Induction of P-450 isoenzyme activities in Syrian golden hamster liver compared to rat liver as probed by the rate of 7-alkoxyresorufin-O-dealkylation

Ring-oxidative biotransformation and drug interactions of propofol in the livers of rats

Propofol, an intravenous anesthetic agent, is widely used for inducing and maintaining anesthesia during surgical procedures and for sedating intensive care unit patients. In the clinic, rapid elimination is one of the major advantages of propofol. Meanwhile, the biotransformation and drug interactions of propofol in rat livers are still little known. In this study, we evaluated the ring-oxidative metabolism of propofol in phenobarbital-treated rat livers and possible drug interactions. Administration of phenobarbital to male Wistar rats significantly increased levels of hepatic cytochrome P450 (CYP) 2B1/2 and microsomal pentoxyresorufin O-dealkylase (PROD) activity. Analyses by high-performance liquid chromatography and liquid chromatography mass spectroscopy revealed that propofol was metabolized by phenobarbital-treated rat liver microsomes into 4-hydroxypropofol. In comparison, PROD activity and 4-hydroxy-propofol production from propofol metabolism were suppressed by orphenodrine, an inhibitor of CYP2B1/2, and a polyclonal antibody against rat CYP2B1/2 protein. Furthermore, exposure of rats to propofol did not affect the basal or phenobarbital-enhanced levels of hepatic CYP2B1/2 protein. Meanwhile, propofol decreased the dealkylation of pentoxyresorufin by phenobarbital-treated rat liver microsomes in a concentration-dependent manner. Taken together, this study shows that rat hepatic CYP2B1/2 plays a critical role in the ring-oxidative metabolism of propofol into 4-hydroxypropofol, and this anesthetic agent can inhibit CYP2B1/2 activity without affecting protein synthesis.

Alkoxyresorufin-O-deethylase activities and polychlorinated biphenyl patterns in shrews as biomarkers in environmental risk assessments: sensitivity and specificity

Alkoxyresorufin-O-deethylase (AROD) biomarkers are useful indicators of the exposure of organisms to dioxin-like compounds. In the current study, an in vivo validation of the use of such biomarkers in shrews was conducted. Furthermore, the use of changes in polychlorinated biphenyl (PCB) patterns as an animal-friendly alternative to AROD biomarkers was evaluated. Two experiments and a field study were conducted in which dose-response relations were established between levels of sigma-PCBs in shrews on one hand and their AROD activities and changes in PCB patterns on the other. We demonstrate that the changes in PCB patterns are as sensitive as the classic AROD biomarkers. The experiments also showed a substrate-specific induction of AROD biomarkers and a related PCB congener-specific metabolism. This implies that congener-specific analysis of PCBs can reveal activities of specific AROD biomarkers. Gender-specific induction of AROD activities in shrews was shown in the field study, whereas the relationship between exposure and changes in PCB patterns did not differ between genders. It is concluded that (i) AROD biomarkers are useful biomarkers to assess exposure of shrews to specific organochlorines and that (ii) changes in PCB patterns can be used as an animal-friendly alternative to these AROD biomarkers.

Dose-response relationships for cytochrome P450 induction by phenobarbital in the cotton rat (Sigmodon hispidus)

The induction of a hepatic pleiotropic response, including increase in liver/body weight ratio, induction of hepatic CYP2B and CYP3A protein and catalytic activity, and hepatic microsomal epoxide hydration activity, was investigated in male cotton rats (Sigmodon hispidus) administered graded dietary concentrations (0-1500 ppm) of phenobarbital (PB) for 14 days. A dose-dependent induction of each endpoint was observed, although plateaus in the various dose-response curves were not obtained, and ED50 values (PB concentrations associated with half-maximal responses) for the various endpoints were not able to be calculated. A maximal 1.31-fold increase, compared to the control value, in live/body weight ratio was observed, while microsomal epoxide hydration activity was increased as much as 3.6-fold by PB administration. Pentoxy- and benzyloxyresorufin O-dealkylation and testosterone 16 beta-hydroxylation activities (considered to be relatively selective for CYP2B in the Norway rat (Rattus norvegicus)), were induced maximally less than five-fold. Testosterone 6 beta-hydroxylation (considered to be relatively selective for CYP3A in R. norvegicus) was induced maximally less than two-fold. Maximal induction of 7-ethoxy-4-trifluoromethyl-coumarin O-deethylation was 18-fold, compared to the control rate. Western blotting studies indicated that hepatic microsomal proteins immunoreactive with polyclonal antisera to R. norvegicus CYP2B1 or CYP3A1 were induced, in a dose-responsive manner, by PB in the cotton rats. These results indicate that the cotton rat responds to PB treatment with a coordinate pleiotropic response similar to that displayed by R. norvegicus, although the substrate specificity of the induced proteins appears to differ between the two rodent species.

