Beneficial cardiac effects of the renin inhibitor aliskiren in spontaneously hypertensive rats

Angiotensin-(1-12): Does It Exist? A Critical Evaluation in Humans, Rats, and Mice

BACKGROUND

Angiotensin-(1-12), measured by a self-developed, polyclonal antibody-based radioimmunoassay, has been suggested to act as an alternative precursor of angiotensin II. A more reliable detection method would be liquid chromatography-tandem mass spectrometry.

METHODS

We set up the quantification of human and murine angiotensin-(1-12) by liquid chromatography-tandem mass spectrometry and then used this method to measure angiotensin-(1-12) in human, rat, and mouse blood samples, as well as in mouse brain, mouse kidney, and rat heart. We also verified ex vivo angiotensin-(1-12) generation and metabolism in human blood samples incubated at 37 °C.

RESULTS

Stabilization of blood in guanidine hydrochloride was chosen for sample collection since this allowed full recovery of spiked angiotensin-(1-12). Angiotensin-(1-12) was undetectable in human blood samples when incubating nonstabilized plasma at 37 °C, while angiotensin-(1-12) added to nonstabilized human plasma disappeared within 10 minutes. Stabilized human blood samples contained angiotensin II, while angiotensin-(1-12) was undetectable. Blood, hearts, and kidneys, but not brains, of wild-type mice and rats contained detectable levels of angiotensin II, while angiotensin-(1-12) was undetectable. In renin knockout mice, all angiotensins, including angiotensin-(1-12), were undetectable at all sites, despite a 50% rise in angiotensinogen. Angiotensin-(1-12) metabolism in human blood plasma was not affected by renin inhibition. Yet, blockade of angiotensin-converting enzyme and aminopeptidase A, but not of chymase, neutral endopeptidase, or prolyl oligopeptidase, prolonged the half-life of angiotensin-(1-12), and angiotensin-converting enzyme inhibition prevented the formation of angiotensin II.

CONCLUSIONS

We were unable to detect intact angiotensin-(1-12) in humans, rats, and mice, either in blood or tissue, suggesting that this metabolite is an unlikely source of endogenous angiotensins.

Blood pressure-independent renoprotective effects of small interference RNA targeting liver angiotensinogen in experimental diabetes

BACKGROUND AND PURPOSE

Small interfering RNA (siRNA) targeting liver angiotensinogen lowers blood pressure, but its effects in hypertensive diabetes are unknown.

EXPERIMENTAL APPROACH

To address this, TGR (mRen2)27 rats (angiotensin II-dependent hypertension model) were made diabetic with streptozotocin over 18 weeks and treated with either vehicle, angiotensinogen siRNA, the AT₁ antagonist valsartan, the ACE inhibitor captopril, valsartan + siRNA or valsartan + captopril for the final 3 weeks. Mean arterial pressure (MAP) was measured via radiotelemetry.

KEY RESULTS

MAP before treatment was 153 ± 2 mmHg. Diabetes resulted in albuminuria, accompanied by glomerulosclerosis and podocyte effacement, without a change in glomerular filtration rate. All treatments lowered MAP and cardiac hypertrophy, and the largest drop in MAP was observed with siRNA + valsartan. Treatment with siRNA lowered circulating angiotensinogen by >99%, and the lowest circulating angiotensin II and aldosterone levels occurred in the dual treatment groups. Angiotensinogen siRNA did not affect renal angiotensinogen mRNA expression, confirming its liver-specificity. Furthermore, only siRNA with or without valsartan lowered renal angiotensin I. All treatments lowered renal angiotensin II and the reduction was largest (>95%) in the siRNA + valsartan group. All treatments identically lowered albuminuria, whereas only siRNA with or without valsartan restored podocyte foot processes and reduced glomerulosclerosis.

CONCLUSION AND IMPLICATIONS

Angiotensinogen siRNA exerts renoprotection in diabetic TGR (mRen2)27 rats and this relies, at least in part, on the suppression of renal angiotensin II formation from liver-derived angiotensinogen. Clinical trials should now address whether this is also beneficial in human diabetic kidney disease.

Conventional Vasopressor and Vasopressor-Sparing Strategies to Counteract the Blood Pressure-Lowering Effect of Small Interfering RNA Targeting Angiotensinogen

Background

A single dose of small interfering RNA (siRNA) targeting liver angiotensinogen eliminates hepatic angiotensinogen and lowers blood pressure. Angiotensinogen elimination raises concerns for clinical application because an angiotensin rise is needed to maintain perfusion pressure during hypovolemia. Here, we investigated whether conventional vasopressors can raise arterial pressure after angiotensinogen depletion.

Methods and Results

Spontaneously hypertensive rats on a low‐salt diet were treated with siRNA (10 mg/kg fortnightly) for 4 weeks, supplemented during the final 2 weeks with fludrocortisone (6 mg/kg per day), the α‐adrenergic agonist midodrine (4 mg/kg per day), or a high‐salt diet (all groups n=6–7). Pressor responsiveness to angiotensin II and norepinephrine was assessed before and after siRNA administration. Blood pressure was measured via radiotelemetry. Depletion of liver angiotensinogen by siRNA lowered plasma angiotensinogen concentrations by 99.2±0.1% and mean arterial pressure by 19 mm Hg. siRNA‐mediated blood pressure lowering was rapidly reversed by intravenous angiotensin II or norepinephrine, or gradually reversed by fludrocortisone or high salt intake. Midodrine had no effect. Unexpectedly, fludrocortisone partially restored plasma angiotensinogen concentrations in siRNA‐treated rats, and nearly abolished plasma renin concentrations. To investigate whether this angiotensinogen originated from nonhepatic sources, fludrocortisone was administered to mice lacking hepatic angiotensinogen. Fludrocortisone did not increase angiotensinogen in these mice, implying that the rise in angiotensinogen in the siRNA‐treated rats must have depended on the liver, most likely reflecting diminished cleavage by renin.

Conclusions

Intact pressor responsiveness to conventional vasopressors provides pharmacological means to regulate the blood pressure–lowering effect of angiotensinogen siRNA and may support future therapeutic implementation of siRNA.

Kidney Angiotensin in Cardiovascular Disease: Formation and Drug Targeting

The concept of local formation of angiotensin II in the kidney has changed over the last 10-15 years. Local synthesis of angiotensinogen in the proximal tubule has been proposed, combined with prorenin synthesis in the collecting duct. Binding of prorenin via the so-called (pro)renin receptor has been introduced, as well as megalin-mediated uptake of filtered plasma-derived renin-angiotensin system (RAS) components. Moreover, angiotensin metabolites other than angiotensin II [notably angiotensin-(1-7)] exist, and angiotensins exert their effects via three different receptors, of which angiotensin II type 2 and Mas receptors are considered renoprotective, possibly in a sex-specific manner, whereas angiotensin II type 1 (AT1) receptors are believed to be deleterious. Additionally, internalized angiotensin II may stimulate intracellular receptors. Angiotensin-converting enzyme 2 (ACE2) not only generates angiotensin-(1-7) but also acts as coronavirus receptor. Multiple, if not all, cardiovascular diseases involve the kidney RAS, with renal AT1 receptors often being claimed to exert a crucial role. Urinary RAS component levels, depending on filtration, reabsorption, and local release, are believed to reflect renal RAS activity. Finally, both existing drugs (RAS inhibitors, cyclooxygenase inhibitors) and novel drugs (angiotensin receptor/neprilysin inhibitors, sodium-glucose cotransporter-2 inhibitors, soluble ACE2) affect renal angiotensin formation, thereby displaying cardiovascular efficacy. Particular in the case of the latter three, an important question is to what degree they induce renoprotection (e.g., in a renal RAS-dependent manner). This review provides a unifying view, explaining not only how kidney angiotensin formation occurs and how it is affected by drugs but also why drugs are renoprotective when altering the renal RAS. SIGNIFICANCE STATEMENT: Angiotensin formation in the kidney is widely accepted but little understood, and multiple, often contrasting concepts have been put forward over the last two decades. This paper offers a unifying view, simultaneously explaining how existing and novel drugs exert renoprotection by interfering with kidney angiotensin formation.

