Lens β-Amyloid Biomarker for Early Detection of Preclinical Alzheimer's Disease in the Framingham Study

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Recent research advances have led to detailed understanding of the pathogenesis of Alzheimer's disease (AD) and development of emerging disease-modifying therapies. Yet effective treatment remains elusive. Repeated failure of AD clinical trials has focused attention on preclinical AD that begins with clinically silent accumulation of β-amyloid (Aβ) in the brain and progresses to onset of cognitive symptoms. Early detection of preclinical AD is now recognized as a prerequisite for effective treatment. Aβ is an accepted “gold standard” AD biomarker. Available methods to assess Aβ burden rely on positron emission tomography (PET) brain scans or cerebrospinal fluid (CSF) analysis. These methods are expensive, invasive, cumbersome, not widely available, and difficult to scale. The NIA has identified development of new, safe, sensitive, cost-efficient, point-of-care technology to detect preclinical AD as a high-priority goal. This project addresses this unmet need by accelerating testing of an innovative drug-device combination eye scanner (Sapphire II) that detects AD-related Aβ in the lens. This novel approach is based on our discovery of AD-specific Aβ lens pathology in patients with pathologically-confirmed AD, but not other non-AD neurodegenerative diseases or normal aging. Moreover, we found that AD-related pathology and phenotypes are expressed far earlier in lens than brain in Framingham Eye Study participants. This and related research led to development of the Sapphire II system that combines a topically-applied Aβ-binding fluorescent ligand (Aftobetin) and a purpose-designed eye scanner with integrated fluorescent lifetime decay spectroscopy analyzer. The eye scanner and ligand reliably measure lens Aβ with high specificity, sensitivity, and signal-to-noise ratio. In Phase 2 clinical trials, the Sapphire II system showed high positive and negative predictive values for AD diagnosis and differentiated mild cognitive impairment (MCI) and clinical AD from normal controls with greater sensitivity and specificity than amyloid-PET scans. This project leverages opportunistic timing of NHLBI-funded basic health exams by adding lens Aβ measurements in well- characterized, community-based longitudinal cohorts in the Framingham Heart Study (FHS). Specifically, we will evaluate lens Aβ burden in two older FHS cohorts (Aim 1; Gen 2, multi-ethnic OmniGen 1) and two middle-aged FHS cohorts (Aim 2; Gen 3, multi-ethnic OmniGen 2), each with longitudinal neuropsychological test battery results, concurrent MRI brains scans, and ancillary datasets relevant to cognitive decline and AD. Lens Aβ measurement will be evaluated using stratified analyses for age, sex, ApoE genotype, and AD risk factors (Aim 3) and computational modeling to construct multi-marker predictive profiles for AD (Aim 4). Results will be used to test our project hypothesis that lens Aβ burden will be elevated in middle-aged and older FHS participants who show evidence of cognitive decline (memory deficits, executive dysfunction), AD neuroimaging biomarkers, or clinical AD. Project results are expected to accelerate clinical introduction of lens Aβ burden as an objective measure to evaluate AD risk, detect preclinical AD, and assess early AD and progression in individual patients.