Cytochrome P450 epoxygenase metabolite, 14,15-EET, protects against isoproterenol-induced cellular hypertrophy in H9c2 rat cell line

We have previously shown that isoproterenol-induced cardiac hypertrophy causes significant changes to cytochromes P450 (CYPs) and soluble epoxide hydrolase (sEH) gene expression. Therefore, in this study, we examined the effect of isoproterenol in H9c2 cells, and the protective effects of 14,15-EET against isoproterenol-induced cellular hypertrophy. Isoproterenol was incubated with H9c2 cells for 24 and 48 h. To determine the protective effects of 14,15-EET, H9c2 cells were incubated with isoproterenol in the absence and presence of 14,15-EET. Thereafter, the expression of hypertrophic markers and different CYP genes were determined by real time-PCR. Our results demonstrated that isoproterenol significantly increased the expression of hypertrophic marker, atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP), parallel to a significant increase in cell surface area. Also, isoproterenol increased the mRNA expression of CYP1A1, CYP1B1, CYP2J3, CYP4F4 and CYP4F5, as well as the gene encoding sEH, EPHX2. On other hand, 14,15-EET significantly attenuated the isoproterenol-mediated induction of ANP, BNP, CYP1A1, CYP2J3, CYP4F4, CYP4F5 and EPHX2. Moreover 14,15-EET prevented the isoproterenol-mediated increase in cell surface area. Interestingly, 20-hydroxyeicosatetraenoic acid (20-HETE) treatment caused similar effects to that of isoproterenol treatment and induced cellular hypertrophy in H9c2 cells. In conclusion, isoproterenol induces cellular hypertrophy and modulates the expression of CYPs and EPHX2 in H9c2 cells. Furthermore, 14,15-EET exerts a protective effect against isoproterenol-induced cellular hypertrophy whereas, 20-HETE induced cellular hypertrophy in H9c2 cells.

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.

Genetic disruption of soluble epoxide hydrolase is protective against streptozotocin-induced diabetic nephropathy

Cytochrome P-450 (CYP) epoxygenases metabolize arachidonic acid into epoxyeicosatrienoic acids (EETs), which play important roles in regulating cardiovascular functions. The anti-inflammatory, antiapoptotic, proangiogenic, and antihypertensive properties of EETs suggest a beneficial role for EETs in diabetic nephropathy. Endogenous EET levels are maintained by a balance between synthesis by CYP epoxygenases and hydrolysis by epoxide hydrolases into physiologically less active dihydroxyeicosatrienoic acids. Genetic disruption of soluble epoxide hydrolase (sEH/EPHX2) results in increased EET levels through decreased hydrolysis. This study investigated the effects of sEH gene disruption on diabetic nephropathy in streptozotocin-induced diabetic mice. Streptozotocin-induced diabetic manifestations were attenuated in sEH-deficient mice relative to wild-type controls, with significantly decreased levels of Hb A(1c), creatinine, and blood urea nitrogen and urinary microalbumin excretion. The sEH-deficient diabetic mice also had decreased renal tubular apoptosis that coincided with increased levels of antiapoptotic Bcl-2 and Bcl-xl, and decreased levels of the proapoptotic Bax. These effects were associated with activation of the PI3K-Akt-NOS3 and AMPK signaling cascades. sEH gene inhibition and exogenous EETs significantly protected HK-2 cells from TNFα-induced apoptosis in vitro. These findings highlight the beneficial role of the CYP epoxygenase-EETs-sEH system in the pathogenesis of diabetic nephropathy and suggest that the sEH inhibitors available may be potential therapeutic agents for this condition.

8,9-Epoxyeicosatrienoic acid inhibits antibody production of B lymphocytes in mice

Epoxyeicosatrienoic acids (EETs), synthesized from arachidonic acid by cytochrome P450 epoxygenases, are converted to dihydroxyeicosatrienoic acids by soluble epoxide hydrolase. EETs exert anti-inflammatory effects. However, the effect of EETs on humoral immunity is poorly understood. The present study is to investigate the potential role of EETs on B cell function and mechanisms. We examined the role of EETs on antibody production of splenic B cells from C57BL/6 and apolipoprotein E-deficient (ApoE−/−) mice by means of ELISA. Of the 4 EET regioisomers, 8,9-EET decreased basal and activation-induced B cell antibody secretion. As well, 8,9-EET significantly inhibited B-cell proliferation and survival, plasma cell differentiation and class-switch recombination. Western blot analysis revealed that lipopolysaccharide-induced nuclear translocation of NF-κB could be attenuated by 8,9-EET. Furthermore, germinal center formation was impaired by 8,9-EET in mice in vivo. 8,9-EET may inhibit B-cell function in vitro and in vivo, which suggests a new therapeutic strategy for diseases with excess B cell activation.

