Cytochrome P450 eicosanoids and cerebral vascular function

Thromboxane-induced cerebral microvascular rarefaction predicts depressive symptom emergence in metabolic disease

Previous studies have suggested that the loss of microvessel density in the peripheral circulation with evolving metabolic disease severity represents a significant contributor to impaired skeletal muscle oxygenation and fatigue-resistance. Based on this and our recent work, we hypothesized that cerebral microvascular rarefaction was initiated from the increased prooxidant and proinflammatory environment with metabolic disease and is predictive of the severity of the emergence of depressive symptoms in obese Zucker rats (OZRs). In male OZR, cerebrovascular rarefaction followed the emergence of elevated oxidant and inflammatory environments characterized by increased vascular production of thromboxane A2 (TxA2). The subsequent emergence of depressive symptoms in OZR was associated with the timing and severity of the rarefaction. Chronic intervention with antioxidant (TEMPOL) or anti-inflammation (pentoxifylline) therapy blunted the severity of rarefaction and depressive symptoms, although the effectiveness was limited. Blockade of TxA2 production (dazmegrel) or action (SQ-29548) resulted in a stronger therapeutic effect, suggesting that vascular production and action represent a significant contributor to rarefaction and the emergence of depressive symptoms with chronic metabolic disease (although other pathways clearly contribute as well). A de novo biosimulation of cerebrovascular oxygenation in the face of progressive rarefaction demonstrates the increased probability of generating hypoxic regions within the microvascular networks, which could contribute to impaired neuronal metabolism and the emergence of depressive symptoms. The results of the present study also implicate the potential importance of aggressive prodromic intervention in reducing the severity of chronic complications arising from metabolic disease.NEW & NOTEWORTHY With clinical studies linking vascular disease risk to depressive symptom emergence, we used obese Zucker rats, a model of chronic metabolic disease, to identify potential mechanistic links between these two negative outcomes. Depressive symptom severity correlated with the extent of cerebrovascular rarefaction, after increased vascular oxidant stress/inflammation and TxA2 production. Anti-TxA2 interventions prevasculopathy blunted rarefaction and depressive symptoms, while biosimulation indicated that cerebrovascular rarefaction increased hypoxia within capillary networks as a potential contributing mechanism.

Neurotrophic Natural Products

Neurotrophins (NGF, BDNF, NT3, NT4) can decrease cell death, induce differentiation, as well as sustain the structure and function of neurons, which make them promising therapeutic agents for the treatment of neurodegenerative disorders. However, neurotrophins have not been very effective in clinical trials mostly because they cannot pass through the blood-brain barrier owing to being high-molecular-weight proteins. Thus, neurotrophin-mimic small molecules, which stimulate the synthesis of endogenous neurotrophins or enhance neurotrophic actions, may serve as promising alternatives to neurotrophins. Small-molecular-weight natural products, which have been used in dietary functional foods or in traditional medicines over the course of human history, have a great potential for the development of new therapeutic agents against neurodegenerative diseases such as Alzheimer's disease. In this contribution, a variety of natural products possessing neurotrophic properties such as neurogenesis, neurite outgrowth promotion (neuritogenesis), and neuroprotection are described, and a focus is made on the chemistry and biology of several neurotrophic natural products.

Connexin and Pannexin Large-Pore Channels in Microcirculation and Neurovascular Coupling Function

Microcirculation homeostasis depends on several channels permeable to ions and/or small molecules that facilitate the regulation of the vasomotor tone, hyperpermeability, the blood–brain barrier, and the neurovascular coupling function. Connexin (Cxs) and Pannexin (Panxs) large-pore channel proteins are implicated in several aspects of vascular physiology. The permeation of ions (i.e., Ca²⁺) and key metabolites (ATP, prostaglandins, D-serine, etc.) through Cxs (i.e., gap junction channels or hemichannels) and Panxs proteins plays a vital role in intercellular communication and maintaining vascular homeostasis. Therefore, dysregulation or genetic pathologies associated with these channels promote deleterious tissue consequences. This review provides an overview of current knowledge concerning the physiological role of these large-pore molecule channels in microcirculation (arterioles, capillaries, venules) and in the neurovascular coupling function.

Endothelial Cells and the Cerebral Circulation

Endothelial cells form the innermost layer of all blood vessels and are the only vascular component that remains throughout all vascular segments. The cerebral vasculature has several unique properties not found in the peripheral circulation; this requires that the cerebral endothelium be considered as a unique entity. Cerebral endothelial cells perform several functions vital for brain health. The cerebral vasculature is responsible for protecting the brain from external threats carried in the blood. The endothelial cells are central to this requirement as they form the basis of the blood-brain barrier. The endothelium also regulates fibrinolysis, thrombosis, platelet activation, vascular permeability, metabolism, catabolism, inflammation, and white cell trafficking. Endothelial cells regulate the changes in vascular structure caused by angiogenesis and artery remodeling. Further, the endothelium contributes to vascular tone, allowing proper perfusion of the brain which has high energy demands and no energy stores. In this article, we discuss the basic anatomy and physiology of the cerebral endothelium. Where appropriate, we discuss the detrimental effects of high blood pressure on the cerebral endothelium and the contribution of cerebrovascular disease endothelial dysfunction and dementia. © 2022 American Physiological Society. Compr Physiol 12:3449-3508, 2022.

Epoxyeicosatrienoic acids and soluble epoxide hydrolase in physiology and diseases of the central nervous system

Epoxyeicosatrienoic acids (EETs) are fatty acid signaling molecules synthesized by cytochrome P450 epoxygenases from arachidonic acid. The biological activity of EETs is terminated when being metabolized by soluble epoxide hydrolase (sEH), a process that serves as a key regulator of tissue EETs levels. EETs act through several signaling pathways to mediate various beneficial effects, including anti-inflammation, anti-apoptosis, and anti-oxidation with relieve of endoplasmic reticulum stress, thereby sEH has become a potential therapeutic target in cardiovascular disease and cancer therapy. Enzymes for EET biosynthesis and metabolism are both widely detected in both neuron and glial cells in the central nervous system (CNS). Recent studies discovered that astrocyte-derived EETs not only mediate neurovascular coupling and neuronal excitability by maintaining glutamate homeostasis but also glia-dependent neuroprotection. Genetic ablation as well as pharmacologic inhibition of sEH has greatly helped to elucidate the physiologic actions of EETs, and maintaining or elevating brain EETs level has been demonstrated beneficial effects in CNS disease models. Here, we review the literature regarding the studies on the bioactivity of EETs and their metabolic enzyme sEH with special attention paid to their action mechanisms in the CNS, including their modulation of neuronal activity, attenuation of neuroinflammation, regulation of cerebral blood flow, and improvement of neuronal and glial cells survival. We further reviewed the recent advance on the potential application of sEH inhibition for treating cerebrovascular disease, epilepsy, and pain disorder.

20-hydroxyeiscosatetraenoic acid may be as a predictor of malignant middle cerebral artery infarction in patients with massive middle cerebral artery infarction

Background

Early identification of massive middle cerebral artery infarction (MCAI) at risk for malignant MCAI (m-MCAI) may be useful in selecting patients for aggressive therapies. The aim of this study was to determine whether CYP metabolites may help to predict impending m-MCAI.

Methods

This is a prospective, two-center observational study in 256 patients with acute massive MCAI. Plasma levels of 20-hydroxyeicosatetraenoic acid (20-HETE), epoxyeicosatrienoic acids, and dihydroxyeicosatrienoic acids were measured at admission. Brain computed tomography (CT) was performed at admission and repeated between day 3 and 7, or earlier if there was neurological deterioration. The primary outcome was m-MCAI. The m-MCAI was diagnosed when follow-up brain CT detected a more than two-thirds space-occupying MCAI with midline shift, compression of the basal cisterns, and neurological worsening.

