Abstract W P196: Post-Stroke Activation of Angiotensin Converting Enzyme 2 is Neuroprotective

Abstract

Background: Recent discoveries point to the angiotensin converting enzyme 2/angiotensin-(1-7)/mas (ACE2-Ang-(1-7)-Mas) axis as a potential target for neuroprotective stroke therapies. Central pre-stroke activation of this axis by infusion of diminazene aceturate (DIZE), an activator of ACE2, improves stroke outcomes in rats. This led us to hypothesize that intraperitoneal (IP) post-stroke injections of DIZE may exert similar Mas-mediated neuroprotection and thus offer additional clinically-relevant evidence to support this approach. We also assessed the direct effects of DIZE on ACE2 activity in brain tissue. Methods: Male SD rats underwent ischemic stroke by endothelin-1-induced middle cerebral artery occlusion and were randomly divided into groups (n=~12/group) that received IP injections of dH2O or DIZE (0.75, 2.5, or 7.5 mg/kg) at 4, 24, and 48 h after stroke, as well as blinded neurological assessments at 4, 24, and 72 h after stroke. Additional groups received pre- and post-stroke intracerebroventricular (ICV) infusion of sterile 0.9% saline or Mas receptor antagonist A-779 in addition to post-stroke control or drug therapy. Immediately after the 72 h tests, animals were euthanized, cerebral infarct size assessed by TTC staining, and tissue harvested for ACE2 activity assay. Data are expressed as mean ± SEM with significance inferred at p<0.05. Results: Mean infarct sizes (%) were significantly decreased by post-stroke IP injections of all doses of DIZE (0.75 mg/kg: 29.9±5.0; 2.5 mg/kg: 27.9±4.2; 7.5 mg/kg: 31.36±4.1) vs. dH2O (41.9±3.8). At 24 h post-stroke, neurologic deficits (Garcia and Bederson scales) were significantly improved in DIZE-treated rats (7.5 mg/kg: 16.7±0.2 and 0.5±0.1) vs. controls (15.5±0.4 and 1.1±0.2). ICV infusion of A-779 in DIZE-treated rats abolished the improvement in infarct size observed in saline infused DIZE-treated rats (A-779: 43.8%±7.5; saline: 25.8±6.7). Addition of DIZE (4 nmol/μg protein) to brain homogenate increased ACE2 activity by more than 3-fold. Conclusions: This suggests that targeting the ACE2/Ang-(1-7)/Mas axis by post-stroke DIZE injections exerts neuroprotection in a Mas-dependent fashion.