Inhibition of muscle insulin-like growth factor I expression by tumor necrosis factor-alpha

The role of TNF-alpha in muscle catabolism is well established, but little is known about the mechanisms of its catabolic action. One possibility could be that TNF-alpha impairs the production of local growth factors like IGF-I. The aim of this study was to investigate whether TNF-alpha can directly inhibit IGF-I gene and protein expression in muscle. First, we investigated whether the acute inflammation induced by endotoxin injection changes IGF-I and TNF-alpha mRNA in rat tibialis anterior muscle. Endotoxin rapidly increased TNF-alpha mRNA (7-fold at 1 h, P < 0.001) and later decreased IGF-I mRNA (-73% at 12 h, P < 0.001). Furthermore, in a model of C2C12 myotubes, TNF-alpha strongly inhibited IGF-I mRNA and protein (-73 and -47% after 72 h, P < 0.001 and P < 0.01, respectively). Other proinflammatory cytokines failed to inhibit IGF-I mRNA. The effect of TNF-alpha on IGF-I mRNA was not mediated by nitric oxide, and the activation of NF-kappaB was insufficient to inhibit IGF-I expression. Taken together, our data suggest that TNF-alpha induced in muscle after LPS injection can locally inhibit IGF-I expression. The inhibition of muscle IGF-I production could contribute to the catabolic effect of TNF-alpha.     

Establishment of a consistent L929 bioassay system for TNF-alpha quantitation to evaluate the effect of lipopolysaccharide, phytomitogens and cytodifferentiation agents on cytotoxicity of TNF-alpha secreted by adherent human mononuclear cells

TUMOR necrosis factor-alpha (TNF-alpha) plays an important role in the pathogenesis of rheumatoid arthritis. The present study was to evaluate the effects of lipopolysaccharide (LPS), phytomitogens and cytodifferentiation agents on cytotoxicity of TNF-alpha secreted by adherent human mononuclear cells (AMC). TNF-alpha cytotoxicity in LPS-treated, phytomitogen-treated, and cytodifferentiation agent-treated AMC supernatants were analyzed by the L929 bioassay system. Our results showed that LPS could induce homogeneous TNF-alpha production by AMC whereas, in addition to TNF-alpha, phytomitogens could also induce other TNF-like factors. Neither methotrexate, retinoic acid nor sodium butyrate can inhibit TNF-alpha cytotoxicity, while hexamethylene bisacetamide could not only inhibit TNF-alpha cytotoxicity but also TNF-alpha inducing ability of LPS to AMC.     

Calcitonin gene-related peptide indirectly inhibits IL-7 responses in pre-B cells by induction of IL-6 and TNF-alpha in bone marrow

Calcitonin gene-related peptide (CGRP) has inflammatory and immunoregulatory properties. CGRP directly inhibits IL-7 induced proliferation in developing B cells and also induces soluble factors that inhibit IL-7 responses. We identified 2 cytokines, IL-6 and TNF-alpha, induced by CGRP, that inhibit IL-7 pre-B cell responses. CGRP induction of IL-6 and TNF-alpha mRNA in long-term bone marrow cultures is transient and IL-6 or TNF-alpha inhibit IL-7 induced colony formation by 60%. When added with CGRP, colony formation is completely inhibited. TNF-alpha directly inhibits IL-7 responses in B220(+)/IgM(-) cells whereas IL-6 inhibits only colony formation with whole bone marrow. This suggests that the effect of IL-6 is mediated by other cells in the bone marrow. These results suggest that the indirect effect of CGRP on IL-7 depends in part on induction of IL-6 and TNF-alpha.     

