Detection of early changes in renal function using 99mTc-MAG3 imaging in a murine model of ischemia-reperfusion injury

Abstract

Accurate determination of renal function in mice is a major impediment to the use of murine models in acute kidney injury. The purpose of this study was to determine whether early changes in renal function could be detected using dynamic gamma camera imaging in a mouse model of ischemia-reperfusion (I/R) injury. C57BL/6 mice (n = 5/group) underwent a right nephrectomy, followed by either 30 min of I/R injury or sham surgery of the remaining kidney. Dynamic renal studies (21 min, 10 s/frame) were conducted before surgery (baseline) and at 5, 24, and 48 h by injection of (99m)Tc-mercaptoacetyltriglycine (MAG3; approximately 1.0 mCi/mouse) via the tail vein. The percentage of injected dose (%ID) in the kidney was calculated for each 10-s interval after MAG3 injection, using standard region of interest analyses. A defect in renal function in I/R-treated mice was detected as early as 5 h after surgery compared with sham-treated mice, identified by the increased %ID (at peak) in the I/R-treated kidneys at 100 s (P < 0.01) that remained significantly higher than sham-treated mice for the duration of the scan until 600 s (P < 0.05). At 48 h, the renal scan demonstrated functional renal recovery of the I/R mice and was comparable to sham-treated mice. Our study shows that using dynamic imaging, renal dysfunction can be detected and quantified reliably as early as 5 h after I/R insult, allowing for evaluation of early treatment interventions.

Fig. 1

Renal function and histology of sham and ischemia-reperfusion (I/R)-treated mice. Blood urea nitrogen (BUN; A) and creatinine concentrations (B) for I/R and sham-treated mice at 5 (n = 5), 24 (n = 5), and 48 h (n = 9) are shown. *P < 0.05 vs. sham. C: renal histology at 5 and 24 h following I/R with classic changes in acute tubular necrosis (arrows) and cast formation (asterisks). Note the minimal cast formation at 5 h following I/R.

Fig. 2

Representative scans from 3 mice following injection of ^99mTc-mercaptoacetyltriglycine (MAG3) at baseline (A) and following I/R (B). Note the rapid uptake of the tracer in the kidneys and appearance in the bladder. The frames are numbered in sequential order, and every 6th frame is shown. Depending on their placement during the experiment, the mouse on the right was injected first (frame 6), following by the mouse in the middle (frame 12), and finally the mouse on the left (frame 18). Note than in B all animals underwent unilateral nephrectomy and contralateral I/R before imaging.

Fig. 3

Percent injected dose (%ID) in the left kidney at baseline and following I/R or sham at 5 (A), 24 (B), and 48 h (C) after surgery: A: at 5 h following unilateral nephrectomy and contralateral I/R in mice, ^99mTc-MAG3 imaging shows severe decreases in renal function (pink line at top). The middle (yellow) line represents sham animals that have undergone unilateral nephrectomy and hence the change from normal animals (blue line at bottom; n = 5 mice/group). A shows a significant difference in the amount of dose retained in the left kidney in I/R vs. sham-treated mice. *P < 0.05 vs. sham and baseline. #P < 0.05 vs. sham. B and C show significant differences between baseline vs. sham and I/R (#P < 0.05), but no significant difference between I/R and sham-treated mice.