The interaction of MRI contrast agents with phospholipids

The molecular interactions of three clinically used MRI contrast agents wit h lipid vesicles, consisting of egg phosphatidylcholine (EPC), have been st udied using high-field NMR techniques. At a molar ratio of one contrast age nt molecule to five phospholipid molecules, a significant increase in the p roton resonance line width occurred for certain lipid head group moieties. A large decrease in the T-1 relaxation times for the head group moieties wa s also observed. These two effects occurred regardless of the ionic status and the chelate structure of the three contrast agents. The structure of th e contrast agents did, however, affect the magnitude of the two NMR paramet er changes. These NMR effects also differed in magnitude amongst the variou s head group entities. The NMR effects were greatest for the head group moi eties at or near the vesicle-water interface. The results are discussed in terms of the structure of the phospholipid-water interface. Since the use o f contrast agents has become routine in clinical MRI, our results are of im portance in terms of the interaction of the agents with physiological surfa ces, many of which contain phospholipids. The understanding of such interac tions should be of value not only for improved diagnostics, but also in the development of new contrast agents.