Differential effects of recombinant interferon alpha on constitutive and inducible cytochrome P450 isozymes in mouse liver

Exposure of cinnamyl alcohol in co-culture of BEAS-2B and dendritic cells: Interaction between CYP450 and cytokines

The prevalence of fragrances in various hygiene products contributes to their sensorial allure. However, fragrances can induce sensitization in the skin or respiratory system, and the mechanisms involved in this process are incompletely understood. This study investigated the intricate mechanisms underlying the fragrance's effects on sensitization response, focusing on the interplay between CYP450 enzymes, a class of drug-metabolizing enzymes, and the adaptive immune system. Specifically, we assessed the expression of CYP450 enzymes and cytokine profiles in culture of BEAS-2B and mature dendritic cells (mDC) alone or in co-culture stimulated with 2 mM of a common fragrance, cinnamyl alcohol (CA) for 20 h. CYP1A1, CYP1A2, CYP1B1, CYP2A6, and CYP2A13 were analyzed by RT-PCR and IL-10, IL-12p70, IL-18, IL-33, and thymic stromal lymphopoietin (TSLP) by Cytometric Bead Array (CBA). Through RT-PCR analysis, we observed that CA increased CYP1A2 and CYP1B1 expression in BEAS-2B, with a further increased in BEAS-2B-mDC co-culture. Additionally, exposure to CA increased IL-12p70 levels in mDC rather than in BEAS-2B-mDC co-culture. In regards to IL-18, level was higher in BEAS-2B than in BEAS-2B-mDC co-culture. A positive correlation between the levels of IL-10 and CYP1B1 was found in mDC-CA-exposed and between IL-12p70 and CYP1A1 was found in BEAS-2B after CA exposure. However, IL-12p70 and CYP1A2 as well as IL-18, IL-33, and CYP1A1 levels were negative, correlated mainly in co-culture control. These correlations highlight potential immunomodulatory interactions and complex regulatory relationships. Overall, exposure to CA enhances CYP450 expression, suggesting that CA can influence immune responses by degrading ligands on xenosensitive transcription factors.

Fragrances as a trigger of immune responses in different environments

Fragrances can cause allergic skin reactions, expressed as allergic contact dermatitis and reactions in the respiratory tract that range from acute temporary upper airway irritation to obstructive lung disease. These adverse health effects may result from the stimulation of a specific (adaptive) immune response. Th1 cells, which essentially produce interleukin-2 (IL-2) and interferon-γ (IFN-γ), play a key role in allergic contact dermatitis and also on allergic sensitization to common allergens (e.g., nickel and fragrance). It has been shown that fragrance allergy leads to Th2/Th22 production of IL-4, IL-5 and IL-13, controlling the development of IgE and mediating hypersensitivity reactions in the lung, such as asthma. Cytokines released during immune response modulate the expression of cytochrome P450 (CYPs) proteins, which can result in alterations of the pharmacological effects of substances in inflammatory diseases. The mechanisms linking environment and immunity are still not completely understood but it is known that aryl hydrocarbon receptor (AhR) is a sensor with conserved ligand-activated transcription factor, highly expressed in cells that controls complex transcriptional programs which are ligand and cell type specific, with CYPs as targeted genes. This review focuses on these important aspects of immune responses of the skin and respiratory tract cells, describing some in vitro models applied to evaluate the mechanisms involved in fragrance-induced allergy.

Effect of interferon-α2b on the expression of various drug-metabolizing enzymes and transporters in co-cultures of freshly prepared human primary hepatocytes

The purpose of this study was to assess the impact of interferon-α2b (IFN-α2b) on the expression of various drug-metabolizing enzymes and transporters in freshly prepared co-cultures (parenchymal and non-parenchymal cells) of human primary hepatocytes. At therapeutically relevant concentrations (from 1000 to 3000 IU/mL), IFN-α2b up-regulated STAT1 (signal transducer and activator of transcription factor 1) mRNA expression. Conversely, three cytochrome P450s (CYP1A2, CYP2B6, CYP2E1), a UDP-glucuronosyltransferase (UGT2B7), a sulphotransferase (SULT1A1) and organic anion transporter (OAT2) were significantly down-regulated (~50%; P < 0.05). Western blot analysis of CYP1A2, UGT2B7 and OAT2 protein supported the mRNA data. Two peroxisome proliferator activator receptor alpha (PPARα)-controlled genes (pyruvate dehydrogenase kinase 4 and adipose differentiation-related protein), CYP3A4 and multidrug resistance-associated protein 2 were significantly up-regulated (up to 223%; P < 0.05). On the other hand, SULT2A1, carboxylesterase 2, organic anion transporting peptide (OATP1B1, OATP1B3, OATP2B1), organic cation transporter 1, P-glycoprotein and breast cancer resistance protein mRNA expression was not significantly affected. Western blot analysis of CYP3A4 supported the mRNA data also. The present results demonstrated complex interactions between IFN-α2b and hepatocytes and the observed down-regulation of CYP1A2, OAT2 and UGT2B7 is consistent with reports of drug interactions between IFN-α2b and drugs such as theophylline, clozapine and gemfibrozil.

Interactions between immune and biotransformation systems in fish: a review

In animals biotransformation and immune system are not totally independent, there are numerous functional interrelationships between these two systems. They are both implicated in the capacity of organisms to resist to a wide variety of environmental components such as viruses, bacteria and xenobiotics. It is known for a long time that the immune system functions as a physiologic system and interacts with all the other components of the organism including nervous or endocrine ones. In the same manner, the biotransformation system (especially the cytochrome P450 monooxygenases) is involved in the regulation of numerous hormone productions. In this way, many studies in mammals have revealed the possible interaction between immune and biotransformation systems. Among these interactions, the capacity of the activation of host defense mechanisms to down-regulate microsomal cytochrome P450 and the role of biotransformation system in the xenobiotic-mediated immunotoxicity have been underlined. Advances in the basic knowledge of fish immune and biotransformation systems should lead to a better understanding of the possible interactions between both systems and should improve fish health monitoring which is a crucial ecotoxicological goal.

