Species and sex differences of testosterone and nifedipine oxidation in liver microsomes of rat, dog and monkey

Comparison of mRNA expression profiles of drug-metabolizing enzymes and transporters in fresh and cryopreserved cynomolgus monkey hepatocytes

In this study, freshly isolated and cryopreserved cynomolgus monkey hepatocytes were seeded on Cell-able^® plates with feeder cells to form spheroids and were cultured for 28 days. As a control, hepatocytes were also cultured with or without feeder cells on collagen-coated plates. We verified the mRNA expression levels of drug-metabolizing enzyme-related genes and the leakage of enzymes (AST, ALT, LDH, and γ-GTP) as indicators of cell survival. As a result, the patterns of target mRNA expression in fresh and cryopreserved hepatocytes were very similar during the culture period between culture methods. mRNA expression levels were highly maintained at day 28 using the 3D spheroid and co-culture methods, demonstrating that these methods are useful for maintenance of liver function. Leakage of AST and ALT was higher at day 3 but decreased at day 14. LDH was not detected, suggesting that the cell viability was also maintained during the culture period. Furthermore, the functional differences between fresh and cryopreserved hepatocytes were not clearly detected. The co-culture method was useful for long-term culture not requiring 3D structure, and the 3D spheroid culture method was effective as well. With these techniques, cynomolgus monkey hepatocytes are expected to exhibit smaller individual differences and high reproducibility.

Study on the pharmacokinetics of deoxyschizandrin and schizandrin in combination with epigallocatechin gallate, a component of green tea, in rats

1. Green tea is commonly used worldwide due to its potential positive health benefits. We have examined the effects of epigallocatechin gallate (EGCG), the most abundant catechin in green tea, on the pharmacokinetics of deoxyschizandrin (DSD) and schizandrin (SD), which are the representative lignans in popular traditional Chinese medicines Fructus schisandrae, in rats. 2. The effects on the transport in Caco-2 cells and metabolism in human liver microsomes (HLMs) of DSD and SD by EGCG were determined to analyze their interactions thoroughly. 3. In pharmacokinetic studies, rats were divided into four groups. Each group was orally treated with DSD alone (Group 1), DSD combined with EGCG (Group 2), SD alone (Group 3) and SD combined with EGCG (Group 4). The pharmacokinetic parameters of DSD and SD in rats were determined by UPLC-MS/MS. 4. The in vivo results indicated that EGCG had no significant influence on the pharmacokinetic behaviors of DSD or SD in rats, which were in accordance with the in vitro transport and metabolism studies. However, there were marked differences between male and female rats among C_max, AUC_0-t, AUC_0-∞ of DSD and SD. This disparity suggested that gender differences might exist in the pharmacokinetic processes of DSD or SD in rats.

Photostabilization studies of antihypertensive 1,4-dihydropyridines using polymeric containers

1,4-dihydropyridine antihypertensives (DHPs) are almost all dispensed in solid pharmaceutical formulations for their easy lability when exposed to light. This paper reports a study on the photoprotective effect of containers in different glassy or polymeric matrices with regard to four known DHPs when in solutions. The samples were subjected to forced degradation by means of a Xenon lamp, in accordance with the international rules on drug stability evaluation. The simultaneous determination of the drugs and their photoproducts was carried out by applying the multivariate curve resolution (MCR) methodology to the spectral data recorded along the irradiation test. This technique was able to determine the kinetic parameters and resolve the spectra of the photoproducts. The time required to reduce by 10% the concentration of the drug (t0.1) was adopted as a criterion to compare the protective ability of the containers. A significant photoprotection for all drugs tested was obtained by the use of polyethylene terephthalate (PET) containers. The best result was achieved for the felodipine solution in blue PET transparent bottle of 0.6mm thickness, reaching an almost complete stabilization up to six hours under stressing irradiation. In contrast, the glass containers, whether or not coloured, did not provide a satisfactory photoprotection of the drugs, showing in any case t0.1 values under 24min. These results can be a good opportunity to design new photoprotective pharmaceutical packaging for DHPs in liquid dosage form.

The effects of endosulfan on cytochrome P450 enzymes and glutathione S-transferases in zebrafish (Danio rerio) livers

Endosulfan, an organochlorine pesticide, has been used worldwide in the past decades. The present study was performed to investigate the effect of endosulfan on liver microsomal cytochrome P450 (CYP) enzymes and glutathione S-transferases (GST) in zebrafish. Male and female zebrafish were separated and exposed to a control and four concentrations of endosulfan (0.01, 0.1, 1, and 10μgL(-1)) and were sampled on days 7, 14, 21, and 28. After exposure to endosulfan, the content of CYP increased and later gradually fell back to control level in most sampling time intervals. A similar tendency was also found in the activities of NADPH-P450 reductase (NCR), aminopyrine N-demethylase (APND) and erythromycin N-demethylase (ERND). GST activities were generally higher in treatment groups than control groups. Regarding sex-based differences, the induction degree of the activity of NCR was generally higher in males than females. Similar differences were also found on the 28th day in the activities of APND and ERND, as well as GST activity on the 7th day. Overall, the present results demonstrate the toxicity at low doses of endosulfan and indicated marked induction of CYP and GST enzymes in zebrafish liver.

