Mechanism and signal transduction of 14 (R), 15 (S)-epoxyeicosatrienoic acid (14,15-EET) binding in guinea pig monocytes

Epoxylipids and soluble epoxide hydrolase in heart diseases

Cardiovascular and heart diseases are leading causes of morbidity and mortality. Coronary artery endothelial and vascular dysfunction, inflammation, and mitochondrial dysfunction contribute to progression of heart diseases such as arrhythmias, congestive heart failure, and heart attacks. Classes of fatty acid epoxylipids and their enzymatic regulation by soluble epoxide hydrolase (sEH) have been implicated in coronary artery dysfunction, inflammation, and mitochondrial dysfunction in heart diseases. Likewise, genetic and pharmacological manipulations of epoxylipids have been demonstrated to have therapeutic benefits for heart diseases. Increasing epoxylipids reduce cardiac hypertrophy and fibrosis and improve cardiac function. Beneficial actions for epoxylipids have been demonstrated in cardiac ischemia reperfusion injury, electrical conductance abnormalities and arrhythmias, and ventricular tachycardia. This review discusses past and recent findings on the contribution of epoxylipids in heart diseases and the potential for their manipulation to treat heart attacks, arrhythmias, ventricular tachycardia, and heart failure.

Cytochrome P450 Metabolism of Polyunsaturated Fatty Acids and Neurodegeneration

Due to the aging population in the world, neurodegenerative diseases have become a serious public health issue that greatly impacts patients' quality of life and adds a huge economic burden. Even after decades of research, there is no effective curative treatment for neurodegenerative diseases. Polyunsaturated fatty acids (PUFAs) have become an emerging dietary medical intervention for health maintenance and treatment of diseases, including neurodegenerative diseases. Recent research demonstrated that the oxidized metabolites, particularly the cytochrome P450 (CYP) metabolites, of PUFAs are beneficial to several neurodegenerative diseases, including Alzheimer's disease and Parkinson's disease; however, their mechanism(s) remains unclear. The endogenous levels of CYP metabolites are greatly affected by our diet, endogenous synthesis, and the downstream metabolism. While the activity of omega-3 (ω-3) CYP PUFA metabolites and omega-6 (ω-6) CYP PUFA metabolites largely overlap, the ω-3 CYP PUFA metabolites are more active in general. In this review, we will briefly summarize recent findings regarding the biosynthesis and metabolism of CYP PUFA metabolites. We will also discuss the potential mechanism(s) of CYP PUFA metabolites in neurodegeneration, which will ultimately improve our understanding of how PUFAs affect neurodegeneration and may identify potential drug targets for neurodegenerative diseases.

Epoxyeicosatrienoic acids protect pancreatic beta cells against pro-inflammatory cytokine toxicity

Pro-inflammatory cytokines contribute to pancreatic beta cell death in the pathogenesis of type 1 diabetes mellitus (DM). Cytochrome P450-derived epoxyeicosatrienoic acids (EETs), produced by selective epoxidation of arachidonic acid, display anti-inflammatory activity in numerous disease models, in part through inhibition of NFκB activity. No studies have directly assessed their roles in cellular models of pancreatic beta cell death and therefore we aimed to investigate the cytoprotective effects of the EET isomers 8(9)-, 11(12)- and 14(15)-EET and their corresponding vicinal diols (dihydroxyeicosatrienoic acids, DHETs) in a model of pro-inflammatory cytokine-toxicity using the rat pancreatic beta cell line BRIN-BD11. Co-treatment of cells with a cocktail of pro-inflammatory cytokines (IL-1β, IFNγ and TNFα) caused a marked increase in caspase activation and a reduction in cell viability, effects attenuated by inclusion of each EET; this was also associated with a reduction in cytokine-induced NFκB activation and nitrite accumulation. Surprisingly, of the DHET derivatives of EETs, 8(9)-DHET conferred similar protective effects against cytokine-induced caspase activation. This data therefore highlights a novel role of EETs and a surprising activity of 8(9)-DHET in attenuating cytokine-toxicity in pancreatic beta cells.

Time-resolved phosphoproteomic analysis elucidates hepatic 11,12-Epoxyeicosatrienoic acid signaling pathways

Epoxyeicosatrienoic acids (EETs) are potent lipid mediators with well-established effects in vascular tissues. Recent studies indicated an emerging role of these eicosanoids in metabolic diseases and the EET signaling pathway was shown to be involved in hepatic insulin sensitivity. However, compared to vascular tissues, there is only limited knowledge about the underlying signaling pathways in the liver. Therefore, we employed an LC-MS/MS-based time-resolved phosphoproteomics approach to characterize 11,12-EET-mediated signaling events in the liver cell line Hepa 1-6. 11,12-EET treatment resulted in the time-dependent regulation of phosphopeptides involved in processes as yet unknown to be affected by EETs, including RNA processing, splicing and translation regulation. Pathway analysis combined with western blot-based validation revealed enhanced AKT/mTOR/p70S6K signaling as demonstrated by increased acute phosphorylation of AKT (Ser473) and p70S6K (Thr389). In addition, 11,12-EET treatment led to differential regulation of phosphopeptides including important mediators of the DNA damage response and we observed a prolonged induction of the etoposide-induced DNA damage marker γH2AX in response to 11,12-EET. In summary, our findings extend current knowledge of 11,12-EET signaling events and emphasize the importance of the AKT/mTOR/p70S6K pathway in hepatic 11,12-EET signaling. Based on the results presented in this study, we furthermore propose a novel role of EET signaling in the regulation of the DNA damage response.

Oxidized Lipids in Persistent Pain States

Chemotherapy, nerve injuries, or diseases like multiple sclerosis can cause pathophysiological processes of persistent and neuropathic pain. Thereby, the activation threshold of ion channels is reduced in peripheral sensory neurons to normally noxious stimuli like heat, cold, acid, or mechanical due to sensitization processes. This leads to enhanced neuronal activity, which can result in mechanical allodynia, cold allodynia, thermal hyperalgesia, spontaneous pain, and may initiate persistent and neuropathic pain. The treatment options for persistent and neuropathic pain patients are limited; for about 50% of them, current medication is not efficient due to severe side effects or low response to the treatment. Therefore, it is of special interest to find additional treatment strategies. One approach is the control of neuronal sensitization processes. Herein, signaling lipids are crucial mediators and play an important role during the onset and maintenance of pain. As preclinical studies demonstrate, lipids may act as endogenous ligands or may sensitize transient receptor potential (TRP)-channels. Likewise, they can cause enhanced activity of sensory neurons by mechanisms involving G-protein coupled receptors and activation of intracellular protein kinases. In this regard, oxidized metabolites of the essential fatty acid linoleic acid, 9- and 13-hydroxyoctadecadienoic acid (HODE), their dihydroxy-metabolites (DiHOMEs), as well as epoxides of linoleic acid (EpOMEs) and of arachidonic acid (EETs), as well as lysophospholipids, sphingolipids, and specialized pro-resolving mediators (SPMs) have been reported to play distinct roles in pain transmission or inhibition. Here, we discuss the underlying molecular mechanisms of the oxidized linoleic acid metabolites and eicosanoids. Furthermore, we critically evaluate their role as potential targets for the development of novel analgesics and for the treatment of persistent or neuropathic pain.

