Age- and sex-related expression of cytochromes p450f and P450g in rat liver

Gonadal hormone modulation of ∆9-tetrahydrocannabinol-induced antinociception and metabolism in female versus male rats

The gonadal hormones testosterone (T) in adult males and estradiol (E2) in adult females have been reported to modulate behavioral effects of ∆⁹-tetrahydrocannabinol (THC). This study determined whether activational effects of T and E2 are sex-specific, and whether hormones modulate production of the active metabolite 11-hydroxy-THC (11-OH-THC) and the inactive metabolite 11-nor-9-carboxy-THC (THC-COOH). Adult male and female rats were gonadectomized (GDX) and treated with nothing (0), T (10-mm Silastic capsule/100g body weight), or E2 (1-mm Silastic capsule/rat). Three weeks later, saline or the cytochrome P450 inhibitor proadifen (25mg/kg; to block THC metabolism and boost THC's effects) was injected i.p.; 1h later, vehicle or THC (3mg/kg females, 5mg/kg males) was injected i.p., and rats were tested for antinociceptive and motoric effects 15-240min post-injection. T did not consistently alter THC-induced antinociception in males, but decreased it in females (tail withdrawal test). Conversely, T decreased THC-induced catalepsy in males, but had no effect in females. E2 did not alter THC-induced antinociception in females, but enhanced it in males. The discrepant effects of T and E2 on males' and females' behavioral responses to THC suggests that sexual differentiation of THC sensitivity is not simply due to activational effects of hormones, but also occurs via organizational hormone or sex chromosome effects. Analysis of serum showed that proadifen increased THC levels, E2 increased 11-OH-THC in GDX males, and T decreased 11-OH-THC (and to a lesser extent, THC) in GDX females. Thus, hormone modulation of THC's behavioral effects is caused in part by hormone modulation of THC oxidation to its active metabolite. However, the fact that hormone modulation of metabolism did not alter THC sensitivity similarly on all behavioral measures within each sex suggests that other mechanisms also play a role in gonadal hormone modulation of THC sensitivity in adult rats.

Sex-different hepaticglycogen content and glucose output in rats

Background

Genes involved in hepatic metabolism have a sex-different expression in rodents. To test whether male and female rat livers differ regarding lipid and carbohydrate metabolism, whole-genome transcript profiles were generated and these were complemented by measurements of hepatic lipid and glycogen content, fatty acid (FA) oxidation rates and hepatic glucose output (HGO). The latter was determined in perfusates from in situ perfusion of male and female rat livers. These perfusates were also analysed using nuclear magnetic resonance (NMR) spectroscopy to identify putative sex-differences in other liver-derived metabolites. Effects of insulin were monitored by analysis of Akt-phosphorylation, gene expression and HGO after s.c. insulin injections.

Results

Out of approximately 3 500 gene products being detected in liver, 11% were significantly higher in females, and 11% were higher in males. Many transcripts for the production of triglycerides (TG), cholesterol and VLDL particles were female-predominant, whereas genes for FA oxidation, gluconeogenesis and glycogen synthesis were male-predominant. Sex-differences in mRNA levels related to metabolism were more pronounced during mild starvation (12 h fasting), as compared to the postabsorptive state (4 h fasting). No sex-differences were observed regarding hepatic TG content, FA oxidation rates or blood levels of ketone bodies or glucose. However, males had higher hepatic glycogen content and higher HGO, as well as higher ratios of insulin to glucagon levels. Based on NMR spectroscopy, liver-derived lactate was also higher in males. HGO was inhibited by insulin in parallel with increased phosphorylation of Akt, without any sex-differences in insulin sensitivity. However, the degree of Thr172-phosphorylated AMP kinase (AMPK) was higher in females, indicating a higher degree of AMPK-dependent actions.

Conclusions

Taken together, males had higher ratios of insulin to glucagon levels, higher levels of glycogen, lower degree of AMPK phosphorylation, higher expression of gluconeogenic genes and higher hepatic glucose output. Possibly these sex-differences reflect a higher ability for the healthy male rat liver to respond to increased energy demands.

Changes in the gene expression and enzyme activity of hepatic cytochrome P450 in juvenile Sprague-Dawley rats

The developmental changes in the hepatic cytochrome P450 (CYP) content, mRNA expression of 12 hepatic CYP subtypes, and the enzyme activities of 5 hepatic CYP subfamilies in rats were investigated using non-treated male and female Sprague-Dawley rats of ages postnatal day (PD) 4, 16, 30 and 8 and 12 weeks. The hepatic proliferation kinetics was also determined by using the phospho-histone H3 (p-histon)-labeled hepatocyte index. The developmental changes in the enzyme activities of hepatic expression of CYP1A and CYP3A in rats were similar to those in humans, although there is no fetal-neonatal dominant CYP3A subtype in rat livers unlike human CYP3A7. On the other hand, the developmental pattern of expression of the CYP2C subfamily differed between humans and rats. Enzyme activity and mRNA expression of each hepatic CYP subtype in rats on PD 30 was similar to that after 8 weeks of age, except in the case of sex-dependent CYP subtypes. The p-histon-labeled hepatocyte index was approximately 10-fold higher in PD 30 rats than in 8-week-old rats. Therefore, the livers of juvenile rats, which have high hepatocellular proliferation activity and a sufficient amount of metabolic enzymes such as CYP, may be more sensitive to the cytotoxic and carcinogenic effects of chemicals than the livers of adult rats. Thus, our results on developmental difference of hepatic CYPs in juvenile rats are useful to identify underlying age-dependent susceptibility of chemical-induced toxicity, and to understand developmental change of chemical disposition.

Detection of initiation activity of 1,2-dimethylhydrazine in in vivo medium-term liver initiation assay system using 4-week-old rats without hepatocellular proliferative stimuli during the test chemical treatment period

We have developed an in vivo medium-term liver initiation assay system to detect initiation activities of chemicals on multi-organ carcinogenesis. However, cell proliferation stimuli during the test chemical treatment period, required in the previously used assay models using adult rats, are laborious; moreover, those cause decrease of hepatic metabolic enzymes and psychological and physical discomfort to animals resulting in inaccurate interpretation. Therefore, we investigated the utility of another in vivo medium-term liver initiation assay model using 4-week-old rats without the cell proliferation stimuli. In this study, we confirmed that 4-week-old and 4.5-week-old male rats have high hepatocyte proliferation activity and similar enzyme activities of hepatic Cytochrome P450 subtypes as compared with 8-week-old male rats. Next, the in vivo medium-term liver initiation assay model using 4-week-old rats without cell proliferation stimuli was evaluated for the detection of the initiation activity of 1,2-dimethylhydrazine (DMH), which is a well-known genotoxic carcinogen. Four-week-old rats were orally administered DMH (single dose, 4 or 16 mg/kg; or 4-day repeat, 1 or 4 mg/kg); subsequently, these rats were treated promotion treatment consisted of administration of 2-acetylaminofluorene and carbon tetrachloride. Four weeks after the first DMH administration, the glutathione S-transferase placental form (GST-P)-positive foci induced by DMH in the liver was measured immunohistochemically. The inductions of GST-P-positive foci in all DMH-treated groups were dose-dependent, duration-dependent and significantly higher than that in non-DMH-treated group. From these results, our assay model was detected the initiation activity of DMH simply, and would be useful to evaluate the carcinogenicity of chemicals.

