Evidence for role of epoxyeicosatrienoic acids in mediating ischemic preconditioning and postconditioning in dog

Prospective for cytochrome P450 epoxygenase cardiovascular and renal therapeutics

Therapeutics for arachidonic acid pathways began with the development of non-steroidal anti-inflammatory drugs that inhibit cyclooxygenase (COX). The enzymatic pathways and arachidonic acid metabolites and respective receptors have been successfully targeted and therapeutics developed for pain, inflammation, pulmonary and cardiovascular diseases. These drugs target the COX and lipoxygenase pathways but not the third branch for arachidonic acid metabolism, the cytochrome P450 (CYP) pathway. Small molecule compounds targeting enzymes and CYP epoxy-fatty acid metabolites have evolved rapidly over the last two decades. These therapeutics have primarily focused on inhibiting soluble epoxide hydrolase (sEH) or agonist mimetics for epoxyeicosatrienoic acids (EET). Based on preclinical animal model studies and human studies, major therapeutic indications for these sEH inhibitors and EET mimics/analogs are renal and cardiovascular diseases. Novel small molecules that inhibit sEH have advanced to human clinical trials and demonstrate promise for cardiovascular diseases. Challenges remain for sEH inhibitor and EET analog drug development; however, there is a high likelihood that a drug that acts on this third branch of arachidonic acid metabolism will be utilized to treat a cardiovascular or kidney disease in the next decade.

Therapeutic potential of omega-3 fatty acid-derived epoxyeicosanoids in cardiovascular and inflammatory diseases

Numerous benefits have been attributed to dietary long-chain omega-3 polyunsaturated fatty acids (n-3 LC-PUFAs), including protection against cardiac arrhythmia, triglyceride-lowering, amelioration of inflammatory, and neurodegenerative disorders. This review covers recent findings indicating that a variety of these beneficial effects are mediated by "omega-3 epoxyeicosanoids", a class of novel n-3 LC-PUFA-derived lipid mediators, which are generated via the cytochrome P450 (CYP) epoxygenase pathway. CYP enzymes, previously identified as arachidonic acid (20:4n-6; AA) epoxygenases, accept eicosapentaenoic acid (20:5n-3; EPA) and docosahexaenoic acid (22:6n-3; DHA), the major fish oil n-3 LC-PUFAs, as efficient alternative substrates. In humans and rodents, dietary EPA/DHA supplementation causes a profound shift of the endogenous CYP-eicosanoid profile from AA- to EPA- and DHA-derived metabolites, increasing, in particular, the plasma and tissue levels of 17,18-epoxyeicosatetraenoic acid (17,18-EEQ) and 19,20-epoxydocosapentaenoic acid (19,20-EDP). Based on preclinical studies, these omega-3 epoxyeicosanoids display cardioprotective, vasodilatory, anti-inflammatory, and anti-allergic properties that contribute to the beneficial effects of n-3 LC-PUFAs in diverse disease conditions ranging from cardiac disease, bronchial disorders, and intraocular neovascularization, to allergic intestinal inflammation and inflammatory pain. Increasing evidence also suggests that background nutrition as well as genetic and disease state-related factors could limit the response to EPA/DHA-supplementation by reducing the formation and/or enhancing the degradation of omega-3 epoxyeicosanoids. Recently, metabolically robust synthetic analogs mimicking the biological activities of 17,18-EEQ have been developed. These drug candidates may overcome limitations of dietary EPA/DHA supplementation and provide novel options for the treatment of cardiovascular and inflammatory diseases.

14,15-EET Suppresses Neuronal Apoptosis in Ischemia-Reperfusion Through the Mitochondrial Pathway

Neuronal apoptosis mediated by the mitochondrial apoptosis pathway is an important pathological process in cerebral ischemia-reperfusion injury. 14,15-EET, an intermediate metabolite of arachidonic acid, can promote cell survival during ischemia/reperfusion. However, whether the mitochondrial apoptotic pathway is involved this survival mechanism is not fully understood. In this study, we observed that infarct size in ischemia-reperfusion injury was reduced in sEH gene knockout mice. In addition, Caspase 3 activation, cytochrome C release and AIF nuclear translocation were also inhibited. In this study, 14,15-EET pretreatment reduced neuronal apoptosis in the oxygen-glucose deprivation and re-oxygenation group in vitro. The mitochondrial apoptosis pathway was also inhibited, as evidenced by AIF translocation from the mitochondria to nucleus and the reduction in the expressions of cleaved-caspase 3 and cytochrome C in the cytoplasm. 14,15-EET could reduce neuronal apoptosis through upregulation of the ratio of Bcl-2 (anti-apoptotic protein) to Bax (apoptosis protein) and inhibition of Bax aggregation onto mitochondria. PI3K/AKT pathway is also probably involved in the reduction of neuronal apoptosis by EET. Our study suggests that 14,15-EET could suppress neuronal apoptosis and reduce infarct volume through the mitochondrial apoptotic pathway. Furthermore, the PI3K/AKT pathway also appears to be involved in the neuroprotection against ischemia-reperfusion by 14,15-EET.

