Cytochrome P450 2C expression and EDHF-mediated relaxation in porcine coronary arteries is increased by cortisol

Maximal exercise and plasma cytochrome P450 and lipoxygenase mediators: a lipidomics study

Epoxides derived from arachidonic acid (AA) are released during exercise and may contribute to vasodilation. However, exercise may also affect circulating levels of other epoxides derived from cytochromes P450 (CYP) monooxygenase and lipoxygenase (LOX) pathways, many of whose exhibit cardiovascular activity in vitro. The effects of exercise on their levels have not been documented. We tested the hypothesis that acute, maximal exercise would influence the plasma concentrations of these vasoactive substances. We measured plasma CYP and LOX mediators derived from both the n − 3 and n − 6 fatty acid (FA) classes in healthy volunteers before, during and after short‐term exhaustive exercise. Lipid mediators were profiled by means of LC–MS/MS tandem mass spectrometry. A maximal Bruce treadmill test was performed to voluntary exhaustion. Exhaustive exercise increased the circulating levels of epoxyoctadecenoic (12,13‐EpOME), dihydroxyeicosatrienoic (5,6‐DHET), dihydroxyeicosatetraenoic acids (5,6‐DiHETE, 17,18‐DiHETE), but had no effect on the majority of CYP and LOX metabolites. Although our calculations of diol/epoxide ratios revealed preferred hydrolysis of epoxyeicosatrienoic acids (EEQs) into their diols (DiHETEs), this hydrolysis was resistant to maximal exercise. Our study is the first documentation that bioactive endogenous n − 3 and n − 6 CYP lipid mediators are released by short‐term exhaustive exercise in humans. In particular, the CYP epoxy‐metabolite status, 12,13‐EpOME/DiHOME, 5,6‐EET/DHET, 5,6‐EEQ/DiHETE and 17,18‐EEQ/DiHETE may contribute to the cardiovascular response during maximal exercise.

The effect of dietary arachidonic acid (ARA) on growth performance, fatty acid composition and expression of ARA metabolism-related genes in larval half-smooth tongue sole (Cynoglossus semilaevis)

The present study was conducted to investigate the effects of dietary arachidonic acid (ARA) on growth performance, fatty acid composition and ARA metabolism-related gene expression in larval half-smooth tongue sole (Cynoglossus semilaevis). Larvae (35 d after hatching, 54 (sem 1) mg) were fed diets with graded concentrations of ARA (0·01, 0·39, 0·70, 1·07, 1·42 and 2·86 % dry weight) five times per d to apparent satiation for 30 d. Results showed that increased dietary ARA concentration caused a significant non-linear rise to a plateau in survival rate, final body weight and thermal growth coefficient, and the maximum values occurred with the 1·42 % ARA treatment. As dietary ARA increased to 1·07 or 1·42 %, activities of trypsin, leucine aminopeptidase and alkaline phosphatase levels increased, but they decreased with higher ARA concentrations. The fatty acid composition of tongue sole larvae was almost well correlated with their dietary fatty acid profiles, and the EPA content of the larvae decreased with increasing dietary ARA. Meanwhile, the partial sequences of COX-1a (cyclo-oxygenase-1a), COX-1b (cyclo-oxygenase-1b), COX-2 (cyclo-oxygenase-2), 5-LOX (5-lipoxygenase) and CYP2J6-like (cytochrome P450 2J6-like) were also obtained. Both COX-2 and 5-LOX mRNA expression levels significantly increased to a plateau in an ‘L’-shaped manner as dietary ARA increased to 1·07 or 1·42 %, but no significant differences were found in the gene expression of COX-1a, COX-1b or CYP2J6-like. These results suggest that 1·07–1·42 % dietary ARA was beneficial to the growth performance of larval tongue sole, and the regulation of dietary ARA on the growth performance of larvae was probably involved in altering the mRNA expression of COX-2 and 5-LOX.

