A Systematic Review of Animal Models of NAFLD Finds High-Fat, High-Fructose Diets Most Closely Resemble Human NAFLD.

BACKGROUND AND AIMS: Animal models of human disease are a key component of translational hepatology research, yet there is no consensus on which model is optimal for NAFLD. APPROACH AND RESULTS: We generated a database of 3,920 rodent models of NAFLD. Study designs were highly heterogeneous, and therefore, few models had been cited more than once. Analysis of genetic models supported the current evidence for the role of adipose dysfunction and suggested a role for innate immunity in the progression of NAFLD. We identified that high-fat, high-fructose diets most closely recapitulate the human phenotype of NAFLD. There was substantial variability in the nomenclature of animal models: a consensus on terminology of specialist diets is needed. More broadly, this analysis demonstrates the variability in preclinical study design, which has wider implications for the reproducibility of in vivo experiments both in the field of hepatology and beyond. CONCLUSIONS: This systematic analysis provides a framework for phenotypic assessment of NAFLD models and highlights the need for increased standardization and replication.

Weight loss, insulin resistance, and study design confound results in a meta-analysis of animal models of fatty liver.

The classical drug development pipeline necessitates studies using animal models of human disease to gauge future efficacy in humans, however there is a low conversion rate from success in animals to humans. Non-alcoholic fatty liver disease (NAFLD) is a complex chronic disease without any established therapies and a major field of animal research. We performed a meta-analysis with meta-regression of 603 interventional rodent studies (10,364 animals) in NAFLD to assess which variables influenced treatment response. Weight loss and alleviation of insulin resistance were consistently associated with improvement in NAFLD. Multiple drug classes that do not affect weight in humans caused weight loss in animals. Other study design variables, such as age of animals and dietary composition, influenced the magnitude of treatment effect. Publication bias may have increased effect estimates by 37-79%. These findings help to explain the challenge of reproducibility and translation within the field of metabolism.

Obesity and diabetes are increasingly common diseases that can lead to other complications such as fatty liver disease. Fatty liver disease affects one in five people and is caused by a built-up of fat in the liver, which can result in scarring of the liver tissue and other serious complications. There is currently no cure for fatty liver disease. Drugs that have been effective in treating the condition in mice, lack efficacy in humans. To better understand why this is the case, Hunter, de Gracia Hahn, Duret, Im et al. conducted a review of over 5,000 published studies, analysing over 600 experiments. Hunter et al. asked which drugs improved fatty liver in mice the most and if they had the same effect in humans. They also tested whether the age of the mice affected the outcome of the experiments. The analyses revealed that the drugs that work best in mice are different to the ones that show some effect in humans. In mice, many of the drugs reduced their weight or lowered their blood sugar levels, which also improved the fatty liver condition. Moreover, drugs appeared to be less effective the older the mice were. However, most of these drugs do not cause weight loss or lower blood sugar levels in humans, suggesting that factors other than the intended action of these drug could affect the outcome of a mouse study. These findings will help shape future research into obesity, diabetes and fatty liver disease using mice. They highlight that results obtained from studies with mice so far do not predict if a drug will work in humans to treat fatty liver disease. Moreover, weight loss seems to be the most important factor linked to how efficiently a drug treats fatty liver disease.