Local renin-angiotensin systems and their interactions with extra-adrenal corticosteroid production

Nebivolol/valsartan combination for the treatment of hypertension: a review

Nebivolol (N) is a β₁-adrenoreceptor antagonist that is approved for treatment of hypertension in the USA. Effective treatment of hypertension is becoming an increasingly difficult process that often requires multiple drug combinations to meet target guidelines. This has resulted in the increasing introduction of multidrug single-pill combinations (SPCs) to facilitate cost and compliance issues. Some of the SPCs have added valsartan (V), an angiotensin receptor blocker, which is an increasingly advocated antihypertensive class. Pharmacological profiles of N and V, alone and combined, are well characterized. In 2007, the SPC of N and V, 5 and 80 mg, respectively, was approved by the US FDA for treatment of hypertension. This paper will summarize and update key issues in pharmacology, clinical use and benefit.

Rationale for nebivolol/valsartan combination for hypertension: review of preclinical and clinical data

To treat hypertension, combining two or more antihypertensive drugs from different classes is often necessary. β-Blockers and renin–angiotensin–aldosterone system inhibitors, when combined, have been deemed ‘less effective’ based on partially overlapping mechanisms of action and limited evidence. Recently, the single-pill combination (SPC) of nebivolol (Neb) 5 mg – a vasodilatory β1-selective antagonist/β3 agonist – and valsartan 80 mg, an angiotensin II receptor blocker, was US Food and Drug Administration-approved for hypertension. Pharmacological profiles of Neb and valsartan, alone and combined, are well characterized. In addition, a large 8-week randomized trial in stages I–II hypertensive patients (N = 4161) demonstrated greater blood pressure-reducing efficacy for Neb/valsartan SPCs than component monotherapies with comparable tolerability. In a biomarkers substudy (N = 805), Neb/valsartan SPCs prevented valsartan-induced increases in plasma renin, and a greater reduction in plasma aldosterone was observed with the highest SPC dose vs. valsartan 320 mg/day. This review summarizes preclinical and clinical evidence supporting Neb/valsartan as an efficacious and well tolerated combination treatment for hypertension.

Angiotensin II type 1a receptor-deficient mice develop angiotensin II-induced oxidative stress and DNA damage without blood pressure increase

Hypertensive patients have an increased risk of developing kidney cancer. We have shown in vivo that besides elevating blood pressure, angiotensin II causes DNA damage dose dependently. Here, the role of blood pressure in the formation of DNA damage is studied. Mice lacking one of the two murine angiotensin II type 1 receptor (AT1R) subtypes, AT1aR, were equipped with osmotic minipumps, delivering angiotensin II during 28 days. Parameters of oxidative stress and DNA damage of kidneys and hearts of AT1aR-knockout mice were compared with wild-type (C57BL/6) mice receiving angiotensin II, and additionally, with wild-type mice treated with candesartan, an antagonist of both AT1R subtypes. In wild-type mice, angiotensin II induced hypertension, reduced kidney function, and led to a significant formation of reactive oxygen species (ROS). Furthermore, genomic damage was markedly increased in this group. All these responses to angiotensin II could be attenuated by concurrent administration of candesartan. In AT1aR-deficient mice treated with angiotensin II, systolic pressure was not increased, and renal function was not affected. However, angiotensin II still led to an increase of ROS in kidneys and hearts of these animals. Additionally, genomic damage in the form of double-strand breaks was significantly induced in kidneys of AT1aR-deficient mice. Our results show that angiotensin II induced ROS production and DNA damage even without the presence of AT1aR and independently of blood pressure changes.

A rare case of juvenile hypertension: coexistence of type 2 multiple endocrine neoplasia -related bilateral pheochromocytoma and reninoma in a young patient with ACE gene polymorphism

BACKGROUND

Pheochromocytoma and reninoma represent two rare diseases causing hypertension. We here reported a rare case of association between type 2 multiple endocrine neoplasia related bilateral pheochromocytoma and reninoma. Moreover, polymorphism of ACE gene, which is known to be related to an increase of cardiovascular risk, has been found in the same patient.

