Regulation of CYP4A1 and peroxisome proliferator-activated receptor alpha expression by interleukin-1beta, interleukin-6, and dexamethasone in cultured fetal rat hepatocytes

Role of PPAR-Allopregnanolone Signaling in Behavioral and Inflammatory Gut-Brain Axis Communications

The gut microbiome regulates emotional behavior, stress responses, and inflammatory processes by communicating with the brain. How and which neurobiological mediators underlie this communication remain poorly understood. PPAR-α (peroxisome proliferator-activated receptor α), a transcription factor susceptible to epigenetic modifications, regulates pathophysiological functions, including metabolic syndrome, inflammation, and behavior. Mood disorders, inflammatory processes, and obesity are intertwined phenomena that are associated with low blood concentrations of the anti-inflammatory and "endogenous tranquilizer" neurosteroid allopregnanolone and poor PPAR-α function. Stress and consumption of obesogenic diets repress PPAR function in brain, enterocytes, lipocytes, and immune modulatory cells favoring inflammation, lipogenesis, and mood instability. Conversely, micronutrients and modulators of PPAR-α function improve microbiome composition, dampen systemic inflammation and lipogenesis, and improve anxiety and depression. In rodent stress models of anxiety and depression, PPAR activation normalizes both PPAR-α expression downregulation and decreased allopregnanolone content and ameliorates depressive-like behavior and fear responses. PPAR-α is known to regulate metabolic and inflammatory processes activated by short-chain fatty acids; endocannabinoids and congeners, such as N-palmitoylethanolamide, drugs that treat dyslipidemias; and micronutrients, including polyunsaturated fatty acids. Both PPAR-α and allopregnanolone are abundantly expressed in the colon, and they exert potent anti-inflammatory actions by blocking the toll-like receptor-4-nuclear factor-κB pathway in peripheral immune cells, neurons, and glia. The perspective that PPAR-α regulation in the colon by gut microbiota or metabolites influences central allopregnanolone content after trafficking to the brain, thereby serving as a mediator of gut-brain axis communications, is examined in this review.

Pemafibrate attenuates pulmonary fibrosis by inhibiting myofibroblast differentiation

BACKGROUND AND OBJECTIVE

Idiopathic pulmonary fibrosis is a chronic progressive disease associated with substantial morbidity and mortality despite advances in medical therapy. Increasing evidence suggests that peroxisome proliferator-activated receptors (PPARs) play important roles in the fibrosis-related diseases and their agonists may become effective therapeutic targets. Pemafibrate is a selective PPARα agonist, but the efficacy against pulmonary fibrosis and mechanisms involved have not been systematically evaluated. Thus, the aims of this study were to explore the role of PPARα in the pulmonary fibrosis and to assess the effect of pemafibrate in vivo and in vitro.

METHODS

The effects of pemafibrate were evaluated in bleomycin-challenged murine pulmonary fibrosis model and transforming growth factor-beta 1 (TGF-β1) stimulated lung fibroblasts.

RESULTS

Bleomycin instillation induced body weight loss, declined lung function, pulmonary fibrosis, and extensive collagen deposition in the mice, accompanied with decreased pulmonary expression of PPARα, all of which were partially improved by pemafibrate at a dose of 2 mg/kg. Besides, pemafibrate effectively inhibits TGF-β1-induced myofibroblast differentiation and extracellular matrix (ECM) production in vivo and in vitro. Furthermore, we showed that pemafibrate not only inhibited pulmonary expression of NLRP3 and cleaved caspase-1 in bleomycin-inhaled mice, but also repressed activation of NLRP3/caspase-1 axis in TGF-β1 stimulated lung fibroblasts.

CONCLUSION

Our data suggest that pemafibrate exerts a marked protection against from the development of pulmonary fibrosis, which could constitute a novel candidate for the treatment for pulmonary fibrosis.

The Glitazars Paradox: Cardiotoxicity of the Metabolically Beneficial Dual PPARα and PPARγ Activation

The most common complications in patients with type-2 diabetes are hyperglycemia and hyperlipidemia that can lead to cardiovascular disease. Alleviation of these complications constitutes the major therapeutic approach for the treatment of diabetes mellitus. Agonists of peroxisome proliferator-activated receptor (PPAR) alpha and PPARγ are used for the treatment of hyperlipidemia and hyperglycemia, respectively. PPARs belong to the nuclear receptors superfamily and regulate fatty acid metabolism. PPARα ligands, such as fibrates, reduce circulating triglyceride levels, and PPARγ agonists, such as thiazolidinediones, improve insulin sensitivity. Dual-PPARα/γ agonists (glitazars) were developed to combine the beneficial effects of PPARα and PPARγ agonism. Although they improved metabolic parameters, they paradoxically aggravated congestive heart failure in patients with type-2 diabetes via mechanisms that remain elusive. Many of the glitazars, such as muraglitazar, tesaglitazar, and aleglitazar, were abandoned in phase-III clinical trials. The objective of this review article pertains to the understanding of how combined PPARα and PPARγ activation, which successfully targets the major complications of diabetes, causes cardiac dysfunction. Furthermore, it aims to suggest interventions that will maintain the beneficial effects of dual PPARα/γ agonism and alleviate adverse cardiac outcomes in diabetes.

