Endotoxin tolerance: independent regulation of interleukin-1 and tumor necrosis factor expression.

The injection of lethal or sublethal doses of bacterial lipopolysaccharide (LPS) into mice results in transient increases in both serum tumor necrosis factor (TNF) and interleukin-1 (IL-1). The peak in serum TNF was detected prior to maximal elevation in endogenous corticosterone and was no longer apparent 3 to 4 h post-LPS injection, a point at which corticosterone and IL-1 levels had significantly increased. The initial increase in serum IL-1 may, in part, be modulated by the preceding TNF peak, as pretreating animals with a monoclonal antibody against murine TNF resulted in a significant decrease in IL-1 levels 3 h post-LPS injection. A second injection of LPS at 20 h failed to result in a secondary TNF peak, suggesting an endotoxin-tolerant state. However, in contrast to TNF, significant increases in serum IL-1 were detected in the endotoxin-tolerant animals following a repeated LPS stimulus. This secondary increase in IL-1 occurred despite the elevation in serum corticosterone. While peritoneal macrophages from endotoxin-tolerant mice demonstrated only a modest 10 to 15% increase in TNF and IL-1 mRNA relative to the levels after the primary 1-h LPS stimulus, a secondary increase in IL-1 but not TNF mRNA in the spleen was apparent following a second LPS injection. The spleen, however, was not essential for the increase in serum IL-1, as endotoxin-tolerant splenectomized mice had comparable increases in IL-1 following a repeated LPS stimulus. These results demonstrate the differential regulation of IL-1 and TNF in vivo during endotoxin tolerance.     

In vivo inhibition of lipopolysaccharide-induced lethality and tumor necrosis factor synthesis by Rhodobacter sphaeroides diphosphoryl lipid A is dependent on corticosterone induction.

Diphosphoryl lipid A from the lipopolysaccharide (LPS) of Rhodobacter sphaeroides (Rs-DPLA) has been demonstrated to block in mice and guinea pigs the increase in the serum tumor necrosis factor (TNF) response induced by highly purified deep rough chemotype LPS from Escherichia coli D31m4 (ReLPS). The present study was designed to determine the role of corticosterone induction by Rs-DPLA and its effect on TNF regulation and survival in lethal endotoxin shock models and to evaluate the ability of Rs-DPLA to induce endotoxin tolerance. Administration of a 100-fold excess of Rs-DPLA 1 h prior to ReLPS administration inhibited the characteristic peak in serum TNF levels induced by LPS. Inhibition was apparent in normal and D-galactosamine (GalN)-sensitized mice and occurred at the pretranslational level, as splenic TNF and interleukin-1 beta mRNAs were present in lower amounts in LPS-stimulated mice pretreated with Rs-DPLA. Consistent with its effects in reducing serum TNF levels, Rs-DPLA pretreatment protected GalN-sensitized mice from a lethal ReLPS challenge. In contrast, Rs-DPLA did not inhibit the increase in the serum TNF response or protect against a lethal ReLPS challenge in parallel experiments with adrenalectomized (Adrex) mice, for which the 50% lethal dose of ReLPS was comparable to that for GalN-sensitized mice. Furthermore, Rs-DPLA appeared to prime Adrex animals and increase the magnitude of the serum TNF response to a suboptimal LPS stimulus. Priming by Rs-DPLA, however, was not observed in normal or GalN-sensitized mice. Although Rs-DPLA by itself was nontoxic and unable to elevate serum TNF levels in any of the models investigated, it did induce a significant increase in the serum corticosterone response and was capable of inducing endotoxin tolerance in normal mice. The inability of Rs-DPLA to protect Adrex mice from a lethal ReLPS stimulus or to inhibit the increase in the serum TNF response suggests that the protective effect of Rs-DPLA in normal or GalN-sensitized animals occurs through corticosterone induction. These results support the concept that endogenous glucocorticoids can modulate the endotoxic effects of LPS by inhibiting the synthesis of inflammatory cytokines.     

