Therapeutic potential for leukocyte elastase in chronic pain states harboring a neuropathic component

Granzyme B in aging and age-related pathologies

Aging is a major risk factor for pathologies that manifest later in life. Much attention is devoted towards elucidating how prolonged environmental exposures and inflammation promote biological (accelerated) tissue aging. Granzymes, a family of serine proteases, are increasingly recognized for their emerging roles in biological aging and disease. Widely recognized as intracellular mediators of cell death, granzymes, particularly granzyme B (GzmB), also accumulate in the extracellular milieu of tissues with age, contributing to chronic tissue injury, inflammation, and impaired healing. Consequently, this has prompted the field to reconsider how GzmB regulation, accumulation, and proteolysis impact health and disease with age. While GzmB is observed in numerous age-related conditions, the current review focuses on mechanistic studies where proof-of-concept has been forwarded.

Unraveling impact and potential mechanisms of baseline pain on efficacy of immunotherapy in lung cancer patients: a retrospective and bioinformatic analysis

Objective

Pain is a prevalent discomfort symptom associated with cancer, yet the correlations and potential mechanisms between pain and the efficacy of cancer immunotherapy remain uncertain.

Methods

Non-small cell lung cancer (NSCLC) patients who received immune checkpoint inhibitors (ICIs) in the inpatient department of Guangdong Provincial Hospital of Chinese Medicine from January 1, 2018, to December 31, 2021, were retrospectively enrolled. Through cox regression analysis, prognostic factors and independent prognostic factors affecting the efficacy of ICIs were identified, and a nomogram model was constructed. Hub cancer-related pain genes (CRPGs) were identified through bioinformatic analysis. Finally, the expression levels of hub CRPGs were detected using an enzyme-linked immunosorbent assay (ELISA).

Results

Before PSM, a total of 222 patients were enrolled in this study. Univariate and multivariate cox analysis indicated that bone metastasis and NRS scores were independent prognostic factors for the efficacy of ICIs. After PSM, a total of 94 people were enrolled in this study. Univariate cox analysis and multivariate cox analysis indicated that age, platelets, Dnlr, liver metastasis, bone metastasis, and NRS scores were independent prognostic factors for the efficacy of ICIs. A nomogram was constructed based on 6 independent prognostic factors with AUC values of 0.80 for 1-year, 0.73 for 2-year, and 0.80 for 3-year survival. ELISA assay results indicated that the level of CXCL12 significantly decreased compared to baseline after pain was relieved.

Conclusion

Baseline pain is an independent prognostic factor affecting the efficacy of ICIs in lung cancer, potentially through CXCL12-mediated inflammation promotion and immunosuppression.

Exploring neuroinflammation: A key driver in neuropathic pain disorders

Inflammation is a fundamental part of the body's natural defense mechanism, involving immune cells and inflammatory mediators to promote healing and protect against harm. In the event of a lesion or disease of the somatosensory nervous system, inflammation, however, triggers a cascade of changes in both the peripheral and central nervous systems, ultimately contributing to chronic neuropathic pain. Substantial evidence links neuroinflammation to various conditions associated with neuropathic pain. This chapter will explore the role of neuroinflammation in the initiation, maintenance, and resolution of peripheral and central neuropathic pain. Additionally, biomarkers of neuroinflammation in humans will be examined, emphasizing their relevance in different neuropathic pain disorders.

New insights in the mechanisms of opioid analgesia and tolerance: Ultramicronized palmitoylethanolamide down-modulates vascular endothelial growth factor-A in the nervous system

Growing evidence suggests that opioid analgesics modulate angiogenesis during pathophysiological processes. Vascular endothelial growth factor-A (VEGF-A) was recently proposed to be involved in pain development. To date, no anti-angiogenic drug is used for pain management. When administered in a bioavailable formulation, (i.e., ultramicronized) N-palmitoylethanolamine (PEA) delays the onset of morphine tolerance, improves morphine analgesic activity and reduces angiogenesis in in vivo models. This study aimed at investigating whether VEGF-A is involved in PEA-induced delay of morphine tolerance. The anti-VEGF-A monoclonal antibody bevacizumab was used as a reference drug. Preemptive and concomitant treatment with ultramicronized PEA delayed morphine tolerance and potentiated the analgesic effect of morphine, while counteracting morphine-induced increase of VEGF-A in the nervous system. Similar results were obtained when bevacizumab was administered together with morphine. Of note, bevacizumab showed an analgesic effect per se. In equianalgesic treatment regimens (obtained through increasing morphine doses and associating PEA), PEA resulted in lower expression of VEGF-A in dorsal root ganglia (DRG) and spinal cord compared to morphine alone. Similar results were observed for plasma levels of the soluble VEGF receptor 1 (sFLT-1). Moreover, in morphine-treated animals, two pain-related genes (i.e., Serpina3n and Eaat2) showed a more than 3-fold increase in their expression at spinal cord and DRG level, with the increase being significantly counteracted by PEA treatment. This study supports the hypothesis that the effects of PEA on morphine analgesia and tolerance may be mediated by the down-modulation of VEGF-A and sFLT-1 in the nervous system and plasma, respectively.