CASE PRESENTATION

A 24 year old Caucasian man came to our attention for severe hypertension, resistant to anti-hypertensive polytherapy. At the age of twenty he had undergone total thyroidectomy with lymphadenectomy for medullary carcinoma. Genetic testing showed a RET mutation of codon 918 (exon 16) not documented in other family members. During the follow-up, a progressive increase of urinary metanephrines and catecholamines was recorded. Our evaluation confirmed the presence of severe hypertension (220/140 mmHg) and a severe increase of urinary catecholamines and metanephrines. Due to the presence of hypokalemia, other causes of hypertension were researched leading to the discovery of hyperreninemia (236 μUI/ml) with mild hyperaldosteronism, and a mild increase of the renal artery resistance at ultrasound. An abdominal MRI showed multiple adrenal masses and a right kidney nodular lesion of about 2 cm. The patient underwent bilateral adrenalectomy and right nephrectomy, and histology confirmed the presence of bilateral pheochromocytoma and right reninoma. The post-surgery laboratory evaluation showed a rapid reduction of the urinary metanephrines while plasma renin level remained low in spite of the bilateral adrenalectomy without any mineralocorticoid supplementation. To further investigate these unusual feature, we performed genetic testing for the ACE gene, which revealed the presence of ACE I/D polymorphism.

CONCLUSION

This unique report describes the association between two rare causes of hypertension in the same patient. Furthermore, the absence of requirement of mineralocorticoid supplementation in spite of bilateral adrenalectomy, represent an uncommon and interest finding.

The multifaceted mineralocorticoid receptor

The primary adrenal cortical steroid hormones, aldosterone, and the glucocorticoids cortisol and corticosterone, act through the structurally similar mineralocorticoid (MR) and glucocorticoid receptors (GRs). Aldosterone is crucial for fluid, electrolyte, and hemodynamic homeostasis and tissue repair; the significantly more abundant glucocorticoids are indispensable for energy homeostasis, appropriate responses to stress, and limiting inflammation. Steroid receptors initiate gene transcription for proteins that effect their actions as well as rapid non-genomic effects through classical cell signaling pathways. GR and MR are expressed in many tissues types, often in the same cells, where they interact at molecular and functional levels, at times in synergy, others in opposition. Thus the appropriate balance of MR and GR activation is crucial for homeostasis. MR has the same binding affinity for aldosterone, cortisol, and corticosterone. Glucocorticoids activate MR in most tissues at basal levels and GR at stress levels. Inactivation of cortisol and corticosterone by 11β-HSD2 allows aldosterone to activate MR within aldosterone target cells and limits activation of the GR. Under most conditions, 11β-HSD1 acts as a reductase and activates cortisol/corticosterone, amplifying circulating levels. 11β-HSD1 and MR antagonists mitigate inappropriate activation of MR under conditions of oxidative stress that contributes to the pathophysiology of the cardiometabolic syndrome; however, MR antagonists decrease normal MR/GR functional interactions, a particular concern for neurons mediating cognition, memory, and affect.

Expression of the renin-angiotensin system in a human placental cell line

BACKGROUND

The renin-angiotensin system (RAS) is present in human placental tissue and participates in regulation of maternal-fetal blood flow during pregnancy. RAS expression in placental tissue is regulated by various hormones and is altered in various disease conditions. An in vitro system is needed to further investigate regulation of the placental RAS. To this end, we studied RAS expression in the human placenta-derived cell line, CRL-7548.

METHODS

CRL-7548 cells were cultured in plastic plates. Total RNA was extracted, reverse transcribed, and amplified by polymerase chain reaction (PCR) with specific primers. Angiotensin II peptide in the culture media was measured by radioimmunoassay. Renin activity was detected by radioimmunoassay measuring angiotensin I generated. Angiotensin receptor type I was detected by Western blot.

