Chemical reduction of 3-oxo and unsaturated groups in fatty acids of diphosphoryl lipid A from the lipopolysaccharide of Rhodopseudomonas sphaeroides. Comparison of biological properties before and after reduction

Structural analysis of a novel lipooligosaccharide (LOS) from Rhodobacter azotoformans

Lipopolysaccharides (LPS) are components of the Gram-negative bacterial cell surface that stimulate the host innate immune system through the Toll-like receptor (TLR) 4-MD-2 complex. Rhodobacter sp. have been reported to produce LPS that lack endotoxic activity, and instead act as antagonists of other endotoxins. In this report, we focused on LPS, especially the lipooligosaccharide (LOS) fraction produced by Rhodobacter azotoformans that shows production of IL-8, but has an inverse correlation with IL-6 production. We analyzed their molecular structure by using mass spectrometry and nuclear magnetic resonance spectroscopy and report a novel LOS consisting of a shorter glycan structure containing glucuronic acid but not heptoses. A novel glycan structure, Glcα(1 → 4)GlcAα(1 → 4)KDOα(2 → 4)[Glcα(1 → 5)]KDOα(2 → 6)[4-phosphate]GlcNβ(1 → 6) GlcNα1-phosphate, was proposed using NMR methods. The structure was consistent with one obtained based on MS. The MS analysis further revealed the existence of structural variation caused by extension with hexoses. The acyl composition in lipid A was suggested to contain three C14 fatty acyl chains (3-OH-14:0 or 3-oxo-14:0 at N2 of GlcN-1, 3-OH-14:0 at N2 of GlcN-2, that carried another 14:1 Δ7 on its β-hydroxyl group) and two C10 fatty acyl chains (3-OH-10:0 at O3 of both GlcN), which are same as those found in lipid A from Rhodobacter sphaeroides.

Natural Products with Toll-Like Receptor 4 Antagonist Activity

Toll-Like Receptors (TLRs) are the innate immunity receptors that play an activating role when interacting with molecules released by bacteria and viruses (PAMPs, pathogen-associated molecular patterns) or with molecules released by injured cells and tissues (DAMPs, danger-associated molecular patterns). TLR triggering leads to the induction of proinflammatory cytokines and chemokines, driving the activation of both innate and adaptive immunity. In particular, Toll-Like Receptor 4 (TLR4) has been described to be involved in the inflammatory processes observed in several pathologies (such as ischemia/reperfusion injury, neuropathic pain, neurodegenerative diseases, and cancer). Molecules obtained by natural sources have been discovered to exert an anti-inflammatory action by targeting TLR4 activation pathways. This review focuses on TLR4 antagonists obtained from bacteria, cyanobacteria, and plants.

LPS-dependent changes in the expression of 57 kDa and 53 kDa cell membrane proteins without participation of CD14

It is widely presumed that in addition to CD14, other molecules are necessary for lipopolysaccharide (LPS)-induced cell activation. In order to shed light on some of the biological and biochemical properties of these molecules, we examined the LPS responsiveness of CD14-negative, ST2 cells. Although ST2 cells do not express CD14 mRNA, they, nonetheless, expressed IL-6 mRNA and synthesized IL-6 protein when incubated with LPS in serum-free medium ( i.e. without soluble CD14). Paxlitacel (Taxol™) also induced IL-6 mRNA expression in ST2 cells, while Rhodobacter sphaeroides diphoshoryl lipid A (RsDPLA) inhibited both LPS- and Taxol-induced expression of IL-6 mRNA. Collectively, these data suggest that LPS, RsDPLA, and Taxol all recognize the same receptor complex on ST2 cells and do not require the participation of CD14. In addition, using antibody raised against the ST2 cell membrane fraction, we detected a set of LPS-specific membrane antigens in murine peritoneal macrophages, including two designated p57 (57 kDa) and p53 (53 kDa). There was no qualitative difference in the expression of p57 and p53 in LPS-responsive, C3H/HeN and LPS-hyporesponsive, C3H/HeJ macrophages. However, after stimulating the macrophages with LPS or Taxol, expression of p57 and p53 was diminished in C3H/HeN macrophages, but not in C3H/HeJ macrophages. Phorbol ester (PMA) and A23187 calcium ionophore did not suppress p57 or p53 expression, and the lipid A precursor, PE406, did not bind to either protein. Thus, p57 and p53 may play important roles in LPS-evoked responses, but they do not appear to serve as LPS receptors.

Rhodobacter sphaeroides diphosphoryl lipid A inhibits interleukin-6 production in CD14-negative murine marrow stromal ST2 cells stimulated with lipopolysaccharide or paclitaxel (taxol)

Paclitaxel (taxol), a microtubule stabilizer with anticancer activity, mimics the actions of lipopolysaccharide (LPS) on murine macrophages in vitro. Recent studies have shown that the Rhodobacter sphaeroides diphosphoryl lipid A (RsDPLA) inhibits both LPS- and paclitaxel-induced activation of murine macrophages, and have suggested that LPS, RsDPLA, and paclitaxel share the same receptor site on murine macrophages. To analyze this receptor site, the present study focused on the interactions between LPS, RsDPLA and paclitaxel in the activation of ST2 cells derived from murine bone marrow stroma. The ST2 cells did not express CD14 mRNA. The cells produced IL-6 molecules and expressed IL-6 mRNA in response to LPS, but did not produce TNF and nitric oxide. Paclitaxel induced IL-6 mRNA expression in ST2 cells. RsDPLA inhibited both LPS- and paclitaxel-induced IL-6 mRNA expression in a dose-dependent manner. These results suggest that LPS, RsDPLA, and paclitaxel are recognized by the same receptor complex on ST2 cells, and that the receptor functions without membrane CD14.

