabolizing enzymes and their activities. In addition, the 7th European amendment to the cosmetic directive forbids the use of animal testing to assess the effectiveness and safety of new cosmetics. This policy has forced the cosmetic industry to develop in vitro tools as alternative methods to animal experiments. Reconstructed human skin models are a part of them. For these reasons, these models have to be characterized and compared with normal human skin in terms of metabolic capabilities. This work presents a review of the L’Oreal research strategy and main results in the characterization of skin metabolic equipment and its catalytic capabilities. Thus, characterization for the expression of several enzymes (CYP450, Esterase, NAT, GST, UGT, SULT…) and their catalytic activities (Apparent Km, Vmax and clearance) in various reconstructed skins were compared to normal human skin samples.