Effect of angiotensin II type 1 receptor blocker on 12-lipoxygenase activity and slit diaphragm protein expression in type 2 diabetic rat glomeruli.

BACKGROUND: The 12-lipoxygenase (12-LO) and angiotensin II (Ang II) interaction plays an important role in diabetic nephropathy (DN). Proteinuria in DN is associated with decreased slit diaphragm proteins including nephrin and P-cadherin. Therefore, we investigated whether Ang II type 1 receptor (AT1) blocker (ARB) regulates 12-LO activity and slit diaphragm protein expression in diabetic rat glomeruli. METHOD: Glomeruli were isolated with the sieving method, and classified into small glomeruli (SG; 75-µm sieve) and large glomeruli (LG; 125-µm sieve). RESULTS: 12(S)-HETE, a lipid product of 12-LO, was increased by Ang II in the glomeruli. Infusion of 12(S)-HETE and Ang II significantly decreased nephrin expression in LG, but increased it in SG compared to control. Glomerular P-cadherin expression was reduced after Ang II and 12(S)-HETE treatment without differences between LG and SG. ARB did not influence glycemic levels but completely abolished the increases in 12(S)-HETE, AT1 expression, and proteinuria in diabetic rats. Nephrin expression was significantly reduced in LG but increased in SG in diabetic rats compared to control. P-cadherin expression decreased in both diabetic LG and SG. The abnormalities of nephrin and P-cadherin were partially but significantly reversed by ARB. CONCLUSION: ARB potentially ameliorates DN via the up-regulation of glomerular nephrin and P-cadherin expression through the inhibition of 12-LO activation in the glomeruli of rats with DN.