Animal Studies

Oxaliplatin is an antineoplastic agent frequently used in the treatment of gastrointestinal tumors. However, it causes dose-limiting sensorimotor neuropathy, referred to as oxaliplatin-induced peripheral neuropathy (OIPN), for which there is no effective treatment. Here, we report that the elevation of neutrophil extracellular traps (NETs) is a pathological change common to both cancer patients treated with oxaliplatin and a murine model of OIPN. Mechanistically, we found that NETs trigger NLR family pyrin domain containing 3 (NLRP3) inflammasome activation and the subsequent release of IL18 by macrophages, resulting in mechanical hyperalgesia. In NLRP3-deficient mice, the mechanical hyperalgesia characteristic of OIPN in our model was reduced. In addition, in the murine model, treatment with the IL18 decoy receptor IL18BP prevented the development of OIPN. We further showed that eicosapentaenoic acid (EPA) reduced NET formation by suppressing the LPS-TLR4-JNK pathway and thereby abolished NLRP3 inflammasome activation and the subsequent secretion of IL18, which markedly prevented oxaliplatin-induced mechanical hyperalgesia in mice. These results identify a role for NET-triggered NLRP3 activation and IL18 release in the development of OIPN and suggest that utilizing IL18BP and EPA could be effective treatments for OIPN.

Extensive extracellular matrix production and increased cell-matrix adhesion by bone marrow stromal cells (BMSCs) are hallmarks of fibrotic alterations in the vertebral bone marrow known as Modic type 1 changes (MC1). MC1 are associated with non-specific chronic low-back pain. To identify treatment targets for MC1, in vitro studies using patient BMSCs are important to reveal pathological mechanisms. For the culture of BMSCs, fibroblast growth factor 2 (FGF2) is widely used. However, FGF2 has been shown to suppress matrix synthesis in various stromal cell populations. The aim of the present study was to investigate whether FGF2 affected the in vitro study of the fibrotic pathomechanisms of MC1-derived BMSCs. Transcriptomic changes and changes in cell-matrix adhesion of MC1-derived BMSCs were compared to intra-patient control BMSCs in response to FGF2. RNA sequencing and quantitative real-time polymerase chain reaction revealed that pro-fibrotic genes and pathways were not detectable in MC1-derived BMSCs when cultured in the presence of FGF2. In addition, significantly increased cell-matrix adhesion of MC1-derived BMSCs was abolished in the presence of FGF2. In conclusion, the data demonstrated that FGF2 overrides key pro-fibrotic features of MC1 BMSCs in vitro. Usage of FGF2-supplemented media in studies of fibrotic mechanisms should be critically evaluated as it could override normally dominant biological and biophysical cues.

Temporomandibular disorders (TMD) include a group of musculoskeletal disorders that may involve increased responsiveness of nociceptive neurons in the central nervous system (i.e. central sensitization). To test this hypothesis further, the present study examined whether, as compared with healthy subjects, patients with chronic TMD have a greater susceptibility to develop secondary mechanical hyperalgesia – a phenomenon that can be confidently attributed to central sensitization.In this case-control study, we assessed the area of secondary mechanical hyperalgesia induced experimentally by delivering high-frequency electrical stimulation (HFS) to the volar forearm skin in 20 participants with chronic TMD and 20 matched healthy controls. HFS consisted in 12 trains of constant-current electrical pulses (5mA) delivered at 42 Hz. The area of secondary mechanical hyperalgesia was evaluated 30 minutes after applying HFS.The area of secondary mechanical hyperalgesia induced by HFS was on average 76% larger in the chronic TMD group (M = 67.7 cm2, SD = 28.2) than in the healthy control group (M = 38.4 cm2, SD = 14.9; p = .0003). Regarding secondary outcomes, there was no group difference in the intensity of secondary mechanical hyperalgesia, but allodynia to cotton after HFS was more frequent in the chronic TMD group.To our knowledge, this is the first study to show that individuals with chronic TMD have an increased susceptibility to develop secondary hyperalgesia in a site innervated extra-trigeminally. Our results contribute to a better understanding of the pathophysiology of chronic TMD.