Patient variation in veterinary medicine--part II--influence of physiological variables

In veterinary medicine, the characterization of a drug's pharmacokinetic properties is generally based upon data that are derived from studies that employ small groups of young healthy animals, often of a single breed. In Part I of the series, we focused on the potential influence of disease processes, stress, pregnancy and lactation on drug pharmacokinetics. In this Part II of the series, we consider other covariates, such as gender, heritable traits, age, body composition, and circadian rhythms. The impact of these factors with respect to predicting the relationship between dose and drug exposure characteristics within an animal population is illustrated through the use of Monte Carlo simulations. Ultimately, an appreciation of these potential influences will improve the prediction of situations when dose adjustments may be appropriate.

Lead and cadmium co-exposure mediated toxic insults on hepatic steroid metabolism and antioxidant system of adult male rats

The redox status and steroid metabolism of liver of adult male rat exposed to lead (Pb) and cadmium (Cd) either alone or in co-exposure (0.025 mg/kg body weight intraperitoneally/15 days) was studied. Pb and Cd significantly accumulated in the liver. The activity of steroid metabolizing enzymes 17-betahydroxysteroid oxidoreductase and uridine diphosphate-glucuronyltransferase were decreased in experimental animals. 17-beta-Hydroxysteroid dehydrogenase was reduced to 33%, 38%, and 24% on treatment of Pb, Cd, and co-exposure (Pb + Cd). Furthermore, the activity of uridine diphosphate-glucuronosyltransferase was significantly reduced to 27% (Pb exposure), 36% (Cd exposure), and 25% (co-exposure of Pb + Cd). Cd exposure exhibited more toxic effect than Pb, while co-exposure demonstrated the least. The activities of antioxidant enzymes, superoxide dismutase, catalase, glutathione reductase, and glucose-6-phosphate dehydrogenase decreased and glutathione peroxidase increased in mitochondrial and post-mitochondrial fractions. The level of lipid peroxidation increased, and cellular glutathione concentration decreased. Hepatic DNA was decreased, whereas RNA content and the activity of alanine transaminase remained unchanged. Histological studies revealed that only Cd-exposed groups exhibited cytotoxic effect. These results suggest that when Pb and Cd are present together in similar concentrations, they exhibited relatively decreased toxic effect when compared to lead and cadmium in isolation with regard to decreased steroid metabolizing and antioxidant enzyme activities. This seems that the toxic effect of these metals is antagonized by co-exposure due to possible competition amongst Pb and Cd for hepatic accumulation.

Contaminant-induced feminization and demasculinization of nonmammalian vertebrate males in aquatic environments

Many chemicals introduced into the environment by humans adversely affect embryonic development and the functioning of the male reproductive system. It has been hypothesized that these developmental alterations are due to the endocrine-disruptive effects of various environmental contaminants. The endocrine system exhibits an organizational effect on the developing embryo. Thus, a disruption of the normal hormonal signals can permanently modify the organization and future function of the male reproductive system. A wide range of studies examining wildlife either in laboratories or in natural settings have documented alterations in the development of males. These studies have begun to provide the causal relationships between embryonic contaminant exposure and reproductive abnormalities that have been lacking in pure field studies of wild populations. An understanding of the developmental consequences of endocrine disruption in wildlife can lead to new indicators of exposure and a better understanding of the most sensitive life stages as well as the consequences of exposure during these periods.

Expression of cytochrome P450 enzymes in hepatic organoid reconstructed by rat small hepatocytes

BACKGROUND AND AIMS

Small hepatocytes (SH), which are hepatic progenitor cells, were isolated from an adult rat liver. SH in a colony sometimes change their shape from small to large and from flat to rising/piled-up. The morphological changes of SH may be correlated with hepatic maturation. Cytochrome P450s (CYP) are drug-metabolizing enzymes and the expression is one of hepatic differentiated functions. However, it is well known that the re-expression and maintenance of CYP activity are very difficult in cultured hepatocytes. We investigated the expression of CYP and the enzymatic activities in long-term cultured SH.

