Protective effect of folic acid on MNNG-induced proliferation of esophageal epithelial cells via the PI3K/AKT/mTOR signaling pathway

Recent research has revealed that N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) constitutes a significant risk factor in the development of esophageal cancer. Several investigations have elucidated the beneficial impact of folic acid (FA) in safeguarding esophageal epithelial cells against MNNG-induced damage. Therefore, we hypothesized that FA might prevent MNNG-induced proliferation of esophageal epithelial cells by interfering with the PI3K/AKT/mTOR signaling pathway. In vivo experiments, we found that FA antagonized MNNG-induced proliferation of rat esophageal mucosal epithelial echinocytes and activation of the PI3K/AKT/mTOR signaling pathway. In our in vitro experiments, it was observed that acute exposure to MNNG for 24 h led to a decrease in proliferative capacity and inhibition of the PI3K/AKT/mTOR signaling pathway in an immortalized human normal esophageal epithelial cell line (Het-1A), which was also ameliorated by supplementation with FA. We successfully established a Het-1A-T-cell line by inducing malignant transformation in Het-1A cells through exposure to MNNG. Notably, the PI3K/AKT2/mTOR pathway showed early suppression followed by activation during this transition. Next, we observed that FA inhibited cell proliferation and activation of the PI3K/AKT2/mTOR signaling pathway in Het-1A-T malignantly transformed cells. We further investigated the impact of 740Y-P, a PI3K agonist, and LY294002, a PI3K inhibitor, on Het-1A-T-cell proliferation. Overall, our findings show that FA supplementation may be beneficial in safeguarding normal esophageal epithelial cell proliferation and avoiding the development of esophageal cancer by decreasing the activation of the MNNG-induced PI3K/AKT2/mTOR signaling pathway.