Applications of in vivo electron paramagnetic resonance (EPR) spectroscopy: measurements of pO2 and NO in endotoxin shock

Applications of Electron Paramagnetic Resonance (EPR) Spectroscopy in the Study of Oxidative Stress in Biological Systems

Electron paramagnetic resonance (EPR) spectroscopy is the most direct and powerful method for the detection and identification of free radicals and other molecules with unpaired electrons. Such species are generated by and are crucial to mechanisms of oxidative stress in biological systems, and EPR spectroscopy offers a unique ability to detect, identify, and quantitate free radicals to aid our understanding of the role of these species in oxidative stress. This chapter outlines the application of EPR spectroscopy to the study of important reactive oxygen and nitrogen molecules in biological systems including their detection in vivo.

Porphyrin containing isoindoline nitroxides as potential fluorescence sensors of free radicals

A series of new spin-labeled porphyrin containing isoindoline nitroxide moieties were synthesized and characterized as potential free radical fluorescence sensors. Fluorescence-suppression was observed in the free-base monoradical porphyrins, whilst the free-base biradical porphyrins exhibited highly suppressed fluorescence about three times greater than the monoradical porphyrins. The observed fluorescence-suppression was attributed to enhanced intersystem crossing resulting from electronexchange between the doublet nitroxide and the excited porphyrin fluorophore. Notably, fluorescencesuppression was not as strong in the related metalated porphyrins, possibly due to insufficient spin coupling between the nitroxide and the porphyrin. Continuous wave EPR spectroscopy of the diradical porphyrins in fluid solution suggests that the nitroxyl-nitroxyl interspin distance is long enough and tumbling is fast enough not to detect dipolar coupling.

Use of electron paramagnetic resonance spectroscopy to evaluate the redox state in vivo

The aim of this article is to provide an overview of how electron paramagnetic resonance (EPR) can be used to measure redox-related parameters in vivo. The values of this approach include that the measurements are made under fully physiological conditions, and some of the measurements cannot be made by other means. Three complementary approaches are used with in vivo EPR: the rate of reduction or reactions of nitroxides, spin trapping of free radicals, and measurements of thiols. All three approaches already have produced unique and useful information. The measurement of the rate of decrease of nitroxides technically is the simplest, but difficult to interpret because the measured parameter, reduction in the intensity of the nitroxide signal, can occur by several different mechanisms. In vivo spin trapping can provide direct evidence for the occurrence of specific free radicals in vivo and reflect relative changes, but accurate absolute quantification remains challenging. The measurement of thiols in vivo also appears likely to be useful, but its development as an in vivo technique is at an early stage. It seems likely that the use of in vivo EPR to measure redox processes will become an increasingly utilized and valuable tool.

Synthesis and properties of novel porphyrin spin probes containing isoindoline nitroxides

We report the synthesis of novel spin-labeled porphyrins containing isoindoline nitroxides (TMIO-APTPP and TMIO-APTSPP) and their manganese complexes (Mn-TMIO-APTPP and Mn-TMIO-APTSPP). These compounds represent potential new tools for electron paramagnetic resonance (EPR) as well as novel spin probes. Both TMIO-APTPP and TMIO-APTSPP have characteristic UV absorption peaks of free base porphyrin, while the characteristic absorption peaks of their manganese complexes Mn-TMIO-APTPP and Mn-TMIO-APTSPP shifted to shorter wavelengths. Electron paramagnetic resonance (EPR) spectroscopy indicated that these compounds all exhibit hyperfine splittings characteristic of EPR spectra of tetramethylisoindoline nitroxides, the typical nitroxide g values of approximately 2.006, and nitrogen isotropic hyperfine coupling constants (a(N) values) of about 14 G (293 K). The observed linewidths (La) for TMIO-APTSPP (0.73 G) and Mn-TMIO-APTSPP (0.65 G) in distilled water are significantly narrower than for TMIO-APTPP (1.475 G) and Mn-TMIO-APTPP (1.55 G) in chloroform.