A phospholipid spin label used as a liposome-associated MRI contrast agent.
Given current clinical use of phospholipid bilayer structures (liposomes/vesicles) as nontoxic drug delivery vehicles, we have addressed the possibility of employing the phospholipids themselves as MRI contrast agents. To this end we have synthesized phosphatidylcholine with a nitroxide spin label replacing one methyl residue of the choline headgroup. This material was mixed with natural phosphatidylcholine in mole ratios from 1:50 to 1:1 and used to prepare sonicated unilamellar vesicles in saline. Expected structural features of these vesicles were verified by freeze-fracture electron microscopy. Proton T1 values of saline were readily decreased to less than 0.3 s by such preparations, yielding a net relaxivity of 0.6 M-1 s-1. The approach seems to be a realistic way of firmly associating a contrast agent of minimal toxicity with ordinary liposomes/vesicles in a manner that is not subject to leakage.
Grant
C W
CW
Department of Biochemistry, University of Western Ontario, London, Canada.
Barber
K R
KR
Florio
E
E
Karlik
S
S
D003287:Contrast Media; D008081:Liposomes; D008279:Magnetic Resonance Imaging; D010713:Phosphatidylcholines; D013113:Spin Labels
D003287:Contrast Media; D008081:Liposomes; D010713:Phosphatidylcholines; D013113:Spin Labels