E5531, a synthetic non-toxic lipid A derivative blocks the immunobiological activities of lipopolysaccharide

Rhodobacter capsulatus PG Lipopolysaccharide Blocks the Effects of a Lipoteichoic Acid, a Toll-Like Receptor 2 Agonist

Lipopolysaccharides (LPS) and lipoteichoic acids (LTA) are the major inducers of the inflammatory response of blood cells caused by Gram-negative and some Gram-positive bacteria. CD14 is a common receptor for LPS and LTA that transfers the ligands to TLR4 and TLR2, respectively. In this work, we have demonstrated that the non-toxic LPS from Rhodobacter capsulatus PG blocks the synthesis of pro-inflammatory cytokines during the activation of blood cells by Streptococcus pyogenes LTA through binding to the CD14 receptor, resulting in the signal transduction to TLR2/TLR6 being blocked. The LPS from Rhodobacter capsulatus PG can be considered a prototype for developing preparations to protect blood cells against the LTA of gram-positive bacteria.

Single Domain Antibody application in bacterial infection diagnosis and neutralization

Increasing antibiotic resistance to bacterial infections causes a serious threat to human health. Efficient detection and treatment strategies are the keys to preventing and reducing bacterial infections. Due to the high affinity and antigen specificity, antibodies have become an important tool for diagnosis and treatment of various human diseases. In addition to conventional antibodies, a unique class of “heavy-chain-only” antibodies (HCAbs) were found in the serum of camelids and sharks. HCAbs binds to the antigen through only one variable domain Referred to as VHH (variable domain of the heavy chain of HCAbs). The recombinant format of the VHH is also called single domain antibody (sdAb) or nanobody (Nb). Sharks might also have an ancestor HCAb from where SdAbs or V-NAR might be engineered. Compared with traditional Abs, Nbs have several outstanding properties such as small size, high stability, strong antigen-binding affinity, high solubility and low immunogenicity. Furthermore, they are expressed at low cost in microorganisms and amenable to engineering. These superior properties make Nbs a highly desired alternative to conventional antibodies, which are extensively employed in structural biology, unravelling biochemical mechanisms, molecular imaging, diagnosis and treatment of diseases. In this review, we summarized recent progress of nanobody-based approaches in diagnosis and neutralization of bacterial infection and further discussed the challenges of Nbs in these fields.

Toll-like receptor (TLRs) agonists and antagonists for COVID-19 treatments

Severe acute respiratory syndrome coronavirus type 2 (SARS-CoV-2) rapidly infects humans and animals which make coronavirus disease 2019 (COVID-19) a grievous epidemic worldwide which broke out in 2020. According to data analysis of the other coronavirus family, for instance severe acute respiratory syndrome SARS coronavirus (SARS-CoV), can provide experience for the mutation of SARS-CoV-2 and the prevention and treatment of COVID-19. Toll-like receptors (TLRs) as a pattern recognition receptor (PRRs), have an indispensable function in identifying the invader even activate the innate immune system. It is possible for organism to activate different TLR pathways which leads to secretion of proinflammatory cytokines such as Interleukin 1 (IL-1), Interleukin 6 (IL-6), Tumor necrosis factor α (TNFα) and type Ⅰ interferon. As a component of non-specific immunity, TLRs pathway may participate in the SARS-CoV-2 pathogenic processes, due to previous works have proved that TLRs are involved in the invasion and infection of SARS-CoV and MERS to varying degrees. Different TLR, such as TLR2, TLR4, TLR7, TLR8 and TLR9 probably have a double-sided in COVID-19 infection. Therefore, it is of great significance for a correctly acknowledging how TLR take part in the SARS-CoV-2 pathogenic processes, which will be the development of treatment and prevention strategies.

Lipopolysaccharide lipid A: A promising molecule for new immunity-based therapies and antibiotics

Lipopolysaccharides (LPS) are the main components of the external leaflet of the Gram-negative outer membrane and consist of three different moieties: lipid A, core oligosaccharide, and O-polysaccharide. The lipid A is a glucosamine disaccharide with different levels of acylation and phosphorylation, beside carrying, in certain cases, additional substituents on the sugar backbone. It is also the main immunostimulatory part of the LPS, as its recognition by the host immune system represents a fundamental event for detection of perilous microorganisms. Moreover, an uncontrolled immune response caused by a large amount of circulating LPS can lead to dramatic outcomes for human health, such as septic shock. The immunostimulant properties of an LPS incredibly vary depending on lipid A chemical structure, and for this reason, natural and synthetic variants of the lipid A are under study to develop new drugs that mimic or antagonise its natural effects. Here, we review past and recent findings on the lipid A as an antibiotic target and immune-therapeutic molecule, with a special attention on the crucial role of the chemical structure and its exploitation for conceiving novel strategies for treatment of several immune-related pathologies.

Toll-like receptor 4 (TLR4) antagonists as potential therapeutics for intestinal inflammation

Gastrointestinal inflammation is a hallmark of highly prevalent disorders, including cancer treatment-induced mucositis and ulcerative colitis. These disorders cause debilitating symptoms, have a significant impact on quality of life, and are poorly managed. The activation of toll-like receptor 4 (TLR4) has been proposed to have a major influence on the inflammatory signalling pathways of the intestinal tract. Inhibition of TLR4 has been postulated as an effective way to treat intestinal inflammation. However, there are a limited number of studies looking into the potential of TLR4 antagonism as a therapeutic approach for intestinal inflammation. This review surveyed available literature and reported on the in vitro, ex vivo and in vivo effects of TLR4 antagonism on different models of intestinal inflammation. Of the studies reviewed, evidence suggests that there is indeed potential for TLR4 antagonists to treat inflammation, although only a limited number of studies have investigated treating intestinal inflammation with TLR4 antagonists directly. These results warrant further research into the effect of TLR4 antagonists in the intestinal tract.

