Evaluation of hepatic integrin αvβ3 expression in non-alcoholic steatohepatitis (NASH) model mouse by ¹⁸F-FPP-RGD₂ PET

Background: Activated hepatic stellate cells (HSCs), which express integrin αvβ3, are a major fibrogenic factor in NASH pathophysiology. ¹⁸F-labeled cyclic arginine-glycine-aspartic acid penta-peptide (¹⁸F-FPP-RGD₂) has been used as a PET probe for tumors expressing integrin αvβ3. The aim of this study was to assess the potential of PET with ¹⁸F-FPP-RGD₂ to detect hepatic integrin αvβ3 expression in non-alcoholic steatohepatitis (NASH) model mice. Results: Thirty-two male C57BL/6 mice aged 6 weeks were fed a choline-deficient, l-amino acid-defined, high-fat diet (CDAHFD) for 3 and 8 weeks. ¹⁸F-FPP-RGD₂ PET imaging of the liver was performed at 3 and 8 weeks after CDAHFD feeding. After PET scanning, levels of hepatic integrin αvβ, 3α-smooth muscle actin (α-SMA), and collagen type 1 alpha 1(col1a1) were measured. Histopathological analysis of hepatic steatosis, inflammation, and fibrosis, as well as blood biochemistry analysis, was also performed. CDAHFD for 3 and 8 weeks produced a moderate-to-severe steatosis and inflammation of the liver in mice. NAFLD activity score (NAS) in mice fed the CDAHFD for 3 and 8 weeks were more than 4 indicating NASH or borderline NASH pathology. Fibrosis was observed only in mice fed the CDAHFD for 8 weeks. PET imaging showed that the hepatic standardized uptake value, SUV_80–90 min, was increased with prolonged CDAHFD feeding compared with the respective controls (CDAHFD 3 weeks 0.32 ± 0.06 vs 0.48 ± 0.05, p < 0.01; CDAHFD 8 weeks 0.35 ± 0.04 vs 0.75 ± 0.07, p < 0.01, respectively). Prolonged CDAHFD feeding increased hepatic mRNA and protein levels of integrin αv and β3 at 3 and 8 weeks. Hepatic ¹⁸F-FPP-RGD₂ uptake and amount of integrin αv and β3 protein were well correlated (r = 0.593, p < 0.05 and r = 0.835, p < 0.001, respectively). Hepatic ¹⁸F-FPP-RGD₂ uptake also showed a positive correlation with Sirius red-positive area. Conclusions: The hepatic uptake of ¹⁸F-FPP-RGD₂ correlated well with integrin αv and β3 expression and histological fibrosis in a mouse model of NASH, suggesting the predictability of fibrosis in NASH pathology.