Assessment of renal function in mice with unilateral ureteral obstruction using 99mTc-MAG3 dynamic scintigraphy

Abstract

Background: Renal scintigraphy using 99mTc-mercaptoacetyltriglycine (99mTc-MAG3) is widely used for the assessment of renal function in humans. However, the application of this method to animal models of renal disease is currently limited, especially in rodents. Here, we have applied 99mTc-MAG3 renal scintigraphy to a mouse model of unilateral ureteral obstruction (UUO) and evaluated its utility in studying obstructive renal disease.

Methods: UUO mice were generated by complete ligation of the left ureter. Sham-operated mice were used as a control. Renal function was investigated on days 0, 1, 3, and 6 post-surgery using dynamic planar imaging of 99mTc-MAG3 activity following retro-orbital injection. Time-activity curves (TACs) were produced for individual kidneys and renal function was assessed by 1) the slope of initial 99mTc-MAG3 uptake (SIU), which is related to renal perfusion; 2) peak activity; and 3) the time-to-peak (TTP). The parameters of tubular excretion were not evaluated in this study as 99mTc-MAG3 is not excreted from UUO kidneys.

Results: Compared to sham-operated mice, SIU was remarkably (>60%) reduced in UUO kidneys at day 1 post surgery and the TACs plateaued, indicating that 99mTc-MAG3 is not excreted in these kidneys. The plateau activity in UUO kidneys was relatively low (~40% of sham kidney's peak activity) as early as day1 post surgery, demonstrating that uptake of 99mTc-MAG3 is rapidly reduced in UUO kidneys. The time to plateau in UUO kidneys exceeded 200 sec, suggesting that 99mTc-MAG3 is slowly up-taken in these kidneys. These changes advanced as the disease progressed. SIU, peak activity and TTPs were minimally changed in contra-lateral kidneys during the study period.

Conclusions: Our data demonstrate that renal uptake of 99mTc-MAG3 is remarkably and rapidly reduced in UUO kidneys, while the changes are minimal in contra-lateral kidneys. The parametric analysis of TACs suggested that renal perfusion as well as tubular uptake is reduced in UUO kidneys. This imaging technique should allow non-invasive assessments of UUO renal injury and enable a more rapid interrogation of novel therapeutic agents and protocols.

Figure 1

Renal structure and histopathology in UUO mice. (A) Representative T1- and T2-weighted coronal MRI images of UUO kidney at day 0, 1, 3 and 6 post obstruction. Renal pelvic space (asterisks) is progressively expanded in the obstructed kidney, and renal medulla (outlined with dotted lines), especially inner medulla and papilla, is remarkably decreased as the disease progresses. Arrows indicate urine. C, cortex; OM, outer medulla (inner stripe); IM, inner medulla; P, papilla. (B) Representative histological sections of mouse kidneys subjected to unilateral ureteral obstruction. Tubulointerstitial region increases markedly over 6 days in UUO kidneys, as indicated by destructive morphology of renal tubules (asterisks) and interstitial fibrosis (arrows). Bar=100 μm. Masson trichrome stain

Figure 2

Representative time-activity curves (TACs) of ^99mTc-MAG3 dynamic renal scintigraphy in normal mice. ^99mTc-MAG3 was retro-orbitally injected to mice and the TACs were established as described in “Materials and Methods”. The slope of initial uptake (SIU) which rises linearly, peak activity, and the time-to-peak (TTP) were determined and used as parameters of renal ^99mTc-MAG3 uptake

Figure 3

Comparison of TACs established by intravenous and retro-orbital ^99mTc-MAG3 injections. (A) Mean TACs established by intravenous (n=7) and retro-orbital (n=12) ^99mTc-MAG3 injections. For intravenous injection, ^99mTc-MAG3 was injected via jugular vein catheter. Values are means ± SE. (B) Comparison of the parameters (SIU, peak activity, and TTP) extracted from the TACs generated by intravenous and retro-orbital ^99mTc-MAG3 injections. No significant difference was found between the two procedures

Figure 4

TACs of ^99mTc-MAG3 dynamic renal scintigraphy in UUO mice. (A) UUO day 0, (B) UUO day 1, (C) UUO day 3, (D) UUO day 6, (E) Sham operation day 0, (F) Sham operation day 6. Values are means ± SE. The numbers of mice are described in Table 1

Figure 5

Representative time-interval images of ^99mTc-MAG3 dynamic renal scintigraphy in UUO mice at 6 days post obstruction. Uptake of the tracer is remarkably reduced in UUO kidney. A) 0–1 min, B) 1–2 min, C) 2–6 min, D) 6–15 min, E) 15–25 min, F) 25–35 min, and G) 35–40 min. R, right; L, left; CL, contralateral kidney

Figure 6

Static ^99mTc-MAG3 imaging of UUO mice kidneys. A) Static SPECT images (a 40-min acquisition) were obtained from UUO day 6 and sham-operated mice kidneys after retro-orbital injection of ^99mTc-MAG3. The excretion of ^99mTc-MAG3 to renal pelvis is not observed in UUO day 6 kidney, while ^99mTc-MAG3 gets into renal pelvis in sham-operated kidney during a 40 min scan. B) Similar findings were observed in UUO day 0 and day 1 kidneys, while ^99mTc-MAG3 was excreted to renal pelvis (arrows) in contralateral kidneys (CL). Representative images are shown

Figure 7

Parametric analysis of ^99mTc-MAG3 dynamic renal scintigraphy obtained from UUO, sham-operated, and non-surgery (control) mice. Values are means ± SE. The numbers of mice are described in Table 1. Note: The time-to-plateau (TTPt) was measured in UUO kidneys

Figure 8

Slope of ascending phase is increased in contralateral kidneys after UUO surgery. A) Graphical depiction of ascending phase window selection in contralateral kidneys at 0 and 6 days post ureteral obstruction. B) The slope of ascending phase (from 50s to peak) was measured for the contralateral kidneys in UUO and sham-operated mice. Values are means ± SE. The numbers of mice are described in Table 1