Search PubMed⌕ Search

Biomedical subjects

E T Morgan

Publications and source records attributed to E T Morgan.

At least 37 records · Page 2Linked to original sources
PubMed1998

Down-regulation of the expression of three major rat liver cytochrome P450S by endotoxin in vivo occurs independently of nitric oxide production.

Endotoxemia results in both the down-regulation of multiple cytochrome P450 genes and the induction of inducible nitric oxide synthase (NOS2). The nitric oxide (NO) released during inflammation has been implicated as the mediator of the decreased catalytic activity and expression of several cytochrome P450 isozymes. We examined the role of NO in the decreases of both gene expression and activity of three major P450s in the endotoxemic Fischer 344 rat. Endotoxin (LPS) treatment suppressed both mRNA and protein expression of P450 2C11, 2E1, and 3A2. Coadministration of the NOS inhibitor aminoguanidine to LPS-treated rats completely inhibited the release of NO into the plasma but did not reverse the down-regulation of expression of any of the P450s examined at three time points. LPS treatment had a biphasic effect on some P450 catalytic activities. The hydroxylation of testosterone at the 2alpha-, 16alpha- and to a lesser extent 6beta-positions, was inhibited 6 hr after LPS treatment and returned to normal by 12 hr. The role of NO in the 6 hr effects could not be assessed due to effects of the aminoguanidine treatment itself. The second phase of decreased P450 activities seen after 24 hr was attributed to the NO-independent decrease in gene expression. Our results suggest that NO is not required for the LPS-evoked down-regulation of P450 2C11, 2E1 and 3A2 mRNA or protein expression. We cannot rule out a possible role for NO in the decreases in P450 activities seen early in the response.

Animals↗
PubMed1998

Physiological and pathophysiological regulation of cytochrome P450.

This article is a report on a symposium sponsored by the American Society for Pharmacology and Experimental Therapeutics and held at the April 1998 Experimental Biology '98 meeting in San Francisco. The presentations focused on the mechanisms of regulation of cytochrome P450 gene expression by developmental factors and by hormones and cytokines, as well as on the interplay between physiological and chemical regulation. Approaches and systems used to address these questions included conditional gene knockouts in mice, primary hepatocyte cultures, immunofluorescence imaging of cells, and cell lines stably expressing reporter gene constructs.

Animals↗
PubMed1997

Regulation of hepatic cytochrome P450 2C11 by glucocorticoids.

Previous studies have shown that the expression of cytochrome P450 2C11 is increased in primary hepatocyte culture in the presence of 10(-8) M dexamethasone (DEX). We and others have demonstrated that injection of rats with DEX resulted in 2C11 repression. In the present study, we show that regulation of 2C11 expression in hepatocytes by glucocorticoids is biphasic. Low concentrations (<10(-8) M) of DEX activate 2C11 expression, while higher concentrations of (>10(-7) M) suppress it. Corticosterone has a similar biphasic effect, although this physiological glucocorticoid was less potent than DEX. The transition between activation and suppression of 2C11 expression happens at glucocorticoid concentrations relevant to the transition between normal and stress levels of the hormones. Both the inductive and suppressive effects of glucocorticoids are blocked by RU486, a glucocorticoid receptor antagonist. We postulate that the biphasic nature of the 2C11 response to glucocorticoids may result in a high sensitivity of this P450 to stressful stimuli.

Animals↗
PubMed1997

Nitric oxide-independent suppression of P450 2C11 expression by interleukin-1beta and endotoxin in primary rat hepatocytes.

