The Role of TNF in Hepatotoxicity

肿瘤坏死因子α(TNFpha)一直以来都是 被证明是内毒素休克的主要介质。一 肿瘤坏死因子诱导的损伤机制是通过激活核因子-kB实现的 以及活性氧物种的产生。我们有 假设2，3，7，8-四氯二苯并二恶英(TCDD) 诱导的内毒素超敏反应和随后的诱导 细胞凋亡可能通过调节肿瘤坏死因子α信号发生 小路。我们实验室最近的努力主要集中在体内 内毒素超敏反应模型及其相互关系的研究进展 肿瘤坏死因子α信号转导与氧化应激。我们已经将 用血清评价法研究TCDD致肝损伤的动力学 酶水平和凋亡细胞的定量，并已评估 关键时间点的基因表达变化。我们有 研究表明，当啮齿动物在内毒素之前使用TCDD治疗时 暴露的毒性显著增加，而且这种抑制作用 放线菌酮阻断TCDD诱导的蛋白质合成 在该模型中对肿瘤坏死因子α的敏感性。核糖核酸酶的表达 与肿瘤坏死因子和Fas凋亡途径相关的基因有 在对照组和治疗组动物的肝组织中进行了定量 使用RT-PCR法。TCDD对内毒素调节的早期调控 Fas的表达及改变肿瘤坏死因子受体1和 核因子kappaB(NFKB)。我们目前正在研究 TCDD对NFKB基因表达的影响初步研究表明 TCDD/内毒素联合治疗改变核 P65亚单位或NFKB易位。虽然高水平的 肝脏中的肿瘤坏死因子α通常与感染性休克有关， 细胞毒性、炎症和/或细胞凋亡， 认识到肿瘤坏死因子α也在调节 肝细胞生长。此前的研究表明， 过氧化物酶体增殖物诱导的肝细胞改变 细胞增殖可能与肿瘤坏死因子α的促有丝分裂活性有关 从激活的库普弗细胞中释放出来。库普弗池的调制 使用限制或阻止细胞因子产生的试剂的活动可能 是对抗肝毒性的重要治疗工具 肿瘤。在罗纳德·瑟曼博士的合作下，我们有 确定用过氧化物酶增殖剂治疗 惠氏14,643激活肝脏中的枯否细胞，刺激 吞噬和增加肿瘤坏死因子α基因表达和 分泌物。这一增长可以受到许多因素的影响 防止库普弗细胞激活的物质，如棕榈酸甲酯， 氯化格拉和尼莫地平。我们还展示了 饮食中的甘氨酸抑制库普弗细胞的激活并防止 脂多糖或硫代巴比妥钠处理后体内肿瘤坏死因子α的产生 惠氏-14,643。该项目之前曾作为Z01的一部分进行过报道 ES 30106 23 LT

Tumor necrosis factor alpha (TNFalpha) has been demonstrated to be a primary mediator of endotoxin shock. One mechanism of TNF-induced injury is via the activation of NF-kB and the generation of reactive oxygen species. We have hypothesized that 2,3,7,8-tetrachlorodibenzodioxin (TCDD) -induced endotoxin hypersensitivity and subsequent induction of apoptosis may occur through modulation of TNFalpha signaling pathways. Recent efforts in our laboratory have focused on in vivo models of endotoxin hypersensitivity and the relationship between TNFalpha signaling and oxidative stress. We have characterized the kinetics of TCDD-induced damage in the liver by evaluating serum enzyme levels and quantitating apoptotic cells, and have evaluated alterations in gene expression at critical time points. We have shown that when rodents are treated with TCDD prior to endotoxin exposure a significant increase in toxicity occurs, and that inhibition of protein synthesis with cycloheximide blocks the TCDD-induced sensitivity to TNFalpha in this model. Expression of mRNAs for genes associated with the TNF and Fas apoptotic pathways have been quantitated in liver tissue from control and treated animals using RT-PCR. TCDD modulated endotoxin-regulated early expression of Fas and altered the expression of TNF receptor 1 and nuclear factor kappa B (NFKB). We are currently examining the effects of TCDD on NFKB expression. Preliminary studies suggest that combined TCDD/endotoxin treatment alters nuclear translocation of the p65 subunit or NFKB. While high levels of TNFalpha in the liver are usually associated with septic shock, cytotoxicity, inflammation and/or apoptosis, there is an increasing awareness that TNFalpha also plays a pivotal role in regulation of hepatocyte growth. Previous studies have suggested that peroxisome proliferator-induced alterations in hepatocyte proliferation may be due to the mitogenic activity of TNFalpha released from activated Kupffer cells. Modulation of Kupffer cell activity with agents that limit or prevent cytokine production could be an important therapeutic tool against hepatic toxicity and neoplasia. In collaboration with Dr. Ronald Thurman we have determined that treatment with the peroxisome proliferator Wyeth-14,643 activates Kupffer cells in the liver, stimulating phagocytosis and increasing TNFalpha gene expression and secretion. This increase can be modulated by a number of factors which prevent Kupffer cell activation, such as methyl palmitate, gadolinium chloride and nimodipine. We have also demonstrated that dietary glycine inhibits Kupffer cells activation and prevents TNFalpha production in vivo following treatment with LPS or Wyeth-14,643. This project was previously reported as part of Z01 ES 30106 23 LT