Inhibitory anti-CYP3A4 peptide antibody: mapping of inhibitory epitope and specificity toward other CYP3A isoforms

An antipeptide antibody has been produced that recognizes CYP3A4 and exhibits greater than 90-95% inhibition on CYP3A4-mediated reactions [Wang RW and Lu AYH (1997) Drug Metab Dispos 25:762-767]. The inhibitory epitope of the 21-amino acid peptide, corresponding to residues 253 to 273 of CYP3A4, has been identified to reside in a 7-amino acid sequence (LEDTQKH: residues 261-267 of CYP3A4). This conclusion was based on the reversal of antibody inhibition of testosterone 6beta-hydroxylation when peptides with overlapping sequence in this region were preincubated with the antibody. In immunoblotting analysis, this antibody did not recognize CYP3A5 or CYP3A7 in microsomes prepared from baculovirus-infected cells containing these two expressed isoforms. In addition, the antipeptide antibody did not inhibit testosterone 6beta-hydroxylation or midazolam 1'- and 4-hydroxylation in microsomes containing expressed CYP3A5 and CYP3A7. Because the corresponding sequence in CYP3A5 (LNDKQKH) and CYP3A7 (LKETQKH) differs from CYP3A4 by only two amino acids, six peptides with either one or two amino acid changes were used to determine which amino acid is essential for antibody-antigen interaction. Our data indicate that Glu, Asp, and Thr in the 7-amino acid sequence of CYP3A4 are critical determinants of selectivity among CYP3A isoforms.

Autoantibodies against cytochromes P-4502E1 and P-4503A in alcoholics

Autoantibodies against soluble liver enzymes have been reported among alcoholics, but the targets of self-reactivity toward membrane proteins of the liver have not been characterized. Previously, among alcoholics, we found antibodies against ethanol-derived radical protein adducts that are dependent on cytochrome P-4502E1 (CYP2E1) for their formation. To further investigate autoantibodies against cytochrome P-450s during alcohol abuse, sera of rats chronically treated with ethanol in the total enteral nutrition model and sera from alcoholics with or without alcohol liver disease and from control subjects were analyzed by enzyme-linked immunosorbent assay and Western blotting for the presence of IgG against rat and human CYP2E1, rat CYP3A1, and human CYP3A4. A time-dependent appearance of IgG against rat CYP3A1 and CYP2E1 was evident during chronic ethanol feeding of rats. Anti-CYP2E1 reactivity showed positive correlation with the levels of hepatic CYP2E1 and was inhibited by the CYP2E1 transcriptional inhibitor chlormethiazole. Screening of the human sera by enzyme-linked immunosorbent assay revealed reactivity against CYP3A4 and CYP2E1 in about 20 to 30% and 10 to 20% of the alcoholic sera, respectively. No difference were noted between sera from alcoholics with or without hepatitis C virus infection, and only very little reactivity was seen in sera from control subjects. Western blotting analysis revealed anti-human CYP2E1 reactivity in 8 of 85 alcoholic sera and 3 of 58 control sera, whereas anti-CYP3A4 reactivity was detected in 18 of 85 alcoholic sera and 4 of 58 control sera, which were different from the sera reactive with CYP2E1. Immunoblot reactivity of CYP3A4-positive alcoholic sera was found against glutathione-S-transferase fusion proteins containing truncated forms of CYP3A4, and such sera were also able to immunoprecipitate in vitro translated CYP3A4. Seven of eight sera showed reactivity toward domains C-terminal of position Ser281, and 1 of 8 sera recognized autoepitopes within the region Thr207-Ser281. These findings indicate that alcoholics develop autoantibodies against CYP2E1 and CYP3A4 that the CYP3A4 C-terminal domain is a target for the autoantibody reactions among a subset of alcoholics. The novel finding of CYP3A4 autoantibodies and their significant expression among alcoholics warrants further investigation. Attention should be given to immune toxicity associated with CYP3A4 autoantibodies and cases of alcohol abuse that are accompanied by exposure to drugs and substances that are CYP3A substrates.

Epitope mapping of monoclonal antibodies against 4-aminobenzoate hydroxylase from Agaricus bisporus

Four monoclonal antibodies (mAbs) against 4-aminobenzoate hydroxylase (EC 1.14.13.27) have been produced (H. Tsuji et al., J. Biol. Chem. 265 (1990) 16064; T. Ogawa et al., Biochim. Biophys. Acta 1115 (1992) 220). Of the mAbs, three mAbs (mAb-A, -B1 and -B2) recognize the FAD-binding domain of the enzyme. In the present study, the epitopes of the mAbs on the enzyme have been examined using pGEX-2T expression systems for DNA fragments encoding various partial amino acid sequences of 4-aminobenzoate hydroxylase. The epitopes for mAb-A, -B1 and -B2 were shown to be on sequences 413-434, 435-460 and 380-413, respectively. These findings suggest that these epitopes for mAb-A, -B1 and -B2 may be close to the isoalloxazine moiety of FAD, which plays a central role in the catalysis of the enzyme.

