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

IL-1 and TNF-α regulation of aryl hydrocarbon receptor (AhR) expression in HSY human salivary cells

OBJECTIVES

Recent findings demonstrate that nuclear receptor - aryl hydrocarbon receptor (AhR) may play an important role in the pathogenesis of Sjögren's syndrome (SS) via involvement in Epstein-Barr virus reactivation. In that study a reporter system was used. Therefore, it was decided to define AhR expression in human salivary cell line (HSY) and its functional regulators.

DESIGN

The expression and functional regulation of AhR was studied in HSY cells. The cells were incubated with dioxin (TCDD) - AhR model inducer, IL-1 and TNF-α. qRT-PCR was applied to assess the expression of AHR, AHRR (AhR repressor), ARNT (AhR nuclear translocator) as well as AhR dependent genes: CYP1A1 and CYP1B1. Enzymatic activity of CYP1A1 and CYP1B1 was evaluated using luciferin-labelled CYPs substrate.

RESULTS

In general, dioxin did not significantly influence the expression of AHR and ARNT, but reduced AHRR level. AhR dependent gene expression, i.e. CYP1A1 and CYP1B1 increased gradually with TCDD incubation time. TNF-α significantly induced AHR along with CYP1A1 and CYP1B1 expression. IL-1β did not affect AHR expression, and had minimal effects on CYP1 mRNA levels. Exposure of HSY cells to TCDD resulted in time-dependent induction of CYP1A1 and CYP1B1 enzymatic activity.

CONCLUSIONS

This study documents functional expression of AhR in HSY as well as induction of AhR and its dependent genes by TNF-α.

Acute toxic responses of the rockfish (Sebastes schlegeli) to Iranian heavy crude oil: feeding disrupts the biotransformation and innate immune systems

To clarify the toxic effects of Iranian Heavy Crude Oil (IHCO) from the "Hebei spirit" oil spill, innate immune toxic effects defending on biotransformation pathway have been investigated on fish exposed to IHCO. Juvenile rockfish were exposed to IHCO in gelatin capsules by feeding. The effects on multiple fish biotransformation enzymes (Cytochrome P4501A and glutathione-S-transferase) and the expression level of the several immune response genes, including interleukin-1beta, granulocyte colony-stimulating factor and Cathepsin L, were measured in the liver, spleen and kidney. The tissue-specific expression patterns of these genes demonstrated that the highest expression levels of Cytochrome P4501A, glutathione-S-transferase, interleukin-1beta, granulocyte colony-stimulating factor, interferon stimulated gene 15 and Cathepsin L were found in the liver and that the TNF receptor was high in spleen. The oil-fed fish had significantly higher concentrations of biliary fluorescent metabolites and Cytochrome P4501A expression during the initial stage (12 ∼ 48 h after exposure) than those in the liver and kidney of the sham group. Similarly, the highest mRNA expression levels of interleukin-1beta and granulocyte colony-stimulating factor were detected in the liver at the early stages of exposure (12 h after exposure). Following exposure, the levels of interferon stimulated gene 15 and granulocyte colony-stimulating factor mRNA remained high at 120 h after exposure in the liver but the levels of interleukin-1beta and Cathepsin L gradually decreased to an expression level equal to or less than the sham group. Our data suggest that the innate immune and hepatodetoxification responses in oil-fed fish were induced at the initial stage of exposure to the IHCO at the same time but several immune-related genes decreased to less than that of the sham group after the initial stage of response. Therefore, immune disturbances in fish exposed to IHCO may allow the pathogens, including the infectious diseases, to more easily affect the oil exposed fish.

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.

The aryl hydrocarbon receptor complex and the control of gene expression

The aryl hydrocarbon receptor (AhR) is a ligand-activated transcription factor that controls the expression of a diverse set of genes. The toxicity of the potent AhR ligand 2,3,7,8-tetrachlorodibenzo-p-dioxin is almost exclusively mediated through this receptor. However, the key alterations in gene expression that mediate toxicity are poorly understood. It has been established through characterization of AhR-null mice that the AhR has a required physiological function, yet how endogenous mediators regulate this orphan receptor remains to be established. A picture as to how the AhR/ARNT heterodimer actually mediates gene transcription is starting to emerge. The AhR/ARNT complex can alter transcription both by binding to its cognate response element and through tethering to other transcription factors. In addition, many of the coregulatory proteins necessary for AhR-mediated transcription have been identified. Cross talk between the estrogen receptor and the AhR at the promoter of target genes appears to be an important mode of regulation. Inflammatory signaling pathways and the AhR also appear to be another important site of cross talk at the level of transcription. A major focus of this review is to highlight experimental efforts to characterize nonclassical mechanisms of AhR-mediated modulation of gene transcription.

