Quantification of Collagenogenesis in Experimental Early-stage Alcoholic Liver Fibrosis using Cis-4-[18F]fluoro-L-Proline microPET

Abstract

Purpose: The diagnosis and quantification of early-stage alcoholic liver fibrosis （ALF） are vital and the objective is to establish a noninvasive PET technique to quantify the collagenogenesis of hepatic stellate cells (HSC) in an ALF mouse model. Methods: To establish the ALF animal model, a liquid alcohol diet (8 weeks), and CCl4 were injected intraperitoneally at 5-8 weeks. A liquid scintillation counter was used to measure [3H]proline uptake by rats HSC in vitro experiment. Collagen type 1 production was tested by ELISA in a culture medium. The expression of type 1 collagen and proline transporters in ex vivo experiments was compared between ALF rats and mice. Different doses of unlabeled proline and benztropine were ex vivo quantified [3H]proline in liver tissues. Tracer uptake in different organs including the liver in ALF and control mice in vivo was quantified using [18F]fluoro-proline microPET/CT Results: The optimal dose and time of [3H]proline uptake by HSC was 19-37MBq/L and 30-90min after culture. Higher [3H]proline uptake and type 1 collagen production in HSC were found in ALF and control rats. There was a high correlation between [3H]proline uptake and type 1 collagen in ALF rats. To cut the costs of tracer usage and imaging in vivo, the mouse-to-rat model was compared. Type 1 collagen levels of ALF mice liver tissue in ex vivo were similar to ALF rats, as was proline transporter protein. Unlabeled proline of type 1 collagen and [3H]proline uptake of ALF mice was blocked by benztropine. In vivo [18F]fluoro-proline PET/CT imaging, SUVmax in the liver, normalized liver/brain and liver/thigh ratio were significantly different between ALF mice and controls and there was a strong positive correlation among these three indexes in ALF mice. Conclusions: [18F]fluoro-proline microPET/CT is feasible to quantify collagenogenesis in HSC in early-stage ALF animal models, which may be used as a promising and reliable noninvasive diagnostic technique.