METHODS

SH were isolated from adult rat livers and SH colonies were collected, replated on new dishes, and then cultured. CYP1A1/2, CYP2B1, CYP3A2, CYP4A1, and CYP2E1 were induced by the addition of 3-methylcholanthrene, phenobarbital, pregnenolone-16alpha-carbonitrile, clofibric acid, and ethanol, respectively. Immunocytochemistry, immunoblots, and enzyme activities were examined.

RESULTS

SH could differentiate into mature hepatocytes by the addition of Matrigel and re-express constitutive CYPs. The expression of CYP1A1/2, CYP2B1, CYP3A2, and CYP4A1 dose-dependently increased and the amounts gradually increased with time in culture, especially in the cells treated with Matrigel. Activities of CYP1A, CYP2B, CYP3A and CYP2E in SH treated with Matrigel induced by each of the inducers were approximately 120-fold, 2.8-fold, 6.4-fold and 0.8-fold higher than in the control.

CONCLUSION

The matured SH could re-express the constitutive CYP and recover inducibility, not only of protein expression but also of enzyme activities.

DDT increases hepatic testosterone metabolism in rats

DDT and its metabolites are considered as endocrine disruptors able to promote hormone-dependent pathologies. We studied the effects of technical-grade DDT on hepatic testosterone metabolism and testosterone hydroxylase activity ratios in the rat. Male and female Wistar rats were treated by gavage with a single dose of technical-grade DDT (0, 0.1, 1, 10, and 100 mg/kg body weight) and killed 24 h later. Hepatic microsomes were incubated with [4-14C]-testosterone and the metabolites were separated by thin-layer chromatography and quantified by radio scanning. DDT increased testosterone biotransformation and modified the profile of metabolites produced in a sex-dependent manner. Males treated with a representative dose (10 mg/kg) produced relatively less androstenedione (AD), 2alpha-hydroxytestosterone (OHT), and 16alpha-OHT but higher 6beta-OHT whereas treated females produced less 7alpha-OHT and AD but higher 6beta-OHT and 6alpha-OHT than their respective controls. In both sexes DDT decreased the relative proportion of AD and increased that of 6beta-OHT suggesting that the androgen-saving pathway was affected. The testosterone 6alpha-/15alpha-OHT ratio, a proposed indicator of demasculinization, was increased in treated males. This effect was in agreement with the demasculinizing ability proposed for DDT. The effects on 6alpha-/16alpha-OHT and 6-dehydrotestosterone/16alpha-OHT ratios followed a similar tendency, with the ratio 6alpha-/16alpha-OHT being the most sensitive marker. Interestingly, these ratios were reduced in treated females suggesting that technical-grade DDT shifted testosterone hydroxylations toward a more masculine pattern. Thus, technical-grade DDT altered the hepatic sexual dimorphism in testosterone metabolism and decreased the metabolic differences between male and female rats.

Influence of recipient gender on intrasplenic fetal liver tissue transplants in rats: cytochrome P450-mediated monooxygenase functions

Rat livers display a sex-specific cytochrome P450 (P450) isoforms expression pattern with consecutive differences in P450-mediated monooxygenase activities, which have been shown to be due to a differential profile of growth hormone (GH) secretion. Parallel to previous investigations on P450 isoforms expression, the aim of the present study was to elucidate the influence of recipient gender on P450-mediated monooxygenase activities in intrasplenic liver tissue transplants in comparison to orthotopic liver. Fetal liver tissue suspensions of mixed gender were transplanted into the spleen of adult male or female syngenic recipients. Four months after grafting transplant-recipients and age-matched controls were treated with beta-naphthoflavone (BNF), phenobarbital (PB), dexamethasone (DEX) or the vehicles and sacrificed 24 or 48 h thereafter. P450-dependent monooxygenase activities were assessed by a series of model reactions for different P450 subtypes in liver and spleen 9000 g supernatants. In spleens of male and female control rats only very low monooxygenase activities were detectable, whereas with most model reactions distinct activities were observed in transplant-containing organs. Livers and transplant-containing spleens from male rats displayed higher basal ethoxycoumarin O-deethylase and testosterone 2alpha-, 2beta-, 6beta-, 14alpha-, 15alpha-, 15beta-, 16alpha-, 16beta- and 17-hydroxylase activities than those from females. On the other hand, like the respective livers, spleens from female transplant-recipients demonstrated more pronounced p-nitrophenol- and testosterone 6alpha- and 7alpha-hydroxylase activities than those from male hosts. With nearly all model reactions gender-specific differences in inducibility by BNF, PB or DEX could be demonstrated in livers as well as in transplant-containing spleens. These results further confirm that the P450 system of intrasplenic liver tissue transplants and the respective orthotopic livers is similarly influenced by recipient gender.