Inhibitory effect of 5,8,11-eicosatrienoic acid on angiogenesis

INTRODUCTION

Cartilage contains high levels of n-9 eicosatrienoic acid (20:3n-9) but no blood vessels. 20:3n-9 might inhibit angiogenesis.

MATERIALS AND METHODS

Angiogenesis was measured in human umbilical vein endothelial cells and diploid fibroblasts. Co-culture was performed with vascular endothelial growth factor-A (VEGF-A, 10 ng/mL) and fatty acids (0.1-10 μmol/L). After 10 days of incubation and immunostaining for endothelial cells, vessel areas were calculated with image analyser software.

RESULTS

Addition of 20:3n-9 and n-3 eicosatrienoic acid (20:3n-3) dose dependently inhibited VEGF-A-stimulated angiogenesis (more than the positive control suramin). Arachidonic, eicosapentaenoic, dihomo-γ-linolenic (20:3n-6) and oleic acids did not affect VEGF-A-stimulated angiogenesis even at 10 μmol/L. Arachidonic and dihomo-γ-linolenic acids enhanced angiogenesis without VEGF-A.

DISCUSSION AND CONCLUSIONS

We suggest that the presence of 20:3n-9 in cartilage may be related to its vessel-free status and that 20:3n-9 may be useful for the treatment of disorders with excessive vasculature.

ACKNOWLEDGEMENTS

This work was partly supported by Polyene Project, Inc.

A soluble epoxide hydrolase inhibitor--8-HUDE increases pulmonary vasoconstriction through inhibition of K(ATP) channels

Epoxyeicosatrienoic acids (EETs), cytochrome P450-derived metabolites of arachidonic acid, are endogenously produced epoxides that act as substrates for the soluble epoxide hydrolase (sEH). Recent studies indicate that EETs increase the tension of rat pulmonary arteries (PAs), and inhibition of sEH augments hypoxic pulmonary vasoconstriction. However, the mechanisms underlying the proconstrictive effects of sEH inhibitors in pulmonary artery smooth muscle cells (PASMCs) are unclear. In the present study, we used a sEH inhibitor, 12-(3-hexylureido) dodec-8-enoic acid (8-HUDE), to examine the ionic mechanisms underlying the constriction of PAs. 8-HUDE increased the tension of rat PAs to 145% baseline in a manner which was effectively eliminated by 10 μmol/L glibenclamide, an inhibitor of ATP-sensitive K(+) (K(ATP)) channels. Whole cell currents of HEK cells transfected with Kir6.1 or SUR2B were activated by K(ATP) channel opener pinacidil, inhibited by K(ATP) channel inhibitor glibenclamide or inhibited by 8-HUDE in a concentration-dependent manner with an IC50 value of 40 uM. In addition, 8-HUDE inhibited the expression of Kir6.1 and SUR2B at both mRNA and protein level in rat PASMCs. These observations suggest that 8-HUDE exerts acute effects on K(ATP) channel activity as well as subacute effects through decreased channel expression, and these effects are, at least in part, via the Kir6.1/SUR2B channel.

11,12-EET increases porto-sinusoidal resistance and may play a role in endothelial dysfunction of portal hypertension

CYP450-dependent epoxyeicosatrienoic acids (EETs) are potent arterial vasodilators, while 20-hydroxyeicosatatraenoic acid (20-HETE) is a vasoconstrictor. We evaluated their role in the control of portal circulation in normal and cirrhotic (CCl(4) induced) isolated perfused rat liver. Phenylephrine (PE) and endothelin-1 (ET-1) increased portal perfusion pressure, as did arachidonic acid (AA), 20-HETE, and 11,12-EET. Inhibition of 20-HETE with 12,12-dibromododecenoic acid (DBDD) did not affect basal pressure nor the responses to PE, ET-1, or AA. However, inhibition of epoxygenase with miconazole caused a significant reduction in the response to ET-1 and to AA, without affecting neither basal pressure nor the response to PE. Hepatic vein EETs concentration increased in response to ET-1, and was increased in cirrhotic, compared to control, livers. 20HETE levels were non-measurable. Miconazole decreased portal perfusion pressure in cirrhotic livers. In conclusion, 20HETE and EETs increase portal resistance; EETs, but not 20-HETE, mediate in part the pressure response to ET-1 in the portal circulation and may be involved in pathophysiology of portal hypertension.

Uptake of dihomo-gamma-linolenic acid by murine macrophages increases series-1 prostaglandin release following lipopolysaccharide treatment

Administration of dihomo-gamma-linolenic acid is useful for atopic dermatitis and atherosclerosis in mice; however, the metabolites of dihomo-gamma-linolenic acid have been little studied. We employed a method which enabled simultaneous analysis of nine prostaglandins using liquid chromatography-tandem mass spectrometry, and determined the concentrations of prostaglandins in the supernatants of cultures of mouse peritoneal macrophages stimulated with lipopolysaccharide after pre-incubation with dihomo-gamma-linolenic acid, arachidonic acid, or eicosapentaenoic acid. Accumulated prostaglandin concentrations from mouse macrophages with dihomo-gamma-linolenic acid uptake increased in a dihomo-gamma-linolenic acid concentration-dependent fashion. These increases were mainly due to prostaglandin D(1) and prostaglandin E(1). The order of accumulated prostaglandin concentrations was dihomo-gamma-linolenic acid>arachidonic acid>eicosapentaenoic acid in supernatants with the same concentration of polyunsaturated fatty acid. Since mouse macrophages can clearly produce series-1 prostaglandins, they must be formed in vivo. These findings suggest that the effects of dihomo-gamma-linolenic acid on diseases may be due to series-1 prostaglandins.

