Diabetes is one of the main risk factors for the development of cardiovascular disease. A central reason for this is the malfunctioning of the endothelial cells of the blood vessels, leading to vasoconstriction and inflammation. Recent evidence suggests that the enzyme arginase is essential for the regulation of endothelial function by modulating the production of nitric oxide and free oxygen radicals. In addition, our research has shown that arginase in red blood cells may play an important role in cardiovascular function during oxygen deprivation. Our hypothesis is that increased activity of arginase in the blood vessel wall and red blood cells in diabetes results in reduced formation of nitric oxide, increased radical formation and vascular damage. The goal is to identify the regulation of arginase and to improve cardiovascular function in diabetes through arginase inhibition. These questions will be addressed first in experimental disease models and then in clinical studies. In experimental studies, the role of arginase in blood vessels and red blood cells in the development of cardiovascular dysfunction under oxygen deprivation will be investigated. In patients with diabetes and vascular complications, the regulation and activity of arginase in blood vessels and red blood cells is being investigated. The effect of arginase blockade on vascular function is being studied in controlled clinical trials. The project may lead to new knowledge about disease mechanisms and new treatment options to improve cardiovascular function and prevent complications in diabetes.