In vivo electron spin resonance analysis of nitroxide radicals injected into a rat by a flexible surface-coil-type resonator as an endoscope- or a stethoscope-like device

Abstract

The flexible surface-coil-type resonator (FSCR) operating in a 700 MHz microwave electron spin resonance (ESR) system was applied to measure the nitroxide radicals at a specific area in rats. The FSCR was composed of a single-turn coil with a diameter of 5 mm and two flexible coaxial lines of 450 mm in length. For an endoscope-like application, the FSCR was inserted into the rectum of the rat and sequential changes in the ESR signals of the intravenously injected nitroxide radical (4-hydroxy-2,2,6,6-tetramethyl-piperidine-1-oxyl; TEMPOL or 3-carbamoyl-2,2,5,5-tetramethylpyrrolidine-1-yloxy; carbamoyl-PROXYL) were measured. The ESR signal intensity of the nitroxide decreased according to first-order kinetics. For a stethoscope-like application, the FSCR was placed at several sites on the abdominal skin of the rats receiving a subcutaneous injection of carbamoyl-PROXYL, and diffusion and/or metabolism of the radical in the skin was observed.

Surface-coil-type resonators for in vivo temporal ESR measurements in different organs of nitroxide-treated rats

“…A 700 MHz microwave ESR spectrometer constructed at our laboratory (already described in detail [4,5]), consisted of a main electromagnet, a pair of field scan coils, a pair of field gradient coils, power supplies, a personal computer, and a 700 MHz microwave ESR unit. The main electromagnet is air-cored, water-cooled, and two-coil Helmholtz designed.…”

“…For this purpose, electron spin resonance (ESR) spectrometers operating around 1 GHz with a surface-coil-type resonator (SCR) have been used [1][2][3][4]. The SCR, composed of a single-turn coil and a transmission line, is equivalent to an LC circuit, where the former provides inductance and the latter capacitance [3].…”

“…This resonator can be positioned in any of several possible sites in living animals. Recently, we succeeded in observing the temporal changes in signal intensity of exogenous TEMPOL in the rectums or on the skin by employing an SCR [4].…”

Evaluation of the hepatic reduction of a nitroxide radical in rats receiving ascorbic acid, glutathione or ascorbic acid oxidase by in vivo electron spin resonance study

“…In vivo ESR detection of exogenous nitroxide radicals at the UHF band can provide real‐time information about the redox status in living animals 1,2 , 4,5 . We have succeeded in investigating temporal changes in the ESR signal of a nitroxide radical, 4‐hydroxy‐2,2,6,6‐tetramethylpiperidin‐1‐oxyl (TEMPOL), in various organs of living rats by employing a surface coil‐type resonator (SCR) 8–10 . The SCR is composed of a single‐turn coil and a transmission line, equivalent to a LC circuit, in which the former provides the inductance, and the latter, the capacitance 11,12 .…”

Determination of Ascorbate Concentration in a Raw Leaf with Electron Spin Resonance Spectroscopy

“…TEMPOL (one of nitroxyl radicals) is stable in air; it has been successfully used as a spin probe at in vivo ESR research projects. 9,10 The reduction of nitroxyl radicals has been studied by many investigators. [11][12][13] Since ascorbate acted as a sole non-enzymatic reducing agent of TEMPOL in biological samples in vitro 14 , we think that it might be useful to measure the TEMPOL reduction rate, from which the ascorbate concentration would be calculated.…”