The cytochromes P450 (CYP) response to allergic inflammation of the lung

The expression of the mouse Cyp family and key inflammatory mediators were examined in a model of ovalbumin (OVA)-induced allergic airway disease. The expression of IL-4, IL-13 and Ccl11 increased during the acute phase of allergic inflammation and decreased with its resolution. Interestingly, the expression of Ccl20 was increased during the resolution phase. The response of the Cyp gene family to the development of allergic inflammation was differential and correlated with the evolution of the inflammatory response. During the acute inflammatory phase the mRNA levels of Cyp2e1, Cyp2f2, Cyp2j6, Cyp4b1, Cyp8a1 and Cypor were decreased while the mRNA levels of Cyp4f18, Cyp5a1 and Cyp7b1 were elevated. With resolution of the inflammation the expression patterns returned to normal. These changes suggest that the Cyp family may play a role in the allergic inflammation by modulating the metabolism of xenobiotics and endogenous compounds such as LTB4, TXA1, PGI2 and native anti-glucocorticoids.

Possible implication of macrophages in the regulation of cytochrome P450 activities in carp (Cyprinus carpio)

Macrophages play a key role in the regulation of cytochrome P450 activity induced by immunostimulants in mammals. We investigated the effects of immunostimulants (LPS, dextran sulfate and tilorone) on biotransformation and macrophage activities in carp. The major effect of LPS was its capacity to inhibit 3-MC-induced cytochrome P450 activities in the liver and head kidney. Basal phase I activities were reduced by tilorone and dextran sulfate in immune organs. Tilorone and dextran sulfate differently modulated total cytochrome P450 contents and P4501A activities suggesting differential sensitivity for P450 classes. In immune organs, tilorone and dextran sulfate inhibited basal EROD activity. Tilorone inhibited 3-MC-induced EROD activity whereas dextran sulfate enhanced this activity. LPS and dextran sulfate increased ROS production by macrophages and all the immunostimulants induced macrophage activating factor (MAF) production. This study demonstrates for the first time in fish the capacity of CYP-regulated immunostimulants to activate macrophages and provides initial insight into the capacity of macrophages to regulate CYP activity induced by immunostimulants in fish.

Modification of the P-Glycoprotein Dependent Pharmacokinetics of Digoxin in Rats by Human Recombinant Interferon-α

PURPOSE

This study was conducted to investigate in vivo the impact of interferon-alpha (IFN)-alpha on P-glycoprotein (P-gp) activity in rats by studying how its administration modifies the bioavailability of digoxin, a fairly pure P-gp substrate.

METHODS

Human recombinant IFN-alpha was given to rats (n = 5-7 per group) daily for 8 days at different doses (IntronA) 10(6), 2.10(6), or 4.10(6) IU kg(-1), s.c.), whereas pegylated-IFN-alpha (ViraferonPeg), 29 microg kg(-1)) was given s.c. three times a week. Rats were then given digoxin (32 microg kg(-1)) i.v. or orally. The pharmacokinetics of digoxin was studied. Intestinal P-gp expression was also examined.

RESULTS

The pharmacokinetics of i.v. administered digoxin was not modified by IFN-alpha, but a dose-dependent increase in areas under the curve (AUCs) was observed in the orally administered digoxin parameters in rats (AUCs: 392 +/- 83 min microg L(-1), p < 0.01 and 550 +/- 97 min microg L(-1), p < 0.001, respectively, vs. 286 +/- 111 min microg L(-1) for control). A decrease in P-gp expression in the ileum (relative intensities: 0.70 +/- 0.19 for 4 Million International Unit (MIU) kg(-1) IFN-alpha-treated animals vs. 1.00 +/- 0.13 for controls, p < 0.05) and mainly in the jejunum (relative intensities: 0.46 +/- 0.13 for 4 MIU kg(-1) IFN-alpha-treated animals vs. 1.00 +/- 0.08 for controls, p < 0.001) was observed.

CONCLUSION

IFN-alpha induces in vivo a significant dose-dependent inhibitory effect on intestinal P-gp activity related to a local decrease in its expression, thereby predicting important clinical consequences when IFN-alpha and other P-gp substrates are associated.

Hepatic (dys-)function during inflammation

It is an understatement to say that the liver is an important organ. Each of the liver cells goes through thousands of complex biochemical interactions that influence all of the other organs in the body. Since the liver is involved with almost all biochemical processes it is no wonder that there are many different diseases that will affect it. A process known to impair liver function, including hepatic drug metabolism, is an infection induced inflammatory response. Infection induced alterations in liver function involve various cell types and their continuous cross-talk, as well as several circulating or locally secreted inflammatory mediators. Three main hepatic cell types contribute to the liver response during inflammation: hepatocytes, Kupffer cells and sinusoidal endothelial cells. In addition, activated neutrophils, which are also recruited in the liver and produce potentially destructive enzymes and oxygen-derived radicals, may further enhance liver injury. This review will focus on the pathway by which Kupffer cells and hepatocytes are activated and how this affects liver function, in particular hepatic drug metabolism.

beta-naphthoflavone induction of CYP1A in brain of juvenile lake trout (Salvelinus namaycush Walbaum)

Many environmental pollutants induce expression of the cytochrome P450 (CYP) 1A subfamily of genes. We integrated cellular and molecular biological techniques to examine the effects of beta-naphthoflavone (BNF) exposure in lake trout brain CYP1A distribution and dynamics. Over a 32-day time-course, real time quantitative reverse transcription polymerase chain reaction (Q-RT-PCR) results showed that CYP1A mRNA induction in response to BNF exposure occurred rapidly and continued to rise in the BNF-treated lake trout after 4 h, with a peak at or after 2 days. Messenger RNA levels fell after 4 days, and this trend continued after 16 days of exposure. In situ hybridization indicated that CYP1A mRNA was universally elevated in the brain of BNF-exposed fish and was mainly expressed in the endothelia and occasionally in the glial cells. CYP1A immunoreactivity was induced in the olfactory bulb and valvula cerebelli of BNF-treated fish. Other brain areas showed constitutive CYP1A immunoreactivity in both control and BNF-treated fish. Some BNF-treated fish contained multifocal hemorrhages in the brain tissue, and these fish had overall depressed CYP1A immunoreactivity in the brain. The relationship between transcriptional and translational effects of BNF exposure in the brain of juvenile lake trout is discussed.

