肝细胞一氧化氮合酶的诱导及动力学研究

目的对内毒素和几种细胞因子诱导肝细胞一氧化氮合酶的协同效应及酶动力学参数进行研究.方法原位预灌流和段原酶循环灌流大鼠肝脏、分离肝实质细胞,观察内毒素、IFN-Y、IFN-α、TNFα、IL-lβ、IL-6及不同组合对肝细胞一氧化氮合酶活性、cGMP及NO2-+NO3的影响,分析酶动力学特征及皮质甾与酶诱导的量效关系.结果内毒素+IFN-v+TNFα+IL-lβ(IL-6)组合诱导酶表达效应最显著;酶参数分析显示Km、Vmax分别为108μmol/L和2632pmol@min1mg-1蛋白质,竞争性抑制剂L-NMMA、L-NNA作用的Ki分别为056μmolL及094μmol/L;诱导时间进程显示iNOS活性表达在9h达到峰值,但cGMP及NO2-NO3-的释放持续增加可维持至l8h;地塞米松和氢化可的松抑制肝细胞酶诱导的IC50分别为35×10-8mol/L和26×10-0mol/L.结论肝细胞诱导性一氧化氮合酶的表达依赖特异多细胞因子协同作用,这种可诱导性特征可能在内毒素血症和败血症休克发病机制中具有重要意义.     

Rat liver slices as a tool to study LPS-induced inflammatory response in the liver

BACKGROUND/AIMS: Inflammation in the liver is a complex interaction between parenchymal and non-parenchymal cells, and therefore can not be studied in vitro in pure cultures of these cells. METHODS: We investigated whether Kupffer cells in the liver slice are still responsive to an inflammatory stimulus of lipopolysaccharide (LPS), and evoke an inflammatory response in the hepatocytes. RESULTS: TNFalpha, IL-1beta and IL-10 were significantly elevated in culture medium of LPS-stimulated rat liver slices. Nitric oxide (NO) production of LPS-treated slices gradually increased from 5 to 24 h (24 h: 81+/-5 microM vs. 14+/-2 microM in control P < 0.05), paralleled by inducible nitric oxide synthase (iNOS) in the hepatocytes, iNOS mRNA was induced after 3 h. NO production but not iNOS induction was significantly inhibited by NOS inhibitors S-methylisothiourea and N(G)-nitro-L-arginine methylester. Both pentoxifylline and dexamethasone inhibited TNFalpha and IL-1beta production, albeit to a different extent, iNOS induction and, as a result thereof, NO production. CONCLUSIONS: These results imply that non-parenchymal cells in liver slices are viable and can be activated by LPS. In addition, it is concluded that the upregulation of iNOS in hepatocytes by LPS is caused by cytokines produced by Kupffer cells because inhibition of TNFalpha and IL-1beta production attenuated iNOS induction.     

Nitric oxide production by hepatocytes contributes to the inhibitory effect of endotoxin on insulin-like growth factor I gene expression

We tested whether endotoxin (lipopolysaccharide, LPS) inhibits IGF-I gene expression in hepatocytes and the possible role of Kupffer cells and nitric oxide (NO) in this effect. LPS decreased IGF-I mRNA in hepatocyte cultures and increased the nitrite + nitrate levels in the culture medium. Furthermore, there was a negative correlation between the IGF-I mRNA and the nitrite+nitrate levels. When hepatocytes were cocultured with Kupffer cells, the inhibitory effect of LPS on IGF-I mRNA was higher than in hepatocyte cultures, but the stimulatory effect on nitrite+nitrate was similar in both conditions. The exogenous NO donated by S-nitroso-n-acetyl-d,l-penicillamide also decreased the IGF-I gene expression in hepatocyte cultures. In addition, two specific inducible NO synthase (iNOS) inhibitors, l-N6-(1-iminoethyl)lysine (l-NIL) and aminoguanidine, prevented the effect of LPS on nitrite+nitrate levels and on IGF-I gene expression in hepatocyte cultures. These data indicate that iNOS-derived NO may cause downregulation of IGF-I gene expression in hepatocytes. However, in cocultures, the iNOS inhibitor l-NIL prevented the effect of LPS on nitrite+nitrate levels, but only attenuated the LPS-induced decrease in IGF-I gene expression. We conclude that in hepatocytes, LPS-induced decrease in IGF-I is mainly due to induction of iNOS, whereas in the presence of Kupffer cells LPS inhibits IGF-I through NO release and through other inhibitory pathways.     