睾酮对内皮细胞妊娠相关血浆蛋白-A mRNA表达的影响

目的:观察睾酮对内皮细胞妊娠相关血浆蛋白-A(PAPP-A)m RNA表达的影响。方法:人原代脐静脉内皮细胞,选择第3~4代生长状态良好的细胞用于实验。实验分组:1空白对照组;2肿瘤坏死因子(TNF)-α(终浓度100μg/L)培养细胞组;3TNF-α(终浓度100μg/L)及睾酮1×10-8mol/L培养细胞组;4睾酮1×10-8mol/L培养细胞组。实验结束后收集各组细胞,用RT-PCR方法检测各组细胞PAPP-A m RNA表达水平。结果:TNF-α作用2 h后,内皮细胞中PAPP-A m RNA表达水平升高(P0.05),且随TNF-α作用时间的延长,PAPP-A表达逐渐升高,在16小时达高峰;睾酮作用后,PAPP-A m RNA表达水平较TNF-α组明显降低(P0.01)。结论:TNF-α上调内皮细胞PAPP-A m RNA的表达,而睾酮抑制了TNF-α对PAPP-A分泌增加的刺激作用。     

Regulation of collagen deposition and lysyl oxidase by tumor necrosis factor-alpha in osteoblasts

Tumor necrosis factor-alpha (TNF-alpha) inhibits osteoblast function in vitro by inhibiting collagen deposition. Studies generally support that TNF-alpha does not inhibit collagen biosynthesis by osteoblasts but that collagen deposition is in some way diminished. The study investigated TNF-alpha regulation of biosynthetic enzymes and proteins crucial for posttranslational extracellular collagen maturation in osteoblasts including procollagen C-proteinases, procollagen C-proteinase enhancer, and lysyl oxidase. The working hypothesis is that such regulation could inhibit collagen deposition by osteoblasts. We report that in phenotypically normal MC3T3-E1 osteoblasts, TNF-alpha decreases collagen deposition without decreasing collagen mRNA levels or procollagen protein synthesis. Analyses of the cell layers revealed that TNF-alpha diminished the levels of mature collagen cross-links, pyridinoline and deoxypyridinoline. Further analyses revealed that the mRNA expression for lysyl oxidase, the determining enzyme required for collagen cross-linking, is down-regulated by TNF-alpha in a concentration- and time-dependent manner by up to 50%. The decrease was accompanied by a significant reduction of lysyl oxidase protein levels and enzyme activity. By contrast, Northern and Western blotting studies revealed that procollagen C-proteinases bone morphogenic protein-1 and mammalians Tolloid and procollagen C-proteinase enhancer were expressed in MC3T3-E1 cells and not down-regulated. The data together demonstrate that TNF-alpha does not inhibit collagen synthesis but does inhibit the expression and activity of lysyl oxidase in osteoblasts, thereby contributing to perturbed collagen cross-linking and accumulation. These studies identify a novel mechanism in which proinflammatory cytokine modulation of an extracellular biosynthetic enzyme plays a determining role in the control of collagen accumulation by osteoblasts.     

Influence of tumor necrosis factor-alpha on the ability of monocytes and lymphocytes to destroy intraerythrocytic Plasmodium falciparum in vitro

It has been shown that administration of TNF-alpha causes an increase of survival of plasmodium-infected mice. However, this anti-parasitic effect cannot be reproduced in vitro upon direct incubation of the cytokine with the parasite. This suggests that TNF-alpha may act through modulation of some plasmodicidal mechanism not yet clarified. We evaluated the effect of exogenous TNF-alpha on the phagocytosis of Plasmodium falciparum-infected erythrocytes by monocytes and its influence on the ability of monocytes and lymphocytes to inhibit parasite growth. The capacity of endogenous TNF-alpha to influence the ability of monocytes to inhibit the parasite was also verified. We found that addition of 33 ng TNF-alpha/mL to cultures of human monocytes and P. falciparum-infected erythrocytes increased the phagocytic index from 3.8 to 7.8 in the presence of serum containing P. falciparum antibody. TNF-alpha increased the capacity of monocyte plus lymphocyte to inhibit parasite growth by about 3 times at 0.5 and 5 ng/mL. Sera from severely ill P. falciparum-infected individuals inhibited the parasite growth, but addition of anti-TNF-alpha antibody was unable to modify this inhibition. These data show that TNF-alpha can increase the phagocytic capacity. This was probably due to an increased expression of Fc receptors on monocytes or to the modulation of Fc receptor signaling pathways by signals originating from the binding of TNF-alpha to its receptors. TNF-alpha also acted on lymphocytes plus monocytes by increasing the inhibition of P. falciparum by a mechanism not related to phagocytosis. These findings suggest that TNF-alpha has a pleiotropic anti-malaria effect and that this protective effect depends on the interplay of different factors, such as monocytes/macrophages, lymphocytes, and antibodies, in addition to other cells and molecules.     

