Enhanced DNA binding and activation of transcription factors NF-kappa B and AP-1 by acetaldehyde in HEPG2 cells

Clostridium perfringens phospholipase C induced ROS production and cytotoxicity require PKC, MEK1 and NFκB activation

Clostridium perfringens phospholipase C (CpPLC), also called α-toxin, is the most toxic extracellular enzyme produced by this bacteria and is essential for virulence in gas gangrene. At lytic concentrations, CpPLC causes membrane disruption, whereas at sublytic concentrations this toxin causes oxidative stress and activates the MEK/ERK pathway, which contributes to its cytotoxic and myotoxic effects. In the present work, the role of PKC, ERK 1/2 and NFκB signalling pathways in ROS generation induced by CpPLC and their contribution to CpPLC-induced cytotoxicity was evaluated. The results demonstrate that CpPLC induces ROS production through PKC, MEK/ERK and NFκB pathways, the latter being activated by the MEK/ERK signalling cascade. Inhibition of either of these signalling pathways prevents CpPLC's cytotoxic effect. In addition, it was demonstrated that NFκB inhibition leads to a significant reduction in the myotoxicity induced by intramuscular injection of CpPLC in mice. Understanding the role of these signalling pathways could lead towards developing rational therapeutic strategies aimed to reduce cell death during a clostridialmyonecrosis.

Regulation of cytochrome P450 4F11 by nuclear transcription factor-κB

Although the mechanisms that regulate CYP4F genes have been and are currently being studied in a number of laboratories, the specific mechanisms for the regulation of these genes are not yet fully understood. This study shows that nuclear factor κB of the light-chain-enhancer in activated B cells (NF-κB) can inhibit CYP4F11 expression in human liver carcinoma cell line (HepG2) as summarized below. Tumor necrosis factor-α (TNF-α), a proinflammatory cytokine, has been shown to activate NF-κB signaling while also activating the c-Jun NH(2)-terminal kinase (JNK) signaling pathway. Other studies have reported that JNK signaling can up-regulate CYP4F11 expression. The results of this study demonstrate that in the presence of TNF-α and the specific NF-κB translocation inhibitor N-[3,5-bis(trifluoromethyl)phenyl]-5-chloro-2-hydroxybenzamide (IMD-0354), there is a greater increase in CYP4F11 expression than that elicited by TNF-α alone, indicating that NF-κB plays an inhibitory role. Moreover, NF-κB stimulation by overexpression of mitogen-activated protein kinase kinase kinase inhibited CYP4F11 promoter expression. CYP4F11 promoter inhibition can also be rescued in the presence of TNF-α when p65, a NF-κB protein, is knocked down. Thus, NF-κB signaling pathways negatively regulate the CYP4F11 gene.

Effects of Feiyanning Decoction on proliferation of lung adenocarcinoma cell line and their production of interleukin-6 and interleukin-8 induced by tumor necrosis factor-alpha

OBJECTIVE

To study the effects of Feiyanning Decoction, a compound traditional Chinese herbal medicine, on proliferation of lung adenocarcinoma cell line A549 cells and their production of interleukin-6 (IL-6) and IL-8 induced by tumor necrosis factor-alpha (TNF-alpha).

METHODS

A549 cells were incubated with rat serum containing Feiyanning Decoction at 15% for 24, 48 and 72 h respectively. The cell proliferation was examined by 2-(2-methoxy-4-nitrophenyl)-3-(4-nitrophenyl)-5-(2, 4-disulfophenyl)-2H-tetrazolium, monosodium salt assay (WST-8). The production of IL-6 and IL-8 was tested by enzyme-linked immunosorbent assay after 48-hour treatment of reagents, and the expressions of IL-6 and IL-8 mRNAs were detected by reverse transcription-polymerase chain reaction.

RESULTS

Serum containing Feiyanning Decoction had obvious inhibitive functions in A549 cell proliferation after 48- and 72-treatment. TNF-alpha (1 microg/L) strongly induced the production of IL-6 and IL-8 as compared with the control serum in A549 cells, and the induced cytokine production was significantly suppressed by 15% serum containing Feiyanning Decoction (P<0.01). In addition, serum containing Feiyanning Decoction could inhibit the mRNA expressions of IL-6 and IL-8 (P<0.01).

CONCLUSION

Feiyanning Decoction can inhibit IL-6 and IL-8 production induced by TNF-alpha. It is therefore expected to be a new strategy for treating lung cancer.

Hepatocyte growth factor protects hepatocytes against oxidative injury induced by ethanol metabolism

Hepatocyte growth factor (HGF) is involved in many cellular responses, such as mitogenesis and apoptosis protection; however, its effect against oxidative injury induced by ethanol metabolism is not well understood. The aim of this work was to address the mechanism of HGF-induced protection against ethanol-generated oxidative stress damage in the human cell line VL-17A (cytochrome P450 2E1/alcohol dehydrogenase-transfected HepG2 cells). Cells were pretreated with 50 ng/ml HGF for 12 h and then treated with 100 mM ethanol for 0-48 h. Some parameters of oxidative damage were evaluated. We found that ethanol induced peroxide formation (3.3-fold) and oxidative damage as judged by lipid peroxidation (5.4-fold). Damage was prevented by HGF. To address the mechanisms of HGF-induced protection we investigated the cellular antioxidant system. We found that HGF increased the GSH/GSSG ratio, as well as SOD1, catalase, and gamma-glutamylcysteine synthetase expression. To explore the signaling pathways involved in this process, VL-17A cells were pretreated with inhibitors against PI3K, Akt, and NF-kappaB. We found that all treatments decreased the expression of the antioxidant enzymes, thus abrogating the HGF-induced protection against oxidative stress. Our results demonstrate that HGF protects cells from the oxidative damage induced by ethanol metabolism by a mechanism driven by NF-kappaB and PI3K/Akt signaling.

Hypertriglyceridemia and hepatic steatosis in senescence-accelerated mouse associate to changes in lipid-related gene expression

Aged rodents show increasing plasma and tissue triglycerides, and reductions in liver peroxisome proliferator-activated receptor alpha (PPARalpha) and its target genes. We determined whether a similar situation is present in a model of accelerated aging, the senescence-accelerated prone (SAM-P8) mouse. Five-month-old SAM-P8 mice were hypertriglyceridemic, and exhibited hepatic steatosis and reduced fatty acid oxidation versus control 5-month-old senescence-accelerated resistant (SAM-R1) mice, with no differences in PPARalpha expression and binding activity; in fact, fenofibrate administration to SAM-P8 mice induced a clear PPARalpha-driven response. Complementary DNA (cDNA) microarray analysis (Affymetrix Mouse Genome 430A 2.0 GeneChip array), Western blot, and electrophoretic mobility shift assay (EMSA) experiments indicated, among other changes, a deficit in farnesoid X receptor (FXR) expression and binding activity in the livers of SAM-P8 mice with respect to SAM-R1 controls. Triglyceride accretion and a deficit in hepatic fatty acid oxidation, features of the aging process in mammals, associate to a deficit in hepatic FXR activity in the SAM-P8 mice.

Alcohol induced hepatic fibrosis: role of acetaldehyde

Alcohol abuse is one of the major causes of liver fibrosis worldwide. Although the pathogenesis of liver fibrosis is a very complex phenomenon involving different molecular and biological mechanisms, several lines of evidence established that the first ethanol metabolite, acetaldehyde, plays a key role in the onset and maintenance of the fibrogenetic process. This review briefly summarizes the molecular mechanisms underlying acetaldehyde pro-fibrogenic effects. Liver fibrosis represents a general wound-healing response to a variety of insults. Although mortality due to alcohol abuse has been constantly decreasing in the past 20 years in Southern Europe and North America, in several Eastern-European countries and Great Britain Alcoholic Liver Disease (ALD) shows a sharply increasing trend [Bosetti, C., Levi, F., Lucchini, F., Zatonski, W.A., Negri, E., La, V.C., 2007. Worldwide mortality from cirrhosis: an update to 2002. J. Hepatol. 46, 827-839]. ALD has a complex pathogenesis, in which acetaldehyde (AcCHO), the major ethanol metabolite, plays a central role. Ethanol is mainly metabolized in the liver by two oxidative pathways. In the first one ethanol is oxidized to acetaldehyde by the cytoplasmic alcohol dehydrogenase enzyme (ADH), acetaldehyde is then oxidized to acetic acid by the mitochondrial acetaldehyde dehydrogenase (ALDH). The second pathway is inducible and involves the microsomal ethanol-oxidizing system (MEOS), in which the oxidation of ethanol to acetaldehyde and acetic acid also leads to generation of reactive oxygen species (ROS). Chronic ethanol consumption significantly inhibits mitochondrial ALDH activity while the rate of ethanol oxidation to acetaldehyde is even enhanced, resulting in a striking increase of tissue and plasma acetaldehyde levels [Lieber, C.S., 1997. Ethanol metabolism, cirrhosis and alcoholism. Clin. Chim. Acta 257, 59-84]. This review will focus on the molecular mechanisms by which acetaldehyde promote liver fibrosis.