Hepatic expression of multiple cytochrome P450 genes is suppressed in the livers of rats undergoing an inflammatory response. Nitric oxide (NO) released during inflammation has been implicated in the decreased activities and expression of several cytochrome P450 isozymes. We examined the role of cytokine-mediated NO release on cytochrome P450 2C11 expression in rat hepatocytes cultured on Matrigel. Lipopolysaccharide (LPS), interleukin-1beta (IL-1beta), IL-6, and tumor necrosis factor-alpha (TNF-alpha), but not interferon-gamma (IFN-gamma), suppressed the expression of P450 2C11 mRNA. Neither IL-6 nor IFN-gamma caused NO release into the medium or induction of inducible nitric oxide synthase (iNOS) mRNA. IL-1beta and LPS were the most effective in causing NO release and iNOS induction, and in down-regulating P450 2C11 mRNA expression. Combinations of the cytokines, IFN-gamma, and LPS produced an additive release of NO but did not synergize to further suppress P450 2C11 mRNA. To investigate the role of NO in the IL-1beta- or LPS-mediated suppression of P450 2C11, N-monomethyl-L-arginine (NMA) was administered at concentrations ranging from 30 to 300 microM. Three hundred micromolar NMA returned NO release back to control levels, but did not affect the IL-1beta- or LPS-mediated down-regulation of P450 2C11 mRNA or protein expression. Our results suggest that NO is not required for IL-1beta- or LPS-mediated down-regulation of P450 2C11 expression in cultured hepatocytes.

Animals↗
PubMed1997

Bimodal regulation of ceramidase by interleukin-1beta. Implications for the regulation of cytochrome p450 2C11.

Interleukin 1beta (IL-1beta) induces the hydrolysis of sphingomyelin (SM) to ceramide (Cer) in primary cultures of rat hepatocytes, and Cer has been proposed to play a role in the down-regulation of cytochrome P450 2C11 (CYP2C11) and induction of alpha1-acid glycoprotein (AGP) by this cytokine (Chen, J., Nikolova-Karakashian, M., Merrill, A. H. & Morgan, E. T. (1995) J. Biol. Chem. 270, 25233-25238). Nonetheless, some of the features of the down-regulation of CYP2C11 do not fit a simple model of Cer as a second messenger as follows: N-acetylsphinganine (C2-DHCer) is as potent as N-acetylsphingosine (C2-Cer) in suppression of CYP2C11; the IL-1beta concentration dependence for SM turnover is different from that for the increase in Cer; and the increase in Cer mass is not equivalent to the amount of SM hydrolyzed nor the time course of SM hydrolysis. In this article, we report that these discrepancies are due to activation of ceramidase by the low concentrations of IL-1beta ( approximately 2.5 ng/ml) that maximally down-regulate CYP2C11 expression, whereas higher IL-1beta concentrations (that induce AGP) do not activate ceramidase and allow Cer accumulation. This bimodal concentration dependence is demonstrated both by in vitro ceramidase assays and in intact hepatocytes using a fluorescence Cer analog, 6-((N-(7-nitrobenz-2-oxa-1, 3-diazol-4-yl)amino)-Cer (NBD-Cer), and following release of the NBD-fatty acid. IL-1beta increases both acid and neutral ceramidase activities, which appear to be regulated by tyrosine phosphorylation because pretreatment of hepatocytes with sodium vanadate increases (and 25 microM genistein reduces) the basal and IL-1beta-stimulated ceramidase activities. Since these findings suggested that sphingosine (and, possibly, subsequent metabolites) is the primary mediator of the down-regulation of CYP2C11 by IL-1beta, the effects of exogenous sphingosine and C2-Cer on expression of this gene were compared. Sphingosine was more potent than C2-Cer in down-regulation of CYP2C11 when added alone or with fumonisin B1 to block acylation of the exogenous sphingosine. Furthermore, the suppression of CYP2C11 by C2-Cer (and C2-DHCer) is probably mediated by free sphingoid bases, rather than the short chain Cer directly, because both are hydrolyzed by hepatocytes and increase cellular levels of sphingosine and sphinganine. From these observations we conclude that sphingosine, possibly via sphingosine 1-phosphate, is a mediator of the regulation of CYP2C11 by IL-1beta in rat hepatocytes and that ceramidase activation provides a "switch" that determines which sphingolipids are elevated by this cytokine to produce multiple intracellular responses.

