A novel species of cytochrome P-450 (P-450ib) specific for the small intestine of rabbits. cDNA cloning and its expression in COS cells

Pharmacogenomics for the efficacy and side effects of antihistamines

Antihistamines, especially H1 antihistamines, are widely used in the treatment of allergic diseases such as urticaria and allergic rhinitis, mainly for reversing elevated histamine and anti-allergic effects. Antihistamines are generally safe, but some patients experience adverse reactions, such as cardiotoxicity, central inhibition, and anticholinergic effects. There are also individual differences in antihistamine efficacy in clinical practice. The concept of individualized medicine has been deeply rooted in people's minds since it was put forward. Pharmacogenomics is the study of the role of inheritance in individual variations in drug response. In recent decades, pharmacogenomics has been developing rapidly, which provides new ideas for individualized medicine. Polymorphisms in the genes encoding metabolic enzymes, transporters, and target receptors have been shown to affect the efficacy of antihistamines. In addition, recent evidence suggests that gene polymorphisms influence urticaria susceptibility and antihistamine therapy. Here, we summarize current reports in this area, aiming to contribute to future research in antihistamines and clinical guidance for antihistamines use in individualized medicine.

Terfenadine metabolism of human cytochrome P450 2J2 containing genetic variations (G312R, P351L and P115L)

The human cytochrome P450 2J2 is involved in several metabolic reactions, including the oxidation of important therapeutics and epoxidation of endogenous arachidonic acid. At least ten genetic variations of P450 2J2 have been identified, but their effects on enzymatic activity have not been clearly characterized. Here, we evaluated the functional effects of three genetic variations of P450 2J2 (G312R, P351L, and P115L). Recombinant enzymes of wild-type and three variant P450 2J2 were heterologously expressed in Escherichia coli and purified. P450 expression levels in the wild-type and two variants (P351L and P115L) were 142-231 nmol per liter culture, while the G312R variant showed no holoenzyme peak in the CO-binding spectra. Substrate binding titrations to terfenadine showed that the wild-type and two variants displayed K_d values of 0.90-2.2 μM, indicating tight substrate binding affinities. Steady-state kinetic analysis for t-butyl methyl hydroxylation of terfenadine indicated that two variant enzymes had similar k_cat and K_m values to wild-type P450 2J2. The locations of mutations in three-dimensional structural models indicated that the G312R is located in the I-helix region near the formal active site in P450 2J2 and its amino acid change affected the structural stability of the P450 heme environment.

Marmoset cytochrome P450 2J2 mainly expressed in small intestines and livers effectively metabolizes human P450 2J2 probe substrates, astemizole and terfenadine

1. Common marmoset (Callithrix jacchus), a New World Monkey, has potential to be a useful animal model in preclinical studies. However, drug metabolizing properties have not been fully understood due to insufficient information on cytochrome P450 (P450), major drug metabolizing enzymes. 2. Marmoset P450 2J2 cDNA was isolated from marmoset livers. The deduced amino acid sequence showed a high-sequence identity (91%) with cynomolgus monkey and human P450 2J2 enzymes. A phylogenetic tree revealed that marmoset P450 2J2 was evolutionarily closer to cynomolgus monkey and human P450 2J2 enzymes, than P450 2J forms in pigs, rabbits, rats or mice. 3. Marmoset P450 2J2 mRNA was abundantly expressed in the small intestine and liver, and to a lesser extent in the brain, lung and kidney. Immunoblot analysis also showed expression of marmoset P450 2J2 protein in the small intestine and liver. 4. Enzyme assays using marmoset P450 2J2 protein heterologously expressed in Escherichia coli indicated that marmoset P450 2J2 effectively catalyzed astemizole O-demethylation and terfenadine t-butyl hydroxylation, similar to human and cynomolgus monkey P450 2J2 enzymes. 5. These results suggest the functional characteristics of P450 2J2 enzymes are similar among marmosets, cynomolgus monkeys and humans.