Pentoxifylline downregulates alpha (I) collagen expression by the inhibition of Ikappabalpha degradation in liver stellate cells

Overproduction of collagen (I) by activated hepatic stellate cells is a critical step in the development of liver fibrosis. It has been established that these cells express interleukin (IL)-6 and respond to this cytokine with an increase in alpha(I) collagen. Pentoxifylline, a methylxanthine derivate, has been reported to have antifibrotic properties, but the mechanism responsible for this effect is unknown. The aim of this study was to determine the effect of pentoxifylline on acetaldehyde-induced collagen production in a rat hepatic stellate cell line (CFSC-2G cells). Cells were treated with 100 microM acetaldehyde and 200 microM pentoxifyline for 3 h. IL-6 and alpha(I) collagen messenger RNA (mRNA) were determined by reverse transcriptase polymerase chain reaction (RT-PCR) assay. NFkappaB activation was determined by electrophoretic mobility shift assay. To corroborate NFkappaB participation in pentoxifylline effect, cells were pretreated with 10 microM TPCK, a NFkappaB inhibitor. IkappaBalpha was determined by Western blot. IL-6 expression decreased significantly in acetaldehyde-pentoxifylline-treated cells. Acetaldehyde-treated cells pretreated with an anti-IL-6 monoclonal antibody did not show any increase in alpha (I) collagen expression. Acetaldehyde-treated cells increased 1.48 times NFkappaB activation, whereas acetaldehyde-pentoxifylline-treated cells decreased NFkappaB activation to control values. TPCK pretreated acetaldehyde cells did not present NFkappaB activation. To corroborate NFkappaB participation in pentoxifylline effect, IkappaBalpha was determined. IkappaBalpha protein level decreased 50% in acetaldehyde-treated cells, while acetaldehyde-pentoxifylline-treated cells showed IkappaBalpha control cells value. The data suggest that acetaldehyde induced alpha(I) collagen and IL-6 expression via NFkappaB activation. Pentoxifylline prevents acetaldehyde-induced alpha(I) collagen and IL-6 expression by a mechanism dependent on IkappaBalpha degradation, which in turn blocks NFkappaB activation.

Dual role of mitochondrial reactive oxygen species in hypoxia signaling: activation of nuclear factor-{kappa}B via c-SRC and oxidant-dependent cell death

Hypoxia is a prominent feature of solid tumor development and is known to stimulate mitochondrial ROS (mROS), which, in turn, can activate hypoxia-inducible transcription factor-1alpha and nuclear factor-kappaB (NF-kappaB). Because NF-kappaB plays a central role in carcinogenesis, we examined the mechanism of mROS-mediated NF-kappaB activation and the fate of cancer cells during hypoxia after mitochondrial reduced glutathione (mGSH) depletion. Hypoxia generated mROS in hepatoma (HepG2, H35), neuroblastoma (SH-SY5Y), and colon carcinoma (DLD-1) cells, leading to hypoxia-inducible transcription factor-1alpha-dependent gene expression and c-Src activation that was prevented in cells expressing a redox-insensitive c-Src mutant (C487A). c-Src stimulation activated NF-kappaB without IkappaB-alpha degradation due to IkappaB-alpha tyrosine phosphorylation that was inhibited by rotenone/TTFA or c-Src antagonism. The c-Src-NF-kappaB signaling contributed to the survival of cells during hypoxia as c-Src inhibition or p65 down-regulation by small interfering RNA-sensitized HepG2 cells to hypoxia-induced cell death. Moreover, selective mGSH depletion resulted in an accelerated and enhanced mROS generation by hypoxia that killed SH-SY5Y and DLD-1 cells without disabling the c-Src-NF-kappaB pathway. Thus, although mROS promote cell survival by NF-kappaB activation via c-Src, mROS overgeneration may be exploited to sensitize cancer cells to hypoxia.

Receptor activated C kinase is down-regulated in the male gonad of the marine bivalve mollusc Mya arenaria exposed to tributyltin (TBT)

This study was aimed at investigating the molecular mechanisms by which tributyltin (TBT) impairs the reproductive processes in the marine bivalve Mya arenaria. The suppression polymerase chain reaction subtractive hybridization (SSH) method was used to identify differentially expressed transcripts in the gonads of adult M. arenaria 72 h after a single injection of 160 ng TBT in the adductor muscle. Subtractive cDNA libraries comprising 322 clones were obtained. These clones were sequenced and corresponded to 55 female and 26 single male non-redundant cDNAs. Following similarity searches in genome databases, some of the transcripts could be assigned to cellular functions including mitochondrial respiration, structural proteins, structure of cytoskeleton, nucleic acid regulation, general metabolism and signal transduction. Among the potentially differentially regulated transcripts, Receptor for activated C kinase 1 (RACK1) represented 6% of the total down-regulated clones in males and the corresponding protein exhibited a high degree of similarity (80%) with the human polypeptide. The RACK1 cDNA from M. arenaria consists of 1085 bp, encoding a 318 deduced polypeptide which contains five internal tryptophan-aspartate (WD) repeats, six putative PKC phosphorylation sites, one tyrosine kinase site, four putative N-myristoylation sites as well as a transmembrane segment spanning amino acid 228-251. A significant down-regulation (by approximately 30% (p<0.05)) of RACK1 expression in male gonads exposed to TBT was confirmed by quantitative real-time RT-PCR. Transcript levels of RACK1 were higher in the female gonads than in the mantle, gills and male gonads. Gene expression as detected by in situ hybridization was strong in mature oocytes comparatively to primary germ cells. RACK1 may be a useful biomarker for TBT exposure in the reproductive system of bivalve molluscs.

Transcriptional regulation of deoxynivalenol-induced IL-8 expression in human monocytes

The trichothecene mycotoxin deoxynivalenol (DON), commonly present in contaminated grains worldwide, induces expression of the chemokine interleukin (IL)-8 in human monocytes. The purpose of this study was to test the hypothesis that DON modulates transcriptional and posttranscriptional regulation of IL-8 expression in the U937 human monocyte model. When U937 cells were transfected with a wild-type IL-8 promoter luciferase construct (-162/+44 IL-8 LUC) and incubated with DON (1 mug/ml) or the positive control, lipopolysaccharide (LPS) (1 mug/ml), there was a significant increase in luciferase expression. Mutation of the nuclear factor-kappaB (NF-kappaB) binding site significantly impaired both DON- and LPS-induced luciferase expression. In contrast, mutating the activator protein-1 binding site resulted in significantly increased DON- and LPS-induced luciferase expression. CCAAT/enhancer-binding protein beta, octamer-1, or NF-kappaB repressing factor binding site mutations did not affect DON-induced luciferase activity. Consistent with reporter studies, the NF-kappaB inhibitor caffeic acid phenethyl ester completely ablated both DON-induced IL-8 mRNA and protein expression. When NF-kappaB subunit binding to a specific IL-8 promoter probe was evaluated by enzyme-linked immunosorbent assay (ELISA), DON was observed to increase p65 binding by 21-fold, have no effect on p50 binding and decrease p52 binding. DON was not found to stabilize IL-8 mRNA in U937 cells. Taken together, these data suggest that DON-induced IL-8 expression is likely to be mediated at the transcriptional level by NF-kappaB, specifically p65, but does not appear to involve mRNA stabilization.

Impairment of hepatic Stat-3 activation and reduction of PPARalpha activity in fructose-fed rats

Fructose makes up a significant proportion of energy intake in westernized diets; its increased consumption has paralleled the growing prevalence of obesity and metabolic syndrome over the past two decades. In the current study, we demonstrate that fructose administration (10% wt/vol) in the drinking water of rats reduces the trans-activating and trans-repressing activity of the hepatic peroxisome proliferator-activated receptor alpha (PPARalpha). As a consequence, fructose decreases hepatic fatty oxidation and increases pro-inflammatory transcription factor nuclear factor kappaB (NF-kappaB) activity. These changes were not observed in glucose-administered rats (10% wt/vol), although both carbohydrates produced similar changes in plasma adiponectin and in the hepatic expression of transcription factors and enzymes involved in fatty acid synthesis. Fructose-fed, but not glucose-fed, rats were hyperleptinemic and exhibited increased tyrosine phosphorylation of the signal transducer and activator of transcription-3 (STAT-3) transcription factor, although they did not present a similar increase in the serine phosphorylation of nuclear STAT3. Thus, an impairment in the hepatic transduction of the leptin signal could be responsible for the observed alterations in PPARalpha activity in fructose-fed rats. Because PPARalpha activity is lower in human than in rodent liver, fructose ingestion in humans should cause even worse effects, which would partly explain the link between increased consumption of fructose and widening epidemics of obesity and metabolic syndrome.