Structural analysis of the lipid A derived from the lipopolysaccharide of Brucella abortus

Lipopolysaccharide (LPS) of Brucella abortus strain 45/20 was purified using a novel method. Monophosphoryl lipid A (MPLA) was prepared from this LPS, methylated, and purified by high performance liquid chromatography. Chemical, mass spectral, and nuclear magnetic resonance analyses showed that MPLA consists of heptaacyl lipid As with molecular weights of 2095, 2123, 2151 and 2179. They contained the β-1,6-linked 2,3-diamino-2,3,-dideoxy-glucose disaccharide backbone and a phosphate group at the 4' position. Bisphosphoryl lipid A was also prepared and completely O-deacylated. It contained an additional phosphate group, and either 2 hydroxyhexadecanoic, 1 hydroxytetradecanoic, 1 hydroxydodecanoic acids or 2 hydroxyhexadecanoic and 2 hydroxydodecanoic acids, all in amide linkage. The predominant ester-linked fatty acyl group in acyloxyacyl linkage was hexadecanoate.

The purified LPS, bisphosphoryl lipid A, and MPLA from B. abortus showed about 14%, 3% and 1%, respectively, of the B cell mitogen activity of ReLPS from Escherichia coli at 1.0 μg/ml.

Position and configuration of double bonds of lipid A-associated monounsaturated fatty acids of Proteobacferia and Rhodobacter capsulatus 37b4

The double bond of dodecenoic acid in the endotoxin-antagonistically acting lipid A of Rhodobacter capsulatus, strains 37b4 and St Louis, was found to have cis-configuration. The position of the double bond was ω7. The mono-unsaturated fatty acids of lipid A from a number of additionally investigated strains of various species of the α-, β-, and γ-subgroups of Proteobacteria (Agrobacterium spp., Azospirillum spp., Rhizobium meliloti, Rhodobacter sphaeroides, Rhodomicrobium vannielii, Rhodopseudomonas blastica, Rhodospirillum salinarum, Sphaerotilus natans, Thiobacillus spp. and Yersinia enterocolitica) have also cis -configuration with the double bond in the ω7-position (one exception), suggesting the anaerobic pathway of biosynthesis to be common for most of them.

TLR4 antagonist reduces early-stage atherosclerosis in diabetic apolipoprotein E-deficient mice

Although it has been reported that deficiency of toll-like receptor 4 (TLR4) is associated with reduced atherosclerosis in atherosclerosis-prone mice and attenuated pro-inflammatory state in diabetic mice, it remains undetermined whether treatment with a TLR4 antagonist reduces atherosclerosis in nondiabetic or diabetic mice that have TLR4 expression. In this study, we determined the effect of Rhodobacter sphaeroides lipopolysaccharide (Rs-LPS), an established TLR4 antagonist, on early-stage atherosclerosis in nondiabetic and streptozotocin-induced diabetic apolipoprotein E-deficient (Apoe(-/-)) mice. Analysis of atherosclerotic lesions of both en face aortas and cross sections of aortic roots showed that administration of Rs-LPS in 14-week-old diabetic Apoe(-/-) mice for 10 weeks significantly reduced atherosclerotic lesions. Although atherosclerotic lesions in nondiabetic Apoe(-/-) mice appeared to be decreased by Rs-LPS treatment, the difference was not statistically significant. Metabolic study showed that Rs-LPS significantly lowered serum levels of cholesterol and triglycerides in nondiabetic mice but not in diabetic mice. Furthermore, immunohistochemistry studies showed that Rs-LPS inhibited the expression of interleukin 6 and matrix metalloproteinase-9 and reduced the content of monocytes and macrophages in atherosclerotic plaques. Taken together, this study demonstrated for the first time that TLR4 antagonist inhibited vascular inflammation and atherogenesis in diabetic Apoe(-/-) mice and lowered serum cholesterol and triglyceride levels in nondiabetic Apoe(-/-) mice.

A variety of novel lipid A structures obtained from Francisella tularensis live vaccine strain

F. tularensis is a Gram-negative coccobacillus that causes tularemia. Its LPS has nominal biological activity. Currently, there is controversy regarding the structure of the lipid A obtained from F. tularensis live vaccine strain (LVS). Therefore, to resolve this controversy, the purification and structural identification of this LPS was crucial. To achieve this, LPS from F. tularensis LVS was acid hydrolyzed to obtain crude lipid A that was methylated and purified by HPLC and the fractions were analyzed by MALDI-TOF MS. The structure of the major lipid A species was composed of a glucosamine disaccharide backbone substituted with four fatty acyl groups and a phosphate (1-position) with a molecular mass of 1505. The major lipid A component contained 18:0[3-O(16:0)] in the distal subunit and two 18:0(3-OH) fatty acyl chains at the 2- or 3-positions of the reducing subunit. Additional variations in the lipid A species include: heterogeneity in fatty acyl groups, a phosphate or a phosphoryl galactosamine at the 1-position, and a hexose at the 4' or 6' position, some of which have not been previously described for F. tularensis LVS. This analysis revealed that lipid A from F. tularensis LVS is far more complex than originally believed.

Structural analysis of lipopolysaccharides from Gram-negative bacteria

This review covers data on composition and structure of lipid A, core, and O-polysaccharide of the known lipopolysaccharides from Gram-negative bacteria. The relationship between the structure and biological activity of lipid A is discussed. The data on roles of core and O-polysaccharide in biological activities of lipopolysaccharides are presented. The structural homology of some oligosaccharide sequences of lipopolysaccharides to gangliosides of human cell membranes is considered.

Biological properties of the native and synthetic lipid A of Porphyromonas gingivalis lipopolysaccharide

INTRODUCTION AND METHODS

A pentaacyl and diphosphoryl lipid A molecule found in the lipid A isolated from Porphyromonas gingivalis lipopolysaccharide (LPS) was chemically synthesized, and its characteristics were evaluated to reconfirm its interesting bioactivities including low endotoxicity and activity against LPS-unresponsive C3H/HeJ mouse cells.

