Nephrectomy, converting enzyme inhibition, and angiotensin peptides

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.

New Approaches Targeting the Renin-Angiotensin System: Inhibition of Brain Aminopeptidase A, ACE2 Ubiquitination, and Angiotensinogen

Despite the availability of various therapeutic classes of antihypertensive drugs, hypertension remains poorly controlled, in part because of poor adherence. Hence, there is a need for the development of antihypertensive drugs acting on new targets to improve control of blood pressure. This review discusses novel insights (including the data of recent clinical trials) with regard to interference with the renin-angiotensin system, focusing on the enzymes aminopeptidase A and angiotensin-converting enzyme 2 (ACE2) in the brain, as well as the substrate of renin- angiotensinogen-in the liver. It raises the possibility that centrally acting amino peptidase A inhibitors (eg, firibastat), preventing the conversion of angiotensin II to angiotensin III in the brain, might be particularly useful in African Americans and patients with obesity. Firibastat additionally upregulates brain ACE2, allowing the conversion of angiotensin II to its protective metabolite angiotensin-(1-7). Furthermore, antisense oligonucleotides or small interfering ribonucleic acids suppress hepatic angiotensinogen for weeks to months after 1 injection and thus could potentially overcome adherence issues. Finally, interference with ACE2 ubiquitination is emerging as a future option for the treatment of neurogenic hypertension, given that ubiquitination resistance might upregulate ACE2 activity.

Angiotensinogen Suppression: A New Tool to Treat Cardiovascular and Renal Disease

Multiple types of renin-angiotensin system (RAS) blockers exist, allowing interference with the system at the level of renin, angiotensin-converting enzyme, or the angiotensin II receptor. Yet, in particular, for the treatment of hypertension, the number of patients with uncontrolled hypertension continues to rise, either due to patient noncompliance or because of the significant renin rises that may, at least partially, overcome the effect of RAS blockade (RAS escape). New approaches to target the RAS are either direct antisense oligonucleotides that inhibit angiotensinogen RNA translation, or small interfering RNA (siRNA) that function via the RNA interference pathway. Since all angiotensins stem from angiotensinogen, lowering angiotensinogen has the potential to circumvent the RAS escape phenomenon. Moreover, antisense oligonucleotides and small interfering RNA require injections only every few weeks to months, which might reduce noncompliance. Of course, angiotensinogen suppression also poses a threat in situations where the RAS is acutely needed, for instance in women becoming pregnant during treatment, or in cases of emergency, when severe hypotension occurs. This review discusses all preclinical data on angiotensinogen suppression, as well as the limited clinical data that are currently available. It concludes that it is an exciting new tool to target the RAS with high specificity and a low side effect profile. Its long-term action might revolutionize pharmacotherapy, as it could overcome compliance problems. Preclinical and clinical programs are now carefully investigating its efficacy and safety profile, allowing an optimal introduction as a novel drug to treat cardiovascular and renal diseases in due time.

Perivascular Adipose Tissue in Vascular Function: Does Locally Synthesized Angiotensinogen Play a Role?

ABSTRACT

In recent years, perivascular adipose tissue (PVAT) research has gained special attention in an effort to understand its involvement in vascular function. PVAT is recognized as an important endocrine organ that secretes procontractile and anticontractile factors, including components of the renin-angiotensin-aldosterone system, particularly angiotensinogen (AGT). This review critically addresses the occurrence of AGT in PVAT, its release into the blood stream, and its contribution to the generation and effects of angiotensins (notably angiotensin-(1-7) and angiotensin II) in the vascular wall. It describes that the introduction of transgenic animals, expressing AGT at 0, 1, or more specific location(s), combined with the careful measurement of angiotensins, has revealed that the assumption that PVAT independently generates angiotensins from locally synthesized AGT is incorrect. Indeed, selective deletion of AGT from adipocytes did not lower circulating AGT, neither under a control diet nor under a high-fat diet, and only liver-specific AGT deletion resulted in the disappearance of AGT from blood plasma and adipose tissue. An entirely novel scenario therefore develops, supporting local angiotensin generation in PVAT that depends on the uptake of both AGT and renin from blood, in addition to the possibility that circulating angiotensins exert vascular effects. The review ends with a summary of where we stand now and recommendations for future research.

Nanoparticle-Mediated Angiotensin-(1-9) Drug Delivery for the Treatment of Cardiac Hypertrophy

Ang-(1-9) peptide is a bioactive vasodilator peptide that prevents cardiomyocyte hypertrophy in vitro and in vivo as well as lowers blood pressure and pathological cardiovascular remodeling; however, it has a reduced half-life in circulation, requiring a suitable carrier for its delivery. In this work, hybrid nanoparticles composed of polymeric nanoparticles (pNPs) based on Eudragit^® E/Alginate (EE/Alg), and gold nanospheres (AuNS), were developed to evaluate their encapsulation capacity and release of Ang-(1-9) under different experimental conditions. Hybrid pNPs were characterized by dynamic light scattering, zeta potential, transmission and scanning electron microscopy, size distribution, and concentration by nanoparticle tracking analysis. Nanometric pNPs, with good polydispersity index and colloidally stable, produced high association efficiency of Ang-(1-9) and controlled release. Finally, the treatment of neonatal cardiomyocytes in culture with EE/Alg/AuNS 2% + Ang-(1-9) 20% pNPs decreased the area and perimeter, demonstrating efficacy in preventing norepinephrine-induced cardiomyocyte hypertrophy. On the other hand, the incorporation of AuNS did not cause negative effects either on the cytotoxicity or on the association capacity of Ang-(1-9), suggesting that the hybrid carrier EE/Alg/AuNS pNPs could be used for the delivery of Ang-(1-9) in the treatment of cardiovascular hypertrophy.

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.

Angiotensin generation in the brain: a re-evaluation

The existence of a so-called brain renin-angiotensin system (RAS) is controversial. Given the presence of the blood-brain barrier, angiotensin generation in the brain, if occurring, should depend on local synthesis of renin and angiotensinogen. Yet, although initially brain-selective expression of intracellular renin was reported, data in intracellular renin knockout animals argue against a role for this renin in angiotensin generation. Moreover, renin levels in brain tissue at most represented renin in trapped blood. Additionally, in neurogenic hypertension brain prorenin up-regulation has been claimed, which would generate angiotensin following its binding to the (pro)renin receptor. However, recent studies reported no evidence for prorenin expression in the brain, nor for its selective up-regulation in neurogenic hypertension, and the (pro)renin receptor rather displays RAS-unrelated functions. Finally, although angiotensinogen mRNA is detectable in the brain, brain angiotensinogen protein levels are low, and even these low levels might be an overestimation due to assay artefacts. Taken together, independent angiotensin generation in the brain is unlikely. Indeed, brain angiotensin levels are extremely low, with angiotensin (Ang) I levels corresponding to the small amounts of Ang I in trapped blood plasma, and Ang II levels at most representing Ang II bound to (vascular) brain Ang II type 1 receptors. This review concludes with a unifying concept proposing the blood origin of angiotensin in the brain, possibly resulting in increased levels following blood-brain barrier disruption (e.g. due to hypertension), and suggesting that interfering with either intracellular renin or the (pro)renin receptor has consequences in an RAS-independent manner.