IL-1 receptor antagonist therapy mitigates placental dysfunction and perinatal injury following Zika virus infection

Zika virus (ZIKV) infection during pregnancy causes significant adverse sequelae in the developing fetus, and results in long-term structural and neurologic defects. Most preventive and therapeutic efforts have focused on the development of vaccines, antivirals, and antibodies. The placental immunologic response to ZIKV, however, has been largely overlooked as a target for therapeutic intervention. The placental inflammatory response, specifically IL-1β secretion and signaling, is induced by ZIKV infection and represents an environmental factor that is known to increase the risk of perinatal developmental abnormalities. We show in a mouse model that maternally administrated IL-1 receptor antagonist (IRA; Kineret, or anakinra), following ZIKV exposure, can preserve placental function (by improving trophoblast invasion and placental vasculature), increase fetal viability, and reduce neurobehavioral deficits in the offspring. We further demonstrate that while ZIKV RNA is highly detectable in placentas, it is not correlated with fetal viability. Beyond its effects in the placenta, we show that IL-1 blockade may also directly decrease fetal neuroinflammation by mitigating fetal microglial activation in a dose-dependent manner. Our studies distinguish the role of placental inflammation during ZIKV-infected pregnancies, and demonstrate that maternal IRA may attenuate fetal neuroinflammation and improve perinatal outcomes.

Molecular Actions of PPARα in Lipid Metabolism and Inflammation

Peroxisome proliferator-activated receptor α (PPARα) is a nuclear receptor of clinical interest as a drug target in various metabolic disorders. PPARα also exhibits marked anti-inflammatory capacities. The first-generation PPARα agonists, the fibrates, have however been hampered by drug-drug interaction issues, statin drop-in, and ill-designed cardiovascular intervention trials. Notwithstanding, understanding the molecular mechanisms by which PPARα works will enable control of its activities as a drug target for metabolic diseases with an underlying inflammatory component. Given its role in reshaping the immune system, the full potential of this nuclear receptor subtype as a versatile drug target with high plasticity becomes increasingly clear, and a novel generation of agonists may pave the way for novel fields of applications.

Lipid Use and Misuse by the Heart

The heart utilizes large amounts of fatty acids as energy providing substrates. The physiological balance of lipid uptake and oxidation prevents accumulation of excess lipids. Several processes that affect cardiac function, including ischemia, obesity, diabetes mellitus, sepsis, and most forms of heart failure lead to altered fatty acid oxidation and often also to the accumulation of lipids. There is now mounting evidence associating certain species of these lipids with cardiac lipotoxicity and subsequent myocardial dysfunction. Experimental and clinical data are discussed and paths to reduction of toxic lipids as a means to improve cardiac function are suggested.

PPARs: Protectors or Opponents of Myocardial Function?

Over 5 million people in the United States suffer from the complications of heart failure (HF), which is a rapidly expanding health complication. Disorders that contribute to HF include ischemic cardiac disease, cardiomyopathies, and hypertension. Peroxisome proliferator-activated receptors (PPARs) are members of the nuclear receptor family. There are three PPAR isoforms: PPARα, PPARγ, and PPARδ. They can be activated by endogenous ligands, such as fatty acids, as well as by pharmacologic agents. Activators of PPARs are used for treating several metabolic complications, such as diabetes and hyperlipidemia that are directly or indirectly associated with HF. However, some of these drugs have adverse effects that compromise cardiac function. This review article aims to summarize the current basic and clinical research findings of the beneficial or detrimental effects of PPAR biology on myocardial function.

Quercetin and allopurinol reduce liver thioredoxin-interacting protein to alleviate inflammation and lipid accumulation in diabetic rats

BACKGROUND AND PURPOSE

Thioredoxin-interacting protein (TXNIP), a regulator of cellular oxidative stress, has been associated with activation of NOD-like receptor 3 (NLRP3) inflammasome, inflammation and lipid metabolism, suggesting it has a role in the pathogenesis of non-alcoholic fatty liver disease (NAFLD) in diabetes. In this study we investigated whether TXNIP is involved in type 1 diabetes-associated NAFLD and whether antioxidants, quercetin and allopurinol, alleviate NAFLD by targeting TXNIP.

EXPERIMENTAL APPROACH

Diabetes was induced in male Sprague-Dawley rats by a single i.p. injection of 55 mg · kg⁻¹ streptozotocin. Quercetin and allopurinol were given p.o. to diabetic rats for 7 weeks. Hepatic function, oxidative stress, inflammation and lipid levels were determined. Rat BRL-3A and human HepG2 cells were exposed to high glucose (30 mM) in the presence and absence of antioxidants, TXNIP siRNA transfection or caspase-1 inhibitor, Ac-YVAD-CMK.

