Evidence of a specific interaction between new synthetic antisepsis agents and CD14

Nanolevel Immunomodulators in Sepsis: Novel Roles, Current Perspectives, and Future Directions

Sepsis represents a profound challenge in critical care, characterized by a severe systemic inflammatory response which can lead to multi-organ failure and death. The intricate pathophysiology of sepsis involves an overwhelming immune reaction that disrupts normal host defense mechanisms, necessitating innovative approaches to modulation. Nanoscale immunomodulators, with their precision targeting and controlled release capabilities, have emerged as a potent solution to recalibrate immune responses in sepsis. This review explores the recent advancements in nanotechnology for sepsis management, emphasizing the integration of nanoparticulate systems to modulate immune function and inflammatory pathways. Discussions detail the development of the immune system, the distinct inflammatory responses triggered by sepsis, and the scientific principles underpinning nanoscale immunomodulation, including specific targeting mechanisms and delivery systems. The review highlights nanoformulation designs aimed at enhancing bioavailability, stability, and therapeutic efficacy, which shows promise in clinical settings by modulating key inflammatory pathways. Ultimately, this review synthesizes the current state of knowledge and projects future directions for research, underscoring the transformative potential of nanolevel immunomodulators for sepsis treatment through innovative technologies and therapeutic strategies.

Investigation of TLR4 Antagonists for Prevention of Intestinal Inflammation

Activation of toll-like receptor 4 (TLR4) has been shown to be a major influence on the inflammatory signalling pathways in intestinal mucositis (IM), as demonstrated by TLR4 knock-out mice. Pharmacological TLR4 inhibition has thus been postulated as a potential new therapeutic approach for the treatment of IM but specific TLR4 inhibitors have yet to be investigated. As such, we aimed to determine whether direct TLR4 antagonism prevents inflammation in pre-clinical experimental models of IM. The non-competitive and competitive TLR4 inhibitors, TAK-242 (10 µM) and IAXO-102 (10 µM), respectively, or vehicle were added to human T84, HT-29, and U937 cell lines and mouse colonic explants 1 h before the addition of lipopolysaccharide (LPS) (in vitro: 100 µg/mL; ex vivo: 10 µg/mL), SN-38 (in vitro: 1 µM or 1 nM; ex vivo: 2 µM), and/or tumour necrosis factor-alpha (TNF-α) (5 µg/mL). Supernatant was collected for human IL-8 and mouse IL-6 enzyme-linked immunosorbent assays (ELISAs), as a measure of inflammatory signalling. Cell viability was measured using XTT assays. Explant tissue was used in histopathological and RT-PCR analysis for genes of interest: TLR4, MD2, CD14, MyD88, IL-6, IL-6R, CXCL2, CXCR1, CXCR2. SN-38 increased cytostasis compared to vehicle (P < 0.0001). However, this was not prevented by either antagonist (P > 0.05) in any of the 3 cell lines. Quantitative histological assessment scores showed no differences between vehicle and treatment groups (P > 0.05). There were no differences in in vitro IL-8 (P > 0.05, in all 3 cells lines) and ex vivo IL-6 (P > 0.05) concentrations between vehicle and treatment groups. Transcript expression of all genes was similar across vehicle and treatment groups (P > 0.05). TLR4 antagonism using specific inhibitors TAK-242 and IAXO-102 was not effective at blocking IM in these pre-clinical models of mucositis. This work indicates that specific epithelial inhibition of TLR4 with these compounds is insufficient to manage mucositis-related inflammation. Rather, TLR4 signalling through immune cells may be a more important target to prevent IM.

Antinociceptive and modulatory effect of pathoplastic changes in spinal glia of a TLR4/CD14 blocking molecule in two models of pain in rat

The role of spinal glia in the development and maintenance of chronic pain has become over the last years a subject of increasing interest. In this regard, toll-like receptor 4 (TLR4) signaling has been proposed as a major trigger mechanism. Hence, in this study we explored the implications of TLR4 inhibition in the periphery and primarily in the CNS, focusing on the impact this inhibition renders in pain development and glia activation in the dorsal horn in two models of pain. Making use of a synthetic cluster of differentiation 14 (CD14)/TLR4 antagonist, the effect of TLR4 blockade on tactile allodynia and heat hyperalgesia was evaluated in osteoarthritic and postoperative rat models. An in vitro parallel artificial membrane permeation assay was performed to determine the proneness of the drug to permeate the blood-brain barrier prior to systemic and central administration. Findings suggest a dominant role of peripheral TLR4 in the model of incisional pain, whilst both peripheral and central TLR4 seem to be responsible for osteoarthritic pain. That is, central and peripheral TLR4 may be differently involved in the etiopathology of diverse types of pain what potentially seems a promising approach in the management of pain.

