Prolonged treatment with angiotensin 1-7 improves endothelial function in diet-induced obesity

Abstract

Objective: The renin-angiotensin system peptides are critically involved in the regulation of endothelial function with important pathological implications. Angiotensin (Ang) 1-7 has many beneficial effects in the vasculature that modulate the cardiovascular risk. Here, we tested the hypothesis that Ang 1-7 has a protective role against the endothelial defects associated with diet-induced obesity (DIO) in mice.

Methods: Ang 1-7 (with or without Ang II) was delivered subcutaneously for 4 weeks using osmotic minipumps. Vascular studies were performed using aortic rings. Arterial pressure and heart rate were measured in separate cohorts of mice by telemetry.

Results: First, we examined whether chronic administration of Ang 1-7 improves the vascular dysfunctions caused by Ang II. Subcutaneous coinfusion of Ang 1-7 significantly attenuates Ang II-induced endothelial dysfunctions. In addition, DIO mice have significant impairment in the endothelium-dependent relaxation. The contractile responses induced by various stimuli, including serotonin and endothelin-1, were differentially altered in DIO mice. Notably, DIO mice treated with Ang 1-7 for 4 weeks displayed significant improvement in the endothelial function as indicated by the increased acetylcholine-induced relaxation. Consistent with this, chronic treatment with Ang 1-7 reversed the increased aortic expression of NAD(P)H oxidase subunits (p22(phox) and p47(phox)) and plasma TBARS associated with DIO mice. In contrast, treatment with Ang 1-7 did not normalize the altered contractions associated with DIO mice.

Conclusion: Our data demonstrate a novel role for Ang 1-7 in improving obesity-associated endothelial dysfunction.

FIGURE 1

Ang 1–7 improves Ang II-induced endothelial dysfunction. Comparison of the vasodilation induced by the endothelial-dependent dilator acetylcholine (ACh, a) and endothelial-independent NO donor sodium nitroprusside (SNP, b) in aortic rings from mice treated with vehicle, Ang II or Ang II along with Ang 1–7 for 4 weeks before the study. Precontraction of the aortic rings was induced using Pgf_2α and relaxation was expressed as a percentage of the precontraction. ^*P <0.05 vs. vehicle, ^†P <0.05 vs. both Ang II and vehicle (n ≥ 6 per group).

FIGURE 2

Ang II-induced alteration in vascular contraction was not affected by Ang 1–7 treatment. Contractile responses induced by receptor-dependent agonists, serotonin (5-HT, a) and endothelin-1 (ET-1, b), or receptor-independent constrictor, potassium chloride (KCl, c) in aortic rings from mice treated with vehicle, Ang II or Ang II along with Ang 1–7 for 4 weeks before the study. ^*P <0.05 vs. vehicle (n ≥ 6 per group).

FIGURE 3

Ang II-induced hypertension was not affected by Ang 1–7 treatment. Radiotelemetry arterial pressure [AP: diastolic (a), mean (b) and systolic (c)] and heart rate (HR, d) at baseline and 4 weeks after infusion of Ang II with or without Ang 1–7 in mice. ^*P <0.05 vs. baseline (n = 5–7 per group).

FIGURE 4

Comparison of body weight between diet-induced obese mice and lean controls with or without Ang 1–7 treatment. Body weight was greater in DIO mice relative to lean controls. Ang 1–7 treatment for 4 weeks had no significant effect on body weight in DIO mice. ^*P <0.05 vs. lean control mice (n ≥ 8 per group).

FIGURE 5

Ang 1–7 improves endothelial function in diet-induced obese mice. (a, b) Comparison of the vasodilation induced by the endothelial-dependent acetylcholine (ACh, a) and endothelial-independent sodium nitroprusside (SNP, b) in aortic rings obtained from lean and DIO mice. (c, d) Effect of 4-week treatment with Ang 1–7 on the aortic rings relaxation induced by ACh (c) and SNP (d) in DIO mice. Precontraction of the aortic rings was induced using Pgf_2α and relaxation was expressed as a percentage of the precontraction. ^*P <0.05 vs. lean mice, ^†P <0.05 vs. DIO-vehicle group (n ≥ 6 per group).

FIGURE 6

Ang 1–7 has no effect on the altered contractile responses in diet-induced obese mice. (a–c) Comparison of the contractile responses induced by receptor-dependent agonists, serotonin (5-HT, a) and endothelin-1 (ET-1, b), or receptor-independent constrictor, potassium chloride (KCl, c) in aortic rings obtained from lean and DIO mice. (d–f) Effect of 4-week treatment with Ang 1–7 on the aortic rings contraction induced by receptor-dependent agonists, serotonin (5-HT, d) and endothelin-1 (ET-1, e), or receptor-independent constrictor, potassium chloride (KCl, f) in DIO mice. ^*P <0.05 vs. lean mice (n ≥ 6 per group).

FIGURE 7

Ang 1–7 abolishes the upregulation of NAD(p)H oxidase in the aorta and circulating TBARS in diet-induced obese mice. (a, b) Elevated RNA expression levels of p22^phox (a) and p47^phox (b) subunits of NAD(p)H oxidase in the aorta of DIO mice, which can be normalized by chronic Ang 1–7 treatment. (c) DIO mice exhibited elevated plasma concentration of TBARS relative to lean controls and this was normalized by chronic Ang 1–7 treatment. ^*P <0.05 vs. lean mice and DIO along with Ang 1–7 (n = 4–15 per group).