[Diabetic nephropathy and low molecular weight advanced glycation end-product in urine]

Glucose reacts non-enzymatically with amino groups of proteins to produce diverse groups of protein-bound moieties with cross-linking properties called advanced glycation end-products (AGEs). A large number of studies suggest that tissue and circulating AGEs, especially those bound to small peptides, play an important role in the pathogenesis and development of diabetic complications. The aim of the present study was to evaluate AGE-peptide levels in the urine in various stages of diabetic nephropathy and to analyze structures of AGEs generated in vivo. Urine samples were obtained from 100 type-2 diabetic patients with various stages of nephropathy, 39 non-diabetic patients with renal dysfunction, and 20 control subjects with neither diabetes nor renal disease. Low molecular weight peptides (< 10 kDa) isolated from each sample were used. With the use of size-exclusion HPLC monitored by AGE-specific fluorescence, three main fluorescence peaks were detected at molecular weights of 6,000 Da, 2,500 Da, and 300 Da. The fluorescence intensity of total AGE-peptide and 6,000 Da peak AGE-peptide is enhanced together with the development of renal dysfunction in diabetic patients, which strongly correlated with the level of serum creatinine. There was no difference in total urinary AGE between diabetic and non-diabetic hemodialysis patients, suggesting that insufficient clearance during dialysis is more important than AGE production. A competitive ELISA using a polyclonal anti-AGE antibody, anion-exchange HPLC, and reversed-phase HPLC were performed on the peaks appearing in size-exclusive HPLC to further characterize the AGE composition. The 300 Da product was specific to diabetic patients with chronic renal failure and hemodialysis patients, which may be a good marker to distinguish diabetic from non-diabetic renal failures. We also speculated that because of its low molecular weight, the 300 Da product might represent the final degradation product of AGE-peptides in the kidney.