Inflammatory signaling and aryl hydrocarbon receptor mediate synergistic induction of interleukin 6 in MCF-7 cells

The pleiotropic cytokine interleukin 6 (IL-6) is involved in immune cell homeostasis. Additionally, IL-6 expression and signaling in tumor cells have been shown to elicit both protumor and antitumor properties. There is a plethora of mechanistic knowledge regarding how IL-6 signal transduction translates to biological responses. However, there is little understanding as to what factors control IL-6 expression within a tumor cell environment. The studies presented herein show that, in MCF-7 breast and ECC-1 endocervical cancer cells, the stimulation of aryl hydrocarbon receptor (AHR) activity, in combination with IL-1beta or phorbol 12-myristate 13-acetate (PMA) treatment, results in a marked synergistic induction of IL-6 levels over what is seen without AHR activation. Chromatin immunoprecipitation experiments suggest that the regulation of IL-6 mRNA expression occurs at the chromatin level, as AHR presence on the IL-6 promoter was observed in response to treatment with AHR ligand. Synergistic induction of IL-6 expression was sustained for 72 hours, with accumulation of IL-6 protein reaching levels 4.8-fold above IL-1beta treatment alone. In addition, transcriptional regulation of the prototypic AHR responsive gene Cyp1a1 was negatively regulated by PMA and IL-1beta treatment. Silencing of RELA expression alleviated IL-1beta-mediated repression of AHR transcriptional activity, whereas PMA-mediated repression was maintained. Additionally, small interfering RNA studies reveal that AHR and RELA are necessary for synergistic induction of IL-6. The findings presented here reveal the AHR as a potential therapeutic target for selective modulation of IL-6 expression in some tumor cell types. The data also suggest a possible previously unrecognized mechanism of AHR-mediated tumor promotion.

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.

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.

Endotoxin contamination in commercially available pokeweed mitogen contributes to the activation of murine macrophages and human dendritic cell maturation

Commercially available pokeweed mitogen (PWM) has been reported to activate macrophages, leading to production of proinflammatory cytokines and nitric oxide (NO). However, we found that polymyxin B (PMB), a specific inhibitor of endotoxin activity, inhibited the PWM-induced expression of proinflammatory cytokines and NO and the activation of Toll-like receptor 4 (TLR4). A kinetic-turbidimetric Limulus amebocyte lysate assay demonstrated that commercial PWM contained substantial endotoxin, over 10(4) endotoxin units/mg of the PWM. A PWM repurified by PMB-coupled beads no longer induced the expression of proinflammatory cytokines, TLR4 activation, or dendritic cell maturation. However, the repurified PWM remained able to induce proliferation of human lymphocytes, which is a representative characteristic of PWM. These results suggest that commercial PWM might be contaminated with a large amount of endotoxin, resulting in the attribution of misleading immunological properties to PWM.

Interleukin-1alpha and tumor necrosis factor alpha modulate cytochrome P450 activities in carp (Cyprinus carpio)

In mammals, it has been shown that the activation of host defense mechanisms down-regulates microsomal cytochrome P450 by the liberation of cytokines. We investigated the effect of interleukin-1alpha (IL1alpha) and tumor necrosis factoralpha (TNFalpha) on constitutive and 3-methylcholanthrene (3-MC)-induced biotransformation activities in carp. We have first measured the time course response of ethoxyresorufine O-decthylase (EROD) activity in liver, head kidney, and spleen 1, 2, 3, 5, and 7 days after intraperitoneal injection of a prototypical Cyp 1A inducer (3-MC). This activity was compared to the rate of 3-MC accumulation in all organs tested. A correlation between a diminution of EROD activity and an increase in 3-MC concentration in each organ was observed. We have also tested the effects of two inflammatory cytokines (IL1alpha and TNFalpha) on biotransformation activities. Intravenous injection of these compounds resulted in a marked depression of 3-MC-induced glutathione S-transferase activity in all organs tested and in 3-MC-increased cytochrome P450 content in the liver and head kidney. TNFalpha produced an increase in basal EROD activity in the liver and head kidney. Taken together, these results suggested that, as in mammals, the activation of host defense mechanisms regulates microsomal cytochrome P450 and related enzymes in fish.

Induction of cellular oxidative stress by aryl hydrocarbon receptor activation

The aryl hydrocarbon receptor (AHR) has long been associated with the induction of a battery of genes involved in the metabolism of foreign and endogenous compounds. Depending on experimental conditions, AHR can mediate either activation or amelioration of chemical toxicity. For the past decade, evidence has mounted that AHR is associated with a cellular oxidative stress response that must be considered when evaluating the mechanism of action of xenobiotics capable of activating AHR, or capable of metabolic activation by enzymes encoded by genes under control of AHR. In this review, we have evaluated the diverse mechanisms by which AHR generates an oxidative stress response, including inflammation, antioxidant and prooxidant enzymes and cytochrome P450. A review of the regulation of Ahr transcription and functional polymorphisms especially related to oxidative stress is also included. We have carefully avoided placing a value judgment on the degree of toxicity produced by such a response, in view of the realization that an oxidative response is involved in many normal physiological processes. Since the interface between physiological, adaptive and toxicological responses elicited by the AHR-mediated oxidative stress response is not clearly defined, it behooves the researcher to evaluate both toxicological and physiological features of the response.