Human serum albumin-based probes for molecular targeting of macrophage scavenger receptors

Abstract

Mona Ahmed,1 Roland Baumgartner,2 Silvia Aldi,3 Philip Dusart,4 Ulf Hedin,1 Björn Gustafsson,1 Kenneth Caidahl1,51Department of Molecular Medicine and Surgery, Karolinska Institutet, SE 17176, Stockholm, Sweden; 2Department of Medicine Solna, Karolinska Institutet, SE 17176, Stockholm, Sweden; 3Section for Medical Inflammation Research, Department of Medical Biochemistry and Biophysics, Karolinska Institutet, SE 17177, Stockholm, Sweden; 4Department of Cellular and Clinical Proteomics, Science for Life Laboratory, Kungliga Tekniska Högskolan (KTH), SE 17165, Stockholm, Sweden; 5Department of Molecular and Clinical Medicine, Institute of Medicine, Sahlgrenska Academy, University of Gothenburg, SE 41345, Gothenburg, SwedenBackground: Inflammation and accumulation of macrophages are key features of unstable atherosclerotic plaques. The ability of macrophages to take up molecular probes can be exploited in new clinical imaging methods for the detection of unstable atherosclerotic lesions. We investigated whether modifications of human serum albumin (HSA) could be used to target macrophages efficiently in vitro.Materials and methods: Maleylated and aconitylated HSA were compared with unmodified HSA. Fluorescent or radiolabeled (89Zr) modified HSA was used in in vitro experiments to study cellular uptake by differentiated THP-1 cells and primary human macrophages. The time course of uptake was evaluated by flow cytometry, confocal microscopy, real-time microscopy and radioactivity measurements. The involvement of scavenger receptors (SR-A1, SR-B2, LOX-1) was assessed by knockdown experiments using RNA interference, by blocking experiments and by assays of competition by modified low-density lipoprotein.Results: Modified HSA was readily taken up by different macrophages. Uptake was mediated nonexclusively via the scavenger receptor SR-A1 (encoded by the MSR1 gene). Knockdown of CD36 and ORL1 had no influence on the uptake. Modified HSA was preferentially taken up by human macrophages compared with other vascular cell types such as endothelial cells and smooth muscle cells.Conclusions: Modified 89Zr-labeled HSA probes were recognized by different subsets of polarized macrophages, and maleylated HSA may be a promising radiotracer for radionuclide imaging of macrophage-rich inflammatory vascular diseases.Keywords: atherosclerosis, inflammation, macrophage, molecular imaging, scavenger receptor, zirconium  

Keywords

• atherosclerosis
• inflammation
• macrophage
• molecular imaging
• scavenger receptor
• zirconium