Abstract
Insulin resistance is a key driver of metabolic disorders, including type 2 diabetes and non-alcoholic fatty liver disease (NAFLD), progressing to non-alcoholic steatohepatitis (NASH). This study investigated the effects of geniposide (GP) on insulin sensitivity and hepatic fibrosis in a high-fat diet (HFD)-induced NASH model. C57BL/6 mice were fed an HFD for five weeks and subsequently divided into normal chow (NC), HFD, HFD with GP 50 mg/kg (GP50), and HFD with GP 100 mg/kg (GP100) groups. The treatments were administered orally for 12 weeks. GP treatment significantly reduced body weight as well as epididymal fat and liver weights, while no differences were observed in food intake. Improvements in glucose and lipid metabolism were observed in oral glucose tolerance tests, homeostatic model assessment of insulin resistance (HOMA-IR), and blood lipid profiles. Histological analyses revealed that GP suppressed adipocyte hypertrophy and hepatic lipid accumulation and hepatic fibrosis. To further elucidate molecular mechanisms of GP, quantitative real-time polymerase chain reaction (qRT-PCR) analysis was conducted in the liver tissue. GP downregulated expression of inflammatory markers, including F4/80, tumor necrosis factor (TNF)-α, and interleukin (IL)-6. GP treatment modulated genes involved in insulin signaling including Janus kinase 2 (JAK2), insulin receptor (INSR), insulin receptor substrate 2 (IRS-2), and protein kinase B (AKT1) gene expression levels. This suggests GP suppresses inflammation and mitigates insulin resistance by activating the INSR-IRS2-Akt pathway. Additionally, GP enhanced adenosine monophosphate-activated protein kinase (AMPK) expression, suggesting its potential role in improving glucose and lipid metabolism. In conclusion, GP improves insulin resistance, inflammation, and hepatic fibrosis, highlighting its therapeutic potential for NASH and related metabolic disorders.