New Lipid Mediators in Retinal Angiogenesis and Retinopathy

Retinal diseases associated with vascular destabilization and the inappropriate proliferation of retinal endothelial cells have major consequences on the retinal vascular network. In extreme cases, the development of hypoxia, the upregulation of growth factors, and the hyper-proliferation of unstable capillaries can result in bleeding and vision loss. While anti-vascular endothelial growth factor therapy and laser retinal photocoagulation can be used to treat the symptoms of late stage disease, there is currently no treatment available that can prevent disease progression. Cytochrome P450 enzymes metabolize endogenous substrates (polyunsaturated fatty acids) to bioactive fatty acid epoxides that demonstrate biological activity with generally protective/anti-inflammatory and insulin-sensitizing effects. These epoxides are further metabolized by the soluble epoxide hydrolase (sEH) to fatty acid diols, high concentrations of which have vascular destabilizing effects. Recent studies have identified increased sEH expression and activity and the subsequent generation of the docosahexaenoic acid-derived diol; 19,20-dihydroxydocosapentaenoic acid, as playing a major role in the development of diabetic retinopathy. This review summarizes current understanding of the roles of cytochrome P450 enzyme and sEH–derived PUFA mediators in retinal disease.

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.

P450 Eicosanoids and Reactive Oxygen Species Interplay in Brain Injury and Neuroprotection

Significance: Eicosanoids are endogenous lipid mediators that play important roles in brain function and disease. Acute brain injury such as that which occurs in stroke and traumatic brain injury increases the formation of eicosanoids, which, in turn, exacerbate or diminish injury. In chronic neurodegenerative diseases such as Alzheimer's disease and vascular dementia (VD), eicosanoid synthetic and metabolizing enzymes are altered, disrupting the balance between neuroprotective and neurotoxic eicosanoids. Recent Advances: Human and experimental studies have established the opposing roles of hydroxy- and epoxyeicosanoids and their potential utility as diagnostic biomarkers and therapeutic targets in neural injury. Critical Issues: A gap in knowledge remains in understanding the cellular and molecular mechanisms underlying the neurovascular actions of specific eicosanoids, such as specific isomers of epoxyeicosatrienoic (EETs) and hydroxyeicosatetraenoic acids (HETEs). Future Directions: EETs and HETEs exert their actions on brain cells by targeting multiple mechanisms, which include surface G-protein coupled receptors. The identification of high-affinity receptors for EETs and HETEs and their cellular localization in the brain will be a breakthrough in our understanding of these eicosanoids as mediators of cell-cell communications and contributors to brain development, function, and disease. Antioxid. Redox Signal. 28, 987-1007.

Orally Active Epoxyeicosatrienoic Acid Analogs

Biologically active epoxyeicosatrienoic acid (EET) regioisomers are synthesized from arachidonic acid by cytochrome P450 epoxygenases of endothelial, myocardial, and renal tubular cells. EETs relax vascular smooth muscle and decrease inflammatory cell adhesion and cytokine release. Renal EETs promote sodium excretion and vasodilation to decrease hypertension. Cardiac EETs reduce infarct size after ischemia-reperfusion injury and decrease fibrosis and inflammation in heart failure. In diabetes, EETs improve insulin sensitivity, increase glucose tolerance, and reduce the renal injury. These actions of EETs emphasize their therapeutic potential. To minimize metabolic inactivation, 14,15-EET agonist analogs with stable epoxide bioisosteres and carboxyl surrogates were developed. In preclinical rat models, a subset of agonist analogs, termed EET-A, EET-B, and EET-C22, are orally active with good pharmacokinetic properties. These orally active EET agonists lower blood pressure and reduce cardiac and renal injury in spontaneous and angiotensin hypertension. Other beneficial cardiovascular actions include improved endothelial function and cardiac antiremodeling actions. In rats, EET analogs effectively combat acute and chronic kidney disease including drug- and radiation-induced kidney damage, hypertension and cardiorenal syndrome kidney damage, and metabolic syndrome and diabetes nephropathy. The compelling preclinical efficacy supports the prospect of advancing EET analogs to human clinical trials for kidney and cardiovascular diseases.

Functional screening for G protein-coupled receptor targets of 14,15-epoxyeicosatrienoic acid

Epoxyeicosatrienoic acids (EETs) are potent vasodilators that play important roles in cardiovascular physiology and disease, yet the molecular mechanisms underlying the biological actions of EETs are not fully understood. Multiple lines of evidence suggest that the actions of EETs are in part mediated via G protein-coupled receptor (GPCR) signaling, but the identity of such a receptor has remained elusive. We sought to identify 14,15-EET-responsive GPCRs. A set of 105 clones were expressed in Xenopus oocyte and screened for their ability to activate cAMP-dependent chloride current. Several receptors responded to micromolar concentrations of 14,15-EET, with the top five being prostaglandin receptor subtypes (PTGER2, PTGER4, PTGFR, PTGDR, PTGER3IV). Overall, our results indicate that multiple low-affinity 14,15-EET GPCRs are capable of increasing cAMP levels following 14,15-EET stimulation, highlighting the potential for cross-talk between prostanoid and other ecosanoid GPCRs. Our data also indicate that none of the 105 GPCRs screened met our criteria for a high-affinity receptor for 14,15-EET.

The role of epoxyeicosatrienoic acids in the cardiovascular system

There is increasing evidence suggesting that epoxyeicosatrienoic acids (EETs) play an important role in cardioprotective mechanisms. These include regulating vascular tone, modulating inflammatory responses, improving cardiomyocyte function and reducing ischaemic damage, resulting in attenuation of animal models of cardiovascular risk factors. This review discusses the current knowledge on the role of EETs in endothelium-dependent control of vascular tone in the healthy and in subjects with cardiovascular risk factors, and considers the pharmacological potential of targeting this pathway.

Arachidonic acid monooxygenase: Genetic and biochemical approaches to physiological/pathophysiological relevance

Studies with rat genetic models of hypertension pointed to roles for the CYP2C and CYP4A arachidonic acid epoxygenases and ω-hydroxylases in tubular transport, hemodynamics, and blood pressure control. Further progress in defining their physiological functions and significance to human hypertension requires conclusive identifications of the relevant genes and proteins. Here we discuss unequivocal evidence of roles for the murine Cyp4a14, Cyp4a10, and Cyp2c44 genes in the pathophysiology of hypertension by showing that: (a) Cyp4a14(-/-) mice develop sexually dimorphic hypertension associated with renal vasoconstriction, and up-regulated expression of Cyp4a12a and pro-hypertensive 20-hydroxyeicosatetraenoic acid (20-HETE) levels, and b) Cyp4a10(-/-) and Cyp2c44(-/-) mice develop salt sensitive hypertension linked to downregulation or lack of the Cyp2c44 epoxygenase, reductions in anti-hypertensive epoxyeicosatrienoic acids (EETs), and increases in distal sodium reabsorption. Based on these studies, the human CYP4A11 and CYPs 2C8 and 2C9 genes and their products are identified as potential candidates for studies of the molecular basis of human hypertension.

