Mitogenic activity and signaling mechanism of 2-(14,15- epoxyeicosatrienoyl)glycerol, a novel cytochrome p450 arachidonate metabolite

Arachidonic acid is an essential constituent of cell membranes that is esterified to the sn-2 position of glycerophospholipids and is released from selected phospholipid pools by tightly regulated phospholipase cleavage. Metabolism of the released arachidonic acid by the cytochrome P450 enzyme system (cP450) generates biologically active compounds, including epoxyeicosatrienoic acids (EETs) and hydroxyeicosatetraenoic acids. Here we report that 2-(14,15-epoxyeicosatrienoyl)glycerol (2-14,15-EG), a novel cP450 arachidonate metabolite produced in the kidney, is a potent mitogen for renal proximal tubule cells. This effect is mediated by activation of tumor necrosis factor alpha-converting enzyme (ADAM17), which cleaves membrane-bound transforming growth factor alpha (proTGF-alpha) and releases soluble TGF-alpha as a ligand that binds and activates epidermal growth factor receptor (EGFR). The present studies additionally demonstrate that the structurally related 14,15-EET stimulates release of soluble heparin-binding EGF-like growth factor as an EGFR ligand by activation of ADAM9, another member of the ADAM family. Thus, in addition to the characterization of 2-14,15-EG's mitogenic activity and signaling mechanism, our study provides the first example that two structurally related biologically active lipid mediators can activate different metalloproteinases and release different EGFR ligands in the same cell type to activate EGFR and stimulate cell proliferation.

Cyclooxygenase (COX)-1 and COX-2 participate in 5,6-epoxyeicosatrienoic acid-induced contraction of rabbit intralobar pulmonary arteries

Epoxyeicosatrienoic acids (EETs) have been reported to contract intralobar pulmonary arteries (PA) of the rabbit in a cyclooxygenase (COX)-dependent manner. In the present study, we observed that COX-1 and COX-2 isoforms were expressed in freshly isolated PA of healthy rabbits. We examined the hypothesis that both COX isoforms participate in 5,6-EET-induced contraction of rabbit intralobar PA. Selective inhibition of COX-1 with 300 nM 5-(4-chlorophenyl)-1-(4-methoxyphenyl)-3-(trifluoromethyl)-1H-pyrazole (SC-560) prevented 5,6-EET (1x10(-8)-1x10(-5) M)-induced contractions of isolated intralobar rabbit PA rings in a manner similar to that observed with the nonselective cyclooxygenase inhibitor indomethacin at 10 microM. Selective inhibition of COX-2 with either 100 nM 5-bromo-2-(4-fluorophenyl)-3-(4-methylsulfonyl) thiophene (DUP-697) or 3 microM N-(2-cyclohexyloxy-4-nitrophenyl) methanesulfonamide (NS-398) shifted the EC50 value of 5,6-EET-induced PA contraction to the right but with considerably lower efficacy than SC-560. In rabbit PA, 5,6-EET-induced contraction was primarily dependent on COX-1 activity. Differential metabolism of 5,6-EET by COX-1 and COX-2 does not explain the primary dependence of PA contraction on COX-1 activity because 5,6-EET was metabolized similarly by both COX isoforms. COX-1 and -2 were expressed primarily in PA endothelium where COX-1 expression was dense and uniform, whereas COX-2 expression was sparse and nonuniform. 5,6-EET-induced PA contraction was endothelium-dependent. These results suggest that 5,6-EET-induced contraction is primarily dependent on COX-1 activity.

Cyclic AMP-dependent modulation of cardiac L-type Ca2+ and transient outward K+ channel activities by epoxyeicosatrienoic acids

The three major enzyme systems, cyclo-oxygenase, lipoxygenase, and cytochrome P450 (P450/CYP), metabolize arachidonic acid (AA) to biologically active compounds. P450 and its associated monooxygenase activities have been identified in mammalian cardiac tissue, including humans. The four regioisomeric eicosanoids, 5,6-, 8,9-, 11,12-, and 14,15-epoxyeicosatrienoic acids (EETs) of AA metabolites derived by P450 epoxygenases have shown to possess potent biological effects in numerous tissues. In the coronary circulation the EETs are leading candidates for endothelial-derived hyperpolarizing factors that hyperpolarize vascular smooth muscle cells by opening Ca2+-activated K+ channels. Recently, the effects of the CYP pathways and their metabolites on cardiac ischemia-reperfusion injury have been evaluated in animal models. Some of these AA metabolites are cardioprotective and some are detrimental. However, EETs appear to be cardioprotective in CYP2J2 transgenic mice and in a canine ischemic model. Multiple effects of EETs on cardiac ion channels have been observed, such as activation of ATP-sensitive K+ channels and L-type Ca2+ channels in cardiomyocytes and inhibition of cardiac Na+ channels and L-type Ca2+ channels reconstructed in planar lipid bilayers. This brief review summarizes EET-induced modulation of cardiac ion channels.

