Pharmacology/Drug Development

Mirogabalin (MGB, Tarlige), an inhibitor of the αδ-1 subunit of voltage-gated Ca (Ca) channels, is used as a way to alleviate peripheral neuropathic pain and diabetic neuropathy. However, to what extent MGB modifies the magnitude, gating, and/or hysteresis of various types of plasmalemmal ionic currents remains largely unexplored. In pituitary tumor (GH) cells, we found that MGB was effective at suppressing the peak (transient, ) and sustained (late, ) components of the voltage-gated Na current () in a concentration-dependent manner, with an effective IC of 19.5 and 7.3 μM, respectively, while the value calculated on the basis of minimum reaction scheme was 8.2 μM. The recovery of inactivation slowed in the presence of MGB, although the overall current-voltage relation of was unaltered; however, there was a leftward shift in the inactivation curve of the current. The magnitude of the window () or resurgent () evoked by the respective ascending or descending ramp pulse (V) was reduced during cell exposure to MGB. MGB-induced attenuation in or was reversed by the further addition of tefluthrin, a pyrethroid insecticide known to stimulate . MGB also effectively lessened the strength of voltage-dependent hysteresis of persistent in response to the isosceles triangular V. The cumulative inhibition of evoked by pulse train stimulation, was enhanced in its presence. Taken together, in addition to the inhibition of Ca channels, the Na channel attenuation produced by MGB might have an impact in its analgesic effects occurring in vivo.

Low back pain (LBP), caused by intervertebral disc (IVD) degeneration, is a major contributor to global disability. In its healthy state, the IVD is a tough and well-hydrated tissue, able to act as a shock absorber along the spine. During degeneration, the IVD is hit by a cell-driven cascade of events, which progressively lead to extracellular matrix (ECM) degradation, chronic inflammation, and pain. Current treatments are divided into palliative care (early stage degeneration) and surgical interventions (late-stage degeneration), which are invasive and poorly efficient in the long term. To overcome these limitations, alternative tissue engineering and regenerative medicine strategies, in which soft biomaterials are used as injectable carriers of cells and/or biomolecules to be delivered to the injury site and restore tissue function, are currently being explored. Self-assembling peptide hydrogels (SAPHs) represent a promising class of synthetic biomaterials able to merge the strengths of both natural and synthetic hydrogels for biomedical applications. Inherent features, such as shear-thinning behaviour, high biocompatibility, ECM biomimicry, and tuneable physiochemical properties make these hydrogels appropriate and functional tools to tackle IVD degeneration. This review will describe the pathogenesis of IVD degeneration, list biomaterials requirements to attempt IVD repair, and focus on current peptide hydrogel materials exploited for this purpose.

The distinction between glial painful and protective pathways is unclear and the possibility to finely modulate the system is lacking. Focusing on painful neuropathies, we studied the role of interleukin 1α (IL-1α), an alarmin belonging to the larger family of damage-associated molecular patterns endogenously secreted to restore homeostasis. The treatment of rat primary neurons with increasing dose of the neurotoxic anticancer drug oxaliplatin (0.3-100μM, 48 h) induced the release of IL-1α. The knockdown of the alarmin in neurons leads to their higher mortality when co-cultured with astrocytes. This toxicity was related to increased extracellular ATP and decreased release of transforming growth factor β1, mostly produced by astrocytes. In a rat model of neuropathy induced by oxaliplatin, the intrathecal treatment with IL-1α was able to reduce mechanical and thermal hypersensitivity both after acute injection and continuous infusion. Ex vivo analysis on spinal purified astrocyte processes (gliosomes) and nerve terminals (synaptosomes) revealed the property of IL-1α to reduce the endogenous glutamate release induced by oxaliplatin. This protective effect paralleled with an increased number of GFAP-positive cells in the spinal cord, suggesting the ability of IL-1α to evoke a positive, conservative astrocyte phenotype. Endogenous IL-1α induces protective signals in the cross-talk between neurons and astrocytes. Exogenously administered in rats, IL-1α prevents neuropathic pain in the presence of spinal glutamate decrease and astrocyte activation.

The N-methyl-D-aspartate (NMDA) receptors are heteromeric cation channels involved in memory, learning, and synaptic plasticity. The dysfunction associated with NMDA receptors results in neurodegenerative conditions. The conantokins comprise a family of Conus venom peptides that induce sleep upon intracranial injection into young mice and are known to be NMDA receptor antagonists. This work comprehensibly documents the conantokins that have been characterized to date, focusing on the biochemistry, solution structures in the presence or absence of divalent cations, functions as selective NMDA receptor antagonists, and structure-activity relationships. Furthermore, the applications of conantokins as potential therapeutics for certain neurological conditions, including neuropathic pain, epilepsy, and ischemia that are linked to NMDA receptor dysfunction are reviewed.

