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Results for “Cytochrome P-450 CYP2B1”

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At least 19 recordsLinked to original sources

PubMed1992

Anti-P450lpr antiserum inhibits specific monooxygenase activities in LPR house fly microsomes.

Monooxygenase activity in microsomes from the LPR strain of house fly (Musca domestica L.) was inhibited by anti-P450lpr, and antiserum specific for house fly cytochrome P450lpr. Anti-P450lpr did not inhibit house fly cytochrome P450 reductase or rat cytochrome P450 monooxygenase assays, consistent with specific inhibition of P450lpr. Anti-P450lpr inhibited the ability of cytochrome P450 reductase to reduce carbon monoxide treated LPR microsomal cytochrome P450, up to 49% of the total, showing that inhibition of cytochrome P450 reduction is the major mechanism of inhibition. Anti-P450lpr inhibited 98% of methoxyresorufin-O-demethylase activity and all the benzo(a)pyrene hydroxylase activity in LPR microsomes, but none of the pentoxyresorufin-O-dealkylase activity. The antiserum partially inhibited ethoxyresorufin-O-dealkylase and ethoxycoumarin-O-dealkylase activity. These results demonstrate that methoxyresourfin-O-demethylase activity and benzo(a)pyrene hydroxylase activity are characteristic substrates for P450lpr activity in the LPR strain of house fly.

7-Alkoxycoumarin O-Dealkylase↗

PubMed1992

Suppressive effect of interleukin-1 on pulmonary cytochrome P450 and superoxide anion production.

Interleukin-1 has been shown to prolong the survival of rats exposed to lethal concentrations of oxygen. This oxygen tolerance has been attributed by some workers to an increase of manganese superoxide dismutase. We report here that the administration of interleukin-1 to male adult rats results in (i) significant decrease of pulmonary cytochrome P450 at 24 and 72 hours, (ii) decrease of P450 IIB1 mRNA at 24 and 72 hours and (iii) significant decrease of superoxide anion generation from pulmonary microsomes isolated from treated rats. To the best of our knowledge, this is the first report to demonstrate these effects of interleukin-1 on pulmonary P450 and its oxidase activity (O2- generation). On the basis of these results and several earlier reports in which various P450 depressants have been shown to depress superoxide production from microsomes and to prolong the lives of rodents in hyperoxia, we conclude that oxygen tolerance induced by interleukin-1 administration is likewise mediated, at least in part, by reduced generation of superoxide anion from cytochrome P450 monooxygenase system.

Animals↗

PubMed1992

Inhibition and induction of cytochrome P450 2B1 in rat liver by promazine and chlorpromazine.

Phenothiazine tranquilizers have been associated with pharmacokinetic drug interactions in man. In this study the in vivo and in vitro effects of the clinically important phenothiazines promazine (PZ) and chlorpromazine (CPZ) on drug oxidations catalysed by specific cytochrome P450 (P450) enzymes were investigated in the rat. In vitro, the two drugs were relatively ineffective inhibitors of constitutive P450 activities, but were inhibitory toward the principal phenobarbital-inducible P450 2B1 and, to a lesser extent, P450 1A1. Administration of PZ and CPZ to male rats did not markedly influence the total microsomal P450 content of the liver. However, the quantitatively important male-specific P450 2C11 was down-regulated by CPZ and concomitant induction of P450 2B1 and associated 7-pentylresorufin O-depentylase activity were noted. A small increase in the activity of microsomal 7-ethylresorufin O-deethylase was also observed following administration of both drugs to rats, suggesting induction of P450 1A1/2. Considered together, it is apparent that the two phenothiazines are preferential inhibitors and inducers of P450 2B1 in rat liver. Drug interactions in humans involving phenothiazines may reflect a combined effect of induction and inhibition processes as well as down-regulation of other P450s, such as that produced by CPZ on P450 2C11.

