In vivo ESR observation of bioradical metabolites in living animals

Summary

L-band ESR spectroscopy with a loop-gap resonator demonstrated the first in vivo detection of a “bioradical”, generated from the metabolism of nitrosobenzene in live mice, A broad three-line ESR spectrum (a_N = 11.6 G) was detected in the buttocks or stomach region of a mouse after intramuscular or intraperitoneal injection of 0.2 mmol/kg nitrosobenzene. The signal intensity reached a maximum at 20 to 30 min and remained constant well beyond twelve hours. When muscle tissue was doped with nitrosobenzene and excised within 5 min, a similar three-line spectrum was also detected at X-band, which was preceded by the rapid growth and subsequent decay of a spectrum identical to that of the phenylhydronitroxide radical. A model system containing nitrosobenzene and unsaturated fatty acids yielded an identical three-line spectrum which came from the radical adduct of nitrosobenzene across double bonds. These results suggest that one of the first possible targets of nitroso compounds in vivo may be regions of polyunsaturated fatty acid clusters in fat or membranes. From the success in detecting “bioradicals” generated by pollutants in vivo, two- and three-dimensional visualization of localized bioradicals seems quite feasible.