Cytochrome P450 induction in feral Cricetid rodents: a review of field and laboratory investigations

The constitutive and inducible hepatic cytochromes P450 of various feral Cricetid rodents (family Cricetidae, comprising various New World rats and mice, hamsters, gerbils and voles), have been examined in a relatively limited number of field and laboratory investigations. These studies, reviewed herein, have employed substrates and immunochemical reagents that are diagnostic for individual P450 subfamilies of Rattus norvegicus (the common laboratory species derived from the Norway rat, a member of the family Muridae). The results have demonstrated that the feral rodents display hepatic responses to prototypic CYP1A inducers (3-methylcholanthrene, beta-naphthoflavone) similar to those displayed by R. norvegicus and Mus musculus (the common laboratory species derived from the house mouse, another member of the family Muridae). At least one study has demonstrated the induction, by ethanol, of a protein immunochemically similar to CYP2E1 in a Cricetid rodent. In Cricetid rodents, phenobarbital-type inducers cause the induction of a hepatic protein immunologically similar to that primarily induced (CYP2B) in R. norvegicus and M. musculus. The proteins induced in the Cricetid rodents, however, exhibit striking differences in substrate specificity, compared to the proteins induced in R. norvegicus. These results indicate that the previously described differences between the P450 induction responses exhibited by the commonly utilized laboratory species R. norvegicus and M. musculus (family Muridae) and the Syrian hamster and gerbil (family Cricetidae) are observed as a generality for members of the Cricetid family of rodents.

Differential induction of isozymes of drug-metabolizing enzymes by butylated hydroxytoluene in mice and Chinese hamsters

Induction of isozymes of drug-metabolizing enzymes by butylated hydroxytoluene (BHT) was studied in the male ddY mouse and Chinese hamster. In mice given 0.05 and 0.15% BHT in the diet for 14 days cytochrome P-450 contents and the activities of uridine diphosphate-glucuronyl transferase (UDP-GT) and pentoxyresorufin O-dealkylase were markedly increased, while in those fed 0.15% BHT testosterone 6 alpha-, 16 alpha- and 16 beta-hydroxylases were greatly increased, which indicated induction of cytochrome P-450 isozymes of the CYP2B family. Western blot analysis also showed an increased level of the isozyme immunorelated to rat CYP2B2 by BHT feeding. The activities of aryl hydrocarbon hydroxylase, ethoxycoumarin O-deethylase (ECOD), erythromycin N-demethylase and glutathione S-transferase (GST) remained unchanged. In Chinese hamsters given 0.05 and 0.15% BHT in the diet for 14 days activities of ECOD and GST were induced, but cytochrome P-450 contents and the activities of other enzymes were unaffected. Testosterone 15 alpha-hydroxylase was induced in hamsters fed 0.15% BHT. These findings suggested that BHT administration in the hamster induced CYP2A2-type isozyme, which was confirmed by Western blot analysis. BHT treatment enhanced activation of benzo[a] pyrene (B[a]P) as determined by the mutagenicity test, especially in Chinese hamsters. The results suggest that BHT treatment induces specific isozymes of drug-metabolizing enzymes and might modify the expression of toxicities of other chemicals.

Induction of CYP2B1 mediated pentoxyresorufin O-dealkylase activity in different species, sex and tissue by prototype 2B1-inducers

