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

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.

Role of meningeal mast cells in intrathecal morphine-evoked granuloma formation

BACKGROUND

Intrathecal morphine forms granulomas that arise from the adjacent arachnoid membrane. The authors propose that these inflammatory cells exit the meningeal vasculature secondary to meningeal mast cell degranulation.

METHODS

Three sets of experiments were accomplished in dogs: (1) ex vivo meningeal mast cell degranulation (histamine release was measured ex vivo from canine dura incubated with opiates); (2) in vivo cutaneous mast cell degranulation (flare areas on the dog abdomen were measured after subcutaneous opiates); and (3) in vivo granuloma pharmacology. Dogs with lumbar intrathecal catheters received infusion of intrathecal saline or intrathecal morphine. Intrathecal morphine dogs received (1) no other treatment (control); (2) twice-daily subcutaneous naltrexone; (3) intrathecal co-infusion of cromolyn; or (4) twice-daily subcutaneous cromolyn for the 24- to 28-day study course.

RESULTS

Morphine but not fentanyl evoked dural histamine release, which was blocked by cromolyn but not naloxone. Wheal/flare was produced by subcutaneous morphine, methadone, hydromorphone, but not fentanyl, and was unaffected by naltrexone but prevented by cromolyn. Granulomas occurred in all dogs receiving intrathecal morphine (15 of 15); subcutaneous naltrexone had no effect on granulomas (six of six) but was reduced by concurrent intrathecal cromolyn (zero of five) or twice-daily subcutaneous cromolyn (one of five).

CONCLUSIONS

The pharmacology of cutaneous/dural mast cell degranulation and intrathecal granulomas are comparable, not mediated by opioid receptors, and reduced by agents preventing mast cell degranulation. If an agent produces cutaneous mast cell degranulation at concentrations produced by intrathecal delivery, the agent may initiate granulomas.

Reactive microglia after taste nerve injury: comparison to nerve injury models of chronic pain

The chorda tympani (CT), which innervates taste buds on the anterior portion of the tongue, is susceptible to damage during inner ear surgeries. Injury to the CT causes a disappearance of taste buds, which is concurrent with significant microglial responses at central nerve terminals in the nucleus of the solitary tract (nTS). The resulting taste disturbances that can occur may persist for months or years, long after the nerve and taste buds have regenerated. These persistent changes in taste sensation suggest alterations in central functioning and may be related to the microglial responses. This is reminiscent of nerve injuries that result in chronic pain, where microglial reactivity is essential in maintaining the altered sensation (i.e., pain). In these models, methods that diminish microglial responses also diminish the corresponding pain behavior. Although the CT nerve does not contain nociceptive pain fibers, the microglial reactivity after CT damage is similar to that described in pain models. Therefore, methods that decrease microglial responses in pain models were used here to test if they could also affect microglial reactivity after CT injury. Treatment with minocycline, an antibiotic that dampens pain responsive microglia, was largely ineffective in diminishing microglial responses after CT injury. In addition, signaling through the toll-like 4 receptor (TLR4) does not seem to be required after CT injury as blocking or deleting TLR4 had no effect on microglial reactivity. These results suggest that microglial responses following CT injury rely on different signaling mechanisms than those described in nerve injuries resulting in chronic pain.

Effects of short-term exposure to environmentally relevant concentrations of different pharmaceutical mixtures on the immune response of the pond snail Lymnaea stagnalis

Pharmaceuticals are pollutants of potential concern in the aquatic environment where they are commonly introduced as complex mixtures via municipal effluents. Many reports underline the effects of pharmaceuticals on immune system of non target species. Four drug mixtures were tested, and regrouped pharmaceuticals by main therapeutic use: psychiatric (venlafaxine, carbamazepine, diazepam), antibiotic (ciprofloxacine, erythromycin, novobiocin, oxytetracycline, sulfamethoxazole, trimethoprim), hypolipemic (atorvastatin, gemfibrozil, benzafibrate) and antihypertensive (atenolol, furosemide, hydrochlorothiazide, lisinopril). Their effects were then compared with a treated municipal effluent known for its contamination, and its effects on the immune response of Lymnaea stagnalis. Adult L. stagnalis were exposed for 3 days to an environmentally relevant concentration of the four mixtures individually and as a global mixture. Effects on immunocompetence (hemocyte viability and count, ROS and thiol levels, phagocytosis) and gene expression were related to the immune response and oxidative stress: catalase (CAT), superoxide dismutase (SOD), glutathione reductase (GR), Selenium-dependent glutathione peroxidase (SeGPx), two isoforms of the nitric oxide synthetase gene (NOS1 and NOS2), molluscan defensive molecule (MDM), Toll-like receptor 4 (TLR4), allograft inflammatory factor-1 (AIF) and heat-shock protein 70 (HSP70). Immunocompetence was differently affected by the therapeutic class mixtures compared to the global mixture, which increased hemocyte count, ROS levels and phagocytosis, and decreased intracellular thiol levels. TLR4 gene expression was the most strongly increased, especially by psychiatric mixture (19-fold), while AIF-1, GR and CAT genes were downregulated. A decision tree analysis revealed that the immunotoxic responses caused by the municipal effluent were comparable to those obtained with the global pharmaceutical mixture, and the latter shared similarity with the antibiotic mixture. This suggests that pharmaceutical mixtures in municipal effluents represent a risk for gastropods at the immunocompetence levels and the antibiotic group could represent a model therapeutic class for municipal effluent toxicity studies in L. stagnalis.