Animals↗

PubMed1992

Benzo[e]pyrene elicits changes in the biochemical activities and chromatographic behavior of murine hepatic cytochromes P-450 that are distinct from those induced by 2,3,7,8-tetrachlorodibenzo-p-dioxin.

The objective of this study was to examine the potential for a specific ligand of carcinogen binding protein (CBP) to induce changes in the overall character of hepatic microsomal cytochromes P-450 (P450) and to compare potential changes with those induced by an Ah receptor ligand. Benzo[e]pyrene (BeP) was previously shown to bind CBP with high affinity and Ah receptor with low affinity. In contrast, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) binds Ah receptor avidly and CBP weakly. Hepatic microsomes were prepared from C57BL/6J (B6) and DBA/2J (D2) mice treated with corn oil, BeP or TCDD. Relative to corn oil controls, pretreatment of B6 mice with BeP or TCDD increased the nmol P450/mg microsomal protein content 26 and 28%, respectively. In D2 mice, nmol P450/mg microsomal protein was increased 23% in the BeP pretreatment, while TCDD pretreatment had no effect relative to the corn oil controls. For the O-alkyl ethers of resorufin, rates of metabolism (per nmol P450) were affected differently in B6 and D2 by BeP pretreatment. Pentoxyresorufin O-dealkylase activity was reduced to 44% of control activity in B6 mice and increased 39% relative to controls in D2 mice. BeP pretreatment had no effect on ethoxyresorufin O-dealkylase activity in B6 mice, while this activity was decreased to 58% of controls in D2 mice. Additionally, benzyloxyresorufin O-dealkylase activity was reduced to 65% of control levels in B6 mice and not affected in D2 mice. Methoxyresorufin O-dealkylase activity was reduced in both strains to an average of 55% of control values. As expected, TCDD pretreatment resulted in increases of all O-dealkylations measured in both strains of mouse. For both inbred strains of mouse, anion exchange chromatography revealed a P450 peak associated with BeP pretreatment that was not present in chromatograms generated with corn oil or TCDD pretreatments. Results of enzyme linked immunosorbant assays also indicated that the pattern of P450 isoenzyme expression associated with BeP pretreatment was distinct from that associated with TCDD pretreatment. Overall, these data show that treatment with a specific ligand of CBP induces changes the biochemical activities and chromatographic behavior of P450 isozymes in murine hepatic microsomes. Moreover, they indicate that changes in P450 occurring after treatment with a CBP ligand are distinct from those changes that are associated with treatment with an Ah receptor ligand (TCDD). Differences between B6 and D2 strains suggest that the hepatic P450 changes occurring in response to pretreatment with a CBP ligand may be influenced by the presence of Ah receptor.

Animals↗

PubMed1992

Mechanism of antimutagenicity of wheat sprout extracts.

In this paper we have demonstrated that wheat sprout extract, which has been shown to be antimutagenic towards benzo[a]pyrene (BP), reduced formation of BP metabolites by hepatic microsomes of either benzo[a]pyrene- or phenobarbital-treated rats as analyzed in high-pressure liquid chromatography (HPLC). Comparing the time dependence of profiles and values of BP metabolites, formed in experiments in which the same dose of wheat sprout extract was added to the incubation medium, it has been observed that the later this extract was added the higher the percent of BP that was metabolized. In a bacterial test (cytochrome P450 induction assay) high inhibition of mutagenic activity of cyclophosphamide and ethidium bromide, in the presence of wheat sprout extract, reflected decreased levels of cytochromes P4502B1 and P4501A1 respectively. Decreased levels of both cytochromes P4501A1 and P4502B1 were also observed in either wheat sprout extract- or wheat sprout extract plus benzo[a]pyrene-treated rats. In all of these studies it has been observed that wheat sprout extract displays much more affinity for cytochrome P4501A1 than for the P4502B1 form. On the other hand the wheat sprout extract had higher affinity for carcinogen binding protein (4S protein) than for the aryl hydrocarbon receptor. The strong inhibition of BP mutagenicity and BP metabolism with non-chlorophyllic wheat sprout extract suggests that chlorophyll is not the main compound responsible for the antimutagenic activity of wheat sprout extract. The similar chromatographic behavior of both the main inhibitory fraction, obtained from wheat sprout extract, and two pure glycosides of apigenin--shaftoside, purified from wheat sprout extract and synthetic swertisine--suggests that antimutagenic compound(s) contained in the wheat sprout extract belong(s) to this family of flavonoids.

