ABSTRACT
Activity-induced pain is common in those with chronic musculoskeletal pain and limits participation in daily activities and exercise. Our laboratory developed a model of activity-induced pain and shows that depletion of muscle macrophages prevents development of hyperalgesia. Adenosine triphosphate (ATP) is released from fatiguing muscle and activates purinergic receptors (P2X), and P2X4 receptors are expressed on macrophages. We hypothesized that exercise releases ATP to activate P2X4 receptors on muscle macrophages, which subsequently release interleukin-1ß (IL-1ß) to produce hyperalgesia. In an animal model of activity-induced pain, using male and female C57BL6/J mice, we show increased expression of P2X4 on muscle macrophages, and blockade of P2X4 receptors in muscle prevented development of hyperalgesia. Using a lentivirus expressing an artificial micro-RNA to P2X4 under the control of a CD68 promoter, we decreased expression of P2X4 mRNA in cultured macrophages, decreased expression of P2X4 protein in muscle macrophages in vivo, and prevented development of activity-induced hyperalgesia. We further show that macrophages primed with LPS differentially released IL-1ß when treated with ATP in neutral or acidic pH. Lastly, blockade of IL-1ß in muscle prevented development of hyperalgesia in this model. Thus, our data suggest that P2X4 receptors could be a valid pharmacological target to control activity-induced muscle pain experienced by patients with chronic musculoskeletal pain.
Subject(s)
Hyperalgesia/metabolism , Macrophages/metabolism , Muscles/metabolism , Myalgia/metabolism , Receptors, Purinergic P2X4/metabolism , Adenosine Triphosphate/pharmacology , Animals , Cells, Cultured , Disease Models, Animal , Female , Gene Knockdown Techniques , Hyperalgesia/complications , Interleukin-1beta/metabolism , Lipopolysaccharides , Macrophages/drug effects , Male , Mice, Inbred C57BL , Myalgia/complicationsABSTRACT
We evaluated if a nanostructured thermoreversible Pluronic F127-based hydrogel incorporated with Hyptis pectinata leaf essential oil (NE-EOH) produces a long-lasting anti-hyperalgesic effect on chronic muscle pain in an animal model. We induced chronic muscle pain by injecting the gastrocnemius with saline injections. Paw and muscle withdrawal thresholds and motor performance were evaluated after treatment and compared with morphine, diazepam, or vehicle. Naloxone and methysergide administration tested the involvement of opioid and serotonin receptors, respectively. Sites of action in the central nervous system for the NE-EOH were examined by measuring substance P (SP) levels in the spinal cord and Fos protein in the brainstem. NE-EOH increased paw and muscle withdrawal thresholds when compared with vehicle but had no effect on motor function. This analgesic effect was reversed by both naloxone and methysergide. NE-EOH decreased elevated substance P levels and reduced Fos-labeled neurons in the spinal cord and increased the number of Fos-labeled neurons in the periaqueductal gray (PAG), nucleus raphe magnus (NRM), and locus coeruleus (LC). NE-EOH was shown to produce a lasting anti-hyperalgesic effect. It uses opioid and serotonin receptors, activates brainstem inhibitory pathways, and reduces the release of excitatory neurotransmitters in the spinal cord and is a substance with potential to be used in the treatment of noninflammatory pain conditions. Graphical Abstract.
Subject(s)
Analgesics/therapeutic use , Chronic Pain/drug therapy , Oils, Volatile/therapeutic use , Plant Extracts/therapeutic use , Analgesics/pharmacology , Animals , Chronic Pain/metabolism , Disease Models, Animal , Hydrogel, Polyethylene Glycol Dimethacrylate , Lamiaceae , Male , Mice , Oils, Volatile/pharmacology , Pain Measurement , Periaqueductal Gray/drug effects , Periaqueductal Gray/metabolism , Plant Extracts/pharmacology , Proto-Oncogene Proteins c-fos/metabolism , Spinal Cord/drug effects , Spinal Cord/metabolism , Substance P/metabolismABSTRACT
Muscle pain is a common medical problem that is difficult to treat. One nonpharmacological treatment used is acupuncture, a procedure in which fine needles are inserted into body points with the intent of relieving pain and other symptoms. Here we investigated the effects of manual acupuncture (MA) on modulating macrophage phenotype and interleukin-10 (IL-10) concentrations in animals with muscle inflammation. Carrageenan, injected in the gastrocnemius muscle of mice, induces an inflammatory response characterized by mechanical hyperalgesia and edema. The inflammation is initially a neutrophilic infiltration that converts to a macrophage-dominated inflammation by 48 h. MA of the Sanyinjiao or Spleen 6 (SP6) acupoint reduces nociceptive behaviors, heat, and mechanical hyperalgesia and enhanced escape/avoidance and the accompanying edema. SP6 MA increased muscle IL-10 levels and was ineffective in reducing pain behaviors and edema in IL-10 knockout (IL-10(-/-)) mice. Repeated daily treatments with SP6 MA induced a phenotypic switch of muscle macrophages with reduced M1 macrophages (pro-inflammatory cells) and an increase of M2 macrophages (anti-inflammatory cells and important IL-10 source). These findings provide new evidence that MA produces a phenotypic switch in macrophages and increases IL-10 concentrations in muscle to reduce pain and inflammation.