Immunotoxicity of surface waters contaminated by municipal effluents to the snail Lymnaea stagnalis

The immunotoxic effects of surface waters contaminated by a municipal effluent dispersion plume were examined in the snail Lymnaea stagnalis. Snails were exposed to surface waters where changes in hemocyte counts, viability, levels of reactive oxygen species (ROS), reduced thiols and phagocytic activity were tracked following exposure periods of 3h and 3 and 7d. Changes in mRNA expression of some genes in the hemocytes were also assessed after 7d of exposure, as follows: genes coding for catalase (CAT), superoxide dismutase (SOD), glutathione reductase (GSR), selenium-dependent glutathione peroxidase (SeGPX), two isoforms of the nitric oxide synthetase (NOS1 and NOS2), molluscan defensive molecule (MDM), toll-like receptor 4 (TLR4), allograft inflammatory factor-1 (AIF), and heat-shock protein 70 (HSP70). At the sites closest to the discharge point, exposure led to impaired hemocyte viability and intracellular thiol levels and also an increase of hemocyte count, ROS levels and phagocytosis. Phagocytosis and ROS levels in hemocytes were correlated with heterotrophic bacterial counts in snails. We found four genes with increased mRNA expression as a response to exposure of municipal wastewaters: TLR4 (6-fold), HSP70 (2-fold), SeGPx (4-fold) and CAT (2-fold). Immunocompetence responses were analyzed by canonical analysis to seek out relationships with mRNA expression of the genes involved in stress, pattern recognition, cellular and humoral responses. The data revealed that genes involved in oxidative stress were strongly involved with immunocompetence and that the resulting immune responses were influenced both by the bacterial and pollutant loadings of the effluent.

Medication-overuse headache and opioid-induced hyperalgesia: A review of mechanisms, a neuroimmune hypothesis and a novel approach to treatment

Introduction

Patients with chronic headache who consume large amounts of analgesics are often encountered in clinical practice. Excessive intake of analgesics is now considered to be a cause, rather than simply a consequence, of frequent headaches, and as such the diagnosis “medication-overuse headache” (MOH) has been formulated. Despite the prevalence and clinical impact of MOH, the pathophysiology behind this disorder remains unclear and specific mechanism-based treatment options are lacking.

Discussion

Although most acute headache treatments have been alleged to cause MOH, here we conclude from the literature that opioids are a particularly problematic drug class consistently associated with worsening headache. MOH may not be a single entity, as each class of drug implicated may cause MOH via a different mechanism. Recent evidence indicates that chronic opioid administration may exacerbate pain in the long term by activating toll-like receptor-4 on glial cells, resulting in a pro-inflammatory state that manifests clinically as increased pain. Thus, from the available evidence it seems opioid-overuse headache is a phenomenon similar to opioid-induced hyperalgesia, which derives from a cumulative interaction between central sensitisation, due to repeated activation of nociceptive pathways by recurrent headaches, and pain facilitation due to glial activation.

Conclusion

Treatment strategies directed at inhibiting glial activation may be of benefit alongside medication withdrawal in the management of MOH.