Interleukin 1 beta markedly stimulates nitric oxide formation in the absence of other cytokines or lipopolysaccharide in primary cultured rat hepatocytes but not in Kupffer cells

To investigate whether a single inflammatory cytokine could stimulate nitric oxide formation in the absence of other cytokines or lipopolysaccharide (LPS), NO was measured by the redox chemiluminescence method in primary cultured rat hepatocytes and in rat Kupffer cells. Interleukin (IL) 1 beta, but neither IL-6, tumor necrosis factor alpha (TNF-alpha), interferon gamma (IFN-gamma), nor LPS stimulated NO formation in a dose-dependent manner and induced half-maximal effects at 30 pmol/L. Maximal stimulation was achieved at 12 to 16 hours after the addition of 1 nmol/L of IL-1 beta, and was 50- to 60-fold above basal levels in rat hepatocytes. The combined effect of these cytokines with LPS or IFN-gamma on NO formation was also examined. Neither LPS nor IFN-gamma affected the IL-1 beta-induced NO formation. TNF-alpha, however, stimulated IL-1 beta-induced NO formation, while IL-6 inhibited it, although independently these cytokines had no effect on NO formation. None of the cytokines tested stimulated NO formation in cultured rat Kupffer cells. In hepatocytes, the NO formation induced by IL-l beta was blocked by both the NO synthase (NOS) inhibitor N^G-monomethyl-L-arginine (L-NMMA) and by IL-1 receptor antagonist (IL-1ra). Furthermore, IL-1 beta markedly increased NOS activity, and this increase in activity was accompanied by the expression of inducible NOS (iNOS) messenger RNA (mRNA). This study clearly demonstrated that IL-1 beta markedly stimulates NO formation in hepatocytes, in the absence of other cytokines or LPS. (Hepatology 1996 Apr;23(4):797-802)     

Altered response to inflammatory cytokines in hepatic energy metabolism in inducible nitric oxide synthase knockout mice

BACKGROUND/AIMS: Production of nitric oxide (NO) in the liver is believed to be a critical factor for carbohydrate and energy metabolism in endotoxin shock. The present study focuses on the involvement of NO produced by inducible nitric oxide synthase (iNOS) in glycogen synthesis and energy metabolism stimulated by insulin.METHODS: Primary hepatocytes prepared from wild-type and iNOS knockout (iNOS(-/-)) mice were employed.RESULTS: Incubation of wild-type hepatocytes with a combination of cytokines (interleukin-1beta, tumor necrosis factor-alpha and interferon-gamma) and lipopolysaccharide (cytokines/LPS) inhibited insulin-stimulated glycogen synthesis and adenosine triphosphate (ATP) increase, and decreased the ketone body ratio (KBR) at 8-12 h, concomitant with expression of iNOS protein and NO production. While the glycogen synthesis was suppressed by cytokines/LPS, reduction of the ATP increase and a decrease in KBR by cytokines/LPS were not observed in iNOS(-/-) hepatocytes. Further, N(G)-monomethyl-L-arginine, a NOS inhibitor, reversed the inhibition of ATP increase and decrease in KBR by cytokines/LPS, but not the inhibition of glycogen synthesis. Conversely, addition of S-nitroso-N-acetylpenicillamine, a NO donor, inhibited the insulin-stimulated ATP increase synthesis in iNOS(-/-) hepatocytes, but not the insulin-stimulated glycogen synthesis.CONCLUSIONS: These results demonstrate that NO mediates the suppression of insulin-stimulated energy metabolism, but not glycogen synthesis, in cytokines/LPS-treated hepatocytes.     