Monoclonal antibodies to 2,4-dichlorophenol hydroxylase as probes for the 2,4-D-degradative phenotype

Two different monoclonal antibodies (MAb) were raised against 2,4-dichlorophenol hydroxylase (DCP-hydroxylase) of Ralstonia eutropha JMP134 (pJP4), the second enzyme in the 2,4-D-degradative pathway of this bacterium. The utility of these antibodies in detecting and characterizing 2,4-D-degrading soil bacteria was investigated. One MAb (F6) reacted with DCP-hydroxylase from 27 out of 36 strains tested, while the other (MAb C3) reacted with only 17 isolates. When used with the colony blot technique, MAb F6 was useful for detecting cross-reacting strains on plates of pure cultures or of mixtures containing nondegraders even when 2,4-D degraders were outnumbered 60 to 1. 2,4-D-degrading strains could also be detected from plates spread with enrichment cultures but not from primary isolation plates spread from soil dilutions, presumably because the ratio of degraders to nondegraders was too low. Colonies of some strains that were very distantly related genetically, but produced functionally similar DCP-hydroxlase enzymes, were detected by MAb F6. This result suggests that MAbs could be useful for detecting functionally similar proteins expressed from tfdB analogs, even in the absence of detectable DNA homology between the genes encoding them.

L-kynurenine 3-monooxygenase from mitochondrial outer membrane of pig liver: purification, some properties, and monoclonal antibodies directed to the enzyme

We have purified L-kynurenine 3-monooxygenase from pig liver mitochondria using a procedure involving seven steps composed of (1) preparation of mitochondrial outer membrane, (2) preparation of the zwitterionic detergent, 3-[(3-cholamidopropyl)dimethylammonio]-1-propane sulfonate (Chaps) insoluble outer membrane material, (3) extraction of the enzyme with beta-octylglucoside, (4) ammonium sulfate fractionation, (5) DEAE-Sepharose CL-6B chromatography, (6) Matrex gel orange A affinity chromatography, and (7) high-performance liquid chromatography (HPLC) gel filtration. The final preparation had an about 160-fold purified enzyme activity with a yield of 0.8%. The apparent molecular mass of the aggregated form of the native enzyme was determined to be close to 300 kDa by HPLC gel filtration in the presence of 0.005% Triton X-100. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) showed a main protein band with an apparent molecular mass of about 49 kDa. The enzyme was found to be about 86% pure by the criterion of SDS-PAGE. The dissociated form of the enzyme contains 1 mol of non-covalently bound FAD/mol of protein monomer. The UV/visible spectrum had absorption peaks at 275, 384, and 450 nm, typical of a simple flavoprotein. Five inhibitory monoclonal antibodies against the enzyme were obtained. They could stain moderately a single protein band (49 kDa) in a Western blot.

Two cytochromes P450 are major hepatocellular autoantigens in autoimmune polyglandular syndrome type 1

BACKGROUND & AIMS

Liver disease has been described in 10%-15% of patients with autoimmune polyglandular syndrome type 1 (APS-1). After the discovery of cytochrome P450 1A2 (CYP1A2) as a hepatocellular autoantigen in liver-kidney microsomal autoantibody (LKM)-positive patients with APS-1, the investigation of antiliver antibodies was extended to 11 Sardinian patients with APS-1.

METHODS

Indirect immunofluorescence and Western blotting analysis were performed to study the antiliver antibodies.

RESULTS

Immunofluorescence revealed LKM antibodies in 3 patients with APS-1, 1 of whom died of fulminant hepatitis. Western blotting showed a liver microsomal protein band of approximately 51 kilodaltons in the LKM-positive sera of these 3 patients. Western blotting performed with recombinant cytochrome P450 enzymes allowed the identification of CYP2A6 as a specific target antigen.

CONCLUSIONS

LKM antibodies in APS-1 sera are specifically directed against CYP1A2 or CYP2A6, but their diagnostic and prognostic significance for liver disease remain to be determined.

