Importance of intracellular Angiotensin II in vascular smooth muscle cell apoptosis: Inhibition by the Angiotensin AT1 receptor antagonist irbesartan

Angiotensin-(1-7) abrogates angiotensin II-induced proliferation, migration and inflammation in VSMCs through inactivation of ROS-mediated PI3K/Akt and MAPK/ERK signaling pathways

The proliferation, migration and inflammation of vascular smooth muscle cells (VSMCs) contribute to the pathogenesis and progression of several cardiovascular diseases such as atherosclerosis and hypertension. Angiotensin (Ang)-(1–7) and Ang II are identified to be involved in regulating cardiovascular activity. The present study is designed to determine the interaction between Ang-(1–7) and Ang II on VSMCs proliferation, migration and inflammation as well as their underlying mechanisms. We found that Ang-(1–7) significantly suppressed the positive effects of Ang II on VSMCs proliferation, migration and inflammation, as well as on induction of the phosphorylation of Akt and ERK1/2 and increase of superoxide anion level and NAD(P)H oxidase activity in VSMCs, whereas Ang-(1–7) alone had no significant effects. This inhibitory effects of Ang-(1–7) were abolished by Mas receptor antagonist A-779. In addition, Ang II type 1 (AT₁) receptor antagonist losartan, but not A-779, abolished Ang II induced VSMCs proliferation, migration and inflammation responses. Furthermore, superoxide anion scavenger N-acetyl-L-cysteine (NAC) or NAD(P)H oxidase inhibitor apocynin inhibited Ang II-induced activation of Akt and ERK1/2 signaling. These results indicate that Ang-(1–7) antagonizes the Ang II-induced VSMC proliferation, migration and inflammation through activation of Mas receptor and then suppression of ROS-dependent PI3K/Akt and MAPK/ERK signaling pathways.

Angiotensin-(1-7) counteracts the effects of Ang II on vascular smooth muscle cells, vascular remodeling and hemorrhagic stroke: Role of the NFкB inflammatory pathway

Angiotensin (Ang)-(1-7) is a potential vasoprotective peptide. In the present study, we investigated its counteractive effects to Ang II on vascular smooth muscle cells (VSMCs) and intracerebral hemorrhagic stroke (ICH) through inflammatory mechanism. In in vitro experiments, human brain VSMCs (HBVSMCs) were treated with vehicle, Ang II, Ang II+Ang-(1-7), Ang II+A-779 or Ang II+Ang-(1-7)+A-779 (Mas receptor antagonist). HBVSMC proliferation, migration and apoptosis were determined by methyl thiazolyltetrazolium, wound healing assay and flow cytometry, respectively. In in vivo experiments, C57BL/6 mice were divided into vehicle, Ang II, Ang II+Ang-(1-7), Ang II+A-779 or Ang II+Ang-(1-7)+A-779 groups before they were subjected to collagenase-induced ICH or sham surgery. Hemorrhage volume and middle cerebral artery (MCA) remodeling were determined by histological analyses. Levels of NFκB, inhibitor of κBα (IκBα), tumor necrosis factor-α (TNF-α), monocyte chemoattractant protein 1 (MCP-1) and interleukin (IL-8) were measured by western blot or ELISA. We found that 1) Ang II increased HBVSMC migration, proliferation and apoptosis, and increased the blood pressure (BP), neurological deficit score, MCA remodeling and hemorrhage volume in ICH mice. 2) Ang-(1-7) counteracted these effects of Ang II, which was independent of BP, with the down-regulation of NFκB, up-regulation of IκBα, and decreased levels of TNF-α, MCP-1 and IL-8. 3) The beneficial effects of Ang-(1-7) could be abolished by A-779. In conclusion, Ang-(1-7) counteracts the effects of Ang II on ICH via modulating NFκB inflammation pathway in HBVSMCs and cerebral microvessels.

Protective effect of irbesartan, an angiotensin II receptor antagonist, alone and in combination with aspirin on middle cerebral artery occlusion model of focal cerebral ischemia in rats

The present study was designed to test pretreatment multiple doses of irbesartan (IRB) 50 mg, aspirin (ASP) 100 mg and the combination of both drugs for 7 days on middle cerebral artery—occluded (MCAO) rats. Focal cerebral ischemia was induced by MCA occlusion for 2 hours followed by reperfusion for 22 hours. After 24 hours of ischemia, grip strength and locomotor activity tests were performed. Animals were immediately sacrificed, infarct volume was measured followed by the estimation of markers of oxidative stress in the whole brains. Locomotor activity and grip strength were improved in IRB- and ASP-treated rats. Infarct volume was reduced in both IRB and ASP pretreatment as compared with MCAO rats. An elevation of thiobarbituric acid reactive substance (TBARS) and a reduction in glutathione (GSH) and antioxidant enzymes viz. superoxide dismutase (SOD) and catalase were observed following MCAO. Pretreatment of IRB and ASP showed the reduction in TBARS, elevation in GSH, SOD and catalase levels as compared with MCAO rats. The protective effects of IRB, an angiotensin II receptor antagonist having affinity for AT1 receptor subtypes, could be due to inhibition of AT 1 receptor expression in addition to its neuroprotective and free radical scavenging properties in cerebral ischemia. Further, it may be possible that the combination of IRB and ASP may be useful as an add-on therapy and would yield beneficial effects, if administered immediately following the ischemia in reducing the severity of the neurological deficits. However, our results are preliminary, further studies with posttreatment of IRB and ASP are required to provide more firm view.

Role of Angiotensin II in the Remodeling Induced by a Chronic Increase in Flow in Rat Mesenteric Resistance Arteries

Angiotensin II is a potent growth factor involved in arterial wall homeostasis. In resistance arteries, chronic increases in blood flow induce a rise in diameter associated with arterial wall hypertrophy. Nevertheless, the role of angiotensin II in this remodeling is unknown. We investigated the effect of blocking angiotensin II production or receptor activation on flow-induced remodeling of mesenteric resistance arteries. Arteries were ligated in vivo to generate high-flow arteries compared with normal flow (control) vessels located at a distance. Arteries were isolated after 1 week for in vitro analysis. Arterial diameter, media surface, endothelial NO synthase expression, superoxide production, and extracellular signal–regulated kinase 1/2 phosphorylation were higher in high-flow than in control arteries. Angiotensin-converting enzyme inhibition (perindopril) and angiotensin II type 1 receptor blockade (candesartan) prevented arterial wall hypertrophy without affecting diameter enlargement. The nonselective vasodilator hydralazine had no effect on remodeling. Although perindopril and candesartan increased endothelial NO synthase expression in high-flow arteries, hypertrophy remained in rats treated with N G -nitro- l -arginine methyl ester and mice lacking endothelial NO synthase. Perindopril and candesartan reduced oxidative stress in high-flow arteries, but superoxide scavenging did not prevent hypertrophy. Both Tempol and the absence of endothelial NO synthase prevented the rise in diameter in high-flow vessels. Extracellular signal–regulated kinase 1/2 activation in high-flow arteries was prevented by perindopril and candesartan and not by hydralazine. Extracellular signal–regulated kinase 1/2 inhibition in vivo (U0126) prevented hypertrophy in high-flow arteries. Thus, a chronic rise in blood flow in resistance arteries induces a diameter enlargement involving NO and superoxide, whereas hypertrophy was associated with extracellular signal–regulated kinase 1/2 activation by angiotensin II.