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.

Detection of EETs and HETE-generating cytochrome P-450 enzymes and the effects of their metabolites on myometrial and vascular function

Cytochrome P-450 (CYP450) enzymes of the CYP2 and -4 family in humans metabolize arachidonic acid to generate bioactive epoxyeicosatrienenoic acids (EETs) and hydroxyeicosatetrenoic acids (HETEs). We report significantly higher levels of CYP 2J2 protein expression following the onset of labor (n = 6, P < 0.05), implying increased EET-generating capacity within the uterus. Myometrial relaxation to 8,9-EET and 5,6-EET was observed, with the latter being inhibited by preincubation with 1 muM paxilline and is supported by whole cell recordings showing a modest effect of 5,6-EET on myometrial outward-current density (n = 4, P < 0.05). Only 5,6-EET of the EETs tested affected vascular reactivity (n = 6). Both 12- and 20-HETE (n = 5-6) caused vasoconstriction of partially depolarized blood vessels, with glibenclamide (n = 5) enhancing the effect of 12-HETE alone. Our findings signify a role for CYP2C9/19, -2J2, and -4A11/22 in late pregnancy, possibly related to the synthesis of lipid metabolites and downstream effects on vascular remodeling in the term pregnant uterus. The presence of CYP4A11/22 and their resultant procontractile metabolites could argue either a role in the control and initiation of labor and/or modification of the vascular delivery system to influence blood flow to the laboring uterus. The differential effects of the EETs and HETEs in the pregnant human uterus identify the CYP pathway as a novel modulator of myometrial and vascular physiology during late pregnancy.

[Promotive effects of epoxyeicosatrienoic acids (EETs) on proliferation of tumor cells]

BACKGROUND & OBJECTIVE

Epoxyeicosatrienoic acids (EETs) are generated from arachidomic acid by cytochrome P450(CYP). Previous studies revealed very strong and selective expression of CYP expoxygenase in human cancer tissues, but almost none in adjacent normal tissues. This study was to investigate the promotive effect of EETs on proliferation of tumor cells and the possible mechanisms.

METHODS

Four tumor cell lines, Tca-8113, A549, Ncl-H446 and HepG2, were treated with different concentrations of EETs (8,9-EET, 11,12-EET and 14,15-EET) for 12, 24, 48 and 72 h, respectively. Cell proliferation was measured using the MTT assay. The effect of exogenous EETs on cell cycle of Tca-8113 cells was assessed by flow cytometry. Signal transduction inhibitors of PI3K (LY294002), MAPKK (PD98059), MAPK (apigenin) and PKC (H7) were used to block EETs-induced cell proliferation. Expressions of the total protein and phosphorylated ERK1/2 and Akt were determined by Western blot.

RESULTS

EETs promoted proliferation of tumor cells compared with the control and vehicle group in a dose-and time-dependent manner (P<0.01). Incubation of tumor cells with EETs markedly increased the cell number at S/G2-M phase. The percentages of Tca-8113 cells at S and G2-M phases were (49.7+/-7.5%) vs. (17.2+/-9.7%) (P<0.01) and (21.0+/-5.3%) vs. (4.9+/-7.3%), respectively(P<0.01) with and without the treatment of 11,12-EET. EETs incubation significantly enhanced phosphorylation of MARK as well as PI3K/Akt in tumor cells. LY294002, PD98059, apigenine and H7 reduced the stimulative effect of EETs on cell proliferation.

CONCLUSION

EETs possess the promotive effect on proliferation of tumor cells via activation of MAPK and PI3K/Akt signal pathways.

