Rifampin inhibits Toll-like receptor 4 signaling by targeting myeloid differentiation protein 2 and attenuates neuropathic pain

The emerging role of adaptor proteins in regulating innate immunity of sepsis

Sepsis is a life-threatening syndrome caused by a dysregulated immune response. A large number of adaptor proteins have been found to play a pivotal role in sepsis via protein-protein interactions, thus participating in inflammatory cascades, leading to the generation of numerous inflammatory cytokines, as well as oxidative stress and regulated cell death. Although available strategies for the diagnosis and management of sepsis have improved, effective and specific treatments are lacking. This review focuses on the emerging role of adaptor proteins in regulating the innate immunity of sepsis and evaluates the potential value of adaptor protein-associated therapeutic strategy for sepsis.

Biological role of mitochondrial TLR4-mediated NF-κB signaling pathway in central nervous system injury

Previous studies suggested that central nervous system injury is often accompanied by the activation of Toll-like receptor 4/NF-κB pathway, which leads to the upregulation of proapoptotic gene expression, causes mitochondrial oxidative stress, and further aggravates the inflammatory response to induce cell apoptosis. Subsequent studies have shown that NF-κB and IκBα can directly act on mitochondria. Therefore, elucidation of the specific mechanisms of NF-κB and IκBα in mitochondria may help to discover new therapeutic targets for central nervous system injury. Recent studies have suggested that NF-κB (especially RelA) in mitochondria can inhibit mitochondrial respiration or DNA expression, leading to mitochondrial dysfunction. IκBα silencing will cause reactive oxygen species storm and initiate the mitochondrial apoptosis pathway. Other research results suggest that RelA can regulate mitochondrial respiration and energy metabolism balance by interacting with p53 and STAT3, thus initiating the mitochondrial protection mechanism. IκBα can also inhibit apoptosis in mitochondria by interacting with VDAC1 and other molecules. Regulating the biological role of NF-κB signaling pathway in mitochondria by targeting key proteins such as p53, STAT3, and VDAC1 may help maintain the balance of mitochondrial respiration and energy metabolism, thereby protecting nerve cells and reducing inflammatory storms and death caused by ischemia and hypoxia.

Effect of rifampicin on TLR4-signaling pathways in the nucleus accumbens of the rat brain during abstinence of long-term alcohol treatment

AIMS

The treatment with the antibiotic rifampicin (Rif) led to a decrease in the frequency of neurodegenerative pathologies. There are suggestions that the mechanism of action of Rif may be mediated by its effect on toll-like receptor (TLR)4-dependent pathways. We evaluated the expression status of TLR4-dependent genes during abstinence from long-term alcohol treatments in the nucleus accumbens (NAc) of the rat brain, and also studied the effects of Rif to correct these changes.

METHODS

The long-term alcohol treatment was performed by intragastric delivery of ethanol solution. At the end of alcohol treatment intraperitoneal injections of Rif (100 mg/kg) or saline were made. Extraction of the brain structures was performed on the 10th day of abstinence from alcohol. We used the SYBR Green qPCR method to quantitatively analyze the relative expression levels of the studied genes.

RESULTS

The long-term alcohol treatment promotes an increase in the level of TLR4 mRNA and mRNA of its endogenous ligand high-mobility group protein B1 during abstinence drop alcohol in NAc of rats. The use of Rif in our study led to a decrease in the increased expression of high-mobility group protein B1, Tlr4, and proinflammatory cytokine genes (Il1β, Il6) in the NAc of the rat brain during abstinence of long-term alcohol treatment. In addition, Rif administration increased the decreased mRNA levels of anti-inflammatory cytokines (Il10, Il11).

CONCLUSION

The data obtained indicate the ability of Rif to correct the mechanisms of the TLR4 system genes in the NAc of the rat brain during alcohol abstinence.

Andrographolide inhibits the activation of spinal microglia and ameliorates mechanical allodynia

Andrographolide (Andro), a labdane diterpene, possesses anti-inflammatory properties and has been used to treat numerous inflammatory diseases. Novel findings revealed that Andro might be vital in regulating pain. However, the contribution of Andro to chronic inflammatory pain has yet to be determined, and its underlying mechanism of action remains unknown. In this study, we observed that Andro attenuated mechanical allodynia in inflammatory pain mice induced by injecting complete Freund's adjuvant (CFA) into the right hind paws. This analgesic effect of Andro is mainly dependent on its inhibition of microglial overactivation and the release of proinflammatory cytokines (TNF and IL-1β) in lumbar spinal cords of inflammatory pain model mice. More importantly, our data in vivo and in vitro revealed a negative role for Andro in regulating the TLR4/NF-κB signaling pathway, which might contribute to the inhibition of spinal microglial activation and proinflammatory cytokines production, and the improvement of paw withdrawal thresholds in a mouse model of chronic inflammatory pain evoked by CFA. We further found the potential interaction of Andro with TLR4/myeloid differentiation factor 2 heterodimer using molecular modeling, implying that TLR4 might be a potential target for Andro to exert an analgesic effect. Taken together, our findings demonstrated that the modulation of spinal microglial activation by Andro might be substantially conducive to managing chronic pain triggered by neuroinflammation.

Revolutionizing control strategies against Mycobacterium tuberculosis infection through selected targeting of lipid metabolism

Lipid species play a critical role in the growth and virulence expression of Mycobacterium tuberculosis (Mtb), the causative agent of tuberculosis (TB). During Mtb infection, foamy macrophages accumulate lipids in granulomas, providing metabolic adaptation and survival strategies for Mtb against multiple stresses. Host-derived lipid species, including triacylglycerol and cholesterol, can also contribute to the development of drug-tolerant Mtb, leading to reduced efficacy of antibiotics targeting the bacterial cell wall or transcription. Transcriptional and metabolic analyses indicate that lipid metabolism-associated factors of Mtb are highly regulated by antibiotics and ultimately affect treatment outcomes. Despite the well-known association between major antibiotics and lipid metabolites in TB treatment, a comprehensive understanding of how altered lipid metabolites in both host and Mtb influence treatment outcomes in a drug-specific manner is necessary to overcome drug tolerance. The current review explores the controversies and correlations between lipids and drug efficacy in various Mtb infection models and proposes novel approaches to enhance the efficacy of anti-TB drugs. Moreover, the review provides insights into the efficacious control of Mtb infection by elucidating the impact of lipids on drug efficacy. This review aims to improve the effectiveness of current anti-TB drugs and facilitate the development of innovative therapeutic strategies against Mtb infection by making reverse use of Mtb-favoring lipid species.

The effect of rifampicin on expression of the toll-like receptor system genes in the forebrain cortex of rats prenatally exposed to alcohol

Ethanol causes long-term changes in the toll-like receptor (TLR) system, promoting activation of neuroinflammation pathways. Alcohol use during pregnancy causes neuroinflammatory processes in the fetus; this can lead to the development of symptoms of fetal alcohol spectrum disorder (FASD). Our study has shown that prenatal alcohol exposure (PAE) induced long-term changes in the TLR system genes (Tlr3, Tlr4, Ticam, Hmgb1, cytokine genes) in the forebrain cortex of rat pups. Administration of rifampicin (Rif), which can reduce the level of pro-inflammatory mediators in various pathological conditions of the nervous system, normalized the altered expression level of the studied TLR system genes. This suggests that Rif can prevent the development of persistent neuroinflammatory events in the forebrain cortex of rat pups caused by dysregulation in the TLR system.

A clindamycin acetylated derivative with reduced antibacterial activity inhibits articular hyperalgesia and edema by attenuating neutrophil recruitment, NF-κB activation and tumor necrosis factor-α production

We recently demonstrated that clindamycin exhibits activities in acute and chronic models of pain and inflammation. In the present study, we investigated the effects of clindamycin and a clindamycin acetylated derivative (CAD) in models of acute joint inflammation and in a microbiological assay. Joint inflammation was induced in mice by intraarticular (i.a.) injection of zymosan or lipopolysaccharide (LPS). Clindamycin or CAD were administered via the intraperitoneal route 1 h before zymosan or LPS. Paw withdrawal threshold, joint diameter, histological changes, neutrophil recruitment, tumor necrosis factor-α (TNF-α) production and phosphorylation of the IκBα and NF-κB/p65 were evaluated. In vitro assays were used to measure the antibacterial activity of clindamycin and CAD and also their effects on zymosan-induced TNF-α production by RAW264.7 macrophages. Clindamycin exhibited activity against Staphylococcus aureus and Salmonella Typhimurium ATCC® strains at much lower concentrations than CAD. Intraarticular injection of zymosan or LPS induced articular hyperalgesia, edema and neutrophil infiltration in the joints. Zymosan also induced histological changes, NF-κB activation and TNF-α production. Responses induced by zymosan and LPS were inhibited by clindamycin (200 and 400 mg/kg) or CAD (436 mg/kg). Both clindamycin and CAD inhibited in vitro TNF-α production by macrophages. In summary, we provided additional insights of the clindamycin immunomodulatory effects, whose mechanism was associated with NF-κB inhibition and reduced TNF-α production. Such effects were extended to a clindamycin derivative with reduced antibacterial activity, indicating that clindamycin derivatives should be investigated as candidates to drugs that could be useful in the management of inflammatory and painful conditions.