The induction of CYP2B1 mediated pentoxyresorufin O-dealkylase (PROD) activity by various xenobiotics was explored in liver, kidney and lung from a variety of animal species of both sexes, in order to gain insights into the substrate specificity of induced CYPs. Marked species- and sex-related differences in the inducibility of PROD activity by tested chemicals were observed, the mouse being always more responsive when compared to hamster or rat. Induction by sodium phenobarbital (NaPB) led to a conspicuous increase in all situations, up to approximately 38-fold in female rat and mouse liver, with the exception of hamster kidney where PROD activity was only slightly affected. Unexpectedly, both sodium barbital (NaB) and phorone (PHR) moderately induce CYP2B1 isoforms in rat, the extent being highest in female kidney (PHR, 14-fold increase) and male lung (NaB, 4.5-fold). The degree of induction was maximal in the liver with some exceptions occurring in male mice where NaB induced up to 46- and 115-fold increases in lung and kidney and PHR up to 115-fold in kidney. Minimal, although significant induction of PROD activity following treatment with trans-1,2-dichloroethylene (1,2-DCE) occurred in all situations with the exception of hamster kidney and lung. Therefore, caution should be exercised when using PROD activity as specific enzymatic assay to probe CYP2B1-like induction.

Differential modulation of hepatic cytochrome P-450 enzymes in rat and Syrian hamster by 4'-trifluoromethyl-2,3,4,5-tetrachlorobiphenyl

The effects of a single injection (40 mg/kg) of 4'-trifluoromethyl-2,3,4,5-tetrachlorobiphenyl (CF3) on hepatic cytochrome P-450 monooxygenases were assessed in rat and syrian hamster. The CF3 treatment significantly increased the total amount of cytochrome P-450 in both species. In rats, CF3 treatment caused marked increases in ethoxyresorufin O-deethylase (EROD), arylhydrocarbon hydroxylase (AHH), and testosterone 7 alpha-hydroxylase activities but significantly reduced the activities of benzphetamine N-demethylase (BzND), erythromycin N-demethylase (ErND), testosterone 6 beta, 16 alpha, and 16 beta-hydroxylase, and formation of androstenedione. Administration of CF3 to hamsters strongly induced the activities of EROD, AHH, BzND, testosterone 15 alpha, and 16 alpha-hydroxylases, and androstenedione production, whereas ErND, testosterone 6 beta, and 7 alpha-hydroxylases were decreased. Administration of CF3 to rats induced the CYP1A family proteins and CYP2A1, while CF3 reduced the level of CYP2B1, and, to a lesser extent, of CYP6 beta 2. In hamsters, CF3 treatment significantly induced the CYP1A2, CYP2A1, CYP2A8, and CYP2B1 isozymes, whereas the CYP6 beta 2 level was decreased. The ability of hepatic microsomes to activate aflatoxin B1 and benzo(a)pyrene was elevated by CF3 treatment in hamsters, while activation of aflatoxin B1 was decreased in microsomes from CF3-treated rats. These results showed differences in the CF3-induced pattern of rat and hamster cytochrome P-450 monooxygenases.

Tissue and sex-dependent differences in CYP2A activities in hamsters

Three enzymatic activities of the CYP2A subfamily, coumarin 7-hydroxylase (COH), testosterone 15 alpha-hydroxylase (T15 alpha OH) and testosterone 7 alpha-hydroxylase (T7 alpha OH), were characterized in liver, kidney and lung microsomes from control, pyrazole (PYR), 3-methylcholanthrene (MC) and phenobarbital (PB) treated female and male Syrian golden hamsters. Sex-dependent changes in the enzymatic activities were found. Among control animals COH and T15 alpha OH activities were higher in males. T7 alpha OH activity was five times higher in female kidneys than in males. Inducers changed this metabolic profile. MC and PB were potent CYP2A inducers in extrahepatic tissues: significant increases were found in COH (5-fold) and T15 alpha OH (12-fold) activities in female MC lung microsomes and T7 alpha OH (7-fold) in MC male kidney microsomes. PB increased significantly activities of COH (5-fold), T15 alpha OH (3-fold) and T7 alpha OH (10-fold) in male kidney microsomes. All inducers significantly increased T7 alpha OH activity in male kidney microsomes but decreased hepatic T7 alpha OH activity in both sexes. PYR treatment decreased hepatic CYP2A activities. Anti-mouse CYP2A4/5 antibody inhibited COH activity by a variable extent depending on the tissue and pretreatment and recognised three 52-, 49-, 48-kDa bands in liver and two major bands in kidney (48 and 49 kDa) and lung (49 and 52 kDa) microsomes. COH and T15 alpha OH activities correlated well with 49 kDa protein (r = 0.95 and r = 0.99, respectively) in lung microsomes.(ABSTRACT TRUNCATED AT 250 WORDS)