Induction of Lethal Shock and Tolerance by Porphyromonas gingivalis Lipopolysaccharide in d-Galactosamine-Sensitized C3H/HeJ Mice

Lipopolysaccharide (LPS) obtained from Porphyromonas gingivalis was found to exhibit marked lethal toxicity in galactosamine-sensitized C3H/HeJ mice. Although no lethality was observed in mice intraperitoneally challenged with 1 mg of P. gingivalis LPS without galactosamine, when they were sensitized with 30 mg of galactosamine, challenge with 1 and 10 micrograms of LPS resulted in 67 and 100% lethality, respectively. The lethal dose of LPS was almost the same in LPS-responsive C57BL/6 mice and non-LPS-responsive C3H/HeJ mice. Furthermore, when 1 microgram of P. gingivalis LPS was administered to each mouse 90 min before the challenge with the same LPS with galactosamine, tolerance to the lethal action of LPS was induced, and the mice were completely protected from death, even at a dose 100-fold greater than the lethal dose of LPS. Neither a lethal effect nor induction of tolerance to the lethality of P. gingivalis LPS was exhibited by Salmonella LPS in galactosamine-sensitized C3H/HeJ mice. A protein-LPS complex derived from Pseudomonas aeruginosa, which exhibited strong lethality and induced tolerance to a subsequent challenge with a lethal dose of LPS in galactosamine-sensitized LPS-responsive mice, did not exhibit lethal toxicity in galactosamine-sensitized C3H/HeJ mice and failed to induce tolerance in these mice to the lethality of P. gingivalis LPS. These results indicate that P. gingivalis LPS plays the central role in the activation of non-LPS-responsive C3H/HeJ mice.     

Colchicine prevents tumor necrosis factor-induced toxicity in vivo.

Tumor necrosis factor (TNF) toxicity was induced in vivo by intravenous administration of 15 micrograms of recombinant murine TNF-alpha per kg to galactosamine-sensitized mice. Within 8 h, the animals developed a fulminant hepatitis. Intravenous administration of 0.5 mg of colchicine per kg at 19 and 4 h prior to TNF challenge protected the animals against hepatitis. Lipopolysaccharide (LPS)-stimulated, bone marrow-derived macrophages from C3H/HeN mice released significant amounts of TNF in vitro. When such macrophages were intravenously given to LPS-resistant galactosamine-sensitized C3H/HeJ mice, these animals died within 24 h. Preincubation of these transferred macrophages with colchicine did not suppress the LPS-inducible TNF release from these cells. Concordantly, administration of macrophages exposed to colchicine in vitro resulted in full lethality. However, in vivo pretreatment of C3H/HeJ mice with colchicine 19 and 4 h prior to the transfer of LPS-stimulated macrophages prevented lethality. In LPS-responsive NMRI mice which had been protected against galactosamine-LPS-induced hepatitis by pretreatment with colchicine, TNF was still released into the blood. We conclude from our findings that the in vivo protection by colchicine is mediated by blocking TNF action on target cells while the effector cells of LPS toxicity, i.e., the macrophages, remain responsive.     

Toll-like receptor 2- and 6-mediated stimulation by macrophage-activating lipopeptide 2 induces lipopolysaccharide (LPS) cross tolerance in mice,which results in protection from tumor necrosis factor alpha but in only partial protection from lethal LPS doses

Patients or experimental animals previously exposed to lipopolysaccharide (LPS) become tolerant to further LPS challenge. We investigated the potential of the macrophage-activating lipopeptide 2 (MALP-2) to induce in vivo cross tolerance to tumor necrosis factor alpha (TNF-alpha) and LPS. MALP-2-induced tolerance could be of practical interest, as MALP-2 proved much less pyrogenic in rabbits than LPS. Whereas LPS signals via Toll-like receptor 4 (TLR4), MALP-2 uses TLR2 and TLR6. LPS-mediated cytokine release was studied in mice pretreated with intraperitoneal injections of MALP-2. No biologically active TNF-alpha could be detected in the serum of MALP-2-treated animals when challenged with LPS 24 or 72 h later, whereas suppression of LPS-dependent interleukin (IL)-6 lasted for only 24 h. Protection from lethal TNF-alpha shock was studied in galactosamine-treated mice. Dose dependently, MALP-2 prevented death from lethal TNF-alpha doses in TLR4(-/-) but not in TLR2(-/-) mice, with protection lasting from 5 to 24 h. To assay protection from LPS, mice were pretreated with MALP-2 doses of up to 10 micro g. Five and 24 h later, the animals were simultaneously sensitized and challenged by intravenous coinjection of galactosamine and a lethal dose of 50 ng of LPS. There was only limited protection (four of seven mice survived) when mice were challenged 5 h after MALP-2 pretreatment, and no protection when mice were challenged at later times. The high effectiveness of MALP-2 in suppressing TNF-alpha, the known ways of biological inactivation, and low pyrogenicity make MALP-2 a potential candidate for clinical use.     