Advances in immunomodulatory strategies for host-directed therapies in combating tuberculosis

Tuberculosis (TB) maintains its infamous status regarding its detrimental effect on global health, causing the highest mortality by a single infectious agent. The presence of resistance and immune compromising disease favours the disease in maintaining its footing in the health care burden despite various anti-TB drugs used to fight it. Main factors contributing to resistance and difficulty in treating disease include prolonged treatment duration (at least 6 months) and severe toxicity, which further leads to patient non-compliance, and thus a ripple effect leading to therapeutic non-efficacy. The efficacy of new regimens demonstrates that targeting host factors concomitantly with the Mycobacterium tuberculosis (M.tb) strain is urgently required. Due to the huge expenses and time required of up to 20 years for new drug research and development, drug repurposing may be the most economical, circumspective, and conveniently faster journey to embark on. Host-directed therapy (HDT) will dampen the burden of the disease by acting as an immunomodulator, allowing it to defend the body against antibiotic-resistant pathogens whilst minimizing the possibility of developing new resistance to susceptible drugs. Repurposed drugs in TB act as host-directed therapies, acclimatizing the host immune cell to the presence of TB, improving its antimicrobial activity and time taken to get rid of the disease, whilst minimizing inflammation and tissue damage. In this review, we, therefore, explore possible immunomodulatory targets, HDT immunomodulatory agents, and their ability to improve clinical outcomes whilst minimizing the risk of drug resistance, through various pathway targeting and treatment duration reduction.

Pharmaceutical Development of Nanostructured Vesicular Hydrogel Formulations of Rifampicin for Wound Healing

Chronic wounds exhibit elevated levels of inflammatory cytokines, resulting in the release of proteolytic enzymes which delay wound-healing processes. In recent years, rifampicin has gained significant attention in the treatment of chronic wounds due to an interesting combination of antibacterial and anti-inflammatory effects. Unfortunately, rifampicin is sensitive to hydrolysis and oxidation. As a result, no topical drug product for wound-healing applications has been approved. To address this medical need two nanostructured hydrogel formulations of rifampicin were developed. The liposomal vesicles were embedded into hydroxypropyl methylcellulose (HPMC) gel or a combination of hyaluronic acid and marine collagen. To protect rifampicin from degradation in aqueous environments, a freeze-drying method was developed. Before freeze-drying, two well-defined hydrogel preparations were obtained. After freeze-drying, the visual appearance, chemical stability, residual moisture content, and redispersion time of both preparations were within acceptable limits. However, the morphological characterization revealed an increase in the vesicle size for collagen-hyaluronic acid hydrogel. This was confirmed by subsequent release studies. Interactions of marine collagen with phosphatidylcholine were held responsible for this effect. The HPMC hydrogel formulation remained stable over 6 months of storage. Moving forward, this product fulfills all criteria to be evaluated in preclinical and clinical studies.

Anti-nociceptive effects of magnolol via inhibition of TRPV1/P2Y and TLR4/NF-κB signaling in a postoperative pain model

AIMS

The current study explored the anti-nociceptive activity of magnolol in post-incisional inflammatory nociceptive pain.

MAIN METHODS

Preliminary, the anti-inflammatory, antioxidant, and cytoprotective potential of magnolol were confirmed against hydrogen peroxide (H₂O₂)-induced PC12 cells. Next, an in-vivo model of planter incision surgery was established in BALB/c mice. Tramadol 50 mg/kg intraperitoneal (i.p.) and magnolol (0.1, 1, 10 mg/kg i.p. + 10 mg/kg intra planter) were administered after plantar incision surgery and behavior parameters were measured.

KEY FINDINGS

The results indicate that magnolol significantly suppressed post-incision-induced mechanical allodynia, thermal hyperalgesia, and paw edema. Magnolol promisingly inhibited post-incision induces nitric oxide (NO), malondialdehyde (MDA), eosinophil peroxidase (EPO), and neutrophil infiltration. Magnolol strongly attenuated post-incision inducing the release of tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β) and inhibited deoxyribonucleic acid (DNA) fragmentation. Magnolol markedly reverses post-incisional histopathological changes and biochemical composition of the incised paw. Magnolol markedly down-regulated post-incisional increase expression of transient receptor potential vanilloid 1 (TRPV1), purinergic (P2Y) nociceptors as well as toll-like receptor 4 (TLR4), nuclear factor kappa light chain enhancer of activated B cell (NF-κB), cyclooxygenase-2 (COX-2) and inducible nitric oxide synthase (iNOS) while upregulating the expression of inhibitor of nuclear kappa B alpha (IκB-α).

SIGNIFICANCE

The present study strongly suggests that magnolol significantly suppressed post-incisional inflammatory nociceptive pain by targeting TRPV1/P2Y and TLR4/NF-κB signaling.

Delamanid suppresses CXCL10 expression via regulation of JAK/STAT1 signaling and correlates with reduced inflammation in tuberculosis patients

Background

Apart from bactericidal effects, anti-tuberculosis drugs can interfere with the host’s immune system. In this study, we analyzed the role of delamanid (DLM), an inhibitor of mycolic acid synthesis of mycobacterial cell wall, on human macrophages.

Methods

Based on a cohort of multidrug-resistant tuberculosis (MDR-TB) patients treated with DLM, the levels of C-reaction protein (CRP) and cytokines in the plasma were monitored using immunoturbidimetric assay and flow cytometry, respectively. We investigated the role of DLM on CXCL10 expression in U937 cell model using the following methods: cell viability assay, reverse transcription-quantitative polymerase chain reaction, enzyme linked immunosorbent assay, immunoblot, and transwell co-culture assay.

Results

A total of 23 MDR-TB patients were included, comprising of 13 patients treated with optimized background therapeutic regimen (OBR) plus DLM regimen (OBR+DLM) and 10 patients treated with OBR plus placebo. DLM administration was associated with a significant reduce in circulating CRP level. Correspondingly, after treatment, the level of CXCL10 in patients treated with OBR+DLM was significantly lower than that with control. Using cell model, DLM dramatically suppressed CXCL10 expression, which majorly depended on inhibiting the JAK/STAT pathway, and impaired the migration of PBMCs.

Conclusion

Our data firstly demonstrate that DLM suppresses CXCL10 expression via regulation of JAK2/STAT1 signaling and correlates with reduced inflammation in MDR-TB patients. DLM could be used as a potential drug for immunotherapy of patients with overactive immune response due to CXCL10.

Neuronal toll like receptor 9 contributes to complete Freund’s adjuvant-induced inflammatory pain in mice

Toll like receptor 9 (TLR9) is a critical sensor for danger-associated molecular patterns (DAMPs) and a crucial marker of non-sterile/sterile inflammation among all TLRs. However, the significance of TLR9 in inflammatory pain remains unclear. Here, we subcutaneously injected Complete Freund’s adjuvant (CFA) into the plantar surface of the hind paw, to established a mouse model of inflammatory pain, and we examined expression and distribution of TLR9 in this model. There was a significant increase of TLR9 mRNA and reduction of mechanical paw withdrawal threshold in mice intraplantar injected with CFA. By contrast, mechanical paw withdrawal threshold significantly increased in mice treated with TLR9 antagonist ODN2088. Furthermore, TLR9 is found predominantly distributed in the neurons by immunofluorescence experiment. Accordingly, neuronal TLR9 downregulation in the spinal cord prevented CFA-induced persistent hyperalgesia. Overall, these findings indicate that neuronal TLR9 in the spinal cord is closely related to CFA-induced inflammatory pain. It provides a potential treatment option for CFA-induced inflammatory pain by applying TLR9 antagonist.

