Potentiation and suppression of mouse liver cytochrome P-450 isozymes during the acute-phase response induced by bacterial endotoxin

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.

The role of the immune system in nevirapine-induced subclinical liver injury of a rat model

In this study, the role of the immune system in nevirapine- (NVP-) induced subclinical liver injury was investigated by observing for changes of some immune parameters during the initial stages of NVP-induced hepatotoxicity in a rat model. In the acute phase, two test-groups of 10 Sprague-Dawley rats each were administered with bacterial lipopolysaccharide (LPS) or saline (S) intraperitoneally, followed by oral NVP, after which 5 rats from each group were sacrificed at 6 and 24 hours. For the chronic phase, two groups of 15 rats each received daily NVP, and on days 7, 14, and 21, five rats from each group were administered with either LPS or S, followed by that day's NVP dose, and were sacrificed 24 hours later. NVP caused liver injury up to seven days and progressively increased IL-2 and IFN-γ levels and lymphocyte count over the 21 days. NVP-induced liver injury was characterized by apoptosis and degeneration changes, while, for LPS, it was cell swelling, leukostasis, and portal inflammation. Coadministration of NVP and LPS attenuated NVP-induced liver injury. In conclusion, the immune system is involved in NVP toxicity, and the LPS effects may lay the clue to development of therapeutic strategies against NVP-induced hepatotoxicity.

Effect of sulfur dioxide inhalation on CYP2B1/2 and CYP2E1 in rat liver and lung

Sulfur dioxide (SO2) is a ubiquitous air pollutant, present in low concentrations in the urban air and in higher concentrations in the working environment. In this study, we investigated the effects of inhaled SO2 on the O-dealkylase of pentoxyresorufin (PROD) and p-nitrophenol hydroxylases (p-NP) activities and mRNA levels of CYP2B1/2 and CYP2E1 in the lung and liver of Wistar rats. Male Wistar rats were housed in exposure chambers and treated with 14.11 +/- 1.53, 28.36 +/- 2.12, and 56.25 +/- 4.28 mg/m3 SO2 for 6 h/day for 7 days, while control rats were exposed to filtered air in the same condition. The mRNAs of CYP2B1/2 and -2E1 were analyzed in livers and lungs by using reverse-transcription polymerase chain reaction (RT-PCR). Our results showed that the PROD activities and mRNA of CYP2B1/2 were decreased in livers and lungs of rats exposed to SO2. The p-NP activities and mRNA of CYP2E1 were decreased in lungs but not in livers of rats exposed to SO2. Total liver microsomal cytochrome P-450 (CYP) contents were diminished in SO2-exposed rats. These results lead to two conclusions: (1) SO2 exposure can suppress CYP2B1/2 and CYP2E1 in lungs and CYP2B1/2 in livers of rats, thus modifying the liver and lung toxication/detoxication potential, and (2) the total liver microsomal CYP contents were diminished, although the activity and mRNA expression of CYP2E1 in rat livers were not affected by SO2 exposure.

Genomic profiling in nuclear receptor-mediated toxicity

Nuclear receptors (NRs) are attractive drug targets due to their role in regulation of a wide range of physiologic responses. In addition to providing therapeutic value, many pharmaceutical agents along with environmental chemicals are ligands for NRs and can cause adverse health effects that are directly related to activation of NRs. Identifying the molecular events that produce a toxic response may be confounded by the fact that there is a significant overlap in the biological processes that NRs regulate. Microarrays and other methods for gene expression profiling have served as useful, sensitive tools for discerning the mechanisms by which therapeutics and environmental chemicals invoke toxic effects. The capability to probe thousands of genes simultaneously has made genomics a prime technology for identifying drug targets, biomarkers of exposure/toxicity and key players in the mechanisms of disease. The complex intertwining networks regulated by NRs are hard to probe comprehensively without global approaches and genomics has become a key technology that facilitates our understanding of NR-dependent and -independent events. The future of drug discovery, design and optimization, and risk assessment of chemical toxicants that activate NRs will inevitably involve genomic profiling. This review will focus on genomics studies related to PPAR, CAR, PXR, RXR, LXR, FXR, and AHR.

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.

Effect of sulfur dioxide inhalation on CYP1A1 and CYP1A2 in rat liver and lung

Sulfur dioxide (SO2) is a ubiquitous air pollutant, presents in low concentrations in the urban air, and in higher concentrations in the working environment. In the present study, male Wistar rats were housed in exposure chambers and treated with 14.00+/-1.53, 28.00+/-2.12 and 56.00+/-4.28 mg/m3 SO2 for 6 h/day for 7 days, while control rats were exposed to filtered air in the same condition. Highly specific substrates were used as probes of cytochrome P4501A1 (CYP1A1) and cytochrome P4501A2 (CYP1A2). The mRNA levels of CYP1A1 and 1A2 were analyzed in livers and lungs by using a real-time reverse transcription-polymerase chain reaction (real-time RT-PCR) assay. Our results showed that the activities and mRNA levels of P450 were decreased in livers and lungs of rats exposed to SO2. In the liver, a decrease down to 0.68- and 0.64-fold in the CYP1A1 activity, probed by the O-deethylation of ethoxyresorufin (EROD), was observed at higher dose of SO2 (28 and 56 mg/m3); Similarly, CYP1A1 mRNA levels were reduced in livers of rats exposed to SO2 at 28 and 56 mg/m3. For livers, CYP1A2-mediated methoxyresorufin O-demethylase activity (MROD) was unaltered by SO2 at low concentrations, except for a significant decrease in the rats exposed to SO2 at 56 mg/m3 (0.79-fold); however, SO2 at higher concentrations significantly decreased levels of CYP1A2 (28 and 56 mg/m3) (p<0.05). Significant inhibition of both EROD and MROD was observed in lungs of rats exposed to SO2 at 28 and 56mg/m3. CYP1A1 activity was repressed 0.62- and 0.53-fold, while CYP1A2 activity was reduced to 0.74- and 0.55-fold in lungs, respectively. SO2 at higher concentrations (28 and 56 mg/m3) decreased significantly pulmonary CYP1A1 and 1A2 mRNA levels relative to control animals. Furthermore, the decreases of activities and mRNA levels of these P450 enzymes caused by SO2 at different concentrations in lungs and livers of rats followed linear dose-response curves. These results lead to the conclusion that SO2 exposure can reduce CYP1A1 and 1A2 in lungs and livers of rats and ROS and/or cytokines might act as mediators of this effect according to previous studies performed in mice. Reduction of hepatic and pulmonary CYPlAl and lA2 expression during SO2 exposure may be part of an adaptive response by the liver and lung to minimize cell damage.

