Soluble epoxide inhibition is protective against cerebral ischemia via vascular and neural protection

Soluble epoxide hydrolase activity regulates inflammatory responses and seizure generation in two mouse models of temporal lobe epilepsy

Neuroinflammation is known to be involved in epileptogenesis with unclear mechanisms. Inhibition of soluble epoxide hydrolase (sEH) seems to offer anti-inflammatory protection to ischemic brain injury in rodents. Thus, it is hypothesized that sEH inhibition might also affect the neuroinflammatory responses caused by epileptic seizures. In the present study, we investigated the involvement of sEH in neuroinflammation, seizure generation and subsequent epileptogenesis using two mouse models of temporal lobe epilepsy. Experimental epileptic seizures were induced by either pilocarpine or electrical amygdala kindling in both wild-type (WT) C57BL/6 mice and sEH knockout (sEH KO) mice. The sEH expression in the hippocampus was detected by immunohistochemistry and Western blot analysis. The effects of the sEH hydrolase inhibitors, 12-(3-adamantan-1-yl-ureido)-dodecanoic acid (AUDA) and N-[1-(1-oxopropyl)-4-piperidinyl]-N'-[4-(trifluoromethoxy) phenyl)-urea (TPPU), and of the genetic deletion of sEH on seizure-induced neuroinflammatory responses and the development of epilepsy were evaluated. In the hippocampus of WT mice, sEH was mainly expressed in astrocytes (GFAP(+)), neurons (NeuN(+)) and scattered microglia (Iba-1(+)) in the regions of CA1, CA3 and dentate gyrus. Expression of sEH was significantly increased on day 7, 14, 21 and 28 after pilocarpine-induced status epilepticus (SE). Administration with sEH inhibitors attenuated the SE-induced up-regulation of interleukin-1β (IL-1β) and interleukin-6 (IL-6), the degradation of EETs, as well as IκB phosphorylation. Following treatment with AUDA, the frequency and duration of spontaneous motor seizures in the pilocarpine-SE mice were decreased and the seizure-induction threshold of the fully kindled mice was increased. Up-regulation of hippocampal IL-1β and IL-6 was found in both WT and sEH KO mice after successful induction of SE. Notably, sEH KO mice were more susceptible to seizures than WT mice. Seizure related neuroinflammation and ictogenesis were attenuated by pharmacological inhibition of sEH enzymatic activity but not by sEH genetic deletion. Therefore, sEH may play an important role in the generation of epilepsy. Furthermore, the effectiveness of AUDA in terms of anti-inflammatory and anti-ictogenesis properties suggests that it may have clinical therapeutic implication for epilepsy in the future, particularly when treating temporal lobe epilepsy.

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.

Inhibition of soluble epoxide hydrolase prevents renal interstitial fibrosis and inflammation

The pathophysiological events that lead to renal interstitial fibrogenesis are incompletely understood. Epoxyeicosatrienoic acid (EET), an arachidonic acid metabolite, has anti-inflammatory and profibrinolytic functions. Soluble epoxide hydrolase (sEH) converts EET to less active dihydroxyeicosatrienoic acid. Here, we tested the hypothesis that sEH deficiency would prevent tubulointerstitial fibrosis and inflammation induced by unilateral ureteral obstruction (UUO) in mouse kidneys. The loss of sEH enhanced levels of EET regioisomers and abolished tubulointerstitial fibrosis as demonstrated by reduced collagen deposition and myofibroblast formation at 3 and 10 days after UUO. The inflammatory response was prevented as demonstrated by decreased influx of neutrophil and macrophage, expression of inflammatory cytokines, and chemotactic factors in sEH-deficient UUO kidneys. Pharmacological inhibition of sEH also prevented inflammation and fibrosis after UUO. Next, we delved into the molecular mechanisms piloting the beneficial effects of sEH deficiency in renal fibrosis. UUO upregulated profibrotic factors associated with transforming growth factor (TGF)-β1/Smad3 signaling, oxidative stress, and NF-κB activation, and downregulated antifibrotic factors including peroxisome proliferator-activated receptor (PPAR) isoforms, especially PPARγ, but the loss of sEH prevented these adverse effects in UUO kidneys. Furthermore, administration of PPAR antagonists enhanced myofibroblast formation and activation of Smad3 and NF-κB p65, effects that were prevented by sEH deficiency in UUO kidneys. These data demonstrate that loss of sEH promotes anti-inflammatory and fibroprotective effects in UUO kidneys via activation of PPAR isoforms and downregulation of NF-κB, TGF-β1/Smad3, and inflammatory signaling pathways. Our data suggest the potential use of sEH inhibitors in treating fibrotic diseases.

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.

Mechanism of protection by soluble epoxide hydrolase inhibition in type 2 diabetic stroke

Inhibition of soluble epoxide hydrolase (sEH) is a potential target of therapy for ischemic injury. sEH metabolizes neuroprotective epoxyeicosatrienoic acids (EETs). We recently demonstrated that sEH inhibition reduces infarct size after middle cerebral artery occlusion (MCAO) in type 1 diabetic mice. We hypothesized that inhibition of sEH would protect against ischemic injury in type 2 diabetic mice. Type 2 diabetes was produced by combined high-fat diet, nicotinamide and streptozotocin in male mice. Diabetic and control mice were treated with vehicle or the sEH inhibitor t-AUCB then subjected to 60-min MCAO. Compared to chow-fed mice, high fat diet-fed mice exhibited an upregulation of sEH mRNA and protein in brain, but no differences in brain EETs levels were observed between groups. Type 2 diabetic mice had increased blood glucose levels at baseline and throughout ischemia, decreased laser-Doppler perfusion of the MCA territory after reperfusion, and sustained larger cortical infarcts compared to control mice. t-AUCB decreased fasting glucose levels at baseline and throughout ischemia, improved cortical perfusion after MCAO and significantly reduced infarct size in diabetic mice. We conclude that sEH inhibition, as a preventative treatment, improves glycemic status, post-ischemic reperfusion in the ischemic territory, and stroke outcome in type 2 diabetic mice.

