Tumor Necrosis Factor in Alcohol Enhanced Endotoxin Liver Injury

Endotoxin administration causes liver injury. Patients with alcoholic liver disease frequently have portal vein and systemic endotoxemia, and some investigators have suggested that endotoxin plays an etiologic role in alcoholic liver injury. Many of the metabolic effects of endotoxin are mediated by the cytokine tumor necrosis factor (TNF). It was the purpose of this study to determine whether TNF plays a role in ethanol-enhanced endotoxin liver injury. Rats were fed either a diet in which 36% of the calories were from ethanol or an isocaloric control diet. After 6 weeks, groups of 10 rats were intravenously injected with either saline, 1 mg/kg endotoxin, or 30 micrograms/kg of a prostaglandin E1 (PGE1) analogue + 1 mg/kg endotoxin 24 hr prior to sacrifice. Ethanol/endotoxin-treated rats had significantly higher liver enzyme levels (ALT: 1064 +/- 355 IU/liter, AST: 2024 +/- 515 IU/liter) compared with isocaloric/endotoxin controls (ALT: 237 +/- 54 IU/liter, AST: 602 +/- 80 IU/liter). Ethanol/endotoxin rats also had significantly higher peak serum TNF concentrations (992 +/- 200 units/ml) compared with isocaloric/endotoxin controls (344 +/- 96 units/ml). Pretreatment of ethanol/endotoxin rats with PGE1 caused significant attenuation of liver injury (ALT: 267 +/- 64 IU/liter, AST: 612 +/- 77 IU/liter) and a diminished serum TNF response. In contrast to chronic ethanol administration, acute gavage with 2 mg/kg ethanol (30% w/v) followed by intravenous injection of 2 mg/kg endotoxin produced significantly lower peak serum TNF concentrations (401 +/- 76 units/ml) than gavage with distilled water (1152 +/- 208 units/ml).(ABSTRACT TRUNCATED AT 250 WORDS)     

Chronic ethanol consumption alters the glutathione/glutathione peroxidase-1 system and protein oxidation status in rat liver

BACKGROUND: Alcohol-induced liver damage is associated with oxidative stress, which might be linked to disturbances in liver antioxidant defense mechanisms. The effect of chronic ethanol consumption on the mitochondrial and cytosolic glutathione/glutathione peroxidase-1 (GSHPx-1) system and oxidative modification of proteins was therefore studied in the rat. METHODS: Male Sprague-Dawley rats were fed liquid diets that provided 36% total calories as ethanol for at least 31 days. Pair-fed controls received isocaloric diets with ethanol calories substituted with maltose-dextrins. Mitochondrial and cytosolic fractions were prepared from livers and assayed for GSHPx-1 and glutathione reductase activities and total and oxidized concentrations of glutathione. Catalase activity was measured in the postmitochondrial supernatant. Levels of GSHPx-1, lactate dehydrogenase, and the beta subunit of the F1 portion of the ATP synthase protein were determined by western blot analysis. Concentrations of mitochondrial and cytosolic protein carbonyls were measured to assess ethanol-induced oxidation of proteins. RESULTS: Chronic ethanol consumption significantly decreased cytosolic and mitochondrial GSHPx-1 activities by 40% and 30%, respectively. Levels of GSHPx-1 protein in cytosol were unaffected by ethanol feeding, whereas there was a small decrease in GSHPx-1 protein levels in mitochondria isolated from ethanol-fed rats. Glutathione reductase activities were increased in both intracellular compartments and catalase activity was increased as a consequence of ethanol exposure. Cytosolic total glutathione was mildly decreased, whereas ethanol feeding increased mitochondrial levels of total glutathione. Chronic ethanol feeding significantly increased both cytosolic and mitochondrial concentrations of protein carbonyls by 30% and 60%, respectively. CONCLUSIONS: This study demonstrates that chronic ethanol-induced alterations in the glutathione/GSHPx-1 antioxidant system might promote oxidative modification of liver proteins, namely those of the mitochondrion, which could contribute to the adverse effects of ethanol on the liver.     

Alcohol, Tumor Necrosis Factor, and Tuberculosis

Alcohol exerts potent suppressive effects on the immune system that significanty increase host susceptibility to a variety of infections, particularly pneumonia. Historically, tuberculosis has been strongly associated with alcohol abuse. Although the relationship between alcohol abuse and tuberculosis is widely appreciated, the basic mechanisms by which alcohol immunosuppresses the host remain to be clarified. A major obstacle in furthering our understanding of this association has been the difficulty in distinguishing between the effects of alcohol per se and the other frequent sequelae of alcoholism such as nutritional deficiencies, liver disease, cigarette smoking, hygienic factors, and lifestyle. This article focuses on the role of tumor necrosis factor-alpha (TNF) in host defense and how alcohol modulates the activity of this important cytokine. While TNF's role in mediating the lethal consequences of infection has been the subject of much conjecture, this review focuses on the emerging evidence that TNF is an essential factor in the normal immune response to numerous infections, including tuberculosis.     