Results

In total of 256 enrolled patients, 77 (30.1%) patients developed m-MCAI. Among the 77 patients with m-MCAI, 60 (77.9%) patients died during 3 months of stroke onset. 20-HETE level on admission was significantly higher in patients with m-MCAI than those without m-MCAI. There was an increase in the risk of m-MCAI with increase of 20-HETE levels. The third and fourth quartiles of 20-HETE levels were independent predictors of m-MCAI (OR: 2.86; 95% CI: 1.16 – 6.68; P = 0.025, and OR: 4.23; 95% CI: 1.35 – 8.26; P = 0.002, respectively).

Conclusions

Incidence of m-MCAI was high in patients with massive MCAI and the prognosis of m-MCAI is very poor. Elevated plasma 20-HETE may be as a predictor for m-MCAI in acute massive MCAI, and it might useful in clinical practice in therapeutic decision making.

Angiotensin II Disrupts Neurovascular Coupling by Potentiating Calcium Increases in Astrocytic Endfeet

Background Angiotensin II (Ang II), a critical mediator of hypertension, impairs neurovascular coupling. Since astrocytes are key regulators of neurovascular coupling, we sought to investigate whether Ang II impairs neurovascular coupling through modulation of astrocytic Ca2+ signaling. Methods and Results Using laser Doppler flowmetry, we found that Ang II attenuates cerebral blood flow elevations induced by whisker stimulation or the metabotropic glutamate receptors agonist, 1S, 3R-1-aminocyclopentane-trans-1,3-dicarboxylic acid (P<0.01). In acute brain slices, Ang II shifted the vascular response induced by 1S, 3R-1-aminocyclopentane-trans-1,3-dicarboxylic acid towards vasoconstriction (P<0.05). The resting and 1S, 3R-1-aminocyclopentane-trans-1,3-dicarboxylic acid-induced Ca2+ levels in the astrocytic endfeet were more elevated in the presence of Ang II (P<0.01). Both effects were reversed by the AT1 receptor antagonist, candesartan (P<0.01 for diameter and P<0.05 for calcium levels). Using photolysis of caged Ca2+ in astrocytic endfeet or pre-incubation of 1,2-Bis(2-aminophenoxy)ethane-N,N,N',N'-tetra-acetic acid tetrakis (acetoxymethyl ester), we demonstrated the link between potentiated Ca2+ elevation and impaired vascular response in the presence of Ang II (P<0.001 and P<0.05, respectively). Both intracellular Ca2+ mobilization and Ca2+ influx through transient receptor potential vanilloid 4 mediated Ang II-induced astrocytic Ca2+ elevation, since blockade of these pathways significantly prevented the intracellular Ca2+ in response to 1S, 3R-1-aminocyclopentane-trans-1,3-dicarboxylic acid (P<0.05). Conclusions These results suggest that Ang II through its AT1 receptor potentiates the astrocytic Ca2+ responses to a level that promotes vasoconstriction over vasodilation, thus altering cerebral blood flow increases in response to neuronal activity.

Polymorphisms in genes related to oxidative stress and inflammation: Emerging links with the pathogenesis and severity of Cerebral Cavernous Malformation disease

Cerebral Cavernous Malformation (CCM) is a cerebrovascular disease of genetic origin affecting 0.5% of the population and characterized by abnormally enlarged and leaky capillaries that predispose to seizures, neurological deficits, and intracerebral hemorrhage (ICH). CCM occurs sporadically or is inherited as dominant condition with incomplete penetrance and highly variable expressivity. Three disease genes have been identified: KRIT1 (CCM1), CCM2 and CCM3. Previous results demonstrated that loss-of-function mutations of CCM genes cause pleiotropic effects, including defective autophagy, altered reactive oxygen species (ROS) homeostasis, and enhanced sensitivity to oxidative stress and inflammatory events, suggesting a novel unifying pathogenetic mechanism, and raising the possibility that CCM disease onset and severity are influenced by the presence of susceptibility and modifier genes. Consistently, genome-wide association studies (GWAS) in large and homogeneous cohorts of patients sharing the familial form of CCM disease and identical mutations in CCM genes have led to the discovery of distinct genetic modifiers of major disease severity phenotypes, such as development of numerous and large CCM lesions, and susceptibility to ICH. This review deals with the identification of genetic modifiers with a significant impact on inter-individual variability in CCM disease onset and severity, including highly polymorphic genes involved in oxidative stress, inflammatory and immune responses, such as cytochrome P450 monooxygenases (CYP), matrix metalloproteinases (MMP), and Toll-like receptors (TLR), pointing to their emerging prognostic value, and opening up new perspectives for risk stratification and personalized medicine strategies.

PET imaging of soluble epoxide hydrolase in non-human primate brain with [18F]FNDP

Purpose

Soluble epoxide hydrolase (sEH) is a promising candidate positron emission tomography (PET) imaging biomarker altered in various disorders, including vascular cognitive impairment (VCI), Alzheimer’s disease (AD), Parkinson’s disease (PD), stroke, and depression, known to regulate levels of epoxyeicosatrienoic acids (EETs) and play an important role in neurovascular coupling. [¹⁸F]FNDP, a PET radiotracer for imaging sEH, was evaluated through quantitative PET imaging in the baboon brain, radiometabolite analysis, and radiation dosimetry estimate.

Methods

Baboon [¹⁸F]FNDP dynamic PET studies were performed at baseline and with blocking doses of the selective sEH inhibitor AR-9281 to evaluate sEH binding specificity. Radiometabolites of [¹⁸F]FNDP in mice and baboons were measured by high-performance liquid chromatography. Regional brain distribution volume (V_T) of [¹⁸F]FNDP was computed from PET using radiometabolite-corrected arterial input functions. Full body distribution of [¹⁸F]FNDP was studied in CD-1 mice, and the human effective dose was estimated using OLINDA/EXM software.

Results

[¹⁸F]FNDP exhibited high and rapid brain uptake in baboons. AR-9281 blocked [¹⁸F]FNDP uptake dose-dependently with a baseline V_T of 10.9 ± 2.4 mL/mL and a high-dose blocking V_T of 1.0 ± 0.09 mL/mL, indicating substantial binding specificity (91.70 ± 1.74%). The V_ND was estimated as 0.865 ± 0.066 mL/mL. The estimated occupancy values of AR-9281 were 99.2 ± 1.1% for 1 mg/kg, 88.6 ± 1.3% for 0.1 mg/kg, and 33.8 ± 3.8% for 0.02 mg/kg. Murine biodistribution of [¹⁸F]FNDP enabled an effective dose estimate for humans (0.032 mSv/MBq). [¹⁸F]FNDP forms hydrophilic radiometabolites in murine and non-human primate plasma. However, only minute amounts of the radiometabolites entered the animal brain (< 2% in mice).

Conclusions

[¹⁸F]FNDP is a highly sEH-specific radiotracer that is suitable for quantitative PET imaging in the baboon brain. [¹⁸F]FNDP holds promise for translation to human subjects.

A novel interaction between soluble epoxide hydrolase and the AT1 receptor in retinal microvascular damage

Clinical studies have suggested that the renin-angiotensin system (RAS) may be a promising therapeutic target in treating diabetic retinopathy (DR). While AT1 receptor blockade decreased the incidence of DR in the DIRECT trial, it did not reduce the DR progression. Lack of understanding of the molecular mechanism of retinal microvascular damage induced by RAS is a critical barrier to the use of RAS blockade in preventing or treating DR. The purpose of this study is to investigate the interaction between soluble epoxide hydrolase (sEH) and the AT1 receptor in Angiotensin II (Ang II)- and diabetes-induced retinal microvascular damage. We demonstrate that Ang II increases retinal sEH levels, which is blunted by an AT1 blocker; administration of 11,12-epoxyeicosatrienoic acid (EET) exacerbates intravitreal Ang II-induced retinal albumin leakage; while sEH knockout (KO) and blockade reduce Ang II-induced retinal vascular remodeling, sEH KO causes retinal vascular leakage in Ang II-sEH KO mice; and sEH KO potentiates diabetes-induced retinal damage via promoting retinal vascular endothelial growth factor (VEGF) but reducing expression of tight junction proteins (ZO-1 and occludin). Our studies hold the promise of providing a new strategy, the use of combined EETs blockade with AT1 blocker, to prevent or reduce DR.