Angiotensin II Short-Loop Feedback: Is There a Role of Ang II for the Regulation of the Renin System In Vivo?

The activity of the renin-angiotensin-aldosterone system is triggered by the release of the protease renin from the kidneys, which in turn is controlled in the sense of negative feedback loops. It is widely assumed that Ang II (angiotensin II) directly inhibits renin expression and secretion via a short-loop feedback by an effect on renin-producing cells (RPCs) mediated by AT₁ (Ang II type 1) receptors. Because the concept of such a direct short-loop negative feedback control, which originates mostly from in vitro experiments, has not yet been systematically proven in vivo, we aimed to test the validity of this concept by studying the regulation of renin synthesis and secretion in mice lacking Ang II-AT₁ receptors on RPCs. We found that RPCs of the kidney express Ang II-AT₁ receptors. Mice with conditional deletion of Ang II-AT₁ receptors in RPCs were normal with regard to the number of renin cells, renal renin mRNA, and plasma renin concentrations. Renin expression and secretion of these mice responded to Ang I (angiotensin I)-converting enzyme inhibition and to Ang II infusion like in wild-type (WT) controls. In summary, we did not obtain evidence that Ang II-AT₁ receptors on RPCs are of major relevance for the normal regulation of renin expression and secretion in mice. Therefore, we doubt the existence of a direct negative feedback function of Ang II on RPCs.

Regulation and Functions of the Renin-Angiotensin System in White and Brown Adipose Tissue

The renin angiotensin system (RAS) is a major regulator of blood pressure, fluid, and electrolyte homeostasis. RAS precursor angiotensinogen (Agt) is cleaved into angiotensin I (Ang I) and II (Ang II) by renin and angiotensin converting enzyme (ACE), respectively. Major effects of Ang II, the main bioactive peptide of this system, is mediated by G protein coupled receptors, Angiotensin Type 1 (AGTR1, AT1R) and Type 2 (AGTR2, AT2R) receptors. Further, the discovery of additional RAS peptides such as Ang 1-7 generated by the action of another enzyme ACE2 identified novel functions of this complex system. In addition to the systemic RAS, several local RAS exist in organs such as the brain, kidney, pancreas, and adipose tissue. The expression and regulation of various components of RAS in adipose tissue prompted extensive research into the role of adipose RAS in metabolic diseases. Indeed, animal studies have shown that adipose-derived Agt contributes to circulating RAS, kidney, and blood pressure regulation. Further, mice overexpressing Agt have high blood pressure and increased adiposity characterized by inflammation, adipocyte hypertrophy, and insulin resistance, which can be reversed at least in part by RAS inhibition. These findings highlight the importance of this system in energy homeostasis, especially in the context of obesity. This overview article discusses the depot-specific functions of adipose RAS, genetic and pharmacological manipulations of RAS, and its applications to adipogenesis, thermogenesis, and overall energy homeostasis. © 2017 American Physiological Society. Compr Physiol 7:1137-1150, 2017.

The vasoprotective axes of the renin-angiotensin system: Physiological relevance and therapeutic implications in cardiovascular, hypertensive and kidney diseases

The renin-angiotensin system (RAS) is undisputedly one of the most prominent endocrine (tissue-to-tissue), paracrine (cell-to-cell) and intracrine (intracellular/nuclear) vasoactive systems in the physiological regulation of neural, cardiovascular, blood pressure, and kidney function. The importance of the RAS in the development and pathogenesis of cardiovascular, hypertensive and kidney diseases has now been firmly established in clinical trials and practice using renin inhibitors, angiotensin-converting enzyme (ACE) inhibitors, type 1 (AT₁) angiotensin II (ANG II) receptor blockers (ARBs), or aldosterone receptor antagonists as major therapeutic drugs. The major mechanisms of actions for these RAS inhibitors or receptor blockers are mediated primarily by blocking the detrimental effects of the classic angiotensinogen/renin/ACE/ANG II/AT₁/aldosterone axis. However, the RAS has expanded from this classic axis to include several other complex biochemical and physiological axes, which are derived from the metabolism of this classic axis. Currently, at least five axes of the RAS have been described, with each having its key substrate, enzyme, effector peptide, receptor, and/or downstream signaling pathways. These include the classic angiotensinogen/renin/ACE/ANG II/AT₁ receptor, the ANG II/APA/ANG III/AT₂/NO/cGMP, the ANG I/ANG II/ACE2/ANG (1-7)/Mas receptor, the prorenin/renin/prorenin receptor (PRR or Atp6ap2)/MAP kinases ERK1/2/V-ATPase, and the ANG III/APN/ANG IV/IRAP/AT₄ receptor axes. Since the roles and therapeutic implications of the classic angiotensinogen/renin/ACE/ANG II/AT₁ receptor axis have been extensively reviewed, this article will focus primarily on reviewing the roles and therapeutic implications of the vasoprotective axes of the RAS in cardiovascular, hypertensive and kidney diseases.

Is angiotensin-(3-4) (Val-Tyr), the shortest angiotensin II-derived peptide, opening new vistas on the renin-angiotensin system?

Angiotensin-(3−4) (Ang-(3−4) or Val-Tyr) is the shorter angiotensin (Ang) II-derived peptide, formed through successive hydrolysis that culminates with the release of Val-Tyr as a dipeptide. It is formed both in plasma and in kidney from Ang II and Ang III, and can be considered a component of the systemic and organ-based renin–angiotensin system. It is potently antihypertensive in humans and rats, and its concerted actions on proximal tubule cells culminate in the inhibition of fluid reabsorption, hyperosmotic urinary excretion of Na⁺. At the renal cell signaling level, Ang-(3−4) counteracts Ang II-type 1 receptor-mediated responses by acting as an allosteric enhancer in Ang II-type 2 receptor populations that target adenosine triphosphate-dependent Ca²⁺ and Na⁺ transporters through a cyclic adenosine monophosphate-activated protein kinase pathway.

Brain Renin-Angiotensin System: Does It Exist?

Because of the presence of the blood-brain barrier, brain renin-angiotensin system activity should depend on local (pro)renin synthesis. Indeed, an intracellular form of renin has been described in the brain, but whether it displays angiotensin (Ang) I-generating activity (AGA) is unknown. Here, we quantified brain (pro)renin, before and after buffer perfusion of the brain, in wild-type mice, renin knockout mice, deoxycorticosterone acetate salt-treated mice, and Ang II-infused mice. Brain regions were homogenized and incubated with excess angiotensinogen to detect AGA, before and after prorenin activation, using a renin inhibitor to correct for nonrenin-mediated AGA. Renin-dependent AGA was readily detectable in brain regions, the highest AGA being present in brain stem (>thalamus=cerebellum=striatum=midbrain>hippocampus=cortex). Brain AGA increased marginally after prorenin activation, suggesting that brain prorenin is low. Buffer perfusion reduced AGA in all brain areas by >60%. Plasma renin (per mL) was 40× to 800× higher than brain renin (per gram). Renin was undetectable in plasma and brain of renin knockout mice. Deoxycorticosterone acetate salt and Ang II suppressed plasma renin and brain renin in parallel, without upregulating brain prorenin. Finally, Ang I was undetectable in brains of spontaneously hypertensive rats, while their brain/plasma Ang II concentration ratio decreased by 80% after Ang II type 1 receptor blockade. In conclusion, brain renin levels (per gram) correspond with the amount of renin present in 1 to 20 μL of plasma. Brain renin disappears after buffer perfusion and varies in association with plasma renin. This indicates that brain renin represents trapped plasma renin. Brain Ang II represents Ang II taken up from blood rather than locally synthesized Ang II.

