Comparison of n-acetyl-β- d-glucosaminidase and alanine aminopeptidase activities for evaluation of microangiopathy in diabetes mellitus

Abstract

The activities of urinary n-acetyl-β- d-glucosaminidase (NAG) and alanine aminopeptidase (AAP) were measured in 207 diabetic patients and 57 healthy controls, and the relationship of these enzymes to different stages of diabetic microangiopathy was studied. Diabetics with clinical proteinuria had higher urinary NAG and AAP (17.7 ± 1.9 and 42.8 ± 4.9 U/g creatinine, mean ± SE, respectively) than healthy controls (1.8 ± 0.1 and 10.0 ± 0.4) or diabetics without proteinuria. Among diabetics without proteinuria, NAG excretion in those with retinopathy was slightly higher than in those without (6.4 ± 0.5 v 5.4 ± 0.4), and AAP in those with retinopathy was significantly higher than in those without (23.0 ± 1.5 v 17.4 ± 0.8, P < 0.01). Urinary albumin measured by radioimmunoassay and lysozyme in diabetics with retinopathy but without proteinuria was higher than those without retinopathy ( P < 0.001 and P < 0.01). The increase in albumin was the greatest in diabetics with long duration of the disease (≥8 years); however, NAG and AAP increased more significantly in those with high hemoglobin A 1c than in patients with long duration. Although urinary NAG correlated moderately with AAP ( r = .70, P < 0.001), the coefficient of correlation between AAP and albumin was greater than that between NAG and albumin in diabetics without proteinuria and in healthy subjects ( r = .47 and P < 0.001 v r = .32 and P < 0.001). These results indicate that urinary NAG and AAP can be used to diagnose the onset and to follow the development of diabetic vascular complications. AAP appears to be more useful for this purpose.