Renoprotective Effects of Small Interfering RNA Targeting Liver Angiotensinogen in Experimental Chronic Kidney Disease

[Figure: see text].

No evidence for brain renin-angiotensin system activation during DOCA-salt hypertension

Brain renin-angiotensin system (RAS) activation is thought to mediate deoxycorticosterone acetate (DOCA)-salt hypertension, an animal model for human primary hyperaldosteronism. Here, we determined whether brainstem angiotensin II is generated from locally synthesized angiotensinogen and mediates DOCA-salt hypertension. To this end, chronic DOCA-salt-hypertensive rats were treated with liver-directed siRNA targeted to angiotensinogen, the angiotensin II type 1 receptor antagonist valsartan, or the mineralocorticoid receptor antagonist spironolactone (n = 6-8/group). We quantified circulating angiotensinogen and renin by enzyme-kinetic assay, tissue angiotensinogen by Western blotting, and angiotensin metabolites by LC-MS/MS. In rats without DOCA-salt, circulating angiotensin II was detected in all rats, whereas brainstem angiotensin II was detected in 5 out of 7 rats. DOCA-salt increased mean arterial pressure by 19 ± 1 mmHg and suppressed circulating renin and angiotensin II by >90%, while brainstem angiotensin II became undetectable in 5 out of 7 rats (<6 fmol/g). Gene silencing of liver angiotensinogen using siRNA lowered circulating angiotensinogen by 97 ± 0.3%, and made brainstem angiotensin II undetectable in all rats (P<0.05 vs. non-DOCA-salt), although brainstem angiotensinogen remained intact. As expected for this model, neither siRNA nor valsartan attenuated the hypertensive response to DOCA-salt, whereas spironolactone normalized blood pressure and restored brain angiotensin II together with circulating renin and angiotensin II. In conclusion, despite local synthesis of angiotensinogen in the brain, brain angiotensin II depended on circulating angiotensinogen. That DOCA-salt suppressed circulating and brain angiotensin II in parallel, while spironolactone simultaneously increased brain angiotensin II and lowered blood pressure, indicates that DOCA-salt hypertension is not mediated by brain RAS activation.

An overview of the classical and tissue-derived renin-angiotensin-aldosterone system and its genetic polymorphisms in essential hypertension

The renin-angiotensin-aldosterone system (RAAS) is a specific hormonal cascade implicated in the blood pressure control and sodium balance regulation. Several components of this pathway have been identified including renin, angiotensinogen, angiotensin-converting enzyme, angiotensins with a wide range of distinct subtypes and receptors, and aldosterone. The RAAS is not only confined to the systemic circulation but also exists locally in specific tissues such as the heart, brain, and blood vessels with a particular paracrine action. Alteration of RAAS function can contribute to the development of hypertension and the emergence of its associated end-organ damage. Genotypic variations of the different genes of RAAS cascade have been linked to the susceptibility to essential hypertension. Accordingly, to understand the pathogenesis of essential hypertension and its related complications, deep insight into the physiological and genetic aspects of RAAS with its different components and pathways is necessary. In this review, we aimed to illustrate the physiological and genetic aspects of RAAS and the underlying mechanisms which link this system to the predisposition to essential hypertension.

Effect of direct renin inhibition on vascular function after long-term treatment with aliskiren in hypertensive and diabetic patients

OBJECTIVE

We tested the hypothesis that chronic treatment with the direct renin inhibitor aliskiren improves vascular function in resistance and conduit arteries of type two diabetic and hypertensive patients.

METHOD

Sixteen patients with mild essential hypertension and with a previous diagnosis of noninsulin-dependent diabetes mellitus were included in the study. Patients were then randomized to aliskiren (150 mg once daily, n = 9), or ramipril (5 mg once daily, n = 7). Each patient underwent a biopsy of the subcutaneous tissue and small arteries were dissected and mounted on a pressurized micromyograph to evaluate endothelium dependent vasorelaxation in response to acetylcholine ± N omega-nitro-L-arginine methyl ester hydrochloride in vessels precontracted with norepinephrine. Endothelial function has been quantified also in large conduit arteries by flow-mediated dilation.

RESULTS

A similar office blood pressure-lowering effect was observed with the two drugs, although changes in DBP were not statistically significant in the ramipril group. Aliskiren significantly improved endothelium-dependent relaxation in subcutaneous resistance arteries, as well as increased flow-mediated dilation in conduit arteries, whereas the effects induced by ramipril did not reach statistical significance. Only aliskiren significantly increased the expression of p1177-endothelial nitric oxide synthase in the endothelium. Both aliskiren and ramipril had a negligible effect on markers of oxidative stress.

CONCLUSION

Aliskiren restored endothelial function and induced a more prompt peripheral vasodilation in hypertensive and diabetic patients possibly through the increased production of nitric oxide via the enhanced expression and function of the active phosphorylated form of endothelial nitric oxide synthase.

Aliskiren improves renal morphophysiology and inflammation in Wistar rats with 2K1C renovascular hypertension

Hypertension is characterized by persistent elevated blood pressure levels, one of the leading causes of death in the world. Renovascular hypertension represents the most common cause of secondary hypertension, and its progress is associated with overactivation of the renin angiotensin aldosterone system (RAAS), causing systemic and local changes. Aliskiren is a renin-inhibiting drug that optimizes RAAS suppression. In this sense, the objective of the present study was to analyze the morphophysiology of the left kidney in Wistar rats with renovascular hypertension after treatment with Aliskiren. Parameters such as systolic blood pressure, urinary creatinine and protein excretion, renal cortex structure and ultrastructure, fibrosis and tissue inflammation were analyzed. Our results showed that the hypertensive animals treated with Aliskiren presented a reestablishment of blood pressure, expression of renin, and renal function, as well as a remodeling of morphological alterations through the reduction of fibrosis. The treatment regulated the laminin expression and decreased pro-inflammatory cytokines, restoring the integrity of the glomerular filtration barrier. Therefore, our findings suggest that Aliskiren has a renoprotective effect acting on the improvement of the morphology, physiology and pathology of the renal cortex of animals with renovascular hypertension.