Identification of hepatitis C virus inhibitors targeting different aspects of infection using a cell-based assay

With 2 to 3% of the worldwide population chronically infected, hepatitis C virus (HCV) infection continues to be a major health care burden. Unfortunately, current interferon-based treatment options are not effective in all patients and are associated with significant side effects. Consequently, there is an ongoing need to identify and develop new anti-HCV therapies. Toward this goal, we previously developed a cell-based HCV infection assay for antiviral compound screening based on a low-multiplicity-of-infection approach that uniquely allows for the identification of antiviral compounds that target cell culture-derived HCV (HCVcc) at any step of the viral infection cycle. Using this assay, here we report the screening of the NCI Diversity Set II library, containing 1,974 synthesized chemical compounds, and the identification of compounds with specific anti-HCV activity. In combination with toxicity counterscreening, we identified 30 hits from the compound library, 13 of which showed reproducible and dose-dependent inhibition of HCV with mean therapeutic indices (50% cytotoxic concentration [CC(50)]/50% effective concentration [EC(50)]) of greater than 6. Using HCV pseudotype and replicon systems of multiple HCV genotypes, as well as infectious HCVcc-based assembly and secretion analysis, we determined that different compounds within this group of candidate inhibitors target different steps of viral infection. The compounds identified not only will serve as biological probes to study and further dissect the biology of viral infection but also should facilitate the development of new anti-HCV therapeutic treatments.

Opioid activation of toll-like receptor 4 contributes to drug reinforcement

Opioid action was thought to exert reinforcing effects solely via the initial agonism of opioid receptors. Here, we present evidence for an additional novel contributor to opioid reward: the innate immune pattern-recognition receptor, toll-like receptor 4 (TLR4), and its MyD88-dependent signaling. Blockade of TLR4/MD2 by administration of the nonopioid, unnatural isomer of naloxone, (+)-naloxone (rats), or two independent genetic knock-outs of MyD88-TLR4-dependent signaling (mice), suppressed opioid-induced conditioned place preference. (+)-Naloxone also reduced opioid (remifentanil) self-administration (rats), another commonly used behavioral measure of drug reward. Moreover, pharmacological blockade of morphine-TLR4/MD2 activity potently reduced morphine-induced elevations of extracellular dopamine in rat nucleus accumbens, a region critical for opioid reinforcement. Importantly, opioid-TLR4 actions are not a unidirectional influence on opioid pharmacodynamics, since TLR4(-/-) mice had reduced oxycodone-induced p38 and JNK phosphorylation, while displaying potentiated analgesia. Similar to our recent reports of morphine-TLR4/MD2 binding, here we provide a combination of in silico and biophysical data to support (+)-naloxone and remifentanil binding to TLR4/MD2. Collectively, these data indicate that the actions of opioids at classical opioid receptors, together with their newly identified TLR4/MD2 actions, affect the mesolimbic dopamine system that amplifies opioid-induced elevations in extracellular dopamine levels, therefore possibly explaining altered opioid reward behaviors. Thus, the discovery of TLR4/MD2 recognition of opioids as foreign xenobiotic substances adds to the existing hypothesized neuronal reinforcement mechanisms, identifies a new drug target in TLR4/MD2 for the treatment of addictions, and provides further evidence supporting a role for central proinflammatory immune signaling in drug reward.

An emerging new paradigm in opioid withdrawal: a critical role for glia-neuron signaling in the periaqueductal gray

The chronic use of opiates (i.e., narcotics such as the natural derivatives of opium including morphine or codeine) or opioids (i.e., semisynthetic derivatives of opium and other molecules that activate opioid receptors) induces dependence, which is associated with various specific behavioral and somatic signs after their withdrawal or after the administration of an opioid antagonist. Among the brain regions implicated in opiate dependence and withdrawal, the periaqueductal gray area (PAG) appears to be critical in regulating the complex signs and symptoms of opioid withdrawal. Numerous neurochemical mechanisms in the PAG have been identified that may contribute to the opioid withdrawal syndrome. Accumulating evidence suggests that glial activation leading to the release of proinflammatory molecules acting on neurons is important in the complex syndrome of opioid dependence and withdrawal. This paper focuses on the recent advances in our understanding of the vital role that glia-neuron interactions play in opioid dependence and withdrawal within the PAG. We summarize those neurochemical mechanisms associated with opioid withdrawal including the recently defined importance of TNFα release from activated glial cells that communicate with TNF receptors on PAG neurons.

Systems biology approaches to toll-like receptor signaling

Toll-like receptor (TLR) signaling pathways constitute an evolutionarily conserved host defense system that protects against a broad range of infectious agents. Modeling of TLR signaling has been carried out at several levels. Structural models of TLRs and their adaptors, which utilize a small number of structural domains to recognize a diverse range of pathogens, provide a starting point for understanding how pathogens are recognized and signaling events initiated. Various experimental and computational techniques have been used to construct models of downstream signal transduction networks from the measurements of gene expression and chromatin structure under resting and perturbed conditions along with predicted regulatory sequence motifs. Although a complete and accurate mathematical model of all TLR signaling pathways has yet to be derived, many important modules have been identified and investigated, enhancing our understanding of innate immune responses. Extensions of these models based on emerging experimental techniques are discussed. © 2012 Wiley Periodicals, Inc.