Dietary α-Lactalbumin protects against thioacetamide-induced liver cirrhosis by maintaining gut-liver axis function in rats

We tested the hypothesis that α-lactalbumin inhibits the disruption of intestinal barrier function and liver cirrhosis by restoring gut-liver axis function in thioacetamide (TAA) -treated rats. Rat diets were supplemented with α-lactalbumin replacing 50% of dietary protein. After consuming α-lactalbumin for one week, rats were intraperitoneally injected with TAA twice a week for 14 weeks. The α-lactalbumin-enriched diet significantly inhibited the elevation of plasma alanine aminotransferase, aspartate aminotransferase, and hyaluronic acids. The supplement significantly reduced plasma lipopolysaccharide levels and increased occludin mRNA level. Hepatic fibrosis and regenerative nodules was developed and intestinal villi were shortened by TAA; α-Lactalbumin attenuated these histopathological changes. These results indicated that α-lactalbumin improved intestinal barrier function, suppressing endotoxin levels. These data also suggested that α-lactalbumin ameliorated the impairment of the gut-liver axis by TAA, inhibiting the development of liver cirrhosis.

Disaccharide-Based Anionic Amphiphiles as Potent Inhibitors of Lipopolysaccharide-Induced Inflammation

Despite significant advances made in the last decade in the understanding of molecular mechanisms of sepsis and in the development of clinically relevant therapies, sepsis remains the leading cause of mortality in intensive care units with increasing incidence worldwide. Toll-like receptor 4 (TLR4)-a transmembrane pattern-recognition receptor responsible for propagating the immediate immune response to Gram-negative bacterial infection-plays a central role in the pathogenesis of sepsis and chronic inflammation-related disorders. TLR4 is complexed with the lipopolysaccharide (LPS)-sensing protein myeloid differentiation-2 (MD-2) which represents a preferred target for establishing new anti-inflammatory treatment strategies. Herein we report the development, facile synthesis, and biological evaluation of novel disaccharide-based TLR4⋅MD-2 antagonists with potent anti-endotoxic activity at micromolar concentrations. A series of synthetic anionic glycolipids entailing amide-linked β-ketoacyl lipid residues was prepared in a straightforward manner by using a single orthogonally protected nonreducing diglucosamine scaffold. Suppression of the LPS-induced release of interleukin-6 and tumor necrosis factor was monitored and confirmed in human immune cells (MNC and THP1) and mouse macrophages. Structure-activity relationship studies and molecular dynamics simulations revealed the structural basis for the high-affinity interaction between anionic glycolipids and MD-2, and highlighted two compounds as leads for the development of potential anti-inflammatory therapeutics.

In vivo Proinflammatory Cytokine Production by CD-1 Mice in Response to Equipotential Doses of Rhodobacter capsulatus PG and Salmonella enterica Lipopolysaccharides

The capacities of relatively nontoxic lipopolysaccharide (LPS) from Rhodobacter capsulatus PG and highly potent LPS from Salmonella enterica serovar Typhimurium to evoke proinflammatory cytokine production have been compared in vivo. Intravenous administration of S. enterica LPS at a relatively low dose (1 mg/kg body weight) led to upregulation of TNF-α, IL-6, and IFN-γ production by non-sensitized CD-1 mice. LPS from R. capsulatus PG used at a four-times higher dose than that from S. enterica elicited production of almost the same amount of systemic TNF-α; therefore, the doses of 4 mg/kg LPS from R. capsulatus PG and 1 mg/kg LPS from S. enterica were considered to be approximately equipotential doses with respect to the LPS-dependent TNF-α production by CD-1 mice. Rhodobacter capsulatus PG LPS was a weaker inducer of the production of TNF-α, IL-6, and IFN-γ, as compared to the equipotential dose of S. enterica LPS. Administration of R. capsulatus PG LPS before S. enterica LPS decreased production of IFN-γ, but not of TNF-α and IL-6, induced by S. enterica LPS. Rhodobacter capsulatus PG LPS also suppressed IFN-γ production induced by S. enterica LPS when R. capsulatus PG LPS had been injected as little as 10 min after S. enterica LPS, but to a much lesser extent. Rhodobacter capsulatus PG LPS did not affect TNF-α and IL-6 production induced by the equipotential dose of S. enterica LPS. In order to draw conclusion on the endotoxic activity of particular LPSs, species-specific structure or arrangement of the animal or human immune systems should be considered.

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.

Progress in the synthesis and biological evaluation of lipid A and its derivatives

Lipid A is one of the core structures of bacterial lipopolysaccharides (LPSs), and it is mainly responsible for the strong immunostimulatory activities of LPS through interactions with the Toll-like receptors and other molecules in the human immune system. To obtain structurally homogeneous and well-defined lipid As and its derivatives in quantities meaningful for various biological studies and applications, their chemical synthesis has become a focal point. This review has provided a survey of significant progresses made in the synthesis of lipid A, and its derivatives that carry diverse saturated and unsaturated lipids, have the phosphate group at its reducing end replaced with a more stable phosphate or carboxyl group, or lack the reducing end phosphate or both phosphate groups, as well as progresses in the synthesis of LPS analogs and other lipid A conjugates. These synthetic molecules have facilitated the elucidation of the structure-activity relationships of lipid A useful for the design and development of lipid A based therapeutics, such as those utilized to treat sepsis, and other medical applications, for example the use of monophosphoryl lipid A as a carrier molecule for the study of fully synthetic self-adjuvanting conjugate vaccines. These topics are also briefly covered in the current review.

