Role of capsaicin-sensitive nerves and tachykinins in mast cell tryptase-induced inflammation of murine knees

Randomized controlled trials of the effects of capsaicin or menthol on irritable bowel syndrome: a systematic review and meta-analysis

Irritable bowel syndrome (IBS) is a common intestinal disease characterized by abdominal pain, abdominal distension and irregular defecation frequency, and it has had a high incidence and low cure rate in recent years. Visceral hypersensitivity (VH) is one of the main physiological indicators of IBS, and TRPV1 and TRPM8 (transient receptor potential vanilloid 1 and melastatin 8) play crucial roles in VH and are widely distributed in the intestine, significantly impacting abdominal pain in IBS patients. Under the guidance of PRISMA, four databases were systematically searched at the outset, including PubMed, Web of Science, Embase, and Cochrane Library. Randomized controlled trials (RCTs) reporting specific abdominal pain scores (rather than the incidence rate) in IBS patients receiving capsaicin or menthol (agonist of TRPV1 and TRPM8) interventions were included. A meta-analysis was conducted on the retrieved studies, which consisted of three articles on capsaicin and five articles on menthol, to compare the efficacy of capsaicin and menthol in alleviating abdominal pain in IBS patients under conditions of low heterogeneity. The results demonstrated that menthol had a significant effect in relieving abdominal pain in IBS patients. Conversely, although the effect of capsaicin was not statistically significant, two studies involving long-term capsaicin intervention suggested its potential to reduce VH and subsequently relieve abdominal pain, which may be attributed to the up-regulation of the TRPV1 receptor in the gastrointestinal tract of individuals with IBS.

Osteosarcoma-Induced Pain Is Mediated by Glial Cell Activation in the Spinal Dorsal Horn, but Not Capsaicin-Sensitive Nociceptive Neurons: A Complex Functional and Morphological Characterization in Mice

Bone cancer and its related chronic pain are huge clinical problems since the available drugs are often ineffective or cannot be used long term due to a broad range of side effects. The mechanisms, mediators and targets need to be identified to determine potential novel therapies. Here, we characterize a mouse bone cancer model induced by intratibial injection of K7M2 osteosarcoma cells using an integrative approach and investigate the role of capsaicin-sensitive peptidergic sensory nerves. The mechanical pain threshold was assessed by dynamic plantar aesthesiometry, limb loading by dynamic weight bearing, spontaneous pain-related behaviors via observation, knee diameter with a digital caliper, and structural changes by micro-CT and glia cell activation by immunohistochemistry in BALB/c mice of both sexes. Capsaicin-sensitive peptidergic sensory neurons were defunctionalized by systemic pretreatment with a high dose of the transient receptor potential vanilloid 1 (TRPV1) agonist resiniferatoxin (RTX). During the 14- and 28-day experiments, weight bearing on the affected limb and the paw mechanonociceptive thresholds significantly decreased, demonstrating secondary mechanical hyperalgesia. Signs of spontaneous pain and osteoplastic bone remodeling were detected both in male and female mice without any sex differences. Microglia activation was shown by the increased ionized calcium-binding adapter molecule 1 (Iba1) immunopositivity on day 14 and astrocyte activation by the enhanced glial fibrillary acidic protein (GFAP)-positive cell density on day 28 in the ipsilateral spinal dorsal horn. Interestingly, defunctionalization of the capsaicin-sensitive afferents representing approximately 2/3 of the nociceptive fibers did not alter any functional parameters. Here, we provide the first complex functional and morphological characterization of the K7M2 mouse osteosarcoma model. Bone-cancer-related chronic pain and hyperalgesia are likely to be mediated by central sensitization involving neuroinflammation via glial cell activation in the spinal dorsal horn, but not the capsaicin-sensitive sensory neuronal system.

The multifaceted role of mast cells in joint inflammation and arthritis

OBJECTIVE

To review current knowledge surrounding the role of mast cells in joint inflammation and arthritis.

METHOD

Narrative review.