CONCLUSION

Hypertriglyceridemia and hepatic steatosis induced by fructose ingestion result from a reduction in the hepatic catabolism of fatty acids driven by a state of leptin resistance.

Acetaldehyde promotes rapamycin-dependent activation of p70(S6K) and glucose uptake despite inhibition of Akt and mTOR in dopaminergic SH-SY5Y human neuroblastoma cells

Alcohol intake is one of the important lifestyle factors for the risk of insulin resistance and type 2 diabetes. Acetaldehyde, the major ethanol metabolite which is far more reactive than ethanol, has been postulated to participate in alcohol-induced tissue injury although its direct impact on insulin signaling is unclear. This study was designed to examine the effect of acetaldehyde on glucose uptake and insulin signaling in human dopaminergic SH-SY5Y cells. Akt, mammalian target of rapamycin (mTOR), ribosomal-S6 kinase (p70(S6K)), the eukaryotic translation initiation factor 4E (eIF4E)-binding protein 1 (4E-BP1) and insulin receptor substrate (IRS)-2 were evaluated by Western blot analysis. Glucose uptake and apoptosis were measured using [(3)H]-2-deoxyglucose uptake and caspase-3 assay, respectively. Short-term exposure (12 h) of acetaldehyde (150 muM) facilitated glucose uptake in a rapamycin-dependent manner without affecting apoptosis, IRS-2 expression and insulin-stimulated glucose uptake in SH-SY5Y cells. Acetaldehyde suppressed basal and insulin-stimulated Akt phosphorylation without affecting total Akt expression. Acetaldehyde inhibited mTOR phosphorylation without affecting total mTOR and insulin-elicited response on mTOR phosphorylation. Rapamycin, which inhibits mTOR leading to inactivation of p70(S6K), did not affect acetaldehyde-induced inhibition on phosphorylation of Akt and mTOR. Interestingly, acetaldehyde enhanced p70(S6K) activation and depressed 4E-BP1 phosphorylation, the effect of which was blunted and exaggerated, respectively, by rapamycin. Collectively, these data suggested that acetaldehyde did not adversely affect glucose uptake despite inhibition of insulin signaling cascade at the levels of Akt and mTOR, possibly due to presence of certain mechanism(s) responsible for enhanced p70(S6K) phosphorylation.

Aldehydes release zinc from proteins. A pathway from oxidative stress/lipid peroxidation to cellular functions of zinc

Oxidative stress, lipid peroxidation, hyperglycemia-induced glycations and environmental exposures increase the cellular concentrations of aldehydes. A novel aspect of the molecular actions of aldehydes, e.g. acetaldehyde and acrolein, is their reaction with the cysteine ligands of zinc sites in proteins and concomitant zinc release. Stoichiometric amounts of acrolein release zinc from zinc-thiolate coordination sites in proteins such as metallothionein and alcohol dehydrogenase. Aldehydes also release zinc intracellularly in cultured human hepatoma (HepG2) cells and interfere with zinc-dependent signaling processes such as gene expression and phosphorylation. Thus both acetaldehyde and acrolein induce the expression of metallothionein and modulate protein tyrosine phosphatase activity in a zinc-dependent way. Since minute changes in the availability of cellular zinc have potent effects, zinc release is a mechanism of amplification that may account for many of the biological effects of aldehydes. The zinc-releasing activity of aldehydes establishes relationships among cellular zinc, the functions of endogenous and xenobiotic aldehydes, and redox stress, with implications for pathobiochemical and toxicologic mechanisms.

Different response of senescent female Sprague-Dawley rats to gemfibrozil and rosiglitazone administration

Eighteen-month-old Sprague-Dawley rats present age-related alterations in lipid and glucose metabolism and are resistant to the effect of PPARalpha-activating hypolipidemic drugs, such as gemfibrozil. We tested if these animals were responsive to the administration of rosiglitazone, an insulin-sensitizer acting on PPARgamma. We determined in 18-month-old female Sprague-Dawley rats treated for 21 days with a daily dose of 3mg gemfibrozil/kg or 3mg rosiglitazone/kg: (i) plasma concentrations of total cholesterol (TC), triglycerides (TG), nonesterified fatty acids (NEFA), glucose, insulin and leptin, (ii) hepatic concentrations of TG, NEFA and cholesteryl esters (CE), and (iii) the liver expression and binding activity of peroxisome proliferator-activated receptor alpha (PPARalpha), and several of its target genes, hepatic nuclear factor-4 (HNF-4), and liver X receptor alpha (LXRalpha). Although gemfibrozil induced mild effects on hepatic PPARalpha, HNF-4, and LXRalpha, only rosiglitazone significantly reduced plasma TG (59%), glucose (19%), insulin (61%), and leptin (66%), and liver TG (43%), CE (49%), and NEFA (27%). These changes were associated to an increased body weight gain and a decrease in visceral fat (8.7-fold and 37% vs. control females, respectively). The beneficial effect of rosiglitazone treatment in 18-month-old female rats could be related to a direct effect on white adipose tissue.

Atorvastatin reverses age-related reduction in rat hepatic PPARalpha and HNF-4

Old rats are resistant to fibrate-induced hypolipidemia owing to a reduction in hepatic peroxisome proliferator-activated receptor alpha (PPARalpha). We tested whether the age-related decrease in PPARalpha is prevented by atorvastatin (ATV), a hypolipidemic statin. We determined the activity and expression of Liver X receptor alpha (LXRalpha) and PPARalpha in the liver of 18-month-old rats treated with 10 mg kg(-1) of ATV for 21 days. We measured fatty acid oxidation (FAO), the expression of PPARalpha-target genes, liver triglyceride (TG) and cholesteryl ester (CE) contents and plasma concentrations of TG, cholesterol, glucose, nonesterified fatty acids (NEFA), insulin and leptin. While old female rats were practically unresponsive, ATV-treated old males showed lower liver TG (-41%) and CE (-48%), and plasma TG (-35%), glucose (-18%) and NEFA (-39%). Age-related alterations in LXRalpha expression and binding activity were reverted in ATV-treated old males. These changes were related to an increase in hepatic FAO (1.2-fold), and PPARalpha mRNA (2.2-fold), PPARalpha protein (1.6-fold), and PPARalpha-binding activity. Hepatic nuclear factor-4 (HNF-4) and chicken ovalbumin upstream-transcription factor-II participate in the transcriptional regulation of the PPARalpha gene, while peroxisome proliferator-activated receptor gamma coactivator 1 (PGC-1) behaves as a PPAR coactivator. Ageing reduced the hepatic content of HNF-4 (74%) and PGC-1 (77%) exclusively in male rats. ATV administration to old males enhanced the hepatic expression and binding activity (two-fold) of HNF-4. ATV-induced changes in hepatic HNF-4 and PPARalpha may be responsible for the improvement of the lipid metabolic phenotype produced by ATV administration to senescent male rats.

Anti-inflammatory Effect of Pitavastatin on NF-.KAPPA.B Activated by TNF-.ALPHA. in Hepatocellular Carcinoma Cells

As nuclear factor-kappa B (NF-kappaB) is essential for promoting inflammation-associated cancer, it is a potential target for cancer prevention in chronic inflammatory diseases. Here we examined the anti-inflammatory effect of pitavastatin, a 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitor, on NF-kappaB activated by TNF-alpha in hepatocellular carcinoma (HCC) cells. Western blot revealed that the treatment of Huh 7 cells with pitavastatin at 0.1 microM inhibited the nuclear expression of NF-kappaB p65 induced by TNF-alpha. Furthermore, electrophoretic mobility shift assay showed that after the cells were incubated with pitavastatin alone or with pitavastatin and TNF-alpha for 24 h, pitavastatin significantly decreased the DNA binding activity of NF-kappaB induced by TNF-alpha. Subsequently, luciferase assay revealed that pitavastatin suppressed the transcriptional activity of the NF-kappaB promoter, which was clearly related to the HMG-CoA reductase activity because the addition of mevalonic acid (MEV) elevated the TNF-alpha activity. Moreover, the Rho kinase inhibitor Y27632 had no major effect on the NF-kappaB inhibitory activity of pitavastatin. The inhibitory effect of pitavastatin is possibly independent of the Rho kinase pathway in inflammation-associated HCC cells is. Finally, the addition of TNF-alpha significantly increased IL-6 protein production, which was suppressed by the addition of pitavastatin. These results suggest that pitavastatin at a low dose (0.1 microM) inhibits NF-kappaB activation and decreases IL-6 production induced by TNF-alpha, and is therefore expected to be a new strategy for treating HCC.