Effects of 5-oxo-ETE and 14,15-EET on reactivity and Ca2+ sensitivity in guinea pig bronchi

The reactivity and Ca2+ sensitivity of fresh as well as organ-cultured guinea pig bronchi challenged with 5-oxo-ETE and 14,15-EET were compared. Tension measurements, performed on fresh and 3-day cultured bronchi, revealed that the contractile responses to 5-oxo-ETE were largely increased in cultured explants, while 14,15-EET induced larger relaxations on Carbamylcholine (CCh) pre-contracted explants. In fresh bronchi, the contractile responses to 5-oxo-ETE were inhibited by 10 microM indomethacin whereas the relaxing responses induced by 14,15-EET were amplified in the presence of COX inhibitors. COX down expression resulted in a lack of indomethacin effect in cultured explants. One micromolar 5-oxo-ETE increased Ca2+ sensitivity in beta-escin-permeabilized cultured explants, while 1 microM Y-27632 abolished this hypersensitivity. In contrast, 1 microM 14,15-EET significantly reduced the Ca2+ hypersensitivity developed by cultured bronchi. In conclusion, pre-treatment of cultured guinea pig bronchi for 48 h with these eicosanoids modifies the pharmacological responsiveness and Ca2+ sensitivity of these cultured explants.

Regulation of endothelial nitric-oxide synthase activity through phosphorylation in response to epoxyeicosatrienoic acids

Endothelial nitric oxide synthase (eNOS) is a key enzyme in NO-mediated cardiovascular homeostasis and its activity is modulated by a variety of hormonal and mechanical stimuli via phosphorylation modification. Our previous study has demonstrated that epoxyeicosatrienoic acids (EETs), the cytochrome P450 (CYP)-dependent metabolites of arachidonic acid, could robustly up-regulate eNOS expression. However, the molecular mechanism underlying the effects of EETs on eNOS remains elusive. Particularly, whether and how EETs affect eNOS phosphorylation is unknown. In the present study, we investigated the effects of EETs on eNOS phosphorylation with cultured bovine aortic endothelial cells (BAECs). BAECs were either treated with exogenous EETs or infected with recombinant adeno-associated virus (rAAV) carrying CYP2C11-CYPOR, CYP102 F87V mutant and CYP2J2, respectively, to increase endogenous EETs. Both addition of EETs and CYP epoxygenase transfection markedly increased eNOS phosphorylation at its Ser1179 and Thr497 residues. Inhibition of phosphatidylinositol 3-kinase (PI3K) with LY294002 prevented EETs-induced increases of eNOS-Ser(P)1179 but had no effect on the phosphorylation status of Thr497. However, inhibitors of protein kinase B (Akt), mitogen-activated protein kinase (MAPK) and MAPK kinase could block phosphorylation of eNOS at both sites. Inhibition of these kinases also attenuated the up-regulation of eNOS expression by EETs. Finally, administration of viral CYP epoxygenases expression vectors into rats enhanced eNOS phosphorylation and function in vivo. Thus, in addition to up-regulating eNOS expression, EETs also augment eNOS function by enhancing eNOS phosphorylation. EETs-induced up-regulation of eNOS phosphorylation and expression appears to involve in both PI3K/Akt and MAPK pathways.

Emerging mechanisms for growth and protection of the vasculature by cytochrome P450-derived products of arachidonic acid and other eicosanoids

Arachidonic acid (AA) is an essential fatty acid that is metabolized by cyclooxygenase (COX), lipoxygenase (LOX) or cytochrome P450 (CYP) enzymes to generate eicosanoids which in turn mediate a number of biological activities including regulation of angiogenesis. While much information on the effects of COX and LOX products is known, the physiological relevance of the CYP-derived products of AA are less well understood. CYP enzymes are highly expressed in the liver and kidney, but have also been detected at lower levels in the brain, heart and vasculature. A number of these enzymes, including members of the CYP 4 family, predominantly catalyze conversion of AA to 20-hydroxyeicosatetraenoic acid (20-HETE) while the CYP epoxygenases generate mainly epoxyeicosatrienoic acids (EETs). This review will focus on the emerging roles of inhibitors of eicosanoid production with emphasis on the CYP pathways, in the regulation of angiogenesis and tumor growth. We also discuss current observations describing the protective effects of EETs for survival of the endothelium.

