Novel Use of PLGA Microspheres to Create an Animal Model of Glaucoma with Progressive Neuroretinal Degeneration

Abstract

Progressive degeneration of neuroretinal tissue with maintained elevated intraocular pressure (IOP) to simulate chronic glaucoma was produced by intracameral injections of poly (lactic-co-glycolic) acid (PLGA) microspheres (Ms) in rat eyes. The right eye of 39 rats received different sizes of PLGA-Ms (2 µL suspension; 10% w/v): 14 with 38–20 µm Ms (Ms38/20 model) and 25 with 20–10 µm particles (Ms20/10 model). This novel glaucoma animal model was compared to the episcleral vein sclerosis (EPI) model (25 eyes). Injections were performed at baseline, two, four and six weeks. Clinical signs, IOP, retina and optic nerve thicknesses (using in vivo optical coherence tomography; OCT), and histological studies were performed. An IOP increment was observed in all three groups, however, the values obtained from the PLGA-Ms injection resulted lower with a better preservation of the ocular surface. In fact, the injection of Ms20/10 created a gentler, more progressive, and more sustained increase in IOP. This IOP alteration was correlated with a significant decrease in most OCT parameters and in histological ganglion-cell count for the three conditions throughout the eight-week follow-up. In all cases, progressive degeneration of the retina, retinal ganglion cells and optic nerve, simulating chronic glaucoma, was detected by OCT and corroborated by histological study. Results showed an alternative glaucoma model to the well-known episcleral vein model, which was simpler to perform, more reproducible and easier to monitor in vivo.

Chronic Glaucoma Using Biodegradable Microspheres to Induce Intraocular Pressure Elevation. Six-Month Follow-Up

“…To compare retinal morphological alterations between the Ms20/10 and EPI models, six rat eyes (3 LEs and 3 REs) for each glaucoma model were analyzed after 6 months of increased chronic IOP. A similar RGC loss was previously demonstrated in both models by using the Brn3a marker [ 20 ]. In this study, we performed a more exhaustive evaluation of the retina with different markers in order to analyze the aggressivity of each model.…”

“…Ms20/10 preparation was as described in [ 20 ]. The PLGA (D,L-lactide-co-glycolide) (50:50; inherent viscosity: 0.16–0.24 dL/g; Evonik España, Granollers, Spain) Ms were obtained using the oil-in-water (O/W) emulsion solvent extraction-evaporation technique.…”

“…Twenty-five rats received a 2 µL [ 20 , 22 ] PLGA Ms20/10 (10% w/v ) suspension injected into the anterior chamber of the right eye (RE) using a Hamilton ® syringe and glass micropipette via corneal superotemporal puncture, applied at baseline and biweekly for the first month and then once monthly until week 20. Thus, a total of 7 intraocular injections were performed in the study ( Figure 1 ).…”

“…Neuroretinal structures were studied with the Spectralis OCT device (Heidelberg ® Engineering, Heidelberg, Germany) and with a contact lens adapted to the rat cornea to obtain higher-quality recordings. It was performed at baseline and at weeks 8, 12, 18 and 24 after the start of the study, as earlier behavior had been evaluated in our previous paper [ 20 ]. Automatic segmentation protocols such as retina posterior pole (R), retinal nerve fiber layer (RNFL) and ganglion cell layer (GCL) were used.…”

“…For this purpose, we created a modified chronic glaucoma model through intracameral injection of biodegradable poly (co-lactic-glycolic acid) (PLGA) microspheres by using two different size fractions (10–20 µm and 20–38 µm). The 10–20 µm (Ms20/10 model) fraction was selected as the optimal range to promote a progressive and sustained increase in rat eye IOP over 8 weeks of follow-up [ 20 ]. This pre-trabecular model was compared with that produced by sclerosis of the aqueous humor outflow pathway [ 21 ].…”