Acute psychological and physical stress transiently enhances brachial artery flow-mediated dilation stimulated by exercise-induced increases in shear stress

Exercise elevates conduit artery shear stress and stimulates flow-mediated dilation (FMD). However, little is known regarding the impact of acute psychological and physical stress on this response. The purpose of this study was to examine the impact of the Trier Social Stress Test (TSST (speech and arithmetic tasks)) and a cold pressor test (CPT) with and without social evaluation (SE) on exercise-induced brachial artery FMD (EX-FMD). A total of 59 healthy male subjects were randomly assigned to 1 of 3 conditions: TSST, CPT, or CPT with SE. During 6 min of handgrip exercise, brachial artery EX-FMD was assessed before and 15 and 35 min poststress with echo and Doppler ultrasound. Shear stress was estimated as shear rate, calculated as brachial artery mean blood velocity/brachial artery diameter. Results are means ± SD. All conditions elicited significant physiological stress responses. Salivary cortisol increased from 4.6 ± 2.4 nmol/L to 10.0 ± 5.0 nmol/L (p < 0.001; condition effect: p = 0.292). Mean arterial pressure increased from 98.6 ± 12.1 mm Hg to 131.9 ± 18.7 mm Hg (p < 0.001; condition effect: p = 0.664). Exercise shear rate did not differ between conditions (p = 0.592), although it was modestly lower poststress (prestress: 72.3 ± 4.5 s−1; 15 min poststress: 70.8 ± 5.4 s−1; 35 min poststress: 70.6 ± 6.1 s−1; trial effect: p = 0.011). EX-FMD increased from prestress to 15 min poststress in all conditions (prestress: 6.2% ± 2.8%; 15 min poststress: 7.9% ± 3.2%; 35 min poststress: 6.6% ± 2.9%; trial effect: p < 0.001; condition effect: p = 0.611). In conclusion, all conditions elicited similar stress responses that transiently enhanced EX-FMD. This response may help to support muscle perfusion during stress.

Cytochrome P450 and ischemic heart disease: current concepts and future directions

INTRODUCTION

The P450 enzymes (P450s) mediate the biotransformation of several drugs, steroid hormones, eicosanoids, cholesterol, vitamins, fatty acids and bile acids, many of which affect cardiovascular homeostasis. Experimental studies have demonstrated that several P450s modulate important steps in the pathogenesis of ischemic heart disease (IHD).

AREAS COVERED

This article discusses the current knowledge on i) the expression of P450s in cardiovascular and renal tissues; ii) the role of P450s in the pathophysiology of IHD, in particular the modulation of blood pressure and cardiac hypertrophy, coronary arterial tone, ischemia-reperfusion injury and the metabolism of cardiovascular drugs; iii) the available evidence from observational studies on the association between P450 gene polymorphisms and risk of myocardial infarction (MI); and iv) suggestions for further research in this area.

EXPERT OPINION

P450s exert important modulatory effects in experimental models of IHD and MI. However, observational studies have provided conflicting results on the association between P450 genetic polymorphisms and MI. Further, adequately powered studies are required to ascertain the biological and clinical impact of P450s on clinical IHD end-points, that is, fatal and nonfatal MI, revascularization and long-term outcomes post MI. Pharmacogenetic substudies of recently completed cardiovascular clinical trials might represent an alternative strategy in this context.

Inducible endothelium-derived hyperpolarizing factor: role of the 15-lipoxygenase-EDHF pathway

Endothelium-derived hyperpolarizing factors (EDHFs) regulate vascular tone by contributing to the vasorelaxations to shear stress and endothelial agonists such as bradykinin and acetylcholine. 15(S)-Hydroxy-11,12-epoxyeicosatrienoic acid (15-H-11,12-EETA) and 11(R),12(S),15(S)-trihydroxyeicosatrienoic acid (11,12,15-THETA) are endothelial metabolites of the 15-lipoxygenase (15-LO) pathway of arachidonic acid metabolism and are EDHFs. 11,12,15-THETA activates small conductance, calcium-activated potassium channels on smooth muscle cells causing membrane hyperpolarization, and relaxation. Expression levels of 15-LO in the endothelium regulate the activity of the 15-LO/15-H-11,12-EETA/11,12,15-THETA pathway and its contribution to vascular tone. Regulation of its expression is by transcriptional, translational, and epigenetic mechanisms. Hypoxia, hypercholesterolemia, atherosclerosis, anemia, estrogen, interleukins, and possibly other hormones increase 15-LO expression. An increase in 15-LO results in increased synthesis of 15-H-11,12-EETA and 11,12,15-THETA, increased membrane hyperpolarization, and enhanced contribution to relaxation by endothelial agonists. Thus, the 15-LO pathway represents the first example of an inducible EDHF. In addition to 15-LO metabolites, a number of chemicals have been identified as EDHFs and their contributions to vascular tone vary with species and vascular bed. The reason for multiple EDHFs has evaded explanation. However, EDHF functioning as constitutive EDHFs or inducible EDHFs may explain the need for chemically and biochemically distinct pathways for EDHF activity and the variation in EDHFs between species and vascular beds. This new EDHF classification provides a framework for understanding EDHF activity in physiological and pathological conditions.