Pseudoginsenoside-F11 (PF11) exerts anti-neuroinflammatory effects on LPS-activated microglial cells by inhibiting TLR4-mediated TAK1/IKK/NF-κB, MAPKs and Akt signaling pathways

Pseudoginsenoside-F11 (PF11), an ocotillol-type ginsenoside, has been shown to possess significant neuroprotective activity. Since microglia-mediated inflammation is critical for induction of neurodegeneration, this study was designed to investigate the effect of PF11 on activated microglia. PF11 significantly suppressed the release of ROS and proinflammatory mediators induced by LPS in a microglial cell line N9 including NO, PGE2, IL-1β, IL-6 and TNF-α. Moreover, PF11 inhibited interaction and expression of TLR4 and MyD88 in LPS-activated N9 cells, resulting in an inhibition of the TAK1/IKK/NF-κB signaling pathway. PF11 also inhibited the phosphorylation of Akt and MAPKs induced by LPS in N9 cells. Importantly, PF11 significantly alleviated the death of SH-SY5Y neuroblastoma cells and primary cortical neurons induced by the conditioned-medium from activated microglia. At last, the effect of PF11 on neuroinflammation was confirmed in vivo: PF11 mitigated the microglial activation and proinflammatory factors expression obviously in both cortex and hippocampus in mice injected intrahippocampally with LPS. These findings indicate that PF11 exerts anti-neuroinflammatory effects on LPS-activated microglial cells by inhibiting TLR4-mediated TAK1/IKK/NF-κB, MAPKs and Akt signaling pathways, suggesting its therapeutic implication for neurodegenerative disease associated with neuroinflammation.

Pattern recognition receptors in equine endotoxaemia and sepsis

Pattern recognition receptors (PRRs) on host cells detect pathogens to activate innate immunity which, in turn, initiates inflammatory and adaptive immune responses. Successful activation of PRRs is, therefore, critical to controlling infections and driving pathogen‐specific adaptive immunity, but overactivity of PRRs causes systemic inflammation, which is detrimental to the host. Here we review the PRR literature as it relates to horses and speculate on the role PRRs may play in sepsis and endotoxaemia.

From agonist to antagonist: structure and dynamics of innate immune glycoprotein MD-2 upon recognition of variably acylated bacterial endotoxins

The human immune response to an infection by Gram-negative bacteria involves detection of lipopolysaccharides (LPS), also known as endotoxins, which comprise the bacterial outer cell wall. Distinct from mammalian glycolipid structures, LPS have a conserved chemical pattern that is recognized by the pattern recognition receptor complex formed by myeloid differentiation protein 2 (MD-2) and toll-like receptor 4 (TLR4). A remarkable immune-mediated structure-toxicity relationship has been defined that relates to the number of acyl chains in the endotoxin. While there is a clear correlation between endotoxin acylation and elicited agonist or antagonist responses, the 3D structural basis of this relationship remains unclear. In order to explore, at atomic-resolution, the effects of a range of chemically distinct endotoxins on the structure and dynamics of their MD-2·endotoxin complexes, we examined a series of variably acylated lipid A molecules from Escherichia coli and Neisseria meningitidis in complex with human MD-2. Through the application of molecular dynamics simulations, in concert with experimental data, we have identified specific structural and dynamic features of the MD-2-endotoxin complexes that may control dimerization of TLR4 molecules. As dimerization is central to the release of downstream chemical mediators, the results provide a structural foundation for the ability of endotoxins to act as either agonists or antagonists of the TLR4 pathway.

Lactobacillus plantarum lipoteichoic acid down-regulated Shigella flexneri peptidoglycan-induced inflammation

Bacterial peptidoglycans (PGNs) are recognized by the host's innate immune system. This process is mediated by the NOD/CARD family of proteins, which induces inflammation by activating nuclear factor (NF)-κB. Excessive activation of monocytes by Shigella flexneri PGN (flexPGN) leads to serious inflammatory diseases such as intestinal bowel diseases (IBD) and Crohn's disease. In this study, we examined whether Lactobacillus plantarum lipoteichoic acid (pLTA) could attenuate the pro-inflammatory signaling induced by flexPGN in human monocytic THP-1 cells. Compared to control THP-1 cells, pLTA-tolerant cells showed a significant reduction in TNF-α and IL-1β production in response to flexPGN. We also examined the inhibition of NF-κB and the activation of mitogen-activated protein kinase (MAPK) in pLTA-tolerant cells. We found that the expression of NOD2 in pLTA-tolerant cells was down-regulated at the mRNA and protein levels, suggesting that pLTA is a potent modulator of the pro-inflammatory NOD2-related signaling pathways induced by flexPGN. Together, these data indicate that pLTA induces cross-tolerance against flexPGN. Notably, these effects are related not only to IL-1 signaling, which is known to play a role in LPS tolerance, but also to NOD-Rick signaling. This study provides insight into how commensal microflora may contribute to homeostasis of the host intestinal tract.