Effects of epoxyeicosatrienoic acids on levels of eNOS phosphorylation and relevant signaling transduction pathways involved

Endothelial nitric oxide synthase (eNOS) is a key enzyme responsible for the regulation of vascular homeostasis. Many humor factors and mechanical forces can affect eNOS activity via phosphorylation modification but the mechanisms involved vary with stimuli applied. We have demonstrated that cytochrome P450 (CYP) epoxygenase-dependent metabolites of arachidonic acid, epoxyeicosatrienoic acids (EETs), can robustly up-regulate eNOS expression and its activity, however the relevant signaling pathways responsible for activity regulation are not well known. In this study, we explored the role of PI3 kinase (PI3K)/protein kinase B (Akt) signaling pathway in eNOS expression and its phosphorylation in response to EETs via direct addition of EETs into cultured bovine aorta endothelial cells (BAECs) and recombinant adeno-associated virus-mediated transfection of CYP epoxygenase genes CYPF87V and CYP2C11 to produce endogenous EETs followed by co-treatment with PI3K or Akt inhibitor. Results show that both exogenous and endogenous EETs could remarkably enhance eNOS expression and its phosphorylation at Ser1179 and Thr497 residues; PI3K inhibitor LY294002 could inhibit EETs-induced increase in eNOS-Ser(P)1179 but had no effect on the change of eNOS-Thr(P)497, while Akt inhibitor could attenuate the increase in phosphor-eNOS at both residues; both of the two inhibitors could block EETs-enhanced eNOS expression. These results lead to conclusions: (i) EETs-mediated regulation of eNOS activity may be related with the changes of phosphorylation level at eNOS-Ser1179 via P13K/Akt and eNOS-Thr497 via Akt; (ii) PI3K/Akt signaling pathway is involved in the up-regulation of eNOS expression by EETs.

Cytochrome P450 2C9-induced angiogenesis is dependent on EphB4

OBJECTIVE

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

METHODS AND RESULTS

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

CONCLUSIONS

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

[Protective effects of 11,12-epoxyeicosatrienoic acid preconditioning and postconditioning on myocardial ischemia/reperfusion injury in rats]

To explore the effects of 11,12-epoxyeicosatrienoic acid (11,12-EET) preconditioning and postconditioning on myocardial ischemia/reperfusion (IR) injury in rats, the IR injury model was built by stopping perfusion for 40 min followed by reperfusion for 30 min, and the changes of mitochondrial functions, myocardial metabolism and function were measured. Langendorff-perfused isolated rat hearts were divided into 4 groups: control group, persistently perfused with Krebs-Henseleit (K-H) fluid for 100 min; IR group, stopped perfusion for 40 min followed by reperfusion for 30 min; Pre-EET group, preconditioned with 6.24×10(-9) mol/L 11,12-EET for 5 min twice before subjected to ischemia; Post-EET group, postconditioned with 6.24×10(-9) mol/L 11,12-EET for 30 s twice before reperfusion. The computer-based electrophysiological recording system was used to measure the changes of maximal rate of the pressure increase in contract phase (+dp/dt(max)), maximal rate of the pressure decrease in diastole phase of heart (-dp/dt(max)), left ventricular end-diastolic pressure (LVEDP) and difference of left ventricular pressure (DLVP). The activities of lactate dehydrogenase (LDH) in effluent, Ca(2+)-ATPase, Na(+)-K(+)-ATPase and succinate dehydrogenase (SDH) in mitochondria were measured with colorimetry method; superoxide dismutase (SOD) activity was measured with hydroxylamine method and malondialdehyde (MDA) content in myocardial tissues was measured with TBA method. The results showed that: (1) Compared with that in the control group, the myocardial functions, the values of SOD, SDH and Na(+)-K(+)-ATPase were decreased in IR group (P<0.05); the values of LDH, MDA and Ca(2+)-ATPase were increased (P<0.05) in IR group. (2) Compared with that in IR group, the values of SDH and Na(+)-K(+)-ATPase were increased (P<0.05) and the value of Ca(2+)-ATPase was decreased (P<0.05) in both Pre-EET and Post-EET groups. But no significant differences were detected between Pre-EET and Post-EET groups. (3) Compared with IR treatment, both 11,12-EET preconditioning and postconditioning caused significant decreases in MDA content and leakage of LDH, amendment of heart functions and increases in SOD activity (P<0.05). But there were no significant differences between 11,12-EET preconditioning and postconditioning. These results indicate that 11,12-EET preconditioning and postconditioning can protect myocardium from IR injury by improving mitochondrial functions, up-regulating the activities of Na(+)-K(+)-ATPase and SDH, and down-regulating the activity of Ca(2+)-ATPase in mitochondria. Moreover, 11,12-EET preconditioning and postconditioning also elevate the activity of SOD and reduce the content of MDA, suggesting that 11,12-EET can depress the oxidative stress in IR rat heart.

