An antagonist of platelet-activating factor suppresses endotoxin-induced tumor necrosis factor and mortality in mice pretreated with carrageenan

Strategies to improve drug development for sepsis

Sepsis, a common and potentially fatal systemic illness, is triggered by microbial infection and often leads to impaired function of the lungs, kidneys or other vital organs. Since the early 1980s, a large number of therapeutic agents for the treatment of sepsis have been evaluated in randomized controlled clinical trials. With few exceptions, the results from these trials have been disappointing, and no specific therapeutic agent is currently approved for the treatment of sepsis. To improve upon this dismal record, investigators will need to identify more suitable therapeutic targets, improve their approaches for selecting candidate compounds for clinical development and adopt better designs for clinical trials.

Animal models of sepsis

Sepsis remains a common, serious, and heterogeneous clinical entity that is difficult to define adequately. Despite its importance as a public health problem, efforts to develop and gain regulatory approval for a specific therapeutic agent for the adjuvant treatment of sepsis have been remarkably unsuccessful. One step in the critical pathway for the development of a new agent for adjuvant treatment of sepsis is evaluation in an appropriate animal model of the human condition. Unfortunately, the animal models that have been used for this purpose have often yielded misleading findings. It is likely that there are multiple reasons for the discrepancies between the results obtained in tests of pharmacological agents in animal models of sepsis and the outcomes of human clinical trials. One of important reason may be that the changes in gene expression, which are triggered by trauma or infection, are different in mice, a commonly used species for preclinical testing, and humans. Additionally, many species, including mice and baboons, are remarkably resistant to the toxic effects of bacterial lipopolysaccharide, whereas humans are exquisitely sensitive. New approaches toward the use of animals for sepsis research are being investigated. But, at present, results from preclinical studies of new therapeutic agents for sepsis must be viewed with a degree of skepticism.

Inhibition of in vitro tumor cell proliferation by cytokines induced by combinations of TLR or TLR and TCR agonists

The objective of this study was to learn from in vitro studies how to better utilize Toll-like receptor (TLR) agonists in controlling tumor growth. One of the primary effects of TLR agonists is induction of cytokine and chemokine production. In order to identify combinations of cytokines or chemokines with optimal ability to inhibit in vitro tumor cell proliferation, a panel of 17 recombinant human or mouse cytokines that have minimal effect on primary cell survival, were tested individually or in combinations of 2, 3 or 4 on a panel of human and mouse chemotherapy sensitive and resistant tumor cell lines. A combination of high (>10 ng/ml) levels of IFNgamma with moderate concentrations of TNFalpha>IFNalpha>IL-6=IL-8 was most effective at inhibiting in vitro tumor cell viability and proliferation with minimal effect on primary cells. We also observed that similar cytokine profile could be induced in vitro PBMC culture by using certain combinations of TLR-TLR and TLR-TCR agonists. Thus, concomitant activation of TLR7/8 with TLR4 or TLR 7/8 with T cell receptor (TCR) in PBMC, amongst all possible paired TLR-TLR and TLR-TCR agonist combinations, produced cytokine mix high in IFNgamma, in combination with IFNalpha, IL-6, IL-8, TNFalpha. Such cytokine mix was equal or more effective tumor cell killing and inhibition of tumor cell proliferation than the best rec-cytokine mixture tested. These results suggest that, TLR and/or TCR agonists combinations generate an optimal mixture of cytokines and chemokines competent in regulating in vitro tumor growth, and imply that realizing such "right cytokine induction" in vivo might be more efficacious than that with individual cytokines or TLR agonists induced cytokine mix.

Effects of epidural anaesthesia on surgical stress-induced immunosuppression during upper abdominal surgery

BACKGROUND

Previously, we have demonstrated that surgical stress rapidly induced transient hyporesponsiveness of blood cells to endotoxin and that monocyte mCD14 and HLA-DR expression decreased soon after the start of surgery under general anaesthesia. This study was designed to investigate the effects of epidural anaesthesia on surgical stress-induced immunosuppression in patients undergoing upper abdominal surgery.

METHODS

After having obtained informed consent, patients were randomly allocated to receive general anaesthesia (Group G) or general anaesthesia with epidural anaesthesia (Group E). Perioperative changes in neutrophil phagocytic activity, neutrophil respiratory burst activity, monocyte mCD14 and HLA-DR expression, plasma IL-10 concentration, and the LPS-induced TNF-alpha production in whole blood were measured.

