Oxidative Damage Caused by Trimethylamine Oxide to Human Skin Fibroblasts and Protective Effect of Vitamin C against It

This study aimed to clarify the oxidative damage in human skin fibroblasts (HSF) treated with trimethylamine oxide (TMAO) and to elucidate its pro-aging effect in skin cells in terms of antioxidant indicators, levels of inflammatory cytokines, levels of collagen and matrix metalloproteinases, and mRNA expression of related genes. The results showed that TMAO treatment significantly increased the levels of reactive oxygen species (ROS) and malondialdehyde (MDA), and decreased the content of reduced glutathione, superoxide dismutase (SOD) activity, and total antioxidant capacity (TAC) in HSF cells (P < 0.05). TMAO treatment was found to significantly elevate the mRNA levels of inflammatory cytokines, including tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6), and matrix metalloproteinase-1 (MMP-1), and decrease the mRNA transcript levels of collagen synthesis-related genes and the inducible nitric oxide synthase (iNOS) gene by reverse transcription-quantitative polymerase chain reaction (RT-qPCR) and enzyme-linked immunosorbent assay (ELISA). Western blot analysis showed that the protein expression level of phosphorylated p65 (p-p65) significantly increased (P < 0.05). Vitamin C (VC) was able to protect against TMAO-induced oxidative stress in HSF cells, and reduce inflammation and collagen loss. These results indicated that TMAO can produce oxidative stress in HSF cells, which may activate the signaling pathway of nuclear factor kappa-B (NF-κB), promote NF-κB phosphorylation in HSF cells, induce inflammatory responses, reduce collagen synthesis, and accelerate collagen degradation, thus possibly promoting skin cell aging.