[Effects of 11, 12-epoxyeicosatrienoic acid preconditioning and postconditioning on Ca(2+)- handling proteins in myocardial ischemia/reperfusion injury in rats]

OBJECTIVE

To investigate the effects of 11, 12-epoxyeicosatrienoic acid (11, 12-EET) preconditioning and postconditioning on Ca(2+)-handling proteins in myocardial ischemia/reperfusion (IR) injury in rats and reveal the effects and mechanism of 11, 12-EET on cardioprotection. METHODS The IR injury model was built by stopping perfusion for 40 minutes followed by reperfusion for 30 minutes. The isolated Langendorff-perfused rat hearts were divided into 4 groups: control group, IR group, EET preconditioning (Pre-EET) group and EET postconditioning (Post-EET) group. The computer-based electrophysiological recorder system was used to measure the changes of the maximal rate of pressure increased in the contraction phase (+dp/dt(max)), the maximal rate of pressure decreased in the diastole phase (-dp/dt(max)), the left ventricular end diastolic pressure (LVEDP) and the difference of left ventricular pressure (delta LVP). The activity of Ca(2+)-ATPase in sarcoplasmic reticulum was measured with colorimetric method. Reverse transcription-polymerase chain reaction was used to assess the gene expression of C(a2+)-handling protein [sarcoplasic reticulum Ca(2+)-ATPase (SERCA), phospholamban (PLB), ryanodine receptor type 2 (RyR,), and 1, 4, 5-trisphosphate inositol receptor type 2 (IP3 R2) ] mRNAs level.

RESULTS

Compared with IR group, the myocardial functions, the value of Ca(2+)-ATPase, and the expressions of IP3 R2 mRNA were significantly increased and the expression of PLB mRNA was significantly decreased in both Pre-EET group and Post-EET group (P < 0.05, P < 0.01). And the expression of SERCA mRNA was significantly increased in Pre-EET group (P < 0. 05). However, no significant differences were detected between Pre-EET and Post-EET groups. Moreover, the expression of RyR2 mRNA was not significantly different among all groups.

CONCLUSIONS

11, 12-EET preconditioning and post-conditioning can protect myocardium from IR injury by elevating the activity of Ca(2+)-ATPase in sarcoplasmic reticulum, up-regulating the expression of IP3 R2 mRNA, and down-regulating the expression of PLB mRNA. Moreover, up-regulating the expression of SERCA mRNA maybe one of mechanisms of 11, 12-EET preconditioning on cardio protection against IR injury.

Epoxyeicosatrienoic acids regulate Trp channel dependent Ca2+ signaling and hyperpolarization in endothelial cells

OBJECTIVE

An initial step in endothelium-derived hyperpolarizing factor-mediated responses is endothelial cell hyperpolarization. Here we address the mechanisms by which cytochrome P450 (CYP)-derived epoxyeicosatrienoic acids (EETs) contribute to this effect in native and cultured endothelial cells.

METHODS AND RESULTS

In native CYP2C-expressing endothelial cells, bradykinin elicited a Ca(2+) influx that was potentiated by the soluble epoxide hydrolase inhibitor, 1-adamantyl-3-cyclohexylurea (ACU), and attenuated by CYP inhibition. Similar effects were observed in cultured endothelial cells overexpressing CYP2C9, but not in CYP2C9-deficient cells, and were prevented by the EET antagonist 14,15-epoxyeicosa-5(Z)-enoic acid as well as by the cAMP antagonist, Rp-cAMPS. The effects on Ca(2+) were mirrored by prolongation of the bradykinin-induced hyperpolarization. Ruthenium red and the combination of charybdotoxin and apamin prevented the latter effect, suggesting that Trp channel activation increases Ca(2+) influx and prolongs the activation of Ca(2+)-dependent K(+) (K(Ca)) channels. Indeed, overexpression of CYP2C9 enhanced the agonist-induced translocation of a TrpC6-V5 fusion protein to caveolin-1-rich areas of the endothelial cell membrane, which was prevented by Rp-cAMPS and mimicked by 11,12-EET.

CONCLUSIONS

Elevated EET levels regulate Ca(2+) influx into endothelial cells and the subsequent activation of K(Ca) channels, via a cAMP/PKA-dependent mechanism that involves the intracellular translocation of Trp channels.

EET displays anti-inflammatory effects in TNF-alpha stimulated human bronchi: putative role of CPI-17

The aim of the present study was to investigate the anti-inflammatory effects of 14,15-epoxyeicosatrienoic acid (EET) on reactivity and Ca(2+) sensitivity in TNF-alpha-stimulated human bronchi. Tension measurements performed on either control, TNF-alpha-, or TNF-alpha + EET-pretreated bronchi revealed that 100 nM 14,15-EET pretreatments significantly reduced the reactivity of TNF-alpha-pretreated tissues to contractile agonists. EET also normalized the relaxing response to isoproterenol in TNF-alpha-treated bronchi. Pretreatment with 100 nM 14,15-EET prevented TNF-alpha-induced IkappaBalpha degradation, as demonstrated by an increase in IkappaBalpha protein levels on Western blot analysis. The anti-inflammatory properties of EET were mediated by the inhibition of IkappaBalpha degradation, suggesting a lower activation of NF-kappaB. The Ca(2+) sensitivity of TNF-alpha-stimulated bronchi was also evaluated on beta-escin-permeabilized preparations. Observed mean responses demonstrated that EET pretreatments abolished Ca(2+) hypersensitivity developed by TNF-alpha-stimulated bronchial explants. Moreover, 14,15-EET significantly reduced PDBu-induced Ca(2+) sensitivity in TNF-alpha-stimulated bronchi. Western blot and RT-PCR analyses revealed that CPI-17 protein and transcript levels were increased in TNF-alpha-treated bronchi, as opposed to being decreased in the presence of 14,15-EET. This eicosanoid also reduced U-46619-induced Ca(2+) sensitivity, which is related to the activation of Rho-kinase pathway. These results were also correlated with an increase in protein staining and transcription level of p116(Rip), a RhoA inhibitory-binding protein. Altogether, these data demonstrate that 14,15-EET is a potent modulator of the hyperreactivity triggered by TNF-alpha in human airway smooth muscle cells.

