Abstract: Objective To explore the expression characteristics of retinol⁃binding protein 4 (RBP4) in hepatocellular carcinoma (HCC) and liver fibrosis (LF), as well as its clinical significance. Methods The TCGA database was used to analyze the expression level of RBP4 in HCC and its relationship with clinicopathological characteristics and prognosis. Multi⁃response monitoring (MRM) mass spectrometry was used to quantify the serum RBP4 protein expression in 24 HCC patients, 10 chronic hepatitis B (CHB) patients, 10 LF patients and 13 healthy control (HC) population. A high⁃purity anti⁃RBP4 monoclonal antibody was prepared by hybridoma, and the protein expression level of RBP4 protein in the liver tissues of 11 HCC patients was detected by immunohistochemistry (IHC).  Results The results of TCGA dataset analysis showed that the expression levels of RBP4 protein level in HCC tissues were significantly reduced compared to normal liver tissues (P<0.0001). RBP4 expression correlated with the stage, pathological grade and ethnicity (all P<0.05). The prognosis of HCC patients with high RBP4 expression was significantly better than that of patients with low RBP4 expression (all P<0.05). The results of serum MRM mass spectrometry showed that serum RBP4 protein level in HCC and LF groups were significantly lower than those in the HC and CHB groups (all P<0.001). The high⁃purity anti⁃RBP4 monoclonal antibody was prepared with a titer of 1∶729 000 and could specifically recognize RBP4 protein. The results of IHC showed that the expression levels of RBP4 in HCC tissues and LF tissues were significantly lower than that in adjacent tissues (all P<0.0001), in LF tissues were significantly lower than that in HCC tissues (P<0.05). Conclusions Compared with normal tissues, RBP4 is downregulated in HCC and LF tissues, and is associated with poor prognosis and fibrotic progression. 

Key words: Hepatocellular carcinoma, RBP4, Monoclonal antibody, Liver fibrosis