Induction of cytochrome P-448 activity as exemplified by the O-deethylation of ethoxyresorufin. Effects of dose, sex, tissue and animal species

Evaluation of the precision-cut liver and lung slice systems for the study of induction of CYP1, epoxide hydrolase and glutathione S-transferase activities

The principal objective was to ascertain whether precision-cut tissue slices can be used to evaluate the potential of chemicals to induce CYP1, epoxide hydrolase and glutathione S-transferase activities, all being important enzymes involved in the metabolism of polycyclic aromatic hydrocarbons. Precision-cut rat liver and lung slices were incubated with a range of benzo[a]pyrene concentrations for various time periods. A rise in the O-deethylation of ethoxyresorufin was seen in both liver and lung slices exposed to benzo[a]pyrene, which was accompanied by increased CYP1A apoprotein levels. Pulmonary CYP1B1 apoprotein levels and hepatic mRNA levels were similarly enhanced. Elevated epoxide hydrolase and glutathione S-transferase activities were also observed in liver slices following incubation for 24h; similarly, a rise in apoprotein levels of both enzymes was evident, peak levels occurring at the same time point. When mRNA levels were monitored, a rise in the levels of both enzymes was seen as early as 4h after incubation, but maximum levels were attained at 24 h. In lung slices, induction of epoxide hydrolase by benzo[a]pyrene was observed after a 24-h incubation, and at a concentration of 1 microM; a rise in apoprotein levels was seen at this time point. Glutathione S-transferase activity was not inducible in lung slices by benzo[a]pyrene but a modest increase was observed in hepatic slices. Collectively, these studies confirmed CYP1A induction in rat liver slices and established that CYP1B1 expression, and epoxide hydrolase and glutathione S-transferase activities are inducible in precision-cut tissue slices.

Systems biology in drug safety and metabolism: integration of microarray, real-time PCR and enzyme approaches

The last decade has seen a rapid expansion in the field of functional genomics, due mainly to the global gene expression profiling capabilities provided by techniques, such as microarray analysis. Application of these technologies in fields as diverse as plant research, to public health and environmental sciences, forensic science and drug research, shows the versatility of these tools and the promise they hold for revolutionizing research in the life sciences. In drug discovery, attempts have been made to use functional genomics in target identification and validation, lead selection and optimization, and in preclinical studies to predict clinical outcome. These studies have provided a plethora of data and undoubtedly expanded our understanding of genetic alterations in diseased and non-diseased states, but the benefits that these technologies hold have not yet been fully realized. This review discusses how a comprehensive approach to gene regulation studies, a 'systems biology' approach, is being applied in a drug development setting to address mechanism-based questions and issues raised by regulatory authorities.

Hepatic vitamin a depletion is a sensitive marker of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) exposure in four rodent species

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD)-treated animals show altered retinoid homeostasis and exhibit signs of toxicity similar to those of vitamin A-deficient animals. In this study we established dose-response curves for sublethal oral doses of TCDD and hepatic vitamin A gain in four rodent species. This was done to evaluate any potential correlation between decreased hepatic vitamin A gain and other TCDD-induced effects, particularly depressed body weight gain and hepatic CYP1A induction. Young Hartley guinea pigs, Sprague-Dawley rats, C57BL/6 mice, and Golden Syrian hamsters were given single oral doses of TCDD at up to 2.5, 100, 1000, and 1000 microg/kg bw, respectively, and killed 28 days after treatment. Hepatic vitamin A gain was decreased 25% compared to controls at estimated doses of 0.1, 0.9, 1.1 and 3.6 microg/kg bw in guinea pigs, hamsters, rats, and mice, respectively. CYP1A induction and hepatic vitamin A gain were affected at similar dose levels and showed similar, but inverse dose-response curves in each of the four species, consistent with the hypothesis that altered vitamin A homeostasis is Ah-receptor mediated. In addition, there was an apparent correlation between the dose-response curves for decreased hepatic vitamin A gain and decreased body weight gain in all species. Taken together with the known importance of vitamin A in body weight regulation, this result was consistent with a contributing role for altered retinoid homeostasis in the wasting syndrome induced by TCDD.