The renin-angiotensin-aldosterone system and its therapeutic targets

The renin-angiotensin-aldosterone system (RAAS) plays a pivotal role in the regulation of blood pressure and body fluid homeostasis and is a mainstay for the treatment of cardiovascular and renal diseases. Angiotensin II and aldosterone are the two most powerful biologically active products of the RAAS, inducing all of the classical actions of the RAAS including vasoconstriction, sodium retention, tissue remodeling and pro-inflammatory and pro-fibrotic effects. In recent years, new components of the RAAS have been discovered beyond the classical pathway that have led to the identification of depressor or so-called protective RAAS pathways and the development of novel therapies targeting this system. Moreover, dual inhibitors which block the RAAS and other systems involved in the regulation of blood pressure or targeting upstream of angiotensin II by selectively deleting liver-derived angiotensinogen, the precursor to all angiotensins, may provide superior treatment for cardiovascular and renal diseases and revolutionize RAAS-targeting therapy.

Revisiting the Brain Renin-Angiotensin System-Focus on Novel Therapies

Purpose of Review

Although an independent brain renin-angiotensin system is often assumed to exist, evidence for this concept is weak. Most importantly, renin is lacking in the brain, and both brain angiotensinogen and angiotensin (Ang) II levels are exceptionally low. In fact, brain Ang II levels may well represent uptake of circulating Ang II via Ang II type 1 (AT₁) receptors.

Recent Findings

Nevertheless, novel drugs are now aimed at the brain RAS, i.e., aminopeptidase A inhibitors should block Ang III formation from Ang II, and hence diminish AT₁ receptor stimulation by Ang III, while AT₂ and Mas receptor agonists are reported to induce neuroprotection after stroke. The endogenous agonists of these receptors and their origin remain unknown.

Summary

This review addresses the questions whether independent angiotensin generation truly occurs in the brain, what its relationship with the kidney is, and how centrally acting RAS blockers/agonists might work.

Mycophenolate Mofetil Attenuates DOCA-Salt Hypertension: Effects on Vascular Tone

Inflammation is increasingly recognized as a driver of hypertension. Both genetic and pharmacological inhibition of B and T cells attenuates most forms of experimental hypertension. Accordingly, the immunosuppressive drug mycophenolate mofetil (MMF) reduces blood pressure in the deoxycorticosterone acetate (DOCA-) salt model. However, the mechanisms by which MMF prevent hypertension in the DOCA-salt model remain unclear. Recent studies indicate that immunosuppression can inhibit sodium transporter activity in the kidney, but its effect on vascular tone is not well characterized. Therefore, the aim of the present study was to analyze the vascular and renal tubular effects of MMF in the DOCA-salt model in rats (4 weeks without uninephrectomy). Co-treatment with MMF attenuated the rise in blood pressure from day 11 onward resulting in a significantly lower telemetric mean arterial pressure after 4 weeks of treatment (108 ± 7 vs. 130 ± 9 mmHg, P < 0.001 by two-way analysis of variance). MMF significantly reduced the number of CD3⁺ cells in kidney cortex and inner medulla, but not in outer medulla. In addition, MMF significantly reduced urinary interferon-γ excretion. Vascular tone was studied ex vivo using wire myographs. An angiotensin II type 2 (AT₂) receptor antagonist blocked the effects of angiotensin II (Ang II) only in the vehicle group. Conversely, L-NAME significantly increased the Ang II response only in the MMF group. An endothelin A receptor blocker prevented vasoconstriction by endothelin-1 in the MMF but not in the vehicle group. MMF did not reduce the abundances of the kidney sodium transporters NHE3, NKCC2, NCC, or ENaC. Together, our ex vivo results suggest that DOCA-salt induces AT₂ receptor-mediated vasoconstriction. MMF prevents this response and increases nitric oxide availability. These data provide insight in the antihypertensive mechanism of MMF and the role of inflammation in dysregulating vascular tone.

Aliskiren Improves Ischemia- and Oxygen Glucose Deprivation-Induced Cardiac Injury through Activation of Autophagy and AMP-Activated Protein Kinase

Aliskiren is a direct renin inhibitor that has been effective in anti-hypertension. We investigated whether aliskiren could improve the ischemia-induced cardiac injury and whether the autophagy was involved in this effect. A myocardial infarction (MI) model was created by the ligation of the left anterior coronary artery in C57J/BL6 mice. They were treated for 1, 3, 7, and 14 days with vehicle or aliskiren (25 mg/kg/day via subcutaneous injection). In vivo, the MI mice exhibited worse cardiac function by echocardiographic assessment and showed larger myocardial scarring by light microscopy, whereas aliskiren treatment reversed these effects, which were also associated with the changes in caspase-3 and Bcl-2 expression as well as in the number of apoptotic cells. Aliskiren increased autophagy, as demonstrated by LC3B-II expression and transmission electron microscopy. Furthermore, H9c2 cardiomyocytes were employed as an in vitro model to examine the effects of aliskiren on apoptosis and autophagy under oxygen glucose deprivation (OGD)-induced injury. Aliskiren significantly increased cell viability in a dose-dependent manner. The beneficial effects of aliskiren were associated with decreased apoptosis and mitochondrial membrane potential as well as increased autophagy via increased autophagosome formation. We also found that aliskiren-induced cardiomyocyte survival occurred via AMP-activated protein kinase (AMPK)-dependent autophagy. Taken together, these results indicated that aliskiren increased cardiomyocyte survival through increased autophagosomal formation and decreased apoptosis and necrosis via modulating AMPK expression. AMPK-dependent autophagy may represent a novel mechanism for aliskiren in ischemic cardiac disease therapy.

Beneficial Effects of Combined AT1 Receptor/Neprilysin Inhibition (ARNI) Versus AT1 Receptor Blockade Alone in the Diabetic Eye

Purpose

Dysfunction of the renin-angiotensin system (RAS) contributes to pathogenesis of diabetic retinopathy (DR). Yet RAS blockers have only limited beneficial effects on progression of DR in clinical trials. The natriuretic peptide system offsets RAS, so that enhancing the activity of this system on top of RAS blockade might be beneficial. Neprilysin has an important role in the degradation of natriuretic peptides. Therefore, we hypothesize that dual angiotensin receptor-neprilysin inhibition (ARNI) may outperform angiotensin receptor blocker (ARB) in protection against DR. We tested this hypothesis in streptozotocin-induced diabetic transgenic (mRen2)27 rats.

Methods

Adult male diabetic (mRen2)27 rats were followed for 5 or 12 weeks. Treatment with vehicle, irbesartan (ARB), or ARB combined with the neprilysin inhibitor thiorphan (irbesartan+thiorphan [ARNI]) occurred during the final 3 weeks. Retinal cell death, gliosis, and capillary loss were evaluated. Real-time polymerase chain reaction (RT-PCR) analyses were performed to quantify the retinal level of inflammatory cell markers.

Results

Both ARB- and ARNI-treated groups showed similarly reduced retinal apoptotic cell death, gliosis, and capillary loss compared to the vehicle-treated group in the 5-week study. Treatment with ARNI reduced the expression of inflammatory markers more than ARB treatment in the 5-week study. In the 12-week study, ARNI treatment showed significantly more reduction in apoptotic cell death (51% vs. 25% reduction), and capillary loss (68% vs. 43% reduction) than ARB treatment.

Conclusions

Treatment with ARNI provides better protection against DR in diabetic (mRen2)27 transgenic rats, compared to ARB alone. This approach may be a promising treatment option for patients with DR.

