Biomedical subjects

P E Levi

Publications and source records attributed to P E Levi.

At least 19 recordsLinked to original sources

PubMed1998

Molecular cloning, sequence, and expression of mouse flavin-containing monooxygenases 1 and 5 (FMO1 and FMO5).

Full-length cDNA clones encoding FMO1 and FMO5 have been isolated from a library constructed with mRNA from the liver of a female CD-1 mouse. The derived sequence of FMO1 contains 2310 bases: 1596 in the coding region, 301 in the 5'-flanking region, and 413 in the 3'-flanking region. The sequence for FMO5 consists of 3168 bases; 1599 in the coding region, 812 in the 5'-flanking region, and 757 in the 3'-flanking region. The sequence of FMO1 encodes a protein of 532 amino acids with a predicted molecular weight of 59.9 kDa and shows 83.3% identity to human FMO1 and 83-94% identity to other FMO1 homologs. FMO5 encodes a protein of 533 amino acids with a predicted molecular weight of 60.0 kDa and 84.1% identity to human FMO5 and 83-84% identity to other FMO5 orthologs. Two GxGxxG putative pyrophosphate binding domains exist beginning at positions 9 and 191 for FMO1, and 10 and 192 for FMO5. Mouse FMO1 and FMO5 were expressed in E. coli and show similar mobility to the native proteins as determined by SDS-PAGE. The expressed FMO1 protein showed activity toward methimazole, and FMO5 was active toward noctylamine. In addition, FMO1 was shown to metabolize radiolabeled phorate, whereas FMO5 showed no activity toward phorate.

Animals↗

PubMed1997

Molecular cloning, sequencing, and expression in Escherichia coli of mouse flavin-containing monooxygenase 3 (FMO3): comparison with the human isoform.

The sequence of mouse flavin-containing monooxygenase 3 (FMO3) was obtained from several clones isolated from a mouse liver cDNA library. The nucleotide sequence of mouse FMO3 was 2020 bases in length containing 37 bases in the 5' flanking region, 1602 in the coding region, and 381 in the 3' flanking region. The derived protein sequence consisted of 534 amino acids including the putative flavin adenine dinucleotide and NADP+ pyrophosphate binding sites (characteristic of mammalian FMOs) starting at positions 9 and 191, respectively. The mouse FMO3 protein sequence was 79 and 82% identical to the human and rabbit FMO3 sequences, respectively. Mouse FMO3 was expressed in Escherichia coli and compared to E. coli expressed human FMO3. The FMO3 proteins migrated with the same mobility ( approximately 58 kDa) as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and immunoblotting. The expressed FMO3 enzymes (mouse and human forms) were sensitive to heat and reacted in a similar manner toward metal ions and detergent. Catalytic activities of mouse and human FMO3 were high toward the substrate methimazole; however, in the presence of trimethylamine and thioacetamide, FMO-dependent methimazole oxidation by both enzymes was reduced by greater than 85%. Other substrates which inhibited methimazole oxidation were thiourea and thiobenzamide and to a lesser degree N,N-dimethylaniline. When probed with mouse FMO3 cDNA, FMO3 transcripts were detected in hepatic mRNA samples from female mice, but not in samples from males. FMO3 was detected in mRNA samples from male and female mouse lung, but FMO3 message was not detected in mouse kidney sample from either gender. Results of immunoblotting confirmed the tissue- and gender-dependent expression of mouse FMO3.

Amino Acid Sequence↗

PubMed1997

Regulation of mouse liver flavin-containing monooxygenases 1 and 3 by sex steroids.

Based on enzyme activity, protein levels, and mRNA levels, we have previously demonstrated the female-predominant, female-specific, and gender-independent expression in mouse liver of FMO forms 1, 3, and 5, respectively. This study investigated the roles of testosterone, 17 beta-estradiol, and progesterone in the regulation of hepatic FMOs. FMO expression was examined in gonadectomized CD-1 mice, normal CD-1 mice receiving hormonal implants, and gonadectomized mice receiving various hormonal treatments. Following castration of males, hepatic FMO activity levels were significantly increased and serum testosterone levels significantly decreased; however, administration of physiological levels of testosterone to castrated animals returned FMO activity and testosterone concentrations to control levels. When sexually intact and ovariectomized female mice were treated with testosterone, their hepatic FMO activity levels were reduced to those of their male counterparts, concomitant with high serum testosterone levels. In males, castration dramatically increased FMO3 and FMO1 expression, and testosterone replacement to castrated males resulted in ablation of FMO3 expression. In addition, testosterone administration to females (sexually intact and gonadectomized animals) reduced FMO1 expression and obviated FMO3 expression. In females, ovariectomy alone slightly reduced FMO activity, indicative of a possible stimulatory role of female sex steroids; however, female FMO isozyme expression was relatively unchanged, and hormone replacement therapy to ovariectomized females had no discernible effect. In males and females, FMO5 levels were unaffected by gonadectomy or hormone administration, thus indicating a sex hormone-independent mechanism of regulation for this isoform. Interestingly, FMO1 protein levels were increased in sexually intact males following treatment with 17 beta-estradiol; however, only a slight increase in FMO3 protein level was observed. No positive hormone effectors of female FMO expression were identified.

