Evidence that tricyclic small molecules may possess toll-like receptor and myeloid differentiation protein 2 activity

TLR4 inhibitors through inhibiting (MYD88-TRIF) pathway, protect against experimentally-induced intestinal (I/R) injury

Intestinal ischemia/reperfusion (I/R) injury is a serious condition that causes intestinal dysfunction and can be fatal. Previous research has shown that toll-like receptor 4 (TLR4) inhibitors have a protective effect against this injury. This study aimed to investigate the protective effects of TLR4 inhibitors, specifically cyclobenzaprine, ketotifen, amitriptyline, and naltrexone, in rats with intestinal (I/R) injury. Albino rats were divided into seven groups: vehicle control, sham-operated, I/R injury, I/R-cyclobenzaprine (10 mg/kg body weight), I/R-ketotifen (1 mg/kg body weight), I/R-amitriptyline (10 mg/kg body weight), and I/R-naltrexone (4 mg/kg body weight) groups. Anesthetized rats (urethane 1.8 g/kg) underwent 30 min of intestinal ischemia by occluding the superior mesenteric artery (SMA), followed by 2 h of reperfusion. Intestinal tissue samples were collected to measure various parameters, including malondialdehyde (MDA), nitric oxide synthase (NO), myeloperoxidase (MPO), superoxide dismutase (SOD), TLR4, intercellular adhesion molecule-1 (ICAM-1), nuclear factor kappa bp65 (NF-ĸBP65), monocyte chemoattractant protein-1 (MCP-1), tumor necrosis factor-α (TNF-α), macrophages CD68, myeloid differentiation factor 88 (MYD88), and toll interleukin receptor-domain-containing adaptor-inducing interferon β (TRIF). The use of TLR4 inhibitors significantly reduced MDA, MPO, and NO levels, while increasing SOD activity. Furthermore, it significantly decreased TLR4, ICAM-1, TNF-α, MCP-1, MYD88, and TRIF levels. These drugs also showed partial restoration of normal cellular structure with reduced inflammation. Additionally, there was a decrease in NF-ĸBP65 and macrophages CD68 staining compared to rats in the I/R groups. This study focuses on how TLR4 inhibitors enhance intestinal function and protect against intestinal (I/R) injury by influencing macrophages CD86 through (MYD88-TRIF) pathway, as well as their effects on oxidation and inflammation.

Amitriptyline efficacy in decreasing implant-induced foreign body reaction

Beyond its actions on the nervous system, amitriptyline (AM) has been shown to lower inflammatory, angiogenic, and fibrogenic markers in a few pathological conditions in human and in experimental animal models. However, its effects on foreign body reaction (FBR), a complex adverse healing process, after biomedical material implantation are not known. We have evaluated the effects of AM on the angiogenic and fibrogenic components on a model of implant-induced FBR. Sponge disks were implanted subcutaneously in C57BL/6 mice, that were treated daily with oral administration of AM (5 mg/kg) for seven consecutive days in two protocols: treatment was started on the day of surgery and the implants were removed on the seventh day after implantation and treatment started 7 days after implantation and the implants removed 14 after implantation. None of the angiogenic (vessels, Vascular endothelial growth factor (VEGF), and interleukin-1β (IL-1β) or fibrogenic parameters (collagen, TGF-β, and fibrous capsule) and giant cell numbers analyzed were attenuated by AM in 7-day-old implants. However, AM was able to downregulate angiogenesis and FBR in 14-day-old implants. The effects of AM described here expands its range of actions as a potential agent capable of attenuating fibroproliferative processes that may impair functionality of implantable devices.

Bupivacaine inhibits the TLR4- and TLR2-Myd88/NF-κB pathways in human leukocytes

Local anesthetics have anti-inflammatory effects. Because most previous experiments were performed with supra-therapeutic concentrations, we measured the effects of clinically relevant concentrations of bupivacaine on the Toll like receptor 4 (TLR4)- and TLR2-myeloid differentiation primary response 88 (MyD88)-nuclear factor kappa-light-chain-enhancer of activated B cell (NF-κB) pathways. We measured tumor necrosis factor alpha (TNF-α) and prostaglandin E2 (PGE2) release, p38 mitogen-activated protein kinase (MAP-kinase) phosphorylation and translocation of NF-κB in human peripheral blood mononuclear cells (hPBMCs) and human monocytes challenged with lipopolysaccharide (LPS) or tripalmitoylated lipopeptide Pam3CysSerLys4 (Pam3CSK4) in the presence or absence of bupivacaine. Similarly, we measured the effect of bupivacaine on HEK293 cells expressing the hTLR4 and the hTLR2 genes and challenged with LPS or Pam3CSK4. Finally, molecular docking simulations of R(+)- and S(-)-bupivacaine binding to the TLR4-myeloid differentiation protein 2 (MD-2) complex and to the TLR2/TLR1 heterodimer were performed. In PBMCs, bupivacaine from 0.1 to 100 μM inhibited LPS-induced TNF-α and PGE2 secretion, phosphorylation of p38 and nuclear translocation of NF-κB in monocytes. Bupivacaine similarly inhibited the effects of Pam3CSK4 on TNF-α secretion. Bupivacaine inhibited the effect of LPS on HEK293 cells expressing the human TLR4 receptor and the effect of Pam3CSK4 on HEK293 cells expressing the human TLR2 receptor. Molecular docking showed that bupivacaine binds to the MD-2 co-receptor of TLR4 and to the TLR2 receptor. Contrary to numerous experiments performed with supratherapeutic doses, our results were obtained with concentrations of bupivacaine as low as 0.1 μM. We conclude that bupivacaine modulates the inflammatory reactions such as those observed after surgery or trauma, at least partly by inhibiting the TLR4- and TLR2-NF-κB pathways.

Involvement of TLR2-TLR4, NLRP3, and IL-17 in pain induced by a novel Sprague-Dawley rat model of experimental autoimmune encephalomyelitis