Role of cytochrome P450 metabolites of arachidonic acid in regulation of corporal smooth muscle tone in diabetic and older rats

This study examined the role of cytochrome P450 (CYP) metabolites of arachidonic acid (AA) to rat corporal smooth muscle tone. 11, 12-Epoxyeicosatrienoic acid (EET) (10(-11)-10(-6 )M) produced dose-dependent relaxation of rat (control; 10 weeks old) corpus cavernosum with a pD(2) value of 8.8+/-0.2 and a maximal relaxation of 80+/-9%, whereas 20-hydroxyeicosatetraenoic (20-HETE) did not have an effect. EET-mediated relaxation of corpus cavernosum was attenuated by 71+/-3%, 55+/-2%, 53+/-5% and 84+/-3% in the presence of nitro-L-arginine methyl ester (L-NAME) (10(-4) M), an inhibitor of nitric oxide (NO) synthase, iberiotoxin (5 x 10(-8) M), an inhibitor of calcium-activated potassium (BK) channels, glibenclamide (10(-5) M), an inhibitor of ATP-sensitive K(+) channels or 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ) (10(-5) M), an inhibitor of soluble guanylyl cyclase, respectively. EET-mediated relaxation of rat corpus cavernosum was significantly less in the streptozotocin (STZ)-treated (diabetic) and 30 weeks old (older) animals compared to control. Carbachol (10(-9)-10(-4) M)-induced relaxation was significantly reduced whereas phenylephrine (PE) (10(-9)-5 x 10(-3) M)-induced contraction was significantly increased in the cavernosum strips from old and diabetic rats compared to the control. Pre-incubation of the cavernosum strips obtained from control, older or diabetic rats with N-hydroxy-N'-(4-butyl-2-methyl-phenyl)-formamidine (HET0016), a selective inhibitor of 20-HETE synthesis, or 1-cyclohexyl-3-dodecyl urea (CDU), a specific inhibitor of soluble epoxide hydrolase (sEH) resulted in a significant attenuation of PE-induced contraction and improvement in carbachol-induced relaxation. We conclude that 11, 12-EET-induced relaxation of the rat corpus cavernosum involves activation of cGMP/NO pathway as well as activation of ATP-sensitive K(+) channels and BK channels. These results also suggest that inhibition of 20-HETE production or reduction of EET inactivation may have therapeutic potential to prevent erectile dysfunction associated with diabetes and aging.

Electrophysiological properties of cardiomyocytes isolated from CYP2J2 transgenic mice

CYP2J2 is abundant in cardiac tissue and active in the biosynthesis of eicosanoids such as epoxyeicosatrienoic acids (EETs). To determine the effects of CYP2J2 and its eicosanoid products in the heart, we characterized the electrophysiology of single cardiomyocytes isolated from adult transgenic (Tr) mice with cardiac-specific overexpression of CYP2J2. CYP2J2 Tr cardiomyocytes had a shortened action potential. At 90% repolarization, the action potential duration (APD) was 30.6 +/- 3.0 ms (n = 22) in wild-type (Wt) cells and 20.2 +/- 2.3 ms (n = 19) in CYP2J2 Tr cells (p < 0.005). This shortening was probably due to enhanced maximal peak transient outward K(+) currents (I(to,peak)), which were 38.6 +/- 2.8 and 54.4 +/- 4.9 pA/pF in Wt and CYP2J2 Tr cells, respectively (p < 0.05). In contrast, the late portion of the transient outward K(+) current (I(to,280ms)), the slowly inactivating outward K(+) current (I(K,slow)), and the voltage-gated Na(+) current (I(Na)) were not significantly altered in CYP2J2 Tr cells. N-Methylsulphonyl-6-(2-proparglyloxy-phenyl)hexanamide (MS-PPOH), a specific inhibitor of EET biosynthesis, significantly reduced I(to,peak) and increased APD in CYP2J2 Tr cardiomyocytes but not in Wt cells. Intracellular dialysis with a monoclonal antibody against CYP2J2 also significantly reduced I(to,peak) and increased APD in CYP2J2 Tr cardiomyocytes. Addition of 11,12-EET or 8-bromo-cAMP significantly reversed the MS-PPOH- or monoclonal antibody-induced changes in I(to,peak) and APD in CYP2J2 Tr cells. Together, our data demonstrate that shortening of the action potential in CYP2J2 Tr cardiomyocytes is associated with enhanced I(to,peak) via an EET-dependent, cAMP-mediated mechanism.