NADPH-dependent metabolism of 17beta-estradiol and estrone to polar and nonpolar metabolites by human tissues and cytochrome P450 isoforms

The endogenous estrogens, 17beta-estradiol (E(2)) and estrone (E(1)), undergo extensive metabolism in animals and humans, and a large number of their hydroxylated and keto metabolites have been identified in biological samples. The formation of most of the oxidative estrogen metabolites is catalyzed by cytochrome P450 (CYP) enzymes. Precise knowledge of the CYP-mediated formation of these metabolites, particularly those with unique biological activities (e.g., 4-hydroxy-E(2), 16alpha-hydroxy-E(1), 15alpha-hydroxy-E(2), 16-epiestriol, and 2-methoxyestradiol) in human liver and extrahepatic target tissues and cells, would add significantly to our understanding of the diverse biological functions that are associated with endogenous estrogens. In this article, we review recent results on the NADPH-dependent metabolism of endogenous estrogens to polar (hydroxylated and keto) metabolites as well as to nonpolar metabolites by human tissues and recombinant human CYP isoforms. The available data show that a large number of polar and nonpolar metabolites of E(2) and E(1) are formed by human tissues, and a variety of human CYP isoforms are involved in the NADPH-dependent formation of polar as well as nonpolar estrogen metabolites. These enzymes have varying degrees of catalytic activity and distinct regioselectivity.

Skf 525-A induces cocaine N-demethylase, ethoxyresorufin O-deethylase, and pentoxyresorufin O-dealkylase activities by induction of cytochrome p-450 2B in female B6C3F1 mice

Studies demonstrated that cocaine-induced immunosuppression is mediated by metabolites of cocaine. Although SKF 525-A inhibited cocaine N-demethylation in liver S9 fractions isolated from female B6C3F1 mice, our study showed that pretreatment of mice with SKF 525-A potentiated cocaine-induced suppression of the antibody response to sheep red blood cells. An increase in formaldehyde generation was subsequently shown following incubation of cocaine with the S9 fractions prepared from SKF 525-A-treated mice, indicating the possibility of cytochrome P-450 (CYP) induction. Therefore, the inductive effects of SKF 525-A on CYP enzyme activities and proteins were investigated in female B6C3F1 mice to elucidate the potentiation of cocaine-induced immunosuppression by SKF 525-A. When SKF 525-A was administered at 10, 20, or 40 mg/kg/d intraperitoneally for 7 consecutive days, both ethoxyresorufin O-deethylase and pentoxyresorufin O-dealkylase activities were induced dose-dependently. Furthermore, the induction of enzymatic activity was time dependent. Meanwhile, when the type of isozyme induced by SKF 525-A was analyzed by Western immunoblotting with monospecific anti-CYP 1A and anti-CYP 2B antibodies, only the CYP 2B appeared to be induced. From in vitro inhibition studies with monoclonal antibodies, it was confirmed that the induced activity of ethoxyresorufin O-deethylase by SKF 525-A was due to increased levels of CYP 2B proteins. Our present results provide an explanation for the potentiation of cocaine-induced immunosuppression by repeated exposure to SKF 525-A. Our results also indicate that ethoxyresorufin O-deethylase, a selective substrate for CYP 1A, may also be catalyzed by CYP 2B.

Induction of drug-metabolizing enzymes: a path to the discovery of multiple cytochromes P450

This article provides a personal account of the discovery of the induced synthesis of drug-metabolizing enzymes and of subsequent research that led to the discovery of multiple cytochromes P450 with different catalytic activities. The manuscript also emphasizes the role of environmental factors (in addition to genetic polymorphisms) in explaining person-to-person and day-to-day differences in rates and pathways of drug metabolism that occur in the human population.

Species and gender differences in the formation of an active metabolite of a substituted 2,4-thiazolidinedione insulin sensitizer

1. The metabolism of a substituted 2,4-thiazolidinedione (P1) with dual PPARalpha/gamma activity was evaluated in male and female rats, dogs and monkeys. A para-hydroxylated metabolite (M1) with potent PPARgamma-selective agonist, was a major circulating drug-related component in female rats, dogs and monkeys, but not in male rats (M1-to-P1 exposure ratio of <1, 3-5, 5 and 5-11 in male rat, monkey, female rat, and dog, respectively). 2. M1 (%) formed in vitro (5, 53, 57-65, 67 and 67% in male rat, monkey, female rat, dog, and human liver microsomes, respectively), rank ordered with M1 (%) formed in vivo (24-45, 53-57, 78, 75-85%, for male rat, monkey, female rat and dog, respectively, after oral administration of P1). 3. The plasma clearance of M1 was higher in male rats (32 ml min(-1) kg(-1) compared with 6, 7 and 2 ml min(-1) kg(-1) in female rat, male monkey and male dogs, respectively). 4. The low amounts of M1 observed in male rats, with the appearance of products of the cleavage of the propyl group between the phenyl groups was probably due to the presence of the sex-specific CYP2C11, which cleaves P1 at the propyl bridge. None of the CYPs present in female rats cleaved P1 at this site and M1 was only produced by CYP2C6. In humans, only CYP2C8 and the polymorphic CYP2C19 produced M1.

NADPH-dependent metabolism of estrone by human liver microsomes

We characterized the NADPH-dependent metabolism of estrone (E1) by liver microsomes of 21 male and 12 female human subjects. The structures of 11 hydroxylated or keto metabolites of E1 formed by human liver microsomes were identified by chromatographic and mass spectrometric analyses. 2-Hydroxylation of E1 was the dominant metabolic pathway with all human liver microsomes tested. E1 is more prone to form catechol estrogens (particularly 4-OH-E1) than 17beta-estradiol (E2) and the average ratio of E1 4-hydroxylation to 2-hydroxylation (0.24) was slightly higher than the ratio of E2 4- to 2-hydroxylation (0.20, P < 0.001). An unidentified monohydroxylated E1 metabolite (y-OH-E1) was found to be one of the major metabolites formed by human liver microsomes of both genders. 6beta-OH-E1, 16alpha-OH-E1, and 16beta-OH-E1 were also formed in significant quantities. 16alpha-hydroxylation was not a major pathway for E1 metabolism. The overall profiles for the E1 metabolites formed by male and female human liver microsomes were similar, and their average rates were not significantly different. Hepatic CYP3A4/5 activity in both male and female liver microsomes correlated strongly with the rates of formation of several hydroxyestrogen metabolites. The dominant role of hepatic CYP3A4 and CYP3A5 in the formation of these hydroxyestrogen metabolites was further confirmed by incubations of human CYP3A4 or CYP3A5 with [3H]E1 and NADPH. Notably, human CYP3A5 has very high relative activity for E1 4-hydroxylation, exceeding its activity for E1 2-hydroxylation by approximately 100%. It will be of interest to determine the potential biological functions associated with any of the E1 metabolites identified in our present study.

Expression and distribution of CYP2C enzymes in rat basal ganglia

The function and integrity of the basal ganglia is modulated by sex steroids whose activity may be controlled by P450 enzymes, such as members of the CYP2C subfamily. The expression of CYP2C enzymes in rat basal ganglia was examined by immunohistochemistry along with some of the factors that might control their expression. Whereas no CYP2C11 or CYP2C12 immunoreactivity was detected in the basal ganglia of either male or female rats, marked CYP2C13 immunoreactivity was evident in neurones of the subthalamic nucleus, substantia nigra, and interpeduncular nucleus. Strong CYP2C13 immunoreactivity was also expressed in the cortex, olfactory tubercle, hippocampus, dentate gyrus, hypothalamic nuclei, medial habenular nucleus, red nucleus, and medial forebrain bundle. Similar results were found in male and female rats. Following 6-hydroxydopamine lesioning of the nigro-striatal tract, tyrosine hydroxylase immunoreactivity was absent and CYP2C13 immunoreactivity was decreased markedly in the substantia nigra pars compacta, implying its presence in dopaminergic neurones. Modulation of sex steroids, using castrated rats, had no effect on the number of CYP2C13 positive neurones in the substantia nigra pars compacta. These results indicate that CYP2C13 protein is constitutively and widely expressed in rat brain. However, its expression is not sex-specific and is unaffected by castration. The role of CYP2C13 in brain is unknown but it may be involved in the generation of neurosteroids and catecholoestrogens.