The Systems Biology of Drug Metabolizing Enzymes and Transporters: Relevance to Quantitative Systems Pharmacology

Quantitative systems pharmacology (QSP) has emerged as a transformative science in drug discovery and development. It is now time to fully rethink the biological functions of drug metabolizing enzymes (DMEs) and transporters within the framework of QSP models. The large set of DME and transporter genes are generally considered from the perspective of the absorption, distribution, metabolism, and excretion (ADME) of drugs. However, there is a growing amount of data on the endogenous physiology of DMEs and transporters. Recent studies—including systems biology analyses of “omics” data as well as metabolomics studies—indicate that these enzymes and transporters, which are often among the most highly expressed genes in tissues like liver, kidney, and intestine, have coordinated roles in fundamental biological processes. Multispecific DMEs and transporters work together with oligospecific and monospecific ADME proteins in a large multiorgan remote sensing and signaling network. We use the Remote Sensing and Signaling Theory (RSST) to examine the roles of DMEs and transporters in intratissue, interorgan, and interorganismal communication via metabolites and signaling molecules. This RSST‐based view is applicable to bile acids, uric acid, eicosanoids, fatty acids, uremic toxins, and gut microbiome products, among other small organic molecules of physiological interest. Rooting this broader perspective of DMEs and transporters within QSP may facilitate an improved understanding of fundamental biology, physiologically based pharmacokinetics, and the prediction of drug toxicities based upon the interplay of these ADME proteins with key pathways in metabolism and signaling. The RSST‐based view should also enable more tailored pharmacotherapy in the setting of kidney disease, liver disease, metabolic syndrome, and diabetes. We further discuss the pharmaceutical and regulatory implications of this revised view through the lens of systems physiology.

L-arginine supplementation and thromboxane synthase inhibition increases cerebral blood flow in experimental cerebral malaria

Cerebral malaria pathogenesis involves vascular dysfunction with low nitric oxide (NO) bioavailability, vasoconstriction and impaired vasodilation, leading to ischemia, tissue hypoxia and ultimately death. Cerebral blood flow (CBF) involves NO and other pathways, including arachidonic acid (AA)-derived metabolites. Here we show that mice with experimental cerebral malaria (ECM) by P. berghei ANKA showed marked decreases in CBF (as assessed by laser speckle contrast imaging - LSCI) and that administration of L-arginine supplementation (50 mg/kg) and/or of the thromboxane synthase inhibitor Ozagrel (100 mg/kg) induced immediate increases in CBF. L-arginine in combination with artesunate (32 mg/kg) induced immediate reversal of brain ischemia in the short-term (1 hour), but the effect subsided after 3 and 6 hours. Neither L-arginine nor Ozagrel reversed blood brain barrier breakdown. Mice with ECM showed brain levels of selected AA-derived metabolites with a vasoconstrictor profile, with increased levels of 8-isoprostanes, 20-HETE and 14,15-DHET, whereas mice infected with a non-ECM-inducing strain of P. berghei (NK65) showed a vasodilator profile, with normal levels of 20-HETE and 14,15-DHET and increased levels of PGE2. L-arginine is capable of partially reversing cerebral ischemia and AA metabolites may play a role in the cerebrovascular dysfunction in ECM.

The arachidonic acid monooxygenase: from biochemical curiosity to physiological/pathophysiological significance

The initial studies of the metabolism of arachidonic acid (AA) by the cytochrome P450 (P450) hemeproteins sought to: a) elucidate the roles for these enzymes in the metabolism of endogenous pools of the FA, b) identify the P450 isoforms involved in AA epoxidation and ω/ω-1 hydroxylation, and c) explore the biological activities of their metabolites. These early investigations provided a foundation for subsequent efforts to establish the physiological relevance of the AA monooxygenase and its contributions to the pathophysiology of, for example, cancer, diabetes, hypertension, inflammation, nociception, and vascular disease. This retrospective analyzes the history of some of these efforts, with emphasis on genetic studies that identified roles for the murine Cyp4a and Cyp2c genes in renal and vascular physiology and the pathophysiology of hypertension and cancer. Wide-ranging investigations by laboratories worldwide, including the authors, have established a better appreciation of the enzymology, genetics, and physiologic roles for what is now known as the third branch of the AA cascade. Combined with the development of analytical and pharmacological tools, including robust synthetic agonists and antagonists of the major metabolites, we stand at the threshold of novel therapeutic approaches for the treatment of renal injury, pain, hypertension, and heart disease.

14,15-epoxyeicosatrienoic acid produced by cytochrome P450s enhances neurite outgrowth of PC12 and rat hippocampal neuronal cells

Polyunsaturated fatty acids, such as arachidonic acid, are accumulated in brain and induce neuronal differentiation. Arachidonic acid is metabolized to epoxyeicosatrienoic acids (EETs) and hydroxyeicosatetraenoic acids (HETEs) by cytochrome P450s. In this study, we found that 14,15-EET and 20-HETE-enhanced NGF-induced rat pheochromocytoma PC12 cell neurite outgrowth even at the concentration of 100 nmol L-1. LC-MS analysis revealed that 14,15-EET was effectively produced from arachidonic acid by rat CYP2C11, 2C13, and 2C23, and these P450s were expressed in PC12 cells. An inhibitor of these P450s, ketoconazole, inhibited neurite outgrowth, whereas inhibition of soluble epoxide hydrolase, which hydrolyzes EETs to their corresponding diols enhanced neurite outgrowth. To determine the mechanism of neurite formation enhancement by arachidonic acid metabolites, we focused on transient receptor potential (TRP) channels expressed in PC12 cells. The TRPV4 inhibitor HC067047, but not the TRPV1 inhibitor capsazepine, inhibited the effects of 14,15-EET on neurite outgrowth of PC12. Furthermore, 14,15-EET increased the cytosolic calcium ion concentration and this increase was inhibited by HC067047. 14,15-EET also enhanced neurite outgrowth of primary cultured neuron from rat hippocampus. This study suggests that arachidonic acid metabolites produced by P450 contribute to neurite outgrowth through calcium influx.

Cerebral artery myogenic reactivity: The next frontier in developing effective interventions for subarachnoid hemorrhage

Aneurysmal subarachnoid hemorrhage (SAH) is a devastating cerebral event that kills or debilitates the majority of those afflicted. The blood that spills into the subarachnoid space stimulates profound cerebral artery vasoconstriction and consequently, cerebral ischemia. Thus, once the initial bleeding in SAH is appropriately managed, the clinical focus shifts to maintaining/improving cerebral perfusion. However, current therapeutic interventions largely fail to improve clinical outcome, because they do not effectively restore normal cerebral artery function. This review discusses emerging evidence that perturbed cerebrovascular "myogenic reactivity," a crucial microvascular process that potently dictates cerebral perfusion, is the critical element underlying cerebral ischemia in SAH. In fact, the myogenic mechanism could be the reason why many therapeutic interventions, including "Triple H" therapy, fail to deliver benefit to patients. Understanding the molecular basis for myogenic reactivity changes in SAH holds the key to develop more effective therapeutic interventions; indeed, promising recent advancements fuel optimism that vascular dysfunction in SAH can be corrected to improve outcome.

Soluble epoxide hydrolase as a therapeutic target for pain, inflammatory and neurodegenerative diseases

Eicosanoids are biologically active lipid signaling molecules derived from polyunsaturated fatty acids. Many of the actions of eicosanoid metabolites formed by cyclooxygenase and lipoxygenase enzymes have been characterized, however, the epoxy-fatty acids (EpFAs) formed by cytochrome P450 enzymes are newly described by comparison. The EpFA metabolites modulate a diverse set of physiologic functions that include inflammation and nociception among others. Regulation of EpFAs occurs primarily via release, biosynthesis and enzymatic transformation by the soluble epoxide hydrolase (sEH). Targeting sEH with small molecule inhibitors has enabled observation of the biological activity of the EpFAs in vivo in animal models, greatly contributing to the overall understanding of their role in the inflammatory response. Their role in modulating inflammation has been demonstrated in disease models including cardiovascular pathology and inflammatory pain, but extends to neuroinflammation and neuroinflammatory disease. Moreover, while EpFAs demonstrate activity against inflammatory pain, interestingly, this action extends to blocking chronic neuropathic pain as well. This review outlines the role of modulating sEH and the biological action of EpFAs in models of pain and inflammatory diseases.