Endotoxin detection--from limulus amebocyte lysate to recombinant factor C

Gram negative bacterial endotoxin is a biological pyrogen that causes fever when introduced intravenously. The endotoxin, also known as lipopolysaccharide (LPS), is found in the outer membrane of Gram-negative bacteria. During Gram-negative sepsis, endotoxin stimulates host macrophages to release inflammatory cytokines. However, excessive inflammation causes multiple organ failure and death. Endotoxins, which are ubiquitous pathogenic molecules, are a bane to the pharmaceutical industry and healthcare community. Thus early and sensitive detection of endotoxin is crucial to prevent endotoxaemia. The limulus amebocyte lysate (LAL) has been widely used for ~30 years for the detection of endotoxin in the quality assurance of injectable drugs and medical devices. The LAL constitutes a cascade of serine proteases which are triggered by trace levels of endotoxin, culminating in a gel clot at the end of the reaction. The Factor C, which normally exists as a zymogen, is the primer of this coagulation cascade. In vivo, Factor C is the perfect biosensor, which alerts the horseshoe crab of the presence of a Gram-negative invader. The hemostatic end-point entraps the invader, killing it and limiting further infection. However, as an in vitro endotoxin detection tool, variations in the sensitivity and specificity of LAL to endotoxin, and the dwindling supply of horseshoe crabs are posing increasing challenges to the biotechnology industry. This has necessitated the innovation of an alternative test for endotoxin. Thus, Factor C became the obvious, albeit tricky target for the recombinant technology effort. This chapter documents the backwater of mining the natural blood lysate of the endangered species to the monumental effort of genetic engineering, to produce recombinant Factor C (rFC). The rFC is a 132 kDa molecule, which was produced as a proenzyme inducible by the presence of trace levels of endotoxin. The rFC forms the basis of the "PyroGene" kit, which is a novel micro-enzymatic endotoxin diagnostic assay for high-throughput screens of endotoxin. Using the rFC, Lonza Inc. has spawned the "PyroSense" which serves as checkpoints of the biotechnology production line. Thus, from cloning to commercial applications, the rFC has initiated a new era in endotoxin-testing for the quality assurance of biomedical products and for the healthcare industry, whilst sparing the endangered horseshoe crabs.

Molecular structure of endotoxins from Gram-negative marine bacteria: an update

Marine bacteria are microrganisms that have adapted, through millions of years, to survival in environments often characterized by one or more extreme physical or chemical parameters, namely pressure, temperature and salinity. The main interest in the research on marine bacteria is due to their ability to produce several biologically active molecules, such as antibiotics, toxins and antitoxins, antitumor and antimicrobial agents. Nonetheless, lipopolysaccharides (LPSs), or their portions, from Gram-negative marine bacteria, have often shown low virulence, and represent potential candidates in the development of drugs to prevent septic shock. Besides, the molecular architecture of such molecules is related to the possibility of thriving in marine habitats, shielding the cell from the disrupting action of natural stress factors. Over the last few years, the depiction of a variety of structures of lipids A, core oligosaccharides and O-specific polysaccharides from LPSs of marine microrganisms has been given. In particular, here we will examine the most recently encountered structures for bacteria belonging to the genera Shewanella, Pseudoalteromonas and Alteromonas, of the gamma-Proteobacteria phylum, and to the genera Flavobacterium, Cellulophaga, Arenibacter and Chryseobacterium, of the Cytophaga-Flavobacterium-Bacteroides phylum. Particular attention will be paid to the chemical features expressed by these structures (characteristic monosaccharides, non-glycidic appendages, phosphate groups), to the typifying traits of LPSs from marine bacteria and to the possible correlation existing between such features and the adaptation, over years, of bacteria to marine environments.

The cellular Toll-like receptor 4 antagonist E5531 can act as an agonist in horse whole blood

Sepsis and endotoxaemia are important causes of morbidity and mortality in humans. Research on sepsis focuses on rodent models most of which are poorly responsive to lipopolysaccharide (LPS), and thus do not mimic very well the high sensitivity of humans. Therefore, there is a need to develop more clinically relevant models. Horses suffer from a similar endotoxaemic syndrome to humans with high morbidity and mortality. LPS analogues that act as antagonists at Toll-like receptor 4 (TLR4) are being developed as novel treatments for endotoxaemia. Due to differences in recognition of ligands by TLR4 from different mammalian species, individual LPS molecules may act as agonists in some species and antagonists in others. The synthetic lipid A analogue E5531 is an antagonist at TLR4 in humans and mice, but its effects at TLR4 from other species are unknown. In the studies reported here, Escherichia coli LPS is a full agonist on equine bone marrow macrophage-like cells and its effects are antagonised by E5531. Similarly, E. coli LPS is an agonist and E5531 an antagonist on monocytes isolated from peripheral blood of healthy horses and human embryonic kidney (HEK) cells, transiently transfected to express horse TLR4 and its associated cell surface proteins MD2 and CD14. In contrast, both E. coli LPS and E5531 behave as agonists in horse whole blood by inducing production of equivalent amounts of the inflammatory mediator prostaglandin. This finding suggests that modification of E5531 may occur in whole blood, for example, deacylation, which alters its activity. This comparative study has revealed a novel pharmacological action of E5531 and emphasises the importance of extending studies of this nature beyond the normal rodent models.

Influence of lipopolysaccharides and lipids A from some marine bacteria on spontaneous and Escherichia coli LPS-induced TNF-alpha release from peripheral human blood cells

Some endotoxic properties of lipopolysaccharides (LPS) and lipids A (LA) from the marine bacteria Marinomonas communis ATCC 27118(T), Marinomonas mediterranea ATCC 700492(T), and Chryseobacterium indoltheticum CIP 103168(T) were studied. The preparations tested were shown to have high 50% lethal doses (4 microg per mouse for LPS from M. mediterranea and more than 12 microg per mouse for two other LPS and LA from C. indoltheticum) and were moderate (371 +/- 37 pg/ml at 10 microg/ml of C. indoltheticum LPS), weak (148 +/- 5 pg/ml at 1 microg/ml of M. mediterranea LPS), and zero (LA and LPS from M. communis and LA from C. indoltheticum) inducers of tumor necrosis factor alpha (TNF-alpha) release from peripheral human blood cells. The capacity of the LA and LPS samples from marine bacteria to inhibit TNF-alpha release induced by LPS from Escherichia coli O55 : B5 (10 ng/ml) was also studied.