Isolation and characterisation of human proximal tubular cells derived from kidney cortical segments

1. Human renal proximal tubular cells (HPTC) were isolated by collagenase digestion and purified following filtration and isopycnic Percoll density centrifugation. This method used cortical tissue obtained from surgical nephrectomies and was both rapid and simple, providing a preparation of cells with high viability (> 93 +/- 3%) and recovery (16 +/- 7 x 10(6) cells g-1 of cortical tissue). 2. Characterisation of the isolated cells showed that, in terms of morphology, enzyme profile, transport systems and hormonal responsiveness, they were > 95% proximal tubular. The transport systems obeyed Michaelis-Menten kinetics, with the kinetic parameters of the glucose transport system (Km = 2.5mM, Vmax = 7.7 nmol min-1 mg-1 protein) suggesting a higher proportion of PT cells originating from the S1-S2 segment of the nephron. Isolated HPTC also maintained levels of reduced glutathione (GSH) (11.9 +/- 3.2 nmol mg-1 protein) and exhibited cytochrome P450-dependent activity, levels of spectrally determined P450 being 0.22 +/- 0.07 nmol mg-1 protein. 3. These results demonstrate the isolation of a viable and functioning homogeneous preparation of HPTC from cortical tissue, with potential for use in short term pharmacological, physiological and toxicological studies.

Cytochrome P450 activities in pure and co-cultured rat hepatocytes. Effects of model inducers

The stability and inducibility of several P450 activities (namely, P450 1A1; 2A1, 2B1/2, 2C11, and 3A1) were studied in rat hepatocytes co-cultured with the MS epithelial cell line derived from monkey kidney. The results revealed that these monooxygenase activities were systematically higher in co-cultures than in conventional hepatocyte cultures. Pure cultures showed a rapid loss of monooxygenase activities, which were undetectable after 5 days. In contrast, all isozymes assayed were measurable in co-cultured hepatocytes on Day 7 (about 15 to 40% of the initial activities of Day 0 of culture). The beneficial effects of the co-culture system seemed to be more selective for certain cytochrome P450 isoforms, with P450 1A1 and 3A1 being the best stabilized isozymes after 1 wk. A clear response to inducers was observed in co-cultures, each isozyme showing a different induction pattern. 3-Methylcholanthrene produced a strong increase in P450 1A1 (7-ethoxyresorufin O-deethylase) activity and a low increase in P450 2A1 (testosterone 7 alpha-hydroxylation), whereas no changes were observed in the other activities. Phenobarbital treatment resulted in increases in P450 2B1/2 (7-pentoxyresorufin O-depentylase and 16 alpha- and 16 beta-hydroxylation of testosterone) activities, while minor effects were observed on P450 3A1 (testosterone 6 beta-hydroxylation) activity. Dexamethasone markedly increased P450 3A1 (testosterone 6 beta- and 15 beta-hydroxylation) activity and, to a lesser extent, P450 2B1/2 (16 beta-hydroxylation).

Effect of 2,3,7,8-tetrachlorodibenzoy-p-dioxin on the hepatic 7-ethoxyresorufin O-deethylase activity in four rodent species

Temporal and dose-related effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on hepatic 7-ethoxyresorufin O-deethylase (EROD) activity were investigated in young male Hartley guinea pigs, Sprague-Dawley rats, C57Bl/6 mice, DBA/2 mice and Golden Syrian hamsters. Animals were terminated 1, 7, 14, 28, 56 and 112 days after the administration of a single i.p. dose of TCDD. The maximal induction of EROD activity, at doses producing a similar toxic and limited lethal effect in all species/strains, was 42-, 18-, 7- and 3-fold in rats, DBA/2 mice, C57Bl/6 mice and guinea pigs, respectively. No treatment-related induction of EROD activity was observed in hamsters. Generally, maximal induction occurred 1-4 weeks after injection in all species. The guinea pig alone maintained the same magnitude of induction of EROD activity throughout the study. Observed toxic effects, i.e., lethality, loss of body weight gain, liver enlargement and thymic atrophy, did not correlate with the TCDD-induced hepatic EROD activity. The obtained results suggest that the fold induction of cytochrome P450 1A1 activity is not a critical event for the expression of the lethal effect of TCDD in rodents.