Treatment of Myocardial Ischemia/Reperfusion Injury by Ischemic and Pharmacological Postconditioning

Timely reperfusion is the only way to salvage ischemic myocardium from impending infarction. However, reperfusion also adds a further component to myocardial injury such that the ultimate infarct size is the result of both ischemia- and reperfusion-induced injury. Modification of reperfusion can attenuate reperfusion injury and thus reduce infarct size. Ischemic postconditioning is a maneuver of repeated brief interruption of reperfusion by short-lasting coronary occlusions which results in reduced infarct size. Cardioprotection by ischemic postconditioning is mediated through delayed reversal of acidosis and the activation of a complex signal transduction cascade, including triggers such as adenosine, bradykinin, and opioids, mediators such as protein kinases and, notably, mitochondrial function as effector. Inhibition of the mitochondrial permeability transition pore appears to be a final signaling step of ischemic postconditioning. Several drugs which recruit in part such signaling steps of ischemic postconditioning can induce cardioprotection, even when the drug is only administered at reperfusion, that is, there is also pharmacological postconditioning. Ischemic and pharmacological postconditioning have been translated to patients with acute myocardial infarction in proof-of-concept studies, but further mechanistic insight is needed to optimize the conditions and algorithms of cardioprotection by postconditioning.

TRPV4 channels: physiological and pathological role in cardiovascular system

TRPV4 channels are non-selective cation channels permeable to Ca(2+), Na(+), and Mg(2+) ions. Recently, TRPV4 channels have received considerable attention as these channels are widely expressed in the cardiovascular system including endothelial cells, cardiac fibroblasts, vascular smooth muscles, and peri-vascular nerves. Therefore, these channels possibly play a pivotal role in the maintenance of cardiovascular homeostasis. TRPV4 channels critically regulate flow-induced arteriogenesis, TGF-β1-induced differentiation of cardiac fibroblasts into myofibroblasts, and heart failure-induced pulmonary edema. These channels also mediate hypoxia-induced increase in proliferation and migration of pulmonary artery smooth muscle cells and progression of pulmonary hypertension. These channels also maintain flow-induced vasodilation and preserve vascular function by directly activating Ca(2+)-dependent KCa channels. Furthermore, these may also induce vasodilation and maintain blood pressure indirectly by evoking the release of NO, CGRP, and substance P. The present review discusses the evidences and the potential mechanisms implicated in diverse responses including arteriogenesis, cardiac remodeling, congestive heart failure-induced pulmonary edema, pulmonary hypertension, flow-induced dilation, regulation of blood pressure, and hypoxic preconditioning.

Pharmacological postconditioning with lactic acid and hydrogen rich saline alleviates myocardial reperfusion injury in rats

This study investigated whether pharmacological postconditioning with lactic acid and hydrogen rich saline can provide benefits similar to that of mechanical postconditioning. To our knowledge, this is the first therapeutic study to investigate the co-administration of lactic acid and hydrogen. SD rats were randomly divided into 6 groups: Sham, R/I, M-Post, Lac, Hyd, and Lac + Hyd. The left coronary artery was occluded for 45 min. Blood was withdrawn from the right atrium to measure pH. The rats were sacrificed at different time points to measure mitochondrial absorbance, infarct size, serum markers and apoptotic index. Rats in Lac + Hyd group had similar blood pH and ROS levels when compared to the M-Post group. Additionally, the infarct area was reduced to the same extent in Lac + Hyd and M-Post groups with a similar trends observed for serum markers of myocardial injury and apoptotic index. Although the level of P-ERK in Lac + Hyd group was lower, P-p38/JNK, TNFα, Caspase-8, mitochondrial absorbance and Cyt-c were all similar in Lac + Hyd and M-Post groups. The Lac and Hyd groups were able to partially mimic this protective role. These data suggested that pharmacological postconditioning with lactic acid and hydrogen rich saline nearly replicates the benefits of mechanical postconditioning.

Molecular basis of cardioprotection: signal transduction in ischemic pre-, post-, and remote conditioning

Reperfusion is mandatory to salvage ischemic myocardium from infarction, but reperfusion per se contributes to injury and ultimate infarct size. Therefore, cardioprotection beyond that by timely reperfusion is needed to reduce infarct size and improve the prognosis of patients with acute myocardial infarction. The conditioning phenomena provide such cardioprotection, insofar as brief episodes of coronary occlusion/reperfusion preceding (ischemic preconditioning) or following (ischemic postconditioning) sustained myocardial ischemia with reperfusion reduce infarct size. Even ischemia/reperfusion in organs remote from the heart provides cardioprotection (remote ischemic conditioning). The present review characterizes the signal transduction underlying the conditioning phenomena, including their physical and chemical triggers, intracellular signal transduction, and effector mechanisms, notably in the mitochondria. Cardioprotective signal transduction appears as a highly concerted spatiotemporal program. Although the translation of ischemic postconditioning and remote ischemic conditioning protocols to patients with acute myocardial infarction has been fairly successful, the pharmacological recruitment of cardioprotective signaling has been largely disappointing to date.

