Further evidence for tubular dysfunction in insulin dependent diabetes

There is evidence that increased excretion of urinary enzymes and low-molecular mass proteins indicate impaired tubular function. The excretion of N-acetyl-beta-D-glucosaminidase (NAG), lysozyme, and ribonuclease in Type I diabetic patients with (n = 19) and without (n = 17) persistent proteinuria (urinary protein excretion greater than 0.5 g/day) was investigated and compared with this excretion in 30 weight- and gender-matched nondiabetic subjects without renal disease. Urinary NAG excretion was significantly higher in diabetic patients with and without persistent proteinuria (1.16 +/- 0.09 and 3.19 +/- 1.2 Umol/L creatinine, respectively) compared to controls (0.37 +/- 0.03 Umol/L creatinine p less than 0.01). In addition, the urinary excretion of lysozyme and ribonuclease was significantly increased in diabetic patients. Urinary NAG was found to correlate positively with albuminuria and proteinuria (r = 0.95 and 0.93, respectively), as well as with ribonuclease and lysozyme (r = 0.93 and 0.60; p less than 0.01) in patients with persistent proteinuria. Furthermore, NAG excretion was significantly related to the duration of diabetes (r = 0.36; p less than 0.05). No relationship existed between urinary NAG and serum creatinine, beta-2-microglobulin, and degree of metabolic control (HbA7). The lysozyme excretion, but not NAG excretion, was significantly related to hypertension in patients with clinical proteinuria. In conclusion, our results suggest a relationship between the development of tubular dysfunction and the impairment of glomerular function in diabetic nephropathy. An increased excretion of NAG and low-molecular mass proteins may indicate early nephropathy