Characterization of multiple human cytochrome P-450 1 cDNAs. The chromosomal localization of the gene and evidence for alternate RNA splicing

Permanent uncoupling of male-specific CYP2C11 transcription/translation by perinatal glutamate

Perinatal exposure of rats and mice to the typically reported 4mg/g bd wt dose of monosodium glutamate (MSG) results in a complete block in GH secretion as well as obesity, growth retardation and a profound suppression of several cytochrome P450s, including CYP2C11, the predominant male-specific isoform--all irreversible effects. In contrast, we have found that a lower dose of the food additive, 2mg/g bd wt on alternate days for the first 9days of life results in a transient neonatal depletion of plasma GH, a subsequent permanent overexpression of CYP2C11 as well as subnormal (mini) GH pulse amplitudes in an otherwise normal adult masculine episodic GH profile. The overexpressed CYP2C11 was characterized by a 250% increase in mRNA, but only a 40 to 50% increase in CYP2C11 protein and its catalytic activity. Using freshly isolated hepatocytes as well as primary cultures exposed to the masculine-like episodic GH profile, we observed normal induction, activation, nuclear translocation and binding to the CYP2C11 promoter of the GH-dependent signal transducers required for CYP2C11 transcription. The disproportionately lower expression levels of CYP2C11 protein were associated with dramatically high expression levels of an aberrant, presumably nontranslated CYP2C11 mRNA, a 200% increase in CYP2C11 ubiquitination and a 70-80% decline in miRNAs associated, at normal levels, with a suppression of CYP2C expression. Whereas the GH-responsiveness of CYP2C7 and CYP2C6 as well as albumin was normal in the MSG-derived hepatocytes, the abnormal expression of CYP2C11 was permanent and irreversible.

Cytochrome P450 CYP3A in marsupials: cloning and identification of the first CYP3A subfamily member, isoform 3A70 from Eastern gray kangaroo (Macropus giganteus)

Australian marsupials are unique fauna that have evolved and adapted to unique environments and thus it is likely that their detoxification systems differ considerably from those of well-studied eutherian mammals. Knowledge of these processes in marsupials is therefore vital to understanding the consequences of exposure to xenobiotics. Cytochromes P450 (CYPs) are critically important in the oxidative metabolism of a diverse array of both xenobiotics and endogenous substrates. In this study we have cloned and characterized CYP3A70, the first identified member of the CYP3A gene subfamily from Eastern gray kangaroo (Macropus giganteus). A 1665 base pair kangaroo hepatic CYP3A complete cDNA, designated CYP3A70, was cloned by reverse transcription-polymerase chain reaction approaches, which encodes a protein of 506 amino acids. The CYP3A70 cDNA shares approximately 71% nucleotide and 65% amino acid sequence homology to human CYP3A4 and displays high sequence similarity to other published mammalian CYP3As from human, monkey, cow, pig, dog, rat, rabbit, mouse, hamster, and guinea pig. Transfection of the CYP3A70 cDNAs into 293T cells resulted in stable cell lines expressing a CYP3A immuno-reactive protein that was recognized by a goat anti-human CYP3A4 polyclonal antibody. The anti-human CYP3A4 antibody also detected immunoreactive proteins in liver microsomes from all test marsupials, including the kangaroo, koala, wallaby, and wombat, with multiple CYP3A immunoreactive bands observed in kangaroo and wallaby tissues. Relatively, very low CYP catalytic activity was detected for the kangaroo CYP3A70 cDNA-expressed proteins (19.6 relative luminescent units/μg protein), which may be due to low protein expression levels. Collectively, this study provides primary molecular data regarding the Eastern kangaroo hepatic CYP3A70 gene and enables further functional analyses of CYP3A enzymes in marsupials.

Cytochrome P450 CYP3A in marsupials: cloning and characterisation of the second identified CYP3A subfamily member, isoform 3A78 from koala (Phascolarctos cinereus)

Cytochromes P450 (CYPs) are critically important in the oxidative metabolism of a diverse array of xenobiotics and endogenous substrates. Previously, we cloned and characterised the CYP2C, CYP4A, and CYP4B gene subfamilies from marsupials and demonstrated important species-differences in both activity and tissue expression of these CYP enzymes. Recently, we isolated the Eastern grey kangaroo CYP3A70. Here we have cloned and characterised the second identified member of marsupial CYP3A gene subfamily, CYP3A78 from the koala (Phascolarctos cinereus). In addition, we have examined the gender-differences in microsomal erythromycin N-demethylation activity (a CYP3A marker) and CYP3A protein expression across test marsupial species. Significant differences in hepatic erythromycin N-demethylation activity were observed between male and female koalas, with the activity detected in female koalas being 2.5-fold higher compared to that in male koalas (p<0.01). No gender-differences were observed in tammar wallaby or Eastern grey kangaroo. Immunoblot analysis utilising anti-human CYP3A4 antibody detected immunoreactive proteins in liver microsomes from all test male and female marsupials including the koala, tammar wallaby, and Eastern grey kangaroo, with no gender-differences detected across test marsupials. A 1610 bp koala hepatic CYP3A complete cDNA, designated CYP3A78, was cloned by reverse transcription-polymerase chain reaction approaches. It displays 64% nucleotide and 57% amino acid sequence identity to the Eastern grey kangaroo CYP3A70. The CYP3A78 cDNA encodes a protein of 515 amino acids, shares approximately 68% nucleotide and 56% amino acid sequence identity to human CYP3A4, and displays high sequence similarity to other published mammalian CYP3As from human, monkey, cow, pig, dog, rat, rabbit, mouse, hamster, and guinea pig. Collectively, this study provides primary molecular data regarding koala hepatic CYP3A78 gene and enables further functional analyses of CYP3A enzymes in marsupials. Given the significant role that CYP3A enzymes play in the metabolism of both endogenous and exogenous compounds, the clone provides an important step in elucidating the metabolic capacity of marsupials.

