Recent advances using pharmacotherapy greatly expand treatment options for diabetic retinopathy. Intravitreal anti-VEGF immunotherapy has proven to be effective in resolving both neovascular diabetic retinopathy (DR) and diabetic macular edema (DME). However, several large clinical studies reveal that about 40% of patients do not respond to anti-VEGF therapy. Moreover, anti- VEGF treatment is directed at the very late stage in the disease, when full reversal of retinal damage is difficult. Thus, finding novel strategies to cure this complication is paramount. The diabetic metabolic insult leading to retinal vascular degeneration involves initial endothelial cell damage due to low-grade chronic inflammation that is then inadequately repaired due to compromised availability and functionality of bone marrow derived circulating angiogenic cells (CACs). Normally migration to the site of endothelial injury and homing by CACs participates in the retinal vascular repair process. We previously demonstrated that bone marrow pathology with CAC dysfunction precedes and is necessary for retinal vascular degeneration in diabetes. The molecular metabolic link connecting both initial inflammation in the retina and dysfunctional CACs involves activation of acid sphingomyelinase (ASM), the central enzyme of sphingolipid signaling, converting sphingomyelin into pro-inflammatory and pro-apoptotic ceramide. Sphingomyelin is preferentially concentrated on the outer leaflet of the plasma membrane of all mammalian cells. Stress-induced ASM secretion leads to generation of ceramide therein. Once generated, ceramide, due to hydrophobic forces, hydrogen bonding and van der Waal forces, spontaneously coalesces into ceramide-rich platforms (0.5-5.0 mm diameter), macrodomains into which proteins insert and multimerize for the purpose of transmembrane signal transmission. The outcome of this process in retinal endothelial cells, is pro-inflammatory and apoptotic signaling. To intervene therapeutically in microvascular inflammation and apoptosis, our program developed a set of anti-ceramide antibodies. These antibodies are highly specific for ceramide and highly effective in binding monomeric ceramide generated on the surface of endothelial and other cells thereby preventing cytokine receptor clustering and pro-inflammatory and apoptotic signaling. The current application we will employ 6B5 anti-ceramide single chain variable fragment (scFv) to prevent endothelial cell activation and subsequent damage in the retina and to improve retinal vascular repair by correcting the function of bone marrow derived CACs.
Despite recent advances using pharmacotherapy that greatly expanded treatment options for diabetic retinopathy, the cure for this blinding complication is not yet achieved. We identified activation of ASM, the enzyme converting sphingomyelin into ceramide, as a key element affecting both diabetes-induced vascular damage and bone marrow derived circulating angiogenic cell mediated repair of retinal vasculature. This proposal will test therapeutic potential of functional inhibition of ceramide signaling using anti-ceramide immunotherapy.