Synergistic effect of tumor necrosis factor-alpha- and diphtheria toxin-mediated cytotoxicity in sensitive and resistant human ovarian tumor cell lines

Recent studies have demonstrated that diphtheria toxin (DTX) also mediates target cell lysis, and the mechanism of cytotoxicity has many features similar to those of cytotoxicity mediated by TNF-alpha. Thus, we hypothesized that DTX and TNF-alpha, used in combination, may result in either additive or synergistic cytotoxic activity. This was examined on three human ovarian carcinoma cell lines chosen for their differing sensitivities to TNF-alpha and DTX, i.e., 222, which is sensitive to both TNF-alpha and DTX, 222TR, a TNF-alpha-resistant DTX-sensitive variant of 222, and SKOV-3, which is resistant to both DTX and TNF-alpha. The simultaneous use of DTX and TNF-alpha at suboptimal concentrations resulted in synergistic cytotoxic activity against all three lines tested, thus overcoming the TNF-alpha resistance of 222TR and the double resistance of SKOV-3. DNA fragmentation was observed in all three lines treated with DTX and TNF-alpha and occurred as early as 4 h after treatment. Cycloheximide, actinomycin D, or emetine, at concentrations causing greater than 90% protein synthesis inhibition, did not result in cytotoxicity alone or synergy with TNF-alpha, suggesting that synergy by DTX was not due to its ability to inhibit protein synthesis. The use of energy poisons and pH conditions that inhibit DTX-mediated cytotoxicity resulted in the abrogation of synergy. These findings show that the two cytotoxic agents TNF-alpha and DTX, when used at suboptimal concentrations, synergize in their cytotoxic activity against sensitive and resistant cell lines. Because the SKOV-3 cell line used here is also resistant to chemotherapeutic drugs, combination treatment with DTX and TNF-alpha may be beneficial in overcoming drug resistance.     

Tumor necrosis factor-alpha is induced through phorbol ester--and glycated human albumin-dependent pathway in THP-1 cells

Tumor necrosis factor-alpha (TNF-alpha) is involved in insulin resistance. Since the fact that peroxisome proliferator-activated receptor gamma (PPARgamma) ligands inhibit the induction of TNF-alpha by phorbol ester, but not by lipopolysaccharide (LPS), suggests two pathways to induce TNF-alpha, we investigated the mechanisms of glycated human albumin (GHA)- or phorbol ester-induced TNF-alpha in THP-1 cells. GHA induced TNF-alpha release in differentiated THP-1 cells, while phorbol ester induced TNF-alpha release in undifferentiated cells but did not induce TNF-alpha in differentiated cells. Forskolin (adenylate cyclase activator) affected more the GHA-induced TNF-alpha release than the phorbol 12-myristate 13-acetate (PMA)-induced one in undifferentiated cells. Staurosporine [protein kinase-C (PK-C) inhibitor] and PD98059 [mitogen-activated protein kinase inhibitor (MAPK)] only partially inhibited GHA-induced TNF-alpha. Catalase completely inhibited GHA-induced TNF-alpha release; however, superoxide dismutase (SOD) had no effect. These results suggest at least two pathways to induce TNF-alpha (phorbol ester- and GHA-dependent ways) and that GHA-induced TNF-alpha release is through predominantly catalase-dependent way in differentiated THP-1 cells.     

