Cytochrome P450 2C9-derived epoxyeicosatrienoic acids induce angiogenesis via cross-talk with the epidermal growth factor receptor (EGFR)

Gene expression profiling in the remnant kidney model of wild type and kinin B1 and B2 receptor knockout mice

Angiotensin-converting enzyme inhibitors are the most efficient pharmacologic agents to delay the development of end-stage renal disease (ESRD). This is a multipharmacologic approach that inhibits angiotensin II formation while increasing kinin concentrations. Considerable attention has been focused on the role of decreased angiotensin II levels; however, the role of increased kinin levels is gaining in interest. Kinins affect cellular physiology by interacting with one of two receptors being the more inducible B1 and the more constitutive B2 receptors. This study utilizes the mouse remnant kidney of 20 weeks duration as a model of ESRD. Whole mouse genome microarrays were used to evaluate gene expression in the remnant kidneys of wild type, B1 and B2 receptor knockout animals. The microarray data indicate that gene families involved in vascular damage, inflammation, fibrosis, and proteinuria were upregulated, whereas gene families involved in cell growth, metabolism, lipid, and protein biosynthesis were downregulated in the remnant kidneys. Interestingly, the microarray analyses coupled to histological evaluations are suggestive of a possible protective role of kinins operating through the B2 receptor subtype in this model of renal disease. The results highlight the potential of microarray technology for unraveling complex mechanisms contributing to chronic renal failure.

Peroxisomal proliferator-activated receptor-alpha-dependent inhibition of endothelial cell proliferation and tumorigenesis

The peroxisomal proliferator-activated nuclear receptor-alpha (PPARalpha), the target for most hypolipidemic drugs in current clinical use, regulates the transcription of genes involved in lipid metabolism and transport, and energy homeostasis. More recently, PPARalpha and its ligands have been implicated in inflammatory responses and the regulation of cell proliferation. PPARalpha also regulates the expression of Cyp4a fatty acid omega-hydroxylases and Cyp2c arachidonic acid epoxygenase genes. To study the role of the PPARalpha receptor and of its Cyp2c epoxygenase gene target in tumorigenesis, we treated mice injected with tumor cells with Wy-14,643, a PPARalpha-selective ligand. Compared with untreated controls, Wy-14643-treated animals showed marked reductions in tumor growth and vascularization, which were accompanied by decreases in the plasma levels of pro-angiogenic epoxygenase metabolites (EETs), hepatic EET biosynthesis, and Cyp2c epoxygenase expression. All these Wy-14643-induced responses were absent in PPARalpha(-/-) mice and are thus PPARalpha-mediated. Primary cultures of mouse lung endothelial cells treated with Wy-14643 showed reductions in cell proliferation and in the formation of capillary-like structures. These effects were absent in cells obtained from PPRAalpha(-/-) mice and reversed by the addition of EETs. These results identify important anti-angiogenic and anti-tumorigenic roles for PPARalpha, characterize the contribution of its Cyp2c epoxygenases gene target to these responses, and suggest potential anti-cancer roles for this nuclear receptor and its ligands.

Fluid Shear Stress and NO Decrease the Activity of the Hydroxy-Methylglutaryl Coenzyme A Reductase in Endothelial Cells via the AMP-Activated Protein Kinase and FoxO1

The rate-limiting enzyme for cholesterol synthesis, the hydroxy-methylglutaryl coenzyme A reductase (HCR), is phosphorylated by the AMP-activated protein kinase (AMPK). As shear stress activates the AMPK in endothelial cells, we determined whether it affects HCR activity and subsequent HCR-dependent signaling. Shear stress (12 dynes cm(-2)) rapidly increased the phosphorylation and activity (6.5- and 4-fold, respectively) of the AMPK in cultured endothelial cells and the activated AMPK phosphorylated the HCR in vitro. Moreover, shear stress and the AMPK activator 5-aminoimidazole-4-carboxamide ribonucleoside (AICAR) attenuated endothelial HCR activity by 37% and 33%, respectively. Inhibition of NO production attenuated the acute shear stress-induced phosphorylation of the AMPK and the decrease in HCR activity. Prolonged shear stress (18 hours) led to a significant (50%) decrease in HCR mRNA expression that was dependent on NO, AMPK, and the subsequent phosphorylation and degradation of FoxO1a. Correspondingly, the downregulation of FoxO (small interfering RNA) decreased HCR expression. Prolonged shear stress also attenuated the bradykinin-induced activation of Ras and extracellular signal-regulated kinase 1/2, a phenomenon that was comparable to the effects of cerivastatin and that was reversed by mevalonate and thus attributed to HCR inhibition. A decrease (35%) in HCR expression was also detected in femoral arteries from mice following voluntary exercise, and the bradykinin-induced vasodilatation of the mouse hindlimb was attenuated by both exercise and the HCR inhibitor cerivastatin. These data indicate that fluid shear stress regulates the activity and expression of the HCR in endothelial cells and determines responsiveness to stimuli, such as bradykinin via a mechanism involving NO, AMPK, FoxO1a, and p21Ras.

Epoxyeicosatrienoic acids, cell signaling and angiogenesis

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

Beyond vasodilatation: non-vasomotor roles of epoxyeicosatrienoic acids in the cardiovascular system

Epoxyeicosatrienoic acids (EETs), derived from arachidonic acid by cytochrome P450 epoxygenases, are potent vasodilators that function as endothelium-derived hyperpolarizing factors in some vascular beds. EETs are rapidly metabolized by soluble epoxide hydrolase to form dihydroxyeicosatrienoic acids (DHETs). Recent reports indicate that EETs have several important non-vasomotor regulatory roles in the cardiovascular system. EETs are potent anti-inflammatory agents and might function as endogenous anti-atherogenic compounds. In addition, EETs and DHETs might stimulate lipid metabolism and regulate insulin sensitivity. Thus, pharmacological inhibition of soluble epoxide hydrolase might be useful not only for hypertension but also for abating atherosclerosis, diabetes mellitus and the metabolic syndrome. Finally, although usually protective in the systemic circulation, EETs might adversely affect the pulmonary circulation.

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.

