Accepted

Joint pain is the major clinical symptom of arthritis that affects millions of people. Controlling the excitability of knee-innervating dorsal root ganglion (DRG) neurons (knee neurons) could potentially provide pain relief. Therefore, our objective was to evaluate whether the newly engineered adeno-associated virus (AAV) serotype, AAV-PHP.S, can deliver functional artificial receptors to control knee neuron excitability following intra-articular knee injection.

Deafferentation pain (DP), a typical neuropathic pain, occurs due to peripheral or central sensory nerve injury, which causes abnormal discharge of the upstream neurons or C fibers. Current treatment methods for DP have multiple side effects. Bone marrow mesenchymal stem cells (BMSC) have been used to treat neuropathic pain because of their ability to regulate neuroinflammation. Glial cell-derived neurotrophic factor (GDNF) is a neurotrophic mediator that exerts neuroprotective effects in neurological diseases. In this study, we investigated whether DP could be alleviated by BMSCs and the underlying mechanism. In vitro study, microglia was stimulated by lipopolysaccharide and then co-cultured with BMSC, GDNF or siRNA GDNF-BMSC. In vivo study, BMSC or siRNA GDNF-BMSC was transplanted intramedullarily on the 21st day after DP surgery. The expression of inflammatory-related factors were detected by RT-PCR and ELISA, RT-PCR,flow cytometry and immunofluorescence staining were performed to detect the expression of microglial surface markers, and Western blot was used to detect the expression levels of p-NF-kb, pPI3K, and pAKT. The pain-related behavioral changes were detected 7 days after transplantation. ELISA and RT-PCR results showed that the production of inflammatory cytokines in lipopolysaccharide-stimulated microglia and DP model plasma was downregulated, while anti-inflammatory mediators were upregulated significantly following pretreatment with BMSCs or GDNF. Flow cytometry, immunofluorescence staining, and RT-PCR results showed that BMSCs inhibited the microglial M1 phenotype and promoted the M2 phenotype by secreting GDNF. Furthermore, modulation functions of BMSCs involve inhibiting NF-κB while promoting PI3K /AKT signaling pathway activation. We found that our in vivo DP model was completely deafferent and BMSC administration clearly alleviated symptoms of DP. This function was also, at least partly, achieved by GDNF. The present studies demonstrate that BMSC can inhibit neuroinflammation by transforming microglial destructive M1 phenotype into regenerative M2 phenotype, and thus alleviate DP,likely by suppressing the NF-κB signaling pathway while promoting the PI3K/AKT signaling pathway activation through producing GDNF. The present findings are in support of the potential therapeutic application of BMSCs and the pharmaceutical application of GDNF for DP.

Capsaicin is the most abundant pungent molecule identified in red chili peppers, and it is widely used for food flavoring, in pepper spray for self-defense devices and recently in ointments for the relief of neuropathic pain. Capsaicin and several other related vanilloid compounds are secondary plant metabolites. Capsaicin is a selective agonist of the transient receptor potential channel, vanilloid subfamily member 1 (TRPV1). After exposition to vanilloid solution, Caenorhabditis elegans wild type (N2) and mutants were placed on petri dishes divided in quadrants for heat stimulation. Thermal avoidance index was used to phenotype each tested C. elegans experimental groups. The data revealed for the first-time that capsaicin can impede nocifensive response of C. elegans to noxious heat (32-35 °C) following a sustained exposition. The effect was reversed 6 h post capsaicin exposition. Additionally, we identified the capsaicin target, the C. elegans transient receptor potential channel OCR-2 and not OSM-9. Further experiments also undoubtedly revealed anti-nociceptive effect for capsaicin analogues, including olvanil, gingerol, shogaol and curcumin.