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.

Human kidney pericytes produce renin

Pericytes, perivascular cells embedded in the microvascular wall, are crucial for vascular homeostasis. These cells also play diverse roles in tissue development and regeneration as multi-lineage progenitors, immunomodulatory cells and as sources of trophic factors. Here, we establish that pericytes are renin producing cells in the human kidney. Renin was localized by immunohistochemistry in CD146 and NG2 expressing pericytes, surrounding juxtaglomerular and afferent arterioles. Similar to pericytes from other organs, CD146⁺CD34^–CD45^–CD56^– renal fetal pericytes, sorted by flow cytometry, exhibited tri-lineage mesodermal differentiation potential in vitro. Additionally, renin expression was triggered in cultured kidney pericytes by cyclic AMP as confirmed by immuno-electron microscopy, and secretion of enzymatically functional renin, capable of generating angiotensin I. Pericytes derived from second trimester human placenta also expressed renin in an inducible fashion although the renin activity was much lower than in renal pericytes. Thus, our results confirm and extend the recently discovered developmental plasticity of microvascular pericytes, and may open new perspectives to the therapeutic regulation of the renin-angiotensin system.

Biochemical evaluation of the renin-angiotensin system: the good, bad, and absolute?

The renin-angiotensin system (RAS) constitutes a key hormonal system in the physiological regulation of blood pressure through peripheral and central mechanisms. Indeed, dysregulation of the RAS is considered a major factor in the development of cardiovascular pathologies, and pharmacological blockade of this system by the inhibition of angiotensin-converting enzyme (ACE) or antagonism of the angiotensin type 1 receptor (AT1R) offers an effective therapeutic regimen. The RAS is now defined as a system composed of different angiotensin peptides with diverse biological actions mediated by distinct receptor subtypes. The classic RAS comprises the ACE-ANG II-AT1R axis that promotes vasoconstriction; water intake; sodium retention; and increased oxidative stress, fibrosis, cellular growth, and inflammation. In contrast, the nonclassical RAS composed primarily of the ANG II/ANG III-AT2R and the ACE2-ANG-(1-7)-AT7R pathways generally opposes the actions of a stimulated ANG II-AT1R axis. In lieu of the complex and multifunctional aspects of this system, as well as increased concerns on the reproducibility among laboratories, a critical assessment is provided on the current biochemical approaches to characterize and define the various components that ultimately reflect the status of the RAS.

Recent insights and therapeutic perspectives of angiotensin-(1-9) in the cardiovascular system

Chronic RAS (renin-angiotensin system) activation by both AngII (angiotensin II) and aldosterone leads to hypertension and perpetuates a cascade of pro-hypertrophic, pro-inflammatory, pro-thrombotic and atherogenic effects associated with cardiovascular damage. In 2000, a new pathway consisting of ACE2 (angiotensin-converting enzyme2), Ang-(1-9) [angiotensin-(1-9)], Ang-(1-7) [angiotensin-(1-7)] and the Mas receptor was discovered. Activation of this novel pathway stimulates vasodilation, anti-hypertrophy and anti-hyperplasia. For some time, studies have focused mainly on ACE2, Ang-(1-7) and the Mas receptor, and their biological properties that counterbalance the ACE/AngII/AT1R (angiotensin type 1 receptor) axis. No previous information about Ang-(1-9) suggested that this peptide had biological properties. However, recent data suggest that Ang-(1-9) protects the heart and blood vessels (and possibly the kidney) from adverse cardiovascular remodelling in patients with hypertension and/or heart failure. These beneficial effects are not modified by the Mas receptor antagonist A779 [an Ang-(1-7) receptor blocker], but they are abolished by the AT2R (angiotensin type 2 receptor) antagonist PD123319. Current information suggests that the beneficial effects of Ang-(1-9) are mediated via the AT2R. In the present review, we summarize the biological effects of the novel vasoactive peptide Ang-(1-9), providing new evidence of its cardiovascular-protective activity. We also discuss the potential mechanism by which this peptide prevents and ameliorates the cardiovascular damage induced by RAS activation.

Origin of the Y chromosome influences intrarenal vascular responsiveness to angiotensin I and angiotensin (1-7) in stroke-prone spontaneously hypertensive rats

The lineage of the Y chromosome accounts for up to 15 to 20 mm Hg in arterial pressure. Genes located on the Y chromosome from the spontaneously hypertensive rat (SHR) are associated with the renin-angiotensin system. Given the important role of the renin-angiotensin system in the renal regulation of fluid homeostasis and arterial pressure, we hypothesized that the origin of the Y chromosome influences arterial pressure via interaction between the intrarenal vasculature and the renin-angiotensin system. Sixteen-week-old normotensive rats (Wistar Kyoto [WKY]), spontaneously hypertensive stroke-prone rat (SHRSP), and 2 reciprocal Y consomic rat strains, 1 comprising the WKY autosomes and X chromosome with the Y chromosome from the hypertensive rat strain (WKY.SPGlaY) and vice versa (SP.WKYGlaY), were examined. SP.WKYGlaY had lower systolic blood pressure than SHRSP (195±5 versus 227±8 mm Hg; P<0.03), whereas WKY.SPGlaY had higher systolic blood pressure compared with WKY (157±3 versus 148±3 mm Hg; P<0.05), measured by radiotelemetry. Compared with WKY rats, SHRSP had higher plasma angiotensin(1-7) (Ang (1-7)):Ang II ratio (WKY: 0.13±0.01 versus SHRSP: 1.33±0.4; P<0.005), greater angiotensin II receptor type 2 and Mas receptor mRNA expression, and a blunted renal constrictor response to intrarenal Ang I and Ang(1-7) infusions. Introgression of the normotensive Y chromosome into the SHRSP background (SP.WKYGlaY) restored responses in the SHRSP to WKY levels, evidenced by a reduction in plasma Ang(1-7):Ang II ratio (SP.WKYGlaY: 0.24±0.02; P<0.01), angiotensin II receptor type 2, and Mas receptor mRNA expression and an increased vasoconstrictor response to intrarenal Ang I and Ang(1-7) infusion. This study demonstrates that the origin of the Y chromosome significantly impacts the renal vascular responsiveness and therefore may influence the long-term renal regulation of blood pressure.