TRPV1 and TRPV4 channels: potential therapeutic targets for ischemic conditioning-induced cardioprotection

Besides the involvement of TRPV channels in exhibiting various cellular functions including thermoregulation, pain perception, maintenance of bone homeostasis and gastrointestinal function; certain studies have also implicated the putative role of these channels in mediating ischemic conditioning-induced cardioprotection. The potential role of TRPV1 channels in different forms of ischemic conditioning (pre/post/remote)-induced cardioprotection has been described by employing TRPV1 knockout mice and various pharmacological modulators. The cardioprotective effects of TRPV1 activation during ischemic conditioning have been linked with increased CGRP, substance P release and augmented ALOX expression. Furthermore, the role of TRPV4 channels in mediating preconditioning-induced preservation of vascular function in terms restoring NO- and further improving EDH(F)-mediated endothelial relaxation has been described. The present review discusses the putative role of TRPV1 and TRPV4 channels in mediating different forms of conditioning (pre/post/remote)-induced cardioprotection along with the possible mechanisms. Future perspectives have also been described to fully understand the cascade of signaling and contribution of TRPV channel activation during myocardial ischemic conditioning.

Inhibition of Rho-kinase by fasudil restores the cardioprotection of ischemic postconditioninng in hypercholesterolemic rat heart

Ischemic postconditioning (IPoC) reduces lethal reperfusion injury under normal conditions, but its effectiveness is blocked by hypercholesterolemia. The present study aimed to determine whether the inhibition of Rho‑kinase by fasudil restores the cardioprotection of IPoC in the hypercholesterolemic rat heart, and to elucidate the potential mechanisms underlying this process. The isolated rat hearts underwent 30 min global ischemia and 120 min reperfusion. IPoC was induced by six cycles of 10 sec ischemia and 10 sec reperfusion at the onset of the reperfusion. Fasudil was administered 15 min prior to ischemia, and wortmannin and L‑NAME were administered following IPoC. The myocardial infarct size, apoptosis, myocardial nitric oxide (NO) content and Rho‑kinase activity, as well as the activation of the phosphatidylinositol 3‑kinase/Akt/endothelial nitric oxide synthase (PI3K/Akt/eNOS) pathway, were examined. The results revealed that IPoC and 1 µM fasudil treatment alone failed to reduce the infarct size and apoptosis rate. However, IPoC combined with 1 µM fasudil treatment or 10 µM fasudil treatment alone restored the cardioprotection as evidenced by the decreasing in infarct size and apoptosis rate, whereas it was blocked by the administration of wortmannin or L‑NAME. Furthermore, IPoC combined with 1 µM fasudil treatment also enhanced the phosphorylation of Akt and eNOS and conferred a significant increase in the content of NO. By contrast, no significant improvements were demonstrated in the phosphorylation of Akt and eNOS, as well as myocardial NO content when treated with 1 µM fasudil and IPoC alone. The inhibition of Rho‑kinase by fasudil was able to restore the cardioprotection of IPoC in the hypercholesterolemic rat heart. The underlying mechanisms involved in this process appear to be mediated by the activation of the PI3K/Akt/eNOS signal pathway and an increase in the myocardial NO content.

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".

Ischemic postconditioning-mediated miRNA-21 protects against cardiac ischemia/reperfusion injury via PTEN/Akt pathway

Background

Ischemic postconditioning (IPost) protects the reperfused heart from infarction which has drawn much attention recently. However, studies to date have rarely investigated the role of microRNAs (miRNAs) in IPost. The aims of this study were to investigate whether miR-21 is involved in the protective effect of IPost against myocardial ischemia-reperfusion (I/R) injury and disclose the potential molecular mechanisms involved.

Methods and Results

We found that miR-21 was remarkably up-regulated in mouse hearts after IPost. To determine the protective role of IPost-induced miR-21 up-regulation, the mice were divided into the following four groups: I/R group; I/R+IPost group (I/R mice treated with IPost); Antagomir-21+IPost+I/R group (I/R mice treated with anagomir-21 and IPost); Scramble+IPost+I/R group (I/R mice treated with scramble and IPost). The results showed IPost could reduce I/R injury-induced infarct size of the left ventricle, improve cardiac function, and prevent myocardial apoptosis, while knockdown of miR-21 with antagomir-21 could reverse these protective effects of IPost against mouse I/R injury. Furthermore, we confirmed that miR-21 plays a protective role in myocardial apoptosis through PTEN/Akt signaling pathway, which was abrogated by the PI3K inhibitor LY294002. The protective effect of miR-21 on myocardial apoptosis was further revealed in mouse hearts after IPost treatment in vivo.

Conclusions

Our data clearly demonstrate that miR-21 is involved in IPost-mediated cardiac protection against I/R injury and dysfunction through the PTEN/Akt signaling pathway in vivo. Identifying the beneficial roles of IPost-regulated miRNAs in cardiac protection, which may be a rational target selection for ischemic cardioprotection.

