Interleukin-6: an emerging regulator of pathological pain

Challenges in translational drug research in neuropathic and inflammatory pain: the prerequisites for a new paradigm

AIM

Despite an improved understanding of the molecular mechanisms of nociception, existing analgesic drugs remain limited in terms of efficacy in chronic conditions, such as neuropathic pain. Here, we explore the underlying pathophysiological mechanisms of neuropathic and inflammatory pain and discuss the prerequisites and opportunities to reduce attrition and high-failure rate in the development of analgesic drugs.

METHODS

A literature search was performed on preclinical and clinical publications aimed at the evaluation of analgesic compounds using MESH terms in PubMed. Publications were selected, which focused on (1) disease mechanisms leading to chronic/neuropathic pain and (2) druggable targets which are currently under evaluation in drug development. Attention was also given to the role of biomarkers and pharmacokinetic-pharmacodynamic modelling.

RESULTS

Multiple mechanisms act concurrently to produce pain, which is a non-specific manifestation of underlying nociceptive pathways. Whereas these manifestations can be divided into neuropathic and inflammatory pain, it is now clear that inflammatory mechanisms are a common trigger for both types of pain. This has implications for drug development, as the assessment of drug effects in experimental models of neuropathic and chronic pain is driven by overt behavioural measures. By contrast, the use of mechanistic biomarkers in inflammatory pain has provided the pharmacological basis for dose selection and evaluation of non-steroidal anti-inflammatory drugs (NSAIDs).

CONCLUSION

A different paradigm is required for the identification of relevant targets and candidate molecules whereby pain is coupled to the cause of sensorial signal processing dysfunction rather than clinical symptoms. Biomarkers which enable the characterisation of drug binding and target activity are needed for a more robust dose rationale in early clinical development. Such an approach may be facilitated by quantitative clinical pharmacology and evolving technologies in brain imaging, allowing accurate assessment of target engagement, and prediction of treatment effects before embarking on large clinical trials.

Inhibition of interleukin-6 function attenuates the central sensitization and pain behavior induced by osteoarthritis

Chronic pain is the most prominent and disabling symptom in the patients with osteoarthritis (OA), and the underlying mechanism largely remains unclear. Interleukin-6 (IL-6), a proinflammatory cytokine, is critically involved in the development and maintenance of central sensitization in several rodent models of chronic pain. The present study aims to elucidate the IL-6 mediated neurological adaptation in dorsal horn in the rat with monosodium iodoacetate (MIA) - induced OA. Significant upregulation of IL-6 expression was detected in the dorsal horn in the modeled rats. Blockade of IL-6 function by tocilizumab markedly suppressed the activation of astrocytes and microglia in the ipsilateral dorsal horn, reduced c-Fos immunoreactivity in dorsal horn neurons, and attenuated the upregulation of glutamate receptor subunits GluR1 and NR2B in dorsal horn in the rats with MIA-induced OA. It was further reported that administration of tocilizumab significantly improved the performance in weight-bearing test and mitigated the mechanical allodynia in the modeled rats. These data illustrated spinal IL-6 mediated mechanism underlying the chronic pain, and proposed the potential therapeutic effect of tocilizumab on the chronic pain in the setting of OA.

Pain in ankylosing spondylitis: a neuro-immune collaboration

Clinicians have commonly differentiated chronic back pain into two broad subsets: namely, non-inflammatory (or mechanical) back pain and inflammatory back pain. As the terminology suggests, the latter category, in which ankylosing spondylitis (AS) is prominent, presupposes a close link between pain and inflammation. Advances in research into the genetics and immunology of AS have improved our understanding of the inflammatory processes involved in this disease, and have led to the development of potent anti-inflammatory biologic therapeutic agents. However, evidence from clinical trials and from biomarker and imaging studies in patients with AS indicate that pain and inflammation are not always correlated. Thus, the assumption that pain in AS is a reliable surrogate marker for inflammation might be an over-simplification. This Review provides an overview of current concepts relating to neuro-immune interactions in AS and summarizes research that reveals an increasingly complex interplay between the activation of the immune system and pain pathways in the nervous system. The different types of pain experienced by patients with AS, insights from brain imaging studies, neurological mechanisms of pain, sex bias in pain and how the immune system can modify pain in patients with AS are also discussed.