The vascular renin-angiotensin system contributes to blunted vasodilation induced by transient high pressure in human adipose microvessels

Increased intraluminal pressure can reduce endothelial function in resistance arterioles; however, the mechanism of this impairment is unknown. The purpose of this study was to determine the effect of local renin-angiotensin system inhibition on the pressure-induced blunting of endothelium-dependent vasodilation in human adipose arterioles. Arterioles (100-200 μm) were dissected from fresh adipose surgical specimens, cannulated onto glass micropipettes, pressurized to an intraluminal pressure of 60 mmHg, and constricted with endothelin-1. Vasodilation to ACh was assessed at 60 mmHg and again after a 30-min exposure to an intraluminal pressure of 150 mmHg. The vasodilator response to ACh was significantly reduced in vessels exposed to 150 mmHg. Exposure of the vessels to the superoxide scavenger polyethylene glycol-SOD (100 U/ml), the ANG II type 1 receptor antagonist losartan (10(-6) mol/l), or the angiotensin-converting enzyme inhibitor captopril (10(-5) mol/l) prevented the pressure-induced reduction in ACh-dependent vasodilation observed in untreated vessels. High intraluminal pressure had no effect on papaverine-induced vasodilation or ANG II sensitivity. Increased intraluminal pressure increased dihydroethidium fluorescence in cannulated vessels, which could be prevented by polyethylene glycol-SOD or losartan treatment and endothelial denudation. These data indicate that high intraluminal pressure can increase vascular superoxide and reduce nitric oxide-mediated vasodilation via activation of the vascular renin-angiotensin system. This study provides evidence showing that the local renin-angiotensin system in the human microvasculature may be pressure sensitive and contribute to endothelial dysfunction after acute bouts of hypertension.

Angiotensin-(1-7) and angiotensin-(1-9): function in cardiac and vascular remodelling

The RAS (renin-angiotensin system) is integral to cardiovascular physiology; however, dysregulation of this system largely contributes to the pathophysiology of CVD (cardiovascular disease). It is well established that AngII (angiotensin II), the main effector of the RAS, engages the AT1R (angiotensin type 1 receptor) and promotes cell growth, proliferation, migration and oxidative stress, all processes which contribute to remodelling of the heart and vasculature, ultimately leading to the development and progression of various CVDs, including heart failure and atherosclerosis. The counter-regulatory axis of the RAS, which is centred on the actions of ACE2 (angiotensin-converting enzyme 2) and the resultant production of Ang-(1-7) [angiotensin-(1-7)] from AngII, antagonizes the actions of AngII via the receptor Mas, thereby providing a protective role in CVD. More recently, another ACE2 metabolite, Ang-(1-9) [angiotensin-(1-9)], has been reported to be a biologically active peptide within the counter-regulatory axis of the RAS. The present review will discuss the role of the counter-regulatory RAS peptides Ang-(1-7) and Ang-(1-9) in the cardiovascular system, with a focus on their effects in remodelling of the heart and vasculature.

(Pro)renin and its receptors: pathophysiological implications

Tissue angiotensin generation depends on the uptake of circulating (kidney-derived) renin and/or its precursor prorenin [together denoted as (pro)renin]. Since tissue renin levels are usually somewhat higher than expected based upon the amount of (renin-containing) blood in tissue, an active uptake mechanism has been proposed. Several candidates have been evaluated in the past three decades, including a renin-binding protein, the mannose 6-phosphate/insulin-like growth factor II receptor and the (pro)renin receptor. Although the latter seemed the most promising, its nanomolar affinity for renin and prorenin is several orders of magnitude above their actual (picomolar) levels in blood, raising doubt on whether (pro)renin–(pro)renin receptor interaction will ever occur in vivo. A wide range of in vitro studies have now demonstrated (pro)renin-receptor-induced effects at nanomolar renin and prorenin concentrations, resulting in a profibrotic phenotype. In addition, beneficial in vivo effects of the putative (pro)renin receptor blocker HRP (handle region peptide) have been observed, particularly in diabetic animal models. Despite these encouraging results, many other studies have reported either no or even contrasting effects of HRP, and (pro)renin-receptor-knockout studies revealed lethal consequences that are (pro)renin-independent, most probably due to the fact that the (pro)renin receptor co-localizes with vacuolar H+-ATPase and possibly determines the stability of this vital enzyme. The present review summarizes all of the recent findings on the (pro)renin receptor and its blockade, and critically compares it with the other candidates that have been proposed to mediate (pro)renin uptake from blood. It ends with the conclusion that the (pro)renin–(pro)renin receptor interaction, if it occurs in vivo, is limited to (pro)renin-synthesizing organs such as the kidney.

Olmesartan attenuates the development of heart failure after experimental autoimmune myocarditis in rats through the modulation of ANG 1-7 mas receptor

Angiotensin-converting enzyme 2 (ACE-2) is a membrane-associated carboxy-peptidase catalyzes the conversion of the vasoconstrictor angiotensin (ANG)-II to the vasodilatory peptide ANG 1-7. In view of the expanding axis of the renin angiotensin system, we have investigated the cardioprotective effects of olmesartan (10mg/kg/day) in experimental autoimmune myocarditis. Olmesartan treatment effectively suppressed the myocardial protein expressions of inflammatory markers in comparison to the vehicle-treated rats. However, the protein and mRNA levels of ACE-2 and ANG 1-7, and its receptor Mas were upregulated in olmesartan treated group compared to vehicle-treated rats. Olmesartan medoxomil treatment significantly decreased the expression levels of phospho-p38 mitogen-activated protein kinase (MAPK), phospho-JNK, phospho-ERK and phospho-(MAPK) activated protein kinase-2 than with those of vehicle-treated rats. Moreover, vehicle-treated rats were shown to be up-regulated protein expressions of NADPH oxidase subunits (p47phox, p67phox and Nox-4), myocardial apoptotic markers and endoplasmic reticulum stress markers in comparison to those of normal and all these effects are expectedly down-regulated by an olmesartan. In addition, attenuated protein levels of phosphatidylinositol-3-kinase (PI3K) and phospho-Akt in the vehicle-treated EAM rats were prevented by olmesartan treatment. Our results suggest that beneficial effects of olmesartan treatment was more effective therapy in combating the inflammation, oxidative stress, apoptosis and signaling pathways associated with heart failure at least in part via the modulation of ANG 1-7 mas receptor.

Aliskiren increases bradykinin and tissue kallikrein mRNA levels in the heart

1. Aliskiren is a renin inhibitor with an IC(50) of 0.6 nmol/L for human renin, 4.5 nmol/L for mouse renin and 80 nmol/L for rat renin. 2. In the present study, we compared the effects of aliskiren (10 mg/kg per day), the angiotensin-converting enzyme inhibitor perindopril (0.2 mg/kg per day) and their combination on angiotensin and bradykinin peptides in female heterozygous (mRen-2)27 rats, transgenic for the mouse renin gene. 3. All three treatments produced similar reductions in systolic blood pressure, heart weight and plasma aldosterone levels and reduced angiotensin II levels in lung, but only perindopril and the combination reduced angiotensin II levels in kidney of (mRen-2)27 rats. In contrast, aliskiren and the combination, but not perindopril alone, increased cardiac bradykinin levels. Aliskiren increased immunostaining for tissue kallikrein in the heart and reduced cardiac fibrosis. 4. We investigated the mechanism underlying the increase in bradykinin levels following aliskiren treatment in Sprague-Dawley rats, in which aliskiren has a lower potency for renin inhibition. Aliskiren (10 mg/kg per day) reduced renal angiotensin levels within 24 h, but treatment for > 24 h was required to increase cardiac bradykinin levels. Moreover, 3 mg/kg per day aliskiren increased cardiac bradykinin levels, but did not reduce renal angiotensin levels. Aliskiren did not potentiate the hypotensive effects of bradykinin; however, it increased tissue kallikrein, but not plasma kallikrein, mRNA levels in the heart. 5. These data demonstrate that the aliskiren-induced increase in cardiac bradykinin levels is independent of renin inhibition and changes in bradykinin metabolism, but is associated with increased tissue kallikrein gene expression.