Protein biomarkers in the plasma of workers occupationally exposed to polycyclic aromatic hydrocarbons

Polycyclic aromatic hydrocarbons (PAHs) form a chemical family containing several hundred compounds, including benzo[a]pyrene and pyrene. They are usually produced by the incomplete burning of coal, oil, gas, garbage, or other organic substances like tobacco or charbroiled meat. Exposure to PAH causes tumors, primarily in the lung, the bladder, and the skin. To investigate the differentially expressed proteins resultant from PAH exposure, the protein expression in human plasma was analyzed using two-dimensional electrophoresis (2-DE). The plasma exposed to PAH was obtained from 48 waste gas pollution measurers working at an automobile emission inspection center. The 1-hydroxypryene (1-OHP) level, which is the urinary PAH metabolite used for evaluation of PAH exposure, was 0.28 micromol/mol creatinine in PAH exposure groups, and 0.078 micromol/mol creatinine in unexposed groups (control, n = 33). A protein upregulated by PAH (putative capacitative calcium entry channel) and five overexpressed proteins (two fibrinogen gamma-A chain precursors, a hemopexin precursor, an albumin precursor, and T-cell receptor beta chain C region) were identified with matrix assisted laser desorption/ionization-time of flight-mass spectrometry (MALDI-TOF-MS) and confirmed with tandem MS (MS/MS) and Western blotting. The putative capacitative calcium entry channel was partially validated with a laboratory made antibody of a representative peptide fragment in PAH-exposed human plasma samples.

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.

Systemic Inflammation-Associated Glucocorticoid Resistance and Outcome of ARDS

Dysregulated systemic inflammation with excess activation of pro-inflammatory transcription factor nuclear factor-kappaB (NF-kappaB)-activated by inflammatory signals-compared to the anti-inflammatory transcription factor glucocorticoid receptor-alpha (GRalpha)-activated by endogenous or exogenous glucocorticoids (GCs)-is an important pathogenetic mechanism for pulmonary and extrapulmonary organ dysfunction in patients with acute respiratory distress syndrome (ARDS). Activation of one transcription factor in excess of the binding (inhibitory) capacity of the other shifts cellular responses toward increased (dysregulated) or decreased (regulated) transcription of inflammatory mediators over time. Recent data indicate that failure to improve in ARDS (unresolving ARDS) is frequently associated with failure of the activated GRs to downregulate the transcription of inflammatory cytokines despite elevated levels of circulating cortisol, a condition defined as systemic inflammation-associated acquired GC resistance; it is potentially reversible with prolonged GC supplementation. In the first part of this paper, after a brief description of inflammation in ARDS and our model of translational research, we review the two cellular signaling pathways that are central to the regulation of inflammation-the stimulatory NF-alphaB and the inhibitory GRalpha. In the second part, we review findings of recent studies indicating that excessive inflammatory activity in patients with unresolving ARDS may induce noncompensated GC resistance in target organs. In the third part, we review factors affecting cellular response to GC and potential mechanisms involved in inflammation-associated GC resistance.

Hepatic expression of multiple acute phase proteins and down-regulation of nuclear receptors after acute endotoxin exposure

Acute systemic lipopolysaccharide (endotoxin, LPS) exposure, which can lead to septic shock, enhances the hepatic expression of inflammatory and acute-phase proteins (APPs). To better understand how LPS aggravates damage, changes in hepatic gene expression after a single LPS dose was screened by using microarrays for 1176 rat genes. We detected more than 20 new potential LPS-induced APPs. Following acute LPS challenge, significant up-regulation of the steady-state mRNA levels of several important early transcription factors, such as c-jun and STAT3, and cytokine-associated genes, was observed. In contrast, RT-PCR analysis revealed marked down-regulation of the nuclear receptors RXRalpha, PXR, FXR, LXR, PPARalpha and CAR. Also genes encoding lipolytic, antioxidant as well as drug- and alcohol-metabolizing enzymes were down-regulated. These data suggest that acute LPS treatment induces important early transcription factors and co-ordinately down-regulates nuclear receptors, and that this results in altered expression of a large number of downstream genes.

Down-regulation of phenobarbital-induced cytochrome P4502B mRNAs and proteins by endotoxin in mice: independence from nitric oxide production by inducible nitric oxide synthase

Multiple hepatic cytochrome P450 enzymes are down-regulated at the mRNA and protein levels during inflammation and infection. A body of evidence suggests that nitric oxide (NO) produced from inducible NO synthase (NOS2) is responsible for some of these effects. The current study was designed to examine the NO dependencies of the down-regulation of phenobarbital-induced CYP2B mRNAs and proteins by bacterial endotoxin (lipopolysaccharide, LPS) treatment in vivo, using an NOS2-null mouse model. Treatment of C57/BL6 mice with 0.3 mg/kg of LPS maximally suppressed phenobarbital-induced CYP2B9 and 2B10 mRNAs measured 12 hr after injection, whereas 1-10 mg/kg of LPS was required to elevate NO production. Down-regulation of CYP2B mRNAs by 1 mg/kg of LPS was equivalent in wild-type and NOS2-null mice. No effect of LPS in the dose range of 0.3 to 10 mg/kg was observed on microsomal CYP2B protein levels measured 12 hr after treatment, whereas 1 mg/kg of LPS suppressed CYP2B proteins 24 hr after treatment in both wild-type and NOS2-null mice. We conclude that the main mechanism for the down-regulation of CYP2B proteins in mouse liver following moderate- or high-dose LPS treatment is via NO-independent suppression of CYP2B9 and 2B10 mRNAs. Unlike rat hepatocytes, the contribution of a rapid, NO-dependent mechanism of CYP2B protein suppression in mouse liver appears to be minor or non-existent.

