Table 1.

Considerations in assessment of validity of preclinical models of NASH

Characteristic	Comment
Genetics: Single gene knock out or knock in Genetic background of mouse	Need to relate to gene knock out or gain in function in humans and if it involves all humans This important to understand differences between strains and also with human disease given the same environmental manipulation
Diet: Caloric content Macronutrient composition Cholesterol content	Forced feeding induces stress and needs to be considered. Total calories consumed should be within relevant boundaries
	Should broadly resemble that in human obesity Humans do not generally exceed 0.1–0.2%
Physiological requirements: Development of Obesity Development of systemic inflammation (adipose tissue inflammation) Development of insulin resistance Development of dyslipidemia	The extrahepatic features are very relevant to human disease by setting up increased free fatty acid delivery and increased systemic inflammatory cytokine exposure.
Histological requirements: Development of mainly macrovesicular steatosis Lobular inflammation Hepatocellular ballooning +/− Mallory Denk bodies Pericellular fibrosis Fibrosis progression in pattern resembling human disease	Most papers on mouse models do not provide unequivocal evidence of hepatocellular ballooning the hallmark lesion of NASH. This is critical to determine if the model truly develops steatohepatitis. It is not possible to show NAS or SAF in these models without clear cut evidence of steatohepatitis. Progression to cirrhosis is ideal and a key endpoint in preclinical models.
Cell signaling requirements: Increased de novo lipogenesis Altered mitochondrial function Increased UPR signaling Inflammatory signaling Apoptotic signaling Fibrogenic signaling	These are key pathways in human disease and preclinical models must be validated to demonstrate activation of these pathways amongst others. The relationship of these pathway activation to histological course of the disease must be defined.
Transcriptomic validation: Concordance with human disease transcriptome at various stages of development	This further strengthens the evidence that the disease in the model resembles human disease
Metabolomic validation: Concordance with human disease at various stages of development	Provides physiological read out of similarity of disease to human disease.