Amidohydrolases↗
PubMed1997

Regulation of cytochromes P450 during inflammation and infection.

Hepatic P450 activities are profoundly affected by various infectious and inflammatory stimuli, and this has clinical and toxicological consequences. Whereas the expression of most P450s in the liver is suppressed, some are induced. Many of the effects observed in vivo can be mimicked by pro-inflammatory cytokines and IFNs, and P450s are differentially regulated by these agents. Therefore, different cytokine profiles and concentrations in the vicinity of the hepatocyte in different models of inflammation may result in qualitatively and quantitatively different effects on populations of P450s. In addition to cytokines, glucocorticoids may have an important role in P450 regulation in stress conditions, including that caused by inflammatory stimuli. Although in many cases the decreases in activity are due primarily to a down-regulation of P450 gene transcription, it is likely that modulation of RNA and protein turnover, as well as enzyme inhibition, contributes to some of the observed effects. The mechanisms whereby these effects are produced may also vary with both the P450 under study and the time course of the effect. The complexity of the P450 response to inflammation and infection means that all of the above factors must be considered when trying to predict the effect of a given infectious or inflammatory condition on the clinical or toxic response of humans or animals to an administered drug or toxin. The question of whether the down-regulation of the hepatic P450 system to inflammation or infection is a homeostatic or pathological response cannot be answered at present. It is difficult to discern the physiological benefit of reducing hepatic P450 activities, unless it is to prevent the generation of reactive oxygen species generated by uncoupled catalytic turnover of the enzymes. On the other hand, as we proposed some years ago [64], the suppression of P450 may be due to the liver's need to utilize its transcriptional machinery and energy for the synthesis of APPs involved in the inflammatory response. In that case, one could ask why the organism has gone to the trouble of employing differential mechanisms for suppression of P450. One answer could be that the response evolved after the divergence of many of the P450 genes, necessitating the evolution of multiple redundant mechanisms for P450 suppression. In contrast to the down-regulation of P450s in the liver, the induction of several forms in this and other tissues suggests a more specific homeostatic role of these effects, e.g., in generation or catabolism of bioactive metabolites.

Animals↗
PubMed1997

Differential inductive and suppressive effects of endotoxin and particulate irritants on hepatic and renal cytochrome P-450 expression.

Inflammatory stimuli such as bacterial lipopolysaccharide (LPS) have been shown to down-regulate the mRNA and protein expression of hepatic cytochrome P-450 (P-450) isozymes 2C11, 2C12, 2E1 and 3A2 and to induce the mRNA expression of the P-450 4A subfamily. In this study, we examined the effects of irritants on the hepatic and renal expression of P-450 2C11, 2E1 and 3A2 and the 4A subfamily in the rat. Fischer 344 rats were administered doses of SiO2 (Celite), BaSO4, kaolin and LPS intraperitoneally and killed after different times for hepatic and renal RNA and microsome isolation. The administration of each irritant was found to suppress hepatic P-450 2C11 mRNA and protein and to induce P-450 4A1, 4A2 and 4A3 mRNA expression while having no significant effect on P-450 2E1 or 3A2. P-450 4A2, 4A3 and 2E1 mRNAs were all induced in the kidney cortices of the irritant- and LPS-treated rats. The effects of BaSO4 and SiO2 were found to be dose dependent. Chlorzoxazone-6-hydroxylase activity increased in the kidneys of irritant-treated rats, which is consistent with an increased expression of P-450 2E1. All irritants were found to induce the mRNA for the acute-phase protein fibrinogen; however, in contrast to LPS treatment, none of the irritants that were tested induced hepatic inducible nitric oxide synthase mRNA expression. These findings demonstrate the induction of renal P-450 isozymes after irritant and LPS administration. The findings of this study also suggest that different inflammatory stimuli affect the individual P-450 isozymes differentially.

Animals↗
PubMed1996

Suppression of rat hepatic microsomal cytochromes P450 by cyclophosphamide is correlated with plasma thyroid hormone levels and displays differential strain sensitivity.