Cytochrome P450 2J2: distribution, function, regulation, genetic polymorphisms and clinical significance

Cytochrome P450 2J2 (CYP2J2) is an enzyme mainly found in human extrahepatic tissues, with predominant expression in the cardiovascular systems and lower levels in the intestine, kidney, lung, pancreas, brain, liver, etc. During the past 15 years, CYP2J2 has attracted much attention for its epoxygenase activity in arachidonic acid (AA) metabolism. It converts AA to four epoxyeicosatrienoic acids (EETs) that have various biological effects, especially in the cardiovascular systems. In recent publications, CYP2J2 is shown highly expressed in various human tumor cells, and its EET metabolites are demonstrated to implicate in the pathologic development of human cancers. CYP2J2 is also a human CYP that involved in phase I xenobiotics metabolism. Antihistamine drugs and many other compounds were identified as the substrates of CYP2J2, and studies have demonstrated that these substrates have a broad structural diversity. CYP2J2 is found not readily induced by known P450 inducers; however, its expression could be regulated in some pathological conditions, might through the activator protein-1(AP-1), the AP-1-like element and microRNA let-7b. Several genetic mutations in the CYP2J2 gene have been identified in humans, and some of them have been shown to have potential associations with some diseases. With the increasing awareness of its roles in cancer disease and drug metabolism, studies about CYP2J2 are still going on, and various inhibitors of CYP2J2 have been determined. Further studies are needed to delineate the roles of CYP2J2 in disease pathology, drug development and clinical practice.

Characterization of four new mouse cytochrome P450 enzymes of the CYP2J subfamily

The cytochrome P450 superfamily encompasses a diverse group of enzymes that catalyze the oxidation of various substrates. The mouse CYP2J subfamily includes members that have wide tissue distribution and are active in the metabolism of arachidonic acid (AA), linoleic acid (LA), and other lipids and xenobiotics. The mouse Cyp2j locus contains seven genes and three pseudogenes located in a contiguous 0.62 megabase cluster on chromosome 4. We describe four new mouse CYP2J isoforms (designated CYP2J8, CYP2J11, CYP2J12, and CYP2J13). The four cDNAs contain open reading frames that encode polypeptides with 62-84% identity with the three previously identified mouse CYP2Js. All four new CYP2J proteins were expressed in Sf21 insect cells. Each recombinant protein metabolized AA and LA to epoxides and hydroxy derivatives. Specific antibodies, mRNA probes, and polymerase chain reaction primer sets were developed for each mouse CYP2J to examine their tissue distribution. CYP2J8 transcripts were found in the kidney, liver, and brain, and protein expression was confirmed in the kidney and brain (neuropil). CYP2J11 transcripts were most abundant in the kidney and heart, with protein detected primarily in the kidney (proximal convoluted tubules), liver, and heart (cardiomyocytes). CYP2J12 transcripts were prominently present in the brain, and CYP2J13 transcripts were detected in multiple tissues, with the highest expression in the kidney. CYP2J12 and CYP2J13 protein expression could not be determined because the antibodies developed were not immunospecific. We conclude that the four new CYP2J isoforms might be involved in the metabolism of AA and LA to bioactive lipids in mouse hepatic and extrahepatic tissues.

Molecular cloning and enzymatic characterization of sheep CYP2J

Cytochrome P450 (CYP) 2Js have been studied in various mammals, but not in sheep, as an animal model used to test veterinary drug metabolism. Sheep CYP2J was cloned from liver messenger RNA (mRNA) by RACE. The cDNA, after modification at its N- and C-terminals, was expressed in Escherichia coli and the sheep CYP2J protein, purified by chromatography, was 80% homologous to human and monkey CYP2J2. Reverse transcriptase-polymerase chain reaction (RT-PCR) experiments showed that CYP2J mRNA was expressed in liver, cortex, respiratory and olfactory mucosa, heart, bronchi, lung, spleen, small intestine and kidney. The purified enzyme was catalytically active towards aminopyrine, all-trans-retinoic acid, and particularly arachidonic acid forming 20-HETE, 19-HETE, and 18-HETE (about 86% of the total) and 14,15-, 11,12-, 8,9-, and 5,6-EETs (cis-epoxyeicosatrienoic acids; about 14% of total), with a regioselectivity similar to that shown by the mammalian CYP2J2s.

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.