KEY RESULTS

Quercetin and allopurinol significantly inhibited the TXNIP overexpression, activation of NLRP3 inflammasome, down-regulation of PPARα and up-regulation of sterol regulatory element binding protein-1c (SREBP-1c), SREBP-2, fatty acid synthase and liver X receptor α, as well as elevation of ROS and IL-1β in diabetic rat liver. These effects were confirmed in hepatocytes in vitro and it was further shown that TXNIP down-regulation contributed to the suppression of NLRP3 inflammasome activation, inflammation and changes in PPARα and SREBPs.

CONCLUSIONS AND IMPLICATIONS

Inhibition of hepatic TXNIP by quercetin and allopurinol contributes to the reduction in liver inflammation and lipid accumulation under hyperglycaemic conditions. The targeting of hepatic TXNIP by quercetin and allopurinol may have therapeutic implications for prevention of type 1 diabetes-associated NAFLD.

Distinct alterations in ATP-binding cassette transporter expression in liver, kidney, small intestine, and brain in adjuvant-induced arthritic rats

Pathophysiological changes of infection or inflammation are associated with alterations in the production of numerous absorption, distribution, metabolism and excretion-related proteins. However, little information is available on the effects of inflammation on the expression levels and activities of ATP-binding cassette (ABC) transporters. We examined the effect of acute (on day 7) and chronic (on day 21) inflammation on the expression of ABC transporters in some major tissues in rat. Adjuvant-induced arthritis (AA) in rats was used as an animal model for inflammation. The mRNA levels of mdr1a and mdr1b encoding P-glycoprotein (P-gp) decreased significantly in livers of AA rats on day 21. Hepatic protein levels of P-gp, Mrp2, and Bcrp decreased significantly in membranes but not homogenates of AA rats after 7 days and after 21 days of treatment with adjuvant. Contrary to liver, protein levels of P-gp and Mrp2, but not Bcrp in kidney, increased significantly in membranes. The biliary excretion of rhodamine 123 was decreased in rats with chronic inflammation owing to decreases in efflux activities of P-gp. Our results showed that the expression of transporters in response to inflammation was organ dependent. In particular, hepatic and renal P-gp and Mrp2 exhibited opposite changes in membrane protein levels.

A clinical therapeutic protein drug-drug interaction study: coadministration of denosumab and midazolam in postmenopausal women with osteoporosis

Drug–disease interactions involving therapeutic proteins that target cytokines and potentially impact cytochrome P450 (CYP) enzymes have been of increased interest to drug regulatory agencies and industry sponsors in recent years. This parallel-group open-label study evaluated the effects of the monoclonal antibody denosumab, an inhibitor of the cytokine RANKL, on the pharmacokinetics of the probe CYP3A4 substrate midazolam in postmenopausal women with osteoporosis. The pharmacokinetics of a 2 mg oral dose of midazolam was evaluated on days 1 and 16. Subjects in Group A received a 60 mg subcutaneous dose of denosumab on day 2, 2 weeks before the second midazolam dose, while subjects in Group B did not. For Group A (n = 17), point estimates for the ratio of least square means for midazolam exposures based on maximum observed plasma concentration (C_max) and areas under the plasma concentration–time curve (AUCs) on day 16 versus day 1 ranged from 1.02 to 1.04 and 90% confidence intervals were within 0.80–1.25. No period effect was observed for Group B (n = 8). Midazolam and denosumab coadministration was safe and well tolerated. Inhibition of the cytokine RANKL by denosumab does not affect CYP3A4 in postmenopausal women with osteoporosis and will not alter the pharmacokinetics of drugs metabolized by this enzyme. These results are consistent with data suggesting that RANKL does not impact markers of inflammation and represent the first clinical data demonstrating a lack of effect on CYP3A4 of a therapeutic protein that is a cytokine modulator.

Cardiac lipotoxicity: molecular pathways and therapeutic implications

Diabetes and obesity are both associated with lipotoxic cardiomyopathy exclusive of coronary artery disease and hypertension. Lipotoxicities have become a public health concern and are responsible for a significant portion of clinical cardiac disease. These abnormalities may be the result of a toxic metabolic shift to more fatty acid and less glucose oxidation with concomitant accumulation of toxic lipids. Lipids can directly alter cellular structures and activate downstream pathways leading to toxicity. Recent data have implicated fatty acids and fatty acyl coenzyme A, diacylglycerol, and ceramide in cellular lipotoxicity, which may be caused by apoptosis, defective insulin signaling, endoplasmic reticulum stress, activation of protein kinase C, MAPK activation, or modulation of PPARs.

