Sensory neuron BRAF mediates opioid-induced hyperalgesia and tolerance via presynaptic NMDA receptor hyperactivity.

Summary

Morphine drives BRAF translocation to nociceptor central terminals where it augments MEK-ERK signaling and presynaptic NMDAR hyperactivity; BRAF physically associates with NMDARs in rat and human spinal cords. Pharmacologic BRAF/MEK inhibition or DRG-specific Braf deletion reverses NMDAR hyperactivity, enhances morphine analgesia, and mitigates opioid-induced hyperalgesia and tolerance, suggesting repurposing BRAF inhibitors.

Key Findings

• Morphine promoted DRG-to-spinal translocation of monomeric BRAF, increasing MEK-ERK phosphorylation at nociceptor terminals.
• BRAF physically interacted with NMDARs in rat and human spinal cords and drove presynaptic NMDAR hyperactivity.
• Vemurafenib reversed morphine-induced NMDAR phosphorylation and α2δ-1-bound NMDAR synaptic localization and abolished presynaptic NMDAR hyperactivity.
• DRG-specific Braf knockout normalized NMDAR phosphorylation/trafficking and reduced hyperalgesia and tolerance while enhancing morphine analgesia.

Clinical Implications

Co-therapy with BRAF or MEK inhibitors could enhance opioid analgesia while reducing hyperalgesia and tolerance; dose, safety, and oncologic adverse effects of BRAF inhibitors must be carefully evaluated before perioperative or chronic pain applications.

Limitations

• Preclinical animal study; no clinical trial data on efficacy or safety of BRAF/MEK inhibition for opioid-sparing analgesia.
• Potential off-target/systemic effects and oncologic toxicity profiles of BRAF inhibitors may limit perioperative applicability.

Future Directions

Early-phase clinical trials testing low-dose or peripherally restricted BRAF/MEK inhibitors as adjuncts to opioids in acute and chronic pain; biomarker-driven stratification (e.g., DRG BRAF signaling markers) and longitudinal safety monitoring.