Presence of aspartic dipeptides with β peptide bond and/or D-aspartyl residue in rat blood after ingestion of porcine liver protein hydrolysate

Abstract

Background: Formulated liver protein hydrolysate (LPH) was prepared from porcine liver protein. Animal experiments have demonstrated that oral administration of LPH ameliorates alcohol-induced liver toxicity, as well as exercise- and concanavalin A-induced low locomotor activity in mice. The peptides responsible for the beneficial effect have not yet been identified. Recently, presence of food-derived peptides in human blood has been detected post ingestion of other food protein hydrolysates. The peptides absorbed into blood circulation system have been associated with the biological response post ingestion, as they can reach target organs. The objective of the present study was to identify the food-derived peptides in rat blood after ingestion of LPH.

Results: In the in vitro exopeptidase digest of LPH, pyroglutamyl, prolyl, hydroxyprolyl, and aspartic dipeptides were identified. The aspartic peptides (Asp-Val, Asp-Ile, Asp-Leu, and Asp-Phe) showed multiple peaks by LC-MS/MS, indicating the presence of isomers. Four isomers with L- and D-aspartyl residues, and α and β peptide bonds were present in each sequence. After administration of LPH, the amounts of unusual aspartic dipeptides with β peptide bond and/or D-aspartyl residue significantly increased in rat plasma, while those of the other usual aspartic peptides did not.

Conclusions: Indigestible isomerized aspartic di-peptides are released by in vitro exopeptidase digestion of LPH. These peptides are also generated by in vivo digestion and absorption process and increase in blood of rat upon ingestion of LPH.  

Keywords: Liver protein hydrolysate, isopeptide, bioavailability, β peptide bond, isomerization, D-aspartyl residue.