Acetaldehyde-induced interleukin-1beta and tumor necrosis factor-alpha production is inhibited by berberine through nuclear factor-kappaB signaling pathway in HepG2 cells

Alcoholic liver disease (ALD) is one of the most common liver diseases in the world. Increased levels of proinflammatory cytokines, including interleukin-1beta (IL-1beta) and tumor necrosis factor-alpha (TNF-alpha), have been correlated with the patients affected by ALD. However, the direct effect of alcohol in the induction of IL-1beta and TNF-alpha has not been clarified. In this study, we demonstrated that acetaldehyde, the metabolic product of ethanol, was able to induce IL-1beta and TNF-alpha production in HepG2 cells. Nuclear factor-kappaB (NF-kappaB), the transcription factor involved in the regulation of cytokine production, was also activated by acetaldehyde through inhibitory kappaB-alpha (IkappaB-alpha) phosphorylation and degradation. However, the NF-kappaB inhibitors, such as aspirin, cyclosporin A and dexamethasone, inhibited both the acetaldehyde-induced NF-kappaB activity and the induced cytokine production. Therefore, these data suggested that acetaldehyde stimulated IL-1beta and TNF-alpha production via the regulation of NF-kappaB signaling pathway. By screening 297 controlled Chinese medicinal herbs supervised by Committee on Chinese Medicine and Pharmacy at Taiwan, we found that Coptis chinensis (Huang-Lien) and Phellodendron amurense (Huang-Po) were capable of inhibiting acetaldehyde-induced NF-kappaB activity. Berberine, the major ingredient of these herbs, abolished acetaldehyde-induced NF-kappaB activity and cytokine production in a dose-dependent manner. Moreover, its inhibitory ability was through the inhibition of induced IkappaB-alpha phosphorylation and degradation. In conclusion, we first linked the acetaldehyde-induced NF-kappaB activity to the induced proinflammatory cytokine production in HepG2 cells. Our findings also suggested the potential role of berberine in the treatment of ALD.

Differential effect of interleukin-10 on hepatocyte apoptosis

Current data suggests that hepatocyte apoptosis is an essential feature contributing to several chronic liver diseases. It has been shown that IL-10 has diverse and potentially pleiotropic actions that suggest that it may have a direct effect on apoptosis. It has been established that NF-kappaB activation is essential to protect hepatocytes from apoptosis. The purpose of the present work is to evaluate the effect of the anti-inflammatory cytokine, IL-10 on the activation of NF-kappaB in primary cultured rat hepatocytes and hepatoblastoma (HepG2) cell line and explore its consequences on apoptosis. Apoptosis was induced by TNF-alpha and cicloheximide in HepG2 hepatoblastoma cells and by ethanol and a glutathione depletor in primary cultured rat hepatocytes. NF-kappaB activation was determined by EMSA. IL-10 increased ethanol induced apoptosis in primary culture rat hepatocytes (28%). These effects were enhanced when the cells were pre-treated with IL-10 under conditions of oxidative stress (glutathione depletion). The effects of IL-10 on primary cultured hepatocytes were independent of NF-kappaB activation. When apoptosis was induced by cicloheximide and TNF-alpha in hepatoblastoma cells, pretreatment with IL-10 was accompanied by a decrease of 38% in apoptosis. IL-10 did not have any effect on the signaling cascade of apoptosis but caused a significant increase in NF-kappaB activation. When NF-kappaB activation was inhibited by sulfazalazine the decrease in apoptosis was reversed. The present study demonstrates the importance of differential cell marking when trying to characterize the effects of cytokines in their contribution to liver cell apoptosis. The study provides insight into the mechanisms by which IL-10 affects apoptosis through a differential effect on NF-kappaB activation.

Sexual dimorphism in lipid metabolic phenotype associated with old age in Sprague-Dawley rats

PURPOSE

Aged male rats show a decrease in liver PPARalpha. We aimed to determine if the sexual dimorphism in lipid metabolism observed in the PPARalpha-/- mouse is also present in senescent rats.

RESULTS

Eighteen-month old rats were obese and presented high plasma NEFA concentrations. Old male rats were more hypercholesterolemic and hyperleptinemic than females, presenting a higher content in hepatic triglycerides and cholesteryl esters, while 18-month old females were more hypertriglyceridemic than males. Although PPARalpha expression and binding activity was reduced in liver from old male and female rats, the mRNA for a PPARalpha target gene, such as CPT-I, was reduced in old males (-56%), while increased by 286% in old females. LXRalpha protein was increased, and its binding activity was decreased in livers of old males, while livers of old females showed an increase in DGAT1 (2.6-fold) and DGAT2 (4.9-fold) mRNA, with respect to 3-month old animals. The increases in DGAT1 and DGAT2 mRNAs matched in old females those of plasma (3.1-fold) and liver triglycerides (5.0-fold).

CONCLUSIONS

These features disclose a marked sexual dimorphism in lipid metabolism associated to old age in rats that can be partially attributed not only to an age-related decrease in liver PPARalpha expression, but also to changes in other hepatic transcription factors and enzymes, such as liver X receptor alpha (LXRalpha) and diacylglycerol acyltransferases (DGAT).

Differential modulation of interleukin 8 by interleukin 4 and interleukin 10 in HepG2 cells treated with acetaldehyde

BACKGROUND/AIM

Pro-inflammatory cytokines and chemokines, such as interleukin (IL) 8, are important mediators of hepatic injury and repair following an insult. The purpose of this work was to study the regulation of IL-8 by IL-10 and IL-4 in HepG2 cells treated with acetaldehyde (Ac).

METHODS

HepG2 cells were pretreated with IL-10 or IL-4 before exposure to Ac, examining IL-8 expression by reverse transcription polymerase chain reaction and Western blot.

RESULTS

Ac treatment produced an increment in IL-8 induction and secretion that was prevented by IL-4 pretreatment, while IL-10 pretreatment failed to decrease Ac-induced IL-8 production. Consistent with these findings Ac increased NF-kappa B and AP-1 activation that were prevented by IL-4 but not by IL-10, findings accompanied by greater I kappa B-alpha levels in IL-4 but not IL-10 pretreated cells. In contrast to the pro-inflammatory role of IL-10 in HepG2, IL-10 did not show any change in the activation of NF-kappa B by Ac in WRL-68 cells, a human fetal hepatic cell line. Moreover, IL-10 did not induce the degradation of I kappa B-alpha in cellular extract from rat primary cultured cells.

CONCLUSIONS

While the present findings demonstrate the anti-inflammatory role of IL-4 in preventing the expression of IL-8 by Ac, the regulation of chemokines by anti-inflammatory cytokines is complex and depends on the cellular lineage.

Effects of acetaldehyde and TNF alpha on the inhibitory kappa B-alpha protein and nuclear factor kappa B activation in hepatic stellate cells

AIMS

Increased plasma tumour necrosis alpha (TNFalpha) and elevated monocyte nuclear factor kappa B (NF-kappaB) are associated with liver injury and inflammation in models of alcoholic liver disease and are found to be elevated in monocytes of patients with alcoholic hepatitis. Acetaldehyde enhances, whereas TNFalpha inhibits, transcription of the type I collagen promoters and type I collagen production. NF-kappaB, an inhibitor of the type I collagen promoters, is increased by both acetaldehyde and TNFalpha. This study determined the effects of acetaldehyde in comparison to the effects of TNFalpha on inhibitory kappa B-alpha (IkappaB-alpha) protein and NF-kappaB activation in hepatic stellate cells.

METHODS

Activated rat hepatic stellate cells in culture were exposed to acetaldehyde or TNFalpha for short periods of time, following which the cells were harvested for the determination of IkappaB-alpha protein, IkappaB-alpha kinase activity and nuclear NF-kappaB.

RESULTS

Acetaldehyde increased IkappaB-alpha kinase activity and decreased IkappaB-alpha after 10 min of exposure, with recovery towards control levels at 20 min. In contrast, TNFalpha resulted in higher IkappaB-alpha kinase activity at 20 min than at 10 min, and similar low IkappaB-alpha at 10 and 20 min. Both acetaldehyde and TNFalpha enhanced nuclear NF-kappaB (p65), but acetaldehyde alone also increased NF-kappaB (p50).