Cytochrome P450 epoxygenase pathway of polyunsaturated fatty acid metabolism

Polyunsaturated fatty acids (PUFA) are oxidized by cytochrome P450 epoxygenases to PUFA epoxides which function as potent lipid mediators. The major metabolic pathways of PUFA epoxides are incorporation into phospholipids and hydrolysis to the corresponding PUFA diols by soluble epoxide hydrolase. Inhibitors of soluble epoxide hydrolase stabilize PUFA epoxides and potentiate their functional effects. The epoxyeicosatrienoic acids (EETs) synthesized from arachidonic acid produce vasodilation, stimulate angiogenesis, have anti-inflammatory actions, and protect the heart against ischemia-reperfusion injury. EETs produce these functional effects by activating receptor-mediated signaling pathways and ion channels. The epoxyeicosatetraenoic acids synthesized from eicosapentaenoic acid and epoxydocosapentaenoic acids synthesized from docosahexaenoic acid are potent inhibitors of cardiac arrhythmias. Epoxydocosapentaenoic acids also inhibit angiogenesis, decrease inflammatory and neuropathic pain, and reduce tumor metastasis. These findings indicate that a number of the beneficial functions of PUFA may be due to their conversion to PUFA epoxides. This article is part of a Special Issue entitled "Oxygenated metabolism of PUFA: analysis and biological relevance".

The role of cytochrome P450 epoxygenases in retinal angiogenesis

PURPOSE

The purpose of this study was to investigate the role(s) of cytochrome P450 epoxygenases (CYPs) and their products, the epoxyeicosatrienoic acids (EETs), in hypoxia-induced VEGF production and pathologic retinal angiogenesis.

METHODS

Human retinal astrocytes, Müller cells, and retinal microvascular endothelial cells (HRMEC) were exposed to hypoxia, and relative CYP2C expression was measured by RT-PCR. Astrocyte and Müller cell VEGF production was measured by ELISA after exposure to hypoxia and treatment with the general CYP inhibitor, SKF-525a. Human retinal microvascular endothelial cells were treated with the CYP product, 11,12-epoxyeicosatrienoic acid [EET], or SKF-525a in the presence or absence of VEGF. Proliferation of HRMEC and tube formation were assayed. Oxygen-induced retinopathy (OIR) was induced in newborn rats. Retinal CYP2C11 and CYP2C23 expression were measured by RT-PCR. The OIR rats received SKF-525a by intravitreal injection and preretinal neovascularization (NV) was quantified. Retinal VEGF protein levels were measured by ELISA.

RESULTS

Human retinal astrocytes were the only cells to exhibit significant induction of CYP2C8 and CYP2C9 mRNA expression by hypoxia. Astrocytes, but not Müller cells, exhibited reduced hypoxia-induced VEGF production when treated with SKF-525a. 11,12-EET induced HRMEC proliferation and tube formation, and SKF-525a inhibited VEGF-induced proliferation. Oxygen-induced retinopathy induced expression of CYP2C23, but had no effect on CYP2C11. SKF-525a inhibited retinal NV and reduced retinal VEGF levels in OIR rats.

CONCLUSIONS

The CYP-derived 11,12-EET may exhibit a proangiogenic biological function in the retina following stimulation by hypoxia in astrocytes. Inhibition of CYP may provide a rational therapy against retinal NV, because it can reduce VEGF production and VEGF-induced angiogenic responses in endothelial cells.

The biological actions of 11,12-epoxyeicosatrienoic acid in endothelial cells are specific to the R/S-enantiomer and require the G(s) protein

Cytochrome P450-derived epoxides of arachidonic acid [i.e., the epoxyeicosatrienoic acids (EETs)] are important lipid signaling molecules involved in the regulation of vascular tone and angiogenesis. Because many actions of 11,12-cis-epoxyeicosatrienoic acid (EET) are dependent on the activation of protein kinase A (PKA), the existence of a cell-surface G(s)-coupled receptor has been postulated. To assess whether the responses of endothelial cells to 11,12-EET are enantiomer specific and linked to a potential G protein-coupled receptor, we assessed 11,12-EET-induced, PKA-dependent translocation of transient receptor potential (TRP) C6 channels, as well as angiogenesis. In primary cultures of human endothelial cells, (±)-11,12-EET led to the rapid (30 seconds) translocation a TRPC6-V5 fusion protein, an effect reproduced by 11(R),12(S)-EET, but not by 11(S),12(R)-EET or (±)-14,15-EET. Similarly, endothelial cell migration and tube formation were stimulated by (±)-11,12-EET and 11(R),12(S)-EET, whereas 11(S),12(R)-EET and 11,12-dihydroxyeicosatrienoic acid were without effect. The effects of (±)-11,12-EET on TRP channel translocation and angiogenesis were sensitive to EET antagonists, and TRP channel trafficking was also prevented by a PKA inhibitor. The small interfering RNA-mediated downregulation of G(s) in endothelial cells had no significant effect on responses stimulated by vascular endothelial growth or a PKA activator but abolished responses to (±)-11,12-EET. The downregulation of G(q)/11 failed to prevent 11,12-EET-induced TRPC6 channel translocation or the formation of capillary-like structures. Taken together, our results suggest that a G(s)-coupled receptor in the endothelial cell membrane responds to 11(R),12(S)-EET and mediates the PKA-dependent translocation and activation of TRPC6 channels, as well as angiogenesis.

Role of cytochrome P450-mediated arachidonic acid metabolites in the pathogenesis of cardiac hypertrophy

A plethora of studies have demonstrated the expression of cytochrome P450 (CYP) and soluble epoxide hydrolase (sEH) enzymes in the heart and other cardiovascular tissues. In addition, the expression of these enzymes is altered during several cardiovascular diseases (CVDs), including cardiac hypertrophy (CH). The alteration in CYP and sEH expression results in derailed CYP-mediated arachidonic acid (AA) metabolism. In animal models of CH, it has been reported that there is an increase in 20-hydroxyeicosatetraenoic acid (20-HETE) and a decrease in epoxyeicosatrienoic acids (EETs). Further, inhibiting 20-HETE production by CYP ω-hydroxylase inhibitors and increasing EET stability by sEH inhibitors have been proven to protect against CH as well as other CVDs. Therefore, CYP-mediated AA metabolites 20-HETE and EETs are potential key players in the pathogenesis of CH. Some studies have investigated the molecular mechanisms by which these metabolites mediate their effects on cardiomyocytes and vasculature leading to pathological CH. Activation of several intracellular signaling cascades, such as nuclear factor of activated T cells, nuclear factor kappa B, mitogen-activated protein kinases, Rho-kinases, Gp130/signal transducer and activator of transcription, extracellular matrix degradation, apoptotic cascades, inflammatory cytokines, and oxidative stress, has been linked to the pathogenesis of CH. In this review, we discuss how 20-HETE and EETs can affect these signaling pathways to result in, or protect from, CH, respectively. However, further understanding of these metabolites and their effects on intracellular cascades will be required to assess their potential translation to therapeutic approaches for the prevention and/or treatment of CH and heart failure.

