Cytoprotective Effects of Brimonidine in an Induced Pluripotent Stem Cell (iPSC)-Derived Retinal Pigment Epithelium (RPE) Model of Age-Related Macular Degeneration (AMD)

Abstract

Purpose : Brimonidine (brimo) drug delivery system (DDS) has been evaluated as a long-acting therapy for the treatment of geographic atrophy (GA) secondary to AMD. Our objective was to delineate the role of brimo as a cytoprotective agent using a human iPSC-derived RPE in vitro model of dry AMD.

Methods : RPE cells were differentiated from iPSC derived from healthy or albino individuals. iPSC-RPE monolayers were matured for 6 to 8 weeks using a previously published protocol that supports the development of key RPE phenotypic features, including polarized expression of RPE specific markers and cytokine secretion, transepithelial potential and resistance, fluid transport and phagocytosis (Sharma et al., 2019). The effects of melanin binding were assessed by comparing supernatant and cell-associated brimo concentrations in pigmented versus albino iPSC-RPE. Pigmented iPSC-RPE were then challenged with complement-competent human serum (CC-HS) to mimic AMD-like conditions. Challenge with CC-HS induces loss of transepithelial resistance, disrupted RPE morphology and sub-RPE lipid deposition. These changes are characteristic to the phenotypic changes of the RPE in dry AMD. We assessed brimo’s ability to prevent CC-HS-induced phenotypic changes.

Results : Dose-dependent binding of brimo to melanin was observed in pigmented iPSC-RPE cells with 2- to 6-fold lower brimo concentrations in the supernatant after 24 hr incubation compared to albino RPE cells. No brimo-induced cytotoxicity was observed at concentrations up to 30 mM. Subsequent experiments were conducted at concentrations of 0.3 and 3 mM. Pretreatment of iPSC-RPE cells with brimo prevented CC-HS-induced transepithelial resistance reduction and deposition of lipid droplets. Further, we observed partial restoration of cyclic adenosine monophosphate (cAMP) and intracellular calcium levels in CC-HS-challenged iPSC-RPE cells treated with 3mM brimo. These data suggest that brimo has cytoprotective properties and preserves key functional RPE characteristics, restoring homeostatic mechanisms in cells challenged by an AMD-like insult.

Conclusions : In conclusion, our results demonstrate the cytoprotective effects of brimo in a validated model of complement-mediated RPE AMD-like physiology and support development of brimo drug delivery system (DDS) as a novel therapeutic for GA secondary to AMD.

This is a 2021 ARVO Annual Meeting abstract.