[The effect of rifampicin on the system of Toll-like receptors in the nucleus accumbens of the brain of long-term alcoholized rats during alcohol withdrawal]

Nucleus accumbens (NAc) is the ventral part of the striatum of the brain; it is an important part of the mesolimbic pathway involved in the reward system that mediates the formation of various forms of addiction, in particular alcohol addiction. Neuroimaging data and in vitro studies indicate the development of a pronounced neurodegenerative process in the NAc, with long-term alcohol use, but the key mechanisms mediating this process remain unknown. In recent years, the attention of researchers has been focused on studying the system of Toll-like receptors (TLRs), the increased activity of which is clearly shown in the cerebral cortex and hippocampus during prolonged alcohol exposure, but there is a need to study the role of this system in other brain structures. In this study, we have shown that prolonged alcohol exposure (2 months) with moderate doses of ethanol (2 g/kg) promotes a pronounced increase in the expression of the Tlr4 gene and its endogenous ligand Hmgb1 in NAc during the period of alcohol withdrawal in rats. Injections of rifampicin (100 mg/kg) reduced the elevated expression level of Hmgb1, Tlr4, as well as pro-inflammatory cytokine genes (IL1β, IL6), while the administration of the drug increased the reduced level of mRNA of anti-inflammatory cytokines (IL10, IL11).

Pentamidine Alleviates Inflammation and Lipopolysaccharide-Induced Sepsis by Inhibiting TLR4 Activation via Targeting MD2

Toll-like receptor 4 (TLR4) is a pattern-recognition receptor (PRR) that can recognize lipopolysaccharides (LPS) and initiate the immune response, to protect the body from infection. However, excessive activation of TLR4 induced by LPS leads to substantial release of pro-inflammatory factors, which may bring a cytokine storm in the body and cause severe sepsis. Existing molecules specialized in sepsis therapy are either in clinical trials or show mediocre effects. In this study, pentamidine, an approved drug used in the treatment of trypanosomiasis, was identified as a TLR4 antagonist. Saturation transferred difference (STD)-NMR spectra indicated that pentamidine directly interacted with TLR4's co-receptor myeloid differentiation protein 2 (MD2) in vitro. Cellular thermal shift assay (CETSA) showed that pentamidine binding decreased MD2 stability, which was supported by in silico simulations that pentamidine binding rendered most regions of MD2 more flexible. Pentamidine was found to inhibit the formation of the TLR4/MD2/MyD88 complex and the activation of the TLR4 signaling axes of NF-κB and MAPKs, therefore blocking LPS-induced TLR4 signaling downstream of the pro-inflammatory factors NO, TNF-α, and IL-1β. The bioisosteric replacement of the methylene group at the center 13' site of pentamidine by the ether oxygen group significantly decreased its interactions with MD2 and abolished its TLR4 antagonist activity. Furthermore, pentamidine enhanced the survival rate of septic mice and exerted an anti-inflammatory effect on organs. All these data provide strong evidence that pentamidine may be an effective drug in alleviating inflammation and sepsis.

Mechanism of anti-inflammatory effects of Rifampicin in an ex vivo culture system of Hidradenitis Suppurativa

Hidradenitis suppurativa (HS) is a chronic inflammatory skin disease of the hair follicles leading to painful lesions, associated with increased levels of pro-inflammatory cytokines. Numerous guidelines recommend antibiotics like clindamycin and rifampicin in combination, as first-line systemic therapy in moderate to severe forms of inflammation. HS has been proposed to be mainly an auto-inflammatory disease associated with but not initially provoked by bacteria. Therefore, it has to be assumed that the pro-inflammatory milieu previously observed in HS skin is not solely dampened by the bacteriostatic inhibition of DNA-dependent RNA polymerase. To further clarify the mechanism of anti-inflammatory effects of rifampicin, ex vivo explants of lesional HS from 8 HS patients were treated with rifampicin, and its effect on cytokine production, immune cells as well as the expression of Toll-like receptor 2 (TLR2) were investigated. Analysis of cell culture medium of rifampicin treated HS explants revealed an anti-inflammatory effect of rifampicin that significantly inhibiting interleukin (IL)-1β, IL-6, IL-8, IL-10, and tumour necrosis factor (TNF) -α production. Immunohistochemistry of the rifampicin-treated explants suggested a tendency for it to reduce the expression of TLR2 while not affecting the number of immune cells.

Activation of the Hippocampal LXRβ Improves Sleep-Deprived Cognitive Impairment by Inhibiting Neuroinflammation

Sleep deprivation (SD) leads to cognitive impairment due to neuroinflammation associated with impaired hippocampal neuronal plasticity and memory processes. Liver X receptors (LXRs), including LXRα and LXRβ isoforms, are crucial for synaptic plasticity and neuroinflammation. However, the potential roles of LXRs in the pathogenesis of cognitive impairment induced by SD remain unclear. We revealed that SD resulted in LXRβ reduction in the hippocampus, which was associated with upregulated expression of high mobility group box 1 (HMGB1)/toll-like receptor 4 (TLR4)/NF-κB p65, and knockdown of hippocampal LXRβ by shRNA (shLXRβ) led to cognitive impairment. GW3965, a dual agonist for both LXRα and LXRβ, ameliorated SD-induced cognitive impairment by inhibiting microglia activation, suppressing HMGB1/TLR4/NF-κB p65 pathway, and ultimately affecting the hippocampal expression of inflammatory cytokines in SD mice. LXRβ knockdown by shLXRβ abrogated the GW3965-mediated inhibition of the HMGB1/TLR4/NF-κB p65 pathway, therefore, abolishing the cognitive improvement. Moreover, inhibition of HMGB1 by glycyrrhizin (GLY) synergistic promoted GW3965-mediated anti-inflammation in activated microglia after lipopolysaccharide (LPS)/ATP stimulation and facilitated the cognitive improvement after GW administration by activating LXRβ. All the data suggested that GW3965 ameliorated impaired cognition in SD mice by suppressing the HMGB1/TLR4/NF-κB p65 pathway followed LXRβ activation. This study correlates a deficit of LXRβ in cognitive dysfunction in SD associated with HMGB1 inflammatory pathway in hippocampus, and LXRs may serve as a potential therapeutic target for cognitive impairment with anti-inflammation.

Structure-activity relationship study of dihydroartemisinin C-10 hemiacetal derivatives as Toll-like receptor 4 antagonists

Dihydroartemisinin (DHA), a natural product isolated from the traditional Chinese herb Artemisia annua and one of the clinical frontline drugs against malarial infections, has recently been discovered as a Toll-like Receptor 4 (TLR4) antagonist. However, the TLR4 antagonistic activity of DHA is modest and it exhibits cellular toxicity. In this work, the structure-activity relationship (SAR) of DHA as TLR4 antagonist was explored. Since destroying the sesquiterpene endoperoxide scaffold substantially compromised the TLR4 antagonistic activity and molecular dynamics analysis showed that the C-10 hydroxyl group formed a hydrogen bond with E72 of myeloid differentiation factor 2 (MD2) to prevent it moving deeper into MD2, SAR of DHA was focused on the C-10 hemiacetal position. With extending the length of the linear alkane chain at C10 position, the TLR4 antagonistic activity of DHA analogs increased first and then decreased with the best TLR4 antagonism occurring at the length of the carbon chain of 3-4 carbons. In contrast, the cellular toxicity of DHA analogs was raised with the increasing length of the linear alkane chain. The TLR4 antagonistic activity of DHA derivatives with substituted halogen as the terminal functional group decreased with the decrease of electronegativity of the substituted halogen, which implies the electron-rich functional group at the end of the alkane chain appears preferred. Therefore, DHA derivative 2k with alkynyl as the end functional group, exhibited 14 times more potent TLR4 antagonistic activity than DHA. Moreover, 2k showed less cellular toxicity than DHA. Cellular signaling characterizations indicated that 2k inhibited LPS-induced TLR4 dimerization and endocytosis and suppressed LPS-induced NF-κB but not MAPKs activation, culminating in blocking LPS-induced TLR4 signaling downstream pro-inflammatory factors NO and IL-1β. Further, 2k was active in vivo; it significantly increased and prolonged morphine analgesia. Collectively, this study provides a structural guidance to reposition DHA derivatives as TLR4 antagonists.

Rifampicin ameliorates lipopolysaccharide-induced cognitive and motor impairments via inhibition of the TLR4/MyD88/NF-κB signaling pathway in mice

OBJECTIVES

Aberrant microglial responses promote neuroinflammation in neurodegenerative diseases. However, rifampicin's effect on cognitive and motor sequelae of inflammation remains unknown. Therefore, we investigated whether rifampicin exerts neuroprotection against lipopolysaccharide (LPS)-induced cognitive and motor impairments.