Cytochrome P4502A6 (CYP2A6) expression in human hepatocellular carcinoma

The hepatic cytochrome P4502A6 (CYP2A6) enzyme mediates the oxidative metabolism of several procarcinogens that have liver as their primary target. Mouse models indicate that liver tumors invariably overexpress CYP2A forms, and that inflammation and cirrhosis may regulate the CYP2A expression pattern. In this study, the distribution of the CYP2A6 protein was investigated in a series of 24 human hepatocellular carcinoma (HCC) samples by immunohistochemical analysis. A polyclonal antibody was raised in chicken against CYP2A5, the mouse orthologue of CYP2A6. The antibody was characterized and found to be specific for CYP2A members. In DBA/2 mouse liver, a strong increase of CYP2A5 protein amount, localized in the perivenous region, occurred in response to treatment with pyrazole. In human HCC samples, overexpression of CYP2A6 protein was associated with the presence of chronic inflammation and cirrhosis. CYP2A6 protein was observed in 9 of 16 (56%) of samples with non-neoplastic hepatocytes and in 10 of 24 (42%) HCC samples. The staining for CYP2A6 protein was very heterogeneous in tumor cells, suggesting that increased expression of CYP2A6 occurred in a distinct subpopulation of neoplastic cells. In Kaplan-Meyer survival analysis, there was a tendency toward a more favorable prognosis in patients with CYP2A6-positive tumors in comparison with patients with CYP2A6-negative tumors. These data suggest that, in human HCC, in contrast to mouse liver tumors, CYP2A6 overexpression is not an invariable phenotype.

Comparison of CYP2A6 catalytic activity on coumarin 7-hydroxylation in human and monkey liver microsomes

Comparison of 7-hydroxylation of coumarin, a CYP2A6 substrate, in human and African green and cynomolgus monkey liver microsomes was made by means of an HPLC assay with UV detection. In human liver microsomes, the Km and Vmax values for the metabolic conversion were 2.1 microM and 0.79 nmol/mg/min, respectively. While African green monkey showed Km and Vmax values of 2.7 microM and 0.52 nmol/mg/min, which were similar to human, higher Km and Vmax values were found in cynomolgus monkey. Coumarin 7-hydroxylation in human and African green monkey was selectively inhibited by methoxsalen and pilocarpine (CYP2A6 inhibitors) but not by other inhibitors, i.e. alpha-naphthoflavone (CYP1A1), orphenadrine (CYP2B6), sulfaphenazole (CYP2C9), quinidine (CYP2D6) and ketoconazole (CYP3A4). Immunoinhibition results supported CYP2A6 involvement in human and its homolog in monkey in coumarin 7-hydroxylation, as only anti-CYP2A6, but not CYP2B1, CYP2C13, CYP2D6, CYP2E1 or CYP3A antibodies, inhibited this conversion. African green monkey was found to be similar to human in catalytic activity of coumarin 7-hydroxylation and response to CYP2A6 inhibitors or antibody inhibition. However, the monkey CYP2A6 is not identical to the human in that Ki values were different, and differences were observed with some CYP2A6 inhibitors, such as nicotine and methoxsalen, suggesting that, under some circumstances, studies of nicotine kinetics and drug taking behavior in monkey may not be comparable to human.

Identity of bovine growth hormone and peptidylglycine monooxygenase

The C-terminal alpha-amidation of peptides is one of the most important events in prohormone and neuropeptide processing. Peptide amidation is a two-step process catalyzed by peptidylglycine (hydroxylating) monooxygenase (B. A. Eipper et al., 1983, Proc. Natl. Acad. Sci. USA 80, 5144-5148) followed by dismutation of the resultant hydroxylated peptide to peptide amide and glyoxylate, stimulated by alpha-hydroxyglycine amidating dealkylase (K. Takahashi et al., 1990, Arch. Biochem. Biophys. 169, 524-530). Previous reports on peptidylglycine monooxygenase from bovine pituitary have generated substantial disagreement as to its molecular size. We have reinvestigated the purification of this enzyme and we find that peptidylglycine monooxygenase activity from fresh bovine pituitary is entirely due to a previously unrecognized catalytic function of growth hormone (somatotropin).

Inhibitory anti-peptide antibody against human CYP3A4

An inhibitory anti-peptide antibody was raised against a 21-amino acid peptide (VKRMKESRLEDTQKHRVDFLQ) corresponding to residues 253-273 of human cytochrome P450 3A4. High titer antibodies were produced by rabbits immunized with this peptide coupled to keyhole limpet hemocyanin, as judged by ELISA. Anti-peptide antibody recognized a single protein band in microsomes prepared from cells expressing recombinant human CYP3A4 in immunoblotting analysis. No immunodetectable proteins were found in microsomes containing other cytochrome P450 isoforms. In addition, the antibody did not recognize CYP3A5, a closely related isoform in the CYP3A family. In human liver microsomes, only one protein band which comigrated with human CYP3A4 was recognized by this antibody and the relative blotting intensity of this protein band correlated significantly with human CYP3A4-catalyzed testosterone 6 beta-hydroxylase activities (r = 0.96). More importantly, this antibody exhibited greater than 90-95% inhibition of testosterone 6 beta-hydroxylation, while other cytochrome P450-mediated reactions in human liver microsomes were not inhibited. Because of its specificity and inhibitory potency, this anti-peptide antibody should be a valuable tool in evaluating the role of CYP3A in mediating in vitro metabolism of therapeutic agents.