Identification and Partial Characterization of a Novel CYP2C9 Splicing Variant Encoding a Protein Lacking Eight Amino Acid Residues

CYP2C9 is known as an enzyme responsible for the metabolism of various clinically important drugs. Recently, we cloned a cDNA corresponding to a CYP2C9 splicing variant (SV), which seemed to have an open reading frame of a protein with 482 amino acid residues. To investigate whether or not the SV can be translated as a functionally active protein, we expressed the CYP2C9SV in insect cells, and spectrophotometric and enzymatic properties were characterized. The CYP2C9SV protein showed a typical reduced CO-difference spectrum, indicating that the translated protein binds a heme moiety. However, CYP2C9SV did not metabolize tolbutamide or diclofenac at all, suggesting that the SV protein appeared to lack the ability to catalyze reactions mediated by CYP2C9. Although the CYP2C9SV mRNA was detected in all human liver samples examined in this study by real-time PCR, the level was generally low, ranging between 0.7 and 9.6% of the normal CYP2C9 mRNA. These results suggest that the CYP2C9SV protein is unlikely to contribute to CYP2C9 activities, although it appears to be expressed in most individuals.

Action of epoxyeicosatrienoic acids on cellular function

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

Distribution of soluble epoxide hydrolase, cytochrome P450 2C8, 2C9 and 2J2 in human malignant neoplasms

Soluble epoxide hydrolase (sEH) is a bifunctional enzyme with a C-terminal epoxide hydrolase activity and an N-terminal phosphatase activity. Arachidonic acid epoxides, previously suggested to be involved in apoptosis, oncogenesis and cell proliferation, are generated by cytochrome P450 epoxygenases and are good substrates of the sEH C-terminal domain. In addition, the N-terminal phosphatase domain hydrolyzes isoprenoid mono- and pyrophosphates, which are involved in cell signaling and apoptosis. Here we provide a comprehensive analysis of the distribution of sEH, CYP2C8, 2C9 and 2J2 in human neoplastic tissues using tissue micro-arrays. The human neoplastic tissue micro-arrays provide a well-controlled side by side analysis of a wide array of neoplastic tissues and their surrounding normal tissue controls. Many of the neoplastic tissues showed altered expression of these enzymes as compared to normal tissues. Altered expression was not limited to the neoplastic tissues but also found in the surrounding non-neoplastic tissues. For example, sEH expression in renal and hepatic malignant neoplasms and surrounding non-neoplastic tissues was found to be significantly decreased, whereas expression was found to be increased in seminoma as compared to normal tissues. Our study warrants further investigation of the role of altered expression of these enzymes in neoplastic tissues.

11,12-epoxyeicosatrienoic acid stimulates heme-oxygenase-1 in endothelial cells

As epoxyeicosatrienoic acids (EETs), particularly 11,12-EET, and the heme oxygenase/carbon monoxide (HO/CO) system share overlapping biological activities, we examined a possible link between 11,12-EET and HO activity in endothelial cells. Confocal microscopy analysis of immunostaining of HO-1 and HO-2 in cultured endothelial cells treated with 11,12-EET (1 microM) showed an increase in florescence of HO-1 protein in the various cellular compartments, but not of HO-2. Incubation of endothelial cells with 11,12-EET (1 microM) for 24 h increased the level of HO-1 protein by about three-fold. Similarly, incubation of endothelial cells with 8,9-EET and sodium nitroprussiate, a known inducer of HO-1, increased HO-1 protein without any effect on HO-2. Upregulation of HO-1 by 11,12-EET, as well as 8,9-EET, was associated with an increase in HO activity, which was inhibited by stannous mesoporphirin (10 microM). Incubation of rat aortas with 11,12-EET (1 microM for 60 min) increased HO activity. These findings identify a novel effect of EETs on endothelial HO-1 and indicate that the signaling pathway of EETs in endothelial cells is possibly via an increase in HO-1 expression and activity.

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.

CYP1A in TCDD toxicity and in physiology-with particular reference to CYP dependent arachidonic acid metabolism and other endogenous substrates

Toxicologic and physiologic roles of CYP1A enzyme induction, the major biochemical effect of aryl hydrocarbon receptor activation by TCDD and other receptor ligands, are unknown. Evidence is presented that CYP1A exerts biologic effects via metabolism of endogenous substrates (i.e., arachidonic acid, other eicosanoids, estrogens, bilirubin, and melatonin), production of reactive oxygen, and effects on K(+) and Ca(2+) channels. These interrelated pathways may connect CYP1A induction to TCDD toxicities, including cardiotoxicity, vascular dysfunction, and wasting. They may also underlie homeostatic roles for CYP1A, especially when transiently induced by common chemical exposures and environmental conditions (i.e., tryptophan photoproducts, dietary indoles, and changes in oxygen tension).

Meeting report: ISN forefronts in nephrology on endothelial biology and renal disease: from bench to prevention

This ISN-sponsored Forefront in Nephrology meeting, which has brought together 120 scientists from 21 countries, has been concerned with various aspects of endothelial function and dysfunction and their contribution to progression of chronic kidney disease and/or its cardiovascular complications. The following themes were discussed in great depth: (1) phenotypical changes in the vascular endothelium - permeability, senescence, and apoptosis; (2) regulation of endothelial nitric oxide (NO) synthase function - caveolar and shear stress mechanisms, epigenetic regulation, S-nitrosylation, and Rho-kinase regulation; (3) oxidative stress and hypoxia-induced changes; (4) organellar dysfunction - lysosomes, mitochondria, and endoplasmic reticulum; (5) NO-independent mechanisms of vasomotion - epoxides, heme oxygenase-1 and carbon monoxide, thromboxane, tumor necrosis factor-alpha, and uric acid; (6) endothelial crosstalk with podocytes, monocytes, smooth muscle cells, and platelets; (7) candidate clinical biomarkers of endothelial dysfunction - functional testing of macro- and micro-vascular functions, surrogate markers, circulating detached endothelial cells, and endothelial precursor cells; and culminated in Round Table discussion on the diagnosis of endothelial dysfunction and its treatment options. In conclusion, this meeting has focused on several key problems of endothelial cell pathobiology relevant to chronic kidney disease.

