Decreasing Insulin Resistance Reduces Early Progressive Proteinuria by Decreasing Renal Hyperfiltration and Inflammation in Obese Dahl Salt‐Sensitive Rats

Abstract

Prepubertal/childhood obesity (PPO) is quickly becoming an epidemic and is considered a major risk factor for proteinuria. Previous studies have demonstrated that insulin resistance alters renal hemodynamics leading to inflammation and renal injury in obese adults. However, studies examining the relationship between insulin resistance and renal hyperfiltration (RH) and inflammation in obese children are lacking. Recently, we reported that insulin resistance in the obese Dahl salt‐sensitive leptin receptor mutant (SSLepRmutant) rat is associated with progressive proteinuria and RH prior to puberty. Therefore, the aim of the present study was to examine whether decreasing insulin resistance with metformin will reduce proteinuria in SSLepRmutant rats. Four‐week‐old SS and SSLepRmutant rats were separated into 4 groups (n=5/group) and treated with either vehicle (PBS) or metformin (300 mg/kg/day, ip) for 4 weeks. Blood glucose levels were similar among the groups throughout the study (≤ 120 mg/dL). However, at the end of study, plasma insulin levels were significantly elevated in SSLepRmutant rats vs SS rats (9±2 vs 1±0.2 ng/ml respectively; p<0.05), and glucose tolerance was significantly impaired in SSLepRmutant rats compared to values measured in SS rats. Chronic treatment with metformin markedly reduced plasma insulin (2±1 ng/ml; p<0.05) and improved glucose tolerance in SSLepRmutant rats. At baseline, proteinuria was significantly higher in SSLepRmutant rats vs SS rats and remained elevated throughout the study (449±123 vs 25±7 mg/day, respectively; p<0.05). Metformin treatment significantly decreased proteinuria in SSLepRmutant rats (177±80 mg/day; p<0.05) with no effect in SS rats (36±13 mg/day). We observed a significant increase in creatinine clearance (CCr) in SSLepRmutant rats vs SS rats indicating RH (3.3±0.4 ml/min vs 1.9±0.1 ml/min, respectively; p<0.05). Chronic treatment with metformin significantly decreased CCr in SSLepRmutant rats (1.3±0.2 ml/min; p<0.05) while not affecting SS rats. Renal histology revealed marked glomerular injury in vehicle‐treated SSLepRmutant compared to SS rats, and treatment with metformin reduced glomerular injury in SSLepRmutant rats. We observed a significant increase in the renal infiltration of stimulatory dendritic cells and macrophages in vehicle‐treated SSLepRmutant rats compared to their SS counterparts, and metformin reduced the infiltration of these immune cells only in SSLepRmutant rats. MIP3α (pro‐inflammatory cytokine) was significantly increased and IL‐4 (anti‐inflammatory cytokine) was markedly decreased in the kidneys of SSLepRmutant rats compared to their SS counterparts (23±3 vs 5±1 ng/mg and 11±2 vs 54±5 ng/mg, respectively; p<0.05). Treatment with metformin decreased renal MIP3α (10±2 ng/mg; p<0.05), while increasing renal IL‐4 (26±5 ng/mg) in SSLepRmutant rats. These data suggest that decreasing insulin resistance reduces RH, proteinuria, and inflammation and may be therapeutically useful in managing renal injury during PPO.