Nitric oxide: prospects and perspectives of in vivo detection by L-band EPR spectroscopy.

This paper discusses, compares and evaluates various in vivo EPR methods of detection of nitric oxide (NO). In particular the various classes of agents are: Fe(II)-dithiocarbamate derivative complexes of MGD (N-methyl-D-glucamine dithiocarbamate) and DTCS [N-(dithiocarboxy)sarcosine], stable imidazolineoxy N-oxides and nitronyl N-oxides, and NO-sensitive chars. As a specific example direct, real-time, in vivo measurements of nitric oxide (NO) in mice are described with the water soluble metal chelator complex (MGD)2-Fe(II), as monitored at L-band EPR. The three-line EPR spectrum of [(MGD)2-Fe(II)-NO] was observed non-invasively in both control animals injected with the preformed product [(MGD)2-Fe(II)-NO] and from lipopolysaccharide (LPS) treated mice subsequently injected with (MGD)2-Fe(II) complex. The [(MGD)2-Fe(II)-NO] spectrum was markedly suppressed after administration of phenyl N-tert-butyl nitrone (PBN) prior to LPS injection as PBN inhibits the expression of inducible nitric oxide synthase (iNOS). When 15N-arginine was administered to LPS-treated mice, an EPR spectrum consisting of both three- and two-line EPR signals (due to (MGD)2-Fe(II)-14NO and (MGD)2-Fe(II)-15NO respectively) was observed, confirming that the trapped NO was generated through the NOS enzyme and not other chemical routes.