Strain differences in cytochrome P450 (P450) expression were investigated in Sprague-Dawley (SDs) compared with Fischer 344s (F344s) rats after administration of cyclophosphamide (CPA). Animals received a single dose of CPA with sacrifice occurring 6 days post-treatment. At 130 mg/kg, male F344s displayed a greater sensitivity to CPA, as evidenced by a 68% loss of total hepatic microsomal P450 compared with only 35% in SDs. The most dramatic change in P450 was the loss of 2C11 (84% in F344s, 52% in SDs). In the SD, individual rat 2C11 activity was correlated (r2 = 0.76), with the level of plasma thyroxine in that animal. In male F344s administered CPA at 50 mg/kg, 43 and 44% losses in 2C11 activity (P < .05) and thyroxine (P < .01), respectively, were observed, whereas activities characteristic of P450s 2C11, 3A2, 2A2, 2C6 and 2E1/1A2 were unaffected in SDs at this dose. CPA also produced suppression of P450 in female SDs, including female-specific 2C12. Correlation was observed between the loss of P450 expression and change in body weight after treatment in both male and female animals, suggesting that CPA downregulates P450 expression secondary to decreased caloric intake. The anorectic effect of CPA is believed to result from potent central nervous system stimulation, accompanied by a state of adaptive hypothyroidism. It has been reported that CPA produces "feminization" of P450 expression in male rats. However, our findings suggest the alternative explanation that the effects of CPA on P450 expression result from decreased caloric intake.

Animals↗
PubMed1996

Suppression of constitutive cytochrome P450 gene expression by epidermal growth factor receptor ligands in cultured rat hepatocytes.

In rat hepatocytes cultured on Matrigel, incubation with epidermal growth factor (EGF) or transforming growth factor-alpha for 24 hr suppressed the constitutive expression of cytochrome P450 (CYP) 2C11 mRNA by 60-70%. The growth factors were maximally effective at concentrations of 10-30 ng/ml. These agents also suppressed the expression of CYP2C11 protein measured 48-72 hr after addition to the medium. Significant suppression of CYP2C11 mRNA was first seen 8 hr after EGF addition to the medium, was maximal by 16 hr, and persisted for at least 36 hr. The suppression of CYP2C11 mRNA by EGF was comparable in magnitude with that produced by interleukin (IL)-1, but greater than that by IL-6. The suppressive effects of EGF and IL-1 on CYP2C11 mRNA were additive, suggesting that the signaling pathways for suppression of CYP2C11 by EGF and IL-1 are different.

Animals↗
PubMed1996

Endotoxemia in rats is associated with induction of the P4504A subfamily and suppression of several other forms of cytochrome P450.

Bacterial lipopolysaccharide (LPS) has been previously shown to down-regulate the mRNA and protein expression of the hepatic cytochrome P450 (P450) isozymes 2C11 and 2C12. In this study, we examined the effects of LPS on the constitutive expression of P4503A2, P4502E1, and the P4504A subfamily in the rat. Fischer 344 and Sprague-Dawley rats were each administered 1 mg/kg LPS intraperitoneally and killed for hepatic RNA and microsome isolation at different times. LPS treatment was found to suppress P4502C11, P4503A2, and P4502E1 protein and mRNA expression in both strains of rat. Total microsomal P450 levels decreased by 30%, which was smaller than the effects on the levels of individual isozymes. The magnitude of suppression exhibited in the Sprague-Dawley rats, however, seemed to be more variable than that in the F344 strain. The mRNAs of all three of the P4504A subfamily members were induced 2- to 6-fold in the F344 rat livers after LPS administration. P4504A3 protein expression increased 2-fold, whereas P4504A1/2 protein levels decreased by 30%. Lauric acid omega-hydroxylase activity increased 1.6-fold in LPS-treated Fischer 344 rats and omega-1-hydroxylase activity decreased by 38%. In the Sprague-Dawley strain, however, decreases were seen in both omega- and omega-1-hydroxylase activities after LPS treatment. Our data demonstrate that LPS administration induces P4504A subfamily mRNA and P4504A3 protein expression. Furthermore, our findings also suggest strain differences in both suppression and induction of P450s between the Sprague-Dawley and F344 rats.