Molecular mechanism underlying the TLR4 antagonistic and antiseptic activities of papiliocin, an insect innate immune response molecule

SignificanceSimilar to mammalian TLR4/MD-2, the Toll9/MD-2-like protein complex in the silkworm, Bombyx mori, acts as an innate pattern-recognition receptor that recognizes lipopolysaccharide (LPS) and induces LPS-stimulated expression of antimicrobial peptides such as cecropins. Here, we report that papiliocin, a cecropin-like insect antimicrobial peptide from the swallowtail butterfly, competitively inhibits the LPS-TLR4/MD-2 interaction by directly binding to human TLR4/MD-2. Structural elements in papiliocin, which are important in inhibiting TLR4 signaling via direct binding, are highly conserved among insect cecropins, indicating that its TLR4-antagonistic activity may be related to insect Toll9-mediated immune response against microbial infection. This study highlights the potential of papiliocin as a potent TLR4 antagonist and safe peptide antibiotic for treating gram-negative sepsis.

TLR4 Antagonism Reduces Movement-Induced Nociception and ATF-3 Expression in Experimental Osteoarthritis

Introduction

Toll-like receptor 4 (TLR4) is a pattern recognition receptor involved in the detection of pathogen-associated molecular patterns (PAMPs), but also a "danger-sensing" receptor that recognizes host-derived endogenous molecules called damage-associated molecular patterns (DAMPs). The involvement of TLR4 in rheumatic diseases is becoming evident, as well as its potential role as a target for therapeutic intervention. Moreover, increasing evidence also suggests that TLR4 is implicated in chronic pain states. Thus, in this study, we evaluated whether a systemic administration of a synthetic antagonist of TLR4 (TLR4-A1) could decrease nociception and cartilage degradation in experimental osteoarthritis (OA). Furthermore, as the activation transcription factor (ATF)-3 serves as a negative regulator for TLR4-stimulated inflammatory response, we also evaluated the effect of TLR4 inhibition on ATF-3 expression in primary afferent neurons at the dorsal root ganglia (DRG).

Methods

OA was induced in adult male Wistar rats through an intra-articular injection of 2 mg of sodium mono-iodoacetate (MIA) into the left knee. From days 14 to 28 after OA induction, animals received an intraperitoneal injection of either TLR4-A1 (10 mg/kg) or vehicle. Movement- and loading-induced nociception was evaluated in all animals, by the Knee-Bend and CatWalk tests, before and at several time-points after TLR4-A1/vehicle administration. Immunofluorescence for TLR4 and ATF-3 was performed in L3-L5 DRG. Knee joints were processed for histopathological evaluation.

Results

Administration of TLR4-A1 markedly reduced movement-induced nociception in OA animals, particularly in the Knee-Bend test. Moreover, the increase of ATF-3 expression observed in DRG of OA animals was significantly reduced by TLR4-A1. However, no effect was observed in cartilage loss nor in the neuronal cytoplasmic expression of TLR4 upon antagonist administration.

Conclusion

The TLR4 antagonist administration possibly interrupts the TLR4 signalling cascade, thus decreasing the neurotoxic environment at the joint, which leads to a reduction in ATF-3 expression and in nociception associated with experimental OA.

Nanotools for Sepsis Diagnosis and Treatment

Sepsis is one of the leading causes of death worldwide with high mortality rates and a pathological complexity hindering early and accurate diagnosis. Today, laboratory culture tests are the epitome of pathogen recognition in sepsis. However, their consistency remains an issue of controversy with false negative results often observed. Clinically used blood markers, C reactive protein (CRP) and procalcitonin (PCT) are indicators of an acute-phase response and thus lack specificity, offering limited diagnostic efficacy. In addition to poor diagnosis, inefficient drug delivery and the increasing prevalence of antibiotic-resistant microorganisms constitute significant barriers in antibiotic stewardship and impede effective therapy. These challenges have prompted the exploration for alternative strategies that pursue accurate diagnosis and effective treatment. Nanomaterials are examined for both diagnostic and therapeutic purposes in sepsis. The nanoparticle (NP)-enabled capture of sepsis causative agents and/or sepsis biomarkers in biofluids can revolutionize sepsis diagnosis. From the therapeutic point of view, currently existing nanoscale drug delivery systems have proven to be excellent allies in targeted therapy, while many other nanotherapeutic applications are envisioned. Herein, the most relevant applications of nanomedicine for the diagnosis, prognosis, and treatment of sepsis is reviewed, providing a critical assessment of their potentiality for clinical translation.

Inhibition of the cluster of differentiation 14 innate immunity pathway with IAXO-101 improves chronic microelectrode performance

OBJECTIVE

Neuroinflammatory mechanisms are hypothesized to contribute to intracortical microelectrode failures. The cluster of differentiation 14 (CD14) molecule is an innate immunity receptor involved in the recognition of pathogens and tissue damage to promote inflammation. The goal of the study was to investigate the effect of CD14 inhibition on intracortical microelectrode recording performance and tissue integration.

APPROACH

Mice implanted with intracortical microelectrodes in the motor cortex underwent electrophysiological characterization for 16 weeks, followed by endpoint histology. Three conditions were examined: (1) wildtype control mice, (2) knockout mice lacking CD14, and (3) wildtype control mice administered a small molecule inhibitor to CD14 called IAXO-101.