Induction of CYP1A and cyp2-mediated arachidonic acid epoxygenation and suppression of 20-hydroxyeicosatetraenoic acid by imidazole derivatives including the aromatase inhibitor vorozole

Cytochrome P450 (P450) enzymes metabolize the membrane lipid arachidonic acid to stable biologically active epoxides [eicosatrienoic acids (EETs)] and 20-hydroxyeicosatetraenoic acid (20-HETE). These products have cardiovascular activity, primarily acting as vasodilators and vasoconstrictors, respectively. EET formation can be increased by the prototype CYP1A or CYP2 inducers, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) or phenobarbital (PB), respectively. We report here that imidazole derivative drugs: the anthelminthics, albendazole and thiabendazole; the proton pump inhibitor, omeprazole; the thromboxane synthase inhibitor, benzylimidazole; and the aromatase (CYP19) inhibitor vorozole (R76713, racemate; and R83842, (+) enantiomer) increased hepatic microsomal EET formation in a chick embryo model. Albendazole increased EETs by transcriptional induction of CYP1A5 and the others by combined induction of CYP1A5 and CYP2H, the avian orthologs of mammalian CYP1A2 and CYP2B, respectively. All inducers increased formation of the four EET regioisomers, but TCDD and albendazole had preference for 5,6-EET and PB and omeprazole for 14,15-EET. Vorozole, benzylimidazole, and TCDD also suppressed 20-HETE formation. Vorozole was a remarkably effective and potent inducer of multiple hepatic P450s at a dose range which overlapped its inhibition of ovarian aromatase. Increased CYP1A activity in mouse Hepa 1-6 and human HepG2 cells by vorozole and other imidazole derivatives demonstrated applicability of the findings to mammalian cells. The findings suggest that changes in P450-dependent arachidonic acid metabolism may be a new source of side effects for drugs that induce CYP1A or CYP2. They demonstrate further that in vivo induction of multiple hepatic P450s produces additive increases in arachidonic acid epoxygenase activity and can occur concurrently with inhibition of ovarian aromatase activity.

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.

Endothelium-Derived Epoxyeicosatrienoic Acids and Vascular Function

Epoxyeicosatrienoic acids (EETs) are epoxides of arachidonic acid generated by cytochrome P450 (CYP) epoxygenases. The activation of CYP epoxygenases in endothelial cells is an important step in the NO and prostacyclin-independent vasodilatation of several vascular beds, and EETs have been identified as an endothelium-derived hyperpolarizing factor. However, EETs also exert membrane potential-independent effects and modulate several signaling cascades that affect endothelial cell proliferation and angiogenesis. This review summarizes the role of CYP-derived EETs in endothelium-derived hyperpolarizing factor-mediated responses and highlights the evidence indicating that EETs are important second messengers involved in endothelial cell signaling pathways related to angiogenesis.

Cytochrome p450 2C (CYP2C) in ischemic heart injury and vascular dysfunctionThis paper is one of a selection of papers published in this Special Issue, entitled Young Investigator's Forum

The cytochrome p450 2C (CYP2C) monooxygenase family is a key player in the generation of epoxyeicosatrienoic acids. It has recently become apparent that CYP plays an important role in cardiovascular physiology and contributes to the pathogenesis of various cardiovascular diseases. In particular, several studies have demonstrated a role for these enzymes in cardiac ischemia and reperfusion injury. The current review summarizes the role of the CYP epoxygenase, CYP2C9, in ischemic heart disease and vascular homeostasis.

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

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

Chick chorioallantoic membrane as an in vivo model to study vasoreactivity: characterization of development-dependent hyperemia induced by epoxyeicosatrienoic acids (EETs)

Shell-less culture of chick chorioallantoic membrane (CAM) of developing chicken embryos is a useful model to evaluate the effects of vascular agents. We assessed the response of CAM vessels to epoxyeicosatrienoic acids (EETs), derivatives of the essential fatty acid arachidonic acid, that have a number of important biological functions, including dilation of microvessels in the coronary, cerebral, renal, and mesenteric circulations. Three of four regioisomers of EETs, 14,15-, 11,12-, and 8,9-EET, induced a characteristic dose-dependent acute hyperemia within 4 min after application on 10-day-old CAMs. This response was marked in early stages of development (between days 8 and 10), but the frequency and intensity of the response were reduced after 11 days of development. Histological examination demonstrated that the hyperemia was not due to extravasation of erythrocytes. However, many capillaries were distended and contained densely packed erythrocytes as compared to uniformly arranged vessels and erythrocytes in untreated CAMs. Transmission electron microscopy showed the basal laminae surrounding capillaries remained intact, similar to those in vehicle-treated or untreated CAM tissue. The hyperemia was specific to EETs since we did not observe it to be induced by other vasodilators such as nitric oxide or prostacyclin. In conclusion, we report a novel vascular response to EETs using the CAM as an in vivo model. These lipids specifically distend a subset of capillaries in a dose- and development-dependent manner.

Cytochrome P450 epoxygenases 2C8 and 2C9 are implicated in hypoxia-induced endothelial cell migration and angiogenesis

Recent studies suggest that cytochrome P450 (CYP) epoxygenase-derived epoxyeicosatrienoic acids (EETs) elicit cell proliferation and promote angiogenesis. The aim of this study was to determine the role of CYP 2C8/9-derived EETs in the process of angiogenesis under hypoxic conditions. In human endothelial cells, hypoxia enhanced the activity of the CYP 2C9 promoter, increased the expression of CYP 2C mRNA and protein and augmented 11,12-EET production. In Transwell assays, the migration of endothelial cells pre-exposed to hypoxia to increase CYP expression was abolished by CYP 2C antisense oligonucleotides as well as by the CYP inhibitor MS-PPOH and the EET antagonist 14,15-epoxyeicosa-5(Z)-enoic acid (EEZE). Similar findings were obtained in porcine coronary artery endothelial cells. CYP 2C9 overexpression in endothelial cells increased the association of PAK-1 with Rac, a response also elicited by the CYP 2C9 product 11,12-EET. Matrix metalloprotease (MMP) activity was increased in CYP-2C9-overexpressing cells and correlated with increased invasion through Matrigel-coated Transwell chambers: an effect sensitive to the CYP 2C9 inhibitor sulfaphenazole as well as to EEZE and the MMP inhibitor GM6001. In in vitro angiogenesis models, the EET antagonist inhibited tube formation induced by CYP 2C9 overexpression as well as that in endothelial cells exposed to hypoxia to increase CYP 2C expression. Furthermore, in the chick chorioallantoic membrane assay, EEZE abolished hypoxia-induced angiogenesis. Taken together, these data indicate that CYP 2C-derived EETs significantly affect the sequence of angiogenic events under hypoxic conditions.