Animals↗

PubMed1992

Absence of interactions on hepatic retention and 7-ethoxyresorufin-O-deethylation activity after co-administration of 1,2,3,7,8-pentachlorodibenzo-p-dioxin and 2,4,5,2',4',5'-hexachlorobiphenyl.

Interactions between 1,2,3,7,8-pentachlorodibenzo-p-dioxin (PnCDD) and 2,4,5,2',4',5'-hexachlorobiphenyl (HxCB) on hepatic retention of PnCDD and on cytochrome P450 related enzyme activities were studied in male C57BL/6J mice. Animals received 8 nmol PnCDD/kg orally, alone or in combination with 1-416 mumol HxCB/kg. Co-administration of HxCB did not alter the hepatic retention of PnCDD or the 7-ethoxyresorufin-O-deethylation (EROD) activity induced by PnCDD as observed after 1 week. A small antagonistic effect on total cytochrome P450 content and 7-pentoxyresorufin-O-depentylation (PROD) activity was observed at a dose of 8 nmol PnCDD/kg and 1 mumol HxCB/kg. Furthermore, a significant induction of PROD activity by PnCDD was found. This was not expected, since PROD activity is considered to be a specific marker for CYP2b related enzyme activity and this type of cytochrome P450 is not induced by polychlorinated dibenzo-p-dioxins such as PnCDD. It is concluded that, under these short-term experimental conditions, no toxicokinetic basis was found to explain the antagonistic effects on hepatic cytochrome P450 related activities observed in the present study or in other studies.

Animals↗

PubMed1992

Liver microsomal alkoxyphenoxazone O-dealkylases of white Leghorn chickens: response to mixed function oxidase inducers.

1. The cytochrome P-450 substrates, methoxy-, ethoxy-, pentoxy- and benzyloxyphenoxazone were investigated in liver microsomes of phenobarbital- and beta-napththoflavone-induced White Leghorn chickens and compared to the rat mammalian model. 2. Thirty-two-fold increases in benzyloxyphenoxazone O-dealkylase and 27-fold increases in ethoxyphenoxazone O-dealkylase activities were observed in beta-naphthoflavone-treated chickens compared to only an 18-fold increase in ethoxyphenoxazone O-dealkylase activity in beta-naphthoflavone-treated rats. 3. Decreases in pentoxy- and benzyloxyphenoxazone O-dealkylase activities were observed in phenobarbital-treated chickens in contrast to increases of 197-fold in pentoxy- and 98-fold in benzyloxyphenoxazone O-dealkylases in the phenobarbital-treated rats.

Animals↗

PubMed1992

Mechanisms of glucagon-induced increases in rates of cytochrome P450-dependent pentoxyphenoxazone O-depentylation in cultured rat conceptuses.

Inclusions of glucagon (1.0 or 2.0 microM, final concentrations) in the media of cultured whole rat conceptuses resulted in concentration-dependent increases in measured rates of O-depentylation of pentoxyphenoxazone in cell-free preparations of conceptal tissues. Enzymic activities were assayed 24 h after initial exposure of the conceptuses to glucagon on day 10 of gestation. Glucagon elicited increases in tissue levels of cAMP that were parallel to those produced by 3-isobutyl-1-methylxanthine over the same time period. Tissue cAMP levels were maximal after 2 h, rapidly returned to control levels and were also equal to background levels in controls after the 24 h culture period. Dibutyryl cAMP, 3-isobutyl-1-methylxanthine, theophylline, and RO201724, a cAMP-selective phosphodiesterase inhibitor, each produced 75 to 100% increases in O-dealkylase activity. Dibutyryl cGMP and two phosphodiesterase inhibitors, enoximone (cGMP-inhibited) and zaprinast (cGMP-specific), each failed to produce statistically significant increases in O-depentylase activity. The O-depentylase was tentatively identified as a conceptus-specific P450 cytochrome that is synthesized predominantly in tissues of the visceral yolk sac. The results indicated that glucagon may upregulate a unique, xenobiotic-biotransforming P450(s) via a long-term mechanism(s) specifically involving tissue cAMP.