Interleukin-1beta, interleukin-6, tumour necrosis factor-alpha and interferon-gamma released by a viral infection and an aseptic inflammation reduce CYP1A1, 1A2 and 3A6 expression in rabbit hepatocytes

Inflammation reduces activity and expression of hepatic cytochrome P450 (P450) and therefore diminishes drug biotransformation. This study aimed to identify the serum mediators triggered by a viral infection and an aseptic inflammation that downregulate P450 isoforms. Incubation of hepatocytes with serum from rabbits with a turpentine-induced inflammation or humans with a viral infection decreased the amount of cytochrome 1A1 (CYP1A1), 1A2 and 3A6 mRNA and apoproteins. By serum fractionation and immuno-neutralization, we showed that in the aseptic inflammation, interleukin-6 and, to a lesser degree, interleukin-1beta are involved in the downregulation of all three isoforms. In serum from humans with a viral infection, interleukin-1beta, interleukin-6, interferon-gamma and tumour necrosis factor-alpha contribute to the downregulation of P450 isoforms. CYP1A1 and 1A2 are regulated by serum mediators at the transcriptional level, while the expression of CYP3A6 appears to be under the control of pre- and posttranscriptional mechanisms.

Moricizine, an antiarrhythmic agent, as a potent inhibitor of hepatic microsomal CYP1A

We examined the inhibitory effect of moricizine (MOR) on hepatic cytochrome P-450 (CYP) in mice. Spectrophotometric analysis revealed that MOR had a relatively high affinity for CYP molecules. MOR most potently inhibited the CYP1A1-dependent ethoxyresorufin O-deethylation and the CYP1A2-dependent methoxyresorufin O-demethylation, among the metabolic reactions mediated by CYP1A, CYP2A, CYP2B, CYP2C, CYP2D, CYP2E, and CYP3A subfamilies expressed in untreated and CYP-inducer-treated hepatic microsomes. The inhibition constants (K(i)) for ethoxyresorufin and methoxyresorufin O-dealkylations were 0.43 and 0.98 micromol/l, respectively. These K(i) values were one to three orders of magnitude lower than those of cimetidine (CIM) and mexiletine (MEX) that have been accepted as the clinical inhibitors of CYP1A2 and were below the therapeutic serum concentration of MOR. Theophylline 3-demethylation and 8-hydroxylation in untreated hepatic microsomes, clinical probes for CYP1A2 activities, were subjected to marked and competitive inhibition by MOR with K(i) values similar to that of methoxyresorufin O-demethylation, and the inhibitory potency of MOR was much higher than those of CIM and MEX. In addition, the zoxazolamine paralysis time, an in vivo measure of the hepatic CYP1A2 capacity, was markedly prolonged by pretreatment of mice with MOR rather than CIM and MEX, while the prolonging effect of MOR on the pentobarbital sleeping time, an indicator of the metabolic function of phenobarbital-inducible CYP species, was not so pronounced as compared with the zoxazolamine paralysis time. These results indicate that MOR acts as a potent and preferential inhibitor of hepatic CYP1A enzymes in vitro and in vivo.

Paraquat detoxicative system in the mouse liver postmitochondrial fraction

We examined the paraquat detoxicative system in mouse livers. The survival rate of mice receiving 50 mg/kg paraquat was 41% at 7 days and significantly rose to 88, 64, 69% with pretreatment with phenytoin, phenobarbital, and rifampicin, respectively. Phenytoin induced activity in NADPH-cytochrome P450 reductase, CYP3A, CYP2B, and CYP2C that was 3 to 4 times higher than that of the controls. Phenobarbital induced CYP2B and rifampicin induced CYP3A, respectively, in addition to NADPH-cytochrome P450 reductase. 3-Methylcholanthrene did not induce these enzymes and did not alter the survival rate. All the mice pretreated with CoCl(2) (a CYP synthesis inhibitor) or SKF 525-A (a CYP inhibitor) were dead after 5 days, and troleandomycin (a CYP3A-specific inhibitor) also reduced the survival rate. When cell homogenates were incubated with paraquat and NADPH, paraquat decreased and its metabolic intermediate paraquat-monopyridone was formed. Troleandomycin inhibited the decrease in paraquat and increased the monopyridone. After making a subfraction of the homogenate, monopyridone was produced in the postmicrosomal 105,000g supernatant, but not in the microsomes. The pretreatment of mice with phenytoin decreased the monopyridone in the postmitochondrial fraction, but did not affect the supernatant. These results indicated that paraquat was first metabolized in the postmicrosomal supernatant into monopyridone, and that may have been subsequently hydroxylated by the microsomes. Repeated intravenous injections of alpha-tocopherol to paraquat-loaded mice significantly reduced the paraquat mortality and when these mice were pretreated with rifampicin, 100% of them survived. These studies demonstrate that postmitochondrial fractions play an important role in paraquat detoxication metabolism, and that the combination of CYP induction and alpha-tocopherol administration is highly useful for the survival of paraquat-exposed mice.

Role of cytokines in the lipopolysaccharide-evoked depression of cytochrome P450 in the brain and liver

A role for cytokines as mediators of the depression in cytochrome P450 activity in brain and liver during CNS inflammation is proposed. Lipopolysaccharide (LPS) was given directly into the lateral ventricle of the brain to mimic a localized CNS infection. CYP1A activity and protein in both brain and liver were depressed in response to this treatment. The administration of the pro-inflammatory cytokines tumor necrosis factor-alpha (TNF-alpha), interleukin-1beta (IL-1beta), and interferon-gamma (IFN-gamma) directly into the lateral ventricle emulated the effects of LPS on CYP1A activity only in the brain. In contrast, these centrally administered cytokines did not produce a concomitant loss of CYP1A activity in the liver. Significant levels of several cytokines (TNF-alpha, IL-1beta, and IFN-gamma) were produced in the serum of animals following intracerebroventricular (i.c.v.) administration of LPS. This production of peripheral cytokines by LPS could not be mimicked by the i.c.v. injection of IL-1beta or TNF-alpha. These results suggest that induction of cytokines in the brain may play a direct role in the depression of CYP1A activity in the CNS following the administration of LPS into the lateral ventricle. The production of cytokines within the brain does not appear to participate in the signaling process in the brain that leads to the concomitant loss of CYP1A activity in the liver. The subsequent production of cytokines in peripheral tissues, however, does appear to play a role in the loss of cytochrome P450 in the liver.

Alteration of drug biotransformation and elimination during infection and inflammation

During infection or inflammation, the expression of cytochrome P450 and its dependent biotransformation pathways are modified. This results in a change in the capacity of the liver to handle drugs and in alterations in the production and elimination of endogenous substances throughout the body. The majority of the CYP isoforms are modified at pre-translational steps in protein synthesis, and, in most cases, cytokines are involved as mediators of the response. Recent information suggests that inflammatory responses that are localized to the CNS cause a loss of CYP within the brain. This is accompanied by a parallel down-regulation of CYP in peripheral organs that is mediated by a signaling pathway between the brain and periphery. This review covers the loss that occurs in the major mammalian CYP families in response to infection/inflammation and the mediator pathways that are key to this response.

