Unusual regioselectivity and active site topology of human cytochrome P450 2J2

The oxidation of six derivatives of terfenadone by recombinant human CYP2J2 (CYP = cytochrome P450) was studied by high-performance liquid chromatography coupled to mass spectrometry (MS) using tandem MS techniques and by 1H NMR spectroscopy. CYP2J2 exhibited a surprising regioselectivity in favor of the hydroxylation of the substrate terminal chain at the weakly reactive homobenzylic position. In contrast, hydroxylation of the same substrates by CYP3A4 mainly occurred on the most chemically reactive sites of the substrates (N-oxidation and benzylic hydroxylation). A 3D homology model of CYP2J2 was constructed using recently published structures of CYP2A6, CYP2B4, CYP2C8, CYP2C9, and CYP2D6 as templates. In contrast with other CYP2 structures, it revealed an active site cavity with a severely restricted access of substrates to the heme through a narrow hydrophobic channel. Dynamic docking of terfenadone derivatives in the CYP2J2 active site allowed one to interpret the unexpected regioselectivity of the hydroxylation of these substrates by CYP2J2, which is mainly based on this restricted access to the iron. The structural features that have been found to be important for recognition of substrates or inhibitors by CYP2J2 were also interpreted on the basis of CYP2J2-substrate interactions in this model.

Electrophysiological properties of cardiomyocytes isolated from CYP2J2 transgenic mice

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

Altered mechanisms of endothelium-dependent dilation in skeletal muscle arterioles with genetic hypercholesterolemia

With most cardiovascular disease risk factors, endothelium-dependent dilation of skeletal muscle resistance arterioles is compromised, although with hypercholesterolemia, impairments to reactivity are not consistently observed. Using apolipoprotein E (ApoE) and low-density lipoprotein receptor (LDLR) gene deletion male mouse models of hypercholesterolemia at 20 wk of age, we tested the hypothesis that arteriolar dilation would be maintained due to an increased stimulus-induced production of dilator metabolites via cyclooxygenase and cytochrome P-450 epoxygenase pathways. Arterioles from both strains demonstrated mild reductions in dilation to hypoxia and acetylcholine versus responses in C57/Bl/6J (C57) controls. However, although inhibition of nitric oxide synthase (NOS) attenuated dilation in arterioles from C57 controls, this effect was absent in ApoE or LDLR strains. In contrast, cyclooxygenase-dependent portions of dilator reactivity were maintained across the three strains. Notably, although combined NOS and cyclooxygenase inhibition abolished arteriolar responses to hypoxia and acetylcholine in C57 controls, significant reactivity remained in ApoE and LDLR strains. Whereas inhibition of cytochrome P-450 omega-hydroxylase and epoxygenases had no effect on this residual reactivity in ApoE and LDLR strains, inhibition of 12/15-lipoxygenase with nordihydroguaiaretic acid abolished the residual reactivity. With both hypoxic and methacholine challenges, arteries from ApoE and LDLR strains demonstrated an increased production of both 12(S)- and 15(S)-hydroxyeicosatetraenoic acid, end products of arachidonic acid metabolism via 12/15-lipoxygenase, a response that was not present in C57 controls. These results suggest that with development of hypercholesterolemia, mechanisms contributing to dilator reactivity in skeletal muscle arterioles are modified such that net reactivity to endothelium-dependent stimuli is largely intact.