Steroid inhibited Serpina3n expression which was positively correlated with the degrees of spinal cord injury

Aims

The aim of our project was to identify proteins associated with the extent of spinal cord injury (SCI) and subsequent long-term neurological recovery.

Methods

Through proteomic analysis, we identified proteins that are differentially expressed specifically in the acute phase of injury. We analyzed the concentrations of differentially expressed proteins in serum and the injured spinal cord segment by ELISA.

Results

Serpina3n protein expression in the injured spinal cord segment was increased 101-fold at 12 h after severe SCI and 89-fold at 12 h after mild SCI, as determined by LC‒MS/MS. In the mild and severe SCI groups, serum Serpina3n levels began to increase at 12 h and peaked at 24 h. At 12 h, 24 h and 3 d after injury, serum Serpina3n protein levels were significantly correlated with the severity of injury (12 h: r = 0.6034, P = 0.008; 24 h: r = 0.7542, P = 0.0003; 3 d: r = 0.862, P < 0.001). Serum Serpina3n levels at 2 h, 24 h and 3 d post injury were significantly correlated with long-term neurological recovery at 28 d after SCI (2 h: r = -0.5781, P = 0.012; 24 h: r = -0.5912, P = 0.0098; 3 d: r = -0.7792, P < 0.0001). Methylprednisolone treatment would decrease the serum Serpina3n levels in mice with mild and severe SCI compared with those in placebo-group mice at 12 h and 24 h after SCI. The serum Serpina3n concentration in the severe SCI group was significantly reduced on the third day after steroid treatment.

Conclusion

Taken together, these data suggest that serpina3n may be a circulating biomarker of acute SCI and may be closely associated with injury severity and long-term motor function recovery.

The dorsal root ganglion as a target for neurorestoration in neuropathic pain

Neuropathic pain is a severe and chronic condition widely found in the general population. The reason for this is the extensive variety of damage or diseases that can spark this unpleasant constant feeling in patients. During the processing of pain, the dorsal root ganglia constitute an important region where dorsal root ganglion neurons play a crucial role in the transmission and propagation of sensory electrical stimulation. Furthermore, the dorsal root ganglia have recently exhibited a regenerative capacity that should not be neglected in the understanding of the development and resolution of neuropathic pain and in the elucidation of innovative therapies. Here, we will review the complex interplay between cells (satellite glial cells and inflammatory cells) and factors (cytokines, neurotrophic factors and genetic factors) that takes place within the dorsal root ganglia and accounts for the generation of the aberrant excitation of primary sensory neurons occurring in neuropathic pain. More importantly, we will summarize an updated view of the current pharmacologic and nonpharmacologic therapies targeting the dorsal root ganglia for the treatment of neuropathic pain.

The role of neuroinflammation in the transition of acute to chronic pain and the opioid-induced hyperalgesia and tolerance

Current evidence suggests that activation of glial and immune cells leads to increased production of proinflammatory mediators, creating a neuroinflammatory state. Neuroinflammation has been proven to be a fundamental mechanism in the genesis of acute pain and its transition to neuropathic and chronic pain. A noxious event that stimulates peripheral afferent nerve fibers may also activate pronociceptive receptors situated at the dorsal root ganglion and dorsal horn of the spinal cord, as well as peripheral glial cells, setting off the so-called peripheral sensitization and spreading neuroinflammation to the brain. Once activated, microglia produce cytokines, chemokines, and neuropeptides that can increase the sensitivity and firing properties of second-order neurons, upregulating the signaling of nociceptive information to the cerebral cortex. This process, known as central sensitization, is crucial for chronification of acute pain. Immune-neuronal interactions are also implicated in the lesser-known complex regulatory relationship between pain and opioids. Current evidence suggests that activated immune and glial cells can alter neuronal function, induce, and maintain pathological pain, and disrupt the analgesic effects of opioid drugs by contributing to the development of tolerance and dependence, even causing paradoxical hyperalgesia. Such alterations may occur when the neuronal environment is impacted by trauma, inflammation, and immune-derived molecules, or when opioids induce proinflammatory glial activation. Hence, understanding these intricate interactions may help in managing pain signaling and opioid efficacy beyond the classical pharmacological approach.