The 2,4-dichlorophenol hydroxylase of Alcaligenes eutrophus JMP134 is a homotetramer

2,4-Dichlorophenol hydroxylase (DCP-hydroxylase) is a key enzyme in the pathway for degradation of 2,4-dichlorophenoxyacetic acid (2,4-D) in many bacteria. In Alcaligenes eutrophus JMP134, DCP-hydroxylase was reported to consist of two dissimilar types of subunit of 66 and 45 kDa, a structure which is different from that in other bacteria. Using a different procedure involving affinity purification and ion-exchange chromatography, we have purified active enzyme from JMP134 and show that it has a native molecular mass of approximately 245 kDa and consists of a single type of subunit of 66 kDa, similar to all other flavoprotein monooxygenase enzymes. A 45-kDa polypeptide, found in partially purified enzyme preparations, was not required for enzyme activity but had some serologic and N-terminal amino acid sequence similarity to the 66-kDa enzyme subunit.

Pituitary control of proliferation and differentiation of Leydig cells and their putative precursors in immature hypophysectomized rat testis

The objective of this study was to determine the effects of pituitary hormones (luteinizing hormone [LH], follicle-stimulating hormone [FSH], growth hormone [GH], and prolactin [PRL]) on interstitial cell proliferation and differentiation in the testis of immature hypophysectomized rats. Macrophages, Leydig cells, precursor mesenchymal cells, endothelial lymphatic cells, and myoid cells were studied. Our experimental approach was aimed at determining whether changes in a cellular subpopulation observed after pituitary hormone treatments were the result of division of existing cells in the population, of differentiation of interstitial precursor cells, or both. In this context, it must be stressed that our data reflected the effects of hormones to prevent the decline of cells due to hypophysectomy rather than their recovery. Macrophage proliferation was taken into account because macrophages closely resemble Leydig cells and are known to proliferate after hormonal treatment. A double-labeling procedure (acid phosphatase and anti-bromodeoxyuridine [anti-BUdR]) revealed that LH, FSH, and PRL increased the number of testicular macrophages 105-, 104-, and 103-fold, respectively, in hypophysectomized rats compared to hypophysectomized control animals. BUdR incorporation in testicular macrophages was greater after PRL treatment than after LH and FSH supplementation. In contrast, we were unable to demonstrate any effect of rat GH on the macrophage population. Light microscopic analysis of plastic embedded sections of treated rat testis revealed that LH increased the numbers of Leydig, precursor mesenchymal, and myoid cells 6-, 4-, and 1.3-fold, respectively. LH also stimulated BUdR incorporation into all interstitial cell types. PRL administration increased both the number of Leydig and precursor mesenchymal cells (each 3-fold) but decreased the number of endothelial lymphatic cells (1.5-fold) when compared to the control animals. In contrast, FSH did not increase the number and proliferation of Leydig cells but exerted a slight proliferative effect on the other interstitial cell populations. In GH-treated rats, the number of precursor mesenchymal cells increased two fold above the control rats. GH also exerted slight proliferative effects on both precursor mesenchymal and myoid cells. Immunohistochemical studies of steroidogenic enzymes in the testicular interstitium of treated rats demonstrated the presence of steroidogenic enzymes, not only in Leydig and precursor mesenchymal cells, but also in some (1%-2%) endothelial lymphatic cells and myoid cells. This may indicate that both of these cell types are also constitutively equipped to perform steroidogenesis or that they are precursor cells undergoing differentiation. Taken together, changes in the number of Leydig cells in our animal model appeared more likely to be dependent on the transformation of precursor cells than on division of preexisting mature Leydig cells.

Interindividual variability in catalytic activity and immunoreactivity of three major human liver cytochrome P450 isozymes

OBJECTIVE

Interindividual variations in immunoreactivity and function of three major human drug metabolising P450 monooxygenases has been investigated in liver microsomes from 42 Caucasians (kidney donors or liver biopsies).