The transcriptional regulation of the human CYP2C genes

In humans, four members of the CYP2C subfamily (CYP2C8, CYP2C9, CYP2C18, and CYP2C19) metabolize more than 20% of all therapeutic drugs as well as a number of endogenous compounds. The CYP2C enzymes are found predominantly in the liver, where they comprise approximately 20% of the total cytochrome P450. A variety of xenobiotics such as phenobarbital, rifampicin, and hyperforin have been shown to induce the transcriptional expression of CYP2C genes in primary human hepatocytes and to increase the metabolism of CYP2C substrates in vivo in man. This induction can result in drug-drug interactions, drug tolerance, and therapeutic failure. Several drug-activated nuclear receptors including CAR, PXR, VDR, and GR recognize drug responsive elements within the 5' flanking promoter region of CYP2C genes to mediate the transcriptional upregulation of these genes in response to xenobiotics and steroids. Other nuclear receptors and transcriptional factors including HNF4alpha, HNF3gamma, C/EBPalpha and more recently RORs, have been reported to regulate the constitutive expression of CYP2C genes in liver. The maximum transcriptional induction of CYP2C genes appears to be achieved through a coordinative cross-talk between drug responsive nuclear receptors, hepatic factors, and coactivators. The transcriptional regulatory mechanisms of the expression of CYP2C genes in extrahepatic tissues has received less study, but these may be altered by perturbations from pathological conditions such as ischemia as well as some of the receptors mentioned above.

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.

Cytochrome P450 Epoxygenase CYP2J2 and the Risk of Coronary Artery Disease

Cytochrome P450 (CYP) enzyme 2J2, an epoxygenase predominantly expressed in the heart, metabolizes arachidonic acid to biologically active eicosanoids. One of the CYP2J2 products, 11,12-epoxyeicosatrienoic acid, has several vasoprotective effects. A frequent promoter polymorphism of CYP2J2 decreases gene expression and is associated with coronary artery disease. This association supports the vascular protective role of CYP-derived eicosanoids in cardiovascular disease.

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.

Possible pathomechanisms of sudden infant death syndrome: key role of chronic hypoxia, infection/inflammation states, cytokine irregularities, and metabolic trauma in genetically predisposed infants