RESULTS

The synthesized P. gingivalis lipid A (synthetic Pg-LA) exhibited strong activities almost equivalent to those of Escherichia coli-type synthetic lipid A (compound 506) in all assays on LPS-responsive mice, and cells. LPS and native lipid A of P. gingivalis displayed overall endotoxic activities, but its potency was reduced in comparison to the synthetic analogs. In the assays using C3H/HeJ mouse cells, the LPS and native lipid A significantly stimulated splenocytes to cause mitosis, and peritoneal macrophages to induce tumor necrosis factor-alpha and interleukin-6 production. However, synthetic Pg-LA and compound 506 showed no activity on the LPS-unresponsive cells. Inhibition assays using some inhibitors including anti-human Toll-like receptor 2 (TLR2) and TLR4/MD-2 complex monoclonal antibodies showed that the biological activity of synthetic Pg-LA was mediated only through the TLR4 signaling pathway, which might act as a receptor for LPS, whereas TLR2, possibly together with CD14, was associated with the signaling cascade for LPS and native lipid A of P. gingivalis, in addition to the TLR4 pathway.

CONCLUSION

These results suggested that the moderated and reduced biological activity of P. gingivalis LPS and native lipid A, including their activity on C3H/HeJ mouse cells via the TLR2-mediated pathway, may be mediated by bioactive contaminants or low acylated molecules present in the native preparations having multiple lipid A moieties.

Structure of a novel lipid A obtained from the lipopolysaccharide of Caulobacter crescentus

Caulobacter crescentus CB15 is a dimorphic bacterium that is best known as a prokaryotic model for cell development. However, it is also being exploited in biotechnology, where the crystalline surface (S-layer) protein secretion system has been adapted for heterologous protein display or secretion. Because the S-layer attaches to the cell surface via lipopolysaccharide (LPS) and since the LPS represents a potential endotoxin contaminant of recombinant proteins, the lipid A component was examined in detail. LPS was acid hydrolyzed to obtain crude lipid A, which was methylated and purified by HPLC. HPLC peak fractions were analyzed by mass spectrometry and nuclear magnetic resonance spectroscopy. The structure of the major lipid A of C. crescentus comprised the tetrasaccharide backbone α-D-GalpA-(1→4)-β-D-DAG-(1→6)-α-D-DAG-(1→1)-α-D-GalpA substituted with six fatty acids, and a molecular mass of 1875 (GalpA, galactopyranuronic acid; DAG, 2,3-diamino-2,3-dideoxyglucopyranose). No phosphate residues were detected. The major lipid A component had 12:0[3-O[Δ5-12:1(3-OH)]] and 12:0[3-O(Δ5-12:1)] fatty acyl chains at either the 3′- or the 2′ positions of the distal subunit DAG B, and 12:0(3OH) and 12:0[3,6-(OH) 2] fatty acyl chains at 3- and 2- positions of the reducing end subunit DAG A, respectively. In addition, several other variations in the structure were observed. The LPS was evaluated for TNF-α inducing activity and consistent with its unusual lipid A structure (relative to that of enteric bacteria), the activity was reduced by greater than 100-fold as compared to Escherichia coli ReLPS. This and other evidence suggests the potential application of this lipid A as a vaccine adjuvant or the suitability of Caulobacter displaying antigens for formulation of whole cell vaccines.

[Identification and structural analysis of a glycophospholipid component from the venom of ant Paraponera clavata]

The venom of South American ant Paraponera clavata and its low-molecular-mass fraction were shown to possess insectotoxic and pore-forming activities. A number of glycophospholipid components were isolated from this ant venom by means of gel filtration and reversed-phase chromatography. Some of the compounds cause conductivity fluctuations in lipid bilayer membranes within the ranges 3-25 pS and 200-400 pS at concentrations of 10(-6) to 10(-7) M. N-Acetylglucosamine, a fatty acid, and phosphoric acid residues were found in their structures. A full structure, 3-myristoyl-2-acetamido-2-deoxy-alpha-D-glucopyranosyl phosphate, was elucidated for one of the compounds by the use of 1H, 13C, and 31P NMR spectroscopy and mass spectrometry.

Syntheses of glucose derivatives of E5564-related compounds and their LPS-antagonistic activities

Glucose analogues 6, 12, 17b, 19a, and 19b of E5564 were synthesized, and their LPS-antagonistic activities were measured. The antagonistic activities (IC(50)) on LPS-induced TNFalpha production of these five compounds toward human whole blood were 72.8, 3.0, 0.9, 7.5, and 1.4nM, respectively. Inhibitory doses (ID(50)) of compounds 12, 17b, 19a, and 19b on TNFalpha production induced by co-injection of galactosamine and LPS in C3H/HeN mice in vivo were measured. The values of these compounds were 0.9, ND (not determined), 1.6, and 0.9mg/kg, respectively.

Regulation of cellular caveolin-1 protein expression in murine macrophages by microbial products

Previously, we reported that expression of caveolin-1 in elicited peritoneal mouse macrophages was up-regulated by remarkably low (1.0-pg/ml) concentrations of Escherichia coli O111 lipopolysaccharide (LPS). Here we report that increases in caveolin-1 expression are manifested by different types of LPS, LPS-mimetic taxol, and heat-killed E. coli and to a much lesser extent by zymosan, polysaccharide-peptidoglycan, and heat-killed Staphylococcus aureus. Rhodobacter sphaeroides lipid A (RsDPLA) could not induce caveolin-1 expression in macrophages. Interestingly, polymyxin B (5 microg/ml) and RsDPLA show only a limited capacity to inhibit LPS-induced caveolin-1 expression. These findings suggest that expression of caveolin-1 in response to LPS may only partially be dependent upon lipid A. Recombinant tumor necrosis factor alpha marginally induces caveolin-1, suggesting that the ability of LPS to regulate caveolin-1 is not mediated primarily through an autocrine/paracrine mechanism involving this cytokine. Under conditions in which cellular levels of caveolin-1 are profoundly induced, no significant changes in TLR4 expression are observed. Of interest, caveolin-1 appears to localize to two cellular compartments, one associated with lipid rafts and a second associated with TLR4. Gamma interferon treatment inhibits the induction of caveolin-1 by LPS in macrophages. Inhibition of the p38 kinase-dependent pathway, but not the extracellular signal-regulated kinase pathway, effectively reduced the ability of LPS to mediate caveolin-1 up-regulation. Lactacystin, a potent inhibitor of the proteasome pathway, significantly modulates LPS-independent caveolin-1 expression, and lactacystin inhibits LPS-triggered caveolin-1 responses. These studies suggest that caveolin-1 up-regulation in response to LPS is likely to be proteasome dependent and triggered through the p38 kinase pathway.

