Targeted Demineralization of Sub-RPE Calcifications using Anti-Elastin DTPA-HSA Nanoparticles in a Progeroid Mouse Model
Frank Rutsch, Yvonne Nitschke, Theresa Begasse, Peter Heiduschka, Nicole Eter, Uwe Hansen, Joseph Deering, Marc Mckee, Klaus Langer
Affiliation(s):
Department Of General Pediatrics, Muenster University Children’s Hospital, Muenster, Germany And Intec, Center For Medical Genetics, Ghent, Belgium
Objective: Calcification of sub-retinal pigment epithelial (sub-RPE) deposits is strongly linked to retinal drusen biogenesis and accelerated progression of age-related macular degeneration (AMD). Despite its clinical significance, therapeutic options for AMD remain limited. In this study, we established a mouse model that recapitulates sub-RPE calcification to evaluate a novel, targeted drug delivery system designed to actively resolve these mineral deposits.
Methods: Ttw/ttw mice carrying a truncating mutation in Enpp1 received a high-phosphate diet to accelerate ectopic calcification. Eyes were studied by optical coherence tomography (OCT), fluorescein angiography, and retinal function by electroretinography (ERG). Eye calcification was examined by Alizarin red staining, X-ray microscopy, and electron microscopy. Mineral deposits were analyzed by energy-dispersive X-ray spectroscopy (EDS). Calcium content was chemically quantified by the O-cresolphthalein-complexon method. For treatment, the chelating agent diethylenetriaminepentaacetic acid (DTPA) was covalently bound to human serum albumin (HSA)-based nanoparticles (NPs). NP surface was modified by an anti-elastin antibody to target elastin in Bruch’s membrane (BM). NPs were injected twice per week at a concentration of 20 µg/g body weight starting from 10 weeks of age (4 injections in total) into the lateral tail vein of ttw/ttw mice.
Results: Calcified sub-RPE deposits were evident at 9 weeks of age in ttw/ttw mice fed a high-phosphate diet, and calcifications were more pronounced at 12 weeks of age. EDS confirmed the presence of calcium phosphate-rich mineral phases. Ocular calcifications were absent in wild type (WT) mice. Ttw/ttw mice with sub-RPE calcifications displayed decreased amplitudes of ERG a- and b-waves compared to control WT mice. Ocular calcium content in ttw/ttw mice treated with systemically administered NPs targeted to BM was equal to ocular calcium content in WT mice (Figure 1), suggesting resolution of sub-RPE calcifications in ttw/ttw mice.
Conclusion: In ttw/ttw mice, a high-phosphate diet induces calcified sub-RPE deposits that mimic key pathological features of AMD. To treat these calcifications, systemic delivery of DTPA-HSA-NPs — functionalized with antibodies targeting Bruch’s membrane elastin — shows significant therapeutic potential. This strategy will be further validated within the collaborative REPAIR (Regenerative application of nanoparticular substances to resolve retinal calcification) project, which explores the potential of nanoparticles to dissolve retinal mineral deposits through different applications.