RESULTS

Specific mRNA for angiotensin, renin, angiotensin converting enzyme, and angiotensin receptor type I was detected by real-time PCR. Renin activity was detected in the placental cell lysate, and angiotensin II peptide, the final product of the RAS system, was detected in cell culture media by radioimmunoassay. Angiotensin receptor type I was identified as a 41 kDa protein in cell lysates by Western blot.

CONCLUSIONS

These results demonstrate that all necessary components of the classic RAS are expressed in the human placental cell line CRL-7548. This cell line may prove useful as an in vitro system for studying RAS regulation in the placenta.

Extra-adrenal glucocorticoids and mineralocorticoids: evidence for local synthesis, regulation, and function

Glucocorticoids and mineralocorticoids are steroid hormones classically thought to be secreted exclusively by the adrenal glands. However, recent evidence has shown that corticosteroids can also be locally synthesized in various other tissues, including primary lymphoid organs, intestine, skin, brain, and possibly heart. Evidence for local synthesis includes detection of steroidogenic enzymes and high local corticosteroid levels, even after adrenalectomy. Local synthesis creates high corticosteroid concentrations in extra-adrenal organs, sometimes much higher than circulating concentrations. Interestingly, local corticosteroid synthesis can be regulated via locally expressed mediators of the hypothalamic-pituitary-adrenal (HPA) axis or renin-angiotensin system (RAS). In some tissues (e.g., skin), these local control pathways might form miniature analogs of the pathways that regulate adrenal corticosteroid production. Locally synthesized glucocorticoids regulate activation of immune cells, while locally synthesized mineralocorticoids regulate blood volume and pressure. The physiological importance of extra-adrenal glucocorticoids and mineralocorticoids has been shown, because inhibition of local synthesis has major effects even in adrenal-intact subjects. In sum, while adrenal secretion of glucocorticoids and mineralocorticoids into the blood coordinates multiple organ systems, local synthesis of corticosteroids results in high spatial specificity of steroid action. Taken together, studies of these five major organ systems challenge the conventional understanding of corticosteroid biosynthesis and function.

Superoxide anion and hydrogen peroxide-induced signaling and damage in angiotensin II and aldosterone action

The formation of reactive oxygen species (ROS) can be induced by xenobiotic substances, such as redox cycling molecules, but also by endogenous substances such as hormones and cytokines. Recent research shows the importance of ROS in cellular signaling. Here, the signaling pathways of the two blood pressure-regulating hormones angiotensin II and aldosterone are presented, focusing on both their physiological effects and the change of signaling owing to the action of increased concentrations or prolonged exposure. When present in high concentrations, both angiotensin II and aldosterone, as various other endogenous substances, activate NADPH oxidase, which produces superoxide. In this review the generation of superoxide anions and hydrogen peroxide in cells stimulated with angiotensin II or aldosterone, as well as the subsequently induced signaling processes and DNA damage is discussed.

Mineralocorticoid and glucocorticoid receptors in sciatic nerve function and regeneration

The contribution of the two corticosteroid (mineralocorticoid and glucocorticoid) receptor (MR and GR) pathways to the function and regeneration of the sciatic nerve was investigated. We found that the corticosterone-inactivating enzyme 11β-hydroxysteroid dehydrogenase type 2 (HSD2) was up-regulated 7 days after lesion in freeze-injured nerve. The maintenance of a low intracellular level of corticosterone by HSD2 activity in the regenerating nerve is concordant with the improvement of nervous function in injured animals (as measured by walking ability) after treatment by the GR antagonist mifepristone and with the reduction in GR participation in accumulation of the mRNA for numerous endogenous genes (from the renin-angiotensin system and other classical mineralocorticoid-responsive genes), in the same animals. Furthermore, using the MR antagonist spironolactone, we demonstrated that MR plays an active role in the function of the intact sciatic nerve: MR is required for walking ability and participates in the control of the accumulation of the mRNA for several endogenous genes. However, after injury, changes in gene expression cannot be fully explained by changes in MR/GR activity, due to an HSD2 effect, and other signalling pathway(s) induced by the lesion likely combine with the effect of the corticosteroid receptors.