Expression of CYP3A4 mRNA Is Correlated With CYP3A4 Protein Level and Metabolic Activity in Human Liver

A relatively large amount of human liver tissue was required to determine the exact activity of human hepatic CYP3A. Although, the quantity of available human liver tissue samples is limited. We measured levels of CYP3A4 mRNA by RT-PCR with a radiolabeled primer specific for CYP3A4 and compared mRNA expression with CYP3A4 protein level and metabolic activity in liver. The level of CYP3A4 mRNA was correlated with the levels of CYP3A4 protein and activity. Our results suggest that CYP3A4 protein and activity levels can be predicted from CYP3A4 mRNA levels determined by RT-PCR and using a very small amount of liver tissue.

Species Difference in Nisoldipine Oxidation Activity in the Small Intestine

Species difference in nisoldipine oxidation activities was investigated using small intestinal microsomes of rats, guinea pigs, dogs, monkeys and humans. The oxidation activities were estimated by measuring metabolites formation (BAY o 3199 and BAY r 9425) of nisoldipine. For the preparation of small intestinal microsomes of various animal species, the effect of protease inhibitors was preliminarily investigated. The formation of BAY o 3199 significantly increased in the rat small intestinal microsomes prepared with trypsin inhibitor. Using the trypsin inhibitor-treated small intestinal microsomes of various animals, metabolic intrinsic clearances (CL(int, in vitro)) for BAY o 3199 and BAY r 9425 formations were estimated based on an Eadie-Hofstee plot. The total CL(int,in vitro) estimated by the sum of CL(int, in vitro) for both formations in the small intestines of all species was much lower than that in the liver. There was a marked species difference in the nisoldipine oxidation activities in the small intestines, with the rank order being humans=monkeys>dogs>rats>guinea pigs, versus the following order in the liver: rats>monkeys=guinea pigs>humans>dogs. The formations of both BAY o 3199 and BAY r 9425 in the human intestinal microsomes were inhibited by pretreatment with troleandomycin (TAO) and antiserum against CYP3A4. Similar inhibition profile by TAO was obtained from the monkey intestinal microsomes. These results implied that monkeys would be a good predictor of human small intestinal metabolism for CYP3A4 substrates.

Neonatal low- and high-dose exposure to estradiol benzoate in the male rat: II. Effects on male puberty and the reproductive tract

Environmental contaminants with estrogenic properties have been cause for heightened concern about their possible role in inducing adverse health effects. Brief exposure of rodents to high doses of natural estrogens early in life results in permanent alterations of the male reproductive tissues, but the question of whether environmentally relevant doses can cause the same effects remains controversial. The current project was designed to determine the dose-response relationship between neonatal estradiol exposure and the development of the male reproductive tract in the rat. Neonatal male Sprague-Dawley (SD) and Fisher 344 (F344) rats were exposed to beta-estradiol-3-benzoate (EB) at concentrations ranging from 0.015 microg/kg body weight (BW) to 15.0 mg/kg BW and 0.15 microg/kg BW to 1.5 mg/kg BW, respectively. Results showed an inverted U-shaped dose-response profile for testis and epididymis weights in 35-day-old SD rats, with increased organ sizes at the low-dose end of the treatment. This effect was transient and was not sustained into adulthood. Increased hepatic testosterone hydroxylase activities in low-dose animals suggest an advancement of puberty as the cause for increased reproductive organ weights. On postnatal day (PND) 90, a stimulatory low-dose response to EB was present in SD rat testicular and epididymal weights, however at one order of magnitude lower dose than that seen on PND 35, suggesting a separate effect. All SD male reproductive tract organs and serum hormones showed a permanent inhibitory response to high doses of neonatal EB. F344 rats exhibited greater estrogen sensitivity on PND 90. Despite this heightened responsiveness, F344 rats did not exhibit a low-dose effect for any endpoint. These low-dose responses to estradiol are organ and strain specific.

Rapid high-performance liquid chromatographic method for the separation of hydroxylated testosterone metabolites

A rapid high-performance liquid chromatography (HPLC) method is described for the quantitation of hydroxytestosterone metabolites. The method combines a Hypersil BDS C18 analytical column (10 cm x 0.46 cm) and a linear mobile phase (1.25 ml/min) gradient of tetrahydrofuran-acetonitrile-water (10:10:80, v/v) changing to tetrahydrofuran-acetonitrile-water (14:14:72, v/v) over 10 min then remaining isocratic for 3 min. The total run time for the chromatographic separation of eight metabolites of testosterone is 15 min. Detection by UV is linear between 300 ng/ml and 10 microg/ml with a limit of detection on column of 300 ng/ml. A method for the direct HPLC analysis of liver microsomal incubates of [14C]testosterone is also briefly described and when combined with the HPLC method, offers a distinct advantage over previously reported methods for the rapid screening of testosterone hydroxylase activity in rat and human liver microsomes.

