Abstract
Imidazole dipeptides are generally present in animal foods as a mixture of anserine and carnosine. When ingested orally, both dipeptides are absorbed from the intestinal tract and immediately hydrolyzed to their constituent amino acids in blood. A reversed phase-HPLC method using acetonitrile solvent was developed for the quantification of imidazole dipeptides and their metabolites in blood. However, due to the overlapping of serum components and deproteinizing reagents, it was difficult to simultaneously determine the plasma levels of these compounds, especially that of 1- or 3-methyl histidine, using this system. To solve this, we modified the solvent and used an isocratic condition without acetonitrile to prolong the retention time of imidazole dipeptides and their metabolites. Consequently, this system was able to quantify imidazole dipeptides and their related metabolites without removal of the deproteinizing reagents. Further, we evaluated whether there are differences in plasma concentrations and bioavailability of different commercial products. Alterations in plasma levels of imidazole dipeptides and related compounds in 10 normal volunteers who orally ingested two different commercial products in a double-blinded and crossover study were measured using the modified method. Although the plasma levels of anserine were only 1/10 of 1-methyl histidine, the Cmax of anserine was observed at 40 min after ingestion and was similar for both commercial products. There were no differences in the bioavailability and plasma levels of the related compounds of the two commercial imidazole dipeptides. These results indicate that the modified HPLC method was applicable for the simultaneous and precise determination of human plasma levels of imidazole dipeptides and their metabolites.