20-Iodo-14,15-epoxyeicosa-8(Z)-enoyl-3-azidophenylsulfonamide: photoaffinity labeling of a 14,15-epoxyeicosatrienoic acid receptor

Endothelium-derived epoxyeicosatrienoic acids (EETs) relax vascular smooth muscle by activating potassium channels and causing membrane hyperpolarization. Recent evidence suggests that EETs act via a membrane binding site or receptor. To further characterize this binding site or receptor, we synthesized 20-iodo-14,15-epoxyeicosa-8(Z)-enoyl-3-azidophenylsulfonamide (20-I-14,15-EE8ZE-APSA), an EET analogue with a photoactive azido group. 20-I-14,15-EE8ZE-APSA and 14,15-EET displaced 20-(125)I-14,15-epoxyeicosa-5(Z)-enoic acid binding to U937 cell membranes with K(i) values of 3.60 and 2.73 nM, respectively. The EET analogue relaxed preconstricted bovine coronary arteries with an ED(50) comparable to that of 14,15-EET. Using electrophoresis, 20-(125)I-14,15-EE8ZE-APSA labeled a single 47 kDa band in U937 cell membranes, smooth muscle and endothelial cells, and bovine coronary arteries. In U937 cell membranes, the 47 kDa radiolabeling was inhibited in a concentration-dependent manner by 8,9-EET, 11,12-EET, and 14,15-EET (IC(50) values of 444, 11.7, and 8.28 nM, respectively). The structurally unrelated EET ligands miconazole, MS-PPOH, and ketoconazole also inhibited the 47 kDa labeling. In contrast, radiolabeling was not inhibited by 8,9-dihydroxyeicosatrienoic acid, 5-oxoeicosatetraenoic acid, a biologically inactive thiirane analogue of 14,15-EET, the opioid antagonist naloxone, the thromboxane mimetic U46619, or the cannabinoid antagonist AM251. Radiolabeling was not detected in membranes from HEK293T cells expressing 79 orphan receptors. These studies indicate that vascular smooth muscle, endothelial cells, and U937 cell membranes contain a high-affinity EET binding protein that may represent an EET receptor. This EET photoaffinity labeling method with a high signal-to-noise ratio may lead to new insights into the expression and regulation of the EET receptor.

Epoxyeicosatrienoic acids enhance axonal growth in primary sensory and cortical neuronal cell cultures

It has recently been reported that soluble epoxide hydrolase (sEH), the major enzyme that metabolizes epoxyeicosatrienoic acids (EETs), is expressed in axons of cortical neurons; however, the functional relevance of axonal sEH localization is unknown. Immunocytochemical analyses demonstrate predominant axonal localization of sEH in primary cultures of not only cortical but also sympathetic and sensory neurons. Morphometric analyses of cultured sensory neurons indicate that exposure to a regioisomeric mixture of EETs (0.01-1.0 μM) causes a concentration-dependent increase in axon outgrowth. This axon promoting activity is not a generalized property of all regioisomers of EETs as axonal growth is enhanced in sensory neurons exposed to 14,15-EET but not 8,9- or 11,12-EET. 14,15-EET also promotes axon outgrowth in cultured cortical neurons. Co-exposure to EETs and either of two structurally diverse pharmacological inhibitors of sEH potentiates the axon-enhancing activity of EETs in sensory and cortical neurons. Mass spectrometry indicates that sEH inhibition significantly increases EETs and significantly decreases dihydroxyeicosatrienoic acid metabolites in neuronal cell cultures. These data indicate that EETs enhance axon outgrowth and suggest that axonal sEH activity regulates EETs-induced axon outgrowth. These findings suggest a novel therapeutic use of sEH inhibitors in promoting nerve regeneration.

Vanilloid and melastatin transient receptor potential channels in vascular smooth muscle

The mammalian transient receptor potential (TRP) superfamily consists of six subfamilies that are defined by structural homology: TRPC (conventional or canonical), TRPV (vanilloid), TRPM (melastatin), TRPA (ankyrin), TRPP (polycystin), and TRPML (mucoliptin). This review focuses on channels belonging to the vanilloid (V) and melastatin (M) TRP subfamilies. The TRPV subfamily consists of six members (TRPV1-6) and the TRPM subfamily has eight (TRPM1-8). The basic biophysical properties of these channels are briefly described. All of these channels except TRPV5, TRPV6, and TRPM1 are reportedly present in arterial smooth muscle from various segments of the vasculature. Studies demonstrating involvement of TRPV1, TRPV2, TRPV4, TRPM4, TRPM7, and TRPM8 in regulation of arterial smooth muscle function are reviewed. The functions of TRPV3, TRPM2, TRPM3, and TRPM6 channels in arterial myocytes have not been reported.

Epoxyeicosatrienoic acids and endothelium-dependent responses

Epoxyeicosatrienoic acids (EETs) are cytochrome P450 metabolites of arachidonic acid that are produced by the vascular endothelium in response to agonists such as bradykinin and acetylcholine or physical stimuli such as shear stress or cyclic stretch. In the vasculature, the EETs have biological actions that are involved in the regulation of vascular tone, hemostasis, and inflammation. In preconstricted arteries in vitro, EETs activate calcium-activated potassium channels on vascular smooth muscle and the endothelium causing membrane hyperpolarization and relaxation. These effects are observed in a variety of arteries from experimental animals and humans; however, this is not a universal finding in all arteries. The mechanism of EET action may vary. In some arteries, EETs are released from the endothelium and are transferred to the smooth muscle where they cause potassium channel activation, hyperpolarization, and relaxation through a guanine nucleotide binding protein-coupled mechanism or transient receptor potential (TRP) channel activation. In other arteries, EETs activate TRP channels on the endothelium to cause endothelial hyperpolarization that is transferred to the smooth muscle by gap junctions or potassium ion. Some arteries use a combination of mechanisms. Acetylcholine and bradykinin increase blood flow in dogs and humans that is inhibited by potassium channel blockers and cytochrome P450 inhibitors. Thus, the EETs are endothelium-derived hyperpolarizing factors mediating a portion of the relaxations to acetylcholine, bradykinin, shear stress, and cyclic stretch and regulate vascular tone in vitro and in vivo.

