Abstract
Purpose :
The arginase isoforms (A1 & A2) are involved in the pathogenesis of diabetic retinopathy (DR) through a complex relationship with the endothelial and inducible forms of nitric oxide synthase (eNOS & iNOS), which compete with arginase for L-arginine, their common substrate. While eNOS produces nitric oxide to mediate vasodilation, iNOS is expressed under conditions of stress, mediating immune activation that perpetuates inflammation and oxidative stress. With the type 2 diabetic db/db mouse model, we investigated our hypothesis that administration of A1 will halt DR progression by reducing iNOS activity through depletion of L-arginine, thus limiting oxidative stress and inflammation.
Methods :
Pegylated arginase-1 (PEG-A1) or PEG-5000 (control) was given via intraperitoneal injection thrice weekly for two weeks (25 mg/kg/dose) in db/db mice between the ages of 16 and 24 weeks (n=11/group). Visual acuity and contrast sensitivity were assessed via Optokinetic tracking. Whole eyes, retinas, and plasma were collected, and globes sectioned for immunofluorescence (IF). IF was performed for A1, markers of inflammation and oxidative stress including IL-6, 3-nitrotyrosine (3-NT), and 4HNE, and for vascular tight junction protein ZO-1. Retina lysates were used to western blot for inflammasome proteins, oxidative stress products, inflammation, and hypoxia, including A1, A2, iNOS, IL-1β, TNF-α, and 4-HNE. Data was analyzed via unpaired t-tests and values of p<0.05 were considered significant.
Results :
Untreated db/db mice exhibited impaired visual acuity (p<0.01), higher visual contrast sensitivity thresholds (p<0.05), marked elevation in retinal A1 (p<0.001), iNOS (p<0.05), IL-1β (p<0.05), and 4HNE (p<0.01), and increased retinal albumin extravasation (p<0.0001) compared to lean controls. PEG-A1 treatment significantly improved visual acuity (p<0.01), visual contrast sensitivity (p<0.05), and reduced iNOS (p<0.01), 3-NT (p<0.05), 4HNE (p<0.01), IL-1β (p<0.01), and TNF-α expression (p<0.05) in db/db mice compared to controls. Additionally, ZO-1 integrity was increased (p<0.05) and albumin leakage decreased (p<0.05) in retinas of PEG-A1 treated db/db mice.
Conclusions :
Systemic PEG-A1 administration in db/db mice resulted in improved visual function, increased blood-retinal-barrier integrity, and reduced inflammation and oxidative stress compared to PEG-5000 controls.
This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.