Modulation of lipopolysaccharide-induced macrophage gene expression by Rhodobacter sphaeroides lipid A and SDZ 880.431

Taxol: a promising endotoxin research tool

Recently, endotoxin research has benefited from the cross fertilization of two fields of study. Investigation into the cellular actions of the anticancer drug, taxol, has suggested novel tools with which to investigate the signaling apparatus that mediates macrophage activation by bacterial lipopolysaccharide. 2 In turn, this research may ultimately cause a re-examination of the belief that microtubules are the singular molecular target for taxol and suggest additional potential mechanisms for the antineoplastic actions of taxoids. The aim of this chapter is to review the actions of taxol on macrophages and the evidence that taxol engages the LPS signaling apparatus. Microtubule-independent targets for taxol are proposed, as is the use of taxol as a novel tool for endotoxin research.

Lipopolysaccharide from Rhodobacter sphaeroides is an agonist in equine cells

Endotoxemia is associated with the principal causes of death in adult horses and equine neonates and, therefore, veterinary researchers are expending efforts to identify new therapeutic interventions that might be beneficial in these animals. Endotoxin antagonists inhibit interaction of endotoxin with cellular receptors and may be beneficial in the treatment of endotoxemia and sepsis. Diphosphoryl lipid A from Rhodobacter sphaeroides ( RsDPLA) is a potent antagonist of enteric LPS in human cells, but is an agonist in hamster cells. In this study, the effect of lipopolysaccharide from R. sphaeroides ( RsLPS) on equine whole blood and isolated monocyte preparations was investigated by comparing tumor necrosis factor (TNF) production in response to RsLPS and Escherichia coli O55:B5 LPS. Our results indicate that RsLPS is a potent agonist in equine cells, which precludes therapeutic use of this agent in equine patients. In contrast to the results in equine cells, RsLPS did not elicit TNF production by itself, and inhibited the response to E. coli O55:B5 LPS in a human monocytic cell line.

Regulation of gene expression and nitric oxide production in murine macrophages by the serine/threonine phosphatase inhibitor okadaic acid

LPS-stimulated macrophages produce cytokines which, at appropriate levels, direct successful immune responses against harmful pathogens. However, excessive cytokine production, as seen in endotoxemia, results in pathophysiological damage to the host. Therefore, understanding mechanisms of cytokine regulation may aid the development of strategies designed to control cytokine production during an ongoing immune response. We have examined the role of okadaic acid-sensitive phosphatases in the production of cytokines and nitric oxide by macrophages. Okadaic acid induces TNFα, IL-1β, IL-6, IFN-β, and IP-10, but not IL-10 or IL-12 (p40) mRNA. Okadaic acid differentially regulates the expression of LPS-inducible IL-10 and IL-12 (p40) mRNA. These findings suggest that okadaic acid-sensitive phosphatases are key regulators of cytokine production in unstimulated and immune-activated macrophages. Finally, okadaic acid inhibits iNOS mRNA and nitric oxide production by macrophages activated by LPS and IFN-γ.

Mammalian Lipopolysaccharide Receptors Incorporated into the Retroviral Envelope Augment Virus Transmission

The orally transmitted retrovirus mouse mammary tumor virus (MMTV) requires the intestinal microbiota for persistence. Virion-associated lipopolysaccharide (LPS) activates Toll-like receptor 4 (TLR4), stimulating production of the immunosuppressive cytokine IL-10 and MMTV evasion of host immunity. However, the mechanisms by which MMTV associates with LPS remain unknown. We find that the viral envelope contains the mammalian LPS-binding factors CD14, TLR4, and MD-2, which, in conjunction with LPS-binding protein (LBP), bind LPS to the virus and augment transmission. MMTV isolated from infected mice lacking these LBPs cannot engage LPS or stimulate TLR4 and have a transmission defect. Furthermore, MMTV incorporation of a weak agonist LPS from Bacteroides, a prevalent LPS source in the gut, significantly enhances the ability of this LPS to stimulate TLR4, suggesting that MMTV intensifies these immunostimulatory properties. Thus, an orally transmitted retrovirus can capture, modify, and exploit mammalian receptors for bacterial ligands to ensure successful transmission.