WITHDRAWN: Cytochrome P450 CYP3A in marsupials: Characterisation of the first identified CYP3A subfamily member, isoform 3A70 from Eastern grey kangaroo (Macropus giganteus)

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Pulmonary cytochrome P450 enzymes belonging to the CYP4B subfamily from an Australian marsupial, the tammar wallaby (Macropus eugenii)

Cytochromes P450 (CYPs) are critically important in the oxidative metabolism of a diverse array of xenobiotics and endogenous substrates. We have previously reported the cloning and characterisation of the koala CYP4A15, the first reported member of the CYP4 family from marsupials, and have demonstrated important species differences in CYP4A activity and tissue expression. In the present study, the cloning of CYP4B1 in the wallaby (Macropus eugenii) and their expression across marsupials is described. Rabbit anti-mouse CYP4B1 antibody detected immunoreactive proteins in lung and liver microsomes from all test marsupials, with relative weak signal detected from the koala, suggesting a species-specific expression. Microsomal 2-aminofluorene bio-activation (a CYP4B1 marker) in wallaby lung was comparable to that of rabbit, with significant higher activities detected in wallaby liver and kidneys compared to rabbit. A 1548bp wallaby lung CYP4B complete cDNA, designated CYP4B1, which encodes a protein of 510 amino acids and shares 72% nucleotide and 69% amino acid sequence identity to human CYP4B1, was cloned by polymerase chain reaction approaches. The results demonstrate the presence of wallaby CYP4B1 that shares several common features with other published CYP4Bs; however the wallaby CYP4B1 cDNA contains four extra amino acid residues at the NH₂-terminal, a fundamentally conserved transmembrane anchor of all eukaryote CYPs.

An Interethnic Comparison of Polymorphisms of the Genes Encoding Drug-Metabolizing Enzymes and Drug Transporters: Experience in Singapore

Much of the interindividual variability in drug response is attributable to the presence of single nucleotide polymorphisms (SNPs) in genes encoding drug-metabolizing enzymes and drug transporters. In recent years, we have investigated the polymorphisms in a number of genes encoding phase I and II drug-metabolizing enzymes including CYPIA1, CYP3A4, CYP3A5, GSTM1, NAT2, UGT1A1, and TPMT and drug transporter (MDR1) in three distinct Asian populations in Singapore, namely the Chinese, Malays, and Indians. Significant differences in the frequencies of common alleles encoding these proteins have been observed among these three ethnic groups. For example, the frequency of the variant A2455G polymorphism of CYP1A1 was 28% in Chinese and 31% in Malays, but only 18% in Indians. CYP3A4*4 was detected in two of 110 Chinese subjects, but absent in Indians and Malays. Many Chinese and Malays (61-63%) were homozygous for the GSTM1*0 null genotype compared with 33% of Indians. The frequency of the UGTIA1*28 allele was highest in the Indian population (35%) compared to similar frequencies that were found in the Chinese (16%) and Malay (19%) populations. More importantly, our experience over the years has shown that the pharmacogenetics of these drug-metabolizing enzymes and MDR1 in the Asian populations are different from these in the Caucasian and African populations. For example, the CYP3A4*1B allele, which contains an A-290G substitution in the promoter region of CYP3A4, is absent in all three Asian populations of Singapore studied, but occurs in more than 54% of Africans and 5% of Caucasians. There were no difference in genotype and allelic variant frequencies in exon 12 of MDR1 between the Chinese, Malay, and Indian populations. When compared with other ethnic groups, the distribution of the wild-type C allele in exon 12 in the Malays (34.2%) and Indians (32.8%) was relatively high and similar to the Japanese (38.55%) and Caucasians (41%) but different from African-Americans (15%). The frequency of wild-type TT genotype in Asians (43.5% to 52.1%) and Japanese (61.5%) was much higher than those found in Caucasians (13.3%). All the proteins we studied represent the primary hepatic or extrahepatic enzymes, and their polymorphic expression may be implicated in disease risk and the disposition of drugs or endogenous substances. As such, dose requirements of certain drugs may not be optimal for Asian populations, and a second look at the factors responsible for this difference is necessary.

Hepatic cytochrome P450 enzymes belonging to the CYP2C subfamily from an Australian marsupial, the koala (Phascolarctos cinereus)

Cytochromes P450 (CYPs) are critically important in the oxidative metabolism of a diverse array of xenobiotics and endogenous substrates. We have previously reported that the obligate Eucalyptus feeder koala (Phascolarctos cinereus) exhibits a higher hepatic CYP2C activity as compared to non-Eucalyptus feeders human or rat, with stimulation of CYP2C activity by cineole. In the present study, we examine CYP2C expression by immunohistochemistry and describe the identification and cloning of koala CYP2Cs. Utilising anti-rat CYP2C6 antibody, the expression of CYP2C was found to be uniform across the hepatic sections, being consistent with that observed in human and rat. Two 1647 and 1638 bp koala liver CYP2C complete cDNAs, designated CYP2C47 and CYP2C48 respectively, were cloned by cDNA library screening. The koala CYP2C cDNAs encode a protein of 495 amino acids. Three additional partial CYP2C sequences were also identified from the koala, indicating the multiplicity of the CYP2C subfamily in this unique marsupial species. The results of this study demonstrate the presence of koala hepatic CYP2Cs that share several common features with other published CYP2Cs; however CYP2C47 and CYP2C48 contain four extra amino acid residues at the NH2-terminal, a transmembrane anchor which was reported being a fundamentally conserved structure core of all eukaryote CYP enzymes.

Alternative splicing within the human cytochrome P450 superfamily with an emphasis on the brain: the convolution continues

The human cytochrome P450 (CYP) superfamily of enzymes regulate hepatic phase 1 drug metabolism and subsequently play a significant role in pharmacokinetics, drug discovery and drug development. Alternative splicing of the cytochrome CYP gene transcripts enhances gene diversity and may play a role in transcriptional regulation of certain CYP proteins. Tissue-specific alternative splicing of CYPs is significant for its potential to add greater dimension to differential drug metabolism in hepatic and extrahepatic tissues, such as the brain, and to our understanding of the CYP family. This review provides an overview of tissue-specific splicing patterns, splicing types, regulation and the functional diversities between liver and splice variant CYP proteins and further explores the relevance of tissue-specific alternative splicing of CYPs in the nervous system.

