REN and diabetic kidney disease: Among several pathogenetic mechanisms of diabetic nephropathy including advanced glycated end-product formation, an enhanced PKC pathway, the polyol pathway, the hexosamine pathway, and the renin-angiotensin (RA) system [10], oxidative stress plays an important role in the development of diabetic nephropathy, while the suppression of oxidative stress ameliorates renal damage [12–15].