Altered regulation of Cyp1a-1 gene expression during cultivation of mouse hepatocytes in primary culture

Effects of cytochrome P450 1A substrate (difloxacin) on enzyme gene expression and pharmacokinetics in crucian carp (hybridized Prussian carp)

Cytochrome P450s (CYPs) play a prominent role in drug metabolism and biotransformation which are distributed in liver of aquatic animals. However, limited information is available about CYP genes involved in drug metabolism in fish. In the present study, we explore CYP1A characterization for DIF metabolism. Firstly, we cloned and characterized the full-length cDNA sequence of a CYP1A gene from crucian carp (hybridized Prussian carp), the predicted protein sequence for CYP1A comprise 496 amino acids. The heme-binding region of the CYP1A, encompassing the amino acid sequence GLGKRRCIG, which is identical to the same region of other homologues. Secondly, we studied the difloxacin (DIF) kinetics and the effects of DIF on their corresponding CYP1A mRNA levels in liver of crucian carp. CYP1A1 mRNA expression was analyzed by real-time PCR, and DIF concentration was determined by reversed-phase high-performance liquid chromatography (RP-HPLC). Results showed that the concentration of DIF in liver reached its peak (67.70 mg kg(-1)) at 0.5h, while the CYP1A1 gene expression was at the lowest point. CYP1A mRNA was down-regulated by 6.5 mg ml(-1) DIF in the liver of crucian carp. Thus, our work confirmed that DIF is both the substrate and inhibitor of CYP1A. The information provided a model for the potential utility of gene expression analysis and drug metabolization in fish.

Activation of CYP1A1 gene expression during primary culture of mouse hepatocytes

Expression of CYP1A1 mRNA in mouse hepatocytes in primary culture was investigated. The expression was obvious on day 3 of culture without addition of any known ligands of the aryl hydrocarbon receptor and increased with culture period. Removal of insulin from and addition of hydrogen peroxide to the medium enhanced and suppressed the expression, respectively. The CYP1A1 mRNA expression was also enhanced in the presence of anti-oxidant, t-butylhydroquinone, in the medium. Several kinds of kinase inhibitors markedly increased the CYP1A1 mRNA expression. In contrast, the inhibitory expression was prolonged in the presence of okadaic acid, a potent inhibitor of serine/threonine phosphatase PP1 and PP2. These observations suggest that there might be a repressive pathway in the regulation of CYP1A1 mRNA expression and that the presently observed expression pathway differs at several points from those previously reported, such as ligand-activated aryl hydrocarbon receptor- or omeprazole-mediated expression. Modulation of CYP1A2 mRNA expression after exposing hepatocytes to agents affecting phosphorylation pathways differed from that of CYP1A1 mRNA. This implies that regulatory pathways for CYP1A1 and CYP1A2 expression may differ.

Sex-associated expression of mouse hepatic and renal CYP2B enzymes by glucocorticoid hormones

The expression of Cyp2b9 and Cyp2b10 genes was investigated in kidney, liver, and cultured hepatocytes of adult C57BL/6NCrj mice. The constitutive expression level of CYP2B mRNA in kidney was higher in female than in male mice, as it was in the liver where more CYP2B9 than CYP2B10 was expressed in the females, and more CYP2B10 was expressed in the males. After treatment with dexamethasone (Dex), induction of CYP2B10 mRNA and protein in the kidneys was far greater in male than in female mice. In contrast to Dex, phenobarbital (PB), pregnenolone-16 alpha-carbonitrile (PCN), and 1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane (DDT) did not induce the expression of the Cyp2b gene in the kidneys of either sex. In the liver, PB, PCN, and DDT induced both CYP2B9 and CYP2B10 in both sexes to the same extent, whereas Dex induced only CYP2B10 and simultaneously suppressed CYP2B9. Dex-inducible expression of CYP2B mRNA was decreased by 11 beta-[4-dimethylamino]phenyl-17 beta-hydroxy-17-[1-propynyl]estra-4,9-dien-3-one (RU-486), in both the kidneys and liver from male mice, and in cultured hepatocytes. However, RU-486 itself induced the expression of CYP2B mRNA in female liver and cultured hepatocytes. Interestingly, RU-486 increased PB-inducible expression of these species in cultured hepatocytes. Gonadectomy increased the expression of CYP2B mRNA in untreated male liver, but suppressed Dex-induced expression in the kidneys of both sexes. These observations suggest that (a) there are multiple regulatory pathways in the expression of Cyp2b genes, one of which used by Dex is mediated via the glucocorticoid receptor, which is different from that used by PB, and (b) sex hormones play a role in the regulation of the sex-dependent expression of Cyp2b genes in the mouse.

