Anti-inflammatory effects of angiotensin-(1-7) in ischemic stroke
Introduction
Stroke is the fourth leading cause of death in the United States and a major cause of serious, long-term disability (Roger et al., 2012). While there have been many efforts to develop therapeutic approaches for stroke, very little progress has been made to counteract stroke damage and limit long-term disability. Mounting evidence indicates that the renin-angiotensin system (RAS) is a potential therapeutic target for ischemic stroke, as over activation of the angiotensin converting enzyme/angiotensin II/angiotensin II type 1 receptor (ACE/Ang II/AT1R) arm of the RAS is highly involved in the processes that induce cerebral damage following ischemia. Specifically, numerous studies in animal models of experimental stroke have shown that ACE inhibitors and AT1R blockers (ARBs) decrease cortical/subcortical infarct size and the ensuing neurological deficits in animal models of stroke (Groth et al., 2003; Thone-Reineke et al., 2006). Importantly, a number of human clinical trials have also indicated that ACE inhibitors and ARBs can reduce cardiovascular risk and prevent stroke (Dahlöf et al., 2002; Papademetriou et al., 2004; Reboldi et al., 2008).
While Ang II acting via AT1R activation is well known to exert deleterious actions in stroke and other cardiovascular diseases, there is accumulating evidence that the more recently discovered angiotensin converting enzyme 2/angiotensin-(1-7)/Mas (ACE2/Ang-(1-7)/Mas) axis of the RAS exerts beneficial actions in several cardiovascular diseases (Santos et al., 2008; Ferreira et al., 2010). Activating this protective arm of the RAS appears to have potential for treating hypertension, hypertension related pathology, pulmonary hypertension, myocardial infarction, and heart failure based on its ability to counteract the ACE/Ang II/AT1R axis (Castro-Chaves et al., 2010). In the brain, Ang-(1-7) is primarily generated by the action of ACE2 on Ang II, and its effects are mediated by its receptor, Mas (Santos et al., 2003). In recent studies, we demonstrated that the intracerebral damage and neurological deficits elicited by endothelin-1 (ET-1)-induced middle cerebral artery occlusion (MCAO), a model of ischemic stroke, are significantly reduced by intracerebroventricular (ICV) administration of either exogenous Ang-(1-7) or an activator of ACE2, prior to and during the stroke period (Mecca et al., 2011). These beneficial actions of Ang-(1-7) were not due to inhibition of the effects of ET-1 on cerebral vasoconstriction or effects on cerebral blood flow.
The aim of the present study was to investigate the mechanism of this Ang-(1-7) induced cerebroprotection, as understanding these processes would further support the rationale for activating the ACE2/Ang-(1-7)/Mas axis as a potential stroke therapy. Since stroke-induced cerebral damage includes an excessive intracerebral pro-inflammatory response leading to neuronal death (Jin et al., 2010; Iadecola and Anrather, 2011; Lambertsen et al., 2012), in the current study we investigated whether the cerebroprotective actions of Ang-(1-7) in ischemic stroke are associated with anti-inflammatory actions of this peptide.
Section snippets
Animals and ethical approval
For the experiments described here, we used adult male Sprague Dawley (SD) rats (250–275 g) or FVB mice (25–30 g) purchased from Charles River Farms (Wilmington, MA, USA). In addition, Sprague Dawley pups (derived from in-house breeding colony) were used to generate the cell cultures. Brains from FVB/N-Mas-deficient (Mas−/−) mice were obtained from Dr. Michael Bader (Max Delbrück Center for Molecular Medicine, Berlin, Germany) and Dr. Robson Santos (Federal University of Minas Gerais, Belo
Ang-(1-7) reduces intracerebral infarct size 24 h after ET-1-induced MCAO
Previously we demonstrated that ICV treatment with Ang-(1-7) prior to and during induction of ischemic stroke via ET-1-induced MCAO (Mecca et al., 2011) decreased the size of the intracerebral infarct and improved performance on several neurological exams, when measured 72 h after MCAO. Furthermore, in the same study we demonstrated that Ang-(1-7) did not alter blood pressure, percent change in MCA branch vessel diameter or percent change in cerebral blood flow (Mecca et al., 2011). Using the
Discussion
In this study we investigated potential mechanisms that underlie the cerebroprotective action of Ang-(1-7) in ischemic stroke. The major novel findings are: (i) Ang-(1-7) blunts the increases in the levels of iNOS, pro-inflammatory cytokines and CD11b (a marker of macrophage/microglial activation) that occur in the ipsilateral hemisphere following MCAO-induced ischemic stroke; (ii) Ang-(1-7) blunts LPS-induced increases in NO production in cultured glia (mixed culture of microglia and
Acknowledgments
This work was supported by grants from the American Heart Association Greater Southeast Affiliate (09GRNT2060421), the American Medical Association, and from the University of Florida Clinical and Translational Science Institute. Robert Regenhardt received predoctoral fellowship support from the University of Florida Multidisciplinary Training Program in Hypertension (T32 HL-083810). Adam Mecca is a NIH/NINDS, NRSA predoctoral fellow (F30 NS-060335). Support from University of Florida HHMI
References (38)
- et al.
Cardiovascular morbidity and mortality in the Losartan Intervention For Endpoint reduction in hypertension study (LIFE): a randomised trial against atenolol
Lancet
(2002) - et al.
Astrocytes are active players in cerebral innate immunity
Trends Immunol.
(2007) - et al.
Analysis of glial secretome: the long pentraxin PTX3 modulates phagocytic activity of microglia
J. Neuroimmunol.
(2010) - et al.
SDF-1alpha up-regulates interleukin-6 through CXCR4, PI3K/Akt, ERK, and NF-kappaB-dependent pathway in microglia
Eur. J. Pharmacol.
(2009) - et al.
Stroke prevention with the angiotensin II type 1-receptor blocker candesartan in elderly patients with isolated systolic hypertension: the Study on Cognition and Prognosis in the Elderly (SCOPE)
J. Am. Coll. Cardiol.
(2004) - et al.
(Pro)renin receptors and angiotensin converting enzyme 2/angiotensin-(1-7)/Mas receptor axis in human aortic valve stenosis
Atherosclerosis
(2011) - et al.
Effects of monocyte chemoattractant protein 1 on blood-borne cell recruitment after transient focal cerebral ischemia in mice
Neuroscience
(2009) - et al.
Microglial activation in stroke: therapeutic targets
Neurotherapeutics
(2010) - et al.
Isolation and characterization of a new cellular oncogene encoding a protein with multiple potential transmembrane domains
Cell
(1986) - et al.
Central administration of angiotensin-(1-7) stimulates nitric oxide release and upregulates the endothelial nitric oxide synthase expression following focal cerebral ischemia/reperfusion in rats
Neuropeptides
(2008)