RESULTS

Mast cells (MCs) are commonly observed in the synovium of the joint, particularly surrounding blood vessels and nerve endings. Some studies have reported increased MC number and degranulation in patients with osteoarthritis (OA). In two studies, MCs were the only immune cell type found in higher concentrations in synovium of OA patients compared to rheumatoid arthritis patients. Activation of MCs in OA includes signaling pathways such as immunoglobulin E/Fc epsilon Receptor 1 (IgE/FcεR1), immunoglobulin G/Fc gamma receptor (IgG/FcγR), complement, and toll-like cell surface receptor-mediated signaling, resulting in context-dependent release of either pro-inflammatory and/or anti-inflammatory mediators within the joint. Activation of MCs results in the release of pro-inflammatory mediators that ultimately contribute to inflammation of the synovium, bone remodeling, and cartilage damage. However, some studies have proposed that MCs can also exhibit anti-inflammatory effects by secreting mediators that inactivate pro-inflammatory cytokines such as interleukin 6 (IL-6).

CONCLUSIONS

MCs may play a role in mediating synovial inflammation and OA progression. However, the mechanisms governing MC activation, the downstream pro- and/or anti-inflammatory effects, and their impact on osteoarthritis pathogenesis remains to be elucidated and requires extensive further study. Furthermore, it is important to establish the pathways of MC activation in OA to determine whether MCs exhibit varying phenotypes as a function of disease stage. Ultimately, such research is needed before understanding whether MCs could be targeted in OA treatments.

Systematic comparisons of various markers for mast cell activation in RBL-2H3 cells

Mast cell activation plays a key role in various allergic diseases and anaphylaxis. Several methods/techniques can be used for detection of mast cell activation. However, there was no previous systematic evaluation to compare the efficacy of each method/technique. The present study thus systematically compared various markers for mast cell activation induced by IgE cross-linking. The widely used RBL-2H3 mast cells were sensitized with anti-DNP (dinitrophenyl) IgE overnight and activated with DNP-BSA (bovine serum albumin) for up to 4 h. The untreated cells and those with anti-DNP IgE sensitization but without DNP-BSA activation served as the controls. Intracellular calcium level gradually increased to ~2-fold at 1 h, reached its peak (~5-fold) at 2 h, and returned to the basal level at 3-h post-activation. The increases in cellular tryptase level (by Western blotting) (~0.3- to 0.4-fold) and average cell size (~2.5-fold) and decrease of nucleus/cytoplasm ratio (~0.4- to 0.5-fold) were marginal at all time-points. By contrast, β-hexosaminidase release and CD63 expression (by both flow cytometry and immunofluorescence detection/localization), secreted tryptase level (by Western blotting), and tryptase expression (by immunofluorescence detection/localization) stably and obviously increased (~10-fold as compared with the untreated control and sensitized-only cells or detectable only after activation). Based on these data, the stably obvious increases (by ≥ 10-fold) in β-hexosaminidase release, CD63 expression (by both flow cytometry and immunofluorescence staining), secreted tryptase level (by Western blotting), and tryptase expression (by immunofluorescence staining) are recommended as the markers of choice for the in vitro study of mast cell activation using RBL-2H3 cells.

Protease Activated Receptors and Arthritis

The catabolic and destructive activity of serine proteases in arthritic joints is well known; however, these enzymes can also signal pain and inflammation in joints. For example, thrombin, trypsin, tryptase, and neutrophil elastase cleave the extracellular N-terminus of a family of G protein-coupled receptors and the remaining tethered ligand sequence then binds to the same receptor to initiate a series of molecular signalling processes. These protease activated receptors (PARs) pervade multiple tissues and cells throughout joints where they have the potential to regulate joint homeostasis. Overall, joint PARs contribute to pain, inflammation, and structural integrity by altering vascular reactivity, nociceptor sensitivity, and tissue remodelling. This review highlights the therapeutic potential of targeting PARs to alleviate the pain and destructive nature of elevated proteases in various arthritic conditions.

Involvement of Mast Cells in the Pathophysiology of Pain

Mast cells (MCs) are immune cells and are widely distributed throughout the body. MCs are not only classically viewed as effector cells of some allergic diseases but also participate in host defense, innate and acquired immunity, homeostatic responses, and immunoregulation. Mounting evidence indicates that activation of MCs releasing numerous vasoactive and inflammatory mediators has effects on the nervous system and has been involved in different pain conditions. Here, we review the latest advances made about the implication of MCs in pain. Possible cellular and molecular mechanisms regarding the crosstalk between MC and the nervous system in the initiation and maintenance of pain are also discussed.