RESULTS

Surgical stress rapidly depressed neutrophil phagocytic activity, monocyte mCD14 and HLA-DR expression, and LPS-induced TNF-alpha production ex vivo (P < 0.05 vs preoperation) in both Group G and Group E. In contrast, the plasma IL-10 concentration increased significantly 2 h after the start of surgery (P < 0.05) in both groups. There were no significant differences between the two groups. The neutrophil respiratory burst activity did not change during the operation in either group.

CONCLUSION

This study showed that the innate immune system is suppressed from the early period of upper abdominal surgery. Subgroup analysis suggested that epidural anaesthesia to T4 dermatome as well as general anaesthesia may not protect patients from this immunosuppression. These results in part explain the impairment of host-defense mechanisms seen in the perioperative period.

Signaling via platelet-activating factor receptors accounts for the impairment of neutrophil migration in polymicrobial sepsis

Sepsis is a systemic inflammatory response that results from the inability of the immune system to limit bacterial spread during an ongoing infection. Recently, we have documented an impaired neutrophil migration toward the infectious focus in severe sepsis. This impairment seems to be mediated by circulating cytokines, chemokines, and NO. Platelet-activating factor (PAF) plays an important role in the orchestration of different inflammatory reactions, including the release of cytokines, chemokines, and free radicals. Using a PAFR antagonist, PCA-4248, and PAFR-deficient mice, we investigated whether signaling via PAFR was relevant for the failure of neutrophils to migrate to the site of infection after lethal sepsis caused by cecum ligation and puncture in mice. In PAFR-deficient mice or mice pretreated with PCA-4248 (5 mg/kg) and subjected to lethal sepsis, neutrophil migration failure was prevented, and bacterial clearance was more efficient. There was also reduced systemic inflammation (low serum cytokine levels), lower nitrate levels in plasma, and higher survival rate. Altogether, the results firmly establish a role for PAFR in mediating the early impairment of neutrophil migration toward the infectious focus. Blockade of PAFR may prevent the establishment of severe sepsis.

Increment of Plasma Soluble CD14 Level in Carrageenan-Primed Endotoxin Shock Model Mice

CD14 is membrane-associating or free soluble glycoprotein which recognizes lipopolysaccharide (LPS) and is assumed to be involved in the onset of endotoxin shock. There are some reports suggesting the relationship between increased expression of CD14 in infectious or inflammatory diseases. However, little has been reported concerning the soluble CD14 (sCD14) level, especially in mice. In this study, we measured the plasma level of sCD14, TNF-alpha and IL-6 in the iota-carrageenan (CAR)-primed endotoxin shock model in addition to the D-galactosamine (D-galN)-primed endotoxin shock model mice. It was confirmed that all mice were dead within 12 h after a higher dose of LPS-treatment in both animal models. The level of TNF-alpha, IL-6 and sCD14 significantly increased in the CAR-primed endotoxin shock model mice. However, the D-galN-primed endotoxin shock model mice showed only a slight increment of TNF-alpha and IL-6 level, and sCD14 was below the detectable level. In the examination using several doses of LPS in CAR-primed model mice, IL-6 and sCD14 were increased dependent on the LPS dose, but TNF-alpha remained at an almost equal level at any dose of LPS in this study condition. In conclusion, the production of TNF-alpha, IL-6 and sCD14 was significantly enhanced in the CAR-primed model mice, compared to the D-galN-primed model mice. Therefore, these data indicate the possibility that the sCD14 level did not increase consistently, even under a fatal condition in endotoxin shock. Also, CAR-primed endotoxin shock would be an important experimental model to examine the elevation mechanisms for sCD14 and IL-6 production.

A platelet activating factor receptor antagonist inhibits cytokine production in human whole blood by bacterial toxins and live bacteria

We previously reported that a platelet-activating factor receptor (PAFR) antagonist (TCV-309) suppressed lipopolysaccharide (LPS)-induced mortality and tumor necrosis factor (TNF) production in mice. However, the effect of TCV-309 on cytokine production induced by Staphylococcus enterotoxin B (SEB) or live bacteria has not been reported. In this study we investigated the effect of TCV-309 on cytokine production in human whole blood induced by LPS, SEB, and both Gram-positive and -negative bacteria. Human whole blood diluted 5:1 (980 microL) was placed in the wells of a 24-well plate. Ten microliters of LPS, SEB, Escherichia coli O18 K(+), or Staphylococcus aureus were added to each well. After incubation at 37 degrees C for 6 h, TNF, interleukin (IL)-6, and IL-8 in the culture medium were measured. TCV-309 did not affect the growth of either E. coli or S. aureus bacteria in the culture medium for the 6 h incubation. LPS, SEB, and both E. coli and S. aureus induced TNF, IL-6, and IL-8 in human whole blood. TCV-309 significantly inhibited the production of TNF, IL-6, and IL-8 induced by LPS, SEB, and bacteria. A PAFR antagonist suppressed cytokine production induced by LPS, SEB, and both Gram-positive and -negative bacteria in human whole blood. A PAFR plays an important role of producing proinflammatory cytokines induced by both toxins and live bacteria.