Chronic hypoxia, viral infections/bacterial toxins, inflammation states, biochemical disorders, and genetic abnormalities are the most likely trigger of sudden infant death syndrome (SIDS). Autopsy studies have shown increased pulmonary density of macrophages and markedly more eosinophils in the lungs accompanied by increased T and B lymphocytes. The elevated levels of immunoglobulins, about 20% more muscle in the pulmonary arteries, increased airway smooth muscle cells, and increased fetal hemoglobin and erythropoietin are evidence of chronic hypoxia before death. Other abnormal findings included mucosal immune stimulation of the tracheal wall, duodenal mucosa, and palatine tonsils, and circulating interferon. Low normal or higher blood levels of cortisol often with petechiae on intrathoracic organs, depleted maternal IgG antibodies to endotoxin core (EndoCAb) and early IgM EndoCAb triggered, partial deletions of the C4 gene, and frequent IL-10-592*A polymorphism in SIDS victims as well as possible hypoxia-induced decreased production of antiinflammatory, antiimmune, and antifibrotic cytokine IL-10, may be responsible for the excessive reactions to otherwise harmless infections. In SIDS infants, during chronic hypoxia and times of infection/inflammation, several proinflammatory cytokines are released in large quantities, sometimes also representing a potential source of tissue damage if their production is not sufficiently well controlled, eg, by pituitary adenylate cyclase-activating polypeptide (PACAP) and vasoactive intestinal polypeptide (VIP). These proinflammatory cytokines down-regulate gene expression of major cytochrome P-450 and/or other enzymes with the specific effects on mRNA levels, protein expression, and enzyme activity, thus affecting metabolism of several endogenous lipophilic substances, such as steroids, lipid-soluble vitamins, prostaglandins, leukotrienes, thromboxanes, and exogenous substances. In SIDS victims, chronic hypoxia, TNF-alpha and other inflammatory cytokines, and arachidonic acid (AA) as well as n-3 polyunsaturated fatty acids (FA), stimulated and/or augmented superoxide generation by polymorphonuclear leukocytes, which contributed to tissue damage. Chronic hypoxia, increased amounts of nonheme iron in the liver and adrenals of these infants, enhanced activity of CYP2C9 regarded as the functional source of reactive oxygen species (ROS) in some endothelial cells, and nicotine accumulation in tissues also intensified production of ROS. These increased quantities of proinflammatory cytokines, ROS, AA, and nitric oxide (NO) also resulted in suppression of many CYP450 and other enzymes, eg, phosphoenolpyruvate carboxykinase (PEPCK), an enzyme important in the metabolism of FA during gluconeogenesis and glyceroneogenesis. PEPCK deficit found in SIDS infants (caused also by vitamin A deficiency) and eventually enhanced by PACAP lipolysis of adipocyte triglycerides resulted in an increased FA level in blood because of their impaired reesterification to triacylglycerol in adipocytes. In turn, the overproduction and release of FA into the blood of SIDS victims could lead to the metabolic syndrome and an early phase of type 2 diabetes. This is probably the reason for the secondary overexpression of the hepatic CYP2C8/9 content and activity reported in SIDS infants, which intensified AA metabolism. Pulmonary edema and petechial hemorrhages often present in SIDS victims may be the result of the vascular leak syndrome caused by IL-2 and IFN-alpha. Chronic hypoxia with the release of proinflammatory mediators IL-1alpha, IL-1beta and IL-6, and overloading of the cardiovascular and respiratory systems due to the narrowing airways and small pulmonary arteries of these children could also contribute to the development of these abnormalities. Moreover, chronic hypoxia of SIDS infants induced also production of hypoxia-inducible factor 1alpha (HIF-1alpha), which stimulated synthesis and release of different growth factors by vascular endothelial cells and intensified subclinical inflammatory reactions in the central nervous system, perhaps potentiated also by PACAP and VIP gene mutations. These processes could lead to the development of brainstem gliosis and disorders in the release of neuromediators important for physiologic sleep regulation. All these changes as well as eventual PACAP abnormalities could result in disturbed homeostatic control of the cardiovascular and respiratory responses of SIDS victims, which, combined with the nicotine effects and metabolic trauma, finally lead to death in these often genetically predisposed children.

Multilocus analysis of hypertension: a hierarchical approach

While hypertension is a complex disease with a well-documented genetic component, genetic studies often fail to replicate findings. One possibility for such inconsistency is that the underlying genetics of hypertension is not based on single genes of major effect, but on interactions among genes. To test this hypothesis, we studied both single locus and multilocus effects, using a case-control design of subjects from Ghana. Thirteen polymorphisms in eight candidate genes were studied. Each candidate gene has been shown to play a physiological role in blood pressure regulation and affects one of four pathways that modulate blood pressure: vasoconstriction (angiotensinogen, angiotensin converting enzyme - ACE, angiotensin II receptor), nitric oxide (NO) dependent and NO independent vasodilation pathways and sodium balance (G protein-coupled receptor kinase, GRK4). We evaluated single site allelic and genotypic associations, multilocus genotype equilibrium and multilocus genotype associations, using multifactor dimensionality reduction (MDR). For MDR, we performed systematic reanalysis of the data to address the role of various physiological pathways. We found no significant single site associations, but the hypertensive class deviated significantly from genotype equilibrium in more than 25% of all multilocus comparisons (2,162 of 8,178), whereas the normotensive class rarely did (11 of 8,178). The MDR analysis identified a two-locus model including ACE and GRK4 that successfully predicted blood pressure phenotype 70.5% of the time. Thus, our data indicate epistatic interactions play a major role in hypertension susceptibility. Our data also support a model where multiple pathways need to be affected in order to predispose to hypertension.

