A novel role for P450 eicosanoids in the neurogenic control of cerebral blood flow in the rat

Abstract

The P450 eicosanoids epoxyeicosatrienoic acids (EETs) are endogenous lipid mediators produced in the brain by P450 epoxygenases and metabolized through multiple pathways, including soluble epoxide hydrolase (sEH). Epoxyeicosatrienoic acids play important functions in the brain, including regulation of cerebral blood flow and protection from ischaemic brain injury. We previously demonstrated that ischaemic preconditioning induces cytochrome P450 2C11 epoxygenase (CYP2C11) expression in the brain, and that pharmacological inhibition and genetic deletion of sEH increases EETs and protects against stroke-induced brain damage. However, the expression profiles of CYP2C11 and sEH in normal brain remain unknown. In agreement with previous reports in peripheral vessels, we here demonstrate by immunofluorescence double-labelling that within cerebral parenchymal microvessels, sEH-immunoreactivity (IR) is localized to the vascular smooth muscle layer. Unexpectedly, however, analysis of large cerebral conduit arteries such as the middle cerebral artery revealed CYP2C11 and sEH expression in extrinsic perivascular nerves. Double-labelling studies revealed that CYP2C11-and sEH-IR predominantly colocalized with neuronal nitric oxide synthase-IR within perivascular nerve fibres. Significant colocalization for CYP2C11 and sEH was also observed with the parasympathetic markers vasoactive intestinal peptide and choline actetyltransferase, in addition to the sensory fibre markers calcitonin gene-related peptide and substance P. No colocalization was observed for either CYP2C11 or sEH with the sympathetic nerve markers dopamine β-hydroxylase or neuropeptide Y. The presence of enzymes involved in production and inactivation of EETs within extrinsic parasympathetic and sensory vasodilator fibres suggests a novel role for EETs in the neurogenic control of cerebral arteries.

Differential Expression of Cytochrome P450 Enzymes from the CYP2C Subfamily in the Human Brain

“…There is also evidence that specific CYP2C forms are expressed in the rodent brain, including the cortex and hippocampus (Alkayed et al, 1996;Luo et al, 1998;Riedl et al, 2000;Iliff et al, 2007). CYP2C11 expressed in astrocytes and perivascular neurons was proposed to be an arachidonic acid epoxygenase involved in the regulation of cerebral blood flow in rats (Alkayed et al, 1996;Iliff et al, 2007).…”

“…CYP2C11 expressed in astrocytes and perivascular neurons was proposed to be an arachidonic acid epoxygenase involved in the regulation of cerebral blood flow in rats (Alkayed et al, 1996;Iliff et al, 2007). Human CYP2C family enzymes may play a similar role in regulating cerebral blood flow (Gervasini et al, 2004); CYP2C8 and CYP2C9 were shown to have arachidonic acid epoxygenase activity (Rifkind et al, 1995) and CYP2C9 has been suggested to regulate blood flow in skeletal muscle during exercise (Hillig et al, 2003).…”

“…Given the role of CYP2C forms in the metabolism of a number of drugs affecting the central nervous system (Guengerich, 2005), it is of significant interest to characterize their expression in the brain. Moreover, CYP2C enzymes in animals have been proposed to contribute to the regulation of cerebral blood flow via generation of epoxyeicosatrienoic acid metabolites from arachidonic acid (Alkayed et al, 1996;Iliff et al, 2007). Although a few studies have been undertaken to detect CYP2C transcript expression in the human brain (McFayden et al, 1998;Klose et al, 1999;Dauchy et al, 2008;Dutheil et al, 2009), the detection of CYP2C proteins has been limited by the paucity of human brain tissue and form-specific antibodies.…”

Two Pools of Epoxyeicosatrienoic Acids in Humans

“…They were present in both SR and SS and highly significant in all subjects together. Previously reported relationships between epoxyeicosatrienoic acids and the autonomic nervous system include (1) arachidonic acid mediated by endogenous 5,6-EET, which can be blocked by CYP450 inhibitors and restored by exogenous 5, ; (2) coexpression of epoxygenases and sEH in brain parasympathetic perivascular nerves 21 ; and (3) production of EETs by sympathetic superior cervical ganglia neurons in culture. 22 Mechanisms for these interactions have not been elucidated, and there is no evidence for either catecholamine stimulation of epoxygenases or for EET-induced norepinephrine release from sympathetic terminals in whole animals or humans.…”

Interaction among <i>CYP2C8</i>, <i>EPHX2</i>, and <i>CYP4A11</i> Gene Variants Significantly Increases the Risk for Ischemic Stroke in Chinese Populations

“…The CYP2C8 rs17110453 polymorphism may decrease the activity of CYP2C8, thereby decreasing the levels of circulating EET metabolites. Pharmacological inhibition or genetic deletion of sEH (encoded by the EPHX2 gene) has been shown to increase EET levels and protect against stroke-induced brain injury 49,50) . Furthermore, certain gene polymorphisms of human EPHX2 have been shown to increase sEH activity and thereby increase the incidence of IS 21) .…”