Up to 92% of patients suffering from multiple sclerosis (MS) experience pain, most without adequate treatment, and many report pain long before motor symptoms associated with MS diagnosis. In the most commonly studied rodent model of MS, experimental autoimmune encephalomyelitis (EAE), motor impairments/disabilities caused by EAE can interfere with pain testing. In this study, we characterize a novel low-dose myelin-oligodendrocyte-glycoprotein (MOG)-induced Sprague-Dawley (SD) model of EAE-related pain in male rats, optimized to minimize motor impairments/disabilities. Adult male SD rats were treated with increasing doses of intradermal myelin-oligodendrocyte-glycoprotein (MOG1-125) (0, 4, 8, and 16 μg) in incomplete Freund's adjuvant (IFA) vehicle to induce mild EAE. Von Frey testing and motor assessments were conducted prior to EAE induction and then weekly thereafter to assess EAE-induced pain and motor impairment. Results from these studies demonstrated that doses of 8 and 16 μg MOG1-125 were sufficient to produce stable mechanical allodynia for up to 1 month in the absence of hindpaw motor impairments/disabilities. In the follow-up studies, these doses of MOG1-125, were administered to create allodynia in the absence of confounded motor impairments. Then, 2 weeks later, rats began daily subcutaneous injections of the Toll-like receptor 2 and 4 (TLR2-TLR4) antagonist (+)-naltrexone [(+)-NTX] or saline for an additional 13 days. We found that (+)-NTX also reverses EAE-induced mechanical allodynia in the MOG-induced SD rat model of EAE, supporting parallels between models, but now allowing a protracted timecourse to be examined completely free of motor confounds. Exploring further mechanisms, we demonstrated that both spinal NOD-like receptor protein 3 (NLRP3) and interleukin-17 (IL-17) are necessary for EAE-induced pain, as intrathecal injections of NLRP3 antagonist MCC950 and IL-17 neutralizing antibody both acutely reversed EAE-induced pain. Finally, we show that spinal glial immunoreactivity induced by EAE is reversed by (+)-NTX, and that spinal demyelination correlates with the severity of motor impairments/disabilities. These findings characterize an optimized MOG-induced SD rat model of EAE for the study of pain with minimal motor impairments/disabilities. Finally, these studies support the role of TLR2-TLR4 antagonists as a potential treatment for MS-related pain and other pain and inflammatory-related disorders.

Dual effect of amitriptyline in the control of vascular tone: Direct blockade of calcium channel in smooth muscle cells and reduction of TLR4-dependent NO production in endothelial cells

BACKGROUND AND PURPOSE

Amitriptyline (AM) is a classical and typical tricyclic antidepressant drug. Despite its well-known effects on the nervous system, it has been described to work as a TLR4 antagonist and several clinical works suggested some unexpected cardiovascular effects. The role of amitriptyline on vascular tone is not clear, thus we hypothesized that amitriptyline has a double effect on vascular tone by both endothelial TLR4-dependent nitric oxide down-regulation and calcium channel blockade in smooth muscle cells.

EXPERIMENTAL APPROACH

Changes in isometric tension were recorded on a wire myograph. NO production was evaluated by fluorescence microscopy and flow cytometry in the mouse aorta and EAhy926 cells using DAF fluorescence intensity. Calcium influx was evaluated in A7r5 cells by flow cytometry. Western blot was used to analyze eNOS and nNOS phosphorylation.

KEY RESULTS

AM reduced PE-induced contraction by calcium influx diminution in smooth muscle cells (F/F₀ = 225.6 ± 15.9 and 118.6 ± 17.6 to CT and AM, respectively). AM impaired Ach-dependent vasodilation (Emax = 95.8 ± 1.4; 78.1 ± 1.8; 60.4 ± 2.9 and -7.4 ± 1.0 for CT, 0.01, 0,1 and 1 μmol/L AM, respectively) through reduction of calcium influx and NO availability and TLR4 antagonism in a concentration-dependent manner. AM or TLR4 gene deletion significantly reduced NO production (Fluorescence = 9503 ± 871.7, 2561 ± 282, 4771 ± 728 and 1029 ± 103 to CT, AM, TLR4^-/- and AM + TLR4^-/-, respectively) by an increase in nNOS^ser852 and reduction in eNOS^ser1177 phosphorylation in endothelial cells.

CONCLUSIONS AND IMPLICATIONS

Our data show that amitriptyline impaired vascular function through two different mechanisms: blockade of TLR4 in endothelial cells and consequent decrease in NO production and calcium influx reduction in smooth muscle and endothelial cells. We also suggest, for the first time, nNOS activity reduction by AM in non-neuronal cells.

MyD88: At the heart of inflammatory signaling and cardiovascular disease

Cardiovascular disease is a leading cause of death worldwide and is associated with systemic inflammation. In depth study of the cell-specific signaling mechanisms mediating the inflammatory response is vital to improving anti-inflammatory therapies that reduce mortality and morbidity. Cellular damage in the cardiovascular system results in the release of damage associated molecular patterns (DAMPs), also known as "alarmins," which activate myeloid cells through the adaptor protein myeloid differentiation primary response 88 (MyD88). MyD88 is broadly expressed in most cell types of the immune and cardiovascular systems, and its role often differs in a cardiovascular disease context and cell specific manner. Herein we review what is known about MyD88 in the setting of a variety of cardiovascular diseases, discussing cell specific functions and the relative contributions of MyD88-dependent vs. independent alarmin triggered inflammatory signaling. The widespread involvement of these pathways in cardiovascular disease, and their largely unexplored complexity, sets the stage for future in depth mechanistic studies that may place MyD88 in both immune and non-immune cell types as an attractive target for therapeutic intervention in cardiovascular disease.

Amitriptyline blocks innate immune responses mediated by TLR4 & IL1R: preclinical and clinical evidence in OA and gout

Background and Purpose

Osteoarthritis, a major cause of disability in developed countries does not have effective treatment. Activation of TLR4 and innate immune response factors contribute to osteoarthritis progressive cartilage degradation. There are no clinically available TLR4 inhibitors. Interestingly, the antidepressant amitriptyline could block this receptor. Thus, we evaluated amitriptyline anti‐TLR4 effects on human osteoarthritis chondrocytes in order to repurpose it as an inhibitor of innate immune response in joint inflammatory pathologies.

Experimental Approach

Using in silico docking analysis, RT‐PCR, siRNA, elisa, proteomics and clinical data mining of drug consumption, we explored the clinical relevance of amitriptyline blockade of TLR4‐mediated innate immune responses in human osteoarthritis chondrocytes.

Key Results

Amitriptyline bound TLR4 but not IL‐1 receptor. Interestingly, amitriptyline binding to TLR4 inhibited TLR4‐ and IL‐1 receptor‐mediated innate immune responses in human osteoarthritis chondrocytes, synoviocytes and osteoblasts cells. Amitriptyline reduced basal innate immune responses and promoted anabolic effects in human osteoarthritis chondrocytes. Supporting its anti‐innate immune response effects, amitriptyline down‐regulated basal and induced expression of NLRP3, an inflammasome member from IL‐1 receptor signalling linked to osteoarthritis and gout pathologies. Accordingly, mining of dissociated and aggregated drug consumption data from 107,172 elderly patients (>65 years) revealed that amitriptyline consumption was significantly associated with lower colchicine consumption associated with inflammatory gout flare treatment.

Conclusion and Implications

Amitriptyline blocks TLR4‐, IL‐1 receptor and NLRP3‐dependent innate immune responses. This together with clinical data amitriptyline could be repurposed for systemic or local innate immune response management in diverse joint inflammatory pathologies.

Examination and characterisation of the effect of amitriptyline therapy for chronic neuropathic pain on neuropeptide and proteomic constituents of human cerebrospinal fluid

INTRODUCTION

Amitriptyline is prescribed to reduce the intensity of chronic neuropathic pain. There is a paucity of validated in vivo evidence in humans regarding amitriptyline's mechanism of action. We examined the effect of amitriptyline therapy on cerebrospinal fluid (CSF) neuropeptides and proteome in patients with chronic neuropathic pain to identify potential mechanisms of action of amitriptyline.