CONCLUSIONS

TNFalpha and acetaldehyde independently activate NF-kappaB by rapid enhancement of IkappaB-alpha kinase activity and degradation of IkB-alpha protein. Increased TNFalpha is the principal mechanism for the elevation of NF-kappaB in severe alcoholic hepatitis. The elevation of NF-kappaB due to TNFalpha enhance liver injury, but inhibit fibrogenesis. In contrast, the effect of acetaldehyde in activating NF-kappaB is associated with increases in both liver injury and fibrogenesis, indicating that the effects of acetaldehyde on fibrogenesis are mediated by cytokines and by trans-acting factors other than NF-kappaB.

Critical role of mitochondrial glutathione in the survival of hepatocytes during hypoxia

Hypoxia is known to stimulate reactive oxygen species (ROS) generation. Because reduced glutathione (GSH) is compartmentalized in cytosol and mitochondria, we examined the specific role of mitochondrial GSH (mGSH) in the survival of hepatocytes during hypoxia (5% O2). 5% O2 stimulated ROS in HepG2 cells and cultured rat hepatocytes. Mitochondrial complex I and II inhibitors prevented this effect, whereas inhibition of nitric oxide synthesis with Nomega-nitro-L-arginine methyl ester hydrochloride or the peroxynitrite scavenger uric acid did not. Depletion of GSH stores in both cytosol and mitochondria enhanced the susceptibility of HepG2 cells or primary rat hepatocytes to 5% O2 exposure. However, this sensitization was abrogated by preventing mitochondrial ROS generation by complex I and II inhibition. Moreover, selective mGSH depletion by (R,S)-3-hydroxy-4-pentenoate that spared cytosol GSH levels sensitized rat hepatocytes to hypoxia because of enhanced ROS generation. GSH restoration by GSH ethyl ester or by blocking mitochondrial electron flow at complex I and II rescued (R,S)-3-hydroxy-4-pentenoate-treated hepatocytes to hypoxia-induced cell death. Thus, mGSH controls the survival of hepatocytes during hypoxia through the regulation of mitochondrial generation of oxidative stress.

Prevention of age-related changes in rat cortex transcription factor activator protein-1 by hypolipidemic drugs

We sought to investigate if, similar to what has been described in other rodent tissues, ageing changes the activity of several transcription factors, namely signal transducer and activator of transcription, nuclear factor-kappa B (NFkappaB), activated protein-1 (AP-1) and peroxisome proliferator-activated receptor (PPAR), in cortex of Sprague-Dawley rats. We also investigated if the administration of two hypolipidemic drugs, gemfibrozil (GFB) and atorvastatin (ATV), could prevent those changes. To this purpose, we determined the expression and binding activity of these transcription factors in cortex samples from 3-month and 18-month old male and female rats, and in 18-month old rats of both sexes treated for 21 days with a daily dose of 3mg GFB/kg or 10mg ATV/kg. Ageing increased rat cortex NFkappaB binding activity by 35-40%, and decreased by 22-26% the amount of PPARalpha in rats of both sexes, while cortex AP-1 binding activity and c-Jun content were reduced only in old females (-26 and -50%, respectively). Cortex cyclooxigenase-2 (COX-2) and receptor for activated C-kinase 1 (RACK1) expression was also reduced by old age. Hypolipidemic drugs prevented the age-related decrease of cortex AP-1 in old females and increased AP-1 binding activity and c-Jun protein in cortex from both old male and female rats. GFB increased also by 80% the cortex PPARalpha content in old males. Our data indicate that 18-month old rats show signs of cortex biochemical deterioration related to the ageing process, and that hypolipidemic drug administration partially prevents the appearance of some of the age-related changes in cortex biochemistry.

Glutathione depletion impairs myogenic differentiation of murine skeletal muscle C2C12 cells through sustained NF-kappaB activation

Skeletal muscle differentation is a complex process regulated at multiple levels. This study addressed the effect of glutathione (GSH) depletion on the transition of murine skeletal muscle C2C12 myoblasts into myocytes induced by growth factor inactivation. Cellular GSH levels increased within 24 hours on myogenic stimulation of myoblasts due to enhanced GSH synthetic rate accounted for by stimulated glutamate-L-cysteine ligase (also known as gamma-glutamylcysteine synthetase) activity. In contrast, the synthesis rate of GSH using gamma-glutamylcysteine and glutamate as precursors, which reflects the activity of the GSH synthetase, did not change during differentiation. The stimulation of GSH stores preceded the myogenic differentiation of C2C12 myoblasts monitored by expression of muscle-specific genes, creatine kinase (CK), myosin heavy chain (MyHC), and MyoD. The pattern of DNA binding activity of NF-kappaB and AP-1 in differentiating cells was similar both displaying an activation peak at 24 hours after myogenic stimulation. Depletion of cellular GSH levels 24 hours after stimulation of differentiation abrogated myogenesis as reflected by lower CK activity, MyHC levels, MyoD expression, and myotubes formation, effects that were reversible on GSH replenishment by GSH ethyl ester (GHSEE). Moreover, GSH depletion led to sustained activation of NF-kappaB, while GSHEE prevented it. Furthermore, inhibition of NF-kappaB activation restored myogenesis despite GSH depletion. Thus, GSH contributes to the formation of myotubes from satellite myoblasts by ensuring inactivation of NF-kappaB, and hence maintaining optimal GSH levels may be beneficial in restoring muscle mass in chronic inflammatory disorders.

Identification of a novel NF-kappaB-binding site with regulation of the murine alpha2(I) collagen promoter

Hepatic fibrosis is due to the increased synthesis and deposition of type I collagen. Acetaldehyde activates type I collagen promoters. Nuclear factor kappaB (NF-kappaB) was previously shown to inhibit expression of murine alpha(1)(I) and human alpha(2)(I) collagen promoters. The present study identifies binding of NF-kappaB, present in nuclear extracts of stellate cells, to a region between -553 and -537 of the murine alpha(2)(I) collagen promoter. The NF-kappaB (p65) expression vector inhibited promoter activity. Mutation of the promoter at the NF-kappaB-binding site increased basal promoter activity and abrogated the activating and inhibitory effects of transforming growth factor beta and tumor necrosis factor alpha, respectively, on promoter activity. Acetaldehyde increased IkappaB-alpha kinase activity and phosphorylated IkappaB-alpha, NF-kappaB nuclear protein, and its binding to the promoter. However, the activating effect of acetaldehyde was not affected by the mutation of the promoter. In conclusion, although acetaldehyde increases the binding of NF-kappaB to the murine alpha(2)(I) collagen promoter, this binding does not mediate the activating effect of acetaldehyde on promoter activity. The effects of acetaldehyde in increasing the translocation of NF-kappaB to the nucleus with increased DNA binding activity may be important in mediating the effects of acetaldehyde on other genes.

Activation of Activator Protein 1 and Extracellular Signal-Regulated Kinases in Human Hepatocellular Transformation

Hepatocellular carcinoma is one of the most common tumors worldwide. Activator protein 1 (AP-1) is a nuclear transcription factor, and its transactivation is required for transformation in several cell lines. However, no direct correlation between AP-1 activity and human hepatocellular transformation has been proved. Here we analyzed the role of AP-1 on the 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced human hepatocellular transformation. TPA promoted the formation of anchorage-independent colonies, induced the AP-1 activity, and enhanced the DNA-binding ability of AP-1 in human hepatocytes. The phosphorylation of extracellular signal-regulated protein kinases (ERKs) was increased by TPA and the TPA-induced AP-1 activity was inhibited by PD98059, indicating that TPA-induced AP-1 activation was via ERK pathway. Moreover, retinoic acid and PD98059, which inhibited the AP-1 activity, abolished the TPA-induced transformation. Our findings indicated that AP-1 and ERKs activations were required for TPA-induced human hepatocellular transformation. These studies suggested that AP-1 could be the target for the development of antihepatocellular transformation agents.

The Mouse RACK1 Gene Is Regulated by Nuclear Factor-κB and Contributes to Cell Survival

Receptor for activated C kinase 1 (RACK1) is a multifunctional, WD motif-containing protein important in regulating several cell surface receptors and intracellular protein kinases. To better understand its function, we cloned the mouse RACK1 gene and found it contains eight exons and seven introns, and maps to mouse chromosome 11B1.2-1.3. Promoter analysis identified NF-kappaB as an important transcription factor for promoter activity. In PC-12 cells, nerve growth factor (NGF), which activates nuclear factor-kappaB (NF-kappaB), maintained RACK1 levels and promoted cell survival in serum-free medium. Inhibitors of NF-kappaB activation blocked NGF-stimulated survival and RACK1 expression, whereas transgenic expression of RACK1 promoted survival in cells deprived of serum and NGF. Thus, RACK1 gene expression is induced by NF-kappaB and RACK1 contributes to NF-kappaB-mediated cell survival.