METHODS

A mouse model of LPS-induced cognitive and motor impairment was established. Adult C57BL/6 mice were injected intraperitoneally with 25 mg/kg rifampicin 30 min before intraperitoneal microinjection of LPS (750 μg/kg) daily until study end. Treatments and behavioral experiments were performed once daily for 7 days. Behavioral tests and pathological/biochemical assays were performed to evaluate LPS-induced damage to the hippocampus and substantia nigra (SN).

RESULTS

Rifampicin attenuated LPS-induced cognitive and motor impairments, based on performance in the behavioral tests. Rifampicin suppressed the release of pro-inflammatory mediators, including tumor necrosis factor-α, interleukin-1β, and prostaglandin E₂ in the serum and nitric oxide (NO) in brain tissue, and cyclooxygenase-2 and inducible nitric oxide synthase levels. Immunofluorescence revealed that rifampicin inhibited LPS-induced microglial activation in the hippocampus and SN, thus protecting the neurons. Rifampicin inhibited the activation of the toll-like receptor 4 (TLR4)/myeloid differentiation primary response 88 (MyD88)/nuclear factor kappa B (NF-κB) signaling pathway. Rifampicin downregulated TLR4 and MyD88 protein levels and inhibited NF-κB inhibitor alpha and NF-κB inhibitor kinase beta phosphorylation, thus reducing p65 nuclear transfer by inhibiting NF-κB signaling activation in LPS-treated mice.

CONCLUSION

Rifampicin protects against LPS-induced neuroinflammation and attenuates cognitive and motor impairments by inhibiting the TLR4/MyD88/NF-κB signaling pathway. Our findings might aid the development of novel therapies to treat progressive neurodegenerative diseases.

Heme Causes Pain in Sickle Mice via Toll-Like Receptor 4-Mediated Reactive Oxygen Species- and Endoplasmic Reticulum Stress-Induced Glial Activation

Aims: Lifelong pain is a hallmark feature of sickle cell disease (SCD). How sickle pathobiology evokes pain remains unknown. We hypothesize that increased cell-free heme due to ongoing hemolysis activates toll-like receptor 4 (TLR4), leading to the formation of reactive oxygen species (ROS) and endoplasmic reticulum (ER) stress. Together, these processes lead to spinal microglial activation and neuroinflammation, culminating in acute and chronic pain. Results: Spinal heme levels, TLR4 transcripts, oxidative stress, and ER stress were significantly higher in sickle mice than controls. In vitro, TLR4 inhibition in spinal cord microglial cells attenuated heme-induced ROS and ER stress. Heme treatment led to a time-dependent increase in the characteristic features of sickle pain (mechanical and thermal hyperalgesia) in both sickle and control mice; this effect was absent in TLR4-knockout sickle and control mice. TLR4 deletion in sickle mice attenuated chronic and hypoxia/reoxygenation (H/R)-evoked acute hyperalgesia. Sickle mice treated with the TLR4 inhibitor resatorvid; selective small-molecule inhibitor of TLR4 (TAK242) had significantly reduced chronic hyperalgesia and had less severe H/R-evoked acute pain with quicker recovery. Notably, reducing ER stress with salubrinal ameliorated chronic hyperalgesia in sickle mice. Innovation: Our findings demonstrate the causal role of free heme in the genesis of acute and chronic sickle pain and suggest that TLR4 and/or ER stress are novel therapeutic targets for treating pain in SCD. Conclusion: Heme-induced microglial activation via TLR4 in the central nervous system contributes to the initiation and maintenance of sickle pain via ER stress in SCD. Antioxid. Redox Signal. 34, 279-293.

Paeonol ameliorates CFA-induced inflammatory pain by inhibiting HMGB1/TLR4/NF-κB p65 pathway

The enhanced release of inflammatory cytokines mediated by high mobility group box1 (HMGB1) leads to pain sensation, and has been implicated in the etiology of inflammatory pain. Paeonol (PAE), a major active phenolic component in Cortex Moutan, provides neuroprotective efficacy via exerting anti-inflammatory effect. However, the role and mechanism of PAE in inflammatory pain remain to be fully clarified. In this study, we showed that PAE treatment significantly ameliorated mechanical and thermal hyperalgesia of mice induced by complete Freund's adjuvant (CFA). The analgesic effect of PAE administration was associated with suppressing the enhanced expression of HMGB1 as well as the downstream signaling molecules including toll-like receptor 4 (TLR4), the nuclear NF-κB p65, TNF-α and IL-1β after CFA insult in the anterior cingulate cortex (ACC), a key brain region responsible for pain processing. Furthermore, inhibition of HMGB1 activity by glycyrrhizin (GLY), an HMGB1 inhibitor, alleviated CFA-induced pain and also facilitated PAE-mediated analgesic effect in mice along with the decreased expression of TLR4, NF-κB p65, TNF-α and IL-1β upon CFA injury. Collectively, we showed PAE exerted analgesic effect through inhibiting the HMGB1/TLR4/NF-κB p65 pathway and subsequent generation of cytokines TNF-α and IL-1β in the ACC.

Rifampicin impairs adipogenesis by suppressing NRF2-ARE activity in mice fed a high-fat diet

Prolonged treatment with rifampicin (RFP), a first-line antibacterial agent used in the treatment of drug-sensitive tuberculosis, may cause various side effects, including metabolic disorders. The nuclear factor (erythroid-derived 2)-like 2 (NFE2L2, also known as NRF2) plays an essential regulatory role in cellular adaptive responses to stresses via the antioxidant response element (ARE). Our previous studies discovered that NRF2 regulates the expression of CCAAT-enhancer-binding protein β (Cebpb) and peroxisome proliferator-activated receptor gamma (Pparg) in the process of adipogenesis. Here, we found that prolonged RFP treatment in adult male mice fed a high-fat diet developed insulin resistance, but reduced fat accumulation and decreased expression of multiple adipogenic genes in white adipose tissues. In 3 T3-L1 preadipocytes, RFP reduced the induction of Cebpb, Pparg and Cebpa at mRNA and protein levels in the early and/or later stage of hormonal cocktail-induced adipogenesis. Mechanistic investigations demonstrated that RFP inhibits NRF2-ARE luciferase reporter activity and expression of NRF2 downstream genes under normal culture condition and in the early stage of adipogenesis in 3 T3-L1 preadipocytes, suggesting that RFP can disturb adipogenic differentiation via NRF2-ARE interference. Taken together, we demonstrate a potential mechanism that RFP impairs adipose function by which RFP likely inhibits NRF2-ARE pathway and thereby interrupts its downstream adipogenic transcription network.

Bioorthogonal Correlative Light-Electron Microscopy of Mycobacterium tuberculosis in Macrophages Reveals the Effect of Antituberculosis Drugs on Subcellular Bacterial Distribution

Bioorthogonal correlative light-electron microscopy (B-CLEM) can give a detailed overview of multicomponent biological systems. It can provide information on the ultrastructural context of bioorthogonal handles and other fluorescent signals, as well as information about subcellular organization. We have here applied B-CLEM to the study of the intracellular pathogen Mycobacterium tuberculosis (Mtb) by generating a triply labeled Mtb through combined metabolic labeling of the cell wall and the proteome of a DsRed-expressing Mtb strain. Study of this pathogen in a B-CLEM setting was used to provide information about the intracellular distribution of the pathogen, as well as its in situ response to various clinical antibiotics, supported by flow cytometric analysis of the bacteria, after recovery from the host cell (ex cellula). The RNA polymerase-targeting drug rifampicin displayed the most prominent effect on subcellular distribution, suggesting the most direct effect on pathogenicity and/or viability, while the cell wall synthesis-targeting drugs isoniazid and ethambutol effectively rescued bacterial division-induced loss of metabolic labels. The three drugs combined did not give a more pronounced effect but rather an intermediate response, whereas gentamicin displayed a surprisingly strong additive effect on subcellular distribution.