METHODS

Patients with lumbar radicular neuropathic pain were selected for inclusion with clinical and radiological signs and a >50% reduction in pain in response to a selective nerve root block. Baseline (pre-treatment) and 8-week (post-treatment) pain scores with demographics were recorded. CSF samples were taken at baseline (pre-treatment) and 8 weeks after amitriptyline treatment (post-treatment). Proteome analysis was performed using mass spectrometry and secreted cytokines, chemokines and neurotrophins were measured by enzyme-linked immunosorbent assay (ELISA).

RESULTS

A total of 9/16 patients experienced a >30% reduction in pain after treatment with amitriptyline and GO analysis demonstrated that the greatest modulatory effect was on immune system processes. KEGG analysis also identified a reduction in PI3K-Akt and MAPK signalling pathways in responders but not in non-responders. There was also a significant decrease in the chemokine eotaxin-1 (p ​= ​0.02) and a significant increase in the neurotrophin VEGF-A (p ​= ​0.04) in responders.

CONCLUSION

The CSF secretome and proteome was modulated in responders to amitriptyline verifying many pre-clinical and in vitro models. The predominant features were immunomodulation with a reduction in pro-inflammatory pathways of neuronal-glia communications and evidence of a neurotrophic effect.

Targeting Toll like Receptors in Cancer: Role of TLR Natural and Synthetic Modulators

Background:

Toll like receptors (TLRs) are a group of transmembrane receptors belonging to the broad class pattern recognition receptors (PRR), involved in recognition of Pathogen Associated Molecular Patterns (PAMPs) thereby inducing an immune response. Apart from these exogenous PAMPs, numerous endogenous PAMPs are also ligands for various TLRs thereby activating the TLR dependent immune response, subsequently leading to the onset of an inflammatory response. Prolonged activation of TLR by these endogenous PAMPs leads to chronic inflammatory insults to the body and which in turn alters the proliferative patterns of the cells, which ultimately leads to the development of cancer.

Objectives:

The present review aims to provide a detailed outline of the differential roles of various TLRs in cancer and the possible use of them as a therapeutic target.

Methods:

Data were collected from PubMed/Sciencedirect/Web of Science database and sorted; the latest literature on TLRs was incorporated in the review.

Results:

Among the different TLRs, few are reported to be anti-neoplastic, which controls the cell growth and multiplication in response to the endogenous signals. On the contrary, numerous studies have reported the procarcinogenic potentials of TLRs. Hence, TLRs have emerged as a potential target for the prevention and treatment of various types of cancers. Several molecules, such as monoclonal antibodies, small molecule inhibitors and natural products have shown promising anticancer potential by effectively modulating the TLR signalling.

Conclusion:

Toll-like receptors play vital roles in the process of carcinogenesis, hence TLR targeting is a promising approach for cancer prevention.

Molecular Biology of Opioid Analgesia and Its Clinical Considerations

Understanding the molecular biology of opioid analgesia is essential for its proper implementation and mechanistic approach to its modulation in order to maximize analgesia and minimize undesired effects. By appreciating the molecular mechanisms intrinsic to opioid analgesia, one can manipulate a molecular target to augment or diminish a specific effect using adjuvant drugs, select an appropriate opioid for opioid rotation or define a molecular target for new opioid drug development. In this review, we present the cellular and molecular mechanisms of opioid analgesia and that of the associated phenomena of tolerance, dependence, and hyperalgesia. The specific mechanisms highlighted are those that presently can be clinically addressed.

Amitriptyline Reduces Sepsis-Induced Brain Damage Through TrkA Signaling Pathway

Sepsis can induce acute and chronic changes in the central nervous system termed sepsis-associated encephalopathy (SAE). Not only cognitive deficits but also anxiety, depression, and post-traumatic stress disorder are common in severe sepsis survivors. In this study, we demonstrated that amitriptyline, a classic tricyclic antidepressant, reduced sepsis-induced brain damage through the tropomyosin receptor kinase A (TrkA) signaling pathway. Amitriptyline ameliorated neuronal loss assessed by Nissl staining in a mouse cecal ligation and puncture (CLP)-induced sepsis model. Furthermore, amitriptyline reduced early gliosis assessed by immunofluorescence and late cognitive deficits assessed by the Morris water maze (MWM) test. Moreover, amitriptyline treatment attenuated oxidative stress indicated by less superoxide dismutase (SOD) and catalase (CAT) activity consumption and malondialdehyde (MDA) accumulation. Interestingly, those protective effects of amitriptyline could be abolished by GW441756, a TrkA signaling pathway inhibitor. Immunoblot directly showed that TrkA signaling pathway-associated proteins, such as Akt and GSK3β, were involved in the neuroprotective effects of amitriptyline. Thus, amitriptyline appears to be an encouraging candidate to treat cognitive deficits and depression after severe sepsis.

Neuroimmune mechanisms of pain: Basic science and potential therapeutic modulators

This narrative review aims to describe the role of peripheral and central immune responses to tissue and nerve damage in animal models, and to discuss the use of immunomodulatory agents in clinical practice and their perioperative implications. Animal models of pain have demonstrated that nerve injury activates immune signalling pathways that drive aberrant sensory processes, resulting in neuropathic and chronic pain. This response involves the innate immune system. T lymphocytes are also recruited. Glial cells surrounding the damaged nerves release cytokines and proinflammatory mediators that activate resident immune cells and recruit circulatory immune cells. Toll-like receptors on the glial cells play a crucial role in the pathogenesis of chronic pain. Animal models indicate an immune mechanism of neuropathic pain. Analgesic drugs and anaesthetic agents have varied effects on the neuroimmune interface. Evidence of a neuroimmune interaction is mainly from animal studies. Human studies are required to evaluate the clinical implications of this neuroimmune interaction.

An investigation into the modulation of T cell phenotypes by amitriptyline and nortriptyline

Amitriptyline is prescribed for treating the symptoms of neuroinflammatory disorders including neuropathic pain and fibromyalgia. As amitriptyline has evidence of modulating the neuroimmune interface; the effects of amitriptyline treatment on T-cell phenotype and function were examined in vitro. Peripheral blood mononuclear cells(PBMCs) were isolated and treated with amitriptyline, nortriptyline and a combination of both drugs. Toxicity for T-cells was assessed by Annexin V/Propidium Iodide staining. Activation status and cytokine expression by T-cells post treatment was assessed by flow cytometry. The levels of secreted cytokines, chemokines and neurotrophins were measured by ELISA in the supernatants. There was no significant increase in T-cell death following 24 or 48 h compared to controls. There were significantly lower frequencies of CD8⁺ T-cells after treatment with amitriptyline, nortriptyline and a combination of both compared to a Vehicle Control(VC)(p<0.001). The frequencies of naive CD8⁺CD45RA⁺ cells were significantly lower after amitriptyline, nortriptyline and a combination of both (p<0001). The frequencies of CD27⁺CD4⁺(p<0.05) and CD27⁺CD8⁺(p<0.01) T-cells were also significantly lower following combination drug treatment. Significantly lower frequencies of IFN-γ-producing CD8⁺ T-cells were observed with all treatment combinations(p<0.05) and frequencies of IL-17-producing CD4⁺ and CD8⁺ T-cells were significantly lower following amitriptyline treatment (p<0.05). Frequencies of Natural Killer T-cells were significantly higher following treatment with nortriptyline (p<0.05). Significantly higher levels of IL-16 (p<0.001) and lower levels of TNF-β (p<0.05) were observed in supernatants. This data indicates that both amitriptyline and nortriptyline modulate the phenotype and function of T-cells and this may have clinical relevance in the pathologies of its off-label applications.