A comparative study of constitutive and induced alkoxyresorufin O-dealkylation and individual cytochrome P450 forms in cynomolgus monkey (Macaca fascicularis), human, mouse, rat and hamster liver microsomes

The expression of constitutive and inducible cytochrome P450 forms was measured in cynomolgus monkey liver and compared with man, rat, mouse and hamster. Four alkoxyresorufin O-dealkylation (AROD) activities widely used as indicators of P450 induction were measured: methoxyresorufin O-demethylation (MROD), ethoxyresorufin O-deethylation (EROD), pentoxyresorufin O-dealkylation (PROD) and benzyloxyresorufin O-dealkylation (BROD). In monkeys there were no sex-differences in untreated, phenobarbitone (PB)- or beta-naphthoflavone (BNF)-treated animals in AROD activities, or in individual P450 proteins detected by immunoblotting. Basal MROD and EROD activities varied by less than 7-fold between the five species, but the comparative pattern of basal MROD, EROD, PROD and BROD activities (the "MEPB profile") was very species-specific, with monkeys being similar to rats but different from man, mouse and hamster. The induction of AROD activities by PB and BNF was also highly species-specific. Monkeys expressed constitutive proteins immunorelated to the CYP1A, CYP2A, CYP2B, CYP2C and CYP3A sub-families (human CYP2A6 cross-reacted with the anti-rat CYP2B1 antibodies used, and so CYP2A and CYP2B forms could not be separately identified in the monkey). Single constitutive immunoblot bands were identified in monkey for CYP1A (54 kDa), CYP2A/CYP2B (51 kDa) and CYP3A (51 kDa), respectively, but two strong (51 and 52 kDa) plus two weak (49 and 49.5 kDa) bands were shown for CYP2C. Human liver expressed CYP1A2 (54 kDa), CYP2A6 (51 kDa), CYP3A4 (50.5 kDa) and three CYP2C9-immunorelated protein bands (48, 50 and 54 kDa). In monkeys BNF induced the 54 kDa CYP1A protein and CYP1A-dependent MROD, EROD and PROD activities (18-, 15- and 6-fold increases in activity, respectively), whereas PB strongly induced the 51 kDa CYP2A/CYP2B protein but did not induce PROD activity. PB also induced non-constitutive CYP2A/CYP2B protein bands at 49 and 52 kDa in some monkeys. BROD activity was induced less that four-fold by either PB or BNF in monkeys. In conclusion, cynomolgus monkeys expressed a range of constitutive CYP1A, CYP2A or CYP2B, CYP2C and CYP3A proteins similar to man, and a range of AROD monooxygenase reaction rates similar to both man and rat, but the basal MEPB profile of AROD activities in monkeys was more similar to rat than to man. MROD and EROD were good measures of CYP1A induction by polycyclic aromatic hydrocarbons in cynomolgus monkeys, but neither PROD nor BROD were indices of CYP2B induction by PB.

Differences in the effects of model inducers of cytochrome P450 on the biotransformation of scoparone in rat and hamster liver

The hamster is known to display very high rates of monooxygenase-mediated biotransformation. In comparison with other species little knowledge has been gathered with respect to the nature of its cytochrome P450 enzymes and their respective inducibility. We studied the consequences of induction of P450 enzymes in rats and Syrian golden hamsters using the regioselective oxidative O-demethylation of the coumarin derivative scoparone. This metabolic conversion indicates differential effects of P450 inducers in the rat, in which various types of inducers cause different shifts in the isoscopoletin/scopoletin metabolite ratio (I/S-ratio). Liver microsomes from hamster not treated with P450 inducers oxidized scoparone much more efficiently than liver microsomes of untreated rats. In rat liver microsomes total demethylation rates of scoparone increased upon in vivo treatment with phenobarbital or beta-naphthoflavone. Phenobarbital reduced the I/S-ratio whereas beta-naphthoflavone caused an increase in this ratio. In hamster liver microsomes both phenobarbital and beta-naphthoflavone treatments resulted in a decrease in the I/S ratio. In this species the total scoparone demethylation rate was not much affected by phenobarbital, but beta-naphthoflavone caused a huge increase in over-all scoparone biotransformation. In both species, dexamethasone, isoniazid and clofibrate were much less effective. In contrast to the rat, in the hamster the scoparone biotransformation profile cannot be used to differentiate between phenobarbital- or beta-naphthoflavone-treated animals.

