Use of spin-traps during warm ischemia-reperfusion in rat liver: comparative effect on energetic metabolism studied using31P nuclear magnetic resonance

Detection of free radicals by electron spin resonance (ESR) proves the involvement of reactive oxygen species (ROS) in reperfused organ injuries. Spin-traps are known to ameliorate hemodynamic parameters in an isolated postischemic heart. The effects of 5 mmol/L DMPO (5,5-dimethyl-1-pyrroline-N-oxide) or DEPMPO (5-(diethylphosphoryl)-5-methyl-1-pyrrolineN-oxide) on intracellular pH (pHin) and ATP level were evaluated by31P nuclear magnetic resonance on isolated rat liver submitted to 1 hour of warm ischemia and reperfusion. At the end of the reperfusion period, during which pHin recovered to its initial value (7.16±0.03) in all groups, the ATP recovery level (expressed in percentage of initial value) was similar in controls and DEPMPO (60%±5%,n=6 and 54%±4%,n=6, respectively), but only 37%±1% in DMPO-treated livers (n=6) (p<0.05 versus controls andp<0.05 versus DEPMPO). Oxidative phosphorylation was not affected by an addition of nitrones on isolated mitochondria extracted from livers not submitted to ischemia-reperfusion. In contrast, mitochondria extracted at the end of the ischemia-reperfusion showed an impairment in the phosphorylation parameters, particularly in the presence of DMPO. Mass spectrum of ischemic liver perchloric acid extracts evidenced probable catabolites in treated groups. The differences in the effect of the two nitrones on energetic metabolism may be explained by the production of deleterious catabolites by DMPO as compared to DEPMPO. Even though a specific radical scavenging effect could be operative in the liver, our results indicate that catabolic effects were predominant. The absence of deleterious effects of DEPMPO in contrast to DMPO on the liver energetic metabolism was evidenced, allowing the use of DEPMPO for ESR detection.