Collagen type I gel cultures of adult rat hepatocytes as a screening induction model for cytochrome P450-dependent enzymes

Albumin secretion, expression of cytochrome P450 dependent mono-oxygenases (CYPs) and their inducibility by well-known inducers were evaluated during 1 week in collagen type I gel sandwich and immobilisation cultures of adult primary rat hepatocytes. Albumin secretion increased during culture time and, following an initial decrease, CYP biotransformation activities remained stable for at least 7 days. Better preservation results were observed in the collagen gel sandwich culture than in the immobilisation model. The inducibility of CYPs by beta-naphthoflavone (beta-NF), 3- methylcholanthrene (3-MC), phenobarbital (PB) and dexamethasone (DEX) was studied in both collagen gel hepatocyte cultures. Exposure of the cells to either 5microM 3-MC or 25 microM beta-NF, added to the culture medium, resulted in strong increases of CYP1A1/2 activity in both culture models. Treatment with PB (3.2 mM) resulted in an increase in the CYP2B activity and a higher hydroxylation of testosterone in the 16alpha-position (CYP2B1/2 and CYP2C11), the 7alpha-position (CYP2A1/2), and the 6beta-position (CYP3A1). DEX (10 microM) markedly increased testosterone 6beta- and 7alpha-hydroxylation. Expression and induction experiments of CYP proteins exposed to these molecules confirmed the results of the CYP activity measurements. The patterns of CYP induction in collagen gel cultures of rat hepatocytes were similar to those observed in vivo. Consequently, collagen gel cultures and, more specifically, collagen gel sandwich cultures seem to be suitable as in vitro models for evaluating xenobiotics as potential inducers of CYP-enzymes.

Comparative in vitro metabolism of indinavir in primates--a unique stereoselective hydroxylation in monkey

1. The in vitro metabolism of indinavir (CRIXIVAN, MK-0639, L-735,524), an HIV protease inhibitor, was evaluated using liver microsomes from cynomolgus monkey, rhesus monkey, chimpanzee and human. Indinavir exhibited marked species differences in metabolism. The overall rate of indinavir metabolism varied > 4-fold among primates (84 pmol/min/mg protein in cynomolgus monkey versus 20.4 pmol/min/mg protein in human) and followed the rank order: cynomolgus monkey > rhesus monkey > chimpanzee > human. 2. The cis-(indan)hydroxylated metabolite of indinavir was formed only in cynomolgus and rhesus monkey livers, whereas trans-(indan)hydroxylation and N-dealkylation were observed as the major metabolites in all primates tested. Inhibition studies with P450-selective inhibitors (ketoconazole, quinine, quinidine) and monoclonal antibodies (against CYP2D6 or CYP3A4) indicated that a cytochrome P450 isoform of the CYP2D subfamily is involved in the formation of the unique cis-(indan) hydroxylated metabolite in monkey, whereas all other oxidative metabolites, including the trans-(indan)hydroxylated metabolite, are formed by CYP3A isoform(s). 3. The present study has demonstrated that monkeys were unique in their abilities to form the stereoselective metabolite and were not appropriate surrogates for the qualitative prediction of indinavir metabolism in human.

A comparison of the effect of five phenothiazines on hepatic CYP isoenzymes in rats

We examined the influence of five phenothiazine derivatives on the activity and the expression of hepatic cytochrome P450 (CYP) 1A, 2B, 2C6, 2C11, 2E1 and 3A2 in male Sprague-Dawley rats. Twenty mg/kg of phenothiazine, chlorpromazine, and thioridazine, or 1 mg/kg of trifluoperazine and perphenazine was administered intraperitoneally for 4 consecutive days. Phenothiazine increased the total CYP content and induced CYP1A, CYP2B, and CYP3A. Western blot analysis showed marked induction of CYP1A1 by phenothiazine. Chlorpromazine induced CYP2B, and CYP3A without a significant increase in the CYP content. Thioridazine decreased the total CYP content and reduced CYP2C11, CYP2E1, and CYP3A. Neither trifluoperazine nor perphenazine significantly altered the catalytic activity or the protein level of any enzyme examined. These results suggest that the antipsychotic phenothiazine derivatives examined here hardly affect CYP1A at the pharmacological doses, while phenothiazine does induce it. Although a relatively short period and small dose of administration might counteract the influence, trifluoperazine and perphenazine have less effect on CYP subfamilies than chlorpromazine or thioridazine.

