ADVANCED GLYCOSYLATION END-PRODUCTS IN PATIENTS WITH DIABETIC NEPHROPATHY

Background. Glucose reacts nonenzymatically with proteins in vivo, chemically forming covalently attached glucose-addition products and cross-links between proteins. The excessive accumulation of rearranged late-glucose-addition products, or advanced glycosylation end products (AGEs), is believed to contribute to the chronic complications of diabetes mellitus. Methods. To elucidate the relation of AGEs to diabetic complications, we used a radioreceptor assay to measure serum and tissue AGEs in diabetic (Types I and II) and nondiabetic patients with different levels of renal function. Serum AGEs were measured as a low-molecular-weight (less-than-or-equal-to 10 kd) peptide fraction and a high-molecular-weight (> 10 kd) protein fraction. Results. The mean (+/- SD) AGE content of samples of arterial-wall collagen from 9 diabetic patients was significantly higher than that of samples from 18 nondiabetic patients (14.5 +/- 5.2 vs. 3.6 +/- 1.5 AGE units per milligram, P < 0.001). Moreover, diabetic patients with end-stage renal disease had almost twice as much AGE in tissue as diabetic patients without renal disease (21.3 +/- 2.8 vs. 11.5 +/- 1.9 AGE units per milligram, P < 0.001). The AGE levels in both serum fractions were elevated in the patients with-diabetes, and the levels of AGE peptides correlated directly with serum creatinine (P < 0.001) and inversely with creatinine clearance (P < 0.005), suggesting that levels of AGE peptides increased with the severity of diabetic nephropathy. In six patients with diabetes who required hemodialysis, the levels of AGE peptides were five times higher than in eight normal subjects (82.8 +/- 9.4 vs. 15.6 +/- 3.4 AGE units per milliliter, P < 0.001). In another group of diabetic patients, the mean serum creatinine level decreased by 75 percent during a session of hemodialysis, whereas the level of AGE peptides decreased by only 24 percent. Serum levels of AGE peptides were normal in two patients with normal serum creatinine levels after renal transplantation. Conclusions. AGEs accumulate at a faster-than-normal rate in arteries and the circulation of patients with diabetes; the increase in circulating AGE peptides parallels the severity of renal functional impairment in diabetic nephropathy.