METHODS

Diclofenac 4'-hydroxylation, dextromethorphan O-demethylation and midazolam 1'-hydroxylation, measured by HPLC in incubates, were used as probes to determine CYP2C9, CYP2D6 and CYP3A4 function kinetics, respectively. Immunoquantification of the three isoforms was achieved by Western blotting, using rabbit polyclonal antibodies raised against human CYP2C9 and human CYP3A4, and mouse monoclonal antibody raised against human CYP2D6.

RESULTS

Diclofenac 4'-hydroxylation exhibited Michaelis-Menten kinetics with kM = 3.4 mumol.l-1 and Vmax = 45 nmole.mg-1 P.h-1. Relative immunoreactivity of CYP2C9 was correlated with Vmax and CL(int). Dextromethorphan O-demethylation in EM (extensive metabolisers) liver microsomes also showed Michaelis-Menten kinetics, with kM = 4.4 mumol.l-1 and Vmax = 5.0 nmol.mg-1 P.h-1. Relative immunoreactivity of CYP2D6 was correlated with Vmax and CL(int). Midazolam 1'-hydroxylation also exhibited Michaelis-Menten kinetics with kM = 3.3 mumol.l-1 and Vmax = 35 nmol.mg-1 P.h-1. Relative immunoreactivity of CYP3A4 was correlated with Vmax and CL(int). Immunoreactivity and function were correlated for each isozyme, but there was no cross correlation between isozymes.

CONCLUSION

The velocity of metabolite formation (Vmax) by the three major human drug metabolising P450 monoxygenases is correlated with their immunoreactivity in liver microsomes. Interindividual variation was much larger for Vmax than kM. Interindividual variability was more pronounced for CYP2D6, probably due to the presence of several different functional alleles in the population of extensive metabolisers.

Characterization of Drosophila tyramine beta-hydroxylase gene and isolation of mutant flies lacking octopamine

Octopamine is likely to be an important neuroactive molecule in invertebrates. Here we report the molecular cloning of the Drosophila melanogaster gene, which encodes tyramine beta-hydroxylase (TBH), the enzyme that catalyzes the last step in octopamine biosynthesis. The deduced amino acid sequence of the encoded protein exhibits 39% identity to the evolutionarily related mammalian dopamine beta-hydroxylase enzyme. We generated a polyclonal antibody against the protein product of T beta h gene, and we demonstrate that the TBH expression pattern is remarkably similar to the previously described octopamine immunoreactivity in Drosophila. We further report the creation of null mutations at the T beta h locus, which result in complete absence of TBH protein and blockage of the octopamine biosynthesis. T beta h-null flies are octopamine-less but survive to adulthood. They are normal in external morphology, but the females are sterile, because although they mate, they retain fully developed eggs. Finally, we demonstrate that this defect in egg laying is associated with the octopamine deficit, because females that have retained eggs initiate egg laying when transferred onto octopamine-supplemented food.

Identification, purification, and characterization of the molecular forms of Aplysia californica peptidylglycine alpha-amidating enzyme

Peptidylglycine alpha-amidating enzyme (PAM; EC 1.14.17.3) is responsible for the conversion of peptides with a COOH-terminal glycine into alpha-amidated peptides, a posttranslational modification often required for biological activity and/or increased stability. Such an activity able to convert the model peptide D-Tyr-Val-Gly into D-Tyr-Val-amide was found to be present in the marine mollusk Aplysia californica. Examination of this amidating activity as well as its immunoreactivity demonstrates that (1) it can be found mainly in the atrial gland, heart, and CNS but is barely detectable in the hepatopancreas and gonads, (2) it requires as essential cofactors copper, molecular oxygen, and ascorbate, and (3) it exists in at least two molecular forms, a soluble and a membrane-bound form. Purification of this activity from the atrial gland was accomplished using Cu(2+)-chelating Sepharose, gel permeation, and hydroxyapatite chromatography. In addition, using polyclonal antibodies raised against various parts of the rat amidating enzyme, we demonstrate that numerous immunologically recognized regions are conserved in both the soluble and membrane-bound Aplysia californica PAM.

Ethnic-related differences in coumarin 7-hydroxylation activities catalyzed by cytochrome P4502A6 in liver microsomes of Japanese and Caucasian populations

