Familial and phenotypic associations of the aldosterone Renin ratio

Familial Aggregation and Heritability of Aldosteronism with Cardiovascular Events

CONTEXT

To date, the effect of positive family history as a risk factor of primary aldosteronism (PA) is largely unknown. Studies have failed to distinguish the heritability of PA as well as the associations between positive family history of PA and clinical outcomes.

OBJECTIVES

We quantified the prevalence, the extent of familial aggregation, the heritability of PA among family members of patients with PA, and the association between positive PA family history and major cardiovascular events (MACE).

DESIGN AND SETTINGS

Using the Taiwan National Health Insurance Database, 30 245 077 National Health Insurance beneficiaries (both alive and those deceased between January 1, 1999, and December 31, 2015) were identified.

RESULTS

We identified 7902 PA patients. Forty-four had PA (0.3%) among 10 234 individuals with affected parents, 2298 with affected offspring, 1924 with affected siblings, and 22 with affected twins. A positive family history was associated with the adjusted relative risk (RR) (95% confidence interval [CI]) of 11.60 (7.63-17.63) for PA in people with an affected first-degree relative. In subgroup analysis, the risk for PA across all relationships (parent, siblings, offspring, and spouse) showed highly significant differences to PA without family history. The accountability for phenotypic variance of PA was 51.0% for genetic factors, 24.9% for shared environmental factors, and 24.1% for nonshared environmental factors. PA patients with an affected first-degree relative were associated with an increased risk for composite major cardiovascular events (RR 1.31; 95% CI 1.24-1.40, P < .001) compared with PA patients without family history.

CONCLUSION

Familial clustering of PA exists among a population-based study, supporting a genetic susceptibility leading to PA. There is increased coaggregation of MACE in first-degree relatives of PA patients. Our findings suggest a strong genetic component in the susceptibility of PA, involving different kinships.

Plasma Aldosterone After Seated Saline Infusion Test Outperforms Captopril Test at Predicting Clinical Outcomes After Adrenalectomy for Primary Aldosteronism

OBJECTIVE

The saline infusion test (SIT) and the captopril test (CT) are widely used as confirmatory tests for primary aldosteronism (PA). We hypothesized that post-SIT and post-CT plasma aldosterone concentrations (PAC) indicate the severity of aldosterone-producing adenoma (APA) and might predict clinical outcome.

METHODS

We recruited 216 patients with APA in the Taiwan Primary Aldosteronism Investigation (TAIPAI) registry who received both seated SIT and CT as confirmatory tests. The data of 143 patients who underwent adrenalectomy with complete follow-up after diagnosis were included in the final analysis. We determined the proportion of patients achieving clinical success in accordance with the Primary Aldosteronism Surgical Outcome consensus. Logistic regression analysis was conducted to identify preoperative factors associated with cure of hypertension.

RESULTS

Complete clinical success was achieved in 48 (33.6%) patients and partial clinical success in 59 (41.2%) patients; absent clinical success was seen in 36 (25.2%) of 143 patients. Post-SIT PAC but not post-CT PAC was independently associated with clinical outcome. Higher levels of post-SIT PAC had a higher likelihood of clinical benefit (complete plus partial clinical success; odds ratio = 1.04 per ng/dl increase, 95% confidence interval = 1.01, 1.06; P = 0.004). Patients with post-SIT PAC > 25 ng/dl were more likely to have a favorable clinical outcome after adrenalectomy. This cutoff value translated into a positive predictive value of 86.0%.

CONCLUSIONS

We suggest that post-SIT PAC is a better predictor than post-CT PAC for clinical success in PA post adrenalectomy.

Sex Difference in the Association Between Subtype Distribution and Age at Diagnosis in Patients With Primary Aldosteronism

Primary aldosteronism (PA) is the most frequent cause of secondary hypertension. Adrenal vein sampling (AVS) is an established method for finding patients with the unilateral subtype of PA, for which adrenalectomy is an applicable treatment. In this study, we analyzed a large database of patients with PA who underwent adrenal vein sampling, to investigate the sex differences in the impact of age at diagnosis on the subtype and cause of PA. In 2122 patients, women with the unilateral subtype were younger than men with the same subtype and women with the bilateral subtype. Younger age and older age were associated with unilateral PA in women and men, respectively. After stratification by tertiles of age, there was a trend of decreased and increased incidence of unilateral PA with aging in women and men, respectively. Male sex was a predictor of unilateral PA in middle-aged and older patients but not in younger patients. We also found that obesity, a known factor associated with idiopathic hyperaldosteronism, was positively associated with bilateral PA in younger patients but not in older patients. These findings suggest that the proportion of operable patients with unilateral PA differs depending on the combination of sex and age, and that other than obesity, the cause of PA is also associated with the bilateral subtype in older patients.