MAIN RESULTS

The CD14 knockout mice exhibited acute but not chronic improvements in intracortical microelectrode performance without significant differences in endpoint histology. Mice receiving IAXO-101 exhibited significant improvements in recording performance over the entire 16 week duration without significant differences in endpoint histology.

SIGNIFICANCE

Full removal of CD14 is beneficial at acute time ranges, but limited CD14 signaling is beneficial at chronic time ranges. Innate immunity receptor inhibition strategies have the potential to improve long-term intracortical microelectrode performance.

Understanding the Role of Innate Immunity in the Response to Intracortical Microelectrodes

Intracortical microelectrodes exhibit enormous potential for researching the nervous system, steering assistive devices and functional electrode stimulation systems for severely paralyzed individuals, and augmenting the brain with computing power. Unfortunately, intracortical microelectrodes often fail to consistently record signals over clinically useful periods. Biological mechanisms, such as the foreign body response to intracortical microelectrodes and self-perpetuating neuroinflammatory cascades, contribute to the inconsistencies and decline in recording performance. Unfortunately, few studies have directly correlated microelectrode performance with the neuroinflammatory response to the implanted devices. However, of those select studies that have, the role of the innate immune system remains among the most likely links capable of corroborating the results of different studies, across laboratories. Therefore, the overall goal of this review is to highlight the role of innate immunity signaling in the foreign body response to intracortical microelectrodes and hypothesize as to appropriate strategies that may become the most relevant in enabling brain-dwelling electrodes of any geometry, or location, for a range of clinical applications.

Human αS1-casein induces IL-8 secretion by binding to the ecto-domain of the TLR4/MD2 receptor complex

BACKGROUND

The milk protein α_S1-casein was recently reported to induce secretion of proinflammatory cytokines via Toll-like receptor 4 (TLR4). In this study, α_S1-casein was identified as binder of theTLR4 ecto domain.

METHODS

IL-8 secretion after stimulation of TLR4/MD2 (myeloid differentiation factor 2)/CD14 (cluster of differentiation 14)-transfected HEK293 cells (TLR4⁺) and Mono Mac 6 cells (MM6) with recombinant α_S1-casein, or LPS as control was monitored. Binding of α_S1-casein to TLR4 was quantified by microscale thermophoresis (MST).

RESULTS

α_S1-casein induced secretion of IL-8 in TLR4⁺ cells and in MM6 cells with a six-times higher final IL-8 concentration in supernatants. IL-8 secretion was inhibited by intracellular TLR4-domain antagonist TAK-242 with an IC₅₀-value of 259.6 nM, by ecto-domain TLR4 antagonistic mianserin with 10-51 μM and by anti-CD14-IgA. The binding constants (K_D) of α_S1-casein to the TLR4, MD2, and CD14 were 2.8 μM, 0.3 μM and 2.7 μM, respectively. Finally, α_S1-casein showed a higher affinity to TLR4/MD2 (K_D: 2.2 μM) compared to LPS (K_D: 8.2 μM).

CONCLUSION

Human α_S1-casein induced proinflammatory effects are dependent upon binding to the TLR4 ectodomain and the presence of CD14. α_S1-casein displayed stronger TLR4 agonistic activity than LPS via a different mode of action.

GENERAL SIGNIFICANCE

Breast milk protein α_S1-casein is a proinflammatory cytokine.

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.

The synthetic glycolipid-based TLR4 antagonist FP7 negatively regulates in vitro and in vivo haematopoietic and non-haematopoietic vascular TLR4 signalling

TLRs, including TLR4, have been shown to play a crucial role in cardiovascular inflammatory-based diseases. The main goal of this study was to determine the potential of FP7, a synthetic glycolipid active as a TLR4 antagonist, to modulate haematopoietic and non-haematopoietic vascular TLR4 pro-inflammatory signalling. HUVEC, human THP-1 monocytes, THP-1-derived macrophages, mouse RAW-264.7 macrophages and Angiotensin II-infused apolipoprotein E-deficient mice were in vitro and in vivo models, respectively. Western blotting, Ab array and ELISA approaches were used to explore the effect of FP7 on TLR4 functional activity in response to bacterial LPS (in vitro) and endogenous ligands of sterile inflammation (in vitro and in vivo). Following activation of TLR4, in vitro and in vivo data revealed that FP7 inhibited p38 MAPK and p65 NF-kB phosphorylation associated with down-regulation of a number of TLR4-dependent pro-inflammatory proteins. In addition to inhibition of LPS-induced TLR4 signalling, FP7 negatively regulated TLR4 activation in response to ligands of sterile inflammation (hydroperoxide-rich oxidised LDL, in vitro and Angiotensin II infusion, in vivo). These results demonstrate the ability of FP7 to negatively regulate in vitro and in vivo haematopoietic and non-haematopoietic vascular TLR4 signalling both in humans and mice, suggesting the potential therapeutic use of this TLR4 antagonist for pharmacological intervention of vascular inflammatory diseases.

