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R H Tukey

Publications and source records attributed to R H Tukey.

At least 37 records · Page 2Linked to original sources
PubMed1997

Characterization of rabbit UDP-glucuronosyltransferase UGT1A7: tertiary amine glucuronidation is catalyzed by UGT1A7 and UGT1A4.

A rabbit liver UDP-glucuronosyltransferase cDNA that is related to human and rat UGT1A7 has been identified. The predicted amino acid sequence of the UGT1A71 displays 80% similarity to that encoded by human HP4 (UGT1A9), but 81% to that predicted for human UGT1A7 and 77% to the rat UGT1A7 (UGTA2). The exons encoding human UGT1A7 and rat UGTA2 are the seventh of the series of cassette exons that flank the 3' common exon series of the UGT1A locus. Southern blot analysis demonstrates that the exon sequence encoding UGT1A71 is part of a larger cluster of highly related genes. The UGT1A71 RNA is expressed in both neonatal and adult liver, and unlike rat UGT1A2 which is inducible with Ah receptor ligands such as polycyclic aromatic hydrocarbons, rabbit UGT1A7 is not regulated when animals are exposed to these inducers. Following expression of UGT171 in COS-1 cells, glucuronidation activity was identified for small phenolic molecules like 4-nitrophenyl, bulky phenols as represented by 4-hydroxybiphenol and octylgallate, as well as 4-hydroxyestrone. In addition, UGT1A71 possesses catalytic activity toward tertiary amines like the tricyclic antidepressant imipramine. The pattern of UGT1A71 glucuronidation is similar to that observed for human UGT1A9, except tertiary amines are not subject to glucuronidation by human UGT1A9. Glucuronidation of tertiary amines is catalyzed principally by human UGT1A4 as well as rabbit UGT1A4. Although rabbit UGT1A7 catalyzes the formation of quarternary ammonium glucuronides, the Vmax is considerably less than that observed for rabbit UGT1A4. Overall, the characterization of rabbit UGT1A7 suggests that this protein represents the ortholog of the human UGT1A7, which to date has not been identified.

Amines↗
PubMed1997

Characterization of rabbit UDP-glucuronosyltransferase UGT1A7: tertiary amine glucuronidation is catalyzed by UGT1A7 and UGT1A4.

A rabbit liver UDP-glucuronosyltransferase cDNA that is related to human and rat UGT1A7 has been identified. The predicted amino acid sequence of the UGT1A7l displays 80% similarity to that encoded by human HP4 (UGT1A9), but 81% to that predicted for human UGT1A7 and 77% to the rat UGT1A7 (UGTA2). The exons encoding human UGT1A7 and rat UGTA2 are the seventh of the series of cassette exons that flank the 3' common exon series of the UGT1A locus. Southern blot analysis demonstrates that the exon sequence encoding UGT1A7l is part of a larger cluster of highly related genes. The UGT1A7l RNA is expressed in both neonatal and adult liver, and unlike rat UGT1A2 which is inducible with Ah receptor ligands such as polycyclic aromatic hydrocarbons, rabbit UGT1A7l is not regulated when animals are exposed to these inducers. Following expression of UGT1A7l in COS-1 cells, glucuronidation activity was identified for small phenolic molecules like 4-nitrophenol, bulky phenols as represented by 4-hydroxybiphenol and octylgallate, as well as 4-hydroxyestrone. In addition, UGT1A7l possesses catalytic activity toward tertiary amines like the tricyclic antidepressant imipramine. The pattern of UGT1A7l glucuronidation is similar to that observed for human UGT1A9, except tertiary amines are not subject to glucuronidation by human UGT1A9. Glucuronidation of tertiary amines is catalyzed principally by human UGT1A4 as well as rabbit UGT1A4. Although rabbit UGT1A7l catalyzes the formation of quarternary ammonium glucuronides, the Vmax is considerably less than that observed for rabbit UGT1A4. Overall, the characterization of rabbit UGT1A7l suggests that this protein represents the ortholog of the human UGT1A7, which to date has not been identified.

Amines↗
PubMed1997

Differential down-regulation of the UDP-glucuronosyltransferase 1A locus is an early event in human liver and biliary cancer.

