Abstract
Lysosomal enzymes function optimally in acidic environments, and elevation of lysosomal pH can impede their ability to degrade material delivered to lysosomes through autophagy or phagocytosis. We hypothesize that abnormal lysosomal pH is a key aspect in diseases of accumulation and that restoring lysosomal pH will improve cell function. The propensity of nanoparticles to end up in the lysosome makes them an ideal method of delivering drugs to lysosomes. This study asked whether acidic nanoparticles could traffic to lysosomes, lower lysosomal pH and enhance lysosomal degradation by the cultured human retinal pigmented epithelial cell line ARPE-19. Acidic nanoparticles composed of poly (DL-lactide-co-glycolide) (PLGA) 502 H, PLGA 503 H and poly (DL-lactide) (PLA) colocalized to lysosomes of ARPE-19 cells within 60 min. PLGA 503 H and PLA lowered lysosomal pH in cells compromised by the alkalinizing agent chloroquine when measured 1 hr. after treatment, with acidification still observed 12 days later. PLA enhanced binding of Bodipy-pepstatin-A to the active site of cathepsin D in compromised cells. PLA also reduced the cellular levels of opsin and the lipofuscin-like autofluorescence associated with photoreceptor outer segments. These observations suggest the acidification produced by the nanoparticles was functionally effective. In summary, acid nanoparticles lead to a rapid and sustained lowering of lysosomal pH and improved degradative activity.
Highlights
While the propensity of nanoparticles to accumulate in lysosomes can frustrate many, they are ideally suited to treat lysosomal defects
While the effect of chloroquine was dose dependent over this range (Supplemental Figure S1), we have previously found 10 mM produces relatively constant effects on lysosomal pH without leading to cell death
Nanoparticles have great promise for drug delivery, but their delivery to the correct target is critical. This study turns their propensity for lysosomal accumulation into an advantage, and demonstrates that acidic nanoparticles can lower the pH of compromised lysosomes to improve degradative function
Summary
While the propensity of nanoparticles to accumulate in lysosomes can frustrate many, they are ideally suited to treat lysosomal defects. In this regard, the lysosomes of retinal pigment epithelial (RPE) cells represent a prime target. The elevated pH can impair the activity of hydrolytic enzymes such as cathepsin D and lysosomal acid lipase, leading to a decline in lysosomal degradative capacity [9,10,11]. Incomplete degradation of phagocytic and autophagic material leads to the accumulation of autofluorescent lipofuscin which itself is often associated with retinal degenerations [12,13,14]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
