LACK OF EFFECT OF COPPER ON ADVANCED MAILLARD REACTION AND GLUCOSE AUTOXIDATION AT PHYSIOLOGICAL CONCENTRATIONS OF ALBUMIN

This study examines the possible action of copper on advanced glycatio n. Copper has been shown to induce fluorescence due to advanced-glycat ed-end-products (AGEs) on albumin incubated with glucose, and this was interpreted as activation of the glucose or Amadori product (AP) auto xidation. We glycated albumin (60 g/L) to several levels with increasi ng concentrations of glucose. The dialysed glucose-free glycated album in was then incubated with 1.5 mu mol/L copper or 1 mmol/L diethylenet riaminepentaacetic acid (DTPA), plus or minus glucose. The production of AP, measured as furosine, was similar whether DTPA or copper was pr esent in the incubation medium. It linearly increased as a function of time and glucose concentration in both cases up to a maximum (furosin e around 20 mmol/g protein), indicating saturation of the free NH2 res idues on the protein. The fluorescence due to AGEs increased linearly over time for glycated albumin incubated without glucose, and exponent ially when glucose was added to the incubation medium. This fluorescen ce was also unaffected by DTPA or copper for a glucose concentration b elow 125 mmol/L and initial furosine below 10 mmol/g. However copper c aused a slight activation in samples with very high glucose (1.25 mol/ L) and furosine (30-40 mmol/g) concentrations. We therefore find no ef fect of copper in this experiment, because the copper concentration is lower and the albumin higher than that used in previous studies. In t hese conditions, albumin chelates copper and inhibits its oxidative ac tivity. The protein concentrations used in most in vitro studies showi ng a copper effect were below 10 g/L with copper often above 10 mu mol /L, so that copper may act oxidatively. As the lens and arterial wall have high protein concentrations, copper should have no action on prot ein glycation in vivo, unless altered protein structure impedes the in activation of copper by chelation.