Cytochrome P450 induction and metabolism of alkoxyresorufins, ethylmorphine and testosterone in cultured hepatocytes from goats, sheep and cattle

Very little is known of cytochrome P450 (P450) patterns and enzyme characteristics in food-producing animal species. Oxidative metabolism of alkoxyresorufins, ethylmorphine (EtM) and testosterone (TST) was used to monitor the effects of the P450 inducers phenobarbital (PB), beta-naphthoflavone (BNF), dexamethasone (DEX) and triacetyloleandomycin (TAO) in primary cultured hepatocytes from goats, sheep and cattle. BNF effectively and specifically induced ethoxyresorufin deethylase (> 20-fold), indicating the presence of an inducible P450 1A form, and down-regulated EtM demethylation and most selected TST hydroxylations. In non-induced hepatocyte cultures, TST was metabolized to 6 beta-, 2 beta-, 12 beta-, and 11 alpha-hydroxy-TST (OHT). PB and, to a lesser extent, DEX non-specifically induced all OHT formations, and EtM demethylation. TAO almost completely inhibited OHT formation and EtM demethylation. These results indicate the involvement of principally one P450 form, or a restricted number of related P450 forms, presumably belonging to the P450 3A subfamily. In western blot analysis, cross reactivity was found with rat anti-P450 3A1 and anti-sheep P450 3A. A more specific PB effect was observed for 16 alpha-OHT, which may be formed though a ruminant P450 2B form. None of the inducers influenced pentoxyresorufin depentylase (PROD) or EtM O-deethylation. Metabolite patterns and inducibility of selected activities in ruminant hepatocytes are in accordance with previous findings in goats in vivo. Cytochrome P450 characteristics in ruminants appear to differ from those in rats whereas similarities to the situation in humans appear to exist.

Mutagenicity of chrysene, its methyl and benzo derivatives, and their interactions with cytochromes P-450 and the Ah-receptor; relevance to their carcinogenic potency

The genotoxicity in the Ames test of chrysene, of its six methyl and of two benzo-derivatives, and their ability to induce rat hepatic CYP1A and epoxide hydrolase activities, and stimulate their own bioactivation were determined. The primary objective is to provide a rationale for the higher carcinogenic potency of 5-methylchrysene when compared to that of the parent compound and the other methyl isomers. In the presence of Aroclor 1254-induced hepatic microsomes chrysene, its 5- and 4-methyl derivatives and to a lesser extent the 2- and 3-methyl derivatives and benzo[c]chrysene elicited a positive mutagenic response. Chrysene, all derivatives studied and especially benzo[c]chrysene were potent inducers of rat hepatic CYP1A1 activity as exemplified by the O-deethylation of ethoxyresorufin (30-180-fold when activities are expressed per nmol of total cytochrome P-450). All compounds studied displaced [3H]TCDD from the cytosolic Ah receptor at a concentration of 10(-10)-10(-9) M. Benzo[c]chrysene and to a lesser extent 6-methylchrysene were the only compounds capable of stimulating epoxide hydrolase activity, but the effect was modest. None of the compounds studied could induce its own activation to mutagens in the Ames test. The present findings indicate that the higher carcinogenic potency of 5-methylchrysene cannot be related to its mutagenic potential or its ability to enhance its own activation through induction of CYP1A1 and epoxide hydrolase activities.

Induction of 7-ethoxyresorufin-O-deethylase (EROD) activity in mice foetuses by the PCB-congener 3,3',4,4'-tetrachlorobiphenyl

1. 3,3',4,4'-Tetrachlorobiphenyl (TCB) induces liver microsomal 7-ethoxyresorufin-O-deethylase (EROD) activity, and this P450 isoform, i.e. CYP 1, is involved in the metabolism of TCB. 2. TCB administered i.p. to pregnant mice (5-25 mg/kg) induced foetal as well as maternal hepatic EROD activity; in all cases the maternal induced activity was higher than the foetal activity. EROD activity of TCB-induced foetuses increased with developmental age, but decreased with the length of time after treatment. 3. Strain differences were seen; in control mice and TCB-treated dams NMRI > C57BL in EROD activity, but in transplacentally TCB-treated foetuses, C57BL > NMRI. EROD activity in non-pregnant control C57BL mice was higher than in pregnant ones, whereas no activity was seen in control foetuses. 4. Results indicate that TCB at a certain dose can induce foetal metabolism, but that earlier observed foetal accumulation at lower TCB doses is probably a consequence of transplacental transport of maternally-produced metabolites.

