Acute and chronic pain resulting from injury, surgery, or disease afflicts >100 million Americans each year, having a severe impact on mood, mental health, and quality of life. The lack of structural and functional information for most ion channels, many of which play key roles in the detection and transmission of noxious stimuli, means that there remain unidentified therapeutic targets for pain management. This study focuses on the TRPC4 ion channel, which is involved in the tissue-specific and stimulus-dependent regulation of intracellular Ca2+ signaling. Rats with a transposon-mediated TRPC4-knockout mutation displayed tolerance to visceral pain induced by colonic mustard oil (MO) exposure, but not somatic or neuropathic pain stimuli. Moreover, wild type rats treated with a selective TRPC4 antagonist (ML-204) prior to MO exposure mimicked the behavioral responses observed in TRPC4-knockout rats. Significantly, ML-204 inhibited visceral pain-related behavior in a dose-dependent manner without noticeable adverse effects. These data provide evidence that TRPC4 is required for detection and/or transmission of colonic mustard oil visceral pain sensation. In the future, inhibitors of TRPC4 signaling may provide a highly promising path for the development of first-in-class therapeutics for this visceral pain, which may have fewer side effects and less addictive potential than opioid derivatives.

Background Patients with temporomandibular joint disorders (TMD), reactive arthritis, and rheumatoid arthritis often have combined etiology of hereditary and microenvironmental factors contributing to joint pain. Multiple clinical and animal studies indicate “double-hit” inflammatory insults can cause chronic inflammation. The first inflammatory insult primes the immune system and subsequent insults elicit amplified responses. The present “double hit” study produced a chronic orofacial pain model in mice with genetic deletion of both TNFα receptors (TNFR1/R2−/−), investigating the main nociceptive signaling pathways in comparisons to wild type mice. Methods An initial inflammatory insult was given unilaterally into the temporomandibular joint (TMJ). Secondary hypersensitivity was tested on the skin over the TMJ throughout the experiment. Three weeks later after complete reversal of hypersensitivity, a second inflammatory insult was imposed on the colon. Pharmacological interventions were tested for efficacy after week 10 when hypersensitivity was chronic in TNFR1/R2−/− mice. Serum cytokines were analyzed Days 1, 14, and Week 18. Results The double hit insult produced chronic hypersensitivity continuing through the four month experimental timeline in the absence of TNFα signaling. P2X7 and NMDA receptor antagonists temporarily attenuated chronic hypersensitivity. Serum cytokine/chemokine analysis on Day 14 when CFA induced hypersensitivity was resolved identified increased levels of pro-inflammatory cytokines CCL2, CXCL9, CXCL10, RANTES and decreased levels of anti-inflammatory cytokines IL-1ra and IL-4 in TNFR1/R2−/− compared to WT mice. Conclusions These data suggest a causal feed-forward signaling cascade of these little studied cytokines have the potential to cause recrudescence in this orofacial inflammatory pain model in the absence of TNFα signaling.

Background Nitric oxide synthase (iNOS) is induced in hepatocytes by shock and inflammatory stimuli. Excessive NO from iNOS mediates shock-induced hepatic injury and death so understanding the regulation of iNOS will help elucidate the pathophysiology of septic shock. In vitro, cytokines induce iNOS expression through activation of signaling pathways including mitogen-activated protein kinases and Nuclear Factor κB. Cytokines also induce calcium (Ca2+) mobilization and activate calcium-mediated intracellular signaling pathways, typically through activation of calmodulin-dependent kinases (CaMK). Calcium regulates NO production in macrophages but the role of calcium and calcium-mediated signaling in hepatocyte iNOS expression has not been defined. Materials and Methods Primary rat hepatocytes were isolated, cultured, and induced to produce NO with proinflammatory cytokines. Calcium mobilization and Ca2+-mediated signaling were altered with ionophore, Ca2+ channel blockers, and inhibitors of CaMK. Results The Ca2+ ionophore A23187 suppressed cytokine-stimulated NO production while EGTA and nifedipine increased NO production, iNOS mRNA, and iNOS protein expression. Inhibition of CaMK with KN93 and CBD increased NO production but the calcineurin inhibitor FK 506 decreased iNOS expression. Conclusions These data demonstrate that calcium-mediated signaling regulates hepatocyte iNOS expression and does so through a mechanism independent of calcineurin. Changes in intracellular calcium levels may regulate iNOS expression during hepatic inflammation induced by pro-inflammatory cytokines.