Abstract-The aim of this study was to explore the effects of the renin inhibitor aliskiren in streptozotocin-diabetic TG(mRen-2)27 rats. Furthermore, we investigated in vitro the effect of aliskiren on the interactions between renin and the (pro)renin receptor and between aliskiren and prorenin. Aliskiren distributed extensively to the kidneys of normotensive (non)diabetic rats, localizing in the glomeruli and vessel walls after 2 hours exposure. In diabetic TG(mRen-2)27 rats, aliskiren (10 or 30 mg/kg per day, 10 weeks) lowered blood pressure, prevented albuminuria, and suppressed renal transforming growth factor-␤ and collagen I expression versus vehicle. Aliskiren reduced (pro)renin receptor expression in glomeruli, tubules, and cortical vessels compared to vehicle (in situ hybridization). In human mesangial cells, aliskiren (0.1 mol/L to 10 mol/L) did not inhibit binding of 125 I-renin to the (pro)renin receptor, nor did it alter the activation of extracellular signal-regulated kinase 1/2 by renin (20 nmol/L) preincubated with aliskiren (100 nmol/L) or affect gene expression of the (pro)renin receptor. Evidence was obtained that aliskiren binds to the active site of prorenin. The above results demonstrate the antihypertensive and renoprotective effects of aliskiren in experimental diabetic nephropathy. The evidence that aliskiren can reduce in vivo gene expression for the (pro)renin receptor and that it may block prorenin-induced angiotensin generation supports the need for additional work to reveal the mechanism of the observed renoprotection by this renin inhibitor. Key Words: aliskiren Ⅲ renin inhibitor Ⅲ TG(mRen-2)rat Ⅲ diabetic nephropathy Ⅲ (pro)renin receptor A central role for the renin-angiotensin-aldosterone system (RAAS) in the pathogenesis of diabetic nephropathy (DN) is widely accepted, based largely on the attenuation of DN by angiotensin (Ang) converting enzyme inhibitors (ACEi) 1 and Ang II receptor blockers (ARB). 2 However, these agents do not halt renal decline, possibly because of insufficient suppression of the intrarenal RAAS. Theoretically, agents that more effectively suppress the RAAS should confer improved tissue protection over current treatments for DN. Renin inhibitors, by acting at the point of activation of the RAAS cascade, may represent such agents. Aliskiren is a potent inhibitor of human renin; it lowers blood pressure (BP) in patients with mild-moderate hypertension 3,4 and shows cardiorenal protection in hypertensive double transgenic rats expressing human genes for renin and angiotensinogen. 5

In this report we investigate the molecular mechanisms that contribute to tissue damage following ischemia and ischemia coupled with reperfusion (ischemia/ reperfusion) in the rat heart and kidney. We observe the activation of three stress-inducible mitogen-activated protein (MAP) kinases in these tissues: p38 MAP kinase and the 46-and 55-kDa isoforms of Jun N-terminal kinase (JNK 46 and JNK 55 ). The heart and kidney show distinct time courses in the activation of p38 MAP kinase during ischemia but no activation of either JNK 46 or JNK 55 . These two tissues also respond differently to ischemia/reperfusion. In the heart we observe activation of JNK 55 and p38 MAP kinase, whereas in the kidney all three kinases are active. We also examined the expression pattern of two stress-responsive genes, c-Jun and ATF3. Our results indicate that in the heart both genes are induced by ischemia and ischemia/reperfusion. However, in the kidney c-Jun and ATF3 expression is induced only by ischemia/reperfusion. To correlate these molecular events with tissue damage we examined DNA laddering, a common marker of apoptosis. A significant increase in DNA laddering was evident in both heart and kidney following ischemia/reperfusion and correlated with the pattern of kinase activation, supporting a link between stress kinase activation and apoptotic cell death in these tissues.

Background-Angiotensin