Absence of nuclear factor kappaB inhibition by NSAIDs in hepatocytes

The inhibition of NFкB signaling and inflammatory response as a strategy for blunting bile acid-induced hepatic and renal toxicity

The cholestatic liver injury could occur in response to a variety of diseases or xenobiotics. Although cholestasis primarily affects liver function, it has been well-known that other organs such as the kidney could be influenced in cholestatic patients. Severe cholestasis could lead to tissue fibrosis and organ failure. Unfortunately, there is no specific therapeutic option against cholestasis-induced organ injury. Hence, finding the mechanism of organ injury during cholestasis could lead to therapeutic options against this complication. The accumulation of potentially cytotoxic compounds such as hydrophobic bile acids is the most suspected mechanism involved in the pathogenesis of cholestasis-induced organ injury. A plethora of evidence indicates a role for the inflammatory response in the pathogenesis of several human diseases. Here, the role of nuclear factor-kB (NFkB)-mediated inflammatory response is investigated in an animal model of cholestasis. Bile duct ligated (BDL) animals were treated with sulfasalazine (SSLZ, 10 and 100 mg/kg, i.p) as a potent inhibitor of NFkB signaling. The NFkB proteins family activity in the liver and kidney, serum and tissue levels of pro-inflammatory cytokines, tissue biomarkers of oxidative stress, serum markers of organ injury, and the liver and kidney histopathological alterations and fibrotic changes. The oxidative stress-mediated inflammatory-related indices were monitored in the kidney and liver at scheduled time intervals (3, 7, and 14 days after BDL operation). Significant increase in serum and urine markers of organ injury, besides changes in biomarkers of oxidative stress and tissue histopathology, were evident in the liver and kidney of BDL animals. The activity of NFkB proteins (p65, p50, p52, c-Rel, and RelB) was significantly increased in the liver and kidney of cholestatic animals. Serum and tissue levels of pro-inflammatory cytokines (IL-1β, IL-2, IL-6, IL-7, IL-12, IL-17, IL-18, IL-23, TNF-α, and INF-γ) were also higher than sham-operated animals. Moreover, TGF- β, α-SMA, and tissue fibrosis (Trichrome stain) were evident in cholestatic animals' liver and kidneys. It was found that SSLZ (10 and 100 mg/kg/day, i.p) alleviated cholestasis-induced hepatic and renal injury. The effect of SSLZ on NFkB signaling and suppression of pro-inflammatory cytokines could play a significant role in its protective role in cholestasis. Based on these data, NFkB signaling could receive special attention to develop therapeutic options to blunt cholestasis-induced organ injury.

Evidence for the Involvement of the Master Transcription Factor NF-κB in Cancer Initiation and Progression

Nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) is responsible for the regulation of a large number of genes that are involved in important physiological processes, including survival, inflammation, and immune responses. At the same time, this transcription factor can control the expression of a plethora of genes that promote tumor cell proliferation, survival, metastasis, inflammation, invasion, and angiogenesis. The aberrant activation of this transcription factor has been observed in several types of cancer and is known to contribute to aggressive tumor growth and resistance to therapeutic treatment. Although NF-κB has been identified to be a major contributor to cancer initiation and development, there is evidence revealing its role in tumor suppression. This review briefly highlights the major mechanisms of NF-κB activation, the role of NF-κB in tumor promotion and suppression, as well as a few important pharmacological strategies that have been developed to modulate NF-κB function.

20-Hydroxyeicosatetraenoic acid inhibits ATP-induced COX-2 expression via peroxisome proliferator activator receptor-α in vascular smooth muscle cells

BACKGROUND AND PURPOSE

20-Hydroxyeicosatetraenoic acid (20-HETE), formed from arachidonate by cytochrome P450, regulates vascular smooth muscle cell (VSMC) function. Because 20-HETE may activate peroxisome proliferator activator receptors (PPARs) and may participate in inflammatory responses, we asked whether 20-HETE may inhibit cyclooxygenase 2 (COX-2) expression by activating PPARs in VSMC.

EXPERIMENTAL APPROACH

Quiescent neonatal VSMC (R22D cell line), were incubated with 20-HETE, synthetic ligands of PPARs, or inhibitors of the extracellular signal regulated kinase (ERK1/2), c-jun N-terminal kinase and the transcription factor activated protein-1 before adding ATPγS. mRNA and protein expression of COX-2 and the promoter luciferase activity of COX-2 and PPAR response element were determined.