Syntheses of glucose analogues of E5564 as a highly potent anti-sepsis drug candidate

Glucose analogues 5 and 9 of E5564 were synthesized, and their LPS-antagonistic activities were measured. The inhibitory activities (IC50) on LPS-induced TNFalpha production of these two compounds towards human whole blood cells were 0.06 and 0.83 nM, respectively. Inhibitory doses (ID50) of compounds 5 and 9 on TNFalpha production induced by coinjection of galactosamine and LPS in C3H/HeN mice in vivo were measured and were 0.55 and <0.20 mg/kg, respectively. And also C3H/HeN mice preinjected with compounds 5 and 9 were protected from lethality induced by coinjection of galactosamine and LPS; out of eight mice preinjected with 1 mg/kg of the compounds, one-six and three of eight mice were protected, respectively.

Influence of CD14 on ligand interactions between lipopolysaccharide and its receptor complex

The interaction of LPS (endotoxin) with the CD14-TLR4 receptor complex modulates the host innate immune response. Several studies using partial structures of LPS have suggested that TLR4 determines the ligand specificity of this complex, and that CD14 indiscriminately serves to deliver the ligand to TLR4. This conclusion has been made despite observations that the response of TLR4(+/+),CD14(-/-) macrophages to LPS is very weak. To determine whether CD14 itself plays a role in specific ligand recognition, the influences of various partial structures of LPS on induction of the proinflammatory cytokine, TNF, by CD14(+/+) and CD14(-/-) macrophages were compared. These studies show that the ligand specificities of CD14(+/+) and CD14(-/-) macrophages are very different. When CD14 is present, the receptor complex shows exquisite specificity for smooth LPS, the major form expressed by Gram-negative bacteria; however, as increasing amounts of carbohydrate are removed from smooth LPS, the sensitivity of CD14(+/+) macrophages decreases as much as 500-fold. In contrast, CD14(-/-) macrophages are unable to distinguish between smooth LPS and its various partial structures. Furthermore, CD14(-/-) macrophages are 150,000-fold less sensitive than CD14(+/+) macrophages to smooth LPS. A similar ability to distinguish the differing LPS structures of various bacteria such as Bacteroides fragilis and Salmonella abortus are observed for CD14(+/+), but not CD14(-/-), macrophages. Thus, CD14(+/+), but not CD14(-/-), macrophages are highly sensitive to stimulation by natural forms of LPS and show the ability to distinguish between various LPS ligands, consistent with CD14 being a highly specific receptor.

The proteasome as a lipopolysaccharide-binding protein in macrophages: differential effects of proteasome inhibition on lipopolysaccharide-induced signaling events

We have developed a novel LPS probe using a highly purified and homogenous preparation of [(3)H] Escherichia coli LPS from the deep rough mutant, which contains a covalently linked, photoactivable 4-p-(azidosalicylamido)-butylamine group. This cross-linker was used to identify the LPS-binding proteins in membranes of the murine-macrophage-like cell line RAW 264.7. The alpha-subunit (PSMA1 C2, 29.5 kDa) and the beta-subunit (PSMB4 N3, 24.36 kDa) of the 20S proteasome complex were identified as LPS-binding proteins. This is the first report demonstrating LPS binding to enzymes such as the proteasome subunits. Functionally, LPS enhanced the chymotrypsin-like activity of the proteasome to degrade synthetic peptides in vitro and, conversely, the proteasome inhibitor lactacystin completely blocked the LPS-induced proteasome's chymotrypsin activity as well as macrophage TNF-alpha secretion and the expression of multiple inflammatory mediator genes. Lactacystin also completely blocked the LPS-induced expression of Toll-like receptor 2 mRNA. In addition, lactacystin dysregulated mitogen-activated protein kinase phosphorylation in LPS-stimulated macrophages, but failed to inhibit IL-1 receptor-associated kinase-1 activity. Importantly, lactacystin also prevented LPS-induced shock in mice. These data strongly suggest that the proteasome complex regulates the LPS-induced signal transduction and that it may be an important therapeutic target in Gram-negative sepsis.

Synthesis of lipid A type carboxymethyl derivatives with ether chains instead of ester chains and their LPS-antagonistic activities

Synthesis of lipid A type carboxymethyl derivatives having ether chains at both the C-3 and C-3' positions and their LPS-antagonistic activities toward human U937 cells are described.

Bacterial lipopolysaccharides and innate immunity

Bacterial lipopolysaccharides (LPS) are the major outer surface membrane components present in almost all Gram-negative bacteria and act as extremely strong stimulators of innate or natural immunity in diverse eukaryotic species ranging from insects to humans. LPS consist of a poly- or oligosaccharide region that is anchored in the outer bacterial membrane by a specific carbohydrate lipid moiety termed lipid A. The lipid A component is the primary immunostimulatory centre of LPS. With respect to immunoactivation in mammalian systems, the classical group of strongly agonistic (highly endotoxic) forms of LPS has been shown to be comprised of a rather similar set of lipid A types. In addition, several natural or derivatised lipid A structures have been identified that display comparatively low or even no immunostimulation for a given mammalian species. Some members of the latter more heterogeneous group are capable of antagonizing the effects of strongly stimulatory LPS/lipid A forms. Agonistic forms of LPS or lipid A trigger numerous physiological immunostimulatory effects in mammalian organisms, but--in higher doses--can also lead to pathological reactions such as the induction of septic shock. Cells of the myeloid lineage have been shown to be the primary cellular sensors for LPS in the mammalian immune system. During the past decade, enormous progress has been obtained in the elucidation of the central LPS/lipid A recognition and signaling system in mammalian phagocytes. According to the current model, the specific cellular recognition of agonistic LPS/lipid A is initialized by the combined extracellular actions of LPS binding protein (LBP), the membrane-bound or soluble forms of CD14 and the newly identified Toll-like receptor 4 (TLR4)*MD-2 complex, leading to the rapid activation of an intracellular signaling network that is highly homologous to the signaling systems of IL-1 and IL-18. The elucidation of structure-activity correlations in LPS and lipid A has not only contributed to a molecular understanding of both immunostimulatory and toxic septic processes, but has also re-animated the development of new pharmacological and immunostimulatory strategies for the prevention and therapy of infectious and malignant diseases.