Maximum renal responses to renin inhibition in healthy study participants: VTP-27999 versus aliskiren

BACKGROUND

Renin inhibition with aliskiren induced the largest increases in renal plasma flow (RPF) in salt-depleted healthy volunteers of all renin-angiotensin system (RAS) blockers. However, given its side-effects at doses higher than 300 mg, no maximum effect of renin inhibition could be established. We hypothesized that VTP-27999, a novel renin inhibitor without major side-effects at high doses, would allow us to establish this.

METHODS AND RESULTS

The effects of escalating VTP-27999 doses (75-600 mg) on RPF, glomerular filtration rate (GFR), and plasma RAS components were compared with those of 300 mg aliskiren in 22 normal volunteers on a low-sodium diet. VTP-27999 dose-dependently increased RPF and GFR; its effects on both parameters at 600 mg (increases of 18 ± 4 and 20 ± 4%, respectively) were equivalent to those at 300 mg, indicating that a maximum had been reached. The effects of 300 mg aliskiren (increases of 13 ± 5 and 8 ± 6%, respectively; P < 0.01 vs. 300 and 600 mg VTP-27999) resembled those of 150 mg VTP-27999. VTP-27999 dose-dependently increased renin, and lowered plasma renin activity and angiotensin II to detection limit levels. The effects of aliskiren on RAS components were best comparable to those of 150 mg VTP-27999.

CONCLUSION

Maximum renal renin blockade in healthy, salt-depleted volunteers, requires aliskiren doses higher than 300 mg, but can be established with 300 mg VTP-27999. To what degree such maximal effects (exceeding those of angiotensin-converting enzyme inhibitors and AT1-receptor blockers) are required in patients with renal disease, given the potential detrimental effects of excessive RAS blockade, remains to be determined.

AT1-receptor blockade, but not renin inhibition, reduces aneurysm growth and cardiac failure in fibulin-4 mice

AIMS

Increasing evidence supports a role for the angiotensin II-AT1-receptor axis in aneurysm development. Here, we studied whether counteracting this axis via stimulation of AT2 receptors is beneficial. Such stimulation occurs naturally during AT1-receptor blockade with losartan, but not during renin inhibition with aliskiren.

METHODS AND RESULTS

Aneurysmal homozygous fibulin-4 mice, displaying a four-fold reduced fibulin-4 expression, were treated with placebo, losartan, aliskiren, or the β-blocker propranolol from day 35 to 100. Their phenotype includes cystic media degeneration, aortic regurgitation, left ventricular dilation, reduced ejection fraction, and fractional shortening. Although losartan and aliskiren reduced hemodynamic stress and increased renin similarly, only losartan increased survival. Propranolol had no effect. No drug rescued elastic fiber fragmentation in established aneurysms, although losartan did reduce aneurysm size. Losartan also increased ejection fraction, decreased LV diameter, and reduced cardiac pSmad2 signaling. None of these effects were seen with aliskiren or propranolol. Longitudinal micro-CT measurements, a novel method in which each mouse serves as its own control, revealed that losartan reduced LV growth more than aneurysm growth, presumably because the heart profits both from the local (cardiac) effects of losartan and its effects on aortic root remodeling.

CONCLUSION

Losartan, but not aliskiren or propranolol, improved survival in fibulin-4 mice. This most likely relates to its capacity to improve structure and function of both aorta and heart. The absence of this effect during aliskiren treatment, despite a similar degree of blood pressure reduction and renin-angiotensin system blockade, suggests that it might be because of AT2-receptor stimulation.

Anti-diabetic and renoprotective effects of aliskiren in streptozotocin-induced diabetic nephropathy in female rats

Since chronic kidney disease due to diabetic nephropathy (DN) is becoming an ever larger health burden worldwide, more effective therapies are desperately needed. In the present study, the anti-diabetic and renoprotective effects of aliskiren have been evaluated in streptozotocin (STZ)-induced DN in rats. DN was induced by a single intraperitoneal injection of STZ (65 mg/kg). Three weeks after STZ, rats were divided into four groups; normal, diabetic, diabetic treated with gliclazide (10 mg/kg/day) for 1 month, and diabetic treated with aliskiren (50 mg/kg/day) for 1 month. At the end of the experiment, mean arterial blood pressure and heart rate were recorded. Rats were then euthanized and serum was separated for determination of glucose, insulin, kidney function tests, superoxide dismutase activity (SOD), adiponectin, and tumor necrosis factor-alpha (TNF-α). One kidney was used for estimation of malondialdehyde (MDA), reduced glutathione (GSH), and nitric oxide (NO) contents. Other kidney was used for histopathological study and immunohistochemical measurement of caspase-3 and transforming growth factor beta (TGF-β). In addition, islets of Langerhans were isolated from normal rats by collagenase digestion technique for in vitro study. Aliskiren normalized STZ-induced hyperglycemia, increased insulin level both in vivo and in vitro, normalized kidney function tests and blood pressure, and alleviated STZ-induced kidney histopathological changes. This could be related to the ability of aliskiren toward preserving hemodynamic changes and alleviating oxidative stress and inflammatory and apoptotic markers induced by STZ in rats. However, aliskiren was more effective than gliclazide in relieving STZ-induced DN. These findings support the beneficial effect of aliskiren treatment in DN which could be attributed to its anti-diabetic, renoprotective, antioxidant, anti-inflammatory, and anti-apoptotic effects. Moreover, clinical studies are required to establish the effectiveness of aliskiren treatment in patients suffering from hypertension and diabetes.

Blood pressure-independent renoprotection in diabetic rats treated with AT1 receptor-neprilysin inhibition compared with AT1 receptor blockade alone

ARNI [dual AT1 (angiotensin II type 1) receptor-neprilysin inhibition] exerts beneficial effects on blood pressure and kidney function in heart failure, compared with ARB (AT1 receptor blockade) alone. We hypothesized that ARNI improves cardiac and kidney parameters in diabetic TGR(mREN2)27 rats, an angiotensin II-dependent hypertension model. Rats were made diabetic with streptozotocin for 5 or 12 weeks. In the final 3 weeks, rats were treated with vehicle, irbesartan (ARB) or irbesartan+thiorphan (ARNI). Blood pressure, measured by telemetry in the 5-week group, was lowered identically by ARB and ARNI. The heart weight/tibia length ratio in 12-week diabetic animals was lower after ARNI compared with after ARB. Proteinuria and albuminuria were observed from 8 weeks of diabetes onwards. ARNI reduced proteinuria more strongly than ARB, and a similar trend was seen for albuminuria. Kidneys of ARNI-treated animals showed less severe segmental glomerulosclerosis than those of ARB-treated animals. After 12 weeks, no differences between ARNI- and ARB-treated animals were found regarding diuresis, natriuresis, plasma endothelin-1, vascular reactivity (acetylcholine response) or kidney sodium transporters. Only ARNI-treated rats displayed endothelin type B receptor-mediated vasodilation. In conclusion, ARNI reduces proteinuria, glomerulosclerosis and heart weight in diabetic TGR(mREN2)27 rats more strongly than does ARB, and this occurs independently of blood pressure.

Suppression of murine autoimmune myocarditis achieved with direct renin inhibition

BACKGROUND

The renin angiotensin system (RAS) plays an important role in the pathogenesis of cardiovascular diseases and inflammation. Myocarditis is an inflammatory disease of the heart, and the role of the RAS in its pathophysiology is unknown. Because the direct renin inhibitor, aliskiren, is thought to block RAS completely, we investigated the cardioprotective effect of aliskiren in mice with experimental autoimmune myocarditis (EAM).