Chronic treatment with progesterone but not medroxyprogesterone acetate restores the endothelial control of vascular tone in the mesenteric artery of ovariectomized rats

OBJECTIVE

To examine whether chronic administration of the natural hormone progesterone or a synthetic progestogen, medroxyprogesterone acetate, to ovariectomized rats affects the endothelial control of arterial tone in the isolated mesenteric artery.

DESIGN

Sham-operated rats received a daily subcutaneous injection of solvent (sesame oil), whereas ovariectomized rats received either sesame oil, progesterone (22 mg kg/day), or medroxyprogesterone acetate (22 mg kg/day) for 4 weeks, according to their respective group.

RESULTS

Phenylephrine-induced contractions were significantly increased (about 200% at 10 microM) by N-nitro-L-arginine, a nitric oxide synthase inhibitor, in intact mesenteric arterial rings from the sham-operated but not from the ovariectomized group. The progesterone but not the medroxyprogesterone treatment restored the potentiating effect of N-nitro-L-arginine on phenylephrine-induced contraction (about 180% at 10 microM). Contractions to phenylephrine were not affected by the combination of charybdotoxin plus apamin, two inhibitors of endothelium-derived hyperpolarizing factor-mediated responses, in all groups. Acetylcholine induced endothelium-dependent relaxations, which were partially inhibited by N-nitro-L-arginine and abolished by the combination of N-nitro-L-arginine plus charybdotoxin and apamin, in all groups. Acetylcholine induced similar charybdotoxin and apamin-sensitive hyperpolarizations in intact mesenteric artery segments from all groups.

CONCLUSIONS

Chronic administration of progesterone, but not medroxyprogesterone, to ovarictomized rats restores the endothelium-dependent attenuation of contractile responses to phenylephrine in mesenteric arterial rings through the endothelial formation of nitric oxide. Thus, an enhancement of the protective effect of endothelial cells on the arterial wall might contribute to the beneficial effect of certain progestogen-containing preparations during hormonal treatment.

Cloning, Expression, and Characterization of Three New Mouse Cytochrome P450 Enzymes and Partial Characterization of Their Fatty Acid Oxidation Activities

The mammalian CYP2C subfamily is one of the largest and most complicated in the cytochrome P450 superfamily. In this report, we describe the organization of the mouse Cyp2c locus, which contains 15 genes and four pseudogenes, all of which are located in a 5.5-megabase region on chromosome 19. We cloned three novel mouse CYP2C cDNAs (designated CYP2C50, CYP2C54, and CYP2C55) from mouse heart, liver, and colon, respectively. All three cDNAs contain open reading frames that encode 490 amino acid polypeptides that are 57 to 95% identical to other CYP2Cs. The recombinant CYP2C proteins were expressed in Escherichia coli after N-terminal modification, partially purified, and shown to be active in the metabolism of both arachidonic acid (AA) and linoleic acid, albeit with different catalytic efficiencies and profiles. CYP2C50 and CYP2C54 metabolize AA to epoxyeicosatrienoic acids (EETs) primarily, and linoleic acid to epoxyoctadecenoic acids (EOAs) primarily, whereas CYP2C55 metabolizes AA to EETs and hydroxyeicosatetraenoic acids and linoleic acid to EOAs and hydroxyoctadecadienoic acids. Northern blotting and reverse transcription-polymerase chain reaction analysis reveal that CYP2C50 transcripts are abundant in liver and heart; CYP2C54 transcripts are present in liver, kidney, and stomach; and CYP2C55 transcripts are abundant in liver, colon, and kidney. Immunoblotting studies demonstrate that CYP2C50 protein is expressed in liver and heart, CYP2C54 protein is detected primarily in liver, and CYP2C55 protein is present primarily in colon. Immunohistochemistry reveals that CYP2C55 is most abundant in surface columnar epithelium in the cecum. We conclude that these new CYP2C enzymes are probably involved in AA and linoleic acid metabolism in mouse hepatic and extrahepatic tissues.