IMPLICATIONS

The platelet-activating factor receptor plays an important role in producing proinflammatory cytokines induced by bacterial toxins, such as lipopolysaccharide,Staphylococcus enterotoxin B, and live Gram-positive and Gram-negative bacteria.

Cytokines in coagulation and thrombosis: a preclinical and clinical review

The cytokine network is a complex and dynamic system, involved in numerous biological responses in the human body. This review of the current literature describes the role of cytokines and their interaction with the coagulation system, specifically in the maintenance of the thrombo-hemorrhagic balance in vivo in human subjects and in animals. In general, cytokines are thrombogenic, but they are amenable to therapeutic manipulations and hence are a potentially attractive tool in the clinician's armamentarium. Studies of the effects of cytokines in vivo are difficult because cytokines act in a very finite microenvironment and, although their actions are significant, they are transient. Most of the available clinical data related to interactions between cytokines and the coagulation system focuses on the role of tumor necrosis factor-alpha and interleukin-1 in septicemia and septic shock. However, several other cytokines and related proteins, such as platelet activating factor and plasminogen activator inhibitor, are also known to influence coagulation and thrombosis. These factors interact closely with cytokines, and have been included in this review for a better understanding of their interactions with traditional cytokines. Studies that utilize cell culture systems do not accurately model the in vivo status of this complex system and, hence, this review has excluded such studies. The role of the cytokine network in coronary artery disease, angiogenesis, or neoplasia has been addressed elsewhere by other workers and is not discussed here. By emphasizing important in vivo interactions, the intention of this review is to serve as an impetus to further translational research, both clinical and in the laboratory.

Reactive oxygen species and endotoxic shock: effect of dimethylthiourea

The effects of endotoxemia on the cardiac function and contractility, oxygen radical production by polymorphonuclear leukocytes (PMNL-CL), cardiac antioxidant reserve (LV-CL), antioxidant enzymes (superoxide dismutase [SOD], catalase, glutathione peroxidase [GSH-P(X)]) and malondialdehyde (MDA); and plasma creatine kinase (CK) and lactate in the absence or presence of dimethylthiourea (DMTU), an antioxidant, in anesthetized dogs were studied. Dogs were assigned to three groups: group 1, control; group II, endotoxin (ET) (5 mg/kg body wt intravenously), and group III, ET + DMTU (500 mg/kg intravenously). ET produced decreases in the cardiac function and contractility, antioxidant reserve, antioxidant enzymes; and increases in PMNL-CL, cardiac MDA, plasma CK, and lactate. Pretreatment with DMTU attenuated the ET-induced cardiac dysfunction and changes in the cardiac MDA, antioxidant reserve, and antioxidant enzymes, PMNL-CL, and plasma CK and lactate levels. These results suggest that reactive oxygen species may be involved in the deterioration of cardiac function and contractility, and cellular injury during endotoxic shock and that antioxidants may be of value in the treatment of endotoxic shock.

Surgical stress induces endotoxin hyporesponsiveness and an early decrease of monocyte mCD14 and HLA-DR expression during surgery

It is generally accepted that major surgery is associated with severe alterations of the host-defense mechanisms. We investigated the effect of surgical stress on the immune system. Specifically, we studied the relationship between perioperative lipopolysaccharide (LPS) hyporesponsiveness and monocyte human leukocyte antigen-DR (HLA-DR) and CD14 expression during the perioperative period in 20 patients who underwent partial gastrectomy. This study demonstrated that surgical stress rapidly depressed monocyte mCD14 and HLA-DR expression in comparison with preanesthesia levels. Monocyte mCD14 expression recovered to preoperative levels on the first postoperative day, and monocyte HLA-DR expression recovered by the seventh postoperative day. Consistent with our previous study, LPS-induced tumor necrosis factor (TNF)-alpha production ex vivo was significantly suppressed from the beginning of the operation. On the contrary, the plasma interleukin-10 concentration started to increase after the surgical incision was made. LPS hyporesponsiveness was least at the end of the operation and returned to preoperative levels on the first postoperative day. In conclusion, the present study demonstrated that LPS responsiveness, plasma interleukin-10 concentration, and monocytes mCD14 and HLA-DR expression altered from the early period of surgery. These alterations may be related to the impairment of the immune system during the perioperative period.