Comparative pharmacodynamics of CYP2B induction by phenobarbital in the male and female F344/NCr rat

The phenobarbital dose-CYP2B induction response relationships and pharmacodynamics of CYP2B induction have been characterized in female and male F344/NCr rats. The ED50 and EC50 values for the induction, by phenobarbital, of hepatic CYP2B1 or 2B1/2B2 protein or associated catalytic activities (benzyloxy- or pentoxyresorufin O-dealkylation or testosterone 16 beta-hydroxylation) were 2- to 7-fold higher in the female than in the male rat, indicating a somewhat decreased potency for this effect in the female rat. In contrast, the maximal induction, expressed as the ratio of induced activity to control activity, was as great or greater in the female rat than in the male. Thus, any difference in the responsiveness of female rats to hepatic CYP2B induction by phenobarbital, compared to male rats, is reflected in potency but not degree of induction of catalytic activity or immunoreactive protein.

N-benzylimidazole-mediated changes in hepatic drug-metabolizing enzyme activities in Ah-responsive and Ah-non-responsive mice

1. The inductive effect of N-benzylimidazole (NBI) on hepatic microsomal and cytosolic drug-metabolizing enzyme activities in aryl hydrocarbon (Ah)-responsive C57BL/6N (B6) and Ah-non-responsive DBA/2N (D2) mouse strains was determined and compared with that caused by beta-naphthoflavone (BNF). 2. Relative Ah-responsiveness of the two strains was confirmed by measurement of BNF-induced ethoxyresorufin deethylase (EROD) activity and ELISA immunoquantification. BNF markedly induced EROD activity only in the Ah-responsive B6 mouse strain (65-fold increase). 3. NBI (150 mg/kg per day for 3 days) increased cytochrome P450 concentration similarly in both strains (40 and 60% in B6 and D2 strains, respectively). Compared with BNF treatment of the B6 strain, increases in EROD activity following NBI treatment were only minor. In addition, EROD activity increases were greater in the Ah-nonresponsive D2 strain (300%) than in the Ah-responsive B6 strain (100%) suggesting the possibility of an induction mechanism different from that of recognized Ah receptor agonists. 4. Induction of UDP-glucuronosyltransferase activity (p-nitrophenol acceptor) by BNF was greater in the Ah-responsive B6 strain than in the Ah-non-responsive D2 strain. NBI failed to induce this activity in either strain. 5. Induction of glutathione S-transferase activity towards 1-chloro-2,4-dinitrobenzene following NBI treatment occurred to the same extent (25% increase) as that seen following BNF treatment, in the Ah-responsive B6 strain. Neither xenobiotic affected this activity in the Ah-non-responsive D2 strain. 6. Although NBI is a major inducer, possessing Ah-like inducing properties in rat, it caused only minor changes in murine drug metabolizing enzymes.(ABSTRACT TRUNCATED AT 250 WORDS)

Purification and characterization of an acetone-inducible cytochrome P-450 from hamster liver microsomes

A form of cytochrome P-450 has been purified to electrophoretic homogeneity from the hepatic microsomes of Syrian golden hamsters treated with acetone. This P-450 form, designated ha P-450j, had an M(r) of approximately 55,000, bound dimethyl sulphoxide and exhibited a CO-reduced absorbance maximum at 451 nm. The absolute spectra of its oxidized form indicated that ha P-450j was predominantly in the low-spin state. In a reconstituted system, ha P-450j showed relatively low catalytic activities towards 7-ethoxycoumarin, 7-ethoxyresorufin, aminopyrine, ethylmorphine and benzphetamine, whereas it catalysed the oxidation of aniline, acetone and thiobenzamide with a high catalytic-centre activity. In addition, ha P-450j catalysed at a high rate the high-affinity component of dimethylnitrosamine N-demethylase; in contrast, only the low-affinity component of diethylnitrosamine N-de-ethylase was efficiently catalysed. The addition of cytochrome b5 to the reconstitution system decreased the Km value for dimethylnitrosamine N-demethylase by a factor of 5 and increased the Vmax. value, and slightly enhanced the other activities. Thiobenzamide and diethyldithiocarbamate were found to be the most effective inhibitors of the ha-P-450j-dependent aniline hydroxylation. Polyclonal antibodies against rat P-450j recognized ha P-450j in immunoblots of control and treated hamster liver microsomes. Treatment of hamsters with acetone increased the apparent abundance of ha P-450j in microsomes, whereas phenobarbital and beta-naphthoflavone did not induce it. Analysis of N-terminal amino acid sequences demonstrated that ha P-450j has a high degree of sequence identity with rat P-450j. All the evidence presented in this study indicates that ha P-450j could represent the hamster orthologue of the previously described CYP2E1(s) of other species.

