A role for substance P and acid-sensing ion channel 1a in prolotherapy with dextrose-mediated analgesia in a mouse model of chronic muscle pain.

ABSTRACT: Prolotherapy is widely used in pain control and tissue repair in pain medicine. The classical mode is injection with hypertonic dextrose in muscle or perimysium. However, the analgesic mechanism is still not known. Here, we successfully established dextrose-mediated antinociception in a mouse model of fibromyalgia. The antinociceptive effects of dextrose injections were evaluated in a mouse model of fibromyalgia, in which bilateral chronic mechanical hyperalgesia was induced by unilateral intramuscular acid injection. The injectant (dextrose), dose (≥5%), and volume (>10 μL), but not osmolarity, were essential for the prolotherapy. Further studies showed that the activation of acid-sensing ion channel 1a (ASIC1a), neural activation, and the release of substance P from muscle afferents were required in the dextrose-induced reduction of mechanical hypersensitivity. Both pharmacological blockade and genetic deletion of ASIC1a or substance P as well as lidocaine abolished the dextrose-induced antinociception in mice with chronic hyperalgesia. Moreover, intramuscular dextrose injection induced phosphorylated extracellular signal-regulated kinase expression in dorsal root ganglion neurons expressing substance P; the phosphorylated extracellular signal-regulated kinase expression was inhibited by the ASIC1a antagonist PcTx1. The optimal settings for prolotherapy in fibromyalgia-like pain are dextrose dependent and volume dependent, and the peripheral antinociception involves ASIC1a and substance P signaling in muscle afferents. This study suggests a possible mechanism of action of dextrose prolotherapy in noninflammatory muscle pain such as fibromyalgia and provides insights into treating other types of chronic pain.