AN IMPROVED METHOD FOR EVALUATION OF NEPHROTOXICITY BY ASSAY OF URINARY N-ACETYL-BETA-D-GLUCOSAMINIDASE (NAG) ACTIVITY

Reaction conditions of N-acetyl-beta-D-glucosaminictase (EC 3.2.1.30; NAG) determination in untreated urine samples were studied, using 4-ni trophenyl-N-acetyl-beta-D-glucosaminide (PNP-NAG) as substrate. Final concentrations of 8 mmol of PNP-NAG, 25 mmol of acetate, or 100 mmol o f citrate (pH 4.80 at 37 degrees C) per liter and a sample/reagent vol ume ratio of 1/18 were found to be optimum. The within-run and between -run precision was excellent, with CVs averaging 2.67 and 4.55%, respe ctively. Reference values for urinary NAG activity assayed by this met hod were established for untimed human urine specimens from 206 health y subjects. The normal reference interval (mean +/- 1SD) was 0.15-15.0 5 (4.51 +/- 3.02) U per gram creatinine. By this method, urinary NAG a ctivity can be measured over a wide range (up to 200 U/L) in untreated urine samples with high sensitivity. Urine samples need no pretreatme nt, and two reagent solutions are enough for measurement of NAG activi ty The method is thus suitable for use with various automated analyzer s. Finally, this method requires only to 25 mu L Of untreated urine. T herefore, it is appropriate for evaluating nephrotoxicity in human (es pecially neonates and infants) and small animal models by assay of uri nary NAG activity.