CYP2J2 overexpression protects against arrhythmia susceptibility in cardiac hypertrophy

Maladaptive cardiac hypertrophy predisposes one to arrhythmia and sudden death. Cytochrome P450 (CYP)-derived epoxyeicosatrienoic acids (EETs) promote anti-inflammatory and antiapoptotic mechanisms, and are involved in the regulation of cardiac Ca(2+)-, K(+)- and Na(+)-channels. To test the hypothesis that enhanced cardiac EET biosynthesis counteracts hypertrophy-induced electrical remodeling, male transgenic mice with cardiomyocyte-specific overexpression of the human epoxygenase CYP2J2 (CYP2J2-TG) and wildtype littermates (WT) were subjected to chronic pressure overload (transverse aortic constriction, TAC) or β-adrenergic stimulation (isoproterenol infusion, ISO). TAC caused progressive mortality that was higher in WT (42% over 8 weeks after TAC), compared to CYP2J2-TG mice (6%). In vivo electrophysiological studies, 4 weeks after TAC, revealed high ventricular tachyarrhythmia inducibility in WT (47% of the stimulation protocols), but not in CYP2J2-TG mice (0%). CYP2J2 overexpression also enhanced ventricular refractoriness and protected against TAC-induced QRS prolongation and delocalization of left ventricular connexin-43. ISO for 14 days induced high vulnerability for atrial fibrillation in WT mice (54%) that was reduced in CYP-TG mice (17%). CYP2J2 overexpression also protected against ISO-induced reduction of atrial refractoriness and development of atrial fibrosis. In contrast to these profound effects on electrical remodeling, CYP2J2 overexpression only moderately reduced TAC-induced cardiac hypertrophy and did not affect the hypertrophic response to β-adrenergic stimulation. These results demonstrate that enhanced cardiac EET biosynthesis protects against electrical remodeling, ventricular tachyarrhythmia, and atrial fibrillation susceptibility during maladaptive cardiac hypertrophy.

Aging, estrogen loss and epoxyeicosatrienoic acids (EETs)

Inflammation is a key element in many cardiovascular diseases. Both estrogen loss, caused by menopause, and aging have inflammatory consequences. Epoxyeicosatrienoic acids (EETs) are anti-inflammatory molecules synthesized by various cytochrome P450 (Cyp) enzymes from arachidonic acid. EETs are in the third (Cytochrome P450) pathway of arachindonic acid metabolism, others being cyclooxygenases and lipoxygenases. We hypothesized that aging and estrogen loss would reduce levels of anti-inflammatory EETs. Adult (6 mo) and aged (22 mo) ovariectomized rats with (OP) and without (Ovx) 17-∃-estradiol replacement were used in this study. Mass spectrometry was used to measure levels of EETs and their metabolites, dihydroxyeicosatrienoic acids (DHETs). Levels of Cyp2C2, Cyp2C6, and Cyp2J2, the principal Cyps responsible for EETs synthesis, as well as soluble epoxide hydrolase (sEH), which metabolizes EETS to DHETs, were determined via western blot. Overall Cyp levels decreased with age, though Cyp2C6 increased in the liver. sEH was increased in the kidney with estrogen replacement. Despite protein changes, no differences were measured in plasma or aortic tissue levels of EETs. However, plasma 14,15 DHET was increased in aged Ovx, and 5,6 DHET in adult OP. In conclusion neither aging nor estrogen loss decreased the anti-inflammatory EETs in the cardiovascular system.

Roles of endothelial nitric oxide synthase (eNOS) and mitochondrial permeability transition pore (MPTP) in epoxyeicosatrienoic acid (EET)-induced cardioprotection against infarction in intact rat hearts