Effects of chronic cytochrome P-450 inhibition on the course of hypertension and end-organ damage in Ren-2 transgenic rats

The aim of the present study was to evaluate the effects of inhibition of cytochrome P-450 (CYP) activity by 1-aminobenzotriazole (ABT) and by CoCl(2), first, on the development of hypertension when treatment was started in young male heterozygous Ren-2 transgenic rats (TGR) and, second, on blood pressure (BP) when treatment was started in adult TGR with established hypertension. Normotensive Hannover Sprague-Dawley (HanSD) rats served as controls. In addition, the renal cortical activities of omega-hydroxylase, the enzyme catalyzing the formation of 20-hydroxyeicosatetraenoic acid (20-HETE), and of epoxygenase, the enzyme responsible for epoxyeicosatrienoic acids (EETs) production, and urinary excretion of 20-HETE and EETs in TGR and HanSD rats were assessed. TGR have higher renal tissue omega-hydroxylase activity and urinary excretion of 20-HETE but have significantly lower renal epoxygenase activity and urinary excretion of EETs than HanSD rats. Treatment of young TGR with ABT and CoCl(2) attenuated the development of hypertension and cardiac hypertrophy and prevented glomerulosclerosis. Administration of ABT and CoCl(2) in adult TGR decreased BP, cardiac hypertrophy, but did not reduce glomerulosclerosis. Our data suggest that altered production and/or action of CYP-derived metabolites play a permissive role in the development and maintenance of hypertension in TGR by enhancing ANG II-induced vasoconstriction.

CYP2J2 and CYP2C8 polymorphisms and coronary heart disease risk: the Atherosclerosis Risk in Communities (ARIC) study

OBJECTIVE

The cytochromes P450 epoxygenases CYP2J2 and CYP2C8 synthesize epoxyeicosatrienoic acids, which regulate endothelial function. We sought to determine if genetic variation in CYP2J2 and CYP2C8 was associated with coronary heart disease risk.

METHODS

We genotyped 2065 Atherosclerosis Risk in Communities study participants (1085 incident coronary heart disease cases, 980 noncases) for polymorphisms in CYP2J2 and CYP2C8. Using a case-cohort design, associations between genotype and incident coronary heart disease risk were evaluated using proportional hazards regression. The influence of cigarette smoking on these associations was also evaluated. False discovery rate q-values were estimated to minimize the impact of the multiple statistical comparisons completed. All analyses were race stratified.

RESULTS

The CYP2J2 G-50T polymorphism variant -50T allele was associated with significantly lower risk of incident coronary heart disease in African-Americans (adjusted hazard rate ratio 0.58, 95% confidence interval 0.35-0.96, P=0.036, q=0.051); however, no significant association was observed in Caucasians. Overall, the I264M, I269F, and K399R polymorphisms in CYP2C8 were not significantly associated with risk of incident coronary heart disease. In Caucasians, the relationship between the I264M and K399R polymorphisms and incident coronary heart disease risk was significantly modified by cigarette smoking status (P for interaction=0.008, q=0.064), with the highest risk observed in smokers carrying at least one variant allele.

CONCLUSIONS

The G-50T polymorphism in CYP2J2 may be an important risk factor for the development of coronary heart disease events in African-Americans, whereas cigarette smoking may modify the relationship between the I264M and K399R polymorphisms in CYP2C8 and coronary heart disease risk in Caucasians. Confirmation of these findings in an independent population is warranted.

Promoter polymorphism G-50T of a human CYP2J2 epoxygenase gene is associated with common susceptibility to asthma

BACKGROUND

Cytochrome P-450 2J2 (CYP2J2) has recently been shown to be an important enzyme in the metabolism of epoxygenase-derived eicosanoids that play important functional roles in pulmonary physiology and may contribute to the pathogenesis of asthma.

STUDY OBJECTIVE

The focus of our pilot study was to evaluate whether common polymorphism G-50T within the proximal promoter of human CYP2J2 gene is associated with the susceptibility to bronchial asthma.

DESIGN AND PARTICIPANTS

A total of 429 unrelated Russian subjects were recruited in this case-control study, including 215 sex-matched and age-matched patients with asthma and 214 healthy control subjects. The blood samples were analyzed for genetic polymorphism G-50T in the CYP2J2 gene by polymerase chain reaction followed by restriction fragment length polymorphism analysis.

