Morphology, binding behavior and MR-properties of paramagnetic collagen-binding liposomes

Collagen is an important component of the extracellular matrix (ECM) and plays an important role in normal tissue maturation and in pathological processes such as atherosclerosis and myocardial infarction. The diagnostics of the latter diseases using MRI could strongly benefit from the use of collagen-specific contrast agents. The current study aimed to develop a bimodal liposomal MR contrast agent that was functionalized with CNA35, a collagen adhesion protein of the Staphylococcus aureus bacterium. The liposomes were characterized in terms of CNA35 protein conjugation and loading. The overall morphology was assessed with DLS and cryo-TEM, while cryo-TEM tomography was used to visualize the protein coverage of the liposomes. The binding properties of the contrast agent were investigated using a fluorescence assay based on the rhodamine content of the liposomes. The bulk relaxivity was determined using regular relaxometry while the MR-properties of liposomes in their bound state were studied using NMR depth profiling. This CNA35 functionalized contrast agent and the set of in vitro experiments we performed indicate the potential of this technology for in vivo molecular imaging of collagen.