High-Resolution Multi-Elemental Metallomic Mapping of the Adult Human Eye in Aged Adults and Alzheimer’s Disease

Abstract

Purpose: : We previously identified amyloid-β (Aβ) deposition, amyloid pathology, and co-localizing supranuclear cataracts in Alzheimer’s disease (AD) and Down Syndrome (DS) subjects (Goldstein, Lancet, 2003, Moncaster, Plos One, 2010). Metal-mediated Aβ aggregation in brain and lens is a major contributor to AD pathogenesis and the basis for a clinically proven therapeutic strategy (Lannfelt, Lancet Neurol., 2008). Mapping the microanatomy of essential and trace elements in the adult human eye has been limited by technical barriers. Here we develop a new technique, High-Resolution Metallomic Imaging Mass Spectrometry (HR-MIMS), to map the metallome of the adult human eye in AD and age-matched controls.

Methods: : Intact human eyes and same-subject through the Boston Univ Alzheimer’s Disease Center brain bank and NDRI (Philadelphia, PA). Brains were evaluated by NIA protocol. Eye were flash frozen and analyzed in a custom cryogenic cell by nanosecond laser ablation and magnetic sector field ICP-MS (Center for Biometals & Metallomics). Laser ablation: wavelength, 213 nm; rate, 5-50 µms-1; spot size, 100 micron (scanning) to 10 micron (high-resolution). MIMS analysis was conducted on surround to establish elemental background and calibrated with NIST standards.

Results: : High resolution metallomic maps generated from AD and age-matched control eyes demonstrated unique elemental and isotopic distribution patterns. Zinc was confirmed in the subequatorial supranucleus of the lens, the same region implicated in AD-linked Aβ accumulation and cataractogenesis. Retinal zinc demonstrated a laminar distribution corresponding to cytoarchitectonic organization. Retinal iron revealed a vascular distribution. The trabecular meshwork demonstrated high levels of zinc, copper, and iron. These findings are consistent with our previous low-resolution analyses by X-ray fluorescence microscopy.

Conclusions: : We deployed HR-MIMS analysis to generate detailed quantitative spatial distribution maps of essential and trace elements in adult human eyes at 10-100 micron spatial resolution. This study confirms a role for zinc as a pathogenic contributor to AD-linked pathology in the lens and brain.

Keywords: pathology: human • cataract • pathobiology