IL-1 Mediates Chronic Stress-Induced Hyperalgesia Accompanied by Microglia and Astroglia Morphological Changes in Pain-Related Brain Regions in Mice

Chronic stress causes several pain conditions including fibromyalgia. Its pathophysiological mechanisms are unknown, and the therapy is unresolved. Since the involvement of interleukin-1 (IL-1) has been described in stress and inflammatory pain but no data are available regarding stress-induced pain, we studied its role in a chronic restraint stress (CRS) mouse model. Female and male C57Bl/6J wild-type (WT) and IL-1αβ-deficient (knock-out: IL-1 KO) mice were exposed to 6 h of immobilization/day for 4 weeks. Mechanonociception, cold tolerance, behavioral alterations, relative thymus/adrenal gland weights, microglia ionized calcium-binding adaptor molecule 1 (IBA1) and astrocyte glial fibrillary acidic protein (GFAP) integrated density, number and morphological transformation in pain-related brain regions were determined. CRS induced 15–20% mechanical hyperalgesia after 2 weeks in WT mice in both sexes, which was significantly reduced in female but not in male IL-1 KOs. Increased IBA1+ integrated density in the central nucleus of amygdala, primary somatosensory cortex hind limb representation part, hippocampus cornu ammonis area 3 (CA3) and periaqueductal gray matter (PAG) was present, accompanied by a cell number increase in IBA1+ microglia in stressed female WTs but not in IL-1 KOs. CRS induced morphological changes of GFAP+ astrocytes in WT but not in KO mice. Stress evoked cold hypersensitivity in the stressed animals. Anxiety and depression-like behaviors, thymus and adrenal gland weight changes were detectable in all groups after 2 but not 4 weeks of CRS due to adaptation. Thus, IL-1 mediates chronic stress-induced hyperalgesia in female mice, without other major behavioral alterations, suggesting the analgesic potentials of IL-1 in blocking drugs in stress-related pain syndromes.

Discovery of novel targets in a complex regional pain syndrome mouse model by transcriptomics: TNF and JAK-STAT pathways

Complex Regional Pain Syndrome (CRPS) represents severe chronic pain, hypersensitivity, and inflammation induced by sensory-immune-vascular interactions after a small injury. Since the therapy is unsatisfactory, there is a great need to identify novel drug targets. Unbiased transcriptomic analysis of the dorsal root ganglia (DRG) was performed in a passive transfer-trauma mouse model, and the predicted pathways were confirmed by pharmacological interventions. In the unilateral L3-5 DRGs 125 genes were differentially expressed in response to plantar incision and injecting IgG of CRPS patients. These are related to inflammatory and immune responses, cytokines, chemokines and neuropeptides. Pathway analysis revealed the involvement of Tumor Necrosis Factor (TNF) and Janus kinase (JAK-STAT) signaling. The relevance of these pathways was proven by abolished CRPS IgG-induced hyperalgesia and reduced microglia and astrocyte markers in pain-associated central nervous system regions after treatment with the soluble TNF alpha receptor etanercept or JAK inhibitor tofacitinib. These results provide the first evidence for CRPS-related neuroinflammation and abnormal cytokine signaling at the level of the primary sensory neurons in a translational mouse model and suggest that etanercept and tofacitinib might have drug repositioning potentials for CRPS-related pain.

Proof-of-Concept for the Analgesic Effect and Thermoregulatory Safety of Orally Administered Multi-Target Compound SZV 1287 in Mice: A Novel Drug Candidate for Neuropathic Pain

SZV 1287 (3-(4,5-diphenyl-1,3-oxazol-2-yl)propanal oxime) is a novel multi-target candidate under preclinical development for neuropathic pain. It inhibits amine oxidase copper containing 3, transient receptor potential ankyrin 1 and vanilloid 1 (TRPV1) receptors. Mainly under acidic conditions, it is transformed to the cyclooxygenase inhibitor oxaprozin, which is ineffective for neuropathy. Therefore, an enterosolvent capsule is suggested for oral formulation, which we investigated for nociception, basic kinetics, and thermoregulatory safety in mice. The antihyperalgesic effect of SZV 1287 (10, 20, 50, and 200 mg/kg, p.o.) was determined in partial sciatic nerve ligation-induced traumatic neuropathy by aesthesiometry, brain and plasma concentrations by HPLC, and deep body temperature by thermometry. Its effect on proton-induced TRPV1 activation involved in thermoregulation was assessed by microfluorimetry in cultured trigeminal neurons. The three higher SZV 1287 doses significantly, but not dose-dependently, reduced neuropathic hyperalgesia by 50% of its maximal effect. It was quickly absorbed; plasma concentration was stable for 2 h, and it entered into the brain. Although SZV 1287 significantly decreased the proton-induced TRPV1-mediated calcium-influx potentially leading to hyperthermia, it did not alter deep body temperature. Oral SZV 1287 inhibited neuropathic hyperalgesia and, despite TRPV1 antagonistic action and brain penetration, it did not influence thermoregulation, which makes it a promising analgesic candidate.

Exploratory and locomotor activity, learning and memory functions in somatostatin receptor subtype 4 gene-deficient mice in relation to aging and sex

The inhibitory neuropeptide somatostatin regulates several functions in the nervous system including memory. Its concentrations decrease by age leading to functional alterations, but there are little known about the receptorial mechanism. We discovered that somatostatin receptor 4 (sst₄) mediates analgesic, anti-depressant, and anti-inflammatory effects without endocrine actions, and it is a unique target for drug development. We investigated the exploratory and locomotor activities and learning and memory functions of male and female sst₄gene-deficient mice compared with their wild-types (WT) at ages of 3, 12, 17 months in the Y-maze test, open field test (OFT), radial-arm maze (RAM) test and novel object recognition (NOR) test. Young sst₄ gene-deficient females visited, repeated, and missed significantly less arms than the WTs in the RAM; males showed decreased exploration in the NOR. Young mice moved significantly more, spend longer time in OFT center, and visited more arms in the Y-maze than older ones. Young WT females spend significantly longer time in the OFT center, visited, missed and repeated more arms of the RAM than males. Old males found more rewards than females. Young males explored longer the novel object than young females and older males in the NOR; the recognition index was smaller in females. We conclude that aging and sex are important factors of behavioral parameters that should be focused on in such studies. Sst₄ is likely to influence locomotion and exploratory behavior only in young mice, but not during normal aging, which is a beneficial feature of a good drug target focusing on the elderly.

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.

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.