When more than 5% of liver cells exhibit bullous steatosis without secondary factors like alcohol or drugs, the condition is known as nonalcoholic fatty liver disease (NAFLD). NAFLD encompasses a range of advancing conditions, including simple hepatic steatosis, nonalcoholic steatohepatitis (NASH), fibrosis, cirrhosis, and hepatocellular carcinoma [1]. NAFLD is a worldwide health issue, affecting approximately 25% of the global population [2].

Ferroptosis is a form of programmed cell death driven by iron dependency and lipid peroxidation. Unlike other forms of cell death, it typically remains unaffected by caspase inhibitors and does not demonstrate morphological alterations in the nucleus or an increase in caspase-3 activity [3]. These features distinguish ferroptosis from previously recognized forms of cell death, including autophagy, necrosis, and apoptosis [4]. Excessive iron accumulation leads to the Fenton reaction, toxic reactive oxygen species (ROS), and lipid peroxidation, which is the hallmark feature of ferroptosis [5]. More and more clinical studies have reported that liver iron accumulation is closely related to the pathogenesis of NASH [6]. Research indicates that interrupting ferroptosis may prevent the progression from NAFLD to NASH. Thus, the ferroptosis mechanism is essential to the NAFLD pathological process [7]. Cells produce lipid peroxide products during ferroptosis, which may exacerbate hepatic inflammation [8]. In turn, the inflammatory environment can further induce ferroptosis, creating a vicious cycle. For example, areas of iron deposition and macrophage-rich inflammatory foci in the liver of NASH patients are closely positively correlated, indicating that inflammation and ferroptosis may promote each other [9]. In addition, the reduction of lipid peroxides related to ferroptosis may help alleviate lipid accumulation, while lipid ROS can aggravate hepatic steatosis by facilitating the development of lipid droplets [10]. As a result, restoration of hepatic iron homeostasis involving ferroptosis and inflammatory response could be a useful strategy against NAFLD symptoms.

A significant member of the nuclear receptor family, the farnesoid X receptor (FXR) is extensively expressed in the small intestine and liver. It plays a crucial role in maintaining the stable equilibrium of hepatic lipid metabolism and glucose homeostasis in the body as the central regulatory hub of bile acid metabolism [11,12]. Research has demonstrated that FXR activation protects against NAFLD by lowering lipid absorption in bile acid-dependent manner and improving liver metabolism via activating FXR and its target gene [13,14]. Recent studies have demonstrated that FXR is an effective transcriptional regulator of ferroptosis. FXR activation in mouse hepatocytes and human induced pluripotent stem cell (iPSC) derived hepatocytes can upregulate a crucial ferroptosis suppressor gene to suppress lipid peroxidation and ferroptosis [15]. Furthermore, FXR protects against cisplatin-induced acute kidney injury by regulating the transcription of genes associated with ferroptosis [3]. Additionally, FXR activation safeguards against ulcerative colitis by inhibiting ferroptosis through both the solute carrier family 7 member 11 (SLC7A11) pathway and the OTU Deubiquitinase, Ubiquitin Aldehyde Binding 1 (OTUB1)/glutathione peroxidase 4 (GPX4) pathway [16]. Together, these findings expand our understanding of FXR as a therapeutic target for NAFLD by demonstrating that it not only suppresses ferroptosis but also exerts anti-inflammatory effects.

Consequently, FXR is considered a promising target for the treatment of NAFLD. However, there is currently a lack of natural compounds capable of effectively activating FXR, inhibiting ferroptosis, and ameliorating inflammatory responses simultaneously. Obeticholic acid (OCA) is one of the FXR agonists that has garnered attention [17]; however, the FDA issued a warning on OCA due to its potential to cause serious liver damage, including death, as well as intense itching. Patients with severe liver impairment should pay particular attention to avoiding overdosing [18]. The therapy and prevention of NAFLD still lack promising approaches. The US Government Approved One New Drug, Resmetirom, in 2024 by the FDA to treat liver fibrosis caused by NASH [19]. This oral selective drug specifically targets thyroid hormone receptor β (THRβ). It does not seem to affect the body weight or glucose metabolism, but it can improve liver fibrosis, reduce liver damage, and decrease liver fat content [20]. Due to the global risk of NAFLD, it is essential to find safer drugs and novel means to alleviate NAFLD.

Hesperetin (HES) is a natural flavonoid in citrus fruits, which is commonly found in grapefruit peel, orange peel, tangerine peel, and other traditional medicinal materials [21]. Numerous studies have shown that HES could inhibit lipid synthesis and alleviate hepatic steatosis by regulating mitochondrial dynamics and inhibiting key enzymes of fatty acid synthesis [22]. At the same time, it can also promote lipolysis and inhibit lipid accumulation by regulating the function of adipocytes, showing its therapeutic potential in anti-NAFLD [23]. In addition, HES can also inhibit ferroptosis and promote the healing of diabetic wounds [24]. Thus, HES has the potential to improve hepatic lipid metabolism. However, whether it can synergistically alleviate NAFLD by targeting and activating FXR, thereby simultaneously inhibiting ferroptosis and inflammatory responses, has not yet been reported in studies. Consequently, the purpose of this study is to determine if HES reduces NAFLD by activating FXR, which simultaneously inhibits inflammatory responses and ferroptosis. To our knowledge, this is the first study to explore the potential role and underlying mechanism of HES as an FXR activator in modulating both ferroptosis and inflammation within the context of NAFLD. Our findings may offer a new candidate compound for FXR-targeted NAFLD therapy.