Potential Roles of Myeloid Differentiation Factor 2 on Neuroinflammation and Its Possible Interventions

Neuroinflammation is the primary response by immune cells in the nervous system to protect against infection. Chronic and uncontrolled neuroinflammation triggers neuronal injury and neuronal death resulting in a variety of neurodegenerative disorders. Therefore, fine tuning of the immune response in the nervous system is now extensively considered as a potential therapeutic intervention for those diseases. The immune cells of the nervous system express Toll-like receptor 4 (TLR4) together with myeloid differentiation factor 2 (MD-2) to protect against the pathogens. Over the last 10 years, antagonists targeting the functional domains of MD-2 have become attractive pharmacological intervention strategies in pre-clinical studies into neuroinflammation and its associated brain pathologies. This review aims to summarize and discuss the roles of TLR4-MD-2 signaling pathway activation in various models of neuroinflammation. This review article also highlights the studies reporting the effect of MD-2 antagonists on neuroinflammation in in vitro and in vivo studies.

Switch Off "Parallel Circuit": Insight of New Strategy of Simultaneously Suppressing Canonical and Noncanonical Inflammation Activation in Endotoxemic Mice

Sepsis is a life-threatening inflammatory disease with a high mortality rate and huge implicative costs. Lipopolysaccharide (LPS) from gram-negative bacteria activates toll-like receptor 4 (TLR4) and may trigger septic shock. However, potent TLR4 inhibitors TAK-242 and Eritoran have been terminated in phase III clinical trials because of inadequate efficacy. Inspired by the recently discovered intracellular, noncanonical LPS receptors, it is considered that TLR4-mediated canonical and caspase-mediated noncanonical inflammation can be seen as a "parallel circuit" to induce sepsis and endotoxemia. Logically, it is proposed that the dual inhibition of caspase-4/5/11 and TLR4 can be a potential novel strategy to develop new therapeutics for sepsis. To verify the strategy, two potential compounds are found: Luteolin and Diacerein with substantial antiinflammatory activity in vitro and in vivo. The results show that the survival rate of endotoxemic mice treated by these compounds is increased remarkably. LPS-induced organ damage is also prevented. Moreover, these compounds result in physical and mental recovery for endotoxemic mice. Notably, Luteolin exhibits better antiinflammatory activity than TAK-242 at comparable TLR4-inhibitory levels. These findings indicate that simultaneous inhibition of TLR4 and caspase-4/5/11 can be an anticipative strategy defeating sepsis and endotoxemia, which can be translated into significant medical and economic benefits.

The antibiotic bedaquiline activates host macrophage innate immune resistance to bacterial infection

Antibiotics are widely used in the treatment of bacterial infections. Although known for their microbicidal activity, antibiotics may also interfere with the host's immune system. Here, we analyzed the effects of bedaquiline (BDQ), an inhibitor of the mycobacterial ATP synthase, on human macrophages. Genome-wide gene expression analysis revealed that BDQ reprogramed cells into potent bactericidal phagocytes. We found that 579 and 1,495 genes were respectively differentially expressed in naive- and M. tuberculosis-infected macrophages incubated with the drug, with an over-representation of lysosome-associated genes. BDQ treatment triggered a variety of antimicrobial defense mechanisms, including phagosome-lysosome fusion, and autophagy. These effects were associated with activation of transcription factor EB, involved in the transcription of lysosomal genes, resulting in enhanced intracellular killing of different bacterial species that were naturally insensitive to BDQ. Thus, BDQ could be used as a host-directed therapy against a wide range of bacterial infections.

Clindamycin inhibits nociceptive response by reducing tumor necrosis factor-α and CXCL-1 production and activating opioidergic mechanisms

Clindamycin, a bacteriostatic semisynthetic lincosamide, is useful in the management of infections caused by aerobic and anaerobic Gram-positive cocci, including bacteremic pneumonia, streptococcal toxic shock syndrome and sepsis. It has been recently demonstrated that clindamycin inhibits in vitro and in vivo inflammatory cytokine production. In the present study, we investigated the effects of clindamycin in acute and chronic models of pain and inflammation in mice and the underlying mechanisms. Intraperitoneal (i.p.) administration of clindamycin (400 mg/kg) increased the animal's latency to exhibit the nociceptive behavior induced by noxious heat (hot plate model). Intrathecal injection of clindamycin (2, 10 and 50 µg) also increased the animals' latency to exhibit the nociceptive behavior. Tactile hypersensitivity and paw edema induced by intraplantar (i.pl.) injection of carrageenan were attenuated by previous administration of clindamycin (200 and 400 mg/kg, i.p.). Clindamycin (100, 200 and 400 mg/kg, i.p.) also attenuated ongoing tactile hypersensitivity and paw edema induced by i.pl. injection of complete Freund's adjuvant (CFA). The antinociceptive activity of clindamycin (400 mg/kg, i.p.) in the hot plate model was attenuated by previous administration of naltrexone (5 and 10 mg/kg, i.p.), but not glibenclamide or AM251. CFA-induced production of TNF-α and CXCL-1 was reduced by clindamycin (400 mg/kg, i.p.). Concluding, clindamycin exhibits activities in acute and chronic models of pain and inflammation. These effects are associated with reduced production of TNF-α and CXCL-1 and activation of opioidergic mechanisms. Altogether, these results indicate that the clindamycin's immunomodulatory effects may contribute to a pharmacological potential beyond its antibiotic property.

Lovastatin inhibits Toll-like receptor 4 signaling in microglia by targeting its co-receptor myeloid differentiation protein 2 and attenuates neuropathic pain

There is growing interest in drug repositioning to find new therapeutic indications for drugs already approved for use in people. Lovastatin is an FDA approved drug that has been used clinically for over a decade as a lipid-lowering medication. While lovastatin is classically considered to act as a hydroxymethylglutaryl (HMG)-CoA reductase inhibitor, the present series of studies reveal a novel lovastatin effect, that being as a Toll-like receptor 4 (TLR4) antagonist. Lovastatin selectively inhibits lipopolysaccharide (LPS)-induced TLR4-NF-κB activation without affecting signaling by other homologous TLRs. In vitro biophysical binding and cellular thermal shift assay (CETSA) show that lovastatin is recognized by TLR4's coreceptor myeloid differentiation protein 2 (MD-2). This finding is supported by molecular dynamics simulations that lovastatin targets the LPS binding pocket of MD-2 and lovastatin binding stabilizes the MD-2 conformation. In vitro studies of BV-2 microglial cells revealed that lovastatin inhibits multiple effects of LPS, including activation of NFkB; mRNA expression of tumor necrosis factor-a, interleukin-6 and cyclo-oxygenase 2; production of nitric oxide and reactive oxygen species; as well as phagocytic activity. Furthermore, intrathecal delivery of lovastatin over lumbosacral spinal cord of rats attenuated both neuropathic pain from sciatic nerve injury and expression of the microglial activation marker CD11 in lumbar spinal cord dorsal horn. Given the well-established role of microglia and proinflammatory signaling in neuropathic pain, these data are supportive that lovastatin, as a TLR4 antagonist, may be productively repurposed for treating chronic pain.

CSF levels of apolipoprotein C1 and autotaxin found to associate with neuropathic pain and fibromyalgia

Objective

Neuropathic pain and fibromyalgia are two common and poorly understood chronic pain conditions that lack satisfactory treatments, cause substantial suffering and societal costs. Today, there are no biological markers on which to base chronic pain diagnoses, treatment choices or to understand the pathophysiology of pain for the individual patient. This study aimed to investigate cerebrospinal fluid (CSF) protein profiles potentially associated with fibromyalgia and neuropathic pain.

Methods

CSF samples were collected from 25 patients with neuropathic pain (two independent sets, n=14 patients for discovery, and n=11 for verification), 40 patients with fibromyalgia and 134 controls without neurological disease from two different populations. CSF protein profiling of 55 proteins was performed using antibody suspension bead array technology.

Results

We found increased levels of apolipoprotein C1 (APOC1) in CSF of neuropathic pain patients compared to controls and there was a trend for increased levels also in fibromyalgia patients. In addition, levels of ectonucleotide pyrophosphatase family member 2 (ENPP2, also referred to as autotaxin) were increased in the CSF of fibromyalgia patients compared to all other groups including patients with neuropathic pain.

Conclusion

The increased levels of APOC1 and ENPP2 found in neuropathic pain and fibromyalgia patients may shed light on the underlying mechanisms of these conditions. Further investigation is required to elucidate their role in maintaining pain and other main symptoms of these disorders.

