Carnosine protects cardiac myocytes against lipid peroxidation products

Endogenous histidyl dipeptides such as carnosine(β-alanine-l-histidine) form conjugates with lipid peroxidation products such as 4-hydroxy-trans- 2-nonenal(HNE and acrolein), chelatemetals, and protect against myocardial ischemic injury. Nevertheless, it is unclear whether these peptides protect against cardiac injury by directly reacting with lipid peroxidation products. Hence, to examine whether changes in the structure of carnosinecould affect its aldehyde reactivity and metal chelatingability, we synthesized methylated analogs of carnosine, balenine (β-alanine-Nτ-methylhistidine) and dimethyl balenine (DMB), and measured their aldehyde reactivity and metal chelatingproperties. We found that methylation of Nτ residue of imidazole ring (balenine) or trimethylation of carnosinebackbone at Nτ residue of imidazole ring and terminal amine group dimethyl balenine (DMB) abolishes the ability of these peptides to react with HNE. Incubation of balenine with acroleinresulted in the formation of single product (m/z 297), whereas DMB did not react with acrolein. In comparison with carnosine, balenine exhibited moderate acroleinquenching capacity. The Fe2+ chelatingability of balenine was higher than that of carnosine, whereas DMB lacked chelatingcapacity. Pretreatment of cardiac myocyteswith carnosineincreased the mean lifetime of myocytessuperfused with HNE or acroleincompared with balenine or DMB. Collectively, these results suggest that carnosineprotects cardiac myocytesagainst HNE and acroleintoxicity by directly reacting with these aldehydes. This reaction involves both the amino group of β-alanyl residue and the imidazole residue of l-histidine. Methylation of these sites prevents or abolishes the aldehyde reactivity of carnosine, alters its metal- chelatingproperty, and diminishes its ability to prevent electrophilic injury.