Immunotherapies in chronic pain through modulation of neuroimmune interactions

It is generally believed that immune activation can elicit pain through production of inflammatory mediators that can activate nociceptive sensory neurons. Emerging evidence suggests that immune activation may also contribute to the resolution of pain by producing distinct pro-resolution/anti-inflammatory mediators. Recent research into the connection between the immune and nervous systems has opened new avenues for immunotherapy in pain management. This review provides an overview of the most utilized forms of immunotherapies (e.g., biologics) and highlight their potential for immune and neuronal modulation in chronic pain. Specifically, we discuss pain-related immunotherapy mechanisms that target inflammatory cytokine pathways, the PD-L1/PD-1 pathway, and the cGAS/STING pathway. This review also highlights cell-based immunotherapies targeting macrophages, T cells, neutrophils and mesenchymal stromal cells for chronic pain management.

Isolation and Characterization of Poeciguamerin, a Peptide with Dual Analgesic and Anti-Thrombotic Activity from the Poecilobdella manillensis Leech

When Poecilobdella manillensis attacks its prey, the prey bleeds profusely but feels little pain. We and other research teams have identified several anticoagulant molecules in the saliva of P. manillensis, but the substance that produces the paralyzing effect in P. manillensis is not known. In this study, we successfully isolated, purified, and identified a serine protease inhibitor containing an antistasin-like domain from the salivary secretions of P. manillensis. This peptide (named poeciguamerin) significantly inhibited elastase activity and slightly inhibited FXIIa and kallikrein activity, but had no effect on FXa, trypsin, or thrombin activity. Furthermore, poeciguamerin exhibited analgesic activity in the foot-licking and tail-withdrawal mouse models and anticoagulant activity in the FeCl₃-induced carotid artery thrombosis mouse model. In this study, poeciguamerin was found to be a promising elastase inhibitor with potent analgesic and antithrombotic activity for the inhibition of pain and thrombosis after surgery or in inflammatory conditions.

Neutrophils infiltrate sensory ganglia and mediate chronic widespread pain in fibromyalgia

Fibromyalgia is a debilitating widespread chronic pain syndrome that occurs in 2 to 4% of the population. The prevailing view that fibromyalgia results from central nervous system dysfunction has recently been challenged with data showing changes in peripheral nervous system activity. Using a mouse model of chronic widespread pain through hyperalgesic priming of muscle, we show that neutrophils invade sensory ganglia and confer mechanical hypersensitivity on recipient mice, while adoptive transfer of immunoglobulin, serum, lymphocytes, or monocytes has no effect on pain behavior. Neutrophil depletion abolishes the establishment of chronic widespread pain in mice. Neutrophils from patients with fibromyalgia also confer pain on mice. A link between neutrophil-derived mediators and peripheral nerve sensitization is already established. Our observations suggest approaches for targeting fibromyalgia pain via mechanisms that cause altered neutrophil activity and interactions with sensory neurons.

Transcriptional Profiling of TGF-β Superfamily Members in Lumbar DRGs of Rats Following Sciatic Nerve Axotomy and Activin C Inhibits Neuropathic Pain

BACKGROUND

Neuroinflammation and cytokines play critical roles in neuropathic pain and axon degeneration/regeneration. Cytokines of transforming growth factor-β superfamily have implications in pain and injured nerve repair processing. However, the transcriptional profiles of the transforming growth factor-β superfamily members in dorsal root ganglia under neuropathic pain and axon degeneration/regeneration conditions remain elusive.

OBJECTIVE

We aimed to plot the transcriptional profiles of transforming growth factor-β superfamily components in lumbar dorsal root ganglia of sciatic nerve-axotomized rats and to further verify the profiles by testing the analgesic effect of activin C, a representative cytokine, on neuropathic pain.

METHODS

Adult male rats were axotomized in sciatic nerves, and lumbar dorsal root ganglia were isolated for total RNA extraction or section. A custom microarray was developed and employed to plot the gene expression profiles of transforming growth factor-β superfamily components. Realtime RT-PCR was used to confirm changes in the expression of activin/inhibin family genes, and then in situ hybridization was performed to determine the cellular locations of inhibin α, activin βC, BMP-5 and GDF-9 mRNAs. The rat spared nerve injury model was performed, and a pain test was employed to determine the effect of activin C on neuropathic pain.

RESULTS

The expression of transforming growth factor-β superfamily cytokines and their signaling, including some receptors and signaling adaptors, were robustly upregulated. Activin βC subunit mRNAs were expressed in the small-diameter dorsal root ganglion neurons and upregulated after axotomy. Single intrathecal injection of activin C inhibited neuropathic pain in spared nerve injury model.

CONCLUSION

This is the first report to investigate the transcriptional profiles of members of transforming growth factor-β superfamily in axotomized dorsal root ganglia. The distinct cytokine profiles observed here might provide clues toward further study of the role of transforming growth factor-β superfamily in the pathogenesis of neuropathic pain and axon degeneration/regeneration after peripheral nerve injury.

