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.

Impact and implications:

Macrophage-mediated inflammation contributes to MASH progression and fibrosis; however, liver biopsy is currently the only tool to assess this response. Thus, the development of non-invasive imaging modalities to identify and follow inflammatory activation is an area of need for patient care. In this study, we leverage molecular imaging using PET radiotracers to follow changes in macrophage composition that are related to MASH disease activity. The results in our preclinical model provide important proof of concept evidence that this approach can be used to diagnose MASH and to follow disease activity in response to intervention. Ongoing studies will evaluate the utility of this modality in humans with MASH.