Structural basis for endotoxin neutralisation and anti-inflammatory activity of thrombin-derived C-terminal peptides

Thrombin-derived C-terminal peptides (TCPs) of about 2 kDa are present in wounds, where they exert anti-endotoxic functions. Employing a combination of nuclear magnetic resonance spectroscopy (NMR), biophysical, mass spectrometry and cellular studies combined with in silico multiscale modelling, we here determine the bound conformation of HVF18 (HVFRLKKWIQKVIDQFGE), a TCP generated by neutrophil elastase, in complex with bacterial lipopolysaccharide (LPS) and define a previously undisclosed interaction between TCPs and human CD14. Further, we show that TCPs bind to the LPS-binding hydrophobic pocket of CD14 and identify the peptide region crucial for TCP interaction with LPS and CD14. Taken together, our results demonstrate the role of structural transitions in LPS complex formation and CD14 interaction, providing a molecular explanation for the previously observed therapeutic effects of TCPs in experimental models of bacterial sepsis and endotoxin shock.

Thrombin-derived C-terminal peptides (TCPs) have anti-endotoxic functions in wounds by binding to bacterial lipopolysaccharide (LPS) and Gram-negative bacteria. Here authors use a spectrum of biophysical techniques to determine the conformation of a TCP in complex with LPS and define the interaction between TCPs and CD14.

Structural insights into pharmacophore-assisted in silico identification of protein-protein interaction inhibitors for inhibition of human toll-like receptor 4 - myeloid differentiation factor-2 (hTLR4-MD-2) complex

Toll-like receptor 4 (TLR4) is a member of Toll-Like Receptors (TLRs) family that serves as a receptor for bacterial lipopolysaccharide (LPS). TLR4 alone cannot recognize LPS without aid of co-receptor myeloid differentiation factor-2 (MD-2). Binding of LPS with TLR4 forms a LPS-TLR4-MD-2 complex and directs downstream signaling for activation of immune response, inflammation and NF-κB activation. Activation of TLR4 signaling is associated with various pathophysiological consequences. Therefore, targeting protein-protein interaction (PPI) in TLR4-MD-2 complex formation could be an attractive therapeutic approach for targeting inflammatory disorders. The aim of present study was directed to identify small molecule PPI inhibitors (SMPPIIs) using pharmacophore mapping-based approach of computational drug discovery. Here, we had retrieved the information about the hot spot residues and their pharmacophoric features at both primary (TLR4-MD-2) and dimerization (MD-2-TLR4*) protein-protein interaction interfaces in TLR4-MD-2 homo-dimer complex using in silico methods. Promising candidates were identified after virtual screening, which may restrict TLR4-MD-2 protein-protein interaction. In silico off-target profiling over the virtually screened compounds revealed other possible molecular targets. Two of the virtually screened compounds (C11 and C15) were predicted to have an inhibitory concentration in μM range after HYDE assessment. Molecular dynamics simulation study performed for these two compounds in complex with target protein confirms the stability of the complex. After virtual high throughput screening we found selective hTLR4-MD-2 inhibitors, which may have therapeutic potential to target chronic inflammatory diseases.

TLR4 Signaling Pathway Modulators as Potential Therapeutics in Inflammation and Sepsis

Toll-Like Receptor 4 (TLR4) signal pathway plays an important role in initiating the innate immune response and its activation by bacterial endotoxin is responsible for chronic and acute inflammatory disorders that are becoming more and more frequent in developed countries. Modulation of the TLR4 pathway is a potential strategy to specifically target these pathologies. Among the diseases caused by TLR4 abnormal activation by bacterial endotoxin, sepsis is the most dangerous one because it is a life-threatening acute system inflammatory condition that still lacks specific pharmacological treatment. Here, we review molecules at a preclinical or clinical phase of development, that are active in inhibiting the TLR4-MyD88 and TLR4-TRIF pathways in animal models. These are low-molecular weight compounds of natural and synthetic origin that can be considered leads for drug development. The results of in vivo studies in the sepsis model and the mechanisms of action of drug leads are presented and critically discussed, evidencing the differences in treatment results from rodents to humans.

Amphiphilic Guanidinocalixarenes Inhibit Lipopolysaccharide (LPS)- and Lectin-Stimulated Toll-like Receptor 4 (TLR4) Signaling

We recently reported on the activity of cationic amphiphiles in inhibiting TLR4 activation and subsequent production of inflammatory cytokines in cells and in animal models. Starting from the assumption that opportunely designed cationic amphiphiles can behave as CD14/MD-2 ligands and therefore modulate the TLR4 signaling, we present here a panel of amphiphilic guanidinocalixarenes whose structure was computationally optimized to dock into MD-2 and CD14 binding sites. Some of these calixarenes were active in inhibiting, in a dose-dependent way, the LPS-stimulated TLR4 activation and TLR4-dependent cytokine production in human and mouse cells. Moreover, guanidinocalixarenes also inhibited TLR4 signaling when TLR4 was activated by a non-LPS stimulus, the plant lectin PHA. While the activity of guanidinocalixarenes in inhibiting LPS toxic action has previously been related to their capacity to bind LPS, we suggest a direct antagonist effect of calixarenes on TLR4/MD-2 dimerization, pointing at the calixarene moiety as a potential scaffold for the development of new TLR4-directed therapeutics.