Here we studied spinal neurotransmitter mechanisms involved in the reduction of mechanical hypersensitivity by inhibition of the amygdaloid central nucleus (CeA) in male and female rats with spared nerve injury (SNI) model of neuropathy. SNI induced mechanical hypersensitivity that was stronger in females. Reversible blocking of the CeA with muscimol (GABA receptor agonist) induced a reduction of mechanical hypersensitivity that did not differ between males and females. Following spinal co-administration of atipamezole (α-adrenoceptor antagonist), the reduction of mechanical hypersensitivity by CeA muscimol was attenuated more in males than females. In contrast, following spinal co-administration of raclopride (dopamine D2 receptor antagonist) the reduction of hypersensitivity by CeA muscimol was attenuated more in females than males. The reduction of mechanical hypersensitivity by CeA muscimol was equally attenuated in males and females by spinal co-administration of WAY-100635 (5-HT receptor antagonist) or bicuculline (GABA receptor antagonist). The CeA muscimol induced attenuation of ongoing pain-like behavior (conditioned place preference test) that was reversed by spinal co-administration of atipamezole in both sexes. The results support the hypothesis that CeA contributes to mechanical hypersensitivity and ongoing pain-like behavior in SNI males and females. Disinhibition of descending controls acting on spinal α-adrenoceptors, 5-HT, dopamine D2 and GABA receptors provides a plausible explanation for the reduction of mechanical hypersensitivity by CeA block in SNI. The involvement of spinal dopamine D2 receptors and α-adrenoceptors in the CeA muscimol-induced reduction of mechanical hypersensitivity is sexually dimorphic, unlike that of spinal α-adrenoceptors in the reduction of ongoing neuropathic pain.

TRPV4 is associated with the development of neuropathic pain, sensory defects, muscular dystrophies, neurodegenerative disorders, Charcot Marie Tooth and skeletal dysplasia. In all these cases, mitochondrial abnormalities are prominent. Here, we demonstrate that TRPV4, localizes to a subpopulation of mitochondria in various cell lines. Improper expression and/or function of TRPV4 induces several mitochondrial abnormalities. TRPV4 is also involved in the regulation of mitochondrial numbers, Ca-levels and mitochondrial temperature. Accordingly, several naturally occurring TRPV4 mutations affect mitochondrial morphology and distribution. These findings may help in understanding the significance of mitochondria in TRPV4-mediated channelopathies possibly classifying them as mitochondrial diseases.

Migraine is a common neuronal disorder characterized by recurrent episodes of headache associated with a higher prevalence in women than men. Several risk factors have been associated with migraine disease as genetic factors, gender, and age. Although understanding migraine pathophysiology is improved, it has been reported that NOD-like receptor protein 3 (NLRP3) inflammasome pathway overactivation can contribute to migraine progression. Therefore, the aim of this study was to investigate the effect of BAY-117082, an NLRP3 inflammasome inhibitor, in a mouse model of nitroglycerin (NTG)-induced migraine. The in vivo model of migraine was induced by intraperitoneal (i.p) injection of NTG (dose of 10 mg/kg). Mice were treated intraperitoneally with BAY-117082 at doses of 1 mg/kg, 5 mg/kg, and 10 mg/kg, 5 min following NTG injection. After 4 h of NTG injection, the whole brain tissue with the rostral spinal cord were collected and used to perform further analysis. Our results demonstrated that BAY-117082 treatments (5 mg/kg and 10 mg/kg) reduced pain attacks, hyperalgesia and photophobia more in female mice NTG-induced. Moreover, the treatment with BAY-117082 significantly reduced histological damage in the trigeminal nerve nucleus in female mice accordingly to significantly decreased in NLRP3 complex components expression levels such as ASC, IL-1β, IL-18, caspase-1 and TNF-α levels. Additionally, the treatment with BAY-117082 at both higher doses significantly modulated CREB/Erk/Akt pathways strictly correlated to the expression of neurotrophic factors. Taken together, obtained results confer new insight into the role of the NLRP3 inflammasome pathway in migraine pathogenesis, suggesting that BAY-117082 could be considered a novel strategy therapeutics for migraine treatment despite unconventional drug use.