Endotoxin downregulates hepatic expression of P-glycoprotein and MRP2 in 2-acetylaminofluorene-treated rats

In liver, the ATP-dependent transporters P-glycoprotein (PGP) and multidrug resistance protein-2 (MRP2) are involved in the secretion of numerous drugs and toxins in bile. Although constitutive levels of PGP and MRP-2 are decreased in rat liver after exposure to endotoxin, it is possible that induced forms of these transporters may be alternately affected. In vitro, the hepatocarcinogen, 2-acetylaminofluorene (AAF) induces expression of PGP and MRP2. Thus, we examined the influence of endotoxin on the expression of PGP and MRP2 in AAF-treated rats. Expression of PGP and MRP2 was analyzed on Westerns and by RT-PCR in livers obtained from endotoxin and control groups. In vivo, AAF treatment significantly induced PGP/mdr1 expression and imposed a significant reduction in the expression of spgp. MRP2 protein and mRNA levels were not altered by AAF administration. Endotoxin administration to both AAF-treated and non-AAF-treated rats elicited significant reductions in the protein and mRNA expression of MRP2 and PGP (P < 0.05). Our data indicate that endotoxin suppresses the overexpression of PGP and constitutive expression of MRP2 in AAF-treated rats. Furthermore, in vivo administration of AAF, which maximally induces PGP does not induce MRP2.

Effect of hepatobiliary disease, chronic hepatitis C and hepatitis B virus infections and interferon-alpha on porphyrin profiles in plasma, urine and faeces

BACKGROUND

Documentation of the profiles of porphyrins in hepatobiliary disease is limited. Strong associations of hepatitis B and C virus infections with porphyria cutanea tarda have suggested causal relationships. This study aimed to determine the nature of porphyrin abnormalities in hepatobiliary disease and the effect of interferon-alpha on porphyrin profiles.

METHODS

Total porphyrins were measured in the plasma, urine and faeces of 83 patients with hepatobiliary disease (37 hepatitis C, 20 hepatitis B, 26 other causes) and 12 clinical controls, and porphyrin profiles were determined by high-performance liquid chromatography.

RESULTS

Porphyrins were elevated in the plasma of 11 and urine of 23 patients with hepatobiliary disease, as a result of elevated coproporphyrin I. This was reflected in increased coproporphyrin I:III ratios. Abnormal total porphyrin levels had a significant negative correlation with plasma albumin, and a positive correlation with bilirubin and alkaline phosphatase, but not with aminotransferases. Total urinary porphyrins were elevated in three control patients, but coproporphyrin I:III ratios were normal. Although not seen in plasma or urine, porphyrins that are specific for porphyria cutanea tarda were found in the faeces of six patients, but this occurred with similar frequency in hepatitis B or C infection (four of 50) as in the clinical controls (two of 12). Interferon-alpha had no effect during or after therapy in six patients with hepatitis C.

CONCLUSIONS

Reduced biliary excretion of coproporphyrin I occurs in more severe cholestasis and/or hepatic dysfunction. A causal relationship between viral liver disease and porphyria cutanea tarda which is unlikely to be precipitated by interferon-alpha, is not supported.

Hepatic drug metabolism and immunostimulation

When host defence mechanisms are stimulated there is a concomitant decrease in cytochrome P450 based drug biotransformation and elimination. This has resulted in a number of clinically important unwanted drug responses in patients with infections or inflammatory responses. The loss in cytochrome P450 is predominantly an effect at the level of the gene expression and the majority of enzyme forms examined to date are involved. Although the effect occurs predominantly in the liver it has been recently shown that inflammatory responses in the brain also cause a loss of the same enzyme forms in that organ. The loss of cytochrome P450 in the brain in response to localised inflammation is accompanied by a similar loss in the liver. The decrease of cytochrome P450 and its dependent drug biotransformation is of concern whenever drugs are used in patients with infections or disease states with an inflammatory component.

Lipopolysaccharide evokes the modulation of brain cytochrome P4501A in the rat

The cytochrome P450 enzyme system is a multigene family of enzymes that is modulated in the liver during systemic inflammatory responses or during infection Several forms of the enzyme are expressed in discrete areas of the brain and likely play a critical role in the metabolism of drugs and endogenous chemicals in the central nervous system (CNS). Even though the brain responds to inflammation in a manner different from most tissues, we examined the possible modification of a major cytochrome P450 form (CYP1A) in the brain during inflammation confined to that organ. Total brain CYP1A activity, as measured by ethoxyresorufin dealkylase (EROD), was downregulated 24 and 48 h following the administration of a single dose of lipopolysaccharide (LPS). Regionally, a similar effect was determined in the cortex, hippocampus and the mid-brain but the activity in the cerebellum was unaffected. The examination of coronal brain sections using an antibody directed against CYP1A indicated that the enzyme was distributed in discrete cells of the hippocampus, thalamus and cortex and in the tanycytes surrounding the third ventricle. In each of these areas, the immunoreactivity was diminished in animals receiving LPS as compared to saline-treated animals. LPS also evoked the expression of the small molecular weight heat shock protein hsp27 throughout the brain indicating the development of an inflammatory response. These studies indicate that inflammation localized to the CNS causes an alteration in the levels and activity of a major cytochrome P450 form in the brain. This could have implications to the metabolism or activation of drugs and endogenous chemicals in the CNS during a disease state that features an inflammatory component.