Low Na intake suppresses expression of CYP2C23 and arachidonic acid-induced inhibition of ENaC

We previously demonstrated that arachidonic acid (AA) inhibits epithelial Na channels (ENaC) through the cytochrome P-450 (CYP) epoxygenase-dependent pathway ( 34 ). In the present study, we tested the hypothesis that low Na intake suppresses the expression of CYP2C23, which is mainly responsible for converting AA to epoxyeicosatrienoic acid (EET) in the kidney ( 11 ) and attenuates the AA-induced inhibition of ENaC. Immunostaining showed that CYP2C23 is expressed in the Tamm-Horsfall protein (THP)-positive and aquaporin 2 (AQP2)-positive tubules. This suggests that CYP2C23 is expressed in the thick ascending limb (TAL) and collecting duct (CD). Na restriction significantly suppressed the expression of CYP2C23 in the TAL and CD. Western blot also demonstrated that the expression of CYP2C23 in renal cortex and outer medulla diminished in rats on Na-deficient diet (Na-D) but increased in those on high-Na diet (4%). Moreover, the content of 11,12-epoxyeicosatrienoic acid (EET) decreased in the isolated cortical CD from rats on Na-D compared with those on a normal-Na diet (0.5%). Patch-clamp study showed that application of 15 μM AA inhibited the activity of ENaC by 77% in the CCD of rats on a Na-D for 3 days. However, the inhibitory effect of AA on ENaC was significantly attenuated in rats on Na-D for 14 days. Furthermore, inhibition of CYP epoxygenase with MS-PPOH increased the ENaC activity in the CCD of rats on a control Na diet. We also used microperfusion technique to examine the effect of MS-PPOH on Na transport in the distal nephron. Application of MS-PPOH significantly increased Na absorption in the distal nephron of control rats but had no significant effect on Na absorption in rats on Na-D for 14 days. We conclude that low Na intake downregulates the activity and expression of CYP2C23 and attenuates the inhibitory effect of AA on Na transport.

[Effect of 11, 12-epoxyeicosatrienoic acids on hypoxia/reoxygenation injury in the human umbilical vein endothelial cells]

OBJECTIVE

To investigate the effects of 11, 12-epoxyeicosatrienoic acids (11, 12-EET) on the degree of hypoxia/reoxygenation injury in human umbilical vein endothelial cells ( HUVECs), and reveal the possible pathway of EET on protection.

METHODS

Primary cultured HUVECs were randomly divided into control group, hypoxia/reoxygenation group, 11, 12-EET control group, 11, 12- EET hypoxia/reoxygenation group, inhibition of extracellular signal-regulated kinase (ERKI/2) group, and inhibition of nitric oxide synthase (NOS) group. Hypoxia/reoxygenation injury model in HUVECs was established by exposure to hypoxia (2% O2, 5% CO2 and 93% N2) for 3 hours, followed by reoxygenation (95% air and 5% CO2) for 1 hour. The evaluation of the endothelial cells were made by immunohistochemistry. The cell viability was monitored by MTT assay. Colorimetry method was used to assay the lactate dehydrogenase (LDH) , malondialdehyde (MDA) and activity of superoxide dismutase (SOD) in culture medium. Western blot was used to detect the expressions of endothelial nitric oxide synthase (eNOS) and phosphorylated ERK1/2 in HUVECs.

RESULTS

11, 12-EET caused minor injury in normal oxygen incubated HUVECs; however, in hypoxia/reoxygenation HUVECs, it raised the cell viability markedly, decreased the LDH release and MDA content, and increased the activity of SOD and the expressions of eNOS and phosphorylated ERK1/2.

CONCLUSIONS

11, 12-EET may prevent against endothelial cell hypoxia/reoxygenation injury. The mechanism may be related to the increased activity of SOD, elimination of oxygen-derived free radicals, and reduction of eNOS and phosphorylated ERK1/2 lesion caused by hypoxia/reoxygenation.

Protein phosphatase 2A and Ca2+-activated K+ channels contribute to 11,12-epoxyeicosatrienoic acid analog mediated mesenteric arterial relaxation