Dysregulated aldosterone secretion in persons of African descent with endothelin-1 gene variants

Compared with persons of European descent (ED), persons of African descent (AD) have lower aldosterone (ALDO) levels, with the assumption being that the increased cardiovascular disease (CVD) risk associated with AD is not related to ALDO. However, the appropriateness of the ALDO levels for the volume status in AD is unclear. We hypothesized that, even though ALDO levels are lower in AD, they are inappropriately increased, and therefore, ALDO could mediate the increased CVD in AD. To test this hypothesis, we analyzed data from HyperPATH - 1,788 individuals from the total cohort and 765 restricted to ED-to-AD in a 2:1 match and genotyped for the endothelin-1 gene (EDN1). Linear regression analyses with adjustments were performed. In the total and restricted cohorts, PRA, ALDO, and urinary potassium levels were significantly lower in AD. However, in the AD group, greater ALDO dysregulation was present as evidenced by higher ALDO/plasma renin activity (PRA) ratios (ARR) and sodium-modulated ALDO suppression-to-stimulation indices. Furthermore, EDN1 minor allele carriers had significantly greater ARRs than noncarriers but only in the AD group. ARR levels were modulated by a significant interaction between EDN1 and AD. Thus, EDN1 variants may identify particularly susceptible ADs who will be responsive to treatment targeting ALDO-dependent pathways (e.g., mineralocorticoid-receptor antagonists).

Primary Aldosteronism With Type 2 Diabetes Mellitus Requires More Antihypertensive Drugs for Blood Pressure Control: A Retrospective Observational Study

Background

Diabetes mellitus (DM) and primary aldosteronism (PA) have been reported to induce drug-resistant hypertension and atherosclerosis. It is likely that blood pressure (BP) control becomes far more difficult in PA patients with DM. However, precise clinical characteristics of PA with type 2 DM especially in the aspect of BP control are not clear.

Methods

The study included 18 patients who were diagnosed as PA with DM and 52 PA patients without DM who matched age and sex and chosen as a control group. We have compared differences in BP control, use of antihypertensive agents and clinical characteristics between PA patients with and without DM.

Results

There was no difference with regard to the duration of hypertension and BP control between either group. Interestingly, the PA with DM group was found to require more antihypertensive agents than the PA without DM group (number of antihypertensive agents used, 2.0 ± 1.5 vs. 1.3 ± 1.1; P < 0.05, respectively). In the 28 patients who underwent measurement of central BP (CBP) values, plasma aldosterone concentration (PAC) was high in the PA with DM group. Furthermore, a positive correlation was shown between PAC and CBP (r = 0.58; P < 0.01); the higher the PAC, the higher the CBP of patient.

Conclusions

These results might suggest that hypertension becomes more difficult to control in PA patients with DM in the future.

Rapid Screening of Primary Aldosteronism by a Novel Chemiluminescent Immunoassay

Measurement of plasma aldosterone and renin concentration, or activity, is useful for selecting antihypertensive agents and detecting hyperaldosteronism in hypertensive patients. However, it takes several days to get results when measured by radioimmunoassay and development of more rapid assays has been long expected. We have developed chemiluminescent enzyme immunoassays enabling the simultaneous measurement of both aldosterone and renin concentrations in 10 minutes by a fully automated assay using antibody-immobilized magnetic particles with quick aggregation and dispersion. We performed clinical validation of diagnostic ability of this newly developed assay-based screening of 125 patients with primary aldosteronism from 97 patients with essential hypertension. Results of this novel assay significantly correlated with the results of radioimmunoassay (aldosterone, active renin concentration, and renin activity) and liquid chromatography-tandem mass spectrometry (aldosterone). The analytic sensitivity of this particularly novel active renin assay was 0.1 pg/mL, which was better than that of radioimmunoassay (2.0 pg/mL). The ratio of aldosterone-to-renin concentrations of 6.0 (ng/dL per pg/mL) provided 92.0% sensitivity and 76.3% specificity as a cutoff for differentiating primary aldosteronism from essential hypertension. This novel measurement is expected to be a clinically reliable alternative for conventional radioimmunoassay and to provide better throughput and cost effectiveness in diagnosis of hyperaldosteronism from larger numbers of hypertensive patients in clinical settings.