Potential Neuroimmune Interaction in Chronic Pain: A Review on Immune Cells in Peripheral and Central Sensitization

Chronic pain is a long-standing unpleasant sensory and emotional feeling that has a tremendous impact on the physiological functions of the body, manifesting itself as a dysfunction of the nervous system, which can occur with peripheral and central sensitization. Many recent studies have shown that a variety of common immune cells in the immune system are involved in chronic pain by acting on the peripheral or central nervous system, especially in the autoimmune diseases. This article reviews the mechanisms of regulation of the sensory nervous system by neutrophils, macrophages, mast cells, B cells, T cells, and central glial cells. In addition, we discuss in more detail the influence of each immune cell on the initiation, maintenance, and resolution of chronic pain. Neutrophils, macrophages, and mast cells as intrinsic immune cells can induce the transition from acute to chronic pain and its maintenance; B cells and T cells as adaptive immune cells are mainly involved in the initiation of chronic pain, and T cells also contribute to the resolution of it; the role of glial cells in the nervous system can be extended to the beginning and end of chronic pain. This article aims to promote the understanding of the neuroimmune mechanisms of chronic pain, and to provide new therapeutic ideas and strategies for the control of chronic pain at the immune cellular level.

Gasdermin D-mediated release of IL-33 from senescent hepatic stellate cells promotes obesity-associated hepatocellular carcinoma

Long-term senescent cells exhibit a secretome termed the senescence-associated secretory phenotype (SASP). Although the mechanisms of SASP factor induction have been intensively studied, the release mechanism and how SASP factors influence tumorigenesis in the biological context remain unclear. In this study, using a mouse model of obesity-induced hepatocellular carcinoma (HCC), we identified the release mechanism of SASP factors, which include interleukin-1β (IL-1β)- and IL-1β-dependent IL-33, from senescent hepatic stellate cells (HSCs) via gasdermin D (GSDMD) amino-terminal-mediated pore. We found that IL-33 was highly induced in senescent HSCs in an IL-1β-dependent manner in the tumor microenvironment. The release of both IL-33 and IL-1β was triggered by lipoteichoic acid (LTA), a cell wall component of gut microbiota that was transferred and accumulated in the liver tissue of high-fat diet-fed mice, and the release of these factors was mediated through cell membrane pores formed by the GSDMD amino terminus, which was cleaved by LTA-induced caspase-11. We demonstrated that IL-33 release from HSCs promoted HCC development via the activation of ST2-positive T_reg cells in the liver tumor microenvironment. The accumulation of GSDMD amino terminus was also detected in HSCs from human NASH-associated HCC patients, suggesting that similar mechanism could be involved in a certain type of human HCC. These results uncover a release mechanism for SASP factors from sensitized senescent HSCs in the tumor microenvironment, thereby facilitating obesity-associated HCC progression. Furthermore, our findings highlight the therapeutic potential of inhibitors of GSDMD-mediated pore formation for HCC treatment.

Drug Repurposing to Target Neuroinflammation and Sensory Neuron-Dependent Pain

Around 20% of the American population have chronic pain and estimates in other Western countries report similar numbers. This represents a major challenge for global health care systems. Additional problems for the treatment of chronic and persistent pain are the comparably low efficacy of existing therapies, the failure to translate effects observed in preclinical pain models to human patients and related setbacks in clinical trials from previous attempts to develop novel analgesics. Drug repurposing offers an alternative approach to identify novel analgesics as it can bypass various steps of classical drug development. In recent years, several approved drugs were attributed analgesic properties. Here, we review available data and discuss recent findings suggesting that the approved drugs minocycline, fingolimod, pioglitazone, nilotinib, telmisartan, and others, which were originally developed for the treatment of different pathologies, can have analgesic, antihyperalgesic, or neuroprotective effects in preclinical and clinical models of inflammatory or neuropathic pain. For our analysis, we subdivide the drugs into substances that can target neuroinflammation or substances that can act on peripheral sensory neurons, and highlight the proposed mechanisms. Finally, we discuss the merits and challenges of drug repurposing for the development of novel analgesics.

Neuro-Immunity and Gut Dysbiosis Drive Parkinson's Disease-Induced Pain

Parkinson's disease (PD) is the second most common neurodegenerative disorder, affecting 1-2% of the population aged 65 and over. Additionally, non-motor symptoms such as pain and gastrointestinal dysregulation are also common in PD. These impairments might stem from a dysregulation within the gut-brain axis that alters immunity and the inflammatory state and subsequently drives neurodegeneration. There is increasing evidence linking gut dysbiosis to the severity of PD's motor symptoms as well as to somatosensory hypersensitivities. Altogether, these interdependent features highlight the urgency of reviewing the links between the onset of PD's non-motor symptoms and gut immunity and whether such interplays drive the progression of PD. This review will shed light on maladaptive neuro-immune crosstalk in the context of gut dysbiosis and will posit that such deleterious interplays lead to PD-induced pain hypersensitivity.

