Oligomeric amyloid-β targeted contrast agent for MRI evaluation of Alzheimer's disease mouse models

Abstract

Background: Oligomeric amyloid beta (oAβ) is a toxic factor that acts in the early stage of Alzheimer's disease (AD) and may initiate the pathologic cascade. Therefore, detecting oAβ has a crucial role in the early diagnosis, monitoring, and treatment of AD.

Purpose: The purpose of this study was to evaluate MRI signal changes in different mouse models and the time-dependent signal changes using our novel gadolinium (Gd)-dodecane tetraacetic acid (DOTA)- ob5 aptamer contrast agent.

Methods: We developed an MRI contrast agent by conjugating Gd-DOTA-DNA aptamer called ob5 to evaluate its ability to detect oAβ deposits in the brain using MRI. A total of 10 control mice, 9 3xTg AD mice, and 11 APP/PS/Tau AD mice were included in this study, with the age of each model being 16 or 36 weeks. A T1-weighted image was acquired at the time points before (0 min) and after injection of the contrast agent at 5, 10, 15, 20, and 25 min. The analyses were performed to compare MRI signal differences among the three groups and the time-dependent signal differences in different mouse models.

Results: Both 3xTg AD and APP/PS/Tau AD mouse models had higher signal enhancement than control mice at all scan-time points after injection of our contrast media, especially in bilateral hippocampal areas. In particular, all Tg AD mouse models aged 16 weeks showed a higher contrast enhancement than those aged 36 weeks. For 3xTg AD and APP/PS/Tau AD groups, the signal enhancement was significantly different among the five time points (0 min, 5 min, 10 min, 15 min, 20 min, and 25 min) in multiple ROI areas, typically in the bilateral hippocampus, left thalamus, and left amygdala.

Conclusion: The findings of this study suggest that the expression of the contrast agent in different AD models demonstrates its translational flexibility across different species. The signal enhancement peaked around 15-20 min after injection of the contrast agent. Therefore, our novel contrast agent targeting oAβ has the potential ability to diagnose early AD and monitor the progression of AD.

Keywords: ApoE mouse model; DNA aptamer; MRI contrast agent; oligomeric amyloid-beta; tau mouse model; time-dependent signal enhancement.

FIGURE 1

Regions-of-interest (ROIs) defined at the right and left amygdala, cortex, thalami, and frontal part and posterior part of the hippocampus.

FIGURE 2

Representative images obtained from Control (A), 3xTg AD (B), and APP/PS/Tau AD (C) mice before and after injection of our proposed contrast agent. For both 3xTg AD (B) and APP/PS/Tau AD (C) mice, T1-weighted images showed a signal increase with our contrast agent from 5 min to 25 min after injection of the contrast agent. Signal enhancement looks higher with 16-week-old mice than with 36-week-old mice for both models.

FIGURE 3

Result of the voxel-based comparison of the signal enhancement between the mouse groups in 5, 10, 15, 20, and 25 min after injection of our proposed contrast agent. Results show comparison between APP/PS/Tau AD and control groups (A), between 3xTg AD and control groups (B), between 16 weeks-aged Tg AD and 16 weeks-aged control mice (C), and between 36 weeks-aged Tg AD and 36 weeks-aged control mice (D), and between 16 weeks-aged Tg AD and 36 weeks-aged Tg AD mice (E).

FIGURE 4

Result of the voxel-based comparison of the signal enhancement between before (pre) and after injection of the proposed contrast agent for the control mouse model group (A), 3xTg AD model group (B), and APP/PS/Tau model group (C). No significant differences were found when signal intensity was compared between other scan-time points after injection of the proposed contrast agent for each mouse model group.

FIGURE 5

Result of region-of-interest (ROI)-based comparison of the signal enhancement between the three mouse groups for each scan-time point. Data list in Supplementary Table S1 as the median (25th −75th percentile) of the signal enhancement at the scanned times of 5, 10, 15, 20, and 25 min after injection of the contrast media.

FIGURE 6

Result of region-of-interest (ROI)-based comparison of the signal enhancement between the scan-time points for Control (A), 3xTg AD (B), and App/PS/Tau AD (C) mouse groups. Data listed in Supplementary Table S5 as the median (25th −75th percentile) of the signal enhancement at the scanned times of 5, 10, 15, 20, and 25 min after injection of the contrast media for each mouse model.

FIGURE 7

Results of immunofluorescence (IF) analysis of 16-week-old mice (A) and 36-week-old mice (B) of control, 3xTg AD, and APP/PS/Tau AD mouse models. The IF analysis showed the deposit pattern of monomer amyloid beta (mAβ) and oligomeric amyloid beta (oAβ) in the brain tissue of AD mouse models. Brain tissues were subjected to immunohistochemistry using antibodies to anti-mAβ (6E10, Biolegend, San Diego, CA, United States) and ob5 aptamer (J&Pharma, Korea) as indicated. The scale bar indicates 500 μm.

FIGURE 8

Distribution of signal enhancement in 3xTg AD and APP/PS/Tau mouse models after injection of low or high-contrast agents in 10 scan-time points. Signal enhancements in AD mouse models were concentrated in the hippocampus C1&C2&C3&DG, hippocampus C3, cortex, and thalamus in both low and high doses of the proposed contrast agent. Signal enhancements in high doses were more extensive than those in low doses.