Effects of the second-generation synthetic lipid A analogue E5564 on responses to endotoxin in [corrected] equine whole blood and monocytes

OBJECTIVE

To evaluate proinflammatory effects of the second-generation synthetic lipid A analogue E5564 on equine whole blood and isolated monocytes and to determine the ability of E5564 to prevent LPS (lipopolysaccharide)-induced procoagulant activity (PCA); tumor necrosis factor (TNF)-alpha production; and mRNA expression of TNF-alpha, interleukin (IL)-1beta, IL-6, and IL-10 by equine monocytes.

SAMPLE POPULATION

Venous blood samples obtained from 19 healthy horses.

PROCEDURES

Whole blood and monocytes were incubated with Escherichia coli O111:B4 LPS, E5564, or E5564 plus E coli O111:B4 LPS. Whole blood and cell supernatants were assayed for TNF-alpha, and cell lysates were assayed to determine PCA. Expression of mRNA for TNF-alpha, IL-1beta, IL-6, and IL-10 by monocytes was determined by use of real-time quantitative PCR assay.

RESULTS

Minimal proinflammatory effects were detected in whole blood and monocytes. In addition, E5564 inhibited LPS-induced PCA and TNF-alpha production in a concentration-dependent manner. Furthermore, E5564 significantly inhibited LPS-induced mRNA expression of TNF-alpha, IL-1beta, and IL-10 and decreased LPS-induced expression of IL-6.

CONCLUSIONS AND CLINICAL RELEVANCE

The second-generation synthetic lipid A analogue E5564 lacked agonist activity in equine whole blood and monocytes and was a potent antagonist of enteric LPS. Therefore, E5564 appeared to be the first lipid A analogue that has potential as an effective therapeutic agent in horses with endotoxemia.

Neutrophil activation by bacterial lipoprotein versus lipopolysaccharide: differential requirements for serum and CD14

Neutrophil activation plays an important role in the inflammatory response to Gram-negative bacterial infections. LPS has been shown to be a major mediator of neutrophil activation which is accompanied by an early down-regulation of L-selectin and up-regulation of CD1lb/CD18. In this study, we investigated whether lipoprotein (LP), the most abundant protein in the outer membrane of bacteria from the family Enterobacteriaceae, can activate neutrophils and whether this activation is mediated by mechanisms that differ from those used by LPS or Escherichia coli diphosphoryl lipid A (EcDPLA). Neutrophil activation was assessed by measuring down-regulation of L-selectin and up-regulation of CD11b/CD18. When comparing molar concentrations of LP vs EcDPLA, LP was more potent (four times) at activating neutrophils. In contrast to LPS/EcDPLA, LP activation of neutrophils was serum independent. However, LP activation of neutrophils was enhanced by the addition of soluble CD14 and/or LPS-binding protein. In the presence of serum, LP activation of neutrophils was inhibited by different mAbs to CD14. This inhibition was significantly reduced or absent when performed in the absence of serum. Diphosphoryl lipid A from Rhodobacter spheroides (RaDPLA) completely inhibited LPS/EcDPLA activation of neutrophils but only slightly inhibited LP activation of neutrophils. These results suggest that LP activation of human neutrophils can be mediated by a mechanism that is different from LPS activation and that LP is a potentially important component in the development of diseases caused by Gram-negative bacteria of the family Enterobacteriaceae.