The relationship of neutrophil elastase and proteinase 3 with risk factors, and chronic complications in type 2 diabetes: A Fenofibrate Intervention and Event Lowering in Diabetes (FIELD) sub-study

INTRODUCTION

Neutrophil elastase (NE) and proteinase 3 (PR3) are novel inflammation biomarkers. We investigated their associations with chronic complications, determinants of biomarker levels and effects of fenofibrate in patients with type 2 diabetes mellitus (T2DM) from Fenofibrate Intervention and Event Lowering in Diabetes study.

METHODS

Plasma NE and PR3 levels were quantified at baseline (n = 2000), and relationships with complications over 5-years assessed. Effects of fenofibrate on biomarker levels (n = 200) were determined at four follow-up visits.

RESULTS

Higher waist-to-hip ratio, homocysteine and C-reactive protein and lower apoA-II were determinants of higher NE and PR3 levels. Higher NE levels were associated with on-trial stroke and cardiovascular mortality, and higher PR3 levels with on-trial stroke, but associations were not significant after adjustment for confounding factors. Although higher NE and PR3 levels were associated with baseline total microvascular disease, only NE levels were associated with on-trial neuropathy or amputation. These associations were not significant after adjusting for multiple comparisons. NE and PR3 levels did not change with fenofibrate.

CONCLUSIONS

In T2DM plasma NE and PR3 levels are associated with vascular risk factors, and total microvascular disease at baseline, but on rigorous analyses were not associated with on-trial complications. Levels were not changed by fenofibrate.

Sulfonated Nonsaccharide Heparin Mimetics Are Potent and Noncompetitive Inhibitors of Human Neutrophil Elastase

Human neutrophil elastase (HNE) is a serine protease that plays vital roles in inflammation, innate immune response, and tissue remodeling processes. HNE has been actively pursued as a drug target, particularly for the treatment of cardiopulmonary diseases. Although thousands of molecules have been reported to inhibit HNE, yet very few are being evaluated in early clinical trials, with sivelestat as the only approved HNE inhibitor. We report here a novel chemotype of sulfonated nonsaccharide heparin mimetics as potent and noncompetitive inhibitors of HNE. Using a chromogenic substrate hydrolysis assay, 14 sulfonated nonsaccharide heparin mimetics were tested for their inhibitory activity against HNE. Only 12 molecules inhibited HNE with IC₅₀ values of 0.22-88.3 μM. The inhibition of HNE by these molecules was salt-dependent. Interestingly, a specific hexa-sulfonated molecule inhibited HNE with an IC₅₀ value of 0.22 μM via noncompetitive mechanism, as demonstrated by Michaelis-Menten kinetics. The hexa-sulfonated derivative demonstrated at least 455-, 221-, 1590-, 21-, and 381-fold selectivity indices over other heparin-binding coagulation proteins including factors IIa, Xa, IXa, XIa, and FXIIIa, respectively. At the highest concentrations tested, the molecule also did not significantly inhibit other serine proteases of plasmin, trypsin, and chymotrypsin. Further supporting its selectivity, the molecule did not show heparin-like effects on clotting times of human plasma. The molecule also did not affect the proliferation of three cell lines at a concentration as high as 10 μM. Interestingly, the hexa-sulfonated molecule also inhibited cathepsin G with an IC₅₀ value of 0.57 μM alluding to a dual anti-inflammatory action. A computational approach was exploited to identify putative binding site(s) for this novel class of HNE inhibitors. Overall, the reported hexa-sulfonated nonsaccharide heparin mimetic serves as a new platform to develop potent, selective, and noncompetitive inhibitors of HNE for therapeutic purposes.

Ulinastatin Exhibits Antinociception in Rat Models of Acute Somatic and Visceral Pain Through Inhibiting the Local and Central Inflammation

Introduction

Ulinastatin, a broad-spectrum serine protease inhibitor, has been widely used to treat various diseases clinically. However, so far, the antinociceptive effect of ulinastatin remains less studied experimentally and the underlying mechanisms of ulinastatin for pain relief remain unclear. This study aimed to find evidence of the analgesic effect of ulinastatin on acute somatic and visceral pain.

Methods

The analgesic effect of ulinastatin on acute somatic and visceral pain was evaluated by using formalin and acetic acid-induced writhing test. The analgesic mechanism of ulinastatin was verified by detecting the peripheral inflammatory cell infiltration and spinal glial activation with hematoxylin-eosin (H&E) and immunohistochemistry staining.