One of the most important processes controlling cellular detoxification is carried out in the endoplasmic reticulum by glucuronidation, and most likely plays an important role in the defense mechanism against chemical-induced carcinogenesis. The human UDP-glucuronosyltransferase UGT1A locus encodes up to 12 unique transferases that are transcribed through selective exon sharing. Little is known about how this locus is regulated in human tissues. We present evidence that the UGT1A gene products are differentially expressed in normal liver tissue, which is composed of hepatocellular and biliary tissue, as well as in malignant and premalignant tumor tissue. In liver, UGT1A1, UGT1A3, UGT1A4, and UGT1A9 are expressed, and are all significantly down-regulated in malignant hepatocellular carcinoma and its premalignant precursor, hepatic adenoma, but not in benign focal nodular hyperplasia. UGT1A6, which is expressed abundantly in liver, is not significantly regulated in liver tumors. UGT1A10, a newly discovered UGT1A gene product, is expressed only in biliary and not hepatocellular tissue and is also significantly down-regulated in cholangiocellular carcinoma. Differential regulation between normal biliary tissue and tumor is also observed with UGT1A4. These findings implicate the regulation of the UGT1A locus as a putative early event in hepatocarcinogenesis that discriminates between benign and malignant hepatotumorigenesis and indicates that a complex mode of cellular control underlies the regulation of this locus.

Base Sequence↗
PubMed1997

Expression and functional domains of rabbit liver UDP-glucuronosyltransferase 2B16 and 2B13.

Southern blot analysis has demonstrated that the 5' portion of the rabbit liver dexamethasone-inducible UDP-glucuronosyltransferase (UGT) 2B13 RNA is related in sequence to a family of UGT genes (Tukey, R. H., Pendurthi, U. R., Nguyen, N. T., Green, M. D., and Tephly, T. R. (1993) J. Biol. Chem. 268, 15260-15266). To identify these additional gene transcripts, rabbit liver cDNA libraries were screened with a 5' conserved 330-base pair UGT2B13 cDNA fragment, resulting in the isolation and characterization of several rabbit liver UGT cDNAs. One such clone, called pGT11, encodes a putative glycoprotein that is 78% similar to rabbit UGT2B13. The new UGT has been designated UGT2B16. The UGT2B16 gene is expressed as a single 4200-base RNA transcript that is regulated only in adult rabbits. The predicted NH2-terminal 25 amino acids of UGT2B16 are identical to that of rabbit liver UGT2B13, with the remainder of the protein being 77% similar to UGT2B13. Expressed UGT2B16 protein in COS-1 cells was active toward 4-hydroxybiphenyl, similar to that of UGT2B13. However, UGT2B16 efficiently conjugated 4-hydroxyestrone and 4-tert-butylphenol, substrates that are not efficiently catalyzed by UGT2B13. To further characterize the structural domains of UGT2B16 and UGT2B13, a series of chimeric cDNAs were constructed that contained portions of both UGT2B16 and UGT2B13. Chimeric 2B163002B13531, which contained the amino-terminal UGT2B16 amino acids 1-300 followed by amino acids 301-531 of UGT2B13, as well as chimeric 2B163582B13531 and 2B164342B13531 proteins, catalyzed the glucuronidation of 4-hydroxyestrone, indicating that the carboxyl terminus of UGT2B13 could substitute for those same regions on UGT2B16. However, the replacement of the carboxyl end of UGT2B13 with 2B16300-531 or 2B16434-531 dramatically impaired the catalytic function of the chimeric proteins. These results indicate that the carboxyl end of UGT2B13 plays an important role in the functional and possible conformational state of the protein.

Amino Acid Sequence↗
PubMed1997

Metabolism of carcinogenic heterocyclic and aromatic amines by recombinant human cytochrome P450 enzymes.