A lifetime of aldosterone excess: long-term consequences of altered regulation of aldosterone production for cardiovascular function

Up to 15% of patients with essential hypertension have inappropriate regulation of aldosterone; although only a minority have distinct adrenal tumors, recent evidence shows that mineralocorticoid receptor activation contributes to the age-related blood pressure rise and illustrates the importance of aldosterone in determining cardiovascular risk. Aldosterone also has a major role in progression and outcome of ischemic heart disease. These data highlight the need to understand better the regulation of aldosterone synthesis and its action. Aldosterone effects are mediated mainly through classical nuclear receptors that alter gene transcription. In classic epithelial target tissues, signaling mechanisms are relatively well defined. However, aldosterone has major effects in nonepithelial tissues that include increased synthesis of proinflammatory molecules and reactive oxygen species; it remains unclear how these effects are controlled and how receptor specificity is maintained. Variation in aldosterone production reflects interaction of genetic and environmental factors. Although the environmental factors are well understood, the genetic control of aldosterone synthesis is still the subject of debate. Aldosterone synthase (encoded by the CYP11B2 gene) controls conversion of deoxycorticosterone to aldosterone. Polymorphic variation in CYP11B2 is associated with increased risk of hypertension, but the molecular mechanism that accounts for this is not known. Altered 11beta-hydroxylase efficiency (conversion of deoxycortisol to cortisol) as a consequence of variation in the neighboring gene (CYP11B1) may be important in contributing to altered control of aldosterone synthesis, so that the risk of hypertension may reflect a digenic effect, a concept that is discussed further. There is evidence that a long-term increase in aldosterone production from early life is determined by an interaction of genetic and environmental factors, leading to the eventual phenotypes of aldosterone-associated hypertension and cardiovascular damage in middle age and beyond. The importance of aldosterone has generated interest in its therapeutic modulation. Disadvantages associated with spironolactone (altered libido, gynecomastia) have led to a search for alternative mineralocorticoid receptor antagonists. Of these, eplerenone has been shown to reduce cardiovascular risk after myocardial infarction. The benefits and disadvantages of this therapeutic approach are discussed.

Drug Insight: eplerenone, a mineralocorticoid-receptor antagonist

Increasing recognition of the role of aldosterone in cardiovascular disease has been supported by a significant body of evidence from animal models. This evidence has been translated into clinical practice, and large-scale, randomized, placebo-controlled trials have confirmed the beneficial effects of mineralocorticoid blockade in patients with heart failure. As a consequence, there has been a resurgence in the use of mineralocorticoid-receptor antagonists in clinical practice that has prompted the search for a potent and specific antagonist without the sexual side effects of spironolactone. Eplerenone, a mineralocorticoid-receptor antagonist with minimal binding to the progesterone and androgen receptors, is now licensed for treatment of heart failure in Europe and heart failure and hypertension in the US; it has also been proposed as a treatment for a variety of cardiovascular conditions. This article reviews the current concepts of the actions of aldosterone at a cellular level. Recent findings regarding its role as a cardiovascular hormone, both in animal models and human studies, are discussed. We also describe the development of mineralocorticoid-receptor blockers following the isolation of aldosterone and discuss the subsequent search for a specific mineralocorticoid antagonist. In addition we detail the effects of eplerenone in a number of clinical situations and outline its potential future applications.