Pattern recognition receptors: a contemporary view on liver diseases

Pattern recognition receptors (PRRs) function as sensors of microbial danger signals enabling the vertebrate host to initiate an immune response. PRRs are present not only in immune cells but also in liver parenchymal cells and the complexity of the cell populations provide unique aspects to pathogen recognition and tissue damage in the liver. This review discusses the role of different PRRs in pathogen recognition in the liver, and focuses on the role of PRRs in hepatic inflammation, cholestasis, ischemia, repair and fibrosis. PRRs as novel therapeutic targets are evaluated.

Genetic Analysis of Innate Immunity

The inflammatory response to microbes--and host perception of microbes in general--is largely initiated by a single class of receptors, named for their similarity to the prototypic Toll receptor of Drosophila. The mammalian Toll-like receptors (TLRs) are ultimately responsible for most phenomena associated with infection. This includes both "good" effects of infection (e.g., the induction of lasting specific immunity to an infectious agent) and "bad" effects of infection (systemic inflammation and shock). Although they are essential for host defense, no other endogenous proteins can match their lethal potential. The TLR complexes transduce the toxicity of lipopolysaccharide (LPS), cysteinyl lipopeptides, and many other molecules of microbial origin. The identification of the TLRs as the key conduit to host awareness of microbial infection was a victory for reductionism, proving that the complexity of infectious inflammation as a phenomenon belies the simplicity of its origins. It was achieved by a classical genetic approach, proceeding from phenotype to gene. Further analysis of the signaling pathways activated by the TLRs has depended on both classical and reverse genetic methods. Additional work will ultimately disclose the extent to which sterile inflammatory diseases are mediated by aberrations in these pathways.

Effects of diesel exhaust particles on human alveolar macrophage ability to secrete inflammatory mediators in response to lipopolysaccharide

Ambient particulate matter (PM) has been shown to be associated with mortality and morbidity. Diesel exhaust particles (DEP) contribute to ambient PM. Alveolar macrophages (AM) are important targets for PM effects in the lung. The effects of DEP exposure on human AM response to lipopolysachharide (LPS; from gram-negative bacteria) challenge in vitro were determined by monitoring the production of interleukin 8 (IL-8), tumor necrosis factor-alpha (TNF-alpha) and prostaglandin E(2) (PGE(2)). The roles of organic compounds and carbonaceous core of DEP in response to LPS were evaluated by comparing the DEPs effect to that of carbon black (CB), a carbonaceous particle with few adsorbed organic compounds. AMs were exposed in vitro to Standard Reference Material (SRM) DEP 2975, SRM DEP 1650, SRM 1975 (a dichloromethane extract of SRM DEP 2975) and CB particles for 24 h. DEPs induced a decreased secretion of IL-8, TNF-alpha and PGE(2) in response to a subsequent LPS stimulation. DEPs also show suppressive effect on the release of inflammatory mediators when stimulated with lipoteichoic acid, a product of gram positive bacteria. In summary, in vitro exposure of human AM to DEPs significantly suppress AM responsiveness to gram-negative and positive bacterial products, which may be a contributing factor to the impairment of pulmonary defense.

MD-2 mediates the ability of tetra-acylated and penta-acylated lipopolysaccharides to antagonize Escherichia coli lipopolysaccharide at the TLR4 signaling complex

We have demonstrated previously that tetra-acylated LPS derived from the oral bacterium, Porphyromonas gingivalis, and penta-acylated msbB LPS derived from a mutant strain of Escherichia coli can antagonize the ability of canonical hexa-acylated E. coli LPS to signal through the TLR4 signaling complex in human endothelial cells. Activation of the TLR4 signaling complex requires the coordinated function of LPS binding protein (LBP), CD14, MD-2, and TLR4. To elucidate the specific molecular components that mediate antagonism, we developed a recombinant human TLR4 signaling complex that displayed efficient LPS-dependent antagonism of E. coli LPS in HEK293 cells. Notably, changes in the expression levels of TLR4 in HEK293 cells modulated the efficiency of antagonism by P. gingivalis LPS. Both soluble (s) CD14 and membrane (m) CD14 supported efficient P. gingivalis LPS-dependent and msbB LPS-dependent antagonism of E. coli LPS in the recombinant TLR4 system. When cells expressing TLR4, MD-2, and mCD14 were exposed to LPS in the absence of serum-derived LBP, efficient LPS-dependent antagonism of E. coli LPS was still observed indicating that LPS-dependent antagonism occurs downstream of LBP. Experiments using immunoprecipitates of sCD14 or sMD-2 that had been pre-exposed to agonist and antagonist indicated that LPS-dependent antagonism occurs partially at sCD14 and potently at sMD-2. This study provides novel evidence that expression levels of TLR4 can modulate the efficiency of LPS-dependent antagonism. However, MD-2 represents the principal molecular component that tetra-acylated P. gingivalis LPS and penta-acylated msbB LPS use to antagonize hexa-acylated E. coli LPS at the TLR4 signaling complex.

A synthetic TLR4 antagonist has anti-inflammatory effects in two murine models of inflammatory bowel disease

Current evidence indicates that the chronic inflammation observed in the intestines of patients with inflammatory bowel disease is due to an aberrant immune response to enteric flora. We have developed a lipid A-mimetic, CRX-526, which has antagonistic activity for TLR4 and can block the interaction of LPS with the immune system. CRX-526 can prevent the expression of proinflammatory genes stimulated by LPS in vitro. This antagonist activity of CRX-526 is directly related to its structure, particularly secondary fatty acyl chain length. In vivo, CRX-526 treatment blocks the ability of LPS to induce TNF-alpha release. Importantly, treatment with CRX-526 inhibits the development of moderate-to-severe disease in two mouse models of colonic inflammation: the dextran sodium sulfate model and multidrug resistance gene 1a-deficient mice. By blocking the interaction between enteric bacteria and the innate immune system, CRX-526 may be an effective therapeutic molecule for inflammatory bowel disease.