Reduced leptin levels in starvation increase susceptibility to endotoxic shock

Malnutrition compromises immune function, reducing resistance to infection. We examine whether the decrease in leptin induced by starvation increases susceptibility to lipopolysaccharide (LPS)- and tumor necrosis factor (TNF)-induced lethality. In mice, fasting for 48 hours enhances sensitivity to LPS. Decreasing the fasting-induced fall in leptin by leptin administration markedly reduced sensitivity to LPS. Although fasting decreases basal leptin levels, LPS treatment increased leptin to the same extent as in fed animals. Fasting increased basal serum corticosterone; leptin treatment blunted this increase. Fasting decreased the ability of LPS to increase corticosterone; leptin restored the corticosterone response to LPS. Serum glucose levels were decreased in fasted mice and LPS induced a further decrease. Leptin treatment affected neither basal glucose nor that after LPS. LPS induced a fivefold greater increase in serum TNF in fasted mice, which was blunted by leptin replacement. In contrast, LPS induced lower levels of interferon-gamma and no differences in interleukin-1beta in fasted compared to fed animals; leptin had no effect on those cytokines. Furthermore, fasting increased sensitivity to the lethal effect of TNF itself, which was also reversed by leptin treatment. Thus, leptin seems to be protective by both inhibiting TNF induction by LPS and by reducing TNF toxicity.     

Differential regulation of lipopolysaccharide-induced interleukin 1 and tumor necrosis factor synthesis: effects of endogenous and exogenous glucocorticoids and the role of the pituitary-adrenal axis

Intraperitoneal injection of a sublethal dose of lipopolysaccharide (LPS) into mice resulted in the appearance of tumor necrosis factor (TNF) in the serum within 45 min. Maximal serum TNF was detected by 1 h, and by 3-4 h TNF levels were no longer significantly above baseline. Injection of mice with an additional dose of LPS at 4 h resulted in no further increase in serum TNF. The in vivo kinetics of TNF appearance correlated with in vitro studies in which TNF mRNA was detected in murine peritoneal macrophages 30 min after LPS stimulation. The increase in serum TNF was not detected in mice treated with dexamethasone, 3 mg/kg, prior to LPS stimulation. The decrease in TNF correlated with the appearance of significant amounts of endogenous serum corticosterone which were maximal by 3 h. Further evidence for the role of endogenous steroids in the modulation of serum TNF levels was obtained in studies with adrenalectomized or hypophysectomized mice. Compared to sham-operated animals, serum TNF levels remain elevated 5 h post LPS stimulation in adrenalectomized or hypophysectomized mice. In contrast with the transient increase in TNF, serum IL 1 was maximal 4 h post LPS injection and remained elevated at 24 h. In vitro studies with primary cultures of human peripheral blood monocytes and human umbilical cord vein endothelial cells demonstrated that LPS-induced monocyte IL 1 levels were reduced approximately 5-fold by 10(-7) M dexamethasone while dexamethasone had only minimal effects on endothelial cell IL 1. Therefore, the in vitro data would suggest that the maintenance of elevated IL 1 levels coincident with the appearance of endogenous corticosteroids during LPS shock is related to the synthesis of IL 1 by both monocyte-macrophages and non-myeloid cell populations including endothelial cells.     

Lipopolysaccharide-tumor necrosis factor-glucocorticoid interactions during cecal ligation and puncture-induced sepsis in mature versus senescent mice.