Interindividual variance of cytochrome P450 forms in human hepatic microsomes: correlation of individual forms with xenobiotic metabolism and implications in risk assessment

Differences in biotransformation activities may alter the bioavailability or efficacy of drugs, provide protection from certain xenobiotic and environmental agents, or increase toxicity of others. Cytochrome P450 (CYP450) enzymes are responsible for the majority of oxidation reactions of drugs and other xenobiotics and differences in their expression may directly produce interindividual differences in susceptibility to compounds whose toxicity is modulated by these enzymes. To rapidly quantify CYP450 forms in human hepatic microsomes, we developed, and applied, an ELISA to 40 samples of microsomes from adult human organ donors. The procedure was reliable and the results were reproducible within normal limits. Protein content for CYP1A, CYP2E1, and CYP3A positively correlated with suitable marker activities. CYP1A, CYP2B, CYP2C6, CYP2C11, CYP2E1, and CYP3A protein content demonstrated 36-, 13-, 11-, 2-, 12-, and 22-fold differences between the highest and lowest samples and the values were normally distributed. Of the forms examined, CYP3A was expressed in the highest amount and it was the only form whose content was correlated with total CYP450 content. Content of other forms was independent of total CYP450. We further determined the contribution of specific forms to the biotransformation of trichloroethylene as a model substrate. CYP2E1 was strongly correlated with chloral hydrate formation from trichloroethylene; CYP2B displayed the strongest correlation with trichloroethanol formation. These data describing the expression and distribution of these forms in human microsomes can be used to extrapolate in vitro derived metabolic rates for toxicologically important reactions, when form selectivity and specific activity are known. This approach may be applied to refine estimates of human interindividual differences in susceptibility for application in human health risk assessment.

The effect of gender, sexual maturation and xenobiotic treatment on the formation of hydroxymethyl metabolites from 7, 12-dimethylbenz[a]anthracene in rat liver microsomes

The effects of age, gender, strain, phenobarbital (PB) treatment and pituitary influence on the regioselective metabolism of 7, 12-dimethylbenz[a]anthracene to hydroxmethyl metabolites were investigated. Studies used hepatic microsomal membranes from immature and mature Long Evans (LE) rats and adult Hooded Lister (HL) animals. Hydroxymethyl metabolites were resolved by both normal and reverse phase HPLC with on-line diode array detection. The CYP isoform(s) responsible for oxidation at the 12 methyl position exhibited no gender or developmental regulation and the rate of formation was not altered following hypophysectomy. PB-treatment of adult rats caused a significant increase in the rate of formation of both male and female animals (29 and 41-fold, respectively) suggesting a major contribution from a PB-inducible isoform, such as CYP2B. The rate of formation of 7OHMe12MBA exhibited no gender dependency in immature animals but was 2-fold greater than that observed for 12OHMe7MBA suggesting that steric hindrance resulting from the adjacent 1,2 benzyl ring favours substrate oxidation at the 7-methyl position. Male predominant formation of 7OHMe12MBA was apparent following sexual maturation of the LE rats and was significantly reduced upon hypophysectomy suggesting the involvement of a male-specific GH dependent isoform e.g. CYP2C11.

Gender-specific metabolism of benz[a]anthracene in hepatic microsomes from Long-Evans and Hooded Lister rats

The cytochrome P450 isoforms responsible for the regio-selective metabolism of benz[a]anthracene (BA) are poorly defined but as with other polycyclic aromatic hydrocarbons (PAHs) may include members of the CYP2C sub-family. Since the expression of some of these is regulated in a gender-specific manner and may be altered by age, rat strain or by phenobarbital treatment, the effects of these variables on metabolism of BA to diols was investigated. These studies used hepatic, microsomal membranes from immature and adult Long-Evans rats and adult Hooded Lister rats. BA-diols were resolved by normal phase HPLC into three discrete peaks identified as benz[a]anthracene-5,6-diol (BA-5,6-diol), benz[a]anthracene-10, 11-diol (BA-10,11-diol) and a mixture of benz[a]anthracene-3,4- and -8,9-diols (BA-3,4-diol and BA-8,9-diol and termed Peak(3/8)). Significant gender-related differences were found in the rates of diol formation in adults of both the Long-Evans and Hooded Lister rat strains. Formation of BA-10,11-diol and to a lesser extent the components of Peak(3/8) were greater in the male compared to female animals by factors of at least 14 and two, respectively. An age-dependent effect is also observed in the Long-Evans rat since these differences are still apparent in prepubertal animals but to a lesser extent (gender ratio male:female BA-10,11-diol 9X; Peak(3/8) 1.4X). In contrast BA-5,6-diol was formed at similar rates by membranes from female and male rats whether mature (Long-Evans and Hooded Lister) or immature (Long-Evans). Phenobarbital treatment of the adult Long-Evans rats resulted in a moderate increase in the formation of each diol other than at the 10,11-position and the induction was not gender specific. The rate of formation of BA-10, 11-diol was decreased in phenobarbital-treated male rats suggesting modulation of a male specific isoform. Measurement of microsomal epoxide hydrolase revealed no gender or age differences and suggests that this enzyme is not rate limiting in BA-diol formation and thus is not responsible for the differences in BA-diol formation observed. The results suggest that CYP2C11 along with a male-specific isoenzyme not regulated by age are important in the formation of BA-10,11-diol and a component(s) of Peak(3/8) in males. CYPs 2B2 and/or 2C6 appear to be involved in formation of BA-5,6-diol in male and female. Identification of the CYPs involved in the regio-selective metabolism of BA may lead to an explanation of the lower carcinogenic potency of this PAH compared to dimethylbenz[a]anthracene and this study provides novel clues concerning the identities of the CYPs, which are important.

Growth hormone-regulated periportal expression of CYP2C7 in rat liver

Most drug- and steroid-metabolizing cytochrome P450 (CYP) enzymes are expressed in the mammalian liver in a characteristic zonated pattern, with high expression in the downstream perivenous (centrilobular) region. Here, we report that CYP2C7, a member of the rat CYP2 family, is expressed preferentially in the opposite, periportal region. CYP2C7 mRNA, as detected by reverse transcription-polymerase chain reaction, was detected almost exclusively in cell lysates obtained from the periportal region, indicating a very steep acinar gradient. The amount of immunoreactive CYP2C7 protein in periportal cell lysates was also higher than in samples from the perivenous region. This gradient was reversed by hypophysectomy, which markedly and selectively reduced the periportal CYP2C7 protein content. Subsequent growth hormone infusion by osmotic minipumps restored the zonation by selectively increasing the amount of periportal CYP2C7 protein. Although hypophysectomy suppressed CYP2C7 mRNA and growth hormone counteracted it, regulation at this level did not appear to occur in a zone-specific fashion. This indicates that growth hormone-mediated zonal regulation of CYP2C7 protein has additional translational or posttranslational components. Ethanol treatment, which has been shown to affect growth hormone levels, significantly induced CYP2C7 mRNA, but not zone specifically. Our results demonstrate that growth hormone up-regulates the CYP2C7 gene by enhancing the expression of the protein specifically in the periportal liver region. Growth hormone may up-regulate other periportally expressed liver genes in a similar fashion.

