肿瘤坏死因子α致暴发性肝功能衰竭小鼠肠上皮细胞凋亡的作用

目的研究肿瘤坏死因子α(TNFα)对暴发性肝功能衰竭(FHF)小鼠肠黏膜上皮细胞凋亡的作用。方法用D-氨基半乳糖(GalN) 脂多糖(LPS)或TNFα造FHF小鼠模型;酶联免疫吸附法测定血清TNFα含量;光学显微镜和电子显微镜观察肠组织;末端转移酶介导的dUTP缺口末端标记法检测肠组织细胞凋亡情况;免疫组织化学法检测肿瘤坏死因子受体I(TNFRⅠ)蛋白在肠组织的表达与分布。结果实验各组动物各时间点光学显微镜下肠黏膜上皮细胞结构均保持完整,电镜下可见肝功能衰竭组有典型的凋亡细胞;对照组、LPS组、GalN组血清TNFα水平几乎正常,凋亡率低且基本没有TNFRⅠ蛋白表达;GalN LPS组血清TNFα水平12h明显升高(P<0.01),且TNFRⅠ蛋白在6h(大肠:2.82e 4±4.60e 3;小肠:1.14e 4±2.13e 3)即有表达,此时肠上皮细胞凋亡不明显,9h和12hTNFRⅠ蛋白表达明显增加,同时肠上皮细胞凋亡也明显。用GalN TNFα造FHF模型,结果也与GalN LPS组类似。应用抗TNFα抗体,可降低TNFRⅠ蛋白表达和减少肠上皮细胞凋亡的发生。结论TNFα能诱导肝功能衰竭小鼠肠上皮细胞凋亡,抗TNFα抗体能阻断这一作用;在FHF的模型动物中,TNFRⅠ蛋白表达增多,TNFRⅠ蛋白表达与肠上皮细胞凋亡在一定程度上呈正相关。

Tumor necrosis factor alpha and enterocyte apoptosis in mice with fulminant hepatic failure

OBJECTIVE: To study the role of tumor necrosis factor-alpha (TNFalpha) on enterocyte apoptosis in the experimental model of fulminant hepatic failure (FHF). METHODS: Liver damage was induced by lipopolysaccharide (LPS)/TNFalpha in D-galactosamine (GalN) sensitized BALB/c mice. Serum TNFalpha levels were determined by enzyme-linked immunosorbent assays (ELISA). The intestinal tissues were studied micro- and ultra-microscopically at 2 h, 6 h, 9 h, 12 h and 24 h time points in mice with fulminant hepatic failure. Enterocyte apoptosis was determined by TUNEL method. The TNFR I expression in the intestinal tissue was tested by immunohistochemistry. RESULTS: (1) Gut mucosa was morphologically normal at every time point in all groups, but typical apoptotic cells could be seen in the experimental groups under the electron microscope. Apoptosis rate of gut mucosal epithelial cells was significantly increased at 6 h (large intestine: 6.47e(-3)+/-2.91e(-4); small intestine: 6.64e(-3)+/-3.78e(-4)), 9 h (large intestine: 6.81e(+4)+/-7.41e(+3); small intestine: 2.58e(+4)+/-2.28e(+3)) and 12 h (large intestine: 4.92e(+4)+/-9.80e(+3); small intestine: 5.24e(+4)+/-3.01e(+3)), and peaked at 12 h in mice with FHF. (2) TNFalpha induced apoptosis of enterocytes in mice with FHF. Anti-TNFalpha inhibited this effect. (3) The integrated OD (IOD) levels of TNFalpha receptor I protein expressed differently in the intestine of mice with GalN/LPS and GalN/ TNFalpha-induced FHF at 9 h after GalN/LPS and GalN/ TNFalpha administration, in comparison with those of the control groups. IOD level of TNFRI changed significantly at 6 h (large intestine: 2.82e(+4)+/-4.60e(+3); small intestine: 1.14e(+4)+/-2.13e(+3)), 9 h (large intestine: 6.81e(+4)+/-7.41e(+3); small intestine: 2.58e(+4)+/-2.28e(+3)) and 12 (large intestine: 4.92e(+4)+/-9.80e(+3); small intestine: 5.24e(+4)+/-3.01e(+3)) hours after GalN/LPS and GalN/ TNFa administration. The expression of TNFR1 protein was significantly higher at 9 and 12 h after GalN/LPS and GalN/TNFa administration than other time points. Protein expression of TNFR1 was positively correlated with enterocyte apoptosis. CONCLUSION: TNFa can induce enterocyte apoptosis in mice with FHF. Anti- TNFalpha IgG can inhibit this role. Excessive TNFRI expression of enterocyte in fulminant hepatic failure can be induced by TNFa, which suggests that TNFalpha can induce apoptosis of enterocyte by up-regulation of TNFRI protein expression.