Ursodeoxycholic acid prevents hepatic cytochrome P450 isozyme reduction in rats with deoxycholic acid-induced liver injury

BACKGROUND/AIMS

Hydrophobic bile acids, such as deoxycholic acid produce cholestatic liver injury. Ursodeoxycholic acid has been shown to be useful in the treatment of cholestatic liver disease.

METHODS

In this study, we investigated the effects of deoxycholic acid or ursodeoxycholic acid (1% of diet, for 14 days) and their combination (1% each) on expression of hepatic cytochrome P450 isozymes, their related enzyme activities and mRNA level in rats.

RESULTS

Adding 1% deoxycholic acid to chow caused a marked increase in serum total bilirubin (47-fold) and total bile acid (8-fold) concentrations and in alkaline phosphatase (2.5-fold, p<0.01) and alanine aminotransferase activities (23.5-fold, p<0.01). Adding the same dose of ursodeoxycholic acid along with the deoxycholic acid mitigated both the rise in serum total bilirubin and bile acid concentrations and that in alkaline phosphatase and alanine aminotransferase activities, although the use of ursodeoxycholic acid alone did not affect any of the above. Feeding 1% deoxycholic acid caused a decrease (48% of control) in total cytochrome P450 content in hepatic microsomes. Addition of 1% ursodeoxycholic acid along with the 1% deoxycholic acid completely prevented the decrease in total cytochrome P450 content. Feeding ursodeoxycholic acid alone did not affect the total cytochrome P450 content. The expression of cytochrome P450 2B1, 2E1, 3A2, 2C6, 2C11 and 4A1 proteins in hepatic microsomes was decreased by deoxycholic acid (44, 51, 23, 59, 30 and 74% of control, respectively). Likewise, the activities of cytochrome P450 2B1 (pentoxyresorufin O-depentylation), 2E1 (aniline p-hydroxylation) and 3A2 (testosterone 6beta-hydroxylation) isozymes and the 3A2 mRNA levels in liver were decreased by deoxycholic acid. Addition of 1% ursodeoxycholic acid to 1% deoxycholic acid also prevented the decrease in these cytochrome P450 proteins, related enzyme activities and mRNA levels in liver.

CONCLUSIONS

These results indicate that, in rats with deoxycholic acid-induced liver injury, ursodeoxycholic acid prevents the decrease in hepatic cytochrome P450 isozymes and suggest that ursodeoxycholic acid is useful for the treatment of liver injury in terms of aiding the normalization of the hepatic drug-metabolizing system.

Multiple cytochrome P-450 subfamilies are co-induced with P-glycoprotein by both phenothiazine and 2-acetylaminofluorene in rats

We studied the effects of two P-glycoprotein (P-gp) inducers, 2-acetylaminofluorene (2-AAF) and phenothiazine (PTZ), administered intraperitoneally, on the activities and content of hepatic cytochrome P-450 (CYP) subfamilies in hepatic microsomes of Sprague-Dawley rats. After 4-day administration of 2-AAF or PTZ, the P-gp content was increased. The total CYP content after PTZ treatment was significantly increased compared with that of controls. The CYP1A, CYP2B and CYP3A2 contents were induced, while the CYP2C6, CYP2C11 and CYP2E1 contents remained unaffected. A marked increase in CYP1A1 was found after administration of each compound. Ethoxyresorufin O-deethylase, pentoxyresorufin O-deethylase, and testosterone 6beta hydroxylation activities showed a significant increase after both 2-AAF and PTZ treatments. In particular, ethoxyresorufin O-deethylase exhibited more than ten times greater activity than that of the controls after the treatments. These results suggest that P-gp inducers affect several CYP subfamilies in addition to CYP3A, which is reported to be up-regulated coordinately with P-gp by a CYP3A inducer.

Carbamazepine induces multiple cytochrome P450 subfamilies in rats

We compared the effect of three different doses (30, 60, and 100 mg/kg) of carbamazepine (CBZ) administered intraperitoneally for 1, 3, and 7 days on the activity and protein content of hepatic cytochrome P450 (CYP) subfamilies in Sprague-Dawley rats. After 3-day- and 7-day administration with CBZ, the total CYP content had increased in a dose-dependent fashion. Among six enzyme activities examined, only aniline hydroxylase activity remained unchanged after 7-day treatment with CBZ. Pentoxyresorufin O-deethylase activity showed the most significant increase and was induced up to 7 days in a time-dependent fashion. Pretreatment of rats with cycloheximide significantly suppressed the pentoxyresorufin O-deethylase induction by one dose of 100 mg/day CBZ. Immunoblot analysis showed a significant correlation between the protein content of each isoenzyme examined and its activity except CYP2E1 after 7-day treatment with CBZ. Similar results were obtained in the mRNA levels of CYP subfamilies. These results suggested that CBZ may induce multiple CYP subfamilies, except CYP2E1, and the activity and the protein content of CYP2B showed the greatest increase with increased CYP2B mRNA.