Benzobicyclooctanes as novel inhibitors of TNF-alpha signaling

A novel series of TNF-alpha inhibitors based on a benzobicyclooctane scaffold is reported. The compounds display good potency in inhibiting TNF-alpha induced apoptosis and NF kappa B activation. Additionally, they are selective for TNF-alpha as they do not inhibit apoptosis induced by soluble Fas ligand. The compounds described here can act as leads for future medicinal chemistry efforts and may also be useful tools for elucidating the TNF-alpha signaling pathway.     

Alpha-fluoro-substituted thalidomide analogues

Thalidomide, (1), has made a remarkable comeback from its days of a sedative with teratogenic properties due to its ability to selectively inhibit TNF-alpha, a key pro-inflammatory cytokine and its clinical benefit in the treatment of cancer. Thalidomide contains one chiral center and is known to be chirally unstable under in vitro and in vivo conditions. It has been hypothesized that different biological properties are associated with each isomer. Thus, chirally stable analogues of thalidomide, alpha-fluorothalidomide, (3) and alpha-fluoro-4-aminothalidomide (4) were prepared by electrophilic fluorination. Analogue 3 was found to be cytotoxic and did not inhibit TNF-alpha production in LPS stimulated hPBMC below toxic concentrations. On the other hand, 4 was non-cytotoxic at the tested concentrations and was found to be 830-fold more potent than thalidomide as TNF-alpha inhibitor.     

Modulation of cytokine release from mononuclear cells by prostacyclin, IL-4 and IL-13

In a previous study, we reported that cicaprost, a stable prostacyclin analogue can inhibit the release of granulocyte-macrophage colony-stimulating factor (GM-CSF) from activated human peripheral mononuclear blood cells (PBMCs). Since interleukin (IL-4) and IL-13 have been shown to inhibit the release of cytokines from PBMCs we tested the hypothesis that prostacyclin in combination with IL-4 or IL-13 can act synergistically to modulate the release of IL-10, generally associated with anti-inflammatory properties, and the pro-inflammatory cytokine tumour necrosis factor alpha (TNF-alpha). For this purpose, PBMCs were isolated over Ficoll, stimulated with lipopolysaccharide (LPS) and incubated in the presence of cicaprost, IL-4 or IL-13. There was a significant reduction in TNF-alpha as well as IL-10 secretion from LPS-stimulated PBMCs following incubation with IL-4 or IL-13. In contrast, cicaprost reduced the secretion of TNF-alpha but led to a slight enhancement of IL-10 release from PBMCs. When LPS-activated PBMCs were incubated in the presence of cicaprost and IL-4 or IL-13 there was a selective, synergistic inhibition of the TNF-alpha release which was not observed for IL-10. Thus, our data suggest that prostacyclin can synergize with cytokines to selectively inhibit the release of pro-inflammatory cytokines from PBMCs.     

Tumor necrosis factor-alpha, sphingomyelinase, and ceramide inhibit store-operated calcium entry in thyroid FRTL-5 cells