Previous work in our laboratory demonstrated increased sensitivity of senescent (24-month-old) mice to cecal ligation and puncture (CLP) sepsis compared with that of mature (12-month-old) mice. In this study the median lethal dose of the strain of Escherichia coli most frequently isolated during CLP sepsis was determined. No significant age-associated difference in the mean lethal dose or the mean survival time was noted; however, sham surgery before injection of E. coli decreased the mean lethal dose by at least 100-fold. With surgical manipulation, the average time to death after bacterial injection simulated more closely that observed after CLP surgery. Host responses to CLP sepsis were investigated by measuring the levels of corticosterone, glucose, and tumor necrosis factor (TNF) in the sera of mature and senescent mice at 2-h intervals after surgery. Corticosterone levels increased gradually during the course of sepsis in mature mice; however, senescent mice demonstrated a pronounced elevation in hormone levels at 2 and 4 h after surgery. At subsequent sampling intervals the corticosterone levels remained elevated, although they were similar for both ages. At all sampling intervals, the glucose levels in serum were lower in senescent mice than in mature mice. Pronounced hypoglycemia (less than 80 mg/dl) was observed in senescent mice at 8 h postsurgery. TNF was detected in serum within a narrow time frame in both age groups at 6, 8, and 10 h postsurgery. Although elevated TNF levels in serum were not seen in every mouse in each group (approximately 50%), the data hinted that senescent animals produced larger quantities of TNF during CLP sepsis than did mature animals. E. coli lipopolysaccharide (1 mg/kg) was injected intraperitoneally, and the TNF levels in serum and peritoneal lavage fluid were measured at 30, 60, and 90 min. Senescent mice demonstrated a level of TNF in serum at 90 min after lipopolysaccharide treatment that was 20-fold higher than that of mature mice (299,877 pg/ml versus 15,594 pg/ml). The amount of TNF produced locally in the peritoneum was also substantially higher in senescent mice than in mature animals (1,716 pg/ml versus 776 pg/ml). The increased production of TNF in senescent animals, despite elevated circulating corticosterone levels, suggested an age-related defect in glucocorticoid-directed downregulation of TNF production. This was confirmed in lipopolysaccharide-treated animals given exogenous dexamethasone.(ABSTRACT TRUNCATED AT 400 WORDS)     

Regulation of serum tumor necrosis factor in glucocorticoid-sensitive and -resistant rodent endotoxin shock models.

Bolus injection of lethal or sublethal doses of endotoxin or lipopolysaccharide (LPS) results in the rapid and transient rise in tumor necrosis factor (TNF) levels in serum in mammals. TNF levels peak between 1 and 2 h after LPS injection in mice and guinea pigs and approach basal levels by 6 h. Although the kinetics of TNF in serum appear similar between these two species, guinea pigs respond to a lethal dose of LPS of 20 mg/kg by producing approximately 10-fold more TNF than mice do. These two endotoxin shock models also differ in their sensitivity to glucocorticoids. TNF levels in serum are not reduced in the lethal endotoxin shock model in guinea pigs after treatment with dexamethasone at 25 mg/kg. In contrast, TNF levels in mouse serum are inhibited by more than 90% after treatment with dexamethasone at 3 mg/kg. Coincident with the TNF peak in serum is a leukopenia which approaches control levels by 6 h in dexamethasone-treated mice, while remaining depressed in dexamethasone-treated guinea pigs. Treatment with dexamethasone at 25 mg/kg did not save guinea pigs from endotoxin lethality, whereas long-term survival of mice under identical conditions was apparent. These results suggest that the relative glucocorticoid resistance observed in guinea pigs is also apparent in a lethal endotoxin shock model in which dexamethasone does not modulate TNF levels or result in increased survival as occurs in mice. The lack of clear efficacy for steroid therapy in human clinical septic shock trials would suggest that the guinea pig endotoxin model may be a more predictive system than the mouse model for the identification of novel agents useful in the treatment of endotoxin shock.     

Chlorpromazine specifically inhibits peripheral and brain TNF production, and up-regulates IL-10 production, in mice.