Pinocembrin protects rats against cerebral ischemic damage through soluble epoxide hydrolase and epoxyeicosatrienoic acids

AIM

To investigate the relationship between cerebroprotection of pinocembrin and epoxyeicosatrienoic acids (EETs) and their regulating enzyme soluble epoxide hydrolase (sEH).

METHODS

Rats underwent middle cerebral artery occlusion (MCAO) to mimic permanent focal ischemia, and pinocembrin was administrated via tail vein injection at 10 min, 4 h, 8 h and 23 h after MCAO. After 24 MCAO, rats were re-anesthetized, and the blood and brain were harvested and analyzed.

RESULTS

Pinocembrin displayed significant protective effects on MCAO rats indicated by reduced neurological deficits and infarct volume. Importantly, co-administration of 0.2 mg·kg(-1) 14, 15-EEZE, a putative selective EET antagonist, weakened the beneficial effects of pinocembrin. 14, 15-EET levels in the blood and brain of rats after 24 h MCAO were elevated in the presence of pinocembrin. In an assay for hydrolase activity, pinocembrin significantly lowered brain sEH activity of MCAO rats and inhibited recombinant human sEH activity in a concentration-dependent manner (IC50, 2.58 μmol·L(-1)). In addition, Western blot and immunohistochemistry analysis showed that pinocembrin at doses of 10 mg·kg(-1) and 30 mg·kg(-1) significantly down-regulated sEH protein in rat brain, especially the hippocampus CA1 region of MCAO rats.

CONCLUSION

Inhibiting sEH and then increasing the potency of EETs may be one of the mechanisms through which pinocembrin provides cerebral protection.

Role of soluble epoxide hydrolase in exacerbation of stroke by streptozotocin-induced type 1 diabetes mellitus

Hyperglycemia worsens stroke, yet rigorous glycemic control does not improve neurologic outcome. An alternative is to target downstream molecular mediator(s) triggered by hyperglycemia but independent of prevailing glycemia. Soluble epoxide hydrolase (sEH) is a potential mediator of injury via its metabolism of neuroprotective epoxyeicosatrienoic acids (EETs). We tested whether hyperglycemia exacerbates cerebral injury by upregulating sEH and decreasing brain EET levels. Type 1 diabetes mellitus was modeled by streptozotocin (STZ; 50 mg/kg per day intraperitoneally, 5 days) in male mice. At 4 weeks, STZ-treated and control mice underwent 45-minute middle cerebral artery occlusion (MCAO) with or without sEH blockade by trans-4-[4-(3-adamantan-1-yl-ureido)-cyclohexyloxy]-benzoic acid (t-AUCB; 1 mg/kg intraperitoneally daily for 6 days before MCAO). The STZ-treated mice had increased sEH mRNA expression in cerebral vessels and decreased EET concentrations in brain. There was no difference in cortical perfusion between groups. The STZ-treated mice sustained larger brain infarct than controls. Pretreatment with t-AUCB eliminated the difference in infarct size and EETs concentration between STZ-treated mice and controls, without altering glycemia. We conclude that type 1 diabetes mellitus upregulates sEH mRNA and decreases concentrations of neuroprotective EETs within the brain, leading to worse stroke outcome. The data indicate that sEH antagonism may be beneficial in the setting of hyperglycemic stroke.

Soluble epoxide hydrolase inhibitor trans-4-[4-(3-adamantan-1-yl-ureido)-cyclohexyloxy]-benzoic acid is neuroprotective in rat model of ischemic stroke

Soluble epoxide hydrolase (sEH) diminishes vasodilatory and neuroprotective effects of epoxyeicosatrienoic acids by hydrolyzing them to inactive dihydroxy metabolites. The primary goals of this study were to investigate the effects of acute sEH inhibition by trans-4-[4-(3-adamantan-1-yl-ureido)-cyclohexyloxy]-benzoic acid (t-AUCB) on infarct volume, functional outcome, and changes in cerebral blood flow (CBF) in a rat model of ischemic stroke. Focal cerebral ischemia was induced in rats for 90 min followed by reperfusion. At the end of 24 h after reperfusion rats were euthanized for infarct volume assessment by triphenyltetrazolium chloride staining. Brain cortical sEH activity was assessed by ultra performance liquid chromatography-tandem mass spectrometry. Functional outcome at 24 and 48 h after reperfusion was evaluated by arm flexion and sticky-tape tests. Changes in CBF were assessed by arterial spin-labeled-MRI at baseline, during ischemia, and at 180 min after reperfusion. Neuroprotective effects of t-AUCB were evaluated in primary rat neuronal cultures by Cytotox-Flour kit and propidium iodide staining. t-AUCB significantly reduced cortical infarct volume by 35% (14.5 ± 2.7% vs. 41.5 ± 4.5%), elevated cumulative epoxyeicosatrienoic acids-to-dihydroxyeicosatrienoic acids ratio in brain cortex by twofold (4.40 ± 1.89 vs. 1.97 ± 0.85), and improved functional outcome in arm-flexion test (day 1: 3.28 ± 0.5 s vs. 7.50 ± 0.9 s; day 2: 1.71 ± 0.4 s vs. 5.28 ± 0.5 s) when compared with that of the vehicle-treated group. t-AUCB significantly reduced neuronal cell death in a dose-dependent manner (vehicle: 70.9 ± 7.1% vs. t-AUCB0.1μM: 58 ± 5.11% vs. t-AUCB0.5μM: 39.9 ± 5.8%). These findings suggest that t-AUCB may exert its neuroprotective effects by affecting multiple components of neurovascular unit including neurons, astrocytes, and microvascular flow.

