Use of a surface-coil-type resonator for in vivo assessment of radical generation in mouse skin during UV irradiation

[BACKGROUND] Ultraviolet (UV) light causes various injuries such as sunburn, inflammation, aging, cancer, etc. There have been little reports about in vivo evidence of generation of free radicals including oxygen radicals during exposure to UV light, although free radicals may be involved in those injuries. In this study, induction of radical reaction was examined in skin of living mouse under UV light by using in vivo ESR spectroscopy with a nitroxyl radical, 3-carbamoyl-2,2,5,5-tetramethylpyrrolidine-N-oxyl (carbamoyl-PROXYL), as a redox probe.[METHODS] An aqueous solution of carbamoyl-PROXYL was injected intravenously to an anesthetized mouse, and L-band ESR spectra of the probe were recorded at the dorsal region of hairless mice with a surface-coil-type resonator.[RESULTS] The intensity of ESR signal for mouse whose skin was removed and then returned was about two-third of the intensity for intact mouse, indicating that the signal of probe in skin should be about one-third of signal observed in intact mouse. The rate of signal decay significantly increased by irradiation with UV light (UV-A+B). The increase of signal decay rate was not observed in mouse with removed, and then returned skin. The increase of signal decay rate was suppressed by pre-administration of a spin trapping reagent, N-t-butyl-alpha-phenylnitrone (PBN), while PBN did not change the decay rate for non-irradiated mouse. There was no relationship between the signal decay rate and physiological parameters (blood velocity and blood mass in skin and body surface temperature). In vitro experiment shows that PBN inhibited only signal reduction of carbamoyl-PROXYL caused by peroxyl radicals.[CONCLUSION] Relation of enhanced signal decay of the probe to the generation of peroxyl radical in skin is suggested. The measurement of radical generation under UV light may be possible by using in vivo ESR spectroscopy with asurface-coil-type resonator and a nitroxyl redox probe.International Symposium on the Instrumentation of EPR Spectroscop