Animals↗
PubMed1995

Regulation of cytochrome P450 2C11 (CYP2C11) gene expression by interleukin-1, sphingomyelin hydrolysis, and ceramides in rat hepatocytes.

Interleukin-1 triggers the down-regulation of several hepatic cytochrome P450 gene products, but the cellular signaling pathways involved are not known. We have examined the role of sphingomyelin hydrolysis to ceramide in the suppression of CYP2C11, a major constitutive form of cytochrome P450, by interleukin-1. Treatment of rat hepatocytes cultured on matrigel with interleukin-1 beta caused a rapid turnover of sphingomyelin and an increase in cellular ceramide, with no change in cellular phosphatidylcholine. The ceramide was composed mainly of a D-erythro-sphingosine backbone, suggesting that it was derived from sphingolipid hydrolysis rather than from increased de novo synthesis. Treatment of the cells with either N-acetyl-D-erythro-sphingosine (C2-ceramide) or bacterial sphingomyelinase suppressed the expression of CYP2C11 and induced the expression of the interleukin-1-responsive alpha 1-acid glycoprotein mRNA. In contrast, the acute-phase gene beta-fibrinogen, which is induced by interleukin-6 but not by interleukin-1, did not respond to C2-ceramide. N-Acetyl-D-erythro-sphinganine mimicked the effect of C2-ceramide on CYP2C11, but not on alpha 1-acid glycoprotein expression. These results are consistent with a role for ceramide or a related sphingolipid in mediating the down-regulation of CYP2C11, the induction of alpha 1-acid glycoprotein, and perhaps other cellular effects of interleukin-1 in hepatocytes.

Acute-Phase Proteins↗
PubMed1995

Suppression of the constitutive expression of cytochrome P-450 2C11 by cytokines and interferons in primary cultures of rat hepatocytes: comparison with induction of acute-phase genes and demonstration that CYP2C11 promoter sequences are involved in the suppressive response to interleukins 1 and 6.

Hepatic expression of various members of the cytochrome P-450 (CYP) superfamily is suppressed during inflammatory responses. We have shown that the specific expression of P-450 2C11 in male rat liver is suppressed transcriptionally by endotoxin treatment. To investigate the molecular mechanisms underlying this phenomenon, we studied the effects of the inflammatory cytokines interleukin (IL)-1, IL-6, tumor necrosis factor-alpha (TNF), interferon (IFN)-alpha, and IFN-gamma on the expression of P-450 2C11 and the mRNAs of two typical acute-phase protein genes, alpha 1-acid glycoprotein (AGP) and fibrinogen, in primary hepatocyte cultures. IL-1, IL-6, TNF, and IFN-alpha all suppressed P-450 2C11 mRNA, whereas IFN-gamma had no effect. IL-1 and TNF were more effective than IL-6 in the suppression of P-450 2C11 mRNA. Whereas IL-1 and IL-6 effects on P-450 2C11 were accompanied by induction of AGP and fibrinogen mRNAs, IFN-alpha and TNF treatments had no effects on AGP. The suppression of P-450 2C11 and the induction of AGP by IL-1 showed similar time courses. The combination of IL-1 and IL-6 showed additivity in suppression of P-450 2C11, at maximally effective concentrations of cytokines. The effects of IL-1 on P-450 2C11 and AGP expression were blocked by IL-1 receptor antagonist protein. We also studied the effects of IL-1 and IL-6 on the transient expression of chloramphenicol acetyl-transferase reporter gene constructs containing 200 or 1287 base pairs of the 5' flanking region of the CYP2C11 gene, transfected into primary hepatocytes. The chloramphenicol acetyltransferase activities in cells transfected with the 200-base pair construct were reduced to about 33% and 58% of control levels by treatment with IL-1 or IL-6, respectively, suggesting that sequences important for cytokine down-regulation lie within the proximal promoter region of the CYP2C11 gene.