Irinotecan: 25 years of cancer treatment

Twenty-five years ago, the cytotoxic drug irinotecan (IRT) was first approved in Japan for the treatment of cancer. For more than two decades, the IRT prodrug has largely contributed to the treatment of solid tumors worldwide. Nowadays, this camptothecin derivative targeting topoisomerase 1 remains largely used in combination regimen, like FOLFIRI and FOLFIRINOX, to treat metastatic or advanced solid tumors, such as colon, gastric and pancreatic cancers and others. This review highlights recent discoveries in the field of IRT and its derivatives, including analogues of the active metabolite SN38 (such as FL118), the recently approved liposomal form Nal-IRI and SN38-based immuno-conjugates currently in development (such as sacituzumab govitecan). New information about the IRT mechanism of action are presented, including the discovery of a new protein target, the single-stranded DNA-binding protein FUBP1. Significant progress has been made also to better understand and manage the main limiting toxicities of IRT, chiefly neutropenia and diarrhea. The role of drug-induced inflammation and dysbiosis is underlined and strategies to limit the intestinal toxicity of IRT are discussed (use of β-glucuronidase inhibitors, plant extracts, probiotics). The detailed knowledge of the metabolism of IRT has enabled the identification of potential biomarkers to guide patient selection and to limit drug-induced toxicities, but no robust IRT-specific therapeutic biomarker has been approved yet. IRT is a versatile chemotherapeutic agent which combines well with a variety of anticancer drugs. It offers a large range of drug combinations with cytotoxic agents, targeted products and immuno-active biotherapeutics, to treat a variety of advanced solid carcinoma, sarcoma and cancers with progressive central nervous system diseases. A quarter of century after its first launch, IRT remains an essential anticancer drug, largely prescribed, useful to many patients and scientifically inspiring.

Structural Modification of the Antidepressant Mianserin Suggests That Its Anti-inflammatory Activity May Be Independent of 5-Hydroxytryptamine Receptors

Antidepressants are increasingly recognized to have anti-inflammatory properties in addition to their ability to treat major depressive disorders. To explore if engagement of 5-hydroxytryptamine (5-HT) receptors was required for the anti-inflammatory effect of the tetracyclic antidepressant mianserin, a series of structural derivatives were generated with the aim of reducing 5-HT receptor binding. Primary human peripheral blood mononuclear cells were used to screen for anti-inflammatory activity. The lead compound demonstrated a significant loss in 5-HT receptor binding, as assessed by non-selective 5-HT binding of radiolabelled serotonin in rat cerebral cortex. However, it retained the ability to inhibit endosomal toll-like receptor 8 signaling in primary human macrophages and spontaneous cytokine production from human rheumatoid synovial tissue equivalent to that previously observed for mianserin. These data demonstrate that the anti-inflammatory mechanism of mianserin may be independent of 5-HT receptor activity. This research offers new insights into the mechanism and structural requirements for the anti-inflammatory action of mianserin.

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.

Differential effect of morphine on gastrointestinal transit, colonic contractions and nerve-evoked relaxations in Toll-Like Receptor deficient mice

Toll-like receptors (TLRs) are expressed in enteric neurons, glia, gastrointestinal (GI) smooth muscle and mucosa, yet their functional roles in the GI tract are not fully understood. TLRs have been linked to many of the undesirable central effects of chronic opioid administration including hyperalgesia and dependence via activation of central microglia. Opioid-induced bowel dysfunction (OIBD) remains a primary reason for the reduction or withdrawal of opioid analgesics. Morphine-induced inhibition of colonic motility was assessed in vivo by GI transit studies and in vitro using isolated colons from wildtype (WT) and TLR deficient mice. Morphine slowed movement of ingested content in WT but this retardation effect was attenuated in TLR4^−/− and TLR2/4^−/−. In isolated colons, morphine reduced amplitude and frequency colonic migrating motor contractions in both WT and TLR2/4^−/−. Electrical field stimulation elicited distal colon relaxation that was potentiated by morphine in WT but not in TLR2/4^−/−. Inhibitory junction potentials were of similar amplitude and kinetics in WT and TLR2/4^−/− distal colon and not altered by morphine. Enteric nerve density and proportion of nitrergic nerves were similar in WT and TLR2/4^−/− distal colon. These data suggest an involvement of TLRs in opioid pharmacodynamics and thus a potential interventional target for OIBD.

Lipopolysaccharide (LPS)-mediated priming of toll-like receptor 4 enhances oxidant-induced prostaglandin E2 biosynthesis in primary murine macrophages

Agonists and pseudo-agonists for toll-like receptor 4 (TLR4) are common in our environment. Thus, human exposure to these agents may result in "priming or sensitization" of TLR4. A body of evidence suggests that LPS-mediated sensitization of TLR4 can increase the magnitude of responses to exogenous agents in multiple tissues. We have previously shown that reactive oxygen and nitrogen species (RONS) stimulate TLR4. There is no evidence that LPS-primed TLR4 can influence the magnitude of responses to oxidants from either endogenous or exogenous sources. In the present study, we directly tested the hypothesis that LPS-primed TLR4 will sensitize primary murine peritoneal macrophages (pM) to oxidant-mediated prostaglandin E2 (PGE₂) production. We used potassium peroxychromate (PPC) and potassium peroxynitrite (PPN) as direct in vitro sources of exogenous RONS. Our results showed that a direct treatment with PPC or PPN alone as sources of exogenous oxidants had a limited effect on PGE₂ biosynthesis. In contrast, pM sensitized by prior incubation with LPS-EK, a TLR4-specific agonist, followed by oxidant stimulation exhibited increased transcriptional and translational expression of cyclooxygenase-2 (COX-2) with enhanced PGE₂ biosynthesis/production only in pM derived from TLR4-WT mice but not in TLR4-KO mice. Thus, we have shown a critical role for LPS-primed TLR4 in oxidant-induced inflammatory phenotypes that have the potential to initiate, propagate and maintain many human diseases.