RESULTS

The frequency of variant allele -50T of the CYP2J2 gene was significantly higher in asthmatic patients than in healthy subjects (odds ratio [OR], 5.04; 95% confidence interval [CI], 1.99 to 12.77; p = 0.0003). In addition, the heterozygous genotype -50GT of the CYP2J2 gene was found to be significantly associated with susceptibility to allergic asthma (OR, 5.40; 95% CI, 2.05 to 14.26; p = 0.0003) as well as nonallergic asthma (OR, 5.77; 95% CI, 1.84 to 18.10; p = 0.004). The associations of the CYP2J2 gene G-50T polymorphism with asthma remained significant after adjustment for age and gender using multiple logistic regression analysis.

CONCLUSIONS

Our data demonstrate for the first time that the CYP2J2 gene might be considered as a novel candidate gene for common susceptibility to asthma and highlight the importance of the P-450 epoxygenase pathway of metabolism of arachidonic acid in the pathogenesis of the disease.

Cytochrome P450 eicosanoids are activators of peroxisome proliferator-activated receptor alpha

Cytochrome P450 (P450) eicosanoids regulate vascular tone, renal tubular transport, cellular proliferation, and inflammation. Both the CYP4A omega-hydroxylases, which catalyze 20-hydroxyeicosatetraenoic acid (20-HETE) formation, and soluble epoxide hydrolase (sEH), which catalyzes epoxyeicosatrienoic acid (EET) degradation to the dihydroxyeicosatrienoic acids (DHETs), are induced upon activation of peroxisome proliferator-activated receptor alpha (PPARalpha) by fatty acids and fibrates. In contrast, the CYP2C epoxygenases, which are responsible for EET formation, are repressed after fibrate treatment. We show here that P450 eicosanoids can bind to and activate PPARalpha and result in the modulation of PPARalpha target gene expression. In transactivation assays, 14,15-DHET, 11,2-EET, and 20-HETE were potent activators of PPARalpha. Gel shift assays showed that EETs, DHETs, and 20-HETE induced PPARalpha-specific binding to its cognate response element. Expression of apolipoprotein A-I was decreased 70% by 20-HETE, whereas apolipoprotein A-II expression was increased up to 3-fold by 11,12-EET, 14,15-DHET, and 20-HETE. In addition, P450 eicosanoids induced CYP4A1, sEH, and CYP2C11 expression, suggesting that they can regulate their own levels. Given that P450 eicosanoids have multiple cardiovascular effects, pharmacological modulation of their formation and/or degradation may yield therapeutic benefits.

Selective, competitive and mechanism-based inhibitors of human cytochrome P450 2J2

Twenty five derivatives of the drugs terfenadine and ebastine have been designed, synthesized and evaluated as inhibitors of recombinant human CYP2J2. Compound 14, which has an imidazole substituent, is a good non-competitive inhibitor of CYP2J2 (IC(50)=400nM). It is not selective towards CYP2J2 as it also efficiently inhibits the other main vascular CYPs, such as CYP2B6, 2C8, 2C9 and 3A4; however, it could be an interesting tool to inhibit all these vascular CYPs. Compounds 4, 5 and 13, which have a propyl, allyl and benzo-1,3-dioxole terminal group, respectively, are selective CYP2J2 inhibitors. Compound 4 is a high-affinity, competitive inhibitor and alternative substrate of CYP2J2 (K(i)=160+/-50nM). Compounds 5 and 13 are efficient mechanism-based inhibitors of CYP2J2 (k(inact)/K(i) values approximately 3000Lmol(-1)s(-1)). Inactivation of CYP2J2 by 13 is due to the formation of a stable iron-carbene bond which occurs upon CYP2J2-catalyzed oxidation of 13 with a partition ratio of 18+/-3. These new selective inhibitors should be interesting tools to study the biological roles of CYP2J2.

The effect of CYP2J2, CYP3A4, CYP3A5 and the MDR1 polymorphisms and gender on the urinary excretion of the metabolites of the H-receptor antihistamine ebastine: a pilot study

AIMS

To determine the effect of gender and the genetic polymorphisms of CYP2J2, CYP3A4, CYP3A5 and MDR1 on the urinary excretion of the H(1) antihistamine ebastine in healthy subjects.

