Renoprotective, anti-oxidative and anti-apoptotic effects of oral low-dose quercetin in the C57BL/6J model of diabetic nephropathy

Abstract

Background: Diabetic nephropathy (DN) is one of the major causes of end-stage renal disease in diabetic patients. Increasing evidence from studies in the rodents has suggested that this disease is associated with increased oxidative stress due to hyperglycemia. In the present study, we evaluated the renoprotective, anti-oxidative and anti-apoptotic effects of the flavonoid quercetin in C57BL/6J model of DN.

Methods: DN was induced by streptozotocin (STZ, 100 mg/kg/day, for 3 days) in adult C57BL/6J mice. Six weeks later, mice were divided into the following groups: diabetic mice treated with quercetin (DQ, 10 mg/kg/day, 4 weeks), diabetic mice treated with vehicle (DV) or non-treated non-diabetic (ND) mice.

Results: Quercetin treatment caused a reduction in polyuria (~45%) and glycemia (~35%), abolished the hypertriglyceridemia and had significant effects on renal function including, decreased proteinuria and high plasma levels of uric acid, urea and creatinine, which were accompanied by beneficial effects on the structural changes of the kidney including glomerulosclerosis. Flow cytometry showed a decrease in oxidative stress and apoptosis in DN mice.

Conclusion: Taken together, these data show that quercetin effectively attenuated STZ-induced cytotoxicity in renal tissue. This study provides convincing experimental evidence and perspectives on the renoprotective effects of quercetin in diabetic mice and outlines a novel therapeutic strategy for this flavonoid in the treatment of DN.

Figure 1

Food (A) and water (B) intake, body weight gain (C) and urine volume (D) in diabetic mice treated with quercetin (DQ) compared to diabetic mice administered vehicle (DV) and non-diabetic (ND) mice. Values are means ± SEM for n = 6–8 mice per group. *p < 0.05 vs. ND, ^# p < 0.05 vs. DV.

Figure 2

Plasma glucose (A), total cholesterol (B) and triglycerides (C) in diabetic mice treated with quercetin (DQ) compared to diabetic mice administered vehicle (DV) and non-diabetic (ND) mice. Values are means ± SEM for n = 6–8 mice per group. *p < 0.05 vs. ND, ^# p < 0.05 vs. DV.

Figure 3

Plasma uric acid (A), urea (B), creatinine (C), proteinuria (D) and creatinine clearance (E) in diabetic mice treated with quercetin (DQ) compared to diabetic mice administered with vehicle (DV) and to non-diabetic (ND) mice. Values are means ± SEM for n = 6–8 mice per group. *p < 0.05 vs. ND, ^# p < 0.05 vs. DV.

Figure 4

Kidney weight/body weight ratio (A), glomerular tuff area (B), glomerulosclerosis (C) in diabetic mice treated with quercetin (DQ) compared to diabetic mice administered with vehicle (DV) and non-diabetic (ND) mice. The mean value of 30 individual glomeruli areas from each kidney were used to calculate the glomerular tuff area and glomerulosclerosis. Micrographs (D) are representative glomerular sections (magnification of 400x) stained with Masson trichrome to identify sclerosis (blue) in each glomerulus. Values are means ± SEM for n = 6–8 mice per group. *p < 0.05 vs. ND, ^# p < 0.05 vs. DV.

Figure 5

Production of superoxide anions. A: representative histograms from flow cytometry analysis using dihydroethidium (DHE) in diabetic mice treated with quercetin (DQ), compared to diabetic mice that received the vehicle (DV) and non-diabetic (ND) mice; the log fluorescence (X-axis) shows the intensity of fluorescence (+) for the number of kidney cells assayed. B: bar graph shows geometric mean fluorescence intensity. *p < 0.05 vs. ND group, ^# p < 0.05 vs. DV group.

Figure 6

Flow cytometric analysis of apoptosis in kidney cells. Each dot plot (A) was constructed using propidium iodide (PI) and annexin V/FITC staining indicating: damaged cells (Q1), cells that are undergoing late apoptosis (Q2), viable cells (Q3) and cells in early apoptosis (Q4). Bar graph B shows the average percentage of PI positive (viable) cells, which were used to quantify apoptosis. Bar graph C shows the average percentage of cells in early and late apoptosis in non-diabetic mice (ND), diabetic mice administered vehicle (DV) and diabetic mice treated with quercetin (DQ). Values are mean ± SEM for 6 to 8 animals per group. *p < 0.05 vs. ND group and ^#p < 0.05 vs. DV group.