Synthesis of lipid A type pyran carboxylic acids with ether chains and their biological activities

Synthesis of lipid A type pyran carboxylic acids having ether chains at both the C-3' and C-4 positions and their bioactivities toward human U937 cells are described.

Haemophilus influenzae stimulates ICAM-1 expression on respiratory epithelial cells

Epithelial cells interact directly with bacteria in the environment and play a critical role in airway defense against microbial pathogens. In this study, we examined the response of respiratory epithelial cells to infection with nontypable Haemophilus influenzae. Using an in vitro cell culture model, we found that epithelial cell monolayers released significant quantities of IL-8 and expressed increased levels of ICAM-1 mRNA and surface protein in response to H. influenzae. In contrast, levels of IL-1beta, TNF-alpha, and MHC class I were not significantly affected, suggesting preferential activation of a specific subset of epithelial genes directed toward defense against bacteria. Induction of ICAM-1 required direct bacterial interaction with the epithelial cell surface and was not reproduced by purified H. influenzae lipooligosaccharide. Consistent with a functional role for this response, induction of ICAM-1 by H. influenzae mediated increased neutrophil adherence to the epithelial cell surface. Furthermore, in an in vivo murine model of airway infection with H. influenzae, increased epithelial cell ICAM-1 expression coincided with increased chemokine levels and neutrophil recruitment in the airway. These results indicate that ICAM-1 expression on human respiratory epithelial cells is induced by epithelial cell interaction with H. influenzae and suggest that an ICAM-1-dependent mechanism can mediate neutrophil adherence to these cells independent of inflammatory mediator release by other cell types. Direct induction of specific epithelial cell genes (such as ICAM-1 and IL-8) by bacterial infection may allow for rapid and efficient innate defense in the airway.

Limited role of ceramide in lipopolysaccharide-mediated mitogen-activated protein kinase activation, transcription factor induction, and cytokine release

The involvement of ceramide in lipopolysaccharide-mediated activation of mouse macrophages was studied. Lipopolysaccharide, cell-permeable ceramide analogs, and bacterial sphingomyelinase led to phosphorylation of the extracellular signal-regulated kinases, c-Jun NH2-terminal kinases, and p38 kinase and induced AP-1 DNA binding in C3H/OuJ (Lpsn) but not in C3H/HeJ (Lpsd) macrophages. Lipopolysaccharide and ceramide mimetics showed distinct kinetics of mitogen-activated protein kinase phosphorylation and AP-1 induction and activated AP-1 complexes with different subunit compositions. Lipopolysaccharide-activated AP-1 consisted of c-Fos, Jun-B, Jun-D, and c-Jun, while C2-ceramide induced Jun-D and c-Jun only. Lipopolysaccharide and, less potently, C2-ceramide or sphingomyelinase, stimulated AP-1-dependent reporter gene transcription in RAW 264.7 cells. Unlike lipopolysaccharide, C2-ceramide failed to activate NF-kappaB and did not induce production of tumor necrosis factor or interleukin-6. The lipopolysaccharide antagonist, Rhodobacter sphae-roides diphosphoryl lipid A, inhibited lipopolysaccharide activation of NF-kappaB and AP-1 but did not block C2-ceramide-induced AP-1. Pretreatment of C3H/OuJ macrophages with C2-ceramide greatly diminished AP-1 induction following subsequent C2-ceramide stimulation. However, lipopolysaccharide-induced transcription factor activation and cytokine release were not influenced. In contrast, lipopolysaccharide pretreatment inhibited both lipopolysaccharide- and C2-ceramide-mediated responses. Thus, ceramide partially mimics lipopolysaccharide in activating the mitogen-activated protein kinases and AP-1 but not in mediating NF-kappaB induction or cytokine production, suggesting a limited role in lipopolysaccharide signaling.

Lipopolysaccharides (LPS) of oral black-pigmented bacteria induce tumor necrosis factor production by LPS-refractory C3H/HeJ macrophages in a way different from that of Salmonella LPS

Some lipopolysaccharide (LPS) preparations from S- or R-form members of the family Enterobacteriaceae and oral black-pigmented bacteria (Porphyromonas gingivalis and Prevotella intermedia) are known to activate LPS-refractory C3H/HeJ macrophages. When contaminating proteins are removed from R-form LPS of Enterobacteriaceae by repurification, however, this ability is lost. In the present study, we investigated the capacity of LPS from P. gingivalis, P. intermedia, Salmonella minnesota, and Salmonella abortusequi to induce production of tumor necrosis factor (TNF) in gamma interferon-primed C3H/HeJ macrophages before and after repurification. P. abortusequi S-LPS was fractionated by centrifugal partition chromatography into two LPS forms: SL-LPS, having homologous long O-polysaccharide chains, and SS-LPS having short oligosaccharide chains. Prior to repurification, all LPS forms except SL-LPS induced TNF production in both C3H/HeJ and C3H/HeN macrophages. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis showed that repurification removed contaminating protein from the preparations, and repurified SS-LPS and S. minnesota Ra-LPS no longer stimulated TNF production in C3H/HeJ macrophages, although C3H/HeN macrophages remained responsive. In contrast, repurified oral bacterial LPS retained the capacity to induce TNF production in C3H/HeJ macrophages. Oral bacterial LPS preparations also were not antagonized by excess inactive, repurified SL-LPS; Ra-LPS; Rhodobacter sphaeroides lipid A, a competitive LPS antagonist, or paclitaxel, an LPS agonist, and they were comparatively resistant to polymyxin B treatment. Nevertheless, oral bacterial LPS was less toxic to D-galactosamine-treated C3H/HeN mice than was LPS from Salmonella. These findings indicate that the active molecule(s) and mode of action of LPS from P. gingivalis and P. intermedia are quite different from those of LPS from Salmonella.

