Unraveling the regulatory mechanisms of tetrandrine in microglial phenotypic transition and neuronal autophagy for relieving diabetic neuropathic pain

Background: Diabetic neuropathic pain (DNP) is a prevalent and debilitating complication of diabetes mellitus, characterized by persistent pain and neuroinflammation. Current treatments often provide inadequate relief, highlighting the need for novel therapeutic strategies targeting its underlying mechanisms. Objectives: This study aimed to investigate the therapeutic potential of tetrandrine (Tet) in alleviating DNP and to elucidate its effects on two key pathological processes: neuronal autophagy and microglial polarization. Methods: To establish the DNP model, rats received an intraperitoneal injection of streptozotocin. Pain behavior was assessed weekly using mechanical withdrawal threshold and thermal withdrawal latency tests. Relevant markers were analyzed via reverse-transcription quantitative real-time polymerase chain reaction, enzyme-linked immunosorbent assay, immunofluorescence, or Western blot. To further investigate the underlying mechanisms, in-vitro experiments were conducted using high glucose-treated neuronal cells and lipopolysaccharide-stimulated BV2 microglia. Results: Tet administration significantly alleviated pain hypersensitivity and neuroinflammation in DNP rats. Mechanistically, this effect might be achieved through a dual modulation of neuroimmune processes and intracellular clearance pathways. Tet shifted microglial polarization from the pro-inflammatory M1 phenotype toward the anti-inflammatory M2 state. Concurrently, it enhanced autophagic activity, as evidenced by an increased LC3-II level and LC3-II/LC3-I ratio, restored expression of the mitophagy-related proteins PINK1 and parkin and reduced p62 accumulation. In-vitro findings corroborated these mechanisms: Tet balanced the expression of M1 and M2 markers in activated microglia and similarly upregulated key autophagy-related proteins (LC3-II, PINK1, parkin) in neurons under high-glucose stress. Conclusion: Tet alleviates DNP, potentially through the concurrent modulation of microglial phenotypic transition and neuronal autophagy. These findings identify Tet as a promising multi-target agent for DNP and elucidate its potential mechanisms of action.