Evidence that immature rat liver is capable of participating in steroidogenesis by expressing 17alpha-hydroxylase/17,20-lyase P450c17

Steroid hydroxylase cytochrome P450c17 has been previously purified from microsomal fractions of immature rat livers. In this study, we investigated the expression of P450c17 in rat livers to understand a role of steroidogenesis in the extrasteroidogenic tissue. Upon immunoblot analysis utilizing liver microsomes from rats, P450c17 was detected in 1 and 3 week old rats but not in adult rats. Data from immunohistochemical studies also showed a similar age-dependent expression of P450c17 and indicated that P450c17 detected in immature rat livers is localized in cells surrounding interlobular veins. This age-dependent expression of P450c17 in rat livers was observed in both sexes. Upon enzymatic analysis utilizing microsomal fractions from livers, levels of 17alpha-hydroxylase and 17,20-lyase activity for pregnenolone and progesterone increased by 3 weeks and dramatically reduced at 7 weeks, which is consistent with the expression level of P450c17. These data clearly indicate that P450c17 is expressed in immature rat liver to produce 17alpha-hydroxysteroids and C19-steroids. Based upon immunoblot analysis, the expression level of P450c17 in immature rat livers was approximately one third of that in testis. Compared expression level of P450c17 and total volume of organs between liver and testis, the total amount of steroid metabolites produced by liver P450c17 could be greater than that produced by gonadal P450c17. Because of the absence of P450c17 in rat adrenal glands, rat liver could be the major site for producing 17alpha-hydroxysteroids and C19-steroids in this particular period of life. Although physiological products formed by P450c17 in liver and their roles remain to be elucidated, this study suggests a large capacity of prepubertal rat liver for participating the production of steroid hormones and a putative importance of 17alpha-hydroxysteroids and C19-steroids, such as cortisol and androstendione, which are generally believed to be minor components of steroid hormones in rodents.

Sex differences in ibogaine antagonism of morphine-induced locomotor activity and in ibogaine brain levels and metabolism

The present study demonstrates that the putative antiaddictive agent ibogaine produces more robust behavioral effects in female than in male rats and that these behavioral differences correlate with higher levels of ibogaine in the brain and plasma of female rats. There were no differences in basal locomotor activity between the sexes, and the response of rats to ibogaine differed between the sexes even in the absence of morphine. Five h after receiving ibogaine (40 mg/kg, i.p.). antagonism of morphine-induced locomotor activity was evident in female but not in male rats. Either 19 h after administration of ibogaine (10-60 mg/kg, i.p.), or one h after administration of noribogaine (5-40 mg/kg, i.p.), a suspected metabolite, antagonism of morphine was significantly greater in female than in male rats. Brain and plasma levels of ibogaine (1 h) and noribogaine (5 h), measured by gas chromatography-mass spectrometry, were greater in females as compared with males receiving the same dose of ibogaine. Levels of both ibogaine and noribogaine were substantially lower at 19 h than at earlier times after ibogaine administration, contrary to a previous study in humans. For both sexes, subcutaneous administration of ibogaine (40 mg/kg, i.p., 19 h) produced greater antagonism of morphine-induced locomotor activity than did a comparable intraperitoneal injection, consistent with previous studies from this laboratory demonstrating that the former route of administration produces higher levels of ibogaine in the brain. These data show that there are sex differences in the effects of ibogaine and that this may be due to decreased bioavailability of ibogaine in males as compared to females.

Chromatographic separation and behavior of microsomal cytochrome P450 and cytochrome b5

The methods used for separation of the multiple mammalian cytochrome P450 enzymes by liquid chromatography are reviewed. In addition to the chromatographic techniques, preparation and handling of samples and prefractionation procedures are considered. Conditions that affect stability and chromatographic resolution of cytochromes P450 are also discussed. Special emphasis is put on useful methods which are not routinely used for P450 separation, such as immobilized metal affinity or hydrophobic-interaction chromatography. Applications of low- and high-pressure methods with regard to preparative and analytical separations are compared. It is shown that high- and medium-pressure ion-exchange chromatography are suitable tools for separation of closely related P450 enzymes, especially when specific detection methods are available. In addition to fractionation of cytochromes P450, the isolation and chromatographic behavior of cytochrome b5 is discussed.

Adult-male-specific S-warfarin (11S-OH) and progesterone (20 beta-OH) keto-reductases in rat hepatic microsomes are not identical

Adult-male-specific reductase activities in rat hepatic microsomes use NADPH to reduce S-warfarin and progesterone to their 11S-OH and 20 beta-OH products, respectively (Apanovitch et al. (1992) Biochem. Biophys. Res. Commun. 184, 338-346). When microsomes were treated with increasing concentrations of detergent, S-warfarin (11S-OH) reductase (SW(11S)R) activity was subject to monophasic activation by Triton X-100, monophasic inhibition by sodium cholate, and, activation followed by inhibition with either CHAPS or dodecyl-beta-D-maltoside. A non-dialyzable, heat-sensitive factor in rat and rabbit sera activates microsomal SW(11S)R activity six- to eight-fold. Similar detergent inhibitions but no detergent or serum activations were observed for progesterone (20 beta-OH) reductase (P(20 beta)R) activity. A significant amount of SW(11S)R activity was lost during purification regardless of whether the detergent used for solubilization was activating or inhibiting. Octyl-Sepharose, hydroxyapatite, DEAE-cellulose and carboxymethyl matrices were used to partially purify SW(11S)R. P(20 beta)R activity co-purified with SW(11S)R and the most purified fraction contained two major and several minor polypeptides. Partially purified SW(11S)R is activated by detergents, serum, and salt. These and previous results indicate that SW(11S)R and P(20 beta)R are not identical even though they are both adult male-specific, integral membrane proteins apparently having their active sites exposed on the cytoplasmic surface of the endoplasmic reticulum.

Quantitation of cytochrome P450 enzymes (CYP1A1/2, 2B11, 2C21 and 3A12) in dog liver microsomes by enzyme-linked immunosorbent assay

1. An enzyme-linked immunosorbent assay (ELISA) using specific antisera has been developed to quantify individual cytochrome P450 (P450) enzymes (1A1/2, 2B11, 2C21 and 3A12) in dog liver microsomes. 2. The specific contents of CYP1A1/2, 2B11, 2C21 and 3A12 in untreated male dog liver microsomes determined by the ELISA were 17, 48, 160 and 69 pmol/mg protein respectively, corresponding to 4, 10, 34 and 15% of total optically determined P450 respectively. These P450 enzymes in untreated female dog liver microsomes showed almost similar amounts and relative proportions to those observed in male dog liver microsomes. 3. The oral treatment of male dogs with phenobarbital (PB), rifampicin (Rif) or beta-naphthoflavone (beta-NF) induced significant increases in the contents of CYP1A1/2 (12-fold by beta-NF), 2B11 (16-fold by PB), 2C21 (2-fold by PB) and 3A12 (5-fold by PB and Rif), resulting in marked proportional alterations of the P450 enzymes in dog liver microsomes. 4. This ELISA method will be a useful tool for investigating possible influences (induct on/suppression) of xenobiotics on the expression of P450 enzymes in dog liver.

Effects of diet and ethanol on the expression and localization of cytochromes P450 2E1 and P450 2C7 in the colon of male rats

Local activation of procarcinogens in target tissues such as the colon by cytochrome P450-dependent microsomal monooxygenases is considered to be an important factor in the etiology of cancer. Diet and alcohol consumption are considered risk factors in colon cancer, and the cytochrome P450 isozymes CYP2E1 and CYP2C7 have been implicated in the biochemical mechanisms underlying colon cancer. The current study was conducted to determine the effects of diet and ethanol consumption on colonic and hepatic expression of these two enzymes. Adult male rat Sprague-Dawley rats were fed rat chow ad lib. or were infused intragastrically with control or ethanol-containing diets. Our results indicate that CYP2E1 is present in colonic epithelial cells, and expression of colonic and hepatic microsomal CYP2E1 and CYP2C7 was increased by chronic ethanol intake. As compared with rats having ad lib. access to standard rat food, rats receiving total enteral nutrition had significant (P < 0.01) reductions of CYP2C7 and slight, but not statistically significant, reductions in the expression of CYP2E1 in colon. Diet and ethanol differentially regulated CYP2E1 and CYP2C7 in a tissue-specific manner such that the ethanol induced CYP2E1 and CYP2C7 in the colon and liver, and the intragastric diet alone had a tendency to induce these isozymes in the liver and reduce them in the colon. These results may provide a partial explanation for the mechanism underlying effects of diet and ethanol on colon cancer.

