Dynamic nuclear polarization studies of redox-sensitive nitroxyl spin probes in liposomal solution.
Overhauser-enhanced magnetic resonance imaging (OMRI) studies of a membrane-permeable nitroxyl spin probe, (2)H-enriched 3-methoxycarbonyl-2,2,5,5-tetramethyl-pyrrolidine-1-oxyl (MC-PROXYL), used in simultaneous molecular imaging is reported. Phantom imaging was performed with liposomal solutions of MC-PROXYL at varying spin probe and liposome concentrations using a field-cycle mode, custom-built OMRI scanner. Dynamic nuclear polarization (DNP) spectra of the liposomal solution of the spin probe, measured at 14.529mT using a 5mT sweep of the electron paramagnetic resonance (EPR) irradiation field showed splitting of the low and high filed hyperfine lines. Spectral measurements using D(2)O and a spin broadening agent, K(3)Fe(CN)(6) confirmed that these peaks originated from water molecules in two different environments, compartmentalized with liposomes. The nuclear Overhauser enhancement measured at different EPR irradiation times and power levels showed reduction in water nuclear magnetic resonance (NMR) signal enhancement in liposomal membrane due to the reduction in the coupling constant, rho. This study illustrates that OMRI can be used to differentiate between the intra- and extra- membrane water by loading the liposome vesicles with a lipid-permeable nitroxyl spin probe.
Department of Bio-functional Science, Faculty of Pharmaceutical Sciences, Kyushu University, Fukuoka 812-8582, Japan.
A Milton Franklin
AM
Benial
Hideo
H
Utsumi
Kazuhiro
K
Ichikawa
Ramachandran
R
Murugesan
Ken-ichi
K
Yamada
Yuichi
Y
Kinoshita
Tatsuya
T
Naganuma
Masahisa
M
Kato
D004578:Electron Spin Resonance Spectroscopy / Q000379:methods*; D008081:Liposomes / Q000737:chemistry*; D015336:Molecular Probe Techniques; D009589:Nitrogen Oxides / Q000032:analysis* / Q000737:chemistry*; D012996:Solutions; D013113:Spin Labels; D014867:Water / Q000737:chemistry*
D008081:Liposomes; D009589:Nitrogen Oxides; D012996:Solutions; D013113:Spin Labels; D014867:Water; C039900:nitroxyl