The effects of hypertension on the cerebral circulation

Maintenance of brain function depends on a constant blood supply. Deficits in cerebral blood flow are linked to cognitive decline, and they have detrimental effects on the outcome of ischemia. Hypertension causes alterations in cerebral artery structure and function that can impair blood flow, particularly during an ischemic insult or during periods of low arterial pressure. This review will focus on the historical discoveries, novel developments, and knowledge gaps in 1) hypertensive cerebral artery remodeling, 2) vascular function with emphasis on myogenic reactivity and endothelium-dependent dilation, and 3) blood-brain barrier function. Hypertensive artery remodeling results in reduction in the lumen diameter and an increase in the wall-to-lumen ratio in most cerebral arteries; this is linked to reduced blood flow postischemia and increased ischemic damage. Many factors that are increased in hypertension stimulate remodeling; these include the renin-angiotensin-aldosterone system and reactive oxygen species levels. Endothelial function, vital for endothelium-mediated dilation and regulation of myogenic reactivity, is impaired in hypertension. This is a consequence of alterations in vasodilator mechanisms involving nitric oxide, epoxyeicosatrienoic acids, and ion channels, including calcium-activated potassium channels and transient receptor potential vanilloid channel 4. Hypertension causes blood-brain barrier breakdown by mechanisms involving inflammation, oxidative stress, and vasoactive circulating molecules. This exposes neurons to cytotoxic molecules, leading to neuronal loss, cognitive decline, and impaired recovery from ischemia. As the population ages and the incidence of hypertension, stroke, and dementia increases, it is imperative that we gain a better understanding of the control of cerebral artery function in health and disease.

Multifunctional role of astrocytes as gatekeepers of neuronal energy supply

Dynamic adjustments to neuronal energy supply in response to synaptic activity are critical for neuronal function. Glial cells known as astrocytes have processes that ensheath most central synapses and express G-protein-coupled neurotransmitter receptors and transporters that respond to neuronal activity. Astrocytes also release substrates for neuronal oxidative phosphorylation and have processes that terminate on the surface of brain arterioles and can influence vascular smooth muscle tone and local blood flow. Membrane receptor or transporter-mediated effects of glutamate represent a convergence point of astrocyte influence on neuronal bioenergetics. Astrocytic glutamate uptake drives glycolysis and subsequent shuttling of lactate from astrocytes to neurons for oxidative metabolism. Astrocytes also convert synaptically reclaimed glutamate to glutamine, which is returned to neurons for glutamate salvage or oxidation. Finally, astrocytes store brain energy currency in the form of glycogen, which can be mobilized to produce lactate for neuronal oxidative phosphorylation in response to glutamatergic neurotransmission. These mechanisms couple synaptically driven astrocytic responses to glutamate with release of energy substrates back to neurons to match demand with supply. In addition, astrocytes directly influence the tone of penetrating brain arterioles in response to glutamatergic neurotransmission, coordinating dynamic regulation of local blood flow. We will describe the role of astrocytes in neurometabolic and neurovascular coupling in detail and discuss, in turn, how astrocyte dysfunction may contribute to neuronal bioenergetic deficit and neurodegeneration. Understanding the role of astrocytes as a hub for neurometabolic and neurovascular coupling mechanisms is a critical underpinning for therapeutic development in a broad range of neurodegenerative disorders characterized by chronic generalized brain ischemia and brain microvascular dysfunction.

Beneficial effects of inhibition of soluble epoxide hydrolase on glucose homeostasis and islet damage in a streptozotocin-induced diabetic mouse model

Soluble epoxide hydrolase (sEH) is an enzyme involved in the metabolism of endogenous inflammatory and anti-apoptotic mediators. In the present study, we determined the effects of the inhibition of sEH on glucose homeostasis and islet damage in mice treated with streptozotocin (STZ), a model of chemical-induced diabetes. STZ increased daily water intake and decreased visceral (spleen and pancreas) weight in mice; sEH inhibition in STZ mice decreased water intake, but did not affect visceral weight. Hyperglycemia induced by STZ treatment in mice was attenuated by inhibiting sEH. The beneficial effects of sEH inhibition were accompanied, after 2 and 4 weeks of initial administration, by improving glucose tolerance. In contrast, sEH inhibition did not affect insulin tolerance. Using LC/MS analysis, neither STZ nor STZ plus sEH inhibition affected pancreatic and plasma ratios of epoxyeicosatrienoic acids (EETs) to dihydroxyeicosatrienoic acids (DHETs), an index of EETs levels. Western blot analysis showed that mouse cytochrome P450 (CYP) 2C enzymes are the major epoxygenases in islets. On day 5 after initial STZ treatment, STZ induced islet cell apoptosis, while sEH inhibition in STZ mice significantly reduced islet cell apoptosis. These studies provide pharmacological evidence that inhibiting sEH activity provides significant protection against islet β-cell damage and improves glucose homeostasis in STZ-induced diabetes.

Förster resonance energy transfer competitive displacement assay for human soluble epoxide hydrolase

The soluble epoxide hydrolase (sEH), responsible for the hydrolysis of various fatty acid epoxides to their corresponding 1,2-diols, is becoming an attractive pharmaceutical target. These fatty acid epoxides, particularly epoxyeicosatrienoic acids (EETs), play an important role in human homeostatic and inflammation processes. Therefore, inhibition of human sEH, which stabilizes EETs in vivo, brings several beneficial effects to human health. Although there are several catalytic assays available to determine the potency of sEH inhibitors, measuring the in vitro inhibition constant (K(i)) for these inhibitors using catalytic assay is laborious. In addition, k(off), which has been recently suggested to correlate better with the in vivo potency of inhibitors, has never been measured for sEH inhibitors. To better measure the potency of sEH inhibitors, a reporting ligand, 1-(adamantan-1-yl)-3-(1-(2-(7-hydroxy-2-oxo-2H-chromen-4-yl)acetyl) piperidin-4-yl)urea (ACPU), was designed and synthesized. With ACPU, we have developed a Förster resonance energy transfer (FRET)-based competitive displacement assay using intrinsic tryptophan fluorescence from sEH. In addition, the resulting assay allows us to measure the K(i) values of very potent compounds to the picomolar level and to obtain relative k(off) values of the inhibitors. This assay provides additional data to evaluate the potency of sEH inhibitors.

