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G. Baltazar, S. Guha, A. M. Laties, U. B. Kompella, C. H. Mitchell; Acidification of RPE Lysosomes by Nanoparticles. Invest. Ophthalmol. Vis. Sci. 2010;51(13):700.
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Lysosomal enzymes require an acidic pH to function optimally, and the lysosomal pH of RPE cells may elevate in disease. Experimentally, elevation of lysosomal pH can lead to the accumulation of lipofuscin-like autofluorescence. As reacidification of the lysosomes can reduce this build-up in RPE cells, approaches to lower the lysosomal pH of compromised RPE cells are of potential benefit. In this regard, we asked whether acidic nanoparticles were delivered to the lysosomes of RPE cells and whether they successfully reacidified these lysosomes.
Acidic nanospheres derived from polylactide were developed. Nanospheres labeled with Nile Red were administered to cultured ARPE-19 cells to examine their internalization and subcellular localization. Additionally, their ability to acidify compromised lysosomes was assessed. ARPE-19 cells grown in 96-well plates were treated on day 0 with 10 µM chloroquine in the presence and absence of unlabeled nanoparticles. The lysosomal pH was determined from the ratio of fluorescence excited at 340 and 380 nm in cells loaded with the dye Lysosensor Yellow-Blue.
Acidic nanoparticles had internalized in ARPE-19 cells within 24 hours. The nanoparticles predominantly co-localized with the LysoTracker stain, indicating they had been delivered to the lysosomes. A single dose of chloroquine elevated the pH of lysosomes for up to 7 days. Two nanosphere formulations were successful in lowering this lysosomal pH by 30-50%, with sustained acidification lasting at least 7 days.
Acidic nanoparticles are internalized by RPE cells and delivered to the lysosomes. A single application of nanoparticles can restore acidity to these compromised cells for at least a week. It remains to be determined whether nanoparticles can improve degradative function and reduce the accumulation of lipofuscin in disordered RPE cells.
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