Novel Approach to Establishing an Aldosterone: Renin Ratio Cutoff for Primary Aldosteronism

Direct renin concentration is replacing plasma renin activity in many laboratories for the investigation of primary aldosteronism, which may have a significant impact on the resulting aldosterone:renin ratios. We sought to develop a population-based approach to establishing an aldosterone:renin ratio cutoff when transitioning between assays. A population-based study was performed in Calgary, Alberta, Canada of 4301 individuals who received testing from January 2012 to November 2015. In 2014, direct renin concentration replaced plasma renin activity in routine testing. We described the prevalence of primary aldosteronism in our population before the change and, using the assumption of disease prevalence stability, determined the corresponding ratio cutoffs after the introduction of the new assay. During the initial portion of the study (using plasma renin activity), 4.9% of those screened were classified as highly probable cases, whereas 10.4% were considered probable and 28.9% possible using locally validated cutoffs. Aldosterone:renin ratio cutoffs were then determined for the direct renin concentration assay. A highly probable case of primary aldosteronism corresponded to a cutoff of >100 pmol L −1 mIU −1 L −1 with hypokalemia. A probable case corresponded to a cutoff of >100 and a possible case to >35 pmol L −1 mIU −1 L −1 . In contrast, cutoffs derived using a conversion factor resulted in significantly higher cutoffs and the potential for missed cases. In conclusion, using large population data, historically consistent aldosterone:renin ratio cutoffs can be established when transitioning between assays. Population-derived cutoffs may be more appropriate for clinical use and less likely to result in false-negative classification than those obtained from conventional direct method comparisons.

Body Mass Index Predicts 24-Hour Urinary Aldosterone Levels in Patients With Resistant Hypertension

Prospective studies indicate that hyperaldosteronism is found in 20% of patients with resistant hypertension. A small number of observational studies in normotensive and hypertensive patients suggest a correlation between aldosterone levels and obesity while others could not confirm these findings. The correlation between aldosterone levels and body mass index (BMI) in patients with resistant hypertension has not been previously investigated. Our objective was to determine whether BMI is positively correlated with plasma aldosterone concentration, plasma renin activity, aldosterone:renin ratio, and 24-hour urinary aldosterone in black and white patients. We performed a cross-sectional analysis of a large diverse cohort (n=2170) with resistant hypertension. The relationship between plasma aldosterone concentration, plasma renin activity, aldosterone:renin ratio, 24-hour urinary aldosterone, and BMI was investigated for the entire cohort, by sex and race (65.3% white, 40.3% men). We demonstrate that plasma aldosterone concentration and aldosterone:renin ratio were significantly correlated to BMI (P<0.0001) across the first 3 quartiles, but not from the 3rd to 4th quartile of BMI. Plasma renin activity was not correlated with BMI. Twenty-four-hour urinary aldosterone was positively correlated across all quartiles of BMI for the cohort (P<0.0001) and when analyzed by sex (men P<0.0001; women P=0.0013) and race (P<0.05), and stronger for men compared with women (r=0.19, P<0.001 versus r=0.05, P=0.431, P=0.028) regardless of race. In both black and white patients, aldosterone levels were positively correlated to increasing BMI, with the correlation being more pronounced in black and white men. These findings suggest that obesity, particularly the abdominal obesity typical of men, contributes to excess aldosterone in patients with resistant hypertension.

Clinical validation for the aldosterone-to-renin ratio and aldosterone suppression testing using simultaneous fully automated chemiluminescence immunoassays

BACKGROUND

As larger numbers of hypertensive patients are screened for primary aldosteronism with the aldosterone-to-renin ratio (ARR), automated analyzers present a practical solution for many laboratories. We report the method-specific ARR cutoff determined with direct, automated chemiluminescence immunoassays allowing the simultaneous measurement of plasma aldosterone concentrations (PACs) and plasma renin concentrations (PRCs).

