AAV-glycine receptor α3 alleviates CFA-induced inflammatory pain by downregulating ERK phosphorylation and proinflammatory cytokine expression in SD rats.

BACKGROUND: Glycine receptors (GlyRs) play key roles in the processing of inflammatory pain. The use of adeno-associated virus (AAV) vectors for gene therapy in human clinical trials has shown promise, as AAV generally causes a very mild immune response and long-term gene transfer, and there have been no reports of disease. Therefore, we used AAV for GlyRα1/3 gene transfer in F11 neuron cells and into Sprague-Dawley (SD) rats to investigate the effects and roles of AAV-GlyRα1/3 on cell cytotoxicity and inflammatory response. METHODS: In vitro experiments were performed using plasmid adeno-associated virus (pAAV)-GlyRα1/3-transfected F11 neurons to investigate the effects of pAAV-GlyRα1/3 on cell cytotoxicity and the prostaglandin E2 (PGE2)-mediated inflammatory response. In vivo experiment, the association between GlyRα3 and inflammatory pain was analyzed in normal rats after AAV-GlyRα3 intrathecal injection and after complete Freund's adjuvant (CFA) intraplantar administration. Intrathecal AAV-GlyRα3 delivery into SD rats was evaluated in terms of its potential for alleviating CFA-induced inflammatory pain. RESULTS: The activation of mitogen-activated protein kinase (MAPK) inflammatory signaling and neuronal injury marker activating transcription factor 3 (ATF-3) were evaluated by western blotting and immunofluorescence; the level of cytokine expression was measured by ELISA. The results showed that pAAV/pAAV-GlyRα1/3 transfection into F11 cells did not significantly reduce cell viability or induce extracellular signal-regulated kinase (ERK) phosphorylation or ATF-3 activation. PGE2-induced ERK phosphorylation in F11 cells was repressed by the expression of pAAV-GlyRα3 and administration of an EP2 inhibitor, GlyRαs antagonist (strychnine), and a protein kinase C inhibitor. Additionally, intrathecal AAV-GlyRα3 administration to SD rats significantly decreased CFA-induced inflammatory pain and suppressed CFA-induced ERK phosphorylation, did not induce obvious histopathological injury but increased ATF-3 activation in dorsal root ganglion (DRGs). CONCLUSIONS: Antagonists of the prostaglandin EP2 receptor, PKC, and glycine receptor can inhibit PGE2-induced ERK phosphorylation. Intrathecal AAV-GlyRα3 administration to SD rats significantly decreased CFA-induced inflammatory pain and suppressed CFA-induced ERK phosphorylation, did not significantly induce gross histopathological injury but elicited ATF-3 activation. We suggest that PGE2-induced ERK phosphorylation can be modulated by GlyRα3, and AAV-GlyRα3 significantly downregulated CFA-induced cytokine activation.

Pre-emptive intrathecal quinidine alleviates spinal nerve ligation-induced peripheral neuropathic pain.

OBJECTIVES: Quinidine, a class I anti-arrhythmic agent, is a sodium channel blocker that is more potent than lidocaine and mexiletine. This study tested pre-emptive intrathecal quinidine to attenuate neuropathic pain induced by lumbar spinal nerve ligation (SNL). METHODS: Ninety-six adult male Sprague-Dawley rats were grouped equally (n=24 per group) as follows: group S (sham), removal of transverse process only; group L, SNL; group Q35, SNL pretreated with intrathecal quinidine 35 mM (50 µl); group Q70, SNL pretreated with intrathecal quinidine 70 mM (50 µl). Neuropathic pain was measured by thermal hyperalgesia and mechanical allodynia. Other measurements included dys-regulation of sodium channel Nav1.3 in dorsal root ganglion (DRG) and spinal microglia activation in spinal dorsal horn. KEY FINDINGS: Spinal nerve ligation induced abnormal mechanical allodynia and thermal hyperalgesia, up-regulated Nav1.3 in DRG, and activated microglia in spinal cord. Group Q70 showed attenuated thermal hyperalgesia (P<0.001) and mechanical allodynia (P<0.05) on postoperative day 5 (POD5) but not on POD7, reversed up-regulated expression of Nav1.3 on POD3 and POD7 in DRG and significantly attenuated microglia activation on POD7 (P=0.032) in spinal cord. CONCLUSIONS: Pretreatment with intrathecal quinidine 70 mM before SNL attenuates nerve ligation-induced neuropathic pain. The duration of the effect is 5 days.