Mast Cell Degranulation and Fibroblast Activation in the Morphine-induced Spinal Mass

Abstract

Editor’s Perspective What We Already Know about This Topic What This Article Tells Us That Is New Background As the meningeally derived, fibroblast-rich, mass-produced by intrathecal morphine infusion is not produced by all opiates, but reduced by mast cell stabilizers, the authors hypothesized a role for meningeal mast cell/fibroblast activation. Using the guinea pig, the authors asked: (1) Are intrathecal morphine masses blocked by opiate antagonism?; (2) Do opioid agonists not producing mast cell degranulation or fibroblast activation produce masses?; and (3) Do masses covary with Mas-related G protein-coupled receptor signaling thought to mediate mast cell degranulation? Methods In adult male guinea pigs (N = 66), lumbar intrathecal catheters connected to osmotic minipumps (14 days; 0.5 µl/h) were placed to deliver saline or equianalgesic concentrations of morphine sulfate (33 nmol/h), 2’,6’-dimethyl tyrosine-(Tyr-D-Arg-Phe-Lys-NH2) (abbreviated as DMT-DALDA; 10 pmol/h; μ agonist) or PZM21 (27 nmol/h; biased μ agonist). A second pump delivered subcutaneous naltrexone (25 µg/h) in some animals. After 14 to 16 days, animals were anesthetized and perfusion-fixed. Drug effects on degranulation of human cultured mast cells, mouse embryonic fibroblast activation/migration/collagen formation, and Mas-related G protein-coupled receptor activation (PRESTO-Tango assays) were determined. Results Intrathecal infusion of morphine, DMT-DALDA or PZM21, but not saline, comparably increased thermal thresholds for 7 days. Spinal masses proximal to catheter tip, composed of fibroblast/collagen type I (median: interquartile range, 0 to 4 scale), were produced by morphine (2.3: 2.0 to 3.5) and morphine plus naltrexone (2.5: 1.4 to 3.1), but not vehicle (1.2: 1.1 to 1.5), DMT-DALDA (1.0: 0.6 to 1.3), or PZM21 (0.5: 0.4 to 0.8). Morphine in a naloxone-insensitive fashion, but not PZM21 or DMT-DALDA, resulted in mast cell degranulation and fibroblast proliferation/collagen formation. Morphine-induced fibroblast proliferation, as mast cell degranulation, is blocked by cromolyn. Mas-related G protein-coupled receptor activation was produced by morphine and TAN67 (∂-opioid agonist), but not by PZM21, TRV130 (mu biased ligand), or DMT-DALDA. Conclusions Opiates that activate Mas-related G protein-coupled receptor will degranulate mast cells, activate fibroblasts, and result in intrathecal mass formation. Results suggest a mechanistically rational path forward to safer intrathecal opioid therapeutics.

The atypical chemokine receptor ACKR3/CXCR7 is a broad-spectrum scavenger for opioid peptides

“…In the light of the present study, it is tempting to speculate that some of these activities may be attributed to the scavenging function of ACKR3 68,69 . Recently, the orphan receptor MRGPRX2 (Mas-related GPCR X2 or MrgX2) was also proposed as an AOR 55,70,71 . It is expressed on mast cells and small diameter neurons in dorsal root and trigeminal ganglia and induces classical G protein signaling in response to micromolar concentrations of pro-dynorphin-derived peptides and well-known synthetic opioid agonists.…”

Biased Opioid Ligands

“…Intrathecal opiate use with drugs like morphine is usually impacted by the risk of producing space-occupying intrathecal masses through Mas-related G-protein coupled receptor (MRGPR) signaling. A recent study by the Yaksh group shows that PZM21 does not produce mast cell degranulation or activation of fibroblasts because it doesn’t activate MRGs, unlike morphine, suggesting that MOR biased ligands could be useful for intrathecal therapies [ 41 ].…”

Characterization of Effect of Repeated Bolus or Continuous Intrathecal Infusion of Morphine on Spinal Mass Formation in the Dog

“…(9) Current work has emphasized the role of a family of Mas-Related G-Protein Coupled Receptors (MRGP-r) in mediating opioid-receptor-independent degranulation of mast cells by morphine (29). In recent studies in the guinea pig, we found that two mu agonists, DMT-DALDA and PZM21, that are not activators of MRGP-r produce little or no mast cell degranulation, do not activate fibroblasts and when infused intrathecally do not produce intrathecal masses (30). Of note, it was recently reported that a spinal mass resected from a patient receiving 50 mg/mL morphine displayed particulates of morphine, in a loculated fluid-filled sac at the catheter tip, suggesting that at concentrations close to solubility in a buffered water environment with restricted diffusion access, particulate formation may occur, and may contribute to the local reaction (31).…”