METHODS

A cardiac α-myosin heavy chain peptide was injected in mice on days 0 and 7. Aliskiren 25mg/kg per day (n=10) or vehicle (n=10) was administered to EAM mice starting on day 0 and the animals were killed on day 21.

RESULTS

Aliskiren significantly prevented the progression of left ventricular wall thickening in EAM hearts compared to the vehicle-treated group. Histologically, the inflammatory cell infiltration and fibrosis area ratios in the aliskiren-treated group were lower than that in the vehicle-treated group. Immunohistochemistry revealed that aliskiren suppressed CD4 positive cell infiltration in EAM hearts compared to vehicle. Moreover, aliskiren decreased mRNA levels of interleukin (IL)-2, interferon-γ, tumor necrosis factor-α, and collagen 1. In vitro study showed that aliskiren inhibited T cell proliferation and IL-2 production induced by myosin stimulation.

CONCLUSION

Our results suggest that aliskiren ameliorates EAM by suppressing T-cell activation and inflammatory cytokines, and has potential as a treatment for myocarditis.

Optimum AT1 receptor-neprilysin inhibition has superior cardioprotective effects compared with AT1 receptor blockade alone in hypertensive rats

Neprilysin inhibitors prevent the breakdown of bradykinin and natriuretic peptides, promoting vasodilation and natriuresis. However, they also increase angiotensin II and endothelin-1. Here we studied the effects of a low and a high dose of the neprilysin inhibitor thiorphan on top of AT1 receptor blockade with irbesartan versus vehicle in TGR(mREN2)27 rats with high renin hypertension. Mean arterial blood pressure was unaffected by vehicle or thiorphan alone. Irbesartan lowered blood pressure, but after 7 days pressure started to increase again. Low- but not high-dose thiorphan prevented this rise. Only during exposure to low-dose thiorphan plus irbesartan did heart weight/body weight ratio, cardiac atrial natriuretic peptide expression, and myocyte size decrease significantly. Circulating endothelin-1 was not affected by low-dose thiorphan with or without irbesartan, but increased after treatment with high-dose thiorphan plus irbesartan. This endothelin-1 rise was accompanied by an increase in renal sodium-hydrogen exchanger 3 protein abundance, and an upregulation of constrictor vascular endothelin type B receptors. Consequently, the endothelin type B receptor antagonist BQ788 no longer enhanced endothelin-1-induced vasoconstriction (indicative of endothelin type B receptor-mediated vasodilation), but prevented it. Thus, optimal neprilysin inhibitor dosing reveals additional cardioprotective effects on top of AT1 receptor blockade in renin-dependent hypertension.

Modulation of the renin-angiotensin-aldosterone system in heart failure

The renin-angiotensin-aldosterone system (RAAS) is well-established and continues to be pursued as a therapeutic target in the treatment of heart failure, predominantly due to the success of agents that block RAAS in clinical trials of systolic heart failure. The optimal treatment of heart failure patients with preserved ejection fraction (HFpEF), however, remains unclear. Early trials of direct renin inhibitors have suggested that these agents may play a role in HFpEF, but recent clinical trial results have not been encouraging. Preliminary trials of angiotensin-receptor/neprilysin inhibitors look promising. Whether results with these or other drugs will alter current recommendations remains to be seen. In this review, we assess the current understanding of the role of RAAS modulation in heart failure.

Treatment of hypertension and renal injury induced by the angiogenesis inhibitor sunitinib: preclinical study

Common adverse effects of angiogenesis inhibition are hypertension and renal injury. To determine the most optimal way to prevent these adverse effects and to explore their interdependency, the following drugs were investigated in unrestrained Wistar Kyoto rats exposed to the angiogenesis inhibitor sunitinib: the dual endothelin receptor antagonist macitentan; the calcium channel blocker amlodipine; the angiotensin-converting enzyme inhibitor captopril; and the phosphodiesterase type 5 inhibitor sildenafil. Mean arterial pressure was monitored telemetrically. After 8 days, rats were euthanized and blood samples and kidneys were collected. In addition, 24-hour urine samples were collected. After sunitinib start, mean arterial pressure increased rapidly by ≈30 mm Hg. Coadministration of macitentan or amlodipine largely prevented this rise, whereas captopril or sildenafil did not. Macitentan, captopril, and sildenafil diminished the sunitinib-induced proteinuria and endothelinuria and glomerular intraepithelial protein deposition, whereas amlodipine did not. Changes in proteinuria and endothelinuria were unrelated. We conclude that in our experimental model, dual endothelin receptor antagonism and calcium channel blockade are suitable to prevent angiogenesis inhibition-induced hypertension, whereas dual endothelin receptor antagonism, angiotensin-converting enzyme inhibitor, and phosphodiesterase type 5 inhibition can prevent angiogenesis inhibition-induced proteinuria. Moreover, the variable response of hypertension and renal injury to different antihypertensive agents suggests that these side effects are, at least in part, unrelated.

Combined renin inhibition/(pro)renin receptor blockade in diabetic retinopathy--a study in transgenic (mREN2)27 rats

Dysfunction of renin-angiotensin system (RAS) contributes to the pathogenesis of diabetic retinopathy (DR). Prorenin, the precursor of renin is highly elevated in ocular fluid of diabetic patients with proliferative retinopathy. Prorenin may exert local effects in the eye by binding to the so-called (pro)renin receptor ((P)RR). Here we investigated the combined effects of the renin inhibitor aliskiren and the putative (P)RR blocker handle-region peptide (HRP) on diabetic retinopathy in streptozotocin (STZ)-induced diabetic transgenic (mRen2)27 rats (a model with high plasma prorenin levels) as well as prorenin stimulated cytokine expression in cultured Müller cells. Adult (mRen2)27 rats were randomly divided into the following groups: (1) non-diabetic; (2) diabetic treated with vehicle; (3) diabetic treated with aliskiren (10 mg/kg per day); and (4) diabetic treated with aliskiren+HRP (1 mg/kg per day). Age-matched non-diabetic wildtype Sprague-Dawley rats were used as control. Drugs were administered by osmotic minipumps for three weeks. Transgenic (mRen2)27 rat retinas showed increased apoptotic cell death of both inner retinal neurons and photoreceptors, increased loss of capillaries, as well as increased expression of inflammatory cytokines. These pathological changes were further exacerbated by diabetes. Aliskiren treatment of diabetic (mRen2)27 rats prevented retinal gliosis, and reduced retinal apoptotic cell death, acellular capillaries and the expression of inflammatory cytokines. HRP on top of aliskiren did not provide additional protection. In cultured Müller cells, prorenin significantly increased the expression levels of IL-1α and TNF-α, and this was completely blocked by aliskiren or HRP, their combination, (P)RR siRNA and the AT1R blocker losartan, suggesting that these effects entirely depended on Ang II generation by (P)RR-bound prorenin. In conclusion, the lack of effect of HRP on top of aliskiren, and the Ang II-dependency of the ocular effects of prorenin in vitro, argue against the combined application of (P)RR blockade and renin inhibition in diabetic retinopathy.