Transactivation of the rat CYP2C13 gene promoter involves HNF-1, HNF-3, and members of the orphan receptor subfamily

The rat CYP2C13 gene (2C13) encodes one of the constitutive male forms of cytochrome P-450 that are involved in steroid metabolism. In addition to being developmentally regulated, the expression of 2C13 is restricted to the liver and suppressed by the female pattern of growth hormone (GH) secretion at the transcriptional initiation level. In this study, we show that the liver-specific expression, but not the regulation by GH, can be reconstituted with 117 bp to 2 kb of 2C13 5' flank. Transactivation of the 2C13 promoter requires both HNF-1 and HNF-3 and is influenced by members of the orphan receptor subfamily of transcription factors. Although HNF-4, ARP-1, EAR-2, and COUP-TF bind to the 2C13 promoter in vitro, overexpression of EAR-2 and COUP-TF, but not of HNF-4 or ARP-1, results in the potentiation of the HNF-3- and HNF-1-supported activity in non-liver cells.

Alterations in cytochrome P-450 levels in adult rats following neonatal exposure to xenobiotics

Neonatal exposure to certain xenobiotics has been shown to alter hepatic metabolism in adult rats in a manner that indicates long-term changes in enzyme regulation. Previously, we have observed changes in adult testosterone metabolism and in cytochrome P-450 (P-450) mRNA levels in animals neonatally exposed to phenobarbital (PB) or diethylstilbestrol (DES). In order to test for other enzyme alterations, we used Western blot procedures for specific P-450s to analyze hepatic microsomes from adult rats (24 wk old) that had been exposed neonatally to DES, PB, 7,12-dimethylbenz[a]anthracene (DMBA), or pregnenolone 16 alpha-carbonitrile (PCN). The most striking effects were observed in the DES-treated males: P-4502C6 and an immunologically similar protein were increased 60 and 90%, respectively, relative to control values, but P-4503A2 was decreased by 44%. No changes were observed in the DES-treated males in levels of P-4502E1, P-4502B, or the male-specific P-4502C13. Adult males neonatally treated with PB had 150% increase in levels of anti-P4502B-reactive protein without significant changes in the other enzymes. The DES- and DMBA-treated females had increased levels of the female-specific P-4502C12 of 38 and 48%, respectively, but no other observed alterations. The results confirm that neonatal exposure to DES or PB can cause alterations in adult hepatic cytochrome P-450 levels but show that these chemicals act on different enzymes. Neonatal DMBA resulted in changes in adult females similar to those produced by the synthetic estrogen DES, but did so at about two-thirds lower dose.

Regulation of liver-specific steroid metabolizing cytochromes P450: cholesterol 7α-hydroxylase, bile acid 6β-hydroxylase, and growth hormone-responsive steroid hormone hydroxylases

The hydroxylation of cholesterol, bile acids, and steroid hormones by liver cytochrome P450 (CYP) enzymes proceeds with a high degree of regiospecificity, and contributes to both biosynthetic and catabolic pathways of sterol metabolism. CYP 7-catalyzed cholesterol 7α-hydroxylation, a key control point of bile acid biosynthesis, is regulated at a pretranslational step, probably transcription initiation, by multiple factors, including liver bile acid and cholesterol levels, thyroid hormone status, and diurnal rhythm. Hydrophobic bile acids, such as lithocholic acid, are converted to less cholestatic derivatives by 6β-hydroxylation carried out by CYP 3A P450s, which also catalyze steroid hormone 6β-hydroxylation reactions. Complex, gender-dependent developmental patterns characterize the expression of steroid 5α-reductase and several rat liver steroid hydroxylase CYPs. Multiple pituitary-dependent factors regulate the expression of these enzymes; of greatest importance are the gonadal steroids and the sex-dependent secretory patterns of growth hormone (GH) that they impart. The continuous presence of GH in circulation, a characteristic of adult female rats, positively regulates expression of the female-specific steroid disulfate 15β-hydroxylase CYP 2C12, while expression of the male-specific steroid 16α- and 2α-hydroxylase CYP 2C11 is stimulated by the intermittent pituitary secretion of GH that occurs in adult male rats. Intermittent GH can stimulate CYP 2C11 gene expression even when the hormone presents to the hepatocyte at a non-physiological pulse amplitude, duration, and frequency, provided that an interpulse interval of no GH (obligatory recovery period) is maintained for at least 2.5 h. GH regulates the expression of the CYP 2C11 and CYP 2C12 genes at the level of transcription initiation. This process is probably mediated by sex-dependent and GH-regulated protein-DNA interactions, such as those observed in the 5'-flank of the CYP 2C12 gene. Thyroid hormone is a second major regulator of liver steroid hydroxylase P450 activity. It regulates these enzymes directly, at a pretranslational step, and indirectly, through its stimulation of pituitary GH secretion and by its positive effects on the expression of the flavoenzyme NADPH-P450 reductase, which catalyzes electron transfer that is obligatory for all microsomal steroid hydroxylation reactions.

Constitutive expression and hormonal regulation of male sexually differentiated cytochromes P450 in primary cultured rat hepatocytes

Experiments, predominantly performed in vivo, have shown that the pattern of growth hormone (GH) release from the pituitary gland is a major regulator of sex-specific cytochromes P450 (P450) in rats and other rodents. However, difficulty in constitutively expressing male-specific forms of P450 using in vitro models, such as primary cell culture, has impeded efforts to examine the direct actions of hormones on these enzyme forms. In the present study mRNA species for the male-specific P450 2C11 and 2C13, but not 3A2, were successfully expressed in primary hepatocytes cultured on a laminin-rich extracellular matrix (matrigel) in a serum-free, chemically defined medium containing insulin as the only hormone. When cells were exposed to GH (100 ng/ml), 2C11 mRNA expression was virtually abolished and 2C13 expression decreased to approximately 50% of control values, demonstrating that the negative regulation of these P450 forms by GH is a direct action on hepatocytes. Dexamethasone (DEX, 10(-8) M) increased the expression of 2C11 to 195% while decreasing 2C13 expression to 25% of control values. When GH and DEX were administered concurrently 2C11 was downregulated, indicating that GH is the dominant regulatory hormone for this form. L-Triiodothyronine (T3) (10(-9) M) suppressed 2C11 (46% of control) but had no effect on 2C13 mRNA expression. The positive regulatory effect of glucocorticoids on 2C11 was also found to occur in vivo and demonstrated to operate predominantly at the transcriptional level. This study demonstrates that primary cultures of hypatocytes are a suitable in vitro model for studies on regulation of some male-specific P450 forms and that GH, DEX, and T3 act directly on hepatocytes at a pretranslational level to regulate these forms.

Brain cytochrome P450 and testosterone metabolism by rat brain subcellular fractions: presence of cytochrome P450 3A immunoreactive protein in rat brain mitochondria

The hydroxylation of testosterone by rat brain subcellular fractions has been studied using an HPLC method with an enhanced resolution for the separation of testosterone and its monohydroxy derivatives. Although the analysis time is longer than that reported for earlier methods, a baseline separation was obtained between all hydroxytestosterones, excepting 6 alpha-hydroxytestosterone and 15 beta-hydroxytestosterone, which were separated using a second chromatography system. This separation was important as rat brain microsomes metabolized testosterone to 15 alpha-, 6 beta-, 15 beta-, 16 beta-, 2 beta-, 1 beta-hydroxytestosterone and androstenedione. Testosterone metabolism was found to be linear with time and protein concentration. The rat brain mitochondrial fraction metabolized testosterone to androstenedione. Small amounts of immunoreactive bands comigrating with purified cytochromes P450j, P450b, and P450p were detected by Western blot analysis in rat brain microsomes, while only an immunoreactive protein related to cytochrome P450p was found in the mitochondrial fractions. Immunoinhibition studies showed that BEA33, a monoclonal antibody to cytochrome P450b and simultaneously recognizing cytochromes P450e and P450a, was able to inhibit the metabolism of testosterone to the 1 beta-, 15 alpha-, 2 beta-, and 6 alpha-hydroxylated metabolites, whereas polyclonal anti-cytochrome P450p did not inhibit the formation of the 6 beta-hydroxytestosterone by rat brain microsomes. The metabolism of testosterone by rat brain microsomal or mitochondrial fractions was refractory to induction by 3-methylcholanthrene or pregnenolone-16 alpha-carbonitrile. Thus, in the brain multiple isozymes of cytochrome P450 are constitutively expressed in different subcellular fractions, which suggests that brain cytochrome P450 may play an important role in the metabolism of endogenous compounds. The significance and role of cytochrome P450p-related protein in the rat brain mitochondrial fraction are yet to be determined.