Differential cumene hydroperoxide sensitivity of cytochrome P-450 enzymes IA1 and IIB1 determined by their way of membrane incorporation

The cytochrome P-450-dependent O-dealkylation of alkoxyresorufins was used to study the effect of cumene hydroperoxide on cytochrome P-450 IIB1 and IA1 in microsomal and reconstituted systems. In liver microsomal systems from respectively phenobarbital and 3-methylcholanthrene pretreated male Wistar rats, cytochrome P-450 IIB1-dependent pentoxyresorufin-O-dealkylation appeared to be more sensitive to cumene hydroperoxide treatment than cytochrome P-450 IA1-dependent ethoxyresorufin-O-dealkylation. This phenomenon was also observed when the cumene hydroperoxide sensitivity of P-450 IIB1 and IA1 was studied in an isosafrole pretreated rat liver microsomal system. The decrease in alkoxy-O-dealkylating activities appeared to proceed by destruction of the cytochrome P-450 component of the enzyme system. Purification and reconstitution of the enzyme system components in a system in which the isolated proteins were not incorporated into a membrane resulted in the disappearance of the difference in sensitivity between the two P-450 enzymes. However, in a reconstituted system with membrane incorporated proteins, again cytochrome P-450 IIB1 expressed a higher sensitivity towards cumene hydroperoxide than cytochrome P-450 IA1. From this it was concluded that the differential cumene hydroperoxide sensitivity of cytochrome P-450 IIB1 and IA1 is not caused by an intrinsic difference in their sensitivity but by a differential effect of membrane incorporation on their cumene hydroperoxide sensitivity.

Maintenance of monooxygenase activities and detection of cytochrome P-450-mediated cytotoxicity in Mongolian gerbil hepatocyte cultures

1. Hepatocytes were isolated from untreated and phenobarbitone (PB)-treated Mongolian gerbils by lobe perfusion. Yields were approx. 20 x 10(6) cells/g liver and viability was 95 +/- 1%. 2. PB treatment significantly increased the total cytochrome P-450 content, and the 7-ethoxycoumarin O-deethylase, p-nitrophenol hydroxylase and coumarin 7-hydroxylase activities, relative to those of untreated gerbils, measured in homogenates of freshly isolated hepatocytes. 3. After 24 h in culture the cytochrome P-450 content of hepatocyte homogenates from both untreated and PB-treated gerbils was 40-45% that of the corresponding values of freshly isolated hepatocytes. This decrease was accompanied by selective losses of cytochrome P-450-dependent enzyme activities. 4. Erythromycin and benzphetamine N-demethylase, and p-nitrophenol hydroxylase, activities were well maintained over 24 h in culture, whilst 7-ethoxycoumarin O-deethylase and coumarin 7-hydroxylase activities were poorly maintained. In general, the stability of the monooxygenase activities measured was improved by BP treatment of gerbils. 5. The toxicity of coumarin, precocene I and precocene II to gerbil hepatocyte cultures was dose-dependent. Precocene II was significantly more toxic to hepatocytes cultured from PB-treated, compared with untreated, gerbils. 6. Gerbil hepatocyte cultures would seem to be appropriate for investigating species differences in metabolism-mediated cytotoxicity.

Comparison of the effects of inducers of cytochrome P450 on Mongolian gerbil and rat hepatic microsomal monooxygenase activities