Fibroblast growth factor-2 is a downstream mediator of phosphatidylinositol 3-kinase-Akt signaling in 14,15-epoxyeicosatrienoic acid-induced angiogenesis

To determine the efficacy of cytochrome P450 2C9 metabolites of arachidonic acid, viz. 5,6-, 8,9-, 11,12-, and 14,15-epoxyeicosatrienoic acids (EETs), in inducing angiogenesis, we have studied their effects on human dermal microvascular endothelial cell (HDMVEC) tube formation and migration. All four EETs stimulated HDMVEC tube formation and migration in a dose-dependent manner. Because 14,15-EET was found to be slightly more efficacious than 5,6-, 8,9-, and 11,12-EETs in stimulating HDMVEC tube formation and migration, we next focused on elucidation of the signaling mechanisms underlying its angiogenic activity. 14,15-EET stimulated Akt and S6K1 phosphorylation in Src- and phosphatidylinositol 3-kinase (PI3K)-dependent manner in HDMVECs. Inhibition of Src and PI3K-Akt-mTOR signaling by both pharmacological and dominant-negative mutant approaches suppressed 14,15-EET-induced HDMVEC tube formation and migration in vitro and Matrigel plug angiogenesis in vivo. In addition, 14,15-EET induced the expression of fibroblast growth factor-2 (FGF-2) in Src- and PI3K-Akt-dependent and mTOR-independent manner in HDMVECs. Neutralizing anti-FGF-2 antibodies completely suppressed 14,15-EET-induced HDMVEC tube formation and migration in vitro and Matrigel plug angiogenesis in vivo. Together, these results show for the first time that Src and PI3K-Akt signaling via targeting in parallel with FGF-2 expression and mTOR-S6K1 activation plays an indispensable role in 14,15-EET-induced angiogenesis.

15(S)-hydroxyeicosatetraenoic acid induces angiogenesis via activation of PI3K-Akt-mTOR-S6K1 signaling

To determine whether the lipoxygenase metabolites of arachidonic acid, 5(S)-, 12(S)-, and 15(S)-hydroxyeicosatetraenoic acids [5(S)-HETE, 12(S)-HETE, and 15(S)-HETE, respectively] are angiogenic, we have studied their effects on human dermal microvascular endothelial cell (HDMVEC) tube formation and migration. All three HETEs stimulated HDMVEC tube formation and migration. Because 15(S)-HETE was found to be more potent than 5(S)-HETE and 12(S)-HETE in HDMVEC tube formation, we next focused on elucidation of the signaling mechanisms underlying its angiogenic activity. 15(S)-HETE stimulated Akt and S6K1 phosphorylation in HDMVEC in a time-dependent manner. Wortmannin and LY294002, two specific inhibitors of phosphatidylinositol 3-kinase (PI3K), blocked both Akt and S6K1 phosphorylation, whereas rapamycin, a specific inhibitor of Akt downstream effector, mammalian target of rapamycin (mTOR), suppressed only S6K1 phosphorylation induced by 15(S)-HETE suggesting that this eicosanoid activates the PI3K-Akt-mTOR-S6K1 signaling in HDMVEC. Wortmannin, LY294002, and rapamycin also inhibited 15(S)-HETE-induced HDMVEC tube formation and migration. In addition, all three HETEs stimulated angiogenesis as measured by in vivo Matrigel plug assay with 15(S)-HETE being more potent. Pharmacologic inhibition of PI3K-Akt-mTOR-S6K1 signaling completely suppressed 15(S)-HETE-induced in vivo angiogenesis. Consistent with these observations, adenoviral-mediated expression of dominant-negative Akt also blocked 15(S)-HETE-induced HDMVEC tube formation and migration and in vivo angiogenesis. Together, these results show for the first time that 15(S)-HETE stimulates angiogenesis via activation of PI3K-Akt-mTOR-S6K1 signaling.

Hypoxic preconditioning and tolerance via hypoxia inducible factor (HIF) 1alpha-linked induction of P450 2C11 epoxygenase in astrocytes

The brain's adaptive response to ischemic preconditioning (IPC) is mediated in part via hypoxia inducible factor (HIF)-responsive genes. We previously showed that IPC induces cytochrome P450 2C11 expression in the brain, associated with protection from stroke. Cytochrome P450 2C11 is an arachidonic acid (AA) epoxygenase expressed in astrocytes, which metabolizes AA to epoxyeicosatrienoic acids (EETs). We tested the hypotheses that hypoxic preconditioning (HPC) induces 2C11 expression in astrocytes via HIF-1alpha, and that the P450 epoxygenase pathway contributes to enhanced astrocyte tolerance to ischemia-like injury induced by oxygen-glucose deprivation (OGD). Primary cultured astrocytes were incubated under normoxic or hypoxic conditions for 1, 3, 6, 24, or 48 h, and protein levels of P450 2C11 and HIF-1alpha were measured by Western blotting. Additionally, 2C11 mRNA was measured by Northern blotting, and binding of HIF-1alpha to 2C11 promoter was evaluated using electrophoretic mobility shift assay (EMSA) with 2C11 promoter DNA containing putative HIF-binding sites. Levels of 2C11 mRNA and protein were significantly increased starting at 3 and 6 h of hypoxia, respectively. The increase in 2C11 expression was preceded by an increase in HIF-1alpha protein at 1 h of hypoxia, and EMSA showed a specific and direct interaction between 2C11 promoter DNA and HIF-1alpha in nuclear extracts from astrocytes. HPC and EETs reduced astrocyte cell death, and P450 epoxygenase inhibition prevented protection by HPC. We conclude that HPC induces tolerance in astrocytes, at least in part, via HIF-1alpha-linked upregulation of P450 2C11.

Cytochrome p450 enzymes and cardiovascular disease

The cytochrome p450 (CYP) superfamily is responsible for the oxidation, peroxidation, and (or) reduction of vitamins, steroids, xenobiotics, and the majority of cardiovascular drugs in an oxygen- and NADPH-dependent manner. Although hepatic CYP have been studied extensively, the role of CYP in cardiovascular physiology and disease is poorly understood. Increasing evidence suggests that these enzymes play an important role in the pathogenesis of a number of cardiovascular diseases. The current review summarizes the understanding as to the role that dysregulated CYP expression and (or) activity may play in the onset and progression of cardiovascular disease.