Lipopolysaccharide and its analog antagonists display differential serum factor dependencies for induction of cytokine genes in murine macrophages

Monocytes/macrophages play a central role in mediating the effects of lipopolysaccharide (LPS) derived from gram-negative bacteria by the production of proinflammatory mediators. Recently, it was shown that the expression of cytokine genes for tumor necrosis factor alpha (TNF-alpha), interleukin-1beta (IL-1beta), and interferon-inducible protein-10 (IP-10) by murine macrophages in response to low concentrations of LPS is entirely CD14 dependent. In this report, we show that murine macrophages respond to low concentrations of LPS ( Collapse

Key Words Collapse

MESH Headings

• Acute-Phase Proteins
• Animals
• Carrier Proteins/pharmacology
• Chemokine CXCL10
• Chemokines, CXC/biosynthesis
• Culture Media, Serum-Free
• Cytokines/biosynthesis
• Disaccharides/pharmacology
• Dose-Response Relationship, Drug
• Escherichia coli
• Female
• Gene Expression Regulation
• Interleukin-1/biosynthesis
• Lipid A/analogs & derivatives
• Lipid A/pharmacology
• Lipopolysaccharide Receptors/genetics
• Lipopolysaccharide Receptors/pharmacology
• Lipopolysaccharides/antagonists & inhibitors
• Lipopolysaccharides/immunology
• Macrophages/immunology
• Male
• Membrane Glycoproteins
• Mice
• Mice, Inbred C3H
• Mice, Knockout
• Monosaccharides/pharmacology
• Tumor Necrosis Factor-alpha/biosynthesis

Collapse

Grants

• R37 AI018797 NIAID NIH HHS
• AI 18797 NIAID NIH HHS
• GM 50870 NIGMS NIH HHS
• R01 GM050870 NIGMS NIH HHS
• R01 AI018797 NIAID NIH HHS
• R56 AI018797 NIAID NIH HHS

Collapse

Affiliation(s)

P Y Perera Department of Microbiology and Immunology, Uniformed Services University of the Health Sciences, Bethesda, Maryland 20814-4799, USA
N Qureshi
W J Christ
P Stütz
S N Vogel

Collapse

Innate immune recognition of bacterial lipopolysaccharide: dependence on interactions with membrane lipids and endocytic movement

Lipopolysaccharide ([LPS], an endotoxin) from most bacterial species provokes a strong inflammatory response in naive animals. LPS from Rhodobacter sphaeroides (RsLPS) has a relatively small hydrophobic region and does not stimulate cells or animals but instead acts as antagonist of LPS action. Here, we show that the activity of RsLPS is transformed from antagonist to full agonist by the addition of chlorpromazine (CPZ) and other cationic membrane-active agents. In addition, while LPS is rapidly transported from the plasma membrane to an intracellular site, we find that RsLPS is not transported but instead remains in the cell periphery. Addition of CPZ also reverses this behavior, causing RsLPS to be transported to a perinuclear site. The data suggest that the interaction of LPS with membrane lipids is influenced by membrane-modifying agents such as CPZ, and these interactions dictate both its intracellular transport and its ability to stimulate cellular responses.

Grain dust-induced lung inflammation is reduced by Rhodobacter sphaeroides diphosphoryl lipid A

To further determine the importance of endotoxin in grain dust-induced inflammation of the lower respiratory tract, we evaluated the efficacy of pentaacylated diphosphoryl lipid A derived from the lipopolysaccharide of Rhodobacter sphaeroides (RsDPLA) as a partial agonist of grain dust-induced airway inflammation. RsDPLA is a relatively inactive compound compared with lipid A derived from Escherichia coli (LPS) and has been demonstrated to act as a partial agonist of LPS-induced inflammation. To assess the potential stimulatory effect of RsDPLA in relation to LPS, we incubated THP-1 cells with RsDPLA (0.001-100 micrograms/ml), LPS (0.02 microgram endotoxin activity/ml), or corn dust extract (CDE; 0.02 microgram endotoxin activity/ml). Incubation with RsDPLA revealed a tumor necrosis factor (TNF)-alpha stimulatory effect at 100 micrograms/ml. In contrast, incubation with LPS or CDE resulted in TNF-alpha release at 0.02 microgram/ml. Pretreatment of THP-1 cells with varying concentrations of RsDPLA before incubation with LPS or CDE (0.02 microgram endotoxin activity/ml) resulted in a dose-dependent reduction in the LPS- or CDE-induced release of TNF-alpha with concentrations of RsDPLA of up to 10 micrograms/ml but not at 100 micrograms/ml. To further understand the role of endotoxin in grain dust-induced airway inflammation, we utilized the unique LPS inhibitory property of RsDPLA to determine the inflammatory response to inhaled CDE in mice in the presence of RsDPLA. Ten micrograms of RsDPLA intratracheally did not cause a significant inflammatory response compared with intratracheal saline. However, pretreatment of mice with 10 micrograms of RsDPLA intratracheally before exposure to CDE (5.4 and 0.2 micrograms/m3) or LPS (7.2 and 0.28 micrograms/m3) resulted in significant reductions in the lung lavage concentrations of total cells, neutrophils, and specific proinflammatory cytokines compared with mice pretreated with sterile saline. These results confirm the LPS-inhibitory effect of RsDPLA and support the role of endotoxin as the principal agent in grain dust causing airway inflammation.