Animals↗

PubMed1992

Role of residue 478 as a determinant of the substrate specificity of cytochrome P450 2B1.

Two allelic variants and eight site-directed mutants of cytochrome P450 2B1 differing at residue 478 have been expressed in COS cells and assayed for androstenedione hydroxylase activities. The 478Gly and 478Ala variants and five mutants (Ser, Thr, Val, Ile, and Leu) exhibited 16 beta-OH:16 alpha-OH ratios ranging from 0.7 to 9.3, whereas the Pro, Glu, and Arg mutants were expressed but inactive. The seven samples active toward androstenedione also exhibited testosterone 16 beta-OH:16 alpha-OH ratios ranging from 0.4 to 2.3. With both steroids, the Gly variant had the highest 16 beta-hydroxylase activity, and the 16 beta-OH:16 alpha-OH ratio increased with the size of aliphatic size chains (Ala, Val, and Ile/Leu). The highest ratio of androgen 15 alpha:16-hydroxylation was observed with the Ser mutant. On the basis of previous work indicating decreased susceptibility of the 478Ala variant in liver microsomal and reconstituted systems to inactivation by chloramphenicol analogs, methodology was refined for monitoring enzyme inactivation in COS cell microsomes. The Gly and Ala variants were inactivated by chloramphenicol with similar rate constants, whereas the Ser and Val mutants were inactivated more slowly, and the Leu mutant was refractory. Only the Gly variant was inactivated by the chloramphenicol analog N-(2-p-nitrophenethyl)chlorofluoroacetamide. Thus, the side chain of residue 478 appears to be a major determinant of enzyme inactivation as well as of androgen hydroxylation.(ABSTRACT TRUNCATED AT 250 WORDS)

Alleles↗

PubMed1992

Chloroform inhibits the development of diethylnitrosamine-initiated, phenobarbital-promoted gamma-glutamyltranspeptidase and placental form glutathione S-transferase-positive foci in rat liver.

In this study we demonstrate that chloroform, a widely used industrial solvent, a medicinal chemical and a common drinking water contaminant, reduces the number of detectable preneoplastic enzyme-altered foci [gamma-glutamyltranspeptidase-positive (GGT+) and placental form glutathione S-transferase-positive (GST-P+)] in the liver of male Fischer 344 rats. The animals were given a partial hepatectomy and 18 h later received a single oral dose of either 0.5 mmol/kg diethylnitrosamine (DENA) or saline. Two weeks later, groups of 12 animals were started on drinking water containing phenobarbital with varying concentrations (200-1800 mg/l) of chloroform fro 12 weeks. Treated and control animals were killed and the number and the volume of GGT+ and GST-P+ expressing hepatic foci were tabulated. The numbers of foci per unit volume (and per unit area), the percent focal volume and the focal liver were reduced by chloroform in a dose-dependent manner. The mean focal volume was not influenced by chloroform. A plausible explanation for these results could be that chloroform exerts its focal inhibitory effect either by selectively killing the putative initiated cells, by retarding the inherent growth rate of enzyme-altered cells or by reducing the effectiveness of the promoter, phenobarbital. The available evidence suggests that the first hypothesis is the most likely explanation for these observations. These results are consistent with earlier studies showing that chloroform inhibits tumorigenesis in rodents.

