Vitamin D3 Attenuates Neuropathic Pain via Suppression of Mitochondria-Associated Ferroptosis by Inhibiting PKCα/NOX4 Signaling Pathway

Aims

Neuropathic pain remains a significant unmet medical challenge due to its elusive mechanisms. Recent clinical observations suggest that vitamin D (VitD) holds promise in pain relief, yet its precise mechanism of action is still unclear. This study explores the therapeutical role and potential mechanism of VitD₃ in spared nerve injury (SNI)-induced neuropathic pain rat model.

Methods

The analgesic effects and underlying mechanisms of VitD₃ were evaluated in SNI and naïve rat models. Mechanical allodynia was assessed using the Von Frey test. Western blotting, immunofluorescence, biochemical assay, and transmission electron microscope (TEM) were employed to investigate the molecular and cellular effects of VitD₃.

Results

Ferroptosis was observed in the spinal cord following SNI. Intrathecal administration of VitD₃, the active form of VitD, activated the vitamin D receptor (VDR), suppressed ferroptosis, and alleviated mechanical nociceptive behaviors. VitD₃ treatment preserved spinal GABAergic interneurons, and its neuroprotective effects were eliminated by the ferroptosis inducer RSL3. Additionally, VitD₃ mitigated aberrant mitochondrial morphology and oxidative metabolism in the spinal cord. Mechanistically, VitD₃ inhibited SNI-induced activation of spinal PKCα/NOX4 signaling. Inhibition of PKCα/NOX4 signaling alleviated mechanical pain hypersensitivity, accompanied by reduced ferroptosis and mitochondrial dysfunction in SNI rats. Conversely, activation of PKCα/NOX4 signaling in naïve rats induced hyperalgesia, ferroptosis, loss of GABAergic interneurons, and mitochondrial dysfunction in the spinal cord, all of which were reversed by VitD₃ treatment.

Conclusions

Our findings provide evidence that VitD₃ attenuates neuropathic pain by preserving spinal GABAergic interneurons through the suppression of mitochondria-associated ferroptosis mediated by PKCα/NOX4 signaling, probably via VDR activation. VitD, alone or in combination with existing analgesics, presents an innovative therapeutic avenue for neuropathic pain.