We have previously shown that chlorpromazine (CPZ) inhibits tumour necrosis factor (TNF) production and protects against endotoxic shock in mice. In this paper we investigated the effect of pretreatment with CPZ, 4 mg/kg i.p. 30 min before, compared with dexamethasone (DEX; 3 mg/kg) on the induction of other endotoxin (lipopolysaccharide; LPS)-induced cytokines in the serum of mice, i.e. interleukin-1 alpha (IL-1 alpha), IL-6 and IL-10, and TNF. We also studied the effect of CPZ on serum and spleen-associated TNF. Both DEX and CPZ inhibited TNF production, whereas induction of IL-1 and IL-6 was inhibited by DEX but not by CPZ. DEX did not affect IL-10, while CPZ potentiated its induction. CPZ also inhibited spleen-associated TNF induction in LPS-treated mice, suggesting an effect on the synthesis of TNF. CPZ inhibited TNF induction by Gram-positive bacteria (heat-killed Staphylococcus epidermidis) and by anti-CD3 monoclonal antibodies. Intraperitoneal administration of CPZ also inhibited the induction of brain-associated TNF induced by intra-cerebroventricular injection of LPS. Therefore, CPZ is a more specific inhibitor of TNF production than DEX; in particular, CPZ increased the induction of IL-10, which is a 'protective' cytokine known to inhibit LPS toxicity and TNF production. CPZ inhibited TNF production in vivo, irrespective of the TNF stimulus used to induce TNF. Finally, CPZ did not induce the 'rebound' effect of DEX that, when given 24 hr before LPS, potentiates TNF production, but it did inhibit TNF production after 24 hr.     

Indirect and selective down-regulation of serum tumor necrosis factor-alpha release by interleukin-1 beta.

A selective inhibition of LPS-induced tumor necrosis factor-alpha (TNF) response in mice was caused by an injection of recombinant human interleukin-1 (IL-1). The decrease in serum TNF level reached 70 to 80 percent of the controls receiving LPS alone when IL-1 was given simultaneously or prior to the challenge. At the same time serum IL-6 release was more elevated. Ex vivo assays have shown that macrophages from IL-1 treated animals did not respond to LPS when stimulated immediately after harvesting but recovered their normal responsiveness after being cultured for 2 hours and then washed. In vitro with or without addition of IL-1, mouse elicited macrophages responded equally to LPS in releasing TNF. In the absence of a direct and lasting effect on TNF-producing cells, the host reaction responsible for the inhibitory effect of IL-1 could be related to the overproduction of corticosterone that occurred after IL-1 injection, since it was not observed in adrenalectomized animals. Indeed the blockade of corticoid secretion by indomethacin prevented the inhibition of TNF production induced by IL-1 administration before LPS challenge. TNF administration did not result in elevation of corticosterone level and in contrast to IL-1 enhanced the TNF response to LPS injection. In vitro and ex vivo assays have shown this enhanced response to LPS was linked to a direct and prolonged effect of TNF on TNF-producing cells. Muramyl dipeptide (MDP) which was used as a known priming agent for enhanced cytokine release had a similar effect on TNF-producing cells.(ABSTRACT TRUNCATED AT 250 WORDS)     

Independent down-regulation of central and peripheral tumor necrosis factor production as a result of lipopolysaccharide tolerance in mice.

Lipopolysaccharide (LPS) induces a variety of central and peripheral effects that are largely mediated by cytokines, including tumor necrosis factor (TNF). Peripheral (intravenous [i.v.]) administration of LPS (2.5 micrograms per mouse) induced TNF levels in the serum and spleen but not in the brain, while central (intracerebroventricular [i.c.v.]) administration of LPS induced TNF production both in the brain and in the periphery. Mice challenged with LPS after LPS pretreatment (35 micrograms per mouse, intraperitoneally, as a single dose on day -3 or as a 4-day treatment on days -5 to -2) were unresponsive in terms of induction of serum TNF. When peripherally LPS-tolerant mice (where LPS pretreatment was given intraperitoneally) were challenged with an i.c.v. dose of LPS, brain (but not serum) TNF was still produced, meaning that the LPS-tolerant state was confined to the periphery. However, if LPS pretreatment was given i.c.v. (35 micrograms, as a single dose), the brain, like the periphery, became LPS tolerant in terms of TNF production. We investigated how tolerance to LPS affected two of its actions, decrease in food intake and induction of serum corticosterone (CS). After an i.v. challenge in peripherally LPS-tolerant mice, no decrease in food intake was observed, but this response was still elicited by an i.c.v. challenge. LPS tolerance reduced the CS response to i.v. and i.c.v. challenge. These results suggest that LPS-induced decrease in food intake might be a fully central effect, while the increase of serum CS might be due to both central and peripheral actions.     

