C-Peptide Ameliorates Particulate Matter 2.5-Induced Skin Cell Apoptosis by Inhibiting NADPH Oxidation

Connecting peptide (C-peptide), a byproduct of insulin biosynthesis, has diverse cellular and biological functions. Particulate matter 2.5 (PM_2.5) adversely affects human skin, leading to skin thickening, wrinkle formation, skin aging, and inflammation. This study aimed to investigate the protective effects of C-peptide against PM_2.5-induced damage to skin cells, focusing on oxidative stress as a key mechanism. C-peptide mitigated NADPH oxidation and intracellular reactive oxygen species (ROS) production induced by PM_2.5. It also suppressed PM_2.5-induced NADPH oxidase (NOX) activity and alleviated PM_2.5-induced NOX1 and NOX4 expression. C-peptide protected against PM_2.5-induced DNA damage, lipid peroxidation, and protein carbonylation. Additionally, C-peptide mitigated PM_2.5-induced apoptosis by inhibiting intracellular ROS production. In summary, our findings suggest that C-peptide mitigates PM_2.5-induced apoptosis in human HaCaT keratinocytes by inhibiting intracellular ROS production and NOX activity.