Implications of central immune signaling caused by drugs of abuse: mechanisms, mediators and new therapeutic approaches for prediction and treatment of drug dependence

In the past two decades a trickle of manuscripts examining the non-neuronal central nervous system immune consequences of the drugs of abuse has now swollen to a significant body of work. Initially, these studies reported associative evidence of central nervous system proinflammation resulting from exposure to the drugs of abuse demonstrating key implications for neurotoxicity and disease progression associated with, for example, HIV infection. However, more recently this drug-induced activation of central immune signaling is now understood to contribute substantially to the pharmacodynamic actions of the drugs of abuse, by enhancing the engagement of classical mesolimbic dopamine reward pathways and withdrawal centers. This review will highlight the key in vivo animal, human, biological and molecular evidence of these central immune signaling actions of opioids, alcohol, cocaine, methamphetamine, and 3,4-methylenedioxymethamphetamine (MDMA). Excitingly, this new appreciation of central immune signaling activity of drugs of abuse provides novel therapeutic interventions and opportunities to identify 'at risk' individuals through the use of immunogenetics. Discussion will also cover the evidence of modulation of this signaling by existing clinical and pre-clinical drug candidates, and novel pharmacological targets. Finally, following examination of the breadth of central immune signaling actions of the drugs of abuse highlighted here, the current known common immune signaling components will be outlined and their impact on established addiction neurocircuitry discussed, thereby synthesizing a common neuroimmune hypothesis of addiction.

Endogenous opiates and behavior: 2010

This paper is the thirty-third consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2010 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior (Section 2), and the roles of these opioid peptides and receptors in pain and analgesia (Section 3); stress and social status (Section 4); tolerance and dependence (Section 5); learning and memory (Section 6); eating and drinking (Section 7); alcohol and drugs of abuse (Section 8); sexual activity and hormones, pregnancy, development and endocrinology (Section 9); mental illness and mood (Section 10); seizures and neurologic disorders (Section 11); electrical-related activity and neurophysiology (Section 12); general activity and locomotion (Section 13); gastrointestinal, renal and hepatic functions (Section 14); cardiovascular responses (Section 15); respiration (Section 16); and immunological responses (Section 17).

Toll-like receptors in chronic pain

Proinflammatory central immune signaling contributes significantly to the initiation and maintenance of heightened pain states. Recent discoveries have implicated the innate immune system, pattern recognition Toll-like receptors in triggering these proinflammatory central immune signaling events. These exciting developments have been complemented by the discovery of neuronal expression of Toll-like receptors, suggesting pain pathways can be activated directly by the detection of pathogen associated molecular patterns or danger associated molecular patterns. This review will examine the evidence to date implicating Toll-like receptors and their associated signaling components in heightened pain states. In addition, insights into the impact Toll-like receptors have on priming central immune signaling systems for heightened pain states will be discussed. The influence possible sex differences in Toll-like receptor signaling have for female pain and the recognition of small molecule xenobiotics by Toll-like receptors will also be reviewed.

Linking pharmacology to clinical reports: cyclobenzaprine and its possible association with serotonin syndrome

The link between cyclobenzaprine (Flexeril) administration and serotonin syndrome (SS) is subject to debate. Establishing such a connection is difficult because of the limited number of case reports available and the almost complete ignorance of its preclinical pharmacology. In this context, evidence is provided here that cyclobenzaprine blocks the serotonin and norepinephrine transporters and binds to another set of five serotonin receptors. SS should be considered when indicative signs occur in the context of cyclobenzaprine use.

Acute Pain Management in Opioid-Tolerant Patients: A Growing Challenge

In Australia and New Zealand, in parallel with other developed countries, the number of patients prescribed opioids on a long-term basis has grown rapidly over the last decade. The burden of chronic pain is more widely recognised and there has been an increase in the use of opioids for both cancer and non-cancer indications. While the prevalence of illicit opioid use has remained relatively stable, the diversion and abuse of prescription opioids has escalated, as has the number of individuals receiving methadone or buprenorphine pharmacotherapy for opioid addiction. As a result, the proportion of opioid-tolerant patients requiring acute pain management has increased, often presenting clinicians with greater challenges than those faced when treating the opioid-naïve.