Different regulation of the expression of mouse hepatic cytochrome P450 2B enzymes by glucocorticoid and phenobarbital

The effect of the synthetic glucocorticoid, dexamethasone, and phenobarbital upon the expression of Cyp2b9 and Cyp2b10, major CYP2B subfamilies in the mouse, was differentiated in C57BL/6 mouse liver and hepatocytes in primary culture. Overall expression was higher in the untreated female liver than in the male liver. More Cyp2b9 than Cyp2b10 mRNA was present in the female liver, whereas the level of Cyp2b10 was higher in the male. Phenobarbital increased Cyp2b10 expression more than did Cyp2b9 in both sexes. Treatment with dexamethasone markedly induced Cyp2b10 expression dose dependently, but simultaneously suppressed Cyp2b9 in both sexes. Evidence of this was obtained both in vivo and in hepatocyte culture. Furthermore, the existence of at least two unknown species of CYP2B, whose expressions were either increased or decreased by dexamethasone was suggested. Adrenalectomy increased the expression of Cyp2b9 and Cyp2b10 mRNAs, especially that of Cyp2b9 in the male liver. In addition, the expression of one unknown species which was constitutively suppressed increased in adrenalectomized male mice. That the treatment of dexamethasone or adrenalectomy altered the expression of CYP2B subfamilies suggests that endogenous glucocorticoid hormone plays a basic role in the constitutive expression of cytochrome P450. Furthermore, the sex-related difference in the expression of Cyp2b9 and Cyp2b10 suggests that sex-dependent secretion of endogeneous modulating factors is involved in the regulatory pathway.

Induction of rat hepatic cytochrome P4501A and P4502B by the methoxsalen

The effect of methoxsalen, the inhibitor of the hepatic mixed function oxidase, on the expression of liver cytochrome P450s was examined in rats. Administration of methoxsalen to rats significantly increased the hepatic content of P450 and activities of microsomal ethoxyresorufin O-deethylase (EROD), methoxyresorufin O-demethylase (MROD), pentoxyresorufin O-dealkylase (PROD), a representative activity of P4501A1, P4501A2 and P4502B1/2, respectively, in a dose-dependent manner. In contrast, there was no effect on the P4502E1 catalyzed aniline hydroxylase. In the time-course experiment, methoxsalen exhibited a biphasic effect on EROD, MROD, and PROD activities, an initial inhibitory phase was followed by a phase of induction following a single treatment. Immunoblot analysis using anti-rat liver P4501A and P4502B revealed that increase in the apoprotein levels of P4501A1/2 and P4502B1/2 by methoxsalen was consistent with those in enzyme activity levels. Levels of mRNA of P4501A1/2 and P4502B1/2 were also increased by methoxsalen in Northern blot analysis. These results demonstrated that methoxsalen acts as an inducer of the hepatic microsomal mixed function oxidase; selective induction of P4501A and P4502B families involved increases in mRNA levels.

Maintenance and activation of Cyp2e-1 gene expression in mouse hepatocytes in primary culture

The expression of Cyp2e-1 mRNA and protein was investigated in the C57BL/6NCrj mouse hepatocytes in primary culture, as well as liver and kidney. The mRNA and protein expression in the liver was in the same range in both sexes and was not affected by orchiectomy or ovariectomy. The mRNA expression was enhanced in the kidney of ovariectomized mice, in which the protein contents were not influenced. Orchiectomy decreased the expression of both mRNA and protein. When the hepatocytes were transferred to primary culture, the amounts of the mRNA were not changed within 24 h and about half remained by day 3. However, the expression was low thereafter. The expression of the protein gradually decreased after the start of culture. Dexamethasone showed a potential as an inducer at more than 10(-8) M. Sex hormones increased the expression of this P-450 species a little in culture, but growth hormone did not. These observations indicated that glucocorticoid hormone plays a role in modifying expression of Cyp2e-1 and that the mouse hepatocyte culture is useful for examining its regulation mechanism.