Results

We found that both of intraperitoneal (i.p.) pre-administration and post-administration of ulinastatin could reduce the total number of flinching and the licking duration following intraplantar formalin injection in a dose-related manner. However, the inhibitory effect of ulinastatin existed only in the second phase (Phase 2) of formalin-induced spontaneous pain response, with no effect in the first phase (Phase 1). The formalin-induced edema and ulcer were also improved by i.p. administration of ulinastatin. Moreover, i.p. administration of ulinastatin was also able to delay the occurrence of acetic acid-induced writhing and reduced the total number of writhes dose-dependently. We further demonstrated that ulinastatin significantly decreased the local inflammatory cell infiltration in injured paw and peritoneum tissue under formalin and acetic acid test separately. The microglial and astrocytic activation in the spinal dorsal horn induced by intraplantar formalin and i.p. acetic acid injection were also dramatically inhibited by i.p. administration of ulinastatin.

Conclusion

Our results for the first time provided a new line of evidence showing that ulinastatin could attenuate acute somatic and visceral pain by inhibiting the peripheral and spinal inflammatory reaction.

A genome-wide screen reveals microRNAs in peripheral sensory neurons driving painful diabetic neuropathy

ABSTRACT

Diabetes is a leading cause of peripheral neuropathy (diabetic peripheral neuropathy, DPN), and uncontrolled long-lasting hyperglycemia leads to severe complications. A major proportion of diabetics develop excruciating pain with a variable course. Mechanisms leading to painful DPN are not completely understood and treatment options limited. We hypothesized that epigenetic modulation at the level of microRNA (miRNA) expression triggered by metabolic imbalance and nerve damage regulates the course of pain development. We used clinically relevant preclinical models, genome-wide screening, in silico analyses, cellular assays, miRNA fluorescent in situ hybridization, in vivo molecular manipulations, and behavioral analyses in the current study. We identified miRNAs and their targets that critically impact on nociceptive hypersensitivity in painful DPN. Our analyses identify miR-33 and miR-380 expressed in nociceptive neurons as critical denominators of diabetic pain and miR-124-1 as a mediator of physiological nociception. Our comprehensive analyses on the putative mRNA targets for miR-33 or miR-124-1 identified a set of mRNAs that are regulated after miR-33 or miR-124-1 overexpression in dorsal root ganglia in vivo. Our results shed light on the regulation of DPN pathophysiology and implicate specific miRNAs as novel therapeutic targets for treating painful DPN.

Sex differences in neuro(auto)immunity and chronic sciatic nerve pain

Chronic pain occurs with greater frequency in women, with a parallel sexually dimorphic trend reported in sufferers of many autoimmune diseases. There is a need to continue examining neuro-immune-endocrine crosstalk in the context of sexual dimorphisms in chronic pain. Several phenomena in particular need to be further explored. In patients, autoantibodies to neural antigens have been associated with sensory pathway hyper-excitability, and the role of self-antigens released by damaged nerves remains to be defined. In addition, specific immune cells release pro-nociceptive cytokines that directly influence neural firing, while T lymphocytes activated by specific antigens secrete factors that either support nerve repair or exacerbate the damage. Modulating specific immune cell populations could therefore be a means to promote nerve recovery, with sex-specific outcomes. Understanding biological sex differences that maintain, or fail to maintain, neuroimmune homeostasis may inform the selection of sex-specific treatment regimens, improving chronic pain management by rebalancing neuroimmune feedback. Given the significance of interactions between nerves and immune cells in the generation and maintenance of neuropathic pain, this review focuses on sex differences and possible links with persistent autoimmune activity using sciatica as an example.

Cathepsin E in neutrophils contributes to the generation of neuropathic pain in experimental autoimmune encephalomyelitis

Pain is a frequent and disabling symptom in patients with multiple sclerosis (MS); however, the underlying mechanisms of MS-related pain are not fully understood. Here, we demonstrated that cathepsin E (CatE) in neutrophils contributes to the generation of mechanical allodynia in experimental autoimmune encephalomyelitis, an animal model of MS. We showed that CatE-deficient (CatE) mice were highly resistant to myelin oligodendrocyte glycoprotein (MOG35-55)-induced mechanical allodynia. After MOG35-55 immunization, neutrophils immediately accumulated in the dorsal root ganglion (DRG). Adoptive transfer of MOG35-55-stimulated wild-type neutrophils into the dorsal root ganglion induced mechanical allodynia in the recipient C57BL/6 mice. However, the pain threshold did not change when MOG35-55-stimulated CatE neutrophils were transferred into the recipient C57BL/6 mice. MOG35-55 stimulation caused CatE-dependent secretion of elastase in neutrophils. Behavioral analyses revealed that sivelestat, a selective neutrophil elastase inhibitor, suppressed mechanical allodynia induced by adoptively transferred MOG35-55-stimulated neutrophils. MOG35-55 directly bound to toll-like receptor 4, which led to increased production of CatE in neutrophils. Our findings suggest that inhibition of CatE-dependent elastase production in neutrophil might be a potential therapeutic target for pain in patients with MS.