The N-hydroxylation of carcinogenic arylamines represents an initial step in their metabolic activation. Animal studies have shown that this reaction is catalyzed by the cytochrome P450 (P450) enzymes P450 1A1 and P450 1A2. In this study, utilizing enzymes expressed in Escherichia coli (and purified) or in human B-lymphoblastoid cells, the catalytic activities of recombinant human P450 1A1, P450 1A2, and P450 3A4 for N-hydroxylation of several carcinogenic arylamines were determined. P450 1A2 from both expression systems catalyzed the N-hydroxylation of 4-aminobiphenyl and the heterocyclic amines, 2-amino-3-methylimidazo[4,5-f/quinoline (IQ), 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx), and 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP). Rates were similar, with values of 1.1-7.8 nmol/min/nmol P450. In contrast, P450 1A1 catalyzed N-hydroxylation of only PhIP, and no activity was observed with P450 3A4. Further kinetic analysis with purified P450 1A2 showed similar Km and Vmax values for N-hydroxylation of the arylamines. Furafylline and fluvoxamine, inhibitors of P450 1A2 activity in human liver microsomes, were found to be inhibitory of the recombinant P450 1A2 N-hydroxylation activity. Results from this study are supportive of a major role for human P450 1A2 in the metabolic activation of arylamines.

Amines↗
PubMed1997

Differential expression of the UGT1A locus in human liver, biliary, and gastric tissue: identification of UGT1A7 and UGT1A10 transcripts in extrahepatic tissue.

Family 1 UDP-glucuronosyltransferases (UGTs) (UGT1A) are encoded by a locus that predicts the existence of at least nine individual proteins. The different proteins are generated by exon-sharing, which results in the production of a family of proteins that contain identical, 245-amino acid, carboxyl-terminal domains and an amino-terminal region of approximately 280 amino acids. The diversity of the UGT1A locus suggests the existence of complex regulation, most likely designed to account for the variable and specific glucuronidation requirements. However, the tissue-specific and extrahepatic regulation of the complete UGT1A locus has not been defined to date. In this study, quantitative duplex reverse transcription-polymerase chain reaction was used to analyze UGT1A RNA expression in 16 hepatic, four biliary, and two gastric human tissue specimens. UGT1A3 and UGT1A6 were found to be expressed in the three tissues, whereas UGT1A5 and UGT1A8 were not expressed. Hepatocellular and biliary tissue expressed UGT1A1 and UGT1A4 but hepatocellular tissue uniquely expressed UGT1A9, whereas biliary tissue expressed UGT1A10. In contrast to hepatocellular tissue, gastric tissue expressed UGT1A7 in addition to UGT1A10. The expression of UGT1A9 in hepatic tissue, UGT1A7 in gastric tissue, and UGT1A10 in biliary and gastric tissue provides evidence for the selective regulation of the UGT1A locus in hepatic and extrahepatic tissues. The newly identified UGT1A7 and UGT1A10 transcripts were cloned and found to be 95.86% identical. Sequence analysis confirmed two proteins with divergent amino termini of 285 residues and identical carboxyl termini of 245 residues. This study provides evidence for hepatic and extrahepatic regulation of the human UGT1A locus and identifies two novel extrahepatic transcripts of the UGT1A family.

Alternative Splicing↗
PubMed1997

Cytochrome P450 1A2 is a hepatic autoantigen in autoimmune polyglandular syndrome type 1.

Autoantibodies directed against proteins of the adrenal cortex and the liver were studied in 88 subjects of Sardinian descent, namely six patients with autoimmune polyendocrine syndrome type 1 (APS1), 22 relatives of APS1 patients, 40 controls with other autoimmune diseases, and 20 healthy controls. Indirect immunofluorescence, using tissue sections of the adrenal cortex, revealed a cytoplasmatic staining pattern in 4 of 6 patients with APS1. Western blotting with adrenal mitochondria identified autoantigens of 54 kDa and 57 kDa, Western blotting with placental mitochondria revealed a 54-kDa autoantigen. The 54-kDa protein was recognized by 4 of 6 patients with APS1 both in placental and adrenal tissue, whereas the 57-kDa protein was detected only by one serum. Using recombinant preparations of cytochrome P450 proteins, the autoantigens were identified as P450 scc and P450 c17. One of six APS1 patients suffered from chronic hepatitis. In this patient, immunofluorescence revealed a centrolobular liver and a proximal renal tubule staining pattern. Western blots using microsomal preparations of human liver revealed a protein band of 52 kDa. The autoantigen was identified as cytochrome P450 1A2 by use of recombinant protein preparations. P450 1A2 represents the first hepatic autoantigen reported in APS1. P450 1A2 usually is not detected by sera of patients with isolated autoimmune liver disease and might be a hepatic marker autoantigen for patients with APS1.