Aspergillus fumigatus-induced early inflammatory response in pulmonary microvascular endothelial cells: Role of p38 MAPK and inhibition by silibinin

Human invasive pulmonary aspergillosis (IPA) is a serious infectious disease mainly caused by Aspergillus fumigatus (A. fumigatus). Pulmonary microvascular endothelial cells (PMVECs) are important ones in the human lung tissue. However, it remains unclear about the role of PMVECs in IPA. In the present study, we cocultured PMVECs with A. fumigatus. We observed that A. fumigatus induced dose- and time-dependent increases of interleukin 6 (IL-6), interleukin 1β (IL-1β) and intercellular adhesion molecule 1 (ICAM-1) concentration in the cultures. Significant increases in IL-6, IL-1β, E-selectin, and ICAM-1 mRNA expression were also observed in the cultures treated with A. fumigatus. While preincubation with SB203580 (10μM) did not cause significant changes in IL-6, IL-1β and ICAM-1 concentration in the cocultures, significant IL-6, IL-1β and ICAM-1 concentration decreases were observed in the cocultures preincubated with SB203580 (20μM). Neither SP600125 (10-20μM) nor PD98059 (10-20μM) caused significant changes in IL-6, IL-1β and ICAM-1 concentration in the cocultures. PCR results also showed that SB203580 (20μM) (neither SP600125 (20μM) nor PD98059 (20μM)) preincubation significantly decreased IL-6, IL-1β, E-selectin and ICAM-1 mRNA expression in the cocultures. In addition, significant p38 MAPK phosphorylation increase was observed in the PMVECs cultures treated with A. fumigatus. Furthermore, silibinin pre-treatment and post-treatment were observed to significantly down-regulate mRNA and protein expression of proinflammatory factors and adhesion molecules in the cocultures. Finally, we observed that silibinin significantly inhibited A. fumigatus-induced p38 MAPK activation in PMVECs. Our results indicated that PMVECs might participate in IPA early inflammation which is mediated by p38 MAPK. Silibinin may inhibit A. fumigatus-induced inflammation in PMVECs through p38 MAPK.

The use of non-steroidal anti-inflammatory drugs in neurological diseases

Non-steroidal anti-inflammatory drugs (NSAIDs) have been in use for many years and constitute a large part of prescriptions issued in daily practice. Although NSAIDs are used for many diseases in neurology, they have also been tested as a new therapeutic option for various other diseases. While their effects on headache and cerebrovascular diseases are well known, little is known about their impact on neurodegenerative diseases. This review discusses the use, effects and safety of NSAIDs in neurological diseases.

The Role of Spinal GABAB Receptors in Cancer-Induced Bone Pain in Rats

Cancer-induced bone pain (CIBP) remains a major challenge in advanced cancer patients because of our lack of understanding of its mechanisms. Previous studies have shown the vital role of γ-aminobutyric acid B receptors (GABABRs) in regulating nociception and various neuropathic pain models have shown diminished activity of GABABRs. However, the role of spinal GABABRs in CIBP remains largely unknown. In this study, we investigated the specific cellular mechanisms of GABABRs in the development and maintenance of CIBP in rats. Our behavioral results show that acute as well as chronic intrathecal treatment with baclofen, a GABABR agonist, significantly attenuated CIBP-induced mechanical allodynia and ambulatory pain. The expression levels of GABABRs were significantly decreased in a time-dependent manner and colocalized mostly with neurons and a minority with astrocytes and microglia. Chronic treatment with baclofen restored the expression of GABABRs and markedly inhibited the activation of cyclic adenosine monophosphate (cAMP)-dependent protein kinase and the cAMP-response element-binding protein signaling pathway.