Induction in vitro and complete coding region sequence of cytochrome P4501A1 cDNA from cultured whole rat conceptuses during early organogenesis

Exposures of cultured whole rat conceptuses during organogenesis to 3-methylcholanthrene (MC; 0.025-25 microM), 5,6-benzoflavone (BNF; 5-100 microM) or benz[a]anthracene (BA; 5-100 microM) were effected by placement of each of these "MC-type" inducing agents in the culture medium at the time of explantation on day 9.5 of gestation. Conceptuses were then cultured for 48 hr and evaluated on day 11.5 for increased expression of inducible conceptal cytochrome P450 (P450). The three agents each elicited concentration-dependent increases in 7,8-benzoflavone (ANF)-inhibitable ethoxyresorufin O-deethylase (EROD) activities and increased P4501A1 mRNA as detected by primer-specific reverse transcriptase-polymerase chain reaction (RT-PCR) in cell-free preparations of the treated, cultured conceptuses. At effective inducing concentrations, dysmorphogenic or other embryotoxic effects were not detectable. At 20 microM concentrations, the three agents exhibited roughly equal induction that was approximately equivalent in magnitude (6- to 13-fold) to that achieved previously with exposures to MC in utero. Additions to the culture medium of 2.5 to 10 microM concentrations of dexamethasone (DEX) did not alter significantly the magnitude of MC-elicited induction in vitro. Repeated full-length sequencing of an RT-PCR-amplified cDNA revealed a coding region sequence identical to that reported for the P4501A1 sequence from adult rat liver. The results provide a basis for investigations, in the absence of maternal influences, of the regulation of mammalian conceptal P4501A1 in intact tissues during organogenesis, a gestational period critical in terms of the dysmorphogenic and other embryotoxic effects of foreign organic chemicals. The results are also pertinent to studies of embryotoxicity, particularly to the transplacental carcinogenicity, mutagenicity and dysmorphogenicity of P4501A1 substrates.

Down regulation of CYP 1A1 by glucocorticoids in trout hepatocytes in vitro

Short-term culture of rainbow trout (Onchorhynchus mykiss) hepatocytes was used to examine the effect of dexamethasone (DEX) on microsomal CYP 1A1 protein content and 7-ethoxyresorufin-O-deethylase (EROD) activity in vitro. Hepatocytes prepared by controlled collagenase digestion and plated at a density of 0.25 x 10(6) cells/cm2 in plastic culture dishes precoated with trout skin extract (7.6 micrograms skin protein/cm2) to facilitate cell attachment were maintained at 16 degrees C. Cells were treated with DEX (10(-9) to 10(-7) M) or vehicle (dimethyl sulfoxide, DMSO) at 24 h. Microsomal CYP 1A1 protein content and EROD activities were measured at 72 h. Both CYP 1A1 protein as measured by Western blots using CYP 1A1 specific anti-sera and EROD activity were significantly lower in DEX (10(-8) to 10(-7) M)-treated hepatocytes compared to untreated (control) or DMSO-treated cells. The effect was dose dependent in that a gradual decrease of CYP 1A1 protein and EROD activities were seen with increasing doses of DEX (10(-8) to 10(-7) M). DEX at 10(-9) M was ineffective. Concomitant addition of 10(-6) M RU486, a type II specific glucocorticoid receptor antagonist, to hepatocytes treated with 10(-7) M DEX abolished the DEX effect. RU486 at 10(-8) M was ineffective. Spironolactone (10(-8) to 10(-6) M), a type I specific glucocorticoid receptor antagonist, did not counteract the DEX effect. RU486 or spironolactone (10(-6) M) alone had no effect on CYP 1A1 under similar conditions. DEX thus down regulates CYP 1A1 in fish cultured hepatocytes and this regulation is mediated through the type II glucocorticoid receptor(s).

Cell-density-dependent expression of Cyp1a2 gene in monolayer-cultured adult mouse hepatocytes

Expression of Cyp1a1 and Cyp1a2 genes was investigated in adult C57BL/6NCrj mouse hepatocytes for up to 5 days after transfer to monolayer culture. CYP1A1 mRNA was substantially induced by treatment with 3-methylcholanthrene during the observation period, independently of the seeded cell density. However, expression of CYP1A2 mRNA was dependent on cell density and was higher in cells cultivated at lower density. With increasing culture period the expression was decreased, so that only negligible levels were evident by day 5, and reduced expression of constitutive and induced CYP-1A2 mRNA became apparent earlier in more densely seeded cells. This was not related to differences in numbers of inducer molecules per cell. While mouse hepatocytes incorporated tritium-labeled thymidine under the given culture conditions, induction of expression of the two Cyp1a genes did not show any direct relationship with DNA synthesizing activity. These observations suggest some role for Cyp1a2 during changes in physiological state.