Epoxyeicosatrienoic acids (EETs) are considered to be endothelium-derived hyperpolarizing factors, and are potent activators of the large-conductance, Ca(2+)-activated K(+) (BK(Ca)) channel in vascular smooth muscle. Here, we investigate the signal transduction pathway involved in the activation of BK(Ca) channels by 11,12-EET and 11,12-EET stable analogs in rat mesenteric vascular smooth muscle cells. 11,12-EET and the 11,12-EET analogs, 11-nonyloxy-undec-8(Z)-enoic acid (11,12-ether-EET-8-ZE), 11-(9-hydroxy-nonyloxy)-undec-8(Z)-enoic acid (11,12-ether-EET-8-ZE-OH) and 11,12-trans-oxidoeicosa-8(Z)-enoic acid (11,12-tetra-EET-8-ZE), caused vasorelaxation of mesenteric resistance arteries. Mesenteric myocyte whole-cell (perforated-patch) currents were substantially (approximately 150%) increased by 11,12-EET and 11,12-EET analogs. Single-channel recordings were conducted to identify the target for 11,12-EET. 11,12-EET and 11,12-EET analogs also increased mesenteric myocyte BK(Ca) channel activity in cell-attached patches. Similar results were obtained in cell-free patches. Baseline mesenteric myocyte BK(Ca) channel activity (NPo) in cell-free patches averaged less than 0.001 at +50 mV and 11,12-EET (1 micromol/L) increased NPo to 0.03+/-0.02 and 11,12-EET analogs (1 micromol/L) increased NPo to 0.09+/-0.006. Inhibition of protein phosphatase 2A (PP2A) activity with okadaic acid (10 nmol/L) completely reversed 11,12-EET stimulated BK(Ca) channel activity and greatly attenuated 11,12-ether-EET-8-ZE mesenteric resistance artery vasorelaxation. 11,12-EET and 11,12-EET analogs increased mesenteric myocyte PP2A activity by 3.5-fold. Okadaic acid and the EET inhibitor, 14,15-epoxyeicosa-5(Z)-enoic acid (14,15-EEZE) inhibited the 11,12-EET mediated increase in PP2A activity. These findings provide initial evidence that PP2A activity contributes to 11,12-EET and 11,12-EET analog activation of mesenteric resistant artery BK(Ca) channels and vasorelaxation.

Participation of epoxygenase activation in saikogenin D-induced inhibition of prostaglandin E(2) synthesis

We examined the effect of saikogenin D on arachidonic acid metabolism in C6 rat glioma cells to clarify its anti-inflammatory mechanism. Incubation of C6 cells with saikogenin D for 20 min resulted in the inhibition of prostaglandin E(2) production and the accumulation of an arachidonic acid metabolite that was found to be 11,12-dihydroxyeicosatrienoic acid, a metabolite of 11,12-epoxyeicosatrienoic acid. C6 cells expressed rat epoxygenase mRNAs, CYP1A1, CYP2B1 and CYP2J3, which converted arachidonic acid to epoxyeicosatrienoic acids. 11,12-Epoxyeicosatrienoic acid inhibited A23187-induced prostaglandin E(2) production and SKF-525A, an inhibitor of epoxygenase, attenuated the saikogenin D-induced inhibition of prostaglandin E(2) production in C6 cells. Furthermore, 11,12-epoxyeicosatrienoic acid and 11,12-dihydroxyeicosatrienoic acid, but not saikogenin D, inhibited the activity of cyclooxygenase in a cell-free condition. These data suggest that saikogenin D activates epoxygenases that rapidly convert arachidonic acid to epoxyeicosanoids and dihydroxyeicosatrienoic acids, and then the metabolites secondarily inhibit prostaglandin E(2) production.

Inhibition of smooth muscle proliferation by urea-based alkanoic acids via peroxisome proliferator-activated receptor alpha-dependent repression of cyclin D1

OBJECTIVE

Proliferation of smooth muscle cells is implicated in cardiovascular complications. Previously, a urea-based soluble epoxide hydrolase inhibitor was shown to attenuate smooth muscle cell proliferation. We examined the possibility that urea-based alkanoic acids activate the nuclear receptor peroxisome proliferator-activated receptor alpha (PPARalpha) and the role of PPARalpha in smooth muscle cell proliferation.

METHODS AND RESULTS

Alkanoic acids transactivated PPARalpha, induced binding of PPARalpha to its response element, and significantly induced the expression of PPARalpha-responsive genes, showing their function as PPARalpha agonists. Furthermore, the alkanoic acids attenuated platelet-derived growth factor-induced smooth muscle cell proliferation via repression of cyclin D1 expression. Using small interfering RNA to decrease endogenous PPARalpha expression, it was determined that PPARalpha was partially involved in the cyclin D1 repression. The antiproliferative effects of alkanoic acids may also be attributed to their inhibitory effects on soluble epoxide hydrolase, because epoxyeicosatrienoic acids alone inhibited smooth muscle cell proliferation.

CONCLUSIONS

These results show that attenuation of smooth muscle cell proliferation by urea-based alkanoic acids is mediated, in part, by the activation of PPARalpha. These acids may be useful for designing therapeutics to treat diseases characterized by excessive smooth muscle cell proliferation.