Targets for Drug Therapy for Autism Spectrum Disorder: Challenges and Future Directions

Autism spectrum disorder (ASD) is a neurodevelopmental disorder characterized by persistent deficits in social communication and interaction and restricted, repetitive patterns of behavior, interests, and activities. Various factors are involved in the etiopathogenesis of ASD, including genetic factors, environmental toxins and stressors, impaired immune responses, mitochondrial dysfunction, and neuroinflammation. The heterogeneity in the phenotype among ASD patients and the complex etiology of the condition have long impeded the advancement of the development of pharmacological therapies. In the recent years, the integration of findings from mouse models to human genetics resulted in considerable progress toward the understanding of ASD pathophysiology. Currently, strategies to treat core symptoms of ASD are directed to correct synaptic dysfunctions, abnormalities in central oxytocin, vasopressin, and serotonin neurotransmission, and neuroinflammation. Here, we present a survey of the studies that have suggested molecular targets for drug development for ASD and the state-of-the-art of medicinal chemistry efforts in related areas.

NLRP3 Inflammasome Contributes to Lipopolysaccharide-induced Depressive-Like Behaviors via Indoleamine 2,3-dioxygenase Induction

BACKGROUND

Inflammation may play a significant role in the pathogenesis of depression, although the molecular target for the treatment of inflammation-mediated depressive symptoms remains to be elucidated. Recent studies have implicated the NLRP3 inflammasome in various psychiatric disorders, including depression. However, the underlying mechanism by which NLRP3 inflammasome activation mediates the progression of depressive-like behaviors remains poorly understood.

METHODS

We examined whether NLRP3 deficiency influenced depressive-like behaviors and cerebral inflammation following systemic administration of lipopolysaccharide in mice. To further assess the contribution of the NLRP3 inflammasome to the progression of depression, we evaluated the effects of NLRP3 signaling on levels of indoleamine 2,3-dioxygenase.

RESULTS

Nlrp3-deficient mice exhibited significant attenuation of depressive-like behaviors and cerebral caspase-1 activation in a lipopolysaccharide-induced model of depression. Treatment with the antidepressant amitriptyline failed to block NLRP3-dependent activation of caspase-1, but inhibited lipopolysaccharide-promoted production of interleukin-1β mRNA via suppressing NF-κB signaling in mouse mixed glial cultures. Interestingly, lipopolysaccharide administration produced NLRP3-dependent increases in indoleamine 2,3-dioxygenase expression and activity of mouse brain. Furthermore, inflammasome-activating stimulations, but not treatment with the inflammasome product interleukin-1β, triggered indoleamine 2,3-dioxygenase mRNA induction in mixed glial cells.

CONCLUSIONS

Our data indicate that the NLRP3 inflammasome is significantly implicated in the progression of systemic inflammation-induced depression. NLRP3-dependent caspase-1 activation produced significant increases in indoleamine 2,3-dioxygenase levels, which may play a significant role in lipopolysaccharide-induced depression. Collectively, our findings suggest that indoleamine 2,3-dioxygenase is a potential downstream mediator of the NLRP3 inflammasome in inflammation-mediated depressive-like behaviors.

Novel Molecular Strategies and Targets for Opioid Drug Discovery for the Treatment of Chronic Pain

Opioid drugs like morphine and fentanyl are the gold standard for treating moderate to severe acute and chronic pain. However, opioid drug use can be limited by serious side effects, including constipation, tolerance, respiratory suppression, and addiction. For more than 100 years, we have tried to develop opioids that decrease or eliminate these liabilities, with little success. Recent advances in understanding opioid receptor signal transduction have suggested new possibilities to activate the opioid receptors to cause analgesia, while reducing or eliminating unwanted side effects. These new approaches include designing functionally selective ligands, which activate desired signaling cascades while avoiding signaling cascades that are thought to provoke side effects. It may also be possible to directly modulate downstream signaling through the use of selective activators and inhibitors. Separate from downstream signal transduction, it has also been found that when the opioid system is stimulated, various negative feedback systems are upregulated to compensate, which can drive side effects. This has led to the development of multi-functional molecules that simultaneously activate the opioid receptor while blocking various negative feedback receptor systems including cholecystokinin and neurokinin-1. Other novel approaches include targeting heterodimers of the opioid and other receptor systems which may drive side effects, and making endogenous opioid peptides druggable, which may also reduce opioid mediated side effects. Taken together, these advances in our molecular understanding provide a path forward to break the barrier in producing an opioid with reduced or eliminated side effects, especially addiction, which may provide relief for millions of patients.

Activation of μ-opioid receptor and Toll-like receptor 4 by plasma from morphine-treated mice

In this study, we quantified the ability of opioids present in biological samples to activate the μ-opioid receptor and TLR4 using cell-based assays. Each assay was standardised, in the presence of plasma, using morphine, its μ receptor-active metabolite morphine-6 glucuronide (M6G) and its μ receptor-inactive, but TLR4-active metabolite morphine-3 glucuronide (M3G). Specificity was verified using antagonists. Morphine- and M6G-spiked plasma samples exhibited μ receptor activation, which M3G-spiked plasma lacked. In contrast, M3G showed moderate but consistent activation of TLR-4. Plasma samples were collected at a number of time points from mice administered morphine (1 or 10mg/kg every 12h for 3days) or saline. Morphine administration led to intermittent μ receptor activation, reversed by μ receptor antagonists, and to TRL4 activation at time points where M3G is measured in plasma. Interestingly, this protocol of morphine administration also led to TLR4-independent NF-κB activation, at time points where M3G was not detected, presumably via elevation of circulating cytokines including, but not limited to, TNFα. Circulating TNFα was increased after three days of morphine administration, and TNFα mRNA elevated in the spleen of morphine-treated mice.

The Effects of the Toll-Like Receptor 4 Antagonist, Ibudilast, on Sevoflurane's Minimum Alveolar Concentration and the Delayed Remifentanil-Induced Increase in the Minimum Alveolar Concentration in Rats

BACKGROUND

Ultralow doses of naloxone, an opioid and toll-like receptor 4 antagonist, blocked remifentanil-induced hyperalgesia and the associated increase in the minimum alveolar concentration (MAC), but not tolerance. The aim was to determine the effects of the toll-like receptor 4 antagonist, ibudilast, on the MAC in the rat and how it might prevent the effects of remifentanil.

METHODS

Male Wistar rats were randomly allocated to 5 treatment groups (n = 7 per group): 10 mg/kg ibudilast intraperitoneally, 240 µg/kg/h remifentanil IV, ibudilast plus remifentanil, remifentanil plus naloxone IV, or saline. The sevoflurane MAC was determined 3 times in every rat and every day (days 0, 2, and 4): baseline (MAC-A) and 2 further determinations were made after treatments, 1.5 hours apart (MAC-B and MAC-C).

RESULTS

A reduction in baseline MAC was produced on day 0 by ibudilast, remifentanil, remifentanil plus ibudilast, remifentanil plus naloxone (P < 0.01), but not saline. Similar effects were found on days 2 and 4. A tolerance to remifentanil was found on days 0, 2, and 4, which neither ibudilast nor naloxone prevented. The MAC increase produced by remifentanil on day 4 (P = 0.001) was prevented by either ibudilast or naloxone.

CONCLUSIONS

Ibudilast, besides reducing the MAC, prevented the delayed increase in baseline MAC produced by remifentanil but not the increase in MAC caused by tolerance to remifentanil.