Kupffer cells promote hepatic steatosis via interleukin-1beta-dependent suppression of peroxisome proliferator-activated receptor alpha activity

Kupffer cells have been implicated in the pathogenesis of various liver diseases. However, their involvement in metabolic disorders of the liver, including fatty liver disease, remains unclear. The present study sought to determine the impact of Kupffer cells on hepatic triglyceride storage and to explore the possible mechanisms involved. To that end, C57Bl/6 mice rendered obese and steatotic by chronic high-fat feeding were treated for 1 week with clodronate liposomes, which cause depletion of Kupffer cells. Loss of expression of marker genes Cd68, F4/80, and Clec4f, and loss of Cd68 immunostaining verified almost complete removal of Kupffer cells from the liver. Also, expression of complement components C1, the chemokine (C-C motif) ligand 6 (Ccl6), and cytokines interleukin-15 (IL-15) and IL-1beta were markedly reduced. Importantly, Kupffer cell depletion significantly decreased liver triglyceride and glucosylceramide levels concurrent with increased expression of genes involved in fatty acid oxidation including peroxisome proliferator-activated receptor alpha (PPARalpha), carnitine palmitoyltransferase 1A (Cpt1alpha), and fatty acid transport protein 2 (Fatp2). Treatment of mice with IL-1beta decreased expression of PPARalpha and its target genes, which was confirmed in primary hepatocytes. Consistent with these data, IL-1beta suppressed human and mouse PPARalpha promoter activity. Suppression of PPARalpha promoter activity was recapitulated by overexpression of nuclear factor kappaB (NF-kappaB) subunit p50 and p65, and was abolished upon deletion of putative NF-kappaB binding sites. Finally, IL-1beta and NF-kappaB interfered with the ability of PPARalpha to activate gene transcription.

CONCLUSION

Our data point toward important cross-talk between Kupffer cells and hepatocytes in the regulation of hepatic triglyceride storage. The effect of Kupffer cells on liver triglycerides are at least partially mediated by IL-1beta, which suppresses PPARalpha expression and activity.

Regulation of peroxisome proliferator-activated receptor-α expression during lung inflammation

Peroxisome proliferator-activated receptor-alpha (PPARalpha) is implicated in the control of airway inflammation. However, little is known so far about PPARalpha expression and regulation in the lung. Our aim was to assess PPARalpha expression in the lung from normal mice, as well as to investigate its regulation during airway inflammation or in response to anti-inflammatory agents. The PPARalpha activator, fenofibrate, the glucocorticoid, dexamethasone or vehicle was administered to normal mice, to mice exposed to tumor necrosis factor-alpha (TNF-alpha) or lipopolysaccharide (LPS) or to ovalbumin (OVA)-sensitized and challenged animals. PPARalpha expression was assessed by quantifying PPARalpha mRNA levels using real-time quantitative PCR after reverse-transcription of total lung RNA. Airway inflammation was evaluated by determining total and differential cell counts, as well as TNF-alpha production in bronchoalveolar lavage fluids. PPARalpha mRNA was found at significant levels in the lung from normal mice. This expression was increased by 65% (p<0.05) and 55% (p<0.05) in animals treated with fenofibrate and dexamethasone, respectively. In mice exposed to TNF-alpha or LPS, as well as in animals sensitized and challenged with OVA, that exhibited airway inflammation, PPARalpha mRNA was decreased by 60% (p<0.05), 43% (p<0.05) and 50% (p<0.05), respectively. In mice exposed to LPS, down-regulation of PPARalpha was maximal at 4h, whereas TNF-alpha production and cell infiltration peaked at 2 and 24h, respectively. In the lung of mice exposed to LPS or OVA and treated with fenofibrate or dexamethasone, PPARalpha down-regulation was suppressed, while airway inflammation was abolished. Our data showed that PPARalpha is constitutively expressed in mouse lung and down-regulated in response to TNF-alpha or upon acute or allergic airway inflammation. Fenofibrate and dexamethasone upregulated PPARalpha in normal lung and suppressed PPARalpha down-regulation associated with airway inflammation. Taken together, our data show that PPARalpha expression is inversely regulated with lung inflammation.

Plasma antioxidants in subjects before hematopoietic stem cell transplantation

Chemo-irradiation induced oxidative damage to vascular endothelium may contribute to pulmonary complications of hematopoietic stem cell transplantation (HSCT). We measured antioxidants, markers of oxidative stress and plasma antioxidant capacity in plasma or serum from 24 subjects at day 7 before HSCT and 20 control subjects. The plasma concentration of extracellular glutathione peroxidase (GPX-3) was significantly reduced in the HSCT subjects compared with controls (HSCT: 98+/-42 microg/ml, control: 169+/-56 microg/ml, P<0.0001). The concentration of gamma-tocopherol was significantly higher in the HSCT subjects compared with controls (HSCT: 207+/-103 microg/dl;

CONTROL

98+/-52 microg/dl; P=0.0002). The plasma concentrations of protein carbonyl, nitrotyrosine, malondialdehyde, alpha-tocopherol, vitamin A, homocysteine, cysteine and cysteinylglycine did not differ between HSCT and control subjects. Plasma from HSCT subjects was as effective as control plasma in quenching menadione-induced intracellular reactive oxygen species production in human microvascular endothelial cells. In summary, subjects before HSCT have significantly reduced plasma concentrations of GPX-3, elevated plasma gamma-tocopherol yet retains the ability to quench an acute oxidative stress. These changes may play a role in chronic oxidative stress in the HSCT population.

Peroxisome proliferator-activated receptor alpha (PPAR alpha) down-regulation in cystic fibrosis lymphocytes

Background

PPARs exhibit anti-inflammatory capacities and are potential modulators of the inflammatory response. We hypothesized that their expression and/or function may be altered in cystic fibrosis (CF), a disorder characterized by an excessive host inflammatory response.