Tumor necrosis factor alpha (TNF-alpha) is a potent inhibitor of proliferation in several cell types, including thyroid FRTL-5 cells. As intracellular free calcium ([Ca2+]i) is a major signal in activating proliferation, we investigated the effect of TNF-alpha on calcium fluxes in FRTL-5 cells. TNF-alpha per se did not modulate resting [Ca2+]i. However, preincubation (10 min) of the cells with 1-100 ng/ml TNF-alpha decreased the thapsigargin (Tg)-evoked store-operated calcium entry in a concentration-dependent manner. TNF-alpha did not inhibit the mobilization of sequestered calcium. To investigate whether the effect of TNF-alpha on calcium entry was mediated via the sphingomyelinase pathway, the cells were pretreated with sphingomyelinase (SMase) prior to stimulation with Tg. SMase inhibited the Tg-evoked calcium entry in a concentration-dependent manner. Furthermore, an inhibition of calcium entry was obtained after preincubation of the cells with the membrane-permeable C2-ceramide and C6-ceramide analogues. The inactive ceramides dihydro-C2 and dihydro-C6 showed only marginal effects. Neither SMase, C2-ceramide, nor C6-ceramide affected the release of sequestered calcium. C2- and C6-ceramide also decreased the ATP-evoked calcium entry, without affecting the release of sequestered calcium. The effect of TNF-alpha and SMase was inhibited by the kinase inhibitor staurosporin and by the protein kinase C (PKC) inhibitor calphostin C but not by down-regulation of PKC. However, we were unable to measure a significant activation of PKC using TNF-alpha or C6-ceramide. The effect of TNF-alpha was not mediated via activation of either c-Jun N-terminal kinase or p38 kinase. We were unable to detect an increase in the ceramide (or sphingosine) content of the cells after stimulation with TNF-alpha for up to 30 min. Thus, one mechanism of action of TNF-alpha, SMase, and ceramide on thyroid FRTL-5 cells is to inhibit calcium entry.     

De novo design TNF-alpha antagonistic peptide based on the complex structure of TNF-alpha with its neutralizing monoclonal antibody Z12

Tumor necrosis factor-alpha (TNF-alpha) antagonists have become therapeutic drugs for immunological diseases including rheumatoid arthritis, inflammatory bowel disease, Crohn's disease, etc. Low molecular weight synthetic peptides can mimic the binding sites of TNF-alpha receptors and block the activity of TNF-alpha. Based on the 3-D complex structure of TNF-alpha with its neutralizing monoclonal antibody (Mab) Z12, an antagonistic peptide (AP) was rationally de novo designed. The designed AP possessed similar structural character and potential bioactivity with Mab Z12. AP could competitively inhibit the binding of Mab Z12 to TNF-alpha, TNF-alpha-meditated caspase activation and TNF-alpha-induced cytotoxicity on murine L929 cells with a dose-dependent fashion. This study highlights the potential of computation-aided method for the design of novel peptides with the ability to block the deleterious biological effects of TNF-alpha.     

Establishment of a cell-based assay for examining the expression of tumor necrosis factor alpha (TNF-α) gene

Tumor necrosis factor alpha (TNF-alpha) is a proinflammatory cytokine produced by activated macrophages and lymphocytes and involved in many inflammatory diseases. Preventing the production or action of TNF-alpha is a potent therapeutic strategy for these inflammatory diseases. Since there is a lack of rapid and effective assay for examining the expression TNF-alpha in macrophages, we attempt to establish a reporter system to assess TNF-alpha gene expression through measuring luciferase activity. In this study, mouse macrophage cell line RAW 264.7 was stably transfected with a luciferase reporter pGL3-TNFPro-UTR, which contains TNF-alpha promoter and 3'-untranslated region (3'-UTR). The TNF-alpha-luciferase reporter cell line is used for assessing the expression of TNF-alpha gene induced by LPS in the presence or absence of chemicals that inhibit the biosynthesis of TNF-alpha such as dexamethasone and emodin, and also for measuring change of expression of TNF-alpha gene under downregulation of the expression of steroid receptor coactivator-3, a modulator for TNF-alpha. The luciferase activity correlated well with the ELISA results for TNF-alpha production, therefore, the TNF-alpha-luciferase reporter cell line is a sensitive, effective tool for studying the expression of TNF-alpha gene.     

