Diagnostic Value of the Aminopeptidase N, N-Acetyl-β-D-Glucosaminidase and Dipeptidylpeptidase IV in Evaluating Tubular Dysfunction in Patients with Glomerulopathies

Aim. The aim of the present study was to investigate the value of the urine cell glycoprotein 1 (PC-1), aminopeptidase N (APN), N-acetyl-β-D-glucosaminidase (NAGA), and dipeptidylpeptidase IV (DPP IV) in the evaluation of tubular damage in patients with primary glomerulonephritis, diabetic nephropathy, and lupus nephritis. Subjects and Methods. PC-1, APN, NAGA, and DPP IV activities were determined in serum, urine, and lymphocytes of 178 subjects, including 10 patients with membranous nephropathy, 38 with IgA nephropathy, 29 with lupus nephritis, 51 with diabetic nephropathy, and 50 control subjects. Results. Urinary PC-1 excretion in IgA nephropathy group was significantly higher (p < 0.05) than in controls. Urinary NAGA excretion was markedly (p < 0.01) higher in membranous nephropathy group, and APN excretion in diabetic nephropathy group was significantly higher (p < 0.01) than in healthy controls. Urinary APN activity was significantly (p < 0.01) higher in both type 1 and type 2 diabetic patients with microalbuminuria, as well as urinary NAGA and DPP IV activities in type 2 diabetics with microalbuminuria (p < 0.01 and p < 0.05, respectively) compared to controls. Serum PC-1 and APN activities were significantly higher than the control level in membranous nephropathy group, as well as serum PC-1 and DPP IV activities in IgA nephropathy patients (p < 0.05). However, significantly lower serum DPP IV and APN activity was observed in type 2 diabetics with microalbuminuria compared to controls (p < 0.05). Conclusion. Damage of tubules in primary glomerulonephritis, lupus nephritis, and diabetic nephropathy is accompanied by a release of several tubular enzymes, with possible diagnostic and prognostic significance. Increased serum PC-1, APN, and DPP IV activities could be also of diagnostic significance.