Liver fibrosis is caused by excessive synthesis and deposition of collagen in the liver extracellular matrix (ECM) due to liver injury. Most types of chronic liver diseases, such as viral hepatitis, alcoholic liver disease, non-alcoholic fatty liver disease and autoimmune hepatitis, could lead to liver fibrosis [1], [2], [3], [4], [5]. Although studies suggested that liver fibrosis is a reversible pathological process, advanced liver fibrosis leads to cirrhosis, liver failure, and portal hypertension, which could usually only be treated by liver transplantation [6], [7]. Therefore, effective drugs to treat liver fibrosis must be urgently developed.

Hepatocyte damage and immune cell infiltration activate the trans-differentiation of hepatic stellate cells (HSCs) into myofibroblasts [8]. It is an important link in the occurrence and development of liver fibrosis. HSCs undergo marked phenotypic activation and acquire fibrotic properties in chronic liver disease, as first described by von Kupffer in 1876. Since then, HSCs were identified as the major collagen-producing cells in the liver. Cytokines, such as transforming growth factor-β1 (TGF-β1), activate HSCs through paracrine and other methods, and they are closely related to the occurrence of liver fibrosis [9]. During liver injury, the production of TGF-β1 could promote and maintain collagen gene expression while upregulating the expression of tissue inhibitors of metalloproteinases, leading to ECM deposition and fibrosis [10]. Hepatocyte or epithelial cell injury and inflammatory response exist in the process of various chronic liver diseases, and liver injury promotes the high expression of platelet-derived growth factor (PDGF)-activated HSCs. Similar to TGF-β1, PDGF causes HSCs proliferation and activation, and it is a key signaling molecule associated with fibrosis progression [11].

Chronic inflammatory responses trigger leukocyte migration to inflammatory tissues. The NLRP3 inflammasome is one of the most important multimeric protein complexes involved in immune system function, it is extensively involved in intracellular inflammatory mechanisms, and it plays an important role in the pathogenesis of liver fibrosis [12]. Studies have found that NLRP3 inflammasome may trigger HSCs activation and is essential for immune defense. The inflammatory response mediated by it plays an important role in chronic liver disease and liver fibrosis. Activated NLRP3 inflammasome could promote the pathological process of liver inflammation and fibrosis, and activated caspase-1, IL-18, and IL-1β are the key to the development of liver fibrosis caused by the activation of NLRP3 inflammasome [13]. Activation of NLRP3 inflammasome leads to the production of proinflammatory cytokines. Proinflammatory factors, such as TNF-α, IL-1β, and IL-6, enable HSCs activation. During activation, the activation signal causes NLRP3 to assemble with ASC and caspase-1 into inflammasomes, and the activated caspase-1 converts pro-IL-1β and pro-IL-18 into mature IL-1β and IL-18. Such a vicious cycle aggravates liver inflammation and liver fibrosis. Intracellular potassium efflux, reactive oxygen species (ROS), mitochondrial dysfunction, and lysosomal damage all stimulate the production of activating signals [14].

Oxidative stress is a phenomenon caused by the increasing accumulation of ROS in cells and the imbalance between an organism’s ability to detoxify these ROS products. ROS could stimulate HSCs by promoting the secretion of fibrotropic factor through inflammatory cells and causing lipid peroxidation on cell surface, ultimately leading to liver fibrosis [15], [16]. Mitochondrial respiratory chain is the main source of subcellular ROS [17]. The human respiratory chain is located in the mitochondrial intima, protecting the basic function of the mitochondria. The electron transport chain in the mitochondrial intima and ATP synthase together form the oxidative phosphorylation system, through which most of the ATP in the cell is produced. Previous studies have demonstrated that mitochondrial ROS production could be driven by the mitochondrial complex I inhibitor rotenone and the complex III inhibitor antimycin A [18]. Therefore, restoring the activity of mitochondrial respiratory chain complexes I and III to inhibit ROS production may be an effective means to alleviate the development of liver fibrosis.

Axitinib is a vascular endothelial growth factor receptor (VEGFR) and PDGF tyrosine kinase inhibitor [19]. It was approved by the U.S. Food and Drug Administration (FDA) on January 27, 2012. This medicine is used to treat advanced renal cell carcinoma and colon cancer after failure of one prior systemic therapy. In recent years [20], researchers have found that small-molecule kinase inhibitors could inhibit cell proliferation and angiogenesis by targeting kinases to exert anti-hepatic fibrosis effects, and substantial positive therapeutic effects have been observed in preclinical animal models of liver fibrosis and patients with liver fibrosis.

Existing studies have shown the possibility of protein kinases being involved in the process of liver fibrosis. On the basis of this possibility, axitinib was explored in this study to inhibit the process of liver fibrosis through the activation of CCl4-induced liver fibrosis mouse model and HSCs and explore its mechanism of action.