IMPLICATIONS

Recent studies demonstrate that surgical stress induces immune dysfunction. We found that surgical stress rapidly decreased monocyte mCD14 and human leukocyte antigen-DR expression, and endotoxin responsiveness. These findings suggest that early changes of the immune system caused by surgical stress contribute to postoperative complications such as sepsis and multiple organ failure.

Measurement of blood clearance time by Limulus G test of Candida-water soluble polysaccharide fraction, CAWS, in mice

The Limulus G test, responsive to beta-1,3-D-glucan, is a well-established method for the detection of invasive fungal infection. We have recently found that Candida albicans released a water-soluble polysaccharide fraction (CAWS) into synthetic medium (Uchiyama et al., FEMS Immunol. Med. Microbiol. 24 (1999) 411-420). CAWS was composed of a mannoprotein-beta-glucan complex and activated Limulus factor G, and thus would be similar to the Limulus active substance in patient's blood. In a preliminary investigation, we have found that CAWS is lethal when administered intravenously in a murine system. In this study, we examined the toxicity and then the fate of CAWS in mice. The lethal toxicity was strain-dependent and strain DBA/2 was the most resistant. The toxicity was, at least in part, reduced by salbutamol sulfate and prednisolone treatment in the sensitive strains. On intravenous administration, the half clearance time (t1/2) was approximately 40 min in mice (DBA/2). On intraperitoneal administration, CAWS appeared in the blood with a peak concentration at 1 h. In order to establish a treatment plan, it is important to demonstrate the onset and the termination of deep-seated mycosis. The Limulus G test is suitable for the above purpose; however, it is necessary to fully understand the fate of beta-1,3-D-glucan in patients' blood.

Suppression of lipopolysaccharide-induced nitric oxide synthase expression by platelet-activating factor receptor antagonists in the rat liver and cultured rat Kupffer cells

Excessive nitric oxide (NO) generated by hepatic cells in response to lipopolysaccharide (LPS) and inflammatory substances (e.g., platelet-activating factor [PAF]) is a key contributor to the pathophysiological outcomes observed in the liver during sepsis. In rats subjected to liver-focused endotoxemia, inducible nitric oxide synthase (iNOS) levels in the intact liver were elevated by 6 hours; cell-specific expression of iNOS messenger RNA (mRNA) was Kupffer cells (KCs), endothelial cells, and hepatocytes. Elevated serum alanine transaminase (ALT) levels at 6 hours confirmed hepatic damage. Pretreatment of endotoxemic rats with PAF receptor antagonists BN 50739 or WEB 2170 reduced serum ALT and iNOS mRNA levels in the intact liver. Pretreatment of cultured KCs with BN 50739 or WEB 2170 inhibited both LPS and PAF-induced iNOS mRNA formation. In addition, LPS-induced iNOS protein levels in KCs pretreated with BN 50739 or WEB 2170 were decreased. Exposure of KCs to either LPS or PAF caused the translocation of the p65 subunit of nuclear factor kappa B (NF-kappaB) into the nucleus and this process was attenuated by BN 50739 and WEB 2170. There was concomitant inhibition of LPS-dependent degradation of the inhibitory protein IkappaBalpha and increase in intracellular Ca(2+) in KC treated with BN 50739 or WEB 2170. Also, in KCs, LPS was able to induce iNOS mRNA expression independent of CD14. This response was inhibited by pretreatment of KCs with either BN 50739 or WEB 2170. Our findings indicate that PAF receptor antagonists convey protection against hepatocellular injury accompanied by a decrease in nitric oxide (NO) formation in the livers of endotoxemic rats.

Platelet-activating factor and arachidonic acid metabolites mediate tumor necrosis factor and eicosanoid kinetics and cardiopulmonary dysfunction during bacteremic shock

OBJECTIVE

Platelet-activating factor (PAF) and eicosanoids are putative mediators of septic shock that are associated with release of tumor necrosis factor (TNF). The purpose of this investigation was to a) examine temporal patterns of TNF and arachidonic acid metabolite release in a porcine model of bacteremic shock and b) selectively block PAF, thromboxane A2, prostacyclin, and leukotrienes to determine the relationships among these inflammatory response mediators and the alterations in cardiorespiratory dysfunction for which they are required.

DESIGN

Prospective, nonrandomized, controlled trial.

SETTING

Laboratory at a university medical center.

SUBJECTS

Thirty-four female Yorkshire swine.