Intracellular versus extracellular inhibition of calpain I causes differential effects on pain in a rat model of joint inflammation

Calpain I is a calcium-dependent cysteine protease which has dual effects on tissue inflammation depending on its cellular location. Intracellularly, calpain I has pro-inflammatory properties but becomes anti-inflammatory when exteriorised into the extracellular space. In this study, the effect of calpain I on joint pain was investigated using the kaolin/carrageenan model of acute synovitis. Evoked pain behaviour was determined by von Frey hair algesiometry and non-evoked pain was measured using dynamic hindlimb weight bearing. Local administration of calpain I reduced secondary allodynia in the acute inflammation model and this effect was blocked by the cell impermeable calpain inhibitor E-64c. Calpain I also blocked the algesic effect of the protease activated receptor-2 (PAR-2) cleaving enzyme mast cell tryptase. The cell permeable calpain blocker E-64d also produced analgesia in arthritic joints. These data suggest that calpain I produces disparate effects on joint pain viz. analgesia when present extracellularly by disarming PAR-2, and pro-algesic when the enzyme is inside the cell.

Update on pain in arthritis

PURPOSE OF REVIEW

Osteoarthritis is a degenerative joint disease that features pain as a hallmark symptom. This review summarises progress and obstacles in our understanding of pain mechanisms in arthritis.

RECENT FINDINGS

Pain phenotypes in osteoarthritis are poorly characterized in clinical studies and animal studies are largely carti-centric. Different animal models incur variable disease progression patterns and activation of distinct pain pathways, but studies reporting both structural and pain outcomes permit better translational insights. In patients, classification of osteoarthritis disease severity is only based on structural integrity of the joint, but pain outcomes do not consistently correlate with joint damage. The complexity of this relationship underlines the need for pain detection in criteria for osteoarthritis classification and patient-reported outcome measures.

SUMMARY

Variable inflammatory and neuropathic components and spatiotemporal evolution underlie the heterogeneity of osteoarthritis pain phenotypes, which must be considered to adequately stratify patients. Revised classification of osteoarthritis at different stages encompassing both structural and pain outcomes would significantly improve detection and diagnosis at both early and late stages of disease. These are necessary advancements in the field that would also improve trial design and provide better understanding of basic mechanisms of disease progression and pain in osteoarthritis.

Capsaicin-Sensitive Peptidergic Sensory Nerves Are Anti-Inflammatory Gatekeepers in the Hyperacute Phase of a Mouse Rheumatoid Arthritis Model

Capsaicin-sensitive peptidergic sensory nerves play complex, mainly protective regulatory roles in the inflammatory cascade of the joints via neuropeptide mediators, but the mechanisms of the hyperacute arthritis phase has not been investigated. Therefore, we studied the involvement of these afferents in the early, "black box" period of a rheumatoid arthritis (RA) mouse model. Capsaicin-sensitive fibres were defunctionalized by pretreatment with the ultrapotent capsaicin analog resiniferatoxin and arthritis was induced by K/BxN arthritogenic serum. Disease severity was assessed by clinical scoring, reactive oxygen species (ROS) burst by chemiluminescent, vascular permeability by fluorescent in vivo imaging. Contrast-enhanced magnetic resonance imaging was used to correlate the functional and morphological changes. After sensory desensitization, both early phase ROS-burst and vascular leakage were significantly enhanced, which was later followed by the increased clinical severity scores. Furthermore, the early vascular leakage and ROS-burst were found to be good predictors of later arthritis severity. We conclude that the anti-inflammatory role of peptidergic afferents depends on their activity in the hyperacute phase, characterized by decreased cellular and vascular inflammatory components presumably via anti-inflammatory neuropeptide release. Therefore, these fibres might serve as important gatekeepers in RA.

Anti-Inflammatory and Analgesic Effects of TRPV1 Polypeptide Modulator APHC3 in Models of Osteo- and Rheumatoid Arthritis

Arthritis is a widespread inflammatory disease associated with progressive articular surface degradation, ongoing pain, and hyperalgesia causing the development of functional limitations and disability. TRPV1 channel is one of the high-potential targets for the treatment of inflammatory diseases. Polypeptide APHC3 from sea anemone Heteractis crispa is a mode-selective TRPV1 antagonist that causes mild hypothermia and shows significant anti-inflammatory and analgesic activity in different models of pain. We evaluated the anti-inflammatory properties of APHC3 in models of monosodium iodoacetate (MIA)-induced osteoarthritis and complete Freund’s adjuvant (CFA)-induced rheumatoid monoarthritis in comparison with commonly used non-steroidal anti-inflammatory drugs (NSAIDs) such as diclofenac, ibuprofen, and meloxicam. Subcutaneous administration of APHC3 (0.1 mg/kg) significantly reversed joint swelling, disability, grip strength impairment, and thermal and mechanical hypersensitivity. The effect of APHC3 was equal to or better than that of reference NSAIDs. Protracted treatment with APHC3 decreased IL-1b concentration in synovial fluid, reduced inflammatory changes in joints, and prevented the progression of cartilage degradation. Therefore, polypeptide APHC3 has the potential to be an analgesic and anti-inflammatory substance for the alleviation of arthritis symptoms.

