Nonalcoholic fatty liver disease (NAFLD) refers to a series of liver diseases caused by excessive accumulation of fat in hepatocytes in people without alcohol, drug abuse or viral infection(Brunt et al., 2015). Metabolic dysfunction-associated steatohepatitis (MASH) is the most serious category of NAFLD, with high risk factors for progression to Cirrhosis and Hepatocellular carcinoma (HCC). About 25% of NAFLD patients have MASH(Younossi et al., 2019). A large amount of evidence shows that MASH is not only closely related to metabolic diseases such as obesity, diabetes and dyslipidemia, but also cardiovascular disease is the main risk factor for death in patients with advanced MASH(Wu et al., 2016; Younossi et al., 2016). Although the world 's first MASH drug Resmetirom has been approved by the FDA, the heavy medical burden has not decreased(Petta et al., 2024). The pathophysiology of MASH is complex and its main pathological features are excessive fat deposition in hepatocytes, abnormal secretion of adipokines, production of inflammatory cytokines and oxidative stress, with lipotoxicity and oxidative stress considered to be the drivers of disease progression, or the underlying cause of the disease(Michelotti et al., 2013; Tilg & Moschen, 2010). Therefore, there is an urgent need to develop therapeutic agents for MASH that are capable of targeting the multiple pathological factors mentioned above.
Fibroblast growth factor 21 (FGF21) is a kind of fibrinoid with a molecular weight of 19.5 kDa, which belongs to endocrine FGFs(Watanabe et al., 2020). As a stress-inducing hormone capable of regulating energy homeostasis and glucolipid metabolism, it is secreted primarily in the liver, but is also expressed in other tissues associated with lipid and glucose metabolism, such as adipose tissue, pancreas and skeletal muscle(Tucker et al., 2019). Studies have found that FGF21 can restore the function of β cells, reduce cytokine-induced β cell apoptosis, and improve insulin resistance(Pan et al., 2019; Wente et al., 2006).On the other hand, it has been reported in the literature that by administering FGF21 to a mouse model of High-fat diet (HFD) induced hepatic disease, a Methionine-choline-deficient (MCD) diet induced hepatic disease, and a mouse model of Type 2 diabetes mellitus (T2DM), it was found that FGF21 not only lowered serum and hepatic triglycerides and cholesterol, and Significantly improved hepatic steatosis, while lowering blood glucose and improving insulin resistance(Bao et al., 2018; Liu et al., 2014; Pan et al., 2021; Rusli et al., 2016). In addition, other pleiotropic pharmacological effects of FGF21 have been reported, such as reduction of inflammatory cytokine infiltration, enhancement of thermogenic factor expression in adipose tissue and induction of adiponectin production(Chikamatsu et al., 2023; Tucker et al., 2019). FGF21 is considered an important potential therapeutic target for MASH and is expected to comprehensively improve the overall pathophysiology associated with MASH. However, the natural FGF21 protein is susceptible to protease degradation in vivo, resulting in its short plasma half-life(Geng et al., 2020). And it still shows low stability when using long-acting and structural modification techniques such as PASylation, PEGylation, albumin fusion and Elastin-like polypeptide (ELP) to modify natural FGF21 protein(Chikamatsu et al., 2023; Gilroy et al., 2018; Schilz et al., 2022). Therefore, in view of its poor pharmacokinetic properties and limitations in clinical application, we should take advantage of its strengths and avoid its weaknesses. We synthesized a new long-acting FGF21 analogue DC2303 by conjugating PASylated FGF21 with a variety of functional side chains modified by fatty acids to achieve dimerization.
Since, the therapeutic effects of DC2303 on MASH and the long-term effects on glycolipid metabolism remain unknown. In this study, we used 60% HFD induced db/db mice to construct a MASH model with obesity and abnormal glycolipid metabolism, and subcutaneously injected DC2303 to evaluate the therapeutic effect on MASH and to investigate its mechanism of action.