The narcotic bowel syndrome: a recent update

OBJECTIVES

The paradoxical development of chronic abdominal pain is an underrecognized side effect of opioid use. Narcotic bowel syndrome (NBS), occurring in a small proportion of chronic opioid users, consists of chronic or intermittent abdominal pain, which often increases in severity despite continued or escalating dosages of opioids prescribed to relieve pain.

METHODS

A PubMed search was conducted using terms such as "narcotic bowel syndrome" and "opioid hyperalgesia" through January 2014.

RESULTS

Abdominal pain is the defining symptom of NBS and is thought to be mediated by central nervous system dysfunction; it should be distinguished from the peripheral side effects of opioids, such as nausea, bloating, intermittent vomiting, abdominal distension, and constipation. This latter cluster of symptoms is called opioid bowel dysfunction, although it may co-occur with NBS. Hypothesized mechanisms of the central effects of opioids on nociception in NBS include spinal cord inflammation and dysfunction in opioid receptor activity and related neuroanatomical substrates. With continued use, ∼6% of patients taking narcotics chronically will develop NBS, with profound consequences in terms of daily function. The primary management paradigm for NBS is a structured opioid withdrawal program accompanied by centrally acting adjunctive therapy comprising antidepressants, benzodiazepines, and clonidine to target pain, anxiety, and depression, and prevent withdrawal effects, in addition to peripherally acting agents such as laxatives (e.g., osmotic laxatives and chloride channel activators) to control transient constipation. Such structured withdrawal programs have been prospectively evaluated in small clinical trials and have met with considerable success in the short term.

CONCLUSIONS

Because rates of NBS are likely to rise, integrated intensive pharmacotherapy and psychosocial interventions are needed to help patients with NBS go off and stay off opioids. These programs will likely also reduce comorbid psychopathology and lead to adequate pain control and improved quality of life.

Opioid adjuvant strategy: improving opioid effectiveness

Opioid analgesics continue to be the mainstay of pharmacologic treatment of moderate to severe pain. Many patients, particularly those suffering from chronic pain, require chronic high-dose analgesic therapy. Achieving clinical efficacy and tolerability of such treatment regimens is hampered by the appearance of opioid-induced side effects such as tolerance, hyperalgesia and withdrawal syndrome. Among the therapeutic options to improve the opioid effectiveness, this current review focuses on strategies combining opioids to other drugs that can modulate opioid-mediated effects. We will discuss about experimental evidences reported for several potential opioid adjuvants, including N-methyl-d-aspartate receptor antagonists, 5-HT7 agonists, sigma-1 antagonists, I2-R ligands, cholecystokinin antagonists, neuropeptide FF-R antagonists and toll-like receptor 4 antagonists.

Centrally Mediated Disorders of Gastrointestinal Pain

Centrally Mediated Abdominal Pain Syndrome (CAPS), formerly known as Functional Abdominal Pain Syndrome, can be distinguished from other functional GI disorders by its strong central component and relative independence from motility disturbances. CAPS is a result of central sensitization with disinhibition of pain signals rather than increased peripheral afferent excitability. A newly described condition, Narcotic Bowel Syndrome (NBS)/Opioid-Induced GI Hyperalgesia, is characterized by the paradoxical development of or increases in abdominal pain associated with continuous or increasing dosages of opioids. Patients only have relief when opioids are withdrawn. We define both conditions in the context of epidemiology, pathophysiology, clinical evaluation and treatment, emphasizing the importance of a physician-patient relationship in all aspects of care.

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.

Antidepressants normalize elevated Toll-like receptor profile in major depressive disorder

RATIONALE

Abnormalities in Toll-like receptor (TLR) expression in depression have been inferred in part from observed increases in TLR4 levels in peripheral blood mononuclear cells (PBMCs) and postmortem brains of depressed and suicidal patients. Our previous study found differences in the TLR expression in PBMCs between healthy controls and patients with major depressive disorder. Normalization of increased TLR4 in PBMCs by cognitive behavior psychotherapy has been reported. However, the effects of antidepressants remain unknown.

OBJECTIVES

Changes in TLR1-9 expression levels of PBMCs were examined in 56 patients with MDD. The 17-item Hamilton Depression Rating Scale (HAMD-17) and mRNA expression levels of TLRs were assessed in parallel with a housekeeping gene using qRT-PCR before and after treatment with antidepressants.

RESULTS

TLR3, TLR4, TLR5, TLR7, TLR8, and TLR9 were expressed at elevated levels in patients with MDD and were significantly decreased by treatment with antidepressants for 4 weeks. Antidepressant treatment completely normalized TLR3, TLR5, TLR7, TLR8, and TLR9 levels, whereas TLR1, TLR2, TLR4, and TLR6 were decreased to below normal levels. A subgroup analysis found that only TLR3 was significantly higher at baseline in the nonremission group. In addition, a multiple linear regression analysis revealed that only low TLR3 before treatment predicted improvement in HAMD-17 scores.

CONCLUSIONS

These findings suggest that antidepressant treatment exerts anti-inflammatory effects in patients with MDD and identify TLR profiles as a predictor of response to antidepressant therapy. Further studies investigating the effects of manipulating individual TLRs on depression are needed to fully elucidate the underlying mechanism.

Select steroid hormone glucuronide metabolites can cause toll-like receptor 4 activation and enhanced pain

We have recently shown that several classes of glucuronide metabolites, including the morphine metabolite morphine-3-glucuronide and the ethanol metabolite ethyl glucuronide, cause toll like receptor 4 (TLR4)-dependent signaling in vitro and enhanced pain in vivo. Steroid hormones, including estrogens and corticosterone, are also metabolized through glucuronidation. Here we demonstrate that in silico docking predicts that corticosterone, corticosterone-21-glucuronide, estradiol, estradiol-3-glucuronide and estradiol-17-glucuronide all dock with the MD-2 component of the TLR4 receptor complex. In addition to each docking with MD-2, the docking of each was altered by pre-docking with (+)-naloxone, a TLR4 signaling inhibitor. As agonist versus antagonist activity cannot be determined from these in silico interactions, an in vitro study was undertaken to clarify which of these compounds can act in an agonist fashion. Studies using a cell line transfected with TLR4, necessary co-signaling molecules, and a reporter gene revealed that only estradiol-3-glucuronide and estradiol-17-glucuronide increased reporter gene product, indicative of TLR4 agonism. Finally, in in vivo studies, each of the 5 drugs was injected intrathecally at equimolar doses. In keeping with the in vitro results, only estradiol-3-glucuronide and estradiol-17-glucuronide caused enhanced pain. For both compounds, pain enhancement was blocked by the TLR4 antagonist lipopolysaccharide from Rhodobacter sphaeroides, evidence for the involvement in TLR4 in the resultant pain enhancement. These findings have implications for several chronic pain conditions, including migraine and temporomandibular joint disorder, in which pain episodes are more likely in cycling females when estradiol is decreasing and estradiol metabolites are at their highest.