利用大肠杆菌鞭毛展示的随机肽库筛选TNF—α拮抗须

TNF－α是一种在机体抗感染,抗肿瘤过程中发挥重要作用的细胞因子,其对机体具有保护和损伤两方面的作用,为了探讨新的抑制TNF－α所致炎症损伤等反应的手段,构建了细菌鞭毛递呈的随机肽库,利用构建得到的肽库,进行TNF－α特异性结合肽的筛选工作。经过5轮筛选及DNA测序,共得到6条小肽编码序列。其中2条序列中含有－V－－N－WG的相同序列框架。进行6条序列与TNF－α结合力的确证后,选择了其中的4条肽序列进行人工化学合成,纯化及鉴定。利用L929细胞及MTT法对4条小肽进行活性测定,检测其对TNF－α的抑制活性。结果表明,在TNF－α对L929细胞毒性为30％左右,含同源序列框架的2条肽可抑制90％左右的TNF－α活性。     

Distinct domains of M-T2, the myxoma virus tumor necrosis factor (TNF) receptor homolog, mediate extracellular TNF binding and intracellular apoptosis inhibition.

The myxoma virus tumor necrosis factor (TNF) receptor homolog, M-T2, is expressed both as a secreted glycoprotein that inhibits the cytolytic activity of rabbit TNF-alpha and as an endoglycosidase H-sensitive intracellular species that prevents myxoma virus-infected CD4+ T lymphocytes from undergoing apoptosis. To compare the domains of M-T2 mediating extracellular TNF inhibition and intracellular apoptosis inhibition, recombinant myxoma viruses expressing nested C-terminal truncations of M-T2 protein were constructed. One mutant, deltaL113, containing intact copies of only two cysteine-rich domains, was not secreted and was incapable of binding rabbit TNF-alpha yet retained full ability to inhibit virus-induced apoptosis of RL-5 cells. Thus, the minimal domain of intracellular M-T2 protein required to inhibit apoptosis is distinct from that required by the extracellular M-T2 for functional TNF-alpha binding and inhibition. This is the first report of a virus-encoded immunomodular protein with two distinct antiimmune properties.     

Transcriptional regulation of TNF-alpha production in neutropenia

Neutropenia has been shown to markedly increase plasma TNF-alpha concentration after LPS injection and to enhance LPS-induced mortality. Experiments reported here demonstrate that the 15-fold higher plasma TNF-alpha concentration elicited by LPS in neutropenic vs. nonneutropenic unanesthetized mice correlated with increased hepatic and splenic, but not pulmonary, TNF-alpha mRNA. Core 2 beta-1,6-N-acetylglucosaminyltransferase-null and CD18-deficient mice also exhibited exaggerated plasma TNF-alpha responses to LPS injection. Findings suggest that extravasated neutrophils inhibit systemic TNF-alpha production and that they do so through organ-selective mechanisms involving CD18 integrin and selectin binding.     

Melanocyte stimulating hormone peptides inhibit TNF-alpha signaling in human dermal fibroblast cells

Alpha-melanocyte stimulating hormone (alpha-MSH) has been identified as a potent anti-inflammatory in various tissues including the skin. It has previously been shown in skin cell keratinocytes and melanocytes/melanoma cells that MSH peptides inhibit TNF-alpha stimulated NF-kappaB activity and intercellular adhesion molecule-1 (ICAM-1) upregulation. However, the precise anti-inflammatory role of MSH peptides in dermal fibroblasts is unclear. Some studies report on pro-inflammatory responses, while others on anti-inflammatory responses. The present study confirms MC1R expression in cultured human dermal fibroblasts and reports that the MSH peptides alpha-MSH and KP(-D-)V inhibit TNF-alpha stimulated NF-kappaB activity and ICAM-1 upregulation, consistent with an anti-inflammatory role. However, involvement of IkappaB-alpha regulation by either peptide was not confirmed, supporting a mechanism independent of the NF-kappaB inhibitor. In conclusion, alpha-MSH and KP(-D-)V peptides have an anti-inflammatory action on dermal fibroblast signaling by inhibiting the pro-inflammatory activity of TNF-alpha in vitro.