Tolerance to lipopolysaccharide promotes an enhanced neutrophil extracellular traps formation leading to a more efficient bacterial clearance in mice

Tolerance to lipopolysaccharide (LPS) constitutes a stress adaptation, in which a primary contact with LPS results in a minimal response when a second exposure with the same stimulus occurs. However, active important defence mechanisms are mounted during the tolerant state. Our aim was to assess the contribution of polymorphonuclear neutrophils (PMN) in the clearance of bacterial infection in a mouse model of tolerance to LPS. After tolerance was developed, we investigated in vivo different mechanisms of bacterial clearance. The elimination of a locally induced polymicrobial challenge was more efficient in tolerant mice both in the presence or absence of local macrophages. This was related to a higher number of PMN migrating to the infectious site as a result of an increased number of PMN from the marginal pool with higher chemotactic capacity, not because of differences in their phagocytic activity or reactive species production. In vivo, neutrophils extracellular trap (NET) destruction by nuclease treatment abolished the observed increased clearance in tolerant but not in control mice. In line with this finding, in vitro NETs formation was higher in PMN from tolerant animals. These results indicate that the higher chemotactic response from an increased PMN marginal pool and the NETs enhanced forming capacity are the main mechanisms mediating bacterial clearance in tolerant mice. To sum up, far from being a lack of response, tolerance to LPS causes PMN priming effects which favour distant and local anti-infectious responses.     

Induction of tolerance to a soluble antigen following irradiation and bone marrow reconstitution

Antigen-specific tolerance was induced in mice by lethal irradiation followed by reconstitution with syngeneic, anti-T-cell-treated bone marrow and injection of the protein antigen lysozyme. Animals tolerized with lysozyme responded normally to a second antigen, sheep red blood cells, and animals treated with the same tolerizing regimen using a different protein antigen, bovine serum albumin, responded normally to lysozyme. Challenge of the tolerant mice with lysozyme covalently coupled to LPS induced an antilysozyme response indicating that if tolerance was expressed on the B-cell level that antigen-specific B-cells were still present. These results eliminate clonal abortion and clonal selection as the mechanism of tolerance generation. The tolerance generated by this procedure is either expressed on the T-cell level or is produced by a state of B-cell clonal anergy which can be overcome by the use of antigen coupled to lipopolysaccharide.     

Growing tumors induce hypersensitivity to endotoxin and tumor necrosis factor.

Lewis lung carcinoma and EMT6 sarcoma growing as solid tumors in mice caused a gradual increase in the susceptibility of the animals to lethal toxicity of endotoxins (lipopolysaccharides [LPS]). By day 15 following inoculation of the tumors, the 50% lethal dose of LPS, which in normal mice was approximately 400 micrograms, decreased to 2 micrograms for the sarcoma-bearing mice and 0.1 microgram for the carcinoma-bearing mice. This sensitization to endotoxin was paralleled by a high sensitization to tumor necrosis factor (TNF). Human recombinant TNF given to normal mice was lethal at about 500 micrograms. It was lethal for 50% of the animals bearing EMT6 or Lewis lung carcinoma tumors in amounts of 4 and 0.01 micrograms, respectively, on day 15 following tumor inoculation. The sensitization of tumor-bearing animals to LPS and TNF was paralleled by marked granulocytosis.     

Enhancement of lipopolysaccharide-induced tumor necrosis factor production in mice by carrageenan pretreatment.

