BACKGROUND AND PURPOSEHypoesthesia is a clinical feature of neuropathic pain. The feature is partly explained by the evidence of epigenetic repression of Nav1.8 sodium channel in the dorsal root ganglion (DRG). EXPERIMENTAL APPROACHWe investigated the possibility of trichostatin A (TSA), valproic acid (VPA) and suberoylanilide hydroxamic acid (SAHA) to reverse the unique C-fibre sensitivity observed following partial ligation of sciatic nerve in mice. KEY RESULTSNerve injury-induced down-regulation of DRG Nav1.8 sodium channel and C-fibre-related hypoesthesia were reversed by TSA, VPA and SAHA treatments, which inhibit histone deacetylase (HDAC), and increase histone acetylation at the regulatory sequence of Nav1.8. CONCLUSIONS AND IMPLICATIONSTaken together, these studies provide the evidence that hypoesthesia and underlying down-regulation of Nav1.8, negative symptoms observed in nerve injury-induced neuropathic pain models are regulated by an epigenetic chromatin remodelling through HDAC-related machineries.

BackgroundFibromyalgia (FM) is characterized by chronic widespread pain, which is often refractory to conventional painkillers. Numerous clinical studies have demonstrated that antidepressants are effective in treating FM pain. We previously established a mouse model of FM-like pain, induced by intermittent cold stress (ICS).ResultsIn this study, we find that ICS exposure causes a transient increase in plasma corticosterone concentration, but not in anxiety or depression-like behaviors. A single intrathecal injection of an antidepressant, such as milnacipran, amitriptyline, mianserin or paroxetine, had an acute analgesic effect on ICS-induced thermal hyperalgesia at post-stress day 1 in a dose-dependent manner. In addition, repeated daily antidepressant treatments during post-stress days 1-5 gradually reversed the reduction in thermal pain threshold, and this recovery was maintained for at least 7 days after the final treatment. In addition, relief from mechanical allodynia, induced by ICS exposure, was also observed at day 9 after the cessation of antidepressant treatment. In contrast, the intravenous administration of these antidepressants at conventional doses failed to provide relief.ConclusionsThese results suggest that the repetitive intrathecal administration of antidepressants permanently cures ICS-induced FM pain in mice.

Increased commercial demand for monoclonal antibodies (mAbs) has resulted in the urgent need to establish efficient production systems. We previously developed a transgenic chicken bioreactor system that effectively produced human cytokines in egg whites using genome-edited transgenic chickens. Here, we describe the application of this system to mAb production. The genes encoding the heavy and light chains of humanized anti-HER2 mAb, linked by a 2A peptide sequence, were integrated into the chicken ovalbumin gene locus using a CRISPR/Cas9 protocol. The knock-in hens produced a fully assembled humanized mAb in their eggs. The mAb expression level in the egg white was 1.4–1.9 mg/mL, as determined by ELISA. Furthermore, the antigen binding affinity of the anti-HER2 mAb obtained was estimated to be equal to that of the therapeutic anti-HER2 mAb (trastuzumab). In addition, antigen-specific binding by the egg white mAb was demonstrated by immunofluorescence against HER2-positive and -negative cells. These results indicate that the chicken bioreactor system can efficiently produce mAbs with antigen binding capacity and can serve as an alternative production system for commercial mAbs.

Pregabalin (PGB) is a valuable therapeutic drug against chronic pain. Here we attempted to perform the combinatorial drug therapy with P-glycoprotein (P-gp) inhibitors to lower therapeutic dosage of PGB in the intermittent cold stress-induced fibromyalgia-like pain model. Single intracerebroventricular (i.c.v.) PGB injection exerted long-lasting anti-hyperalgesic effects for 72 h, while the effect of PGB given intraperitoneally (i.p.) disappeared within 3 h. Importantly, the pretreatment with P-gp inhibitors markedly prolonged the PGB (i.p.) effects, which lasted for 72 h. These results suggest that the combinatorial treatment with P-gp inhibitor enables the prolongation of dose-interval for PGB.

Treatment of fibromyalgia is an unmet medical need. To develop novel therapies for the treatment of fibromyalgia, we explored pain therapeutic actions of existing pharmaceuticals, which inhibit the somatic symptoms frequently observed in fibromyalgia patients. This study first examined the therapeutic actions of pilocarpine, which inhibits dry-eye and dry-mouth symptoms, using an experimental fibromyalgia-like chronic pain model produced by intermittent cold stress (ICS) in mice. A single intraperitoneal and intracerebroventricular, but not intrathecal, pilocarpine administration attenuated ICS-induced thermal hyperalgesia and mechanical allodynia, and this action was abolished by muscarinic antagonist pirenzepine (i.c.v.). Treatment with 1-10 mg/kg donepezil (i.p.), which can easily penetrate into the brain, also showed similar therapeutic effects. Importantly, we found that both pilocarpine and donepezil produced antihyperalgesic effects via supraspinal action. Furthermore, repeated donepezil treatments completely cured the ICS-induced hyperalgesia and allodynia even after the cessation of drug treatments. Acute and chronic treatments of these cholinomimetics had no effects on the nociceptive threshold in control animals. By contrast, the lack of morphine (i.c.v.) analgesia initially observed in the ICS model remained in ICS model mice treated with long-term donepezil. Collectively, these findings suggest that stimulation of the muscarinic cholinergic system effectively inhibits some mechanisms underlying chronic pain in the ICS model, but does not inhibit the lack of descending pain-inhibitory mechanisms, which are driven by central morphine.