Hemokinin-1 as a Mediator of Arthritis-Related Pain via Direct Activation of Primary Sensory Neurons

The tachykinin hemokinin-1 (HK-1) is involved in immune cell development and inflammation, but little is known about its function in pain. It acts through the NK1 tachykinin receptor, but several effects are mediated by a yet unidentified target. Therefore, we investigated the role and mechanism of action of HK-1 in arthritis models of distinct mechanisms with special emphasis on pain. Arthritis was induced by i.p. K/BxN serum (passive transfer of inflammatory cytokines, autoantibodies), intra-articular mast cell tryptase or Complete Freund's Adjuvant (CFA, active immunization) in wild type, HK-1- and NK1-deficient mice. Mechanical- and heat hyperalgesia determined by dynamic plantar esthesiometry and increasing temperature hot plate, respectively, swelling measured by plethysmometry or micrometry were significantly reduced in HK-1-deleted, but not NK1-deficient mice in all models. K/BxN serum-induced histopathological changes (day 14) were also decreased, but early myeloperoxidase activity detected by luminescent in vivo imaging increased in HK-1-deleted mice similarly to the CFA model. However, vasodilation and plasma protein extravasation determined by laser Speckle and fluorescent imaging, respectively, were not altered by HK-1 deficiency in any models. HK-1 induced Ca2+-influx in primary sensory neurons, which was also seen in NK1-deficient cells and after pertussis toxin-pretreatment, but not in extracellular Ca2+-free medium. These are the first results showing that HK-1 mediates arthritic pain and cellular, but not vascular inflammatory mechanisms, independently of NK1 activation. HK-1 activates primary sensory neurons presumably via Ca2+ channel-linked receptor. Identifying its target opens new directions to understand joint pain leading to novel therapeutic opportunities.

Topical Diclofenac, an Efficacious Treatment for Osteoarthritis: A Narrative Review

Multiple head-to-head trials have demonstrated that topical nonsteroidal anti-inflammatory drugs (NSAIDs), including topical diclofenac, provide at least equivalent analgesia, improvement in physical function, and reduction of stiffness compared with oral NSAIDs in osteoarthritis and have fewer systemic adverse events. While efficacy of topical diclofenac in osteoarthritis is well established, understanding of the time to onset of action, duration of effect, and the minimum effective concentration is limited. Factors likely to influence these parameters include drug penetration and localization. Diclofenac concentrations in the joint tissues are likely to be more relevant than plasma concentrations. However, although diclofenac penetrates and is retained in these "effect compartments" at the site of inflammation and drug activity, no specific minimum effective concentration of diclofenac in plasma or synovial tissue has been identified. Recent evidence suggests that a reduction in inflammatory markers may be a better predictor of efficacy than plasma concentrations. This narrative review explores existing evidence in these areas and identifies the gaps where further research is needed. Based on our findings, topical NSAIDs such as diclofenac should be considered as a guideline-supported, generally well-tolerated, and effective first-line treatment option for knee and hand OA, especially for older patients and those who have comorbid conditions and/or risk factors for various systemic (gastrointestinal, hepatic, renal, or cardiovascular) adverse events associated with oral NSAIDs, particularly at high doses and with long-term use.

Regulatory role of capsaicin-sensitive peptidergic sensory nerves in the proteoglycan-induced autoimmune arthritis model of the mouse

Objective

The regulatory role of capsaicin-sensitive peptidergic sensory nerves has been shown in acute inflammation, but little is known about their involvement in T/B-cell driven autoimmune arthritis. This study integratively characterized the function of these nerve endings in the proteoglycan-induced chronic arthritis (PGIA), a translational model of rheumatoid arthritis.