Thromboxane receptor stimulation associated with loss of SKCa activity and reduced EDHF responses in the rat isolated mesenteric artery

1. The possibility that thromboxane (TXA(2)) receptor stimulation causes differential block of the SK(Ca) and IK(Ca) channels which underlie EDHF-mediated vascular smooth muscle hyperpolarization and relaxation was investigated in the rat isolated mesenteric artery. 2. Acetylcholine (30 nm-3 microm ACh) or cyclopiazonic acid (10 microm CPA, SERCA inhibitor) were used to stimulate EDHF-evoked smooth muscle hyperpolarization. In each case, this led to maximal hyperpolarization of around 20 mV, which was sensitive to block with 50 nm apamin and abolished by repeated stimulation of mesenteric arteries with the thromboxane mimetic, U46619 (30 nm-0.1 microm), but not the alpha(1)-adrenoceptor agonist phenylephrine (PE). 3. The ability of U46619 to abolish EDHF-evoked smooth muscle hyperpolarization was prevented by prior exposure of mesenteric arteries to the TXA(2) receptor antagonist 1 microm SQ29548. 4. Similar-sized smooth muscle hyperpolarization evoked with the SK(Ca) activator 100 microm riluzole was also abolished by prior stimulation with U46619, while direct muscle hyperpolarization in response to either levcromakalim (1 microm, K(ATP) activator) or NS1619 (40 microm, BK(Ca) activator) was unaffected. 5. During smooth muscle contraction and depolarization to either PE or U46619, ACh evoked concentration-dependent hyperpolarization (to -67 mV) and complete relaxation. These responses were well maintained during repeated stimulation with PE, but with U46619 there was a progressive decline, so that during a third exposure to U46619 maximum hyperpolarization only reached -52 mV and relaxation was reduced by 20%. This relaxation could now be blocked with charybdotoxin alone. The latter responses could be mimicked with 300 microm 1-EBIO (IK(Ca) activator), an action not modified by exposure to U46619. 6. An early consequence of TXA(2) receptor stimulation is a reduction in the arterial hyperpolarization and relaxation attributed to EDHF. This effect appears to reflect a loss of SK(Ca) activity.

Inhibition of Cytochrome P450 2C9 Improves Endothelium-Dependent, Nitric Oxide–Mediated Vasodilatation in Patients With Coronary Artery Disease

Background— Nitric oxide (NO)– and prostacyclin-independent vasodilatation in several vascular beds has been linked to the activation of cytochrome P450 (CYP) epoxygenases expressed in endothelial cells. However, these enzymes, which generate vasodilator epoxyeicosatrienoic acids, may also produce oxygen-derived free radicals, which attenuate the bioavailability of NO. Here, we studied the involvement of CYP 2C9 in modulating endothelium-dependent and -independent changes in forearm blood flow (FBF) in healthy volunteers and in patients with manifest coronary artery disease.

Methods and Results— The effects of sulfaphenazole, a selective inhibitor of CYP 2C9, on endothelium-dependent (acetylcholine) and endothelium-independent (sodium nitroprusside, SNP) FBF responses were measured by venous occlusion plethysmography in 5 healthy subjects and in 16 patients with angiographically documented stable coronary artery disease. Sulfaphenazole did not modify FBF responses to acetylcholine or SNP in healthy subjects. In contrast, sulfaphenazole markedly and dose-dependently enhanced the FBF response to acetylcholine without affecting the response to SNP. Vitamin C also increased the FBF response to acetylcholine, but this effect was further potentiated by sulfaphenazole. In the presence of N ω -monomethyl- l -arginine, sulfaphenazole failed to significantly improve acetylcholine-induced vasodilatation. The oxidation of serum proteins was enhanced in patients with coronary artery disease, and this effect was significantly attenuated by sulfaphenazole.