Adolescent↗
PubMed1997

Identification of rat and human cytochrome P450 forms involved in the metabolism of the thromboxane A2 receptor antagonist (+)-S-145.

(+)-S-145 [5-(+)-(Z)-7-[(1R, 2S, 3S, 4S)-3-phenylsulfonylaminobicyclo[2.2.1]hept-2-yl]-heptenoic acid] and its beta-oxidized metabolites [two [bisnor or dihydro (DH)-bisnor] or four (tetranor) carbon-shortened products at the carboxyl side chain] are hydroxylated at the C-5 or C-6 position of the bicyclo ring by microsomal monooxygenases. We investigated the oxidative metabolism of (+)-S-145 and its beta-oxidized metabolites with liver microsomes from rats and humans to identify which cytochrome P450 (P450) forms are involved in these reactions. In rats, phenobarbital or dexamethasone treatment significantly increased 5- and 6-hydroxylation activities toward (+)-S-145 and its beta-oxidized metabolites, suggesting the involvement of P4503A forms. Immunoinhibition studies suggested that P4503A2 was mainly responsible for the 5-hydroxylation of (+)-S-145, bisnor, and DH-bisnor and the 6-hydroxylation of bisnor and tetranor. Furthermore, P4502C6, a phenobarbital-inducible 2C form in the rat, was involved in the 6-hydroxylation of (+)-S-145, bisnor, and DH-bisnor. P4502C11, the major constitutive form (male rats), was partly involved in the 5-hydroxylation of DH-bisnor and the 6-hydroxylation of bisnor and DH-bisnor. Reconstitution studies with purified human enzymes and immunoinhibition studies suggest that P4503A4 is primarily involved in the 5-hydroxylation of (+)-S-145 and bisnor and the 6-hydroxylation of tetranor; P4502C9/10 mainly catalyzed the 5-hydroxylation of tetranor and the 6-hydroxylation of (+)-S-145. Results of the present study indicated that the same subfamily P450 forms are responsible for the oxidative metabolism of (+)-S-145 in rats and humans. P4503A enzymes were shown to be involved in the formation of 6-hydroxy tetranor, the main metabolite of S-1452 in vivo.

Animals↗
PubMed1997

Baculovirus-directed expression of rabbit UDP-glucuronosyltransferases in Spodoptera frugiperda cells.

The rabbit liver UDP-glucuronosyltransferase (UGT) cDNAs that encode the 4-hydroxybiphenyl UGT2B13 and 4-nitrophenol UGT1A6 have been cloned into baculovirus. Spodoptera frugiperda (SF-9) cells infected with the UGT recombinant baculovirus produced significant amounts of protein, which was detected by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, immunoblot analysis, and pulse chase with 35S-amino acids. The expression of the UGT proteins in SF-9 cells were detected at approximately 24 hr postinfection, with maximal levels of protein seen at 48 hr. Immunoprecipitation of newly synthesized 35S-labeled proteins demonstrated that the maximal rate of protein synthesis in SF-9 cells infected with the UGT baculovirus occur at 48 hr postinfection, although the proteins are abundant in the cells for up to 96 hr. When compared with the expression levels of the same cDNAs through transient transfection into COS-1 cells, the insect-derived UGT proteins showed nearly 50- to 100-fold greater protein accumulation. Although kinetic analysis demonstrated that turnover rate of the SF-9-expressed proteins were greater than their counterparts in COS-1 cells, K(M) values for UGT1A6 and UGT2B13 in SF-9 and COS-1 cells were similar. Overall, SF-9 cells seem to serve as an efficient expression system for the production of the mammalian UGTs.

Animals↗
PubMed1997

Heterologous expression of human drug-metabolizing enzymes.

This article is a report on a symposium held at the March 1997 meeting of the American Society for Pharmacology and Experimental Therapeutics in San Diego. Current developments in the heterologous expression of cytochrome P450, NADPH-cytochrome P450 reductase, glutathione transferase, and UDP-glucuronosyltransferase enzymes are described. Systems include bacteria, insect cells, and transient and stable mammalian cells. Uses of the products are described for discernment of which enzymes are involved in metabolism of drugs, genotoxicity assays, mutagenesis (for structure-activity relationships), large scale production of enzyme products, antibody production, and production of proteins for biophysical studies.

