Urinary enzyme measurements as early indicators of renal insult in type 2 diabetes

The association between urine microalbumin, alpha1-microglobulin concentration (alpha1MG) and the urinary enzyme activities of alanine aminopeptidase (AAP), N-acetyl-beta-D-glucosaminidase (NAG), alpha-glutathione-S-transferase (alphaGST) and pi-glutathione-S-transferase (piGST) is investigated in 36 type 2 diabetic and 15 age- and sex-matched non-diabetic subjects. Diabetic subjects were grouped into those with microalbuminuria <3 mg/L (group A: 7M/5F), 3-30 mg/L (group B: 5M/7F) and 30-300 mg/L (group C: 6M/6F). While serum creatinine concentration remained within the laboratory reference range (<115 mmol/L) in all experimental groups, alpha1MG excretion increased with the severity of microalbuminuria (control group and groups A, B and C mean [SD] values were 1.3 [0.21], 1.6 [0.11], 2.18 [0.42] and 2.8 [0.51] mg/mmol urinary creatinine, respectively). Activities of NAG (U/mmol creatinine) were significantly elevated in groups A, B and C at 98.7 (8.6), 112.8 (12.9) and 147.4(16.2), respectively, compared with the reference range <35 U/mmol creatinine (group C vs. groups A and B: P < 0.01). Activity of AAP (U/mmol creatinine) was significantly elevated in groups B and C at 7.6 (0.5) and 7.9 (0.6), respectively (both P < 0.001), compared to the control and group A values (2.5 [0.2]). Activity of piGST (U/mmol creatinine) was elevated in groups B and C at 2.6 (0.4) and 2.8 (0.5), respectively (both P < 0.001), compared to the control and group A values (1.1 [0.1]). Similarly, urine piGST activity was also elevated in groups B and C at 2.9 (0.6) and 3.1 (0.5), respectively (both P < 0.001), compared to control and group A values (1.3 [0.1] and 1.4 [0.2]). These results suggests that site-specific urinary biochemical markers provide valuable information about early renal proximal and distal tubular insult that ultimately may precede enhanced glomerular permeability in subjects with type 2 diabetes.