Novel Pharmacokinetic Measurement Using Electron Paramagnetic Resonance Spectroscopy and Simulation of in Vivo Decay of Various Nitroxyl Spin Probes in Mouse Blood

Abstract

A novel approach to measure the time course of paramagnetic spin probe concentration in the circulating blood of a living mouse using X-band (9.4 GHz) electron paramagnetic resonance spectrometer is described. Using this technique, the pharmacokinetics of several nitroxyl spin probes was examined. The decay profiles were also independently simulated using pharmacokinetic properties as well as redox-mediated factors responsible in converting the nitroxyl radicals to the corresponding hydroxylamines. Finally, suitability of nitroxyl radicals as the probes of in vivo redox status and for radioprotection was described. The studies indicate that the six-member piperidine nitroxyls are suitable for estimating redox status in the circulation, whereas the five-member pyrrolidine nitroxyl radicals are suited for tissue redox status determination. For selective protection against radiation of normal tissues rather than cancer/tumor, efficient reoxidation of the hydroxylamine in normal tissue is preferable. Simulation results showed that for carbamoyl-PROXYL, only administration of the radical form might give radioprotection and not the hydroxylamine. However, the hydroxylamine form of TEMPOL, i.e., TEMPOL-H, may give similar radioprotection as the radical form due to efficient reoxidation in vivo.Nitroxyl radicals have been widely used as spin probes for low-frequency in vivo EPR experiments to estimate the biological redox status in living experimental animals (Berliner and Wan, 1989;Ilangovan et al., 2002;Kuppusamy et al., 2002;Yamada et al., 2002;Kasazaki et al., 2003). When a nitroxyl spin probe is administered to a living animal, in vivo EPR signal intensities of the probe show characteristic signal intensity profiles as a function of time in the animal, depending on the organ investigated. Generally, in vivo EPR signal decay rates are obtained based on a suitable region of its decay curve to estimate redox status in the animal .Several nitroxyl radicals have been used in studies that exhibit EPR signal decay profiles, depending on the spin probe used. The decay constant of a spin probe depends on the route of administration (i.e., intravenous, intraperitoneal) and methodology of the analysis (i.e., one-compartment model, two-compartment model) (Kocherginsky and Swartz, 1995). Moreover, species, strains, and gender of the experimental animal was found to affect the EPR signal decay profiles (Kocherginsky and Swartz, 1995;Matsumoto et al., 2000).The following general observations can be summarized from earlier studies. The in vivo EPR signal decay rates of the spin probes are enhanced by reactive oxygen species (Utsumi et al., 1993;Sano et al., 1998;Phumala et al., 1999;Han et al., 2001), such as hydroxyl radical and superoxide, which reduce nitroxyl radical in presence of H atom donor, such as NAD(P)H or glutathione (Samuni et al., 1988;Krishna et al., 1992;Samuni et al., 2002;Takeshita et al., 2002). In contrast, the decay rates are decreased due to reoxidation of the hydroxylamine to the nitroxyl radical un...

Estimation of free radical formation by β-ray irradiation in rat liver

“…In contrast, 16,0000-fold higher dose ratio was given for the in vitro study using the 32 P source, otherwise no EPR signal decay of nitroxyl radical was observed at the same low dose as the in vivo study (data not shown). The in vivo EPR signal decay rate of nitroxyl radical exhibits a biphasic decay curve and is dependent on several factors [17]. Small changes in any one or two factors may influence the faster component of the biphasic decay curve.…”

Kinetics of Tempol for Prevention of Xerostomia Following Head and Neck Irradiation in a Mouse Model

“…Tempol, as with several other nitroxyl radicals, is rapidly reduced in living tissues. Electron paramagnetic resonance spectrometer measurements of active tempol have shown sufficient blood activity levels, when administered i.v., maximally 10 minutes before irradiation (17,18). Therefore, we chose not to test times for systemic tempol administration beyond 10 minutes.…”

Reversible reduction of nitroxides to hydroxylamines: Roles for ascorbate and glutathione

“…Chemical reduction of NR to EPR (electron paramagnetic resonance) -silent hydroxylamines (HA) in many cases is an unfavorable factor that significantly limits their applications in biological systems. On other side, EPR-measured rates of NR reduction have been shown to provide information on tissue redox status [9][10][11], and reactive oxygen species (ROS) generation in vivo [11,12]. In its turn, oxidation of HA to NR also has been used for in vivo EPR detection of ROS [13][14][15].…”