Vascular pharmacology of epoxyeicosatrienoic acids

Epoxyeicosatrienoic acids (EETs) are cytochrome P450 metabolites of arachidonic acid that are produced by the vascular endothelium in responses to various stimuli such as the agonists acetylcholine (ACH) or bradykinin or by shear stress which activates phospholipase A(2) to release arachidonic acid. EETs are important regulators of vascular tone and homeostasis. In the modulation of vascular tone, EETs function as endothelium-derived hyperpolarizing factors (EDHFs). In models of vascular inflammation, EETs attenuate inflammatory signaling pathways in both the endothelium and vascular smooth muscle. Likewise, EETs regulate blood vessel formation or angiogenesis by mechanisms that are still not completely understood. Soluble epoxide hydrolase (sEH) converts EETs to dihydroxyeicosatrienoic acids (DHETs) and this metabolism limits many of the biological actions of EETs. The recent development of inhibitors of sEH provides an emerging target for pharmacological manipulation of EETs. Additionally, EETs may initiate their biological effects by interacting with a cell surface protein that is a G protein-coupled receptor (GPCR). Since GPCRs represent a common target of most drugs, further characterization of the EET receptor and synthesis of specific EET agonists and antagonist can be used to exploit many of the beneficial effects of EETs in vascular diseases, such as hypertension and atherosclerosis. This review will focus on the current understanding of the contribution of EETs to the regulation of vascular tone, inflammation, and angiogenesis. Furthermore, the therapeutic potential of targeting the EET pathway in vascular disease will be highlighted.

20-125Iodo-14,15-epoxyeicosa-5(Z)-enoic acid: a high-affinity radioligand used to characterize the epoxyeicosatrienoic acid antagonist binding site

Epoxyeicosatrienoic acids (EETs) are endothelium-derived metabolites of arachidonic acid. They relax vascular smooth muscle by membrane hyperpolarization. These actions are inhibited by the EET antagonist, 14,15-epoxyeicosa-5(Z)-enoic acid (14,15-EE5ZE). We synthesized 20-(125)iodo-14,15-EE5ZE (20-(125)I-14,15-EE5ZE), a radiolabeled EET antagonist, and characterized its binding to cell membranes. 14,15-EET (10(-9)-10(-5)M) caused a concentration-related relaxation of the preconstricted bovine coronary artery and phosphorylation of p38 in U937 cells that were inhibited by 20-(125)I-14,15-EE5ZE. Specific 20-(125)I-14,15-EE5ZE binding to U937 cell membranes reached equilibrium within 5 min and remained unchanged for 30 min. The binding was saturable and reversible, and it exhibited K(D) and B(max) values of 1.11 +/- 0.13 nM and 1.13 +/- 0.04 pmol/mg protein, respectively. Guanosine 5'-O-(3-thio)triphosphate (10 muM) did not change the binding, indicating antagonist binding of the ligand. Various EETs and EET analogs (10(-10)-10(-5)M) competed for 20-(125)I-14,15-EE5ZE binding with an order of potency of 11,12-EET = 14,15-EET > 8,9-EET = 14,15-EE5ZE > 15-hydroxyeicosatetraenoic acid = 14,15-dihydroxyeicosatrienoic acid. 8,9-Dihydroxyeicosatrienoic acid and 11-hydroxyeicosatetraenoic acid did not compete for binding. The soluble and microsomal epoxide hydrolase inhibitors (1-cyclohexyl-3-dodecyl-urea, elaidamide, and 12-hydroxyl-elaidamide) and cytochrome P450 inhibitors (sulfaphenazole and proadifen) did not compete for the binding. However, two cytochrome P450 inhibitors, N-methylsulfonyl-6-(2-propargyloxyphenyl)hexanamide (MS-PPOH) and miconazole competed for binding with K(i) of 1558 and 315 nM, respectively. Miconazole and MS-PPOH, but not proadifen, inhibited 14,15-EET-induced relaxations. These findings define an EET antagonist's binding site and support the presence of an EET receptor. The inhibition of binding by some cytochrome P450 inhibitors suggests an alternative mechanism of action for these drugs and could lead to new drug candidates that target the EET binding sites.

Epoxyeicosanoid signaling in CNS function and disease

Epoxyeicosatrienoic acids (EETs) are arachidonic acid metabolites of cytochrome P450 epoxygenase enzymes recognized as key players in vascular function and disease, primarily attributed to their potent vasodilator, anti-inflammatory and pro-angiogenic effects. Although EETs' actions in the central nervous system (CNS) appear to parallel those in peripheral tissue, accumulating evidence suggests that epoxyeicosanoid signaling plays different roles in neural tissue compared to peripheral tissue; roles that reflect distinct CNS functions, cellular makeup and intercellular relationships. This is exhibited at many levels including the expression of EETs-synthetic and -metabolic enzymes in central neurons and glial cells, EETs' role in neuro-glio-vascular coupling during cortical functional activation, the capacity for interaction between epoxyeicosanoid and neuroactive endocannabinoid signaling pathways, and the regulation of neurohormone and neuropeptide release by endogenous EETs. The ability of several CNS cell types to produce and respond to EETs suggests that epoxyeicosanoid signaling is a key integrator of cell-cell communication in the CNS, coordinating cellular responses across different cell types. Under pathophysiological conditions, such as cerebral ischemia, EETs protect neurons, astroglia and vascular endothelium, thus preserving the integrity of cellular networks unique to and essential for proper CNS function. Recognition of EETs' intimate involvement in CNS function in addition to their multi-cellular protective profile has inspired the development of therapeutic strategies against CNS diseases such as cerebral ischemia, tumors, and neural pain and inflammation that are based on targeting the cellular actions of EETs or their biosynthetic and metabolizing enzymes. Based upon the emerging importance of epoxyeicosanoids in cellular function and disease unique to neural systems, we propose that the actions of "neuroactive EETs" are best considered separately, and not in aggregate with all other peripheral EETs functions.