INTERVENTIONS

Animals were divided into six experimental groups: five septic groups receiving an infusion of Aeromonas hydrophila at 0.2 mL/kg/hr, gradually increasing to 0.4 mL/kg/hr over 4 hrs. Each of four septic groups was pretreated with a specific mediator inhibitor (PAF receptor antagonist, n = 6; prostacyclin antibody, n = 5; leukotriene synthesis inhibitor, n = 5; and thromboxane receptor antagonist, n = 6). One septic group (n = 6) received no mediator inhibitor and served as a septic control, and one anesthesia control group (n = 6) received no intervention.

MEASUREMENTS AND MAIN RESULTS

PAF receptor blockade significantly increased systemic hypotension and mixed venous oxygen saturation and decreased pulmonary artery pressure, oxygen extraction and consumption, hemoconcentration, and levels of TNF and eicosanoids. Leukotriene inhibition increased mean arterial pressure, pulmonary and systemic vascular resistance indices, and arterial and mixed venous oxygen saturation and reduced pulmonary hypertension, oxygen delivery, oxygen extraction, oxygen consumption, and all measured mediators. Thromboxane receptor blockade lowered TNF and leukotriene levels, ameliorated systemic and pulmonary vasoconstriction, and significantly increased arterial and tissue oxygenation compared with septic controls. Prostacyclin antagonism reduced prostacyclin plasma concentrations, arterial hypoxemia, and oxygen consumption during sepsis and increased circulating leukotriene B4.

CONCLUSIONS

Elevations in plasma TNF predictably precede peak levels of eicosanoids in this model. PAF, leukotrienes, and thromboxane A2 are necessary for pulmonary hypertension during bacteremia. Systemic hypotension and increased vascular permeability are mediated by both leukotrienes and PAF. There are complex interactions among mediators during sepsis and further studies are required to define these relationships.

Carrageenan primes leukocytes to enhance lipopolysaccharide-induced tumor necrosis factor alpha production

We have previously reported that pretreatment with carrageenan (CAR) enhances lipopolysaccharide (LPS)-induced tumor necrosis factor alpha (TNF-alpha) production in and lethality for mice. Whole blood cultured in vitro was used to show that CAR pretreatment results in about a 200-fold increase in LPS-induced TNF-alpha production. CAR by itself did not induce TNF-alpha production. However, CAR-treated cultured medium sensitized whole blood to make more LPS-induced TNF than did saline-treated cultured medium in vitro. It was also demonstrated that CAR pretreatment increases TNF-alpha mRNA levels of both blood cells and peritoneal exudate cells, but not of bone marrow cells. Immunoelectron microscopic analysis revealed that polymorphonuclear leukocytes and macrophages are TNF-alpha-producing cells in CAR-treated mice. In CAR-treated mice, TNF-alpha was seen early after LPS injection in leukocytes in hepatic sinusoids and on the surfaces of endothelial cells. TNF-alpha was also detected late after LPS injection in hepatocytes which become edematous. These results suggest that CAR primes leukocytes to produce TNF-alpha in response to LPS and that they play an important role in the pathogenesis of liver injury.

Oxygen Free Radicals and Endotoxic Shock: Effect of Flaxseed

BACKGROUND: Cardiac dysfunction and tissue injury during endotoxemia may be caused by increased levels of oxygen free radicals. METHODS AND RESULTS: We therefore investigated the effects of endotoxic shock on cardiac function and contractility, plasma creatine kinase (CK) activity and lactate concentration, oxyradical-producing activity of polymorphonuclear leukocytes (PMNL-CL) and white blood corpuscles, antioxidant reserve (cardiac chemiluminescence [LV-CL]), antioxidant enzyme activity (superoxide dismutase, catalase, glutathione peroxidase), cardiac malondialdehyde (MDA) concentration, a lipid peroxidation product, and hemodynamics in the absence or presence of flaxseed treatment in anesthetized dogs. Flaxseed contains lignans that have antioxidant activites and inhibit platelet-activating factor (PAF). The dogs were assigned to three groups: group I, sham control; group II, endotoxin (ET) treated (5 mg/kg intravenously); group III, ET + flaxseed (2 gm/kg/day orally) for 6 days. ET produced a decrease in cardiac function and contractility and antioxidant enzyme levels, and an increase in cardiac MDA and LV-CL, PMNL-CL, and plasma CK and lactate. Pretreatment with flaxseed attenuated the ET-induced cardiac dysfunction and cellular damage. Protection was incomplete for cardiovascular function, plasma CK, and lactate. CONCLUSIONS: These results suggest that oxyradicals and/or PAF may be involved in the deterioration of cardiovascular function and cellular integrity during ET shock and that antioxidant and anti-PAF agents may be effective in the treatment of ET shock.