Analysis of Variance↗

PubMed1992

Potentiation of bromobenzene-induced pneumotoxicity by phenobarbital as determined by bronchoalveolar lavage fluid analysis.

Bromobenzene produces pulmonary, renal and hepatic damage in the rat. Phenobarbital potentiates bromobenzene-induced hepatotoxicity. Studies were initiated to determine if phenobarbital potentiates the pulmonary damage produced by bromobenzene. In a dose ranging study, adult male rats were treated daily for 4 days with phenobarbital (80 mg/kg, ip) and on the fifth day were dosed with 0, 2, 3, or 4 mmoles/kg, ip, bromobenzene. In a larger study phenobarbital was given for 4 days (80 mg/kg, ip), and bromobenzene (3.3 mmoles/kg, ip) was given on the fifth day. Pulmonary damage was assessed 24 hours later in the first study and 12 hours later in the second study by bronchoalveolar lavage fluid analysis (BALF), microsomal mixed function oxidase measurements and histopathological evaluations. BALF biochemical markers employed were gamma-glutamyl transpeptidase (GGT), lactate dehydrogenase (LDH) and total protein. Phenobarbital treatment greatly enhanced bromobenzene-induced GGT and LDH release into the lavage fluid in a dose-dependent manner. Phenobarbital treatment increased microsomal 7-O-dealkylation of both ethoxy- and pentoxyresorufin in the liver without affecting these activities in the lung. Bromobenzene treatment decreased the hepatic microsomal dealkylation of decreased the hepatic microsomal dealkylation of pentoxyresorufin in a dose-dependent manner. Since known rat pulmonary P450 isozymes have been reported to be insensitive to phenobarbital induction, it may be that the toxicity is due to transport of a reactive metabolite(s) formed in the liver to the lung or bromobenzene is activated by some other pulmonary P450 isozyme responsive to phenobarbital.

Analysis of Variance↗

PubMed1992

Two monoclonal antibodies recognizing different epitopes on rat cytochrome IIB1 react with human IIE1.

To identify human cytochromes P450 (P450) in the CYP2B subfamily, 14 human liver microsomal samples were screened by immunoblots developed with monoclonal antibodies that recognized seven distinct epitopes on rat IIB1. Two of these antibodies recognized a protein in all of the samples. This protein was termed P450BE. Using video-imaging densitometry, the levels of P450BE were determined and compared with levels of other P450s. An excellent correlation was seen (r = 0.87) between P450BE and human IIE1. However, rat IIE1 did not react in immunoblot and enzyme-linked immunosorbant assays with the two anti-rat IIB1 monoclonal antibodies. As previously observed, the levels of IIE1 in the samples correlated well (r = 0.88) with the ability of these human liver microsomes to N-demethylate N-nitrosodimethylamine. The levels of P450BE also correlated well (r = 0.91) with the ability of the microsomes to N-demethylate N-nitrosodimethylamine. In addition, excellent correlations were obtained when the levels of P450BE and IIE1 were compared with the ability of the microsomes to O-deethylate ethoxycoumarin (r = 0.87 and r = 0.85, respectively). To identify the protein recognized by the anti-rat IIB1 antibodies, P450BE was purified from microsomes prepared from human liver D. Amino-terminal amino acid sequence analyses of P450BE revealed that the 18-amino acid sequence obtained matched the corresponding sequence of human IIE1. In addition, purified human IIE1 and P450BE migrated with the same apparent molecular weight in polyacrylamide gels. Furthermore, proteolytic maps of P450BE and IIE1, generated with two proteases, were found to be identical. Sequence alignments and antigenicity calculations identified three regions of rat IIB1 as likely candidates for the epitopes shared in common with human IIE1. In conclusion, this study indicates that caution must be taken when interpreting the results of immunochemical assays when species lines are crossed.

Adolescent↗

PubMed1992

Sequence of a novel cytochrome CYP2B cDNA coding for a protein which is expressed in a sebaceous gland, but not in the liver.