Pro-apoptotic protein kinase Cδ is associated with intranuclear inclusions in a transgenic model of Huntington's disease

In order to investigate any effect of truncated mutant huntingtin (tNhtt) aggregation on protein kinase C (PKC) signaling in Huntington's disease (HD), we studied a possible association of PKC isoforms with the aggregates using cellular and transgenic models of HD. In this report we describe an association of mutant tNhtt with at least three PKC isoforms (alpha, delta, zeta), as revealed by co-immunoprecipitation assays and immunocytochemistry in a cellular model of HD (Neuro2a cells expressing tNhtt-150Q-EGFP), as well as a specific association of PKC delta with intranuclear aggregates in a transgenic model (R6/2 mice). Immunoblot analysis of isolated nuclear fractions shows an elevation of nuclear PKC delta in transgenic brain tissue. The observed elevation has a strong similarity with the apoptotic translocation of PKC delta detected in experiments with the mouse neuroblastoma Neuro2a cells. Using a Neuro2a cell line expressing tNhtt with the nuclear localization signal, we demonstrate the association of PKC delta with intranuclear aggregates and present evidence that accumulation of PKC delta in cell nuclei does not depend on mutant htt nuclear translocation. Our results suggest that the association of PKC delta with intranuclear htt-aggregates may affect its apoptotic function in a transgenic model of HD.

Role of protein kinase C in estrogen protection against apoptotic cerebellar cell death in ethanol-withdrawn rats

Results of studies from our laboratory have shown that administration of 17beta-estradiol (E(2)) reduces cerebellar neuronal damage during ethanol withdrawal (EW). In the current study, we examined mechanisms underlying E(2) protection against EW-associated cerebellar damage by assessing apoptotic indicators: DNA fragmentation, caspase-3 activity, and protein kinase C (PKC) activity. Ovariectomized rats, implanted with E(2) or oil pellets, received ethanol [7.5% weight/volume (wt./vol.)] (EW/E(2) group and EW/Oil group, respectively) chronically (for 5 weeks) or control dextrin diet (Dextrin/Oil group). At day 14 of EW, cerebelli were collected for the terminal deoxynucleotidyltransferase (TdT)-mediated dUDP-biotin nick end labeling (TUNEL) assay to detect DNA fragmentation and for immunohistochemistry to detect caspase-3 activation. A separate group of rat cerebelli was prepared to assess for total PKC activity, as well as for activity of a specific PKC isozyme, epsilon (PKCepsilon), by using an in vitro [gamma-(32)P]ATP phosphorylation assay at days 1 and 14 of EW. Results indicated that rats in the EW/Oil group had more DNA fragments and caspase-3-positive neuronal cells than observed for control rats, and these effects were inhibited by E(2) treatment. For total PKC activity at day 1 of EW, rats in the EW/E(2) group had a lower cytosolic PKC activity than observed for either rats in the EW/Oil group or control rats. At day 14 of EW, both EW groups had a lower total PKC activity than observed for control rats. For PKCepsilon activity, rats in the EW/E(2) group had a lower cytosolic PKCepsilon activity than observed for rats in the EW/Oil group or for control rats at day 1, and they had a lower membrane PKCepsilon activity at day 14 of EW than observed for control rats. These findings support the suggestion that E(2) protects against cerebellar neuronal damage in ethanol-withdrawn rats by inhibition of DNA fragmentation and caspase-3 activation, and that reduced PKC activity may be involved in the protection.

Protection by quercetin against cooking oil fumes-induced DNA damage in human lung adenocarcinoma CL-3 cells: role of COX-2

Epidemiological studies have shown that the incidence of lung cancer was associated with exposure to cooking oil fumes (COF) in nonsmoking Taiwanese women. We suspect that quercetin may be a potent inhibitor for reduction of COF-induced DNA damage and prevention of lung cancer development. Comet assay was used to evaluate the DNA damage induced by a relatively low dose of COF (100 g/ml) in human lung adenocarcinoma CL-3 cells. To understand whether quercetin has the most potent protective effect on COF-induced DNA damage, the 50% inhibition concentration of quercetin for COF-induced DNA damage (IC50) was compared with IC50 values of alpha-naphthoflavone(alpha-NF), NS-398, and NaN3 (specific inhibitors) or scavengers of cytochrome P-450 1A1, cyclooxygenase-2 (COX-2),and reactive oxygen species. The IC50 of quercetin was only 1/2, 1/3, and 1/35 of IC50 values of alpha-NF, NS-398, and NaN3,respectively. Clearly, quercetin was the most effective inhibitor of COF-induced DNA damage, followed sequentially by kappa-NF, NS-398, and NaN3. To further elucidate whether inhibition of COF-induced DNA damage of quercetin is mediated through the inhibition of COX-2 gene expression by altering the nuclear factor-kappaB pathway, COX-2 mRNA and its protein expressions induced by COF were evaluated by reverse transcription-polymerase chain reaction and Western blot, respectively. Our data showed that COX-2 mRNA and protein levels were significantly repressed by addition of quercetin in a dose-dependent manner. Gel retardation assay showed that nuclear factor-kappaB DNA binding activity induced by COF was significantly inhibited by quercetin. From our previous and present studies, it is revealed that coexpression of COX-2 and cytochrome P-450 1A1 caused by COF may contribute to genomic instability in lung cancer development. Thus quercetin may act as a potent chemopreventive agent of lung cancer for nonsmoking Taiwanese women.

Environmental exposure and lung cancer among nonsmokers: an example of Taiwanese female lung cancer

Lung cancer is the leading cause of cancer death worldwide and in Taiwan. Cigarette smoking is considered to be the most important risk factor, since about 90% of lung cancer can be related to cigarette smoking. Despite the recent decrease of cigarette smoking, lung cancer is still the leading cause of cancer death in the United States. In Taiwan, only around 50% of lung cancer incidence could be associated with cigarette smoking, particularly less than 10% of Taiwanese women are smokers. Thus, the aetiology of lung cancer for nonsmokers remains unknown. DNA damages including bulky and oxidative damage may be related with mutation of tumor suppressor genes, such as p53 gene. The high DNA adduct levels in female may be associated with frequent exposure to indoor cooking oil fumes (COF) and outdoor heavy air pollution. Oxidative stress induced by COF was also discussed. Different p53 mutation spectra and mutation frequency between genders reflected that different environmental factors may be involved in nonsmoking male and female lung cancer development. Most importantly, our recent report has demonstrated that human papillomavirus (HPV) infection was associated with nonsmoking female lung cancer. Based on our studies with Taiwanese nonsmoking lung cancer as the model, the possible aetiological factors of lung cancer incidence in Taiwanese nonsmokers were elucidated.

Acetaldehyde impairs mitochondrial glutathione transport in HepG2 cells through endoplasmic reticulum stress

BACKGROUND & AIMS

Ethanol impairs the mitochondrial transport of reduced glutathione (GSH), resulting in lower mitochondrial GSH (mGSH) levels. Our purpose was to evaluate the role of acetaldehyde on the regulation of mGSH in HepG2 cells.

METHODS

mGSH levels and transport, mitochondrial membrane microviscosity, and lipid composition were determined in mitochondria isolated from acetaldehyde-treated HepG2 cells.

RESULTS

The major ultrastructural changes of acetaldehyde-treated HepG2 cells included cytoplasmic lipid droplets and appearance of swollen mitochondria. Acetaldehyde depleted the mGSH pool size in a time- and dose-dependent fashion with spared cytosol GSH levels. Kinetics of GSH transport into isolated mitochondria from HepG2 cells showed 2 saturable, adenosine triphosphate-stimulated, high- and low-affinity components. Treatment with acetaldehyde increased the Michaelis constant for the high- and low-affinity components, with a greater impact on the former. These changes were due to increased mitochondrial microviscosity by enhanced cholesterol deposition because preincubation with the fluidizing agent, 2-(2-methoxyethoxy) ethyl 8-(cis-2-n-octylcyclopropyl) octanoate, normalized the initial transport rate of GSH into isolated mitochondria. Isolated mitochondria from rat liver enriched in free cholesterol reproduced the disturbing effects of acetaldehyde on GSH transport. The acetaldehyde-stimulated mitochondrial cholesterol content was preceded by increased levels of endoplasmic reticulum (ER)-responsive gene GADD153 and transcription factor sterol regulatory element-binding protein 1 and mimicked by the ER stress-inducing agents tunicamycin and homocysteine. Finally, the mGSH depletion induced by acetaldehyde sensitized HepG2 cells to tumor necrosis factor (TNF)-alpha-induced apoptosis that was prevented by cyclosporin A, GSH ethyl ester, and lovastatin.