Cytochrome P450 (CYP) 2J2 gene transfection attenuates MMP-9 via inhibition of NF-kappabeta in hyperhomocysteinemia

Hyperhomocysteinemia (HHcy) is associated with atherosclerotic events involving the modulation of arachidonic acid (AA) metabolism and the activation of matrix metalloproteinase-9 (MMP-9). Cytochrome P450 (CYP) epoxygenase-2J2 (CYP2J2) is abundant in the heart endothelium, and its AA metabolites epoxyeicosatrienoic acids (EETs) mitigates inflammation through NF-kappabeta. However, the underlying molecular mechanisms for MMP-9 regulation by CYP2J2 in HHcy remain obscure. We sought to determine the molecular mechanisms by which P450 epoxygenase gene transfection or EETs supplementation attenuate homocysteine (Hcy)-induced MMP-9 activation. CYP2J2 was over-expressed in mouse aortic endothelial cells (MAECs) by transfection with the pcDNA3.1/CYP2J2 vector. The effects of P450 epoxygenase transfection or exogenous supplementation of EETs on NF-kappabeta-mediated MMP-9 regulation were evaluated using Western blot, in-gel gelatin zymography, electromobility shift assay, immunocytochemistry. The result suggested that Hcy downregulated CYP2J2 protein expression and dephosphorylated PI3K-dependent AKT signal. Hcy induced the nuclear translocation of NF-kappabeta via downregulation of IKbetaalpha (endogenous cytoplasmic inhibitor of NF-kappabeta). Hcy induced MMP-9 activation by increasing NF-kappabeta-DNA binding. Moreover, P450 epoxygenase transfection or exogenous addition of 8,9-EET phosphorylated the AKT and attenuated Hcy-induced MMP-9 activation. This occurred, in part, by the inhibition of NF-kappabeta nuclear translocation, NF-kappabeta-DNA binding and activation of IKbetaalpha. The study unequivocally suggested the pivotal role of EETs in the modulation of Hcy/MMP-9 signal.

Cytochrome P450 2C9-induced angiogenesis is dependent on EphB4

OBJECTIVE

Cytochrome P450 (CYP) epoxygenase-derived epoxyeicosatrienoic acids (EETs) are known to stimulate angiogenesis, but the mechanisms involved are incompletely understood. Because EphB4 is involved in vascular development, the aim of this study was to investigate whether, and to what extent, EphB4 is part of the signaling cascade that results in CYP2C9-mediated angiogenesis.

METHODS AND RESULTS

CYP2C9 overexpression as well as stimulation with 11,12-EET (up to 48 hours) time-dependently increased EphB4 expression in endothelial cells. This effect and the activation of the EphB4 promoter were mediated by the phosphatidylinositol-3-kinase (P13-K)/Akt pathway and sensitive to the P13-K inhibitor LY 294002 as well as to simultaneous transfection with dominant-negative Akt. 11,12-EET treatment also increased EphB4 expression in isolated mouse mesenteric arteries as well as in the vessels that developed in 11,12-EET-impregnated Matrigel plugs. Moreover, the CYP2C9-stimulated formation of capillary-like structures in a modified spheroid assay was markedly attenuated by EphB4 downregulation (antisense oligonucleotides). Using a parallel approach in vivo, the inclusion of siRNA directed against EphB4 in EET-impregnated Matrigel plugs prevented endothelial cell invasion and vascularization.

CONCLUSIONS

Our data indicate that EphB4 is a critical component of the CYP2C9- and 11,12-EET-activated signaling cascade that promotes angiogenesis in vitro as well as in vivo.

Epoxyeicosatrienoic acids induce growth inhibition and calpain/caspase-12 dependent apoptosis in PDGF cultured 3T6 fibroblast

Previous studies have demonstrated that arachidonic acid (AA) metabolites released by the cyclooxygenase pathway is involved in serum-induced 3T6 fibroblast cycle progression and proliferation. However, these results also suggest that other AA cascade pathways might be involved. Recently, we also described the role of hydroxyeicosatetraenoic acids, which are produced by cytochrome P450 monooxygenases (CYP), in 3T6 fibroblast growth. AA can be also metabolized by the epoxygenase activity of CYP-producing epoxyeicosatrienoic acids (EETs). Finally, the cytosolic epoxide hydrolases catalyze the hydration of the EETs, transforming them into dihydroxyeicosatetraenoic acids (DHETEs). In this work, we have studied the role of the EETs/DHETEs on 3T6 fibroblasts growth. Our results show that PDGF stimulates 3T6 fibroblast proliferation and [3H]thymidine incorporation, while the addition of 5,6-EET, 8,9-EET, 11,12-EET or 14,15-EET (0.1-1 microM) inhibit these processes. Furthermore, 5,6-DHETE and 11,12-DHETE (0.1-1 microM) also inhibit cell proliferation and DNA synthesis. Interestingly, this growth inhibition was correlated with an induction of apoptosis. Thus, we observed that in the presence of PDGF, EETs or DHETEs (0.1-1 microM) induce phosphatidylserine externalization (as measured by annexin V-binding) and DNA fragmentation (as quantified using a TUNEL assay). Our results show that calpain, as well as caspase-12 and caspase-3, are involved in these events. Therefore, EETs and DHETEs have anti-proliferative and pro-apoptotic effects on PDGF-stimulated 3T6 fibroblasts.

Soluble epoxide hydrolase: a novel therapeutic target in stroke

The P450 eicosanoids epoxyeicosatrienoic acids (EETs) are produced in brain and perform important biological functions, including protection from ischemic injury. The beneficial effect of EETs, however, is limited by their metabolism via soluble epoxide hydrolase (sEH). We tested the hypothesis that sEH inhibition is protective against ischemic brain damage in vivo by a mechanism linked to enhanced cerebral blood flow (CBF). We determined expression and distribution of sEH immunoreactivity (IR) in brain, and examined the effect of sEH inhibitor 12-(3-adamantan-1-yl-ureido)-dodecanoic acid butyl ester (AUDA-BE) on CBF and infarct size after experimental stroke in mice. Mice were administered a single intraperitoneal injection of AUDA-BE (10 mg/kg) or vehicle at 30 mins before 2-h middle cerebral artery occlusion (MCAO) or at reperfusion, in the presence and absence of P450 epoxygenase inhibitor N-methylsulfonyl-6-(2-propargyloxyphenyl) hexanamide (MS-PPOH). Immunoreactivity for sEH was detected in vascular and non-vascular brain compartments, with predominant expression in neuronal cell bodies and processes. 12-(3-Adamantan-1-yl-ureido)-dodecanoic acid butyl ester was detected in plasma and brain for up to 24 h after intraperitoneal injection, which was associated with inhibition of sEH activity in brain tissue. Finally, AUDA-BE significantly reduced infarct size at 24 h after MCAO, which was prevented by MS-PPOH. However, regional CBF rates measured by iodoantipyrine (IAP) autoradiography at end ischemia revealed no differences between AUDA-BE- and vehicle-treated mice. The findings suggest that sEH inhibition is protective against ischemic injury by non-vascular mechanisms, and that sEH may serve as a therapeutic target in stroke.

Regulation of ion transport and blood pressure by cytochrome p450 monooxygenases

PURPOSE OF REVIEW

Past and recent studies of the cytochrome P450 monooxygenase branch of the arachidonate cascade establish a role for this metabolic pathway in the regulation of vascular tone and tubular ion transport. Functional and electrophysiology studies indicate that the P450 eicosanoids participate in the regulation of vascular potassium and renal sodium channels, and of systemic blood pressures.

