Influence of Varying Dietary Protein Levels on Glycation of Albumin, Tryptophan and Valine in the Plasma of Chickens

Glycation is a chemical reaction in which reducing sugars bind non-enzymatically to compounds containing amino groups. Avian species like chickens are hyperglycemic animals and have high body temperature compared to mammalian species, which enables avian species to accelerate the glycation of proteins and amino acids with glucose. Although varying dietary crude protein (CP) levels alter plasma concentrations of proteins and amino acids, the influence of varying CP levels on the glycation of plasma proteins and amino acids has not been studied so far. In the present study, therefore, glycation of albumin, tryptophan and valine in the plasma of chickens fed diets with varying CP levels (0, 10, 20, 40 and 60%) was examined. At the end of the experimental period, blood samples were collected and plasma concentrations of glycoalbumin, glycated tryptophan (tryptophan-Amadori product and (1R, 3S) - 1 - (D - gluco - 1, 2, 3, 4, 5 - pentahydroxypentyl) - 1, 2, 3, 4 - tetrahydro - β - carboline - 3 - carboxylic acid (PHP-THβC)), and valine-Amadori product were measured. Although plasma albumin concentration was reduced along with the decrease in dietary CP levels from 20% to 0%, glycoalbumin in the plasma was increased under such dietary conditions. Similar increase in the ratios of tryptophan-Amadori product to tryptophan and valine-Amadori product to valine in the plasma of chickens fed a protein-free diet was observed. These results suggest that dietary protein deficiency might enhance the non-enzymatic glycation of plasma proteins and amino acids in chickens.