Preferential inhibition of CYP1A enzymes in hepatic microsomes by mexiletine

We examined the inhibitory behavior of theophylline oxidations and a variety of cytochrome P450 (P450)-dependent metabolism in the presence of mexiletine (MEX), using hepatic microsomes from both control mice and mice exposed to beta-naphthoflavone (beta-NF). Theophylline metabolism, which is mainly catalyzed by CYP1A2, was susceptible to competitive inhibition by MEX. The calculated inhibition constants (Ki) for theophylline 3-demethylation and its 8-hydroxylation were 4.3 microM and 8.3 microM, respectively, which are comparable to the recommended therapeutic serum range for MEX. The inhibitory potency of MEX on cytochrome P450-dependent enzyme activities diverged among the several metabolic reactions, which were probes for CYP1A, 2A, 2C, 2D, 2E and 3A subfamilies. The Ki value (6.7 microM) for methoxyresorufin O-demethylation mediated by CYP1A2 agreed with those from theophylline oxidations. These metabolic reactions exhibited the smallest Ki values, 1-3 orders of magnitude lower than activities of other constitutive cytochrome P450 species. Similar degrees of inhibition were observed in CYP1A1, a beta-NF-inducible isoform with a relatively high conformity to CYP1A2. These results indicate that MEX acts as a selective and potent inhibitor of the CYP1A enzymes responsible for oxidative biotransformation of chemicals such as theophylline. This evidence provides a fundamental explanation for the pharmacokinetic interactions experienced in clinical practice.

Distinctive roles of STAT5a and STAT5b in sexual dimorphism of hepatic P450 gene expression. Impact of STAT5a gene disruption

Stat5b gene disruption leads to an apparent growth hormone (GH) pulse insensitivity associated with loss of male-characteristic body growth rates and male-specific liver gene expression (Udy, G. B., Towers, R. P., Snell, R. G., Wilkins, R. J., Park, S. H., Ram, P. A., Waxman, D. J., and Davey, H. W. (1997) Proc. Natl. Acad. Sci. U. S. A. 94, 7239-7244). In the present study, disruption of the mouse Stat5a gene, whose coding sequence is approximately 90% identical to the Stat5b gene, resulted in no loss of expression in male mice of several sex-dependent, GH-regulated liver cytochrome P450 (CYP) enzymes. By contrast, the loss of STAT5b feminized the livers of males by decreasing expression of male-specific CYPs (CYP2D9 and testosterone 16alpha-hydroxylase) while increasing to female levels several female-predominant liver CYPs (CYP3A, CYP2B, and testosterone 6beta-hydroxylase). Since STAT5a is thus nonessential for these male GH responses, STAT5b homodimers, but not STAT5a-STAT5b heterodimers, probably mediate the sexually dimorphic effects of male GH pulses on liver CYP expression. In female mice, however, disruption of either Stat5a or Stat5b led to striking decreases in several liver CYP-catalyzed testosterone hydroxylase activities. Stat5a or Stat5b gene disruption also led to the loss of a female-specific, GH-regulated hepatic CYP2B enzyme. STAT5a, which is much less abundant in liver than STAT5b, and STAT5b are therefore both required for constitutive expression in female but not male mouse liver of certain GH-regulated CYP steroid hydroxylases, suggesting that STAT5 protein heterodimerization is an important determinant of the sex-dependent and gene-specific effects that GH has on the liver.

Modulation of drug-metabolizing systems by bacterial endotoxin in carp liver and immune organs

This report describes a study of the effects of bacterial endotoxin [lipopolysaccharide (LPS)] on cytochrome P450 levels and ethoxyresorufin O-deethylase (EROD) and glutathione S-transferase (GST) activities in liver and two main immune organs of carp: spleen and head kidney. Also studied was the paucity of the carp drug-metabolizing system in an environment subject to pollution by a polycyclic aromatic hydrocarbon, 3-methylcholanthrene (3MC), when fish respond to an immune activation by lipopolysaccharide (LPS). In the presence of bacterial endotoxin the basal cytochrome P450 levels were decreased in liver and spleen. EROD activity was increased in liver and basal GST activity was increased in spleen. When fish were treated concomitantly with 3MC and LPS, a suppression of cytochrome P450 induction in liver and head kidney was observed. EROD activity induced by 3MC was not modified by administration of LPS. GST activity was suppressed by treatment with LPS and inducing agent in liver and head kidney. In the present study it was found that endotoxin can have profound and differential effects on fish basal biotransformation of drugs in the liver and immune organs. Also, the induction of biotransformation enzymes by 3MC was modified when fish responded to an immune stimulation.

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.

3-Methylcholanthrene-induced EROD activity and cytochrome P-450 in immune organs of carp (Cyprinus carpio)

In this study, at first, we determined the optimal assay conditions for Ethoxyresorufin-O-deethylase activity and cytochrome P450 contents in the liver and two immune organs (spleen and head kidney) of carp. The Km values of cytochrome P450 1A activity were identical in the three organs, demonstrating that the enzyme belongs to the same isoform. In a second step, we showed that carp contained endogenous cytochrome P450 and EROD activity in two immune organs like in liver. These enzyme activities can be induced in a dose dependent manner by 3-methylcholanthrene, a specific inducer of cytochrome P450 1A, in the three organs. These results suggest that spleen and head kidney, the important immune organs in teleost fish, may be implicated in biotransformation for a class of contaminants like polycyclic aromatic hydrocarbons. In future, we can study the interaction between immune system and biotransformation system in fish.

Cytochrome P4501A1 and cytochrome P4501A2 are downregulated at both transcriptional and post-transcriptional levels by conditions resulting in interferon-alpha/beta induction

The interferon mediated downregulation of constitutive and inducible cytochrome P450 enzymes occurs through a pretranslational mechanism which depresses the mRNA encoding cytochrome P450s. We measured the transcription rates of CYP1A genes and the turnover of CYP1A mRNA in rats treated with the interferon-alpha/beta inducer polyinosinic acid-polycytidylic acid. The rate of transcription of CYP1A1 and CYP1A2 genes was significantly decreased in hepatic nuclei isolated from male rats treated with polyinosinic acid-polycytidylic acid (10 mg/kg). In addition the rate of degradation of hepatic CYP1A1 and CYP1A2 mRNA was examined following the inhibition of de novo transcription by actinomycin D (1 mg/kg). Messenger RNA levels were analysed by Northern and slot blotting with a 1.2 kb murine CYP1A1 cDNA probe. Interferon significantly augmented the rate of loss of CYP1A1 and CYP1A2 mRNAs suggesting that post-transcriptional degradation of mRNA contributes to the pre-translational events that cause cytochrome P450 downregulation. These results support the involvement of both transcriptional and post-transcriptional mechanisms in the loss of cytochrome P450s mediated by interferon inducers.