Structure of the monophosphoryl lipid A moiety obtained from the lipopolysaccharide of Chlamydia trachomatis

Monophosphoryl lipid A was prepared from the lipopolysaccharide of Chlamydia trachomatis, converted to the methyl ester, and fractionated by reverse-phase high-performance liquid chromatography. The peak fractions were collected and analyzed by mass spectrometry. Matrix-assisted laser desorption/ionization and liquid secondary ion mass spectrometry of the first of two major high-performance liquid chromatographic fractions showed multiple quasi-molecular ions of MNa+ at m/z 1780, 1794, 1808, 1822, and 1836. The positive-ion liquid secondary ion mass spectrometry spectrum also showed a minor series of peaks at m/z 1916, 1930, 1944, 1958, and 1971, consistent with the formation of matrix adducts with 3-nitrobenzyl alcohol. Oxonium ions representing the distal subunit were observed at m/z 1057, 1071, 1085, 1099, and 1113. The second fraction was similarly analyzed and found to contain structural homologs of the first fraction. Based on this study, the major lipid A component of chlamydial lipopolysaccharide is a glucosamine disaccharide that contains five fatty acids and a phosphate in the distal segment. Three fatty acyl groups are in the distal segment, and two are in the reducing end segment. The acyloxyacyl group is located in the distal segment in amide linkage. Two structural series, differing by 14 atomic mass units in the reducing subunit, were observed. Chlamydial lipid A is complex and consists of at least 20 homologous structural components. The relatively low potency of Chlamydia trachomatis lipopolysaccharide in activating lipopolysaccharide-responsive cells might be related to the unusual fatty acid composition of the lipid A moiety.

Helicobacter pylori lipopolysaccharide can activate 70Z/3 cells via CD14

Helicobacter pylori persistently colonizes the human gastrointestinal tract and is associated with chronic gastritis and, in some cases, peptic ulcer disease or gastric neoplasms. One factor in the persistence of this organism may be its inability to elicit a strong inflammatory response. Lipopolysaccharide (LPS) is a proinflammatory substance found in the cell walls of all gram-negative bacteria. H. pylori LPS has been found by several different measures to be less active than LPS from Enterobacteriaceae. This study addresses the role of CD14 and LPS-binding protein in the cellular response to H. pylori LPS. We report that H. pylori LPS activates mammalian cells expressing CD14 at much lower LPS concentrations than those for control cells not expressing CD14. The maximal activation of CD14-70Z/3 cells by H. pylori LPS also requires LPS-binding protein. H. pylori LPS at concentrations as high as 30 microg/ml does not elicit an interleukin-8 (IL-8) response from the epithelial cell line SW620 in the presence of CD14; 10 ng of Escherichia coli LPS per ml elicits a maximal IL-8 response. Furthermore, in contrast to some other types of LPS with little activity, H. pylori LPS does not inhibit the CD14-70Z/3 cell response to E. coli LPS. From these studies, we conclude that H. pylori LPS, though much less active than E. coli LPS, stimulates cells via CD14.

Structural study on the free lipid A isolated from lipopolysaccharide of Porphyromonas gingivalis

The chemical structure of lipid A isolated from Porphyromonas gingivalis lipopolysaccharide was elucidated by compositional analysis, mass spectrometry, and nuclear magnetic resonance spectroscopy. The hydrophilic backbone of free lipid A was found to consisted of beta(1,6)-linked D-glucosamine disaccharide 1-phosphate. (R)-3-Hydroxy-15-methylhexadecanoic acid and (R)-3-hydroxyhexadecanoic acid are attached at positions 2 and 3 of the reducing terminal residue, respectively, and positions 2' and 3' of the nonreducing terminal unit are acylated with (R)-3-O-(hexadecanoyl)-15-methylhexadecanoic acid and (R)-3-hydroxy-13-methyltetradecanoic acid, respectively. The hydroxyl group at position 4' is partially replaced by another phosphate group, and the hydroxyl groups at positions 4 and 6' are unsubstituted. Considerable heterogeneity in the fatty acid chain length and the degree of acylation and phosphorylation was detected by liquid secondary ion-mass spectrometry (LSI-MS). A significant pseudomolecular ion of lipid A at m/z 1,769.6 [M-H]- corresponding to a diphosphorylated GlcN backbone bearing five acyl groups described above was detected in the negative mode of LSI-MS. Predominant ions, however, were observed at m/z 1,434.9 [M-H]- and m/z 1,449.0 [M-H]-, each representing monophosphoryl lipid A lacking (R)-3-hydroxyhexadecanoic and (R)-3-hydroxy-13-methyltetradecanoic acids, respectively. The presence of mono- and diphosphorylated lipid A species was also confirmed by LSI-MS of de-O-acylated lipid A (m/z 955.3 and 1,035.2, respectively).

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.

Diphosphoryl lipid A derived from the lipopolysaccharide (LPS) of Rhodobacter sphaeroides ATCC 17023 is a potent competitive LPS inhibitor in murine macrophage-like J774.1 cells

Pentaacyl diphosphoryl lipid A derived from the nontoxic lipopolysaccharide (LPS) of Rhodobacter sphaeroides ATCC 17023 (RsDPLA) did not induce tumour necrosis factor-alpha nor interleukin-6 release in the murine macrophage-like cell line J774.1. However, it effectively inhibited the induction of these two cytokines by LPS of Salmonella minnesota Re mutant R595 (ReLPS) in a concentration-dependent manner. Maximal inhibition and half-maximal inhibition occurred when the ReLPS to RsDPLA mass ratio was 1:30 and 1:1, respectively. A binding study was performed in the presence of serum to determine whether RsDPLA is competing with ReLPS for LPS binding sites on J774.1 cells. This assay allows the determination of LPS binding to J774.1 cells via a mechanism involving CD14, a receptor for complexes of LPS with LPS binding protein (LBP), and its possible inhibition. The results show that RsDPLA strongly inhibits the binding of 125I-labelled ReLPS to J774.1 cells. Maximal and one-half maximal inhibition of binding occurred when the ReLPS to RsDPLA mass ratios were 1:2.5 and 1:0.5, respectively. It was found that the inhibition of binding by RsDPLA was much stronger than that by unlabelled ReLPS. These results suggest that RsDPLA is competing with ReLPS for CD14-dependent recognition of LPS on J774.1 cells.