Tumor Necrosis Factor/Tumor Necrosis Factor Receptor Family Members That Positively Regulate Immunity

The interactions between members of the tumor necrosis factor (TNF) family and their specific receptors (TNFRs) are influential in controlling cell division, life, and death. Recent evidence suggests that these interactions control the functionality and longevity of many types of cells involved in immune responses. In particular, it has become evident that certain interactions support the clonal expansion and survival of T-cells, B-cells, and dendritic cells and thus are essential for establishing a robust immune response. This review describes select TNF/TNFR family members that principally support activation and survival and prevent excessive cell death of T-cells (OX40L/OX40, 4-1BBL/4-1BB, CD30L/CD30, LIGHT/HVEM, CD70/CD27, and GITRL/GITR), B-cells (BAFF/BAFFR), and dendritic cells (RANKL/RANK). Expression of these ligands and receptors on the cell surface is highly regulated, and communication via them occurs during contact between T-cells and dendritic cells and between T-cells and B-cells.The functional dynamic between these TNF/TNFR members is slowly being unraveled, including whether these molecules act together or sequentially or control different type of immune responses. This review summarizes aspects of these TNF/TNFR interactions that are potentially important to immune responses.     

Nitric Oxide-Mediated Intestinal Injury Is Required for Alcohol-Induced Gut Leakiness and Liver Damage

Background: Alcoholic liver disease (ALD) requires endotoxemia and is commonly associated with intestinal barrier leakiness. Using monolayers of intestinal epithelial cells as an in vitro barrier model, we showed that ethanol‐induced intestinal barrier disruption is mediated by inducible nitric oxide synthase (iNOS) upregulation, nitric oxide (NO) overproduction, and oxidation/nitration of cytoskeletal proteins. We hypothesized that iNOS inhibitors [NG‐nitro‐l ‐arginine methyl ester (l ‐NAME), l ‐N⁶‐(1‐iminoethyl)‐lysine (l ‐NIL)] in vivo will inhibit the above cascade and liver injury in an animal model of alcoholic steatohepatitis (ASH). Methods: Male Sprague–Dawley rats were gavaged daily with alcohol (6 g/kg/d) or dextrose for 10 weeks ± l ‐NAME, l ‐NIL, or vehicle. Systemic and intestinal NO levels were measured by nitrites and nitrates in urine and tissue samples, oxidative damage to the intestinal mucosa by protein carbonyl and nitrotyrosine, intestinal permeability by urinary sugar tests, and liver injury by histological inflammation scores, liver fat, and myeloperoxidase activity. Results: Alcohol caused tissue oxidation, gut leakiness, endotoxemia, and ASH. l ‐NIL and l ‐NAME, but not the d ‐enantiomers, attenuated all steps in the alcohol‐induced cascade including NO overproduction, oxidative tissue damage, gut leakiness, endotoxemia, hepatic inflammation, and liver injury. Conclusions: The mechanism we reported for alcohol‐induced intestinal barrier disruption in vitro — NO overproduction, oxidative tissue damage, leaky gut, endotoxemia, and liver injury — appears to be relevant in vivo in an animal model of alcohol‐induced liver injury. That iNOS inhibitors attenuated all steps of this cascade suggests that prevention of this cascade in alcoholics will protect the liver against the injurious effects of chronic alcohol and that iNOS may be a useful target for prevention of ALD.     

慢性酒精性胰腺炎患者体外肿瘤坏死因子和肿瘤坏死因子受体的诱导

肿瘤坏死因子(TNFa)是急性胰腺炎导致全身多器官损害的一种重要介质。本文研究的目的是了解慢性酒精性胰腺炎TNFa和可溶性肿瘤坏死因子受体p55、p75(sTNFRp55、sTNFRp75)是否升高,及其升高是否是内毒素或酒精的作用。我们对12例慢性酒精性胰腺炎患者和8例健康者用内毒素脂多糖(LPS)和乙醇(Ethanol)刺激后的周围血单核细胞上清液用ELISA方法进行了TNFa、sTNFRp55、p75的检测。LPS刺激后的单核细胞上清液中TNFa、sTNFp55、p75浓度不论是患者还是健康组均较自然表达明显增加,其中sTNFRp55、p75浓度在胰腺炎组较正常组明显增加,P值分别<0.05、<0.001。Ethanol刺激后 TNFa和sTNFRp55的表达在胰腺炎组与正常组之间无差异.但sTNFRp75较正常组增加。我们的结果提示慢性酒精性胰腺炎前炎性介质TNFa和sTNFRp55、p75的诱导与内毒素活化的单核细胞表达有关,而酒精对单核细胞活化不起直接作用。     