Association of soluble epoxide hydrolase gene polymorphism with insulin resistance in type 2 diabetic patients

The insulin resistance found in diabetes is influenced by vascular tone and local blood flow. Endothelial-derived hyperpolarizing factor (EDHF) functions as a potent vasodilator to regulate vascular tone, and its production is regulated by soluble epoxide hydrolase (sEH). In this study, we examined the genotype distribution and allele frequency of sEH gene G860A (Arg287Gln) polymorphism in Japanese subjects (n=499) (non-diabetic subjects, n=205; type 2 diabetic patients, n=294). Also, to accurately evaluate insulin resistance, we performed the euglycemic hyperinsulinemic clamp test for each type 2 diabetic patient (n=86) from whom agreement was obtained, and then examined a possible association of sEH gene G860A polymorphism with insulin resistance status. There was no significant difference in genotype distribution and allele frequency between non-diabetic subjects and type 2 diabetic patients. Interestingly, however, there was close association of sEH gene G860A (Arg287Gln) polymorphism with insulin resistance in type 2 diabetic patients, which was not observed in non-diabetic subjects. These results suggest that sEH and EDHF play some important role in the pathogenesis of insulin resistance found in type 2 diabetes.

Characterization of 5,6- and 8,9-epoxyeicosatrienoic acids (5,6- and 8,9-EET) as potent in vivo angiogenic lipids

The cytochrome P450 arachidonic acid epoxygenase metabolites, the epoxyeicosatrienoic acids (EETs) are powerful, nonregioselective, stimulators of cell proliferation. In this study we compared the ability of the four EETs (5,6-, 8,9-, 11,12-, and 14,15-EETs) to regulate endothelial cell proliferation in vitro and angiogenesis in vivo and determined the molecular mechanism by which EETs control these events. Inhibition of the epoxygenase blocked serum-induced endothelial cell proliferation, and exogenously added EETs rescued cell proliferation from epoxygenase inhibition. Studies with selective ERK, p38 MAPK, or PI3K inhibitors revealed that whereas activation of p38 MAPK is required for the proliferative responses to 8,9- and 11,12-EET, activation of PI3K is necessary for the cell proliferation induced by 5,6- and 14,15-EET. Among the four EETs, only 5,6- and 8,9-EET are capable of promoting endothelial cell migration and the formation of capillary-like structures, events that are dependent on EET-mediated activation of ERK and PI3K. Using subcutaneous sponge models, we showed that 5,6- and 8,9-EET are pro-angiogenic in mice and that their neo-vascularization effects are enhanced by the co-administration of an inhibitor of EET enzymatic hydration, presumably because of reduced EET metabolism and inactivation. These studies identify 5,6- and 8,9-EET as powerful and selective angiogenic lipids, provide a functional link between the EET proliferative chemotactic properties and their angiogenic activity, and suggest a physiological role for them in angiogenesis and de novo vascularization.

Angiotensin II-induced Akt activation is mediated by metabolites of arachidonic acid generated by CaMKII-stimulated Ca2+-dependent phospholipase A2

Angiotensin II (ANG II) promotes vascular smooth muscle cell (VSMC) growth, stimulates Ca2+-calmodulin (CaM)-dependent kinase II (CaMKII), and activates cytosolic Ca2+-dependent phospholipase A2(cPLA2), which releases arachidonic acid (AA). ANG II also generates H2O2and activates Akt, which have been implicated in ANG II actions in VSMC. This study was conducted to investigate the relationship of these signaling molecules to Akt activation in rat aortic VSMC. ANG II increased Akt activity, as measured by its phosphorylation at serine-473. ANG II (200 nM)-induced Akt phosphorylation was decreased by extracellular Ca2+depletion and calcium chelator EGTA and inhibitors of CaM [ N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide] and CaMKII {(2-[ N-(2-hydroxyethyl)]- N-(4-me-thoxybenzenesulfonyl)]amino- N-(4-chlorocinnamyl)- N-methylbenzyl-amine)}. cPLA2inhibitor pyrrolidine-1, antisense oligonucleotide, and retroviral small interfering RNA also attenuated ANG II-induced Akt phosphorylation. AA increased Akt phosphorylation, and AA metabolism inhibitor 5,8,11,14-eicosatetraynoic acid (ETYA) blocked ANG II- and AA-induced Akt phosphorylation (199.03 ± 27.91% with ANG II and 110.18 ± 22.40% with ETYA + ANG II; 405.00 ± 86.22% with AA and 153.97 ± 63.26% with ETYA + AA). Inhibitors of lipoxygenase (cinnamyl-3,4-dihydroxy-α-cyanocinnamate) and cytochrome P-450 (ketoconazole and 17-octadecynoic acid), but not cyclooxygenase (indomethacin), attenuated ANG II- and AA-induced Akt phosphorylation. Furthermore, 5( S)-, 12( S)-, 15( S)-, and 20-hydroxyeicosatetraenoic acids and 5,6-, 11,12-, and 14,15-epoxyeicosatrienoic acids increased Akt phosphorylation. Catalase inhibited ANG II-increased H2O2production but not Akt phosphorylation. Oleic acid, which also increased H2O2production, did not cause Akt phosphorylation. These data suggest that ANG II-induced Akt activation in VSMC is mediated by AA metabolites, most likely generated via lipoxygenase and cytochrome P-450 consequent to AA released by CaMKII-activated cPLA2and independent of H2O2production.

Arachidonic acid cascade in endothelial pathobiology

Arachidonic acid (AA) and its metabolites (eicosanoids) represent powerful mediators, used by organisms to induce and suppress inflammation as a part of the innate response to disturbances. Several cell types participate in the synthesis and release of AA metabolites, while many cell types represent the targets for eicosanoid action. Endothelial cells (EC), forming a semi-permeable barrier between the interior space of blood vessels and underlying tissues, are of particular importance for the development of inflammation, since endothelium controls such diverse processes as vascular tone, homeostasis, adhesion of platelets and leukocytes to the vascular wall, and permeability of the vascular wall for cells and fluids. Proliferation and migration of endothelial cells contribute significantly to new vessel development (angiogenesis). This review discusses endothelial-specific synthesis and action of arachidonic acid derivatives with a particular focus on the mechanisms of signal transduction and associated intracellular protein targets.

