[Hyperbilirubinemia induced oxidative stress resulting in glomerular injury in rats].

Objective: To observe the effect of hyperbilirubinemia on glomerulus of rats, and to explore its dose-response and mechanism.

Methods: Twenty-four adult male Sprague-Dawley (SD) rats were divided into four groups according to the random number table method, with 6 rats in each group. Hyperbilirubinemia rat model was reproduced by intraperitoneal injection of bilirubin once every 12 hours for 4 times, at doses of 50, 100, and 200 mg/kg in low, medium, and high dose bilirubin group (LB group, MB group, HB group), respectively. The rats in negative control group (NC group) were given the same solvent without bilirubin powder. Urine was collected 24 hours after administration, and total protein (TP) level was detected. Then the rats were sacrificed, the blood was collected by cardiac puncture, and the total bilirubin (TBil) and direct bilirubin (DBil) levels were measured by automatic biochemical analyzer. The renal tissue was collected and stained with periodic acid-Schiff (PAS) staine, the glomerular morphology was observed under light microscope, and the glomerular injury score was performed. Podocyte morphology was observed by transmission electron microscopy after uranium acetate and lead citrate double staining. The activity of superoxide dismutase (SOD) and content of malondialdehyde (MDA) were determined by colorimetric method. The expression level of podocyte specific marker Wilms tumor protein-1 (WT-1) was determined by Western blotting.

Results: With the increase of bilirubin dose, the contents of 24-hour urine TP, blood TBil, blood DBil and MDA content in kidney tissue were gradually increased, and the SOD activity and WT-1 expression in kidney tissue were gradually decreased. The differences between LB group, MB group, HB group and NC group were statistically significant [24-hour urine TP (mg): 24.85±2.22, 52.57±3.66, 56.84±3.49 vs. 7.50±1.33; blood TBil (μmol/L): 37.75±2.19, 81.37±2.13, 125.13±9.96 vs. 5.53±0.41; blood DBil (μmol/L): 15.50±1.96, 37.88±1.05, 64.53±2.89 vs. 2.38±0.35; kidney MDA (μmol/g): 3.14±0.65, 5.01±0.28, 7.50±1.08 vs. 2.30±0.20; kidney SOD (kU/g): 95.91±10.43, 57.06±15.90, 37.12±11.72 vs. 113.91±12.16; kidney WT-1 protein (WT-1/GAPDH): 0.280±0.006, 0.239±0.006, 0.198±0.001 vs. 0.361±0.005; all P < 0.05]. It was shown under light microscope that uneven thickness of mesangial membrane and basement membrane of the glomerulus, and some of them were accompanied by hyperplasia and widening. The glomerular injury score increased with the increase in bilirubin dose. The differences between LB group, MB group, HB group and NC group were statistically significant (17.50±1.05, 25.00±1.41, 34.00±1.41 vs. 11.67±0.82, all P < 0.05). Transmission electron microscopy showed that with the increase of bilirubin dose, the damage of glomerular podocytes was aggravated.

Conclusions: Hyperbilirubinemia induced damage to glomerulus in a dose-dependent manner. In the lethal dose range, the higher the dose, the stronger the damage, which might be related to the oxidative stress promoted by bilirubin and the damage of glomerular podocytes.