Hyperspectral Imaging Signatures Detect Amyloidopathy in Alzheimer’s Mouse Retina Well before Onset of Cognitive Decline

Abstract

Amyloidopathic disorders such as Alzheimer's disease present symptomology years after the entrenchment of amyloidogenic imbalance. The pathologic α-helix → β-strand conversion of amyloid β(1-42) and amyloid β(1-40) peptides causes neuronal death in the vicinity. Symptomology often presents only after significant neurodegeneration. This thus warrants early detection of amyloidopathy in Alzheimer's disease. Nonexistent modalities for direct identification and quantitation of soluble amyloid aggregates or (proto)fibrils forced us to undertake the development of a spectrophotometric technique to support ongoing drug design. Key requirements were independence from the need for extraneous staining, unambiguous amyloid aggregate detection, and minimal influence of interpretative errors. A Cytoviva instrument pivotal to this study captures scattering of light of visible-near-infrared (VNIR, 400-1000 nm) wavelengths within each pixel of the microscopic view field. We thus assembled a scattering intensity pattern database that provided "signatures" of amyloid aggregates. Comparison of unknown samples against this database enabled direct detection of amyloid aggregates. The technique was found useful for monitoring retinal and brain amyloidopathy in an ongoing preclinical anti-AD study, attesting to the technique's sensitivity and specificity. Interestingly, the technique was found applicable not just to excised brain tissue but also to isolated mouse retina. With the retina being heralded widely as a (diagnostic) extension of the CNS and retinal amyloidopathy occurring well before that in the brain, this development raises a possibility for the first direct retinal imaging diagnosis of early asymptomatic Alzheimer's disease.

Retinal amyloid pathology and proof-of-concept imaging trial in Alzheimer’s disease

“…In line with the above findings, numerous studies examining the retinas of sporadic and transgenic animal models of AD have reported Aβ deposits, vascular Aβ, pTau, and paired helical filament-tau (PHF-tau), often in association with RGC degeneration, local inflammation (i.e., microglial activation), and impairments of retinal structure and function (11,39,40,42,(45)(46)(47)(48)(49)(50)(51)(52)(53)(54)(55)(56)(57)(58)(59)(60)(61). These studies, which included a variety of transgenic rat and mouse models, as well as the sporadic rodent model of AD, Octodon degus, demonstrated abundant Aβ deposits, mainly in the innermost retinal layers (RGCs and NFL) (40,42,45,49,52,54,57).…”

Ocular indicators of Alzheimer’s: exploring disease in the retina

“…These include the Tg2576, APP/PS1, 3xTg, 5xFAD mice, the TgF344-AD rat, and O. degus [1, 46–48, 107, 117, 134, 148, 150, 152, 154, 178, 184]. It has been reported that levels of Aβ 40 and particularly Aβ 42 are elevated in the retina, as well as in the lens, vitreous humor, and choroid of AD rodent models (Table 2) [1, 46, 47, 117, 148, 150, 154, 178, 184].…”

“…Deposits of insoluble Aβ species and subsequent plaque formation have been documented in the retinas of Tg2576, APP SWE /PS1 ΔE9 , APP SWE /PS1 M146L/L286V , 3xTg, and 5xFAD mice, as well as O. degus [1, 46–48, 107, 108, 117, 134, 139, 152, 184, 187, 188]. In the Tg2576 mouse, plaques have been identified most consistently in retinal layers ranging from the GCL to the ONL, and rarely in the photoreceptors and optic nerve [117, 184].…”

The Eye As a Biomarker for Alzheimer's Disease

“…One such method is hyperspectral imaging, whereby tissue reflectance to a wide range of incident wavelengths are quantified (More and Vince, 2015). Using this technique, More and Vince (2015) were able to determine that Aβ has a unique hyperspectral signature, capable of distinguishing these deposits in ex vivo preparations of brain and retina from a mouse model of AD. More recently, the authors applied this technology to a live mouse retina, demonstrating that the hyperspectral signatures are preserved even when imaged through the ocular media.…”