Duodenal Reflux Leads to Down Regulation of DNA Mismatch Repair Pathway in an Animal Model of Esophageal Cancer

Abstract

Gastroduodenal reflux is implicated in esophageal carcinogenesis. This effect is mediated by reactive oxygen species. We hypothesized that this is mediated by DNA mismatch lesion 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxoG), which is repaired by the Mut Y homologue (MYH). We tested the effect of reflux, either alone or in combination with the human dietary mutagen methyl-n-amyl nitrosamine (MNAN), on DNA damage in adenocarcinoma and squamous cell cancer of the esophagus in a rat model. Reflux was promoted in male Sprague-Dawley rats by duodenoesophageal anastomosis (8 weeks) without gastric bypass. MNAN treatment (25 mg/kg per week intraperitoneally for four doses) commenced at 10 weeks age. Ten animals served as controls. Quantification of 8-oxoG was performed by using immunohistochemistry, and MYH was analyzed by Western blot. Apoptosis was assessed by terminal deoxynucleotide transferase-mediated deoxy uridine triphosphate nick-end labeling (TUNEL), cytochrome C, and caspase. Tumors (adenocarcinoma) developed in 15 (50%) of 30 animals with reflux alone; this increased to 26 (86.6%) of 30 when reflux was combined with MNAN treatment, with tumor histology consistent with adenosquamous and squamous cell cancer. DNA damage, as reflected by positive 8-oxoG staining in reflux groups, was significantly increased compared with control (p < 0.01), and this was maximal in tissues with malignant transformation. Protein levels of the DNA repair enzyme MYH were significantly less in tissues subjected to reflux compared with controls (p < 0.05). TUNEL, cytochrome C, and caspase positivity confirmed increased apoptosis in cancer lesions. Gastroduodenal reflux leads to increased DNA damage and downregulation of the DNA mismatch repair pathway. This pathway has an important role in esophageal carcinogenesis in rats.