METHODS

Method comparisons to commonly employed assays and tandem mass spectrometry were undertaken. Patients were previously diagnosed based on the local ARR cutoff of 1.2 (ng/dl)/(μIU/ml) in samples collected in upright seated position. Lack of aldosterone suppression in response to salt load to less than 5 ng/dl confirmed primary aldosteronism. For the new assays, the optimal ARR cutoff was established in 152 patients with essential hypertension, 93 with primary aldosteronism and 147 normotensive patients. Aldosterone suppression was assessed in 73 essential hypertensive and 46 primary aldosteronism patients.

RESULTS

PAC and PRC were significantly correlated to values determined with currently available methods (P < 0.001). In patients with primary aldosteronism, patients with essential hypertension and controls, mean (95% confidence interval) PAC was 28.4 (25.4-31.8), 6.4 (5.9-6.9) and 6.2 (5.6-6.9) ng/dl, respectively. In the same groups, PRC was 6.6 (5.6-7.7), 12.9 (11.2-14.8) and 26.5 (22.2-31.5) μIU/ml. An ARR cutoff of 1.12 provided 98.9% sensitivity and 78.9% specificity. Employing the new assay aldosterone suppression confirmed the diagnosis of primary aldosteronism and essential hypertension using the cutoff of 5 ng/dl.

CONCLUSION

Our data demonstrate that the new assays present a convenient alternative for the measurement of PAC and PRC on a single automated analyzer. Availability of these simultaneous assays should facilitate screening and diagnosis of primary aldosteronism.

Establishment of reference intervals for aldosterone and renin in a Caucasian population using the newly developed Immunodiagnostic Systems specialty immunoassay automated system

BACKGROUND

Measurement of aldosterone and/or renin is essential to aid the differential diagnosis of secondary hypertension, guide strategy for therapeutic management of hypertension and assess adequacy of mineralocorticoid replacement.

AIM

The objective was to establish normative data for aldosterone and renin using the Immunodiagnostic Systems specialty immunoassay system platform in a Caucasian population.

METHODS

Following informed consent, 365 subjects were recruited to this study. Subjects were ambulatory and attended clinic for blood pressure measurement and phlebotomy between the hours of 7:00 and 11:00. Blood pressure was measured according to the 2013 European Society of Hypertension/Cardiology guidelines. The inclusion criteria: age ≥18 years, BMI <30 kg/m(2), non-pregnant, blood pressure <140/90, normal electrolytes and kidney function and not taking prescribed/over the counter medications. Ninety-four subjects were excluded based on these criteria. A total of 271 volunteers (females n = 145), aged 18-65 years formed the reference cohort. Blood for aldosterone/renin was collected into ethylenediaminetetraacetic acid specimen tubes. Samples were kept at room temperature and transported within 30 min of blood draw to the laboratory for immediate processing (centrifugation, separation and freezing of plasma). Plasma was stored at -20℃ prior to analysis on the Immunodiagnostic Systems specialty immunoassay system instrument.

RESULTS

The established reference intervals in an Irish Caucasian population for renin: females: 6.1-62.7 mIU/L, males: 9.0-103 mIU/L, for aldosterone: females: <138-1179 pmol/L, males: <138-670 pmol/L, respectively.

CONCLUSION

This study demonstrates that reference intervals for aldosterone and renin should be gender specific. These automated immunoassays offer rapid stratification of patients with refractory hypertension and will better facilitate the optimization of therapeutic management.

Unadjusted Plasma Renin Activity as a "First-Look" Test to Decide Upon Further Investigations for Primary Aldosteronism

The authors sought to define the 95th percentile of plasma renin activity (PRA) in a sample of patients with confirmed primary aldosteronism (PA) prior to adjustment of medications as a practical "first-look" test to identify those with very low ultimate likelihood of having PA. The aldosterone to renin ratio (ARR) was measured without adjustment of antihypertensive medications, with further workup as appropriate. Two groups were defined: patients with surgically "confirmed PA" (n=58) and patients with "high-probability PA" (n=59), defined as having any of the following: computed tomography-confirmed adrenal adenoma plus lateralizing adrenal vein sampling (AVS) without surgery, high ARR and hypokalemia but nonlateralizing AVS, or ARR more than four times the upper limit of normal. The PRA 95th percentile was 1.0 ng/mL/h. All outliers had hypokalemia and two had adrenal adenomas. There was no difference between the confirmed and high probability groups. In the absence of highly suspicious clinical features, patients with unadjusted PRA >1.0 ng/mL/h do not warrant further investigation for PA.

