Glycation in food and metabolic transit of dietary AGEs (advanced glycation end-products): studies on the urinary excretion of pyrraline

Abstract

Pyrraline [∊-(2´-formyl-5´-hydroxymethyl-pyrrolyl)-l-norleucin] belongs to the group of AGEs (advanced glycation end-products) formed in the final stage of the Maillard reaction in foods and in vivo. As it is generally accepted that AGEs are pathophysiologically relevant in aging and in diseases such as diabetes and uraemia, physiological consequences resulting from the ingestion of dietary AGEs are discussed, but balance studies for well defined AGEs are still lacking. The aim of our study was to investigate the influence of nutrition on the urinary excretion of pyrraline. After the first day without dietary restrictions, seven healthy volunteers were asked, starting on the morning of day 2, to ingest a diet virtually free of Maillard compounds (i.e. no cooked or roasted foods, no bakery products, no coffee, etc.). Dietary control was stopped on the morning of day 5. We collected 24 h urine samples for these 5 days, which were analysed for free pyrraline by reverse-phase HPLC with UV detection at 297 nm. We found that urinary excretion of free pyrraline was directly affected by the composition of the diet, decreasing from 4.8±1.1 mg/day on day 1 to levels of 1.6, 0.4 and 0.3 mg/day on days 2, 3 and 4 respectively, followed by a significant increase to 3.2±1.4 mg/day on the 5th day. The results of this work prove, for the first time, that urinary excretion of pyrraline is strongly dependent on its dietary intake. Thus the influence of nutrition should be taken into consideration in studies directed to the physiological role of glycation compounds.