Detection of nitrosyl-iron complexes by proton-electron-double-resonance imaging

The nitrogen monoxide radical (NO.) forms paramagnetic mono- and dinitrosyl -iron complexes in biologic tissues. To establish a noninvasive technique f or in vivo NO. imaging, we evaluated the suitability of these complexes as magnetic resonance (MR) contrast agents, making use of the ability of the u npaired electrons of the complexes to enter into dynamic nuclear polarizati on with water protons and hence produce enhancement on images generated by the technique of proton-electron-double-resonance imaging (PEDRI). Phantom solutions of synthetic nitrosyl-iron complexes (NICs) altered the signal in tensity of PEDRI images. The dinitrosyl-iron complex (DNIC) with serum albu min induced a significantly larger signal alteration than the mononitrosyl- iron complex (MNIC) with dithiocarbamate. Exposure of rat liver to sodium n itroprusside (SNP) by ex vivo and in situ perfusion induced a composite X-b and electron spin resonance (ESR) spectrum of the isolated liver characteri stic of a MNIC and DNIC. On storage of the tissue, the MNIC signal disappea red and the DNIC signal intensity increased. Correspondingly, in cross-sect ional PEDRI images taken at room temperature, the SNP-exposed livers initia lly exhibited a weak signal that strongly increased with time. In conclusio n, NICs can be detected using PEDRI and could be exploited for in vivo NO. imaging. (C) 1999 Elsevier Science Inc.