Novel Analgesics with Peripheral Targets

A limited number of peripheral targets generate pain. Inflammatory mediators can sensitize these. The review addresses targets acting exclusively or predominantly on sensory neurons, mediators involved in inflammation targeting sensory neurons, and mediators involved in a more general inflammatory process, of which an analgesic effect secondary to an anti-inflammatory effect can be expected. Different approaches to address these systems are discussed, including scavenging proinflammatory mediators, applying anti-inflammatory mediators, and inhibiting proinflammatory or facilitating anti-inflammatory receptors. New approaches are contrasted to established ones; the current stage of progress is mentioned, in particular considering whether there is data from a molecular and cellular level, from animals, or from human trials, including an early stage after a market release. An overview of publication activity is presented, considering a IuPhar/BPS-curated list of targets with restriction to pain-related publications, which was also used to identify topics.

Neuropathic Pain: From Mechanisms to Treatment

Neuropathic pain caused by a lesion or disease of the somatosensory nervous system is a common chronic pain condition with major impact on quality of life. Examples include trigeminal neuralgia, painful polyneuropathy, postherpetic neuralgia, and central poststroke pain. Most patients complain of an ongoing or intermittent spontaneous pain of, for example, burning, pricking, squeezing quality, which may be accompanied by evoked pain, particular to light touch and cold. Ectopic activity in, for example, nerve-end neuroma, compressed nerves or nerve roots, dorsal root ganglia, and the thalamus may in different conditions underlie the spontaneous pain. Evoked pain may spread to neighboring areas, and the underlying pathophysiology involves peripheral and central sensitization. Maladaptive structural changes and a number of cell-cell interactions and molecular signaling underlie the sensitization of nociceptive pathways. These include alteration in ion channels, activation of immune cells, glial-derived mediators, and epigenetic regulation. The major classes of therapeutics include drugs acting on α₂δ subunits of calcium channels, sodium channels, and descending modulatory inhibitory pathways.

Cytotoxic Immunity in Peripheral Nerve Injury and Pain

Cytotoxicity and consequent cell death pathways are a critical component of the immune response to infection, disease or injury. While numerous examples of inflammation causing neuronal sensitization and pain have been described, there is a growing appreciation of the role of cytotoxic immunity in response to painful nerve injury. In this review we highlight the functions of cytotoxic immune effector cells, focusing in particular on natural killer (NK) cells, and describe the consequent action of these cells in the injured nerve as well as other chronic pain conditions and peripheral neuropathies. We describe how targeted delivery of cytotoxic factors via the immune synapse operates alongside Wallerian degeneration to allow local axon degeneration in the absence of cell death and is well-placed to support the restoration of homeostasis within the nerve. We also summarize the evidence for the expression of endogenous ligands and receptors on injured nerve targets and infiltrating immune cells that facilitate direct neuro-immune interactions, as well as modulation of the surrounding immune milieu. A number of chronic pain and peripheral neuropathies appear comorbid with a loss of function of cellular cytotoxicity suggesting such mechanisms may actually help to resolve neuropathic pain. Thus while the immune response to peripheral nerve injury is a major driver of maladaptive pain, it is simultaneously capable of directing resolution of injury in part through the pathways of cellular cytotoxicity. Our growing knowledge in tuning immune function away from inflammation toward recovery from nerve injury therefore holds promise for interventions aimed at preventing the transition from acute to chronic pain.

MHCII-restricted T helper cells: an emerging trigger for chronic tactile allodynia after nerve injuries

Nerve injury-induced chronic pain has been an urgent problem for both public health and clinical practice. While transition to chronic pain is not an inevitable consequence of nerve injuries, the susceptibility/resilience factors and mechanisms for chronic neuropathic pain after nerve injuries still remain unknown. Current preclinical and clinical studies, with certain notable limitations, have shown that major histocompatibility complex class II–restricted T helper (Th) cells is an important trigger for nerve injury-induced chronic tactile allodynia, one of the most prevalent and intractable clinical symptoms of neuropathic pain. Moreover, the precise pathogenic neuroimmune interfaces for Th cells remain controversial, not to mention the detailed pathogenic mechanisms. In this review, depending on the biology of Th cells in a neuroimmunological perspective, we summarize what is currently known about Th cells as a trigger for chronic tactile allodynia after nerve injuries, with a focus on identifying what inconsistencies are evident. Then, we discuss how an interdisciplinary perspective would improve the understanding of Th cells as a trigger for chronic tactile allodynia after nerve injuries. Finally, we hope that the expected new findings in the near future would translate into new therapeutic strategies via targeting Th cells in the context of precision medicine to either prevent or reverse chronic neuropathic tactile allodynia.

