Major role for ACE-independent intrarenal ANG II formation in type II diabetes

Am J Physiol Renal Physiol 298: F37-F48, 2010. First published October 21, 2009; doi: 10.1152/ajprenal.00519.2009.--Combination therapy of angiotensin-converting enzyme (ACE) inhibition and [AT.sub.1] receptor blockade has been shown to provide greater renoprotection than ACE inhibitor alone in human diabetic nephropathy, suggesting that ACE-independent pathways for ANG II formation are of major significance in disease progression. Studies were performed to determine the magnitude of intrarenal ACE-independent formation of ANG II in type II diabetes. Although renal cortical ACE protein activity [2.1 [+ or -] 0.8 vs. 9.2 [+ or -] 2.1 arbitrary fluorescence units (AFU) x [mg.sup.-1] x [min.sup.-1]] and intensity of immunohistochemical staining were significantly reduced and ACE2 protein activity (16.7 [+ or -] 3.2 vs. 7.2 [+ or -] 2.4 AFU x [mg.sup.-1] x [min.sup.-1]) and intensity elevated, kidney ANG I (113 [+ or -] 241 vs. 110 [+ or -] 45 fmol/g) and ANG II (1,017 [+ or -] 165 vs. 788 [+ or -] 99 fmol/g) levels were not different between diabetic and control mice. Afferent arteriole vasoconstriction due to conversion of ANG I to ANG II was similar in magnitude in kidneys of diabetic (-28 [+ or -] 3% at 1 [micro]M) and control (-23 [+ or -] 3% at 1 [micro]M) mice; a response completely inhibited by AT1 receptor blockade. In control kidneys, afferent arteriole vasoconstriction produced by ANG I was significantly attenuated by ACE inhibition, but not by serine protease inhibition. In contrast, afferent arteriole vasoconstriction produced by intrarenal conversion of ANG I to ANG II was significantly attenuated by serine protease inhibition, but not by ACE inhibition in diabetic kidneys. In conclusion, there is a switch from ACE-dependent to serine protease-dependent ANG II formation in the type II diabetic kidney. Pharmacological targeting of these serine protease-dependent pathways may provide further protection from diabetic renal vascular disease. afferent arteriole; juxtamedullary nephron; db/db mouse; angiotensin-converting enzyme; serine protease; angiotensinogen; angiotensin-converting enzyme 2