Effect of Repeated Injection of Iodixanol on Renal Function in Healthy Wistar Rats Using Functional MRI

Abstract

Purpose: To determine the optimal time interval of repeated intravenous injections of iodixanol in rat model and to identify the injury location and causes of renal damage in vivo.

Materials and methods: Rats were randomly divided into Control group, Group 1 with one iodixanol injection, and Group 2 with two iodixanol injections. Group 2 was subdivided into 3 cohorts according to the interval between the first and second iodixanol injections as 1, 3, and 5 days, respectively. Blood oxygen level-dependent (BOLD) imaging and diffusion weighted imaging (DWI) were performed at 1 hour, 1 day, 3 days, 5 days, and 10 days after the application of solutions.

Results: Compared with Group 1 (7.2%), Group 2 produced a remarkable R2^⁎ increment at the inner stripe of the renal outer medulla by 15.37% (P = 0.012), 14.83% (P = 0.046), and 13.53% (P > 0.05), respectively, at 1 hour after repeated injection of iodixanol. The severity of BOLD MRI to detect renal hypoxia was consistent with the expression of HIF-1α and R2^⁎ was well correlated with HIF-1α expression (r = 0.704). The acute tubular injury was associated with urinary NGAL and increased significantly at 1 day.

Conclusions: Repetitive injection of iodixanol within a short time window can induce acute kidney injury, the impact of which on renal damage in rats disappears gradually 3-5 days after the injections.

Figure 1

The experimental flow chart. This flowchart illustrates the specific measurement protocol and the time points of fMRI, histology, uNGAL, and sCr that occurred.

Figure 2

The four kidney areas corresponding to anatomic image. (a) Resected specimen. (b) T2 image. (c) The ROIs.

Figure 3

Representative R2^∗ maps (baseline, 1 h, 1 day, 3 days, 5 days, and 10 days). All maps are demonstrated on the same window and level settings. 1-day, 3-day, and 5-day subgroups were injected for a second time at different time intervals. Group 1 was injected with iodixanol only once. The intensity of ISOM was larger than the remaining regions, which implies lower level of oxygenation.

Figure 4

Summary of the temporal changes in R2^∗/ADC measurement during a long period of time. (a) R2^∗ time curves. (b) ADC time curves. Notice maximum R2^∗/minimum ADC values appeared at 1 h, followed by gradual regression to a near-complete baseline level over time.

Figure 5

Representative ADC maps (baseline, 1 h, 1 day, 3 days, 5 days, and 10 days). The cortical and medullary ADC in the kidney decreased in Group 2 after iodixanol injection, especially in 1-day subgroup. For each renal region, they significantly decreased at 1 h and thereafter gradually increased upward towards the baseline.

Figure 6

Hematoxylin-Eosin (H&E) stained histological sections of the kidneys in the cortex. Renal histological injury subjected to repeated injection of iodixanol at different time points in 1-day subgroup. Scale bar, 100 μm.

Figure 7

Hematoxylin-Eosin (H&E) stained histological sections of the kidneys in the outer medulla (OSOM and ISOM) at 1 h in different groups. Remarkable changes (swollen, broken down, necrotic, and intraluminal desquamation) were observed in part of proximal tubular and distal convoluted tubular epithelial cells in the OSOM and medullary thick ascending limbs, and medullary collecting ducts in the ISOM. Scale bar indicates 100 μm. Asterisk indicates P < 0.05 (compared with Group 1).

Figure 8

HIF-1α signals changes in ISOM renal zones. HIF-1α was mainly localized in the renal ISOM, especially at 1 h. Marked nuclear accumulation of HIF-1α appears in the 1-day subgroup. Thereafter, staining gradually decreased over time, and they were detectable for 5 days. Asterisk indicates P < 0.05 (compared with Group 1). Scale bar, 50 μm. (a) 1-day subgroup; (b) 3-day subgroup; (c) 5-day subgroup; (d) Group 1; (e) HIF-1α score.

Figure 9

The normalized uNGAL (pg/mg) at different time points during the course of contrast injection (n = 3). There was a significant increase in uNGAL levels in rats at 1 day, 3 days, and 5 days in 1-day subgroup. Asterisk indicates P < 0.05 (compared with baseline).

Figure 10

Correlation of R2^∗ with HIF-1α expression/tubular injury and tubular injury with uNGAL. (a) The correlation between the measured R2^∗ values and HIF-1α expression score in the ISOM. (b) The correlation between the measured R2^∗ values and tubular injury score in ISOM. (c) The correlation between all the measured uNGAL and tubular injury score in ISOM.