We previously demonstrated that 11,12 and 14,15-epoxeicosatrienoic acids (EETs) produce cardioprotection against ischemia-reperfusion injury in dogs and rats. Several signaling mechanisms have been implicated in the cardioprotective actions of the EETs; however, their mechanisms remain largely elusive. Since nitric oxide (NO) plays a significant role in cardioprotection and EETs have been demonstrated to induce NO production in various tissues, we hypothesized that NO is involved in mediating the EET actions in cardioprotection. To test this hypothesis, we used an in vivo rat model of infarction in which intact rat hearts were subjected to 30-min occlusion of the left coronary artery and 2-hr reperfusion. 11,12-EET or 14,15-EET (2.5mg/kg) administered 10min prior to the occlusion reduced infarct size, expressed as a percentage of the AAR (IS/AAR), from 63.9±0.8% (control) to 45.3±1.2% and 45.5±1.7%, respectively. A nonselective nitric oxide synthase (NOS) inhibitor, L-NAME (1.0mg/kg) or a selective endothelial NOS inhibitor, L-NIO (0.30mg/kg) alone did not affect IS/AAR but they completely abolished the cardioprotective effects of the EETs. On the other hand, a selective neuronal NOS inhibitor, nNOS I (0.03mg/kg) and a selective inducible NOS inhibitor, 1400W (0.10mg/kg) did not affect IS/AAR or block the cardioprotective effects of the EETs. Administration of 11,12-EET (2.5mg/kg) to the rats also transiently increased the plasma NO concentration. 14,15-EET (10μM) induced the phosphorylation of eNOS (Ser(1177)) as well as a transient increase of NO production in rat cardiomyoblast cell line (H9c2 cells). When 11,12-EET or 14,15-EET was administered at 5min prior to reperfusion, infarct size was also reduced to 42.8±2.2% and 42.6±1.9%, respectively. Interestingly, L-NAME (1.0mg/kg) and a mitochondrial KATP channel blocker, 5-HD (10mg/kg) did not abolish while a sarcolemmal KATP channel blocker, HMR 1098 (6.0mg/kg) and a mitochondrial permeability transition pore (MPTP) opener, atractyloside (5.0mg/kg) completely abolished the cardioprotection produced by the EETs. 14,15-EET (1.5mg/kg) with an inhibitor of MPTP opening, cyclosporin A (CsA, 1.0mg/kg) produced a greater reduction of infarct size than their individual administration. Conversely, an EET antagonist 14,15-epoxyeicosa-5(Z)-enoic acid (14,15-EEZE, 2.5mg/kg) completely abolished the cardioprotective effects of CsA, suggesting a role of MPTP in mediating the EET actions. Taken together, these results suggest that the cardioprotective effects of the EETs in an acute ischemia-reperfusion model are mediated by distinct mediators depending on the time of EET administration. The cardioprotective effects of EETs administered prior to ischemia were regulated by the activation of eNOS and increased NO production, while sarcKATP channels and MPTP were involved in the beneficial effects of the EETs when administered just prior to reperfusion.

Upregulation of cytochrome P450 2J3/11,12-epoxyeicosatrienoic acid inhibits apoptosis in neonatal rat cardiomyocytes by a caspase-dependent pathway

Short, nonlethal ischemic episodes administered to hearts directly after ischemic events (ischemic postconditioning, IPost) have an advantage over ischemic preconditioning (IPC). The endogenous cytochrome P450 2J3/11,12-epoxyeicosatrienoic acid (CYP2J3/11,12-EET) is upregulated by IPost, but not IPC, in the rat heart. The CYP epoxygenase inhibitor N-methylsulphonyl-6-(2-propargyloxyphenyl) hexanamide (MS-PPOH) reduces the cardioprotective effects of IPost, but not IPC. We proposed that upregulation of CYP2J3/11,12-EET during IPost induces cardioprotection by inhibiting cardiomyocyte apoptosis and that multiple apoptotic signals, including changes in mitochondrial membrane potential (MMP) and mitochondrial permeability transition pore (mPTP) opening, mitochondrial cytochrome c leakage, caspase-3 levels, and levels of protective kinases such as Bcl-2 and Bax, are involved in the process. Neonatal rat cardiomyocytes underwent 3-h hypoxia followed by 2-, 5-, or 6-h reoxygenation (H/R) or three cycles of 5-min reoxygenation followed by 5-min hypoxia before 90-min reoxygenation (HPost); or were transfected with pcDNA3.1-CYP2J3 for 48 h before H/R; or were treated with MS-PPOH for 10 min before HPost. For HPost alone, pcDNA3.1-CYP2J3 transfection attenuated cardiomyocyte apoptosis to 68.4% (p<0.05) of that with H/R. pcDNA3.1-CYP2J3 transfection significantly decreased MMP and inhibited mPTP opening induced by H/R, reduced mitochondrial cytochrome c leakage, cleaved caspase-3 protein expression, and increased the ratio of Bcl-2 to Bax expression. MS-PPOH abolished this effect. Therefore, upregulation of CYP2J3/11,12-EET during HPost is involved in cardioprotection by inhibiting apoptosis via a caspase-dependent pathway, and the apoptosis-suppressive effect may have important clinical implications during HPost.

Common variation in fatty acid genes and resuscitation from sudden cardiac arrest

BACKGROUND

Fatty acids provide energy and structural substrates for the heart and brain and may influence resuscitation from sudden cardiac arrest (SCA). We investigated whether genetic variation in fatty acid metabolism pathways was associated with SCA survival.

METHODS AND RESULTS

Subjects (mean age, 67 years; 80% male, white) were out-of-hospital SCA patients found in ventricular fibrillation in King County, WA. We compared subjects who survived to hospital admission (n=664) with those who did not (n=689), and subjects who survived to hospital discharge (n=334) with those who did not (n=1019). Associations between survival and genetic variants were assessed using logistic regression adjusting for age, sex, location, time to arrival of paramedics, whether the event was witnessed, and receipt of bystander cardiopulmonary resuscitation. Within-gene permutation tests were used to correct for multiple comparisons. Variants in 5 genes were significantly associated with SCA survival. After correction for multiple comparisons, single-nucleotide polymorphisms in ACSL1 and ACSL3 were significantly associated with survival to hospital admission. Single-nucleotide polymorphisms in ACSL3, AGPAT3, MLYCD, and SLC27A6 were significantly associated with survival to hospital discharge.