Acute-Phase Reaction↗
PubMed1994

Selective suppression of cytochrome P-450 gene expression by interleukins 1 and 6 in rat liver.

Inflammatory stimuli suppress constitutive hepatic expression of the CYP2C11 and CYP2C12 genes in male and female rat livers, respectively. We have shown previously that injection of interleukin-1 (IL1), but not interleukin-6 (IL6), to female rats also suppresses CYP2C12. In the present study, we examined the effects of these cytokines on CYP2C12 expression in rat hepatocyte cultures, and their in vivo effects on expression of multiple cytochrome P-450 (P450) gene products in male rat livers. IL1 suppressed the expression of CYP2C12 mRNA and protein in hepatocytes cultured on Matrigel in the presence of growth hormone. No consistent effect of IL6 was observed. Maximal suppression of CYP2C12 mRNA after 24 h of IL1 treatment reached 12 and 32% of control levels in two separate experiments. The approximate ED50 for IL1 was 5 ng/ml. CYP2C12 protein was suppressed to 28% of control levels as early as 12 h after IL1 treatment. Injection of IL1, low doses of dexamethasone, or both, in male rats produced decreases in total P450, and in CYP3A2 and CYP2C11 mRNA and protein expression similar to effects previously seen for CYP2C12 expression in females. CYP2E1 mRNA and protein was significantly suppressed only by the combination of IL1 and dexamethasone. IL6 treatment of male rats down-regulated the CYP2C11 and CYP2E1 mRNAs at a dose of 4.5 micrograms/kg, which was lower than that required to induce haptoglobin mRNA, a prototype acute phase gene product. CYP2C11 protein content of the microsomes was also decreased by IL6 treatment, with a slower time-course than for suppression of its mRNA. No significant effects of IL6 treatment were seen on CYP3A2 mRNA or CYP3A2/1 proteins. These results demonstrate that IL1 and IL6 treatments in vivo differentially affect subsets of P450 gene products in rat liver.

Animals↗
PubMed1994

Selective suppression of rat hepatic cytochrome P450 2C11 by chloramphenicol.

Chloramphenicol produces mechanism-based inactivation of several rat hepatic microsomal P450 enzymes including 2C6, 2C11, 2B1/2 and 3A1/2. A preliminary study by this laboratory reported that 48 hr after in vivo treatment with chloramphenicol (CAP) 2C11 activity remained low, whereas activities catalyzed by 3A2 and 2C6 were almost fully restored (Halpert et al., Biochem. Pharmacol. 37: 3046-3048, 1988). Therefore, in experiments conducted to examine whether CAP affects P450 expression, Sprague-Dawley (SD) rats were treated with CAP (single i.p. injection, 300 mg/kg) and sacrificed at various times post-treatment. The loss of P450 2C6, 2C11 and 3A2 catalytic activities which is characteristic of inactivation was demonstrated 1 hr after CAP administration. However, at 4 and 6 days, 2C11-mediated progesterone 2 alpha-hydroxylase activity remained diminished by 52 and 45%, respectively. Similar decreases in anti-P450 2C11-reactive protein and 2C11 mRNA were observed at 6 days, suggesting that the compound acts at a pretranslational step. Evaluation of 2C11 regulators indicated that CAP causes a decrease in plasma thyroxine level in proportion to the loss of 2C11 activity, whereas testosterone appears to be unaffected. To minimize intragroup variability, the inbred Fischer 344 strain was then examined at 2 and 6 days after CAP treatment. Surprisingly, CAP caused no loss in 2C11 protein, although the compound does inactivate 2C11 in liver microsomes from Fischer 344 rats. These results suggest that CAP alters P450 expression in a manner distinct from previously described compounds.

Animals↗
PubMed1993

Down-regulation of multiple cytochrome P450 gene products by inflammatory mediators in vivo. Independence from the hypothalamo-pituitary axis.

