David Louis Feldman

Effects of Aliskiren on Blood Pressure, Albuminuria, and (Pro)Renin Receptor Expression in Diabetic TG(mRen-2)27 Rats

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-&bgr; 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 &mgr;mol/L to 10 &mgr;mol/L) did not inhibit binding of 125I-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.

Aliskiren, a Human Renin Inhibitor, Ameliorates Cardiac and Renal Damage in Double-Transgenic Rats

We tested the hypothesis that the renin inhibitor aliskiren ameliorates organ damage in rats transgenic for human renin and angiotensinogen genes (double transgenic rat [dTGR]). Six-week-old dTGR were matched by albuminuria (2 mg per day) and divided into 5 groups. Untreated dTGR were compared with aliskiren (3 and 0.3 mg/kg per day)-treated and valsartan (Val; 10 and 1 mg/kg per day)-treated rats. Treatment was from week 6 through week 9. At week 6, all groups had elevated systolic blood pressure (BP). Untreated dTGR showed increased BP (202±4 mm Hg), serum creatinine, and albuminuria (34±5.7 mg per day) at week 7. At week 9, both doses of aliskiren lowered BP (115±6 and 139±5 mm Hg) and albuminuria (0.4±0.1 and 1.6±0.6 mg per day) and normalized serum creatinine. Although high-dose Val lowered BP (148±4 mm Hg) and albuminuria (2.1±0.7 mg per day), low-dose Val reduced BP (182±3 mm Hg) and albuminuria (24±3.8 mg per day) to a lesser extent. Mortality was 100% in untreated dTGR and 26% in Val (1 mg/kg per day) treated rats, whereas in all other groups, survival was 100%. dTGR treated with low-dose Val had cardiac hypertrophy (4.4±0.1 mg/g), increased left ventricular (LV) wall thickness, and diastolic dysfunction. LV atrial natriuretic peptide and β-myosin heavy chain mRNA, albuminuria, fibrosis, and cell infiltration were also increased. In contrast, both aliskiren doses and the high-dose Val lowered BP to a similar extent and more effectively than low-dose Val. We conclude that in dTGR, equieffective antihypertensive doses of Val or aliskiren attenuated end-organ damage. Thus, renin inhibition compares favorably to angiotensin receptor blockade in reversing organ damage in dTGR.

Renin inhibition reduces hypercholesterolemia-induced atherosclerosis in mice

The role of the renin angiotensin system (RAS) in atherosclerosis is complex because of the involvement of multiple peptides and receptors. Renin is the rate-limiting enzyme in the production of all angiotensin peptides. To determine the effects of renin inhibition on atherosclerosis, we administered the novel renin inhibitor aliskiren over a broad dose range to fat-fed LDL receptor-deficient (Ldlr(-/-)) mice. Renin inhibition resulted in striking reductions of atherosclerotic lesion size in both the aortic arch and the root. Subsequent studies demonstrated that cultured macrophages expressed all components of the RAS. To determine the role of macrophage-derived angiotensin in the development of atherosclerosis, we transplanted renin-deficient bone marrow to irradiated Ldlr(-/-) mice and observed a profound decrease in the size of atherosclerotic lesions. In similar experiments, transplantation of bone marrow deficient for angiotensin II type 1a receptors failed to influence lesion development. We conclude that renin-dependent angiotensin production in macrophages does not act in an autocrine/paracrine manner. Furthermore, in vitro studies demonstrated that coculture with renin-expressing macrophages augmented monocyte adhesion to endothelial cells. Therefore, although previous work suggests that angiotensin peptides have conflicting effects on atherogenesis, we found that renin inhibition profoundly decreased lesion development in mice.

Renin inhibitors as novel treatments for cardiovascular disease

The renin–angiotensin system (RAS) plays an important role in the development of cardiovascular diseases such as hypertension and heart failure. Inhibitors of renin (EC 3.4.99.19) block the RAS at its first and rate-limiting step and may therefore offer major potential benefits in blood pressure control. Despite intensive research, however, previous attempts to develop clinically useful renin inhibitors have failed. This review discusses recent patent applications for the development of two novel classes of non-peptide renin inhibitors: 3-alkoxy-4-aryl-piperidines, such as Ro 66-1132 (Hoffmann-La Roche), and alkanecarboxamides, such as aliskiren (SPP-100; Novartis). Both classes are effective in animal models, while results from studies in humans suggest that aliskiren may represent the first in a new class of orally-effective renin inhibitors. Patents claiming the use of renin inhibitors in combination therapy are also discussed.

The Renin Rise With Aliskiren: It’s Simply Stoichiometry

To the Editor: With great interest we read Campbell’s1 interpretation of plasma renin concentration in patients receiving aliskiren. The renin rise appears to be larger than the rise observed during angiotensin (Ang)-converting enzyme inhibition or Ang II receptor blockade.2 Indeed, it has been suggested that this may lead to a rise in Ang II.2 However, neither a rise in Ang II nor the putative subsequent rise in blood pressure have been observed thus far,3 possibly because the apparent renin rise is attributable, at least partly, to an assay-related artifact, allowing prorenin to be detected as renin.3,4 Irrespective of the cause of this rise and whether the rise is exaggerated, an aspect that merits consideration is the renin-aliskiren stoichiometry. Is the number …

Low-dose renin inhibitor and low-dose AT1-receptor blocker therapy ameliorate target-organ damage in rats harbouring human renin and angiotensinogen genes

We studied the effects of extremely low-dose human renin inhibition (aliskiren) with low angiotensin II receptor blockade (losartan) in a novel double-transgenic rat model harbouring both human renin and angiotensinogen genes. We found that low-dose aliskiren and low-dose losartan effectively reduced mortality and target-organ damage with minimal, non-significant, effects on blood pressure (BP). Our data suggest that renin-angiotensin system (RAS) inhibition ameliorates target-organ damage in an Ang II-driven model of hypertension. Direct renin inhibition is equally efficacious in this regard. Our study does not fully answer the question of BP-lowering versus RAS inhibition. This question is important and was at least partially addressed with our low-dose model.