Narcotic bowel syndrome and opioid-induced constipation

Prescription opioid use for chronic non-cancer pain has reached epidemic levels in the USA. With this increased use is the recognition of serious opioid-related gastrointestinal complications such as narcotic bowel syndrome (NBS) and opioid-induced constipation (OIC). NBS consists of a paradoxical worsening of abdominal pain with escalating doses of opioids and is likely mediated by the central nervous system. Therapy requires an intensive multidisciplinary approach to detoxification. OIC is the most common gastrointestinal side effect of opioids. Several novel therapeutics are available to treat OIC that fails to respond to laxative therapy. This review will summarize recent findings on the pathophysiology and treatment approaches to NBS and OIC with a focus on controversies about diagnosis and intervention.

Diagnosis and treatment of narcotic bowel syndrome

With increased prescription of opioids has come increased recognition of adverse consequences, including narcotic bowel syndrome (NBS). Characterized by incompletely controlled abdominal pain despite continued or increasing doses of opioids, NBS is estimated to occur in 4.2-6.4% of patients chronically taking opioids. Patients with NBS have a high degree of comorbid psychiatric illness, catastrophizing and disability; comorbid substance abuse must also be considered among this population. NBS should be distinguished from opioid-induced bowel disorder, which results from the effects of opioids on gastrointestinal motility and secretion. By contrast, the mechanisms of NBS are probably centrally mediated and include glial cell activation, bimodal opioid modulation in the dorsal horn, descending facilitation of pain and the glutaminergic system. Few treatments have been rigorously studied. A trial of opioid detoxification resulted in complete detoxification for the vast majority of patients with reduction in pain symptoms; however, despite improvement in pain, approximately half of patients returned to opioid use within 3 months. Improved strategies are needed to identify patients who will respond to detoxification and remain off opioids. Comorbid psychiatric and substance abuse disorders are barriers to durable response after detoxification and should be actively sought out and treated accordingly. An effective patient-physician relationship is essential.

Sinomenine decreases MyD88 expression and improves inflammation-induced joint damage progression and symptoms in rat adjuvant-induced arthritis

Sinomenine (SIN) is the active principle of the Chinese medical plant Sinomenium acutum which is widely used for the treatment of rheumatoid arthritis (RA) in China. Recently, several groups indicated that myeloid differentiation primary response protein 88 (MyD88) might be associated with disease progression of RA. Here, we observed the effect of SIN on MyD88 expression and showed its therapeutic role in RA. First, immunohistochemical staining in clinical specimens showed that MyD88 was mainly located in characteristic pathological structures of RA synovial tissues. Second, we found that MyD88 was overexpressed in the synovial tissues of the rats with adjuvant-induced arthritis (AIA). Treatment with SIN markedly decreased the expression of MyD88 in AIA rats. Finally, we provided evidences that SIN suppressed inflammation response and inflammation-induced joint destructive progression and arthritis symptoms in AIA rats. Therefore, SIN is an effective therapeutic agent for RA. Targeting MyD88 signaling may provide new methods for the treatment of RA.

Pathological pain and the neuroimmune interface

Reciprocal signalling between immunocompetent cells in the central nervous system (CNS) has emerged as a key phenomenon underpinning pathological and chronic pain mechanisms. Neuronal excitability can be powerfully enhanced both by classical neurotransmitters derived from neurons, and by immune mediators released from CNS-resident microglia and astrocytes, and from infiltrating cells such as T cells. In this Review, we discuss the current understanding of the contribution of central immune mechanisms to pathological pain, and how the heterogeneous immune functions of different cells in the CNS could be harnessed to develop new therapeutics for pain control. Given the prevalence of chronic pain and the incomplete efficacy of current drugs--which focus on suppressing aberrant neuronal activity--new strategies to manipulate neuroimmune pain transmission hold considerable promise.

Atractylenolide-I sensitizes human ovarian cancer cells to paclitaxel by blocking activation of TLR4/MyD88-dependent pathway

Paclitaxel, a known TLR4 ligand, leads to activation of TLR4/MyD88-dependent pathway that mediates chemoresistance and tumor progression in epithelial ovarian carcinoma (EOC). Atractylenolide-I (AO-I), a novel TLR4-antagonizing agent, inhibits TLR4 signaling by interfering with the binding of LPS or paclitaxel to membrane TLR4 of human leukocytes. In this study, AO-I was found to attenuate paclitaxel-induced protein expression of IL-6, VEGF and survivin, and to enhance early apoptosis and growth inhibition in MyD88⁺ EOC cells; AO-I was shown to fit into the hydrophobic pocket of human MD-2 and to partially overlap with the binding site of paclitaxel by docking simulations, suggesting that AO-I may block the MD-2-mediated TLR4/MyD88-dependent paclitaxel signaling in MyD88⁺ EOC cells. Therefore, AO-I could significantly sensitize the response of MyD88⁺ EOC cells to paclitaxel by blocking MD-2-mediated TLR4/MyD88 signaling, and that AO-I-paclitaxel combination could be a promising strategy for the treatment of EOC with a functional TLR4/MyD88/NF-κB pathway.

AChE and RACK1 promote the anti-inflammatory properties of fluoxetine

Selective serotonin reuptake inhibitors (SSRIs) show anti-inflammatory effects, suggesting a possible interaction with both Toll-like-receptor 4 (TLR4) responses and cholinergic signaling through as yet unclear molecular mechanism(s). Our results of structural modeling support the concept that the antidepressant fluoxetine physically interacts with the TLR4-myeloid differentiation factor-2 complex at the same site as bacterial lipopolysaccharide (LPS). We also demonstrate reduced LPS-induced pro-inflammatory interleukin-6 and tumor necrosis factor alpha in human peripheral blood mononuclear cells preincubated with fluoxetine. Furthermore, we show that fluoxetine intercepts the LPS-induced decreases in intracellular acetylcholinesterase (AChE-S) and that AChE-S interacts with the nuclear factor kappa B (NFκB)-activating intracellular receptor for activated C kinase 1 (RACK1). This interaction may prevent NFκB activation by residual RACK1 and its interacting protein kinase PKCβII. Our findings attribute the anti-inflammatory properties of SSRI to surface membrane interference with leukocyte TLR4 activation accompanied by intracellular limitation of pathogen-inducible changes in AChE-S, RACK1, and PKCβII.

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.

Intrathecal injection of adenosine 2A receptor agonists reversed neuropathic allodynia through protein kinase (PK)A/PKC signaling

A single intrathecal dose of adenosine 2A receptor (A2AR) agonist was previously reported to produce a multi-week reversal of allodynia in a chronic constriction injury (CCI) model of neuropathic pain. We aimed to determine if this long-term reversal was induced by A2AR agonism versus more generalized across adenosine receptor subtypes, and begin to explore the intracellular signaling cascades involved. In addition, we sought to identify whether the enduring effect could be extended to other models of neuropathic pain. We tested an A1R and A2BR agonist in CCI and found the same long duration effect with A2BR but not A1R agonism. An A2AR agonist (ATL313) produced a significant long-duration reversal of mechanical allodynia induced by long established CCI (administered 6 weeks after surgery), spinal nerve ligation and sciatic inflammatory neuropathy. To determine if ATL313 had a direct effect on glia, ATL313 was coadministered with lipopolysaccharide to neonatal microglia and astrocytes in vitro. ATL313 significantly attenuated TNFα production in both microglia and astrocytes but had no effect on LPS induced IL-10. Protein kinase C significantly reversed the ATL313 effects on TNFα in vitro in microglia and astrocytes, while a protein kinase A inhibitor only effected microglia. Both intrathecal PKA and PKC inhibitors significantly reversed the effect of the A2AR agonist on neuropathic allodynia. Therefore, A2AR agonists administered IT remain an exciting novel target for the treatment of neuropathic pain.