Epoxyeicosatrienoic acids in cardioprotection: ischemic versus reperfusion injury

Cytochrome P-450 (CYP) epoxygenases and their arachidonic acid (AA) metabolites, the epoxyeicosatrienoic acids (EETs), have been shown to produce increases in postischemic function via ATP-sensitive potassium channels (KATP); however, the direct effects of EETs on infarct size (IS) have not been investigated. We demonstrate that two major regioisomers of CYP epoxygenases, 11,12-EET and 14,15-EET, significantly reduced IS in dogs compared to control (22.1 ± 1.8%), whether administered 15 min before 60 min of coronary occlusion (6.4 ± 1.9%, 11,12-EET; and 8.4 ± 2.4%, 14.15-EET) or 5 min before 3 h of reperfusion (8.8 ± 2.1%, 11,12-EET; and 9.7 ± 1.4%, 14,15-EET). Pretreatment with the epoxide hydrolase metabolite of 14,15-EET, 14,15-dihydroxyeicosatrienoic acid, had no effect. The protective effect of 11,12-EET was abolished (24.3 ± 4.6%) by the KATP channel antagonist glibenclamide. Furthermore, one 5-min period of ischemic preconditioning (IPC) reduced IS to a similar extent (8.7 ± 2.8%) to that observed with the EETs. The selective CYP epoxygenase inhibitor, N-methylsulfonyl-6-(2-propargyloxyphenyl)hexanamide (MS-PPOH), did not block the effect of IPC. However, administration of MS-PPOH concomitantly with N-methylsulfonyl-12,12-dibromododec-11-enanide (DDMS), a selective inhibitor of endogenous CYP ω-hydroxylases, abolished the reduction in myocardial IS expressed as a percentage of area at risk (IS/AAR) produced by DDMS (4.6 ± 1.2%, DDMS; and 22.2 ± 3.4%, MS-PPOH + DDMS). These data suggest that 11,12-EET and 14,15-EET produce reductions in IS/AAR primarily at reperfusion. Conversely, inhibition of CYP epoxygenases and endogenous EET formation by MS-PPOH, in the presence of the CYP ω-hydroxylase inhibitor DDMS blocked cardioprotection, which suggests that endogenous EETs are important for the beneficial effects observed when CYP ω-hydroxylases are inhibited. Finally, the protective effects of EETs are mediated by cardiac KATP channels.

High-calcium vs high-phosphate intake and small artery tone in advanced experimental renal insufficiency

BACKGROUND

Disturbed calcium-phosphorus balance significantly contributes to uraemic changes in large arteries. We examined the influences of high-calcium and high-phosphate intake on small artery tone in experimental renal insufficiency.

METHODS

Sixty-five rats were assigned to 5/6 nephrectomy (NTX) or sham operation. After 15 week disease progression, NTX rats were given high-calcium (3%), high-phosphate (1.5%) or control diet (0.3% calcium, 0.5% phosphate) for 12 weeks. Then isolated segments of small mesenteric arteries were studied using wire and pressure myographs.

RESULTS

Subtotal nephrectomy reduced creatinine clearance by 60% and increased parathyroid hormone (PTH) and phosphate 12-fold and 2.7-fold, respectively. High-phosphate intake further elevated PTH and phosphate (33-fold and 5.5-fold, respectively), while the calcium diet suppressed them (to 3.5 and 62% vs sham, respectively). Ventricular B-type natriuretic peptide synthesis was increased, and blood pressure was 27 and 18 mmHg higher in NTX rats on control and phosphate diet, respectively, than in calcium-fed rats. Vasorelaxation to acetylcholine was impaired by approximately 50% in uraemic rats, and was further deteriorated by high-phosphate intake, whereas the calcium diet improved endothelium-mediated relaxation via nitric oxide and potassium channels. Small arteries of all NTX groups featured eutrophic inward remodelling: wall-to-lumen ratio was increased 1.3-fold without change in cross-sectional area.

CONCLUSION

High-phosphate intake had a detrimental influence on secondary hyperparathyroidism and vasodilatation, whereas high-calcium intake reduced blood pressure and PTH, alleviated volume overload and improved vasorelaxation in experimental renal insufficiency. Therefore, alterations in the calcium-phosphorus balance can significantly modulate small artery tone during impaired kidney function.

Modulation of ACTH-induced cortisol release by polyunsaturated fatty acids in interrenal cells from gilthead seabream, Sparus aurata

Highly unsaturated fatty acids are essential components of cellular membranes of vertebrates and can modulate physiological processes, including membrane transport, receptor function and enzymatic activities. In gilthead sea bream, dietary deficiencies of essential fatty acids of marine fish raise the basal cortisol levels and alter the pattern of cortisol release after stress. The aim of the present study was to clarify the effect of different essential fatty acids on adrenocorticotropic hormone (ACTH)-induced cortisol production and release in fish, through in vitro studies of sea bream interrenal cells maintained in superfusion and incubated with different types of fatty acids and eicosanoid production inhibitors. Results showed the first evidence of the effect of certain fatty acids on cortisol production by ACTH-stimulated interrenal cells in fish. Both arachidonic acid (ARA) and particularly eicosapentaenoic acid (EPA) promoted cortisol production in sea bream interrenal cells. Moreover, incubation with indometacin (INDO) reduced the increased cortisol production induced by EPA and ARA, suggesting mediation by their cyclooxygenase-derived products. Docosahexaenoic acid stimulated cortisol production to a lesser extent than that caused by EPA or ARA, but the inhibitory effect of INDO was not as marked as it was for the other fatty acids. In contrast, supplementation with dihomogammalinolenic acid reduced cortisol production, denoting the inhibitor effect of this fatty acid in cortisol secretion.

