Fast food diet mouse: novel small animal model of NASH with ballooning, progressive fibrosis, and high physiological fidelity to the human condition

Abstract

Although there are small animal platforms that recapitulate some of the histological features of nonalcoholic fatty liver disease, there are no small animal models of nonalcoholic steatohepatitis (NASH) with consistent hepatocellular ballooning and progressive fibrosis that also exhibit fidelity to the human condition physiologically. We examined the metabolic and histological effects of a diet on the basis of the composition of "fast food" (high saturated fats, cholesterol, and fructose). Mice (n = 8 in each group) were assigned to diets as follows: 1) standard chow (SC), i.e., 13% energy as fat [1% saturated fatty acids (SFA)], 2) high fat (HF), i.e., 60% energy as fat (1% SFA), and 3) fast food (FF), i.e., 40% energy as fat (12% SFA, 2% cholesterol). All three diets were supplemented with high fructose. All diets produced obesity. The HF and FF diets produced insulin resistance. Liver histology was normal in animals fed the SC diet. Steatohepatitis with pronounced ballooning and progressive fibrosis (stage 2) was observed in mice fed the FF diet. Although the HF diet produced obesity, insulin resistance, and some steatosis; inflammation was minimal, and there was no increase in fibrosis. The FF diet produced a gene expression signature of increased fibrosis, inflammation, and endoplasmic reticulum stress and lipoapoptosis. A diet based on high cholesterol, high saturated fat, and high fructose recapitulates features of the metabolic syndrome and NASH with progressive fibrosis. This represents a novel small animal model of fibrosing NASH with high fidelity to the human condition. These results highlight the contribution of dietary composition to the development of nonalcoholic fatty liver disease and NASH.

Fig. 1.

Weight change over time in animals fed standard chow (SC), fast food (FF), and high-fat (HF) diets. Although initial rate of increment in weight was greatest for FF animals, by 6 mo, weights of FF and HF animals were statistically and numerically similar. Weight did not increase significantly in SC animals. *Statistically significantly (P = 0.02–0.001) greater for FF and HF than SC.

Fig. 2.

Hematoxylin-eosin (H&E, left)- and Masson's trichrome (right)-stained sections of liver tissue from SC, FF, and HF animals. There was no steatosis in mice reared on the SC diet. All FF animals developed cellular ballooning, paracinar steatosis, and intra-acinar inflammation commonly associated with severe nonalcoholic steatohepatitis (NASH). Although animals reared on the HF diet also showed evidence of steatosis, steatosis was largely microvesicular, and there was little or no evidence of inflammation. Only FF mice developed fibrosis, which occurred in a perisinusoidal and pericellular pattern.

Fig. 3.

Top: higher-magnification view of Masson's trichrome-stained sections from FF mice. Bottom: high-magnification view of representative hepatocellular ballooning (arrows). Hepatocellular ballooning has been difficult to recreate consistently in small animal models of NASH.

Fig. 4.

Collagen staining with picrosirius red (left), anti-smooth muscle actin (ASMA, middle), and lumican (right) in SC, FF, and HF animals. On digital image analysis, collagen-stained area was significantly more abundant (2-fold, P < 0.05) in FF than HF and SC animals. Staining for ASMA (P < 0.05) and lumican (P < 0.01) was also significantly more abundant in FF than HF or SC animals. *Statistically significant compared with HF and SC.