Methods

PPARα, β and γ mRNA levels were measured in peripheral blood cells of CF patients and healthy subjects via RT-PCR. PPARα protein expression and subcellular localization was determined via western blot and immunofluorescence, respectively. The activity of PPARα was analyzed by gel shift assay.

Results

In lymphocytes, the expression of PPARα mRNA, but not of PPARβ, was reduced (-37%; p < 0.002) in CF patients compared with healthy persons and was therefore further analyzed. A similar reduction of PPARα was observed at protein level (-26%; p < 0.05). The transcription factor was mainly expressed in the cytosol of lymphocytes, with low expression in the nucleus. Moreover, DNA binding activity of the transcription factor was 36% less in lymphocytes of patients (p < 0.01). For PPARα and PPARβ mRNA expression in monocytes and neutrophils, no significant differences were observed between CF patients and healthy persons. In all cells, PPARγ mRNA levels were below the detection limit.

Conclusion

Lymphocytes are important regulators of the inflammatory response by releasing cytokines and antibodies. The diminished lymphocytic expression and activity of PPARα may therefore contribute to the inflammatory processes that are observed in CF.

Ingestion of a tea rich in catechins leads to a reduction in body fat and malondialdehyde-modified LDL in men

BACKGROUND

Catechins, the major component of green tea extract, have various physiologic effects. There are few studies, however, on the effects of catechins on body fat reduction in humans. It has been reported that the body mass index (BMI) correlates with the amount of malondialdehyde and thiobarbituric acid-reactive substances in the blood.

OBJECTIVE

We investigated the effect of catechins on body fat reduction and the relation between oxidized LDL and body fat variables.

DESIGN

After a 2-wk diet run-in period, healthy Japanese men were divided into 2 groups with similar BMI and waist circumference distributions. A 12-wk double-blind study was performed in which the subjects ingested 1 bottle oolong tea/d containing 690 mg catechins (green tea extract group; n = 17) or 1 bottle oolong tea/d containing 22 mg catechins (control group; n = 18).

RESULTS

Body weight, BMI, waist circumference, body fat mass, and subcutaneous fat area were significantly lower in the green tea extract group than in the control group. Changes in the concentrations of malondialdehyde-modified LDL were positively associated with changes in body fat mass and total fat area in the green tea extract group.

CONCLUSION

Daily consumption of tea containing 690 mg catechins for 12 wk reduced body fat, which suggests that the ingestion of catechins might be useful in the prevention and improvement of lifestyle-related diseases, mainly obesity.

Role of redox imbalance in the molecular mechanisms responsible for immunosenescence

The elderly suffer impairments to their immune system, evidenced by higher susceptibility to infections, cancer, and many diseases believed to be autoimmune in nature. A dysregulated overexpression of many proinflammatory cytokines also occurs with aging, as does the synthesis of enzymes that control expression of inflammatory lipid mediators and reactive oxygen species. An inappropriate activation of redox-controlled transcription factors, like nuclear factor-kappaB, occurs in many tissues from aged donors, and has been linked to excesses in cellular oxidative stress. Recently, the peroxisome proliferator-activated receptor-alpha (PPARalpha) has been evaluated for its effects on inflammatory and adaptive immune processes. PPARalpha provides redox-balancing influences on various lymphoid cell types and their inducible responses. We recently discovered that PPARalpha transiently suppresses the transcription of gamma-interferon (IFNgamma) by inhibiting the induction of T-bet. We now report that PPARalpha expression in CD4+ T cells is affected by the aging process. Lower PPARalpha levels are present in aged CD4+ T cells, and appear responsible for the suppressed interleukin-2 and exaggerated IFNgamma responses by these cells. Restoration of PPARalpha, T-bet, interleukin-2, and IFNgamma responses was found in T cells from aged animals supplemented with vitamin E, suggesting that interventions that focus on restoring redox balance might benefit the ailing aged immune system.

Increased reactive oxygen species production down-regulates peroxisome proliferator-activated alpha pathway in C2C12 skeletal muscle cells

Generation of reactive oxygen species may contribute to the pathogenesis of diseases involving intracellular lipid accumulation. To explore the mechanisms leading to these pathologies we tested the effects of etomoxir, an inhibitor of carnitine palmitoyltransferase I which contains a fatty acid-derived structure, in C2C12 skeletal muscle cells. Etomoxir treatment for 24 h resulted in a down-regulation of peroxisome proliferator-activated receptor alpha (PPARalpha) mRNA expression, achieving an 87% reduction at 80 microm etomoxir. The mRNA levels of most of the PPARalpha target genes studied were reduced at 100 microm etomoxir. By using several inhibitors of de novo ceramide synthesis and C(2)-ceramide we showed that they were not involved in the effects of etomoxir. Interestingly, the addition of triacsin C, a potent inhibitor of acyl-CoA synthetase, to etomoxir-treated C2C12 skeletal muscle cells did not prevent the down-regulation in PPARalpha mRNA levels, suggesting that the active form of the drug, etomoxir-CoA, was not involved. Given that saturated fatty acids may generate reactive oxygen species (ROS), we determined whether the addition of etomoxir resulted in ROS generation. Etomoxir increased ROS production and the activity of the well known redox transcription factor NF-kappaB. In the presence of the pyrrolidine dithiocarbamate, a potent antioxidant and inhibitor of NF-kappaB activity, etomoxir did not down-regulate PPARalpha mRNA in C2C12 skeletal muscle cells. These results indicate that ROS generation and NF-kappaB activation are responsible for the down-regulation of PPARalpha and may provide a new mechanism by which intracellular lipid accumulation occurs in skeletal muscle cells.