The major phenobarbital-inducible rat hepatic cytochromes P-450, CYP2B1 and CYP2B2, are the paradigmatic members of a cytochrome P-450 gene subfamily that contains at least seven additional members. Specific oligonucleotide probes for these genomic members of the CYP2B subfamily were used to assess their tissue-specific expression. In Northern-blot analysis a probe specific to gene 4 (which is designated now as CYP2B12) hybridized to a single mRNA present in the preputial gland, an organ which is used as a model for sebaceous glands, but did not hybridize to mRNA isolated from the liver or from five other tissues of untreated or Aroclor 1254-treated rats. The cDNA sequence for the CYP2B12 RNA was determined from overlapping cDNA clones and contained a long open reading frame of 1476 bp. The nucleotide sequence of the CYP2B12 cDNA was 85% similar to the sequence of the CYP2B1 cDNA in its coding region and was different from any CYP2B cDNA characterized until now. The cDNA-derived primary structure of the CYP2B12 protein contains a signal sequence for its insertion into the endoplasmic reticulum and the putative haem-binding site characteristic of cytochromes P-450. A part of the potential haem pocket of CYP2B12 was identical with a similar structure in a bacterial protocatechuate dioxygenase. In immunoblot analysis of preputial-gland microsomes, antibodies against CYP2B1 recognized a single abundant protein with a lower apparent molecular mass than that of CYP2B1. Our results demonstrate that the CYP2B12 protein has the potential to be enzymically active and are the first demonstration that a member of the CYP2B subfamily is expressed exclusively and at high levels in an extrahepatic organ.

Amino Acid Sequence↗

PubMed1992

Effects of the oxazolidinedione anticonvulsants trimethadione and dimethadione and the barbiturate homolog 5,5-dimethylbarbituric acid on N-nitrosodiethylamine-initiated renal and hepatic carcinogenesis in the F344/NCr rat.

The oxazolidinedione anticonvulsant trimethadione (3,5,5-trimethyl-2,4-oxazolidinedione, TMO) as well as its major metabolite, dimethadione (5,5-dimethyl-2,4-oxazolidinedione, DMO), and a structural analog from the barbiturate series, 5,5-dimethylbarbituric acid (DMB), were fed to F344/NCr male rats previously given a single initiating injection of N-nitrosodiethylamine (NDEA). The known promoter, phenobarbital (5-ethyl-5-phenylbarbituric acid, PB), was employed in this study as a positive control. At dosage levels equimolar to 500 ppm PB, none of the three compounds promoted development of hepatocellular adenomas or carcinomas, in contrast to PB. The two oxazolidinedione analogs and DMB caused minimal or no induction of cytochrome P450 isozyme 2B1 (CYP2B1)-mediated alkoxyresorufin O-dealkylase activities following short-term (2 weeks) feeding to separate groups of 6-week-old male F344/NCr rats, in contrast to the dramatic induction caused by PB. Promotion of neither thyroid nor renal neoplasia was observed following prolonged feeding of any of the tested compounds, although a significantly higher frequency of premalignant renal cortical tubular lesions (dysplasias) was seen in rats exposed to TMO following NDEA initiation than in those treated with NDEA alone. These studies provide important additional data on structure/liver tumor promoting activity relationships, and yield further evidence that within this group of structurally related anticonvulsants, it is possible to separate anticonvulsant activity from tumor promoting activity in the rat liver.

Animals↗

PubMed1992

Tissue-specific expression, induction, and inhibition through metabolic intermediate-complex formation of guinea pig cytochrome P450 belonging to the CYP2B subfamily.