TLR-2 is involved in airway epithelial cell response to air pollution particles

Primary cultures of normal human airway epithelial cells (NHBE) respond to ambient air pollution particulate matter (PM) by increased production of the cytokine IL-8, and the induction of several oxidant stress response genes. Components of ambient air PM responsible for stimulating epithelial cells have not been conclusively identified, although metal contaminants, benzo[a]pyrene and biological matter have been implicated. Stimulation of IL-8 release from NHBE with coarse (PM(2.5-10)), fine (PM2.5), and UF particle fractions has shown that the coarse particle fraction has the greatest effect on the epithelial cells as well as alveolar macrophages (AM). Since this fraction concentrates fugitive dusts and particle-associated microbial matter, it was hypothesized that NHBE may recognize PM through microbial pattern recognition receptors TLR2 and TLR4, as has been previously shown with AM. NHBE were shown to release IL-8 when exposed to a Gram-positive environmental isolate of Staphylococcus lentus, and lower levels when exposed to Gram-negative Pseudomonas spp. Comparison of TLR2 and TLR4 mRNA expression in NHBE and AM showed that NHBE express similar levels of TLR2 mRNA as the AM, but expressed very low levels of TLR4. When NHBE were stimulated with PM(2.5-10), PM2.5, and UF PM, in the presence or absence of inhibitors of TLR2 and TLR4 activation, a blocking antibody to TLR2 inhibited production of IL-8, while TLR4 antagonist E5531 or the LPS inhibitor Polymixin B had no effect. Furthermore, effects on expression of TLR2 and TLR4 mRNA, as well as the stress protein HSP70 was assessed in NHBE exposed to PM. TLR4 expression was increased in these cells while TLR2 mRNA levels were unchanged. Hsp70 was increased by PM(2.5-10) > PM2.5 > UF PM suggesting the possibility of indirect activation of TLR pathway by this endogenous TLR2/4 agonist.

Detailed structure of lipid A isolated from lipopolysaccharide from the marine proteobacterium Marinomonas vaga ATCC 27119

The chemical structure of a novel lipid A, the major component of the lipopolysaccharide from the marine gamma-proteobacterium Marinomonas vaga ATCC 27119(T), was determined by compositional analysis, NMR spectroscopy, and MS. It was found to be beta-1,6-glucosaminobiose 1-phosphate acylated with (R)-3-[dodecanoyl(dodecenoyl)oxy]decanoic acid [C10 : 0 (3O-C12 : 0 [3O-C12 : 1])] or (R)-3-(decanoyloxy)decanoic acid [C10 : 0 (3O-C10 : 0)], (R)-3-hydroxydecanoic acid [C10 : 0 (3OH)], and (R)-3-[(R)-3-hydroxydecanoyloxy]decanoic acid (C10 : 0 [3O-[C10 : 0 (3OH)]]) at the 2, 3, and 2' positions, respectively. It showed low lethal toxicity, which is probably related to specific structural attributes. The absence of a fatty acid at the 3' position and a phosphoryl group at the 4' position and also the presence of an amide-linked (R)-3-hydroxyalkanoic acid that is further O-acylated with another (R)-3-hydroxyalkanoic acid, distinguish M. vaga lipid A from other such molecules.

Inferences, questions and possibilities in Toll-like receptor signalling

The Toll-like receptors (TLRs) are the key proteins that allow mammals--whether immunologically naive or experienced--to detect microbes. They lie at the core of our inherited resistance to disease, initiating most of the phenomena that occur in the course of infection. Quasi-infectious stimuli that have been used for decades to study inflammatory mechanisms can activate the TLR family of proteins. And it now seems that many inflammatory processes, both sterile and infectious, may depend on TLR signalling. We are in a good position to apply our understanding of TLR signalling to a range of challenges in immunology and medicine.

Molecular mechanisms of macrophage activation and deactivation by lipopolysaccharide: roles of the receptor complex

Bacterial lipopolysaccharide (LPS), the major structural component of the outer wall of Gram-negative bacteria, is a potent activator of macrophages. Activated macrophages produce a variety of inflammatory cytokines. Excessive production of cytokines in response to LPS is regarded as the cause of septic shock. On the other hand, macrophages exposed to suboptimal doses of LPS are rendered tolerant to subsequent exposure to LPS and manifest a profoundly altered response to LPS. Increasing evidence suggests that monocytic cells from patients with sepsis and septic shock survivors have characteristics of LPS tolerance. Thus, an understanding of the molecular mechanisms underlying activation and deactivation of macrophages in response to LPS is important for the development of therapeutics for septic shock and the treatment of septic shock survivors. Over the past several years, significant progress has been made in identifying and characterizing several key molecules and signal pathways involved in the regulation of macrophage functions by LPS. In this paper, we summarize the current findings of the functions of the LPS receptor complex, which is composed of CD14, Toll-like receptor 4 (TLR4), and myeloid differentiation protein-2 (MD-2), and the signal pathways of this LPS receptor complex with regard to both activation and deactivation of macrophages by LPS. In addition, recent therapeutic approaches for septic shock targeting the LPS receptor complex are described.