KEY RESULTS

Pretreatment with 20-HETE (5-10 µM) significantly inhibited ATPγS-induced COX-2 mRNA and protein expression in VSMC. The inhibitory effect of 20-HETE on COX-2 expression was mimicked by WY14643, a PPARα ligand and inhibited by MK886, a PPARα inhibitor or by transfection of shRNA for PPARα. Both 20-HETE and WY14643 significantly increased the PPAR-response element luciferase activity. Furthermore, ATPγS-induced activation of the COX-2 promoter containing the activated protein-1 site was also inhibited by pretreatment with 20-HETE, which was reversed by MK886 or by transfection with shRNA for PPARα.

CONCLUSIONS AND IMPLICATIONS

The PPARα may mediate the inhibitory effects of 20-HETE on COX-2 expression through a negative cross-talk between PPARα and the COX-2 promoter.

Acetylsalicylic acid-induced oxidative stress, cell cycle arrest, apoptosis and mitochondrial dysfunction in human hepatoma HepG2 cells

It is widely accepted that non-steroidal anti-inflammatory drugs (NSAIDs), including aspirin, reduce the risk of cancer. The anti-cancer and anti-inflammatory effects of NSAIDs are associated with the inhibition of prostaglandin synthesis and cyclooxygenase-2 activity. Several other mechanisms which contribute to the anti-cancer effect of these drugs in different cancer models both in vivo and in vitro are also presumed to be involved. The precise molecular mechanism, however, is still not clear. We investigated, therefore, the effects of acetylsalicylic acid (ASA, aspirin) on multiple cellular and functional targets, including mitochondrial bioenergetics, using human hepatoma HepG2 cancer cells in culture. Our results demonstrate that ASA induced G0/G1 cell cycle arrest and apoptosis in HepG2 cells. ASA increased the production of reactive oxygen species, reduced the cellular glutathione (GSH) pool and inhibited the activities of the mitochondrial respiratory enzyme complexes, NADH-ubiquinone oxidoreductase (complex I), cytochrome c oxidase (complex IV) and the mitochondrial matrix enzyme, aconitase. Apoptosis was triggered by alteration in mitochondrial permeability transition, inhibition of ATP synthesis, decreased expression of the anti-apoptotic protein Bcl-2, release of cytochrome c and activation of pro-apoptotic caspase-3 and the DNA repairing enzyme, poly (-ADP-ribose) polymerase (PARP). These findings strongly suggest that ASA-induced toxicity in human hepatoma HepG2 cells is mediated by increased metabolic and oxidative stress, accompanied by mitochondrial dysfunction which result in apoptosis.

Eriocalyxin B inhibits nuclear factor-kappaB activation by interfering with the binding of both p65 and p50 to the response element in a noncompetitive manner

Nuclear factor-kappaB (NF-kappaB) has been recognized to play a critical role in cell survival and inflammatory processes. It has become a target for intense drug development for the treatment of cancer, inflammatory, and autoimmune diseases. Here, we describe a potent NF-kappaB inhibitor, eriocalyxin B (Eri-B), an ent-kauranoid isolated from Isodon eriocalyx, an anti-inflammatory remedy. The presence of two alpha,beta-unsaturated ketones give this compound the uniqueness among the ent-kauranoids tested. Eri-B inhibited the NF-kappaB transcriptional activity but not that of cAMP response element-binding protein. It suppressed the transcription of NF-kappaB downstream gene products including cyclooxygenase-2 and inducible nitric-oxide synthase induced by tumor necrosis factor-alpha or lipopolysaccharide in macrophages and hepatocarcinoma cells. Chromatin immunoprecipitation assay indicated that Eri-B selectively blocked the binding between NF-kappaB and the response elements in vivo without affecting the nuclear translocation of the transcription factor. Down-regulation of the endogenous p65 protein sensitized the cells toward the action of the compound. Furthermore, in vitro binding assays suggested that Eri-B reversibly interfered with the binding of p65 and p50 subunits to the DNA in a noncompetitive manner. In summary, this study reveals the novel action of a potent NF-kappaB inhibitor that could be potentially used for the treatment of a variety of NF-kappaB-associated diseases. Modification of the structure of this class of compounds becomes the key to the control of the behavior of the compound against different cellular signaling pathways.