Hepatic cytochrome P450 induction in goats. Effects of model inducers on the metabolism of alkoxyresorufins, testosterone and ethylmorphine, and on apoprotein and mRNA levels

Male and female African dwarf goats were treated orally with phenobarbital (PB) or triacetyloleandomycin (TAO), or subcutaneously with beta-naphthoflavone (BNF). Hepatic microsomal cytochrome P450 content was increased by PB and TAO, but not by BNF. PB effects on P450 activities were non-selective: ethoxyresorufin deethylase (EROD) and pentoxyresorufin depentylase (PROD), hydroxylation of testosterone (TST) and demethylation of ethylmorphine (ETM) were all induced by a factor of 2-3. A similar non-selective induction was observed with TAO, except for EROD and PROD (no effects). After PB and TAO treatment, increased levels of a protein cross-reactive with anti-sheep P450 3A and 2B were found. Thus, in dwarf goats, both PB and TAO appeared to be P450 3A inducers. Selective PB effects related to a P450 2B form on PROD are lacking but 16 alpha-hydroxylation of TST was induced markedly. At the mRNA level, PB induced an mRNA that showed good sequence homology with a human P450 3A4 cDNA probe, rather than with a rat 3A1 probe. BNF selectively induced EROD, whereas TST hydroxylation and ETM dealkylation were inhibited. With BNF-treated animals, increased concentrations of a protein cross-reactive with anti-rat P450 1A1/1A2 and of an mRNA that showed homology with a human 1A1 cDNA probe, but not with a mouse 1A1/1A2 probe, were observed.

Scoparone O-demethylase assay is not useful to differentiate the effects of model inducers of cytochrome P-450 in rabbit and guinea pig liver

Coumarin derivative, scoparone (6,7-dimethoxycoumarin), is regioselectively O-demethylated into isoscopoletin (I) and scopoletin (S). This oxidation is inversely influenced by cytochrome P-450 inducers in the rat such as 3-methylcholantrene (3-MC) and phenobarbital (PB). The I/S ratio is higher than 1.5 with 3-MC treatment whereas it is lower than 0.5 with PB treatment. With regards to this contrasting effect, it has been suggested that the I/S ratio should be useful to differentiate between the effects of these types of inducers. We studied the consequences of in vivo PB and 3-MC treatment on scoparone biotransformation in guinea pig and rabbit. In these two species, at the basal state, scoparone biotransformation was enhanced in comparison to the rat. Moreover, in these untreated animals, two other metabolites were formed. After 3-MC or PB treatment, scoparone metabolism is, in contrast to the rat, inappropriate to differentiate between the P-450 profile of other animals.

Effects of inhibition and induction of cytochrome P-450 isozymes on hyperoxic lung injury in rats

Pulmonary oxygen toxicity most likely results from excessive production of reactive oxygen species. The role of the cytochromes P-450 in this process is controversial because these enzymes have been reported both to enhance hyperoxic lung injury and to protect from the damaging effects of 100% oxygen. We sought to further determine the role of the cytochromes P-450 in hyperoxic lung injury by inhibiting and inducing pulmonary cytochrome P-450 isozymes in rats. Treatment with the cytochrome P-450 inhibitor cimetidine or 8-methoxypsoralen did not improve survival or reduce lung edema in rats exposed to 100% oxygen. The activity of cytochrome P-450IIB1, the major pulmonary cytochrome P-450 isozyme in rats, was clearly inhibited by 8-methoxypsoralen. beta-Naphthoflavone (beta NF), a selective inducer of cytochrome P-450IA1, was administered in two-dose and five-dose regimens. The two-dose regimen produced significant and sustained induction of cytochrome P-450IA1 activity, but survival in these rats was not improved when exposed to 100% oxygen. In rats treated with five doses of beta NF, a small increase in survival time was found from 71.1 +/- 8.7 to 88.0 +/- 20.2 h; however, there was no difference in the induction of cytochrome P-450IA1 activity between this five-dose regimen and the two-dose regimen. The small improvement in survival after five doses of beta NF is thus unrelated to cytochrome P-450IA1 induction. We conclude that neither inhibition of cytochrome P-450IIB1 activity nor induction of cytochrome P-450IA1 activity protects adult rats against hyperoxic lung injury.