Genetic polymorphisms in the cytochromes P-450 (1A1, 2E1), microsomal epoxide hydrolase and glutathione S-transferase M1, T1, and P1 genes, and their relationship with chronic bronchitis and relapsing pneumonia in children

The purpose of this study was to investigate the possible roles of the genes functioning in xenobiotic metabolism and antioxidant pathways in the development of severe chronic lung disease in children. Polymorphisms in the genes encoding CYP1A1, CYP2E1, EPHX1, GSTM1, GSTT1, and GSTP1 were investigated in cases of Tatar children with chronic bronchitis (n=129) and relapsing pneumonia (n=50) and in cases of ethnically matched healthy individuals (n=227) living in the city of Ufa, the Republic of Bashkortostan (South Ural region of Russia), by polymerase chain reaction-restriction fragment length polymorphism (PCR-RLFP) method. The frequency of the *2C allele of the CYP1A1 gene was significantly higher in patients than in the healthy control group (chi2=15.02, P=0.0007, Pcor=0.0021). This allele was associated with a higher risk of chronic bronchitis in children (OR 4.14, 95% CI 1.83-9.53; Pcor=0.0024). Similar results were obtained in cases of patients with relapsing pneumonia (OR 3.86, 95% CI 1.34-10.95; Pcor=0.027 for the *2C allele of the CYP1A1 gene). The frequency of the *5B allele of the CYP2E1 gene was higher in the relapsing pneumonia patients (7.0 vs 1.98% in the control group; chi2=5.68, P=0.018, Pcor=0.054; OR 3.72, 95% CI 1.21-11.24). The increase in the GSTT1 gene deletion was significant only in cases of chronic bronchitis (39.53 compared to 21.15% in the control group; chi2=12.96, P=0.001, Pcor=0.003; OR 2.44, 95% CI 1.48-4.04). Our results show that the presence of the GSTM1 gene deletion is unfavorable for the development of chronic lung disease in females (chi2=9.57; P=0.0029, Pcor=0.0116) and was associated with increased risk (OR 2.44, 95% CI 1.36-4.38). The distribution of EPHX1 and GSTP1 gene genotypes was similar in the control and patient groups. Our findings indicate that the polymorphisms of the CYP1A1, CYP2E1, and GSTT1 genes probably play a substantial part in susceptibility to severe airway and lung injury in cases of children with chronic bronchitis and relapsing pneumonia.

Inter-individual variation in the metabolic activation of the antimalarial biguanides

The aryl-biguanides proguanil and chlorproguanil were developed as part of a collaborative programme between ICI and the Liverpool School of Tropical Medicine during the 1940s. The compounds were characterized by their absence of host toxicity. However, the rapid development of parasite resistance to the actions of these drugs and the development of the 4-aminoquinoline, chloroquine, severely limited their use. The subsequent widespread development of parasite resistance to chloroquine, together with the observations that the magnitude of dihydrofolate reductase inhibitor resistance (the site of action of the biguanides) developed to pyrimethamine is not directly correlated with biguanide resistance(1,2). has resulted in renewed interest in these drugs. In particular, proguanil is now the drug of choice for malaria prophylaxis, in combination with chloroquine; used in combination with a suitable sulphonamide, it may be of value in malaria therapy.

Establishment of ten strains of genetically engineered Salmonella typhimurium TA1538 each co-expressing a form of human cytochrome P450 with NADPH-cytochrome P450 reductase sensitive to various promutagens

We newly developed 10 Salmonela typhimurium TA1538 strains each co-expressing a form of human cytochrome P450s (P450 or CYP) together with NADPH-cytochrome P450 reductase (CPR) for highly sensitive detection of mutagenic activation of mycotoxins, polycyclic aromatic hydrocarbons, heterocyclic amines, and aromatic amines at low substrate concentrations. Each form of P450 (CYP1A1, CYP1A2, CYP2A6, CYP2C8, CYP2C9, CYP2C19, CYP2D6, CYP2E1, CYP3A4 or CYP3A5) expressed in the TA1538 cells efficiently catalyzed the oxidation of a representative substrate. Aflatoxin B1 was mutagenically activated effectively by CYP1A1, CYP1A2, and CYP3A4 and weakly by CYP2A6 and CYP2C8 expressed in S. typhimurium TA1538. CYP1A1 and CYP1A2 were responsible for the mutagenic activation of 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) and 2-acetylaminofluorene. Benzo[a]pyrene was also activated efficiently by CYP1A1 and weakly by CYP1A2, CYP2C9, CYP2C19, and CYP3A4 expressed in TA1538. These results suggest that the newly developed S. typhimurium TA1538 strains are applicable for detecting the activation of promutagens of which mutagenic activation is not or weakly detectable with N-nitrosamine-sensitive YG7108 strains expressing human P450s.

Genetic polymorphisms of CYP2C8 in Japanese population

CYP2C8 plays important roles in metabolizing therapeutic drugs and endogenous compounds. Although genetic polymorphisms of CYP2C8 were reported, there is little information on CYP2C8 polymorphisms in the Japanese population. In the present study, we screened for previously described polymorphisms in the coding region of this gene using polymerase chain reaction (PCR)-restriction fragment length polymorphism or allele specific-PCR analyses. Eleven polymorphisms of CYP2C8*2 (I269F), CYP2C8*3 (R139K, K399R), CYP2C8*4 (I264M), CYP2C8*5 (frameshift), T130N, E154D, N193K, K249R, L390S, P404A, and H411L have been comprehensively investigated in at least 200 Japanese individuals. A single subject was heterozygous for CYP2C8*5, and the allele frequency was calculated as 0.0025. The other single nucleotide polymorphisms (SNPs) were not found in the Japanese subjects in the present study. Thus, it appears that the frequencies of these alleles in Japanese are extremely low. In addition, concerning the SNPs of T130N, E154D, N193K, K249R, and H411L, it remains clear that these alleles exist as polymorphisms or represent sequence errors or cloning artifacts. Although several SNPs such as CYP2C8*2, CYP2C8*3, CYP2C8*4, and P404A have been reported to reduce the enzymatic activity, pharmacokinetic abnormalities of drugs metabolized by polymorphic CYP2C8 might be rare in Japanese.

Pharmacogenetics of the major polymorphic metabolizing enzymes

There is increasing information available on the existence of polymorphisms in genes encoding xenobiotic metabolizing enzymes and the functional significance of many of these. In addition to genes long recognized as being polymorphic, such as CYP2D6, CYP2C19 and CYP2C9, there is now information available on the existence of polymorphisms in other cytochrome P450 genes such as CYP2A6, CYP2B6 and CYP2C8. With respect to phase II metabolism, polymorphisms in GSTM1, GSTT1, NAT2 and TPMT are well understood but information is also emerging on other GST polymorphisms and on polymorphisms in the UDP-glucuronosyltransferases and sulfotransferases. The availability of comprehensive information on the occurrence and functional significance of polymorphisms affecting drug metabolism should facilitate their application to pharmacogenomic profiling.