Hyperbaric oxygenation and 20-hydroxyeicosatetreanoic acid inhibition reduce stroke volume in female diabetic Sprague-Dawley rats

NEW FINDINGS

What is the central question of this study? Is there a beneficial effect and what are the mechanisms of acute and multiple hyperbaric oxygenation (HBO₂ ) exposures on the outcome of cerebral tissue injury induced by a transient middle cerebral artery occlusion model in diabetic female rats? Are 20-hydroxyeicosatetreanoic acid and epoxyeicosatrienoic acids involved? What is the main finding and its importance? Equal reduction of cortical and total infarct size in rats treated with HBO₂ and HET0016 (20-hydroxyeicosatetreanoic acid production inhibitor) and significant mRNA upregulation of epoxyeicosatrienoic acid-producing enzymes (Cyp2J3 and Cyp2C11) in treated groups suggest that HBO₂ and HET0016 are highly effective stroke treatments and that cytochrome P450 metabolites are involved in this therapeutic effect. We evaluated the effects of acute and repetitive hyperbaric oxygenation (HBO₂ ), 20-hydroxyeicosatetreanoic acid (20-HETE) inhibition by N-hydroxy-N'-(4-butyl-2methylphenyl)-formamidine (HET0016) and their combination on experimental stroke outcomes. Streptozotocin-induced type 1 diabetic Sprague-Dawley female rats (n = 42; n = 7 per group), were subjected to 30 min of transient middle cerebral artery occlusion (t-MCAO)-reperfusion and divided into the following groups: (1) control group, without treatment; and groups exposed to: (2) HBO₂ ; (3) multiple HBO₂ (HBO₂ immediately and second exposure 12 h after t-MCAO); (4) HET0016 pretreatment (1 mg kg^-1 , 3 days before t-MCAO) combined with HBO₂ after t-MCAO; (5) HET0016 treatment (1 h before, during and for 6 h after t-MCAO); and (6) HET0016 treatment followed by HBO₂ after t-MCAO. Messenger RNA expression of CYP2J3, CYP2C11, CYP4A1, endothelial nitric oxide synthase and epoxide hydrolase 2 was determined by real-time qPCR. Cortical infarct size and total infarct size were equally and significantly reduced in HBO₂ - and HET0016-treated rats. Combined treatment with HET0016 and HBO₂ provided no significant additive effect compared with HET0016 treatment only. Messenger RNA of Cyp2J3 was significantly increased in all study groups, and mRNA of Cyp2C11 was significantly increased in the multiple HBO₂ group and the HET0016 treatment followed by HBO₂ group, compared with the control group. Expression of endothelial nitric oxide synthase was significantly increased after HBO₂ treatments, and expression of epoxide hydrolase 2 was increased in all groups compared with the control group. In diabetic female Sprague-Dawley rats, HBO₂ and HET0016 are highly effective stroke treatments, suggesting the involvement of cytochrome P450 metabolites and the NO pathway in this therapeutic effect.

Cytochrome P450 eicosanoids in cerebrovascular function and disease

Cytochrome P450 eicosanoids play important roles in brain function and disease through their complementary actions on cell-cell communications within the neurovascular unit (NVU) and mechanisms of brain injury. Epoxy- and hydroxyeicosanoids, respectively formed by cytochrome P450 epoxygenases and ω-hydroxylases, play opposing roles in cerebrovascular function and in pathological processes underlying neural injury, including ischemia, neuroinflammation and oxidative injury. P450 eicosanoids also contribute to cerebrovascular disease risk factors, including hypertension and diabetes. We summarize studies investigating the roles P450 eicosanoids in cerebrovascular physiology and disease to highlight the existing balance between these important lipid signaling molecules, as well as their roles in maintaining neurovascular homeostasis and in acute and chronic neurovascular and neurodegenerative disorders.

Epoxyeicosatrienoic Acids are Mediated by EPHX2 Variants and may be a Predictor of Early Neurological Deterioration in Acute Minor Ischemic Stroke

Aim: To investigatethe association of plasma epoxyeicosatrienoic acids (EETs) with early neurologic deterioration (END), and whether EETs are mediated by EPHX2 variants in patients with minor ischemic stroke (MIS).

Method: This was a prospective, multi-center observational study in patients with acute MIS in the Chinese population.Plasma EETs levels were measured on admission. Single nucleotide polymorphisms (SNPs) of EPHX2rs751141 were genotyped using mass spectrometry. The primary outcome was END within 10 days after admission. END was defined as an increase in NIHSS of 2 or more points. The degree of disability was assessed using the modified Rankin Scale (mRS) at 3 months after admission.

Results: A total of 322 patients were enrolled, of which 85 patients (26.4%) experienced END. The mean EETs level was 64.1 ± 7.5 nmol/L. EETs levels were significantly lower in patients with END compared to patients without END. Frequency of EPHX2 rs751141 GG was higher in patients with END than in patients without END, and EPHX2 rs751141 GG genotype was associated with lower EETs levels. Low level (< 64.4 nmol/L) of EETs was an independent predictor of END (first and second quartiles) in multivariate analyses. END was associated with a higher risk of poor outcome (mRS scores 3–6) at 3 months.

Conclusion: END is fairly common and associated with poor outcomes in acute MIS. EPHX2 variants may mediate EETs levels, and low levels of EETs may be a predictor for END in acute MIS.

The effects of sEH inhibitor on depression-like behavior and neurogenesis in male mice

Currently antidepressants take several weeks to be effective, which is one of the main reasons why patients with depression quit therapy. In the present study, we examine the acute and subacute effects of soluble epoxide hydolase (sEH) inhibitor (sEHI), a compound shown to have antidepressant effects, on mice. We found that acute administration of sEHI TPPU decreases immobility time in the forced swimming test and reduces latency to feed in the novelty suppressed-feeding test in adult male mice. Intraperitoneal administration of TPPU for seven days also increased interaction time of socially defeated mice in the social defeat test. Hippocampal BDNF expression and cell proliferation in the dentate gyrus increased six and 24 hours after TPPU treatment, respectively. Improvement in antidepressant behavior and cell proliferation were inhibited by BDNF-trkB antagonist K252a, which suggests that anti-depressant effects of sEHI may be involved in BDNF signaling. Taken together, our findings suggest that sEHI may provide a rapid antidepressant effect through alterations to BDNF-trkB signaling in the hippocampus and may provide an alternative to current slow-acting antidepressants. © 2017 Wiley Periodicals, Inc.

Clinical Implications of 20-Hydroxyeicosatetraenoic Acid in the Kidney, Liver, Lung and Brain: An Emerging Therapeutic Target

Cytochrome P450-mediated metabolism of arachidonic acid (AA) is an important pathway for the formation of eicosanoids. The ω-hydroxylation of AA generates significant levels of 20-hydroxyeicosatetraenoic acid (20-HETE) in various tissues. In the current review, we discussed the role of 20-HETE in the kidney, liver, lung, and brain during physiological and pathophysiological states. Moreover, we discussed the role of 20-HETE in tumor formation, metabolic syndrome and diabetes. In the kidney, 20-HETE is involved in modulation of preglomerular vascular tone and tubular ion transport. Furthermore, 20-HETE is involved in renal ischemia/reperfusion (I/R) injury and polycystic kidney diseases. The role of 20-HETE in the liver is not clearly understood although it represents 50%-75% of liver CYP-dependent AA metabolism, and it is associated with liver cirrhotic ascites. In the respiratory system, 20-HETE plays a role in pulmonary cell survival, pulmonary vascular tone and tone of the airways. As for the brain, 20-HETE is involved in cerebral I/R injury. Moreover, 20-HETE has angiogenic and mitogenic properties and thus helps in tumor promotion. Several inhibitors and inducers of the synthesis of 20-HETE as well as 20-HETE analogues and antagonists are recently available and could be promising therapeutic options for the treatment of many disease states in the future.