Stereochemistry and innate immune recognition: (+)-norbinaltorphimine targets myeloid differentiation protein 2 and inhibits toll-like receptor 4 signaling

Deregulation of innate immune TLR4 signaling contributes to various diseases including neuropathic pain and drug addiction. Naltrexone is one of the rare TLR4 antagonists with good blood-brain barrier permeability and showing no stereoselectivity for TLR4. By linking 2 naltrexone units through a rigid pyrrole spacer, the bivalent ligand norbinaltorphimine was formed. Interestingly, (+)-norbinaltorphimine [(+)-1] showed ∼25 times better TLR4 antagonist activity than naltrexone in microglial BV-2 cell line, whereas (-)-norbinaltorphimine [(-)-1] lost TLR4 activity. The enantioselectivity of norbinaltorphimine was further confirmed in primary microglia, astrocytes, and macrophages. The activities of meso isomer of norbinaltorphimine and the molecular dynamic simulation results demonstrate that the stereochemistry of (+)-1 is derived from the (+)-naltrexone pharmacophore. Moreover, (+)-1 significantly increased and prolonged morphine analgesia in vivo. The efficacy of (+)-1 is long lasting. This is the first report showing enantioselective modulation of the innate immune TLR signaling.-Zhang, X., Peng, Y., Grace, P. M., Metcalf, M. D., Kwilasz, A. J., Wang, Y., Zhang, T., Wu, S., Selfridge, B. R., Portoghese, P. S., Rice, K. C., Watkins, L. R., Hutchinson, M. R., Wang, X. Stereochemistry and innate immune recognition: (+)-norbinaltorphimine targets myeloid differentiation protein 2 and inhibits toll-like receptor 4 signaling.

Identification of novel analgesics through a drug repurposing strategy

The identification of new indications for approved or failed drugs is a process called drug repositioning or drug repurposing. The motivation includes overcoming the productivity gap that exists in drug development, which is a high-cost–high-risk process. Repositioning also includes rescuing drugs that have safely entered the market but have failed to demonstrate sufficient efficiency for the initial clinical indication. Considering the high prevalence of chronic pain, the lack of sufficient efficacy and the safety issues of current analgesics, repositioning seems to be an attractive approach. This review presents example of drugs that already have been repositioned and highlights new technologies that are available for the identification of additional compounds to stimulate the curiosity of readers for further exploration.

Innate Immune Signaling and Alcohol Use Disorders

Innate immune signaling is an important feature in the pathology of alcohol use disorders. Alcohol abuse causes persistent innate immune activation in the brain. This is seen in postmortem human alcoholic brain specimens, as well as in primate and rodent models of alcohol consumption. Further, in vitro models of alcohol exposure in neurons and glia also demonstrate innate immune activation. The activation of the innate immune system seems to be important in the development of alcohol use pathology, as anti-immune therapies reduce pathology and ethanol self-administration in rodent models. Further, innate immune activation has been identified in each of the stages of addiction: binge/intoxication, withdrawal/negative affect, and preoccupation/craving. This suggests that innate immune activation may play a role both in the development and maintenance of alcoholic pathology. In this chapter, we discuss the known contributions of innate immune signaling in the pathology of alcohol use disorders, and present potential therapeutic interventions that may be beneficial for alcohol use disorders.

Activation of GABAB Receptor Suppresses Diabetic Neuropathic Pain through Toll-Like Receptor 4 Signaling Pathway in the Spinal Dorsal Horn

Diabetic neuropathic pain (DNP) is a prevalent complication in diabetes patients. Neuronal inflammation and activation of Toll-like receptor 4 (TLR4) are involved in the occurrence of DNP. However, the underlying mechanisms remain unclear. Downregulation of gamma-aminobutyric acid B (GABA_B) receptor contributes to the DNP. GABA_B receptor interacts with NF-κB, a downstream signaling factor of TLR4, in a neuropathic pain induced by chemotherapy. In this study, we determined the role of TLR4/Myd88/NF-κB signaling pathways coupled to GABA_B receptors in the generation of DNP. Intrathecal injection of baclofen (GABA_B receptor agonist), LPS-RS ultrapure (TLR4 antagonist), MIP (MyD88 antagonist), or SN50 (NF-κB inhibitor) significantly increased paw withdrawal threshold (PWT) and paw withdrawal thermal latency (PWTL) in DNP rats, while intrathecal injection of saclofen (GABA_B receptor blocker) decreased PWT and PWTL in DNP rats. The expression of TLR4, Myd88, NF-κBp65, and their downstream components IL-1 and TNF-α was significantly higher in the spinal cord tissue in DNP rats compared to control rats. Following inhibition of TLR4, Myd88, and NF-κB, the expression of IL-1 and TNF-α decreased. Activation of GABA_B receptors downregulated the expression of TLR4, Myd88, NF-κBp65, IL-1, and TNF-α. Blockade of GABA_B receptors significantly upregulated expression of TLR4, Myd88, NF-κBp65, IL-1, and TNF-α. These data suggest that activation of the TLR4/Myd88/NF-κB signaling pathway is involved in the occurrence of DNP in rats. Activation of GABA_B receptor in the spinal cord may suppress the TLR4/Myd88/NF-κB signaling pathway and alleviate the DNP.

Dissecting the Innate Immune Recognition of Opioid Inactive Isomer (+)-Naltrexone Derived Toll-like Receptor 4 (TLR4) Antagonists

The opioid inactive isomer (+)-naltrexone is one of the rare Toll-like receptor 4 (TLR4) antagonists with good blood-brain barrier (BBB) permeability, which is a lead with promising potential for treating neuropathic pain and drug addiction. (+)-Naltrexone targets the lipopolysaccharides (LPS) binding pocket of myeloid differentiation protein 2 (MD-2) and blocks innate immune TLR4 signaling. However, the details of the molecular interactions of (+)-naltrexone and its derivatives with MD-2 are not fully understood, which hinders the ligand-based drug discovery. Herein, in silico and in vitro assays were performed to elucidate the innate immune recognition of the opioid inactive (+)-isomers. The results showed that the conserved LPS binding pocket of MD-2 accommodated these opioid inactive (+)-isomers. The calculated binding free energies of (+)-naltrexone and its derivatives in complex with MD-2 correlated well with their experimental binding affinities and TLR4 antagonistic activities. Hydrophobic residues in the MD-2 cavity interacted directly with these (+)-naltrexone based TLR4 antagonists and principally participated in ligand binding. Increasing the hydrophobicity of substituted group at N-17 improved its TLR4 antagonistic activity, while charged groups disfavored the binding with MD-2. Molecular dynamics (MD) simulations showed the binding of (+)-naltrexone or its derivatives to MD-2 stabilized the "collapsed" conformation of MD-2, consequently blocking the binding and signaling of TLR4. Thermodynamics and dynamic analysis showed the topology of substituted group at N-17 of (+)-naltrexone affected the binding with MD-2 and TLR4 antagonistic activity. This study provides a molecular insight into the innate immune recognition of opioid inactive (+)-isomers, which would be of great help for the development of next-generation of (+)-opioid based TLR4 antagonists.

DREADDed microglia in pain: Implications for spinal inflammatory signaling in male rats

The absence of selective pharmacological tools is a major barrier to the in vivo study of microglia. To address this issue, we developed a G_q- and G_i-coupled Designer Receptor Exclusively Activated by a Designer Drug (DREADD) to enable selective stimulation or inhibition of microglia, respectively. DREADDs under a CD68 (microglia/macrophage) promoter were intrathecally transfected via an AAV9 vector. Naïve male rats intrathecally transfected with G_q (stimulatory) DREADDs exhibited significant allodynia following intrathecal administration of the DREADD-selective ligand clozapine-N-oxide (CNO), which was abolished by intrathecal interleukin-1 receptor antagonist. Chronic constriction injury-induced allodynia was attenuated by intrathecal CNO in male rats intrathecally transfected with G_i (inhibitory) DREADDs. To explore mechanisms, BV2 cells were stably transfected with G_q or G_i DREADDs in vitro. CNO treatment induced pro-inflammatory mediator production per se from cells expressing G_q-DREADDs, and inhibited lipopolysaccharide- and CCL2-induced inflammatory signaling from cells expressing G_i-DREADDs. These studies are the first to manipulate microglia function using DREADDs, which allow the role of glia in pain to be conclusively demonstrated, unconfounded by neuronal off-target effects that exist for all other drugs that also inhibit glia. Hence, these studies are the first to conclusively demonstrate that in vivo stimulation of resident spinal microglia in intact spinal cord is a) sufficient for allodynia, and b) necessary for allodynia induced by peripheral nerve injury. DREADDs are a unique tool to selectively explore the physiological and pathological role of microglia in vivo.