Differential effect of pentoxifylline on lipopolysaccharide-induced downregulation of cytochrome P450

It is now established that inflammatory stimuli such as lipopolysaccharides (LPS) and polyinosinic acid:polycytidylic (polyIC) suppress hepatic expression of cytochrome P450 (P450) genes in rat liver. Previous studies have suggested that LPS- or polyIC-induced downregulation of P450 was due to endogenously released inflammatory cytokines such as tumor necrosis factor-alpha (TNF-alpha), interleukin-1, interleukin-6, and interferons (IFNs). To improve our understanding of the role of inflammatory cytokines in mediating P450 depression, we investigated the possibility of preventing P450 downregulation with pentoxifylline. Pentoxifylline has been shown to inhibit LPS-induced TNF-alpha production by suppression of TNF-alpha gene expression. The present study shows that in uninduced male rats pentoxifylline selectively prevents the downregulation of microsomal P4501A2 and P4502B caused by LPS. No protective effect of pentoxifylline on the downregulation of P4502E1 and P4503A1/2 was observed. PolyIC-induced downregulation of P4501A2, P4502B, P4502E1, and P4503A1/2 was not affected by pentoxifylline. These results suggest that the LPS-induced downregulation of P4501A2 and P4502B is mediated to a large extent by TNF-alpha. Other cytokines might be involved in the suppression of P4502E1 and P4503A1/2. The fact that polyIC-induced downregulation is not protected by pentoxifylline is further evidence that this agent acts via a selective induction of IFNs.

Modulation of constitutive and inducible hepatic cytochrome(s) P-450 by interferon beta in mice

AIMS/METHODS

Interferon beta is used as a therapeutic agent, but its effects on the hepatic cytochrome P-450-dependent drug metabolizing system have not yet been characterized. We investigated the effect of interferon beta on cytochrome P-450 in mice.

RESULTS

Interferon beta (2 x 10(5) units/mouse) significantly reduced total hepatic cytochrome P-450 (20%) and the activity of NADPH cytochrome C reductase (12%) 24 h after administration; lower doses had no such effect. Various monooxygenase activities were slightly reduced, the one most affected being 7-ethoxycoumarin O-deethylase (29%). In phenobarbital-treated mice, interferon beta reduced the induction of total cytochrome P-450 (22%), the activities of pentoxyresorufin O-dealkylase (38%), benzyloxyresorufin O-dealkylase (30%), erythromycin N-demethylase (30%), 7-ethoxycoumarin O-deethylase (16%) and cytochrome P-450 2B1 (33%) and 3A (45%) proteins. In beta-naphthoflavone-treated mice, interferon beta lowered the induction of total cytochrome P-450 (18%), the activities of ethoxyresorufin O-deethylase (31%) and of 7-ethoxycoumarin O-deethylase (25%) and of cytochrome P-450 1A1 protein (31%).

CONCLUSIONS

Thus it appears that induced cytochrome(s) P-450 were susceptible to interferon beta, this effect not being influenced by the type of inducer. Since various members of the same cytochrome P-450 subfamilies catalyze oxidation of drugs in humans, our findings have potential significance as regards the fate of drugs or exogenous compounds given to patients receiving interferon beta.

Interferon-mediated changes in the expression of CYP1A1 in human B lymphoblastoid (AHH-1 TK +/-) cells

The expression of constitutive and inducible cytochrome P450s has been shown to be downregulated by interferon through an unknown pretranslational mechanism that depresses the mRNA encoding P450 apoproteins. To establish an association between gene transcription and P450 apoprotein downregulation by interferon, we studied the effect of recombinant interferon (IFN-alpha 2a) on CYP1A1 in human B lymphoblastoid cell lines. The cHoI cell line expresses inducible native CYP1A1, while the genetically engineered derivative h1A1 v2 expresses a noninducible extrachromosomal vector-derived human CYP1A1 cDNA lacking the CYP1A1 promoter region. We characterized CYP1A1 activity, apoprotein, and mRNA by ethoxyresorufin O-deethylase activity, Western immunoblotting, and Northern blot analysis, respectively. In cHoI cells, following induction with dibenz[a,h]anthracene, interferon depressed CYP1A1 apoprotein and mRNA levels by 55 and 76%, respectively, with no detectable changes in enzyme activity. In h1A1 v2, however, interferon increased CYP1A1 activity, apoprotein, and mRNA. The depression of CYP1A1 mRNA and apoprotein levels incHoI cells, in contrast with the increase observed in h1A1 v2 cells, suggests that nuclear mechanisms are essential for interferon-mediated depression of inducible P450s. From our preliminary results we propose that interferon-mediated downregulation of CYP1A1 may result from inhibition of gene transcription.

Effects of streptolysin O, picibanil (OK 432) and interferon alpha 2A on cytochrome P-450-dependent monooxygenases and arylamine N-acetyltransferase in rat liver

Streptolysin O, a thiol-activated exotoxin from group A beta-haemolytic streptococci, caused a dose-dependent depression of aniline hydroxylase, aminopyrine N-demethylase and ethylmorphine N-demethylase activities when added into the hepatic microsomal mixtures from male rats at concentrations 0.02-0.4 HU/mL in vitro. The activities of 7-ethoxycoumarin O-deethylase, 7-ethylresorufin O-deethylase and 7-pentylresorufin O-depentylase were not altered with the used concentrations of the toxin. Specific antibody against haemolytic action of streptolysin O added to incubation mixtures in vitro was not able to protect streptolysin-sensitive monooxygenases from the inhibition. The addition of streptolysin O (0.01-0.8 HU/mL) into the cytosol-containing medium did not significantly influence the activity of procainamide N-acetyltransferase. Immunomodulators picibanil (OK 432) and human recombinant interferon alpha 2A which are known to suppress oxidative metabolism in vivo in humans and animals, were without effect either on the cytochrome P-450-dependent monooxygenases or on the N-acetyltransferase activity when administered in vitro at the doses real in their clinical application (0.001-0.1 KE/mL of picibanil and 10-500 U/mL of alpha-interferon).

Mechanisms of interleukin-2-induced depression of hepatic cytochrome P-450 in mice

Interleukin-2 (15 micrograms/mouse, i.p. twice daily for 4 days and once on the 5th day) significantly lowered cytochrome P-450 and heme content and increased heme oxygenase mRNA accumulation; the activities of 7-ethoxycoumarin O-deethylase, ethoxy- and pentoxyphenoxazone O-dealkylases were decreased. The activity of the type O form of hepatic xanthine oxidase increased, but there was no increase in lipid peroxide, expressed in terms of microsomal malondialdehyde. In vivo inactivation of xanthine oxidase activity by feeding mice with tungstate did not substantially change the degree of interleukin-2-induced cytochrome P-450 depression, suggesting that the two processes are not causally linked. Induction of tolerance to endotoxin by a 4-day pretreatment with lipopolysaccharide resulted in 50% protection against this depression despite inhibition of the interleukin-2 induced formation of tumor necrosis factor. This suggests that the release of tumor necrosis factor per se does not fully account for the depression of cytochrome P-450. Dexamethasone, already used in patients to reduce the toxicity of interleukin-2 therapy, provided full protection against the cytochrome P-450 depression.