Effects of testosterone and estrogen on hepatic levels of cytochromes P450 2C7 and P450 2C11 in the rat

The effects of exogenous hormone treatment on the expression of cytochromes P450 2C7 and P450 2C11 were studied in neonatally gonadectomized and sham-operated male and female rats. Hepatic levels of cytochrome P450 2C7 were found to be two- to threefold higher in intact adult female versus male rats. Neonatal gonadectomy resulted in a reversal of the relative cytochrome P450 2C7 levels in male and female animals at maturity. Expression of this isozyme was restored in ovariectomized females by estradiol treatment. Furthermore, neonatal and/or pubertal administration of estradiol to intact male rats induced cytochrome P450 2C7 to adult female levels. On the other hand, administration of testosterone at all times examined had no effect in intact female rats, but decreased cytochrome P450 2C7 to normal levels in neonatally castrated males treated during adulthood. Neonatal testosterone treatment also increased hepatic cytochrome P450 2C7 content in both ovariectomized females and intact males. These results indicate that estrogen is required for full expression of cytochrome P450 2C7 while the effect of testosterone is ambiguous. In comparison, neonatal gonadectomy of male rats abolished the adult expression of cytochrome P450 2C11. Normal levels were restored only by treatment with testosterone during adulthood. Neonatal testosterone treatment did not induce cytochrome P450 2C11 levels in gonadectomized rats of either sex. In contrast, neonatal estrogen treatment suppressed cytochrome P450 2C11 expression in intact adult male rats to the same extent as neonatal castration. These results indicate that androgen exposure during the adult, and not the neonatal, phase is essential for full expression of cytochrome P450 2C11.

The metabolism of 2,4-dibromo [6,7-3H]17 beta-oestradiol in the rat: ring-A dibromination blocks male-specific 15 alpha-hydroxylation and catechol formation

The metabolism in the rat of 2,4-dibromo-17 beta-oestradiol (2,4-DBE2), a compound of potential use for tumour imaging and assessment, has been studied. 2,4-DB[6,7-3H]E2 was synthesized by bromination of [6,7-3H]E2 with N-bromosuccinimide, and administered (40 micrograms/kg, i.v.) to anaesthetized male and female rats. Metabolites were rapidly and extensively excreted in bile (60 and 82% of the dose over 1 and 6 h, respectively). No unchanged compound was excreted. 2,4-DBE2 was almost entirely oxidized to 2,4-DB-oestrone; which was largely eliminated as its glucuronide but partly (approx. 30%) metabolized to 2,4-DB-16 alpha-hhydroxyoesterone and, to a minor extent, 2,4-DB-oestriol. No products of either oxidative or reductive debromination were detected. Neither of the two oxidative transformations of 2,4-DBE2 in the rat, in contrast with those of exogenous E2, was sex-selective, and 2,4-DB-oestrone underwent less extensive hydroxylation than oestrone formed from E2. In female rats, the substituents selectively redirected the principal site of hydroxylation from C-2 to C-16, whereas in males they had no significant effect on the existing 16 alpha-hydroxylation but did block the major pathway, 15 alpha-hydroxylation. Thus the sexual differentiation of E2 oxidative metabolism was abolished by direct blockage causing metabolic switching to a latent reaction in the female rat and long-range inhibition of the vicinal hydroxylation in the male rat.

Sexual differentiation and regulation of cytochrome P-450 CYP2C7

The multigene family of proteins known as the cytochrome P-450-dependent monooxygenases play a central role in the metabolism of hormones and foreign compounds. As part of our studies into the function and regulation of these proteins we have isolated a little studied constitutively expressed isozyme CYP2C7 and have investigated its substrate specificity and mode of regulation. Interestingly the haem of this enzyme in its isolated form is almost 100% in the high spin state. The enzyme was active in the metabolism of a range of model resorufin substrates, but exhibits highest activity towards benzyloxyresorufin. Indeed, this isozyme appears to play a significant role in the metabolism of this substrate in microsomal samples from untreated male rats. Tissue distribution studies indicated that CYP2C7 was expressed in liver, kidney and possibly muscle tissue. Cytochrome P-450 CYP2C7 could not be significantly induced by any of a wide range of known modulators of cytochrome P-450 expression at the mRNA level, however some significant changes in protein expression were observed. Some of the agents used (e.g., diethylnitrosamine and carbon tetrachloride) caused a significant reduction in the expression of this protein. In agreement with other reports where mRNA levels were measured we found that the level of CYP2C7 protein expression was sexually differentiated. Female rats express two to three times the level found in males, the sex difference being reversible by hypophysectomy.

Induction of cytochrome P450 isozymes in rat liver by methyl n-alkyl ketones and n-alkylbenzenes. Effects of hydrophobicity of inducers on inducibility of cytochrome P450

The effects of methyl n-alkyl ketones and n-alkylbenzenes on hepatic cytochrome P450s in vivo and in vitro were investigated. Male rats were treated with acetone, methyl ethyl ketone, methyl n-propyl ketone, methyl n-butyl ketone, benzene, toluene, ethylbenzene, n-propylbenzene, or n-butylbenzene. The methyl n-alkyl ketones induced the metabolic activities of hepatic microsomes toward aminopyrine, 7-ethoxycoumarin, and aniline. n-Alkylbenzenes induced aminopyrine and 7-ethoxycoumarin metabolic activities. Testosterone 2 beta- and 6 beta-hydroxylation activities were induced by ketones with a long side chain such as methyl n-butyl ketone. Testosterone 2 alpha-hydroxylation activity was decreased by treatment with methyl n-butyl ketone. Testosterone 16 beta-hydroxylation activity was induced by treatment with methyl n-alkyl ketones. The inducibility was dependent on the length of the side chain. Testosterone 16 beta-hydroxylation activity also was induced by n-alkylbenzenes. These results indicate that the levels of multiple forms of cytochrome P450 were changed by treatment with these chemicals. P450IIE1, an acetone-inducible form, was induced by methyl n-alkyl ketones or n-alkylbenzenes. The inducibility did not depend on the length of the side chain of these chemicals. P450IIB1 and IIB2, both phenobarbital-inducible forms, were induced with methyl n-alkyl ketones and n-alkylbenzenes to an extent depending on the length of the side chain of these chemicals. Thus, the hydrophobicity of the inducer affected phenobarbital-type induction but not the induction of P450IIE1. We further investigated the interactions of ketone and benzene derivatives with cytochrome P450 in vitro. Testosterone hydroxylation activities of hepatic microsomes were measured in the presence of methyl n-alkyl ketones and n-alkylbenzenes. Methyl n-alkyl ketones inhibited testosterone 16 beta-hydroxylation activity. n-Alkylbenzenes inhibited 2 beta-, 6 beta-, 15 alpha-, 16 alpha-, and 16 beta-hydroxylation activities. Testosterone hydroxylation activities were inhibited by these chemicals depending on the length of the side chain. n-Alkylbenzenes were stronger inhibitors than methyl n-alkyl ketones, n-Butylbenzene was the strongest inhibitor of these activities. These results indicate that hydrophobicity was important in the interaction of these chemicals with cytochrome P450, and that there is some relationship between the inducibility of cytochrome P450 and its interaction with inducers.