Animals↗

PubMed1997

Regulation of hepatic CYP1A isozymes by piperonyl butoxide and acenaphthylene in the mouse.

The regulation of CYP1A1 and CYP1A2 isozymes by piperonyl butoxide (PBO) and acenaphthylene (ACN) was studied in the liver of male C57BL/6 and DBA/2 mice. These two cytochrome P450 genes are known to be regulated by the aromatic hydrocarbon-responsive receptor (AHR); however, it has been suggested that CYP1A2 is also induced by an AHR-independent mechanism. In this study, PBO induced hepatic CYP1A1 considerably more in C57BL/6 (Ahrb-I) than in DBA/2 (Ahrd) mice. In addition, the superinduction of CYP1A1 in wildtype hepa1c1c7 cells, which is AHR-dependent, resulted from PBO and cycloheximide treatment of the cells. In other studies in this laboratory using AHR knock-out (AHR-/-) mice, a hybrid of 129/SV and C57BL/6 strains, no induction of CYP1A1 occurred with PBO or ACN. [D.-Y. Ryu, P.E. Levi, P. Fernandez-Salguero, F.J. Gonzalez, E. Hodgson, Mol. Pharmacol., 50 (1996) 443-446.] ACN, however, did not induce CYP1A1 under the experimental conditions used. These results suggest that PBO, but not ACN, induces CYP1A1 through a weak activation of AHR. On the other hand, hepatic CYP1A2 mRNA and hnRNA were induced by PBO in both C57BL/6 and DBA/2 strains, but were not induced by ACN, a strong inducer of CYP1A2 in the B6C3F1 strain. However, both PBO and ACN induced CYP1A2 in AHR-/- mice. It is assumed, therefore, that the transcriptional induction of CYP1A2 by PBO and ACN is AHR-independent. In addition, the induction of CYP1A2 by ACN depends upon the strain of mice. Immunohistochemical studies for CYP1A1/CYP1A2 apoproteins showed that PBO induced CYP1A1/CYP1A2 around the central veins as did 3-methylcholanthrene (3-MC). The induction of CYP1A1/CYP1A2 by ACN, however, was not observed, consistent with the northern blot results.

Acenaphthenes↗

PubMed1996

Xenobiotic biotransforming enzymes in the central nervous system: an isoform of flavin-containing monooxygenase (FMO4) is expressed in rabbit brain.

The flavin-containing monooxygenase (FMO, EC 1.14.13.8) is involved in the metabolism of a number of important xenobiotics including many which affect the central nervous system (CNS). Recently, reports in the literature concerning the amount, activity, location, and isozyme characteristics of this enzyme in the brain have presented conflicting evidence. In order to resolve some of the controversy surrounding FMO in the brain, a highly sensitive method for the detection of flavin-containing monooxygenase (FMO) mRNA in whole brain was employed. A poorly conserved region of FMO transcripts was used to design five sets of oligonucleotide primers. Each primer set was specific for one of the five currently known isoforms of FMO. Four and five isoforms, respectively, are expressed in rabbit liver and kidney, as determined by reverse transcription-polymerase chain reaction. However, only one set of primers amplified a specific rabbit brain cDNA fragment. The sequence of the amplification produced affirmed its identity as a segment of FMO4 cDNA. Thus, the FMO of rabbit brain may consist of a single, as yet uncharacterized isozyme and, contrary to several recent reports, is likely to be expressed at low levels.

Animals↗

PubMed1996

Pesticides: an important but underused model for the environmental health sciences.

