Molecular imaging of macrophage composition and dynamics in MASLD

Background & Aims: Metabolic-dysfunction associated steatohepatitis (MASH) is associated with obesity and diabetes, and is linked to liver fibrosis and cardiovascular disease. Identification of patients who have MASH is challenging and the development of non-invasive strategies to diagnose and follow this condition is an important unmet need. Recent studies in mouse and humans have identified that significant changes occur in liver macrophage composition during MASH progression; namely, resident Kupffer cells decrease in number while recruited monocyte-derived macrophages increase. Methods: We developed peptide radiotracers targeted to C-C motif chemokine receptor 2 (CCR2) and CD163 to conduct positron emission tomography (PET) imaging of recruited vs . resident macrophages, respectively. Mice were placed on a MASH- inducing diet and non-invasive PET imaging of the liver was performed with tissue confirmation studies using flow cytometry and immunofluorescence. Statistical analyses were conducted using Student's t tests, Pearson correlational analysis, and linear regression. Results: Using a mouse model of MASH, we found that the liver uptake of both CCR2 and CD163 radiotracers detected an increase in recruited cells and a decrease in resident macrophages. These findings correlated well with tissue macrophage content assessed by flow cytometry with an r value of 0.77 (p = 0.002) and 0.78 (p = 0.001) for CCR2 and CD163, respectively. Serial imaging with these radiotracers at several time points during MASH progression and regression revealed good correlation between liver macrophage composition and PET signal intensity. Conclusion: We demonstrate that novel PET radiotracers targeting CCR2 and CD163 can be used to image macrophage composition in MASH. Non-invasive molecular imaging of inflammation has the potential for diagnosis and monitoring of disease activity in humans with MASH. (c) 2024 The Author(s). Published by Elsevier B.V. on behalf of European Association for the Study of the Liver (EASL). This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).