Diastrophic dysplasia sulfate transporter (SLC26A2) is expressed in the adrenal cortex and regulates aldosterone secretion

Elucidation of the molecular mechanisms leading to autonomous aldosterone secretion is a prerequisite to define potential targets and biomarkers in the context of primary aldosteronism. After a genome-wide association study with subjects from the population-based Cooperative Health Research in the Region of Augsburg F4 survey, we observed a highly significant association (P=6.78×10(-11)) between the aldosterone to renin ratio and a locus at 5q32. Hypothesizing that this locus may contain genes of relevance for the pathogenesis of primary aldosteronism, we investigated solute carrier family 26 member 2 (SLC26A2), a protein with known transport activity for sulfate and other cations. Within murine tissues, adrenal glands showed the highest expression levels for SLC26A2, which was significantly downregulated on in vivo stimulation with angiotensin II and potassium. SLC26A2 expression was found to be significantly lower in aldosterone-producing adenomas in comparison with normal adrenal glands. In adrenocortical NCI-H295R cells, specific knockdown of SLC26A2 resulted in a highly significant increase in aldosterone secretion. Concomitantly, expression of steroidogenic enzymes, as well as upstream effectors including transcription factors such as NR4A1, CAMK1, and intracellular Ca(2+) content, was upregulated in knockdown cells. To substantiate further these findings in an SLC26A2 mutant mouse model, aldosterone output proved to be increased in a sex-specific manner. In summary, these findings point toward a possible effect of SLC26A2 in the regulation of aldosterone secretion potentially involved in the pathogenesis of primary aldosteronism.

Progress in the identification of responsible genes and molecular mechanisms in primary aldosteronism

Aldosterone, the mineralocorticoid hormone, plays an important role in blood regulation. Autonomous secretion of aldosterone is known as primary aldosteronism (PA), the most common cause of secondary hypertension. PA comprises a group of heterogenous disorders which makes their classification and management challenging. With the advent of the genomic era several germline and somatic mutations have been identified that are involved in the pathogenesis of primary aldosteronism. This article will review our current knowledge of the genetic mechanisms of familial hyperaldosterism, somatic mutations in genes encoding electrolyte channels and other potential genetic mechanisms implicated in the dysregulation of aldosterone production from in vitro and animal models. There is potential for novel targeted therapies and diagnosis for subsets of patient. The challenges to achieve them are highlighted in this review.

Mild Adrenal Steroidogenic Defects and ACTH-Dependent Aldosterone Secretion in High Blood Pressure: Preliminary Evidence

Introduction. Adrenal glands play a major role in the control of blood pressure and mild defects of steroidogenesis and/or inappropriate control of mineralocorticoid production have been reported in high blood pressure (HBP). Patients and Methods. We used a specific protocol for the evaluation of 100 consecutive patients with inappropriate or recent onset HBP. Specific methods were used to confirm HBP and to diagnose secondary forms of HBP. In addition we tested adrenal steroidogenesis with the common cosyntropin test, modified to include the simultaneous measurement of renin and aldosterone besides 17-hydroxyprogesterone (17OHP) and 11-deoxycortisol (S). Results. Secondary forms of HBP were diagnosed in 32 patients, including 14 patients with primary hyperaldosteronism (PA) (14%) and 10 patients with pheochromocytoma (10%). Mild defects of the 21-hydroxylase (21OHD) and 11-hydroxylase (11OHD) enzymes were common (42%). ACTH-dependent aldosterone secretion was found in most patients (54%) and characteristically in those with mild defects of adrenal steroidogenesis (>60%), PA (>75%), and otherwise in patients with apparent essential HBP (EHBP) (32%). Discussion. Mild defects of adrenal steroidogenesis are common in patients with HBP, occurring in almost half of the patients. In those patients as well as in patients with apparent EHBP, aldosterone secretion is commonly dependent on ACTH.

