Activation of the Nrf2 Signaling Pathway by Tetrahydroberberine Suppresses Ferroptosis and Enhances Functional Recovery Following Spinal Cord Injury

Recent research has identified ferroptosis, a newly recognized form of programmed cell death, is a crucial factor in spinal cord injury (SCI). Tetrahydroberberine (THB) is a tetrahydroisoquinoline alkaloid derived from the tuber of the poppy family plant, Corydalis, which is recognized for its antioxidant and neuroprotective properties. Despite these attributes, the potential protective effects of THB against SCI are yet to be thoroughly investigated. Therefore, the aim of this study was to elucidate the protective effects and underlying mechanisms of action of THB in SCI. A mouse model of SCI was used for the in vivo experiments. Functional recovery was evaluated using the Basso Mouse Scale (BMS), footprint analysis, and hematoxylin and eosin (HE), Masson's trichrome, and Nissl staining. Lipid peroxidation was quantified using malondialdehyde (MDA), glutathione (GSH), and superoxide dismutase (SOD). The expression levels of the nuclear factor erythroid 2-related factor 2 (Nrf2) signaling pathway and ferroptosis markers were analyzed using western blot (WB) and immunofluorescence (IF) staining. To further elucidate the mechanism through which THB inhibits ferroptosis, an in vitro ferroptosis model was established in PC12 cells using RSL3, a known ferroptosis activator. THB markedly improved tissue and motor function restoration in mice post-SCI, with the BMS score increasing by approximately 50% compared with that in the control group. Lipid peroxidation assays revealed that THB significantly reduced MDA levels and increased GSH and SOD levels. Both in vivo and in vitro experiments demonstrated that THB significantly activated the Nrf2 pathway and inhibited ferroptosis in mice and in PC12 cells. This protective effect was reversed by the Nrf2 inhibitor, ML385, as evidenced by suppression of the Nrf2 pathway, increased lipid peroxidation, and elevated ferroptosis levels. Our in vivo and in vitro experiments indicate that THB promotes functional recovery after SCI by activating the Nrf2 signaling pathway, which attenuates lipid peroxidation and suppresses ferroptosis, thereby contributing to neuronal survival. Our findings contribute to a more comprehensive understanding of how THB exerts its recovery effects in SCI and demonstrate the potential of THB as a novel therapeutic strategy for the clinical management of SCI.