The role of neutrophils in neuro-immune modulation

Neutrophils are peripheral immune cells that represent the first recruited innate immune defense against infections and tissue injury. However, these cells can also induce overzealous responses and cause tissue damage. Although the role of neutrophils activating the immune system is well established, only recently their critical implications in neuro-immune interactions are becoming more relevant. Here, we review several aspects of neutrophils in the bidirectional regulation between the nervous and immune systems. First, the role of neutrophils as a diffuse source of acetylcholine and catecholamines is controversial as well as the effects of these neurotransmitters in neutrophil's functions. Second, neutrophils contribute for the activation and sensitization of sensory neurons, and thereby, in events of nociception and pain. In addition, nociceptor activation promotes an axon reflex triggering a local release of neural mediators and provoking neutrophil activation. Third, the recruitment of neutrophils in inflammatory responses in the nervous system suggests these immune cells as innovative targets in the treatment of central infectious, neurological and neurodegenerative disorders. Multidisciplinary studies involving immunologists and neuroscientists are required to define the role of the neurons-neutrophils communication in the pathophysiology of infectious, inflammatory, and neurological disorders.

A patenting perspective on human neutrophil elastase (HNE) inhibitors (2014-2018) and their therapeutic applications

INTRODUCTION

Human neutrophil elastase (HNE) is involved in a variety of serious chronic diseases, especially cardiopulmonary pathologies. For this reason, the regulation of HNE activity represents a promising therapeutic approach, which is evident by the development of a number of new and selective HNE inhibitors, both in the academic and pharmaceutical environments.

AREAS COVERED

The present review analyzes and summarizes the patent literature regarding human neutrophil elastase inhibitors for the treatment of cardiopulmonary diseases over 2014-2018.

EXPERT OPINION

HNE is an interesting and defined target to treat various inflammatory diseases, including a number of cardiopulmonary pathologies. The research in this field is quite active, and a number of HNE inhibitors are currently in various stages of clinical development. In addition, new opportunities for HNE inhibitor development stem from recent studies demonstrating the involvement of HNE in many other inflammatory pathologies, including rheumatoid arthritis, inflammatory bowel disease, skin diseases, and cancer. Furthermore, the development of dual HNE/proteinase 3 inhibitors is being pursued as an innovative approach for the treatment of neutrophilic inflammatory diseases. Thus, these new developments will likely stimulate new and increased interest in this important therapeutic target and for the development of novel and selective HNE inhibitors.

Evoked hypoalgesia is accompanied by tonic pain and immune cell infiltration in the dorsal root ganglia at late stages of diabetic neuropathy in mice

Diabetic peripheral neuropathy is a major debilitating late complication of diabetes, which significantly reduces the quality of life in patients. Diabetic peripheral neuropathy is associated with a wide spectrum of sensory abnormalities, where in loss of sensation or hypoalgesia to applied external stimuli is paradoxically accompanied by debilitating tonic spontaneous pain. In numerous studies on animal models of diabetic peripheral neuropathy, behavioural measurements have been largely confined to analysis of evoked withdrawal to mechanical and thermal stimuli applied to dermatomes, whereas spontaneous, on-going pain has not been widely studied. In the Streptozotocin model of type 1 diabetes, we employed the Conditioned Place Preference test to assess tonic pain. Our results indicate that both phases, that is, early evoked hypersensitivity (i.e. 5–7 weeks post-Streptozotocin) as well as late stage hypoalgesia (i.e. 17–20 weeks post-Streptozotocin) are accompanied by significant tonic pain in mice with diabetic peripheral neuropathy. We also report on the temporal relation between on-going pain and neuropathological changes in the dorsal root ganglia of mice with diabetic peripheral neuropathy up to 6 months post-Streptozotocin. Neither early hypersensitivity nor late hypoalgesia were associated with markers of cellular stress in the dorsal root ganglia. Whereas significant neutrophil infiltration was observed in the dorsal root ganglia over both early and late stages post-Streptozotocin, T-cell infiltration in the dorsal root ganglia was prominent at late stages post-Streptozotocin. Thus, longitudinal analyses reveal that similar to patients with chronic diabetic peripheral neuropathy, mice show tonic pain despite sensory loss after several months in the Streptozotocin model, which is accompanied by neuroimmune interactions in the dorsal root ganglia.