CONCLUSIONS

Acetaldehyde sensitizes HepG2 cells to TNF-alpha by impairing mGSH transport through an ER stress-mediated increase in cholesterol.

Ganglioside GD3 sensitizes human hepatoma cells to cancer therapy

Ganglioside GD3 (GD3) has emerged as a modulator of cell death pathways due to its ability to interact with mitochondria and disable survival pathways. Because NF-kappaB activation contributes to cancer therapy resistance, this study was undertaken to test whether GD3 modulates the response of human hepatoblastoma HepG2 cells to radio- and chemotherapy. NF-kappaB was activated in HepG2 cells shortly after therapeutic doses of ionizing radiation or daunorubicin treatment that translated into up-regulation of kappaB-dependent genes. These effects were accompanied by minimal killing of HepG2 cells by either ionizing radiation or daunorubicin. However, GD3 pretreatment blocked the nuclear translocation of active kappaB members, without effect on Akt phosphorylation, induced by either treatment. The suppression of kappaB-dependent gene induction by GD3 was accompanied by enhanced apoptotic cell death caused by these therapies. Furthermore, the combination of GD3 plus ionizing radiation stimulated the formation of reactive species followed by the mitochondrial release of cytochrome c and Smac/Diablo and caspase 3 activation. Pretreatment with cyclosporin A before radiotherapy protected HepG2 cells from the therapeutic combination of GD3 plus ionizing radiation. These findings underscore a key role of mitochondria in the response of tumor cells to cancer therapy and highlight the potential relevance of GD3 to overcome resistance to cancer therapy by combining its dual action as a mitochondria-interacting and NF-kappaB-inactivating agent.

The antioxidant (-)-epigallocatechin-3-gallate inhibits activated hepatic stellate cell growth and suppresses acetaldehyde-induced gene expression

Activated hepatic stellate cells (HSC) are the primary source of excessive production of extracellular matrix during liver fibrogenesis. Although the underlying mechanisms remain incompletely understood, it is widely accepted that oxidative stress plays a critical role in liver fibrogenesis. Suppression of HSC growth and activation, as well as induction of apoptosis, have been proposed as therapeutic strategies for treatment and prevention of this disease. In the present report, we elucidated, for the first time, effects of the antioxidant (-)-epigallocatechin-3-gallate (EGCG), a major (and the most active) component of green tea extracts, on cultured HSC growth and activation. Our results revealed that EGCG significantly inhibited cultured HSC growth by inducing cell cycle arrest and apoptosis in a dose- and time-dependent manner. In addition, EGCG markedly suppressed the activation of cultured HSC as demonstrated by blocking transforming growth factor-beta signal transduction and by inhibiting the expression of alpha1(I) collagen, fibronectin and alpha-smooth muscle actin genes induced by acetaldehyde, the most active metabolite of ethanol. Furthermore, EGCG reacted differently in the inhibition of nuclear factor-kappaB activity between cultured HSC with or without acetaldehyde stimulation. Taken together, our results indicated that EGCG was a novel and effective inhibitor for activated HSC growth and activation in vitro. Further studies are necessary to evaluate the effect of this polyphenol in prevention of quiescent HSC activation in vivo, and to further elucidate the underlying mechanisms.

Suppression of nuclear factor-kappa B activity by nitric oxide and hyperoxia in oxygen-resistant cells

Inhaled nitric oxide (iNO) is used clinically to treat pulmonary hypertension in newborns, often in conjunction with hyperoxia (NO/O2). Prolonged exposure to NO/O2 causes synergistic lung injury and death of lung epithelial cells. To explore the mechanisms involved, oxygen-resistant HeLa-80 cells were exposed to NO +/- O2. Exposure to NO and O2 induced a synergistic cytotoxicity, accompanied with apoptotic characteristics, including elevated caspase-3-like activity, Annexin V incorporation, and nuclear condensation. This apoptosis was associated with a synergistic suppression of NF-kappaB activity. Cells lacking functional NF-kappaB p65 subunit were more sensitive to NO/O2 than their wild type counterparts. This injury was partially rescued by transfection with a p65 expression construct, suggesting an inverse relationship between NF-kappaB and susceptibility to the cytotoxicity of NO/O2. Despite the reduced NF-kappaB activity in cells exposed to NO +/- O2, IkappaBalpha was degraded, suggesting that pathways regulating the steady-state levels of IkappaB were not involved. However, exposure to NO/O2 caused a marked reduction in nuclear localization and an increase in protein carbonyl formation of NF-kappaB p65 subunit. These results suggest that NO/O2-induced apoptosis occurs by suppressing NF-kappaB activity.

Divergent role of ceramide generated by exogenous sphingomyelinases on NF-kappa B activation and apoptosis in human colon HT-29 cells

This study examined the role of ceramide generated by exogenous sphingomyelinases (SMases) on transcription nuclear factor-kappa B (NF-kappa B) activation and apoptosis in human colon epithelial HT-29 cells. Exogenous neutral (N) and acidic (A) SMase activated NF-kappa B with different kinetics, accounting for the diverse pattern of DNA binding of NF-kappa B complexes activated by tumor necrosis factor-alpha (TNF). NSMase activated predominantly RelA/p52 and RelA/p50 dimers within 30 min, while ASMase activated the p50/p50 homodimer by 20 h. The predominant activation of RelA-containing kappa B complexes by TNF or NSMase paralleled the induction of interleukin-8. HT-29 cells were sensitive to ASMase and TNF but resistant to NSMase. However, the apoptotic potential of NSMase was masked by NF-kappa B, as its prior inactivation sensitized HT-29 cells to NSMase. Thus, the generation of ceramide by exogenous SMases participates differentially in inflammation and apoptosis.

Cyclooxygenase-2 and presenilin-1 gene expression induced by interleukin-1beta and amyloid beta 42 peptide is potentiated by hypoxia in primary human neural cells

Lipid messengers and amyloid beta (Abeta) peptides generated by cyclooxygenase-2 (COX-2) and presenilin-1 (PS1) mediate pro-inflammatory signaling and neural degeneration in Alzheimer's disease (AD) brain. This study provides data showing that the COX-2 and PS1 genes each transcribe rare, highly labile RNA species that display early response gene behavior in human neural (HN) cells in primary culture, down-regulation during human neural development, and up-regulation in AD neocortex and hippocampal CA1. Together, interleukin-1beta and amyloid beta42 peptide [IL-1beta+Abeta42] synergistically activated COX-2 and PS1 gene expression preceded by increases in AP1-, STAT1alpha-, and in particular NF-kappaBp50/p65- and HIF-1alpha-DNA binding. These events were markedly potentiated by hypoxia and blocked by the antioxidant alpha-phenyl-N-tert-butyl nitrone. Broad transcription profiling further indicated that hypoxia-induced, [IL-1beta+Abeta42]-treated HN cells display robust induction of COX-2 and PS1 as well as a pro-inflammatory gene family that includes NF-kappaBp50/p105, IL-1beta precursor, and cytosolic phospholipase A2 genes. These findings indicate a novel [IL-1beta+Abeta42]-mediated, hypoxia-enhanced, free radical-triggered gene program that drives inflammatory gene signaling and suggest a mechanism by which hypoxia during aging contributes episodically to amyloidogenesis, inflammation, and AD pathophysiology.

Acetaldehyde activates Jun/AP-1 expression and DNA binding activity in human oral keratinocytes

Oral cancer is a significant health problem, particularly among individuals that ingest alcohol in combination with the use of tobacco products. The enhanced development of tobacco-initiated oral cancers by ethanol suggests that ethanol or one of its metabolites may act as a type of tumor promoter. Nevertheless, the mechanisms underlying the ability of ethanol to enhance oral carcinogenesis remain unclear. We hypothesize that acetaldehyde, the first metabolite of ethanol, may activate the expression and/or activity of Jun/AP-1 in oral keratinocytes analogous to the phorbol ester TPA and other tumor promoters in epidermal keratinocytes. To test this hypothesis, we treated HPV immortalized, non-tumorigenic human oral keratinocytes with acetaldehyde at various concentrations and for various times and measured several parameters of Jun/AP-1expression and function. Our results indicated that c-Jun mRNA and protein levels increased in the acetaldehyde treated cells compared to untreated control cells. Moreover, Jun/AP-1 DNA binding activity was rapidly activated by acetaldehyde in a dose-dependent fashion. The increases in Jun protein and AP-1 DNA binding activity were accompanied by increased transactivation of an AP-1 responsive reporter construct as well as increased transcript levels of a candidate AP-1 responsive gene, stromelysin 3. The levels of acetaldehyde employed were minimally toxic to the cells as determined by MTT assays. Thus, acetaldehyde was found to activate the expression and activity of an oncogenic transcription factor in HPV-initiated cells. Taken together, these results suggest that acetaldehyde may participate, at least in part, in the promotion stage of oral carcinogenesis.