Angiotensin II type 2 receptor agonists: where should they be applied?

INTRODUCTION

Angiotensin II, the active endproduct of the renin-angiotensin system (RAS), exerts its effects via angiotensin II type 1 and type 2 (AT(1), AT(2)) receptors. AT(1) receptors mediate all well-known effects of angiotensin II, ranging from vasoconstriction to tissue remodeling. Thus, to treat cardiovascular disease, RAS blockade aims at preventing angiotensin II-AT(1) receptor interaction. Yet RAS blockade is often accompanied by rises in angiotensin II, which may exert beneficial effects via AT(2) receptors.

AREAS COVERED

This review summarizes our current knowledge on AT(2) receptors, describing their location, function(s), endogenous agonist(s) and intracellular signaling cascades. It discusses the beneficial effects obtained with C21, a recently developed AT(2) receptor agonist. Important questions that are addressed are do these receptors truly antagonize AT(1) receptor-mediated effects? What about their role in the diseased state and their heterodimerization with other receptors?

EXPERT OPINION

The general view that AT(2) receptors exclusively exert beneficial effects has been challenged, and in pathological models, their function sometimes mimics that of AT(1) receptors, for example, inducing vasoconstriction and cardiac hypertrophy. Yet given its upregulation in various pathological conditions, the AT(2) receptor remains a promising target for treatment, allowing effects beyond blood pressure-lowering, for example, in stroke, aneurysm formation, inflammation and myocardial fibrosis.

Perivascular adipose tissue from human systemic and coronary vessels: the emergence of a new pharmacotherapeutic target

Fat cells or adipocytes are distributed ubiquitously throughout the body and are often regarded purely as energy stores. However, recently it has become clear that these adipocytes are engine rooms producing large numbers of metabolically active substances with both endocrine and paracrine actions. White adipocytes surround almost every blood vessel in the human body and are collectively termed perivascular adipose tissue (PVAT). It is now well recognized that PVAT not only provides mechanical support for any blood vessels it invests, but also secretes vasoactive and metabolically essential cytokines known as adipokines, which regulate vascular function. The emergence of obesity as a major challenge to our healthcare systems has contributed to the growing interest in adipocyte dysfunction with a view to discovering new pharmacotherapeutic agents to help rescue compromised PVAT function. Very few PVAT studies have been carried out on human tissue. This review will discuss these and the hypotheses generated from such research, as well as highlight the most significant and clinically relevant animal studies showing the most pharmacological promise.

LINKED ARTICLES

This article is part of a themed section on Fat and Vascular Responsiveness. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2012.165.issue-3.

Intracardiac intracellular angiotensin system in diabetes

The renin-angiotensin system (RAS) has mainly been categorized as a circulating and a local tissue RAS. A new component of the local system, known as the intracellular RAS, has recently been described. The intracellular RAS is defined as synthesis and action of ANG II intracellularly. This RAS appears to differ from the circulating and the local RAS, in terms of components and the mechanism of action. These differences may alter treatment strategies that target the RAS in several pathological conditions. Recent work from our laboratory has demonstrated significant upregulation of the cardiac, intracellular RAS in diabetes, which is associated with cardiac dysfunction. Here, we have reviewed evidence supporting an intracellular RAS in different cell types, ANG II's actions in cardiac cells, and its mechanism of action, focusing on the intracellular cardiac RAS in diabetes. We have discussed the significance of an intracellular RAS in cardiac pathophysiology and implications for potential therapies.

Lipid partitioning after uninephrectomy

This longitudinal study addressed the sequential events and metabolic consequences of lipid partitioning following uninephrectomy. Adult male Sprague-Dawley rats were randomized into sham operation (n = 15) or left uninephrectomy (UNX, n = 18). At 1 and 3 months post nephrectomy, three rats from each group were killed for histopathological examination of adipocyte differentiation and lipid accumulation. Renal protein expression of the lipogenic peroxisome proliferator-activated receptor-γ (PPAR-γ), HMG-CoA reductase (HMGCR), and adiponectin receptor was detected by Western blot and immunofluorescence microscopy. Blood lipids, glucose, insulin, and renal functions were longitudinally measured up to 10 months after operation. The UNX rats progressively developed lipodystrophy of subcutaneous and visceral adipose depots with failure of adipocyte differentiation and lipid storage, followed by blood lipid elevation and ectopic lipid deposition with cellular lipid peroxidation, and renal adipogenesis with chronic inflammatory infiltration. Despite having standard diet, normal food consumption and normal body weight, the uninephrectomized rats with defective lipid partitioning manifested a myriad of homeostatic disturbances including insulin resistance, hyperglycemia, adiponectin resistance, and upregulation of PPAR-γ and HMGCR. Abnormal lipid partitioning from adipose depots to circulation and non-adipose tissues and non-adipocytic cells contributes to homeostatic disturbances and lipogenic activation.

Cardioprotective effects of telmisartan against heart failure in rats induced by experimental autoimmune myocarditis through the modulation of angiotensin-converting enzyme-2/angiotensin 1-7/mas receptor axis

Angiotensin-converting enzyme-2 (ACE-2) is a homolog of ACE that preferentially forms angiotensin-(ANG)-1-7 from angiotensin II (ANG II). We investigated the cardioprotective effects of telmisartan, a well-known angiotensin receptor blockers (ARBs) against experimental autoimmune myocarditis (EAM). EAM was induced in Lewis rats by immunization with porcine cardiac myosin. The rats were divided into two groups and treated with telmisartan (10 mg/kg/day) or vehicle for 21 days. Myocardial functional parameters were significantly improved by treatment with telmisartan compared with vehicle-treated rats. Telmisartan lowered myocardial protein expressions of NADPH oxidase subunits 3-nitrotyrosine, p47phox, p67 phox, Nox-4 and superoxide production significantly than vehicle-treated rats. In contrast myocardial protein levels of ACE-2, ANG 1-7 mas receptor were upregulated in the telmisartan treated group compared with those of vehicle-treated rats. The myocardial protein expression levels of tumor necrosis factor receptor (TNFR)-associated factor (TRAF)-2, C/EBP homologous protein (CHOP) and glucose-regulated protein (GRP) 78 were decreased in the telmisartan treated rats compared with those of vehicle-treated rats. In addition, telmisartan treatment significantly decreased the protein expression levels of phospho-p38 mitogen-activated protein kinase (MAPK), phospho-JNK, phospho-ERK and phospho (MAPK) activated protein kinase-2 than with those of vehicle-treated rats. Moreover, telmisartan significantly decreased the production of proinflammatory cytokines, myocardial apoptotic markers and caspase-3 positive cells compared with those of vehicle-treated rats. Therefore, we suggest that telmisartan was beneficial protection against heart failure in rats, at least in part by suppressing inflammation, oxidative stress, ER stress as well as signaling pathways through the modulation of ACE2/ANG1-7/Mas receptor axis.