Differential effect of cytokines on the phenobarbital or 3-methylcholanthrene induction of P450 mediated monooxygenase activity in cultured rat hepatocytes

Cultured rat hepatocytes have been used to compare the relative activities of cytokines to inhibit the phenobarbital (PB) or 3-methylcholanthrene (MC) induction of cytochrome P4502B1 and 2B2 (P4502B1/2) or P4501A1 and 1A2 (P4501A1/2), respectively. Recombinant cytokines tested were human interleukin-6 (IL-6), interleukin-1 alpha and -beta (IL-1 alpha and IL-1 beta, respectively), and rat gamma-interferon (INF gamma). Hepatocytes were cultured in the presence of 2 mM PB or 1 microgram MC/mL culture medium for 24 hr with or without the cytokines. Benzyloxyresorufin and ethoxyresorufin O-dealkylase (BROD and EROD, respectively) activities were determined as indices of P4502B1/2 and P4501A1/2, respectively. All cytokines produced a concentration-dependent inhibition of the PB induction of BROD activity. IL-1 beta and IL-6 were approximately equipotent with IC50 values of 1-2 U/mL, causing greater than 90% inhibition of PB induction of BROD activity at a concentration of 50 U/mL culture medium. IL-1 alpha tended to be less active. PB induction of BROD activity was also inhibited by INF gamma, but higher concentrations (62.5 to 500 U/mL culture medium) were required. All cytokines were less effective in inhibiting the MC induction of EROD activity than the PB induction of BROD activity. IL-1 beta and IL-6, at 50 U/mL culture medium, inhibited EROD induction by only 35% compared with the greater than 90% inhibitory effect on the PB induction of BROD activity. INF gamma was ineffective in inhibiting EROD activity at the concentrations studied. Western immunoblot analysis indicated that the cytokines prevented the ability of the inducers to increase the expression of P4502B1/2 and P4501A1/2 immunoreactive proteins, and this effect correlated with their inhibitory effect on induction of enzyme activity. The results suggest that inducible isoforms of cytochrome P450 differ in their susceptibility to regulation by the cytokines, and that cytokines possess differential activity to inhibit the induction of P450 isoforms, with IL-1 beta and IL-6 being the most effective.

Nitric oxide and intracellular heme

Figure 2 depicts a working hypothesis for these results. Activation of .NO synthesis results in nitrogen oxide-induced loss of protein-bound heme from CYP proteins, which remain relatively intact. This heme liberation results in a decrease in heme synthesis (decreased ALAS) and an increase in heme degradation (increased HO). In addition, .NO synthesis results in direct inhibition of ferrochelatase, which further contributes to inhibition of heme synthesis. There also appears to be a mechanism to repair or resynthesize CYP after .NO synthesis is inhibited. Finally, a result of this effect may be protection against cellular injury, since increased HO is an important response against cellular injury from a variety of insults.

Cytokine therapeutics: lessons from interferon alpha

Cytokines are soluble proteins that allow for communication between cells and the external environment. Interferon (IFN) alpha, the first cytokine to be produced by recombinant DNA technology, has emerged as an important regulator of growth and differentiation, affecting cellular communication and signal transduction pathways as well as immunological control. This review focuses on the biological and clinical activities of the cytokine. Originally discovered as an antiviral substance, the efficacy of IFN-alpha in malignant, viral, immunological, angiogenic, inflammatory, and fibrotic diseases suggests a spectrum of interrelated pathophysiologies. The principles learned from in vivo studies will be discussed, particularly hairy cell leukemia, chronic myelogenous leukemia, certain angiogenic diseases, and hepatitis. After the surprising discovery of activity in a rare B-cell neoplasm, IFN-alpha emerged as a prototypic tumor suppressor protein that represses the clinical tumorigenic phenotype in some malignancies capable of differentiation. Regulatory agencies throughout the world have approved IFN-alpha for treatment of 13 malignant and viral disorders. The principles established with this cytokine serve as a paradigm for future development of natural proteins for human disease.

Effects of interferon-alpha monotherapy on hepatic drug metabolism in cancer patients

1. The influence of interferon-alpha (IFN alpha) on the clearances of theophylline (TH), antipyrine (AP) and hexobarbitone (HB) was studied in seven cancer patients given IFN alpha as their only treatment. In addition, IFN alpha effects on drug clearance were correlated with changes in serum inflammatory cytokines and acute phase proteins. 2. A 'baseline' study was performed by administering an oral drug 'cocktail' of TH (150 mg), AP (250 mg) and HB (250 mg) with saline injected simultaneously and again 24 h later. One week later, an 'acute' study was performed at the initiation of IFN alpha therapy, 3 x 10(6) units injected with the drug cocktail and again 24 h later. After 2 weeks of IFN alpha treatment three times per week, a 'chronic' study was performed with IFN alpha injected the day prior to, simultaneously with, as well as 24 h after the drug cocktail. 3. Plasma samples were collected over 48 h and the clearances of TH, AP and HB were estimated. Serum samples were collected at various times for the measurement of tumor necrosis factor (TNF), interleukin-1 (IL-1), interleukin-6 (IL-6), C-reactive protein (C-RP) and alpha 1-acid glycoprotein (AGP). 4. IFN alpha caused a 33% decrease in the oral clearance of TH during the chronic study compared with baseline (P < or = 0.05). Although IFN alpha inhibited TH clearance by 16% during the acute study and AP clearance by 20-21% during both acute and chronic studies, these changes did not reach statistical significance. IFN alpha caused minimal changes in HB clearance. There were no chronic effects of IFN alpha on serum cytokines or acute phase proteins. 5. The findings confirm that the most commonly used dose of IFN alpha inhibits the hepatic clearance in humans of some but not all drugs and that this inhibition persists during IFN alpha therapy. Because inhibition was not associated with increases in serum cytokines or acute phase proteins, the mechanism by which IFN alpha inhibits cytochrome P450 activities in vivo does not appear to involve inflammatory mediators such as TNF. IL-1 or IL-6.

