The influence of L-arginine on the regulation of epidermal arginase.

Topical preparations containing urea are firmly established in dermatological therapy and nursing care therapy. In addition, urea is frequently used as an inactive ingredient with disinfecting, keratoplastic and penetration-promoting action in topical preparations. Despite good tolerance and ensured action, particularly the irritating effect on erosive, exudative or strongly inflammatory skin restricts its application. Endogenic urea is synthesised from L-arginine by an extra-hepatic arginase in keratinocytes. This enzymatic reaction is subject to regulation by manganese ions and the intracellular L-arginine concentration. L-Arginine is predominantly transported into the cell by a membrane transport system that is dependent on the membrane potential. By incubating keratinocyte cultures in different concentrations of L-arginine and manganese chloride, it could be shown that the keratinocytic urea synthesis can be increased. In relevant concentrations, L-arginine and manganese chloride do not exhibit any proliferation-inhibiting action, do not trigger any apoptosis or necrosis, and are stable. An increase in the expression of arginase cannot be detected using L-arginine. The application of L-arginine alone or in combination with manganese chloride increases the endogenous intrakeratinocytic urea synthesis and thus offers an option for topical therapeutic application in cases of dry skin conditions.