Pharmacological characterization of LPS and opioid interactions at the toll-like receptor 4

BACKGROUND AND PURPOSE

Previous work in our laboratory showed opioid agents inhibit cytokine expression in astrocytes. Recently, Watkins and colleagues hypothesized that opioid agonists activate toll-like receptor 4 (TLR4) signalling, which leads to neuroinflammation. To test this hypothesis, we characterized LPS and opioid effects on TLR4 signalling in reporter cells.

EXPERIMENTAL APPROACH

NF-κB reporter cells expressing high levels of TLR4 were used to compare LPS and opioid effects on NF-κB activation, a pathway activated by TLR4 stimulation.

KEY RESULTS

LPS increased TLR4 signalling in a concentration-dependent manner and was antagonized by LPS antagonist (LPS-RS, from Rhodobacter sphaeroides). A concentration ratio analysis showed that LPS-RS was a competitive antagonist. The opioid agonists, morphine and fentanyl, produced minor activation of TLR4 signalling when given alone. When tested following LPS stimulation, opioid agonists inhibited NF-κB activation but this inhibition was not blocked by the general opioid antagonist, naloxone, nor by the selective μ opioid receptor antagonist, β-FNA. Indeed, both naloxone and β-FNA also inhibited NF-κB activation in reporter cells. Further examination of fentanyl and β-FNA effects revealed that both opioid agents inhibited LPS signalling in a non-competitive fashion.

CONCLUSIONS AND IMPLICATIONS

These results show that LPS-RS is a competitive antagonist at the TLR4 complex, and that both opioid agonists and antagonists inhibit LPS signalling in a non-competitive fashion through a non-GPCR, opioid site(s) in the TLR4 signalling pathway. If confirmed, existing opioid agents or other drug molecules more selective at this novel site may provide a new therapeutic approach to the treatment of neuroinflammation.

Blocking toll-like receptor 2 and 4 signaling during a stressor prevents stress-induced priming of neuroinflammatory responses to a subsequent immune challenge

Acute and chronic stressors sensitize or prime the neuroinflammatory response to a subsequent peripheral or central immunologic challenge. However, the neuroimmune process(es) by which stressors prime or sensitize subsequent neuroinflammatory responses remains unclear. Prior evidence suggested that toll-like receptors (TLRs) might be involved in the mediation of primed neuroinflammatory responses, but the role of TLRs during a stressor has never been directly tested. Here, a novel TLR2 and TLR4 antagonist, OxPAPC, was used to probe the contribution of TLRs in the stress sensitization phenomenon. OxPAPC has not previously been administered to the brain, and so its action in blocking TLR2 and TLR4 action in brain was first verified. Administration of OxPAPC into the CNS prior to stress prevented the stress-induced potentiation of hippocampal pro-inflammatory response to a subsequent peripheral LPS challenge occurring 24 h later. In addition, in vivo administration of OxPAPC prior to stress prevented the sensitized pro-inflammatory response from isolated microglia following administration of LPS ex vivo, further implicating microglia as a key neuroimmune substrate that mediates stress-induced sensitized neuroinflammation.

Identification of substituted pyrimido[5,4-b]indoles as selective Toll-like receptor 4 ligands

A cell-based high-throughput screen to identify small molecular weight stimulators of the innate immune system revealed substituted pyrimido[5,4-b]indoles as potent NFκB activators. The most potent hit compound selectively stimulated Toll-like receptor 4 (TLR4) in human and mouse cells. Synthetic modifications of the pyrimido[5,4-b]indole scaffold at the carboxamide, N-3, and N-5 positions revealed differential TLR4 dependent production of NFκB and type I interferon associated cytokines, IL-6 and interferon γ-induced protein 10 (IP-10) respectively. Specifically, a subset of compounds bearing phenyl and substituted phenyl carboxamides induced lower IL-6 release while maintaining higher IP-10 production, skewing toward the type I interferon pathway. Substitution at N-5 with short alkyl substituents reduced the cytotoxicity of the leading hit compound. Computational studies supported that active compounds appeared to bind primarily to MD-2 in the TLR4/MD-2 complex. These small molecules, which stimulate innate immune cells with minimal toxicity, could potentially be used as adjuvants or immune modulators.

Frank A. Beach award: programming of neuroendocrine function by early-life experience: a critical role for the immune system

Many neuropsychiatric disorders are associated with a strong dysregulation of the immune system, and several have a striking etiology in development as well. Our recent evidence using a rodent model of neonatal Escherichia coli infection has revealed novel insight into the mechanisms underlying cognitive deficits in adulthood, and suggests that the early-life immune history of an individual may be critical to understanding the relative risk of developing later-life mental health disorders in humans. A single neonatal infection programs the function of immune cells within the brain, called microglia, for the life of the rodent such that an adult immune challenge results in exaggerated cytokine production within the brain and associated cognitive deficits. I describe the important role of the immune system, notably microglia, during brain development, and discuss some of the many ways in which immune activation during early brain development can affect the later-life outcomes of neural function, immune function, and cognition.

Glucuronic acid and the ethanol metabolite ethyl-glucuronide cause toll-like receptor 4 activation and enhanced pain

We have previously observed that the non-opioid morphine metabolite, morphine-3-glucuronide, enhances pain via a toll-like receptor 4 (TLR4) dependent mechanism. The present studies were undertaken to determine whether TLR4-dependent pain enhancement generalizes to other classes of glucuronide metabolites. In silico modeling predicted that glucuronic acid alone and ethyl glucuronide, a minor but long-lasting ethanol metabolite, would dock to the same MD-2 portion of the TLR4 receptor complex previously characterized as the docking site for morphine-3-glucuronide. Glucuronic acid, ethyl glucuronide and ethanol all caused an increase in TLR4-dependent reporter protein expression in a cell line transfected with TLR4 and associated co-signaling molecules. Glucuronic acid-, ethyl glucuronide-, and ethanol-induced increases in TLR4 signaling were blocked by the TLR4 antagonists LPS-RS and (+)-naloxone. Glucuronic acid and ethyl glucuronide both caused allodynia following intrathecal injection in rats, which was blocked by intrathecal co-administration of the TLR4 antagonist LPS-RS. The finding that ethyl glucuronide can cause TLR4-dependent pain could have implications for human conditions such as hangover headache and alcohol withdrawal hyperalgesia, as well as suggesting that other classes of glucuronide metabolites could have similar effects.