The effect of sepsis during parenteral nutrition on hepatic microsomal function in rats

STUDY OBJECTIVE

To investigate the effect of sepsis during parenteral nutrition on hepatic cytochrome P450 (CYP) activity in rats.

DESIGN

Prospective, randomized, controlled study.

SETTING

University-based animal research laboratory.

ANIMALS

Twenty adult male Sprague-Dawley rats.

INTERVENTION

The animals were cannulated intravenously and randomized to receive parenteral nutrition (PN), intravenous live Escherichia coli 4 x 10(8) colony-forming units/100 g body weight for 2 consecutive days with PN (PNEC), or chow (CH).

MEASUREMENTS AND MAIN RESULTS

Both PN alone and PNEC resulted in a progressive decline in hepatic CYP concentration compared with CH (0.53 +/- 0.10, 0.41 +/- 0.17, and 0.35 +/- 0.14 nmol/mg microsomal protein, respectively, p < 0.05). Parenteral nutrition alone was associated with a 57% decrease in isoenzyme ethoxycoumarin-O-deethylase activity (ECOD) compared with CH, but sepsis did not further decrease ECOD activity any more than PN alone (0.103 +/- 0.049, 0.044 +/- 0.018, and 0.050 +/- 0.020 nmol/mg microsomal protein/min, respectively, p < 0.05).

CONCLUSION

Hepatic CYP concentration declines with PN and is further decreased when compounded by sepsis. The disproportional decrease in ECOD activity relative to CYP concentration with PN is unchanged by sepsis, indicating a selective alteration in hepatic isoenzymes by PN.

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.

Cytokine-mediated suppression of cytochrome P450 1A1 in Hepa-1c1c7 cells by pokeweed mitogen

This study investigated the effects of pokeweed mitogen (PWM) on the regulation of cytochrome P450 (P450) 1A1 expression in an in vitro model, using murine hepatoma cell line Hepa-1c1c7 and murine macrophage cell line RAW 264.7 cell cultures. PWM added directly to Hepa-1c1c7 cells had no effect on 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)-induced P450 1A1-specific 7-ethoxyresorufin O-deethylase (EROD) activity. However, TCDD-induced EROD activity and P450 1A1 mRNA levels were markedly suppressed when Hepa-1c1c7 cells were cultured with PWM-treated conditioned media from RAW 264.7 in a dose-dependent manner. Concomitant treatment with PWM and pentoxifylline, a TNFalpha synthesis inhibitor, to RAW 264.7 cells decreased the suppressive effects of PWM on TCDD-induced EROD activity. In PWM-exposed RAW 264.7 cell cultures, TNFalpha and IL-6 levels increased in a dose-dependent fashion. When antibodies to TNFalpha or/and IL-6 were added to PWM-treated conditioned media from RAW 264.7, the suppression of EROD activity was inhibited. These results suggested the suppression of P450 1A1 by PWM was mediated exclusively by TNFalpha and IL-6, released from macrophages.

Nitric oxide exerts feedback inhibition on EDHF-induced coronary arteriolar dilation in vivo

We tested the hypothesis that nitric oxide (NO) inhibits endothelium-derived hyperpolarizing factor (EDHF)-induced vasodilation via a negative feedback pathway in the coronary microcirculation. Coronary microvascular diameters were measured using stroboscopic fluorescence microangiography. Bradykinin (BK)-induced dilation was mediated by EDHF, when NO and prostaglandin syntheses were inhibited, or by NO when EDHF and prostaglandin syntheses were blocked. Specifically, BK (20, 50, and 100 ng. kg(-1). min(-1) ic) caused dose-dependent vasodilation similarly before and after administration of N(G)-monomethyl-L-arginine (L-NMMA) (3 micromol/min ic for 10 min) and indomethacin (Indo, 10 mg/kg iv). The residual dilation to BK with L-NMMA and Indo was completely abolished by suffusion of miconazole or an isosmotic buffer containing high KCl (60 mM), suggesting that this arteriolar vasodilation is mediated by the cytochrome P-450 derivative EDHF. BK-induced dilation was reduced by 39% after inhibition of EDHF and prostaglandin synthesis, and dilation was further inhibited by combined blockade with L-NMMA to a 74% reduction in the response. This suggests an involvement for NO in the vasodilation. After dilation to BK was assessed with L-NMMA and Indo, sodium nitroprusside (SNP, 1-3 microgram. kg(-1). min(-1) ic), an exogenous NO donor, was administered in a dose to increase the diameter to the original control value. Dilation to BK was virtually abolished when administered concomitantly with SNP during L-NMMA and Indo (P < 0.01 vs. before SNP), suggesting that NO inhibits EDHF-induced dilation. SNP did not affect adenosine- or papaverine-induced arteriolar dilation in the presence of L-NMMA and Indo, demonstrating that the effect of SNP was not nonspecific. In conclusion, our data are the first in vivo evidence to suggest that NO inhibits the production and/or action of EDHF in the coronary microcirculation.