Selective enhancement of LPS-induced serum TNF-alpha production by carrageenan pretreatment in mice

1. Bacterial lipopolysaccharide (LPS)-induced increases in serum cytokines (TNF-alpha, IL-1 and IL-6) and hypothermia were studied in mice sensitized by carrageenan pretreatment and compared with mice sensitized with heat-killed P. acnes or IFN-gamma, all given IP at appropriate intervals (24 hr, 7 days and 12-18 hr, respectively) before LPS. 2. In mice with localized peritoneal inflammation induced by carrageenan, peak TNF-alpha levels (1.5-2 h after LPS) were markedly enhanced after both doses of LPS tested (50 and 200 microg/mouse IP). However, IL-1beta levels were not changed and IL-6 levels were decreased only after the higher dose of LPS. Hypothermia showed weak and inconsistent changes in carrageenan-sensitized mice. 3. IL-1beta levels in spleen lysates were higher but paralleled those in the serum, being increased in IFN-gamma-sensitized but not in carrageenan-sensitized mice. The levels of both TNF-alpha and IL-1beta were high in the peritoneum of carrageenan-sensitized mice, suggesting that the increased serum TNF-alpha did not emanate from the peritoneum. 4. In mice sensitized with the other two agents, as expected, the levels of all three cytokines increased, but peak levels were attained at the same times post-LPS (TNF-alpha: 1-1.5 hr; IL-1: 3-4 hr; IL-6: 3-4 hr). In addition, hypothermia was increased with both of these methods of sensitization. 5. The lack of consistent correlation of the levels of cytokines studied, particularly TNF-alpha, with the degree of hypothermia, raises questions as to their causative role in its induction in these models. 6. The mechanisms underlying these models of sensitization are clearly different, and further understanding of these mechanisms would aid in the interpretation of the effects of drugs in the models.

Involvement of nuclear factor-kappa B in platelet-activating factor-mediated tumor necrosis factor-alpha expression

Tumor necrosis factor (TNF)-alpha and platelet-activating factor (PAF) are important mediators of inflammatory reactions, and their release is controlled by a positive feedback network. However, the regulatory mechanisms underlying the interaction of these two molecules are unknown. Within 10 min of the injection of lipopolysaccharide (LPS) into C57BL/6 mice, effects inducible by PAF such as anaphylactic shock-like symptoms, disseminated intravascular coagulation, and hemorrhage in renal medullae were observed, and all these pathological changes were prevented by the PAF antagonist, BN 50739. The plasma level of PAF after LPS injection reached a peak at 5 min. TNF-alpha gene expression was evident 20 min after LPS injection and was maximal at 40 min, and the level of serum TNF-alpha reached a peak at 1 h. Pretreatment with BN 50739 inhibited LPS-induced TNF-alpha gene expression and protein synthesis in a dose-dependent manner. Injection of PAF or treatment of the macrophage cell line, J774A.1, with PAF activated the transcription factor, nuclear factor (NF)-kappa B, which is essential for inducible TNF-alpha transcription. The activation of NF-kappa B by PAF preceded the LPS-mediated TNF-alpha gene expression. Pretreatment with BN 50739 inhibited LPS-induced mobilization of NF-kappa B in a dose-dependent manner in vivo as well as in vitro. These data suggest that PAF, which is released immediately or shortly after LPS injection, induces the expression of TNF-alpha through the activation of NF-kappa B.

A protective role of platelet-activating factor in murine candidiasis

Platelet-activating factor (PAF) is a potent phospholipid-derived modulator of immunological and inflammatory processes. In this study, the role of exogenous and endogenous PAF in resistance to infection with Candida albicans was investigated. Administration of PAF following a lethal challenge of C. albicans significantly protected mice from death and reduced the number of organisms in the kidneys. Neutralization of endogenous PAF with the PAF antagonist BN50739 shortened the mean survival time and increased the number of C. albicans cells per kidney. Shortly after infection of mice (30 min), significant levels of PAF were detected in the serum. PAF-induced protection appears to be mediated through the actions of tumor necrosis factor alpha (TNF-alpha), since pretreatment with anti-TNF-alpha before each injection of PAF abrogated the majority of PAF-induced enhanced resistance. Administration of PAF in vivo elevated serum TNF-alpha levels and TNF-alpha mRNA expression in the kidney. Production of TNF-alpha was markedly diminished by pretreatment with the PAF antagonist BN50739 prior to infection with C. albicans. We conclude that PAF, which is produced during infection with C. albicans, plays an important role in determining the level of resistance to this infectious microorganism. This effect of PAF appears to be mediated, at least in part, through the induction of TNF-alpha.