CONCLUSIONS

Our findings indicate that variants in genes important in fatty acid metabolism are associated with SCA survival in this population.

Abdominal surgical incision induces remote preconditioning of trauma (RPCT) via activation of bradykinin receptors (BK2R) and the cytochrome P450 epoxygenase pathway in canine hearts

OBJECTIVE

Recently, a novel observation was made in which nonischemic trauma at a site remote from the heart produced by a transverse abdominal incision resulted in a marked reduction of infarct size (IS) in the mouse heart via activation of sensory nerve fibers in the skin and subsequent activation of bradykinin 2 receptors (BK2R). This phenomenon was termed remote preconditioning of trauma (RPCT). Since RPCT may have potential clinical implications we attempted to confirm these findings in a large animal model, the dog. The epoxyeicosatrienoic acids (EETs) have also recently been shown to be antinociceptive and have been shown to mimic ischemic preconditioning (IPC) and postconditioning (POC) in dogs, therefore, we tested the role of the EETs in RPCT.

METHODS

Anesthetized adult mongrel dogs of either sex were subjected to 60 min of left anterior descending (LAD) coronary artery occlusion followed by 3 h of reperfusion. In all groups except the controls (no slit), a transverse slit (9 cm) was applied to the abdominal wall of the dog being careful to only slit the skin. Subsequently, 15 min after the slit the heart was subjected to the ischemia/reperfusion protocol.

RESULTS

In the control dogs, the IS as a percent of the area at risk (AAR) was 22.5 ± 2.4%, whereas in the dogs subjected to the slit alone the IS/AAR was reduced to 9.2 ± 1.2% (*P < 0.01). The BR2R blocker, HOE 140 (50 ug/kg, iv) given 10 min prior to the slit, completely abolished the protective effects of RCPT as did pretreatment with 14,15-EEZE, a putative EET receptor blocker or pretreatment with the selective EET synthesis inhibitor, MSPPOH.

CONCLUSIONS

These results suggest that BK and the EETs share cardioprotective properties in a large animal model of RPCT.

Factors mediating remote preconditioning of trauma in the rat heart: central role of the cytochrome p450 epoxygenase pathway in mediating infarct size reduction

The present study further identified factors involved in the cardioprotective phenomenon of remote preconditioning of trauma (RPCT) with special emphasis on the role of the epoxyeicosatrienoic acids (EETs) in mediating this phenomenon. Remote preconditioning of trauma was produced by an abdominal incision only through the skin. Subsequently, all rats were subjected to 30 minutes of left coronary artery occlusion followed by 2 hours of reperfusion and the infarct size was determined. Remote preconditioning of trauma produced a reduction in infarct size expressed as a percentage of the area at risk from 63.0% ± 1.1% to 44.7% ± 1.4%; P < .01 versus control. To test the 3 major triggers of classical preconditioning in mediating RPCT, blockers of the bradykinin B2 receptor (B2BK), (S)-4-[2-[Bis(cyclohexylamino)methyleneamino]-3-(2-naphthalenyl)-1-oxopropylamino]benzyl tributyl phosphonium (WIN 64338, 1 mg/kg, iv), or HOE 140 (50 μg/kg, iv), the nonselective opioid receptor blocker, naloxone (3 mg/kg, iv), or the adenosine A1 receptor blocker, 8-Cyclopentyl-1,3-dipropylxanthine (DPCPX, 1 mg/kg, iv) were administered 10 minutes prior to RPCT. Only the 2 B2BK selective antagonists blocked RPCT (60.2% ± 1.1%, WIN 64338; 62.3% ± 2.0%, HOE 140). To test EETs in RPCT, we administered the EET receptor antagonist 14,15-Epoxyeicosa-5(Z)-enoic acid (14,15-EEZE, 2.5 mg/kg, iv) or the EET synthesis inhibitor, N-(Methylsulfonyl)-2-(2-propynyloxy)-benzenehexanamide (MSPPOH, 3.0 mg/kg, iv) 10 minutes prior to RPCT. In both groups, the EET antagonists completely blocked RPCT (62.0% ± 0.8%, 14,15-EEZE; 61.8% ± 1.0%, MSPPOH). The EET antagonists also blocked the effect of B2BK activation. We also determined whether the sarcolemmal K(ATP) or the mitochondrial K(ATP) channel mediate RPCT by pretreating rats with 1-[5-[2-(5-Chloro-o-anisamido)ethyl]-2-methoxyphenyl]sulfonyl-3 methylthiourea, sodium salt (HMR 1098) or 5-hydroxydecanoic acid (5-HD), respectively. Interestingly, 5-HD blocked RPCT (64.7% ± 1.3%), whereas, HMR 1098 did not (50.3% ± 1.3%). The 2 EET antagonists completely blocked capsaicin-induced cardioprotection. These results clearly suggest that EETs mediate RPCT-, bradykinin- and capsaicin-induced cardioprotection in rat hearts.