METHODS

Eighty-nine Caucasians were studied. The presence of polymorphisms in genes known to be involved in ebastine metabolism and transport (CYP2J2*2,*3,*4,*6,*7, CYP3A4*1B, CYP3A5*3, *6 and MDR1(ABCB1)(C3435T)) was assessed by means of PCR-restriction fragment length polymorphism and sequencing methods. Genotype was correlated with the urinary excretion of the main ebastine metabolites (desalkylebastine and carebastine) under basal conditions and after administration of grapefruit juice.

RESULTS

Women excreted statistically greater amounts of desalkylebastine in urine (mean +/- SD (95% confidence intervals, 95% CI), 23.0 +/- 19.5 (18.1, 27.9) micromol) than men (12.4 +/- 11.0 (7.9, 16.9)), (mean difference: 10.6 (2.4, 18.7), P < 0.005). The CYP2J2, CYP3A4 and CYP3A5 analysed polymorphisms did not greatly affect ebastine metabolite excretion. The MDR1(C3435T) polymorphism was found to affect both the urinary excretion of the active metabolite carebastine (32.3 +/- 18.3 (23.1, 41.4), 22.8 +/- 14.7 (18.6, 27.0) and 21.5 +/- 15.3 (14.7, 28.3) for CC, CT and TT carriers, respectively; P < 0.05) and the grapefruit juice-induced inhibition of its transport/formation (mean fold-decrease +/- SD (95% CI), 1.5 +/- 0.8 (1.0, 2.0), 1.1 +/- 0.9 (0.7, 1.4) and 0.9 +/- 0.4 (0.6, 1.2) for CC, CT and TT carriers, respectively; P = 0.01).

CONCLUSIONS

Gender and the presence of the MDR1(C3435T) polymorphism both influence the excretion of ebastine metabolites in urine.

Evidence for Association of Polymorphisms in CYP2J2 and Susceptibility to Essential Hypertension

OBJECTIVE

Evidence from animal models and human studies suggests that CYP2J2 plays a mechanistic role in the development of hypertension. The present study aims to investigate the potential genetic contribution of the CYP2J2 gene to the etiology of essential hypertension (EH) and individual blood pressure.

METHODS

We selected eight polymorphisms in/or around the CYP2J2 gene and performed a case-control association study involving 841 Han Chinese subjects, including 415 unrelated hypertensives and 426 age-, gender- and area-matched normotensives.

RESULTS

Three functionally identified variants (CYP2J2 *2, *7 and CYP2J2 *8) and SNP rs11572182 represented rare polymorphisms in Han Chinese. However, the difference in rs1155002 genotype distribution between hypertensive and healthy subjects was close to significance (P = 0.06) in the whole sample. Interestingly, significant evidence for an association with rs1155002 was found in females when stratified by gender. In females, the TT homozygote of rs1155002 seems to be a risk factor for hypertension (p = 0.014). In addition, ANOVA analysis suggested TT carriers had significantly higher systolic blood pressure (p = 0.016). The genotype frequencies for rs10493270, rs1180273 and rs1324491 revealed no statistically significant differences. Likewise, four-marker haplotype frequencies showed no significant differences between cases and controls.

CONCLUSION

Our data provide strong evidence that the CYP2J2 gene is a susceptibility factor for essential hypertension, especially in females, and influences individual systolic blood pressure in the Chinese Han population.