Lipopolysaccharide interaction with cell surface Toll-like receptor 4-MD-2: higher affinity than that with MD-2 or CD14

Toll-like receptors (TLRs) are innate recognition molecules for microbial products, but their direct interactions with corresponding ligands remain unclarified. LPS, a membrane constituent of gram-negative bacteria, is the best-studied TLR ligand and is recognized by TLR4 and MD-2, a molecule associated with the extracellular domain of TLR4. Although TLR4-MD-2 recognizes LPS, little is known about the physical interaction between LPS and TLR4-MD-2. Here, we demonstrate cell surface LPS-TLR4-MD-2 complexes. CD14 greatly enhances the formation of LPS-TLR4-MD-2 complexes, but is not coprecipitated with LPS-TLR4-MD-2 complexes, suggesting a role for CD14 in LPS loading onto TLR4-MD-2 but not in the interaction itself between LPS and TLR4-MD-2. A tentative dissociation constant (Kd) for LPS-TLR4-MD-2 complexes was approximately 3 nM, which is approximately 10-20 times lower than the reported Kd for LPS-MD-2 or LPS-CD14. The presence of detergent disrupts LPS interaction with CD14 but not with TLR4-MD-2. E5531, a lipid A antagonist developed for therapeutic intervention of endotoxin shock, blocks LPS interaction with TLR4-MD-2 at a concentration 100 times lower than that required for blocking LPS interaction with CD14. These results reveal direct LPS interaction with cell surface TLR4-MD-2 that is distinct from that with MD-2 or CD14.

Stimulation of Toll-like receptor 4 by lipopolysaccharide during cellular invasion by live Salmonella typhimurium is a critical but not exclusive event leading to macrophage responses

Invasion of macrophages by salmonellae induces cellular responses, with the bacterial inducers likely to include a number of pathogen-associated molecular patterns. LPS is one of the prime candidates, but its precise role in the process, especially when presented as a component of live infecting bacteria, is unclear. We thus investigated this question using the lipid A antagonist E5531, the macrophage-like cell line RAW 264.7, and primary macrophage cultures from C3H/HeJ and Toll-like receptor 4(-/-) (TLR-4(-/-)) mice. We show that LPS presented on live salmonellae provides an essential signal, via functional TLR-4, for macrophages to produce NO and TNF-alpha. Furthermore, the mitogen-activated protein kinase c-Jun N-terminal kinase and p38 are activated, and the transcription factor NF-kappa B is translocated to the nucleus when RAW 264.7 cells are presented with purified LPS or live salmonellae. Purified LPS stimulates rapid, transitory mitogen-activated protein kinase activation that is inhibited by E5531, whereas bacterial invasion stimulates delayed, prolonged activation, unaffected by E5531. Both purified LPS and bacterial invasion caused translocation of NF-kappa B, but whereas E5531 always inhibited activation by purified LPS, activation by bacterial invasion was only inhibited at later time points. In conclusion, we show for the first time that production of NO and TNF-alpha is critically dependent on activation of TLR-4 by LPS during invasion of macrophages by salmonellae, but that different patterns of activation of intracellular signaling pathways are induced by purified LPS vs live salmonellae.

Characterization of a novel lipid-A from Rhizobium species Sin-1. A unique lipid-A structure that is devoid of phosphate and has a glycosyl backbone consisting of glucosamine and 2-aminogluconic acid

The structure of the lipid-A from Rhizobium species Sin-1, a nitrogen-fixing Gram-negative bacterial symbiont of Sesbania, was determined by composition, nuclear magnetic resonance spectroscopic, and mass spectrometric analyses. The lipid-A preparation consisted of a mixture of structures due to differences in fatty acylation and in the glycosyl backbone. There were two different disaccharide backbones. One disaccharide consisted of a distal glucosaminosyl residue beta-linked to position 6 of a proximal 2-aminoglucono-1,5-lactonosyl residue, and in the second disaccharide, the proximal residue was 2-amino-2,3-dideoxy-d-erythro-hex-2-enono-1,5-lactone. For both disaccharides, the distal glucosamine was acylated at C-2' primarily with beta-hydroxypalmitate (beta-OHC16:0) which, in turn, was O-acylated with 27-hydroxyoctacosanoic acid. For some of the lipid-A molecules, the distal glucosaminosyl residue was also acylated at C-3' with beta-hydroxymyristate (beta-OHC14:0), whereas other molecules were devoid of this acyl substituent. Both the 2-aminoglucono-1,5-lactonosyl and 2-amino-2,3-dideoxy-d-erythro-hex-2-enono-1,5-lactonosyl residues were acylated at C-2, primarily with beta-OHC16:0. Minor amounts of lipid-A molecules contained beta-OHC14:0 at C-3 and/or beta-hydroxystearate (beta-OHC18:0) or beta-hydroxyoctadecenoate (beta-OHC18:1) as the C-2 and C-2' N-acyl substituents.

Involvement of microbial components and toll-like receptors 2 and 4 in cytokine responses to air pollution particles

Inhalation of particulate matter (PM) may result in exacerbation of inflammatory airways disease, including asthma. Results from this laboratory have shown that the coarse inhalable particle fraction (PM(2.5-10)) is responsible for most of the PM effects on human airway macrophages (AM), including induction of cytokine production. Endotoxins associated with these particles account for a large part of their potency, as activity of PM can be inhibited by polymixin B and an activating moiety bound by lipopolysaccharide (LPS)-binding protein (LBP). The hypothesis behind the present study was that not only particle-bound LPS, but also Gram-negative (Gram-) and Gram-positive (Gram+) bacteria are responsible for PM-induced stimulation of AM, and therefore that PM are likely to activate receptors involved in recognition of microbes. Low level contamination of model pollution particles with environmental Staphyloccocus, Streptococcus, and Pseudomonas species was found to confer cytokine-inducing activity on inactive particles. Only one Gram- bacterium was sufficient for significant stimulatation of 100 AM, whereas at least three times more Gram+ bacteria were required for a similar level of response. Cytokine responses induced by PM as well as Gram+ and Gram- bacteria were inhibited by anti-CD14 antibody and required the presence of LBP-containing serum. The involvement of Toll-like receptor (TLR) 2 and 4 in recognition of PM(2.5-10) was investigated in transfected Chinese hamster ovary cells expressing CD14 and TLR2 or TLR4. TLR4 was found to be involved in PM(2.5-10) and Pseudomonas-induced activation, whereas TLR2 activation was induced by both Gram+ and Gram- bacteria and by PM. The synthetic lipid A analog E5531 fully inhibited the response to purified LPS and partially inhibited the response to PM and Pseudomonas. In contrast, E5531 had no effect on the response to Staphylococcus. Taken together, these results implicate microbial components as important players in AM-dependent inflammatory responses to PM.