CYP-eicosanoids--a new link between omega-3 fatty acids and cardiac disease?

Fish oil omega-3 fatty acids such as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) protect against arrhythmia and sudden cardiac death by largely unknown mechanisms. Recent in vitro and in vivo studies demonstrate that arachidonic acid (AA) metabolizing cytochrome P450-(CYP) enzymes accept EPA and DHA as efficient alternative substrates. Dietary EPA/DHA supplementation causes a profound shift of the cardiac CYP-eicosanoid profile from AA- to EPA- and DHA-derived epoxy- and hydroxy-metabolites. CYP2J2 and other CYP epoxygenases preferentially epoxidize the ω-3 double bond of EPA and DHA. The corresponding metabolites, 17,18-epoxy-EPA and 19,20-epoxy-DHA, dominate the CYP-eicosanoid profile of the rat heart after EPA/DHA supplementation. The (ω-3)-epoxyeicosanoids show highly potent antiarrhythmic properties in neonatal cardiomyocytes, suggesting that these metabolites may specifically contribute to the cardioprotective effects of omega-3 fatty acids. This hypothesis is discussed in the context of recent findings that revealed CYP-eicosanoid mediated mechanisms in cardiac ischemia-reperfusion injury and maladaptive cardiac hypertrophy.

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.

Epoxyeicosatrienoic acids are endogenous regulators of vasoactive neuropeptide release from trigeminal ganglion neurons

Epoxyeicosatrienoic acids (EETs) are bioactive eicosanoids produced from arachidonic acid by cytochrome P450 epoxygenases. We previously described the expression of cytochrome P450-2J epoxygenase in rat trigeminal ganglion neurons and that EETs signaling is involved in cerebrovascular dilation resulting from perivascular nerve stimulation. In this study, we evaluate the presence of the EETs signaling pathway in trigeminal ganglion neurons and their role in modulating the release of calcitonin gene-related peptide (CGRP) by trigeminal ganglion neurons. Liquid chromatography tandem mass spectrometry identified the presence of each of the four EETs regio-isomers within primary trigeminal ganglion neurons. Stimulation for 1 h with the transient receptor potential vanilloid-1 channel agonist capsaicin (100 nmol/L) or depolarizing K(+) (60 mmol/L) increased CGRP release as measured by ELISA. Stimulation-evoked CGRP release was attenuated by 30 min pre-treatment with the EETs antagonist 14,15-epoxyeicosa-5(Z)-enoic acid (14,15-EEZE, 10 μmol/L). K(+) stimulation elevated CGRP release 2.9 ± 0.3-fold above control levels, whereas in the presence of 14,15-EEZE K(+)-evoked CGRP release was significantly reduced to 1.1 ± 0.2-fold above control release (p < 0.01 anova, n = 6). 14,15-EEZE likewise attenuated capsaicin-evoked CGRP release from trigeminal ganglion neurons (p < 0.05 anova, n = 6). Similarly, pre-treatment with the cytochrome P450 epoxygenase inhibitor attenuated stimulation-evoked CGRP release. These data demonstrate that EETs are endogenous constituents of rat trigeminal ganglion neurons and suggest that they may act as intracellular regulators of neuropeptide release, which may have important clinical implications for treatment of migraine, stroke and vasospasm after subarachnoid hemorrhage.

Evidence that the acute phase of ischemic preconditioning does not require signaling by the A 2B adenosine receptor

Ischemic preconditioning (IPC) is a protective phenomenon in which brief ischemia renders the myocardium resistant to subsequent ischemic insults. Here, we used A(2B)AR gene knock-out (A(2B)KO)/β-galactosidase reporter gene knock-in mice and the A(2B)AR antagonist ATL-801 to investigate the potential involvement of the A(2B)AR in IPC, focusing on the acute phase of protection. Cardioprotection provided by acute IPC elicited by two 3-min occlusion/3-min reperfusion cycles was readily apparent in an isolated, Langendorff-perfused mouse heart model in studies using hearts from A(2B)KO mice. IPC equivalently improved the recovery of contractile function following 20 min of global ischemia and 45 min of reperfusion in both WT and A(2B)KO hearts by ~30-40%, and equivalently decreased the release of cardiac troponin I during the reperfusion period (from 5969 ± 925 to 1595 ± 674 ng/g and 4376 ± 739 to 2278 ± 462 ng/g using WT and A(2B)KO hearts, respectively). Similarly, the infarct size-reducing capacity of acute IPC in an in vivo model of infarction was fully manifested in experiments using A(2B)KO mice, as well as in experiments using rats pretreated with ATL-801. We did observe, however, a marked reduction in infarct size in rats following administration of the selective A(2B)AR agonist BAY 60-6583 (~25% reduction at a dose of 1.0mg/kg). While supportive of its concept as a cardioprotective receptor, these experiments indicate that the mechanism of the early phase of IPC is not dependent on signaling by the A(2B)AR. We present the idea that the A(2B)AR may contribute to the later stages of IPC dependent on the induction of stress-responsive genes.