Aliskiren-attenuated myocardium apoptosis via regulation of autophagy and connexin-43 in aged spontaneously hypertensive rats

There are controversies about the mechanism of myocardium apoptosis in hypertensive heart disease. The aim of this study was to investigate the relationship among autophagy, Cx43 and apoptosis in aged spontaneously hypertensive rats (SHRs) and establish whether Aliskiren is effective or not for the treatment of myocardium apoptosis. Twenty-one SHRs aged 52 weeks were randomly divided into three groups, the first two receiving Aliskiren at a dose of 10 and 25 mg/kg/day respectively; the third, placebo for comparison with seven Wistar-Kyoto (WKY) as controls. After a 2-month treatment, systolic blood pressure (SBP), heart to bw ratios (HW/BW%) and angiotensin II (AngII) concentration were significantly enhanced in SHRs respectively. Apoptotic cardiomyocytes detected with TUNEL and immunofluorescent labelling for active caspase-3 increased nearly fourfolds in SHRs, with a decline in the expression of survivin and AKT activation, and an increase in caspase-3 activation and the ratio of Bax/Bcl-2. Myocardium autophagy, detected with immunofluorescent labelling for LC3-II, increased nearly threefolds in SHRs, with the up-regulation of Atg5, Atg16L1, Beclin-1 and LC3-II. The expression of Cx43 plaque was found to be down-regulated in SHRs. Aliskiren significantly reduced SBP, HW/BW%, AngII concentration and the expression of AT(1)R. Thus, Aliskiren protects myocardium against apoptosis by decreasing autophagy, up-regulating Cx43. These effects showed a dose-dependent tendency, but no significance. In conclusion, the myocardium apoptosis developed during the hypertensive end-stage of SHRs could be ameliorated by Aliskiren via the regulation of myocardium autophagy and maladaptive remodelling of Cx43.

Deterioration of kidney function by the (pro)renin receptor blocker handle region peptide in aliskiren-treated diabetic transgenic (mRen2)27 rats

Dual renin-angiotensin system (RAS) blockade in diabetic nephropathy is no longer feasible because of the profit/side effect imbalance. (Pro)renin receptor [(P)RR] blockade with handle region peptide (HRP) has been reported to exert beneficial effects in various diabetic models in a RAS-independent manner. To what degree (P)RR blockade adds benefits on top of RAS blockade is still unknown. In the present study, we treated diabetic TGR(mREN2)27 rats, a well-established nephropathy model with high prorenin levels [allowing continuous (P)RR stimulation in vivo], with HRP on top of renin inhibition with aliskiren. Aliskiren alone lowered blood pressure and exerted renoprotective effects, as evidenced by reduced glomerulosclerosis, diuresis, proteinuria, albuminuria, and urinary aldosterone levels as well as diminished renal (P)RR and ANG II type 1 receptor expression. It also suppressed plasma and tissue RAS activity and suppressed cardiac atrial natriuretic peptide and brain natriuretic peptide expression. HRP, when given on top of aliskiren, did not alter the effects of renin inhibition on blood pressure, RAS activity, or aldosterone. However, it counteracted the beneficial effects of aliskiren in the kidney, induced hyperkalemia, and increased plasma plasminogen activator-inhibitor 1, renal cyclooxygenase-2, and cardiac collagen content. All these effects have been linked to (P)RR stimulation, suggesting that HRP might, in fact, act as a partial agonist. Therefore, the use of HRP on top of RAS blockade in diabetic nephropathy is not advisable.

Direct renin inhibition with aliskiren protects against myocardial ischemia/reperfusion injury by activating nitric oxide synthase signaling in spontaneously hypertensive rats

BACKGROUND

We tested the hypothesis that direct renin inhibition with aliskiren protects against myocardial ischemia/reperfusion (I/R) injury in spontaneously hypertensive rats (SHR), and examined the mechanism by which this occurs.

METHODS AND RESULTS

Male SHR were treated (orally, 4 weeks) with saline or aliskiren (30 or 60 mg kg(-1) day(-1)) and subjected to 30 minutes of left anterior descending coronary artery occlusion followed by 6 or 24 hours of reperfusion. Only the higher dose significantly lowered systolic blood pressure, the lower dose causing a smaller apparent lowering that was nonsignificant. Despite this difference in blood pressure-lowering effect, both doses increased the ejection fraction and fractional shortening and reduced myocardial infarct size equally. I/R decreased cardiac expression of phosphatidylinositol 3-kinase (PI3K), phospho-Akt and phospho-endothelial nitric oxide synthase (phospho-eNOS), but increased expression of inducible nitric oxide synthase (iNOS); these changes were all abrogated by aliskiren. Moreover, aliskiren decreased superoxide anion generation and increased cyclic guanosine-3',5'-monophosphate, an index of bioactive nitric oxide, in myocardium. It also decreased the expression of myocardial matrix metalloproteinase-2, matrix metalloproteinase-9, and tissue inhibitor of metalloproteinases-1 (TIMP-1) following I/R. In a Langendorff heart preparation, the detrimental cardiac effects of I/R were abrogated by aliskiren, and these protective effects were abolished by NOS or PI3K inhibition. In a parallel study, although specific iNOS inhibition reduced plasma malondialdehyde and myocardial superoxide anion generation, it did not affect the deleterious effects of I/R on myocardial structure and function.

CONCLUSIONS

Direct renin inhibition protects against myocardial I/R injury through activation of the PI3K-Akt-eNOS pathway.

K+-induced natriuresis is preserved during Na+ depletion and accompanied by inhibition of the Na+-Cl- cotransporter

During hypovolemia and hyperkalemia, the kidneys defend homeostasis by Na(+) retention and K(+) secretion, respectively. Aldosterone mediates both effects, but it is unclear how the same hormone can evoke such different responses. To address this, we mimicked hypovolemia and hyperkalemia in four groups of rats with a control diet, low-Na(+) diet, high-K(+) diet, or combined diet. The low-Na(+) and combined diets increased plasma and kidney ANG II. The low-Na(+) and high-K(+) diets increased plasma aldosterone to a similar degree (3-fold), whereas the combined diet increased aldosterone to a greater extent (10-fold). Despite similar Na(+) intake and higher aldosterone, the high-K(+) and combined diets caused a greater natriuresis than the control and low-Na(+) diets, respectively (P < 0.001 for both). This K(+)-induced natriuresis was accompanied by a decreased abundance but not phosphorylation of the Na(+)-Cl(-) cotransporter (NCC). In contrast, the epithelial Na(+) channel (ENaC) increased in parallel with aldosterone, showing the highest expression with the combined diet. The high-K(+) and combined diets also increased WNK4 but decreased Nedd4-2 in the kidney. Total and phosphorylated Ste-20-related kinase were also increased but were retained in the cytoplasm of distal convoluted tubule cells. In summary, high dietary K(+) overrides the effects of ANG II and aldosterone on NCC to deliver sufficient Na(+) to ENaC for K(+) secretion. K(+) may inhibit NCC through WNK4 and help activate ENaC through Nedd4-2.

The (pro)renin receptor blocker handle region peptide upregulates endothelium-derived contractile factors in aliskiren-treated diabetic transgenic (mREN2)27 rats

BACKGROUND

Elevated prorenin levels associate with microvascular complications in patients with diabetes mellitus, possibly because prorenin affects vascular function in diabetes mellitus, for example by generating angiotensins following its binding to the (pro)renin receptor [(P)RR]. Here we evaluated whether the renin inhibitor aliskiren, with or without the putative (P)RR antagonist handle region peptide (HRP) improved the disturbed vascular function in diabetic TGR(mREN2)27 rats, a high-prorenin, high-(P)RR hypertensive model.