Identification and regulation of a new vertebrate cytochrome P450 subfamily, the CYP2Ps, and functional characterization of CYP2P3, a conserved arachidonic acid epoxygenase/19-hydroxylase

Three genes cloned from Fundulus heteroclitus (killifish) define a new P450 subfamily, CYP2P. Structurally, the CYP2Ps are related to fish CYP2Ns and mammalian CYP2Js. CYP2P transcripts are expressed predominantly in liver and intestine. CYP2P3 coexpressed with P450 oxidoreductase in a baculovirus system catalyzed benzphetamine-N-demethylation and arachidonic acid oxidation, forming 14,15-, 11,12-, and 8,9-epoxyeicosatrienoic acids and 19-hydroxyeicosatetraenoic acid. CYP2P3 regio- and enantioselectivities with arachidonic acid were remarkably similar to human CYP2J2 and rat CYP2J3. Epoxyeicosatrienoic acids and their corresponding hydration products, the dihydroxyeicosatrienoic acids, were detected in killifish liver and intestine, indicating metabolism of arachidonic acid by killifish P450s in vivo. Levels of these products in killifish intestine were higher than those in mammalian intestine. 12-O-Tetradecanoyl phorbol 13-acetate suppressed expression of CYP2P2 and CYP2P3 in killifish intestine; fasting itself suppressed expression of CYP2P2/3 but not CYP2P1. In rat intestine fasting similarly depressed the levels of CYP2J proteins. The CYP2Ps and the CYP2Js appear to be derived from a common ancestral gene, likely a fatty acid monooxygenase.

Molecular cloning and characterization of mouse CYP2J6, an unstable cytochrome P450 isoform

A cDNA encoding a new cytochrome P450 was cloned from a mouse liver library. Sequence analysis revealed that this 2046-bp cDNA encodes a 501-amino acid polypeptide that is 72-94% identical to other CYP2J subfamily P450s and is designated CYP2J6. Northern analysis demonstrated that CYP2J6 transcripts are abundant in the small intestine and present at lower levels in other mouse tissues. In situ hybridization revealed that CYP2J6 mRNAs are present in luminal epithelial cells of the gastrointestinal mucosa. The CYP2J6 cDNA was expressed in Sf9 cells using baculovirus. The heterologously expressed CYP2J6 protein displayed a typical P450 CO-difference spectrum; however, the protein was unstable as evidenced by the loss of the Soret maxima at 450nm and the appearance of a 420nm peak when CYP2J6-expressing cells were disrupted by mechanical homogenization, sonication, or freeze-thaw. Immunoblotting of mouse microsomes with the anti-human CYP2J2 IgG, which cross-reacts with rodent CYP2Js, demonstrated the presence of multiple distinct murine CYP2J immunoreactive proteins in various tissues. Immunoblotting with an antibody to a CYP2J6-specific peptide detected a prominent 55-57kDa protein in Sf9 cell extracts expressing recombinant CYP2J6 but did not detect a protein of similar molecular mass in mouse small intestinal microsomes. Mixing experiments demonstrated that recombinant CYP2J6 is degraded rapidly in the presence of small intestinal microsomes consistent with proteolysis at highly sensitive sites. Sf9 cells, which express both CYP2J6 and NADPH-P450 oxidoreductase, metabolized benzphetamine but not arachidonic acid. We conclude that CYP2J6 is an unstable P450 that is active in the metabolism of benzphetamine, but not arachidonic acid.

Impact of incorporating the 2C5 crystal structure into comparative models of cytochrome P450 2D6

Cytochrome P450 2D6 (CYP2D6) metabolizes approximately one third of the drugs in current clinical use. To gain insight into its structure and function, we have produced four different sets of comparative models of 2D6: one based on the structures of P450s from four different microorganisms (P450 terp, P450 eryF, P450 cam, and P450 BM3), another on the only mammalian P450 (2C5) structure available, and the other two based on alternative amino acid sequence alignments of 2D6 with all five of these structures. Principal component analysis suggests that inclusion of the 2C5 crystal structure has a profound effect on the modeling process, altering the general topology of the active site, and that the models produced differ significantly from all of the templates. The four models of 2D6 were also used in conjunction with molecular docking to produce complexes with the substrates codeine and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP); this identified Glu 216 [in the F-helix; substrate recognition site (SRS) 2] as a key determinant in the binding of the basic moiety of the substrate. Our studies suggest that both Asp 301 and Glu 216 are required for metabolism of basic substrates. Furthermore, they suggest that Asp 301 (I-helix, SRS-4), a residue thought from mutagenesis studies to bind directly to the basic moiety of substrates, may play a key role in positioning the B'-C loop (SRS-1) and that the loss of activity on mutating Asp 301 may therefore be the result of an indirect effect (movement of the B'-C loop) on replacing this residue.