Cytochrome P450 and matrix metalloproteinase genetic modifiers of disease severity in Cerebral Cavernous Malformation type 1

BACKGROUND

Familial Cerebral Cavernous Malformation type 1 (CCM1) is an autosomal dominant disease caused by mutations in the Krev Interaction Trapped 1 (KRIT1/CCM1) gene, and characterized by multiple brain lesions. CCM lesions manifest across a range of different phenotypes, including wide differences in lesion number, size and susceptibility to intracerebral hemorrhage (ICH). Oxidative stress plays an important role in cerebrovascular disease pathogenesis, raising the possibility that inter-individual variability in genes related to oxidative stress may contribute to the phenotypic differences observed in CCM1 disease. Here, we investigated whether candidate oxidative stress-related cytochrome P450 (CYP) and matrix metalloproteinase (MMP) genetic markers grouped by superfamilies, families or genes, or analyzed individually influence the severity of CCM1 disease.

METHODS

Clinical assessment and cerebral susceptibility-weighted magnetic resonance imaging (SWI) were performed to determine total and large (≥5mm in diameter) lesion counts as well as ICH in 188 Hispanic CCM1 patients harboring the founder KRIT1/CCM1 'common Hispanic mutation' (CCM1-CHM). Samples were genotyped on the Affymetrix Axiom Genome-Wide LAT1 Human Array. We analyzed 1,122 genetic markers (both single nucleotide polymorphisms (SNPs) and insertion/deletions) grouped by CYP and MMP superfamily, family or gene for association with total or large lesion count and ICH adjusted for age at enrollment and gender. Genetic markers bearing the associations were then analyzed individually.

RESULTS

The CYP superfamily showed a trend toward association with total lesion count (P=0.057) and large lesion count (P=0.088) in contrast to the MMP superfamily. The CYP4 and CYP8 families were associated with either large lesion count or total lesion count (P=0.014), and two other families (CYP46 and the MMP Stromelysins) were associated with ICH (P=0.011 and 0.007, respectively). CYP4F12 rs11085971, CYP8A1 rs5628, CYP46A1 rs10151332, and MMP3 rs117153070 single SNPs, mainly bearing the above-mentioned associations, were also individually associated with CCM1 disease severity.

CONCLUSIONS

Overall, our candidate oxidative stress-related genetic markers set approach outlined CYP and MMP families and identified suggestive SNPs that may impact the severity of CCM1 disease, including the development of numerous and large CCM lesions and ICH. These novel genetic risk factors of prognostic value could serve as early objective predictors of disease outcome and might ultimately provide better options for disease prevention and treatment.

Cyclooxygenase- and cytochrome P450-derived eicosanoids in stroke

Arachidonic acid (AA) is metabolized by cyclooxygenase (COX) and cytochrome P450 (CYP) enzymes into eicosanoids, which are involved in cardiovascular diseases and stroke. Evidence has demonstrated the important functions of these eicosanoids in regulating cerebral vascular tone, cerebral blood flow, and autoregulation of cerebral circulation. Although COX-2 inhibitors have been suggested as potential treatments for stroke, adverse events, including an increased risk of stroke, occur following long-term use of coxibs. It is important to note that prolonged treatment with rofecoxib increased circulating levels of 20-hydroxyeicosatetraenoic acid (20-HETE), and 20-HETE blockade is a possible strategy to prevent coxib-induced stroke events. It appears that 20-HETE has detrimental effects in the brain, and that its blockade exerts cerebroprotection against ischemic stroke and subarachnoid hemorrhage (SAH). There is clear evidence that activation of EP2 and EP4 receptors exerts cerebroprotection against ischemic stroke. Several elegant studies have contributed to defining the importance of stabilizing the levels of epoxyeicosatrienoic acids (EETs), by inhibiting or deleting soluble epoxide hydrolase (sEH), in stroke research. These reports support the notion that sEH blockade is cerebroprotective against ischemic stroke and SAH. Here, we summarize recent findings implicating these eicosanoid pathways in cerebral vascular function and stroke. We also discuss the development of animal models with targeted gene deletion and specific enzymatic inhibitors in each pathway to identify potential targets for the treatment of ischemic stroke and SAH.

20-HETE is associated with unfavorable outcomes in subarachnoid hemorrhage patients

Emerging evidence has suggested that patients experiencing aneurysmal subarachnoid hemorrhage (aSAH) develop vascular dysregulation as a potential contributor to poor outcomes. Preclinical studies have implicated the novel microvascular constrictor, 20-hydroxyeicosatetraenoic acid (20-HETE) in aSAH pathogenesis, yet the translational relevance of 20-HETE in patients with aSAH is largely unknown. The goal of this research was to determine the relationship between 20-HETE cerebrospinal fluid (CSF) levels, gene variants in 20-HETE synthesis, and acute/long-term aSAH outcomes. In all, 363 adult patients (age 18 to 75) with aSAH were prospectively recruited from the University of Pittsburgh Medical Center neurovascular Intensive Care Unit. Patients were genotyped for polymorphic variants and cytochrome P450 (CYP)-eicosanoid CSF levels were measured over 14 days. Outcomes included delayed cerebral ischemia (DCI), clinical neurologic deterioration (CND), and modified Rankin Scores (MRS) at 3 and 12 months. Patients with CND and unfavorable 3-month MRS had 2.2- and 2.7-fold higher mean 20-HETE CSF levels, respectively. Patients in high/moderate 20-HETE trajectory groups (35.7%) were 2.5-, 2.1-, 3.1-, 3.3-, and 2.1-fold more likely to have unfavorable MRS at 3 months, unfavorable MRS at 12 months, mortality at 3 months, mortality at 12 months, and CND, respectively. These results showed that 20-HETE is associated with acute and long-term outcomes and suggest that 20-HETE may be a novel target in aSAH.

A multimodal disease modifying approach to treat neuropathic pain--inhibition of soluble epoxide hydrolase (sEH)

Both neuronal and non-neuronal mechanisms have been proposed to contribute to neuropathic pain (NP). All currently approved treatments for NP modulate neuronal targets and provide only symptomatic relief. Here we review evidence that inhibition of soluble epoxide hydrolase (sEH), the enzyme that degrades epoxyeicosatrienoic acids (EETs), has potential to be a multimodal, disease modifying approach to treat NP: (1) EET actions involve both endogenous opioid system and the GABAergic systems thus provide superior pain relief compared to morphine or gabapentin, (2) EETs are directly anti-inflammatory and inhibit expression of inflammatory cytokines and adhesion molecules thus can prevent continued nerve damage; and (3) EETs promote nerve regeneration in cultured neurons. Thus, an sEH inhibitor will not only provide effective pain relief, but would also block further nerve damage and promote healing.

Effect of Natural Polyphenols on CYP Metabolism: Implications for Diseases

Cytochromes P450 (CYPs) are a large group of hemeproteins located on mitochondrial membranes or the endoplasmic reticulum. They play a crucial role in the metabolism of endogenous and exogenous molecules. The activity of CYP is associated with a number of factors including redox potential, protein conformation, the accessibility of the active site by substrates, and others. This activity may be potentially modulated by a variety of small molecules. Extensive experimental data collected over the past decade point at the active role of natural polyphenols in modulating the catalytic activity of CYP. Polyphenols are widespread micronutrients present in human diets of plant origin and in medicinal herbs. These compounds may alter the activity of CYP either via direct interactions with the enzymes or by affecting CYP gene expression. The polyphenol-CYP interactions may significantly alter the pharmacokinetics of drugs and thus influence the effectiveness of chemical therapies used in the treatment of different types of cancers, diabetes, obesity, and cardiovascular diseases (CVD). CYPs are involved in the oxidation and activation of external carcinogenic agents, in which case the inhibition of the CYP activity is beneficial for health. CYPs also support detoxification processes. In this case, it is the upregulation of CYP genes that would be favorable for the organism. A CYP enzyme aromatase catalyzes the formation of estrone and estradiol from their precursors. CYPs also catalyze multiple reactions leading to the oxidation of estrogen. Estrogen signaling and oxidative metabolism of estrogen are associated with the development of cancer. Thus, polyphenol-mediated modulation of the CYP's activity also plays a vital role in estrogen carcinogenesis. The aim of the present review is to summarize the data collected over the last five to six years on the following topics: (1) the mechanisms of the interactions of CYP with food constituents that occur via the direct binding of polyphenols to the enzymes and (2) the mechanisms of the regulation of CYP gene expression mediated by polyphenols. The structure-activity relationship relevant to the ability of polyphenols to affect the activity of CYP is analyzed. The application of polyphenol-CYP interactions to diseases is discussed.

