Dissociation between urinary pyrraline and pentosidine concentrations in diabetic patients with advanced nephropathy

It has been reported that the concentrations of both pyrraline and pentosidine, well-characterized advanced glycation end products, are increased in the urine of diabetic patients. To determine factors that influence the urinary excretion of pyrraline or pentosidine, we compared pyrraline or pentosidine concentrations with glycemic-control indexes, urinary albumin excretion, and urinary beta2-microglobulin in patients with type 2 diabetes. The study was conducted in 39 age-matched healthy control subjects and 50 diabetic patients, including 22 patients with normoalbuminuria, 15 with microalbuminuria, and 13 with macroalbuminuria. Both urinary pyrraline and pentosidine were measured in early-morning urine specimens with the use of high-pressure liquid chromatography. The urinary pentosidine concentration was significantly higher in diabetic patients than in control subjects (P < .01). In contrast, the urinary pyrraline concentration was significantly lower in diabetic patients than in control subjects (P < .001). Urinary pentosidine concentrations were greater in diabetic patients with macroalbuminuria and microalbuminuria than in those with normoalbuminuria. However, urinary pyrraline concentrations were significantly lower in diabetic patients with advanced nephropathy. Both the hemoglobin A(1c) (HbA(1c)) and the preceding year's mean HbA(1c) were lower in patients with macroalbuminuria than in those with normoalbuminuria or microalbuminuria. Urinary pyrraline, but not pentosidine, showed a significantly positive correlation with the preceding year's mean HbA(1c) (P < 0.01). Multivariate analysis disclosed that urinary beta-2-microglobulin was independently correlated with the urinary concentrations of pentosidine and pyrraline (P < .05 for both). We conclude that the urinary concentration of pentosidine is greater in diabetic patients with overt nephropathy, whereas the urinary pyrraline concentration is significantly lower in diabetic patients with overt nephropathy. Because urinary pyrraline is more directly influenced by glycemia than by pentosidine, the difference in glycemic control among diabetic patients with various grades of nephropathy may be responsible for a dissociation between urinary pyrraline and pentosidine concentrations in patients with overt diabetic nephropathy.