Methods

Peptidergic afferents were defunctionalized by resiniferatoxin (RTX) pretreatment in BALB/c mice, PGIA was induced by repeated antigen challenges. Hind paw volume, arthritis severity, grasping ability and the mechanonociceptive threshold were monitored during the 17-week experiment. Myeloperoxidase activity, vascular leakage and bone turnover were evaluated by in vivo optical imaging. Bone morphology was assessed using micro-CT, the intertarsal small joints were processed for histopathological analysis.

Results

Following desensitization of the capsaicin-sensitive afferents, ankle edema, arthritis severity and mechanical hyperalgesia were markedly diminished. Myeloperoxidase activity was lower in the early, but increased in the late phase, whilst plasma leakage and bone turnover were not altered. Desensitized mice displayed similar bone spurs and erosions, but increased trabecular thickness of the tibia and bony ankylosis of the spine. Intertarsal cartilage thickness was not altered in the model, but desensitization increased this parameter in both the non-arthritic and arthritic groups.

Conclusion

This is the first integrative in vivo functional and morphological characterization of the PGIA mouse model, wherein peptidergic afferents have an important regulatory function. Their overall effect is proinflammatory by increasing acute inflammation, immune cell activity and pain. Meanwhile, their activation decreases spinal ankylosis, arthritis-induced altered trabecularity, and cartilage thickness in small joints.

Electronic supplementary material

The online version of this article (10.1186/s12974-018-1364-5) contains supplementary material, which is available to authorized users.

Complex Role of Capsaicin-Sensitive Afferents in the Collagen Antibody-Induced Autoimmune Arthritis of the Mouse

Capsaicin-sensitive afferents have complex regulatory functions in the joints orchestrated via neuropeptides. This study aimed to determine their role in the collagen-antibody induced rheumatoid arthritis model. Capsaicin-sensitive nerves were defunctionalized by the capsaicin receptor agonist resiniferatoxin in C57Bl/6 mice. Arthritis was induced by the ArithroMab antibody cocktail and adjuvant. Arthritis was monitored by measuring body weight, joint edema by plethysmometry, arthritis severity by clinical scoring, mechanonociceptive threshold by plantar esthesiometry, thermonociceptive threshold by hot plate, cold tolerance by paw withdrawal latency from 0 °C water. Grasping ability was determined by the wire-grid grip test. Bone structure was evaluated by in vivo micro-CT and histology. Arthritic animals developed a modest joint edema, mechanical and cold hyperalgesia, weight loss, and a diminished grasping function, while thermal hyperalgesia is absent in the model. Desensitised mice displayed reduced arthritis severity, edema, and mechanical hyperalgesia, however, cold hyperalgesia was significantly greater in this group. Arthritic controls displayed a transient decrease of bone volume and an increased porosity, while bone density and trabecularity increased in desensitised mice. The activation of capsaicin-sensitive afferents increases joint inflammation and mechanical hyperalgesia, but decreases cold allodynia. It also affects inflammatory bone structural changes by promoting bone resorption.

Evidence for Transient Receptor Potential (TRP) Channel Contribution to Arthritis Pain and Pathogenesis

Based on clinical and preclinical evidence, Transient Receptor Potential (TRP) channels have emerged as potential drug targets for the treatment of osteoarthritis, rheumatoid arthritis, and gout. This review summarizes the relevant data supporting a role for various TRP channels in arthritis pain and pathogenesis, as well as the current state of pharmacological efforts to ameliorate arthritis symptoms in patient populations.

Intra-articular Injections of Platelet-Rich Plasma Releasate Reduce Pain and Synovial Inflammation in a Mouse Model of Osteoarthritis

BACKGROUND

Osteoarthritis (OA) is a degenerative joint disease leading to pain and disability for which no curative treatment exists. A promising biological treatment for OA is intra-articular administration of platelet-rich plasma (PRP). PRP injections in OA joints can relieve pain, although the exact working mechanism is unclear.

PURPOSE

To examine the effects of PRP releasate (PRPr) on pain, cartilage damage, and synovial inflammation in a mouse OA model.

STUDY DESIGN

Controlled laboratory study.

METHODS

OA was induced unilaterally in the knees of male mice (n = 36) by 2 intra-articular injections of collagenase at days -7 and -5. At day 0, pain was measured by registering weight distribution on the hindlimbs, after which mice were randomly divided into 2 groups. Mice received 3 intra-articular injections of PRP or saline in the affected knee. Seven mice per group were euthanized at day 5 for assessment of early synovial inflammation and cartilage damage. Pain in the remaining mice was registered for a total of 3 weeks. These mice were euthanized at day 21 for assessment of cartilage damage and synovial inflammation on histological evaluation. Antibodies against iNOS, CD163, and CD206 were used to identify different subtypes of macrophages in the synovial membrane.

