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

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. 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 5 to assess cerebral 12/15-LOX expression, vessel constrictions, platelet activation, microthrombi, neurodegeneration, infarction, cortical perfusion, and 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. 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. 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.