The prevalence of nonalcoholic fatty liver disease (NAFLD) is increasing, with ~24% of the US and European populations estimated to be affected. NAFLD is defined as the presence of fat in liver parenchyma without inflammation, but in the absence of excess alcohol consumption. In many NAFLD cases, a more aggressive form of fatty liver disease develops: Nonalcoholic steatohepatitis (NASH). NASH is associated with liver inflammation, and there is potential for extensive fibrosis to develop, leading eventually to cirrhosis. NAFLD and NASH are therefore increasingly important public health concerns, yet treatment options remain limited.
Although lifestyle management can be effective in bringing NAFLD and NASH under control, it is very difficult to implement and maintain in practice. Therefore, there is an urgent need to develop a deeper understanding of the disease and how it progresses, and to provide additional treatment solutions. Animal models developed through diet manipulation are critically important for achieving these aims. At Envigo, we have a number of diet options available to NAFLD/NASH researchers. Our nutritionists are also available to assist researchers in identifying the diet that best fits their specific research goal.
What dietary manipulations are used to induce NAFLD/NASH in rodents?
In rodents, there are two commonly used methods that can either induce obesity, metabolic syndrome, and mild NASH, or isolate the hepatic features of NASH without recapitulating metabolic symptoms such as obesity and insulin resistance. Some of the diet options available for each of these methods are described below:
Inducing obesity, metabolic syndrome, and mild NAFLD/NASH
+ Western or fast food style diets typically contain 40 - 45% kcal from milkfat (a fat source high in palmitate) with added cholesterol (0.15 - 2%) and are high in sucrose (>30%).
+ Obesity, metabolic syndrome, and simple steatosis can occur within nine weeks, and increased hepatic inflammation after 12 weeks.
+ More complex disease (fibrosis, hepatic ballooning) requires longer feeding periods (9+ months).
+ Increasing dietary sucrose (~41%) and cholesterol (~1.25%) accelerates the NASH phenotype with steatosis, inflammation and hepatocyte ballooning observed within 12 weeks.
+ In addition to feeding a high fat diet, providing a glucose/fructose mixture in the drinking water may further promote NASH development.
+ The American Lifestyle-Induced Obesity Syndrome (ALIOS) model involves feeding the “American fast food” diet, which is high in trans-fats and sugar.
+ Insulin resistance, elevated ALT levels, and steatosis occurs within 16 weeks. Increased inflammation and early development of fibrosis have been observed at 6 months.
+ Severe steatosis with fibrosis and inflammation develops after 12 months of feeding.
+ Adding cholesterol (0.2%) to the American Fast Food diet may accelerate NASH phenotype development.
+ A glucose/fructose solution is also added to the drinking water, and sedentary behaviour is promoted by removing the overhead cage feeders.
+ The Fructose, Palmitate, Cholesterol and Trans-Fat (FPC) diet contains high sucrose (~34%) with 1.25% cholesterol and 52% kcal from fat using a mixture of fat sources including milkfat, palmitic acid and hydrogenated vegetable oil (providing trans-fats).
+ Originally developed to accelerate the development of the NASH phenotype with metabolic features.
+ Insulin resistance and NAFLD with inflammation, hepatocyte death, and fibrosis developed in mice fed the FPC within 16 weeks.
+ In addition to feeding the FPC, the model provides a glucose/fructose mixture in the drinking water to further promote NASH development.
In all the diets listed above, feeding over longer time periods can induce mild NASH symptoms, including steatosis, fibrosis and inflammation.
Inducing more severe hepatic NAFLD/NASH without obesity or metabolic syndrome
+ Atherogenic diets that are high in fat with cholesterol (1 – 1.25%) and cholate (0.5% sodium cholate or cholic acid) have been useful in inducing NASH.
+ These diets typically induce hepatic inflammation with early fibrosis.
+ Metabolic changes similar to human NASH are not expect with animals typically maintaining normal body weights.
+ Methionine and choline deficient (MCD) diets are amino acid defined diets deficient in methionine and choline with high sucrose levels and ~10% corn oil.
+ Steatosis, increased serum alanine aminotransferase, inflammation, and hepatic fat oxidation occur within three weeks, and fibrosis can be observed after six weeks.
+ Metabolic syndrome does not develop and progressive weight loss is typical for this diet type.
In summary, diets that can recapitulate the metabolic and mild hepatic components of NAFLD require long term feeding (4-12 months). Additional manipulations can include adding a glucose/fructose solution to the drinking water and promotion of sedentary behavior. Diets to induce more severe hepatic NASH, but without metabolic symptoms, can commonly induce hepatic inflammation and early fibrosis within three weeks.
New diets can be formulated in order to investigate novel dietary models of NAFLD/NASH, and Envigo is continuing to evolve our models with the goal of recapitulating both metabolic and hepatic symptoms common to human disease. If you’re interested in using these models, a Teklad nutritionist can work with you to help formulate a diet that would work for your research needs.
Please contact us to learn more about our Teklad diets.