These mechanisms include hexosamine pathway, activation of protein kinase C, oxidative stress, pathological effects of the renin–angiotensin–aldosterone system (RAAS), advanced glycation end product (AGE) formation, inflammation and modification of circulating macromolecules, etc., which may influence not only the development of DR, but also the progress of atherosclerosis [35]. Here, REN is linked to atherosclerosis.