Enhanced induction of cytochrome P450 enzymes and CAR binding in TNF (p55(-/-)/p75(-/-)) double receptor knockout mice following phenobarbital treatment

Phenobarbital (PB) is a well characterized inducer of cytochrome P450 (P450) 2B and 3A subfamilies. Several proinflammatory cytokines have been shown to negatively modulate the induction of P450 by PB. In addition, PB is known to elicit an inflammatory mitogenic effect on the liver. To date, no studies have evaluated the PB induction profile of hepatic P450 in the absence of an intact tumor necrosis factor-alpha (TNFalpha) response. To test the hypothesis that endogenous TNFalpha signaling modulates hepatic P450 induction by PB in vivo, PB induction was examined in TNF (p55(-/-)/p75(-/-)) double receptor knockout mice (ko-TNF) and wild-type mice (wt-TNF). CYP2B- and CYP3A-associated activities and protein content were induced to a significantly greater extent (p < 0.05) in ko-TNF mice compared with wt-TNF mice. In parallel with enhanced CYP2B induction, an apparent elevation in the nuclear accumulation of the principal regulatory protein for transcription of CYP2B genes, the constitutively activated receptor (CAR), was detected in ko-TNF nuclear extracts following PB treatment. Additionally, nuclear factor kappa-B binding was induced by PB in wt-TNF mice, but not in ko-TNF mice, indicating that the hepatic inflammatory response following PB treatment differed between wt-TNF and ko-TNF mice. These data demonstrate that endogenous TNFalpha signaling modulates PB induction of hepatic CYP2B and CYP3A isoforms in vivo. Further, the data presented herein suggest that endogenous TNFalpha signaling influences PB induction of CYP2B through inhibition of CAR nuclear accumulation.

Transcriptional regulation of CYP2C9 gene. Role of glucocorticoid receptor and constitutive androstane receptor

Although cytochrome P450 2C9 (CYP2C9) is a major CYP expressed in the adult human liver, its mechanism of regulation is poorly known. In previous work, we have shown that CYP2C9 is inducible in primary human hepatocytes by xenobiotics including dexamethasone, rifampicin, and phenobarbital. The aim of this work was to investigate the molecular mechanism(s) controlling the inducible expression of CYP2C9. Deletional analysis of CYP2C9 regulatory region (+21 to -2088) in the presence of various hormone nuclear receptors suggested the presence of two functional response elements, a glucocorticoid receptor-responsive element (-1648/-1684) and a constitutive androstane receptor-responsive element (CAR, -1783/-1856). Each of these were characterized by co-transfection experiments, directed mutagenesis, gel shift assays, and response to specific antagonists RU486 and androstanol. By these experiments we located a glucocorticoid-responsive element imperfect palindrome at -1662/-1676, and a DR4 motif at -1803/-1818 recognized and transactivated by human glucocorticoid receptor and by hCAR and pregnane X receptor, respectively. Identification of these functional elements provides rational mechanistic basis for CYP2C9 induction by dexamethasone (submicromolar concentrations), and by phenobarbital and rifampicin, respectively. CYP2C9 appears therefore to be a primary glucocorticoid-responsive gene, which in addition, may be induced by xenobiotics through CAR/pregnane X receptor activation.

Cytochrome P450 and antioxidant activity in interleukin-6 knockout mice after induction of the acute-phase response

Hepatic cytochrome P450 (CYP) expression and antioxidant activity have been shown to decrease following endotoxin (lipopolysaccharide [LPS]) or proinflammatory cytokine administration. Using mice deficient in interleukin-6 (IL-6), the role of IL-6 in the regulation of hepatic CYP activity, glutathione (GSH) metabolism, and catalase (CAT) activity was analyzed after LPS administration. Administration of LPS produced comparable decreases in hepatic CYP3A activity in WT B6x129 (WT) mice and IL-6 knockout mice. No decrease was observed for CYP2D9 activity after LPS administration in either WT or IL-6 knockout mice. LPS administration significantly increased hepatic and renal CYP2E1 and CYP4A activity in WT mice, with no effect in IL-6 knockout mice. CYP2A12 activity increased in IL-6 knockout, mice with no change in WT mice after LPS administration. LPS administration had no significant effect on hepatic GSH reductase, GST peroxidase, GSH-S-transferase (GST), or total GSH in either WT or IL-6 knockout. However, hepatic CAT activity was significantly reduced in WT mice after LPS administration, with no effect in IL-6 knockout mice. These results support IL-6 as a critical mediator of the effects of LPS on specific hepatic and renal CYP activities and hepatic CAT activity.