Nitric oxide: orchestrator of endothelium-dependent responses

The present review first summarizes the complex chain of events, in endothelial and vascular smooth muscle cells, that leads to endothelium-dependent relaxations (vasodilatations) due to the generation of nitric oxide (NO) by endothelial nitric oxide synthase (eNOS) and how therapeutic interventions may improve the bioavailability of NO and thus prevent/cure endothelial dysfunction. Then, the role of other endothelium-derived mediators (endothelium-derived hyperpolarizing (EDHF) and contracting (EDCF) factors, endothelin-1) and signals (myoendothelial coupling) is summarized also, with special emphasis on their interaction(s) with the NO pathway, which make the latter not only a major mediator but also a key regulator of endothelium-dependent responses.

Protection of salvianolic acid A on rat brain from ischemic damage via soluble epoxide hydrolase inhibition

Epoxyeicosatrienoic acids (EETs) and their regulating enzyme soluble epoxide hydrolase (sEH) have been associated with ischemic stroke. Salvianolic acid A (SAA) is proved to display potent cerebroprotection. However, little information is available about the link between them. This study aimed to investigate whether SAA exhibits its protective effects in rats subjected to middle cerebral artery occlusion (MCAO) through sEH and EETs. The results showed that SAA treatment ameliorated neurological deficits and reduced infarct volume. Notably, the beneficial effects of SAA were attenuated by co-administration of (14,15-epoxyeicosa-5(Z)-enoic acid (14,15-EEZE)), a putative selective EETs antagonist. Furthermore, SAA increased the 14,15-EET levels in the blood and brain of sham and MCAO rats. Assay for hydrolase activity showed that 1 and 3 mg/kg of SAA significantly diminished brain sEH activity of MCAO rats. A fluorescent assay in vitro indicated that SAA could inhibit recombinant human sEH activity in a concentration-dependent manner (IC(50) = 1.62 μmol/l). Immunohistochemical analysis showed that SAA at the doses of 1 and 3 mg/kg significantly decreased sEH protein expression in hippocampus CA1 region of MCAO rats. In conclusion, cerebral protection of SAA is mediated, at least in part, via inhibiting sEH to increase EETs levels.

Impact of soluble epoxide hydrolase and epoxyeicosanoids on human health

The presence of epoxyeicosatrienoic acids (EETs) in tissues and their metabolism by soluble epoxide hydrolase (sEH) to 1,2-diols were first reported 30 years ago. However, appreciation of their importance in cell biology and physiology has greatly accelerated over the past decade with the discovery of metabolically stable inhibitors of sEH, the commercial availability of EETs, and the development of analytical methods for the quantification of EETs and their diols. Numerous roles of EETs in regulatory biology now are clear, and the value of sEH inhibition in various animal models of disease has been demonstrated. Here, we review these results and discuss how the pharmacological stabilization of EETs and other natural epoxy-fatty acids could lead to possible disease therapies.

EET signaling in cancer

Inflammation and angiogenesis in the tumor microenvironment are increasingly implicated in tumorigenesis. Endogenously produced lipid autacoids, locally acting small-molecule mediators, play a central role in inflammation and tissue homeostasis. These lipid mediators, collectively referred to as eicosanoids, have recently been implicated in cancer. Although eicosanoids, including prostaglandins and leukotrienes, are best known as products of arachidonic acid metabolism by cyclooxygenases and lipoxygenases, arachidonic acid is also a substrate for another enzymatic pathway, the cytochrome P450 (CYP) system. This eicosanoid pathway consists of two main branches: ω-hydroxylases which converts arachidonic acid to hydroxyeicosatetraenoic acids (HETEs) and epoxygenases which converts it to four regioisomeric epoxyeicosatrienoic acids (EETs; 5,6-EET, 8,9-EET, 11,12-EET, and 14,15-EET). EETs regulate inflammation and vascular tone. The bioactive EETs are produced predominantly in the endothelium and are mainly metabolized by soluble epoxide hydrolase to less active dihydroxyeicosatrienoic acids. EET signaling was originally studied in conjunction with inflammatory and cardiovascular disease. Arachidonic acid and its metabolites have recently stimulated great interest in cancer biology. To date, most research on eicosanoids in cancer has focused on the COX and LOX pathways. In contrast, the role of cytochrome P450-derived eicosanoids, such as EETs and HETEs, in cancer has received little attention. While CYP epoxygenases are expressed in human cancers and promote human cancer metastasis, the role of EETs (the direct products of CYP epoxygenases) in cancer remains poorly characterized. In this review, the emerging role of EET signaling in angiogenesis, inflammation, and cancer is discussed.

Delivery of AAV2-CYP2J2 protects remnant kidney in the 5/6-nephrectomized rat via inhibition of apoptosis and fibrosis

The cytochrome P450 epoxygenase, CYP2J2, converts arachidonic acid to four regioisomeric epoxyeicosatrienoic acids (EETs), which are highly abundant in the kidney and considered renoprotective. Accumulating evidence suggests that EETs are important in regulating renal and cardiovascular function. Further, EETs have been confirmed to exert diverse biological activities including potent vasodilation; fibrinolytic properties; and antiinflammatory, antiapoptotic, and mitogenic effects. In the current study, we investigated the effects of overexpression of CYP2J2 via recombinant adeno-associated virus (rAAV) in protection against renal damage in a rat 5/6 nephrectomy (5/6-Nx) model of chronic renal failure. The rAAV-CYP2J2 gene delivery in vivo increased EET generation; attenuated the rise in blood pressure; and reduced the levels of proteinuria, serum creatinine, and blood urea nitrogen. Morphological analysis indicated that rAAV-CYP2J2 gene delivery reduced 5/6 nephrectomy-induced glomerular sclerosis, tubular dilatation, luminal protein cast formation, and tubulointerstitial fibrosis. rAAV-CYP2J2 gene delivery also significantly lowered collagen I and IV deposition, as well as renal cell apoptosis detected by TUNEL staining, caspase-3 activity, and the loss of mitochondrial membrane potential (ΔΨ(m)). Furthermore, rAAV-CYP2J2 gene delivery regulated the level of protein expression including transforming growth factor (TGF)-β(1)/SMADs; matrix metalloproteinases (MMPs); mitogen-activated protein kinases (MAPKs); and apoptosis-related proteins Bax, Bcl-2, and Bcl-x(L). Together, these findings demonstrated that rAAV-CYP2J2 gene delivery can protect remnant kidney against renal injury in 5/6-Nx rats by inhibiting apoptosis and fibrosis via regulation of protein expression including TGF-β(1)/SMADs, MMPs, MAPKs, and apoptosis-related proteins.

