Renin-angiotensin system blockers protect pancreatic islets against diet-induced obesity and insulin resistance in mice.

BackgroundThe associations between obesity, hypertension and diabetes are well established, and the renin-angiotensin system (RAS) may provide a link among them. The effect of RAS inhibition on type 2 diabetes is still unclear; however, RAS seems to play an important role in the regulation of the pancreas and glucose intolerance of mice fed high-fat (HF) diet.MethodsC57BL/6 mice fed a HF diet (8 weeks) were treated with aliskiren (50 mg/kg/day), enalapril (30 mg/kg/day) or losartan (10 mg/kg/day) for 6 weeks, and the protective effects were extensively compared among groups by morphometry, stereological tools, immunostaining, Western blotting and hormonal analysis.ResultsAll RAS inhibitors significantly attenuated the increased blood pressure in mice fed a HF diet. Treatment with enalapril, but not aliskiren or losartan, significantly attenuated body mass (BM) gain, glucose intolerance and insulin resistance, improved the alpha and beta cell mass and prevented the reduction of plasma adiponectin. Furthermore, enalapril treatment improved the protein expression of the pancreatic islet Pdx1, GLUT2, ACE2 and Mas receptors. Losartan treatment showed the greatest AT2R expression.ConclusionOur findings indicate that ACE inhibition with enalapril attenuated several of the deleterious effects of the HF diet. In summary, enalapril appears to be responsible for the normalization of islet morphology and function, of alpha and beta cell mass and of Pdx1 and GLUT2 expression. These protective effects of enalapril were attributed, primarily, to the reduction in body mass gain and food intake and the enhancement of the ACE2/Ang (1-7) /Mas receptor axis and adiponectin levels

Representative Western blotting analysis of pancreatic islets for Pdx1 and GLUT2 expression (A) and their densitometry analysis (B – Pdx1; C – GLUT2).

<p>Average values were measured, and equal protein loading was confirmed by probing blots with beta actin antibodies. Each is, expressed as a percentage of the SC counterpart. Data are reported as the means ± SEM, n=9; <i>P</i><0.05, one-way ANOVA and post-hoc of Holm-Sidak test: [a] compared to SC; [b] compared to untreated HF; [c] compared to HF-A, and [d] compared to HF-E.</p

Systolic blood pressure evolution.

<p>Data are reported as the means ± SEM, n=8; <i>P</i><0.05, one-way ANOVA and post-hoc of Holm-Sidak test: a ≠ SC; b ≠ HF; c ≠ HF-A, and d ≠ HF-E.</p

Pancreatic steatosis.

<p>Representative light micrographs of pancreatic sections (stain, hematoxylin and eosin; same magnification, bar = 150 µm) showing normal pancreatic tissues and a pancreatic islets (arrows) in the SC group (A). The HF diet group (B), with a large infiltration of fat (open arrows) between pancreatic lobules (interlobular fat) and within exocrine tissue (intralobular fat). </p

Western blotting analysis illustration (A) of pancreatic islets for renin (B), ACE (C), AT1R (D), and AT2R (E) expressions.

<p>Average values were measured, and equal protein loading was confirmed by probing blots with beta actin antibodies. Each is expressed as a percentage of the SC counterpart. Data are reported as the means ± SEM, n=9; <i>P</i><0.05, one-way ANOVA and post-hoc of Holm-Sidak test: a ≠ SC; b ≠ HF; c ≠ HF-A and d ≠ HF-E.</p

Western blotting analysis (A) of pancreatic islet for ACE2 (B), and <i>Mas</i> receptor (C) expression.

<p>Average values were measured, and equal protein loading was confirmed by probing blots with beta actin antibodies and is expressed as a percentage of the SC counterpart. Data are reported as the means ± SEM, n=9; <i>P</i><0.05, one-way ANOVA and post-hoc of Holm-Sidak test: a ≠ SC; b ≠ HF; c ≠ HF-A and d ≠ HF-E.</p

Beta cell immunohistochemistry.

<p>Photomicrographs show islets with immunoperoxidase (brown)-stained insulin (counterstained with hematoxylin, same magnification, bar = 50 µm). The SC group (A) shows smaller islets than the untreated HF group and a normal pattern of islet distribution, with beta cells restricted to the core of this structure. The untreated HF group (B) shows an increase in insulin immunoreactive-positive beta cells, representing an augmentation of beta cell mass, pancreatic islets hypertrophy, and a complete disarrangement of beta and non-beta cell distributions (arrows). Treatment with enalapril (C) displays a partial restoration of normal patterns of islet cell distributions (arrows) and islet size.</p

BM evolution over the course of the experimental period.

<p>Weeks 1–8 correspond to the period of the induction of obesity and insulin resistance, and weeks 8–14 correspond to the treatment phase. Values are means ± SEM, n=15. Significant differences between the groups are indicated using symbols (<i>P</i><0.05), as determined by a one-way ANOVA and a post-hoc Holm-Sidak test: a ≠ SC; b ≠ HF; c ≠ HF-A, and d ≠ HF-E.</p