Olmesartan Induces Renoprotective Effects by Stimulating Angiotensin Type 2 Receptors and Reducing Oxidative Stress in Diabetic Nephropathy

BACKGROUND: Angiotensin receptor blockers reduce the progression of diabetic nephropathy primarily by inhibiting angiotensin type 1 (AT(1)) receptors. In the present study, we investigated the role of angiotensin type 2 (AT(2)) receptors on the renoprotective effects of olmesartan in diabetic nephropathy. METHODS: Six-week-old mice were treated with streptozotocin and divided into four groups: the OLM group (mice treated with olmesartan), the OLM+Ang II group (mice treated with olmesartan and angiotensin II), the OLM+PD group (mice treated with olmesartan and the AT(2) antagonist PD 123319), and the vehicle group. Nondiabetic mice were used as controls. We measured blood glucose levels and urinary excretions of albumin and 8-hydroxy-2'-deoxyguanosine (8-OHdG), which is a marker for oxidative stress. RESULTS: Although urinary albumin excretion in the OLM and OLM+Ang II groups showed a tendency to be reduced compared to the vehicle group, it was significantly lower compared to the OLM+PD group. Urinary excretion of 8-OHdG was also significantly lower in the OLM and OLM+Ang II groups compared to the OLM+PD group. CONCLUSIONS: In diabetic nephropathy, the renoprotective effects of olmesartan are due not only to the blockade of AT(1) receptors, but also to a reduction in oxidative stress via stimulation of AT(2) receptors.