Immobilized metal affinity chromatography as a means of fractionating microsomal cytochrome P-450 isozymes

Fractionation of microsomal cytochrome P-450s is usually done by chromatography on ion-exchange resins and hydroxyapatite. The resolution of the great number of similar P-450 isozymes, however, requires additional methods based on different separation parameters. For this purpose immobilized-metal affinity chromatography (IMAC) was applied to the separation of P-450 isozymes. The method in its application to rat liver microsomes is described in detail. For method optimization and for the reproducibility of analytical fractionations a completely automatic fast protein liquid chromatographic system especially designed for IMAC is presented. Optimization is done with respect to the choice of the immobilized metal ion and the elution conditions. The chromatographic resolution is markedly enhanced by using segmented vs. linear gradients. The efficiency of P-450 resolution is demonstrated by sodium dodecyl sulphate polyacrylamide gel electrophoresis and immunoblotting, verifying the different retention behaviours of the isozymes. However, for all the isozymes analysed so far, reactivity with one particular polyclonal antibody is observed with more than two IMAC fractions of a single run. This may be explained in part by the occurrence of isozymic forms distinguishable by the pattern of chymotryptic peptides. Hence IMAC appears to be suitable for the separation of closely related isozyme forms.

Gene structure and expression of the rat cytochrome P450IIC13, a polymorphic, male-specific cytochrome in the P450IIC subfamily

The male-specific CYP2C13 gene has been isolated from two independent rat genomic libraries. This gene spans more than 50 kb and contains eight introns which are subject to the GT-AG rule. Two allelic forms of the CYP2C13 gene were identified. Determination of the exonic sequences revealed that one of them encodes cytochrome P450(+g) and the other encodes cytochrome P450(-g). Using allele-specific restriction enzyme sites, a good correlation between the genotype and the phenotype of CYP2C13 was shown. Nucleotide substitutions between the (+g) and the (-g) genes exist not only in the exons but also in the introns and the 5'-flanking region. Although five nucleotide differences were identified within 287 base pairs of the (+g) and (-g) 5'-flanking regions, the transcription initiation sites were identical. In addition to a canonical TATA box located 31 base pairs upstream of the start site of transcription, putative binding sites for the liver-enriched and liver-specific transcription factors HNF1/LF-B1/APF, HNF3, HNF4/AF-1, C/EBP, LAP, and eH-TF/TGT3 and the ubiquitous factors NF-1 and OTF-1 were identified.

Age-dependent expression of cytochrome P-450s in rat liver

Age-related changes in the levels of multiple forms of cytochrome P-450 as well as in the testosterone hydroxylation activities of hepatic microsomes of male and female rats of different ages from 1 week to 104 weeks (24 months) were investigated. The total cytochrome P-450 measured photometrically did not change much with age in either male and female rats. Testosterone 2 alpha-, 2 beta-, 6 beta-, 15 alpha-, 16 beta-hydroxylation activities of male rats were much higher than those in female rats and were induced developmentally. These activities in male rats declined with aging to the very low level in female rats by 104 weeks of age. Testosterone 7 alpha-hydroxylation activity was maximum at 3 weeks of age in rats of both sexes. The levels of individual cytochrome P-450s were measured by immunoblotting. P450IA1 and IA2 (3-methylcholanthrene-inducible forms) and P450IIB1 and IIB2 (phenobarbital-inducible forms) were detected at low levels in rats of both sexes at all ages. P450IIA2, IIC11 and IVA2 were detected in male rats only and were induced developmentally. These male-specific forms disappeared in male rat liver at 104 weeks of age. P450IIC12, a typical female-specific form, was induced developmentally in female rats and was also detected in male rats at 3 and 104 weeks of age. P450IIIA2 (testosterone 6 beta-hydroxylase) was induced developmentally in male rats, but disappeared when the rats were 104 weeks of age. In female rats, P450IIIA2 was detected only at 1 and 3 weeks of age. P450IIA1, IIC6, IIE1 and IVA3 were detected in rats of both sexes at any age. P450IIC6 and IVA3 were induced developmentally and detected at a similar level in rats of both sexes. The level of P450IIA1 was maximum at 3 weeks of age in rats of both sexes. The changes in the level of P450IIE1 during aging were small compared with the changes in other cytochrome P-450s used in this study. These observations provide concrete evidence to our earlier hypothesis that each of the forms of cytochrome P-450 in male rats alter with aging in different patterns resulting in a practical feminization of over-all cytochrome P-450 composition at old age.

Effects of RP 52028 and phenobarbital on mRNA levels of inducible and constitutive sex-specific cytochrome P450 isozymes in rat liver

Sex-related differences in basal levels of mRNA coding for various cytochrome P450 isozymes and their inducibility by 1-(2-chlorophenyl)-N-methyl-N-(1-methylpropyl)-3- isoquinoline carboxamide (RP 52028) in comparison to phenobarbital (PB) were investigated in Sprague-Dawley rats. We observed that the inducible isozymes, namely cytochromes P450IIB1/2 and P450IIIA1/2 were barely detectable in non-induced animal livers. On the contrary, mRNAs coding for two constitutive forms of cytochrome, P450IIC7 and IIC11, were expressed at a high level in untreated rats in a sex-dependent manner. Cytochrome P450IIC11 mRNA was present in male rats only whereas P450IIC7 was expressed in both sexes but at a higher level in female rats. RP 52028 had a dose-dependent inducing effect on the P450IIB1/2 and IIIA1/2 isoforms in both sexes. After administration of a high dose (500 mg/kg), this molecule exhibited a pattern of induction similar to that of PB. Increases in the accumulation of these IIB1/2 and IIIA1/2 messengers were correlated with protein data, suggesting that RP 52028, like PB, induces these isozymes mainly through a pretranslational regulatory mechanism. On the other hand, PB and RP 52028 caused only a slight increase, less pronounced than in Wistar rats, in the mRNA level of the constitutive female-predominant P450IIC7, indicating a strain-related difference in inducibility of this isozyme. RP 52028 had no effect on P450IIC11 mRNA level in male rat liver, in contrast to the decreasing effect obtained with PB. Furthermore, the non-correlated changes in P450IIC11 mRNA level and microsomal testosterone 2 alpha-hydroxylase activity after treatment with RP suggests that this molecule modulates the expression of P450IIC11 at a posttranscriptional level only.

Novel stereoselectivity of rat liver cytochrome(s) P450 toward enantiomers of the trans-1,2-dihydrodiol of triphenylene

Metabolism of 3H-labeled (+)-(S,S)- and (-)-(R,R)-1,2-dihydrodiols of triphenylene by rat liver microsomes and 11 purified isozymes of cytochrome P450 in a reconstituted monooxygenase system has been examined. Although both enantiomers were metabolized at comparable rates, the distribution of metabolites between phenolic dihydrodiols and bay-region, 1,2-diol 3,4-epoxide diastereomers varied substantially with the different systems. Treatment of rats with phenobarbital (PB) or 3-methylcholanthrene (MC) caused a slight reduction or less than a twofold increase, respectively, in the rate of total metabolism (per nanomole of cytochrome P450) of the enantiomeric dihydrodiols compared to microsomes from control rats. Among the 11 isozymes of cytochrome P450 tested, only cytochromes P450c (P450IA1) and P450d (P450IA2) had significant catalytic activity. With either enantiomer of triphenylene 1,2-dihydrodiol, both purified cytochrome P450c (P450IA1) and liver microsomes from MC-treated rats formed diol epoxides and phenolic dihydrodiols in approximately equal amounts. Purifed cytochrome P450d (P450IA2), however, formed bay-region diol epoxides and phenolic dihydrodiols in an 80:20 ratio. Interestingly, liver microsomes from control or PB-treated rats produced only diol epoxides and little or no phenolic dihydrodiols. The diol epoxide diastereomers differ in that the epoxide oxygen is either cis (diol epoxide-1) or trans (diol epoxide-2) to the benzylic 1-hydroxyl group. With either purified cytochromes P450 (isozymes c or d) or liver microsomes from MC-treated rats, diol epoxide-2 is favored over diol epoxide-1 by at least 4:1 when the (-)-enantiomer is the substrate, while diol epoxide-1 is favored by at least 5:1 when the (+)- enantiomer is the substrate. In contrast, with liver microsomes from control or PB-treated rats, formation of diol epoxide-1 relative to diol epoxide-2 was favored by at least 2:1 regardless of the substrate enantiomer metabolized. This is the first instance where the ratio of diol epoxide-1/diol epoxide-2 metabolites is independent of the dihydrodiol enantiomer metabolized. Experiments with antibodies indicate that a large percentage of the metabolism by microsomes from control and PB-treated rats is catalyzed by cytochrome P450p (P450IIIA1), resulting in the altered stereoselectivity of these microsomes compared to that of the liver microsomes from MC-treated rats.