Inflammation and interleukin-6 mediate reductions in the hepatic expression and transcription of the mdr1a and mdr1b Genes

In order to elucidate the mechanisms involved in the downregulation of mdr 1 gene expression reported in experimentally-induced inflammation, we examined the effects of experimentally-induced inflammation and interleukin-(IL-) 6 on transcriptional control of the mdr1 genes in rats. RNA, nuclear extracts, and nuclear protein fractions were isolated from livers harvested from saline or turpentine-treated male Sprague-Dawley rats or from IL-6 treated or nontreated (controls) cultured rat hepatocytes. mdr gene expression and regulation was examined by RT-PCR, mRNA stability studies, nuclear run-on analysis of transcription, and gel shift analysis of promoter-transcription factor interaction. As compared to controls, significantly lower levels of mdr1a and mdr1b mRNA and significantly decreased mdr1a and mdr1b transcription rates were observed in livers isolated from the turpentine-treated rats. In vitro treatments of cultured hepatocytes with IL-6 also suppressed mdr1a and mdr1b mRNA expression and imposed similar reductions in mdr1a and mdr1b transcriptional activity. Significant effects of IL-6 on mdr1 mRNA stability were not seen. Our results indicate that reductions in mdr1 expression in experimental models of inflammation likely occurs through altered gene transcription. Furthermore, as IL-6 was found to decrease mdr1 expression and gene transcription rates in vitro, this cytokine is likely involved in the reduction of mdr1 expression that is seen in vivo during an acute inflammatory response.

Cytochrome P450 inactivation by serum from humans with a viral infection and serum from rabbits with a turpentine-induced inflammation: the role of cytokines

Serum from humans with an acute upper respiratory viral infection and from rabbits with turpentine-induced inflammation reduce the catalytic activity of hepatic cytochrome P450 (P450). The aim of this study was to identify the serum mediators responsible for the decrease in P450 activity. Rabbit and human sera were fractionated by size exclusion chromatography and the fractions tested for their ability to reduce the activity and amount of P450 after 4 h of incubation with hepatocytes from turpentine-treated rabbits (H(INF)). Rabbit and human sera decreased P450 activity by around 40% without any change in the amount of CYP1A1 and 1A2 apoproteins. In rabbit serum, the fraction containing proteins of M(r) 23-15 kDa decreased P450 content by 41%, but did not alter the amount of the apoproteins. Anti-IL-6 antibody added to the M(r) 23-15 kDa fraction restored P450 content to 97% of control values, while anti-IL-1beta, TNF-alpha and IFN-gamma antibodies had no effect. Supporting the role of IL-6, incubation of H(INF) in the presence of IL-6 for 4 h reduced P450 content by 40%. In human serum, the fraction containing proteins of M(r) >95 kDa lowered P450 content by 43% without modifying the amounts of CYP1A1/2. Neutralization experiments showed that IFN-gamma, IL-6, and IL-1beta contributed to the decrease in P450 content. In conclusion, the present results demonstrate that IL-6, and IFN-gamma, IL-6 and IL-1beta are the serum mediators released in vivo by a turpentine-induced inflammatory reaction in the rabbit and an upper respiratory viral infection in humans, respectively, inactivating hepatic P450.

15-Deoxy-Delta(12,14)-prostaglandin J(2), a ligand for peroxisome proliferator-activated receptor-gamma, induces apoptosis in JEG3 choriocarcinoma cells

Apoptosis has been described in placental (trophoblast) tissues during both normal and abnormal pregnancies. We have studied the effects of the cyclopentenone prostaglandins (PGs) on trophoblast cell death using JEG3 choriocarcinoma cells. PGJ(2), Delta(12)PGJ(2), and 15-deoxy-Delta(12,14)-PGJ(2) (15dPGJ(2)) (10 microM) significantly reduced mitochondrial activity (MTT assay) over 16 h by 17.4 +/- 4.7%, 28 +/- 9.3%, and 62.5 +/- 2.8%, respectively (mean +/- sem), while PGA(2) and PGD(2) had no effect. The synthetic PPAR-gamma ligand ciglitizone (12.5 microM) had a potency similar to 15dPGJ(2) (69 +/- 3% reduction). Morphological examination of cultures treated with PGJ(2) and its derivatives revealed the presence of numerous cells with dense, pyknotic nuclei, a hallmark of apoptosis. FACS analysis revealed an abundance (approximately 40%) of apoptotic cells after 16-h treatment with 15dPGJ(2) (10 microM). The caspase inhibitor ZVAD-fmk (5 microM) significantly diminished the apoptotic effects of Delta(12)PGJ(2) and 15dPGJ(2). JEG3 cells expressed PPAR-gamma mRNA by Northern analysis. These novel findings imply a role for PPAR-gamma ligands in various processes associated with pregnancy and parturition.