肿瘤坏死因子α诱导脑血管内皮细胞产生病理性一氧化氮的实验研究

目的探讨肿瘤坏死因子α（TNF—α）作用于脑血管内皮细胞产生病理性一氧化氮（NO）的机制。方法体外培养肿瘤坏死因子受体（TNFR1）基因敲除的小鼠脑血管内皮细胞（BVEC／RI）和野生型小鼠脑血管内皮细胞（BVEC）,分别给予5ng／ml TNF-α刺激24h后,应用PCR技术、Western blot方法、硝酸还原酶法,测定两种细胞的诱导型一氧化氮合酶（iNOS）基因mRNA和蛋白表达量以及所分泌的一氧化氮（NO）含量。结果①给予TNF—α刺激后,野生型BVEC的iNOS mRNA表达增加,BVEC／RI的iNOS mRNA表达未出现明显变化。②给予TNF—α刺激后,野生型BVEC的iNOS蛋白表达量（0．91±0．08）高于未给予TNF-α的BVEC（0．15±0．02）,差异有统计学意义,P〈0．05;BVEC／RI的iNOS蛋白表达量（0．21±0．06）与未给予TNF—α的BVEC／RI（0．30±0．05）相比,差异无统计学意义,P〉0．05。③给予TNF-α刺激后,野生型BVEC的NO含量[（58．6±2．6）μxmol／L]高于未给予TNF—α的BVEC[（18．1±4．3）μmol／L],差异有统计学意义,P〈0．05;BVEC／RI的NO含量[（21．2±3．5）μmol／L]与未给予TNF-α的BVEC／RI[（16．9±3．4）μmol／L]相比,差异无统计学意义,P〉0．05。结论TNF—α可能通过作用于脑血管内皮细胞TNFR1增加iNOS表达,从而增加病理性NO产生。     

Induction of inducible nitric oxide synthase,argininosuccinate synthase,and GTP cyclohydrolase I in arthritic joints of human tumor necrosis factor-alpha transgenic mice

OBJECTIVE: Transgenic mice that express human tumor necrosis factor-alpha (Tg197 h-TNF-alpha) develop polyarthritis at 3 to 4 weeks of age leading to severe joint destruction at 8 to 10 weeks of age. Studies have suggested that inducible nitric oxide synthase (iNOS) activity can modulate the progression of arthritis. We investigated the induction of iNOS together with argininosuccinate synthase (AS) and GTP cyclohydrolase I (GTPCH), 2 of the rate-limiting enzymes for high output NO generation, in the Tg197 h-TNF-alpha transgenic model of arthritis. METHODS: We used 4 and 8-week-old Tg197 h-TNF-alpha transgenic mice and wild-type CBA C57B1/6 control mice to investigate the expression of iNOS with respect to that of AS, GTPCH, and 3-nitrotyrosine by quantitative RT-PCR and immunocytochemistry. Urinary NO metabolites were analyzed using a chemiluminescence assay. RESULTS: Inducible NOS, AS, and GTPCH mRNA was found in all study groups; however, only iNOS mRNA showed a clear increase in 4-week-old Tg197 h-TNF-alpha transgenics in comparison to age matched wild-type controls. Abundant iNOS protein expression was found in macrophages and vascular smooth muscle cells in hyperplastic synovium and pannus. AS expression was found in vascular endothelium and fibroblasts of the inflammatory synovium and pannus. GTPCH immunoreactivity was mostly restricted to macrophages in inflammatory synovium. Localization of 3-nitrotyrosine overlapped with that of iNOS, indicating formation of reactive nitrogen species. Consistent with the high output NO generation, there was a 5-fold increase in urinary NO metabolites in 8-week-old Tg197 h-TNF-alpha transgenic mice. CONCLUSION: We characterized the Tg197 h-TNF-alpha transgenic model of inflammatory arthritis in terms of high output NO-generating pathway, and showed that both AS and GTPCH are intimately associated with inflammatory arthritis. The concomitant induction of AS and GTPCH with that of iNOS suggests that they may be important modulators of arthritis, and that they may represent novel targets for modulation of disease activity.     

