In vivo imaging of oxidative stress in ischemia-reperfusion renal injury using electron paramagnetic resonance

Abstract

Oxidative stress during ischemia-reperfusion acute renal failure (IR-ARF) was noninvasively evaluated with in vivo electron paramagnetic resonance (EPR) imaging. Female ICR mice underwent left nephrectomy and 30-min ischemia-reperfusion of the right kidney. Oxidative stress was evaluated as organ reducing activity with the half-lives of the spin probe 3-carbamoyl-2,2,5,5-tetramethylpyrrolidine-1-oxyl (carbamoyl-PROXYL) using 1) conventional L-band EPR, which showed organ-reducing activity in the whole abdominal area; and 2) EPR imaging, which showed semiquantitative but organ-specific reducing activity. The results were compared with the reducing activity of organ homogenate and phosphatidylcholine hydroperoxide (PC-OOH) concentrations. Half-lives of carbamoyl-PROXYL in the whole upper abdominal area, measured by L-band EPR, were prolonged on day 3 after ischemia-reperfusion and recovered to the level of nontreated mice on day 7. This trend resembled closely that of serum creatinine and blood urea nitrogen concentration. The EPR imaging-measured carbamoyl-PROXYL half-life was also prolonged on day 3 in both the kidney and the liver. However, in the kidney this showed only partial recovery on day 7. In the liver, this convalescence was more remarkable. The ex vivo studies of organ reducing activity and PC-OOH agreed with the results from EPRI, but not with those from L-band EPR. These results indicate that renal reducing activity shows only partial recovery on day 7 after ischemia-reperfusion, when serum creatinine and blood urea nitrogen have recovered. EPR imaging is an appropriate and useful method for the noninvasive evaluation of oxidative stress in the presence of renal injury.

In Vivo Imaging of Renal Redox Status during Azelnidipine Treatment

“…In agreement with our previous studies (7,12), the plots of signal intensities were fitted to a straight line on a semi-logarithmic scale indicating that in vivo Carbamoyl-PROXYL reduction obeyed first order kinetics during the time measured (typical signal decay curves are shown in Fig. 2A).…”

“…Measurements with L-band EPR were conducted by a method previously reported (12). Briefly, Carbamoyl-PROXYL (300 mmol/L, 2 mL/kg) was injected into the mice through the tail vein 10 min after pentobarbital anesthesia.…”

“…The detailed method for the measurement of organ-reducing activity by EPRI was established in our previous reports (7,12). EPR images were obtained every 300 s until approximately 20 min after the Carbamoyl-PROXYL injection.…”

“…To rule out this phenomenon, changes of the Carbamoyl-PROXYL half-life by the addition of a free radical specific scavenger were measured (12). Superoxide dismutase (SOD, 4 U/g) or mannitol was injected intravenously into the three groups of mice after 2 weeks of treatment.…”

“…As such, the measurement of spin probe-reducing activity by EPR may yield information about tissue radical reducing activity, redox status and biological status. Using in vivo EPR and EPR imaging technique (EPRI), we have previously succeeded with noninvasive evaluations of renal antioxidative status in various disease models (7,9,12,13). We have improved the in vivo EPR application step-by-step in our previous reports and proved its accuracy for renal redox measurements.…”