The EuroSciCon's 2015 Innate Immunity Summit

The EuroSciCon's 2015 Innate Immunity Summit, London, UK, 17–19 November 2015

A first line of defense against viral infection is prompted by the innate immune system. Viruses activate both extracellular and intracellular events that lead to a war between the virus and the host. In addition to vaccines which induce adaptive T- and B-cell response in readiness for infection, other therapies that potentiate the host immune response are in development, such as those that induce an increase in restriction factor activity or diminish inflammation through Toll-like receptors’ antagonists. Other modulators of immune response, such as thymosin α-1, contribute to the inhibition of HIV-1 and human T lymphotropic virus 1 infection. Understanding the mechanisms by which the innate immune response combats pathogen invasion will enable the generation of novel therapeutic strategies to cure viral infection.

Small-Molecule Carbohydrate-Based Immunostimulants

In this review, we discuss small-molecule, carbohydrate-based immunostimulants that target Toll-like receptor 4 (TLR-4) and cluster of differentiation 1D (CD1d) receptors. The design and use of these molecules in immunotherapy as well as results from their use in clinical trials are described. How these molecules work and their utilization as vaccine adjuvants are also discussed. Future applications and extensions for the use of these analogues as therapeutic agents will be outlined.

Glycolipid-based TLR4 Modulators and Fluorescent Probes: Rational Design, Synthesis, and Biological Properties

The cationic glycolipid IAXO-102, a potent TLR4 antagonist targeting both MD-2 and CD14 co-receptors, has been used as scaffold to design new potential TLR4 modulators and fluorescent labels for the TLR4 receptor complex (membrane TLR4.MD-2 dimer and CD14). The primary amino group of IAXO-102, not involved in direct interaction with MD-2 and CD14 receptors, has been exploited to covalently attach a fluorescein (molecules 1 and 2) or to link two molecules of IAXO-102 through diamine and diammonium spacers, obtaining 'dimeric' molecules 3 and 4. The structure-based rational design of compounds 1-4 was guided by the optimization of MD-2 and CD14 binding. Compounds 1 and 2 inhibited TLR4 activation, in a concentration-dependent manner, and signaling in HEK-Blue TLR4 cells. The fluorescent labeling of murine macrophages by molecule 1 was inhibited by LPS and was also abrogated when cell surface proteins were digested by trypsin, thus suggesting an interaction of fluorescent probe 1 with membrane proteins of the TLR4 receptor system.

Therapeutic Developments Targeting Toll-like Receptor-4-Mediated Neuroinflammation

Toll-like receptors (TLRs) have been shown to play an important role in the immune system, which warrants study of their remarkable potential as pharmacological targets. Activation of TLRs requires participation from specific pathogen-associated molecular patterns (PAMPs) and accessory proteins such as myeloid differentiation protein 2 (MD2), lipopolysaccharide binding protein (LBP), and cluster differentiation antigen 14 (CD14). Assembly of the TLR4-MD2-LPS complex is essential in TLR4 activation. Recent studies have revealed that TLR4 activation is a significant trigger of signal transmission pathways in the nervous system, which could result in chronic pain as well as opioid tolerance and dependence. Researchers of the molecular structure of TLRs and their accessory proteins have opened a door to syntheses of TLRs agonists and antagonists, such as eritoran. Small-molecule modulators of TLR4, such as MD2-I and tricyclic antidepressants, offer more promising prospects than peptides, given their convenience in oral administration and lower cost. Herein we mainly discuss the mechanisms and clinical prospects of TLR4 agonists and antagonists.

Mannoside Glycolipid Conjugates Display Anti-inflammatory Activity by Inhibition of Toll-like Receptor-4 Mediated Cell Activation

Inhibition of excessive Toll-like receptor 4 (TLR4) signaling is a therapeutic approach pursued for many inflammatory diseases. We report that Mannoside Glycolipid Conjugates (MGCs) selectively blocked TLR4-mediated activation of human monocytes and monocyte-derived dendritic cells (DCs) by lipopolysaccharide (LPS). They potently suppressed pro-inflammatory cytokine secretion and maturation of DCs exposed to LPS, leading to impaired T cell stimulation. MGCs did not interfere with LPS and could act in a delayed manner, hours after LPS stimulation. Their inhibitory action required both the sugar heads and the lipid chain, although the nature of the sugar and the structure of the lipid tail could be modified. They blocked early signaling events at the cell membrane, enhanced internalization of CD14 receptors, and prevented colocalization of CD14 and TLR4, thereby abolishing NF-κB nuclear translocation. When the best lead conjugate was tested in a mouse model of LPS-induced acute lung inflammation, it displayed an anti-inflammatory action by suppressing the recruitment of neutrophils. Thus, MGCs could serve as promising leads for the development of selective TLR4 antagonistic agents for inflammatory diseases.