Inflammatory stimuli suppress constitutive hepatic expression of the CYP2C11 and CYP2C12 genes in male and female rat livers, respectively. Because growth hormone (GH) is an important regulator of P450 gene expression in the rat, the effects of bacterial endotoxin injection in hypophysectomized rats were compared to those in normal animals. In intact females, 0.2 mg/kg endotoxin suppressed total P450 and hepatic expression of CYP2C6, CYP2C7, CYP2C12, and CYP2E1 mRNAs, as well as CYP2C12 and CYP2E1 proteins, measured 16 hr later. CYP2C7 and CYP2E1 mRNAs were most affected (17 and 13% of untreated levels, respectively). Endotoxin treatment also induced the mRNA for the hepatic acute phase protein, haptoglobin, to 260% of control female levels. In hypophysectomized females supplemented with GH infusion, endotoxin caused the same or greater effects on expression of the P450 and haptoglobin gene products than were observed in the intact animals. It is concluded that the P450 suppression observed after endotoxin administration can occur independently of an effect on pituitary hormone secretion.

Acute-Phase Reaction↗
PubMed1992

Differences in glycogen, lipids, and enzymes in livers from rats flown on COSMOS 2044.

Livers from rats flown aboard COSMOS 2044 were analyzed for protein, carbohydrate (glycogen), and lipids as well as the activities of a number of key enzymes involved in metabolism of these compounds and xenobiotics. The major differences between the flight group and the synchronous control were elevations in microsomal protein, liver glycogen content, tyrosine aminotransferase, and tryptophan oxygenase and reductions in sphingolipids and the rate-limiting enzyme of heme biosynthesis, delta-aminolevulinic acid synthase. These results provide further evidence that spaceflight has pronounced and diverse effects on liver function; however, some of the results with samples from COSMOS 2044 differed notably from those from previous spaceflights. This may be due to conditions of spaceflight and/or the postflight recovery period for COSMOS 2044.

Amino Acids↗
PubMed1991

Suppression of P450IIC12 gene expression and elevation of actin messenger ribonucleic acid levels in the livers of female rats after injection of the interferon inducer poly rI.poly rC.

Interferons and interferon inducers cause a reduction in hepatic microsomal cytochrome P450 [AH, reduced-flavoprotein: oxygen oxidoreductase (RH hydroxylating), EC 1.14.14.1] content and drug-metabolizing activities in experimental animals. In the present study, the acute effects of administration of the interferon inducer polyriboinosinic acid.polyribocytidylic acid (poly rI.poly rC) to female rats on expression of the microsomal apoprotein and hepatic mRNA for P450IIC12, a constitutive enzyme comprising a significant fraction of the total P450 in untreated female rats, were examined. Poly rI.poly rC treatment (10 mg/kg, i.p.) caused a suppression of P450IIC12 apoprotein that was of greatest magnitude (47% of control levels) 24 hr after injection. P450IIC12 was still suppressed significantly (P less than 0.05) 48 hr after treatment. The time courses of suppression and recovery of P450IIC12 protein, as well as the magnitude of the effect, were similar to those of total microsomal P450 measured spectrophotometrically. P450IIC12 mRNA levels were also suppressed by the poly rI.poly rC treatment, reaching 29% of control values within 24 hr. Comparison of the kinetics of suppression of the P450IIC12 mRNA and apoprotein indicated that at least part of the suppression of the protein is mediated pretranslationally. However, the existence of a posttranslational component could not be excluded. Concomitant with the suppression of P450IIC12, actin mRNA content was found to be elevated by at least 3.6-fold in the livers of poly rI.poly rC-treated female rats, with the maximum effect occurring 12 hr after injection of the drug. This effect of poly rI.poly rC on expression of actin mRNA appeared to be at least partially sex-specific, since in a previous study [Morgan ET and Norman CA, Drug Metab Dispos 18: 649-653, 1990] a significant effect of the interferon inducer on actin expression was not observed in livers of male rats.

Actins↗