Innate immune recognition of lipopolysaccharide by endothelial cells

OBJECTIVE

The endothelium is an active component of the innate immune response to bacterial invasion. Endothelial cells comprise mechanisms to recognize structural patterns expressed by pathogens and subsequently initiate the transcription of inflammatory genes. The purpose of this article is to summarize the molecular processes that underlie the endothelial innate immune response to microbial components, with a particular focus on responses to Gram-negative bacterial lipopolysaccharide.

DATA SOURCES

Personal observations and review of the literature as revealed by the National Library of Medicine.

DATA SUMMARY AND CONCLUSION

Endothelial cells recognize the presence of microbial components such as lipopolysaccharide via a receptor complex that contains at least three important cell surface components: CD14, Toll-like receptor-4, and MD-2. CD14 and MD-2 exist as soluble receptor components and are thought to bind to both lipopolysaccharide and Toll-like receptor-4, whereas Toll-like receptor-4 itself is the transmembrane signal transducer. Single-point mutations in MD-2 or the cytoplasmic portion of Toll-like receptor-4 abrogate the response to lipopolysaccharide. The composition of this receptor and the recruitment and activation of various cytoplasmic proteins afford at least five levels of ligand specificity and suggest that there are at least as many potential therapeutic targets for Toll-like receptor-mediated inflammatory states, including sepsis.

Endotoxin antagonism: conceptual basis and therapeutic potential

Since antiquity, physicians have beheld infections with deep consternation, knowing that a local lesion can have horrific systemic effects. Even in modern times, these effects have generally been impossible to control. Until recently, their ultimate cause was not well understood. Now, within the space of only a few years, the proximal cause of sepsis has been identified. Paralogous members of the Toll-like receptor (TLR) family sense infection and ignite the systemic inflammatory reaction that is known as sepsis. The question at hand has become a practical one: can this understanding be exploited to a therapeutic advantage?

Membrane perturbing properties of sucrose polyesters

Sucrose polyester (SPE), in the form of sucrose octaesters and sucrose hexaesters of palmitic (16:0), stearic (18:0), oleic (18:1cis), and linoleic (18:2cis) acids, have many uses. Applications include: a non-caloric fat substitute, detoxification agent, and oral contrast agent for human abdominal (MRI) magnetic resonance imaging. However, it has been shown that the ingestion of SPE was shown to generate a depletion of physiologically important lipidic vitamins and other lipophilic molecules. In order to better understand, at the molecular level, the type of interaction between SPE and lipid membrane, we have, first synthesized different type of labelled and non-labelled SPEs. Secondly, we have studied the effect of SPEs on multilamellar dispersions of dielaidoylphosphatidylethanolamine (DEPE) and dipalmitoylphosphocholine (DPPC) as a function of temperature, SPE composition and concentration. The effects of SPEs were studied by differential scanning calorimetry (DSC), X-ray diffraction, 2H and 31P NMR spectroscopy. At low concentration (< 1 mol%) all of the SPEs lowered the bilayer to the inverted hexagonal phase transition temperature of DEPE and induced the formation of a cubic phase in a composition dependent manner. At the same low concentration, SPEs in DPPC induce the formation of a non-bilayer phase as seen by 31P NMR. Order parameter measurements of DPPC-d62/SPE mixtures show that the SPE effect on the DPPC monolayer thickness is dependent on the SPE, concentration, chains length and saturation level. At higher concentration (> or = 10 mol%) SPE are very potent DEPE bilayer to HII phase transition promoters, although at that concentration the SPE have lost the ability to form cubic phases. SPEs have profound effects on the phase behaviour of model membrane systems, and may be important to consider when developing current and potential industrial and medical applications.

Consequences of interaction of a lipophilic endotoxin antagonist with plasma lipoproteins

E5531, a novel synthetic lipid A analogue, antagonizes the toxic effects of lipopolysaccharide, making it a potential intravenously administered therapeutic agent for the treatment of sepsis. This report describes the distribution of E5531 in human blood and its activity when it is associated with different lipoprotein subclasses. After in vitro incubation of [(14)C]E5531 with blood, the great majority (>92%) of material was found in the plasma fraction. Analysis by size-exclusion and affinity chromatographies and density gradient centrifugation indicates that [(14)C]E5531 binds to lipoproteins, primarily high-density lipoproteins (HDLs), with distribution into low-density lipoproteins (LDLs) and very low density lipoproteins (VLDLs) being dependent on the plasma LDL or VLDL cholesterol concentration. Similar results were also seen in a limited study of [(14)C]E5531 administration to human volunteers. The potency of E5531 in freshly drawn human blood directly correlates to increasing LDL cholesterol levels. Finally, preincubation of E5531 with plasma or purified lipoproteins indicated that binding to HDL resulted in a time-dependent loss of drug activity. This loss in activity was not observed with drug binding to LDLs or to VLDLs or chylomicrons. Taken together, these results indicate that E5531 binds to plasma lipoproteins, making its long-term antagonistic potency dependent on the plasma lipoprotein composition.