Hepatic and renal cytochrome P-450s in spontaneously hypertensive rats

The differences in the levels of cytochrome P-450s in hepatic and renal microsomes between spontaneously hypertensive rats (SHR) and normotensive control rats (Wistar Kyoto rats, WKY) were investigated by Western blotting with a specific antibody. Differences in the metabolic activity of the microsomes were also studied. In hepatic microsomes, the content of P450 PB-1 (IIIA2) was 140% higher in SHR than in WKY and the content of P450 IF-3 (IIA1) in SHR was one-seventh that in WKY. The differences reflected the increase in testosterone 6 beta-hydroxylation activity and decrease in testosterone 7 alpha-hydroxylation activity in hepatic microsomes of SHR. The level of P450 K-5 (IVA2) in hepatic microsomes of SHR was 4-times that in microsomes of WKY. The levels of other cytochrome P-450s in SHR were not very different from those in WKY. In renal microsomes, the levels of three renal cytochrome P-450s, P450 K-2, K-4, and K-5, were measured. The level of P450 K-5 (fatty acid omega-hydroxylase) in SHR was 50% higher than that in WKY and the difference reflected the increase in lauric acid omega- and (omega-1)-hydroxylation activities of the renal microsomes of SHR. The levels of P450 K-2 and K-4 did not differ in both rats.

Regulation of the expression of the sex-specific isoforms of cytochrome P-450 in rat liver

The hepatic metabolism of steroid hormones and of xenobiotics frequently depends on the expression of the sex-specific isoforms of cytochrome P-450 and on differences in sex hormones. Following biochemical, immunological and molecular biological investigations, it was shown that in adult rat liver there exist at least four male-specific and one female-specific isoforms of cytochrome P-450. The designation of these sex-specific genes is IIC11, IIIA2, IIC13 and IIA2 in males, and IIC12 in females. The irreversible programming of the expression of these isoforms of cytochrome P-450 in adulthood occurs during the perinatal period of life, and is named enzyme imprinting. One of the main factors that regulates the expression of the sex-specific isoforms of cytochrome P-450 is the level of androgens in the blood. Castration of adult rats decreased the level of the male isoforms of cytochrome P-450 and the activity of the monooxygenase enzyme system that remained higher than in intact females. The mechanism of enzyme imprinting can be explained as follows: neonatal androgens program the secretion of hypothalamic hormones, somatostatin and growth-hormone-releasing factor. These factors determine the type of growth hormone secretion in adult rats, and this controls the type of sex-specific isoforms of cytochrome P-450 expressed in adulthood. Metabolic regulation similar to that outlined above was shown to occur for several metabolism-dependent chemical carcinogens. Such a pathway may explain the different sensitivity displayed by male and female rats to treatment with these carcinogenic agents. One possible way of modulating the expression of some isoforms of cytochrome P-450 in adult rats is by treating neonates with specific xenobiotics that change the constitutive expression of neonatal androgens. It appears that this enzyme imprinting plays an important role in determining the individual sensitivity to the carcinogenic effects of chemicals.

Analytical fractionation of microsomal cytochrome P-450 isoenzymes from rat liver by high-performance ion-exchange chromatography

Ion-exchange Fast Protein Liquid Chromatography (FPLC) on Mono Q and Mono S was optimized for the analytical separation of microsomal cytochrome P-450 species from rat liver. The effects of detergent, pH, gradient profile and column load on resolution are demonstrated. Successive application of anion- and cation-exchange chromatography leads to eleven separated P-450 fractions. The altered microsomal P450 pattern after treatment of rats with various inducers is reflected by distinct elution profiles. Sodium dodecyl sulphate-polyacrylamide gel electrophoresis and enzymatic analysis imply that several FPLC fractions contain more than one P-450 species. Preliminary results are presented showing the suitability of immobilized metal affinity chromatography (MAC) for general P-450 fractionation and thus for the further resolution of Mono Q and Mono S fractions. Scale-up for preparative P-450 fractionation is easily done by adapting the optimized analytical FPLC procedures to Q- and S-Sepharose Fast Flow.

Changes in the amount of cytochrome P450s in rat hepatic microsomes with starvation

The effects of starvation on the composition of 12 different cytochrome P450s in rat hepatic microsomes were studied with a specific antibody. Changes in the metabolic activity of the microsomes were studied at the same time. P450 DM (P450j) was induced 2.5-fold by a 48-h starvation and its increase reflected the increase of metabolic activity of hepatic microsomes toward aniline, 7-ethoxycoumarin, and N-nitrosodimethylamine. P450 K-5, the major renal cytochrome P450 in untreated male rat, was also induced 2.5-fold by a 48-h starvation. P450 UT-2 (P450h) and P450 UT-5 (P450g), typical male-specific forms, decreased with starvation. P450 UT-2 had high testosterone 2 alpha- and 16 alpha-hydroxylation activities. These activities of hepatic microsomes were reduced with the decrease in P450 UT-2. P450 PB-1, testosterone 6 beta-hydroxylase, was increased time-dependently by starvation. P450 UT-4 (RLM2), a minor male-specific form, was not changed by starvation. P450 PB-2 (P450k), present in both sexes, was changed little by starvation. P450 PB-4 (P450b) and P450 PB-5 (P450e) are strongly induced in rat liver by phenobarbital in coordinate fashion. Starvation increased P450 PB-4 12-fold but reduced P450 PB-5 to 22% of the control level. P450 MC-1 (P450d) was decreased by starvation. P450 MC-5 (P450c) was barely detected in control rats and was not changed by starvation. P450 IF-3 (P450a), rich in immature rats, was increased by starvation, accompanied by an increase in testosterone 7 alpha-hydroxylation activity in the hepatic microsomes. We further investigated whether new cytochrome P450s appeared upon starvation by comparison of chromatographic profiles of cytochrome P450 from starved rats with those of cytochrome P450 from control rats using HPLC. Three new cytochrome P450s were detected in the starved rats. These cytochrome P450s were purified to homogeneity. One of them was P450 DM, judging from spectral properties, catalytic activity, and the NH2-terminal sequence. The two other forms were designated P450 3b and 4b. The minimum molecular weights of P450 3b and 4b were 53,000 and 52,000, respectively, and their CO-reduced absorption maxima were at 449 and 452 nm, respectively. P450 3b metabolized aminopyrine, N-nitrosodimethylamine, 7-ethoxycoumarin, and lauric acid, but with low activity. P450 4b was efficient in lauric acid omega- and (omega-1)-hydroxylation only. The spectral properties, catalytic activity, peptide map, and NH2-terminal sequence of P450 4b agreed with those of P450 K-5. P450 3b was a new cytochrome P450, judged by these criteria.