TRPV1 Agonist Capsaicin Enhances Oxidative-Stress Resistance and Regeneration in Dorsal Root Ganglia and Schwann Cells.

Neurodegeneration and oxidative stress are central drivers of immune-mediated neuropathies. Capsaicin, the active ingredient in chili pepper and a direct agonist of the transient receptor potential vanilloid (TRPV1) channel, is used clinically to treat neuropathic pain. We previously demonstrated immunomodulatory and antioxidative effects of capsaicin in experimental autoimmune neuritis in vivo and Schwann cells (SC) in vitro. However, the molecular mechanisms underlying the maintenance of axonal integrity in dorsal root ganglion (DRG) and SC homeostasis remain unclear. In this study, we described the effects of capsaicin on DRG and SC in vitro under both naïve and S-Nitroso-N-acetyl-DL-penicillamine (SNAP)-induced oxidative stress conditions. Capsaicin induced an upregulation of the antioxidative cascade involving Nrf2, Ho-1, and Nqo1 in naïve DRG neurons and restored axonal growth under preventive and therapeutic settings. Preventive treatment enhanced catalase expression, whereas treatment increased regeneration-associated Gap43 and Atf3. Inhibition of TRPV1 with capsazepine partly attenuated the protective effect of axonal outgrowth, indicating TRPV1-mediated neuroprotection. In SC, capsaicin increased mitochondrial ATP production and spare respiratory capacity, inducing a transient Nrf2-dependent antioxidant response. Capsaicin suppressed expression of myelination markers under basal conditions but promoted expression of myelination- and repair-associated markers under oxidative stress. The findings support capsaicin as a regulator of neuronal and Schwann cell oxidative stress adaptation.