Development of human growth hormone-treated chimeric mice with humanized livers for an evaluation model of drug-induced fatty liver disease

Chimeric mice with humanized livers were used to evaluate drug-induced liver injury (DILI). However, lipid accumulation is observed in the human hepatocytes of chimeric mice because of human growth hormone deficiency (GHD), which is an obstacle in the evaluation of drug-induced fatty liver disease (DIFLD), a common type of DILI. Previously, we showed that lipid droplets were reduced by the administration of human growth hormone (h-GH) to chimeric mice. Although h-GH administration reduces the lipid droplets, an optimal h-GH treatment method for assessing DIFLD has not yet been developed. This study investigated the appropriate h-GH dosage required to reduce lipid droplets and reproduce physiological conditions in humans. Moreover, the LXR agonist TO901317 was administered to h-GH-treated chimeric mice to evaluate the new h-GH treatment's effectiveness for DIFLD assessment. The results in blood h-GH levels, oil-red O liver sections, and gene expression levels in the liver suggested that 0.25 mg/kg/day would be an appropriate h-GH dosage to reduce lipid droplets and reproduce human physiological condition. At this dose, TO901317-induced lipid accumulation and lipid synthesis-related gene expression in humanized livers in a dose-dependent manner, suggesting that this new mouse model could be useful for evaluating human DIFLD. In summary, the administration of h-GH at an appropriate dosage regulated lipid homeostasis in the humanized livers of chimeric mice and h-GH-administered chimeric mice may represent a highly sensitive evaluation model for human DIFLD. The study also suggests a correlation between GH levels and lipid metabolism, potentially related to conditions like GHD and aging.