Involvement of CYP2J2 on the intestinal first-pass metabolism of antihistamine drug, astemizole

Orally administered astemizole is well absorbed but undergoes an extensive first-pass metabolism to O-desmethylastemizole. Desmethylastemizole is formed in the human microsomal systems of the small intestine as well as the liver, which suggests the role of cytochromes P450 (P450s) in the first-pass metabolism of astemizole. Human P450s involved in the O-demethylation of astemizole have, however, not been identified, and the involvement of twelve known drug-metabolizing P450s were denied. During the course of the P450 identification study, higher activities of the astemizole O-demethylation in the rabbit small intestine than in the liver (about 3-fold) were found. These data suggest the possible involvement of CYP2J, since P450 included in this subfamily is dominantly expressed in the small intestine of rabbits. Therefore, CYP2J2 cDNA has been isolated from the human cDNA library and expressed in COS-1 cells. A clear activity of astemizole O-demethylation was detected in recombinant CYP2J2 with K(m) = 0.65 microM and V(max) = 1129 pmol/nmol P450/min. Expression of the immunoreactive protein with CYP2J2 antibody was detected in the small intestine and liver. Expression levels of the immunoreactive protein with the CYP2J2 antibody in the small intestine were well correlated with the activities of the astemizole O-demethylation (r = 0.901, n = 5, p < 0.05). The CYP2J2 substrates, arachidonic acid and ebastine, strongly inhibited the microsomal astemizole O-demethylation in the human small intestines and recombinant CYP2J2. These results indicate the involvement of CYP2J2 in the presystemic elimination of astemizole in the human small intestine.

Cloning of CYP2J2 gene and identification of functional polymorphisms

CYP2J2 is abundant in cardiovascular tissue and active in the metabolism of arachidonic acid to eicosanoids that possess potent anti-inflammatory, vasodilatory, and fibrinolytic properties. We cloned and sequenced the entire CYP2J2 gene (approximately 40.3 kb), which contains nine exons and eight introns. We then sequenced the CYP2J2 exons and intron-exon boundaries in 72 healthy persons representing African, Asian, and European/white populations as part of the National Institutes of Health/National Institute of Environmental Health Sciences Environmental Genome Single Nucleotide Polymorphism Program. A variety of polymorphisms were found, four of which resulted in coding changes (Arg158Cys, Ile192Asn, Asp342Asn, and Asn404Tyr). A fifth variant (Thr143Ala) was identified by screening a human heart cDNA library. All five variant cDNAs of CYP2J2 were generated by site-directed mutagenesis and expressed in Sf9 insect cells by using a baculovirus system. The recombinant wild-type and variant CYP2J2 proteins immunoreacted with peptide-based antibodies to CYP2J2 and displayed typical cytochrome P450 (P450) CO-difference spectra; however, the Asn404Tyr and Ile192Asn variants also had prominent spectral peaks at 420 nm. The ability of these variants to metabolize arachidonic acid and linoleic acid was compared with that of wild-type CYP2J2. Three variants (Asn404Tyr, Arg158Cys, and Thr143Ala) showed significantly reduced metabolism of both arachidonic acid and linoleic acid. The Ile192Asn variant showed significantly reduced activity toward arachidonic acid only. The Asp342Asn variant showed similar metabolism to wild-type CYP2J2 for both endogenous substrates. Based on these data, we conclude that allelic variants of the human CYP2J2 gene exist and that some of these variants result in a P450 protein that has reduced catalytic function. Insofar as CYP2J2 products have effects in the cardiovascular system, we speculate that these variants may be functionally relevant.

Cytochrome P450 CYP2J9, a new mouse arachidonic acid omega-1 hydroxylase predominantly expressed in brain

A cDNA encoding a new cytochrome P450 was isolated from a mouse brain library. Sequence analysis reveals that this 1,958-base pair cDNA encodes a 57-58-kDa 502-amino acid polypeptide that is 70-91% identical to CYP2J subfamily P450s and is designated CYP2J9. Recombinant CYP2J9 was co-expressed with NADPH-cytochrome P450 oxidoreductase (CYPOR) in Sf9 cells using a baculovirus system. Microsomes of CYP2J9/CYPOR-transfected cells metabolize arachidonic acid to 19-hydroxyeicosatetraenoic acid (HETE) thus CYP2J9 is enzymologically distinct from other P450s. Northern analysis reveals that CYP2J9 transcripts are present at high levels in mouse brain. Mouse brain microsomes biosynthesize 19-HETE. RNA polymerase chain reaction analysis demonstrates that CYP2J9 mRNAs are widely distributed in brain and most abundant in the cerebellum. Immunoblotting using an antibody raised against human CYP2J2 that cross-reacts with CYP2J9 detects a 56-kDa protein band that is expressed in cerebellum and other brain segments and is regulated during postnatal development. In situ hybridization of mouse brain sections with a CYP2J9-specific riboprobe and immunohistochemical staining with the anti-human CYP2J2 IgG reveals abundant CYP2J9 mRNA and protein in cerebellar Purkinje cells. Importantly, 19-HETE inhibits the activity of recombinant P/Q-type Ca(2+) channels that are known to be expressed preferentially in cerebellar Purkinje cells and are involved in triggering neurotransmitter release. Based on these data, we conclude that CYP2J9 is a developmentally regulated P450 that is abundant in brain, localized to cerebellar Purkinje cells, and active in the biosynthesis of 19-HETE, an eicosanoid that inhibits activity of P/Q-type Ca(2+) channels. We postulate that CYP2J9 arachidonic acid products play important functional roles in the brain.

