Phenotypical heterogeneity in responder and nonresponder male ApoE*3Leiden.CETP mice

The metabolic syndrome (MetS) is a major health issue worldwide and is associated with obesity, insulin resistance, and hypercholesterolemia. Several animal models were used to describe the MetS; however, many of them do not mimic well the MetS pathophysiology in humans. The ApoE*3Leiden.CETP mouse model overcomes part of this limitation, since they have a humanised lipoprotein metabolism and a heterogeneous response to MetS, similar to humans. The reported heterogeneity among them and their common classification refer to responder (R) and nonresponder (NR) mice; R mice show increased body weight, cholesterol, and triglycerides levels, whereas NR mice do not show this expected phenotype when fed a Western type diet. To define better the differences between R and NR mice, we focused on feeding behavior, body weight gain, glucose tolerance, and lipid parameters, and on an extensive pathological examination along with liver histology analysis. Our data confirmed that R mice resemble the pathological features of the human MetS: obesity, dysplipidemia, and glucose intolerance. NR mice do not develop the full dysmetabolic phenotype because of a severe inflammatory hepatic condition, which may heavily affect liver function. We conclude that R and NR mice are metabolically different and that NR mice have indications of severely impaired liver function. Hence, it is critical to identify and separate the respective mice to decrease data heterogeneity. Clinical chemistry and histological analysis should be used to confirm retrospectively the animals' classification. Moreover, we point out that NR mice may not be an appropriate control for studies involving ApoE*3Leiden.CETP R mice. NEW & NOTEWORTHY When compared with some other animal models, ApoE*3Leiden.CETP mice are better models to describe the metabolic syndrome. However, there is phenotypic heterogeneity between "responder" and "nonresponder" mice, the latter showing some evidence of hepatic pathology. A full phenotypic characterization and eventually postmortem analysis of the liver are warranted.