1. Basal cytochrome P450 content (nmol/mg protein) was higher in gerbil (1.10 +/- 0.01) than in rat (0.81 +/- 0.05) hepatic microsomes. Pretreatment of gerbils with phenobarbitone and beta-naphthoflavone increased P450 contents by 200% and 60% respectively. 2. 7-Ethoxycoumarin O-deethylase, coumarin 7-hydroxylase and 4-nitrophenol hydroxylase activities were generally higher in gerbil liver microsomes, whereas erythromycin N-demethylase, and 7-ethoxyresorufin and 7-pentoxyresorufin O-dealkylase activities were higher in rat microsomes. Microsomal benzphetamine N-demethylase activities were similar in both species. 3. Induction of specific cytochrome P450 isozymes increased similar monooxygenase activities of rat and gerbil microsomes. Phenobarbitone, beta-naphthoflavone, isoniazid and pregnenolone 16 alpha-carbonitrile principally increased benzphetamine N-demethylase, 7-ethoxyresorufin O-deethylase, 4-nitrophenol hydroxylase and erythromycin N-demethylase activities respectively. 4. Constitutive 7-ethoxyresorufin and 7-pentoxyresorufin O-dealkylase activities were markedly lower in gerbil microsomes compared with rat microsomes, and pretreatment of gerbils with cytochrome P450 inducers did not significantly increase these activities. 5. Hepatic microsomal coumarin 7-hydroxylase activities were approximately 30-200 times greater (depending on the inducer) in the gerbil than in rat. The gerbil, due to is high coumarin 7-hydroxylase activity, would appear to be a more appropriate species than rat for investigations of coumarin metabolism and toxicity relevant to humans.

Effect of acetone administration on renal, pulmonary and hepatic monooxygenase activities in hamster

Administration of acetone in drinking water to Syrian Golden hamsters for 9-10 days altered microsomal P-450 dependent monooxygenase activities in the liver and the kidney but not in the lung. While hepatic microsomal NADPH-cytochrome c reductase was unaffected, cytochrome b5 and P-450 content increased (about 100%) in liver but not in kidney. Furthermore acetone treatment resulted in an increase of microsomal reverse type I binding with DMSO and in an increase in the P-450IIE1-linked renal and hepatic activities such as aniline hydroxylase (AnH) and p-nitrophenol hydroxylase (pNPH). The SDS-PAGE analysis confirmed the induction in acetone-treated microsomes of a hepatic protein with the M.W. of ethanol inducible P-450IIE1 of hamster. The acetone treatment however, unlike ethanol, induced other activities such as benzphetamine N-demethylase and ethoxycoumarin O-deethylase in liver and aminopyrine N-demethylase in kidney. No change of ethoxyresorufin O-deethylase and pentoxyresorufin O-depentylase was observed in either renal or hepatic microsomes. Addition of acetone in vitro had an inhibitory effect on pNPH by hepatic microsomes from control or acetone induced hamsters, while AnH was not affected. Interruption of acetone administration for 24 h resulted in a return of AnH and pNPH activities to essentially basal levels in the liver suggesting a rapid turnover of the hamster P-450IIE1 (ham P-450j). Our results indicate that, as found in rat, acetone is a good inducer of the P-450IIE1 (ham P-450j) in hamster in both the liver and kidney. However other P-450 forms, such as, probably, the renal and hepatic P-450IIB1, are also induced. Thus acetone-treated hamsters, which, in certain respects, show a qualitatively different induction pattern from that reported for ethanol, can be used as an useful animal model to study the toxicity of certain xenobiotics.

Comparison of polychlorinated dibenzodioxin levels with hepatic mixed-function oxidase induction in great blue herons

As part of the Canadian Wildlife Service monitoring of great blue herons in British Columbia, eggs were collected from three colonies with low, intermediate, and high levels of PCDD and PCDF contamination: Nicomekl, Vancouver, and Crofton, respectively. One egg from each nest was used for chemical analysis by GC-MS; the others were hatched. Liver microsomes were prepared from the heron chicks and used for determination of cytochrome P-450-dependent activities. No erythromycin N-demethylase activity was found in any sample. Ethoxyresorufin O-dealkylase activity in the Nicomekl group was similar to that in pigeons, a control altricial species. The ethoxyresorufin activity in the herons from the Crofton colony was 2.6-fold higher than in the Nicomekl group. The Vancouver colony was intermediate. No difference among the three heron colonies was found in pentoxyresorufin O-dealkylase activity, although levels were 20-33 times that in the pigeon. Chemical analysis was carried out on paired heron eggs. Vancouver and Crofton eggs contained 13.5 and 21 times the levels of 2,3,7,8-TCDD compared to the Nicomekl group. The Crofton eggs contained higher levels of several other contaminants also. A highly significant correlation (p less than .001) was found between ethoxyresorufin O-dealkylase and 2,3,7,8-TCDD concentrations. The correlation coefficient did not change when ethoxyresorufin O-dealkylase was compared to total chemical contamination using several toxic equivalency factors. Multiple regression analysis resulted in only one predictor variable for ethoxyresorufin O-dealkylase: 2,3,7,8-TCDD.