Mas receptors in modulating relaxation induced by perivascular adipose tissue

AIMS

Perivascular adipose tissue (PVAT) is known to secrete vascular relaxation factors, and angiotensin 1-7 [Ang-(1-7)] acting on the endothelium is one of the endothelium-dependent relaxation factors. Mas protein is the receptor for Ang-(1-7). Using aorta from Mas-knockout (K/O) and wild type (FVB) mice, we wished to establish the essential role of Mas receptors in mediating the endothelium-dependent relaxation response induced by relaxation factors from PVAT.

MAIN METHODS

Thoracic aortic rings from K/O and FVB mice were prepared with or without PVAT (PVAT+ and PVAT-) and/or intact endothelium (E+) or with the endothelium removed (E-) for functional studies. The contraction and relaxation responses of these vessels to agonist in the presence of different receptor antagonists were studied.

KEY FINDINGS

PVAT attenuated the contraction induced by phenylephrine (PHE) in the presence of endothelium only in vessels from FVB mice. Mas receptor antagonists D-Ala-Ang-(1-7) (A779) or D-Pro(7)-Ang-(1-7) enhanced the contraction induced by PHE only in vessels from FVB mice. Ang-(1-7) caused a relaxation response only in E+vessels from FVB mice. Transfer of donor solution from PVAT+ vessels to PVAT- recipient vessels caused a relaxation response among FVB vessels and not among vessels from K/O mice.

SIGNIFICANCE

Mas receptors are essential in mediating the endothelium-dependent relaxation response induced by PVAT, therefore highlighting the important role of Ang-(1-7) in the control of vascular functions through PVAT.

Simultaneous determination of atorvastatin, amlodipine, ramipril and benazepril in human plasma by LC-MS/MS and its application to a human pharmacokinetic study

A rapid, simple, sensitive and specific LC-MS/MS method has been developed and validated for the simultaneous estimation of atorvastatin (ATO), amlodipine (AML), ramipril (RAM) and benazepril (BEN) using nevirapine as an internal standard (IS). The API-4000 LC-MS/MS was operated under the multiple-reaction monitoring mode using electrospray ionization. Analytes and IS were extracted from plasma by simple liquid-liquid extraction technique using ethyl acetate. The reconstituted samples were chromatographed on C(18) column by pumping 0.1% formic acid-acetonitrile (15:85, v/v) at a flow rate of 1 mL/min. A detailed validation of the method was performed as per the FDA guidelines and the standard curves were found to be linear in the range of 0.26-210 ng/mL for ATO; 0.05-20.5 ng/mL for AML; 0.25-208 ng/mL for RAM and 0.74-607 ng/mL for BEN with mean correlation coefficient of ≥0.99 for each analyte. The intra-day and inter-day precision and accuracy results were well with in the acceptable limits. A run time of 2.5 min for each sample made it possible to analyze more than 400 human plasma samples per day. The developed assay method was successfully applied to a pharmacokinetic study in human male volunteers.

New insights and perspectives on intrarenal renin-angiotensin system: focus on intracrine/intracellular angiotensin II

Although renin, the rate-limiting enzyme of the renin-angiotensin system (RAS), was first discovered by Robert Tigerstedt and Bergman more than a century ago, the research on the RAS still remains stronger than ever. The RAS, once considered to be an endocrine system, is now widely recognized as dual (circulating and local/tissue) or multiple hormonal systems (endocrine, paracrine and intracrine). In addition to the classical renin/angiotensin I-converting enzyme (ACE)/angiotensin II (Ang II)/Ang II receptor (AT₁/AT₂) axis, the prorenin/(Pro)renin receptor (PRR)/MAP kinase axis, the ACE2/Ang (1-7)/Mas receptor axis, and the Ang IV/AT₄/insulin-regulated aminopeptidase (IRAP) axis have recently been discovered. Furthermore, the roles of the evolving RAS have been extended far beyond blood pressure control, aldosterone synthesis, and body fluid and electrolyte homeostasis. Indeed, novel actions and underlying signaling mechanisms for each member of the RAS in physiology and diseases are continuously uncovered. However, many challenges still remain in the RAS research field despite of more than one century's research effort. It is expected that the research on the expanded RAS will continue to play a prominent role in cardiovascular, renal and hypertension research. The purpose of this article is to review the progress recently being made in the RAS research, with special emphasis on the local RAS in the kidney and the newly discovered prorenin/PRR/MAP kinase axis, the ACE2/Ang (1-7)/Mas receptor axis, the Ang IV/AT₄/IRAP axis, and intracrine/intracellular Ang II. The improved knowledge of the expanded RAS will help us better understand how the classical renin/ACE/Ang II/AT₁ receptor axis, extracellular and/or intracellular origin, interacts with other novel RAS axes to regulate blood pressure and cardiovascular and kidney function in both physiological and diseased states.

Angiotensin1-9 antagonises pro-hypertrophic signalling in cardiomyocytes via the angiotensin type 2 receptor

The renin–angiotensin system (RAS) regulates blood pressure mainly via the actions of angiotensin (Ang)II, generated via angiotensin converting enzyme (ACE). The ACE homologue ACE2 metabolises AngII to Ang1-7, decreasing AngII and increasing Ang1-7, which counteracts AngII activity via the Mas receptor. However, ACE2 also converts AngI to Ang1-9, a poorly characterised peptide which can be further converted to Ang1-7 via ACE. Ang1-9 stimulates bradykinin release in endothelium and has antihypertrophic actions in the heart, attributed to its being a competitive inhibitor of ACE, leading to decreased AngII, rather than increased Ang1-7. To date no direct receptor-mediated effects of Ang1-9 have been described. To further understand the role of Ang1-9 in RAS function we assessed its action in cardiomyocyte hypertrophy in rat neonatal H9c2 and primary adult rabbit left ventricular cardiomyocytes, compared to Ang1-7. Cardiomyocyte hypertrophy was stimulated with AngII or vasopressin, significantly increasing cell size by approximately 1.2-fold (P < 0.05) as well as stimulating expression of the hypertrophy gene markers atrial natriuretic peptide, brain natriuretic peptide, β-myosin heavy chain and myosin light chain (2- to 5-fold, P < 0.05). Both Ang1-9 and Ang1-7 were able to block hypertrophy induced by either agonist (control, 186.4 μm; AngII, 232.8 μm; AngII+Ang1-7, 198.3 μm; AngII+Ang1-9, 195.9 μm; P < 0.05). The effects of Ang1-9 were not inhibited by captopril, supporting previous evidence that Ang1-9 acts independently of Ang1-7. Next, we investigated receptor signalling via angiotensin type 1 and type 2 receptors (AT1R, AT2R) and Mas. The AT1R antagonist losartan blocked AngII-induced, but not vasopressin-induced, hypertrophy. Losartan did not block the antihypertrophic effects of Ang1-9, or Ang1-7 on vasopressin-stimulated cardiomyocytes. The Mas antagonist A779 efficiently blocked the antihypertrophic effects of Ang1-7, without affecting Ang1-9. Furthermore, Ang1-7 activity was also inhibited in the presence of the bradykinin type 2 receptor antagonist HOE140, without affecting Ang1-9. Moreover, we observed that the AT2R antagonist PD123,319 abolished the antihypertrophic effects of Ang1-9, without affecting Ang1-7, suggesting Ang1-9 signals via the AT2R. Radioligand binding assays demonstrated that Ang1-9 was able to bind the AT2R (pKi = 6.28 ± 0.1). In summary, we ascribe a direct biological role for Ang1-9 acting via the AT2R. This has implications for RAS function and identifying new therapeutic targets in cardiovascular disease.