Bacterial lipopolysaccharide induces expression of the stress response genes hop and H411

CD14-transfected Chinese hamster ovary K1 fibroblasts (CHO/CD14) respond to lipopolysaccharide (LPS) by metabolizing arachidonic acid and with translocation of NF-kappaB to the nucleus. Although previous experiments failed to identify the production of tumor necrosis factor-alpha and interleukin (IL)-1beta by CHO/CD14 cells, LPS did induce the expression of IL-6 mRNA and the subsequent release of the IL-6 protein. To identify additional LPS-inducible genes, a cDNA library derived from LPS-stimulated CHO/CD14 cells was screened by subtractive hybridization. Fourteen genes were found to be expressed differentially, and two were analyzed in detail: hop (Hsp70/Hsp90-organizing protein), which is the hamster homologue of the stress-inducible yeast gene, STI1, and clone H411, which encodes a novel LPS-inducible growth factor. In response to LPS, the expression of Hop mRNA was also increased in both the murine macrophage cell line, RAW 264.7, as well as in primary hamster macrophages. This suggested that the up-regulation of Hop expression is part of the macrophage stress response to LPS. Clone H411 encodes a protein in the epidermal growth factor-like repeat protein family. Overexpression of H411 cDNA in the RAW 264.7 macrophage cell line promoted an increased growth rate, suggesting that expression of H411 is part of the proliferative cell response to LPS. Both Hop and H411 represent novel gene products not previously recognized as part of the complex biological response to endotoxin.

Microtubule-disrupting agents inhibit nitric oxide production in murine peritoneal macrophages stimulated with lipopolysaccharide or paclitaxel (Taxol)

Paclitaxel (Taxol), a yew-derived antimitotic agent which binds to microtubules, can mimic certain effects of lipopolysaccharide (LPS) on macrophages from LPS responder mouse strains. The production of nitric oxide (NO) by the peritoneal macrophages of LPS responder C3H/HeN mice stimulated with taxol or LPS was partially, but not completely, suppressed by microtubule-disrupting agents, such as colchicine, podophyllotoxin, vinblastine, and nocodazole, but not by lumicolchicine, an inactive derivative of colchicine. Inducible NO synthase protein expression induced by taxol and LPS in the macrophages was also suppressed by colchicine, but colchicine did not suppress the transcription of iNOS mRNA in the macrophages after stimulation with taxol or LPS. These findings suggest that microtubules function in the posttranscriptional processes of iNOS protein expression rather than in the transcriptional process of iNOS mRNA and the synthetic process of NO molecules.

Lipoteichoic acid preparations of gram-positive bacteria induce interleukin-12 through a CD14-dependent pathway

Interleukin 12 (IL-12) strongly augments gamma interferon production by natural killer (NK) and T cells. IL-12 also promotes effective cell-mediated immune responses, which are particularly important against intracellular bacteria such as Listeria monocytogenes. While the lipopolysaccharide (LPS) of gram-negative bacteria induces monocyte production of IL-12, the relevant gram-positive components which induce IL-12 production are uncharacterized. We used the human monocytic cell line THP-1 to study IL-12 induction by gram-positive bacteria. Muramyl dipeptides as well as the major muramyl tetrapeptide component of Streptococcus pneumoniae were inactive for inducing IL-12. In contrast, lipoteichoic acid (LTA), a predominant surface glycolipid of gram-positive bacteria, potently induced IL-12 p40 gene expression. A competitive LPS antagonist, Rhodobacter sphaeroides LPS, inhibited LTA-induced IL-12 production, suggesting a common pathway for LPS and LTA in IL-12 activation. Pretreatment of cells with anti-CD14 monoclonal antibody blocked both LPS and LTA induction of IL-12 p40 expression. LTA also induced Thl development in naive CD4 T cells by an IL-12-dependent mechanism, indicating direct induction of physiologic levels of IL-12. Together, these results show that LTA is a potent surface structure of gram-positive bacteria which induces IL-12 in monocytes through a CD14-mediated pathway.