Rat mesenteric arterial dilator response to 11,12-epoxyeicosatrienoic acid is mediated by activating heme oxygenase

11,12-Epoxyeicosatrienoic acid (11,12-EET), a potent vasodilator produced by the endothelium, acts on calcium-activated potassium channels and shares biological activities with the heme oxygenase/carbon monoxide (HO/CO) system. We examined whether activation of HO mediates the dilator action of 11,12-EET, and that of the other EETs, on rat mesenteric arteries. Dose-response curves (10(-9) to 10(-6) M) to 5,6-EET, 8,9-EET, 11,12-EET, 14,15-EET, and ACh (10(-9) to 10(-4) M) were evaluated in preconstricted (10(-6) mol/l phenylephrine) mesenteric arteries (<350 microm diameter) in the presence or absence of 1) the cyclooxygenase inhibitor indomethacin (2.8 microM), 2) the HO inhibitor chromium mesoporphyrin (CrMP) (15 microM), 3) the soluble guanylyl cyclase (GC) inhibitor ODQ (10 microM), and 4) the calcium-activated potassium channel inhibitor iberiotoxin (25 nM). The vasodilator response to 11,12-EET was abolished by CrMP and iberiotoxin, whereas indomethacin and ODQ had no effect. In contrast, the effect of ACh was attenuated by ODQ but not by CrMP. The vasodilator effect of 8,9-EET, like that of 11,12-EET, was greatly attenuated by HO inhibition. In contrast, the mesenteric vasodilator response to 5,6-EET was independent of both HO and GC, whereas that to 14,15-EET demonstrated two components, an HO and a GC, of equal magnitude. Incubation of mesenteric microvessels with 11,12-EET caused a 30% increase in CO release, an effect abolished by inhibition of HO. We conclude that the rat mesenteric vasodilator action of 11,12-EET is mediated via an increase in HO activity and an activation of calcium-activated potassium channels.

Glial cells dilate and constrict blood vessels: a mechanism of neurovascular coupling

Neuronal activity evokes localized changes in blood flow. Although this response, termed neurovascular coupling, is widely used to monitor human brain function and diagnose pathology, the cellular mechanisms that mediate the response remain unclear. We investigated the contribution of glial cells to neurovascular coupling in the acutely isolated mammalian retina. We found that light stimulation and glial cell stimulation can both evoke dilation or constriction of arterioles. Light-evoked and glial-evoked vasodilations were blocked by inhibitors of cytochrome P450 epoxygenase, the synthetic enzyme for epoxyeicosatrienoic acids. Vasoconstrictions, in contrast, were blocked by an inhibitor of omega-hydroxylase, which synthesizes 20-hydroxyeicosatetraenoic acid. Nitric oxide influenced whether vasodilations or vasoconstrictions were produced in response to light and glial stimulation. Light-evoked vasoactivity was blocked when neuron-to-glia signaling was interrupted by a purinergic antagonist. These results indicate that glial cells contribute to neurovascular coupling and suggest that regulation of blood flow may involve both vasodilating and vasoconstricting components.

Protective effects of epoxyeicosatrienoic acids on human endothelial cells from the pulmonary and coronary vasculature

Epoxyeicosatrienoic acids (EETs) are cytochrome P-450 (CYP) metabolites synthesized from the essential fatty acid arachidonic acid to generate four regioisomers, 14,15-, 11,12-, 8,9-, and 5,6-EET. Cultured human coronary artery endothelial cells (HCAECs) contain endogenous EETs that are increased by stimulation with physiological agonists such as bradykinin. Because EETs are known to modulate a number of vascular functions, including angiogenesis, we tested each of the four regioisomers to characterize their effects on survival and apoptosis of HCAECs and cultured human lung microvascular endothelial cells (HLMVECs). A single application of physiologically relevant concentration of 14,15-, 11,12-, and 8,9-EET but not 5,6-EET (0.75-300 nM) promoted concentration-dependent increase in cell survival of HLMVECs and HCAECs after removal of serum. The lipids also protected the same cells from death via the intrinsic, as well as extrinsic, pathways of apoptosis. EETs did not increase intracellular calcium concentration ([Ca2+]i) or phosphorylate mitogen-activated protein kinase p44/42 when applied to these cells, and their protective action was attenuated by the phosphotidylinositol-3 kinase inhibitor wortmannin (10 microM) but not the cyclooxygenase inhibitor indomethacin (20 microM). Our results demonstrate for the first time the capacity of EETs to enhance human endothelial cell survival by inhibiting both the intrinsic, as well as extrinsic, pathways of apoptosis, an important underlying mechanism that may promote angiogenesis and endothelial survival during atherosclerosis and related cardiovascular ailments.