CYP2C8 polymorphisms in Caucasians and their relationship with paclitaxel 6alpha-hydroxylase activity in human liver microsomes

Published cDNA sequences suggest the existence of non-synonymous single nucleotide polymorphisms in the cytochrome P450 CYP2C8. To determine whether these polymorphisms could be confirmed in a Caucasian population and to investigate whether additional polymorphisms occur in the coding and upstream regions of this gene, we screened for previously described and for novel polymorphisms using PCR-RFLP and SSCP analysis. We confirmed the existence of two of the previously detected polymorphisms which give rise to the amino acid substitutions I264M and K399R, respectively, but failed to detect three others in our population. We also confirmed that a recently identified polymorphism (R139K) is linked to K399R (CYP2C8*3) in our study population. The allele frequencies for the I264M (CYP2C8*4 allele) and the CYP2C8*3 allele were 0.075 and 0.15, respectively. Three novel polymorphisms (T-370G, C-271A and T1196C/L390S) were also detected with the upstream polymorphisms showing allele frequencies of 0.061 and 0.196, respectively, but the L390S polymorphism detected only in a single subject. An additional single subject was heterozygous for a polymorphism recently described in African-Americans (A805T; CYP2C8*2 allele). The functional significance of the two upstream polymorphisms and the CYP2C8*3 and CYP2C8*4 alleles was investigated in human liver microsomes. Samples heterozygous for CYP2C8*3 showed significantly lower paclitaxel 6alpha-hydroxylase activity compared with wild-type samples. Median activity associated with CYP2C8*4 also appeared lower than the wild-type but the difference was not significant. There was no evidence that either upstream polymorphism gave rise to altered CYP2C8 expression.

Genetic polymorphisms and metabolism of endocrine disruptors in cancer susceptibility

Epidemiological studies have estimated that approximately 80% of all cancers are related to environmental factors. Individual cancer susceptibility can be the result of several host factors, including differences in metabolism, DNA repair, altered expression of tumor suppressor genes and proto-oncogenes, and nutritional status. Xenobiotic metabolism is the principal mechanism for maintaining homeostasis during the body's exposure to xenobiotics. The balance of xenobiotic absorption and elimination rates in metabolism can be important in the prevention of DNA damage by chemical carcinogens. Thus the ability to metabolize and eliminate xenobiotics can be considered one of the body's first protective mechanisms. Variability in individual metabolism has been related to the enzymatic polymorphisms involved in activation and detoxification of chemical carcinogens. This paper is a contemporary literature review on genetic polymorphisms involved in the metabolism of endocrine disruptors potentially related to cancer development.

Nominal growth hormone pulses in otherwise normal masculine plasma profiles induce intron retention of overexpressed hepatic CYP2C11 with associated nuclear splicing deficiency

Restoration of circulating masculine GH profiles at minipulse amplitudes (i.e. approximately 10% of normal) to hypophysectomized male rats and neonatal administration of monosodium glutamate (MSG), producing a similar plasma GH profile, both result in an overexpression (approximately 200-300%) of CYP2C11 messenger RNA (mRNA), the predominant hepatic cytochrome P450 (CYP) drug-metabolizing enzyme in adult male rats. Coincident with the severalfold elevation in transcript level is a modest 10-30% overexpression of CYP2C11 protein and its catalytic activities. Using hepatic tissue from adult, neonatally MSG-treated rats, we have cloned a variant species of CYP2C11 mRNA containing all of the essential elements of a full-length complementary DNA, including initiating codon, termination codon, and polyadenylase tail. In addition, the transcript contains a 742-bp intervening sequence (identical to the complete terminal intron) between the last and penultimate exons, and an intron-specific oligo probe for Northern blotting demonstrates the presence of the variant transcript in liver of MSG-treated rats. Associated with the overexpression and intron retention of the transcript is a 50% reduction in the nuclear splicing capacity of the liver for model precursor CYP2C11 mRNA. It is proposed that this splicing defect may be a consequence of the mini-GH pulses (secreted in otherwise normal masculine plasma profiles) signaling abnormal processing of precursor CYP2C11 mRNA to produce a substantial portion of intron retained, nontranslatable transcript.

Cloning and expression of murine CYP2Cs and their ability to metabolize arachidonic acid

Five murine cytochrome P450 (CYP) 2C cDNAs were cloned and characterized, including four new members of this subfamily: CYP2C37, CYP2C38, CYP2C39, and CYP2C40. The cDNAs ranged from 1716 to 1812 bp in length and encoded polypeptides of 490 amino acid residues except for CYP2C40, which contained an additional glutamic acid residue at the carboxyl terminus. The amino acid identity of the murine CYP2Cs ranged from 69 to 92%, while the overall amino acid identity was 60%; however, within the six putative substrate recognition sites the identity was only 25 to 41%, suggesting possible differences in substrate specificity and product profiles. The CYP2C cDNAs were expressed in Escherichia coli following modification of the N-terminus. All five recombinant CYP2Cs metabolized arachidonic acid, but with different metabolic profiles and catalytic rates. Based on coelution with authentic standards on reverse-phase HPLC, themajor metabolites were tentatively identified asfollows: CYP2C29 and CYP2C39 produced 14, 15-cis-epoxyeicosatrienoic acid (EET); CYP2C37 produced 12-hydroxyeicosatetraenoic acid (HETE); CYP2C38 produced 11,12-EET; and CYP2C40 produced an unidentified metabolite that coeluted with 16-,17-, and 18-HETEs. The turnover numbers for CYP2C29, CYP2C37, CYP2C38, CYP2C39, and CYP2C40 were 0.34, 1.12, 5.15, 0.51, and 0.15 nmol/nmol/min, respectively. Reverse transcriptase-polymerase chain reaction demonstrated the presence of CYP2C29 mRNA in liver as well as in extrahepatic tissues including brain, kidney, lung, heart, and intestine. CYP2C38 and CYP2C40 were found in liver, brain, kidney, and intestine, with trace amounts in lung and heart, while CYP2C37 and CYP2C39 appeared to be liver specific.

