In vivo imaging of curcumin labeled amyloid beta deposits in retina using fluorescence scanning laser ophthalmoscopy in an Alzheimer mouse model

Abstract

Purpose : Alzheimer’s disease (AD) is a chronic progressive neurodegenerative illness that is the commonest cause of dementia. A hallmark of AD is amyloid beta (Ab) plaques detected on neuropathology, or expensive clinical tests in patients who are in advanced stages of disease. A non-invasive method of screening for these plaques could allow for early detection and treatment of asymptomatic patients. A fluoroprobe is required in order to visualize the ocular Ab deposits. Ab deposits in the eye can act as surrogate marker for early-stages of AD. In this longitudinal study, we use a mouse model of AD to detect ocular Ab load in the mouse retina.

Methods : Transgenic (Tg) AD mouse models were followed between 5 months to 18 months of age. Curcumin (a fluorophore that binds to Ab) formulations were delivered to the target-in vivo site via tail-vein injections into each mouse (n=10) once every ~ 3 months. Retinal images of the right eye were acquired using a custom fluorescence Scanning Laser Ophthalmoscope (fSLO), before and 2 hours after curcumin injection. The Ab load was quantified by fluorescence index, computed by segmenting and counting the number of pixels in fluorescent specks in each image. The specks were detected by intensity-based median-filtering and thresholding. At 18 months of age, the mice were sacrificed and Ab load was measured ex vivo on Tg brain and eye tissue using scanning confocal microscopy imaging and immunohistochemistry.

Results : While there was a trend towards higher fluorescence with increasing mouse age, the mean fluorescence index ratio was greater after curcumin injection compared to before (mean of 2.78 vs. 0.556 respectively, p = 0.004) at each time point. Funduscopic detection of Ab deposits in the mouse eyes correlated with the scanning confocal microscopy imaging of the eye cups from the 18-month-old mice. Curcumin labeling of Tg mouse eye cross sections showed positive staining in the inner layers of the retina.

Conclusions : The retina and brain of the Tg mice readily express Ab deposits, which are then detected using fSLO, confocal microscopy, and immunohistochemistry. These findings suggest that using in vivo fSLO live imaging of curcumin in the retina may be a novel and non-invasive method of detecting ocular amyloid beta, and potentially a novel method of predicting and diagnosing early AD.

This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.