Modulating LPS signal transduction at the LPS receptor complex with synthetic Lipid A analogues

Sepsis, defined as a clinical syndrome brought about by an amplified and dysregulated inflammatory response to infections, is one of the leading causes of death worldwide. Despite persistent attempts to develop treatment strategies to manage sepsis in the clinical setting, the basic elements of treatment have not changed since the 1960s. As such, the development of effective therapies for reducing inflammatory reactions and end-organ dysfunction in critically ill patients with sepsis remains a global priority. Advances in understanding of the immune response to sepsis provide the opportunity to develop more effective pharmaceuticals. This article details current information on the modulation of the lipopolysaccharide (LPS) receptor complex with synthetic Lipid A mimetics. As the initial and most critical event in sepsis pathophysiology, the LPS receptor provides an attractive target for antisepsis agents. One of the well-studied approaches to sepsis therapy involves the use of derivatives of Lipid A, the membrane-anchor portion of an LPS, which is largely responsible for its endotoxic activity. This article describes the structural and conformational requirements influencing the ability of Lipid A analogues to compete with LPS for binding to the LPS receptor complex and to inhibit the induction of the signal transduction pathway by impairing LPS-initiated receptor dimerization.

Chemistry of lipid A: at the heart of innate immunity

In many Gram-negative bacteria, lipopolysaccharide (LPS) and its lipid A moiety are pivotal for bacterial survival. Depending on its structure, lipid A carries the toxic properties of the LPS and acts as a potent elicitor of the host innate immune system via the Toll-like receptor 4/myeloid differentiation factor 2 (TLR4/MD-2) receptor complex. It often causes a wide variety of biological effects ranging from a remarkable enhancement of the resistance to the infection to an uncontrolled and massive immune response resulting in sepsis and septic shock. Since the bioactivity of lipid A is strongly influenced by its primary structure, a broad range of chemical syntheses of lipid A derivatives have made an enormous contribution to the characterization of lipid A bioactivity, providing novel pharmacological targets for the development of new biomedical therapies. Here, we describe and discuss the chemical aspects regarding lipid A and its role in innate immunity, from the (bio)synthesis, isolation and characterization to the molecular recognition at the atomic level.

Trehalose- and glucose-derived glycoamphiphiles: small-molecule and nanoparticle Toll-like receptor 4 (TLR4) modulators

An increasing number of pathologies have been linked to Toll-like receptor 4 (TLR4) activation and signaling, therefore new hit and lead compounds targeting this receptor activation process are urgently needed. We report on the synthesis and biological properties of glycolipids based on glucose and trehalose scaffolds which potently inhibit TLR4 activation and signaling in vitro and in vivo. Structure-activity relationship studies on these compounds indicate that the presence of fatty ester chains in the molecule is a primary prerequisite for biological activity and point to facial amphiphilicity as a preferred architecture for TLR4 antagonism. The cationic glycolipids here presented can be considered as new lead compounds for the development of drugs targeting TLR4 activation and signaling in infectious, inflammatory, and autoimmune diseases. Interestingly, the biological activity of the best drug candidate was retained after adsorption at the surface of colloidal gold nanoparticles, broadening the options for clinical development.

Modulation of CD14 and TLR4·MD-2 activities by a synthetic lipid A mimetic

Monosaccharide lipid A mimetics based on a glucosamine core linked to two fatty acid chains and bearing one or two phosphate groups have been synthesized. Compounds 1 and 2, each with one phosphate group, were practically inactive in inhibiting LPS-induced TLR4 signaling and cytokine production in HEK-blue cells and murine macrophages, but compound 3, with two phosphate groups, was found to be active in efficiently inhibiting TLR4 signal in both cell types. The direct interaction between compound 3 and the MD-2 coreceptor was investigated by NMR spectroscopy and molecular modeling/docking analysis. This compound also interacts directly with the CD14 receptor, stimulating its internalization by endocytosis. Experiments on macrophages show that the effect on CD14 reinforces the activity on MD-2·TLR4 because compound 3's activity is higher when CD14 is important for TLR4 signaling (i.e., at low LPS concentration). The dual targeting of MD-2 and CD14, accompanied by good solubility in water and lack of toxicity, suggests the use of monosaccharide 3 as a lead compound for the development of drugs directed against TLR4-related syndromes.

Toll-like receptor 4 (TLR4) modulation by synthetic and natural compounds: an update

Toll-like receptor 4 (TLR4), together with MD-2, binds bacterial endotoxins (E) with high affinity, triggering formation of the activated homodimer (E.MD-2.TLR4)2. Activated TLR4 induces intracellular signaling leading to activation of transcription factors that result in cytokine and chemokine production and initiation of inflammatory and immune responses. TLR4 also responds to endogenous ligands called danger associated molecular patterns (DAMPs). Increased sensitivity to infection and a variety of immune pathologies have been associated with either too little or too much TLR4 activation. We review here the molecular mechanisms of TLR4 activation (agonism) or inhibition (antagonism) by small organic molecules of both natural and synthetic origin. The role of co-receptors MD-2 and CD14 in the TLR4 modulation process is also discussed. Recent achievements in the field of chemical TLR4 modulation are reviewed, with special focus on nonclassical TLR4 ligands with a chemical structure different from that of lipid A.