Enhanced expression of renal endothelin-converting enzyme-1 and endothelin-A-receptor mRNA in rats with interstitial fibrosis following ureter ligation.

Endothelin-1 (ET-1) has been implicated in many chronic renal glomerular diseases. The purpose of this study was to investigate whether the levels of mRNA expression of endothelin-converting enzyme-1 (ECE-1) and endothelin-A- and -B- (ET(A) and ET(B)) receptors are altered during the progression of interstitial fibrosis following ureter ligation. Rats were subjected to left ureter ligation or a sham operation and euthanized 5 days afterward. Kidneys were fixed in Carnoys fixative, embedded in paraffin, and sectioned for assessment of interstitial fibrosis by staining for collagen III using immunofluorescence techniques. The area occupied by collagen staining was quantified by image analysis. Kidneys from obstructed rats showed a 54% increase in the area occupied by collagen III staining compared to the contralateral kidney, and an 89% increase compared to sham-operated kidneys. The mRNA levels of ECE-1, as well as ET(A)- and ET(B)-receptors in the kidney were analyzed by Northern blots. It was found that the ECE-1 and ET(A)-receptor mRNA levels in kidneys subjected to ureter ligation increased by 92% and 71%, respectively, when compared with those obtained from the contralateral kidneys. In contrast, mRNA levels of ET(B)-receptors were not significantly different between the two groups. These results suggest that ET-1, through interaction with the ET(A)-receptors, may play a role in the progression of interstitial fibrosis following ureter ligation.

Direct Renin Inhibition Prevents Cardiac Dysfunction in a Diabetic Mouse Model: Comparison With an Angiotensin Receptor Antagonist and Angiotensin-Converting Enzyme Inhibitor.

Hyperglycaemia up-regulates intracellular AngII (angiotensin II) production in cardiac myocytes, effects of which are blocked more effectively by renin inhibition than ARBs (angiotensin receptor blockers) or ACEis (angiotensin-converting enzyme inhibitors). In the present study, we determined whether renin inhibition is more effective at preventing diabetic cardiomyopathy than an ARB or ACEi. Diabetes was induced in adult mice for 10 weeks by STZ (streptozotocin). Diabetic mice were treated with insulin, aliskiren (a renin inhibitor), benazeprilat (an ACEi) or valsartan (an ARB) via subcutaneous mini-pumps. Significant impairment in diastolic and systolic cardiac functions was observed in diabetic mice, which was completely prevented by all three RAS (renin-angiotensin system) inhibitors. Hyperglycaemia significantly increased cardiac oxidative stress and circulating inflammatory cytokines, which were blocked by aliskiren and benazeprilat, whereas valsartan was partially effective. Diabetes increased cardiac PRR (prorenin receptor) expression and nuclear translocation of PLZF (promyelocytic zinc finger protein), which was completely prevented by aliskiren and valsartan, and partially by benazeprilat. Renin inhibition provided similar protection of cardiac function to ARBs and ACEis. Activation of PLZF by PRR represented a novel mechanism in diabetic cardiomyopathy. Differential effects of the three agents on oxidative stress, cytokines and PRR expression suggested subtle differences in their mechanisms of action.

PKPD modelling of the interrelationship between mean arterial BP, cardiac output and total peripheral resistance in conscious rats

The homeostatic control of arterial BP is well understood with changes in BP resulting from changes in cardiac output (CO) and/or total peripheral resistance (TPR). A mechanism‐based and quantitative analysis of drug effects on this interrelationship could provide a basis for the prediction of drug effects on BP. Hence, we aimed to develop a mechanism‐based pharmacokinetic‐pharmacodynamic (PKPD) model in rats that could be used to characterize the effects of cardiovascular drugs with different mechanisms of action (MoA) on the interrelationship between BP, CO and TPR.

Renin Inhibition Reverses Renal Disease in Transgenic Mice by Shifting the Balance Between Profibrotic and Antifibrotic Agents

Aliskiren, a direct renin inhibitor, is a novel antihypertensive drug. To study whether aliskiren can reverse chronic kidney disease, we administered it to renin transgenic mice, a strain characterized by elevated blood pressure and a slow decline of renal function, mimicking well the progression of hypertensive chronic kidney disease. Ten-month-old transgenic mice were treated either with aliskiren or placebo for 28 days. Age-matched wild-type mice treated or not with aliskiren were considered as normotensive controls. Aliskiren reduced blood pressure to wild-type levels from as early as day 14. Proteinuria and cardiac hypertrophy and fibrosis were also normalized. Renal interstitial fibrosis and inflammation were significantly ameliorated in aliskiren-treated mice (shown by the decrease of proinflammatory and profibrotic markers), and the phenotypes of tubular epithelial cells and podocytes were restored as evidenced by the reappearance of cellular proteins characteristic of normal phenotype of these cells. Profibrotic p38 and Erk mitogen-activated protein kinases were highly activated in placebo-treated transgenic animals. Aliskiren treatment cancelled this activation. This nephroprotection was not attributed to the antihypertensive activity of aliskiren, because blood pressure normalization after treatment with hydralazine failed to induce the regression of renal fibrosis. Direct inhibition of renin can restore renal function and structure in aged hypertensive animals with existing proteinuria. This finding suggests that, in addition to antihypertensive action, aliskiren can be also used to treat chronic kidney disease.