Contribution of epoxyeicosatrienoic acids to flow-induced dilation in arteries of male ERalpha knockout mice: role of aromatase

We studied the roles of estrogen receptors (ER) and aromatase in the mediation of flow-induced dilation (FID) in isolated arteries of male ERalpha-knockout (ERalpha-KO) and wild-type (WT) mice. FID was comparable between gracilis arteries of WT and ERalpha-KO mice. In WT arteries, inhibition of NO and prostaglandins eliminated FID. In ERalpha-KO arteries, N(omega)-nitro-L-arginine methyl ester (L-NAME) inhibited FID by approximately 26%, whereas indomethacin inhibited dilations by approximately 50%. The remaining portion of the dilation was abolished by additional administration of 6-(2-proparglyoxyphenyl)hexanoic acid (PPOH) or iberiotoxin, inhibitors of epoxyeicosatrienoic acid (EET) synthesis and large-conductance potassium channels, respectively. By using an electrophysiological technique, we found that, in the presence of 10 dyne/cm(2) shear stress, perfusate passing through donor vessels isolated from gracilis muscle of ERalpha-KO mice subjected to L-NAME and indomethacin elicited smooth muscle hyperpolarization and a dilator response of endothelium-denuded detector vessels. These responses were prevented by the presence of iberiotoxin in detector or PPOH in donor vessels. Gas chromatography-mass spectrometry (GC-MS) analysis indicated a significant increase in arterial production of EETs in ERalpha-KO compared with WT mice. Western blot analysis showed a significantly reduced endothelial nitric oxide synthase expression but enhanced expressions of aromatase and ERbeta in ERalpha-KO arteries. Treatment of ERalpha-KO arteries with specific aromatase short-interfering RNA for 72 h, knocked down the aromatase mRNA and protein associated with elimination of EET-mediation of FID. Thus, FID in male ERalpha-KO arteries is maintained via an endothelium-derived hyperpolarizing factor/EET-mediated mechanism compensating for reduced NO mediation due, at least in part, to estrogen aromatized from testosterone.

Polymorphisms in the human soluble epoxide hydrolase gene EPHX2 linked to neuronal survival after ischemic injury

Single nucleotide polymorphisms (SNPs) in the human EPHX2 gene have recently been implicated in susceptibility to cardiovascular disease, including stroke. EPHX2 encodes for soluble epoxide hydrolase (sEH), an important enzyme in the metabolic breakdown of arachidonic acid-derived eicosanoids referred to as epoxyeicosatrienoic acids (EETs). We previously demonstrated that EETs are protective against ischemic cell death in culture. Therefore, we tested the hypothesis that polymorphisms in the human EPHX2 gene alter sEH enzyme activity and affect neuronal survival after ischemic injury in vitro. Human EPHX2 mutants were recreated by site-directed mutagenesis and fused downstream of TAT protein transduction domain. Western blot analysis and immunocytochemistry staining revealed high-transduction efficiency of human TAT-sEH variants in rat primary cultured cortical neurons, associated with increased metabolism of 14,15-EET to corresponding 14,15-dihydroxyeicosatrienoic acid. A human variant of sEH with Arg103Cys amino acid substitution, previously demonstrated to increase sEH enzymatic activity, was associated with increased cell death induced in cortical neurons by oxygen-glucose deprivation (OGD) and reoxygenation. In contrast, the Arg287Gln mutation was associated with reduced sEH activity and protection from OGD-induced neuronal cell death. We conclude that sequence variations in the human EPHX2 gene alter susceptibility to ischemic injury and neuronal survival in a manner linked to changes in the hydrolase activity of the enzyme. The findings suggest that human EPHX2 mutations may in part explain the genetic variability in sensitivity to ischemic brain injury and stroke outcome.

Epoxyeicosatrienoic acids affect electrolyte transport in renal tubular epithelial cells: dependence on cyclooxygenase and cell polarity