Multivalent glycoconjugates as anti-pathogenic agents

Multivalency plays a major role in biological processes and particularly in the relationship between pathogenic microorganisms and their host that involves protein-glycan recognition. These interactions occur during the first steps of infection, for specific recognition between host and bacteria, but also at different stages of the immune response. The search for high-affinity ligands for studying such interactions involves the combination of carbohydrate head groups with different scaffolds and linkers generating multivalent glycocompounds with controlled spatial and topology parameters. By interfering with pathogen adhesion, such glycocompounds including glycopolymers, glycoclusters, glycodendrimers and glyconanoparticles have the potential to improve or replace antibiotic treatments that are now subverted by resistance. Multivalent glycoconjugates have also been used for stimulating the innate and adaptive immune systems, for example with carbohydrate-based vaccines. Bacteria present on their surfaces natural multivalent glycoconjugates such as lipopolysaccharides and S-layers that can also be exploited or targeted in anti-infectious strategies.

Reviewing and identifying amino acids of human, murine, canine and equine TLR4 / MD-2 receptor complexes conferring endotoxic innate immunity activation by LPS/lipid A, or antagonistic effects by Eritoran, in contrast to species-dependent modulation by lipid IVa

There is literature evidence gathered throughout the last two decades reflecting unexpected species differences concerning the immune response to lipid IVa which provides the opportunity to gain more detailed insight by the molecular modeling approach described in this study. Lipid IVa is a tetra-acylated precursor of lipid A in the biosynthesis of lipopolysaccharide (LPS) in Gram-negative bacteria. Lipid A of the prototypic E. coli-type is a hexa-acylated structure that acts as an agonist in all tested mammalian species by innate immunorecognition via the Toll-like receptor 4 (TLR4)/myeloid differentiation factor 2 (MD-2) receptor complex. In contrast, lipid IVa is proinflammatory in mouse cells (agonism) but it remains inactive to human macrophages and even antagonizes the action of potent agonists like E. coli-type lipid A. This particular ambivalent activity profile of lipid IVa has been confirmed in other mammalian species: in equine cells Lipid IVa also acts in a weak agonistic manner, whereas being inactive and antagonizing the lipid A-induced activation of canine TLR4/MD-2. Intriguingly, the respective TLR4 amino acid sequences of the latter species are more identical to the human (67%, 68%) than to the murine (62%, 58%) ortholog. In order to address the unpaired activity-sequence dualism for human, murine, canine and equine species regarding the activity of lipid IVa as compared to LPS and lipid A and, we review the literature and computationally pinpoint the differential biological effects of lipid IVa versus LPS and lipid A to specific amino acid residues. In contrast to lipid IVa the structurally related synthetic compound Eritoran (E5564) acts consistently in an antagonistic manner in these mammalian species and serves as a reference ligand for molecular modeling in this study. The combined evaluation of data sets provided by prior studies and in silico homology mapping of differential residues of TLR4/MD-2 complexes lends detailed insight into the driving forces of the characteristic binding modes of the lipid A domain in LPS and the precursor structure lipid IVa to the receptor complex in individual mammalian species.

The crystal structure of human soluble CD14 reveals a bent solenoid with a hydrophobic amino-terminal pocket

Human monocyte differentiation Ag CD14 is a pattern recognition receptor that enhances innate immune responses to infection by sensitizing host cells to bacterial LPS (endotoxin), lipoproteins, lipoteichoic acid, and other acylated microbial products. CD14 physically delivers these lipidated microbial products to various TLR signaling complexes that subsequently induce intracellular proinflammatory signaling cascades upon ligand binding. The ensuing cellular responses are usually protective to the host but can also result in host fatality through sepsis. In this work, we have determined the x-ray crystal structure of human CD14. The structure reveals a bent solenoid typical of leucine-rich repeat proteins with an amino-terminal pocket that presumably binds acylated ligands including LPS. Comparison of human and mouse CD14 structures shows great similarity in overall protein fold. However, compared with mouse CD14, human CD14 contains an expanded pocket and alternative rim residues that are likely to be important for LPS binding and cell activation. The x-ray crystal structure of human CD14 presented in this article may foster additional ligand-bound structural studies, virtual docking studies, and drug design efforts to mitigate LPS-induced sepsis and other inflammatory diseases.

Cationic lipids activate intracellular signaling pathways

Cationic liposomes are commonly used as a transfection reagent for DNA, RNA or proteins and as a co-adjuvant of antigens for vaccination trials. A high density of positive charges close to cell surface is likely to be recognized as a signal of danger by cells or contribute to trigger cascades that are classically activated by endogenous cationic compounds. The present review provides evidence that cationic liposomes activate several cellular pathways like pro-apoptotic and pro-inflammatory cascades. An improved knowledge of the relationship between the cationic lipid properties (nature of the lipid hydrophilic moieties, hydrocarbon tail, mode of organization) and the activation of these pathways opens the way to the use and design of cationic tailored for a specific application (e.g. for gene transport or as adjuvants).

