Imidazole dipeptides (IDPs), including carnosine, anserine, and balenine, are functional food ingredients found in meats. They have been reported to exhibit high antioxidant activity. 2-Oxo-imidazole dipeptides (2-oxo-IDPs) are present in trace amounts in various tissues and show notably higher antioxidant activity compared with IDPs. Trace amounts of 2-oxo-IDPs are also present in commercial IDP reagents, suggesting that they affect the antioxidant activity of IDPs. Trace amounts of 2-oxo-IDPs were detected in IDP reagents from various manufacturers by HPLC. Some reagents with trace amounts of 2-oxo-IDPs exhibited higher antioxidant activity in a DPPH radical-scavenging assay compared with high-purity IDP reagents devoid of 2-oxo-IDPs. Therefore, it is important to use highly purified IDP reagents to measure antioxidant activity accurately. The antioxidant activity of highly purified IDPs and 2-oxocarnosine (2-oxo-Car) was evaluated through their ability to protect protein and DNA from ROS. 2-Oxo-Car markedly inhibited the protein and DNA degradation by ClO− and ONOO− compared with IDPs. Moreover, 2-oxo-Car was not cytotoxic, even at high concentrations, and suppressed pyocyanin-induced ROS generation in C2C12 cells compared with IDPs and glutathione. Overall, 2-oxo-IDPs are effective antioxidants and are equivalent or superior to known water-soluble antioxidants, such as glutathione and vitamin C.
Yamada et al. (Sun,) studied this question.