Conclusions— The CYP 2C9 inhibitor sulfaphenazole enhances endothelium-dependent vasodilator responses in patients with manifest coronary artery disease. This effect seems to be related to an increase in the bioavailability of NO, probably as a consequence of an attenuated generation of reactive oxygen species by CYP 2C9 in endothelial cells.

Mechanistic Role of Cytochrome P450 Monooxygenases in Oxidized Low-Density Lipoprotein–Induced Vascular Injury

Oxidized low-density lipoprotein (oxLDL) is an important risk factor for vascular injury. Its role on coronary vasoconstriction remains speculative. Endothelial monooxygenases (cytochrome P450s [CYPs]) are regulators of vascular tonus through production of epoxy fatty acids. We investigated the effects of oxLDL on CYP monooxygenases in human arterial coronary endothelial cells and explanted healthy and atherosclerotic aortae. We found oxLDL to induce radical oxygen species production via the action of NADPH oxidase NOX4. Intracellular radical oxygen species production prompted reduced protein expression of the transcriptional regulator nuclear factor 1 (NF-1). We identified novel DNA binding sites for NF-1 in promoter regions of CYPs. DNA binding of NF-1 was confirmed by electromobility shift assays. OxLDL repressed DNA binding of NF-1 and diminished transcript level of CYP genes targeted by this factor. The production of endothelial-derived hyperpolarization factor, a key regulator of vascular tonus, was also reduced. Repression of CYP monooxygenases was reversed, and production of endothelial-derived hyperpolarization factor was normalized after treatment of endothelium with the lectin-like oxLDL receptor antagonist κ-carrageenan or blocking of LOX-1 with a specific antibody. This suggests a mechanistic role of CYP monooxygenases in oxLDL-induced vascular injury. Therapy of endothelial dysfunction through LOX-1 receptor antagonism will be an interesting avenue to explore. The full text of this article is available online at http://www.circresaha.org.

Involvement of CYP 2C9 in Mediating the Proinflammatory Effects of Linoleic Acid in Vascular Endothelial Cells

OBJECTIVE

Polyunsaturated fatty acids such as linoleic acid are well known dietary lipids that may be atherogenic by activating vascular endothelial cells. In the liver, fatty acids can be metabolized by cytochrome P450 (CYP) enzymes, but little is known about the role of these enzymes in the vascular endothelium. CYP 2C9 is involved in linoleic acid epoxygenation, and the major product of this reaction is leukotoxin (LTX). We investigated the role of CYP-mediated mechanisms of linoleic acid metabolism in endothelial cell activation by examining the effects of linoleic acid or its oxidized metabolites such as LTX and leukotoxin diol (LTD).

METHODS

The effect of linoleic acid on CYP 2C9 gene expression was studied by RT-PCR. Oxidative stress was monitored by measuring DCF fluorescence and intracellular glutathione levels, and electrophoretic mobility shift assay was carried out to study the activation of oxidative stress sensitive transcription factors. Analysis of oxidized lipids was carried out by liquid chromatography/mass spectrometry.

RESULTS

Linoleic acid treatment for six hours increased the expression of CYP 2C9 in endothelial cells. Linoleic acid-mediated increase in oxidative stress and activation of AP-1 were blocked by sulfaphenazole, a specific inhibitor of CYP 2C9. The linoleic acid metabolites LTX and LTD increased oxidative stress and activation of transcription factors only at high concentrations.

CONCLUSION

Our data show that CYP 2C9 plays a key role in linoleic acid-induced oxidative stress and subsequent proinflammatory events in vascular endothelial cells by possibly causing superoxide generation through uncoupling processes.