Synthetic molecules and functionalized nanoparticles targeting the LPS-TLR4 signaling: A new generation of immunotherapeutics

Toll-like receptor 4 (TLR4), the receptor of bacterial endotoxins in mammalians, plays a pivotal role in the induction of innate immunity and inflammation. TLR4 activation by bacterial lipopolysaccharide (LPS) is achieved by the coordinate and sequential action of three other proteins, the lipopolysaccharide binding protein (LBP), the cluster differentiation antigen CD14, and the myeloid differentiation protein (MD-2) receptors, that bind LPS and present it in a monomeric form to TLR4 by forming the activated [TLR4·MD-2·LPS]2 complex. Small molecules and nanoparticles active in modulating the TLR4 signal by targeting directly the MD-2·TLR4 complex or by interfering in other points of the TLR4 signaling are presented in this paper. These compounds have great pharmacological interest as vaccine adjuvants, immunotherapeutics, anti-sepsis, and anti-inflammatory agents.

Therapeutic targeting of innate immunity with Toll-like receptor 4 (TLR4) antagonists

Early recognition of invading bacteria by the innate immune system has a crucial function in antibacterial defense by triggering inflammatory responses that prevent the spread of infection and suppress bacterial growth. Toll-like receptor 4 (TLR4), the innate immunity receptor of bacterial endotoxins, plays a pivotal role in the induction of inflammatory responses. TLR4 activation by bacterial lipopolysaccharide (LPS) is achieved by the coordinate and sequential action of three other proteins, LBP, CD14 and MD-2 receptors, that bind lipopolysaccharide (LPS) and present it to TLR4 by forming the activated (TLR4-MD-2-LPS)(2) complex. Small molecules active in modulating the TLR4 activation process have great pharmacological interest as vaccine adjuvants, immunotherapeutics or antisepsis and anti-inflammatory agents. In this review we present natural and synthetic molecules active in inhibiting TLR4-mediated LPS signalling in humans and their therapeutic potential. New pharmacological applications of TLR4 antagonists will be also presented related to the recently discovered role of TLR4 in the insurgence and progression of neuropathic pain and sterile inflammations.

Exploring the LPS/TLR4 signal pathway with small molecules

The identification of the bacterial endotoxin receptors for innate immunity, most notably TLR4 (Toll-like receptor 4), has sparked great interest in therapeutic manipulation of the innate immune system. In the present mini-review, several natural and synthetic molecules that modulate the TLR4-mediated LPS (lipopolysaccharide) signalling in animals and humans are considered, and their mechanisms of action are discussed. The process of LPS sensing and signal amplification in humans is based on the sequential action of specific receptors situated in the extracellular side of the innate immunity cells, which bind and transfer LPS to TLR4: LBP (LPS-binding protein), CD14, MD-2 (myeloid differentiation protein 2). We classified the compounds active on TLR4 pathway depending on the specific molecular targets (LPS, LBP, CD14, MD-2 or TLR4). Small molecules developed by our group are described that inhibit LPS-stimulated TLR4 activation by selectively targeting the LPS-CD14 interaction. These compounds have an interesting antiseptic shock, anti-inflammatory and anti-neuropathic pain activity in vivo.

The cationic amphiphile 3,4-bis(tetradecyloxy)benzylamine inhibits LPS signaling by competing with endotoxin for CD14 binding

The identification of the bacterial endotoxin receptors for innate immunity, most notably the Toll-like receptor 4 (TLR4), has sparked great interest in therapeutic manipulation of innate immune system. We have recently developed synthetic molecules that have been shown to inhibit TLR4 activation in vitro and in vivo. Here we present the synthesis and the biological characterization of a new molecule, the cationic amphiphile 3,4-bis(tetradecyloxy)benzylamine, with a structure strictly related to the previously developed TLR4 modulators. This compound is able to inhibit in a dose-dependent manner the LPS-stimulated TLR4 activation in HEK cells. In order to characterize the mechanism of action of this compound, we investigated possible interactions with the extracellular components that bind and shuttle LPS to TLR4, namely LBP, CD14, and MD-2. This compound inhibited LBP/CD14-dependent LPS transfer to MD-2.TLR4, resulting in reduced formation of a (LPS-MD-2-TLR4)(2) complex. This effect was due to inhibition of the transfer of LPS from aggregates in solution to sCD14 with little or no effect on LPS shuttling from LPS/CD14 to MD-2. This compound also inhibited transfer of LPS monomer from full-length CD14 to a truncated, polyhistidine tagged CD14. Taken together, our findings strongly suggest that this compound inhibits LPS-stimulated TLR4 activation by competitively occupying CD14 and thereby reducing the delivery of activating endotoxin to MD-2.TLR4.