Epoxides and soluble epoxide hydrolase in cardiovascular physiology

Epoxyeicosatrienoic acids (EETs) are arachidonic acid metabolites that importantly contribute to vascular and cardiac physiology. The contribution of EETs to vascular and cardiac function is further influenced by soluble epoxide hydrolase (sEH) that degrades EETs to diols. Vascular actions of EETs include dilation and angiogenesis. EETs also decrease inflammation and platelet aggregation and in general act to maintain vascular homeostasis. Myocyte contraction and increased coronary blood flow are the two primary EET actions in the heart. EET cell signaling mechanisms are tissue and organ specific and provide significant evidence for the existence of EET receptors. Additionally, pharmacological and genetic manipulations of EETs and sEH have demonstrated a contribution for this metabolic pathway to cardiovascular diseases. Given the impact of EETs to cardiovascular physiology, there is emerging evidence that development of EET-based therapeutics will be beneficial for cardiovascular diseases.

Reno-protective mechanisms of epoxyeicosatrienoic acids in cardiovascular disease

Cardiovascular disease (CVD) is the leading cause of mortality worldwide, and it is well known that end-stage renal disease (ESRD) is a profound consequence of the progression of CVD. Present treatments only slow CVD progression to ESRD, and it is imperative that new therapeutic strategies are developed to prevent the incidence of ESRD. Because epoxyeicosatrienoic acids (EETs) have been shown to elicit reno-protective effects in hypertensive animal models, the current review will focus on addressing the reno-protective mechanisms of EETs in CVD. The cytochrome P-450 epoxygenase catalyzes the oxidation of arachidonic acid to EETs. EETs have been identified as endothelium-derived hyperpolarizing factors (EDHFs) with vasodilatory, anti-inflammatory, antihypertensive, and antiplatelet aggregation properties. EETs also have profound effects on vascular migration and proliferation and promote angiogenesis. The progression of CVD has been linked to decreased EETs levels, leading to the concept that EETs should be therapeutically targeted to prevent end-organ damage associated with CVD. However, EETs are quickly degraded by the enzyme soluble epoxide hydrolase (sEH) to their less active diols, dihydroxyeicosatrienoic acids (DHETs). As such, one way to increase EETs level is to inhibit their degradation to DHETs by using sEH inhibitors. Inhibition of sEH has been shown to effectively reduce blood pressure and organ damage in experimental models of CVD. Another approach to target EETs is to develop EET analogs with improved solubility and resistance to auto-oxidation and metabolism by sEH. For example, stable ether EET analogs dilate afferent arterioles and lower blood pressure in hypertensive rodent animal models. EET agonists also improve insulin signaling and vascular function in animal models of metabolic syndrome.

Improvement of endothelium-dependent vasodilations by SKA-31 and SKA-20, activators of small- and intermediate-conductance Ca2+ -activated K+ -channels

AIM

Endothelial membrane hyperpolarization mediated by KCa3.1 and KCa2.3 channels has been demonstrated to initiate endothelium-derived hyperpolarizing factor (EDHF)-type vasodilations. Moreover, pharmacological potentiation of KCa3.1/KCa2.3 channels has been suggested to improve EDHF-type vasodilations. Herein, we determined whether the KCa3.1/KCa2.3 activator SKA-31 and its derivative SKA-20 improve endothelial dysfunction in KCa3.1-/- and NOS3-/- mice.

METHODS

Membrane potentials were measured using patch-clamp electrophysiology on carotid artery (CA) endothelial cells (CAEC) from wild-type (wt) and KCa3.1-/- mice. Endothelium-dependent vasodilations were determined by pressure myography in CA.

RESULTS

SKA-31 (1 μm) activated KCa3.1 and KCa2.3 channels and induced membrane hyperpolarization in CAEC of wt (ΔMP -45 mV). These responses were significantly reduced in CAEC of KCa3.1-/- (ΔMP -8 mV). SKA-31 (200 nm, 500 nm) and SKA-20 (300 nm) significantly enhanced EDHF vasodilations in wt. SKA-20 also improved vasodilations during NO synthesis. In KCa3.1-/-, the defective EDHF vasodilations were unchanged at 200 nm SKA-31, but were significantly improved at 500 nm. EDHF vasodilations were slightly enhanced at 300 nm SKA-20, but vasodilations during NO synthesis were unchanged. SKA-31 (500 nm) enhanced the impaired endothelium-dependent vasodilation in NOS3-/- mice twofold. Pharmacological inhibition of the soluble epoxide hydrolase by t-AUCB (1 μm) in contrast did not increase ACh-induced EDHF- or NO-mediated vasodilations in wt and KCa3.1-/-.

CONCLUSION

Normal and defective endothelium-dependent vasodilations in murine carotid arteries can be improved by pharmacological enhancement of KCa3.1/KCa2.3 functions. These findings further support the concept that pharmacological activation of endothelial KCa2.3/KCa3.1 could offer a novel endothelium-specific antihypertensive strategy.