1. Interethnic differences in cytochrome P4502A6 (CYP2A6) levels and coumarin 7-hydroxylation activities were determined in liver microsomes of 30 Japanese and 30 Caucasians. 2. Although CYP2A6 levels and coumarin 7-hydroxylation activities varied very significantly in the 60 human samples examined, both CYP2A6 levels and coumarin 7hydroxylation activities were found to be higher in Caucasian than Japanese population. 3. Interestingly, eight of the 30 Japanese examined showed very low or undetectable levels of coumarin 7-hydroxylation activities as well as of CYP2A6 in liver microsomes. All of the Caucasians, however, had significant CYP2A6 levels and variable 7-hydroxylation activities. 4. Kinetic analvsis of coumarin 7-hydroxylation activities in liver microsomes of various human samples suggested that although there were 260-fold differences in Vmax's in 10 human samples examined, the Km's were very similar (2.1 + or - 107 mu M); a value consistent with that obtained (1.2 mu M) with purified CYP2A6 in reconstituted system. 5. The results suggest that CYP2A6 is actually involved in the 7-hydroxylation of coumarin in human liver microsomes, and that interethnic differences in coumarin 7-hydroxylation activities in Japanese and Caucasian population may be ascribed to the differences in expression of CYP2A6 protein.

Sex differences in constitutive level of renal lauric acid hydroxylase activities and CYP4A-related proteins in mice

The constitutive level of renal fatty acid hydroxylase was examined in ddY mice by measuring the activities of lauric acid omega- and (omega-1)-hydroxylase, (LA12H and LA11H respectively). The activities of both LA12H and LA11H of male mice were significantly higher than those of female mice. This sex difference in renal lauric acid hydroxylase (LAH) activity exists in other strains of mice, including Balb/c, C57BL/6, C3H/HeN and C3H/HeJ. Renal LAH activities are at significantly low levels in both sexes of immature animals, but are sexually differentiated in the mature state. In male mice, orchiectomy caused a drastic decrease in renal LAH activities, and the activities were restored by testosterone treatment to above the level of the intact animal. In female mice, ovariectomy and estradiol treatment had no effect on the activities, but testosterone treatment caused an increase in the activities to the level of the intact male animal. These results suggested that testosterone is a key regulatory factor in the level of LAH activity in mouse kidney. The administration of dexamethasone and clofibrate affected the level of LAH activity. The above data are consistent with the level of CYP4A-related proteins (band H and L protein) measured by using anti-rat CYP4A1 antibodies.antibodies. The antibodies inhibited both LA12H and LA11H activities. The level of band H protein was regulated by testosterone and dexamethasone. On the other hand, the level of band L protein was regulated by clofibrate. These results suggest that distinct modes of regulation exist in the level between band H and L protein in mouse kidney.

Epitope mapping studies with human anti-cytochrome P450 3A antibodies

A subset of patients with hypersensitivity reactions to the aromatic anticonvulsants phenytoin, carbamazepine, and phenobarbital have circulating antibodies that recognize members of the rat cytochrome P450 (CYP) 3A subfamily. These antibodies do not recognize related human CYP3A proteins despite the high degree of structural similarity. To investigate the relationship between P450-mediated drug metabolism and the development of anti-P450 antibodies, we initiated epitope mapping studies by screening a library of fusion proteins constructed from rat CYP3A1 with an anti-CYP3A1-positive patient serum sample. Positive signals from colony lifts were confirmed by sodium dodecyl sulfate/polyacrylamide gel electrophoresis and immunoblotting, and a 26-amino acid sequence corresponding to amino acids 342-367 of the CYP3A1 protein (NKAPPTY-DTVMEMEYLDMVLNETLRL) was identified as containing the epitope recognized by IgG3 antibodies in this serum sample. By subjecting inserts from two clones into a second round of library construction and screening by immunoblot analysis, we further defined the epitope to EYLDMVLNETLRL. Single amino acid deletions identified DMVLNETLRL as the minimum amino acid sequence required for antibody binding. The corresponding sequence in the four human CYP3A proteins differs by only one amino acid (DMVVNETLRL) This amino acid is critical to antibody recognition as immunoreactivity of the L361V mutant is markedly reduced. Anti-CYP3A antibodies in nine of nine additional sera also recognized the 13-amino acid epitope; for five of these sera, the minimum antibody binding sequence was DMVLNETLRL. The proximity of this epitope to a region determining substrate specificity may provide the link among reactive metabolite production, hapten formation, and the production of anti-P450 antibodies in anticonvulsant-induced idiosyncratic reactions.