Enzymes↗
PubMed1996

Protein kinase C modulates regulation of the CYP1A1 gene by the aryl hydrocarbon receptor.

Transcriptional activation of the human CYP1A1 gene by halogenated and polycyclic aromatic hydrocarbons is mediated by the aryl hydrocarbon receptor (AhR) complex, a ligand-dependent transcription factor. A competent AhR comprises at least two components following nuclear translocation and DNA binding, the AhR and the AhR nuclear translocator (Arnt) protein, whose combined action on human CYP1A1 gene transcription is shown to be dependent upon functional protein kinase C (PKC). In the present study, we examined the effects of phorbol 12-myristate 13-acetate, a potent PKC activator, on the ligand-induced transcriptional activation of the CYP1A1 gene and cellular function of the AhR in human HepG2 101L cells. The 101L cells carry a stable transgene consisting of 1800 bases of 5'-flanking DNA and the promoter of the human CYP1A1 gene linked to the firefly luciferase structural gene (Postlind, H., Vu, T. P., Tukey, R. H. & Quattrochi, L. C. (1993) Toxicol. Appl. Pharmacol. 118, 255-262). Pretreatment of cells with 12-myristate 13-acetate enhanced ligand-induced CYP1A1 gene expression 2-3-fold. Inhibition of PKC activity blocked directly the transcriptional activation and the transactivation of the CYP1A1 gene, indicating a role for PKC in the AhR-mediated transcriptional activation process. However, the DNA binding activities of the in vitro activated and the induced nuclear AhR as measured by electrophoretic mobility shift analysis were not affected when CYP1A1 transcription was inhibited, indicating the actions of PKC to be a nuclear event that works in concert with or precedes AhR binding to the gene. These results illustrate that PKC is absolutely essential for the cellular and molecular events that control induction of CYP1A1 gene transcription.

Carcinogens↗
PubMed1996

Cytochromes P450, 1A2, and 2C9 are responsible for the human hepatic O-demethylation of R- and S-naproxen.

A preliminary report implicated cytochrome P450 (CYP) 2C9 in the human liver microsomal O-demethylation of S-naproxen, suggesting that this pathway may be suitable for investigation of human hepatic CYP2C9 in vitro. Kinetic and inhibitor studies with human liver microsomes and confirmatory investigations with cDNA-expressed enzymes were undertaken here to define the role of CYP2C9 and other isoforms in the O-demethylation of R- and S-naproxen. All studies utilised a newly developed sensitive and specific HPLC assay that measured the respective O-desmethyl metabolites of R- and S-naproxen in incubations of human liver microsomes and in COS cell lysates. Microsomal R- and S-naproxen O-demethylation kinetics followed Michaelis-Menten kinetics, with respective mean apparent Km values of 123 microM and 143 microM. Sulfaphenazole, a specific inhibitor of CYP2C9, reduced the microsomal O-demethylation of R- and S-naproxen by 43% and 47%, respectively, and the CYP1A2 inhibitor furafylline decreased R- and S-naproxen O-demethylation by 38% and 28%, respectively. R,S-Mephenytoin was a weak inhibitor of R- and S-naproxen O-demethylation, but other CYP isoform specific inhibitors (e.g., coumarin, diethyldithiocarbamate, quinidine, troleandomycin) had little or no effect on these reactions. cDNA-expressed CYP2C9 and CYP1A2 were both shown to O-demethylate R- and S-naproxen. Apparent Km values (92-156 microM) for the reactions catalysed by the recombinant enzymes were similar to those observed for human liver microsomal R- and S-naproxen O-demethylation. The data demonstrate that CYP2C9 and CYP1A2 together account for the majority of human liver R- and S-naproxen O-demethylation, precluding the use of either R- or S-naproxen as a CYP isoform-specific substrate in vitro and in vivo.

Aryl Hydrocarbon Hydroxylases↗
PubMed1996

Autoantibodies against glucuronosyltransferases differ between viral hepatitis and autoimmune hepatitis.