Characterization of CYP2C19 and CYP2C9 from human liver: respective roles in microsomal tolbutamide, S-mephenytoin, and omeprazole hydroxylations

Individuals with drug metabolism polymorphisms involving CYP2C enzymes exhibit deficient oxidation of important therapeutic agents, including S-mephenytoin, omeprazole, warfarin, tolbutamide, and nonsteroidal anti-inflammatory drugs. While recombinant CYP2C19 and CYP2C9 proteins expressed in yeast or Escherichia coli have been shown to oxidize these agents, the capacity of the corresponding native P450s isolated from human liver to do so is ill defined. To that end, we purified CYP2C19, CYP2C9, and CYP2C8 from human liver samples using conventional chromatographic techniques and examined their capacity to oxidize S-mephenytoin, omeprazole, and tolbutamide. Upon reconstitution, CYP2C19 metabolized S-mephenytoin and omeprazole at rates that were 11- and 8-fold higher, respectively, than those of intact liver microsomes, whereas neither CYP2C9 nor CYP2C8 displayed appreciable metabolic activity with these substrates. CYP2C19 also proved an efficient catalyst of tolbutamide metabolism, exhibiting a turnover rate similar to CYP2C9 preparations (2.0-6.4 vs 2.4-4.3 nmol hydroxytolbutamide formed/min/nmol P450). The kinetic parameters of CYP2C19-mediated tolbutamide hydroxylation (Km = 650 microM, Vmax = 3.71 min-1) somewhat resembled those of the CYP2C9-catalyzed reaction (Km = 178-407 microM, Vmax = 2.95-7.08 min-1). Polyclonal CYP2C19 antibodies markedly decreased S-mephenytoin 4'-hydroxylation (98% inhibition) and omeprazole 5-hydroxylation (85% inhibition) by human liver microsomes. CYP2C19 antibodies also potently inhibited (>90%) microsomal tolbutamide hydroxylation, which was similar to the inhibition (>85%) observed with antibodies to CYP2C9. Moreover, excellent correlations were found between immunoreactive CYP2C19 content, S-mephenytoin 4'-hydroxylase activity (r = 0.912; P < 0. 001), and omeprazole 5-hydroxylase activity (r = 0.906; P < 0.001) in liver samples from 13-17 different subjects. A significant relationship was likewise observed between microsomal tolbutamide hydroxylation and CYP2C9 content (r = 0.664; P < 0.02) but not with CYP2C19 content (r = 0.393; P = 0.184). Finally, immunoquantitation revealed that in these human liver samples, expression of CYP2C9 (88. 5 +/- 36 nmol/mg) was 5-fold higher than that of CYP2C19 (17.8 +/- 14 nmol/mg) and nearly 8-fold higher than that of CYP2C8 (11.5 +/- 12 nmol/mg). Our results, like those obtained with recombinant CYP2C enzymes, indicate that CYP2C19 is a primary determinant of S-mephenytoin 4'-hydroxylation and low-Km omeprazole 5-hydroxylation in human liver. Despite its tolbutamide hydroxylase activity, the low levels of hepatic CYP2C19 expression (relative to CYP2C9) may preclude an important role for this enzyme in hepatic tolbutamide metabolism and any polymorphisms thereof.

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.

Fluorescence in situ hybridization analysis of chromosomal localization of three human cytochrome P450 2C genes (CYP2C8, 2C9, and 2C10) at 10q24.1

Chromosomal localization of three human cytochrome P450 genes belonging to the CYP2C subfamily (CYP2C8, 2C9, and 2C10) was identified by fluorescence in situ hybridization (FISH). An original MP-8 clone was used as a DNA probe for the assignment of the CYP2C10 gene, while two cDNA probes, a 1.37 kb fragment of CYP2C8 and a 1.19 kb fragment of CYP2C9, were obtained after amplifying the predicted fragments (MP-20 and MP-4 clones, respectively) by polymerase chain reaction using a single human liver cDNA library. The results showed that three human CYP2C8, 2C9, and 2C10 cDNAs were located at the same subchromosomal region, 10q24.1.

Evidence that CYP2C19 is the major (S)-mephenytoin 4'-hydroxylase in humans

The present study assesses the role of members of the human CYP2C subfamily in the 4'-hydroxylation of (S)-mephenytoin. When recombinant CYP2C proteins were expressed using a yeast cDNA expression system, 2C19 stereospecifically 4'-hydroxylated (S)-mephenytoin with a turnover number at least 10 times higher than that of human liver microsomes. 2C9 (both Ile359 and Leu359 alleles) and 2C18 (Thr385 and Met385 alleles) metabolized this substrate at a rate 100-fold lower than 2C19, and metabolism by these 2C proteins was not stereospecific for the S-enantiomer. 2C8 exhibited very little mephenytoin 4'-hydroxylase activity. In contrast, the Ile359 allele of 2C9 had a high turnover number for the hydroxylation of tolbutamide, while the Leu359 allele was less active toward this substrate. Immunoblot analysis of 16 human liver donor samples indicated that (S)-mephenytoin 4'-hydroxylase activity correlated with the hepatic CYP2C19 content, but it did not correlate with the hepatic content of CYP2C9. Moreover, direct sequencing of the polymerase chain reaction (PCR) products of 2C9 mRNA from six of these human livers through areas of known allelic variations indicated that the identity of the allele of 2C9 (Cys144 vs Arg, Tyr358 vs Cys, Ile359 vs Leu, or Gly417 vs Asp) did not appear to influence (S)-mephenytoin 4'-hydroxylase activity in these samples. These data indicate that 2C19 is the principal determinant of (S)-mephenytoin 4'-hydroxylase activity in human liver.

Molecular biology of human xenobiotic-metabolizing cytochromes P450: role of vaccinia virus cDNA expression in evaluating catalytic function

Mammalian xenobiotic-metabolizing cytochromes P450s are membrane-bound enzymes that use O2 and electrons from NADPH to oxidize their substrates. For most chemical substrates, stable metabolites are produced that are destined for further metabolism and elimination from the cell. These enzymes are also capable of metabolically-converting promutagens and procarcinogens to their active proximate metabolites that can kill and transform cells. The xenobiotic-metabolizing P450s reside with three distinct families of the large P450 super-family. To study the catalytic activities of P450s, particularly human P450s that cannot be easily purified, a cDNA expression system was developed using vaccinia virus. P450 cDNAs incorporated into this lytic virus are efficiently expressed into catalytically-active enzymes that can be used to determine substrate specificities of specific human P450s forms. Activation of the hepatocarcinogen aflatoxin B1 was determined using a series of vaccinia virus-expressed P450s establishing that it is metabolically-activated to a DnA-binding derivative by several human P450 forms, albeit to differing extents.

Cytochrome P450 2C9 is responsible for hydroxylation of the naphthoquinone antimalarial drug 58C80 in human liver

2-(4-t-Butylcyclohexyl)-3-hydroxy-1,4-naphthoquinone (58C80) is an experimental naphthoquinone antimalarial drug which undergoes extensive alky hydroxylation in man. By means of purification, N-terminal amino acid sequencing and inhibition by antibodies and sulfaphenazole, we have identified the form of cytochrome P450 primarily responsible for 58C80 hydroxylation in human liver, P450hB20-27, to be a member of the P450 2C9 subfamily. P450hB20-27 is a low-spin haemoprotein with molecular mass 54 kDa. 58C80 hydroxylation in human liver microsomes was dependent on either NADPH or NADH, with the activity supported by NADH being 35% of that supported by NADPH. With purified P450hB20-27 cytochrome b5 stimulated the NADH-dependent activity 8-fold but inhibited the NADPH-dependent activity by 30%. 58C80 is a novel substrate structure for human P450 2C and these results significantly broaden the range of drugs which have been directly shown (i.e. using a purified enzyme as opposed to expressed cDNA) to be metabolized by human P450 2C forms that are incontrovertibly expressed in human liver in vivo.

