A quantitative map of glutathione in the aging human lens

Changes to cellular metabolism often precede changes to other biomolecules that in turn cause tissue pathologies. In the ocular lens, changes in the spatial distribution and concentration of metabolites that are associated with the aging process are implicated in the development of the primary lens pathology, lens cataract. The development of age-related nuclear cataract is characterised by regional changes to protein cross-linking and protein insolubilisation that subsequently results in cataract formation. In the present study, MALDI FT-ICR imaging mass spectrometry was used to map the metabolome of the aging human ocular lens, and a MALDI imaging mass spectrometry method developed to quantify regional changes to the primary lens antioxidant glutathione (reduced). Spatial segmentation of total metabolite signal intensities showed the lens contains distinct metabolic compartments that change with increasing age. Using the developed absolute quantitation method, glutathione concentrations throughout the lens were mapped with up to 100 mu m spatial resolution, and showed that cortical concentrations (mean = 3.7 mu mol/g tissue in 34 yo) were always higher than nuclear concentrations (mean = 2.8 mu mol/g tissue in 34 yo). In addition, cortical concentrations decreased slightly with increasing lens age (mean = 2.7 mu mol/g tissue in 74 yo), while the decrease in nuclear glutathione concentrations was more pronounced (mean = 0.8 mu mol/g tissue in 74 yo). Finally, ceramides were localised to the lens region that was specifically depleted of glutathione. In summary, MALDI FT-ICR imaging mass spectrometry has allowed age-related changes to human lens metabolites to be mapped with higher spatial resolution than previously possible using alternative techniques. In addition, the multiplex capability of MALDI imaging mass spectrometry has allowed the spatial relationships of these lens metabolites to be established and explored. This approach should aid the development of spatially directed therapies to delay the onset of lens cataract. (C) 2017 Elsevier B.V. All rights reserved.