The Natural Flavonoid Pinocembrin: Molecular Targets and Potential Therapeutic Applications

Pinocembrin is a natural flavonoid compound extracted from honey, propolis, ginger roots, wild marjoram, and other plants. In preclinical studies, it has shown anti-inflammatory and neuroprotective effects as well as the ability to reduce reactive oxygen species, protect the blood-brain barrier, modulate mitochondrial function, and regulate apoptosis. Considering these pharmaceutical characteristics, pinocembrin has potential as a drug to treat ischemic stroke and other clinical conditions. In this review, we summarize its pharmacologic characteristics and discuss its mechanisms of action and potential therapeutic applications.

Genetic markers in the EET metabolic pathway are associated with outcomes in patients with aneurysmal subarachnoid hemorrhage

Preclinical studies show that epoxyeicosatrienoic acids (EETs) regulate cerebrovascular tone and protect against cerebral ischemia. We investigated the relationship between polymorphic genes involved in EET biosynthesis/metabolism, cytochrome P450 (CYP) eicosanoid levels, and outcomes in 363 patients with aneurysmal subarachnoid hemorrhage (aSAH). Epoxyeicosatrienoic acids and dihydroxyeicosatetraenoic acid (DHET) cerebrospinal fluid (CSF) levels, as well as acute outcomes defined by delayed cerebral ischemia (DCI) or clinical neurologic deterioration (CND), were assessed over 14 days. Long-term outcomes were defined by Modified Rankin Scale (MRS) at 3 and 12 months. CYP2C8*4 allele carriers had 44% and 36% lower mean EET and DHET CSF levels (P=0.003 and P=0.007) and were 2.2- and 2.5-fold more likely to develop DCI and CND (P=0.039 and P=0.041), respectively. EPHX2 55Arg, CYP2J2*7, CYP2C8*1B, and CYP2C8 g.36785A allele carriers had lower EET and DHET CSF levels. CYP2C8 g.25369T and CYP2C8 g.36755A allele carriers had higher EET levels. Patients with CYP2C8*2C and EPHX2 404del variants had worse long-term outcomes while those with EPHX2 287Gln, CYP2J2*7, and CYP2C9 g.816G variants had favorable outcomes. Epoxyeicosatrienoic acid levels were associated with Fisher grade and unfavorable 3-month outcomes. Dihydroxyeicosatetraenoic acids were not associated with outcomes. No associations passed Bonferroni multiple testing correction. These are the first clinical data demonstrating the association between the EET biosynthesis/metabolic pathway and the pathophysiology of aSAH.

Epoxyeicosanoids suppress osteoclastogenesis and prevent ovariectomy-induced bone loss

Epoxyeicosatrienoic acids (EETs) are products of arachidonic acid metabolism catalyzed by cytochrome P450 epoxygenases. These small molecules are autocrine and paracrine lipid mediators with important roles in inflammation, cardiovascular function, and angiogenesis. Recent evidence has highlighted EETs as potent promoters of organ regeneration and malignant metastasis. We speculated that EETs might impact osteoclastogenesis and bone loss. Using both in vitro and in vivo studies, we observed that EETs significantly attenuated bone loss and inhibited osteoclast formation and activity, which were associated with a decreased receptor activator of NF-κB ligand (RANKL):osteoprotegerin ratio and serum levels of TNF-α and IL-1β. At the molecular level, EETs abrogated RANKL-induced activation of NF-κB, activator protein-1 (AP-1), and MAPKs, including ERK and JNK, but not p38, during osteoclast formation. EETs also prevented the production of reactive oxygen species (ROS) following RANKL stimulation. As a result, EETs suppressed osteoclast-specific gene expression, including tartrate resistant acid phosphatase (TRAP), cathepsin K (CK), matrix metalloproteinase (MMP)-9, and receptor activator of NF-κB (RANK). In conclusion, our findings demonstrate that EETs inhibit osteoclastogenesis through modulation of multiple pathways both upstream and downstream of RANKL signaling. The administration or stabilized endogenous levels of EETs could represent a novel therapeutic strategy for osteoclast-related disorders, such as rheumatoid arthritis and postmenopausal osteoporosis.

Arachidonic Acid and Cerebral Ischemia Risk: A Systematic Review of Observational Studies

Background

Arachidonic acid (ARA) is a precursor of various lipid mediators. ARA metabolites such as thromboxane A₂ cause platelet aggregation and vasoconstriction, thus may lead to atherosclerotic disease. It is unclear whether dietary ARA influences the ARA-derived lipid mediator balance and the risk for atherosclerotic diseases, such as cerebral ischemia. Considering the function of ARA in atherosclerosis, it is reasonable to focus on the atherothrombotic type of cerebral ischemia risk. However, no systematic reviews or meta-analyses have been conducted to evaluate the effect of habitual ARA exposure on cerebral ischemia risk. We aimed to systematically evaluate observational studies available on the relationship between ARA exposure and the atherothrombotic type of cerebral ischemia risk in free-living populations.

Summary

The PubMed database was searched for articles registered up to June 24, 2014. We designed a PubMed search formula as follows: key words for humans AND brain ischemia AND study designs AND ARA exposure. Thirty-three articles were reviewed against predefined criteria. There were 695 bibliographies assessed from the articles that included both ARA and cerebral ischemia descriptions. Finally, we identified 11 eligible articles and categorized them according to their reporting and methodological quality. We used the Strengthening the Reporting of Observational Studies in Epidemiology Statement (STROBE) checklist to score the reporting quality. The methodological quality was qualitatively assessed based on the following aspects: subject selection, ARA exposure assessment, outcome diagnosis, methods for controlling confounders, and statistical analysis. We did not conduct a meta-analysis due to the heterogeneity among the studies. All eligible studies measured blood ARA levels as an indicator of exposure. Our literature search did not identify any articles that evaluated dietary ARA intake and tissue ARA as assessments of exposure. Seven of the 11 eligible articles were considered to be of low quality. No articles reported a dose-dependent positive association between an increased cerebral ischemia risk and ARA exposure. However, most studies did not assess the risk in each subtype of cerebral ischemia, thus various etiological types of cerebral ischemia risk were involved in their results.

Key Messages

We did not find a positive association between ARA exposure and cerebral ischemia risk. Eligible studies reported inconsistent findings: cerebral ischemia risk did not change or significantly decreased. We could not draw any conclusions due to the limited number of eligible high-quality studies. Further evidence from well-designed observational studies is required. Simultaneously, in order to develop effective preventive measures against cerebral ischemia, it is imperative to establish standardized definitions, nomenclatures, classifications, and diagnostic procedures.

The protective effect of epoxyeicosatrienoic acids on cerebral ischemia/reperfusion injury is associated with PI3K/Akt pathway and ATP-sensitive potassium channels

Epoxyeicosatrienoic acids (EETs), the cytochrome P450 epoxygenase metabolite of arachidonic acid, have been demonstrated to have neuroprotective effect. Phosphatidylinositol 3-kinase (PI3K)/Akt and ATP-sensitive potassium (KATP) channels are thought to be important factors that mediate neuroprotection. However, little is known about the role of PI3K/Akt and KATP channels in brain after EETs administration. In vitro experiment, oxygen-glucose deprivation (OGD) was performed in cultured rat cerebral microvascular smooth muscle cells (SMCs) for 4 h. The effect of 14,15-EET on OGD induced cell apoptosis was examined after reoxygenation. Western blot and real-time PCR were used to analyze the expression of Kir6.1, SUR2B (two subunits of KATP channels) and p-Akt on cerebral microvascular SMCs. In vivo experiments, we use 12-(3-adamantan-1-yl-ureido)-dodecanoic acid [AUDA, a specific soluble epoxide hydrolase (sEH) inhibitor] to confirm the effect of EETs indirectly. Rats were injected intraperitoneally with AUDA before being subjected to middle cerebral artery occlusion (MCAO). We detected the apoptosis and the expression of p-Akt, Kir6.1 and SUR2B in ischemic penumbra. The results showed that EETs protect against cerebral ischemia/reperfusion (I/R) injury and upregulated the expression of p-Akt and Kir6.1 in both of ischemic penumbra and OGD induced cerebral microvascular SMCs. The protective effect was inhibited by Wortmannin (a specific PI3K inhibitor) and Glib (a specific KATP inhibitor) respectively in vitro experiment. In conclusion, these results suggested that the protective effect of EETs on cerebral I/R injury is associated with PI3K/Akt pathway and KATP channels. Furthermore, the PI3K pathway may contribute to mediating KATP channels on cerebral microvascular SMCs.