Molecular cloning, enzymatic characterization, developmental expression, and cellular localization of a mouse cytochrome P450 highly expressed in kidney

A cDNA encoding a new cytochrome P450 was isolated from a mouse liver library. Sequence analysis reveals that this 1,886-base pair cDNA encodes a 501-amino acid polypeptide that is 69-74% identical to CYP2J subfamily P450s and is designated CYP2J5. Recombinant CYP2J5 was co-expressed with NADPH-cytochrome P450 oxidoreductase in Sf9 cells using a baculovirus system. Microsomal fractions of CYP2J5/NADPH-cytochrome P450 oxidoreductase-transfected cells metabolize arachidonic acid to 14,15-, 11,12-, and 8, 9-epoxyeicosatrienoic acids and 11- and 15-hydroxyeicosatetraenoic acids (catalytic turnover, 4.5 nmol of product/nmol of cytochrome P450/min at 37 degrees C); thus CYP2J5 is enzymologically distinct. Northern analysis reveals that CYP2J5 transcripts are most abundant in mouse kidney and present at lower levels in liver. Immunoblotting using a polyclonal antibody against a CYP2J5-specific peptide detects a protein with the same electrophoretic mobility as recombinant CYP2J5 most abundantly in mouse kidney microsomes. CYP2J5 is regulated during development in a tissue-specific fashion. In the kidney, CYP2J5 is present before birth and reaches maximal levels at 2-4 weeks of age. In the liver, CYP2J5 is absent prenatally and during the early postnatal period, first appears at 1 week, and then remains relatively constant. Immunohistochemical staining of kidney sections with anti-human CYP2J2 IgG reveals that CYP2J protein(s) are present primarily in the proximal tubules and collecting ducts, sites where the epoxyeicosatrienoic acids are known to modulate fluid/electrolyte transport and mediate hormonal action. In situ hybridization confirms abundant CYP2J5 mRNA within tubules of the renal cortex and outer medulla. Epoxyeicosatrienoic acids are endogenous constituents of mouse kidney thus providing direct evidence for the in vivo metabolism of arachidonic acid by the mouse renal epoxygenase(s). Based on these data, we conclude that CYP2J5 is an enzymologically distinct, developmentally regulated, protein that is localized to specific nephron segments and contributes to the oxidation of endogenous renal arachidonic acid pools. In light of the well documented effects of epoxyeicosatrienoic acids in modulating renal tubular transport processes, we postulate that CYP2J5 products play important functional roles in the kidney.

P450 subfamily CYP2J and their role in the bioactivation of arachidonic acid in extrahepatic tissues

Historically, there has been intense interest in P450 metabolic oxidation, peroxidation, and reduction of xenobiotics. More recently, there has been a growing appreciation for the role of P450s in the oxidation of lipophilic endobiotics, such as bile acids, fat-soluble vitamins, and eicosanoids. This review details the emerging CYP2J subfamily of P450s and their role as catalysts of arachidonic acid metabolism.

Mapping of the CYP2J cytochrome P450 genes to human chromosome 1 and mouse chromosome 4

CYP2J subfamily cytochromes P450 catalyze the NADPH-dependent oxidation of arachidonic acid to several unique eicosanoids that possess numerous biological activities including modulation of ion transport, control of bronchial and vascular smooth muscle tone, and stimulation of peptide hormone secretion. We have identified sequence variants in the 3' untranslated regions of two mouse Cyp2j genes (Cyp2j5 and Cyp2j6) and used a PCR-based oligonucleotide hybridization assay to map both genes to the central region of chromosome 4 distal to the Jun oncogene. The corresponding human CYP2J gene (CYP2J2) has been assigned to human chromosome 1 on a panel of somatic hybrid cell lines and to 1p31.3-p31.2 by fluorescence in situ hybridization analysis. The proximity of the Cyp2j cluster to the Cyp4a cluster suggests that these genes may be part of a cassette of P450 genes involved in the oxidation of fatty acids.