Differential effect of amyloid β on the cytochrome P450 epoxygenase activity in rat brain

One of the prominent features of Alzheimer's disease is the excessive accumulation of the protein amyloid beta (Aβ) in certain areas of the brain leading to neurodegeneration. Aβ is cytotoxic and disrupts several cytoprotective pathways. Recent literature has demonstrated that certain cytochrome P450 (CYP) products are neuroprotective, including epoxide metabolites of arachidonic acid (AA), epoxyeicosatrienoic acids (EETs). The action of Aβ with respect to regionally produced EETs in the brain has yet to be defined. Epoxygenases metabolize AA into four regioisomers of EETs (14,15-, 11,12-, 8,9- and 5,6-EET). EETs are rapidly degraded into dihydroxyeicosatrienoic acids (DiHETEs) by soluble epoxide hydrolase (sEH). To determine the effect of Aβ on the epoxygenase activity in different regions of the brain, microsomes were prepared from the cerebrum and cerebellum of adult Sprague-Dawley rats and incubated with 1 and 10 μM Aβ for 30 min after which epoxygenase activity assay was performed. Mass spectrometry indicated that incubation with Aβ reduced 14,15-EET production by 30% as compared to vehicle in the cerebrum, but not in the cerebellum. When we separated the cerebrum into cortex and hippocampus, significant decrease in the production of total EETs and DiHETEs were seen in presence of Aβ (81% and 74%) in the cortex. Moreover, 11,12-EET production was decreased to ∼70% of vehicle in both cortex and hippocampus. Epoxygenase activity in the cultured astrocytes and neurons also showed reduction in total EET and DiHETE production (to 80% and ∼70% of vehicle respectively) in presence of Aβ. Altogether, our data suggest that Aβ reduces epoxygenase activity differentially in a region-specific and cell-specific manner. The reduction of cytoprotective EETs by Aβ in the cerebrum may make it more prone to degeneration than the cerebellum. Further understanding of these interactions will improve our ability to protect against the pathology of Alzheimer's disease.

Eicosanoids, β-cell function, and diabetes

Arachidonic acid (AA) is metabolized by cyclooxygenase (COX), lipoxygenase (LOX), and cytochrome P450 (CYP) enzymes into eicosanoids, which are involved in diverse diseases, including type 1 and type 2 diabetes. During the last 30 years, evidence has been accumulated that suggests important functions for eicosanoids in the control of pancreatic β-cell function and destruction. AA metabolites of the COX pathway, especially prostaglandin E(2) (PGE(2)), appear to be significant factors to β-cell dysfunction and destruction, participating in the pathogenesis of diabetes and its complications. Several elegant studies have contributed to the sorting out of the importance of 12-LOX eicosanoids in cytokine-mediated inflammation in pancreatic β cells. The role of CYP eicosanoids in diabetes is yet to be explored. A recent publication has demonstrated that stabilizing the levels of epoxyeicosatrienoic acids (EETs), CYP eicosanoids, by inhibiting or deleting soluble epoxide hydrolase (sEH) improves β-cell function and reduces β-cell apoptosis in diabetes. In this review we summarize recent findings implicating these eicosanoid pathways in diabetes and its complications. 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 diabetes and its complications.

Targeting epoxides for organ damage in hypertension

Epoxyeicosatrienoic acids (EETs) are synthesized from arachidonic acid and EETs have a number of beneficial cardiovascular actions. This has led to the concept that EETs and its metabolic pathway can be therapeutically targeted for hypertension and other cardiovascular diseases. One approach has been to prevent the conversion of EETs to their inactive diols by inhibiting the soluble epoxide hydrolase (sEH) enzyme. Inhibition of sEH has been demonstrated to decrease blood pressure in certain experimental models of hypertension, decrease inflammation, and protect organs from damage associated with hypertension and other cardiovascular diseases. The development of sEH inhibitors has reached the point where they are being evaluated in humans. A second therapeutic approach has been to develop EET agonists. EET agonists have been essential for determining the structure function relationship for EETs and determining cell-signaling mechanisms by which EETs exert their cardiovascular actions. More recently, EET agonists have been administered chronically to experimental animal models of hypertension and metabolic syndrome and have been demonstrated to decrease blood pressure, improve insulin signaling, and improve vascular function. These experimental findings provide evidence for sEH inhibitors and EET agonists as a therapeutic approach for cardiovascular diseases, hypertension, and the associated end-organ damage.

Cytochrome P450 eicosanoids and cerebral vascular function

The eicosanoids 20-hydroxyeicosatetraenoic acid (20-HETE) and epoxyeicosatrienoic acids (EETs), which are generated from the metabolism of arachidonic acid by cytochrome P450 (CYP) enzymes, possess a wide array of biological actions, including the regulation of blood flow to organs. 20-HETE and EETs are generated in various cell types in the brain and cerebral blood vessels, and contribute significantly to cerebral blood flow autoregulation and the coupling of regional brain blood flow to neuronal activity (neurovascular coupling). Investigations are beginning to unravel the molecular and cellular mechanisms by which these CYP eicosanoids regulate cerebral vascular function and the changes that occur in pathological states. Intriguingly, 20-HETE and the soluble epoxide hydrolase (sEH) enzyme that regulates EET levels have been explored as molecular therapeutic targets for cerebral vascular diseases. Inhibition of 20-HETE, or increasing EET levels by inhibiting the sEH enzyme, decreases cerebral damage following stroke. The improved outcome following cerebral ischaemia is a consequence of improving cerebral vascular structure or function and protecting neurons from cell death. Thus, the CYP eicosanoids are key regulators of cerebral vascular function and novel therapeutic targets for cardiovascular diseases and neurological disorders.

Cytochrome P450-derived eicosanoids: the neglected pathway in cancer

Endogenously produced lipid autacoids are locally acting small molecule mediators that play a central role in the regulation of inflammation and tissue homeostasis. A well-studied group of autacoids are the products of arachidonic acid metabolism, among which the prostaglandins and leukotrienes are the best known. They are generated by two pathways controlled by the enzyme systems cyclooxygenase and lipoxygenase, respectively. However, arachidonic acid is also substrate for a third enzymatic pathway, the cytochrome P450 (CYP) system. This third eicosanoid pathway consists of two main branches: ω-hydroxylases convert arachidonic acid to hydroxyeicosatetraenoic acids (HETEs) and epoxygenases convert it to epoxyeicosatrienoic acids (EETs). This third CYP pathway was originally studied in conjunction with inflammatory and cardiovascular disease. Arachidonic acid and its metabolites have recently stimulated great interest in cancer biology; but, unlike prostaglandins and leukotrienes the link between cytochome P450 metabolites and cancer has received little attention. In this review, the emerging role in cancer of cytochrome P450 metabolites, notably 20-HETE and EETs, are discussed.