Induction of hepatic cytochrome P-450 mediated alkoxyresorufin O-dealkylase activities in different species by prototype P-450 inducers

The induction of cytochrome P-450-mediated alkoxyresorufin O-dealkylase activities by various xenobiotics was examined in liver from a variety of animal species in order to gain insights into the substrate specificities of the induced P-450s. We found that forms of cytochrome P-450 capable of mediating the O-dealkylation of the short-chain phenoxazone ethers methoxy-, ethoxy- and propoxyresorufin were highly induced by 3-methylcholanthrene-type inducers and by Aroclor-1254 in all species tested, although there were species differences in the relative turnover rates for the various substrates. For example, in hamster liver the turnover rates for the short-chain resorufin ethers decreased in the following order: methoxy greater than ethoxy much greater than propoxy, while in the rat liver almost the exact opposite order was observed: ethoxy = propoxy much greater than methoxy. In contrast, the degree of induction by phenobarbital-type inducers of isozymes catalyzing the O-dealkylation of pentoxy- or benzyloxyresorufin was highly species-dependent. Thus, F344/NCr rats, B6C3F1 mice and NZB rabbits showed the greatest (greater than 20-fold) induction of these activities, either by phenobarbital or Aroclor-1254, while Mongolian gerbils showed intermediate levels of induction and Syrian golden hamsters exhibited very low induction. In the Japanese quail, phenobarbital- or DDT-treatment resulted in minimal induction of pentoxy- or benzyloxyresorufin O-dealkylase activity, although significant induction of the latter activity occurred following treatment with 5,6-benzoflavone or with Aroclor-1254. Since substrate specificities of most enzymes can be rationalized based upon differences in the steric requirements at the enzyme active site, we employed molecular modeling techniques to calculate the molecular dimensions of the alkoxyresorufins. Surprisingly, the minimal energy conformations in vacuo of each of the resorufin ethers examined are essentially planar. However, alternative configurations, especially for the pentoxy- and benxyloxy-ethers, having greater three-dimensional bulk are also energetically possible.

Effect of pretreatment of male Syrian golden hamsters with 7,8-benzoflavone and with diethylstilbestrol on P-450 isoenzyme activities and on microsomal diethylstilbestrol metabolism

Combined treatment of male Syrian golden hamsters with the synthetic estrogen diethylstilbestrol (DES) and 7,8-benzoflavone (7,8-BF) gives rise to a high incidence of hepatocellular carcinomas, whereas no such tumors are formed with DES alone nor with 7,8-BF alone. To determine whether alterations in DES metabolism may account for the observed hepatocarcinogenicity, we have studied the effect of pretreatment with 7,8-BF alone, DES alone and 7,8-BF plus DES on the levels of hepatic P-450 and cytochrome b5, on the activities of various P-450 isoenzymes and on microsomal DES metabolism. Hepatic P-450 content was significantly increased after pretreatment with 7,8-BF and decreased after DES, while combined pretreatment led to levels similar to those in untreated control animals. Hepatic cytochrome b5 was also elevated in 7,8-BF-treated hamsters; DES pretreatment had no effect, and combined pretreatment led to a slight increase. Four different substrates were used to probe P-450 isoenzyme activity. Aryl hydrocarbon hydroxylase (AHH), 7-ethoxycoumarin-O-deethylase (ECOD), 7-ethoxyresorufin-O-deethylase (EROD) and 7-pentoxyresorufin-O-dealkylase (PROD) were all elevated after 7,8-BF-pretreatment, while DES led to a decrease in these activities with the exception of AHH, where a transient increase which was observed after 8 and 20 weeks of pretreatment was back to control levels after 32 weeks. Combined pretreatment with 7,8-BF and DES led to an intermediate response (slight increase) with AHH, EROD and PROD, but not with ECOD, where a full induction comparable with that observed after 7,8-BF alone was elicited. In spite of the modulation of enzyme levels and activities observed after the various pretreatments, the metabolism of DES in microsomes from pretreated animals was virtually identical with that from controls. Therefore it is concluded that modulation of hepatic DES metabolism is not the reason for the observed hepatotumorigenicity; instead, it is speculated that 7,8-BF is the carcinogenic agent in this tumor model, and DES may act as a promotor.