Contribution of neutrophils to lipopolysaccharide-induced tumor necrosis factor production and mortality in a carrageenan-pretreated mouse model

Carrageenan (CAR) pretreatment primes mice for lipopolysaccharide (LPS)-induced tumor necrosis factor (TNF)-alpha production in sera and increases their mortality rate. To study the contribution of neutrophils in this model, blood neutrophil count was regulated with cyclophosphamide. After LPS challenge, both serum TNF-alpha activity and mortality risk ratio were significantly higher in neutrophilic mice, but significantly lower in neutropenic mice. In vitro, CAR treatment primed for TNF-alpha production of blood neutrophils, but conversely, that of monocytes was suppressed. We suggest that neutrophils are the major cells to produce TNF-alpha and to determine mouse mortality after LPS challenge in the mouse CAR model.

A lipid A analog inhibits LPS-induced cytokine expression and improves survival in endotoxemic mice

It has recently been shown that inactive disaccharidic analogs of lipid A, an essential structure of lipopolysaccharide (LPS), may act as LPS antagonists which would be effective against septic shock induced by gram-negative bacteria endotoxin. In the present study we examined the inhibitory effect of DY-9973, a synthetic monosaccharidic lipid A analog, on LPS-induced cytokine expression in macrophages and lethal toxicity in mice. DY-9973 inhibited TNF-alpha production induced by LPS in human monocytes and monoblastic U937 cells. Expression of cytokine mRNAs such as TNF-alpha and IL-1 beta induced by LPS was inhibited by treatment with DY-9973 in U937 cells. Meanwhile, DY-9973 did not inhibit IL-1 beta-induced TNF-alpha production in U937 cells. TNF-alpha production induced by LPS or IL-1 beta was similarly inhibited by treatment with herbimycin, a tyrosine kinase inhibitor. Pretreatment with DY-9973 inhibited the elevation of serum TNF-alpha activity induced by the injection of LPS and reduced the lethal toxicity of LPS in BCG-primed mice. These results suggest that monosaccharidic lipid A analog such as DY-9973 can inhibit LPS-induced activation of macrophages and that it reduces lethal toxicity of LPS.

Role for intracellular platelet-activating factor in the circulatory failure in a model of gram-positive shock

1. This study investigates the effects of two structurally different antagonists of platelet-activating factor (PAF), BN52021 and WEB2086, on the circulatory and renal failure elicited by lipoteichoic acid (LTA) from Staphylococcus aureus (an organism without endotoxin) in anaesthetized rats. 2. Administration of LTA (10 mg kg-1, i.v.) caused hypotension and vascular hyporeactivity to noradrenaline (1 microgram kg-1, i.v.) WEB2086 (5 mg kg-1, i.v., 20 min before and 150 min after LTA) inhibited the delayed fall in mean arterial blood pressure (at 300 min: 99 +/- 6 mmHg vs. 75 +/- 6 mmHg, P < 0.01) and prevented the decrease in pressor response to noradrenaline (at 300 min: 36 +/- 5 mmHg min vs. 17 +/- 5 mmHg min, P < 0.01). Surprisingly, BN52021 (20 mg kg-1, i.v., 20 min before and 150 min after LTA) neither prevented the hypotension (74 +/- 6 mmHg) nor the vascular hyporeactivity (21 +/- 5 mmHg min). However, BN52021 inhibited the hypotension to injections of PAF as well as the circulatory failure elicited by lipopolysaccharides (10 mg kg-1, i.v.). 3. LTA caused an increase in plasma concentration of creatinine from 39 +/- 5 microM (sham-operated) to 70 +/- 8 microM and urea from 4.7 +/- 0.1 to 13.1 +/- 1.6 mM. The renal failure elicited by LTA was significantly inhibited by WEB2086 (creatinine: 45 +/- 4 microM and urea: 5.7 +/- 0.7 mM), but not by BN52021. 4. The induction of nitric oxide synthase activity in lungs by LTA was attenuated by WEB2086 from 98 +/- 17 to 40 +/- 15 pmol L-citrulline 30 min-1 mg-1 protein (P < 0.01), but not by BN52021 (148 +/- 21 pmol L-citrulline 30 min-1 mg-1 protein). Similarly, WEB2086, but not BN52021, inhibited the increase in plasma nitrite concentration associated with the delayed circulatory failure caused by LTA. The release of tumour necrosis factor-alpha (TNF-alpha) after injection of LTA was not attenuated by WEB2086. 5. The induction of nitrite release by cultured macrophages activated with LTA (10 micrograms ml-1 for 24 h) was inhibited by 74 +/- 4% by WEB2086 (3 x 10(-4) M), but not by BN52021, indicating that only WEB2086 acts on intracellular PAF receptors. 6. Thus, the intracellular release of PAF contributes to the circulatory and renal failure and induction of nitric oxide synthase elicited by LTA in anaesthetized rats. The difference between the two structurally different PAF antagonists in our septic shock models using either LTA or lipopolysaccharide (LPS), shows the importance of models for Gram-positive sepsis in the elucidation of the pathophysiology of septic shock and for the evaluation of potential drugs.