Inter-individual variation of cytochrome P4502J2 expression and catalytic activities in liver microsomes from Japanese and Caucasian populations

The aim of this study was to investigate the inter-individual variations in cytochrome P4502J2 (CYP2J2) and its typical drug oxidation activities in human liver microsomes in both Japanese and Caucasian populations. CYP2J2 contents were determined immunochemically in liver microsomes from 20 Japanese and 29 Caucasian samples using recombinant CYP2J2 commercially available as a standard. Ebastine hydroxylation and astemizole O-demethylation activities were compared. The CYP2J2 genotype was determined by direct sequencing of liver genomic DNA. The mean expression levels of CYP2J2 determined immunochemically in liver microsomes from Japanese and Caucasian samples were 2.0 +/- 1.5 and 1.2 +/- 2.1 pmol CYP2J2 mg-1 protein (mean +/- standard deviation), respectively, accounting for 1.8 +/- 1.1% and 0.52 +/- 0.65% of the total hepatic P450 content (0.15 +/- 0.19 and 0.27 +/- 0.14 nmol P450 mg-1 protein, respectively). The individual variation of the two marker drug oxidation activities could not be fully accounted for by the CYP2J2 contents or currently known CYP2J2 genotypes. The amounts of CYP2J2 in liver microsomes with the CYP2J2*7 allele (-76G>T) were decreased to 39% compared with those of liver microsomes from other individuals. The results indicate that CYP2J2 accounts for approximately 1-2% of total P450 in human liver microsomes. The information about large inter-individual variation of the CYP2J2 suggests that this enzyme plays a significant role in the metabolism of xenobiotics and may be useful in in-silico simulations of drug disposition.

Detection of human CYP2C8, CYP2C9, and CYP2J2 in cardiovascular tissues

The cytochrome P450 (P450) enzymes CYP2C8, CYP2C9, and CYP2J2 metabolize arachidonic acid to epoxyeicosatrienoic acids, which are known to be vital in regulation of vascular tone and cardiovascular homeostasis. Because there is limited information regarding the relative expression of these P450 enzymes in cardiovascular tissues, this study examined the expression of CYP2C8, CYP2C9, and CYP2J2 mRNA and protein in human heart, aorta, and coronary artery samples by real-time polymerase chain reaction, immunoblotting, and immunohistochemistry. CYP2J2 and CYP2C9 mRNA levels were highly variable in human hearts, whereas CYP2C8 mRNA was present in lower abundance. CYP2J2 mRNA was approximately 10(3) times higher than CYP2C9 or CYP2C8 in human heart. However, CYP2C9 mRNA was more abundant than CYP2J2 or CYP2C8 in one ischemic heart. In human aorta, mean CYP2C9 mRNA levels were approximately 50 times higher than that of CYP2J2 and 5-fold higher than that of CYP2C8. In human coronary artery, mean values for CYP2C9 mRNA were approximately 2-fold higher than that of CYP2J2 mRNA and 6-fold higher than that of CYP2C8 mRNA. Immunoblotting results show relatively high levels of CYP2J2 and CYP2C8 protein in human hearts, which was confirmed by immunohistochemistry. CYP2C9 protein was also detected at high levels in one ischemic heart by immunoblotting. CYP2C9 was present at higher levels than CYPJ2 in aorta and coronary artery, whereas CYP2C8 protein was below the limits of detection. The expression of CYP2J2 and CYP2C8 in human heart, and CYPC9 and CYP2J2 in aorta and coronary artery is consistent with a physiological role for these enzymes in these tissues.

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.

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

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

Expression and possible functional roles of cytochromes P450 2J1 (zfCyp 2J1) in zebrafish