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

Rhodobacter sphaeroides lipid A (RsDPLA) and SDZ 880.431 (3-aza-lipid X-4-phosphate) are prototypic lipopolysaccharide (LPS) antagonists. Herein, we examined the ability of these structures to regulate murine macrophage tumor necrosis factor (TNF) secretion and LPS-inducible gene expression (tumor necrosis factor alpha [TNF-alpha], interleukin-1 beta [IL-1 beta], IP-10, type 2 TNF receptor [TNFR-2], D3, and D8 genes). We report that RsDPLA alone (> 1 microgram/ml) induced low levels of TNF-alpha secretion and a selective pattern of gene expression in peritoneal exudate macrophages; SDZ 880.431 alone was completely inactive. When LPS was present at a low concentration (1 ng/ml), RsDPLA and SDZ 880.431 blocked TNF secretion and gene induction in a concentration-dependent fashion. In general, gene induction was measurably reduced by 10 to 30 ng of RsDPLA per ml or 300 ng of SDZ 880.431 per ml, but inhibition could be uniformly overridden by increasing the concentration of LPS. Although induction of all six genes by LPS was suppressed by either inhibitor, effective inhibitor concentrations depended on the gene of interest. Induction of TNFR-2 by LPS was relatively resistant to inhibition by RsDPLA, and induction of TNFR-2 and D3 was relatively resistant to inhibition by SDZ 880.431. When LPS was present at > or = 100 ng/ml, correspondingly high concentrations (> or = 20 micrograms/ml) of either inhibitor influenced gene expression in a bidirectional manner. Under these conditions, LPS-induced expression of IP-10, D3, and D8 was suppressed regardless of the LPS concentration used (concentrations tested up to 50 micrograms/ml), while expression of TNF-alpha mRNA was enhanced about fourfold. In toto, RsDPLA and SDZ 880.431, when present at low concentrations, act in a manner consistent with competitive inhibition of LPS, while at higher concentrations, these structures inhibit certain LPS responses noncompetitively and synergize with LPS for other responses.

Effect of pH on solubility and ionic state of lipopolysaccharide obtained from the deep rough mutant of Escherichia coli

The dissociation of the highly aggregated form of lipopolysaccharide (LPS) from Gram-negative bacteria to the monomeric (or soluble) form is though to be the initial step in the activation of responding cells (macrophages, B-cells, neutrophils, monocytes, and endothelial cells) by LPS. This process is presently not adequately understood. Using the equilibrium dialysis apparatus and a highly purified and well-characterized radiolabeled deep rough chemotype LPS ([14C]ReLPS) from Escherichia coli D31m4, we have examined the effect of pH on its solubility (CT) and ionic states in aqueous media. The solubility range of [14C]ReLPS suspended in 50 mM Tris-HCl-100 mM KCl buffer (or 50 mM MES-100 mM KCl buffer at pH 6.5) was determined to be from (2.91 +/- 0.01) x 10(-8) to (4.55 +/- 0.07) x 10(-8) M over a pH range of 6.50-8.20, respectively. These experimental data satisfactorily fitted the curve generated by the solubility equation CT = S0(1 + K5/[H+])/([H+]/K4' + 1), where S0 is the concentration of the tetraanionic ReLPS, K5 is the dissociation constant of the tetraanionic ReLPS in solution, and K4' is the dissociation constant of the trianionic ReLPS at the surface of the solid particles in suspension. The increase in solubility of ReLPS with increase in pH from 7.00 to 8.20 is primarily caused by the formation of the pentaanionic form from the tetraanions. The pK5 (primarily the second dissociation of the 1-phosphate) of ReLPS was determined to be 8.58 from experimental data.(ABSTRACT TRUNCATED AT 250 WORDS)

Lipopolysaccharide antagonists

Bacterial lipopolysaccharide (LPS) is a potent and pleiotropic stimulus of immune cells. LPS has important clinical relevance because it has a direct role in the pathogenesis of Gram-negative bacterial infection. The lipid A moiety of LPS is responsible for the toxic effects of LPS. The identification of structural analogs and precursors of lipid A, which are apparently competitive antagonists of the biological actions of LPS, is strong evidence that the actions of LPS are mediated by a specific LPS receptor or family of receptors. Identification and analysis of these LPS receptors with LPS antagonists should help to define the pathways of cellular activation by LPS and lead to the development of novel anti-LPS strategies in the therapy of bacterial diseases.

Structural features that influence the ability of lipid A and its analogs to abolish expression of suppressor T cell activity

Lipid A preparations derived from the lipopolysaccharides of several gram-negative bacteria, as well as chemically defined synthetic lipid A's and their analogs (both glucosamine mono- and disaccharides), were used to establish the chemical structures required for (i) abolishing the expression of suppressor T cell (Ts) function and (ii) inducing polyclonal activation of B cells. Salmonella minnesota R595 lipid A (diphosphoryl lipid A) possesses both of these activities. Decreasing the number of phosphate groups in lipid A from two to one (monophosphoryl lipid A) as well as decreasing the fatty acyl content, primarily by removing the residue at the 3 position, resulted in a progressive reduction in toxicity; however, these structural modifications did not influence its ability to abolish the expression of Ts function. Reducing the fatty acyl content from five to four (lipid A precursor IVA or Ia) eliminated the capacity to influence Ts function but not to induce polyclonal activation of B cells. None of the monosaccharide analogs of lipid A examined influenced the expression of Ts activity, although some were able to activate B cells polyclonally. Thus, in order to be able to abolish the expression of Ts function, lipid A (i) must be a glucosamine disaccharide, (ii) may have either one or two phosphate groups, and (iii) must have at least five fatty acyl groups. Also, the chain length of the nonhydroxylated fatty acid, as well as the location of acyloxyacyl groups (2' versus 3' position), may play an important role. These findings indicate that the chemical structures responsible for the toxicity of lipid A differ from those that influence its capacity to abolish the expression of Ts function and to induce polyclonal activation of B cells.

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.