CYP2J subfamily cytochrome P450s in the gastrointestinal tract: expression, localization, and potential functional significance

Our laboratory recently described a new human cytochrome P450 arachidonic acid epoxygenase (CYP2J2) and the corresponding rat homologue (CYP2J3), both of which were expressed in extrahepatic tissues. Northern analysis of RNA prepared from the human and rat intestine demonstrated that CYP2J2 and CYP2J3 mRNAs were expressed primarily in the small intestine and colon. In contrast, immunoblotting studies using a polyclonal antibody raised against recombinant CYP2J2 showed that CYP2J proteins were expressed throughout the gastrointestinal tract. Immunohistochemical staining of formalin-fixed, paraffin-embedded intestinal sections using anti-CYP2J2 IgG and avidin-biotin-peroxidase detection revealed that CYP2J proteins were present at high levels in nerve cells of autonomic ganglia, epithelial cells, intestinal smooth muscle cells, and vascular endothelium. The distribution of this immunoreactivity was confirmed by in situ hybridization using a CYP2J2-specific antisense RNA probe. Microsomal fractions prepared from human jejunum catalyzed the NADPH-dependent metabolism of arachidonic acid to epoxyeicosatrienoic acids as the principal reaction products. Direct evidence for the in vivo epoxidation of arachidonic acid by intestinal cytochrome P450 was provided by documenting, for the first time, the presence of epoxyeicosatrienoic acids in human jejunum by gas chromatography/mass spectrometry. We conclude that human and rat intestine contain an arachidonic acid epoxygenase belonging to the CYP2J subfamily that is localized to autonomic ganglion cells, epithelial cells, smooth muscle cells, and vascular endothelium. In addition to the known effects on intestinal vascular tone, we speculate that CYP2J products may be involved in the release of intestinal neuropeptides, control of intestinal motility, and/or modulation of intestinal fluid/electrolyte transport.

Molecular cloning, expression, and functional significance of a cytochrome P450 highly expressed in rat heart myocytes

A cDNA encoding a P450 monooxygenase was amplified from reverse transcribed rat heart and liver total RNA by polymerase chain reaction using primers based on the 5'- and 3'-end sequences of two rat pseudogenes, CYP2J3P1 and CYP2J3P2. Sequence analysis revealed that this 1,778-base pair cDNA contained an open reading frame and encoded a new 502 amino acid protein designated CYP2J3. Based on the deduced amino acid sequence, CYP2J3 was approximately 70% homologous to both human CYP2J2 and rabbit CYP2J1. Recombinant CYP2J3 protein was co-expressed with NADPH-cytochrome P450 oxidoreductase in Sf9 insect cells using a baculovirus expression system. Microsomal fractions of CYP2J3/NADPH-cytochrome P450 oxidoreductase-transfected cells metabolized arachidonic acid to 14,15-, 11,12-, and 8, 9-epoxyeicosatrienoic acids and 19-hydroxyeicosatetraenoic acid as the principal reaction products (catalytic turnover, 0.2 nmol of product/nmol of cytochrome P450/min at 37 degrees C). Immunoblotting of microsomal fractions prepared from rat tissues using a polyclonal antibody raised against recombinant CYP2J2 that cross-reacted with CYP2J3 but not with other known rat P450s demonstrated abundant expression of CYP2J3 protein in heart and liver. Immunohistochemical staining of formalin-fixed paraffin-embedded rat heart tissue sections using the anti-CYP2J2 IgG and avidin-biotin-peroxidase detection localized expression of CYP2J3 primarily to atrial and ventricular myocytes. In an isolated-perfused rat heart model, 20 min of global ischemia followed by 40 min of reflow resulted in recovery of only 44 +/- 6% of base-line contractile function. The addition of 5 microM 11, 12-epoxyeicosatrienoic acid to the perfusate prior to global ischemia resulted in a significant 1.6-fold improvement in recovery of cardiac contractility (69 +/- 5% of base line, p = 0.01 versus vehicle alone). Importantly, neither 14,15-epoxyeicosatrienoic acid nor 19-hydroxyeicosatetraenoic acid significantly improved functional recovery following global ischemia, demonstrating the specificity of the biological effect for the 11, 12-epoxyeicosatrienoic acid regioisomer. Based on these data, we conclude that (a) CYP2J3 is one of the predominant enzymes responsible for the oxidation of endogenous arachidonic acid pools in rat heart myocytes and (b) 11,12-epoxyeicosatrienoic acid may play an important functional role in the response of the heart to ischemia.