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

Cytochrome P450 (CYP) epoxygenase products, such as 11,12-epoxyeicosatrienoic acid (EET), stimulate endothelial cell proliferation. We set out to identify the signal transduction cascade linking EET generation to enhanced proliferation and angiogenesis. In human endothelial cells overexpressing CYP 2C9, cell number was increased compared with control cells and was inhibited by the CYP 2C9 inhibitor, sulfaphenazole. CYP 2C9 overexpression was associated with the activation of Akt and an increase in cyclin D1 expression, effects that were abolished by the epidermal growth factor (EGF) receptor inhibitor, AG1478, which also prevented the CYP 2C9-induced increase in cell proliferation. Stimulation of EGF receptor overexpressing cells with 11,12-EET or transfection of these cells with CYP 2C9 enhanced the tyrosine phosphorylation of the EGF receptor. Endothelial tube formation in a fibrin gel was significantly enhanced (6-fold) in CYP 2C9 overexpressing cells and was comparable with the tube formation induced by EGF. In the chick chorioallantoic membrane, 11,12-EET stimulated vessel formation (3.5-fold) and induced vessel convergence, an effect that was abolished by cotreatment with either an EGF receptor-neutralizing antibody or AG1478. These results indicate that CYP 2C9-derived EETs stimulate angiogenesis by a mechanism involving the activation of the EGF receptor.

GTP cyclohydrolase 1 downregulation contributes to glucocorticoid hypertension in rats

NO, a potent vasodilator, has been implicated in the pathogenesis of glucocorticoid hypertension. NO synthase requires the cofactor tetrahydrobiopterin for the production of NO. Guanosine-triphosphate (GTP) cyclohydrolase 1 is the rate-limiting enzyme for the production of tetrahydrobiopterin, and in the presence of low levels of tetrahydrobiopterin, NO production is decreased. We have previously shown that tetrahydrobiopterin-dependent vasodilation is impaired in rats with glucocorticoid hypertension. However, the role GTP cyclohydrolase 1 plays in the pathogenesis of glucocorticoid hypertension has not been investigated. Therefore, we tested the hypothesis that downregulation of GTP cyclohydrolase 1 contributes to the development and maintenance of glucocorticoid hypertension in rats. Rats were implanted with dexamethasone (0.79 mg x kg(-1) x d(-1)) or sham-operated, and systolic blood pressures were measured at baseline and after 12 hours, 4 days, or 15 days. Blood pressure increased significantly after dexamethasone treatment. Isometric force generation was measured in endothelium-intact aortic ring segments. Aortas from dexamethasone-treated rats exhibited a significant time-dependent decrease in maximal relaxation to acetylcholine compared with control rats. Incubation with sepiapterin (10(-4) mol/L, 1 hour), which produces tetrahydrobiopterin via a salvage pathway, restored vasodilation to acetylcholine in aortas from 4- and 15-day dexamethasone-treated rats. GTP cyclohydrolase 1 mRNA expression levels also significantly decreased in a time-dependent manner. These results support the hypothesis that downregulation of GTP cyclohydrolase 1 contributes to increased blood pressure in glucocorticoid hypertensive rats.

Cytochrome P450 epoxygenases and vascular tone: novel role for HMG-CoA reductase inhibitors in the regulation of CYP 2C expression

Over the last 10 years it has become increasingly clear that cytochrome P450 (CYP) enzymes expressed within endothelial and vascular smooth muscle cells play a crucial role in the modulation of vascular homeostasis. There is strong evidence suggesting that the activation of a CYP 2C epoxygenase in endothelial cells is an essential step in nitric oxide (NO)- and prostacyclin (PGI(2))-independent vasodilatation of several vascular beds, particularly in the heart and kidney. Moreover, CYP epoxygenase products as well as CYP-derived reactive oxygen species are intracellular signal transduction molecules involved in several signaling cascades affecting numerous cellular processes, including vascular cell proliferation and angiogenesis. Various pharmacological compounds enhance vascular CYP 2C expression. One group of substances which highlight the possible effects of CYP induction in endothelial cells on vascular function are the HMG-CoA reductase inhibitors (statins). Cerivastatin and fluvastatin increase CYP 2C mRNA and protein in native and cultured endothelial cells, and enhance the bradykinin-induced NO/PGI(2)-independent relaxation of arterial segments as well as the generation of reactive oxygen species. However, statins also increase the expression of the endothelial NO synthase by approximately twofold. As a consequence, the probability that NO and reactive oxygen species react to generate peroxynitrite is increased and the treatment of vascular segments with statins resulted in enhanced protein tyrosine nitration. These data highlight the role played by CYP 2C in vascular homeostasis and its potential regulation by cardiovascular drugs.