Cytochrome P450 2J (Cyp2J) subfamilies are recognized as catalysts of arachidonic acid metabolism in extrahepatic tissues of many species. However, to date, no P450 2J have been identified in zebrafish. We describe here a zfCyp2J1 cDNA which encodes a putative protein of 496 amino acids and shares 51%, 51%, 50%, 51% and 50% identity with mouse Cyp2J6, rabbit Cyp2J1, human Cyp2J2, cow Cyp2J2, and rat Cyp2J4, respectively. Despite detectable levels of expression by RT-PCR, no expression was shown by in situ hybridization using whole-mount tissues of the embryos. Gene-specific knockdown by antisense morpholino oligonucleotide had no phenotypic effect on embryonic development. However, over-expression of zfCyp2J1 by injection of the embryos with the cDNA resulted in substantial dose-dependent morphological defects. With adult zebrafish, whole-mount in situ hybridization showed that zfCyp2J1 was expressed predominantly in the brain and gonads. A semi-quantitative RT-PCR analysis further revealed that the zfCyp2J1 transcript was also expressed in the ovary, testis, heart, liver, and kidney. High levels of zfCyp2J1 mRNA were evident in primary growth stage (stage I) oocytes and cortical alveolus stage (stage II) oocytes but nearly undetectable in stage III and matured oocytes. These results suggest that zfCyp2J1 may not be involved in zebrafish embryogenesis but may rather play an important role in the functioning of brain and gonads of the adults. In addition, zfCyp2J1 may play a particularly crucial role in early oocyte maturation.

Regulation of vascular tone during pregnancy: a novel role for the pregnane X receptor

During pregnancy, maternal vascular function is altered through mechanisms that remain unclear. Progesterone synthesis and metabolism are also increased. Progesterone metabolites are potent endogenous ligands for the pregnane X receptor (PXR), a nuclear receptor that induces the expression of hepatic cytochrome P450 enzymes. Cytochrome P450 enzymes located in the vasculature can metabolize arachidonic acid to produce epoxyeicosatrienoic acids, known vasodilators. We hypothesized that PXR is present in vascular tissue and contributes to vascular adaptations to pregnancy. PXR mRNA was detected in mouse mesenteric arteries by quantitative RT-PCR. Constrictor and relaxation responses in wildtype (PXR(+/+)) and PXR-deficient (PXR(-/-)) mice were compared by wire myography. Relative to nonpregnant controls, arteries from pregnant PXR(+/+) mice had reduced sensitivity to phenylephrine-induced constriction (EC(50): 2.77+/-0.32 mumol/L versus 5.13+/-0.36 mumol/L; P=0.009) and enhanced maximal vasorelaxation to bradykinin (26+/-3% versus 44+/-16%; P=0.013). However, these pregnancy adaptations were absent in PXR(-/-) mice. We also hypothesized that PXR is activated by progesterone metabolites. Treatment of PXR(+/+) and PXR(-/-) nonpregnant mice with 5beta-dihydroprogesterone for 7 days enhanced endothelium-dependent relaxation in only the PXR(+/+) mice, similarly to that seen in pregnancy. In treated mice, inhibition of cytochrome P450 epoxygenase activity with N-methylsulphonyl-6-(2-propargyloxyphenyl)hexanamide attenuated vasorelaxation in arteries from PXR(+/+) but not PXR(-/-) mice. We conclude that PXR contributes to the development of vascular adaptations to pregnancy, likely in response to activation by progesterone metabolites, and that PXR-dependent increases in vasorelaxation may be because of activation of cytochrome P450 epoxygenases.

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

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

The cytochromes P450 (CYP) response to allergic inflammation of the lung

The expression of the mouse Cyp family and key inflammatory mediators were examined in a model of ovalbumin (OVA)-induced allergic airway disease. The expression of IL-4, IL-13 and Ccl11 increased during the acute phase of allergic inflammation and decreased with its resolution. Interestingly, the expression of Ccl20 was increased during the resolution phase. The response of the Cyp gene family to the development of allergic inflammation was differential and correlated with the evolution of the inflammatory response. During the acute inflammatory phase the mRNA levels of Cyp2e1, Cyp2f2, Cyp2j6, Cyp4b1, Cyp8a1 and Cypor were decreased while the mRNA levels of Cyp4f18, Cyp5a1 and Cyp7b1 were elevated. With resolution of the inflammation the expression patterns returned to normal. These changes suggest that the Cyp family may play a role in the allergic inflammation by modulating the metabolism of xenobiotics and endogenous compounds such as LTB4, TXA1, PGI2 and native anti-glucocorticoids.