RECENT FINDINGS

Associations between genetically controlled alterations in blood pressure and the activity or transcriptional regulation of renal Cyp2c arachidonic acid epoxygenases and Cyp4a omega-hydroxylases document a role for these enzymes in the pathophysiology of hypertension--a leading cause of cardiovascular, cerebral, and renal morbidity and mortality. Associations between a functional variant of the human CYP4A11 gene and hypertension suggest a potential role for this gene as a determinant of polygenic blood pressure control in humans.

SUMMARY

These results provide new understandings of the role of P450s in renal physiology, as well as conceptually novel approaches for studies of the molecular basis of human hypertension that could lead to new strategies for the early diagnosis and clinical management of this devastating disease.

α2-Adrenergic receptors activate cyclic AMP-response element-binding protein through arachidonic acid metabolism and protein kinase A in a subtype-specific manner

On incubation with epinephrine, PC12 cells stably expressing alpha2-adrenergic receptor (alpha2-AR) undergo morphological and biochemical changes characteristic of neuron-like differentiation. The present study shows that alpha2-AR stimulation increases the phosphorylation of the transcription factor cAMP-response element-binding protein (CREB), the activity of a CRE-reporter plasmid and the expression of cyclin D1 with subtype-dependent efficiency (alpha2A approximately alpha2C >> alpha2B). The effects of epinephrine were mimicked by cell exposure to forskolin or to exogenous arachidonic acid (AA) and they were abrogated by prior treatment with the inhibitor of phospholipase C (PLC) (U73122) or the inhibitor of cytochrome P450-dependent epoxygenase, ketoconazole. On the other hand, treatment of the cells with epinephrine caused activation of protein kinase A (PKA), which was fully abolished by ketoconazole. Inhibition of PKA activity with H89 or ketoconazole abolished the effects of epinephrine on CREB, suggesting that activation of the cAMP/PKA pathway by AA epoxy-derivatives is responsible for CREB activation by alpha2-ARs. The effects of epinephrine were unaffected by LY294002. Furthermore, treatment with staurosporine, tyrphostin AG1478, PP1 or PD98059 did not change the extent of CREB phosphorylation but enhanced its transcriptional activity. Altogether, our results demonstrate that, in PC12 cells, the alpha2-AR subtypes cause phosphorylation and activation of CREB through a pathway involving stimulation of PLC, AA release, generation of epoxygenase derivative and increase of PKA activity. They also suggest attenuation of CREB transcriptional activity by mitogen-activated protein kinase, protein kinase C and Src kinases.

Characterization of 14,15-Epoxyeicosatrienoyl-Sulfonamides as 14,15-Epoxyeicosatrienoic Acid Agonists: Use for Studies of Metabolism and Ligand Binding

Epoxyeicosatrienoic acids (EETs) are cytochrome P450 epoxygenase metabolites of arachidonic acid. EETs mediate numerous biological functions. In coronary arteries, they regulate vascular tone by the activation of smooth muscle large-conductance, calcium-activated potassium (BK(Ca)) channels to cause hyperpolarization and relaxation. We developed a series of 14,15-EET agonists, 14,15-EET-phenyliodosulfonamide (14,15-EET-PISA), 14,15-EET-biotinsulfonamide (14,15-EET-BSA), and 14,15-EET-benzoyldihydrocinnamide-sulfonamide (14,15-EET-BZDC-SA) as tools to characterize 14,15-EET metabolism and binding. Agonist activities of these analogs were characterized in precontraced bovine coronary arterial rings. All three analogs induced concentration-dependent relaxation and were equipotent with 14,15-EET. Relaxations to these analogs were inhibited by the BK(Ca) channel blocker iberiotoxin (100 nM), the 14,15-EET antagonist 14,15-epoxyeicosa-5(Z)-enoylmethylsulfonamide (10 muM), and abolished by 20 mM extracellular K(+). 14,15-EET-PISA is metabolized to 14,15-dihydroxyeicosatrienoyl-PISA by soluble epoxide hydrolase in bovine coronary arteries and U937 cells but not U937 cell membrane fractions. 14,15-EET-P(125)ISA binding to human U937 cell membranes was time-dependent, concentration-dependent, and saturable. The specific binding reached equilibrium by 15 min at 4 degrees C and remained unchanged up to 30 min. The estimated K(d) and B(max) were 148.3 +/- 36.4 nM and 3.3 +/- 0.5 pmol/mg protein, respectively. These data suggest that 14,15-EET-PISA, 14,15-EET-BSA, and 14,15-EET-BZDC-SA are full 14,15-EET agonists. 14,15-EET-P(125)ISA is a new radiolabeled tool to study EET metabolism and binding. Our results also provide preliminary evidence that EETs exert their biological effect through a membrane binding site/receptor.

20-Hydroxyeicosatetraenoic Acid (20-HETE) Stimulates Migration of Vascular Smooth Muscle Cells

AIM

We tested the hypothesis that 20-HETE production contributes to platelet derived growth factor (PDGF)-BB stimulated migration of VSMC in a cell culture model.

METHODS

Studies were performed with A10 cells which are a rat vascular smooth muscle derived cell line. Migration was determined using a Boyden chamber chemotactic assay.

RESULTS

Pre-treatment of cells with two doses of 20-HETE (100 and 500 nM) significantly increased PDGF-BB stimulated VSMC migration by 34-58% of control; whereas, prior incubation of cells with inhibitors of 20-HETE production, 17-ODYA (1-25 M) or HET0016 (100 nM), significantly decreased PDGF-BB stimulated migration by 40-90%. 20-HETE mediated increase in PDGF-BB migration was completely prevented by the 20-HETE antagonist, WIT-002. In order to determine what second messenger pathways are involved in the 20-HETE mediated stimulation of VSM migration, experiments were performed with specific inhibitors of tyrosine kinase (tyrphostin 25, 10 microM), mitogen-activated extracellular signal-regulated kinase (MEK, PD98059, 20 microM and U0126, 10 microM), protein kinase C (Myr-PKC, 50 microM), and phosphoinositide 3-kinases (PI3Ks) (wortmannin, 50 nM). Blockade of MEK and PI3K all abolished the increase in 20-HETE mediated migration.

CONCLUSION

20-HETE stimulates PDGF-mediated VSM migration acting through pathways that involve MEK and PI3K.

Arachidonic acid metabolites as endothelium-derived hyperpolarizing factors

The endothelium regulates vascular tone through the release of a number of soluble mediators, including NO, prostaglandin I2, and endothelium-derived hyperpolarizing factor. Epoxyeicosatrienoic acids are cytochrome P450 epoxygenase metabolites of arachidonic acid. They are synthesized by the vascular endothelium and open calcium-activated potassium channels, hyperpolarize the membrane, and relax vascular smooth muscle. Endothelium-dependent relaxations to acetylcholine, bradykinin, and shear stress that are not inhibited by cyclooxygenase and NO synthase inhibitors are mediated by the endothelium-derived hyperpolarizing factor. In arteries from experimental animals and humans, the non-NO, non-prostaglandin-mediated relaxations and endothelium-dependent hyperpolarizations are blocked by cytochrome P450 inhibitors, calcium-activated potassium channel blockers, and epoxyeicosatrienoic acid antagonists. Acetylcholine and bradykinin stimulate epoxyeicosatrienoic acid release from endothelial cells and arteries. These findings indicate that epoxyeicosatrienoic acids act as endothelium-derived hyperpolarizing factors and regulate arterial tone.