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.

Molecular cloning of monkey liver cytochrome P-450 cDNAs: similarity of the primary sequences to human cytochromes P-450

Three cDNAs coding for monkey cytochrome P-450 (P450) 2C, 2E and 3A (MKmp13, MKj1 and MKnf2, respectively) were isolated from a lambda gt11 cDNA library of a liver from a 3-methylcholanthrene (3MC)-treated crab-eating monkey, using cDNA fragments for human P450 2C, 2E and 3A as respective probes. MKmp13 and MKnf2 were 1901 and 2032 bp long, containing entire coding regions for polypeptides of 490 and 503 residues, respectively. The deduced N-terminal amino acid sequences of MKmp13 and MKnf2 were identical with those of P450-MK1 and P450-MK2, which had been purified from liver microsomes of untreated and polychlorinated biphenyl (PCB)-treated crab-eating monkeys, respectively. MKj1 was 1508 bp long, encoding a polypeptide of 449 residues, which is presumed to lack N-terminal 45 residues as compared with the sequence for human P450 2E1. Northern blot analysis indicated that monkey P450 2C, 2E and 3A mRNAs were expressed constitutively in monkey livers. P450 2E and 3A mRNAs were induced by both 3MC and PCB, while P450 2C mRNA was induced only by PCB. The deduced amino acid sequences of four monkey cytochrome P-450 cDNAs, including P450 1A1 (MKah1) which we isolated previously, were more than 92% identical with those of corresponding human cytochrome P-450 cDNAs.

Characterization of the cytochrome P-450IID subfamily in bovine liver. Nucleotide sequences and microheterogeneity

To elucidate the molecular mechanisms underlying drug detoxification, the structures of the members of the microsomal cytochrome P-450IID subfamily were analyzed by isolating, mapping and sequencing cytochrome P-450IID (CYP2D) cDNA clones from bovine liver. The screening was performed under nonstringent conditions so that most of the P-450IID subfamily members could be obtained. 114 of the 147 positive clones were classified into four groups on the basis of their restriction-enzyme maps. The maps of the four groups were highly similar, however, the clones of one group contained an insertion of approximately 500 bp in the coding region. Analysis of partial nucleotide sequences of several representative clones from each group showed that the bovine P-450IID subfamily in liver consisted of several, not many, highly similar members, differing by less than 7% in their nucleotide sequences. The location of the insertion found in the minor group corresponded to intron 7 and the GT/AG rule was found at the exon/intron boundary, suggesting that intron 7 was retained in this group. The complete nucleotide sequences of two clones from the major group were examined to determine the structures of the P-450IID subfamily in bovine liver. A full-length cDNA clone (1615 bp) and a partial cDNA clone (1538 bp) contained open reading frames encoding 500 and 487 amino acid residues, respectively. The partial clone lacked the nucleotide sequence corresponding to the first 13 N-terminal amino acid residues. The deduced amino acid sequences of the two clones were 98% similar, and 80% and 68% similar to those from human CYP2D6 and rat CYP2D1, respectively. Comparisons of the amino acid sequences of the P-450IID subfamily members showed the highly conserved C-terminal region of their molecules and the high similarity between the members in one species, especially in cattle and man.

The human hepatic cytochromes P450 involved in drug metabolism

The cytochromes P450 are a superfamily of hemoproteins that catalyze the metabolism of a large number of xenobiotics and endobiotics. The type and amount (i.e., the animal's phenotype) of the P450s expressed by the animal, primarily in the liver, thus determine the metabolic response of the animal to a chemical challenge. A majority of the characterized P450s involved in hepatic drug metabolism have been identified in experimental animals. However, recently at least 12 human drug-metabolizing P450s have been characterized at the molecular and/or enzyme level. The characterization of these P450s has made it possible to "phenotype" microsomal samples with respect to their relative levels of the various P450s and their metabolic capabilities. The purpose of this review is to compare and contrast the human P450s involved in drug metabolism with their related forms in the rat and other experimental species.

Cloning and expression of complementary DNAs for multiple members of the human cytochrome P450IIC subfamily

The present study characterizes the profile of cDNAs from the human P450IIC subfamily in a library from one individual, and it describes three new members of this subfamily (IIC17, IIC18, and IIC19) isolated from two human cDNA libraries. cDNA libraries were constructed from two human livers which differed phenotypically in the hepatic content of P450 HLx (IIC8). The library from the phenotypically low HLx individual was screened by using a cDNA for rat liver P450IIC13 and an oligonucleotide probe for human IIC8. One clone, 245c, was isolated which clearly represents a new member of the human P450IIC subfamily (IIC17). This clone lacked the first 358 nucleotides at the N-terminus but was only 91% homologous in its nucleic acid sequence to IIC9 and 79% homologous to IIC8. Near-full-length clones for IIC9 were also isolated from this library, but no clones for IIC8 were found. Northern blots indicated that the mRNA for IIC8 was low or absent in this individual. A second cDNA library (from a liver phenotypically high in HLx) was then screened. Eighty-three essentially full-length (greater than 1.8 kb) clones belonging to the IIC subfamily were isolated from this library. These include full-length clones for two additional new members of the IIC subfamily. Clones 29c and 6b appear to be allelic variants (IIC18), differing by one nucleotide (one amino acid change) in the coding region. Clone 11a represents a full-length clone for a third new P450 (IIC19).(ABSTRACT TRUNCATED AT 250 WORDS)

DNA-expressed human cytochrome P450s: a new age of molecular toxicology and human risk assessment

It has long been recognized that a large degree of species differences exists among drug and carcinogen metabolizing enzymes. In particular, differences in cytochrome P450s, the principal enzymes of metabolic activation of procarcinogens, are widespread and may determine species and individual susceptibility to cancer causing chemicals. Although species differences in both the regulation and catalytic activities of P450s are quite large, roden-based systems are mainly used as the means to determine the degree of hazard of environmental pollutants, pesticides, drugs and other environmental chemicals to humans. During recent years, a large effort has been expended on analyzing directly the structure, properties and catalytic activities of P450s from human tissues. In vitro mutagen testing systems, based on activation by human P450s, are being developed that will supplement other test systems in order to more accurately predict human risk to chemical exposure.

