Superoxide free radical generation by Amadori compounds: the role of acyclic forms and metal ions.

Generation of oxygen free radicals by glycated proteins is widely believed to be one of the causes of oxidative stress in diabetes and aging. Metal ion catalysis is regarded as an essential part of the oxidative mechanism. In this work, we also considered an alternative "metal-free" superoxide radical formation by a number of fructose-amino acids (Amadori compounds) derived from glycine and lysine, which represent the simplest models for early glycated proteins. In the superoxide dismutase-dependent cytochrome c assay, 1 mM Chelex-treated aqueous solutions of monofructose-amino acids 4-6 generated 0.9-3.6 x 10(-10) M s-1 O2*- at pH 7. Surprisingly, the rates of superoxide radical formation in the solutions of difructose-amino acids 7-9 were significantly higher (0.75-5.8 x 10(-9) M s-1 O2*-). The percentage of acyclic sugar anomers (