P450 gene induction by structurally diverse xenochemicals: central role of nuclear receptors CAR, PXR, and PPAR

The biochemistry of foreign compound metabolism and the roles played by individual cytochrome P450 (CYP) enzymes in drug metabolism and in the toxification and detoxification of xenochemicals prevalent in the environment are important areas of molecular pharmacology and toxicology that have been widely studied over the past decade. Important advances in our understanding of the mechanisms through which foreign chemicals impact on these P450-dependent metabolic processes have been made during the past 2 years with several key discoveries relating to the mechanisms through which xenochemicals induce the expression of hepatic P450 enzymes. Roles for three "orphan" nuclear receptor superfamily members, designated CAR, PXR, and PPAR, in respectively mediating the induction of hepatic P450s belonging to families CYP2, CYP3, and CYP4 in response to the prototypical inducers phenobarbital (CAR), pregnenolone 16alpha-carbonitrile and rifampicin (PXR), and clofibric acid (PPAR) have now been established. Two other nuclear receptors, designated LXR and FXR, which are respectively activated by oxysterols and bile acids, also play a role in liver P450 expression, in this case regulation of P450 cholesterol 7alpha-hydroxylase, a key enzyme of bile acid biosynthesis. All five P450-regulatory nuclear receptors belong to the same nuclear receptor gene family (family NR1), share a common heterodimerization partner, retinoid X-receptor (RXR), and are subject to cross-talk interactions with other nuclear receptors and with a broad range of other intracellular signaling pathways, including those activated by certain cytokines and growth factors. Endogenous ligands of each of those nuclear receptors have been identified and physiological receptor functions are emerging, leading to the proposal that these receptors may primarily serve to modulate hepatic P450 activity in response to endogenous dietary or hormonal stimuli. Accordingly, P450 induction by xenobiotics may in some cases lead to a perturbation of endogenous regulatory circuits with associated pathophysiological consequences.

Pharmacodynamics and toxicodynamics of drug action: signaling in cell survival and cell death

In therapeutic response to drugs, the plasma concentration range leads to the establishment of a safe and effective dosage regimen. Our hypothesis is that by studying drug concentration-dependent effect on signal transduction mechanisms, a better understanding of the beneficial pharmacodynamic and adverse toxicodynamic responses elicited by the drug may be achieved. Using two classes of chemopreventive compounds (phenolic antioxidants and isothiocyanates), we illustrate the potential utility of two signal transduction pathways elicited by these agents to predict the pharmacodynamic effect (induction of Phase II drug metabolizing enzymes) and the potential toxicodynamic response (stimulation of caspase activity and cytotoxic cell death). At lower concentration, phenolic antioxidants and isothiocyanates activate mitogen-activated protein kinase (MAPK; extracellular signal-regulated protein kinase 2, ERK2; and c-Jun N-terminal kinase 1, JNK1) in a concentration-and time-dependent manner. The activation of MAPK by these compounds may lead to the induction of cell survival/protection genes such as c-jun, c-fos, or Phase II drug metabolizing enzymes. However, at higher concentrations, these agents activate another signaling molecule, ICE/Ced3 cysteine protease enzymes (caspases) leading to apoptotic cell death. The activation of these pathways may dictate the fate of the cells/tissues upon exposure to drugs or chemicals. At lower concentrations, these compounds activate MAPK leading to the induction of Phase II genes, which may protect the cells/tissues against toxic insults and therefore may enhance cell survival. On the other hand, at higher concentrations, these agents may activate the caspases, which may lead to apoptotic cell death, and have toxicity. Understanding the activation of these and other signal transduction events elicited by various drugs and chemicals may yield insights into the regulation of gene expression of drug metabolizing enzymes and cytotoxicity. Thus, the study of signaling events in cell survival (hemeostasis) and cell death (cytotoxicity) may have practical application during pharmaceutical drug development.

Peroxisome proliferator-activated receptor alpha activation modulates cellular redox status, represses nuclear factor-kappaB signaling, and reduces inflammatory cytokine production in aging

In aged mice, the redox-regulated transcription factor nuclear factor-kappaB (NF-kappaB) becomes constitutively active in many tissues, as well as in cells of the hematopoietic system. This oxidative stress-induced activity promotes the production of a number of pro-inflammatory cytokines, which can contribute to the pathology of many disease states associated with aging. The administration to aged mice of agents capable of activating the alpha isoform of the peroxisome proliferator-activated receptor (PPARalpha) was found to restore the cellular redox balance, evidenced by a lowering of tissue lipid peroxidation, an elimination of constitutively active NF-kappaB, and a loss in spontaneous inflammatory cytokine production. Aged animals bearing a null mutation in PPARalpha failed to elicit these changes following treatment with PPARalpha activators, but remained responsive to vitamin E supplementation. Aged C57BL/6 mice were found to express reduced transcript levels of PPARalpha and the peroxisome-associated genes acyl-CoA oxidase and catalase. Supplementation of these aged mice with PPARalpha activators or with vitamin E caused elevations in these transcripts to levels seen in young animals. Our results suggest that PPARalpha and the genes under its control play a role in the evolution of oxidative stress excesses observed in aging.