Evidence for a role of opioids in epoxyeicosatrienoic acid-induced cardioprotection in rat hearts

We previously demonstrated that several epoxyeicosatrienoic acids (EETs) produce reductions in myocardial infarct size in rats and dogs. Since a recent study demonstrated the release of opioids in mediating the antinociceptive effect of 14,15-EET, we hypothesized that endogenous opioids may also be involved in mediating the cardioprotective effect of the EETs. To test this hypothesis, we used an in vivo rat model of infarction and a rat Langendorff model. In the infarct model, hearts were subjected to 30 min occlusion of the left coronary artery and 2 h reperfusion. Animals were treated with 11,12-EET or 14,15-EET (2.5 mg/kg) alone 15 min before occlusion or with opioid antagonists [naloxone, naltrindole, nor-binaltorphimine (nor-BNI), and d-Phe-Cys-Tyr-d-Trp-Om-Thr-Pen-Thr-NH(2) (CTOP), a nonselective, a selective delta, a selective kappa, and a selective mu receptor antagonist, respectively] 10 min before EET administration. In four separate groups, antiserum to Met- and Leu-enkephalin and dynorphin-A-(1-17) was administered 50 min before the 11,12-EET administration. Infarct size expressed as a percent of the area at risk (IS/AAR) was 63.5 + or - 1.2, 45.3 + or - 1.0, and 40.9 + or - 1.2% for control, 11,12-EET, and 14,15-EET, respectively. The protective effects of 11,12-EET were abolished by pretreatment with either naloxone (60.5 + or - 1.8%), naltrindole (60.8 + or - 1.0%), nor-BNI (62.3 + or - 2.8%), or Met-enkephalin antiserum (63.2 + or - 1.7%) but not CTOP (42.0 + or - 3.0%). In isolated heart experiments, 11,12-EET was administered to the perfusate 15 min before 20 min global ischemia followed by 45 min reperfusion in control hearts or in those pretreated with pertussis toxin (48 h). 11,12-EET increased the recovery of left ventricular developed pressure from 33 + or - 1 to 45 + or - 6% (P < 0.05) and reduced IS/AAR from 37 + or - 4 to 20 + or - 3% (P < 0.05). Both pertussis toxin and naloxone abolished these beneficial effects of 11,12-EET. Taken together, these results suggest that the major cardioprotective effects of the EETs depend on activation of a G(i/o) protein-coupled delta- and/or kappa-opioid receptor.

Review article: epoxyeicosatrienoic acids: novel mediators of cardioprotection

Recent evidence from a number of in vitro and in vivo studies in isolated cells and animal models has suggested that the cytochrome P450 (CYP450) pathway of arachidonic acid (AA) metabolism produces potent cardioprotective metabolites that markedly reduce reversible (myocardial stunning) and irreversible (infarct size [IS]) injury in the ischemic/reperfused heart. The major players in this protective response appear to be the AA metabolites including the regioisomers of 5,6-, 8,9-, 11,12-, and 14,15-epoxyeicosatrienoic acids (EETs). The present review article will discuss the beneficial effects of the EETs on myocardial stunning and IS reduction and consider some of the signaling pathways and cellular mechanisms by which the EETs produce their beneficial effects and the possible therapeutic benefits that may result from activation of this pathway. The results discussed in this review are taken from experiments obtained from 3 diverse species in different laboratories: the mouse, rat, and dog, in which the results were nearly identical qualitatively and quantitatively, suggesting that these findings are likely to be extrapolated to man as well.

Epoxyeicosatrienoic acid analogs and vascular function

Arachidonic acid metabolites, eicosanoids, are key contributors to vascular function and improper eicosanoid regulation contributes to the progression of cardiovascular diseases. Epoxyeicosatrienoic acids (EETs) are synthesized from arachidonic acid by epoxygenase enzymes to four regioisomers, 5,6-EET, 8,9-EET, 11,12-EET, and 14,15-EET. These EETs have interesting beneficial effects like vasodilation, anti-inflammation, and anti-platelet aggregation that could combat cardiovascular diseases. There is mounting evidence that each regioisomeric EET may have unique vascular effects and that the contribution of individual EETs to vascular function differs from organ to organ. Over the past decade EET analogs and antagonists have been synthesized to determine EET structure function relationships and define the contribution of each regioisomeric EET. A number of studies have demonstrated that EET analogs induce vasodilation, lower blood pressure and decrease inflammation. EET antagonists have also been used to demonstrate that endogenous EETs contribute importantly to cardiovascular function. This review will discuss EET synthesis, regulation and physiological roles in the cardiovascular system. Next we will focus on the development of EET analogs and what has been learned about their contribution to vascular function. Finally, the development of EET antagonists and how these have been utilized to determine the cardiovascular actions of endogenous epoxides will be discussed. Overall, this review will highlight the important knowledge garnered by the development of EET analogs and their possible value in the treatment of cardiovascular diseases.