We investigated the effects of epoxyeicosatrienoic acids (EETs) on ion transport in the polarized renal distal tubular cell line, Madin-Darby canine kidney (MDCK) C7. Of the four EET regioisomers (5,6-EET, 8,9-EET, 11,12-EET, and 14,15-EET) studied, only apical, but not basolateral, application of 5,6-EET increased short-circuit current (I(sc)) with kinetics similar to those of arachidonic acid. The ion transport was blocked by preincubation with the cyclooxygenase inhibitor indomethacin or with the chloride channel blocker NPPB. Furthermore, both a Cl(-)-free bath solution and the Ca(2+) antagonist verapamil blocked 5,6-EET-induced ion transport. Although the presence of the PGE(2) receptors EP2, EP3, and EP4 was demonstrated, apically added PGE(2) was ineffective and basolaterally added PGE(2) caused a different kinetics in ion transport compared with 5,6-EET. Moreover, PGE(2) synthesis in MDCK C7 cells was unaffected by 5,6-EET treatment. GC/MS/MS analysis of cell supernatants revealed the presence of the biologically inactive 5,6-dihydroxy-PGE(1) in 5,6-EET-treated cells, but not in control cells. Indomethacin suppressed the formation of 5,6-dihydroxy-PGE(1). 5,6-Epoxy-PGE(1), the precursor of 5,6-dihydroxy-PGE(1), caused a similar ion transport as 5,6-EET. Cytochrome P-450 enzymes homolog to human CYP2C8, CYP2C9, and CYP2J2 protein were detected immunologically in the MDCK C7 cells. Our findings suggest that 5,6-EET affects Cl(-) transport in renal distal tubular cells independent of PGE(2) but by a mechanism, dependent on its conversion to 5,6-epoxy-PGE(1) by cyclooxygenase. We suggest a role for this P450 epoxygenase product in the regulation of electrolyte transport, especially as a saluretic compound acting from the luminal side of tubular cells in the mammalian kidney.

Epoxyeicosatrienoic Acid Relaxing Effects Involve Ca2+-Activated K+Channel Activation and CPI-17 Dephosphorylation in Human Bronchi

The aim of the present study was to provide a mechanistic insight into how 14,15-epoxyeicosatrienoic acid (EET) relaxes organ-cultured human bronchi. Tension measurements, performed on either fresh or 3-d-cultured bronchi, revealed that the contractile responses to 1 microM methacholine and 10 microM arachidonic acid were largely relaxed by the eicosanoid regioisomer in a concentration-dependent manner (0.01-10 microM). Pretreatments with 14,15-epoxyeicosa-5(Z)-enoic acid, a specific 14,15-EET antagonist, prevented the relaxing effect, whereas iberitoxin pretreatments (10 nM) partially abolished EET-induced relaxations. In contrast, pretreatments with 1 microM indomethacin amplified relaxations in explants and membrane hyperpolarizations triggered by 14,15-EET on airway smooth muscle cells. The relaxing responses induced by 14,15-EET were likely related to reduced Ca2+ sensitivity of the myofilaments, because free Ca2+ concentration-response curves performed on beta-escin-permeabilized cultured explants were shifted toward higher [Ca2+] (lower pCa2+ values). 14,15-EET also abolished the tonic responses induced by phorbol-ester-dybutyrate (PDBu) (a protein kinase C [PKC]-sensitizing agent), on both fresh (intact) and beta-escin-permeabilized explants. Western blot analyses, using two specific primary antibodies against CPI-17 and its PKC-dependent phosphorylated isoform (p-CPI-17), confirmed that the eicosanoid interferes with this intracellular process. These data indicate that 14,15-EET hyperpolarizes airway smooth muscle cells and relaxes precontracted human bronchi while reducing Ca2+ sensitivity of fresh and cultured explants. The intracellular effects are related to a PKC-dependent process involving a lower phosphorylation level of CPI-17.

Determinants of 4 alpha-phorbol sensitivity in transmembrane domains 3 and 4 of the cation channel TRPV4

TRPV4, a Ca(2+)-permeable member of the vanilloid subgroup of the transient receptor potential (TRP) channels, is activated by cell swelling and moderate heat (>27 degrees C) as well as by diverse chemical compounds including synthetic 4 alpha-phorbol esters, the plant extract bisandrographolide A, and endogenous epoxyeicosatrienoic acids (EETs; 5,6-EET and 8,9-EET). Previous work identified a tyrosine residue located in the first half of putative transmembrane segment 3 (TM3) as a crucial determinant for the activation of TRPV4 by its most specific agonist 4 alpha-phorbol 12,13-didecanoate (4 alpha-PDD), suggesting that 4 alpha-PDD interacts with the channel through its transmembrane segments. To obtain insight in the 4 alpha-PDD-binding site and in the mechanism of ligand-dependent TRPV4 activation, we investigated the consequences of specific point mutations in TM4 on the sensitivity of the channel to different chemical and physical stimuli. Mutations of two hydrophobic residues in the central part of TM4 (Leu(584) and Trp(586)) caused a severe reduction of the sensitivity of the channel to 4 alpha-PDD, bisandrographolide A, and heat, whereas responses to cell swelling, arachidonic acid, and 5,6-EET remained unaffected. In contrast, mutations of two residues in the C-terminal part of TM4 (Tyr(591) and Arg(594)) affected channel activation of TRPV4 by all stimuli, suggesting an involvement in channel gating rather than in interaction with agonists. Based on a comparison of the responses of WT and mutant TRPV4 to 4 alpha-PDD and different 4 alpha-phorbol esters, we conclude that the length of the fatty acid moiety determines the ligand binding affinity and propose a model for the interaction between 4 alpha-phorbol esters and the TM3/4 region of TRPV4.

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

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