BACKGROUND & AIMS: Approximately 13% of patients with chronic hepatitis D virus (HDV) infection have liver-kidney microsomal antibodies type 3 (LKM-3) directed against family 1 uridine 5'-diphosphate-glucuronosyl-transferases (UGT-1). The aim of this study was to characterize the prevalence and specificity of LKM-3 by recombinant antigen testing systems. METHODS: Enzyme-linked immunosorbent assay (ELISA) and Western blot were performed using baculovirus-generated human UGT-1.1 and -1.6 and rabbit UGT-1.6. Sera from patients with HDV (n = 50), autoimmune hepatitis (AIH) type 2 (n = 50), hepatitis B virus (n = 26), hepatitis C virus (HCV) (n = 25), and LKM-1 autoantibody-positive HCV (n = 14) and sera from normal controls (n = 50) and italian patients with HDV and known LKM-3 autoantibodies were studied. RESULTS: Six percent of patients with HDV from Germany and 8% of patients with type 2 AIH had LKM-3. Sera from italian patients with HDV and patients with AIH type 2 recognized all three recombinant UGT-1. HDV sera from Germany selectively recognized human UGT-1. LKM-3 titers were lower in HDV than in AIH. One patient with AIH had LKM-3 as the only marker of AIH. CONCLUSIONS: This study indicates a molecular target and titer difference of LKM-3 autoantibodies in German subjects with HDV and AIH. It also suggests a geographic target and titer difference of LKM-3 in HDV. LKM-3 are identified as a rare and previously undescribed independent marker of AIH.

Adult↗
PubMed1996

Human cytochrome P450 isoform specificity in the regioselective metabolism of toluene and o-, m- and p-xylene.

The conversion of toluene and o-, m- and p-xylene to their respective side-chain and ring monohydroxylated metabolites by human liver microsomes was investigated. Methyl hydroxylation, to form a benzylalcohol, was the major metabolic pathway for all four methylbenzenes. With the exception of 2,4-dimethylphenol formation from m-xylene, ring hydroxylation accounted for < 5% of total metabolite formation. However, regioselectivity of ring hydroxylation was apparent, with hydroxylation occurring only at positions ortho and/or para to a methyl substituent. Toluene and each xylene isomer exhibited biphasic methylhydroxylation kinetics in human liver microsomes. The high-affinity component of each methylhydroxylation was selectively inhibited by diethyldithiocarbamate and correlated significantly with cytochrome P-4502E1 (CYP2E1) content and activities in a panel of human liver microsomes. cDNA-expressed CYP2E1 was shown to catalyze the formation of each benzylalcohol, with apparent Km values similar to those of the high affinity microsomal reactions. In contrast, the conversion of m-xylene to 2,4-dimethylphenol followed single enzyme Michaelis-Menten kinetics, was inhibited selectively by furafylline, and correlated significantly with known CYP1A2 catalyzed reactions. cDNA-expressed CYP1A2 converted m-xylene to 2,4-dimethylphenol, with an apparent Km similar to that of the microsomal reaction. Although CYP1A2 appears to be responsible for the formation of the minor (phenolic) metabolites of toluene and the xylene isomers, CYP2E1 catalyzed methylhydroxylation will be the major determinant of the clearance of these compounds in humans.

Cytochrome P-450 Enzyme System↗
PubMed1996

Trans-species gene transfer for analysis of glucocorticoid-inducible transcriptional activation of transiently expressed human CYP3A4 and rabbit CYP3A6 in primary cultures of adult rat and rabbit hepatocytes.