The tissue-specific expression and induction of P450GP-1, a constitutive form of cytochrome P450 of the guinea pig classified into the CYP2B subfamily, were studied. Prior to these studies, a P450 form (P450GP-1 PB) was purified from phenobarbital-treated guinea pigs and the properties were compared with those of the P450GP-1. This form was judged to be the same as P450GP-1 existing in untreated animals by comparisons of their N-terminal amino acid sequences, peptide maps, and affinities toward anti-P450GP-1 antibody. Immunostaining of P450GP-1 revealed that the lung and small intestine as well as the liver of untreated guinea pigs contain P450GP-1, while none or only small amounts of this P450 form were observed in the kidney, heart, spleen, urinary bladder, and testis. The amount of liver P450GP-1 protein expressed in untreated guinea pigs was estimated to be 19.4% of the total cytochrome P450 and this form was increased 1.7-fold by phenobarbital treatment. Similarly, intestinal P450GP-1 was increased by phenobarbital treatment. However, lung P450GP-1 was not increased by the treatment. It was also observed that the liver P450GP-1 is induced with SKF-525A to the same extent as with phenobarbital. On the other hand, dexamethsone, p,p'-dichlorodiphenyltrichloroethane, and isosafrole showed no or only a weak ability to increase the liver P450GP-1 content. The drug-metabolizing activities in the liver microsomes of SKF-525A-pretreated guinea pigs were lower than those in phenobarbital-treated animals, although the P450GP-1 protein was induced equally by these treatments. The low activities of SKF-525A-treated animals in the drug metabolisms were attributed to the formation of the metabolic-intermediate complex between P450GP-1 and SKF-525A metabolite. These results permitted us to conclude that the tissue specificity in the expression of guinea pig P450 belonging to the CYP2B subfamily and the inducibility with chemicals are similar to those of rat CYP2B1, although the constitutive expression of guinea pig liver P450GP-1 is much higher than that of CYP2B1.

Amino Acid Sequence↗

PubMed1992

Resistance of murine lung tumors to xenobiotic-induced cytotoxicity.

Studies were performed to test the hypothesis that urethane-induced murine lung tumors exhibit xenobiotic resistance and alterations in pulmonary cytochrome P-450 enzymes. 1,1-Dichloroethylene, naphthalene, and paraquat were administered to tumor-bearing and control mice to elicit acute lung cytotoxicity, and responses were evaluated in tumors (papillary and solid), uninvolved surrounding tissue, and untreated control lung. 1,1-Dichloroethylene (125 mg/kg, i.p.) and naphthalene (225 mg/kg, i.p.) caused preferential necrosis of Clara cells in control lungs and uninvolved tissue of tumor-bearing lungs. In contrast, papillary and solid tumors were both resistant to 1,1-dichloroethylene-induced cytotoxicity. Paraquat (10, 20 mg/kg, i.v.) elicited Clara cell damage in control lungs and uninvolved lung tissue of tumor-bearing mice, with minor disruption of the alveolar epithelium. Neither papillary nor solid tumors sustained any apparent cell damage from paraquat. Immunoblots of P-450 enzymes confirmed constitutive expression of CYP2B1 in control lung and uninvolved lung tissue of tumor-bearing mice, but this P-450 enzyme was not detected in either adenomas or carcinomas. Lung CYP1A1 was inducible by beta-naphthoflavone in non-tumor-bearing mice and uninvolved tissue of tumor-bearing mice; however, inducibility was decreased in adenomas and abolished in carcinomas. These results demonstrate resistance of lung tumor cells to chemically induced cytotoxicity and diminished expression of cytochrome P-450 enzymes in tumors.

Animals↗

PubMed1992

A pleiotropic response to phenobarbital-type enzyme inducers in the F344/NCr rat. Effects of chemicals of varied structure.