Dual effects of acetylsalicylic acid on mast cell degranulation, expression of cyclooxygenase-2 and release of pro-inflammatory cytokines

Several studies have demonstrated that nonsteroidal anti-inflammatory drugs, such as acetylsalicylic acid (ASA), can have inhibitory or enhancing effects on inflammatory cell function. These effects seem independent of cyclooxygenase activity and prostaglandin synthesis inhibition. Here, we examined the effect of ASA on bone marrow-derived mast cells in more detail. ASA blocked the expression of cyclooxygenase-2, the production of tumor necrosis factor-alpha and interleukin-6, and the release of granule mediators from mast cells in a concentration-dependent fashion. Concomitantly, ASA inhibited nuclear factor (NF)-kappaB activity, as well as the phosphorylation and breakdown of the inhibitory protein IkappaB-alpha. We thus propose that the anti-inflammatory effects of ASA in mast cells are due to suppression of IkappaB kinase activity, thereby inhibiting subsequent phosphorylation and degradation of IkappaB-alpha, activation of NF-kappaB, and transcription of proinflammatory cytokines. The inhibition of BMMC degranulation was independent of NF-kappaB activation, however. Interestingly, the expression of cyclooxygenase-2 was not inhibited at 1mM ASA, but was even enhanced significantly. The latter might contribute to the adverse effects of ASA in ASA-sensitive asthmatics.

Nonsteroidal anti-inflammatory agents differ in their ability to suppress NF-kappaB activation, inhibition of expression of cyclooxygenase-2 and cyclin D1, and abrogation of tumor cell proliferation

Nonsteroidal anti-inflammatory drugs (NSAIDs) such as aspirin have been shown to suppress transcription factor NF-kappaB, which controls the expression of genes such as cyclooxygenase (COX)-2 and cyclin D1, leading to inhibition of proliferation of tumor cells. There is no systematic study as to how these drugs differ in their ability to suppress NF-kappaB activation and NF-kappaB-regulated gene expression or cell proliferation. In the present study, we investigated the effect of almost a dozen different commonly used NSAIDs on tumor necrosis factor (TNF)-induced NF-kappaB activation and NF-kappaB-regulated gene products, and on cell proliferation. Dexamethasone, an anti-inflammatory steroid, was included for comparison with NSAIDs. As indicated by DNA binding, none of the drugs alone activated NF-kappaB. All compounds inhibited TNF-induced NF-kappaB activation, but with highly variable efficacy. The 50% inhibitory concentration required was 5.67, 3.49, 3.03, 1.25, 0.94, 0.60, 0.38, 0.084, 0.043, 0.027, 0.024, and 0.010 mM for aspirin, ibuprofen, sulindac, phenylbutazone, naproxen, indomethacin, diclofenac, resveratrol, curcumin, dexamethasone, celecoxib, and tamoxifen, respectively. All drugs inhibited IkappaBalpha kinase and suppressed IkappaBalpha degradation and NF-kappaB-regulated reporter gene expression. They also suppressed NF-kappaB-regulated COX-2 and cyclin D1 protein expression in a dose-dependent manner. All compounds inhibited the proliferation of tumor cells, with 50% inhibitory concentrations of 6.09, 1.12, 0.65, 0.49, 1.01, 0.19, 0.36, 0.012, 0.016, 0.047, 0.013, and 0.008 mM for aspirin, ibuprofen, sulindac, phenylbutazone, naproxen, indomethacin, diclofenac, resveratrol, curcumin, dexamethasone, celecoxib, and tamoxifen, respectively. Overall these results indicate that aspirin and ibuprofen are least potent, while resveratrol, curcumin, celecoxib, and tamoxifen are the most potent anti-inflammatory and antiproliferative agents of those we studied.

Anti-angiogenic therapy in breast cancer

Breast cancer is a worldwide epidemic among women, and one of the most rapidly increasing cancers. Not only the incidence rate but also the death rate is increasing. Despite enthusiastic efforts in early diagnosis, aggressive surgical treatment and application of additional non-operative modalities, its prognosis is still dismal. This emphasizes the necessity to develop new measures and strategies for its prevention. The understanding of the biology of angiogenesis is improving rapidly, offering the hope for more specific vascular targeting of tumor neovasculature. Anti-angiogenic therapy is a promising, relatively new form of cancer treatment using drugs called angiogenesis inhibitors that specifically inhibit new blood vessel growth. Extensive studies conducted over the past few years have recognized that overexpression of COX-2, VEGF in the cancer might be the leading factors, can induce angiogenesis via induction of multiple pro-angiogenic regulators. Breast tumor growth and metastasization are both hormone-sensitive and angiogenesis-dependent. A single angiogenic inhibitor is not capable to inhibit angiogenesis. Therefore, we should select a combination of angiogenesis inhibitors targeting COX-2, VEGF, and bFGF pathway. This article reviews the background and implementation of the current use of angiogenesis inhibitors and discusses the likely therapeutic roles in the early and advanced breast cancer together with its potential for chemoprevention.

