Objective: The renin-angiotensin system affects insulin sensitivity mainly through the angiotensin II type 1 receptor. In this study, the effects of renin inhibition on insulin resistance and adipose tissue dysfunction were explored in type 2 diabetic KK-A(y) mice.
Methods and results: Male KK-A mice were treated with a direct renin inhibitor, aliskiren, administered subcutaneously at a dose of 50 mg/kg per day for 14 days using an osmotic minipump. This dose of aliskiren strongly inhibited plasma renin activity and lowered blood pressure about 17% in KK-A(y) mice. Aliskiren decreased body weight and plasma glucose level, and increased plasma insulin level in a fed condition. Aliskiren also lowered the plasma levels of cholesterol, fatty acids and triglycerides. In the oral glucose tolerant test, the plasma glucose elevation after glucose load was reduced by aliskiren, without a significant change in insulin level. Insulin tolerance test showed that aliskiren enhanced insulin's effect on plasma glucose. Aliskiren also reduced the epididymal adipose tissue mass by 25% and retroperitoneal adipose tissue mass by 35%. In adipose tissue, expression of the insulin receptor was not changed by aliskiren; however, expression of insulin receptor substrate-1, glucose transporter type 4, adiponectin, peroxisome proliferator-activated receptor-gamma and CCAAT/enhancer-binding proteindelta was increased by aliskiren. Moreover, NADPH oxidase activity and expression of inflammatory factors were reduced in adipose tissue. Aliskiren increased the pancreatic beta-cell area in KK-A(y) mice.
Conclusion: These results suggest that renin inhibition by aliskiren improved insulin resistance and adipose tissue dysfunction in type 2 diabetic mice through an increase in insulin sensitivity, insulin secretion and adipocyte differentiation, and a reduction of oxidative stress.