The acute phase response is associated with retinoid X receptor repression in rodent liver

The acute phase response (APR) is associated with decreased hepatic expression of many proteins involved in lipid metabolism. The nuclear hormone receptors peroxisome proliferator-activated receptor alpha (PPARalpha) and liver X receptor (LXR) play key roles in regulation of hepatic lipid metabolism. Because heterodimerization with RXR is crucial for their action, we hypothesized that a decrease in RXR may be one mechanism to coordinately down-regulate gene expression during APR. We demonstrate that lipopolysaccharide (LPS) induces a rapid, dose-dependent decrease in RXRalpha, RXRbeta, and RXRgamma proteins in hamster liver. Maximum inhibition was observed at 4 h for RXRalpha (62%) and RXRbeta (50%) and at 2 h for RXRgamma (61%). These decreases were associated with a marked reduction in RXRalpha, RXRbeta, and RXRgamma mRNA levels. Increased RNA degradation is likely responsible for the repression of RXR, because LPS did not decrease RXRbeta and RXRgamma transcription and only marginally inhibited (38%) RXRalpha transcription. RXR repression was associated with decreased LXRalpha and PPARalpha mRNA levels and reduced RXR x RXR, RXR x PPAR and RXR x LXR binding activities in nuclear extracts. Furthermore, LPS markedly decreased both basal and Wy-14,643-induced expression of acyl-CoA synthetase, a well characterized PPARalpha target. The reduction in hepatic RXR levels alone or in association with other nuclear hormone receptors could be a mechanism for coordinately inhibiting the expression of multiple genes during the APR.

Suppression of cytochrome P450 gene expression in the livers of mice with concanavalin A-induced hepatitis

Cytochrome P450 (CYP) gene expression in the livers of mice with concanavalin A-induced hepatitis was examined. Treatment of mice with concanavalin A (10 mg/kg, i.v.) elevated plasma alanine aminotransaminase activity. In normal liver, CYP1A2, 3A and 2E1 mRNAs were expressed, and concanavalin A treatment differentially suppressed the expression of these CYP genes. Gadolinium chloride (40 mg/kg, i.p.) treatment, which inhibited the concanavalin A-induced elevation of plasma alanine aminotransferase activity without affecting concanavalin A-induced cytokine expression, counteracted the concanavalin A-induced suppression of CYP gene expression in the liver. Kupffer cell function or hepatic injury might contribute to the concanavalin A-induced suppression of CYP gene expression.

Coordinate up-regulation of CYP1A1 and heme oxygenase-1 (HO-1) expression and modulation of delta-aminolevulinic acid synthase and tryptophan pyrrolase activities in pyridine-treated rats

To determine the changes in heme metabolism associated with induction of cytochrome P450 expression by pyridine, we compared the time course of CYP1A expression with the time course of (i) expression of heme oxygenase-1 (HO-1) (EC 1.14.99.3), (ii) activity of delta-aminolevulinic acid synthetase (ALAS) (EC 2.3.1.37), and (iii) heme saturation of tryptophan pyrrolase (TPO) (EC 1.13.11.11) in tissues of rats administered a single 100 or 150 mg/kg i.p. dose of pyridine. Both mRNA and protein of HO-1 and CYP1A1 were induced in the liver, kidney, and lung, with the induction of HO-1 mRNA preceding and paralleling that of CYP1A1 mRNA in the liver and lung but not kidney. Induction of CYP1A1 mRNA expression peaked within 9-12 hr and returned to control levels by 24 hr in all tissues examined, whereas induction of HO-1 mRNA expression was sustained for 48 hr in the lung and liver. In contrast to the transient up-regulation of CYP1A1 mRNA, increased microsomal CYP1A1 protein was sustained in all three tissues. Similar to the induction of HO-1 expression, lipid peroxidation was stimulated by pyridine treatment in the kidney, lung, and liver, but with the stimulation being more persistent in the liver and lung than in the kidney. Increased hepatic CYP1A1 or CYP1A2 activity was preceded by increased activities of HO-1 and ALAS. Pyridine treatment negatively modulated heme saturation of hepatic TPO. The findings indicate that pyridine stimulates the synthesis, utilization, and degradation of heme in a coordinate manner, and suggest that these alterations in heme metabolism may contribute to CYP1A1 induction by pyridine.

Modulation of cytochrome P450 by inflammation in astrocytes

Activation of systemic host defense mechanisms results in the down-regulation of cytochrome P450 enzymes in the liver. This occurs for various induced and constitutive isoforms of cytochrome P450 in response to cytokines such as IFNs, IL-1, IL-6, and TNF-alpha, which are produced during infection. Although the levels of cytochrome P450 in brain regions are low, the enzymes are regionally distributed and may play a critical role in the activation or degradation of drugs and chemicals in localized areas. If activation of the immune response in the CNS by LPS modulates the activity of cytochrome P450 forms in the brain, this may alter normal metabolic pathways or contribute to drug or chemical toxicity. This hypothesis was addressed by examining the effect of LPS on a major cytochrome P450 form in isolated astrocytes obtained from newborn rats. These cells were shown to express CYP1A1/2 when induced by dibenz[a, h]anthracene (DBA) as determined by enzyme activity, immunohistochemistry, and Western blotting. The treatment of these cells with LPS significantly attenuated the activity of these enzymes but had no effect on CYP1A1/2 protein levels as determined by Western blotting. The lack of effect by detoxified LPS indicated the requirement of the lipid A region on LPS to stimulate this response. Pentoxifylline (PNTX) prevented the LPS evoked decrease in CYP1A1/2 activity suggesting that cytokine release was a required component of this effect in astrocytes. These results indicate that stimulation of the immune response by LPS in isolated astrocytes decreases CYP1A1/2 activity. The release of cytokines is implicated in this effect and thought to participate in the functional inhibition of the enzyme as no effect on CYP1A1/2 protein levels was observed.