How is the liver primed or sensitized for alcoholic liver disease?

This article represents the proceedings of a symposium at the 2000 ISBRA Meeting in Yokohama, Japan. The chairs were Hidekazu Tsukamoto and Yoshiyuki Takei. The presentations were (1) Tribute to Professor Rajendar K. Chawla, by Craig J. McClain; (2) Dysregulated TNF signaling in alcoholic liver disease, by Craig J. McClain, S. Joshi-Barve, D. Hill, J Schmidt, I. Deaciuc, and S. Barve; (3) The role of mitochondria in ethanol-mediated sensitization of the liver, by Anna Colell, Carmen Garcia-Ruiz, Neil Kaplowitz, and Jose C. Fernandez-Checa; (4) A peroxisome proliferator (bezafibrate) can prevent superoxide anion release into hepatic sinusoid after acute ethanol administration, by Hirokazu Yokoyama, Yukishige Okamura, Yuji Nakamura, and Hiromasa Ishii; (5) S-adenosylmethionine affects tumor necrosis factor-alpha gene expression in macrophages, by Rajendar K. Chawla, S. Barve, S. Joshi-Barve, W. Watson, W. Nelson, and C. McClain; (6) Iron, retinoic acid and hepatic macrophage TNFalpha gene expression in ALD, by Hidekazu Tsukamoto, Min Lin, Mitsuru Ohata, and Kenta Motomura; and (7) Role of Kupffer cells and gut-derived endotoxin in alcoholic liver injury, by N. Enomoto, K. Ikejima, T. Kitamura, H. Oide, Y. Takei, M. Hirose, B. U. Bradford, C. A. Rivera, H. Kono, S. Peter, S. Yamashina, A. Konno, M. Ishikawa, H. Shimizu, N. Sato, and R. Thurman.

The role of acetaldehyde in the actions of alcohol (update 2000)

BACKGROUND

Recent advances in the field of acetaldehyde (AcH) research have raised the need for a comprehensive review on the role of AcH in the actions of alcohol. This update is an attempt to summarize the available AcH research.

METHODS

The descriptive part of this article covers not only recent research but also the development of the field. Special emphasis is placed on mechanistic analyses, new hypotheses, and conclusions.

RESULTS

Elevated AcH during alcohol intoxication causes alcohol sensitivity, which involves vasodilation associated with increased skin temperature, subjective feelings of hotness and facial flushing, increased heart and respiration rate, lowered blood pressure, sensation of dry mouth or throat associated with bronchoconstriction and allergy reactions, nausea and headache, and also reinforcing reactions like euphoria. These effects seem to involve catecholamine, opiate peptide, prostaglandin, histamine, and/or kinin mechanisms. The contribution of AcH to the pathological consequences of chronic alcohol intake is well established for different forms of cancer in the digestive tract and the upper airways. AcH seems to play a role in the etiology of liver cirrhosis. AcH may have a role in other pathological developments, which include brain damage, cardiomyopathy, pancreatitis, and fetal alcohol syndrome. AcH creates both unpleasant aversive reactions that protect against excessive alcohol drinking and euphoric sensations that may reinforce alcohol drinking. The protective effect of AcH may be used in future treatments that involve gene therapy with or without liver transplantation.

CONCLUSIONS

AcH plays a role in most of the actions of alcohol. The individual variability in these AcH-mediated actions will depend on the genetic polymorphism, not only for the alcohol and AcH-metabolizing enzymes but also for the target sites for AcH actions. The subtle balance between aversive and reinforcing, protecting and promoting factors will determine the overall behavioral and pathological developments.

Alcoholic liver disease

Research has substantiated the role of several mechanisms responsible for alcohol-induced hepatotoxicity. These mechanisms include: oxidative stress and lipid peroxidation; immunogenic processes initiated by formation of protein adducts of acetaldehyde, other aldehydes and 1-hydroxyethyl radicals; and activation of Kupffer cells by endotoxin and subsequent cascade of events that involved cytokines, chemokines, and adhesion molecules. Increasing evidence implicates enhanced intestinal permeability caused by alcohol ingestion as the culprit that leads to endotoxemia. While oxidative stress is important, the principal source of reactive oxygen species that causes alcohol-induced liver injury is hotly debated. Potential sources may include cytochrome P450IIE1, activated Kupffer cells, and mitochondrial electron transfer chain. Apoptosis is likely an important pathway that culminates in hepatocyte cell death. Abstinence, corticosteroids, and enteral nutrition remain the cornerstones in the treatment of alcoholic hepatitis. The efficacies of medications such as S-adenosylmethionine and pentoxifylline will need further confirmation by additional randomized trials before they can be recommended as standard therapies for alcoholic hepatitis.

How is the liver primed or sensitized for alcoholic liver disease?

This article represents the proceedings of a symposium at the 2000 ISBRA Meeting in Yokohama, Japan. The chairs were Hidekazu Tsukamoto and Yoshiyuki Takei. The presentations were (1) Tribute to Professor Rajendar K. Chawla, by Craig J. McClain; (2) Dysregulated TNF signaling in alcoholic liver disease, by Craig J. McClain, S. Joshi-Barve, D. Hill, J Schmidt, I. Deaciuc, and S. Barve; (3) The role of mitochondria in ethanol-mediated sensitization of the liver, by Anna Colell, Carmen Garcia-Ruiz, Neil Kaplowitz, and Jose C. Fernandez-Checa; (4) A peroxisome proliferator (bezafibrate) can prevent superoxide anion release into hepatic sinusoid after acute ethanol administration, by Hirokazu Yokoyama, Yukishige Okamura, Yuji Nakamura, and Hiromasa Ishii; (5) S-adenosylmethionine affects tumor necrosis factor-alpha gene expression in macrophages, by Rajendar K. Chawla, S. Barve, S. Joshi-Barve, W. Watson, W. Nelson, and C. McClain; (6) Iron, retinoic acid and hepatic macrophage TNFalpha gene expression in ALD, by Hidekazu Tsukamoto, Min Lin, Mitsuru Ohata, and Kenta Motomura; and (7) Role of Kupffer cells and gut-derived endotoxin in alcoholic liver injury, by N. Enomoto, K. Ikejima, T. Kitamura, H. Oide, Y. Takei, M. Hirose, B. U. Bradford, C. A. Rivera, H. Kono, S. Peter, S. Yamashina, A. Konno, M. Ishikawa, H. Shimizu, N. Sato, and R. Thurman.

The role of acetaldehyde in the actions of alcohol (update 2000)

BACKGROUND

Recent advances in the field of acetaldehyde (AcH) research have raised the need for a comprehensive review on the role of AcH in the actions of alcohol. This update is an attempt to summarize the available AcH research.

METHODS

The descriptive part of this article covers not only recent research but also the development of the field. Special emphasis is placed on mechanistic analyses, new hypotheses, and conclusions.

RESULTS

Elevated AcH during alcohol intoxication causes alcohol sensitivity, which involves vasodilation associated with increased skin temperature, subjective feelings of hotness and facial flushing, increased heart and respiration rate, lowered blood pressure, sensation of dry mouth or throat associated with bronchoconstriction and allergy reactions, nausea and headache, and also reinforcing reactions like euphoria. These effects seem to involve catecholamine, opiate peptide, prostaglandin, histamine, and/or kinin mechanisms. The contribution of AcH to the pathological consequences of chronic alcohol intake is well established for different forms of cancer in the digestive tract and the upper airways. AcH seems to play a role in the etiology of liver cirrhosis. AcH may have a role in other pathological developments, which include brain damage, cardiomyopathy, pancreatitis, and fetal alcohol syndrome. AcH creates both unpleasant aversive reactions that protect against excessive alcohol drinking and euphoric sensations that may reinforce alcohol drinking. The protective effect of AcH may be used in future treatments that involve gene therapy with or without liver transplantation.

CONCLUSIONS

AcH plays a role in most of the actions of alcohol. The individual variability in these AcH-mediated actions will depend on the genetic polymorphism, not only for the alcohol and AcH-metabolizing enzymes but also for the target sites for AcH actions. The subtle balance between aversive and reinforcing, protecting and promoting factors will determine the overall behavioral and pathological developments.