Metformin exhibits analgesic activity in neuronal cell models and CFA-induced inflammatory pain in mice

Inflammatory pain is mediated by complex interactions between immune signaling and sensory neurons, with prostaglandin E2-dependent pathways playing a central role in nociceptive sensitization. Metformin, a first-line antidiabetic drug, has emerged as a potential non-opioid analgesic due to its pleiotropic anti-inflammatory and neuroprotective properties. In this study, we investigated the analgesic effects of metformin using both an in vitro neuronal sensitization model and an in vivo model of inflammatory pain. In SH-SY5Y neuronal cells, PGE2 exposure significantly reduced Na⁺/K⁺-ATPase activity and increased intracellular cAMP levels. Post-treatment with metformin restored Na⁺/K⁺-ATPase activity and suppressed cAMP elevation in a concentration-dependent manner. In vivo, metformin produced dose-dependent analgesia in mice with complete Freund's adjuvant-induced inflammatory pain, with 0.1 g/kg/day significantly increasing hind paw withdrawal thresholds. Molecular analyses revealed significant downregulation of pain-associated proteins TRPV1 and NaV1.7 in metformin-treated groups, supported by both Western blot and immunohistochemical findings. Histological examination further demonstrated reduced inflammatory cell infiltration and improved tissue recovery. Collectively, these findings indicate that metformin alleviates inflammatory pain by modulating neuronal excitability and inflammatory signaling pathways, highlighting its potential as a non-opioid therapeutic candidate for inflammatory pain management.