Apocynin reduces infarct volume following cerebral ischemia in mice

We tested the effect of apocynin, an NADPH oxidase inhibitor, on cerebral artery production of superoxide (O 2 ‐ ) and hydrogen peroxide (H 2 O 2 ), and on stroke outcome in C57Bl6/J and Nox2 KO mice. Apocynin (300 μM) inhibited NADPH‐induced O 2 ‐ production by ∼40% (n=9, P<0.05), and reduced H 2 O 2 levels by ∼80% (n=6, P<0.05), in cerebral arteries. Interestingly, apocynin also reduced detectable H 2 O 2 by >80% in the absence of arterial tissue. Ischemic stroke was induced by 30 min middle cerebral artery occlusion ( n =79). Mice received vehicle (0.1% DMSO), 2.5 or 5 mg/kg apocynin ip 30 min before ischemia. Mortality at 24 h was 12% in vehicle controls, and 0% (P=0.24) and 41% (P<0.05) in mice treated with 2.5 and 5 mg/kg apocynin, respectively. Infarct volume was reduced by 2.5 mg/kg apocynin by ∼50% (n=8; P <0.05), whereas 5 mg/kg apocynin was ineffective (n=13). Apocynin (2.5 mg/kg) had no effect on infarct volume in Nox2 KO mice, suggesting its protective effect is Nox2‐dependent. Thus, apocynin inhibits cerebral NADPH oxidase, directly scavenges H 2 O 2 , and has a narrow therapeutic window for stroke. As H 2 O 2 is an endogenous cerebral vasodilator, high dose apocynin could compromise blood flow.