CDNA cloning, heterologous expression, and characterization of rat intestinal CYP2J4

The small intestine is the major portal of entry of ingested xenobiotics. Previous studies from this and other laboratories indicated that at least 6 of the 33 xenobiotic metabolizing forms of P450 currently identified are expressed in rat small intestinal epithelial cells. In the present study, a previously unidentified rat P450, designated CYP2J4, was identified in rat small intestine using PCR. The full-length CYP2J4 cDNA contains an open reading frame for a protein of 501 residues and is 72.5 and 75.8% identical to rabbit CYP2J1 and human CYP2J2, respectively, in deduced amino acid sequences. The coding region of CYP2J4 cDNA has been cloned into a baculoviral expression vector (pVL1392) and expressed in cultured Spodoptera frugiperta (SF9) cells. The heterologously expressed CYP2J4 protein displayed a typical p450 CO-difference spectrum, with maximum absorbance at 449 nm. When purified to near electrophoretic homogeneity, it was active toward arachidonic acid in a reconstituted system with NADPH-P450 reductase and phospholipid, producing both hydroxyeicosatetraenoic and epoxyeicosatrienoic acids. RNA blot analysis with CYP2J4 cDNA as a probe detected two mRNA species, about 2.0 and 2.4 kb, respectively, in RNA preparations from liver, intestine, olfactory mucosa, kidney, heart, and lung. The 2.0-kb mRNA species was abundant in liver, small intestine, and olfactory mucosa, whereas the 2.4-kb mRNA species was predominant only in the olfactory mucosa. Immunoblot analysis of microsomal fractions from different rat tissues with a polyclonal anti-peptide antibody to CYP2J4 detected a protein with the same electrophoretic mobility as purified CYP2J4 most abundantly in small intestine and to a lesser extent in liver and other immunoreactive proteins with slightly higher electrophoretic mobility than purified CYP2J4 in a number of tissues, including small intestine, liver, kidney, lung, and olfactory mucosa. The predominant distribution of CYP2J4, which has activity toward arachidonic acid, is provocative, but its physiological function is as yet unknown.

Purification and characterization of rabbit small intestinal cytochromes P450 belonging to CYP2J and CYP4A subfamilies

A new form of P450 designated P450ib2 was purified from rabbit small intestine microsomes. This P450 had properties very similar, to P450ib (CYP2J1), and showed 88% identity with CYP2J1 in its first 20 NH2-terminal amino acid sequence, excluding 3 undetermined residues. Both P450ib and P450ib2 were immunohistochemically detected in the mucosal epitherial cells of the duodenum, jejunum, and ileum in the small intestine, whereas no immunoreactivity was observed in other tissues including liver, kidney, lung, colon, and stomach. The results support that the two closely related P450s are specifically localized in the rabbit small intestine. Another small intestinal P450, P450ia, was found to hydroxylate a wide variety of fatty acids including straight-chain, branched-chain, unsaturated, or hydroxy fatty acids, and prostaglandin A at the omega and (omega-1) positions. P450ia was identical with a rabbit kidney fatty acid omega-hydroxylase, CYP4A7, in its 25 NH2-terminal amino acid sequence, excluding 2 undetermined residues. The results identify P450ia as CYP4A7.