Induction of suppressor of cytokine signaling 3 via HSF-1-HSP70-TLR4 axis attenuates neuroinflammation and ameliorates postoperative pain

Postoperative pain is a common form of acute pain that, if not managed effectively, can become chronic pain. Evidence has shown that glia, especially microglia, mediate neuroinflammation, which plays a vital role in pain sensitization. Moreover, toll-like receptor 4 (TLR4), the tumor necrosis factor receptor (TNF-R), the interleukin-1 receptor (IL-1R), and the interleukin-6 receptor (IL-6R) have been considered key components in central pain sensitization and neuroinflammation. Therefore, we hypothesized that activation of the body's endogenous "immune brakes" will inhibit these receptors and achieve inflammation tolerance as well as relieve postoperative pain. After searching for potential candidates to serve as this immune brake, we identified and focused on the suppressor of cytokine signaling 3 (SOCS3) gene. To regulate SOCS3 expression, we used paeoniflorin to induce heat shock protein 70 (HSP70)/TLR4 signaling. We found that paeoniflorin significantly induced SOCS3 expression both in vitro and in vivo and promoted the efflux of HSP70 from the cytoplasm to the extracellular environment. Furthermore, paeoniflorin markedly attenuated incision-induced mechanical allodynia, and this effect was abolished by small interfering RNAs targeting SOCS3. These findings demonstrated an effective and safe strategy to alleviate postoperative pain.

Rifampicin Alleviates Atopic Dermatitis-Like Response in vivo and in vitro

Atopic dermatitis (AD) is a common inflammatory skin disorder mediated by inflammatory cells, such as macrophages and mast cells. Rifampicin is mainly used for the treatment of tuberculosis. Recently, it was reported that rifampicin has anti-inflammatory and immune-suppressive activities. In this study, we investigated the effect of rifampicin on atopic dermatitis in vivo and in vitro. AD was induced by treatment with 2, 4-dinitrochlorobenzene (DNCB) in NC/Nga mice. A subset of mice was then treated with rifampicin by oral administration. The severity score and scratching behavior were alleviated in the rifampicin-treated group. Serum immunoglobulin E (IgE) and interleukin-4 (IL-4) levels were also ameliorated in mice treated with rifampicin. We next examined whether rifampicin has anti-atopic activity via suppression of mast cell activation. Rifampicin suppressed the release of β-hexosaminidase and histamine from human mast cell (HMC)-1 cultures stimulated with compound 48/80. Treatment with rifampicin also inhibited secretion of inflammatory mediators, such tumor necrosis factor-α (TNF-α) and prostaglandin D₂ (PGD₂), in mast cells activated by compound 48/80. The mRNA expression of cyclooxygenase 2 (COX-2) was reduced in the cells treated with rifampicin in a concentration-dependent manner. These results suggest that rifampicin can be used to treat atopic dermatitis.

Toll-Like Receptor-4 Signaling Drives Persistent Fibroblast Activation and Prevents Fibrosis Resolution in Scleroderma

Significance: This review provides current overview of the emerging role of innate immunity in driving fibrosis, and preventing its resolution, in scleroderma (systemic sclerosis, SSc). Understanding the mechanisms of dysregulated innate immunity in fibrosis and SSc will provide opportunities for therapeutic interventions using novel agents and repurposed existing drugs. Recent Advances: New insights from genomic and genetic studies implicate components of innate immune signaling such as pattern recognition receptors (PRRs), downstream signaling intermediates, and endogenous inhibitors, in fibrosis in SSc. Recent studies distinguish innate immune signaling in tissue-resident myofibroblasts and bone marrow-derived immune cells and define their roles in the development and persistence of tissue fibrosis. Critical Issues: Activation of toll-like receptors (TLRs) and other PRR mechanisms occurs in resident nonimmune cells within injured tissue microenvironments. These cells respond to damage-associated molecular patterns (DAMPs), such as tenascin-C that are recognized as danger signals, and elicit matrix production, cytokine secretion, and myofibroblast transformation and survival. When these responses persist due to constitutive TLR activation or impaired termination by endogenous inhibitors, they interfere with fibrosis resolution. The genetic basis and molecular mechanisms of these phenomena in the context of fibrosis are under current investigation. Future Directions: Precise delineation of the pathogenic DAMPs, their interaction with TLRs and other PRRs, the downstream signaling pathways and transcriptional events, and the fibroblast-specific regulation and function of endogenous inhibitors of innate immunity, will form the foundation for innovative targeted therapies to block fibrosis by reestablishing balanced innate immune signaling in fibroblasts.

The role of neuroimmune signaling in alcoholism

Alcohol consumption and stress increase brain levels of known innate immune signaling molecules. Microglia, the innate immune cells of the brain, and neurons respond to alcohol, signaling through Toll-like receptors (TLRs), high-mobility group box 1 (HMGB1), miRNAs, pro-inflammatory cytokines and their associated receptors involved in signaling between microglia, other glia and neurons. Repeated cycles of alcohol and stress cause a progressive, persistent induction of HMGB1, miRNA and TLR receptors in brain that appear to underlie the progressive and persistent loss of behavioral control, increased impulsivity and anxiety, as well as craving, coupled with increasing ventral striatal responses that promote reward seeking behavior and increase risk of developing alcohol use disorders. Studies employing anti-oxidant, anti-inflammatory, anti-depressant, and innate immune antagonists further link innate immune gene expression to addiction-like behaviors. Innate immune molecules are novel targets for addiction and affective disorders therapies. This article is part of the Special Issue entitled "Alcoholism".

Oral clindamycin and rifampicin combination therapy for hidradenitis suppurativa: a prospective study and 1-year follow-up

BACKGROUND

Limited data exist on the use of systemic antibiotic treatment for hidradenitis supportive (HS).

AIM

To investigate the effectiveness, safety and relapse rate of HS treated with a combination of daily oral clindamycin and rifampicin.

METHODS

This was a prospective, hospital-based study of oral clindamycin 600 mg and rifampicin 600 mg daily for 12 weeks for treatment of HS. Patients were followed up for 1 year to monitor for relapse.

RESULTS

In total, 26 patients with HS received oral clindamycin and rifampicin. Most were overweight or obese (73%), and most were smokers (88%). After 12 weeks, clinical response was noted in 19 patients (73%). Response was associated only with female sex (P = 0.02), and not with body mass index, Hurley stage or lesion location. Eight patients (31%) experienced adverse events. At the 1-year follow-up, there was sustained efficacy in 7 (41%) patients, while 10 (59%) had disease relapse after a mean time of 4.2 months.

CONCLUSIONS

Oral clindamycin with oral rifampicin for 12 weeks is an effective and tolerable regimen for HS.

Systemic TAK-242 prevents intrathecal LPS evoked hyperalgesia in male, but not female mice and prevents delayed allodynia following intraplantar formalin in both male and female mice: The role of TLR4 in the evolution of a persistent pain state

OBJECTIVE

Pain resulting from local tissue injury or inflammation typically resolves with time. Frequently, however, this pain may unexpectedly persist, becoming a pathological chronic state. Increasingly, the innate and adaptive immune systems are being implicated in the initiation and maintenance of these persistent conditions. In particular, Toll-like receptor 4 (TLR4) signaling has been shown to mediate the transition to a persistent pain state in a sex-dependent manner. In the present work, we explored this contribution using the TLR4 antagonist, TAK-242.

METHODS

Male and female C57Bl/6 mice were given intravenous (IV), intrathecal (IT), or intraperitoneal (IP) TAK-242 prior to IT delivery of lipopolysaccharide (LPS), and tactile reactivity was assessed at regular intervals over 72-h. Additional groups of mice were treated with IP TAK-242 prior to intraplantar formalin, and flinching was monitored for 1-h. Tactile reactivity was assessed at 7-days after formalin delivery.

RESULTS

LPS evoked TNF release from male and female macrophages and RAW267.4 cells, which was blocked in a concentration dependent fashion by TAK-242. In vivo, IT LPS evoked tactile allodynia to a greater degree in male than female mice. TAK-242, given by all routes, prevented development of IT LPS-induced tactile allodynia in male animals, but did not reverse their established allodynia. TLR4 deficiency and TAK-242 treatment attenuated IT LPS-induced allodynia in male, but not female mice. In the formalin model, pre-treatment with TAK-242 did not affect Phase 1 or Phase 2 flinching, but prevented the delayed tactile allodynia in both male and unexpectedly in female mice (Phase 3).