Role of epoxyeicosatrienoic acids as autocrine metabolites in glutamate-mediated K+ signaling in perivascular astrocytes

Epoxyeicosatrienoic acids (EETs), synthesized and released by astrocytes in response to glutamate, are known to play a pivotal role in neurovascular coupling. In vascular smooth muscle cells (VSMC), EETs activate large-conductance, Ca(2+)-activated K(+) (BK) channels resulting in hyperpolarization and vasodilation. However, the functional role and mechanism of action for glial-derived EETs are still to be determined. In this study, we evaluated the effect of the synthetic EET analog 11-nonyloxy-undec-8(Z)-enoic acid (NUD-GA) on outward K(+) currents mediated by calcium-activated K(+) channels. Addition of NUD-GA significantly increased intracellular Ca(2+) and outward K(+) currents in perivascular astrocytes. NUD-GA-induced currents were significantly inhibited by BK channel blockers paxilline and tetraethylammonium (TEA) (23.4 ± 2.4%; P < 0.0005). Similarly, NUD-GA-induced currents were also significantly inhibited in the presence of the small-conductance Ca(2+)-activated K(+) channel inhibitor apamin along with a combination of blockers against glutamate receptors (12.8 ± 2.70%; P < 0.05). No changes in outward currents were observed in the presence of the channel blocker for intermediate-conductance K(+) channels TRAM-34. Blockade of the endogenous production of EETs with N-methylsulfonyl-6-(2-propargyloxyphenyl)hexanamide (MS-PPOH) significantly blunted (dl)-1-aminocyclopentane-trans-1,3-dicarboxylic acid (t-ACPD)-induced outward K(+) currents (P < 0.05; n = 6). Both NUD-GA and t-ACPD significantly increased BK channel single open probability; the later was blocked following MS-PPOH incubation. Our data supports the idea that EETs are potent K(+) channel modulators in cortical perivascular astrocytes and further suggest that these metabolites may participate in NVC by modulating the levels of K(+) released at the gliovascular space.

Inhibition of the soluble epoxide hydrolase promotes albuminuria in mice with progressive renal disease

Epoxyeicotrienoic acids (EETs) are cytochrome P450-dependent anti-hypertensive and anti-inflammatory derivatives of arachidonic acid, which are highly abundant in the kidney and considered reno-protective. EETs are degraded by the enzyme soluble epoxide hydrolase (sEH) and sEH inhibitors are considered treatment for chronic renal failure (CRF). We determined whether sEH inhibition attenuates the progression of CRF in the 5/6-nephrectomy model (5/6-Nx) in mice. 5/6-Nx mice were treated with a placebo, an ACE-inhibitor (Ramipril, 40 mg/kg), the sEH-inhibitor cAUCB or the CYP-inhibitor fenbendazole for 8 weeks. 5/6-Nx induced hypertension, albuminuria, glomerulosclerosis and tubulo-interstitial damage and these effects were attenuated by Ramipril. In contrast, cAUCB failed to lower the blood pressure and albuminuria was more severe as compared to placebo. Plasma EET-levels were doubled in 5/6 Nx-mice as compared to sham mice receiving placebo. Renal sEH expression was attenuated in 5/6-Nx mice but cAUCB in these animals still further increased the EET-level. cAUCB also increased 5-HETE and 15-HETE, which derive from peroxidation or lipoxygenases. Similar to cAUCB, CYP450 inhibition increased HETEs and promoted albuminuria. Thus, sEH-inhibition failed to elicit protective effects in the 5/6-Nx model and showed a tendency to aggravate the disease. These effects might be consequence of a shift of arachidonic acid metabolism into the lipoxygenase pathway.

Inhibition or deletion of soluble epoxide hydrolase prevents hyperglycemia, promotes insulin secretion, and reduces islet apoptosis

Soluble epoxide hydrolase (sEH) is an enzyme involved in the metabolism of endogenous inflammatory and antiapoptotic mediators. However, the roles of sEH in diabetes and the pancreas are unknown. Our aims were to determine whether sEH is involved in the regulation of hyperglycemia in diabetic mice and to investigate the reasons for the regulation of insulin secretion by sEH deletion or inhibition in islets. We used two separate approaches, targeted disruption of Ephx2 gene [sEH knockout (KO)] and a selective inhibitor of sEH [trans-4-[4-(3-adamantan-1-ylureido)-cyclohexyloxy]-benzoic acid (t-AUCB)], to assess the role of sEH in glucose and insulin homeostasis in streptozotocin (STZ) mice. We also examined the effects of sEH KO or t-AUCB on glucose-stimulated insulin secretion (GSIS) and intracellular calcium levels in islets. Hyperglycemia in STZ mice was prevented by both sEH KO and t-AUCB. In addition, STZ mice with sEH KO had improved glucose tolerance. More important, when insulin levels were assessed by hyperglycemic clamp study, sEH KO was found to promote insulin secretion. In addition, sEH KO and t-AUCB treatment augmented islet GSIS. Islets with sEH KO had a greater intracellular calcium influx when challenged with high glucose or KCl in the presence of diazoxide. Moreover, sEH KO reduced islet cell apoptosis in STZ mice. These results show not only that sEH KO and its inhibition prevent hyperglycemia in diabetes, but also that sEH KO enhances islet GSIS through the amplifying pathway and decreases islet cell apoptosis in diabetes.