Modulation of drug metabolism in infectious and inflammatory diseases

During inflammation, expression of various P450 genes is modulated differentially. Both the downregulation of some P450s and the induction of others may be the result of a complex interaction involving inflammatory cytokines, stress hormones, and metabolic perturbations. Our results suggest that NO is not an important mediator for the downregulation of CYP2C11 in rat liver.

Differential effects of B- and T-lymphocyte mitogens on cytochrome P450 in mice

Lipopolysaccharide (LPS) is widely used as a B-lymphocyte mitogen and is known to depress expression of the cytochrome P450 (P450). However, there have been no studies regarding to the effects of the other mitogens on the expression of P450. This study investigated the effects of mitogens on the constitutive and inducible expression of mouse hepatic P450. Following treatment with B-lymphocyte mitogens, such as LPS and pokeweed mitogen (PWM), hepatic P450 content was reduced. LPS and PWM also suppressed activities of microsomal ethoxyresorufin O-deethylase, pentoxyresorufin O-dealkylase and aniline hydroxylase, a representative activity of P4501A1/2, P4502B1/2 and P4502E1, respectively, in both constitutive and P450 induced mice. However, there was no effect when treated with T-lymphocyte mitogens, such as concanavalin A and phytohemagglutinin. Suppression of P450 expression in the LPS- or PWM-treated mice occurred and was shown to involve a decrease in P450 protein and mRNA levels in liver. These results suggest that suppressive effects of mitogens on the expression of P450 might be different and that B-lymphocyte mitogens selectively depress the expression of P450.

Identification of glutathione S-transferase isozymes and gamma-glutamylcysteine synthetase as negative acute-phase proteins in rat liver

Because acute infection and inflammation affect drug metabolism and drug-metabolizing enzymes, the effect of the acute-phase response on the expression of glutathione S-transferase (GST) isoenzymes, glutathione synthesis, and several antioxidant enzymes was investigated. Hepatic expression of GST isozymes, positive and negative acute-phase reactants, and antioxidant enzymes were determined by Northern blotting and hybridization with gene-specific oligonucleotide probes after lipopolysaccharide treatment of rats. Lipopolysaccharide caused the expected acute-phase response as judged by the increased expression of positive and decreased expression of negative acute-phase proteins. The messenger RNA (mRNA) expression of the major hepatic rat GST isozymes A1, A2, A3, M1, and M2 was decreased 50% to 90%. Total hepatic GST activity toward 1-chloro-2,4-dinitrobenzene was also significantly decreased. mRNA expression of gamma-glutamylcysteine synthetase (GCS) large subunit and catalase was reduced by approximately 60%. GCS enzyme activity was also decreased, resulting in a 35% decrease in the hepatic content of reduced glutathione 4 days after lipopolysaccharide challenge. Mn-Superoxide dismutase expression was increased 13-fold, and thioredoxin level was elevated 3-fold after lipopolysaccharide challenge. The expression of all parameters determined returned to near control levels 7 days after treatment. Together, these data show that GSTs and GCS are negative acute-phase proteins and that decreased GCS activity results in a decrease in hepatic glutathione content. Thus, in addition to the phase I drug-metabolizing enzymes known to be decreased during the acute-phase response, some phase II enzymes involved in the elimination of xenobiotics and carcinogens are also decreased.

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.

Time-dependent effects of Klebsiella pneumoniae endotoxin on hepatic drug-metabolizing enzyme activity in rats

The time-dependent effects of Klebsiella pneumoniae endotoxin on hepatic cytochrome P450-dependent drug-metabolizing capacity (cytochrome P450 and b5 content, activity of aminopyrine N-demethylase, p-nitroanisole O-demethylase, aniline hydroxylase and benzphetamine N-demethylase) and on the pharmacokinetics of antipyrine have been determined in rats. Measurement of enzyme activity and antipyrine (after intravenous injection of 20 mg kg(-1)) were performed 2, 24 and 96 h after a single intraperitoneal injection of endotoxin (1 mg kg(-1)) and after repeated doses (once daily for 4 days). The contribution of tumour necrosis factor alpha (TNFalpha) to the endotoxin-induced changes was also examined in rats pretreated with granulocyte colony-stimulating factor (G-CSF). The systemic clearance of antipyrine and the activity of hepatic cytochrome P450-dependent drug-metabolizing enzymes were dramatically reduced 24 h after a single injection of endotoxin, but had returned to control levels by 96h. The magnitudes of these decreases in these measurements after repeated doses of endotoxin were similar to those seen 24h after the single dose. The systemic clearance of antipyrine correlated significantly with cytochrome P450 content and aminopyrine N-demethylase activity. In histopathological experiments, moderate hypertrophy of Kupffer cells was observed, with no evidence of severe liver-tissue damage. G-CSF pretreatment suppressed the increased plasma concentrations of TNFalpha produced 2 h after single endotoxin injection, but did not eliminate the endotoxin-induced decrease in the systemic clearance of antipyrine, suggesting that TNFalpha is not the sole component responsible for the reduction of cytochrome P450-mediated drug-metabolizing enzyme activity. These results provide evidence that a single intraperitoneal injection of 1.0 mgkg(-1)K. pneumoniae endotoxin in rats reduces hepatic P450 and b5 levels, and reduces the activity of various cytochrome P450-mediated drug-metabolizing enzymes without causing severe liver-tissue damage. This suggests that the effect of endotoxin on hepatic cytochrome P450-mediated drug-metabolizing isozymes is non-selective.

