Background: In most developed countries, diabetic kidney disease is the most common cause of chronic kidney disease, leading to end-stage renal disease, and it is also associated with cardiovascular diseases, including heart failure, and a higher risk of other microvascular complications. A recent clinical trial indicated that the dipeptidyl peptidase-4 inhibitor linagliptin prevents the occurrence and progression of albuminuria in patients with type 2 diabetes. Thus, this study aimed to elucidate the molecular mechanism underlying the inhibitory effect of linagliptin on albuminuria in diabetic kidney disease. Methods: Control C57BL/6 mice and diabetic Ins2+/Akita mice were orally administered linagliptin (5 mg/kg/ day) every day for 8 weeks. Results: Compared to control mice, Ins2+/Akita mice had markedly elevated blood glucose and HbA1c levels, but there were no significant changes after linagliptin treatment. Furthermore, albuminuria and urinary 8-OHdG levels were significantly increased and glomerular mesangial area was significantly expanded in Ins2+/Akita mice compared to those in control mice; these changes were ameliorated by linagliptin treatment, which also improved the degradation of glomerular endothelial glycocalyx and enhancement of glomerular permeability of macromolecules. The activity of AMP-activated protein kinase and the expression of guanosine 5\u27-triphosphate cyclohydrolase I in human glomerular endothelial cells were significantly lower in high glucose conditions and were improved by linagliptin or GLP-1 administration. Discussion: These results together suggest that linagliptin reduced albuminuria in a blood glucose-independent manner via the reduction of oxidative stress and maintenance of the glycocalyx in endothelial cells. Thus, earlier treatment with linagliptin may slow the progression of diabetic kidney disease