Identification and Characterization of an Ovary-Selective Isoform of Epoxide Hydrolase1

A novel ovary-selective gene was identified by suppression subtractive hybridization (SSH) that is expressed only during the mouse periovulatory phase of a stimulated estrous cycle. Analysis of the protein encoded by the full-length cDNA revealed that the majority of it, with the exception of the first 44 amino acids, matched soluble epoxide hydrolase (Ephx2, referred to as Ephx2A). By comparing the cDNA sequence of this newly identified variant of soluble epoxide hydrolase (referred to as Ephx2B) with the mouse genome database, an exon was identified that corresponds to its unique 5' cDNA sequence. Through the use of an Ephx2A-specific probe, Northern blot analysis revealed that this mRNA was also expressed in the ovary, with the highest level of expression occurring during the luteal phase of a stimulated estrous cycle. In situ hybridization revealed that Ephx2B mRNA expression was restricted to granulosa cells of preovulatory follicles. Ephx2A mRNA expression, however, was detectable in follicles at different stages of development, as well as in the corpus luteum. Total ovarian epoxide hydrolase activity increased following the induction of follicular development, and remained elevated through the periovulatory and postovulatory stages of a stimulated estrous cycle. The change in enzyme activity paralleled the combined mRNA expression profiles for both Ephx2A and Ephx2B, thus supporting a role for epoxide metabolism in ovarian function.

Inhibitors of cytochrome P450 4A suppress angiogenic responses

Cytochrome P450 enzymes of the 4A family (CYP4A) convert arachidonic acid to 20-hydroxyeicosatetraenoic acid (20-HETE) in blood vessels of several vascular beds. The present study examined the effects of inhibiting the formation of 20-HETE with N-hydroxy-N'-(4-butyl-2-methylphenol) formamidine (HET0016) on the mitogenic response of vascular endothelial growth factor (VEGF) in human umbilical vein endothelial cells (HUVECs) in vitro, and on growth factor-induced angiogenesis in the cornea of rats in vivo. HET0016 (10 micromol/L and 20 microg, respectively) abolished the mitogenic response to VEGF in HUVECs and the angiogenic response to VEGF, basic fibroblast growth factor, and epidermal growth factor in vivo by 80 to 90% (P < 0.001). Dibromododecenyl methylsulfonimide (DDMS), a structurally and mechanistically different inhibitor of 20-HETE synthesis, also abolished angiogenic responses when tested with VEGF. Additionally, administration of the stable 20-HETE agonist, 20-hydroxyeicosa-6(Z) 15(Z)-dienoic acid (WIT003) induced mitogenesis in HUVECs and angiogenesis in the rat cornea in vivo. We studied the ability of HET0016 to alter the angiogenic response in the rat cornea to human glioblastoma cancer cells (U251). When administered locally into the cornea, HET0016 (20 microg) reduced the angiogenic response to U251 cancer cells by 70%. These results suggest that a product of CYP4A product, possibly 20-HETE, plays a critical role in the regulation of angiogenesis and may provide a useful target for reduction of pathological angiogenesis.

Biosynthesis of epoxyeicosatrienoic acids varies between polymorphic CYP2C enzymes

Arachidonic acid is oxidized by cytochromes P450 2C (CYP2C) to epoxyeicosatrienoic acids (EETs), possessing vasoactive properties, with 11,12-EET as the endothelium derived hyperpolarization factor. Genetic variants of CYP2C enzymes have altered drug metabolizing capacity. Our primary aim was to determine whether EET biosynthesis differed in human liver microsomes with known CYP2C genotypes. Human liver microsomes (n = 25) of different CYP2C genotypes or yeast-expressed CYP2C enzymes were used. Analysis of metabolites was performed by liquid chromatography/mass spectrometry. Samples genotyped as CYP2C8*3/*3/CYP2C9*2/*2 exhibited a 34% (p < 0.05) decreased EET biosynthesis, compared to other CYP2C8/CYP2C9 haplotypes. Inhibition experiments suggested CYP2C8 and CYP2C9 to be the predominant catalysts of EETs. We found no differences between the three recombinantly expressed CYP2C9 variants, but CYP2C8.1 had lower K(m) than these isoforms. In conclusion, there are genetic differences in the CYP2C-dependent oxidation of arachidonic acid to vasoactive metabolites, of which the relevance to cardiovascular pathophysiology is still unclear.

Selective blockade of the intermediate-conductance Ca2+-activated K+ channel suppresses proliferation of microvascular and macrovascular endothelial cells and angiogenesis in vivo

OBJECTIVE

Ca2+-activated K+ (K(Ca)) channels have been proposed to promote mitogenesis in several cell types. Here, we tested whether the intermediate-conductance K(Ca) channel (IKCa1) and the large-conductance K(Ca) channel (BK(Ca)) contribute to endothelial cell (EC) proliferation and angiogenesis.

MATERIAL AND RESULTS

Function and expression of IKCa1 and BK(Ca)/Slo were investigated by patch-clamp analysis and real-time RT-PCR in human umbilical vein ECs (HUVECs) and in dermal human microvascular ECs 1 (HMEC-1). HMEC-1 expressed IKCa1 and BK(Ca)/Slo, whereas HUVECs expressed IKCa1. A 48-hour exposure to basic fibroblast growth factor (bFGF) augmented IKCa1 current amplitudes and induced a 3-fold increase in IKCa1 mRNA expression in HUVECs and HMEC-1. Vascular endothelial growth factor (VEGF) was also effective in upregulating IKCa1. BK(Ca)/Slo expression and current amplitudes in HMEC-1 were not altered by bFGF. bFGF- and VEGF-induced EC proliferation was suppressed by charybdotoxin, clotrimazole, or the selective IKCa1 blocker 1-[(2-chlorophenyl)diphenylmethyl]-1H-pyrazole (TRAM-34), whereas inhibition of BK(Ca)/Slo by iberiotoxin was ineffective. In the Matrigel plug assay in mice, administration of TRAM-34 for 2 weeks significantly suppressed angiogenesis by approximately 85%.

CONCLUSIONS

bFGF and VEGF upregulate expression of IKCa1 in human ECs. This upregulation of IKCa1 seems to be required for mitogen-induced EC proliferation and angiogenesis in vivo. Selective IKCa1 blocker might be of therapeutic value to prevent tumor angiogenesis.