肝硬化患者肿瘤坏死因子与胰岛素抵抗的相关性

目的探讨肝硬化患者肿瘤坏死因子水平与胰岛素抵抗的关系。方法测定73例肝硬化患者及30例健康人血清肿瘤坏死因子水平及相关临床生化参数,并计算胰岛素敏感指数和体重指数。结果肝硬化组肿瘤坏死因子水平明显高于正常对照组,肿瘤坏死因子与胰岛素水平呈负相关,而与胰岛素敏感指数呈正相关。结论肝硬化患者血清肿瘤坏死因子水平明显升高,其可能作为肝功能的评价指标;肿瘤坏死因子水平与肝硬化患者胰岛素抵抗密切相关。     

ABCA1在冠心病及其发病机制中的研究新进展

动脉粥样硬化(As)是冠心病的主要病因,而泡沫细胞又是As的主要病因,过多的胆固醇在巨噬细胞中积累形成泡沫细胞,因此减少胆固醇的积累从而减少泡沫细胞的形成可能成为治疗As有效的方法。ATP结合盒转运体A1(ABCA1)可使细胞内胆固醇和磷脂转运到载脂蛋白AⅠ(Apo AⅠ)形成高密度脂蛋白前体,使过多的胆固醇进入肝脏重新利用或经胆汁和粪便排出,这个过程就是胆固醇逆转运。ABCA1还能够抑制As的炎症反应,引起血管内皮细胞变化,参与氧化应激反应,可通过多种代谢通路影响As,其不同的基因型对As的影响也不相同。因此,ABCA1在As的发生发展中具有举足轻重的作用。     

酒精性肝硬化患者血清肿瘤坏死因子受体的检测及其临床意义

同特异性免疫测定ELISA法检测了32例酒精性肝硬化患者和10名健康人血清中肿瘤坏死因子受体的水平。酒精性肝硬化患者两种可溶性肿瘤坏死因子受体(P55、P75)均明显高于健康组(P<0.01),肝硬化代偿期与失代偿期患者比较有显著差异(P值分别<0.005,<0.01)。这些结果提示循环中可溶性肿瘤坏死因子受体(STNFR)的水平与肝硬化和疾病的进展程度呈正相关。     

Mitochondrial S-Adenosyl-l-Methionine Transport is Insensitive to Alcohol-Mediated Changes in Membrane Dynamics

Background: Alcohol‐induced liver injury is associated with decreased S‐adenosyl‐l ‐methionine (SAM)/S‐adenosyl‐l ‐homocysteine (SAH) ratio and mitochondrial glutathione (mGSH) depletion, which has been shown to sensitize hepatocytes to tumor necrosis factor (TNF). Aims: As the effect of alcohol on mitochondrial SAM (mSAM) has been poorly characterized, our aim was to examine the status and transport of mSAM in relation to that of mGSH during alcohol intake. Methods: Sprague–Dawley rats were pair fed Lieber–DeCarli diets containing alcohol for 1 to 4 weeks and liver fractionated into cytosol and mitochondria to examine the mSAM transport and its sensitivity to membrane dynamics. Results: We found that cytosol SAM was depleted from the first week of alcohol feeding, with mSAM levels paralleling these changes. Cytosol SAH, however, increased during the first 3 weeks of alcohol intake, whereas its mitochondrial levels remained unchanged. mGSH depletion occurred by 3 to 4 weeks of alcohol intake due to cholesterol‐mediated impaired transport from the cytosol. In contrast to this outcome, the transport of SAM into hepatic mitochondria was unaffected by alcohol intake and resistant to cholesterol‐mediated perturbations in membrane dynamics; furthermore cytosolic SAH accumulation in primary hepatocytes by SAH hydrolase inhibition reproduced the mSAM depletion by alcohol due to the competition of SAH with SAM for mitochondrial transport. However, alcohol feeding did not potentiate the sensitivity to inhibition by SAH accumulation. Conclusions: Alcohol‐induced mSAM depletion precedes that of mGSH and occurs independently of alcohol‐mediated perturbations in membrane dynamics, disproving an inherent defect in the mSAM transport by alcohol. These findings suggest that the early mSAM depletion may contribute to the alterations of mitochondrial membrane dynamics and the subsequent mGSH down‐regulation induced by alcohol feeding.