Role of soluble epoxide hydrolase in age-related vascular cognitive decline

P450 eicosanoids are important regulators of the cerebral microcirculation, but their role in cerebral small vessel disease is unclear. We tested the hypothesis that vascular cognitive impairment (VCI) is linked to reduced cerebral microvascular eicosanoid signaling. We analyzed human brain tissue from individuals formerly enrolled in the Oregon Brain Aging Study, who had a history of cognitive impairment histopathological evidence of microvascular disease. VCI subjects had significantly higher lesion burden both on premortem MRI and postmortem histopathology compared to age- and sex-matched controls. Mass spectrometry-based eicosanoid analysis revealed that 14,15-dihydroxyeicosatrienoic acid (DHET) was elevated in cortical brain tissue from VCI subjects. Immunoreactivity of soluble epoxide hydrolase (sEH), the enzyme responsible for 14,15-DHET formation, was localized to cerebral microvascular endothelium, and was enhanced in microvessels of affected tissue. Finally, we evaluated the genotype frequency of two functional single nucleotide polymorphisms of sEH gene EPHX2 in VCI and control groups. Our findings support a role for sEH and a potential benefit from sEH inhibitors in age-related VCI.

Mechanism of the sex difference in endothelial dysfunction after stroke

Stroke, the number four cause of death in the United States, is a greatly debilitating event resulting from insufficient blood supply to the brain (cerebral ischemia). Endothelial dysfunction, primarily characterized by dampened endothelial- dependent vasodilation, is a major contributor to the development and outcome of stroke. This review discusses the role of soluble epoxide hydrolase (sEH), an enzyme responsible for the degradation of vasoprotective eicosatrienoic acids (EETs), in the context of the cerebral vasculature and its contribution to the sexual dimorphic nature of stroke.

Traumatic brain injury in vivo and in vitro contributes to cerebral vascular dysfunction through impaired gap junction communication between vascular smooth muscle cells

Gap junctions (GJs) contribute to cerebral vasodilation, vasoconstriction, and, perhaps, to vascular compensatory mechanisms, such as autoregulation. To explore the effects of traumatic brain injury (TBI) on vascular GJ communication, we assessed GJ coupling in A7r5 vascular smooth muscle (VSM) cells subjected to rapid stretch injury (RSI) in vitro and VSM in middle cerebral arteries (MCAs) harvested from rats subjected to fluid percussion TBI in vivo. Intercellular communication was evaluated by measuring fluorescence recovery after photobleaching (FRAP). In VSM cells in vitro, FRAP increased significantly (p<0.05 vs. sham RSI) after mild RSI, but decreased significantly (p<0.05 vs. sham RSI) after moderate or severe RSI. FRAP decreased significantly (p<0.05 vs. sham RSI) 30 min and 2 h, but increased significantly (p<0.05 vs. sham RSI) 24 h after RSI. In MCAs harvested from rats 30 min after moderate TBI in vivo, FRAP was reduced significantly (p<0.05), compared to MCAs from rats after sham TBI. In VSM cells in vitro, pretreatment with the peroxynitrite (ONOO(-)) scavenger, 5,10,15,20-tetrakis(4-sulfonatophenyl)prophyrinato iron[III], prevented RSI-induced reductions in FRAP. In isolated MCAs from rats treated with the ONOO(-) scavenger, penicillamine, GJ coupling was not impaired by fluid percussion TBI. In addition, penicillamine treatment improved vasodilatory responses to reduced intravascular pressure in MCAs harvested from rats subjected to moderate fluid percussion TBI. These results indicate that TBI reduced GJ coupling in VSM cells in vitro and in vivo through mechanisms related to generation of the potent oxidant, ONOO(-).

Dietary omega-3 fatty acids modulate the eicosanoid profile in man primarily via the CYP-epoxygenase pathway

Cytochrome P450 (CYP)-dependent metabolites of arachidonic acid (AA) contribute to the regulation of cardiovascular function. CYP enzymes also accept EPA and DHA to yield more potent vasodilatory and potentially anti-arrhythmic metabolites, suggesting that the endogenous CYP-eicosanoid profile can be favorably shifted by dietary omega-3 fatty acids. To test this hypothesis, 20 healthy volunteers were treated with an EPA/DHA supplement and analyzed for concomitant changes in the circulatory and urinary levels of AA-, EPA-, and DHA-derived metabolites produced by the cyclooxygenase-, lipoxygenase (LOX)-, and CYP-dependent pathways. Raising the Omega-3 Index from about four to eight primarily resulted in a large increase of EPA-derived CYP-dependent epoxy-metabolites followed by increases of EPA- and DHA-derived LOX-dependent monohydroxy-metabolites including the precursors of the resolvin E and D families; resolvins themselves were not detected. The metabolite/precursor fatty acid ratios indicated that CYP epoxygenases metabolized EPA with an 8.6-fold higher efficiency and DHA with a 2.2-fold higher efficiency than AA. Effects on leukotriene, prostaglandin E, prostacyclin, and thromboxane formation remained rather weak. We propose that CYP-dependent epoxy-metabolites of EPA and DHA may function as mediators of the vasodilatory and cardioprotective effects of omega-3 fatty acids and could serve as biomarkers in clinical studies investigating the cardiovascular effects of EPA/DHA supplementation.

Deletion of the murine cytochrome P450 Cyp2j locus by fused BAC-mediated recombination identifies a role for Cyp2j in the pulmonary vascular response to hypoxia

Epoxyeicosatrienoic acids (EETs) confer vasoactive and cardioprotective functions. Genetic analysis of the contributions of these short-lived mediators to pathophysiology has been confounded to date by the allelic expansion in rodents of the portion of the genome syntenic to human CYP2J2, a gene encoding one of the principle cytochrome P450 epoxygenases responsible for the formation of EETs in humans. Mice have eight potentially functional genes that could direct the synthesis of epoxygenases with properties similar to those of CYP2J2. As an initial step towards understanding the role of the murine Cyp2j locus, we have created mice bearing a 626-kb deletion spanning the entire region syntenic to CYP2J2, using a combination of homologous and site-directed recombination strategies. A mouse strain in which the locus deletion was complemented by transgenic delivery of BAC sequences encoding human CYP2J2 was also created. Systemic and pulmonary hemodynamic measurements did not differ in wild-type, null, and complemented mice at baseline. However, hypoxic pulmonary vasoconstriction (HPV) during left mainstem bronchus occlusion was impaired and associated with reduced systemic oxygenation in null mice, but not in null mice bearing the human transgene. Administration of an epoxygenase inhibitor to wild-type mice also impaired HPV. These findings demonstrate that Cyp2j gene products regulate the pulmonary vascular response to hypoxia.

In mice and humans, the CYP2J class of cytochrome P450 epoxygenases metabolizes arachidonic acid (AA) to epoxyeicosatrienoic acids (EETs), short-lived mediators with effects on both the pulmonary and systemic vasculature. Genetic dissection of CYP2J function to date has been complicated by allelic expansion in the rodent genome. In this study, the mouse chromosomal locus syntenic to human CYP2J2, containing eight presumed genes and two pseudogenes, was deleted via generation of a recombinant template created by homologous and site-specific recombination steps that joined two precursor bacterial artificial chromosomes (BACs). The Cyp2j null mice were subsequently complemented by transgenic delivery of BAC sequences encoding human CYP2J2. Hypoxic pulmonary vasoconstriction (HPV) and systemic oxygenation during regional alveolar hypoxia were unexpectedly found to be impaired in null mice, but not in null mice bearing the transgenic human allele, suggesting that Cyp2j products contribute to the pulmonary vascular response to hypoxia.

