Effects of High Fat Diet on 4‐NQO‐Induced Changes in a Variety of Tissues in a Mouse Model of Oral Cancer

Abstract

IntroductionA variety of factors, including use of tobacco, diet, gender, and genetics impact cancer risk. Smoking is a risk factor for about 1/3 of all human cancers. It is well established that administration of 4‐nitroquinonline 1‐oxide (4NQO) in drinking water mimics the effects of tobacco and leads to development of oral carcinoma in mice. The purpose of this study was to compare the effects of high and low in saturated fat diets (HF and LF, respectively) on the incidence and severity of 4NQO‐induced cancers. We hypothesized that 4NQO's carcinogenic effects extend beyond oral tissues and will result in pathological changes in organs beyond the oral cavity. We also hypothesized that a HF diet would increase inflammation and tissue changes when compared to the LF diet.Materials and methodsMale and female C57Bl/6 mice (Jackson Labs, 36 each gender), 5 weeks old, were divided into a low fat (10kcal% fat; LF) or HF (60 kcal% fat) diet. Within each dietary group, mice were randomly assigned to one of 3 water treatment groups for 17 weeks: water alone (control); propylene glycol in water (1.25%; PG‐H2O); or 4NQO in PG‐H2O (50 mg/ml; 4NQO). After 17 weeks, all mice were given water alone for 6 weeks prior to euthanasia. Animals were weighed weekly and upon sacrifice. Salivary glands, lungs, liver, kidney, spleen, and portions of the gastrointestinal tract were harvested, formalin fixed, microtome sectioned, and stained with hematoxylin and eosin (H&E) for histological evaluation. Histopathology criteria used for tissue assessment were based on the presence and degree of cellular atypia, tissue hyperplasia and dysplasia, and lymphoid cells infiltration.ResultsHistopathological changes in 4NQO‐treated animals were identified in esophagus (epithelial hyperplasia, dysplasia, inflammation, and development of carcinoma), lungs (significant peribronchial lymphoid cell infiltrates and – characteristic of emphysema – increased in size air spaces), and liver (lymphoid cell infiltrates in portal tracts and liver parenchyma and periportal fibrosis). Kidney, spleen, salivary glands, and pancreas demonstrated little changes based on H&E‐stained tissue analysis. Gender had no significant effect on a degree of 4NQO‐induced tissue pathology. However, HF diet exacerbated pathological changes compared to LF diet. This was particularly evident in liver, with males but not females demonstrating severe steatosis and liver enlargement (3× higher liver index in HF males versus all other treatment groups).ConclusionThis mouse model of oral cancer, initially established to mimic the effects of smoking, may be extended to serve as a model for the effects of tobacco and diet on extra‐oral tissues as well.Support or Funding InformationWe recognize the Midwestern University Deans of the College of Dental Medicine and the Basic Science Division for their support of this research. Student research was supported by the Office of Research and Sponsored Programs and the Biomedical Sciences Division.