Soluble Epoxide Inhibition Is Protective Against Cerebral Ischemia via Vascular and Neural Protection

Inhibition of soluble epoxide hydrolase (SEH), the enzyme responsible for degradation of vasoactive epoxides, protects against cerebral ischemia in rats. However, the molecular and biological mechanisms that confer protection in normotension and hypertension remain unclear. Here we show that 6 weeks of SEH inhibition via 2 mg/day of 12-(3-adamantan-1-yl-ureido) dodecanoic acid (AUDA) in spontaneously hypertensive stroke-prone (SHRSP) rats protects against cerebral ischemia induced by middle cerebral artery occlusion, reducing percent hemispheric infarct and neurodeficit score without decreasing blood pressure. This level of cerebral protection was similar to that of the angiotensin-converting enzyme inhibitor, enalapril, which significantly lowered blood pressure. SEH inhibition is also protective in normotensive Wistar-Kyoto (WKY) rats, reducing both hemispheric infarct and neurodeficit score. In SHRSP rats, SEH inhibition reduced wall-to-lumen ratio and collagen deposition and increased cerebral microvessel density, although AUDA did not alter middle cerebral artery structure or microvessel density in WKY rats. An apoptosis mRNA expression microarray of brain tissues from AUDA-treated rats revealed that AUDA modulates gene expression of mediators involved in the regulation of apoptosis in neural tissues of both WKY and SHRSP rats. Hence, we conclude that chronic SEH inhibition protects against cerebral ischemia via vascular protection in SHRSP rats and neural protection in both the SHRSP and WKY rats, indicating that SEH inhibition has broad pharmacological potential for treating ischemic stroke.Epoxyeicosatrienoic acids (EETs), lipid metabolites produced from arachidonic acid by CYP450 enzymes, are novel mediators that antagonize the sequela of hypertension,¹ match cerebral blood flow to increased neural activity and metabolic demand, promotes angiogenesis,² and protect against ischemia.^3,4 Because ischemic stroke occurs with loss of cerebral blood flow and is strongly associated with hypertension, modulation of epoxide degradation has potential in managing ischemic stroke. Unfortunately, pharmacological utility of exogenous EETs is impractical because the epoxides are rapidly degraded by the soluble epoxide hydrolase (SEH) into their less active diol, dihydroxyeicosatrienoic acids.⁵ In fact, human SEH polymorphisms are linked to the incidence of ischemic stroke,⁶ and this association could be related to modifications in SEH activity, and thus epoxide catabolism.⁷ An alternative strategy that has been used to increase EETs systemically is SEH inhibition.¹We previously showed that the SEH inhibitor 12-(3-adamantan-1-yl-ureido) dodecanoic acid (AUDA) protects against cerebral ischemia in spontaneously hypertensive stroke-prone (SHRSP) rats, an animal model of essential hypertension.⁸ Interestingly, chronic AUDA treatment in SHRSP rats effectively decreased infarct size induced by middle cerebral artery occlusion (MCAO) without decreasing blood pressure.⁸ Although blood pressure is an important variable in controlling infarct size in the SHRSP, the cerebrovasculature is also a key determinant of increased sensitivity to cerebral ischemia and thus infarct size.^9,10 Our study provided preliminary evidence that AUDA protection in the SHRSP involved changes in vascular structure.⁸ More recently, a report suggested that administration of AUDA-butyl ester protects against cerebral ischemic reperfusion injury in normotensive mice by mechanisms that may involve neural protection rather than vascular protection.¹¹ As a result, the contribution of vascular and neural protection to the cerebral protective effects of SEH inhibition during states of hypertension and normotension are unclear and require further investigation. The present study tested the hypothesis that SEH inhibition provides cerebral protection via different mechanisms in normotensive WKY and hypertensive SHRSP rats.