Aerosol Delivery of Thioflavin S Reveals Ab in the Retina of the 5XFAD Model of Alzheimer’s Disease

Abstract

Purpose : The hallmark pathologic features of Alzheimer’s disease (AD) are amyloid beta (Ab) plaques and neurofibrillary tangles found in postmortem brain specimens or with invasive brain imaging in patients with advanced disease. A non-invasive and inexpensive screening method is needed for early detection and treatment of asymptomatic AD patients to improve therapeutic efficacy. The similarities between the brain and retina make the retina a suitable surrogate tissue to assess Ab load in AD. Using a novel aerosol delivery method, Thioflavin S (ThioS), a fluroprobe with high affinity to Ab, was administered to 5XFAD transgenic mouse models of AD to reveal ThioS bound to Ab in the retina.

Methods : 5XFAD (Tg, N=10) and age-matched wildtype (WT, N=18) underwent ThioS (2% w/v in ddH2O) nebulization for a period of 3 hours, repeated for two consecutive days. Animals were transcardially perfused 2 hours after the final nebulization. Eyes and brains were then dissected and processed for paraffin or frozen sectioning. Tissues were coverslipped for confocal microscopy using a Zeiss LSM 800/880. All tissues were scanned at identical settings, using 488nm and 543 nm (ThioS) and 405nm (DAPI, nuclei) wavelengths. Intensity of fluorescence was measure by custom software and normalized to negative control sections, and treated and untreated Tg and WT groups were compared.

Results : Paraffin cross sections and wholemounts revealed ThioS labeling in the nerve fiber (NFL) and ganglion cell layer (GCL) of the nebulized Tg retina, with ganglion cell profiles evident. Nebulized WT retina displayed sporadic labeling in the inner and outer plexiform layers (IPL, OPL). Alternate serial cross sections revealed 6E10 immunolabeling in NFL and GCL of Tg retina. Paired brain and eye tissues comparisons identified consistent Ab and ThioS labeling suggesting ThioS is a robust marker of Ab in the brain and eye of the Tg mouse.

Conclusions : Orally administered fluroprobes such as curcumin derivatives have been used for in vivo visualization of retinal Ab in humans, but suffers from low solubility and poor absorption in the gut. Using aerosol delivery systems may allow an improved method to deliver fluroprobes to bind retinal Ab. Our next step will be in vivo fSLO live imaging of fluroprobe-bound Ab in 5XFAD mice for a non-invasive method of detecting Ab, and potentially a novel method of predicting and diagnosing early AD.

This is a 2020 ARVO Annual Meeting abstract.