Down-regulation of cytochrome P450 mRNAs and proteins in mice lacking a functional NOS2 gene

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 in both gene expression and activity of three P450s in endotoxemic parental and NOS2 knockout mice. Twenty-four hours of endotoxin (LPS) treatment significantly suppressed CYP2C29 and CYP3A11 mRNA expression in both the parental and NOS2 knockout strains. Microsomal CYP2E1, CYP2C-like, and CYP3A-like protein levels were also decreased in both strains of mouse. Similar results were obtained in parental strain endotoxemic mice co-administered the NOS inhibitor aminoguanidine. Six hours after LPS treatment, there was an NO-dependent decrease in testosterone 6beta-hydroxylase activity, because no decreases in activity were observed in the NOS2 knockout mice or in mice co-administered aminoguanidine. LPS also evoked decreases in testosterone 15alpha- and 16beta-hydroxylase activity after 24 hr that were observed in the parental strain and not in NOS2 knockout mice. Our results demonstrate that the down-regulation of CYP2C-like, CYP3A-like and CYP2E1 proteins and mRNAs, in the endotoxemic mouse can occur independently of NO production. We do, however, show that the NO released during endotoxemia is capable of causing decreases in some cytochrome P450 catalytic activities.

Cytokine-mediated down-regulation of CYP1A1 in Hepa1 cells

The activation of host defense mechanisms down-regulates microsomal cytochrome P450 in cell culture, humans, and animals. Investigation into various aspects of this effect using in vivo models has yet to define clearly the role that cytokines play in this phenomenon. The mechanism of down-regulation by immunostimulants, such as lipopolysaccharide (LPS), is explored with an in vitro model, utilizing a murine hepatoma (Hepa1) and a murine macrophage (IC-21) cell line. It is hypothesized that down-regulation of P450 activity by immunostimulants involves the activation of immune cells and the subsequent release of cytokines, such as interleukin-1 (IL-1), interleukin-6 (IL-6), and tumor necrosis factor-alpha (TNF-alpha). The effects of immunostimulation on P450 activity are assessed by ethoxyresorufin O-dealkylase, an assay that measures CYP1A activity in Hepa1 cells. Initial studies demonstrated that LPS added directly to hepatoma cells had no effect on the levels of CYP1A1 activity. In contrast, a significant down-regulation in CYP1A1 activity occurred when hepatoma cells were incubated with monocyte conditioned medium obtained by incubating LPS with IC-21 cells. When pentoxifylline, a TNF-alpha synthesis inhibitor, was co-administered with LPS to macrophages, the down-regulation of CYP1A1 activity was prevented. The direct administration of murine recombinant TNF-alpha to hepatoma cells resulted in a down-regulation of CYP1A1 activity. These results implicated the release of TNF-alpha from macrophages as an important step in the down-regulation of CYP1A1 by LPS.

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.

Nitric oxide and endothelium-derived hyperpolarizing factor: formation and interactions

Nitric oxide (NO) and endothelium-derived hyperpolarizing factor (EDHF) represent the two major endothelial autacoids involved in the local control of vascular tone. Here we describe a novel pathway leading to the calcium-independent activation of the endothelial NO synthase by shear stress and enhanced cellular tyrosine phosphorylation. In addition we present evidence that NO inhibits the formation of EDHF, which we have characterized as a transferable, beta-naphthoflavone-inducible P450-dependent metabolite of arachidonic acid.

Minimal effect of acute experimental hepatitis induced by lipopolysaccharide/D-galactosamine on biotransformation in rats

When administered with D-galactosamine, lipopolysaccharide endotoxins produce a good experimental animal model of hepatitis. This galactosamine plus endotoxin model has been used widely, but the acute effect of this fixed combination of two chemicals on hepatic and extrahepatic biotransformation has not been determined. Therefore, either 2 or 4 hr after a single intraperitoneal dose of 300 mg/kg galactosamine plus 30 micrograms/kg lipopolysaccharide was administered, serum, liver, kidney, intestine, and spleen were collected. Serum enzymes (alanine and aspartate aminotransferases, sorbitol dehydrogenase, and gamma-glutamyltranspeptidase) were elevated dramatically 2 and 4 hr after treatment. Cytochrome P450 monooxygenase activity toward benzo-[a]pyrene was increased in kidney 4 hr after treatment, whereas dealkylation of 7-methoxycoumarin or 7-ethoxyresorufin was unchanged in any tissue at either time point. An increase in UDP-glucuronosyltransferase activity toward 4-methylumbelliferone and 4-hydroxybiphenyl was noted in the intestine. Conjugation of 1-chloro-2,4-dinitrobenzene with glutathione was increased in intestine and spleen 2 hr after treatment. gamma-Glutamyltranspeptidase activity was unaltered in all tissues studied. Reduced glutathione concentrations were increased significantly by different amounts depending on which organs were studied 2 or 4 hr after treatment. These results indicate that galactosamine/lipopolysaccharide-induced liver injury is not accompanied by major effects on the examined biotransformation reactions.

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.

Cytochrome P-450 expression in sudden infant death syndrome

In the human liver, the major rise of the cytochrome P-450 isoform content occurs during the first months following birth (e.g., the high vulnerability period to sudden infant death syndrome (SIDS), a syndrome frequently associated with viral infection and drug hypersensitivity. We examined the expression of individual P-450 isoforms in liver samples collected postmortem from SIDS infants and compared values with those of control adults and children of the same age suffering from various pathologies. Hepatic microsomes were prepared and examined for their content in total P-450, the level of individual isoforms (CYP1A2, CYP2E1, CYP4A, CYP3A, and CYP2C) determined with specific antibodies and for their enzymatic activities. Total RNA was extracted and probed with several CYP cDNAs and oligomers. The overall hepatic P-450 content was not modified in SIDS infants. Among cytochrome P-450 isoforms, only CYP2C was markedly increased. This rise resulted from an accumulation of RNA encoding CYP2C and was associated with a stimulation of diazepam demethylation. The precocious expression of CYP2C in SIDS could result in a higher production of epoxyeicosatrienoic acids in the neonate, believed to act as relaxant of pulmonary smooth muscles. Its consequence might be the induction of fatal apnea in SIDS.