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

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

Hepoxilin Analogs, Potential New Therapeutics in Disease

We have chemically synthesized several stable analogs of the naturally occurring hepoxilins, 12-LO products derived from arachidonic acid, which we found to have promising actions in a variety of test systems of disease. The analogs, PBTs, afford chemical and biological stability to the hepoxilin molecule. This article reviews some of our latest observations with the PBTs in the areas of inflammation (inhibition of the bleomycin-evoked lung fibrosis in mice in vivo), platelet aggregation (antagonism of the thromboxane receptor in human platelets in vitro) and thrombosis (inhibitors in vivo), and cancer (apoptosis of the human leukemia cell line, K562 in vitro and in vivo). The demonstration that the PBTs are active in vivo suggests that they can serve as a platform for their further development as novel therapeutics in disease.

Dietary manipulation implicates lipid signaling in the regulation of germ cell maintenance in C. elegans

Reproduction in C. elegans relies on continuously proliferating germ cells which, during germline development, exit mitosis, undergo meiosis and differentiate into gametes. Supplementing the diet of C. elegans with dihommogamma-linolenic acid (20:3n-6, DGLA), a long chain omega-6 polyunsaturated fatty acid, results in sterile worms that lack germ cells. The effect is remarkably specific for DGLA, as eicosapentaenoic acid (20:5n-3, EPA) and other long-chain polyunsaturated fatty acids with similar physical properties have little or no effect on fertility. Germ cells undergoing mitosis during larval stages are especially sensitive to DGLA, but exposure to DGLA during adulthood also reduces germ cells and brood size, in part by inducing inappropriate apoptosis of meiotic germ cells. Mutant strains with defects in fatty acid desaturation and elongation display altered susceptibility to DGLA, indicating that the sterility effect of the dietary lipid depends on the amount of DGLA present in membranes as well as on the capacity to convert DGLA to other fatty acids. We propose that DGLA produces a signal that interacts with one or more pathways regulating germ cell survival. Our DGLA findings are the first report of a role for a specific fatty acid affecting the development and maintenance of germ cells in C. elegans.

Adenosine2A receptor vasodilation of rat preglomerular microvessels is mediated by EETs that activate the cAMP/PKA pathway

Dilation of rat preglomerular microvessels (PGMV) by activation of adenosine A2A receptors (A2AR) is coupled to epoxyeicosatrienoic acid (EET) release. We have investigated the commonality of this signal transduction pathway, i.e., sequential inhibition of G(salpha), adenylyl cyclase, PKA, and Ca2+-activated K+ (KCa) channel activity, to the vasoactive responses to A2AR activation by a selective A2A agonist, CGS-21680, compared with those of 11,12-EET. Male Sprague-Dawley rats were anesthetized, and microdissected arcuate arteries (110-130 microm) were cannulated and pressurized to 80 mmHg. Vessels were superfused with Krebs solution containing NG-nitro-L-arginine methyl ester (L-NAME) and indomethacin and preconstricted with phenylephrine. We assessed the effect of 3-aminobenzamide (10 microM), an inhibitor of mono-ADP-ribosyltranferases, on responses to 11,12-EET (3 nM) and CGS-21680 (10 microM) and found that both were inhibited by approximately 70% (P<0.05), whereas the response to SNP (10 microM) was unaffected. Furthermore, 11,12-EET (100 nM), like cholera toxin (100 ng/ml), stimulated ADP-ribose formation in homogenates of arcuate arteries compared with control. SQ-22536 (10 microM), an inhibitor of adenylyl cyclase activity, and myristolated PKI (14-22) amide (5 microM), an inhibitor of PKA, decreased activity of 11,12-EET and CGS-21680. Incubation of 11,12-EET (3 nM-3 microM) with PGMV resulted in an increase in cAMP levels (P<0.05). The responses to both 11,12-EET and CGS-21680 were significantly reduced by superfusion of iberiotoxin (100 nM), an inhibitor of KCa channel activity. Thus in rat PGMV activation of A2AR is coupled to EET release upstream of adenylyl cyclase activation and EETs stimulate mono-ADP-ribosyltransferase, resulting in Gsalpha protein activation.