Aldosterone synthesis in salt-wasting congenital adrenal hyperplasia with complete absence of adrenal 21-hydroxylase

BACKGROUND

Congenital adrenal hyperplasia due to 21-hydroxylase deficiency is a disorder of cortisol and aldosterone biosynthesis that results from mutations in the CYP21 gene encoding the adrenal 21-hydroxylase P-450c21. It can cause severe salt wasting in newborns that requires long-term treatment with glucocorticoids and mineralocorticoids. We describe a spontaneous partial recovery from this disorder in a 19-year-old woman who had discontinued treatment.

METHODS

We measured plasma and urinary levels of adrenal hormones, plasma renin activity, and sodium balance longitudinally in the patient and four other patients in whom adrenal hyperplasia had been diagnosed in infancy and in whom DNA analysis had predicted a complete absence of functional P-450c21. The ratio of plasma renin activity to urinary aldosterone was used as a measure of the response of the adrenal zona glomerulosa. Two patients underwent intravenous infusion of [3H]progesterone for the measurement of extraadrenal production of 21-hydroxylated precursors of aldosterone.

RESULTS

The patient who had discontinued her medication excreted a normal amount of aldosterone (20.0 nmol per square meter of body-surface area per day) while following a diet low in sodium. Her ratio of plasma renin activity to urinary aldosterone-18-glucuronide excretion was 1.7 after three days of sodium restriction, as compared with a ratio of 4.7 at the age of nine years (normal range, 0.03 to 0.1). The percentage of extraadrenal conversion of progesterone to deoxycorticosterone was low. The four other patients had variable responses to sodium restriction after the neonatal period (range for plasma renin activity:urinary aldosterone-18-glucuronide, 1.9 to 19.4).

CONCLUSIONS

Although patients with salt-wasting 21-hydroxylase deficiency have functionally equivalent mutations in their CYP21 genes, they may vary from one another and over time in their ability to produce mineralocorticoids. This variation may be attributable to another adrenal enzyme with 21-hydroxylase activity.

Expression of cytochrome P-450 enzymes in cultured human hepatocytes

Hepatocytes from adult and newborn humans were put into primary culture and exposed to phenobarbital, 3-methylcholanthrene, or rifampicin, three well-known inducers of cytochrome P-450 in animals. The expression of four cytochrome P-450 enzymes (or groups of enzymes, namely P-450 IIIA, P-450 IIC8/9/10, P-450 IIE1, and P-450 IA2) was investigated. These enzymes were found to remain expressed during the period of culture studied. Treatment with the inducers for three days resulted in different responses, depending upon the inducer and the enzyme. Phenobarbital and rifampicin increased P-450 IIC8/9/10 mRNA transcripts and the corresponding protein, while 3-methylcholanthrene was ineffective. Both P-450 IIIA mRNA and protein were strongly induced by rifampicin. All of the hepatocytes were found to synthesize P-450 IIIA in response to rifampicin, as shown by immunoperoxidase staining. P-450 IIIA expression was not affected by phenobarbital and was decreased by 3-methylcholanthrene. P-450s IA2 and IIE1 decreased to 25-50% of the initial level during these cultures. P-450 IA2 and ethoxyresorufin O-deethylase activity (which is a monooxygenase activity related to P-450 IA family) were increased only by 3-methylcholanthrene and did not respond to the other inducers. P-450 IIE1 was not induced by any of these compounds. P-450 IIC8/9/10 and P-450 IIIA mRNA levels were also measured in human hepatocytes from one newborn. P-450 IIC8/9/10 was barely expressed in freshly isolated cells but increased dramatically with time in culture. P-450 IIIA transcripts were abundant in both freshly isolated and cultured cells derived from a newborn. These results clearly demonstrate that human hepatocytes continue to express cytochrome P-450 enzymes and respond to inducers in culture. This model system provides a useful approach for investigating the effects of drugs on maturation and expression of drug-metabolizing enzymes in human liver.

The human CYP2F gene subfamily: identification of a cDNA encoding a new cytochrome P450, cDNA-directed expression, and chromosome mapping

A cDNA coding for a P450, designated IIF1, was isolated from a human lung lambda gt11 library by screening with a human IIC9 cDNA probe. The cDNA-encoded IIF1 protein had 491 amino acids and a calculated molecular weight of 55,507. IIF1 cDNA, expressed by using a vaccinia virus vector, produced a cytochrome with a lambda max of 454 nm when reduced and complexed with carbon monoxide. This enzyme was able to dealkylate ethoxycoumarin, propoxycoumarin, and pentoxyresorufin but possessed no activity toward ethoxyresorufin and only trace dearylation activity toward benzyloxyresorufin. A variant cDNA, designated IIF1v, was isolated that was identical with IIF1 except for the loss of two segments of 161 and 388 bp within the cDNA coding region. Two mRNAs, consistent with the predicted size of the IIF1 and IIF1v transcripts, were found at very low abundance in lung specimens by Northern blot analysis. A 2-kb transcript, hybridizing with the human IIF1, was also detected as an abundant mRNA in rat lung. The CYP2F gene subfamily was localized to human chromosome 19 and mouse chromosome 7. On the basis of Southern blotting analysis with multiple restriction enzymes, we conclude that the CYP2F1 gene is flanked by a second highly similar gene.

Alternative splicing of mRNA encoding rat liver cytochrome P450e (P450IIB2)

Cytochrome P450e (P450IIB2) is a phenobarbital(PB)-inducible member of the rat liver P450IIB subfamily. Among P450 cDNA clones previously isolated from a cDNA library made from the liver of a single rat were several that contained P450e inserts, including PB13, PB16, and PB22. By nucleotide sequence analysis, the PB16 and PB22 inserts have now been found to contain an additional 24-bp segment not present in the PB13 insert or in previously reported P450e-coding sequences. According to the published P450e genomic sequence, the 24-bp segment is exactly at the junction of the fifth and the sixth exons and its sequence is identical to the first 24 bp of the fifth intron. Translation of this segment would add 8 amino acid residues to the P450e protein. To detect the alternatively spliced P450e mRNA, a synthetic oligodeoxyribonucleotide (oligo) corresponding to 18 of the 24 bp of the intronic sequence found in the PB16 and PB22 inserts was made. This oligo hybridized with a 2.1-kb RNA on Northern blots of liver RNA from PB- or Aroclor 1254-treated rats. Taken together, these results indicate that individual rats can possess both forms of P450e mRNA and that an alternative splicing mechanism is responsible for their formation.