Angiotensin-(1-9) regulates cardiac hypertrophy in vivo and in vitro

BACKGROUND

Angiotensin-(1-9) is present in human and rat plasma and its circulating levels increased early after myocardial infarction or in animals treated with angiotensin-converting enzyme inhibitor. However, the cardiovascular effects of this peptide are unknown.

OBJECTIVE

To determine whether angiotensin-(1-9) is a novel anti-cardiac hypertrophy factor in vitro and in vivo and whether this peptide is involved in the pharmacological effects of cardiovascular drugs acting on the renin-angiotensin system.

METHODS AND RESULTS

The administration of angiotensin-(1-9) to myocardial infarcted rats by osmotic minipumps (450 ng/kg per min, n = 6) vs. vehicle (n = 8) for 2 weeks decreased plasma angiotensin II levels, inhibited angiotensin-converting enzyme activity and also prevented cardiac myocyte hypertrophy. However, cardiac myocyte hypertrophy attenuation triggered by angiotensin-(1-9) was not modified with the simultaneous administration of the angiotensin-(1-7) receptor antagonist A779 (100 ng/kg per min, n = 6). In experiments in vitro with cultured cardiac myocytes incubated with norepinephrine (10 micromol/l) or with insulin-like growth factor-1 (10 nmol/l), angiotensin-(1-9) also prevented hypertrophy. In other experimental setting, myocardial infarcted rats (n = 37) were randomized to receive either vehicle (n = 12), enalapril (10 mg/kg per day, n = 12) or angiotensin II receptor blocker candesartan (10 mg/kg per day, n = 13) for 8 weeks. Both drugs prevented left ventricle hypertrophy and increased plasma angiotensin-(1-9) levels by several folds. Angiotensin-(1-9) levels correlated negatively with different left ventricular hypertrophy markers even after adjustment for blood pressure reduction.

CONCLUSION

Angiotensin-(1-9) is an effective and a novel anti-cardiac hypertrophy agent not acting via the Mas receptor.

Determinants of CREB degradation and KChIP2 gene transcription in cardiac memory

BACKGROUND

Left ventricular pacing (LVP) to induce cardiac memory (CM) in dogs results in a decreased transient outward K current (I(to)) and reduced mRNA and protein of the I(to) channel accessory subunit, KChIP2. The KChIP2 decrease is attributed to a decrease in its transcription factor, cyclic adenosine monophosphate response element binding protein (CREB).

OBJECTIVE

This study sought to determine the mechanisms responsible for the CREB decrease that is initiated by LVP.

METHODS

CM was quantified as T-wave vector displacement in 18 LVP dogs. In 5 dogs, angiotensin II receptor blocker, saralasin, was infused before and during pacing. In 3 dogs, proteasomal inhibitor, lactacystin, was injected into the left anterior descending artery before LVP. Epicardial biopsy samples were taken before and after LVP. Neonatal rat cardiomyocytes (NRCM) were incubated with H(2)O(2) (50 micromol/l) for 1 hour with or without lactacystin.

RESULTS

LVP significantly displaced the T-wave vector and was associated with increased lipid peroxidation and increased tissue angiotensin II levels. Saralasin prevented T-vector displacement and lipid peroxidation. CREB was significantly decreased after 2 hours of LVP and was comparably decreased in H(2)O(2)-treated NRCM. Lactacystin inhibited the CREB decrease in LVP dogs and H(2)O(2)-treated NRCM. LVP and H(2)O(2) both induced CREB ubiquitination, and the H(2)O(2)-induced CREB decrease was prevented by knocking down ubiquitin.

CONCLUSION

LVP initiates myocardial angiotensin II production and reactive oxygen species synthesis, leading to CREB ubiquitination and its proteasomal degradation. This sequence of events would explain the pacing-induced reduction in KChIP2, and contribute to altered repolarization and the T-wave changes of cardiac memory.

Measurement of plasma renin concentration in cats by use of a fluorescence resonance energy transfer peptide substrate of renin

OBJECTIVE

To evaluate the use of a commercially available 5-carboxyfluorescein-based, intramolecularly quenched, fluorescence resonance energy transfer (FRET) peptide substrate of renin for measurement of plasma renin concentration in cats.

SAMPLE POPULATION

Plasma samples obtained during a previous study of renal autograft ischemia-reperfusion injury in 10 cats and samples of fetal bovine serum containing recombinant human renin (rh-renin).

PROCEDURES

Experiments involving samples of fetal bovine serum containing rh-renin were conducted to identify a suitable control vehicle, optimal substrate concentration, and appropriate duration of incubation. With the use of the identified assay conditions, a standard curve was constructed to allow conversion of relative fluorescent units into values of renin concentration (ng/mL). Subsequently, plasma samples obtained from cats before and after renal autograft ischemia-reperfusion injury were assayed to determine endogenous renin concentration.

RESULTS

Under conditions of a 1:50 substrate dilution and 4-hour incubation period, the assay detected small amounts of rh-renin in fetal bovine serum. A linear relationship (R(2) = 0.996) between the relative fluorescent units generated and exogenous rh-renin concentration was evident. The assay detected renin in plasma samples obtained from cats after renal autograft ischemia-reperfusion, and renin concentrations on days 1 and 2 after transplant differed significantly.

CONCLUSIONS AND CLINICAL RELEVANCE

The study data indicated that the assay involving the FRET peptide substrate of renin is potentially a rapid and specific method for measurement of plasma renin concentration in cats.

Endothelium-dependent relaxation factor released by perivascular adipose tissue

OBJECTIVE

Recent studies have demonstrated that perivascular adipose tissue (PVAT) releases vascular relaxation factor(s), but the identity of this relaxation factor remains unknown. Here, we examined if angiotensin 1-7 [Ang-(1-7)] is one of the relaxation factors released by PVAT.

METHOD

Morphological and functional methods were used to study aorta from adult Wistar rats.

RESULTS

Immunohistochemical staining showed abundant presence of Ang-(1-7) in aortic PVAT. In vessels with PVAT removed but intact endothelium (PVAT - E+), contraction induced by phenylephrine was attenuated by preincubation with Ang-(1-7). PVAT - E+ vessels precontracted with phenylephrine showed a concentration-dependent relaxation response to Ang-(1-7), and this response was abolished by the removal of endothelium. Relaxation response induced by Ang-(1-7) was also prevented by Ang-(1-7) receptor (Mas) antagonist (A779), nitric oxide synthase inhibitor, and nitric oxide scavenger. Ang-(1-7) did not cause a relaxation response in aorta precontracted with KCl, and the relaxation response to Ang-(1-7) was also blocked by calcium-dependent potassium (K(Ca)) channel blockers. Incubation of PVAT + E+ vessels with A779 or angiotensin-converting enzyme 2 inhibitor DX600 or angiotensin-converting enzyme inhibitor enalaprilat increased the contraction induced by phenylephrine. Transfer of donor solution incubated with PVAT + E+ vessel to recipient PVAT - E+ vessel caused a relaxation response. This relaxation response was abolished when donor vessels were incubated with DX600 or enalaprilat or when recipient vessels were incubated with A779.