PERSPECTIVE

Our findings provide, to our knowledge, the first evidence that downregulation of GABABRs contribute to the development and maintenance of CIBP and restored diminished GABABRs attenuate CIBP-induced pain behaviors at least partially by inhibiting the protein kinase/cAMP-response element-binding protein signaling pathway. Therefore, spinal GABABR may become a potential therapeutic target for the management of CIBP.

Ion channels and neuronal hyperexcitability in chemotherapy-induced peripheral neuropathy; cause and effect?

Abstract

Cancer is the second leading cause of death worldwide and is a major global health burden. Significant improvements in survival have been achieved, due in part to advances in adjuvant antineoplastic chemotherapy. The most commonly used antineoplastics belong to the taxane, platinum, and vinca alkaloid families. While beneficial, these agents are frequently accompanied by severe side effects, including chemotherapy-induced peripheral neuropathy (CPIN). While CPIN affects both motor and sensory systems, the majority of symptoms are sensory, with pain, tingling, and numbness being the predominant complaints. CPIN not only decreases the quality of life of cancer survivors but also can lead to discontinuation of treatment, thereby adversely affecting survival. Consequently, minimizing the incidence or severity of CPIN is highly desirable, but strategies to prevent and/or treat CIPN have proven elusive. One difficulty in achieving this goal arises from the fact that the molecular and cellular mechanisms that produce CPIN are not fully known; however, one common mechanism appears to be changes in ion channel expression in primary afferent sensory neurons. The processes that underlie chemotherapy-induced changes in ion channel expression and function are poorly understood. Not all antineoplastic agents directly affect ion channel function, suggesting additional pathways may contribute to the development of CPIN Indeed, there are indications that these drugs may mediate their effects through cellular signaling pathways including second messengers and inflammatory cytokines. Here, we focus on ion channelopathies as causal mechanisms for CPIN and review the data from both pre-clinical animal models and from human studies with the aim of facilitating the development of appropriate strategies to prevent and/or treat CPIN.

Anti-rheumatic drug iguratimod (T-614) alleviates cancer-induced bone destruction via down-regulating interleukin-6 production in a nuclear factor-κB-dependent manner

Cytokines are believed to be involved in a "vicious circle" of progressive interactions in bone metastasis. Iguratimod is a novel anti-rheumatic drug which is reported to have the capability of anti-cytokines. In this study, a rat model was constructed to investigate the effect of iguratimod on bone metastasis and it was found that iguratimod alleviated cancer-induced bone destruction. To further explore whether an anti-tumor activity of iguratimod contributes to the effect of bone resorption suppression, two human breast cancer cell lines MDA-MB-231 and MCF-7 were studied. The effect of iguratimod on tumor proliferation was detected by CCK-8 assay and flow cytometry. The effects of iguratimod on migration and invasion of cancer cells were determined by wound-healing and Transwell assays. Results showed that high dose (30 μg/mL) iguratimod slightly suppressed the proliferation of cancer cells but failed to inhibit their migration and invasion capacity. Interestingly, iguratimod decreased the transcription level of IL-6 in MDA-MB-231 cells in a concentration-dependent manner. Moreover, iguratimod partially impaired NF-κB signaling by suppressing the phosphorylation of NF-κB p65 subunit. Our findings indicated that iguratimod may alleviate bone destruction by partially decreasing the expression of IL-6 in an NF-κB-dependent manner, while it has little effect on the tumor proliferation and invasion.

Targeting glia for bone cancer pain

INTRODUCTION

Bone cancer pain (BCP) remains to be a clinical challenge with limited pharmaceutical interventions. Therefore, novel therapeutic targets for the management of BCP are in desperate need. Recently, a growing body of evidence has suggested that glial cells may play a pivotal role in the pathogenesis of BCP. Areas covered: This review summarizes the recent progress in the understanding of glia in BCP and reveals the potential therapeutic targets in glia for BCP treatment. Expert opinion: Pharmacological interventions inhibiting the activation of glial cells, suppressing glia-derived proinflammatory cytokines, cell surface receptors, and the intracellular signaling pathways may be beneficial for the pain management of advanced cancer patients. However, these pharmacological interventions should not disrupt the normal function of glia cells since they play a vital supportive and protective role in the central nervous system.