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.

Characterization of Ebastine, Hydroxyebastine, and Carebastine Metabolism by Human Liver Microsomes and Expressed Cytochrome P450 Enzymes: Major Roles for CYP2J2 and CYP3A

Ebastine undergoes extensive metabolism to form desalkylebastine and hydroxyebastine. Hydroxyebastine is subsequently metabolized to carebastine. Although CYP3A4 and CYP2J2 have been implicated in ebastine N-dealkylation and hydroxylation, the enzyme catalyzing the subsequent metabolic steps (conversion of hydroxyebastine to desalkylebastine and carebastine) have not been identified. Therefore, we used human liver microsomes (HLMs) and expressed cytochromes P450 (P450s) to characterize the metabolism of ebastine and that of its metabolites, hydroxyebastine and carebastine. In HLMs, ebastine was metabolized to desalkyl-, hydroxy-, and carebastine; hydroxyebastine to desalkyl- and carebastine; and carebastine to desalkylebastine. Of the 11 cDNA-expressed P450s, CYP3A4 was the main enzyme catalyzing the N-dealkylation of ebastine, hydroxyebastine, and carebastine to desalkylebastine [intrinsic clearance (CL(int)) = 0.44, 1.05, and 0.16 microl/min/pmol P450, respectively]. Ebastine and hydroxyebastine were also dealkylated to desalkylebastine to some extent by CYP3A5. Ebastine hydroxylation to hydroxyebastine is mainly mediated by CYP2J2 (0.45 microl/min/pmol P450; 22.5- and 7.5-fold higher than that for CYP3A4 and CYP3A5, respectively), whereas CYP2J2 and CYP3A4 contributed to the formation of carebastine from hydroxyebastine. These findings were supported by chemical inhibition and kinetic analysis studies in human liver microsomes. The CL(int) of hydroxyebastine was much higher than that of ebastine and carebastine, and carebastine was metabolically more stable than ebastine and hydroxyebastine. In conclusion, our data for the first time, to our knowledge, suggest that both CYP2J2 and CYP3A play important roles in ebastine sequential metabolism: dealkylation of ebastine and its metabolites is mainly catalyzed by CYP3A4, whereas the hydroxylation reactions are preferentially catalyzed by CYP2J2. The present data will be very useful to understand the pharmacokinetics and drug interaction of ebastine in vivo.

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.

Variability of CYP2J2 expression in human fetal tissues

CYP2J2 metabolizes arachidonic acid to 20-hydroxyeicosatetraenoic acid and epoxyeicosatrienoic acids (EETs), which play a critical role in the regulation of renal, pulmonary, cardiac, and vascular function. However, the contribution of CYP2J2 to EET formation in the liver remains poorly characterized. Likewise, information is sparse regarding the extent and variability of CYP2J2 expression during human development. This investigation was undertaken to characterize the variability of CYP2J2 expression in fetal liver, heart, kidney, lung, intestine, and brain and in postnatal liver samples. CYP2J2 mRNA expression was measured using quantitative polymerase chain reaction, and immunoreactive CYP2J2 was examined using two anti-CYP2J2 antibodies. CYP2J2 mRNA was ubiquitously expressed in pre- and postnatal samples. Fetal hepatic mRNA expression varied 127-fold (1351 +/- 717 transcripts/ng total RNA), but this variation was reduced to 8-fold after exclusion of four samples with extremely low levels of mRNA. Amounts of immunoreactive protein also varied substantially among samples without an apparent relationship with transcript number or genotype. Western blot analysis revealed a different protein pattern between prenatal and postnatal liver samples. DNA resequencing of selected subjects identified a single novel single-nucleotide polymorphism (CYP2J2*10), which was found in only one subject and therefore did not explain the large variability in CYP2J2 protein content. In vitro expression suggests that the protein product of CYP2J2*10 confers reduced enzymatic activity. Aberrant splicing produces three minor transcripts, which were present in all samples tested. Due to premature termination codons, none encodes functional protein. The mechanisms leading to variable amounts of immunoreactive protein and distinct pre- and postnatal CYP2J2 protein patterns warrant further investigation.