CONCLUSION

Ang-(1-7) released by PVAT acts on the endothelium to cause the release of nitric oxide, and nitric oxide acts as a hyperpolarizing factor through K(Ca) channels to cause relaxation of the blood vessel.

Cardiac Renin levels are not influenced by the amount of resident mast cells

To investigate whether mast cells release renin in the heart, we studied renin and prorenin synthesis by such cells, using the human mast cell lines human mastocytoma 1 and LAD2, as well as fresh mast cells from mastocytosis patients. We also quantified the contribution of mast cells to cardiac renin levels in control and infarcted rat hearts. Human mastocytoma 1 cells contained and released angiotensin I-generating activity, and the inhibition of this activity by the renin inhibitor aliskiren was comparable to that of recombinant human renin. Prorenin activation with trypsin increased angiotensin I-generating activity in the medium only, suggesting release but not storage of prorenin. The adenylyl cyclase activator forskolin, the cAMP analogue 8-db-cAMP, and the degranulator compound 48/80 increased renin release without affecting prorenin. Angiotensin II blocked the forskolin-induced renin release. Angiotensin I-generating activity was undetectable in LAD2 cells and fresh mast cells. Nonperfused rat hearts contained angiotensin I-generating activity, and aliskiren blocked approximately 70% of this activity. A 30-minute buffer perfusion washed away >70% of the aliskiren-inhibitable angiotensin I-generating activity. Prolonged buffer perfusion or compound 48/80 did not decrease cardiac angiotensin I-generating activity further or induce angiotensin I-generating activity release in the perfusion buffer. Results in infarcted hearts were identical, despite the increased mast cell number in such hearts. In conclusion, human mastocytoma 1 cells release renin and prorenin, and the regulation of this release resembles that of renal renin. However, this is not a uniform property of all mast cells. Mast cells appear an unlikely source of renin in the heart, both under normal and pathophysiological conditions.

Genetic models provide unique insight into angiotensin and bradykinin peptides in the extravascular compartment of the heart in vivo

1. There is continuing uncertainty about the tissue compartments where angiotensin and bradykinin peptide formation occurs. Mice with angiotensin-converting enzyme (ACE) expression targeted to the cardiomyocyte membrane provide a unique experimental model to detect ACE substrates in the extravascular compartment of the heart in vivo. 2. Angiotensin (Ang) I and II, bradykinin-(1-7) and bradykinin-(1-9) were measured in blood and cardiac ventricles of wild-type (WT) mice, mice with a non-functional somatic ACE gene promoter (KO), mice homozygous (8/8) and heterozygous (1/8) for cardiomyocyte-targeted ACE expression and a non-functional somatic ACE gene promoter, and mice heterozygous for cardiomyocyte-targeted ACE expression and heterozygous for the WT ACE allele (WT/8). 3. Cardiac AngII levels of 8/8, 1/8, WT/8 and WT mice were higher than KO levels. Cardiac AngII levels in 8/8 and 1/8 mice were also higher than WT levels, but the levels in WT/8 mice were similar to WT levels. Cardiac bradykinin-(1-9) levels of WT, but not 8/8 mice, were lower than in KO mice, whereas bradykinin-(1-7) levels in 8/8 mice were lower than in KO mice. 4. We conclude that AngI and bradykinin-(1-7) are present in the cardiac extravascular compartment of mice lacking vascular ACE and that extravascular ACE produces AngII and metabolises bradykinin-(1-7) in this compartment. The data suggest that the vascular compartment is the main site of AngI and bradykinin-(1-9) formation and metabolism and that vascular ACE may limit AngI entry to the extravascular compartment of WT mice.

Differential regulation of angiotensin-(1-12) in plasma and cardiac tissue in response to bilateral nephrectomy

We examined the effects of 48 h bilateral nephrectomy on plasma and cardiac tissue expression of angiotensin-(1-12) [ANG-(1-12)], ANG I, and ANG II in adult Wistar-Kyoto rats to evaluate functional changes induced by removing renal renin. The goal was to expand the evidence of ANG-(1-12) being an alternate renin-independent, angiotensin-forming substrate. Nephrectomy yielded divergent effects on circulating and cardiac angiotensins. Significant decreases in plasma ANG-(1-12), ANG I, and ANG II levels postnephrectomy accompanied increases in cardiac ANG-(1-12), ANG I, and ANG II concentrations compared with controls. Plasma ANG-(1-12) decreased 34% following nephrectomy, which accompanied 78 and 66% decreases in plasma ANG I and ANG II, respectively (P < 0.05 vs. controls). Contrastingly, cardiac ANG-(1-12) in anephric rats averaged 276 +/- 24 fmol/mg compared with 144 +/- 20 fmol/mg in controls (P < 0.005). Cardiac ANG I and ANG II values were 300 +/- 15 and 62 +/- 7 fmol/mg, respectively, in anephric rats compared with 172 +/- 8 fmol/mg for ANG I and 42 +/- 4 fmol/mg for ANG II in controls (P < 0.001). Quantitative immunofluorescence revealed significant increases in average grayscale density for cardiac tissue angiotensinogen, ANG I, ANG II, and AT(1) receptors of WKY rats postnephrectomy. Faint staining of cardiac renin, unchanged by nephrectomy, was associated with an 80% decrease in cardiac renin mRNA. These changes were accompanied by significant increases in p47(phox), Rac1, and Nox4 isoform expression. In conclusion, ANG-(1-12) may be a functional precursor for angiotensin peptide formation in the absence of circulating renin.

Fat redistribution and adipocyte transformation in uninephrectomized rats

Dyslipidemia complicates renal function leading to disturbances of major homeostatic organs in the body. Here we examined the effect of chronic renal dysfunction induced by uninephrectomy on fat redistribution and lipid peroxidation in rats treated with an angiotensin-converting enzyme (ACE) inhibitor (lisinopril) for up to 10 months. Uninephrectomized rats developed fat redistribution and hypercholesterolemia typical of chronic renal failure when compared with sham-operated rats or lisinopril-treated uninephrectomized rats. The weight of the peri-renal fat was significantly less in the untreated compared to the lisinopril-treated uninephrectomized rats or those rats with a sham operation. We also found that there was a shift of heat-protecting unilocular adipocytes to heat-producing multilocular fat cells in the untreated uninephrectomized rats. Similarly in these rats we found a shift of subcutaneous and visceral fat to ectopic fat with excessive lipid accumulation and lipofuscin pigmentation. Lisinopril treatment prevented fat redistribution or transformation and lipid peroxidation. This study shows that ACE inhibition may prevent the fat anomalies associated with chronic renal dysfunction.