In Vivo Near-Infrared Two-Photon Imaging of Amyloid Plaques in Deep Brain of Alzheimer’s Disease Mouse Model

Abstract

Abnormal deposition of brain amyloid is a major hallmark of Alzheimer's disease (AD). The toxic extracellular amyloid plaques originating from the aberrant aggregation of beta-amyloid (Aβ) protein are considered to be the major cause of clinical deficits such as memory loss and cognitive impairment. Two-photon excited fluorescence (TPEF) microscopy provides high spatial resolution, minimal invasiveness, and long-term monitoring capability. TPEF imaging of amyloid plaques in AD transgenic mice models has greatly facilitated studies of the AD pathological mechanism. However, the imaging of deep cortical layers is still hampered by the conventional amyloid probes with short excitation/emission wavelength. In this work, we report that a near-infrared (NIR) probe, named CRANAD-3, is far superior for deep in vivo TPEF imaging of brain amyloid in comparison with the commonly used short-wavelength probe. Our findings show that the major interference for TPEF signal of the NIR probe is from the autofluorescence of lipofuscin, the "aging-pigment" in the brain. To eliminate the interference, we characterized the lipofuscin fluorescence in the aged brains of AD mice and found that it has unique broad emission and short lifetime. The lipofuscin signal can be clearly separated from the fluorescence of CRANAD-3 and fluorescent protein via a ratio-based unmixing method. Our results demonstrate the great advantages of NIR probes for in vivo deep-tissue imaging of amyloid plaques in AD.

The search for a unique Raman signature of amyloid-beta plaques in human brain tissue from Alzheimer's disease patients

“…[56][57][58][59][60] Its broad fluorescence is also known from retinal imaging in humans 61 and was described as fluorescence source by Chen et al, using two-photon fluorescence on live transgenic mice brain tissue. 62,63 The tiny lipofuscin granulates, usually 0.1 to 5 µm in size, 53,64 accumulate to deposits and fill the cytoplasm of cells, therefore reaching a size of 10 to 20 µm. That matches the size of the main feature described by Michael et al 24 as neuritic plaque in their recent publication.…”

Amyloid‐β Oligomer‐Targeted Gadolinium‐Based NIR/MR Dual‐Modal Theranostic Nanoprobe for Alzheimer's Disease

“…After injection of the NP@SiO 2 @F‐SLOH for 6 h, the cerebral fluorescence of the Tg mice revealed unambiguous age‐dependent intensity differences, as shown in Figure A–D; the older Tg mice showed a stronger fluorescence signal than the younger mice, reflecting the higher amount of Aβ contents in the older mice. [ 3b ] To verify this further, ex vivo fluorescence images of the brain slices were acquired. As seen in Figure 3E–K; and Figure S9 (Supporting Information), the brain slices from the three groups of the Tg mice showed an increase in distinct and intense NIR/upconversion fluorescence clusters of NP@SiO 2 @F‐SLOH compared to those from WT mice.…”

“…[ 2 ] Reports have also shown that the presence of amyloid plaques does not correlate well with the progression of the disease, and the more pathogenic and neurotoxic oligomeric amyloid‐β (Aβ) would be more informative and relevant as a disease biomarker than amyloid plaques. [ 3 ] The use of a powerful imaging technique with molecular sensitivity is crucial to diagnosing, and monitoring the disease progression, and understanding the complex disease process, and evaluating the effectiveness of potential AD drugs. Although the current brain imaging technique of choice, positron emission tomography, allows the visualization of amyloid plaques, it affords limited spatial resolution and requires an invasive radiotracer.…”

“…[ 4b ] In particular, effective and sensitive MRI contrast agents for AD biomarker imaging used in animal models that show potential applications in humans are rarely reported. [ 3b ]…”

“…Despite the limited clinical potential of NIR fluorescent probes for brain amyloid imaging, they were found to be effective and useful for AD mouse model investigations, which has recently led to the development of numerous Aβ‐specific NIR fluorescent probes. [ 3b,7 ] Dual modality imaging is attractive because it can provide complementary and expanded information for more accurate etiological investigation and disease diagnosis. In this work, we report for the first time an easily synthesized Aβ oligomer‐specific Gd 3+ ‐based NP as an effective and sensitive multimodal (MR/NIR) imaging probe for real‐time visualization of Aβ contents in different age groups in AD mouse models and as an Aβ aggregation and reactive oxygen species (ROS) inhibitor for the therapeutic treatment of AD.…”