The effects of a number of phenobarbital-type inducers on selected drug-metabolizing enzymes in male F344/NCr rats were determined by measuring specific catalytic activities and/or by measuring the levels of RNA which hybridize with specific probes for the corresponding genes. The effects on hepatic CYP2B1 were assessed by measuring the levels of CYP2B1-specific RNA and benzyloxyresorufin O-dealkylase and testosterone 16 beta-hydroxylase activities. Levels of CYP3A were monitored by measuring the rate of hydroxylation of testosterone at the 6 beta-position. Microsomal epoxide hydrolase activity was determined by measurement of cellular RNA specific for this form and by assaying the hydrolysis of benzo[a]pyrene-4,5-oxide. UDP-glucuronyltransferase activity was assayed by measuring the glucuronidation of 3-hydroxybenz[a]anthracene. Levels of glutathione S-transferase Ya/Yc were measured by quantifying total cellular RNA coding for the proteins. When male F344/NCr rats were administered various doses of phenobarbital or dichlorodiphenyltrichloroethane (DDT), strong correlations between the induction of CYP2B1 and the induction of epoxide hydrolase or UDP-glucuronyltransferase activities were observed. Treatment of rats with barbiturates, hydantoins, halogenated pesticides such as DDT or alpha-hexachlorocyclohexane, 2,4,5,2',4',5'-hexachlorobiphenyl, CYP2B1 inhibitors such as clotrimazole or clonazepam, or such structurally-diverse compounds as 2-hexanone or diallyl sulfide resulted in induction of CYP2B1-mediated enzyme activity and induction of certain other forms of cytochrome P450, microsomal epoxide hydrolase, at least one form of UDP-glucuronyltransferase, and multiple forms of glutathione S-transferase. This suggests that, as a class, compounds which induce CYP2B1 also induce a coordinate hepatic pleiotropic response which includes induction of these other phase I and phase II drug-metabolizing enzymes.

Animals↗

PubMed1992

Induction of hepatic CYP1A in male F344/NCr rats by dietary exposure to Aroclor 1254: examination of immunochemical, RNA, catalytic, and pharmacokinetic endpoints.

Male F344/NCr rats were exposed to low dietary concentrations of Aroclor 1254 (0-33 ppm) for 7 days, following which the induction of selected hepatic drug metabolizing enzymes was monitored. CYP1A1, measured indirectly by assaying the O-dealkylation of ethoxyresorufin in 9000 g supernatants, was increased 1.5-, 3-, 8-, and 37-fold following 7 days of exposure to 1.0, 3.3, 10, and 33 ppm Aroclor, respectively. In contrast, the O-dealkylation of benzyloxyresorufin, an indirect measure of CYP2B1 activity, was increased approximately 4-fold following exposure to 33 ppm dietary Aroclor. Measurement of the non-P450-mediated activities epoxide hydrolase, DT-diaphorase, and aldehyde dehydrogenase (NADP+, benzaldehyde) revealed < 4-fold inductions following feeding of 33 ppm Aroclor. In view of the relatively high sensitivity of the CYP1A-specific catalytic endpoint as a biomarker for Aroclor exposure, alternative endpoints for detecting induction of this subfamily of P450 were also examined. The extent of in vivo CYP1A induction was assessed by measuring serum concentrations of zoxazolamine 150 min following an intraperitoneal dose of 100 mg/kg body wt. Slight decreases in serum zoxazolamine concentration were observed in rats exposed to as little as 1.0 ppm dietary Aroclor 1254, while profound decreases were seen in rats exposed to > or = to 10 ppm Aroclor. Immunodetection of CYP1A1 protein, with a monoclonal antibody directed against this cytochrome, revealed a 2.9-fold increase in rats exposed to as little as 1.0 ppm Aroclor, and approximately 10- and 44-fold increases following exposure to 3.3 and 10 ppm dietary Aroclor, respectively. Increases in total hepatocellular RNA coding for CYP1A1 and CYP1A2, quantified by hybridization to specific oligonucleotide probes, corresponded well to the increases in hepatic O-dealkylase activity for ethoxyresorufin (CYP1A1) and methoxyresorufin (CYP1A2), respectively. Thus, CYP1A induction, directly or indirectly measured with a variety of endpoints, represents a highly sensitive biomarker for exposure to relatively low doses of Aroclor 1254 in the rat.

Administration, Oral↗