Arachidonic acid activates a functional AP-1 and an inactive NF-kappaB complex in human HepG2 hepatoma cells

Exogenous arachidonic acid (AA) has been shown to induce the antioxidant manganese superoxide dismutase gene by reactive oxygen species (ROS) derived from AA metabolism and the participation of the p38 mitogen-activated protein kinase (MAPK) pathway in human HepG2 hepatoma cells. The goal of this study was to investigate the effect of AA on the activation of the two redox-sensitive transcription factors AP-1 and NF-kappaB in HepG2 cells. Using electrophoretic mobility shift assays, DNA-binding activities of AP-1 and NF-kappaB were markedly increased in AA-treated HepG2 cells. The c-Jun and c-Fos proteins were identified as components of the AA-induced AP-1 complex and their levels were increased. AA-activated NF-kappaB complex was constituted as a p50 homodimer resulting in a nuclear translocation for this protein only. Moreover, no degradation of IkappaBalpha was observed. These results were contrasted to the interleukin-1beta-activated p50/p65 complex used as a positive control. Using 5,8,11,14-eicosatetraynoic acid and inhibitors of AA metabolism, AP-1 and NF-kappaB activation required the lipoxygenase/cytochrome P450 monooxygenase pathways. In addition, antioxidants inhibited the AA-induced AP-1 and NF-kappaB activation, suggesting a role of ROS released from the AA metabolism. In reporter gene assays, AA induced the transcriptional activity of AP-1 but not that of NF-kappaB. Further investigations showed that the AA-induced transcriptional activity of AP-1 was regulated by protein kinase C and p38 MAPK pathways. These results suggest that the functional AP-1 activated by AA and coupled to that of p38 MAPK pathway may play an important role in response to ROS induced by AA metabolism in HepG2 cells without the involvement of the NF-kappaB pathway.

Cyclooxygenase-2 (COX-2) inhibitors sensitize tumor cells specifically to death receptor-induced apoptosis independently of COX-2 inhibition

Cyclooxygenase-2 (COX-2) is involved in diverse processes such as inflammation, carcinogenesis and apoptosis. As COX-2 inhibitors interfere with these processes, inhibition of COX-2 has been suggested as a promising anticancer treatment. However, the role of COX-2 in modulation of apoptosis as well as the death pathways affected by COX-2 inhibitors are poorly characterized. Here we demonstrate that the selective COX-2 inhibitors NS-398 and nimesulide increased TNF sensitivity of TNF-resistant HeLa H21 and TNF-sensitive HeLa D98 cells, although this cytokine induced significant COX-2 activity, as judged by prostaglandin E(2) (PGE(2)) production, only in H21 cells. TNF did also not induce PGE(2) production in MCF-7/casp-3 cells stably expressing COX-2; however, nimesulide strongly enhanced TNF-induced apoptosis in these cells. Furthermore, COX-2 activity in HeLa H21 cells could be inhibited by NS-398 concentrations that were 10 000-fold lower compared to those required for the induction of cell death. Most intriguingly, sensibilization to apoptosis was specifically observed in response to activation of death receptors. Not only TNF-induced cell death but also apoptosis triggered by the CD95 and TRAIL receptors was enhanced by nimesulide. In contrast, apoptosis induced by the anticancer drugs doxorubicine and etoposide that target the mitochondrial death pathway remained unaffected. Together, our data suggest that COX-2 inhibitors overcome apoptosis resistance and selectively sensitize tumor cells to the extrinsic death receptor-induced apoptotic pathway independently of COX-2.

PPARdelta activation induces COX-2 gene expression and cell proliferation in human hepatocellular carcinoma cells

Cyclooxygenase-2 (COX-2) has been suggested to be associated with carcinogenesis. Recently, many studies have shown increased expression of COX-2 in a variety of human malignancies, including hepatocellular carcinoma (HCC). Therefore, it becomes important to know more about what determines COX-2 expression. In this work, we have studied the effect of PPARdelta activation on COX-2 expression using a selective agonist (GW501516) in human hepatocellular carcinoma (HepG2) cells. Activation of PPARdelta resulted in increased COX-2 mRNA and protein expression. The mechanism behind the induction seems to be increased activity of the proximal promoter of the COX-2 gene, spanning nucleotides -327 to +59. The increased COX-2 protein expression and promoter activity induced by the GW501516 was also confirmed in the monocytic cell line THP-1. Induced levels of COX-2 have previously been associated with resistance to apoptosis and increased cell proliferation in many cell types. In HepG2 cells, we observed a dose-dependent increase in cell number by GW501516 treatment for 72h. The levels of PCNA, used as an indicator of cell division were induced, and the cell survival promoting complex p65 (NF-kappaB) was phosphorylated under GW501516 treatment. We conclude that PPARdelta activation in HepG2 cells results in induced COX-2 expression and increased cellular proliferation. These results may suggest that PPARdelta plays an important role in the development of HCC by modulating expression of COX-2.

