Low‐Dose Metformin Treatment Ameliorates Renal Dysfunction and Fibrosis in a Mouse Model of Diabetic Nephropathy

Background Diabetes mellitus is the leading cause of chronic kidney disease and end‐stage renal disease in the United States. About one‐third of patients with diabetes develop renal dysfunction, commonly referred to as diabetic nephropathy. Metformin is a widely prescribed antidiabetic medication for patients with type 2 diabetes; however, its direct effects on the renal function besides normalizing glucose levels in patients with diabetic nephropathy are poorly understood. Thus, the objective of our study was to investigate the effects of a non‐glucose lowering, low‐dose metformin treatment on the diabetic kidney using a genetic mouse model of type 2 diabetes. Methods Our study utilized db/db mice ( Lepr db ) , which harbor a mutation in their leptin receptors, and hence, show the signs and symptoms similar to those experienced in patients with type 2 diabetes. To accelerate the progression of nephropathy, each mouse had their left kidney removed at ten weeks of age. Heterozygous mice were used as a control group for the study. Our study had four treatment groups (n=8 per group): 1) Vehicle‐treated control (non‐diabetic), 2) Metformin‐treated control (non‐diabetic), 3) Diabetic, vehicle‐treated, and 4) Diabetic, metformin‐treated. Mice were treated with either vehicle or metformin (100 mg/kg/day) for four weeks. Fasting blood glucose and urine samples were collected at the beginning and end of the study. Plasma and kidney tissue samples were collected at the end of the study. Markers of renal dysfunction such as elevations in urine albumin‐creatinine ratio (UACR) and plasma creatinine were measured in the samples collected from the study. Alpha‐smooth muscle (α‐SMA), a marker of renal fibrosis, were measured in kidney samples via Western blotting. Results Our results showed that the fasting blood glucose (FBG) levels were elevated in the diabetic mice (470.29 ±73.35 mg/dL) at the beginning of the study and were gradually increased with disease progression (672.57 ±107.88 mg/dL). Our results also demonstrated that low‐dose metformin treatment did not lower FBG levels in diabetic mice (583.38 ±195.77 mg/dL). However, metformin treatment was able to prevent the increase in UACR in diabetic mice (205.3 ±112.5 vs. 117.53 ±61.56 μg albumin/mg creatinine). Results from the plasma creatinine levels show that diabetic mice had increased plasma creatinine levels (0.72 ±0.07 mg/dL) compared to the control mice (0.51 ±0.06 mg/dL). Intriguingly, low‐dose metformin treatment did not prevent the diabetes‐induced elevations in plasma creatinine levels. Western blot analysis for α‐SMA indicated that only the diabetic mice expressed α‐SMA in the kidney and low‐dose metformin treatment diminished renal expression of α‐SMA in diabetic mice. Conclusion Our findings suggest that low‐dose metformin treatment improves renal function, and ameliorates renal fibrosis observed with diabetic nephropathy. Further studies are required to investigate the mechanisms that underlie the nephroprotective effects of low‐dose metformin therapy in diabetic mice. Support or Funding Information Funding This study was supported by intramural funds received from Drake University through Harris Research Endowment, Kresge Endowment, and Provost fund.