Possible biphasic changes of free radicals in ethylene glycol-induced nephrolithiasis in rats

Objective To evaluate the possible role of free radicals in nephrolithiasis in rats induced by ethylene glycol, and to examine the correlation between the urinary enzymes N-acetyl-beta-glucosaminidase (NAG), beta-galactosidase (GAL) and neutral endopeptidase (NEP), and free radical production. Materials and methods Hyperoxaluria was produced in male Wistar rats by adding ethylene glycol to their drinking water. After 7, 21 and 42 days of treatment, urinary oxalate, creatinine clearance and urinary enzymes (NAG, GAL and NEP) were measured. The nitroblue tetrazolium perfusion method was used to locate the sites of free-radical production. Ultrasensitive chemiluminescence was used to directly measure the production of reactive oxygen species (ROS) in vivo. Vitamin E and potassium citrate were fed to rats, in addition to ethylene glycol, to assess their effects on free radical production. Results Urinary oxalate increased significantly and was associated with an increase in NAG and GAL at all sample times. However, urinary NEP activity was unchanged on day 7, although there was four times as much NEP on days 21 and 42 than in the control groups. Formazan particles in the renal cortex were scored as 3+ to 4+ in rats treated for 7 days with ethylene glycol. Blood ROS levels were also higher in this group than in the controls (P<0.01). After vitamin E and potassium citrate treatment, blood ROS levels were lower than in rats treated with ethylene glycol alone. Conclusion Free radicals may be produced in the early stages of nephrolithiasis in rats fed with ethylene glycol. Free radicals occurred mainly in blood and might be associated with NEP inactivation.