Design and biological activity of imidazole-containing peptidomimetics with a broad-spectrum antioxidant activity

Histidine-containing natural dipeptides, such as L-carnosine, were reported to be effective against different oxygen-derived free radicals, and also lipoperoxyl radicals. However, L-carnosine appeared to be uneffective in vivo, due to the presence of ubiquitous specific or semi-specific hydrolytic enzymes. Therefore, a series of peptidomimetics were synthesized in order to confer resistance to enzymatic hydrolysis. Some structural modifications were also done in an attempt to improve the antioxidant power of the molecule, for example, in relation to binding of ferrous ions. The following methods were used for the evaluation of peptidomimetics: The resistance to enzymatic deactivation was determined using either a purified specific enzyme or a multienzymatic system. The free radical scavenging potential was measured by different in vitro methods involving different free radical species and biological targets. Deactivation of lipid hydroperoxides was monitored by HPLC and protection of membrane phospholipids and proteins was demonstrated. The effectiveness of peptidomimetics in vivo was evaluated. It was shown that decarboxylation of L-carnosine results in an important improvement of the resistance towards hydrolytic enzymes. In vitro experiments have demonstrated, for a series of peptidomimetics, free radical scavenging and lipid hydroperoxide deactivating properties similar to or even better than the natural peptide (depending on the experimental design). In addition, the two peptidomimetics beta-alanylhistamine and L-prolylhistamine proved to be far superior in inhibiting the lipid hydroperoxide-mediated cross-linking of a representative protein. Finally, beta-alanylhistamine was able to protect skin enzymes from UV-induced degradation in vivo.