Pesticides are high-volume, widely used, environmental chemicals and there is continuous debate concerning their possible role in many chronic human health effects. Because of their known structures, known rates of application, and the presence of a large occupationally exposed population, they are not only important in their own right but are ideal models for the effects of environmental chemicals on the population in general. For reasons that are not always clear, this potential has not been realized. These exposed populations represent an underused asset in the study of the human health effects of environmental contaminants. Chronic effects thought to involve pesticides include carcinogenesis, neurotoxicity, and reproductive and development effects. In this paper we attempt to summarize this concern and, relying to a large extent on studies in our own laboratory, to indicate the importance and present status of studies of the mammalian metabolism of pesticides and indicate the need for further use of this model. Aspects considered include the role of pesticides as substrates for xenobiotic-metabolizing enzymes such as cytochrome P450 and the flavin-containing monooxygenase and their role as inducers or inhibitors of metabolic enzymes. The interaction of pesticides with complex multienzyme pathways, the role of biological characteristics, particularly gender, in pesticide metabolism, and the special role of pesticides at portals of entry and in target tissues are also considered.

Abnormalities, Drug-Induced↗

PubMed1996

Piperonyl butoxide and acenaphthylene induce cytochrome P450 1A2 and 1B1 mRNA in aromatic hydrocarbon-responsive receptor knock-out mouse liver.

It has been suggested that acenaphthylene (ACN), piperonyl butoxide (PBO) and other methylenedioxyphenyl (benzodioxole) compounds can function as aromatic hydrocarbon-responsive receptor (AHR)-independent inducers of the cytochrome P450 (CYP) 1A2 in mouse liver. Although much indirect evidence has supported this hypothesis, direct proof was lacking until the present study. PBO and ACN were used to examine the expression of CYP1A1, CYP1A2 and CYP1B1 in mouse liver. These three CYP isozymes are included in the AHR battery of proteins. In this study, AHR knock-out mice were dosed intraperitoneally with PBO (200 mg/kg) or ACN (100 mg/kg). Induction of hepatic CYP1A1 by PBO or ACN was not detected by northern blots. In contrast, both CYP1A2 and CYP1B1 mRNA, constitutively expressed at low levels in this tissue, were induced by each compound in the livers of AHR knock-out mice. In addition, the use of heterogenous nuclear RNA reverse transcription-polymerase chain reaction procedures revealed that the transcriptional activities of CYP1A2 were increased by PBO and ACN treatments. These results show that AHR-independent pathway(s) can be involved in induction of CYP1A2 and CYP1B1.

Acenaphthenes↗

PubMed1995

Biphasic responses in synergistic interactions.

Synergistic reactions, as exemplified by the methylenedioxyphenyl (benzodioxole) insecticide synergists, are one of the more studied interactions between toxicants. This group of chemicals includes, in addition to synergists such as piperonyl butoxide, carcinogens such as safrole and isosafrole and many compounds occurring naturally in foods, such as myristicin and piperine. These compounds may function as cytochrome P450 substrates, inhibitors and/or inducers. The biphasic curve in cytochrome P450 activities following a single dose is the result of an initial inhibitory phase followed by a phase of induction, with an eventual return to baseline levels. Both inhibition and induction may be isozyme-specific and different isozymes may be involved in the two activities of the same chemical. Details of these activities are presented and their significance is discussed.

Animals↗

PubMed1995

Regulation of cytochrome P-450 isozymes CYP1A1, CYP1A2 and CYP2B10 by three benzodioxole compounds.

Three benzodioxole (BD) compounds were used to investigate the structural requirement for regulation of the cytochrome P450 isozymes, CYP1A1, CYP1A2 and CYP2B10, in mouse liver. Male mice (C57BL/6) were treated intraperitoneally for 3 days with 5-t-butyl-1,3-benzodioxole (t-BBD), 5-n-butyl-1,3-benzodioxole (n-BBD) and 5-(3-oxobutyl)-1,3-benzodioxole (o-BBD). t-BBD-induced liver microsomes showed the highest pentoxyresorufin O-dealkylation (PROD) activity, while o-BBD induced microsomes showed slightly higher activity in ethoxyresorufin O-deethylation (EROD), benzo[a]pyrene hydroxylation (BaP-OH) and acetanilide hydroxylation (Acet-OH) assays. In vitro enzyme inhibition assays showed that n-BBD inhibited EROD and Acet-OH activities more than either o-BBD or t-BBD, while PROD activity was evenly inhibited by all three compounds. Western and northern blots showed that CYP1A1 was not detectably induced by any of the three BD compounds. The levels of CYP1A2 protein and mRNA were increased in all three treated livers. In addition to CYP1A2 induction, t-BBD also induced the protein and mRNA for CYP2B10.