Induction and inhibition of the in vitro N1-oxidation of 9-benzyladenine and isomeric 9-(nitrobenzyl)adenines

The present study investigated some aspects of the enzymology of the in vitro N1-oxidation of 9-benzyladenine (BA) and isomeric 9-(nitrobenzyl)adenines (NBAs) using various potential inducers and inhibitors of cytochrome P-450 (CYP). When incubated with phenobarbital-induced rabbit hepatic microsomes, the N1-oxidation rates of BA and 9-(4-nitrobenzyl)adenine were about 6- and 2-fold higher than that of the control, respectively; while the N1-oxidation of 9-(2-nitrobenzyl)adenine and 9-(3-nitrobenzyl)adenine was not markedly affected. In contrast, beta-naphthoflavone and Arochlor 1254 showed no inductive effects towards the N1-oxidation of any of these substrates. Using 12 typical CYP inhibitors, it was found that nifedipine (CYP3A inhibitor) and haloperidol (CYP2D inhibitor) showed significant inhibition towards the N1-oxidation of BA and NBAs. Therefore, the N1-oxidation of BA and NBAs is probably catalysed by CYP3A and CYP2D subfamilies. Furthermore, when 9-(4-nitrobenzyl)adenine was incubated with compounds which possessed a certain chemical similarity to the adenine substrate, various degrees of inhibition of N1-oxidation of 9-(4-nitrobenzyl)adenine were observed. These observations allowed a preliminary indication as to the structure-metabolism relationship of 9-substituted adenine derivatives.

Induction of hepatic CYP2B in foetal and neonatal rats after maternal administration of phenobarbital

We examined hepatic cytochrome P450 (CYP) induction in rat foetuses and neonates by phenobarbital administered through placenta or breast feeding. In an intraperitoneal study, phenobarbital was administered intraperitoneally to mother rats once a day for 7 consecutive days before delivery. The livers were removed from foetuses, neonates, and mothers just before and 5 and 10 days after delivery. In oral administration study, water containing phenobarbital was given orally ad libitum from day 13 of pregnancy to 3 weeks after delivery (end of lactation). The livers were removed from neonates and mothers just before and one week after delactation. Phenobarbital administered intraperitoneally increased both the activity and the protein expression of CYP2B in 5-day-old neonates, even though the administration ended before delivery. This increase had disappeared in 10-day-old neonates. In mother rats, phenobarbital increased CYP2B just before and 5 days after delivery, while no increase was detected 10 days after delivery. Phenobarbital administered orally also increased both the activity and the protein expression of CYP2B of neonates and mothers during lactation and this increase also disappeared 1 week after delactation. Neither activity nor protein expression of CYP3A were induced in perinates at any age examined in either administration route. In mother rats, increase in CYP3A was found only just before delivery in the peritoneal administration study. Our results suggest that phenobarbital administered through placenta or breast milk transiently induces hepatic CYP2B in newborn rats but that the influence of phenobarbital does not last long.

Characterization of cytochrome P450 (CYP3A12) induction by rifampicin in dog liver

1. Effects of rifampicin (Rif) on the contents of cytochrome P450 (P450) enzymes (CYP1A1/2, 2B11, 2C21 and 3A12) assessed by enzyme-linked immunosorbent assay and catalytic activities (ethoxyresorufin O-deethylase, and testosterone 6 beta-, 16 alpha- and 16 beta-hydroxylase; 6 beta-, 16 alpha- and 16 beta-OHT) in dog liver microsomes were compared between liver lobes of both the male and female dogs. 2. In the control dogs, the contents of individual P450 enzymes and their activities showed no significant differences between individual liver lobes and between the sexes. 3. Rif treatment (10 mg/kg/day, p.o. for 7 days) induced substantial increases in the content of CYP3A12 and 6 beta- and 16 beta-OHT activities, and slight increases in the content of CYP2B11 and 16 alpha-OHT activity, and their elevated levels were virtually the same between liver lobes. The magnitudes of the elevation of the CYP3A12 level and 6 beta- and 16 beta-OHT activities compared with control levels appeared to be greater in the female dogs. However, the ratios of their magnitudes (CYP3A content/6 beta-OHT activity and CYP3A content/16 beta-OHT activity) showed no differences between the sexes. 4. In both the control and Rif-treated dogs, the activities of 6 beta- and 16 beta-OHT were specifically inhibited by anti-CYP3A12 antiserum, and 16 alpha-OHT activity was specifically inhibited by anti-CYP2B11 and anti-CYP2C21 antiserum. 5. These results indicate that Rif treatment induces the expression of CYP3A12 protein, and correlates well with the elevation of its catalytic activity (6 beta- and 16 beta-OHT), and that the female dog is more responsive to Rif treatment as compared with the male.