METHODS

Telemetry transmitters were implanted to monitor blood pressure. After 3 weeks of treatment, rats were sacrificed, and iliac and mesenteric arteries were removed to evaluate vascular reactivity.

RESULTS

Diabetes mellitus enhanced the contractile response to nitric oxide synthase (NOS) blockade, potentiated the response to phenylephrine, diminished the effectiveness of endothelin type A (ETA) receptor blockade and allowed acetylcholine to display constrictor, cyclo-oxygenase-2 mediated, endothelium-dependent responses in the presence of NOS inhibition and blockers of endothelium-derived hyperpolarizing factors. Aliskiren normalized blood pressure, suppressed renin activity, and reversed the above vascular effects, with the exception of the altered effectiveness of ETA receptor blockade. Remarkably, when adding HRP on top of aliskiren, its beneficial vascular effects either disappeared or were greatly diminished, although HRP did not alter the effect of aliskiren on blood pressure and renin activity.

CONCLUSIONS

Renin inhibition improves vascular dysfunction in diabetic hypertensive rats, and HRP counteracts this effect independently of blood pressure and angiotensin. (P)RR blockade therefore is unlikely to be a new tool to further suppress the renin-angiotensin system (RAS) on top of existing RAS blockers.

New roles for renin and prorenin in heart failure and cardiorenal crosstalk

The renin-angiotensin-aldosterone-system (RAAS) plays a central role in the pathophysiology of heart failure and cardiorenal interaction. Drugs interfering in the RAAS form the pillars in treatment of heart failure and cardiorenal syndrome. Although RAAS inhibitors improve prognosis, heart failure–associated morbidity and mortality remain high, especially in the presence of kidney disease. The effect of RAAS blockade may be limited due to the loss of an inhibitory feedback of angiotensin II on renin production. The subsequent increase in prorenin and renin may activate several alternative pathways. These include the recently discovered (pro-) renin receptor, angiotensin II escape via chymase and cathepsin, and the formation of various angiotensin subforms upstream from the blockade, including angiotensin 1–7, angiotensin III, and angiotensin IV. Recently, the direct renin inhibitor aliskiren has been proven effective in reducing plasma renin activity (PRA) and appears to provide additional (tissue) RAAS blockade on top of angiotensin-converting enzyme and angiotensin receptor blockers, underscoring the important role of renin, even (or more so) under adequate RAAS blockade. Reducing PRA however occurs at the expense of an increase plasma renin concentration (PRC). PRC may exert direct effects independent of PRA through the recently discovered (pro-) renin receptor. Additional novel possibilities to interfere in the RAAS, for instance using vitamin D receptor activation, as well as the increased knowledge on alternative pathways, have revived the question on how ideal RAAS-guided therapy should be implemented. Renin and prorenin are pivotal since these are at the base of all of these pathways.

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.

Targeting the renin-angiotensin-aldosterone system in heart failure

The renin-angiotensin-aldosterone system is a well-established therapeutic target in the treatment of heart failure (HF). Substantial advances have been made with existing agents--angiotensin-converting enzyme (ACE) inhibitors, angiotensin II-receptor blockers (ARBs), and mineralocorticoid-receptor antagonists (MRAs)--and new data continue to emerge. The indication for the use of MRAs has been broadened to include potentially all patients who have HF with reduced ejection fraction (HFrEF), and ACE inhibitors might have a novel application in patients who are at risk of left ventricular dysfunction (those with aortic valvular disease or pacing-induced heart disease). ARBs have been shown to be a beneficial alternative to ACE inhibitors in HFrEF, but their value when added to ACE inhibitors has been questioned. Upstream, direct renin blockade with aliskiren is being pursued in two large trials of HF, despite the premature halting of a third study. A substantial, unmet need remains in patients who have HF with preserved ejection fraction (HFpEF). New data on spironolactone and LCZ696 (a combined ARB and neprilysin inhibitor) show promise for these patients. Results of the TOPCAT study of spironolactone in patients with HFpEF are awaited, and LCZ696 is now being tested in a large trial in patients with HFrEF.

Direct renin inhibitor prevents and ameliorates insulin resistance, aortic endothelial dysfunction and vascular remodeling in fructose-fed hypertensive rats

Angiotensin-converting enzyme inhibitors and angiotensin II type 1 receptor blockers can improve insulin resistance and vascular dysfunction in insulin-resistant rats; however, there are few reports on the effects of direct renin inhibitors on these conditions. We investigated the effects of a direct renin inhibitor, aliskiren, on insulin resistance, aortic endothelial dysfunction and vascular remodeling in fructose-fed hypertensive rats. Male Wistar-Kyoto rats were divided into four groups (n=6 per group) and studied for 8 weeks: Group Con: standard chow diet; group Fru: high-fructose diet (60% fructose); Group FruA: high-fructose diet with concurrent aliskiren treatment (100 mg kg(-1) per day); and Group FruB: high-fructose diet with subsequent aliskiren treatment 4 weeks later. Blood was collected for biochemical assays, and isolated rings of the thoracic aorta were obtained for analysis of vascular reactivity, vascular structure and lipid peroxide. Rats fed with high-fructose diets developed significant systolic hypertension, decreased plasma nitrite (NO(2); nitric oxide metabolite) levels and increased plasma glucose, insulin, triglyceride, total cholesterol and aortic lipid peroxide levels, and aortic wall thickness compared with control rats. Aliskiren treatment, either concurrent or subsequent, elevated plasma NO(2) levels and reduced systolic hypertension, insulin resistance, dyslipidemia, aortic lipid peroxide levels and aortic wall hypertrophy in FHR. The peak endothelium-dependent aortic relaxations were significantly higher in rats that received aliskiren treatment than in those that did not. In conclusion, our findings suggest that aliskiren prevents and ameliorates insulin resistance, aortic endothelial dysfunction and oxidative vascular remodeling in fructose-fed hypertensive rats.

AT1 antagonism and renin inhibition in mice: pivotal role of targeting angiotensin II in chronic kidney disease

The role of the renin-angiotensin system in chronic kidney disease involves multiple peptides and receptors. Exerting antipodal pathophysiological mechanisms, renin inhibition and AT(1) antagonism ameliorate renal damage. However, it is unclear which mechanism exerts better nephroprotection. We compared the renin inhibitor aliskiren with the AT(1) antagonist losartan in mice with chronic kidney disease due to renal ablation. Doses were adjusted to equipotent inhibition of the renin-angiotensin system, determined via a dose-response quantifying plasma and renal renin expression. Six-week treatment with either 500 mg/l drinking water losartan or 50 mg·kg(-1)·day(-1) aliskiren significantly decreased albuminuria, glomerular damage, and transcription rates of renal injury markers to a similar extent. An array analysis comparing renal gene expression of losartan- and aliskiren-treated mice evaluating >34,000 transcripts demonstrated regulation for 14 genes only, with small differences. No superior nephroprotection was found by combining losartan and aliskiren. Compared with plasma concentrations, aliskiren accumulated ∼7- to 29-fold in the heart, liver, lung, and spleen and ∼156-fold in the kidney. After withdrawal, plasma concentrations dropped to zero within 24 h, whereas renal tissue concentrations declined slowly over days. Withdrawal of aliskiren in mice with chronic kidney disease revealed a significantly delayed re-increase in albuminuria compared with withdrawal of losartan. This study demonstrates equieffective nephroprotection of renin inhibition and AT(1) antagonism in mice with chronic kidney disease without additional benefit of combination therapy. These observations underscore the pivotal role of targeting ANG II to reduce renal injury.