Animals↗

PubMed1995

Gender differences in hepatic expression of flavin-containing monooxygenase isoforms (FMO1, FMO3, and FMO5) in mice.

Hepatic flavin-containing monooxygenase (FMO) activity of microsomes from adult CD-1, Swiss-Webster, C57BL/6, and DBA/2 mice was found to be significantly higher in females than in males. Based on protein and mRNA levels in CD-1 mice, FMO forms responsible for the gender difference in FMO activity were FMO1 and FMO3. FMO1 expression was two to three times higher in female mice compared with males; FMO3, however, which was expressed at levels equivalent to FMO1 in female mice, was not detected in males. The expression of FMO5 was approximately equal in both sexes. FMO2 and FMO4 transcripts were not evident in hepatic mRNA from mice. Protein and mRNA levels appear to be coregulated with regard to gender-selective or gender-specific expression of FMO1 or FMO3, respectively. FMO5, which demonstrates no gender-selective expression in mice, may be regulated by different mechanisms. Examination of protein levels among Swiss-Webster, C57BL/6, and DBA/2 strains revealed a gender-dependent expression of FMO isozymes identical to the CD-1 strain.

Animals↗

PubMed1995

Pesticide-metabolizing enzymes.

Pesticides are known to function as substrates, inhibitors and inducers of drug-metabolizing enzymes, with the same compound frequently acting in more than one of these roles. Current studies of phase I metabolism of pesticides include cytochrome P450 (P450) and the flavin-containing monooxygenase (FMO), with particular reference to individual isozymes. In mouse liver, the level of FMO1 is gender dependent, FMO3 is gender specific, while FMO5 appears to be gender independent. The isozyme specificity of methylenedioxyphenyl synergists for induction of P450 in mouse liver involves P450s 1A1, 1A2 and 2B10, including a non-Ah receptor-dependent mechanism for 1A2 induction. The substrate specificity of mouse and human P450 and FMO isozymes is discussed.

Animals↗

PubMed1995

Metabolism of thioridazine by microsomal monooxygenases: relative roles of P450 and flavin-containing monooxygenase.

1. The metabolism of thioridazine by the flavin-containing monooxygenase (FMO) of mouse liver and several P450 isozymes was examined using microsomes, purified FMO, and expressed P450 isozymes. Metabolites were identified by hplc. 2. Thermal inactivation and antibodies to NADPH P450 reductase were used to selectively inactivate FMO and P450 respectively. Inactivation of FMO by heat-treatment reduced the formation of thioridazine-N-oxide and northioridazine, whereas inactivation of P450 resulted in decreased amounts of thioridazine-2-sulphoxide, northioridazine, and thioridazine-5-sulphoxide. 3. Liver microsomes from mouse induced with phenobarbital, 3-methylcholanthrene, or acetone were compared with control microsomes. Phenobarbital induction resulted in increased formation of all metabolites except thioridazine-N-oxide, while retaining a general metabolic profile similar to that achieved with control microsomes. Neither 3-methylcholanthrene nor acetone induction had any effect on the in vitro metabolism of thioridazine. 4. FMO purified from mouse liver produced thioridazine-N-oxide as the major metabolite. 5. Preliminary experiments with commercially prepared microsomes made from cells expressing recombinant human liver P450 2D6 and 3A4 suggested that thioridazine is metabolized by 2D6 but not 3A4.

Animals↗

PubMed1994

Effects of P450 inhibition and induction on the olfactory toxicity of beta,beta'-iminodipropionitrile (IDPN) in the rat.

In addition to the neurotoxic effects of beta,beta'-iminodipropionitrile (IDPN) which have been previously reported by other investigators, the olfactory toxicity of this compound has recently been uncovered in this laboratory. Due to the apparently conflicting observations that the IDPN-induced lesion in the olfactory mucosa is very focal in nature (suggesting site-specific activation) and the observation by other investigators that the behavioral effects of IDPN appear to be due to the parent compound, we initiated studies into the possible role of the cytochrome P450 enzymes in the olfactory toxicity of IDPN. Immunohistochemical studies with antibodies raised against several different P450 isoforms revealed good correlation between IDPN-induced olfactory mucosal degeneration and the localization of a protein immunoreacting with an antibody to P450 2E1. Enzymatic studies revealed that there is approximately five-fold more p-nitrophenol hydroxylation activity in the olfactory mucosa than in the liver on a per milligram microsomal protein basis. Administration of 1% acetone in the drinking water increased the levels of olfactory mucosal 2E1, and the increase in enzyme levels corresponded to increased olfactory toxicity of IDPN; inhibition of P450 activities with either metyrapone or carbon tetrachloride eliminated or significantly decreased the olfactory toxicity of IDPN, respectively. These studies suggest a role for cytochrome P450, specifically the 2E1 isoform, in the activation of IDPN within the nasal mucosa.