Induction of hepatic heme oxygenase-1 by diclofenac in rodents: role of oxidative stress and cytochrome P-450 activity

BACKGROUND/AIMS

The role of oxidative stress in diclofenac hepatotoxicity is still not clear. This study examined whether the drug induced heme oxygenase-1 (HO-1), a stress protein.

METHODS

HO-1 mRNA and HO activity were measured in mouse liver and in rat hepatocytes after treatment with diclofenac parallel to release of serum alanine aminotransferase (ALT) and sorbitol dehydrogenase (SDH) as a marker of hepatic damage.

RESULTS

HO-1 was transcriptionally and dose-dependently induced by diclofenac in mouse liver and rat hepatocytes. HO-1 mRNA, ALT and SDH peaked at the same time. Mechanistic studies revealed that the drug synergized with buthionine sulfoximine (BSO) in lowering hepatic glutathione, increased the formation of reactive oxygen intermediates and activated NF-kappaB and AP-1 in rat hepatocytes. HO-1 induction and hepatic damage were increased by BSO and only HO-1 induction was attenuated by the antioxidant N-acetylcysteine. HO-1 induction was also reduced by the cytochrome P-450 inhibitors ketoconazole and tranylcypromine, concomitantly with a significant decrease in the formation of diclofenac oxidative metabolites, which may give rise to reactive compounds.

CONCLUSIONS

Acute treatment with diclofenac induces HO-1 in rodent hepatocytes. Induction is influenced by changes in the cellular redox states and by cytochrome P-450 activity and gives a new insight into the response of the liver to diclofenac.

Haem oxygenase 1 gene induction by glucose deprivation is mediated by reactive oxygen species via the mitochondrial electron-transport chain

Glucose depletion results in cellular stress and reactive oxygen species (ROS) production, which evokes adaptive and protective responses. One such protective response is the induction of haem oxygenase 1 (HO-1), which catalyses the rate-limiting step in haem degradation, liberating iron, CO and biliverdin. The present study evaluated the role of ROS and the mitochondrial electron-transport chain in the induction of HO-1 by glucose deprivation in HepG2 hepatoma cells. Either N-acetylcysteine, an antioxidant, or deferoxamine, an iron chelator, resulted in a dose-dependent inhibition of HO-1 mRNA and protein induction during glucose deprivation, suggesting a redox- and iron-dependent mechanism. Inhibitors of electron-transport chain complex III, antimycin A and myxothiazol, the ATP synthase inhibitor oligomycin and ATP depletion with 2-deoxyglucose or glucosamine also blocked HO-1 induction. To address the involvement of ROS further, specifically H(2)O(2), we showed that overexpression of catalase completely blocked HO-1 activation by glucose deprivation. In contrast, inhibition of nuclear factor kappa B, mitogen-activated protein kinase (MAPK), protein kinase A, protein kinase C, phosphoinositide 3-kinase, cyclo-oxygenase or cytosolic phospholipase A(2), did not prevent HO-1 induction. These results demonstrate that activation of the HO-1 gene by glucose deprivation is mediated by a 'glucose metabolic response' pathway via generation of ROS and that the pathway requires a functional electron-transport chain.

Selective inhibitors of cyclooxygenase-2 delay the activation of nuclear factor kappa B and attenuate the expression of inflammatory genes in murine macrophages treated with lipopolysaccharide

The effect of rofecoxib, a selective cyclooxygenase-2 inhibitor, on inflammatory signaling has been investigated in elicited murine peritoneal macrophages. Macrophages treated with 10 microM rofecoxib exhibited an important inhibition in the early activation of nuclear factor kappa B (NF-kappa B) and the mitogen-activated protein kinase p38, the extracellular-regulated kinase p44, and the c-Jun N-terminal kinase. Moreover, this drug decreased the protein levels of nitric-oxide synthase-2 and cyclooxygenase-2 in lipopolysaccharide (LPS)-treated macrophages. Rofecoxib delayed and attenuated NF-kappa B activation, which impaired significantly the expression of kappa B-dependent genes. This drug and related coxibs did not affect cell viability and protected against LPS-induced apoptosis through the impairment of the inflammatory response. These data show an additional anti-inflammatory mechanism of selective cyclooxygenase-2 inhibitors through the attenuation of macrophage activation.