Angiotensin AT2R stimulation improves glucose tolerance and insulin sensitivity in obese mice

Objective: The functional role of the AT1-receptor (AT1R) in the development of insulin-resistance (IR) is well understood and it is known that AT1R-blockers (ARBs) improve glucose-intolerance and IR. The metabolic contribution of the AT2-receptor (AT2R) is still controversial. Thus, this study aimed to determine the functional significance of the AT2R for the development of IR and adipose-tissue inflammation using the first non-peptide AT2R-agonist, Compound 21 (C21).

Design and methods: Wild type (WT; C57Bl-6) and AT2R-knockout (AT2R-KO) mice were fed with high fat diet (HFD) or control low fat diet (LFD) (60% kcal from fat or 10% kcal from fat, respectively) for 10 weeks to induce obesity and metabolic changes. Afterwards animals (n=10 per group) were treated according to the following protocol for 4 weeks in addition to the diet: C21 (0,3mg/kg BW i.p.), the ARB Valsartan (3mg/kg BW i.p.), Hydralazine (250mg/l drinking water) or vehicle. Glucose tolerance (GT) und insulin sensitivity (IS) were measured by standard ITT and GTT tests, body fat content by NMR, serum markers by magnetic bead-based multiplex assay. The in vivo study was complemented by in vitro experiments in 3T3L-1 adipocytes and THP-1 macrophages.

Results: GT and IS were impaired by HFD-feeding but significantly improved in mice treated with C21; GT was also improved by Valsartan. Furthermore, TNF-alpha, resistin and serum triglycerides (53.57±5.26mg/dl to 37.16±5.08mg/dl; p<0.05) levels were significantly reduced, and serum levels of incretins GIP and GLP-1 were increased by C21-treatment. Consistent with our in vitro data, C21 treatment increased adiponectin as well as IL-10, and decreased leptin serum levels in a significant manner.

HFD-fed AT2R-KO mice showed significantly enhanced body weight gain (+66.6±4.08% vs. +51.2±1.13%) and total body fat content (8.75±1.23g vs. 6.16±0.28g) when compared to WT-HFD-fed mice. Importantly, metabolic outcome of HFD-fed AT2R-KO mice was not altered by the treatment with C21 pointing to AT2R-specificity of C21 effects.

C21 slightly (-6.38mmHg, p<0.05) and Valsartan strongly (-19.37mmHg, p<0.001) lowered blood-pressure in mice of the HFD groups. However, metabolic effects of C21 and Valsartan were blood pressure-independent as controlled for by the Hydralazine treated group.

Conclusions: The present study demonstrates that direct AT2R-stimulation results in anti-inflammatory actions as well as positive modulation of metabolic markers in a HFD model in mice and related in vitro experiments. These data suggest that the AT2R may be a pharmacological target for improvement of obesity-induced metabolic changes.