Cytochrome P4502C9-derived epoxyeicosatrienoic acids induce the expression of cyclooxygenase-2 in endothelial cells

OBJECTIVE

Cytochrome P450 (CYP) epoxygenases metabolize arachidonic acid to epoxyeicosatrienoic acids (EETs). CYP2C9-derived EETs elicit endothelial cell proliferation and angiogenesis, but the signaling pathways involved are incompletely understood. Because cyclooxygenase-2 (COX-2) is involved in angiogenesis, we determined whether a link exists between CYP2C9 and COX-2 expression.

METHODS AND RESULTS

Human umbilical vein endothelial cells were infected with CYP2C9 sense or antisense adenoviral constructs. Overexpression of CYP2C9 increased COX-2 promoter activity, an effect accompanied by a significant increase in COX-2 protein expression and elevated prostacyclin production. The CYP2C9-induced expression of COX-2 was inhibited by the CYP2C9 inhibitor, sulfaphenazole, whereas 11,12-EET increased COX-2 expression. Overexpression of CYP2C9 and stimulation with 11,12-EET increased intracellular cAMP levels and stimulated DNA-binding of the cAMP-response element-binding protein. The protein kinase A inhibitor, KT5720, attenuated the CYP2C9-induced increase in COX-2 promoter activity and protein expression. Overexpression of CYP2C9 stimulated endothelial tube formation, an effect that was attenuated by the COX-2 inhibitor celecoxib. Identical responses were observed in cells preconditioned by cyclic strain to increase CYP2C expression.

CONCLUSIONS

These data indicate that CYP2C9-derived EETs induce the expression of COX-2 in endothelial cells via a cAMP-dependent pathway and that this mechanism contributes to CYP2C9-induced angiogenesis. Overexpression of cytochrome P450 (CYP) 2C9 in endothelial cells increased cAMP levels, stimulated the cAMP-response element-binding protein, and enhanced cyclooxygenase-2 (COX-2) promoter activity, protein expression, and prostacyclin production. CYP2C9 overexpression stimulated endothelial tube formation, which was attenuated by the COX-2 inhibitor celecoxib. Thus, COX-2 contributes to CYP2C9-induced angiogenesis.

Effect of soluble epoxide hydrolase inhibition on epoxyeicosatrienoic acid metabolism in human blood vessels

We investigated the effects of soluble epoxide hydrolase (sEH) inhibition on epoxyeicosatrienoic acid (EET) metabolism in intact human blood vessels, including the human saphenous vein (HSV), coronary artery (HCA), and aorta (HA). When HSV segments were perfused with 2 micromol/l 14,15-[3H]EET for 4 h, >60% of radioactivity in the perfusion medium was converted to 14,15-dihydroxyeicosatrienoic acid (DHET). Similar results were obtained with endothelium-denuded vessels. 14,15-DHET was released from both the luminal and adventitial surfaces of the HSV. When HSVs were incubated with 14,15-[3H]EET under static (no flow) conditions, formation of 14,15-DHET was detected within 15 min and was inhibited by the selective sEH inhibitors N,N'-dicyclohexyl urea and N-cyclohexyl-N'-dodecanoic acid urea (CUDA). Similarly, CUDA inhibited the conversion of 11,12-[3H]EET to 11,12-DHET by the HSV. sEH inhibition enhanced the uptake of 14,15-[3H]EET and facilitated the formation of 10,11-epoxy-16:2, a beta-oxidation product. The HCA and HA converted 14,15-[3H]EET to DHET, and this also was inhibited by CUDA. These findings in intact human blood vessels indicate that conversion to DHET is the predominant pathway for 11,12- and 14,15-EET metabolism and that sEH inhibition can modulate EET metabolism in vascular tissue.

Transfection and Functional Expression of CYP4A1 and CYP4A2 Using Bicistronic Vectors in Vascular Cells and Tissues

20-hydroxyeicosatetraenoic acid (20-HETE), a CYP4A-derived arachidonic acid metabolite, is a potent vasoconstrictor and a modulator of vascular reactivity. We have shown that CYP4A1 and CYP4A2 are the major CYP4A isoforms expressed in the rat renal microcirculation. In the present study, we constructed two bicistronic vectors, pIRES2-EGFP-4A1 and pIRES2-EGFP-4A2, and examined their functional efficacy in COS-1 and vascular smooth muscle (A7r5) cells and in microdissected rat interlobar arteries. Immunocytochemistry coupled with fluorescence microscopy of pIRES2-EGFP-4A1- or pIRES2-EGFP-4A2-transfected COS-1 and A7r5 cells indicated that both enhanced green fluorescence protein (EGFP) and CYP4A1/4A2 were expressed in 80 to 90% of the cells. Western blot analysis showed a 3- to 5-fold increase of CYP4A1 and CYP4A2 proteins in pIRES2-EGFP-4A1- and pIRES2-EGFP-4A2-transfected cells as compared with control pIRES2-transfected cells. Cells transfected with pIRES2-EGFP-4A1 and pIRES2-EGFP-4A2 catalyzed arachidonic acid omega-hydroxylation to 20-HETE at rates of 0.85 +/- 0.29 and 0.27 +/- 0.04 nmol/10(7) cells/h, respectively. Transfection of interlobar arteries with either plasmid yielded EGFP immunofluorescence that was localized to the intima, media, and adventitia. Arteries transfected with pIRES2-EGFP-4A1 and pIRES2-EGFP-4A2 showed increased vasoreactivity displaying EC50 to phenylephrine of 0.24 +/- 0.07 and 0.11 +/- 0.03 microM, respectively, as compared with arteries transfected with pIRES2-EGFP (1.11 +/- 0.21 microM; n=6, p <0.05). The increased vasoreactivity to phenylephrine was inhibited by N-methylsulfonyl-12,12-dibromododec-11-enamide, an inhibitor of CYP4A-catalyzed reactions, suggesting that a product of CYP4A1 and CYP4A2 catalytic activity contributed to the increased constrictor responsiveness. Removal of the endothelium did not prevent the sensitization to phenylephrine in vessels transfected with the plasmid containing the CYP4A1 cDNA, suggesting that the CYP4A product responsible for the sensitizing effect, presumably 20-HETE, is not of endothelial cell origin.