RESULTS

Mice in the PRPr group increased the distribution of weight on the affected joint in 2 consecutive weeks after the start of the treatment ( P < .05), whereas mice in the saline group did not. At day 21, PRPr-injected knees had a thinner synovial membrane ( P < .05) and a trend toward less cartilage damage in the lateral joint compartment ( P = .053) than saline-injected knees. OA knees treated with saline showed less anti-inflammatory (CD206+ and CD163+) cells at day 5 than healthy knees, an observation that was not made in the PRPr-treated group. A higher level of pain at day 7 was associated with a thicker synovial membrane at day 21. The presence of CD206+ cells was negatively associated with synovial membrane thickness.

CONCLUSION

In a murine OA model, multiple PRPr injections reduced pain and synovial thickness, possibly through modulation of macrophage subtypes.

CLINICAL RELEVANCE

PRPr injections in early OA or shortly after joint trauma can reduce pain and synovial inflammation and may inhibit OA development in patients.

The Neurokinin-1 Receptor Contributes to the Early Phase of Lipopolysaccharide-Induced Fever via Stimulation of Peripheral Cyclooxygenase-2 Protein Expression in Mice

Neurokinin (NK) signaling is involved in various inflammatory processes. A common manifestation of systemic inflammation is fever, which is usually induced in animal models with the administration of bacterial lipopolysaccharide (LPS). A role for the NK1 receptor was shown in LPS-induced fever, but the underlying mechanisms of how the NK1 receptor contributes to febrile response, especially in the early phase, have remained unknown. We administered LPS (120 µg/kg, intraperitoneally) to mice with the Tacr1 gene, i.e., the gene encoding the NK1 receptor, either present (Tacr1+/+ ) or absent (Tacr1-/- ) and measured their thermoregulatory responses, serum cytokine levels, tissue cyclooxygenase-2 (COX-2) expression, and prostaglandin (PG) E2 concentration. We found that the LPS-induced febrile response was attenuated in Tacr1-/- compared to their Tacr1+/+ littermates starting from 40 min postinfusion. The febrigenic effect of intracerebroventricularly administered PGE2 was not suppressed in the Tacr1-/- mice. Serum concentration of pyrogenic cytokines did not differ between Tacr1-/- and Tacr1+/+ at 40 min post-LPS infusion. Administration of LPS resulted in amplification of COX-2 mRNA expression in the lungs, liver, and brain of the mice, which was statistically indistinguishable between the genotypes. In contrast, the LPS-induced augmentation of COX-2 protein expression was attenuated in the lungs and tended to be suppressed in the liver of Tacr1-/- mice compared with Tacr1+/+ mice. The Tacr1+/+ mice responded to LPS with a significant surge of PGE2 production in the lungs, whereas Tacr1-/- mice did not. In conclusion, the NK1 receptor is necessary for normal fever genesis. Our results suggest that the NK1 receptor contributes to the early phase of LPS-induced fever by enhancing COX-2 protein expression in the periphery. These findings advance the understanding of the crosstalk between NK signaling and the "cytokine-COX-2-prostaglandin E2" axis in systemic inflammation, thereby open up the possibilities for new therapeutic approaches.

Estradiol Sensitizes the Transient Receptor Potential Vanilloid 1 Receptor in Pain Responses

Sex differences exist in chronic pain pathologies, and gonadal estradiol (E2) alters the pain sensation. The nocisensor transient receptor potential vanilloid 1 (TRPV1) receptor plays a critical role in triggering pain. Here we examined the impact of E2 on the function of TRPV1 receptor in mice sensory neurons in vitro and in vivo. Both mechano- and thermonociceptive thresholds of the plantar surface of the paw of female mice were significantly lower in proestrus compared with the estrus phase. These thresholds were higher in ovariectomized (OVX) mice and significantly lower in sham-operated mice in proestrus compared with the sham-operated mice in estrus phase. This difference was absent in TRPV1 receptor-deficient mice. Furthermore, E2 potentiated the TRPV1 receptor activation-induced mechanical hyperalgesia in OVX mice. Long pretreatment (14 hours) with E2 induced a significant increase in TRPV1 receptor messenger RNA expression and abolished the capsaicin-induced TRPV1 receptor desensitization in primary sensory neurons. The short E2 incubation (10 minutes) also prevented the desensitization, which reverted after coadministration of E2 and the tropomyosin-related kinase A (TrkA) receptor inhibitor. Our study provides in vivo and in vitro evidence for E2-induced TRPV1 receptor upregulation and sensitization mediated by TrkAR via E2-induced genomic and nongenomic mechanisms. The sensitization and upregulation of TRPV1 receptor by E2 in sensory neurons may explain the greater pain sensitivity in female mice.