The increase in urinary excretion of 6 beta-hydroxycortisol as a marker of human hepatic cytochrome P450IIIA induction

1. Urinary excretion of 6 beta-hydroxycortisol, hepatic microsomal cortisol 6 beta-hydroxylase and the specific content of several forms of cytochrome P450 were measured in 8 to 14 patients before and after treatment with rifampicin (600 mg orally per day for 4 days). 2. Rifampicin treatment produced an average five fold increase in daily excretion of urinary 6 beta-hydroxycortisol. 3. Cortisol 6 beta-hydroxylase activity increased from 15 +/- 6 pmol min-1 mg-1 in organ donors (considered as 'control subjects') to 87 +/- 31 pmol min-1 mg-1 in rifampicin treated patients. 4. Among three forms of human P450 (P450IA, IIC and IIIA), (1), (2), measured by Western blots, only P450IIIA was significantly induced by the antibiotic. 5. Only antibodies against P450IIIA selectively inhibited cortisol 6 beta-hydroxylase in human liver microsomes. 6. Cortisol 6 beta-hydroxylase was correlated with P450IIIA specific content. 7. The urinary level of 6 beta-hydroxycortisol correlated with liver microsomal cortisol 6 beta-hydroxylase and P450IIIA specific content. 8. We conclude that P450IIIA is predominantly responsible for cortisol 6 beta-hydroxylase activity in human liver microsomes and that urinary 6 beta-hydroxycortisol is a marker of the induction of this cytochrome P450.

Comparative aspects of the mammalian cytochrome P450 IV gene family

1. The structures of mammalian cytochrome P-450 isoenzymes have been compared with respect to micro-sequence heterogeneity and their haem-binding cysteinyl peptides. 2. Mechanisms of induction of several P450 gene families are described including transcriptional activation and mRNA stabilization in cytochrome P450 I, II and IV families. 3. The tissue expression and substrate specificity of the cytochrome P450 IV family in liver, kidney and lung have been discussed. 4. The role of hepatic cytochrome P450 IVA1 induction in peroxisome proliferation is presented, and emphasis placed on the identification of susceptible and non-susceptible species.

Isolation of a human cytochrome P-450 reductase cDNA clone and localization of the corresponding gene to chromosome 7q11.2

We have isolated and sequenced cDNA clones that code for rat and human NADPH-dependent cytochrome P-450 reductase. The cDNA coding for the human protein was used to analyse, by Southern blot hybridization, DNA isolated from a panel of 8 independent human-rodent somatic cell hybrids. The results indicate that cytochrome P-450 reductase is encoded by a single gene (POR) located on human chromosome 7(pter-q22). Analysis of human metaphase chromosomes by hybridization in situ confirmed the results and refined the localization to 7q11.2. Northern blot hybridization revealed that in human liver the expression of the gene varies by less than 3-fold between different individuals.

Isolation of a new human fetal liver cytochrome P450 cDNA clone: evidence for expression of a limited number of forms of cytochrome P450 in human fetal livers

From a human fetal liver cDNA library, a new cDNA clone (lambda HFL10) was isolated using an antiserum to P450 HFLa, which has been isolated from livers of human fetuses. Cytochrome P450 cDNAs, namely lambda hPA6, lamda hP2-1, and lambda hPD4 which were highly homologous to cDNA clones, pHY13, Hp1-1, and phP450j, respectively, were also isolated from the cDNA library of human adult livers. Using these cDNA clones as probes together with Lambda HFL10, Northern blot analysis was conducted to determine whether all of these cytochromes were expressed in human fetal livers. The results clearly showed that only P450 HFL10 mRNA was detected in human fetal livers. This result supports the allegation that there is a much more limited number of forms of cytochrome P450 in human fetal livers than in adult livers.

Metabolism of retinol and retinoic acid by human liver cytochrome P450IIC8

Liver microsomes obtained from nine subjects were found to metabolize retinol to polar metabolites, including 4-hydroxyretinol. In a reconstituted monooxygenase system containing human liver P450IIC8, retinol was converted to 4-hydroxyretinol and other polar metabolites, with a Km of 0.071 mM and a Vmax of 1.73 nmol/min/nmol P450. Neither P450IIC9 nor P450IIE1, two other purified human P450s, displayed significant retinol hydroxylase activity. Immunoblots performed with a monospecific antibody directed against human P450IIC8 revealed that appreciable amounts of this enzyme were present in human liver microsomes. The same antibody significantly inhibited retinol metabolism in liver microsomes and in the system reconstituted with P450IIC8. The system reconstituted with P450IIC8 also converted retinoic acid to polar metabolites. Thus, this study shows, for the first time, metabolism of two physiologic substrates by a human liver cytochrome P450 related to a group of "constitutive" rodent P450s believed to participate in the metabolism of endogenous compounds. Through its involvement in vitamin A metabolism, P450IIC8 may participate in maintaining the balance between those vitamin A concentrations that promote cellular integrity (and oppose the development of cancer) and those concentrations that cause cellular toxicity.

Cloning, expression and chromosomal localization of a member of the human cytochrome P450IIC gene sub-family

We have isolated and sequenced a cDNA clone (pB8) that codes for a novel member of the cytochrome P450IIC sub-family of man. Analysis, by Southern blot hybridization, of DNA isolated from a panel of nine independent human-rodent somatic cell hybrids demonstrated that the corresponding gene (CYP2C) is located on human chromosome 10. Northern blot hybridization of RNA isolated from human livers revealed a 10-fold inter-individual variation in the expression of the gene.

The P450 superfamily: updated listing of all genes and recommended nomenclature for the chromosomal loci

In this update we provide a list of the 71 P450 genes and the four P450 pseudogenes that have been characterized as of September 30, 1988. The chromosomal locations of many of these genes are also summarized. A modest revision of the initially proposed nomenclature of the P450 superfamily (Nebert et al., DNA 6, 1-11, 1987) is described specifically for the human and mouse chromosomal loci. The motivation for this revision is to conform to the rules of nomenclature for human and mouse genes. Recommendations for the naming of chromosomal loci include the root symbol "CYP" for human ("Cyp" for mouse), denoting "cytochrome P450." We recommend that this root also be used for other organisms. For a chromosomal locus, the root symbol is followed by an Arabic numeral designating the P450 family, a letter indicating the subfamily, and an Arabic numeral representing the individual gene within the family or subfamily. Numbers of the individual genes usually will be assigned in the order the genes are identified. This system is consistent with our earlier proposed nomenclature for P450 families and gene products from all eukaryotes and prokaryotes.