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CB2 receptor agonist AM1241 regulating the polarization of microglia reduces morphine tolerance through IL-4/STAT6

Di Cui1, Chuhua Yang2, Yuanyuan Zhang2

  • 1Department of Anesthesiology, 3201 Hospital, Hanzhong, China.

Molecular Pain
|August 18, 2025
PubMed
Abstract

Insights

Morphine tolerance in pain management is linked to M1 microglial polarization. A CB2 receptor agonist, AM1241, shifts microglia to an M2 state via the IL-4/STAT6 pathway, effectively reducing morphine tolerance.

Area of Science:

  • Neuroscience
  • Immunology
  • Pharmacology

Background:

  • Morphine is a common analgesic, but its efficacy is limited by the development of tolerance.
  • The precise mechanisms underlying morphine tolerance remain incompletely understood.
  • Microglial polarization plays a critical role in neuroinflammation and may contribute to morphine tolerance.

Purpose of the Study:

  • To investigate the role of microglial polarization in morphine tolerance.
  • To explore the potential of interleukin-4 (IL-4) in modulating microglial polarization to reduce morphine tolerance.
  • To examine the therapeutic effect of a CB2 receptor agonist (AM1241) in mitigating morphine tolerance.

Main Methods:

  • In vitro studies involved culturing cells with morphine, CB2 receptor agonist (AM1241), and antagonists/inhibitors.
  • In vivo studies utilized mice treated with drugs for 7 consecutive days, followed by hot plate tests.
  • Molecular analysis included qPCR for mRNA expression (iNOS, SOCS3, IL-4, STAT6) and Western blot for protein expression (iNOS, SOCS3, p-STAT6, STAT6).
  • Inflammatory cytokine levels were quantified using ELISA kits.

Main Results:

  • Morphine treatment increased M1 markers (iNOS) and pro-inflammatory cytokines while decreasing M2 markers (SOCS3).
  • AM1241 treatment increased IL-4 mRNA and p-STAT6 protein, decreased iNOS, increased SOCS3, and reduced pro-inflammatory cytokines, enhancing IL-10 secretion.
  • AM1241 treatment improved pain relief (increased PWL) and reversed morphine-induced M1 polarization.
  • Inhibition of CB2 or IL-4 pathways reversed the beneficial effects of AM1241.

Conclusions:

  • M1 microglial polarization is a key driver of morphine tolerance.
  • AM1241 promotes M2 microglial polarization through the IL-4/STAT6 signaling pathway.
  • This M2 polarization induced by AM1241 effectively reduces morphine tolerance.
  • Targeting microglial polarization via the IL-4/STAT6 pathway presents a promising strategy for managing morphine tolerance.
Keywords:
Cannabinoid type 2 receptorinflammatory cytokinesmicroglial polarizationmorphine tolerance

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