Abstract WP274: Inhibition of Na+/H+ Exchanger Isoform 1 and/or Voltage Gated Proton Channel Improves Outcomes in an Embolic Stroke Model

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While Na+/H+ exchanger isoform 1 inhibitor (NHEi) has been reported to be neuro- and cardio-protective in experimental stroke and myocardial infarction, respectively, clinical use of NHEi for cardioprotection has stalled due to increased cerebrovascular events. NHEi has been demonstrated to increase Hv1 activity and we recently showed that NHEi activates NADPH oxidase and results in amplified superoxide formation in a voltage gated proton channel Hv1-dependent manner. In the CNS, Hv1 is localized primarily to microglia and deletion of Hv1 is neuroprotective after permanent and transient middle cerebral artery occlusion (MCAO). In the current study, we hypothesized that beneficial effect of NHEi after MCAO will be greater in a rat model lacking Hv1 due to loss of a potentially deleterious increase in Hv1 activation and NADPH oxidase activity. The wild type (WT) and Hv1 knockout (KO) rats (n=4-6) were treated with vehicle or NHEi (KR-32568, 2 mg/kg, i.v.) at 30 min after embolic MCAO. The neurological deficiency, infarct size, HT index, and edema ratio were assessed 3 days after surgery (Table). Compare to WT rats, KO rats had smaller infarct, less edema, and better neurological outcomes as previously found in the suture model. NHEi decreased infarct size and edema in both strains. While there was no significant difference in HT between WT and KO rats, the HT was less in WT rats with NHEi. Functional outcomes were significantly improved with NHEi in WT group, while the KO groups had a trend for a better outcomes with NHEi. These data indicate that NHE inhibition in the acute stroke period is similarly effective in both WT and Hv1 KO animals in providing neurovascular protection. Our data do not support the hypothesis that a deleterious increase in Hv1 dependent NADPH oxidase activity limits the beneficial actions of NHEi in embolic stroke. Further studies are needed to explore the underlying mechanism of the interaction between NHEi and the Hv1 channel in ischemic stroke.

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