Acetone↗

PubMed1993

Regulation of cytochrome P-450 isozymes by methylenedioxyphenyl compounds.

Regulation of cytochrome P-450 isozymes 1a-1, 1a-2, and 2b-10 by methylenedioxyphenyl compounds was studied by measuring levels of mRNA, protein, and enzyme activity in hepatic tissue from C57BL/6 (Ah+) and DBA/2 (Ah-) mice dosed with isosafrole (ISO) or piperonyl butoxide (PBO). Increases in 1a-2 and 2b-10 protein were observed for ISO and PBO in both strains of mice, suggesting an Ah receptor-independent mechanism for induction of these isozymes; 1a-1 induction, however, was seen only in C57 mice. Piperonyl butoxide was the more potent inducing agent in both strains. In C57 mice treated with five dose levels of PBO, induction of 1a-1 mRNA, protein, and enzyme activity were seen at doses equal to or greater than 104 mg/kg, but were not detected at lower doses. With isosafrole, induction of 1a-1 mRNA was observed only at the highest dose tested (400 mg/kg); however, neither 1a-1 protein nor increased enzymatic activity was seen at this dose. Dose-response studies showed maximum inducible levels for 1a-2 and 2b-10 protein, beyond which the mRNAs continued to increase while the protein levels remained constant.

Animals↗

PubMed1992

The flavin-containing monooxygenase in mouse lung: evidence for expression of multiple forms.

The flavin-containing monooxygenase (FMO) was purified from mouse lung microsomes. On SDS-PAGE, the purified enzyme separated as two bands, a major band of 58,000 daltons and a minor band of 59,000 daltons. Antibodies to mouse liver FMO cross-reacted with both bands in the purified preparations, whereas antibodies to rabbit lung FMO cross-reacted only with the major band. In microsomal preparations the major band was recognized by both antibodies, but neither antibody detected the minor band in microsomes. A cDNA encoding the pig liver FMO hybridized with mRNA isolated from mouse liver, kidney, and lung, whereas cDNA encoding the rabbit lung FMO hybridized only with mouse lung and kidney mRNA. Thermal stability studies showed that the FMO preparation purified from mouse lung consisted of a heat-stable and a heat-labile component. The heat-labile component of lung FMO was inhibited competitively by imipramine, whereas the heat-stable component was insensitive to the presence of imipramine. Immunoprecipitation of purified mouse lung FMO with anti-rabbit lung FMO completely removed the protein band reactive to anti-rabbit lung FMO while leaving reactivity to anti-liver FMO. The catalytic and immunochemical differences seen between FMO from rabbit lung and mouse lung appear to result from the expression of at least two forms of FMO in the mouse lung, one similar to the rabbit pulmonary form and one similar to the major mouse liver form of FMO.

Animals↗

PubMed1991

The flavin-containing monooxygenase of mouse kidney. A comparison with the liver enzyme.

Flavin-containing monooxygenase (FMO; EC 1.14.13.8) was purified from mouse kidney microsomes and compared to that isolated from mouse liver microsomes. The purified enzymes from kidney and liver appeared as a single band on sodium dodecyl sulfate-polyacrylamide gel electrophoresis with an apparent molecular weight of 58,000 daltons. On wide range (pH 3.5 to 9.0) isoelectric focusing, FMOs from kidney and liver resolved as a single band with an isoelectric point of 8.2. The enzymes from both kidney and liver have a pH optimum of 9.2. Thiobenzamide-S-oxidation catalyzed by both enzymes was sensitive to inhibition by the competitive inhibitors thiourea and methimazole. At an n-octylamine concentration of 3 mM, thiobenzamide-S-oxidation by the kidney FMO was increased by 122% and that by the liver FMO by 148%. Km and Vmax values were determined and compared between the two tissue enzymes for xenobiotic substrates containing nucleophilic nitrogen, sulfur or phosphorus atoms. In general, for most FMO substrates, Km and Vmax values were similar between kidney and liver FMO with only a few exceptions. The Km and Vmax values for fenthion for kidney were only half of those observed for liver FMO. Fonofos was unusual in having a low Km as well as a low Vmax for both tissue enzymes. Anti-sera developed to the FMO purified from kidney and liver showed cross-reactivity with each purified enzyme as well as with a protein with the same molecular weight as the purified FMO present in both kidney and liver microsomes. These bands showed equal intensity based on an equivalent amount of protein. Analysis of kidney and liver FMO by proteolytic digestion followed by visualization of peptides by silver staining or immunoblotting showed only minor differences between the enzymes of the two tissues. The amino acid composition of both mouse kidney and liver FMO was low in methionine and histidine and rich in aspartate/asparagine, glutamate/glutamine, leucine, valine and glycine. Edman degradation of the purified mouse kidney and liver FMO provided a single amino acid sequence of the NH2-terminus. This sequence matched exactly with the cDNA-deduced sequence reported for the pig and rabbit liver beginning with the fifth amino acid and contained the highly conserved FAD-binding domain Gly-X-Gly-X-X-Gly, commonly found in a number of other FAD-binding proteins. These studies indicate that the renal and hepatic forms of FMO from mouse are similar enzymes that are immunologically related and show only a few minor differences.