一氧化氮可能参与多巴胺对PC12细胞凋亡的诱导作用

目的：探讨多巴胺（DA）诱导的PC12细胞凋亡是否与内源性一氧化氮（NO）生成有关。方法：酶还原法测定NO浓度，RT－PCR法检测诱导型一氧化氮合酶（iNOS)和caspase-3 mRNA表达水平，免疫细胞化学方法和蛋白印迹法分别检测活化型caspase-3蛋白和iNOS蛋白水平。结果：在多巴胺诱导PC12细胞凋亡过程中，iNOS mRNA和蛋白表达明显增加，内源性NO生成增多，caspawse-3mRNA和活化型caspase-3蛋白的表达也明显增加，结论：内源性NO可能参与多巴胺对PC12细胞凋亡的诱导作用。     

Suppressive effects of glucagon-like peptide-1 on interferon-gamma-induced nitric oxide production in insulin-producing cells is mediated by inhibition of tumor necrosis factor-alpha production

During the development of Type 1 diabetes, inflammatory cytokines are known to induce the expression of inducible nitric oxide synthase (iNOS) in pancreatic islets, and subsequent production of nitric oxide (NO) contributes to beta cell destruction. Glucagon-like peptide-1 (GLP-1) has been shown to reduce cytokine-induced apoptosis of beta cells. In this study, we investigated whether GLP-1 affects cytokine-induced NO production, resulting in the inhibition of beta-cell apoptosis. We treated MIN6N8a mouse beta cells with interferon (IFN)-gamma in the presence or absence of GLP-1 and found that IFN-gamma treatment induced iNOS mRNA expression and NO production, which was significantly inhibited by treatment with GLP-1. Blocking of GLP-1 receptor signaling via the cyclic AMP and phosphatidylinositol 3-kinase pathway did not directly affect the suppressive effect of GLP-1 on IFN- gamma-induced iNOS mRNA expression. Further studies revealed that IFN-gamma induced the expression of TNF-alpha mRNA and protein, which synergistically induced NO production, and GLP-1 treatment inhibited this induction of TNF-alpha. To examine whether the reduction of TNF-alpha by GLP-1 treatment plays a role in suppressing NO production, we treated MIN6N8a cells with IFN-gamma in the presence of anti-TNF-alpha neutralizing antibody and found that NO production was reduced. In addition, treatment of mouse islets with GLP-1 inhibited the expression of iNOS and TNFmRNA. These results suggest that GLP-1 inhibits IFN-gamma-induced NO production by suppression of TNF-alpha production.     

HuR binding to cytoplasmic mRNA is perturbed by heat shock

AU-rich elements (AREs) located in the 3' untranslated region target the mRNAs encoding many protooncoproteins, cytokines, and lymphokines for rapid degradation. HuR, a ubiquitously expressed member of the embryonic lethal abnormal vision (ELAV) family of RNA-binding proteins, binds ARE sequences and selectively stabilizes ARE-containing reporter mRNAs when overexpressed in transiently transfected cells. HuR appears predominantly nucleoplasmic but has been shown to shuttle between the nucleus and cytoplasm via a novel shuttling sequence HNS. We report generation of a mouse monoclonal antibody 3A2 that both immunoblots and immunoprecipitates HuR protein; it recognizes an epitope located in the first of HuR's three RNA recognition motifs. This antibody was used to probe HuR interactions with mRNA before and after heat shock, a condition that has been reported to stabilize ARE-containing mRNAs. At 37 degrees C, approximately one-third of the cytoplasmic HuR appears polysome associated, and in vivo UV crosslinking reveals that HuR interactions with poly(A)(+) RNA are predominantly cytoplasmic rather than nuclear. This comprises evidence that HuR directly interacts with mRNA in vivo. After heat shock, 12-15% of HuR accumulates in discrete foci in the cytoplasm, but surprisingly the majority of HuR crosslinks instead to nuclear poly(A)(+) RNA, whose levels are dramatically increased in the stressed cells. This behavior of HuR differs from that of another ARE-binding protein, hnRNP D, which has been implicated as an effector of mRNA decay rather than mRNA stabilization and of the general pre-RNA-binding protein hnRNP A1. We interpret these differences to mean that the temporal association of HuR with ARE-containing mRNAs is different from that of these other two proteins.