INTERACTION OF MRI GADOLINIUM CONTRAST AGENTS WITH PHOSPHOLIPID-BILAYERS AS STUDIED BY 95 GHZ EPR

Interactions of two MRI gadolinium contrast agents, gadolinium ethoxyb enzyl-diethylenetriaminepentaacetate (Gd-EOB-DTPA) and gadolinium N-pe ntyl-1,4,7,10-tetraazacyclododecane-N',N '',N'''-triacetic acid (Gd-DO TA-P), with multibilayer phospholipid dispersions prepared from 1,2-di palmitoyl-sn-glycero-3-phosphatidylcholine (DPPC) have been investigat ed with high resolution EPR spectroscopy at 95 GHz. At a resonance fie ld of 3.3 T, EPR spectra of a small nitroxide probe, 2,2,6,6-tetrameth yl-1-piperidinyloxyl (Tempo), partitioned between aqueous and membrane phases are clearly resolved, making measurements of dynamics paramete rs of the probe accurate and unambiguous. Results show that although t he presence of the more lipophilic contrast agent, Gd-DOTA-P, can be d etected within the bilayer, the structural organization of the membran e remains unaffected even at physiologically high (5 mM) concentration s. The temperature of the main phase transition of the bilayer was als o unaffected to within the 0.4 degrees C accuracy of its determination .