Unraveling the neuroimmune mechanisms for the HIV-1-associated cognitive/motor complex

Infection of the brain with human immunodeficiency virus 1 (HIV-1) often leads to the devastating loss of mental faculties. Surprisingly, HIV-1 elicits such brain dysfunction without significantly infecting neurons, astrocytes and oligodendroglia. The target for HIV-1 in the brain is the macrophage, which usually functions as a phagocytic, antigen-presenting and immune-regulatory cell. How can these cells produce such serious cognitive and motor brain impairments? Here, Hans Nottet and Howard Gendelman propose that HIV-1 penetrates the blood-brain barrier inside differentiating macrophages, which become immune activated once inside the brain, and secrete high levels of neurotoxins. Chronic, subclinical disease results by astrocyte regulation of macrophage effector functions. Ultimately, endogenous control mechanisms break down, leading to motor and mental impairments in some affected subjects.

The inhibitory effects of allopurinol on the production and cytotoxicity of tumor necrosis factor

Allopurinol, a xanthine oxidase inhibitor, impaired the cytotoxic effect of human recombinant tumor necrosis factor (TNF) against WEHI cells. Actinomycin D abolished the inhibition of cytotoxicity by allopurinol. Allopurinol also exerted an inhibitory effect on the production of TNF by human mononuclear cells stimulated by either heat-killed Staphylococcus aureus or E. coli lipopolysaccharide. It is suggested that allopurinol inhibits TNF cytotoxicity by decreasing the level of oxygen free radicals generated (among other mechanisms) by the action of xanthine oxidase. Whatever the mechanism, the fact that allopurinol counteracts the toxicity of TNF can help towards an understanding of the complex nature of TNF toxicity.

Effect of peripheral benzodiazepine receptor ligands on lipopolysaccharide-induced tumor necrosis factor activity in thioglycolate-treated mice

To investigate the effect of peripheral and central benzodiazepine receptor ligands on lipopolysaccharide (LPS)-induced tumor necrosis factor (TNF) activity in mouse macrophages, three types of ligands, 4'-chlorodiazepam (pure peripheral), midazolam (mixed), and clonazepam (pure central), were compared. Midazolam and 4'-chlorodiazepam significantly suppressed LPS (1-microgram/ml)-induced TNF activity in thioglycolate-elicited mouse macrophages. In every concentration examined (0.001 to 100 microM), 4'-chlorodiazepam was the most effective agent, clonazepam was the least effective agent, and midazolam had an effect intermediate between those of the other two ligands. The peripheral benzodiazepine receptor ligands had a dose-dependent suppressive effect, and the 50% inhibitory concentrations were 0.01 microM for 4'-chlorodiazepam and 5 microM for midazolam. Concomitant use of PK 11195 (10 microM), an antagonist of the peripheral benzodiazepine receptor, reversed this suppressive effect with 4'-chlorodiazepam (10 microM) or midazolam (10 microM). PK 11195 showed this antagonistic effect in a dose-dependent manner. Intravenous 4'-chlorodiazepam (5 mg/kg of body weight) significantly suppressed LPS (100-micrograms)-induced TNF activity of sera (2 h postchallenge with LPS) from thioglycolate-treated mice. The present findings suggest that the peripheral benzodiazepine receptor plays an important role in modulating LPS-induced TNF activity in mouse macrophages.

Binding of lysozyme to lipopolysaccharide suppresses tumor necrosis factor production in vivo

Endotoxin (lipopolysaccharide [LPS]) released during gram-negative bacterial infection induces varieties of cytokines which directly and/or indirectly cause shock, disseminated intravascular coagulation, and death. We previously showed that lysozyme (LZM) was an LPS-binding protein and inhibited various immunomodulating activities of LPS. In this study, we examined the effect of LZM on the LPS-triggered septic shock model induced by carrageenan treatment and assessed by tumor necrosis factor production. The data presented in this report strongly suggest that LZM-LPS complex formation completely abrogates tumor necrosis factor production and the mortality caused by LPS and that LZM may be useful for the treatment of endotoxin shock.