Cytochrome P-450- and glutathione-associated enzyme activities in freshly isolated enriched lung cell fractions from beta-naphthoflavone-treated male F344 rats

Xenobiotics metabolized in rat pulmonary tissue are often selectively cytotoxic to individual lung cell populations. A non-homogeneous distribution of xenobiotic biotransformation enzymes, e.g., cytochrome P-450 (P-450)- and glutathione (GSH)-associated enzymes, in rat lung tissue may underlie this observed cell-selective pneumotoxicity. To evaluate this hypothesis, the relative activities of P-450- and GSH-associated enzymes were measured in sonicated, freshly isolated preparations containing enriched complements of individual toxicant-sensitive lung cell types, including non-ciliated bronchiolar epithelial (Clara) cells (24% pure), alveolar type II cells (86% pure) and pulmonary endothelial cells (identified by membrane-associated angiotensin converting enzyme activity). Lung cell fractions were isolated by centrifugal elutriation from male F344 rats that 48 h earlier received a single i.p. injection of either P-450-inducer beta-naphthoflavone (50 mg beta-NF/kg body weight) or corn oil vehicle. The enriched Clara cell fraction possessed (per 10(6) cells) greater P-450 and reduced GSH contents and higher enzyme activities (i.e., NADPH- and NADH cytochrome c reductases, benzyloxy (BROD)-, pentoxy (PROD)- and etoxyresorufin (EROD)-O-dealkylases, GSH transferase, GSH peroxidase, GSH reductase and NADPH quinone oxidoreductase) than either the enriched type II cell or endothelial cell preparations. However, the relative biochemical activities for the enriched fractions (Clara greater than type II greater than endothelial) generally reflected respective sonicate cellular protein content. Treatment of rats with beta-NF resulted in: (a) an induction in EROD activity in the enriched preparations of type II cells, Clara cells and endothelial cells (125-, 89- and 35-fold, respectively); (b) higher NADPH quinone oxidoreductase activities, which were increased to the greatest degree (3-fold) in the enriched type II cell fraction and (c) a small elevation in GSH transferase activity measured in the enriched Clara cell fraction. Although the enriched rat lung cell preparations possessed unique biochemical profiles for constitutive and beta-NF-inducible P-450- and GSH-associated enzymes, additional studies with higher purity preparations (e.g., Clara cells) will be required to more fully evaluate the relationship between relative cellular complements of xenobiotic biotransformation enzymes and pneumotoxicant susceptibility.

Influence of ethanol on microsomal p-nitrophenol hydroxylation and ethoxyresorufin deethylation in rat liver and lung

The ability of ethanol to induce the deethylation of ethoxyresorufin and hydroxylation of p-nitrophenol in rat lung and liver was investigated. The administration of 10% ethanol in the drinking water for 7 d increased hepatic p-nitrophenol hydroxylation twofold whereas ethanol ip (3 ml/kg/d for 7 d) decreased the activity. Both ethanol treatments decreased the activity in the lung. Ethoxyresorufin deethylation was induced in the liver by both ethanol treatments, and in the lung the bolus dosing ip increased the activity four-fold. The results indicate that the lung microsomes have p-nitrophenol hydroxylase and ethoxyresorufin deethylase activities, but only the latter was increased by ethanol treatment.

Induction of the P-450 I family of proteins by polycyclic aromatic hydrocarbons: possible relationship to their carcinogenicity

The hypothesis has been put forward that mutagenic polycyclic aromatic hydrocarbons which induce the P-450 I family of cytochromes, the major enzyme system responsible for their activation, are likely to be carcinogenic. In order to test this hypothesis, rats have been pretreated with a number of polycyclic aromatic hydrocarbons of different mutagenic and carcinogenic potency and hepatic P-450 I activity was monitored using chemical probes such as the O-deethylation of ethoxyresorufin and metabolic activation of Glu-P-1 to mutagens, and immunologically employing polyclonal antibodies against purified rat P-450 I A1. All compounds studied enhanced P-450 I activity and induced P-450 I apoproteins but the extent of induction was very markedly different. The results are discussed with reference to the mutagenicity of these chemicals in the Ames test and their carcinogenicity in the classical mouse skin model. A relationship appears to exist between carcinogenicity of polycyclic aromatic hydrocarbons and their ability to induce hepatic P-450 I activity.