Angiotensin II-induced genomic damage in renal cells can be prevented by angiotensin II type 1 receptor blockage or radical scavenging

Hypertensive patients exhibit elevated cancer incidence, especially of cancers of the kidney. Elevated levels of ANG II, the active peptide of the renin-angiotensin system, regulating blood pressure and cardiovascular homeostasis, are known to cause hypertension and kidney diseases. There is evidence that ANG II is an activator of NAD(P)H oxidase, leading to the formation of free radicals, which are known to participate in the induction of DNA damage. This study was undertaken to characterize ANG II-induced DNA damage. DNA damage was measured by comet assay and micronucleus frequency test. Incubation of pig kidney cells (LLC-PK(1)) in vitro with ANG II concentrations between 85 and 340 nM led to a 6- to 15-fold increase of DNA damage compared with the control as revealed by comet assay analysis. Micronuclei were induced about fourfold compared with the control in pig and rat kidney cells (LLC-PK(1), NRK) and in human promyelocytic cells (HL-60). ANG II-induced DNA damage could be prevented by coincubation with the ANG II type 1 receptor blocker candesartan and the antioxidants N-acetylcysteine and alpha-tocopherol. The ANG II type 2 receptor antagonist PD123319 could not reduce ANG II-induced DNA damage. Measurement of reactive oxygen species (ROS) by flow cytometry showed an enhanced formation after exposure to ANG II and a reduction of ROS after candesartan, N-acetylcysteine, and alpha-tocopherol. The present findings support our hypothesis that ANG II causes DNA damage via ANG II type 1 receptor binding and subsequent formation of oxidative stress.

Angiotensin II Receptor Expression Following Intestinal Transplantation in Mice

BACKGROUND

To further improve the success rate of intestinal transplantation there is a need to find early appearing indicators of rejection. The specific aim of this study was to compare Angiotensin (Ang) II type 1 receptor and Ang II type 2 receptor expression in relation to histological signs of rejection.

METHODS

Mice of the C57BL6 strain with syngeneic intestinal grafts were compared to mice subjected to allogeneic intestinal transplantation with BalbC strain as donors. Local expression of Ang II type 1 and 2 receptor was evaluated using rt-PCR and Western blot and compared to histological picture in grafts and native intestine.

RESULTS

The Ang II type 2 receptor protein expression was markedly up-regulated in the allogeneically transplanted graft from day 1 postoperatively. Histological signs of rejection were not seen until day 6.

CONCLUSION

Intestinal allograft transplantation in mice is associated with a marked up-regulation of the Ang II type 2 receptor. However, the detailed role of the renin-angiotensin system in the immune rejection following intestinal transplantation remains to be clarified.

Synthesis and secretion of angiotensin II by the prostate gland in vitro

The renin angiotensin system has been shown to have tissue-related functions that are distinct from its systemic roles. We showed that angiotensin II type 1 (AT1) receptors are present in mammalian sperm, and angiotensin II stimulates sperm motility and capacitation. In addition, angiotensin II is present in human seminal plasma at concentrations higher than found in blood. In testing the possibility that the prostate may be the source of seminal plasma angiotensin II, mRNA coding for angiotensinogen, (pro)renin, and angiotensin-converting enzyme were identified by RT-PCR in rat and human prostate and in prostate LNCaP cells, as well as the angiotensin receptors types 1 and 2 (AT1 and AT2) in human tissues and AT1 in rat. In human tissue, immunocytochemistry showed cellular colocalization of renin with the AT1 receptor in secretory epithelial cells. Confirmation of the capacity of the prostate to secrete angiotensin II was shown by the detection of immunoreactive angiotensin in media removed from rat prostate organ cultures and LNCaP cells. Rat prostate angiotensin secretion was enhanced by dihydrotestosterone, but LNCaP angiotensin was stimulated by estradiol. This stimulation was blocked by tamoxifen. Rat prostate AT1 receptor expression was much greater in prepuberal than in postpuberal rats but was not affected by a low-sodium diet. It was, however, significantly enhanced by captopril pretreatment. These findings all suggest the independence of prostate and systemic renin angiotensin system regulation. The data presented here suggest that the prostate may be a source of the secreted angiotensin II found in seminal plasma.