Cytochrome P450 epoxygenases provide a novel mechanism for penile erection

Erectile dysfunction (ED) is estimated to affect more than 30 million American men and 152 million men worldwide. Therapeutic agents targeting the nitric oxide/cyclic GMP signaling pathway have successfully treated patients with ED; however, the efficacies of these treatments are significantly lower in specific populations such as patients with diabetes. The goal of this study was to discover and identify new endothelium-derived relaxing factors involved in the regulation of erectile function, providing alternative therapeutic targets for treatment of ED. Immunoblotting results showed that protein expressions of epoxygenases from cytochrome P450 (CYP)2B, 2C and 2J subfamilies, as well as NADPH CYP reductase were present in rat corpora cavernosa, which was confirmed by immunohistochemical analysis. Furthermore, CYP2C was localized in cavernosal endothelial cells using double immunolabeling. CYP epoxygenase activity was analyzed by reverse-phase high-pressure liquid chromatography; and the results showed that 11,12- epoxyeicosatrienoic acid (EET) was the major product metabolized by CYP epoxygenases in rat corpora cavernosa. Inhibition of EETs function by injection of an EETs antagonist into rat penis significantly decreased intracavernosal pressure-induced by electrical stimulation of the major pelvic ganglion in vivo. In conclusion, our results suggest that EETs, produced by CYP epoxygenases, in penile endothelial cells serve as vasodilators. Inhibition of this pathway attenuated erectile function, suggesting that EETs are required for normal erection.

Regulation of potassium channels in coronary smooth muscle by adenoviral expression of cytochromeP-450 epoxygenase

Epoxyeicosatrienoic acids (EETs) are endothelium-derived cytochrome P-450 (CYP) metabolites of arachidonic acid that relax vascular smooth muscle by large-conductance calcium-activated potassium (BKCa) channel activation and membrane hyperpolarization. We hypothesized that if smooth muscle cells (SMCs) had the capacity to synthesize EETs, endogenous EET production would increase BKCachannel activity. Bovine coronary SMCs were transduced with adenovirus coding the CYP Bacillus megaterium -3 (F87V) (CYP BM-3) epoxygenase that metabolizes arachidonic acid exclusively to 14( S),15( R)-EET. Adenovirus containing the cytomegalovirus promoter- Escherichia coli β-galactosidase was used as a control. With the use of an anti-CYP BM-3 (F87V) antibody, a 124-kDa immunoreactive protein was detected only in CYP BM-3-transduced cells. Protein expression increased with increasing amounts of virus. When CYP BM-3-transduced cells were incubated with [14C]arachidonic acid, HPLC analysis detected 14,15-dihydroxyeicosatrienoic acid (14,15-DHET) and 14,15-EET. The identity of 14,15-EET and 14,15-DHET was confirmed by mass spectrometry. In CYP BM-3-transduced cells, methacholine (10−5M) increased 14,15-EET release twofold and BKCachannel activity fourfold in cell-attached patches. Methacholine-induced increases in BKCachannel activity were blocked by the CYP inhibitor 17-octadecynoic acid (10−5M). 14( S),15( R)-EET was more potent than 14( R),15( S)-EET in relaxing bovine coronary arteries and activating BKCachannels. Thus CYP BM-3 adenoviral transduction confers SMCs with epoxygenase activity. These cells acquire the capacity to respond to the vasodilator agonist by synthesizing 14( S),15( R)-EET from endogenous arachidonic acid to activate BKCachannels. These studies indicate that 14( S),15( R)-EET is a sufficient endogenous activator of BKCachannels in coronary SMCs.

Effects of arachidonic acid analogs on FcepsilonRI-mediated activation of mast cells

Polyunsaturated fatty acids (PUFAs) such as arachidonic acid (AA) have been shown to modulate a number of inflammatory disorders. Mast cells play a critical role in the initiation and maintenance of inflammatory responses. However, the effects of PUFAs on mast cell functions have not been fully addressed. We here-in examined the effects of PUFAs on the high affinity IgE receptor (FcepsilonRI)-mediated mast cell activation using RBL-2H3 cells, a rat mast cell line, that were cultured in the medium containing palmitic acid (PA), AA, or the AA analogs mead acid (MA) and eicosapentaenoic acid (EPA). In AA-supplemented cells, the FcepsilonRI-mediated beta-hexosamidase and TNF-alpha release, calcium (Ca(2+)) influx, and some protein tyrosine phosphorylations including Syk and linker for activation of T cells (LAT) were enhanced, whereas, in MA- or PA-supplemented cells, they were not changed when compared with cells cultured in control medium. In EPA-supplemented cells, the enhancements of beta-hexosamidase release and protein tyrosine phosphorylations were observed. Furthermore, in AA- or EPA-supplemented cells, FcepsilonRI-mediated intracellular production of reactive oxygen species (ROS) that is required for the tyrosine phosphorylation of LAT and Ca(2+) influx were enhanced when compared with the other cells. Thus, preincubation of AA or EPA augmented FcepsilonRI-mediated degranulation in mast cells by affecting early events of FcepsilonRI signal transduction, which might be associated with the change of fatty acid composition of the cell membrane and enhanced production of ROS. The results suggest that some PUFAs can modulate FcepsilonRI-mediated mast cell activation and might affect FcepsilonRI/mast cell-mediated inflammation, such as allergic reaction.