Induction of monooxygenase and transferase activities in rat by dietary administration of flavonoids

1. The influence of the dietary flavonoids, chrysin, quercetin, tangeretin, flavone and flavanone, on the components of the rat liver drug-metabolizing enzyme system was examined and compared with two well-known synthetic flavonoids 7,8-benzoflavone and 5,6-benzoflavone. 2. Polyhydroxylated molecules such as quercetin and chrysin, produced no significant changes on phase I and phase II enzyme activities. 3. Flavone was the most potent inducer, and resulted in a mixed type of induction. 7-Ethoxycoumarin O-deethylase (ECOD), 7-ethoxyresorufin O-deethylase (EROD) and pentoxyresorufin depentylase (PROD) activities were increased 2, 30 and 15-fold respectively. p-Nitrophenol UDP-glucuronyltransferase (UDPGT 1), p-hydroxybiphenyl UDP-glucuronyltransferase (UDPGT 2) and glutathione transferase (GST) activities were also induced. 4. Flavanone, which differs from flavone only by the degree of unsaturation of the pyrone ring, produced only a weak increase in monooxygenase activity, but the increase in phase II enzyme activities was as great as that for flavone treatment. 5. Tangeretin displayed a mixed pattern of induction, with increases in ECOD, EROD and PROD, and UDPGT 1 and UDPGT 2 activities, but these were less than with flavone treatment. 6. 7,8-Benzoflavone and 5,6-benzoflavone showed induction patterns similar to those of 3-methylcholanthrene. Nevertheless dietary treatment with 5,6-benzoflavone caused changes which were not as great as those usually described when this compound is administered i.p.

Preferential induction of the rat hepatic P450 I proteins by the food carcinogen 2-amino-3-methyl-imidazo[4,5-f]quinoline

1. Administration of the food carcinogen, 2-amino-3-methyl-imidazo[4,5-f]quinoline (IQ) to rats gave rise to significant dose-dependent increases in the microsomal O-deethylations of ethoxycoumarin and ethoxyresorufin but had no effect on the O-dealkylation of pentoxyresorufin and the NADPH-dependent reduction of cytochrome c, and decreased the N-demethylation of dimethylnitrosamine. Microsomal cytochrome b5 and total cytochrome P-450 levels decreased following the administration of the carcinogen. 2. Hepatic microsomal preparations from IQ-treated animals were much more efficient than control in activating the premutagen 2-amino-6-methyldipyrido[1,2-a:3',2'-d]imidazole to mutagenic intermediates in the Ames test. 3. Immunoquantification of two of the major families of cytochrome P-450, namely P450 I and P450 II B, using ELISA techniques showed that treatment with IQ induced the apoprotein levels of the P450 I family but not of P450 II B. 4. Immunoblot analysis employing polyclonal antibodies against P450 I revealed that IQ induced both isoenzymes of this family, namely P450 I A1 and A2. 5. It is concluded that IQ is an inducer of the rat hepatic monooxygenases, selectively inducing the P450 I family as predicted by a computer-graphic analysis of its dimensions which showed that it is a large, essentially planar, molecule.

Induction of the rat hepatic microsomal mixed-function oxidases by two aza-arenes. A comparison with their non-heterocyclic analogues

The ability of the aza-aromatic polycyclic aromatic hydrocarbons 10-azobenz(a)pyrene and benz(a)acridine to induce the rat hepatic microsomal mixed-function oxidases was compared to that of their non-heterocyclic analogues benz(a)pyrene and benz(a)anthracene respectively. All four hydrocarbons markedly increased the O-deethylations of ethoxyresorufin and ethoxycoumarin, the non-heterocyclic analogues being the more potent. A more modest increase was seen in the O-dealkylation of pentoxyresorufin. All four hydrocarbons induced proteins recognised by antibodies to cytochrome P-450IAI but no increase was seen when antibodies to cytochrome P-450IIB1 were employed. The metabolic activation of benz(a)pyrene and Glu-P-1 to mutagenic intermediates in the Ames test was enhanced by all pretreatments. It is concluded that the aza-aromatic polycyclic hydrocarbons, like their non-heterocyclic analogues, selectively induce the cytochrome P-450I family of proteins.