Contribution of human hepatic cytochrome P450 isoforms to regioselective hydroxylation of steroid hormones

1. Hydroxylation activities toward steroid hormones were determined for eleven forms of human hepatic cytochrome P450s expressed in yeast Saccharomyces cerevisiae cells. Microsomes were prepared from the yeast cells and assayed for their regioselectivity of hydroxylation toward progesterone, pregnenolone, dehydroepiandrosterone (DHEA) and oestrone. 2. 6 beta-Hydroxylation of progesterone was catalysed most efficiently by CYP3A4, followed by CYP2D6. CYP3A4 showed the highest progesterone 16 alpha-hydroxylation activity, followed by CYP1A1 and CYP2D6. 16 alpha-Hydroxylation of pregnenolone was catalysed efficiently by CYP1A1 and CYP3A4. Only CYP3A4 exhibited 16 alpha-hydroxylase activities toward DHEA and oestrone. 3. Addition of nifedipine, a typical substrate of CYP3A4, inhibited the 6 beta- and 16 alpha-hydroxylation of progesterone by CYP3A4. 4. These results suggest that CYP3A4 and CYP1A1 are responsible for the hydroxylation of these endogenous steroids, as well as xenobiotics, in human liver.

Liver damage induced by bile duct ligation affects CYP isoenzymes differently in rats

We examined the influence of liver damage induced by bile duct ligation on the activity and the expression of hepatic cytochrome P450 (CYP) 1A, 2B, 2C6, 2C11, 2E1 and 3A2 in male Sprague-Dawley rats. In the ligation group, testosterone 2 alpha-, 16 alpha-, and 6 beta-hydroxylase activities were severely decreased, whereas ethoxyresorufin O-deethylase and progesterone 21-hydroxylase activities relatively remained. Pentoxyresorufin O-deethylase and chlorzoxazone 6-hydroxylase activities were reduced to approximately one thirds those of control. The protein contents of these isoenzymes expressed in hepatic microsomes of the ligation group were decreased to 45%, 32%, 79%, 13%, 58%, and 23% of control for CYP1A, 2B, 2C6, 2C11, 2E1 and 3A2, respectively. The rank order of magnitude of the influence of bile duct ligation on CYP isoenzymes, assessed by the reduction in the enzyme activity and the protein content, corresponded with each other except CYP1A. The reduction of the enzyme activities significantly correlated with the reduction in the protein contents of different isoenzymes. These results suggested that bile duct ligation affected CYP isoenzyme activities and contents with different extent.

Dexamethasone metabolism in vitro: species differences

Dexamethasone (DEX) is extensively metabolized to 6-hydroxyDEX (6OH-DEX) and side-chain cleaved metabolites in human liver both in vitro and in vivo with CYP3A4 responsible for the formation of 6-hydroxylated products. In the present study, the metabolism of [3H]DEX has been examined in the liver fractions from various mammalian species and metabolite profiles compared with those obtained with human liver microsomes. Metabolites were quantified by radiometric high-pressure liquid chromatography (HPLC) and characterized by liquid chromatography-mass spectrometry (LC-MS) and co-chromatography with chemical standards, where available. 6OH-DEX formation was quantified for each species and the inhibitory potency of ketoconazole at 1 and 20 microM determined. Glycyrrhetinic acid, a specific inhibitor of 11-dehydrogenase, was also used to determine the extent of reductive DEX metabolism. Species differences in metabolite profiles obtained from microsomal incubations were both quantitative and qualitative. 6-Hydroxylation was variable (highest in the hamster) and was not always the major route of metabolism, and formation was sex-specific in the rat (male >> female). The inhibition of 6-hydroxylation (CYP3A) by ketoconazole was variable, and indicates that ketoconazole cannot be regarded as a selective inhibitor of CYP3A proteins in all species. Cytosolic incubations produced similar profiles in different species with the formation of a metabolite (M5) which was inhibited by glycyrrhetinic acid and tentatively identified in this study as 11-dehydro-side-chain cleaved DEX (11DH-9alphaF-A). In conclusion, the male rat gave a metabolite profile which was closest to that seen in the human. However, 6-hydroxylation was most extensive in the hamster which may therefore be a suitable model to use for further studies on DEX metabolism by CYP3A.