Epoxyeicosatrienoic acids, cell signaling and angiogenesis

Epoxyeicosatrienoic acids (EETs) are generated from arachidonic acid by cytochrome P450 (CYP) epoxygenases the expression of which is determined by hemodynamic and pharmacological stimuli as well as by hypoxia. The activation of CYP epoxygenases in endothelial cells is an important step in the vasodilatation that has been attributed to the endothelium-derived hyperpolarizing factor. However, in addition to regulating vascular tone EETs modulate several signaling cascades and affect cell proliferation, cell migration and angiogenesis. These include the epidermal growth factor receptor, tyrosine kinases and phosphatases, mitogen-activated protein kinases, protein kinase A, cyclooxygenase-2 and several transcription factors. To-date however, the importance of EETs in vascular homeostasis has been largely underestimated because of the labile nature of the EET-forming enzymes in cell culture. This also means that the contribution of CYP-derived products in the vast majority of the experimental models based on cell culture systems to address topics related to vascular signaling/homeostasis and angiogenesis has been overlooked.

Action of epoxyeicosatrienoic acids on cellular function

Epoxyeicosatrienoic acids (EETs), which function primarily as autocrine and paracrine mediators in the cardiovascular and renal systems, are synthesized from arachidonic acid by cytochrome P-450 epoxygenases. They activate smooth muscle large-conductance Ca(2+)-activated K(+) channels, producing hyperpolarization and vasorelaxation. EETs also have anti-inflammatory effects in the vasculature and kidney, stimulate angiogenesis, and have mitogenic effects in the kidney. Many of the functional effects of EETs occur through activation of signal transduction pathways and modulation of gene expression, events probably initiated by binding to a putative cell surface EET receptor. However, EETs are rapidly taken up by cells and are incorporated into and released from phospholipids, suggesting that some functional effects may occur through a direct interaction between the EET and an intracellular effector system. In this regard, EETs and several of their metabolites activate peroxisome proliferator-activated receptor alpha (PPARalpha) and PPARgamma, suggesting that some functional effects may result from PPAR activation. EETs are metabolized primarily by conversion to dihydroxyeicosatrienoic acids (DHETs), a reaction catalyzed by soluble epoxide hydrolase (sEH). Many potentially beneficial actions of EETs are attenuated upon conversion to DHETs, which do not appear to be essential under routine conditions. Therefore, sEH is considered a potential therapeutic target for enhancing the beneficial functions of EETs.

Mechanism of rat mesenteric arterial KATP channel activation by 14,15-epoxyeicosatrienoic acid

Recently, we reported that 11,12-epoxyeicosatrienoic acid (11,12-EET) potently activates rat mesenteric arterial ATP-sensitive K+ (KATP) channels and produces significant vasodilation through protein kinase A-dependent mechanisms. In this study, we tried to further delineate the signaling steps involved in the activation of vascular KATP channels by EETs. Whole cell patch-clamp recordings [0.1 mM ATP in the pipette, holding potential (HP) = 0 mV and testing potential (TP) = −100 mV] in freshly isolated rat mesenteric smooth muscle cells showed small glibenclamide-sensitive KATP currents (19.0 ± 7.9 pA, n = 5) that increased 6.9-fold on exposure to 5 μM 14,15-EET (132.0 ± 29.0 pA, n = 7, P < 0.05 vs. control). With 1 mM ATP in the pipette solution, KATP currents (HP = 0 mV and TP = −100 mV) were increased 3.5-fold on exposure to 1 μM 14,15-EET (57.5 ± 14.3 pA, n = 9, P < 0.05 vs. baseline). In the presence of 100 nM iberiotoxin, 1 μM 14,15-EET hyperpolarized the membrane potential from −20.5 ± 0.9 mV at baseline to −27.1 ± 3.0 mV ( n = 6 for both, P < 0.05 vs. baseline), and the EET effects were significantly reversed by 10 μM glibenclamide (−21.8 ± 1.4 mV, n = 6, P < 0.05 vs. EET). Incubation with 5 μM 14,15-epoxyeicosa-5( Z)-enoic acid (14,15-EEZE), a 14,15-EET antagonist, abolished the 14,15-EET effects (31.0 ± 11.8 pA, n = 5, P < 0.05 vs. 14,15-EET, P = not significant vs. control). The 14,15-EET effects were inhibited by inclusion of anti-Gsα antibody (1:500 dilution) but not by control IgG in the pipette solution. The effects of 14,15-EET were mimicked by cholera toxin (100 ng/ml), an exogenous ADP-ribosyltransferase. Treatment with the ADP-ribosyltransferase inhibitors 3-aminobenzamide (1 mM) or m-iodobenzylguanidine (100 μM) abrogated the effects of 14,15-EET on KATP currents. These results were corroborated by vasodilation studies. 14,15-EET dose-dependently dilated isolated small mesenteric arteries, and this was significantly attenuated by treatment with 14,15-EEZE or 3-aminobenzamide. These results suggest that 14,15-EET activates vascular KATP channels through ADP-ribosylation of Gsα.

From endothelium-derived hyperpolarizing factor (EDHF) to angiogenesis: Epoxyeicosatrienoic acids (EETs) and cell signaling

Epoxyeicosatrienoic acids (EETs) are generated from arachidonic acid by cytochrome P450 (CYP) epoxygenases. The expression of CYP epoxygenases in endothelial cells is determined by a number of physical (fluid shear stress and cyclic stretch) and pharmacological stimuli as well as by hypoxia. The activation of CYP epoxygenases in endothelial cells is an important step in the nitric oxide and prostacyclin (PGI2)-independent vasodilatation of several vascular beds and EETs have been identified as endothelium-derived hyperpolarizing factors (EDHFs). However, in addition to regulating vascular tone, EETs modulate several signaling cascades and affect cell proliferation, cell migration, and angiogenesis. Signaling molecules modulated by EETs include tyrosine kinases and phosphatases, mitogen-activated protein kinases, protein kinase A (PKA), cyclooxygenase (COX)-2, and several transcription factors. This review summarizes the role of CYP-derived EETs in cell signaling and focuses particularly on their role as intracellular amplifiers of endothelial cell hyperpolarization as well as in cell proliferation and angiogenesis. The angiogenic properties of CYP epoxygenases and CYP-derived EETs implicate that these enzymes may well be accessible targets for anti-angiogenic as well as angiogenic therapies.