Capsaicin Regulates Mitochondrial Fission to Promote Melanoma Cell Apoptosis

Objective: Capsaicin (CPS) is a major component of the red pepper, and its anti-tumor property has been confirmed. However, the underlying mechanism of this anti-tumor effect has not been fully clarified, so we conducted this study to evaluate the role of mitochondrial fission and subsequent mitochondrial dysfunction in CPS-induced apoptosis of melanoma cells. Methods: Two melanoma cell lines and melanocytes were treated with CPS alone or in combination with ruthenium red (a transient receptor potential vanilloid 1 [TRPV] antagonist), Z-VAD-FMK (a pan-caspase inhibitor), or N-acetyl-L-cysteine (an antioxidant). Cell vitality was tested using a cell counting kit-8 assay. The expression levels of related proteins were examined by Western blotting. Apoptosis, intracellular reactive oxygen species, mitochondrial membrane potential, adenosine triphosphate levels, and mitochondrial dynamics were analyzed by flow cytometry, luminometry, and confocal laser microscopy, respectively, and compared between groups. Results: CPS treatment significantly inhibited the vitality of melanoma cells (For A2058 cells: 0 vs. 120 μmol/L: [100.00% ± 0%] vs. [51.02% ± 6.40%], P < 0.05; For WM35 cells: 0 vs. 120 μmol/L: [100.00% ± 0%] vs. [51.80% ± 3.45%], P < 0.05) but exerted less impact on normal melanocytes. CPS promoted melanoma cell apoptosis through TRPV channels and the caspase cascade. CPS treatment then led to TRPV channel-dependent mitochondrial dysfunction with an increase in reactive oxygen species generation (For A2058 cells: CPS vs. CPS+RR: [2.34 ± 0.30] vs. [1.34 ± 0.12], P < 0.05; For WM35 cells: CPS vs. CPS+RR: [2.25 ± 0.25] vs. [1.65 ± 0.13], P < 0.05), dissipation of the mitochondrial membrane potential (Control vs. CPS: [1.00 ± 0] vs. [0.61 ± 0.08], P < 0.05), and adenosine triphosphate reduction ( P < 0.05). In addition, reactive oxygen species generation contributed to CPS-induced melanoma cell apoptosis. Mitochondrial fission was subsequently proved to connect CPS treatment to mitochondrial dysfunction, which was also TRPV channel-dependent, thereby inducing melanoma cell apoptosis. Conclusion: Our study highlights the role of mitochondrial fission and its related mitochondrial dysfunction in mediating the pro-apoptotic effect of CPS in melanoma. These findings deepen our understanding of the mechanisms underlying the anti-tumor activity of CPS and indicate the clinical relevancy of extending the use of this agent for cancer therapy.