Paclitaxel (Taxol)-induced NF-kappaB translocation in murine macrophages

Interaction of bacterial lipopolysaccharide (LPS) with macrophages results in the induction of a cascade of cytokines that mediate the varied effects of LPS. An early intracellular signaling event that follows receptor engagement is the activation of transcription factor NF-kappaB. Nf-kappaB has been shown to be important for the induction of many LPS-inducible cytokine genes, including tumor necrosis factor alpha, interleukin-1beta, and interleukin-6. Previously, we and others have shown that the antitumor agent paclitaxel (Taxol) is able to mimic bacterial LPS in its ability to activate murine macrophages. In this report, we have extended these findings by demonstrating that paclitaxel, like LPS, is able to stimulate the translocation of primarily p50-p65 heterodimers of NF-kappaB to the nucleus. This activation is dose dependent and requires a concentration of > or =5 microM paclitaxel. The kinetics of NF-kappaB activation by paclitaxel are slower than those of LPS: by 15 min poststimulation, LPS-induced NF-kappaB activation was readily detected, whereas the paclitaxel-induced NF-kappaB activation was minimal. Moreover, paclitaxel- and protein-free LPS-induced translocation of NF-kappaB was seen only in macrophages derived from LPS-responsive C3H/OuJ mice and not from the LPS-hyporesponsive C3H/HeJ mice, a finding that is consistent with those of previous genetic studies linking paclitaxel responsiveness to the Lps gene. Finally, the LPS structural antagonist Rhodobacter sphaeroides diphosphoryl lipid A inhibited both LPS-and paclitaxel-induced NF-kappaB activation, suggesting a common receptor component in this activation.

Enzymatically deacylated lipopolysaccharide (LPS) can antagonize LPS at multiple sites in the LPS recognition pathway

Like other tetraacyl partial structures of lipopolysaccharide (LPS) and lipid A, LPS that has been partially deacylated by acyloxyacyl hydrolase can inhibit LPS-induced responses in human cells. To identify the site(s) of inhibition in the LPS recognition pathway, we analyzed the apparent binding affinities and interactions of 3H-labeled enzymatically deacylated LPS (dLPS) and [3H]LPS with CD14, the LPS receptor, on THP-1 cells. Using (i) incubation conditions that prevented ligand internalization and (ii) defined concentrations of LPS binding protein (LBP), which facilitates LPS and dLPS binding to CD14, we found that dLPS can antagonize LPS in at least three ways. 1) When the concentration of LBP in the medium was suboptimal for promoting LPS-CD14 binding, low concentrations of dLPS were able to compete with LPS for binding CD14, suggesting competition between LPS and dLPS for engaging LBP. 2) When LBP was present in excess, dLPS could compete with LPS for binding CD14, but only at dLPS concentrations that were at or above its KD for binding CD14 (100 ng/ml). 3) In contrast, substoichiometric concentrations of dLPS (1 ng/ml) inhibited LPS-induced (3 ng/ml) interleukin-8 release without blocking LPS binding to CD14. Functional antagonism was possible without competition for cell-surface binding because both LPS-induced interleukin-8 release and dLPS inhibition occurred at concentrations that were far below their respective CD14 binding KD values. In addition to its expected ability to compete with LPS for binding LBP and CD14, dLPS thus potently antagonizes LPS at an undiscovered site that is distal to LPS-CD14 binding in the LPS recognition pathway.

Agonistic and antagonistic activities of bacterially derived Rhodobacter sphaeroides lipid A: comparison with activities of synthetic material of the proposed structure and analogs

Lipid A from the photosynthetic bacterium Rhodobacter sphaeroides (RSLA) has been previously shown to antagonize many of the effects of endotoxins from more pathogenic gram-negative bacteria. We have reported on the synthesis of the proposed structure of RSLA and determined that bacterially derived RSLA is not identical to its proposed structure (W.J. Christ, P. D. McGuinness, O. Asano, Y. Wang, M. A. Mullarkey, M. Perez, L. D. Hawkins, T. A. Blythe, G. R. Dubuc, and A. L. Robidoux, J. Am. Chem. Soc. 116:3637-3638, 1994). Here we report results of analyzing the antagonistic and agonistic activities of bacterially derived RSLA in comparison with the activities of chemically synthesized material of the proposed structure of RSLA and analogs. Results indicated that all compounds were approximately equally potent at inhibiting endotoxin-induced release of tumor necrosis factor alpha from human monocytes and human whole blood as well as endotoxin-induced generation of nitric oxide in murine macrophages. In addition, all compounds were of equivalent potencies at inhibiting the binding of 125I-labelled lipopolysaccharide derivatized with 2-(p-azido-salicylamido) ethyl-1-3'-dithiopropionate to murine macrophages. Higher concentrations of bacterially derived RSLA (10 to 100 microM) were agonistic in human and murine assays. In gamma interferon-treated murine macrophages, agonism was exhibited at concentrations as low as 100 nM. In contrast, all synthetic materials were either dramatically less agonistic or devoid of agonistic activity when tested at concentrations as high as 100 microM. It is possible either that bacterially derived RSLA contains a small amount of a highly agonistic impurity or that the agonistic activity of RSLA is intrinsic to its molecular structure. In either case, these biological results support our previous report concluding that biologically derived RSLA is not identical to synthetic material of its proposed structure.