Lipoxygenase: an emerging target for stroke therapy

Neuroprotection as approach to stroke therapy has recently seen a revival of sorts, fueled in part by the continuing necessity to improve acute stroke care, and in part by the identification of novel drug targets. 12/15- Lipoxygenase (12/15-LOX), one of the key enzymes of the arachidonic acid cascade, contributes to both neuronal cell death and vascular injury. Inhibition of 12/15-LOX may thus provide multifactorial protection against ischemic injury. Targeting 12/15-LOX and related eicosanoid pathways is the subject of this brief review.

Activation of neuronal transient receptor potential vanilloid 1 channel underlies 20-hydroxyeicosatetraenoic acid-induced vasoactivity: role for protein kinase A

A rise in intraluminal pressure triggers vasoconstriction in resistance arteries, which is associated with local generation of the vasoconstrictor 20-hydroxyeicosatetraenoic acid (20-HETE). Importantly, dysregulation of 20-HETE synthesis and activity has been implicated in several cardiovascular disease states, including ischemic disease, hypertension, and stroke; however, the exact molecular pathways involved in mediating 20-HETE bioactivity are uncertain. We investigated whether 20-HETE activates the transient receptor potential vanilloid 1 (TRPV1) and thereby regulates vascular function and blood pressure. We demonstrate that 20-HETE causes dose-dependent increases in blood pressure, coronary perfusion pressure (isolated Langendorff), and pressure-induced constriction of resistance arteries (perfusion myography) that is substantially attenuated in TRPV1 knockout mice and by treatment with the neurokinin 1 receptor antagonist RP67580. Furthermore, we show that both channel activation (via patch-clamping of dorsal root ganglion neurons) and vessel constriction are enhanced under inflammatory conditions, and our findings indicate a predominant role for protein kinase A-mediated sensitization of TRPV1 in these phenomena. Finally, we identify a prominence of these pathway in males compared with females, an effect we relate to reduced protein kinase A-induced phosphorylation of TRPV1. 20-HETE-induced activation of TRPV1, in part, mediates pressure-induced myogenic constriction and underlies 20-HETE-induced elevations in blood pressure and coronary resistance. Our findings identify a novel vasoconstrictor 20-HETE/TRPV1 pathway that may offer potential for therapeutic targeting in cardiovascular diseases associated with elevated 20-HETE implicated in dysregulated organ blood flow, such as stroke or hypertension.

Temporal changes of cytochrome P450 (Cyp) and eicosanoid-related gene expression in the rat brain after traumatic brain injury

BACKGROUND

Traumatic brain injury (TBI) induces arachidonic acid (ArA) release from cell membranes. ArA metabolites form a class of over 50 bioactive eicosanoids that can induce both adaptive and/or maladaptive brain responses. The dynamic metabolism of ArA to eicosanoids, and how they affect the injured brain, is poorly understood due to their diverse activities, trace levels, and short half-lives. The eicosanoids produced in the brain postinjury depend upon the enzymes present locally at any given time. Eicosanoids are synthesized by heme-containing enzymes, including cyclooxygenases, lipoxygenases, and arachidonate monoxygenases. The latter comprise a subset of the cytochrome P450 "Cyp" gene family that metabolize fatty acids, steroids, as well as endogenous and exogenous toxicants. However, for many of these genes neither baseline neuroanatomical nor injury-related temporal expression have been studied in the brain.In a rat model of parietal cortex TBI, Cyp and eicosanoid-related mRNA levels were determined at 6 h, 24 h, 3d, and 7d postinjury in parietal cortex and hippocampus, where dynamic changes in eicosanoids have been observed. Quantitative real-time polymerase chain reaction with low density arrays were used to assay 62 rat Cyps, 37 of which metabolize ArA or other unsaturated fatty acids; 16 eicosanoid-related enzymes that metabolize ArA or its metabolites; 8 eicosanoid receptors; 5 other inflammatory- and recovery-related genes, plus 2 mouse Cyps as negative controls and 3 highly expressed "housekeeping" genes.

RESULTS

Sixteen arachidonate monoxygenases, 17 eicosanoid-related genes, and 12 other Cyps were regulated in the brain postinjury (p < 0.05, Tukey HSD). Discrete tissue levels and distinct postinjury temporal patterns of gene expression were observed in hippocampus and parietal cortex.

CONCLUSIONS

The results suggest complex regulation of ArA and other lipid metabolism after TBI. Due to the temporal nature of brain injury-induced Cyp gene induction, manipulation of each gene (or its products) at a given time after TBI will be required to assess their contributions to secondary injury and/or recovery. Moreover, a better understanding of brain region localization and cell type-specific expression may be necessary to deduce the role of these eicosanoid-related genes in the healthy and injured brain.

Cytochrome P450-mediated metabolism in brain: functional roles and their implications

INTRODUCTION

Cytochromes P450 (P450) and associated monooxygenases are a family of heme proteins involved in metabolism of endogenous compounds (arachidonic acid, eicosanoids and prostaglandins) as also xenobiotics including drugs and environmental chemicals. Liver is the major organ involved in P450-mediated metabolism and hepatic enzymes have been characterized. Extrahepatic organs, such as lung, kidney and brain have the capability for biotransformation through P450 enzymes. Brain, including human brain, expresses P450 enzymes that metabolize xenobiotics and endogenous compounds.

AREAS COVERED

An overview of P450-mediated metabolism in brain is presented focusing on distinct differences seen in expression of P450 enzymes, generation of unique P450 enzymes in brain through alternate splicing and their consequences in terms of metabolism of psychoactive drugs and inflammatory prompts, such as leukotrienes, thus modulating inflammatory response.

EXPERT OPINION

The brain possesses unique P450s that metabolize drugs and endogenous compounds through pathways that are markedly different from that seen in liver indicating that extrapolation directly from liver to brain is not appropriate. It is therefore necessary to characterize the unique brain P450s and their ability to metabolize xenobiotics and endogenous compounds to better understand the functions of this important class of enzymes in brain, especially human brain.

Metabolic products of soluble epoxide hydrolase are essential for monocyte chemotaxis to MCP-1 in vitro and in vivo

Monocyte chemoattractant protein-1 (MCP-1)-induced monocyte chemotaxis is a major event in inflammatory disease. Our prior studies have demonstrated that MCP-1-dependent chemotaxis requires release of arachidonic acid (AA) by activated cytosolic phospholipase A(2) (cPLA(2)). Here we investigated the involvement of AA metabolites in chemotaxis. Neither cyclooxygenase nor lipoxygenase pathways were required, whereas pharmacologic inhibitors of both the cytochrome-P450 (CYP) and the soluble epoxide hydrolase (sEH) pathways blocked monocyte chemotaxis to MCP-1. To verify specificity, we demonstrated that the CYP and sEH products epoxyeiscosatrienoic acids (EETs) and dihydroxyeicosatrienoic acids (DHETs), respectively, restored chemotaxis in the presence of the inhibitors, indicating that sEH-derived products are essential for MCP-1-driven chemotaxis. Importantly, DHETs also rescued chemotaxis in cPLA(2)-deficient monocytes and monocytes with blocked Erk1/2 activity, because Erk controls cPLA(2) activation. The in vitro findings regarding the involvement of CYP/sEH pathways were further validated in vivo using two complementary approaches measuring MCP-1-dependent chemotaxis in mice. These observations reveal the importance of sEH in MCP-1-regulated monocyte chemotaxis and may explain the observed therapeutic value of sEH inhibitors in treatment of inflammatory diseases, cardiovascular diseases, pain, and even carcinogenesis. Their effectiveness, often attributed to increasing EET levels, is probably influenced by the impairment of DHET formation and inhibition of chemotaxis.