Differential effects of human recombinant interleukin-1 beta and dexamethasone on hepatic drug-metabolizing enzymes in male and female rats

Interleukin-1 beta (IL-1) is one of the major inflammation mediators, commonly reported to be an inhibitor of hepatic drug metabolism. We studied the effect of IL-1 treatment on various drug-metabolizing enzymes in male and female rats. IL-1 induced both cytochrome P450 (P450) 3A1 activity and protein in females, but in males, IL-1 repressed P450 3A2 activity, without decreasing the protein. P450 1A1 was impaired in males, but was retained after dexamethasone pretreatment. IL-1 did not change P450 2B1/2 activity and protein, but counteracted their induction by dexamethasone. Uridine diphospho-glucuronosyltransferase (UGT) 1A2 (bilirubin) activity and its induction by dexamethasone were not affected by IL-1 treatment. Both P450 2C11 and epoxide hydrolase activities were repressed by IL-1 treatment, and both activities were impaired after dexamethasone treatment. These results clearly demonstrate that IL-1 acts at different steps of protein synthesis and gene expression. The effect of IL-1 on P450 was isoform-dependent, indicating that IL-1 can act on pretranscriptional events. The discrepancy between the variations of the activities and the protein of P450 3A2 suggests a post-translational regulation. For P450 2C11, 3A1, and for microsomal epoxide hydrolase, but not for P450 1A1 and 2B1/2, IL-1 mimics the glucocorticoid effects. These differential effects can affect the kinetics and the bioavailability of drugs used in pathologies in which IL-1 is increased.

Cytochrome P-450 induction in human lung tumor-derived cell lines. Characterisation and effects of inflammatory mediators

Cytochrome P-450 species (P-450) comprise a polymorphic multigene family of heme-containing enzymes which are essential to the phase-I metabolism of xenobiotics. Induction of P-450 species by drugs and carcinogens has been extensively studied; endogenous regulation of P-450 also occurs during normal development and disease. The aim of this project was to study the in-vitro induction of P-450 and its modulation by inflammatory mediators in the human lung tumor-derived cell lines NCI H322 and NCI H358. The cell lines expressed detectable levels of 7-ethoxyresorufin O-deethylase which could be induced by benzanthracene. After benzanthracene treatment, a protein tentatively identified as isozyme CYP1A1 was detected by Western-blot analysis and a concommitant increase in CYP1A mRNA expression was observed. Optimal induction was observed at a benzanthracene concentration of 5 micrograms/ml with cells grown in RPMI medium containing 10% fetal calf serum. The effects of endotoxin, dexamethasone and five recombinant DNA-derived cytokines, interleukin-1 beta, tumor necrosis factor, and interferons alpha, beta and gamma, on constitutive and benzanthracene-induced ethoxyresorufin O-deethylase activity were examined in NCI H322 cells. Of all the lymphokines studied, only interferon gamma had any marked effect. Administration of this lymphokine strongly suppressed ethoxyresorufin O-deethylase activity in both control and benzanthracene-treated cells.

The suppression of hepatic cytochrome P4504A mRNA mediated by the interferon inducer polyinosinic acid.polycytidylic acid

Interferon and interferon inducers are well known to depress the cytochrome P450-dependent hepatic mixed-function oxidase system and cause a decrease in the capacity of the liver to metabolize drugs and xenobiotics. In this study we have shown that the interferon-mediated changes in an induced form of hepatic cytochrome P450 (CYP4A) are mediated via a depression in the levels of mRNA as assessed by Northern blot and slot blot analyses using a 20-base synthetic oligodeoxyribonucleotide hybridization probe. Rats were pretreated with clofibrate to maximize CYP4A mRNA levels prior to the administration of polyinosinic acid.polycytidylic acid (poly IC), an alpha/beta interferon inducer. Hepatic CYP4A mRNA levels were decreased by 49 and 30% at 6 and 24 hr, respectively, following poly IC administration. In hepatic microsomes cytochrome P450 and functional CYP4A as measured by lauric acid hydroxylation, were not affected at 6 hr, but were depressed by 39 and 27%, respectively, 24 hr following poly IC administration. These results suggest that interferon depresses induced levels of hepatic drug metabolism by lowering the level of cytochrome P450 mRNAs and subsequent synthesis of cytochrome P450 apoproteins.

Effects of interleukin-6 on cytochrome P450-dependent mixed-function oxidases in the rat

Intravenous treatment of male rats with recombinant human interleukin-6 (rhIL6) at 50, 100 and 200 micrograms/kg (corresponding to 4, 8 and 16 x 10(4) U/animal, respectively) reduced the activities of hepatic microsomal cytochrome P450-dependent monoxygenases to varying degrees. Ethylmorphine-N-demethylase activity fell to 53% of control values, an effect similar to that induced by 2.5 mg/kg Escherichia coli lipopolysaccharide (LPS). Ethoxycoumarin-O-deethylase activity was also sensitive to inhibition, whereas IL6 had little effect on the activities of other P450-dependent enzymes, including ethoxyresorufin-O-deethylase. Pentoxyresorufin dealkylase activity, which is representative of the cytochrome P450 IIB 1/2 subfamily, was unaffected by IL6 whereas LPS reduced it to 33.7% of control values. Another hepatocyte-related parameter, serum concentration of alpha 1-acid glycoprotein (AGP), was increased by up to 3.5-fold over baseline by IL6 and 10-fold by LPS. Recombinant human interleukin-1 beta (rhIL1 beta) (10 micrograms/kg, corresponding to 5 x 10(4) U/rat) and recombinant human tumor necrosis factor alpha (rhTNF) (150 micrograms/kg corresponding to 24 x 10(4) U/rat) were both as potent as LPS (2.5 mg/kg) in increasing serum AGP levels and reducing hepatic microsomal monoxygenase activities. IL6 did not potentiate the effects of rhIL1 beta. Hepatic microsomal glucuronyltransferase activities were little affected by LPS and unaffected by rhIL6. Finally, rhIL6 was more potent after i.p. injection than after i.v. or s.c. injection. These results suggest that the effects of LPS, TNF and IL1 on the mixed-function oxidase system in vivo may be due partly to an induction of IL6 in vivo. The different sensitivities of the enzymes to IL6 but not to IL1 or TNF may be due to the involvement of two distinct mechanisms.