Diphosphoryl lipid A from Rhodobacter sphaeroides transiently activates NF-kappa B but inhibits lipopolysaccharide induction of kappa light chain and Oct-2 in the B-cell lymphoma line 70Z/3

Lipopolysaccharide (LPS) is implicated in much of the pathophysiology associated with gram-negative septic shock. One approach to this serious clinical problem is to develop new drugs that antagonize the action of toxic LPS. A model system to study LPS action and test for potential antagonists is readily provided by LPS regulation of the kappa gene in the murine B-cell line 70Z/3. Rhodobacter sphaeroides diphosphoryl lipid A (RsDPLA) effectively blocked toxic LPS induction of kappa light-chain immunoglobulin expression in 70Z/3 cells. Induction of kappa expression by LPS is dependent on the activation of at least two transcription factors, Oct-2 and NF-kappa B. RsDPLA completely repressed the long-term activation of NF-kappa B observed after 24 h of Salmonella typhosa LPS treatment and antagonized activation of oct-2 mRNA expression. However, RsDPLA was not an inert competitor of LPS. RsDPLA alone strongly activated NF-kappa B binding activity by 30 min but not beyond 9 h of treatment. It also induced a small increase in oct-2 mRNA levels. RsDPLA is not simply a weak agonist; we found no graded increase in kappa expression with increasing RsDPLA concentrations up to 50 micrograms/ml. The NF-kappa B complexes activated by RsDPLA and S. typhosa LPS were both composed of the p50-p65 heterodimer. These results suggest that the physiological LPS receptor(s) on B cells transmits qualitatively different signals depending on the nature of the binding ligand and that the fatty acyl groups of LPS play an important role in activating signal transduction.

Toxoplasma gondii soluble antigen induces a subset of lipopolysaccharide-inducible genes and tyrosine phosphoproteins in peritoneal macrophages

Previous studies have shown that macrophages play an important role in both the initiation of protective responses and the effector mechanism of immunity to Toxoplasma gondii. The purpose of this investigation was to characterize the responses of macrophages to a soluble antigen extract of T. gondii tachyzoites (STAg) in comparison with a prototypic macrophage-activating agent, lipopolysaccharide (LPS), and to determine whether STAg-induced signaling requires a functional Lps gene. Toward this end, tumor necrosis factor (TNF) secretion, a panel of six LPS-inducible genes, and protein tyrosine phosphorylation were examined to gain insights into macrophage responses to STAg. STAg stimulated both C3H/OuJ (Lpsn) and C3H/HeJ (Lpsd) macrophages to secrete bioactive TNF-alpha and to express a subset of LPS-inducible genes (encoding TNF-alpha, TNF receptor 2, and interleukin-1 beta). In contrast to LPS, STAg failed to stimulate Lpsn or Lpsd macrophages to express genes encoding IP-10, D3, or D8. STAg also induced a pattern of tyrosine phosphorylation identical to that induced by LPS; mitogen-activated protein kinase 47-kDa and 43-kDa isoforms and a 41-kDa protein of undetermined identity were inducibly phosphorylated. The ability of STAg to induce TNF-alpha, encoded by a subset of LPS-inducible genes, and tyrosine phosphoproteins was not affected by LPS inhibitors, confirming that the macrophage response to the parasite extract could not be attributed to LPS contamination. We propose that STAg, while differing from LPS in the pattern of macrophage genes induced, may share with LPS two signaling pathways that are intact in Lpsd macrophages.