Treatment aims include effective relief of acute pain, prevention of drug withdrawal, assistance with any related social, psychiatric and behavioural issues, and ensuring continuity of long-term care. Pharmacological approaches incorporate the continuation of usual medications (or equivalent), short-term use of sometimes much higher than average doses of additional opioid, and prescription of non-opioid and adjuvant drugs, aiming to improve pain relief and attenuate opioid tolerance and/or opioid-induced hyperalgesia. Discharge planning should commence at an early stage and may involve the use of a ‘Reverse Pain Ladder’ aiming to limit duration of additional opioid use. Legislative requirements may restrict which drugs can be prescribed at the time of hospital discharge. At all stages, there should be appropriate and regular consultation and liaison with the patient, other treating teams and specialist services.

Exploring the neuroimmunopharmacology of opioids: an integrative review of mechanisms of central immune signaling and their implications for opioid analgesia

Vastly stimulated by the discovery of opioid receptors in the early 1970s, preclinical and clinical research was directed at the study of stereoselective neuronal actions of opioids, especially those played in their crucial analgesic role. However, during the past decade, a new appreciation of the non-neuronal actions of opioids has emerged from preclinical research, with specific appreciation for the nonclassic and nonstereoselective sites of action. Opioid activity at Toll-like receptors, newly recognized innate immune pattern recognition receptors, adds substantially to this unfolding story. It is now apparent from molecular and rodent data that these newly identified signaling events significantly modify the pharmacodynamics of opioids by eliciting proinflammatory reactivity from glia, the immunocompetent cells of the central nervous system. These central immune signaling events, including the release of cytokines and chemokines and the associated disruption of glutamate homeostasis, cause elevated neuronal excitability, which subsequently decreases opioid analgesic efficacy and leads to heightened pain states. This review will examine the current preclinical literature of opioid-induced central immune signaling mediated by classic and nonclassic opioid receptors. A unification of the preclinical pharmacology, neuroscience, and immunology of opioids now provides new insights into common mechanisms of chronic pain, naive tolerance, analgesic tolerance, opioid-induced hyperalgesia, and allodynia. Novel pharmacological targets for future drug development are discussed in the hope that disease-modifying chronic pain treatments arising from the appreciation of opioid-induced central immune signaling may become practical.

Features of microglia and neuroinflammation relevant to environmental exposure and neurotoxicity

Microglia are resident cells of the brain involved in regulatory processes critical for development, maintenance of the neural environment, injury and repair. They belong to the monocytic-macrophage lineage and serve as brain immune cells to orchestrate innate immune responses; however, they are distinct from other tissue macrophages due to their relatively quiescent phenotype and tight regulation by the CNS microenvironment. Microglia actively survey the surrounding parenchyma and respond rapidly to changes such that any disruption to neural architecture or function can contribute to the loss in regulation of the microglia phenotype. In many models of neurodegeneration and neurotoxicity, early events of synaptic degeneration and neuronal loss are accompanied by an inflammatory response including activation of microglia, perivascular monocytes, and recruitment of leukocytes. In culture, microglia have been shown to be capable of releasing several potentially cytotoxic substances, such as reactive oxygen intermediates, nitric oxide, proteases, arachidonic acid derivatives, excitatory amino acids, and cytokines; however, they also produce various neurotrophic factors and quench damage from free radicals and excitotoxins. As the primary source for pro-inflammatory cytokines, microglia are implicated as pivotal mediators of neuroinflammation and can induce or modulate a broad spectrum of cellular responses. Neuroinflammation should be considered as a balanced network of processes whereby subtle modifications can shift the cells toward disparate outcomes. For any evaluation of neuroinflammation and microglial responses, within the framework of neurotoxicity or degeneration, one key question in determining the consequence of neuroinflammation is whether the response is an initiating event or the consequence of tissue damage. As examples of environmental exposure-related neuroinflammation in the literature, we provide an evaluation of data on manganese and diesel exhaust particles.

Toll-like receptors as targets for immune disorders

Since the identification of the first Toll-like receptor (TLR) in humans in 1997, understanding of the molecular basis for innate immunity has increased significantly. The TLR family and downstream signalling pathways have been extensively characterised, There is now significant evidence suggesting a role for TLRs in human inflammatory and immune diseases such as rheumatoid arthritis, diabetes, allergy/asthma and atherosclerosis. Various approaches have been taken to identify novel therapeutic agents targeting TLRs including biologics, small molecules and nucleic acid-based drugs. Several are now being evaluated in the clinic and showing promise against various diseases. This review paper outlines the recent advances in the understanding of TLR biology and highlights novel TLR agonists and antagonists in development for the treatment of immune diseases.