Abstract
Purpose :
Imaging mass spectrometry (IMS) is a powerful tool for elucidating spatial distributions of biomolecules such as lipids, metabolites, and proteins in tissues. With low micron spatial resolution, molecular distributions can be localized to specific layers of the human retina and choroid. Furthermore, molecular constituents of retina deposits can be determined. The purpose of this work is to map the distribution of lipids in retina specimens with pathologies, such as deposits and migrating RPE cells, and to correlate molecular images with OCT images.
Methods :
Human donor eyes (80-93 yrs of age) were subjected to ex vivo OCT imaging prior to paraformaldehyde fixation. Serial sections were cut for IMS analysis and adjacent sections were stained with Periodic acid-Schiff and Hematoxylin stains for morphological analysis. IMS was performed at 10-20 µm spatial resolution in positive and negative ion modes on a Bruker Solarix 9.4T FTICR instrument with a modified MALDI source designed for high spatial resolution imaging experiments. Tissue autofluorescence images were also acquired from sections, before and after IMS experiments, to enable precise registration of IMS and optical signals, allowing high-confidence localization of IMS signals to retina layers and extracellular deposits.
Results :
Specific lipid signals observed in IMS images correlate with pathology observed by OCT. Specific pathologies include: drusen, basal laminar deposits, and migrating RPE cells. High spatial resolution IMS combined with registration to autofluorescence and H&E images, enabled definitive localization of signals to the pathological features. An abundant signal observed at (m/z 799.676) was identified as PE-Cer-NMe2(42:1) and localized to RPE apical processes/ outer segments and was also observed with very high abundance in a basal laminar deposit present in a 93 year old eye with AMD. This same lipid was detected in RPE cells that had migrated into the neural retina as detected by OCT and autofluorescence. Distinct lipid signals present in drusen deposits were not homogeneously localized throughout the deposits. Cholesterol and cholesteryl esters (CE 18:2) were detected within and in the membranes surrounding soft drusen in the macula.
Conclusions :
Unique molecular signatures were detected for ectopic retina cells and extracellular deposits and these signals were spatially correlated with retina pathology observed by OCT.
This is a 2020 Imaging in the Eye Conference abstract.