Soluble epoxide hydrolase in atherosclerosis

Like many eicosanoids, epoxyeicosatrienoic acids (EETs) have multiple biological functions, including reduction of blood pressure, inflammation, and atherosclerosis in multiple species. Hydration of EETs by the soluble epoxide hydrolase (sEH) is the major route of their degradation to the less bioactive diols. Inhibition of the sEH stabilizes EETs, thus, enhancing the beneficial effects of EETs. Human data show an association of sEH (Ephx2) gene polymorphisms with increased risk of atherosclerosis and cardiovascular diseases. These data suggest a potential therapeutic effect of sEH inhibitors (sEHI) in the treatment of atherosclerosis. Indeed, two laboratories reported independently that using different sEHIs in apolipoprotein E-deficient mice significantly attenuated atherosclerosis development and aneurysm formation. The antiatherosclerotic effects of sEHI are correlated with elevation in EET levels and associated with reduction of low-density lipoprotein and elevation of high-density lipoprotein cholesterols, as well as attenuation of expression of proinflammatory genes and proteins. In addition, the antihypertensive effects and improvement of endothelial function also contribute to the mechanism of the antiatherosclerotic effects of sEHI. The broad spectrum of biological action of EETs and sEHIs with multiple biological beneficial actions provides a promising new class of therapeutics for atherosclerosis and other cardiovascular diseases.

Soluble epoxide hydrolase inhibition modulates vascular remodeling

The soluble epoxide hydrolase enzyme (SEH) and vascular remodeling are associated with cardiovascular disease. Although inhibition of SEH prevents smooth muscle cell proliferation in vitro, the effects of SEH inhibition on vascular remodeling in vivo and mechanisms of these effects remain unclear. Herein we determined the effects of SEH antagonism in an endothelium intact model of vascular remodeling induced by flow reduction and an endothelium denuded model of vascular injury. We demonstrated that chronic treatment of spontaneously hypertensive stroke-prone rats with 12-(3-adamantan-1-yl-ureido) dodecanoic acid, an inhibitor of SEH, improved the increment of inward remodeling induced by common carotid ligation to a level that was comparable with normotensive Wistar Kyoto rats. Similarly, mice with deletion of the gene responsible for the production of the SEH enzyme (Ephx2(-/-)) demonstrated enhanced inward vascular remodeling induced by carotid ligation. However, the hyperplastic response induced by vascular injury that denudes the endothelium was unabated by SEH inhibition or Ephx2 gene deletion. These results suggest that SEH inhibition or Ephx2 gene deletion antagonizes neointimal formation in vivo by mechanisms that are endothelium dependent. Thus SEH inhibition may have therapeutic potential for flow-induced remodeling and neointimal formation.

Oxidation of the endogenous cannabinoid arachidonoyl ethanolamide by the cytochrome P450 monooxygenases: physiological and pharmacological implications

Arachidonoyl ethanolamide (anandamide) is an endogenous amide of arachidonic acid and an important signaling mediator of the endocannabinoid system. Given its numerous roles in maintaining normal physiological function and modulating pathophysiological responses throughout the body, the endocannabinoid system is an important pharmacological target amenable to manipulation directly by cannabinoid receptor ligands or indirectly by drugs that alter endocannabinoid synthesis and inactivation. The latter approach has the possible advantage of more selectivity, thus there is the potential for fewer untoward effects like those that are traditionally associated with cannabinoid receptor ligands. In that regard, inhibitors of the principal inactivating enzyme for anandamide, fatty acid amide hydrolase (FAAH), are currently in development for the treatment of pain and inflammation. However, several pathways involved in anandamide synthesis, metabolism, and inactivation all need to be taken into account when evaluating the effects of FAAH inhibitors and similar agents in preclinical models and assessing their clinical potential. Anandamide undergoes oxidation by several human cytochrome P450 (P450) enzymes, including CYP3A4, CYP4F2, CYP4X1, and the highly polymorphic CYP2D6, forming numerous structurally diverse lipids, which are likely to have important physiological roles, as evidenced by the demonstration that a P450-derived epoxide of anandamide is a potent agonist for the cannabinoid receptor 2. The focus of this review is to emphasize the need for a better understanding of the P450-mediated pathways of the metabolism of anandamide, because these are likely to be important in mediating endocannabinoid signaling as well as the pharmacological responses to endocannabinoid-targeting drugs.

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.

The Soluble Epoxide Hydrolase Inhibitor AR9281 Decreases Blood Pressure, Ameliorates Renal Injury and Improves Vascular Function in Hypertension

Soluble epoxide hydrolase inhibitors (sEHIs) are demonstrating promise as potential pharmaceutical agents for the treatment of cardiovascular disease, diabetes, inflammation, and kidney disease. The present study determined the ability of a first-inclass sEHI, AR9281, to decrease blood pressure, improve vascular function, and decrease renal inflammation and injury in angiotensin hypertension. Rats were infused with angiotensin and AR9281 was given orally during the 14-day infusion period. Systolic blood pressure averaged 180 ± 5 mmHg in vehicle treated and AR9281 treatment significantly lowered blood pressure to 142 ± 7 mmHg in angiotensin hypertension. Histological analysis demonstrated decreased injury to the juxtamedullary glomeruli. Renal expression of inflammatory genes was increased in angiotensin hypertension and two weeks of AR9281 treatment decreased this index of renal inflammation. Vascular function in angiotensin hypertension was also improved by AR9281 treatment. Decreased afferent arteriolar and mesenteric resistance endothelial dependent dilator responses were ameliorated by AR9281 treatment of angiotensin hypertensive rats. These data demonstrate that the first-in-class sEHI, AR9281, lowers blood pressure, improves vascular function and reduces renal damage in angiotensin hypertension.

Soluble epoxide hydrolase as a therapeutic target for cardiovascular diseases

The cardiovascular effects of epoxyeicosatrienoic acids (EETs) include vasodilation, antimigratory actions on vascular smooth muscle cells and anti-inflammatory actions. These endogenous lipid mediators are broken down into diols by soluble epoxide hydrolase (sEH), and so inhibiting this enzyme would be expected to enhance the beneficial cardiovascular properties of EETs. sEH inhibitors (sEHIs) that are based on 1,3-disubstituted urea have been rapidly developed, and have been shown to be antihypertensive and anti-inflammatory, and to protect the brain, heart and kidney from damage. Although challenges for the future exist - including improving the drug-like properties of sEHIs and finding better ways to target sEHIs to specific tissues - the recent initiation of the first clinical trials of sEHIs has highlighted the therapeutic potential of these agents.