Identification of human liver cytochrome P-450 3A4 as the enzyme responsible for fentanyl and sufentanil N-dealkylation

Alfentanil, sufentanil, and fentanyl are synthetic opioids that are metabolized by oxidative N-dealkylation in the liver. We have previously shown that cytochrome P-450 3A4 (CYP3A4) contributes significantly to human liver microsomal alfentanil oxidation. Since identification of specific drug-metabolizing enzymes allows prediction of the variables affecting drug metabolism, the purpose of the present study was to identify the P-450 enzymes responsible for sufentanil and fentanyl metabolism in human liver microsomes. Microsomal preparations fortified with a reduced nicotinamide-adenine dinucleotide phosphate-generating system were incubated with 0.25 microM 3H-fentanyl or 3H-sufentanil. Rates of N-dealkylated metabolite formation significantly correlated with nifedipine oxidation activity (a marker of CYP3A4 activity) for fentanyl and sufentanil (r = 0.93 and 0.87, n = 18, respectively), but not with the oxidation activity for ethoxyresorufin (CYP1A2), S-mephenytoin (CYP2C19), bufuralol (CYP2D6), or chlorzoxazone (CYP2E1). Gestodene and troleandomycin (chemical inhibitors of CYP3A4) and antibody to CYP3A4 inhibited N-dealkylation of fentanyl and sufentanil. Chemical inhibitors of CYP2C, 2E1, and 2D6 did not inhibit N-dealkylation of fentanyl and sufentanil. Recombinant CYP3A4 expressed in Escherichia coli showed N-dealkylation activity of fentanyl and sufentanil, while expressed CYP1A2, 2C10, and 2E1 enzymes did not. We conclude that CYP3A4 is responsible for fentanyl and sufentanil N-dealkylation in vitro.

Distribution and induction of CYP3A1 and CYP3A2 in rat liver and extrahepatic tissues

Previously, we have shown that highly specific antibodies against cytochrome P450 enzymes can be produced by targeting a 5-amino acid sequence at the C-terminus. Although rat CYP3A1 and CYP3A2 share 89% amino acid sequence similarity, they differ by 3 out of 5 of their C-terminal residues. In an effort to produce antibodies specific to each form, rabbits were immunised with the peptides IITGS and VINGA, corresponding to the C-termini of CYP3A1 and CYP3A2, respectively. Both antibodies bound strongly to hepatic microsomal fraction from rats treated with pregnenolone 16 alpha-carbonitrile (PCN) in enzyme-linked immunosorbent assay. Binding of the anti-IITGS antibody was strongly inhibited by incubation with IITGS, but VINGA was 60 times less effective. Conversely, binding of the anti-VINGA antibody was inhibited by VINGA 100 times more effectively than IITGS. Similar inhibition of antibody binding was also found using immunoblotting. Immunoadsorption using the anti-IITGS antibody yielded a single protein from solubilised hepatic microsomal fraction from PCN-treated rats, which was recognised only by the anti-IITGS antibody. Both antibodies bound to single proteins in the liver which were increased following treatment with PCN, but only the anti-IITGS antibody recognised protein in the lung, small intestine, and kidney of untreated and PCN-treated rats. Also, the binding of the two antibodies to hepatic and extrahepatic microsomal fractions from uninduced and induced rats showed differences in the expression of proteins recognised by the two antibodies, providing further evidence of antibody specificity. Thus, the binding of anti-IITGS and anti-VINGA antibodies is mutually exclusive and consistent with specific binding to their target antigens, CYP3A1 and CYP3A2, respectively. Immunocytochemistry was used to determine the distribution of CYP3A1 and CYP3A2. In the liver of untreated animals, both CYP3A1 and CYP3A2 were found to be expressed in the centrilobular region. However, some CYP3A1 immunoreactivity was also detected in many, but not all, hepatocytes throughout the lobule. However, following treatment of rats with PCN, both CYP3A1 and CYP3A2 were found to be strongly expressed in hepatocytes throughout the lobule, although CYP3A2 showed greater expression in the centrilobular region. PCN treatment was also found to result in induction of CYP3A1 in specific regions of the small intestine, lung, and kidney.

Recurrent episodes of acute hepatitis associated with LKM-1 (cytochrome P450 2D6) antibodies in identical twin brothers

BACKGROUND/AIMS

Liver/kidney microsomal antibodies have been noted in liver disease of different etiology, e.g. in autoimmune hepatitis, chronic hepatitis C and D virus infection and in drug-induced liver disease. Unlike these, acute hepatitis of unknown etiology associated with high-titer liver/kidney microsomal-1 antibodies (cytochrome P450 2D6) is reported in identical twin brothers.

METHODS

Patients were studied using clinical, biochemical, serological and immunological methods, as well as liver biopsy.

RESULTS

The acute icteric episodes were followed by spontaneous remission with complete normalization of liver function tests and liver histology. During the acute phase, serum titer for liver/kidney microsomal-1 antibodies (detected by indirect immunofluorescence, ELISA and Western blot analysis) was exceedingly high and decreased gradually thereafter. Hepatitis C and D virus infection were excluded by repeated serological testing; exposure to drugs or chemicals was not evident. Concomitant autoimmune disease was not detectable. HLA typing for class 1 and 2 antigens was positive for the HLA haplotype DQ2, but negative for HLA B4, B8, DR3 and DR4.

