Longitudinal evaluation of the renal clearance of glycated albumin in the diabetic rat

Abstract

This study has examined glycation of serum albumin and its role in evolving diabetic proteinuria. Renal clearances of endogenous glycated and nonglycated albumin were studied in groups of normal and streptozotocin-induced diabetic Wistar-Kyoto rats over a 32 week period. Concentrations of glycated and nonglycated albumin in serum and urine were measured by rat albumin radioimmunoassay following separation on m-aminophenylboronate affinity columns. Levels of glycated serum albumin in diabetic rats were significantly higher than in normal rats (5.9 ± 0.7% vs 4.4 ± 0.3%, P < 0.05). Median total urinary albumin excretion increased from 120 μg/24 h at baseline to 879 μg/24 h ( P < 0.05) 28–32 weeks after induction of diabetes. The renal clearance of glycated albumin was approximately twice as great as that of nonglycated albumin in both normal ( P < 0.01) and diabetic ( P < 0.01) rats. However, the glycated albumin/nonglycated albumin clearance ratio in diabetic rats did not correlate with duration of diabetes or with the level of albuminuria. These results indicate that glycation of albumin does not contribute disproportionately to the development of proteinuria in the diabetic rat, during which median renal albumin clearance increased 7-fold. Other factors, such as glycation of the glomerular filtration surface, may have a more important role in the pathogenesis of proteinuria in experimental diabetes.