CONCLUSIONS

Together, these results suggest that TAK-242 is a TLR4 antagonist that has efficacy after systemic and intrathecal delivery and confirms the role of endogenous TLR4 signaling in triggering the development of a delayed allodynia in both male and female mice.

Pattern recognition receptors in chronic pain: Mechanisms and therapeutic implications

For the individual, it is vital to promptly detect and recognize a danger that threatens the integrity of the body. Pattern recognition receptors (PRRs) are several classes of protein families originally classified as receptors detecting exogenous pathogens. PRRs are also capable of recognizing molecules released from damaged tissues (damage-associated molecular pattern molecules; DAMPs) and thereby contribute to danger recognition. Importantly, it is now evident that PRRs, such as toll-like receptors (TLRs) and receptors for advanced glycation end products (RAGE), are not only expressed in peripheral immune cells but also present in neurons and glial cells in the nervous system. These PRR-expressing cells work in concert, enabling highly sensitive danger recognition. However, this sensitiveness can act as a double-edged sword. Accumulated evidence has led to the hypothesis that aberrant activation of PRRs may play a crucial role in the pathogenesis of pathological pain. Indeed, numerous studies employing gene deletion or pharmacological inhibition of PRRs successfully reversed or prevented pathological pain in experimental animal models. Furthermore, a number of preclinical studies have shown the therapeutic potential of targeting PRRs for chronic pain. Here, we review the current knowledge regarding the role of PRRs in chronic pain and discuss the promise and challenges of targeting PRRs as a novel therapeutic approach for chronic pain.

Pharmacological characterization of the opioid inactive isomers (+)-naltrexone and (+)-naloxone as antagonists of toll-like receptor 4

BACKGROUND AND PURPOSE

The toll-like receptor TLR4 is involved in neuropathic pain and in drug reward and reinforcement. The opioid inactive isomers (+)-naltrexone and (+)-naloxone act as TLR4 antagonists, reversing neuropathic pain and reducing opioid and cocaine reward and reinforcement. However, how these agents modulate TLR4 signalling is not clear. Here, we have elucidated the molecular mechanism of (+)-naltrexone and (+)-naloxone on TLR4 signalling.

EXPERIMENTAL APPROACH

BV-2 mouse microglial cell line, primary rat microglia and primary rat peritoneal macrophages were treated with LPS and TLR4 signalling inhibitors. Effects were measured using Western blotting, luciferase reporter assays, fluorescence microscopy and ELISA KEY RESULTS: (+)-Naltrexone and (+)-naloxone were equi-potent inhibitors of the LPS-induced TLR4 downstream signalling and induction of the pro-inflammatory factors NO and TNF-α. Similarly, (+)-naltrexone or (+)-naloxone inhibited production of reactive oxygen species and increased microglial phagocytosis, induced by LPS. However, (+)-naltrexone and (+)-naloxone did not directly inhibit the increased production of IL-1β, induced by LPS. The drug interaction of (+)-naloxone and (+)-naltrexone was additive. (+)-Naltrexone or (+)-naloxone inhibited LPS-induced activation of IFN regulatory factor 3 and production of IFN-β. However, they did not inhibit TLR4 signalling via the activation of either NF-κB, p38 or JNK in these cellular models.

CONCLUSIONS AND IMPLICATIONS

(+)-Naltrexone and (+)-naloxone were TRIF-IFN regulatory factor 3 axis-biased TLR4 antagonists. They blocked TLR4 downstream signalling leading to NO, TNF-α and reactive oxygen species. This pattern may explain, at least in part, the in vivo therapeutic effects of (+)-naltrexone and (+)-naloxone.

A genome-wide association study suggests an association of Chr8p21.3 (GFRA2) with diabetic neuropathic pain

Background

Neuropathic pain, caused by a lesion or a disease affecting the somatosensory system, is one of the most common complications in diabetic patients. The purpose of this study is to identify genetic factors contributing to this type of pain in a general diabetic population.

Method

We accessed the Genetics of Diabetes Audit and Research Tayside (GoDARTS) datasets that contain prescription information and monofilament test results for 9439 diabetic patients, among which 6927 diabetic individuals were genotyped by Affymetrix SNP6.0 or Illumina OmniExpress chips. Cases of neuropathic pain were defined as diabetic patients with a prescription history of at least one of five drugs specifically indicated for the treatment of neuropathic pain and in whom monofilament test result was positive for sensory neuropathy in at least one foot. Controls were individuals who did not have a record of receiving any opioid analgesics. Imputation of non‐genotyped SNPs was performed by IMPUTE2, with reference files from 1000 Genomes Phase I datasets.

Results

After data cleaning and relevant exclusions, imputed genotypes of 572 diabetic neuropathic pain cases and 2491 diabetic controls were used in the Fisher's exact test. We identified a cluster in the Chr8p21.3, next to GFRA2 with a lowest p‐value of 1.77 × 10⁻⁷ at rs17428041. The narrow‐sense heritability of this phenotype was 11.00%.

Conclusion

This genome‐wide association study on diabetic neuropathic pain suggests new evidence for the involvement of variants near GFRA2 with the disorder, which needs to be verified in an independent cohort and at the molecular level.

Myeloid differentiation protein 2 facilitates pollen- and cat dander-induced innate and allergic airway inflammation

BACKGROUND

The National Health and Nutrition Examination Survey identified several pollens and cat dander as among the most common allergens that induce allergic sensitization and allergic diseases. We recently reported that ragweed pollen extract (RWPE) requires Toll-like receptor 4 (TLR4) to stimulate CXCL-mediated innate neutrophilic inflammation, which in turn facilitates allergic sensitization and airway inflammation. Myeloid differentiation protein 2 (MD2) is a TLR4 coreceptor, but its role in pollen- and cat dander-induced innate and allergic inflammation has not been critically evaluated.

OBJECTIVE

We sought to elucidate the role of MD2 in inducing pollen- and cat dander-induced innate and allergic airway inflammation.

METHODS

TCM(Null) (TLR4(Null), CD14(Null), MD2(Null)), TLR4(Hi), and TCM(Hi) cells and human bronchial epithelial cells with small interfering RNA-induced downregulation of MD2 were stimulated with RWPE, other pollen allergic extracts, or cat dander extract (CDE), and activation of nuclear factor κB (NF-κB), secretion of the NF-κB-dependent CXCL8, or both were quantified. Wild-type mice or mice with small interfering RNA knockdown of lung MD2 were challenged intranasally with RWPE or CDE, and innate and allergic inflammation was quantified.

RESULTS

RWPE stimulated MD2-dependent NF-κB activation and CXCL secretion. Likewise, Bermuda, rye, timothy, pigweed, Russian thistle, cottonwood, walnut, and CDE stimulated MD2-dependent CXCL secretion. RWPE and CDE challenge induced MD2-dependent and CD14-independent innate neutrophil recruitment. RWPE induced MD2-dependent allergic sensitization and airway inflammation.

CONCLUSIONS

MD2 plays an important role in induction of allergic sensitization to cat dander and common pollens relevant to human allergic diseases.

A Genome-wide Association Study Provides Evidence of Sex-specific Involvement of Chr1p35.1 (ZSCAN20-TLR12P) and Chr8p23.1 (HMGB1P46) With Diabetic Neuropathic Pain

Neuropathic pain is defined as pain arising as a direct consequence of a lesion or a disease affecting the somatosensory system and it affects around 1 in 4 diabetic patients in the UK. The purpose of this genome-wide association study (GWAS) was to identify genetic contributors to this disorder. Cases of neuropathic pain were defined as diabetic patients with a multiple prescription history of at least one of five drugs specifically indicated for the treatment of neuropathic pain. Controls were diabetic individuals who were not prescribed any of these drugs, nor amitriptyline, carbamazepine, or nortriptyline. Overall, 961 diabetic neuropathic pain cases and 3260 diabetic controls in the Genetics of Diabetes Audit and Research Tayside (GoDARTS) cohort were identified. We found a cluster in the Chr1p35.1 (ZSCAN20-TLR12P) with a lowest P value of 2.74 × 10(- 7) at rs71647933 in females and a cluster in the Chr8p23.1, next to HMGB1P46 with a lowest P value of 8.02 × 10(- 7) at rs6986153 in males. Sex-specific narrow sense heritability was higher in males (30.0%) than in females (14.7%). This GWAS on diabetic neuropathic pain provides evidence for the sex-specific involvement of Chr1p35.1 (ZSCAN20-TLR12P) and Chr8p23.1 (HMGB1P46) with the disorder, indicating the need for further research.