Tumor necrosis factor (TNF) is a cytokine which mediates endotoxin shock and causes multiple organ damage. It is thought that macrophage (MP) activation is necessary to increase lipopolysaccharide (LPS)-induced TNF production and lethality. Carrageenan (CAR) is sulfated polygalactose which destroys MP; it is used as a MP blocker. We found that CAR pretreatment can increase both endotoxin-induced TNF production and the mortality rate in mice. The ddY mice (7 to 8 weeks old) were injected intraperitoneally with CAR (5-mg dose) and challenged intravenously with LPS 24 h later. Without CAR pretreatment, LPS doses of less than 10 micrograms did not induce TNF in sera. After pretreatment, however, about 3 x 10(3) to 4 x 10(4) U of TNF per ml was produced after LPS injection at doses of 0.1 to 10 micrograms, respectively. TNF production was significantly increased by CAR pretreatment at LPS doses of more than 10 micrograms. CAR pretreatment rendered the mice more sensitive to the lethal effect of LPS; 50% lethal doses of LPS in CAR-pretreated mice and nonpretreated mice were 26.9 and 227 micrograms, respectively. The mortality of the two groups was significantly different at doses of 50, 100, and 200 micrograms of LPS. CAR increased LPS-induced TNF production and mortality within 2 h, much earlier than MP activators, which needed at least 4 days. Our results made clear that TNF production is enhanced not only by a MP activator but also by a MP blocker.     

Limited involvement of interleukin-6 in the pathogenesis of lethal septic shock as revealed by the effect of monoclonal antibodies against interleukin-6 or its receptor in various murine models.

Several studies in human patients and in laboratory animals have revealed a correlation between serum interleukin (IL)-6 levels and outcome in clinical sepsis and in related animal models, respectively. In the present study, two monoclonal antibodies were used to investigate the contribution of IL-6 in the lethal action of tumor necrosis factor (TNF) and of lipopolysaccharide (LPS) in mice. We studied the potential protective properties of an anti-murine (m) IL-6 antibody and of an anti-mIL-6 receptor antibody. In controlled experiments, we observed that both monoclonal antibodies conferred a dose-dependent protection to a lethal dose of mTNF. Detailed studies with the monoclonal antibodies indicate, however, that protection was no longer observed when the mTNF dose was slightly higher than the lethal dose. Likewise, the anti-IL-6 monoclonal antibody protected against injections of LPS at a lethal-dose concentration, but here too failed to protect against higher doses of LPS. The anti-IL-6 monoclonal antibody was unable to protect against mTNF in mice sensitized by galactosamine, the corticoid receptor antagonist RU38486 or human (h) IL-1 beta. Protection did not correlate with the serum concentrations of IL-6. Finally, we demonstrate that hIL-6 injection did not change the sensitivity of mice towards mTNF. We conclude that, although IL-6 levels may be of value as a marker for the outcome in septic shock, this cytokine contributes only marginally in the pathogenesis leading to death. The small, but real, contribution of IL-6 in some situations might be due to its ability to up-regulate the level of TNF receptors.     

Effect of Peroxisome Proliferator-Activated Receptor Alpha Activators on Tumor Necrosis Factor Expression in Mice during Endotoxemia

Inflammatory mediators orchestrate the host immune and metabolic response to acute bacterial infections and mediate the events leading to septic shock. Tumor necrosis factor (TNF) has long been identified as one of the proximal mediators of endotoxin action. Recent studies have implicated peroxisome proliferator-activated receptor alpha (PPARalpha) as a potential target to modulate regulation of the immune response. Since PPARalpha activators, which are hypolipidemic drugs, are being prescribed for a significant population of older patients, it is important to determine the impact of these drugs on the host response to acute inflammation. Therefore, we examined the role of PPARalpha activators on the regulation of TNF expression in a mouse model of endotoxemia. CD-1 mice treated with dietary fenofibrate or Wy-14,643 had fivefold-higher lipopolysaccharide (LPS)-induced TNF plasma levels than LPS-treated control-fed animals. Higher LPS-induced TNF levels in drug-fed animals were reflected physiologically in significantly lower glucose levels in plasma and a significantly lower 50% lethal dose than those in LPS-treated control-fed animals. Utilizing PPARalpha wild-type (WT) and knockout (KO) mice, we showed that the effect of fenofibrate on LPS-induced TNF expression was indeed mediated by PPARalpha. PPARalpha WT mice fed fenofibrate also had a fivefold increase in LPS-induced TNF levels in plasma compared to control-fed animals. However, LPS-induced TNF levels were significantly decreased and glucose levels in plasma were significantly increased in PPARalpha KO mice fed fenofibrate compared to those in control-fed animals. Data from peritoneal macrophage studies indicate that Wy-14,643 modestly decreased TNF expression in vitro. Similarly, overexpression of PPARalpha in 293T cells decreased activity of a human TNF promoter-luciferase construct. The results from these studies suggest that any anti-inflammatory activity of PPARalpha in vivo can be masked by other systemic effects of PPARalpha activators.     

