In vivo monitoring of hydroxyl radical generation caused by x-ray irradiation of rats using the spin trapping/epr technique

Abstract

Measurement of hydroxyl radical ( OH) in living animals irradiated with ionizing radiation should be required to clarify the mechanisms of radiation injury and the in vivo assessment of radiation protectors, because generation of OH is believed to be one of the major triggers of radiation injury. In this study, OH generation was monitored by spin trapping the secondary methyl radical formed by the reaction of OH with dimethyl sulfoxide (DMSO). Rats were injected intraperitoneally with a DMSO solution of α-phenyl- N- tert-butylnitrone (PBN). X-irradiation of the rats remarkedly increased the six-line EPR signal in the bile. The strengthened signal was detectable above 40 Gy. Use of 13C-substituted DMSO revealed that the signal included the methyl radical adduct of PBN as a major component. The EPR signal of the PBN–methyl radical adduct was completely suppressed by preadministration of methyl gallate, a scavenger of OH but not of methyl radical. Methyl gallate did not reduce the spin adducts to EPR-silent forms. These observations indicate that what we were measuring was OH generated in vivo by x-irradiation. This is the first report of the in vivo monitoring of OH generation at a radiation dose close to what people might receive in the case of radiological accident or radiation therapy.