Effects of phenobarbital and interleukin-6 on cytochrome P4502B1 and 2B2 in cultured rat hepatocytes

The objectives of this study were to characterize further the effects of phenobarbital (PB) on cytochrome P4502B1 and 2B2 (P4502B1/2) enzyme activity and immunoreactivity in rat hepatocytes and to investigate the mechanism(s) mediating the ability of interleukin-6 (IL-6) to inhibit this induction. PB caused a concentration-dependent increase in benzyloxyresorufin O-deethylase (BROD) activity with maximal effects (a 25-fold increase) at concentrations of 0.3 to 1 mM. The induction of BROD activity was linear over 24 hr of exposure. Immunoblot profiles of P4502B1/2 agreed with measurements of enzyme activity. In addition to inducing P4502B1/2, PB (0.75 mM) also increased the levels of P450 reductase by approximately 2-fold following a 24-hr exposure to PB. When IL-6 was added concomitantly with or up to 12 hr after the addition of PB, the PB induction of BROD activity and immunoreactivity was inhibited significantly. When 18 hr elapsed between the time of addition of PB and IL-6, the inhibitory effects of IL-6 were no longer apparent, suggesting that the actions of IL-6 were mediated by early events in the induction process. IL-6 did not affect the PB induction of P450 reductase. To determine whether IL-6 altered the degradation of P4502B1/2, hepatocytes were exposed to PB for 24 hr, then washed, and the loss of BROD activity and immunoreactivity following incubation with a protein synthesis inhibitor was measured. IL-6 did not alter the rate of loss of either enzyme activity or immunoreactivity, indicating that the effects of IL-6 could not be attributed to the enhanced degradation of P4502B1/2. Results suggest that the inhibition of PB-induced BROD activity by IL-6 is due to an action on early cellular and molecular events in the induction process.

Comparison of hepatic and extrahepatic drug-metabolizing enzyme activities in rats given single or multiple challenge infections with Fasciola hepatica

The activity of drug-metabolizing enzymes was compared in liver, kidneys and lungs of rats given single or repetitive fluke infections. Fascioliasis was induced by oral administration of 20 metacercariae of F. hepatica to rats, either 6, or 12 and 6, or 12, 9 and 6 weeks before sacrifice. In the liver of mono-infected rats, significant reductions (24-67%) were observed in microsomal content of cytochrome P450 and all P450-dependent monooxygenases investigated. Conjugations to glutathione or acetate were lowered by 34-50% in these animals. In multiply infected animals, a majority of specific enzymatic activities were unchanged, while some monooxygenase activities such as aminopyrine demethylation or benzo(a)pyrene hydroxylation were increased by 26-76% in the liver of tri-infected rats. A renal compensatory process occurred in all infected groups, since cytochrome P450, benzphetamine demethylation and glutathione conjugation were significantly increased. By contrast, dealkylation of benzphetamine and pentoxyresorufin were decreased in the lungs of monoinfected rats. The development of parasite resistance would account for the recovery of liver drug metabolizing capabilities in multi-infected animals.

Immunostimulating lipopeptide, LtriP (RP 56142): comparison of the effect on hepatic cytochrome P 450 modulation and radioprotection in male and female of three mouse strains

The sex-dependent effect of lauroyl-L-Ala-D-gamma-Glu-L,L-A2pmNH2 (LtriP, RP 56142) on hepatic microsomal cytochromes P 450 (cyt P 450) was studied in three mouse strains NMRI, C3H/OuJ and C3H/HeJ. In NMRI and C3H/OuJ, strains which are responsive to bacterial lipopolysaccharides (LPS-responsive), regardless of the sex of the mouse, significant decrease in the amount of cyt P 450 was observed after LtriP treatment, with a concomitant reduction in ethoxyresorufin-O-deethylase (cyt P 450 1A-dependent) and 7-ethoxycoumarin-O-deethylase activities. This was not seen in C3H/HeJ (LPS-hyporesponsive) mice. These effects may be related to LtriP-dependent cytokine induction, since neither LtriP nor LPS stimulated interleukin-1 (IL-1) secretion by C3H/HeJ macrophages. 11- and 12-hydroxylations (11- and 12-OH) of lauric acid were compared in C3H/OuJ and C3H/HeJ mice. LtriP depressed the total enzymatic conversion of lauric acid in the two strains without modification of the 11/12-OH ratio for C3H/OuJ or male C3H/HeJ mice. However, in females C3H/HeJ mice this decrease was particularly significant and concerned especially the 12-OH activity (a marker of cyt P450 4A family). Although males of the three strains were more sensitive to irradiation than females, LtriP exerted a sex-independent radioprotection on NMRI and C3H/OuJ mice. Its radioprotective effect was illustrated by the preservation of all the enzymatic activities studied in treated NMRI mice, contrary to irradiated control animals. In contrast, for the C3H/HeJ strain, males were not protected by LtriP treatment and, furthermore, females showed a marked sensitization to irradiation. The effects in CH3/HeJ strain implicate LtriP in the control of cyt P 450 induction and of sensitivity to irradiation independently of IL-1 induction.

Selective effects of a bacterial infection (Actinobacillus pleuropneumoniae) on the hepatic clearances of caffeine, antipyrine, paracetamol, and indocyanine green in the pig

1. In order to investigate the effect of a bacterial acute phase response model on drug disposition in vivo, plasma clearances of antipyrine, caffeine, paracetamol and indocyanine green were investigated in the healthy and Actinobacillus pleuropneumoniae-infected pig. 2. Indocyanine green plasma and endogenous creatinine clearance were not changed during the infection, which indicates that hepatic blood flow and renal function were not significantly affected. 3. In the A. pleuropneumoniae-infected pig, plasma clearances of antipyrine and caffeine, both marker substrates for hepatic oxidative biotransformation, were decreased by 72 and 68% respectively. The clearance of paracetamol, a drug mainly glucuronidated in the pig, was reduced by 39%. 4. It is concluded that the most important change in drug elimination during an acute phase response induced by A. pleuropneumoniae is a suppression of oxidative hepatic biotransformation.

