EDN1 and diabetic retinopathy: Thus, TTAs are likely to exert antioxidative and antiproliferative effects on diabetic retinopathy and vasculopathy by suppression of the protein kinase C (PKC) and mitogen-activated protein kinase (MAPK) pathways and, indirectly, by suppressing the overexpression of ppET-1, ECE, ETA receptor and iNOS mRNA.