RESUMO
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.
RESUMO
N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) is a common alkylating agent, which can be experimentally used as a chemical mutagen and carcinogen, extensively existing in the environment. Folic acid (FA), part of the B group of vitamins, plays an important role in defending against inflammation and reducing the risk of cancers. Nevertheless, there is little research on the protective effects of FA against MNNG-induced esophageal inflammation, and its underlying mechanism still remains elusive. Hence, in the present study, we exposed MNNG to SD rats and esophageal cells to establish the esophageal inflammation models. Our research aims to explore the protective roles of FA against esophageal inflammation induced by MNNG via NF-κB pathway by CCK-8, EdU, RT-qPCR, ELISA, H&E, Western blot. Our results revealed that MNNG decreased the viability of esophageal cells, which was restored under FA intervention. Besides, FA relieved the elevation of IL-6, IL-8 and TNF-α in MNNG-induced esophageal inflammation. Moreover, histopathological analysis showed that epithelial spinous cells proliferated in mucous layer, and inflammatory cells were locally infiltrated in the submucosa after MNNG exposure, while the pathological damage of esophageal tissues was gradually alleviated along with increasing FA doses. And Western blot results demonstrated that FA could relieve the rise of phosphorylated IκBα (p-IκBα) and phosphorylated p65 (p-p65) proteins induced by MNNG. Therefore, it is reasonable to believe that FA has a crucial role in preventing MNNG-induced esophageal inflammation through inhibiting the NF-κB pathway, thereby down-regulating the expressions of IL-6, IL-8 and TNF-α.