Studies on the origin of circulating 18-hydroxycortisol and 18-oxocortisol in normal human subjects

18-Hydroxycortisol (18-OHF) and 18-oxocortisol (18-oxoF) are derivatives of cortisol found in primary aldosteronism but whose origin and regulation in normal subjects are uncertain. 18-OHF can be synthesized by zona fasciculata 11-beta hydroxylase; 18-oxoF can only be produced by zona glomerulosa aldosterone synthase (AS). Stably transfected cell lines expressing either CYP11B1 (11beta-hydroxylase) or CYP11B2 (AS) were incubated with cortisol and other substrates over a range of concentrations. Both enzymes could synthesize 18-OHF from cortisol, but only AS could synthesize 18-oxoF. AS was more efficient than 11beta-hydroxylase at 18-hydroxylation. The apparent Michaelis-Menten constant (K(m)) of AS for cortisol was estimated to be 2.6 microm. In five patients with adrenal insufficiency maintained on hydrocortisone, urinary free cortisol and cortisone levels were high; 18-oxoF was detectable in all patients and 18-OHF in three. It is likely that the 18-oxygenated steroids were synthesized from circulating cortisol, either in the zona glomerulosa or at extraadrenal sites. In eight male volunteers, dexamethasone treatment decreased urinary excretion rates of free cortisol, cortisone, 18-OHF, and 18-oxoF, confirming dependence of 18-oxygenated steroid levels on cortisol availability. In both groups, hydrocortisone administration resulted in detectable levels of 18-OHF and raised levels of 18-oxoF. There was close correlation between 18-oxoF and cortisol excretion during hydrocortisone administration in normal subjects (r = 0.86; P < 0.001). These data show, for the first time, that 18-OHF and 18-oxoF can be synthesized from circulating cortisol. The close correlation between 18-oxoF and cortisol suggests that 18-oxoF is normally produced by the action of AS using circulating cortisol as a substrate. Although 18OHF can be synthesized using circulating cortisol as substrate, our data suggest this is normally produced in the zona fasciculata by 11beta-hydroxylase from locally available cortisol.

The −344T>C promoter variant of the gene for aldosterone synthase (CYP11B2) is not associated with cardiovascular risk in a prospective study of UK healthy men

INTRODUCTION

The tissue renin-angiotensin system is implicated in the pathogenesis of coronary artery disease (CAD). As locally synthesised aldosterone is a potential mediator of CAD, we have sought an association of the -344T>C variant of the aldosterone synthase (CYP11B2) gene with CAD events.

METHODS

Subjects comprised of the Second Northwick Park Heart Study (NPHSII), a prospective study of unrelated, healthy middle-aged Caucasian males. CAD events were recorded in 2490 subjects, and defined as a sudden cardiac death, myocardial infarction or coronary artery revascularisation procedure. Mean follow-up was 10.8 years. Aldosterone synthase genotype was determined in 2490 subjects. Power calculation suggests that we have 80% power (at a significance level of 0.05) to detect a difference in hazard ratio (HR) between homozygote groups of 0.45.

RESULTS

One hundred and eighty-seven CAD events were recorded in 2490 subjects. In the group overall, CAD events were independent of genotype with adjusted hazard ratios being 1.00 versus 1.25 versus 0.80 for TT versus TC versus CC genotypes, respectively, P = 0.07. Genotype interactions with smoking and blood pressure were sought. Whilst CAD events were independent of genotype amongst non-smokers, CC genotype in smokers was associated with a reduced risk HR 2.02 versus 2.28 versus 0.82 for TT versus TC versus CC genotypes, P = 0.05 (HR for TT + TC versus CC were 1.77 versus 0.67, P = 0.02). This apparent interaction remained after adjustment for conventional risk factors. No such interaction was found with blood pressure.

CONCLUSIONS

Aldosterone synthase genotype is unrelated to overall CAD events risk. A possible interaction with smoking requires confirmation.