Molecular cloning and expression of CYP2J2, a human cytochrome P450 arachidonic acid epoxygenase highly expressed in heart

A cDNA encoding a human cytochrome P450 arachidonic acid epoxygenase was isolated from a human liver cDNA library. Sequence analysis revealed that this 1,876-base pair cDNA contained an open reading frame and encoded a new 502-amino acid protein designated CYP2J2. Blot hybridization analysis of RNA prepared from human tissues revealed that CYP2J2 was highly expressed in the heart. Recombinant CYP2J2 protein was prepared using the baculovirus expression system and purified to near electrophoretic homogeneity. The enzyme metabolized arachidonic acid predominantly via olefin epoxidation to all four regioisomeric cis-epoxyeicosatrienoic acids (catalytic turnover 65 pmol of product formed/nmol of cytochrome P450/min at 30 degrees C). Epoxidation of arachidonic acid by CYP2J2 at the 14,15-olefin was highly enantioselective for (14R, 15S)-epoxyeicosatrienoic acid (76% optical purity). Immunoblotting of microsomal fractions prepared from human tissues using a polyclonal antibody raised against the recombinant hemoprotein confirmed primary expression of CYP2J2 protein in human heart. The in vivo significance of CYP2J2 was suggested by documenting the presence of epoxyeicosatrienoic acids in the human heart using gas chromatography/mass spectroscopy. Importantly, the chirality of CYP2J2 products matched that of the epoxyeicosatrienoic acid enantiomers present, in vivo, in human heart. We propose that CYP2J2 is one of the enzymes responsible for epoxidation of endogenous arachidonic acid pools in human heart and that epoxyeicosatrienoic acids may, therefore, play important functional roles in cardiac physiology.

Intercellular signals downstream of endothelin receptor-B mediate colonization of the large intestine by enteric neuroblasts

Mice homozygous for the piebald lethal (sl) mutation, which have a complete deletion of endothelin receptor-B, fail to form ganglion cells in the distal large intestine and are nearly devoid of cutaneous melanocytes. These phenotypic features stem from incomplete colonization of the hindgut and skin by neural crest-derived neuroblasts and melanoblasts, respectively. We have used expression of a transgene, dopamine-beta-hydroxylase-nlacZ, to study colonization of the enteric nervous system in sl/sl embryos and sl/sl &lt;--&gt; wild-type chimeric mice. Enteric neuroblasts derived from the vagal neural crest colonize the developing foregut, midgut and distal small intestine of sl/sl embryos in a cranial-to-caudal manner indistinguishable from sl/+ or +/+ embryos. However, colonization of the large intestine is retarded and the distal large intestine is never colonized, a developmental defect identical to that observed in lethal spotted (endothelin-3 deficient) embryos. The coat pigmentation and relative distributions of mutant and wild-type ganglion cells in sl/sl &lt;--&gt; wild-type chimeras indicate that the defect associated with endothelin receptor-B gene deletion is not strictly neuroblast autonomous (independent of environmental factors). Instead, intercellular interactions downstream of the endothelin receptor-B mediate complete colonization of the skin and gut by neural crest cells.

The P450 superfamily: update on new sequences, gene mapping, accession numbers, early trivial names of enzymes, and nomenclature

We provide here a list of 221 P450 genes and 12 putative pseudogenes that have been characterized as of December 14, 1992. These genes have been described in 31 eukaryotes (including 11 mammalian and 3 plant species) and 11 prokaryotes. Of 36 gene families so far described, 12 families exist in all mammals examined to date. These 12 families comprise 22 mammalian subfamilies, of which 17 and 15 have been mapped in the human and mouse genome, respectively. To date, each subfamily appears to represent a cluster of tightly linked genes. This revision supersedes the previous updates [Nebert et al., DNA 6, 1-11, 1987; Nebert et al., DNA 8, 1-13, 1989; Nebert et al., DNA Cell Biol. 10, 1-14 (1991)] in which a nomenclature system, based on divergent evolution of the superfamily, has been described. For the gene and cDNA, we recommend that the italicized root symbol "CYP" for human ("Cyp" for mouse), representing "cytochrome P450," be followed by an Arabic number denoting the family, a letter designating the subfamily (when two or more exist), and an Arabic numeral representing the individual gene within the subfamily. A hyphen should precede the final number in mouse genes. "P" ("p" in mouse) after the gene number denotes a pseudogene. If a gene is the sole member of a family, the subfamily letter and gene number need not be included. We suggest that the human nomenclature system be used for all species other than mouse. The mRNA and enzyme in all species (including mouse) should include all capital letters, without italics or hyphens. This nomenclature system is identical to that proposed in our 1991 update. Also included in this update is a listing of available data base accession numbers for P450 DNA and protein sequences. We also discuss the likelihood that this ancient gene superfamily has existed for more than 3.5 billion years, and that the rate of P450 gene evolution appears to be quite nonlinear. Finally, we describe P450 genes that have been detected by expressed sequence tags (ESTs), as well as the relationship between the P450 and the nitric oxide synthase gene superfamilies, as a likely example of convergent evolution.