CONCLUSIONS

The present observations might suggest a hitherto unreported form of acute hepatitis of unknown etiology, distinct from other liver diseases in which liver/kidney microsomal antibodies have been described so far.

Inhibitory and non-inhibitory monoclonal antibodies to human cytochrome P450 3A3/4

Cytochromes P450 3A3/4 are inordinately important P450 enzymes catalyzing the metabolism of a large variety of clinically useful drugs, steroids, and carcinogens. Two monoclonal antibodies, MAb 3-29-9 and MAb 275-1-2, were prepared to human P450 3A4 from mice immunized with baculovirus-expressed human P450 3A4. MAb 3-29-9 was a powerful inhibitor of the enzymatic activity of P450 3A3/4/5. MAb 3-29-9 inhibited the P450 3A3, 3A4, and 3A5 catalyzed metabolism of substrates of divergent molecular weights, e.g., p-nitroanisole, phenanthrene, diazepam, testosterone, taxol, and cyclosporin. However, MAb 3-29-9 did not give a western blot with P450 3A3 or 3A4. MAb 275-1-2 was non-inhibitory but yielded a strong western blot with P450 3A3 and 3A4 but not with 3A5, and thus distinguished between 3A3/4 and 3A5. The two MAbs did not cross-react with human 2E1, 1A2, 2B6, 2C8, and 2C9; rat 2A1, 3A1/2, 4A1, 4A3, and 2B1; and mouse 1A1 and 1A2. MAb 3-29-9 has been used successfully to measure the quantitative contribution of P450 3A3 and 3A4 to the metabolism of the above-designated substrates in human adult liver. MAb 3-29-9 and MAb 275-1-2 are precise and sensitive reagents for P450 3A studies.

Studies on the metabolism of haloperidol (HP): the role of CYP3A in the production of the neurotoxic pyridinium metabolite HPP+ found in rat brain following ip administration of HP

The levels of haloperidol (HP) and its pyridinium metabolite HPP+ were estimated in plasma and brain tissues of rats treated i.p. with HP (10 mg/kg). HP and HPP+ levels in plasma decreased linearly during the 0-3 hour period following drug administration. On the other hand, HPP+ levels in brain tissues increased gradually during the same period. HPP+ levels in brain tissues increased further when HP (10 mg/kg) was injected for three consecutive days. The formation of HPP+ also was studied in rat brain mitochondrial and liver microsomal preparations. Enzyme activity responsible for the conversion of HP to HPP+ was not found in brain mitochondria. Liver microsomal enzymes catalyzed the oxidation of HP and its tetrahydropyridine dehydration product HPTP to HPP+ with about the same efficiency. Studies employing several cytochrome P450 inhibitors and anti-cytochrome P450 antibodies were carried out in an effort to identify the forms of cytochrome P450 that are responsible for catalyzing the oxidation of HP and HPTP to HPP+. The formation of HPP+ in liver microsomes was strongly inhibited by ketoconazole and nifedipine and by an anti-CYP3A antibody. These results suggest that formation of HPP+ from HP and HPTP in rat liver microsomes is catalyzed mainly by CYP3A although the participation of other P450 forms cannot be ruled out.

Anti-peptide antibodies to the P4502D subfamily in rat, dog and man

1. In order to obtain specific antibodies of the P4502D subfamily, we generated two anti-peptide antibodies against synthetic peptides, DPAQPPRD (peptide A) and DPTQPPRH (peptide B). The sequence of peptide A occurs in rat P4502D2, P4502D4 and human P4502D6, whereas the sequence of peptide B occurs in the dog P4502D subfamily. These sequences are closely related to an epitope of liver/kidney microsomal autoimmune hepatitis. 2. In immunoblotting studies, the anti-peptide antibody against peptide A recognized a 49-KDa protein in microsomes derived from human lymphoblasts expressing P4502D6 and rat liver. It showed no crossreactivity with microsomes from dog liver. In contrast, the anti-peptide antibody against peptide B recognized a 49-KDa protein only in microsomes of dog liver. These indicate that each anti-peptide antibody has the specificity for the respective sequences of the members of P4502D subfamily, with the species investigated herein. 3. In immunoinhibition studies, the anti-peptide antibodies against peptide B inhibited bunitrolol 4-hydroxylation and propranolol 4,5-hydroxylation, which are mediated by the dog P4502D subfamily. These data suggest that the anti-peptide antibodies against peptide B bind to the native and denatured forms of the P4502D subfamily. 4. The present study has demonstrated that the anti-peptide antibodies against this region are useful for studying the members of the P4502D subfamily.