Interindividual variation in the spontaneous and in the glucocorticoid-or rifampicin-inducible expression of the CYP3A cytochromes P450, the dominant froms of this supergene family that catalyze the oxidation of numerous drugs and environmental chemicals in human liver, remains largely unexplained, due in part to the lack of a validated animal model. We analyzed the 5'-flanking sequences of CYP3A genes from the rat (CYP3A23, CYP3A2), rabbit (CYP3A6), and human (CYP3A4, CYP3A5, CYP3A7) and found variable regions separated by three areas (consensus I, II, and III) of sequence homology immediately upstream of their respective promoters. We used trans-species gene transfer in cellulo as a new approach for determining the basis for qualitative differences among species in liver expression of different forms of CYP3A. When we transfected into cultured rat hepatocytes vectors containing 5'-flanking DNA from CYP3A23, CYP3A4, or CYP3A6 genes, we found that CAT activity was induced on treatment with dexamethasone or pregnenolone-16 alpha-carbonitrile only if consensus II sequences were included. Rifampicin treatment had no effect. When the same constructions containing consensus II were transfected into rabbit hepatocytes, increased activity was observed on treatment of the cells with dexamethasone or with rifampicin but not with pregnenolone-16 alpha-carbonitrile. These results suggest that the host cellular environment rather than the structure of the gene dictates the pattern of CYP3A inducibility. The application of this new model system will provide a unique technique for identifying mechanisms of induction and advancing the development of appropriate toxicological models for human safety assessment.

Animals↗
PubMed1995

Metabolism of polycyclic aza-aromatic carcinogens catalyzed by four expressed human cytochromes P450.

The role of human cytochromes P4501A1, -1A2, -3A4, and -3A5 in the metabolism of the polycyclic aza-aromatic hydrocarbons 7-methylbenz(c)acridine and dibenz(aj)acridine was investigated. The regioselectivity of the reactions was determined, as well as the associated stereoselectivity in the production of dihydrodiol metabolites and K-region oxides. Metabolite distributions were also examined in the presence of the epoxide hydrolase inhibitor 1,1,1-trichloropropylene-2,3-oxide and the P450 modulator alpha-naphthoflavone. P4501A2 was most regioselective for the production of the proximate carcinogen; the 3,4-dihydrodiol of 7-methylbenz(c)acridine and P4503A4 showed the highest regioselectivity for K-region oxidation. In contrast, the analogous putative proximate carcinogen of dibenz(aj)acridine was formed with the highest relative abundance by P4503A4, while P4501A2 was most regioselective for K-region oxidation. For both compounds the proximate carcinogens possessed predominantly the 3R,4R-absolute configuration, independent of the P450 catalyzing the reaction. The K-region dihydrodiols of 7-methylbenz(c)acridine were formed with no stereoselectivity, except with P4501A2 which favored production of the S,S isomer. In contrast the K-region dihydrodiol of dibenz(aj)acridine was formed by P4501A1 and P4501A2 as the R,R isomer with almost 100% optical purity. P4501A2 and 3A4 showed no stereoselectivity in the formation of the K-region oxide of 7-methylbenz(c)acridine, while P4501A1 produced the 5R,6S-oxide with low optical purity. For dibenz(aj)acridine 5,6-oxide, P4501A1 predominantly formed 5S,6R-oxide (80% pure). These results emphasize the importance of the composition and levels of expressed P450s of an individual in relation to the activation and detoxification of toxicants.

Acridines↗
PubMed1995

Molecular analysis of autoantigens in hepatitis D.

In contrast to hepatitis B virus infection, autoimmunity is common in chronic hepatitis D. In 1983, microsomal autoantibodies were described that differ from the previously described liver-kidney microsomal (LKM)-1 and LKM-2 antibodies. Therefore, these were named LKM-3. In addition, autoantibodies against basal layer cells of rat forestomach (basal cell layer antibodies (BCLA)) and thymic stellate epithelial cells (stellate epithelial cell antibodies (SECA)), as well as thymic reticular (thymic reticular antibodies) and perithymocytic cells (perithymocytic cell antibodies), were reported to be specifically associated with hepatitis D. Antinuclear antibodies against nuclear membrane lamin C were also found to be specifically associated with chronic hepatitis D. A molecular identification of the nonnuclear antigens has not been achieved apart from the observation that BCLA and SECA both recognize an antigen of 46 kDa and that these antibodies are immunologically cross-reactive. After the identification of cytochrome P450 2D6 as the major LKM-1 antigen and cytochrome P450 2C9 as the LKM-2 antigen, family 1 uridine diphosphate-glucuronosyltransferases have been identified as the molecules expressing the major LKM-3 autoepitope. Future studies will have to assess the possible pathogenetic and diagnostic relevance of these autoantibodies. However, chronic hepatitis D seems to be a good clinical model for the study of virus-induced autoimmunity in man.

Animals↗