Effect of tryptase inhibition on joint inflammation: a pharmacological and lentivirus-mediated gene transfer study

Background

Increasing evidences indicate that an unbalance between tryptases and their endogenous inhibitors, leading to an increased proteolytic activity, is implicated in the pathophysiology of rheumatoid arthritis. The aim of the present study was to evaluate the impact of tryptase inhibition on experimental arthritis.

Methods

Analysis of gene expression and regulation in the mouse knee joint was performed by RT-qPCR and in situ hybridization. Arthritis was induced in male C57BL/6 mice with mBSA/IL-1β. Tryptase was inhibited by two approaches: a lentivirus-mediated heterologous expression of the human endogenous tryptase inhibitor, sperm-associated antigen 11B isoform C (hSPAG11B/C), or a chronic treatment with the synthetic tryptase inhibitor APC366. Several inflammatory parameters were evaluated, such as oedema formation, histopathology, production of IL-1β, -6, -17A and CXCL1/KC, myeloperoxidase and tryptase-like activities.

Results

Spag11c was constitutively expressed in chondrocytes and cells from the synovial membrane in mice, but its expression did not change 7 days after the induction of arthritis, while tryptase expression and activity were upregulated. The intra-articular transduction of animals with the lentivirus phSPAG11B/C or the treatment with APC366 inhibited the increase of tryptase-like activity, the late phase of oedema formation, the production of IL-6 and CXCL1/KC. In contrast, neutrophil infiltration, degeneration of hyaline cartilage and erosion of subchondral bone were not affected.

Conclusions

Tryptase inhibition was effective in inhibiting some inflammatory parameters associated to mBSA/IL-1β-induced arthritis, notably late phase oedema formation and IL-6 production, but not neutrophil infiltration and joint degeneration. These results suggest that the therapeutic application of tryptase inhibitors to rheumatoid arthritis would be restrained to palliative care, but not as disease-modifying drugs. Finally, this study highlighted lentivirus-based gene delivery as an instrumental tool to study the relevance of target genes in synovial joint physiology and disease.

Electronic supplementary material

The online version of this article (doi:10.1186/s13075-017-1326-9) contains supplementary material, which is available to authorized users.

Analgesic and Anti-Inflammatory Effects of the Novel Semicarbazide-Sensitive Amine-Oxidase Inhibitor SzV-1287 in Chronic Arthritis Models of the Mouse

Semicarbazide-sensitive amine oxidase (SSAO) catalyses oxidative deamination of primary amines. Since there is no data about its function in pain and arthritis mechanisms, we investigated the effects of our novel SSAO inhibitor SzV-1287 in chronic mouse models of joint inflammation. Effects of SzV-1287 (20 mg/kg i.p./day) were investigated in the K/BxN serum-transfer and complete Freund's adjuvant (CFA)-evoked active immunization models compared to the reference SSAO inhibitor LJP-1207. Mechanonociception was assessed by aesthesiometry, oedema by plethysmometry, clinical severity by scoring, joint function by grid test, myeloperoxidase activity by luminescence, vascular leakage by fluorescence in vivo imaging, histopathological changes by semiquantitative evaluation, and cytokines by Luminex assay. SzV-1287 significantly inhibited hyperalgesia and oedema in both models. Plasma leakage and keratinocyte chemoattractant production in the tibiotarsal joint, but not myeloperoxidase activity was significantly reduced by SzV-1287 in K/BxN-arthritis. SzV-1287 did not influence vascular and cellular mechanisms in CFA-arthritis, but significantly decreased histopathological alterations. There was no difference in the anti-hyperalgesic and anti-inflammatory actions of SzV-1287 and LJP-1207, but only SzV-1287 decreased CFA-induced tissue damage. Unlike SzV-1287, LJP-1207 induced cartilage destruction, which was confirmed in vitro. SzV-1287 exerts potent analgesic and anti-inflammatory actions in chronic arthritis models of distinct mechanisms, without inducing cartilage damage.