Inhibition of Protein Kinase Cβ Protects against Diabetes-Induced Impairment in Arachidonic Acid Dilation of Small Coronary Arteries

To test the hypothesis that protein kinase C (PKC)beta-induced reactive oxygen species (ROS) underlie the vascular dysfunction in diabetes, we examined the effects of (S)-13[(dimethylamino)-methyl]-10,11-14,15-tetrahydro-4,9:16,21-dimetheno-1H,13H-dibenzo[e,k]pyrrolo[3,4-h][1,4,13]oxadi-azacyclohexadecene-1,3(2H)-dione (LY333531; LY), a specific PKCbeta inhibitor, on arachidonic acid (AA)-mediated dilation in small coronary arteries from streptozotocin-induced diabetic rats. This study was designed to determine whether diabetes impairs AA-induced vasodilation of small coronary arteries and whether this defect could be blunted by dietary treatment with LY. Coronary diameter was measured using videomicroscopy in isolated pressurized vessels. In controls, AA dose dependently dilated coronary arteries, with 1 muM producing 54.7 +/- 3.1% and 30 microM producing 72.0 +/- 3.0% dilation (n = 9). In diabetic rats, 1 microM AA only produced 31.4 +/- 3.8% (n = 8; p < 0.01 versus control) and 30 microM 43.8 +/- 3.7% dilation (n = 8; p < 0.001 versus control). Nitroprusside-mediated vasodilations were similar in control and diabetic rats. In contrast, in diabetic rats receiving LY, AA-mediated coronary dilations were normal. In controls, AA-mediated vasodilation was inhibited by miconazole (an inhibitor of cytochrome P450 epoxygenase) and by iberiotoxin (IBTX, an inhibitor of the large conductance Ca(2+)-activated K(+) channel), but miconazole and IBTX had no effects in diabetic vessels. In diabetic rats receiving LY, the effects of miconazole and IBTX were similar to control. Superoxide dismutase restored responses to AA in diabetic vessels but had no effect in vessels from control or diabetic rats on LY. These results suggest that AA-mediated vasodilation in rat coronary arteries are impaired in diabetic rats due to increases in generation of ROS. LY protects against these defects in diabetes through inhibition of PKCbeta-mediated production of ROS.

Role of vascular heme oxygenase in reduced myogenic reactivity following chronic hypoxia

OBJECTIVE

Exposure to chronic hypoxia (CH) results in a persistent endothelium-dependent vascular smooth muscle hyperpolarization that diminishes vasoconstrictor reactivity. Experiments were performed to test the hypothesis that products of both cytochrome P450 epoxygenase (CYP) and heme oxygenase (HO) are required for the persistent diminished myogenic reactivity following CH.

METHODS

The authors examined myogenic responses of mesenteric arteries isolated from control and CH (48 h; P(B) = 380 mmHg) rats in the presence of a HO inhibitor (zinc protoporphyrin IX; ZnPPIX) or combined HO and CYP epoxygenase inhibition (sulfaphenazole). Arteries were isolated and cannulated and the vascular smooth muscle was loaded with the Ca2+ indicator Fura-2.

RESULTS

Control vessels maintained their internal diameter in response to step increases in intraluminal pressure, whereas arteries from CH animals passively distended. ZnPPIX augmented myogenic reactivity and [Ca2+] in arteries from CH animals. Combined administration of sulfaphenazole and ZnPPIX did not have an additional effect compared to ZnPPIX alone. Myogenic reactivity in control vessels was not altered by ZnPPIX or ZnPPIX + sulfaphenazole.

CONCLUSIONS

HO appears to play a role in regulating myogenic reactivity following CH. Furthermore, these data suggest that products of HO and CYP are both required for the observed attenuation in vasoreactivity following CH.