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.

Endotoxin administration to humans inhibits hepatic cytochrome P450-mediated drug metabolism

In experimental animals, injection of gram-negative endotoxin (LPS) decreases hepatic cytochrome P450-mediated drug metabolism. To evaluate this phenomenon in a human model of gram-negative sepsis, LPS was administered on two consecutive days to healthy male volunteers during which time a cocktail of antipyrine (AP-250 mg), hexobarbital (HB-500 mg), and theophylline (TH-150 mg) was ingested and the apparent oral clearance of each drug determined. Each subject had a control drug clearance study with saline injections. In the first experiment, six subjects received the drug cocktail 0.5 h after the first dose of LPS. In the second experiment, another six subjects received the drug cocktail 0.5 h after the second dose of LPS. In both experiments, LPS caused the expected physiologic responses of inflammation including fever with increases in serum concentrations of TNF alpha, IL-1 beta, IL-6, and acute phase reactants. In the first experiment, only minor decreases in clearances of the probe drugs were observed (7-12%). However in the second experiment, marked decreases in the clearances of AP (35, 95% CI 18-48%), HB (27, 95% CI 14-34%), and TH (22, 95% CI 12-32%) were seen. The decreases in AP clearance correlated with initial peak values of TNF alpha (r = 0.82) and IL-6 (r = 0.86). These data show that in humans the inflammatory response to even a very low dose of LPS significantly decreases hepatic cytochrome P450-mediated drug metabolism and this effect evolves over a 24-h period. It is likely that septic patients with much higher exposures to LPS have more profound inhibition of drug metabolism.

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.

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.

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.

Chemistry and biology of heme. Effect of metal salts, organometals, and metalloporphyrins on heme synthesis and catabolism, with special reference to clinical implications and interactions with cytochrome P-450

Although free porphyrins occur in nature in small quantities, no known function has been assigned to them. In contrast, heme and cobalamin, which are Fe and Co chelates of porphyrins or porphyrin derivatives, respectively, carry out crucial biological functions. Heme is the prosthetic group for a number of hemoproteins. These include myoglobin and hemoglobin, which carry out oxygen binding or transport; mitochondrial cytochromes aa3, b, c, and c3, which are important in transferring electrons; microsomal cytochrome P-450, which catalyzes mixed-function oxidations; catalase, which decomposes H2O2; peroxidase, which activates H2O2; and tryptophan pyrrolase, which catalyzes the oxidation of tryptophan. Recently, heme has also been shown to be the prosthetic group of prostaglandin and peroxide synthetase and indoleamine dioxygenase. The elegant studies of the biochemical pathway for the formation of heme demonstrated the arrangement in the porphyrin macrocycle of the carbon and nitrogen atoms originating from the eight glycine and the succinic acid molecule that are the precursors of porphyrins. There are eight enzymes involved in the synthesis of heme. The first and last three of these enzymes are localized in mitochondria, while the intermediate enzymes are localized in cytosol. The catalytic site of HMOX recognizes metalloporphyrins with central metal atoms other than iron; it favors some of these metalloporphyrins over heme as a potential substrate, sometimes by a large factor, permitting the synthetic heme analogue to serve as a potent competitive inhibitor of HMOX reaction. Since these synthetic metalloporphyrins do not bind molecular oxygen, they are not metabolically degraded by ring rupture and do not add to the body pool of bile pigment. One possible consequence of this competitive inhibition of heme degradation is suppression of bile pigment formation to such a degree that excessive plasma levels of bilirubin may be diminished. The studies of Drummond and Kappas (1981) and later studies in rats, mice, monkeys, and man, and also our studies have proved the latter phenomenon. The compound does not appear to affect the metabolic disposition of preformed bilirubin but inhibits biliary bilirubin excretion derived from the metabolism of endogenous or exogenous heme. Whether some of the effect of Sn-PP on naturally occurring or experimentally induced jaundice in animals reflects diversion of heme to nonheme to oxygenase-dependent pathways of heme metabolism, or whether a pathway which is normally latent becomes activated concurrent with HMOX inhibition is not known.(ABSTRACT TRUNCATED AT 400 WORDS)

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.

Modifications of hepatic alpha-1-acid glycoprotein and albumin gene expression in rats treated with phenobarbital

The serum level of alpha 1-acid glycoprotein (alpha 1-AGP) is significantly increased in various animal species by treatment with cytokines, glucocorticoids and phenobarbital. The mechanisms responsible for the cytokine-induced and glucocorticoid-induced increases are now well documented, but not so in the case of phenobarbital. The main purpose of this study was to assess whether phenobarbital acts on alpha 1-AGP synthesis in the liver at the transcriptional or translational level. Male Dark Agouti rats received 70 mg phenobarbital/kg daily for 7 days. The analysis of total hepatic RNA showed that a single injection of phenobarbital induced an 11-fold increase in phenobarbital-dependent cytochrome P450IIB mRNA, whereas seven injections of phenobarbital were required to induce a maximum 5.5-fold increase in alpha 1-AGP mRNA. Concurrently, the transcription rate of the alpha 1-AGP gene rose 3.5-fold. Hepatocytes isolated after the seventh injection of phenobarbital showed a threefold increased capacity to secrete alpha 1-AGP, corresponding to a 3.2-fold increased alpha 1-AGP mRNA content in the liver. In conditions in which its effect on the induction of alpha 1-AGP synthesis was maximum, phenobarbital caused a 30% reduction in liver albumin mRNA and in albumin secretion by isolated hepatocytes, resulting from a 60-70% reduction in the rate of transcription of the albumin gene measured in isolated nuclei. We conclude that the effect of phenobarbital on alpha 1-AGP and albumin gene expression occurs at the transcriptional rather than the translational level.