Valproic acid inhibits angiogenesis in vitro and in vivo

Valproic acid (VPA) is a widely used antiepileptic agent that is undergoing clinical evaluation for anticancer therapy. We assessed the effects of VPA on angiogenesis in vitro and in vivo. In human umbilical vein endothelial cells, therapeutically relevant concentrations of VPA (0.25 to 1 mM) inhibited proliferation, migration, and tube formation. VPA 1 mM inhibited endothelial cell proliferation by 51 +/- 5%, migration by 86 +/- 11%, and tube formation by 82 +/- 3%. These changes were preceded by the hyperacetylation of histone H4, indicating the inhibition of histone deacetylase (HDAC), and a decreased expression of the endothelial nitric-oxide synthase (eNOS). The inhibition of endothelial cell tube formation by VPA was prevented by addition of the nitric oxide donor (Z)-1-[2-(2-aminoethyl)-N-(2-ammonioethyl)amino]diazen-1-ium-1,2-diolate (DETA NONOate). The anticonvulsive active VPA derivative 2-ethyl-4-methylpentanoic acid, which does not inhibit HDAC, did not affect endothelial cell proliferation, tube formation, or eNOS expression. VPA was also found to inhibit angiogenesis in vivo in the chicken chorioallantoic membrane assay and in a Matrigel plug assay in mice. Embryos from VPA-treated mice showed disturbed vessel formation. These results indicate that therapeutic plasma levels of VPA inhibit angiogenesis by a mechanism involving a decrease in eNOS expression preceded by HDAC inhibition.

Membrane-potential-dependent inhibition of platelet adhesion to endothelial cells by epoxyeicosatrienoic acids

OBJECTIVE

Epoxyeicosatrienoic acids (EETs) are potent vasodilators produced by endothelial cells. In many vessels, they are an endothelium-derived hyperpolarizing factor (EDHF). However, it is unknown whether they act as an EDHF on platelets and whether this has functional consequences.

METHODS AND RESULTS

Flow cytometric measurement of platelet membrane potential using the fluorescent dye DiBac4 showed a resting potential of -58+/-9 mV. Different EET regioisomers hyperpolarized platelets down to -69+/-2 mV, which was prevented by the non-specific potassium channel inhibitor charybdotoxin and by use of a blocker of calcium-activated potassium channels of large conductance (BK(Ca) channels), iberiotoxin. EETs inhibited platelet adhesion to endothelial cells under static and flow conditions. Exposure to EETs inhibited platelet P-selectin expression in response to ADP. Stable overexpression of cytochrome P450 2C9 in EA.hy926 cells (EA.hy2C9 cells) resulted in release of EETs and a factor that hyperpolarized platelets and inhibited their adhesion to endothelial cells. These effects were again inhibited by charybdotoxin and iberiotoxin.

CONCLUSIONS

EETs hyperpolarize platelets and inactivate them by inhibiting adhesion molecule expression and platelet adhesion to cultured endothelial cells in a membrane potential-dependent manner. They act as an EDHF on platelets and might be important mediators of the anti-adhesive properties of vascular endothelium.

Identification of novel roles of the cytochrome p450 system in early embryogenesis: effects on vasculogenesis and retinoic Acid homeostasis

The cytochrome P450-dependent monooxygenase system catalyzes the metabolism of xenobiotics and endogenous compounds, including hormones and retinoic acid. In order to establish the role of these enzymes in embryogenesis, we have inactivated the system through the deletion of the gene for the electron donor to all microsomal P450 proteins, cytochrome P450 reductase (Cpr). Mouse embryos homozygous for this deletion died in early to middle gestation (approximately 9.5 days postcoitum [dpc]) and exhibited a number of novel phenotypes, including the severe inhibition of vasculogenesis and hematopoiesis. In addition, defects in the brain, limbs, and cell types where CPR was shown to be expressed were observed. Some of the observed abnormalities have been associated with perturbations in retinoic acid homeostasis in later embryogenesis. Consistent with this possibility, embryos at 9.5 dpc had significantly elevated levels of retinoic acid and reduced levels of retinol. Further, some of the observed phenotypes could be either reversed or exacerbated by decreasing or increasing maternal retinoic acid exposure, respectively. Detailed analysis demonstrated a close relationship between the observed phenotype and the expression of genes controlling vasculogenesis. These data demonstrate that the cytochrome P450 system plays a key role in early embryonic development; this process appears to be, at least in part, controlled by regional concentrations of retinoic acid and has profound effects on blood vessel formation.

11,12-Epoxyeicosatrienoic acid-induced inhibition of FOXO factors promotes endothelial proliferation by down-regulating p27Kip1

Cytochrome P450-derived epoxyeicosatrienoic acids (EETs) stimulate endothelial cell proliferation and angiogenesis. In this study, we investigated the involvement of the forkhead box, class O (FOXO) family of transcription factors and their downstream target p27Kip1 in EET-induced endothelial cell proliferation. Incubation of human umbilical vein endothelial cells with 11,12-EET induced a time- and dose-dependent decrease in p27Kip1 protein expression, whereas p21Cip1 was not significantly affected. This effect on p27Kip1 protein was associated with decreased mRNA levels as well as p27Kip1 promoter activity. 11,12-EET also stimulated the time-dependent phosphorylation of Akt and of the forkhead factors FOXO1 and FOXO3a, effects prevented by the phosphatidylinositol 3-kinase inhibitor LY 294002. Transfection of endothelial cells with either a dominant-negative or an "Akt-resistant"/constitutively active FOXO3a mutant reversed the 11,12-EET-induced down-regulation of p27Kip1, whereas transfection of a constitutive active Akt decreased p27Kip1 expression independently of the presence or absence of 11,12-EET. To determine whether these effects are involved in EET-induced proliferation, endothelial cells were transfected with the 11,12-EET-generating epoxygenase CYP2C9. Transfection of CYP2C9 elicited endothelial cell proliferation and this effect was inhibited in cells co-transfected with CYP2C9 and either a dominant-negative Akt or constitutively active FOXO3a. Reducing FOXO expression using RNA interference, on the other hand, attenuated p27Kip1 expression and stimulated endothelial cell proliferation. These results indicate that EET-induced endothelial cell proliferation is associated with the phosphatidylinositol 3-kinase/Akt-dependent phosphorylation and inactivation of FOXO factors and the subsequent decrease in expression of the cyclin-dependent kinase inhibitor p27Kip1.