Impact of pioglitazone and bradykinin type 1 receptor antagonist on type 2 diabetes in high-fat diet-fed C57BL/6J mice

Abstract

Aim: Type 2 diabetes (T2D) is a major complication of obesity and a leading cause of morbidity and mortality. Antagonizing bradykinin type 1 receptor (B1R) improved body and tissue fat mass and reversed vascular and adipose tissue inflammation in a rat model of insulin resistance. This study aimed at evaluating further the role of B1R in a mouse model of T2D by comparing the antidiabetic and anti-inflammatory effects of the B1R antagonist SSR240612 (SSR) in adipose tissue with those of pioglitazone (TZD), an activator of peroxisome proliferator-activated receptor gamma.

Methods: C57BL/6J mice were fed with high-fat diet (HFD) or standard diet (control) for 20 weeks. Yet, during the last 4 weeks, HFD-fed mice were administered SSR and TZD (10 mg kg^-1 d^-1 each) as monotherapy or combined therapy subcutaneously. The impact of treatments was measured on metabolic hormones levels (ELISA), adipose tissue inflammatory status and the expression of candidate genes involved in T2D (quantitative real-time polymerase chain reaction and western blot).

Results: SSR240612 and TZD treatments improved hyperglycaemia, hyperinsulinaemia, insulin resistance, adipose tissue inflammation (expression of B1R, chemokine ligand 2, F4/80 and tumour necrosis factor) and modulated adipogenesis (peroxisome proliferator-activated receptor gamma, adipocytes' protein 2 and CD40 expressions) in HFD-fed mice. Yet, SSR was more effective than TZD to reduce visceral fat mass and resistin. TZD/SSR combined treatment had an additive effect to improve insulin sensitivity and glucose intolerance.

Conclusion: Bradykinin type 1 receptor antagonism could represent a promising therapeutic tool in combination with TZD for the treatment of T2D, obesity and insulin resistance.

Keywords: Adipose tissue inflammation; PPARγ; bradykinin B1 receptor; obesity.

Figure 1

Effect of pioglitazone (TZD) and SSR240612 (SSR) on weight gain (a), visceral fat accumulation (c) and adipocytes' size (d) in high‐fat diet (HFD)‐fed mice. Values presented as means ± SEM. ***p ≤ 0.001 versus SD group; ^† p ≤ 0.05; ^†† p ≤ 0.01 versus HFD group. Histology of the adipose tissue is also shown (b).

Figure 2

Glycaemic parameters in mice‐treated groups compared with diabetic mice reported by the intraperitoneal glucose tolerance test (IPGTT) (a) and the intraperitoneal insulin sensitivity test (IPIST) (b) performed at the 20th week of the protocol and after 4 weeks of corresponding treatment. Insulin level (c) was evaluated at the end of the protocol to calculate homeostatic model assessment insulin resistance (HOMA‐IR; d). Values expressed as mean ± SEM. *p ≤ 0.05, ***p ≤ 0.001 versus SD group; ^† p ≤ 0.05; ^††† p ≤ 0.001 versus high‐fat diet (HFD) group.

Figure 3

Fasting plasma levels of leptin (a), adiponectin (b) and resistin (c) assessed by ELISA. Values expressed as mean ± SEM. *p ≤ 0.05, **p ≤ 0.01, ***p ≤ 0.001 versus SD group; ^† p ≤ 0.05 versus high‐fat diet (HFD) group.

Figure 4

Effect of treatments on gene expression in epididymal adipose tissue assessed by quantitative polymerase chain reaction (PCR) for the indicated genes. Data were normalized to Cyclo‐A mRNA level and presented as a value relative to that for SD‐fed mice. Results expressed as means ± SEM. *p ≤ 0.05, **p ≤ 0.01, ***p ≤ 0.001 versus SD group; ^†† p ≤ 0.01; ^††† p ≤ 0.001 versus HFD group.

Figure 5

Effect of pioglitazone (TZD) and SSR240612 (SSR) in high‐fat diet (HFD)‐fed mice on proliferator‐activated receptor gamma (PPARγ) (a), adipocytes' protein 2 (aP2) (b), CD40 (c) and CD154 (d) protein levels in retroperitoneal adipose tissue. Histograms represent western blot and quantitative analysis shown as means ± SEM of four mice per group. *p ≤ 0.05, **p ≤ 0.01 versus SD group; ^† p ≤ 0.05 versus HFD group.