Central infusion of aliskiren prevents sympathetic hyperactivity and hypertension in Dahl salt-sensitive rats on high salt intake

Central infusion of an angiotensin type 1 (AT(1)) receptor blocker prevents sympathetic hyperactivity and hypertension in Dahl salt-sensitive (S) rats on high salt. In the present study, we examined whether central infusion of a direct renin inhibitor exerts similar effects. Intracerebroventricular infusion of aliskiren at the rate of 0.05 mg/day markedly inhibited the increase in ANG II levels in the cerebrospinal fluid and in blood pressure (BP) caused by intracerebroventricular infusion of rat renin. In Dahl S rats on high salt, intracerebroventricular infusion of aliskiren at 0.05 and 0.25 mg/day for 2 wk similarly decreased resting BP in Dahl S rats on high salt. In other groups of Dahl S rats, high salt intake for 2 wk increased resting BP by ∼25 mmHg, enhanced pressor and sympathoexcitatory responses to air-stress, and desensitized arterial baroreflex function. All of these effects were largely prevented by intracerebroventricular infusion of aliskiren at 0.05 mg/day. Aliskiren had no effects in rats on regular salt. Neither high salt nor aliskiren affected hypothalamic ANG II content. These results indicate that intracerebroventricular infusions of aliskiren and an AT(1) receptor blocker are similarly effective in preventing salt-induced sympathetic hyperactivity and hypertension in Dahl S rats, suggesting that renin in the brain plays an essential role in the salt-induced hypertension. The absence of an obvious increase in hypothalamic ANG II by high salt, or decrease in ANG II by aliskiren, suggests that tissue levels do not reflect renin-dependent ANG II production in sympathoexcitatory angiotensinergic neurons.

The vascular endothelial growth factor receptor inhibitor sunitinib causes a preeclampsia-like syndrome with activation of the endothelin system

Angiogenesis inhibition is an established treatment for several tumor types. Unfortunately, this therapy is associated with adverse effects, including hypertension and renal toxicity, referred to as "preeclampsia." Recently, we demonstrated in patients and in rats that the multitarget tyrosine kinase inhibitor sunitinib induces a rise in blood pressure (BP), renal dysfunction, and proteinuria associated with activation of the endothelin system. In the current study we investigated the effects of sunitinib on rat renal histology, including the resemblance with preeclampsia, as well as the roles of endothelin 1, decreased nitric oxide (NO) bioavailability, and increased oxidative stress in the development of sunitinib-induced hypertension and renal toxicity. In rats on sunitinib, light and electron microscopic examination revealed marked glomerular endotheliosis, a characteristic histological feature of preeclampsia, which was partly reversible after sunitinib discontinuation. The histological abnormalities were accompanied by an increase in urinary excretion of endothelin 1 and diminished NO metabolite excretion. In rats on sunitinib alone, BP increased (ΔBP: 31.6±0.9 mm Hg). This rise could largely be prevented with the endothelin receptor antagonist macitentan (ΔBP: 12.3±1.5 mm Hg) and only mildly with Tempol, a superoxide dismutase mimetic (ΔBP: 25.9±2.3 mm Hg). Both compounds could not prevent the sunitinib-induced rise in serum creatinine or renal histological abnormalities and had no effect on urine nitrates but decreased proteinuria and urinary endothelin 1 excretion. Our findings indicate that both the endothelin system and oxidative stress play important roles in the development of sunitinib-induced proteinuria and that the endothelin system rather than oxidative stress is important for the development of sunitinib-induced hypertension.

Endothelial damage and regeneration: the role of the renin-angiotensin-aldosterone system

The renin-angiotensin-aldosterone system (RAAS) is part of the blood pressure regulating system. Its main effector peptide is angiotensin II (Ang II). Although it may induce hypertension, the proinflammatory, profibrotic, and prothrombotic effects are mainly mediated by effects of Ang II on the cellular and molecular level that are independent of blood pressure. Therefore, pharmacotherapeutic intervention within the RAAS is an important treatment modality for patients suffering from cardiovascular diseases, even those who are not hypertensive. In addition to the blood pressure lowering and vasculoprotective (pleiotropic) effects of angiotensin II type 1 (AT(1)) receptor blockers (ARBs), and angiotensin-converting enzyme (ACE) inhibitors, regenerative progenitor cell therapy emerges as an auxiliary therapy to improve regeneration of the vascular endothelium. This review focuses on the growing knowledge about regenerating vascular cells, their response to RAAS effectors, and RAAS-modulating pharmacotherapy in the context of endothelial cell damage and regeneration.

Knocking out angiotensin II in the heart

Despite ongoing medical advances, cardiovascular disease continues to be a leading health concern. The renin-angiotensin system (RAS) plays an important role in regulating cardiovascular function, and is, therefore, the subject of extensive study. Several drugs currently used to treat hypertension and heart failure are designed to target angiotensin II synthesis and function, but thus far, none have been able to completely block the effects of RAS signaling. This review discusses current and emerging approaches towards inhibiting cardiac RAS function in order to further improve cardiovascular disease outcomes.

Handle region peptide counteracts the beneficial effects of the Renin inhibitor aliskiren in spontaneously hypertensive rats

To investigate whether the putative (pro)renin receptor blocker, the handle region peptide (HRP), exerts effects on top of the blood pressure-lowering and cardioprotective effects of the renin inhibitor aliskiren, spontaneously hypertensive rats were implanted with telemetry transmitters to monitor heart rate and mean arterial pressure (MAP). After a 2-week recovery period, vehicle, aliskiren, HRP (100 and 1 mg/kg per day, respectively), and HRP+aliskiren were infused for 3 weeks using osmotic minipumps. Subsequently, the heart was removed to study coronary function according to Langendorff. Baseline MAP and heart rate in vehicle-treated rats were 146±3 mm Hg and 326±4 bpm. HRP did not affect MAP, whereas aliskiren and HRP+aliskiren lowered MAP (by maximally 29±2 and 20±1 mm Hg, respectively) without affecting heart rate. Aliskiren significantly reduced MAP throughout the 3-week infusion period, whereas the blood pressure-lowering effect of HRP+aliskiren returned to baseline within 2 weeks of treatment. In comparison with vehicle, aliskiren increased the endothelium-dependent response to bradykinin and decreased the response to angiotensin II in the coronary circulation, whereas these responses were not altered after treatment with HRP or HRP+aliskiren. HRP did not alter plasma renin activity, plasma angiotensin levels, or the renal angiotensin content, either alone or on top of aliskiren, nor did it alter the aliskiren-induced decrease in renal Ang II type 1 receptor expression. Yet, it did reverse the aliskiren-induced reduction in cardiomyocyte area, without affecting this area when given alone. In conclusion, HRP counteracts the beneficial effects of aliskiren on blood pressure, coronary function, and cardiac hypertrophy in an angiotensin-independent manner.