Amino Acid Sequence↗

PubMed1991

The effect of detergents on the purified flavin-containing monooxygenase of mouse liver, kidney and lungs.

1. The effect of various commonly used membrane solubilizing detergents on the activity of the microsomal xenobiotic metabolizing enzyme, the flavin-containing monooxygenase (FMO) purified from mouse liver, kidney and lungs was determined. 2. Regardless of the type of detergent used, the effect on the enzyme activity was variable depending on the type of substrate used. 3. Emulgen 911 concentrations of up to 10% had very little effect on thiobenzamide-S-oxidation by liver, kidney or lung FMO. 4. While Emulgen 911 increased substrate dependent NADPH oxidation rate by thiourea and thioacetamide, it drastically reduced the activity toward the organophosphorous compounds, disulfoton, fenthion, fonofos and phorate at low concentrations. 5. Activities of fenthion, phorate and fonofos were decreased by 80, 65 and 55% by the inclusion of 0.25% Emulgen 911 in the assay mixture. 6. This decline in FMO activity for phorate was evident regardless of the type of detergent used. In contrast, thiourea dependent NADPH oxidation rate in the presence of various detergents was variable. 7. Thiourea oxidation rate was decreased by cholate and Zwittergent 3-12, whereas it was increased in the presence of Emulgen 911, Triton X-100 and Tween 20. 8. This study shows that before FMO activity is determined in the presence of detergents their effects should be carefully evaluated.

Animals↗

PubMed1990

Differences in induction of hepatic cytochrome P450 isozymes by mice in eight methylenedioxyphenyl compounds.

Eight methylenedioxyphenyl (MDP) compounds were examined for their ability to induce cytochrome P450 (P450) in mouse liver. Induction by safrole, isosafrole, and dihydrosafrole was studied in both C57BL/6N (Ah-responsive) and DBA/2N (Ah-nonresponsive) male mice after IP administration of 200 mg/kg/day MDP compound for 3 days. Hepatic P450 content, ethylmorphine N-demethylase, ethoxy-resorufin O-deethylase, and acetanilide hydroxylase activities were induced to the same extent in both strains of mice. Benzo(a)pyrene hydroxylase activity, however, was not induced in either C57 or DBA mice. The similarity of results in both strains of mice indicated induction of these P450 isozymes by these three MDP compounds is not mediated by the Ah receptor. Induction of P450 by butylbenzodioxole (n-butyl-BD), tertiarybutylbenzodioxole (t-butyl-BD), methylbenzodioxole (methyl-BD), nitrobenzodioxole (nitro-BD), and bromobenzodioxole (bromo-BD) was examined only in C57BL/6N mice. Methyl-BD, nitro-BD, and bromo-BD did not induce hepatic microsomal proteins or selected P450 monooxygenase activities. In contrast, n-butyl-BD, and t-butyl-BD induced P450 content, ethylmorphine N-demethylase, acetanilide hydroxylase, and ethoxyresorufin O-deethylase activities. Benzo(a)pyrene hydroxylase was not induced by any of the treatments. Induction of these P450 activities is consistent with induction of P450 IIB1 and P450 IA2, but not induction of P450 IA1. Western blot analysis with antibodies to P450 isozymes induced with either phenobarbital (Pb) or 3-methylcholanthrene (3-MC) confirmed that both IIB1 and IA2 were induced, but that IA1 was not induced.

Animals↗