Acute and subacute effects of miconazole nitrate on hepatic styrene oxide hydrolase and cytochrome P-450-dependent monooxygenase activities in male and female AKR/J mice

The imidazole-containing anti-fungal drug, miconazole nitrate, was shown to enhance hepatic microsomal styrene oxide hydrolase and inhibit several cytochrome P-450-dependent monooxygenase activities in the AKR/J mouse. Miconazole was a more potent inhibitor of cytochrome P-450-dependent monooxygenase activities in microsomes from male than female mice, and inhibitory potency also varied with substrate. When administered in vivo miconazole nitrate stimulated epoxide hydrolase activity, but had a substrate-dependent biphasic effect on cytochrome P-450-dependent monooxygenase activities. Monooxygenase activities with benzo[a]pyrene and benzphetamine were inhibited to varying degrees in liver homogenate and hepatic microsomes from mice sacrificed 45 min after miconazole administration. After repeated administration of miconazole, liver weight, microsomal protein yield and cytochrome P-450 were increased, as were specific monooxygenase activities with ethoxycoumarin and ethoxyresorufin, but benzphetamine N-demethylase activity was decreased. These results suggested that a metabolite of miconazole was responsible for the inhibition of benzphetamine N-demethylase. It was of special interest that ethoxyresorufin O-deethylase activity was induced in the AKR/J mouse by miconazole, since the AKR/J mouse is not responsive to induction by aromatic hydrocarbons.

Induction of the rat hepatic microsomal mixed-function oxidases by 3 imidazole-containing antifungal agents: selectivity for the cytochrome P-450IIB and P-450III families of cytochromes P-450

Administration of the imidazole antifungal agents ketoconazole, miconazole and clotrimazole gave rise to increases in the microsomal cytochrome P-450 levels and the NADPH-dependent reduction of cytochrome c. Clotrimazole, and to a much lesser extent miconazole and ketoconazole, stimulated the dealkylation of pentoxyresorufin. All 3 agents gave rise to small, but significant increases in the O-deethylation of ethoxycoumarin and ethoxyresorufin. The antifungal-induced O-deethylation of ethoxycoumarin was much more sensitive to inhibition by metyrapone rather than by alpha-naphthoflavone. The binding of metyrapone to reduced microsomes was enhanced by treatment of animals with the 3 antifungal agents, clotrimazole being clearly the most potent. Immunoquantitation of cytochrome P-450 proteins using an ELISA procedure and employing anti-cytochrome P-450c (P-450IA1, P-448 low spin) and P-450b (P-450IIB1) antisera revealed that clotrimazole and miconazole, but not ketoconazole, induced the levels of phenobarbital-induced cytochromes P-450, while none of the antifungal agents increased the levels of cytochrome of P-448 proteins. Similar results were obtained using Western blots employing the above antibodies. On SDS-polyacrylamide gel electrophoresis microsomes derived from animals pretreated with clotrimazole showed intensification of a band at 51 kDa which was identified by Western blotting as the PCN-inducible form of cytochrome P-450 (cytochrome P-450p, P-450III family). Similar, but less pronounced intensification was seen with microsomes from animals pretreated with miconazole and ketoconazole. Furthermore, microsomes from clotrimazole- and ketoconazole-treated animals interacted with erythromycin to yield type I spectra. It is concluded that the imidazole-containing agents clotrimazole and miconazole, and to a much lesser extent ketoconazole, are potent inducers of the rat hepatic microsomal mixed-function oxidases, displaying selectivity towards the P-450IIB (phenobarbital-inducible) and P-450III (PCN-inducible) families of cytochrome P-450 proteins.

7-Ethoxyresorufin-O-deethylase activity in human hair roots: a potential marker for toxifying species of cytochrome P-450 isozymes

Assay systems for the evaluation of carcinogen interaction with human tissues are essential for assessing cancer risk. Human hair roots (HHR) are a readily obtainable epithelial tissue source that have been employed for investigating inherited enzyme activities. In this study HHR were found to possess cytochrome P-450-dependent 7-ethoxyresorufin-O-deethylase (ERD) activity which measures cytochrome P-450 isoenzymes that are highly specific (in the order of greater than 95%) markers for the metabolic activation of many environmental carcinogenic substances such as the polycyclic aromatic hydrocarbons (PAHs). Topical application of PAHs (in liquor carbonis detergens) to the scalp of human volunteers was found to enhance the activity of this enzyme in freshly plucked hair roots. Oral and topical administration of ketoconazole to the same subjects resulted in an appreciable (up to 73%) inhibition of detectable enzyme activity. Our data suggest that measurement of ERD in HHR may be a useful marker for the study of toxifying species of cytochrome P-450 isozymes in human populations.