Normal caloric intake with high-fat diet induces metabolic dysfunction-associated steatotic liver disease and dyslipidemia without obesity in rats

Excessive caloric intake and obesity due to high-fat (HFD) and high-disaccharide (HDD) diets have been recognized as major contributing factors to dyslipidemia and metabolic dysfunction-associated steatotic liver disease (MASLD). However, the effect of HFD and HDD without excessive caloric intake is obscure. The aim of the study was to evaluate the effect of physiological caloric intake delivered through HFD and HDD on liver and lipid profiles. The study was performed on 6-week-old male and female (50/50%) Sprague Dawley rats, receiving either a standard (controls, n = 16), HFD (n = 14) or HDD (n = 14) chow. All groups received the same, standard daily calorie rations, titrated weekly to the age of growing rats, for 12 weeks. A panel of metabolic in vivo measurement were performed, followed by histological, biochemical and molecular biology assays on tissues harvested from sacrificed rats. There was no significant difference between the groups in body weight. In contrast to controls, HFD and HDD groups showed metabolic dysfunction-associated steatohepatitis (MASH) characterized by liver steatosis, inflammation, ballooning of hepatocytes and fibrosis. These changes were more pronounced in the HFD than in the HDD group. The HFD group showed significantly higher serum LDL than controls or HDD rats. Furthermore, the HFD group had higher liver protein levels of low-density lipoprotein receptor (LDLR) but lower plasma levels of proprotein convertase subtilisin/kexin type 9 (PCSK9) than the controls or HDD group. There were no differences between sexes in evaluated parameters. The excessive caloric intake and obesity are not prerequisites for the development of MASH and dyslipidemia in rats. The liver changes induced by the HFD and HDD diets exhibit differences in severity, as well as in the expression patterns of LDLR and PCSK9. Notably, these effects are independent of the sex of the rats.