12/15-Lipooxygenase Inhibition Reduces Microvessel Constriction and Microthrombi after Subarachnoid Hemorrhage in Mice.

Abstract

Background and purpose: Impaired cerebral circulation, induced by blood vessel constrictions and microthrombi, leads to delayed cerebral ischemia after subarachnoid hemorrhage (SAH). 12/15-Lipooxygenase (12/15-LOX) overexpression has been implicated in worsening early brain injury outcomes following SAH. However, it is unknown if 12/15-LOX is important in delayed pathophysiological events after SAH. Since 12/15-LOX produces metabolites that induce inflammation and vasoconstriction, we hypothesized that 12/15-LOX leads to microvessel constriction and microthrombi formation after SAH, and thus 12/15-LOX is an important target to prevent delayed cerebral ischemia.

Methods: SAH was induced in C57BL/6 and 12/15-LOX^-/- mice of both sexes by endovascular perforation. Expression of 12/15-LOX was assessed in brain tissue slices and in vitro. C57BL/6 mice were administered either ML351 (12/15-LOX inhibitor) or vehicle. Mice were evaluated for daily neuroscore and euthanized on day five to assess cerebral 12/15-LOX expression, vessel constrictions, platelet activation, microthrombi, neurodegeneration, infarction, cortical perfusion, and for development of delayed deficits. Finally, the effect of 12/15-LOX inhibition on platelet activation was assessed in SAH patient samples using a platelet spreading assay.

Results: In SAH mice, 12/15-LOX was upregulated in brain vascular cells and there was an increase in 12-S-HETE. Inhibition of 12/15-LOX improved brain perfusion on days 4-5 and attenuated delayed pathophysiological events, including microvessel constrictions, microthrombi, neuronal degeneration, and infarction. Additionally, 12/15-LOX inhibition reduced platelet activation in human and mouse blood samples.

Conclusions: Cerebrovascular 12/15-LOX overexpression plays a major role in brain dysfunction after SAH by triggering microvessel constrictions and microthrombi formation, which reduces brain perfusion. Inhibiting 12/15-LOX may be a therapeutic target to improve outcomes after SAH.