Diabetes is the most common metabolic disorder worldwide with millions suffering from its complications. Any individual with diabetes is at risk of developing diabetic retinopathy (DR), the most common microvascular complication of diabetes. DR is a leading cause of vision loss in working-aged individuals and cause to a great socioeconomic burden. While pan-retinal photocoagulation, intraocular steroid, and anti-VEGF treatments increased patient’s quality of life and visual outcomes, no cure is available at this time.Large-scale clinical trials such as the DCCT/EDIC, ACCORD Eye, WESDR, and the FIELD study outlined the advantageous role of controlling dyslipidemia in addition to glycemic control to treat DR. A combination of Statins and Fibrates significantly slowed the progression of DR over four years in the ACCORD Eye study. The underlying mechanism of how lipid-lowering agents elicit their beneficial effects remains unknown as positive effects on serum lipid levels did not correlate with advantageous DR outcomes. This thesis aimed to further study this paradox and the overall significance of dyslipidemia in DR pathogenesis by examining ocular cholesterol abnormalities and by exploring the impact of ceramides in DR to develop novel and advance current treatments. First, retinal cholesterol crystal (CC) deposition was identified as a unifying pathogenic mechanism causing DR progression. Lipid-lowering drugs such as statins, fibrates, and cyclodextrins were able to remove retinal CCs and rescue pathogenic outcomes in human and bovine cell culture models and db/db diabetic mice.Second, a small clinical study identified a pathological imbalance in increased long to decreased very long chain ceramides in the vitreous of PDR patients compared to healthy controls. Long-chain ceramides were identified to instigate ceramide-rich platform (CRP) formation in retinal endothelial cells (RECs) under diabetogenic conditions. CRP domains caused retinal inflammation and REC apoptosis. To functionally interfere with CRP formation, highly specific anti-ceramide antibodies targeting long-chain ceramides were employed. Anti-ceramide antibodies dispersed CRPs and rescued REC apoptosis. Intravitreal anti-ceramide antibodies rescued retinal inflammation and prevented retinal vascular permeability in a murine ischemia reperfusion model and streptozotocin induced diabetic rats. Systemic anti-ceramide antibody treatment rescued retinal inflammation and prevented retinal vascular permeability in a murine ischemia reperfusion model.Last, the ability of anti-ceramide antibodies to restore functional microvascular repair in DR was examined. CRP formation in circulating angiogenic cells (CACs) drove dysfunctional microvascular repair in streptozotocin induced diabetic mice through a decrease in CAC plasma membrane fluidity. Systemic anti-ceramide antibodies dispersed CRPs, restored CAC migration and vascular repair by rescuing plasma membrane fluidity. Multiple dose systemic anti-ceramide antibodies rescued CAC function and prevented retinal vascular permeability in streptozotocin induced diabetic mice. Conclusively, this thesis outlined the ocular crystallization of cholesterol and ceramide-rich platform formation in RECs and CACs to drive DR progression in diabetes. Lipid-lowering drugs and novel anti-ceramide antibodies were able to combat DR pathogenesis in cell culture and rodent models by intravitreal and systemic treatment methods respectively. These results give insights into early DR pathogenesis and how to tackle them. Strategies outlined in this thesis could readily applied be to the clinic and examined as potential novel therapeutics for DR.
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