Neuropathic pain is a distressing medical condition with few effective treatments, and the role of VEGFA in inflammatory pain has been confirmed in many studies. However, the mechanism by which VEGFA affects neuropathic pain remains unclear. In this study, we demonstrated that VEGFA plays an important role in spare nerve injury (SNI)-induced neuropathic pain, which is mediated by enhanced expression and colocalization of VEGFA, p-AKT and TRPV1 in an SNI-induced neuropathic pain model. Soluble VEGFR1 (sFlt1) relieved mechanical hyperalgesia and the expression of inflammatory markers and also ameliorated the expression of VEGFA, VEGFR2, p-AKT, and TRPV1 in the spinal cord. However, these effects of sFlt1 could be blocked by rpVEGFA and 740 Y-P. Therefore, our study indicates that targeting VEGFA with sFlt1 reduces neuropathic pain development via the AKT/TRPV1 pathway in SNI-induced nerve injury. This study elucidates a new therapeutic target for neuropathic pain.

Sigma receptor is a transmembrane non-GPCR protein expressed mainly in the endoplasmic reticulum (ER) membrane associated with mitochondria. It is classified into two types; Sigma-1 (S1R) and Sigma-2 (S2R) based on their biological functions. S1R has been implicated in many neurological disorders such as anxiety, schizophrenia, and depression. Therefore, S1R ligands possess a variety of potential clinical applications with a great interest in the treatment of neuropathic pain. In this study, we report the discovery of a novel lead compound for S1R binding, based on the thiazolidine-2,4-dione nucleus. We have explored hydrophobic groups of different sizes on both sides of the five-membered ring scaffold guided by the crystal structure of S1R. Six compounds showed more than 50% displacement of the radioligand at 10 µM concentration with compound 6c resulting in 100% displacement and a K of 95.5 nM. Moreover, compounds 6c and 6e showed a significant selectivity over S2R. In addition, molecular docking predicted that all the compounds showed the critical salt bridge with Glu172 with variable degrees of π-stacking interaction with Tyr103. Upon optimization, this series of compounds could represent potential clinically useful S1R ligands for pain management.

Suboptimal control of postoperative pain following knee arthroplasty can slow recovery and reduce patient satisfaction. Intraarticular (IA) administration of bupivacaine and ketorolac offers efficient pain control and minimizes opioid consumption. However, the clinical benefits of this approach are short lived due to rapid clearance of drugs from the joint cavity. Here, we describe a poloxamer based thermoresponsive in situ gelling system for the sustained IA delivery of bupivacaine hydrochloride (BH) and ketorolac tromethamine (KT) following knee surgery in an ovine model. Drug loaded formulations were prepared using poloxamer 407, poloxamer 188 and sodium chloride. In vitro characterization was conducted, followed by in vivo evaluation of sustained drug release and safety in an ovine model of knee joint surgery. Rheological studies revealed a Newtonian-like flow of the developed formulation at room temperature, confirming its injectability, followed by a transition to a viscous gel as temperature approached body temperature. The developed formulation successfully sustained the in vivo release of BH for 72 h and KT for 48 h, as determined by circulating drug levels, compared to 24 and 8 h for marketed drug solutions. The concentrations of BH and KT in the synovial fluids at 72 h were 11.5 and 1.8 times that of marketed products, suggesting a significant increase in the IA residence time. The developed formulation induced a comparable inflammatory response compared to the marketed drug solutions, however a significantly higher chondrotoxicity was observed following administration of the gel formulations. Poloxamers based in situ gelling systems are promising delivery platforms for the sustained and localised IA delivery of BH and KT, with potential clinical benefits in managing the postoperative pain following knee arthroplasty.

Human peripheral neuropathies are poorly understood, and the availability of experimental models limits further research. The PeriTox test uses immature dorsal root ganglia (DRG)-like neurons, derived from induced pluripotent stem cells (iPSC), to assess cell death and neurite damage. Here, we explored the suitability of matured peripheral neuron cultures for the detection of sub-cytotoxic endpoints, such as altered responses of pain-related P2X receptors. A two-step differentiation protocol, involving the transient expression of ectopic neurogenin-1 (NGN1) allowed for the generation of homogeneous cultures of sensory neurons. After >38 days of differentiation, they showed a robust response (Ca-signaling) to the P2X3 ligand α,β-methylene ATP. The clinical proteasome inhibitor bortezomib abolished the P2X3 signal at ≥5 nM, while 50-200 nM was required in the PeriTox test to identify neurite damage and cell death. A 24 h treatment with low nM concentrations of bortezomib led to moderate increases in resting cell intracellular Ca concentration but signaling through transient receptor potential V1 (TRPV1) receptors or depolarization-triggered Ca influx remained unaffected. We interpreted the specific attenuation of purinergic signaling as a functional cell stress response. A reorganization of tubulin to form dense structures around the cell somata confirmed a mild, non-cytotoxic stress triggered by low concentrations of bortezomib. The proteasome inhibitors carfilzomib, delanzomib, epoxomicin, and MG-132 showed similar stress responses. Thus, the model presented here may be used for the profiling of new proteasome inhibitors in regard to their side effect (neuropathy) potential, or for pharmacological studies on the attenuation of their neurotoxicity. P2X3 signaling proved useful as endpoint to assess potential neurotoxicants in peripheral neurons.