Lipopolysaccharide-induced lethality and cytokine production in aged mice.

This study was designed to define the lipopolysaccharide (LPS) sensitivity of aged mice in terms of lethality and cytokine production and to determine down-regulating responses of corticosterone and interleukin 10 (IL-10). The 50% lethal doses of LPS in young (6- to 7-week-old) and aged (98- to 102-week-old) mice were 601 and 93 microg per mouse (25.6 and 1.6 mg per kg of body weight), respectively. Aged mice were approximately 6.5-fold more sensitive to the lethal toxicity of LPS in micrograms per mouse (16-fold more sensitive in milligrams per kilogram) than young mice. Levels in sera of tumor necrosis factor-alpha (TNF-alpha) IL-1alpha, and IL-6 after intraperitoneal injection of 100 microg of LPS peaked at 1.5, 3, and 3 h, respectively, and declined thereafter in both groups of mice. However, the peak values of these cytokines were significantly higher in aged than in young mice (P < 0.05). Gamma interferon (IFN-gamma) was detectable at 3 h, and sustained high levels were still detected after 12 h in both age groups. Although there were no significant differences in levels of IFN-gamma in sera from both groups, aged mice showed higher IFN-gamma levels throughout the 3- to 12-h study period. Administration of increasing doses of LPS revealed that aged mice had a lower threshold to IL-1alpha production than young mice. In addition, aged mice were approximately 4-fold more sensitive to the lethal toxicity of exogenous TNF in units per mouse (10-fold more sensitive in units per kilogram) than young mice. With regard to down-regulating factors, corticosterone amounts were similar at basal levels and no differences in kinetics after the LPS challenge were observed, whereas IL-10 levels in sera were significantly higher in aged mice at 1.5 and 3 h than in young mice (P < 0.01). These results indicate that aged mice are more sensitive to the lethal toxicities of LPS and TNF than young mice. We conclude that a relatively activated, or primed, state for LPS-induced cytokine production, in spite of full down-regulating responses by corticosterone and IL- 10, may explain at least in part LPS sensitivity in aged mice.     

LTD4 augments TNF releasein vivo andin vitro

In vivo data suggest a role of LTD₄ in mediating endotoxin (LPS)-inducible liver injury in galactosamine-sensitized mice. Leukotriene D₄ (LTD₄) was shown to synergize in this model with subtoxic amounts of LPS in inducing hepatitis. Mice challenged i.v. with a subtoxic dose of LPS [50 ng/kg] showed significant TNF serum levels 90 min later which were sixfold increased by coadministration of 50 μg/kg LTD₄. When rat Kupffer cells were challenged with LPS, TNF-α measured in the supernatant was significantly increased by LTD₄ [100 pg–100 ng/ml]. Addition of LTD₄ alone did not result in any detectable TNF formation.Since Kupffer cells are known producers of small amounts of LTD₄, it seems feasible that LTD₄ represents an autocrine stimulus of nonparenchymal liver cells. In fact, different LTD₄ synthesis inhibitors and receptor antagonists attenuated LPS-inducible TNF release of rat Kupffer cells supporting the conclusion that LTD₄ acts as an endogenous autocrine enhancer of liver macrophage TNF release.