A marked proportional rise in IVC aldosterone following cosyntropin administration during AVS is a signal to the presence of adrenal hyperplasia in primary aldosteronism

We hypothesized aldosteronoma responsiveness to cosyntropin may be a characterizing feature that could be determined in addition to standard adrenal vein sampling (AVS) data. We reviewed an AVS database from June 2005 to October 2011 including 65 patients with confirmed primary aldosteronism (PA) who underwent AVS and, if applicable, unilateral adrenalectomy. Patients were divided into confirmed lateralized and non-lateralized groups and subgrouped by histology. Plasma aldosterone in inferior vena cava (IVC) pre- and post-cosyntropin infusion during AVS was measured. Peak aldosterone and proportional change was compared between groups. Baseline and peak IVC aldosterone was higher in lateralized patients but incremental aldosterone rise was much greater in subjects with bilateral hyperplasia. From receiver operator characteristics (ROC) analysis, the optimized diagnostic cut point of peak IVC aldosterone of >649 pmol l(-1) would have a sensitivity of 94% for surgical disease although specificity of just 59%. A 250% increase in IVC aldosterone following cosyntropin would be specific enough to exclude 87% of surgical/lateralized disease. These diagnostic capabilities are similar to other results with non-AVS tests performed for diagnosis of lateralization. Although not specific enough to replace standard AVS interpretation, a marked IVC aldosterone increase after cosyntropin during AVS is a useful additional test to diagnose non-lateralizing forms of PA. Such a calculation requires no additional expense or tests.

Regulation of aldosterone secretion: from physiology to disease

Arterial hypertension is a major cardiovascular risk factor that affects between 10 and 40% of the population in industrialized countries. Primary aldosteronism (PA) is the most common form of secondary hypertension with an estimated prevalence of around 10% in referral centers and 4% in a primary care setting. Despite its high prevalence until recently, the underlying genetic and molecular basis of this common disease had remained largely obscure. Over the past decade, a number of insights have been achieved that have relied on in vitro cellular systems, wild-type and genetically modified in vivo models, as well as clinical studies in well-characterized patient populations. This progress has been made possible by a number of independent technical developments including that of specific hormone assays that allow measurement in small sample volumes as well as genetic techniques that enable high-throughput sequencing of a large number of samples. Furthermore, animal models have provided important insights into the physiology of aldosterone regulation that have served as a starting point for investigation of mechanisms involved in autonomous aldosterone secretion. Finally, national and international networks that have built up registries and biobanks have been instrumental in fostering translational research endeavors in PA. Therefore, it is to be expected that in the near future, further pathophysiological mechanisms that result in autonomous aldosterone secretion will be unraveled.

Plasma renin activity and the aldosterone-to-renin ratio are associated with the development of chronic kidney disease: the Ohasama Study

BACKGROUND

The aldosterone-to-renin ratio (ARR) is used to screen for primary aldosteronism and could be an index for salt sensitivity. The association between ARR and the development of chronic kidney disease (CKD) is completely unknown.

METHOD

A longitudinal observational study involving 689 participants from a general Japanese population (mean age 58.2 years; 68.5% women) who did not have CKD and were not receiving antihypertensive medication at baseline was conducted. The estimated glomerular filtration rate (eGFR) was calculated from serum creatinine levels, and CKD was defined as eGFR less than 60 ml/min per 1.73 m(2) and/or dipstick-positive proteinuria. The associations of baseline plasma renin activity (PRA), plasma aldosterone concentration, and ARR with the development of CKD were examined using Cox proportional hazard regression analysis adjusted for sex, age, BMI, smoking, drinking, history of hypercholesterolemia, diabetes mellitus, and cardiovascular disease, SBP, and baseline eGFR.

RESULTS

During a mean 9.1-year follow-up, 118 participants developed CKD. A 1 standard deviation increment in the natural log-transformed (ln) ARR was positively associated with the incidence of CKD (hazard ratio 1.29, P = 0.012). LnPRA showed an inverse association (hazard ratio 0.76, P = 0.007). Meanwhile, plasma aldosterone concentration was not associated with CKD. Individuals who developed CKD had significantly lower baseline PRA (0.97 vs. 1.14 ng/ml per h; P = 0.03) and higher baseline ARR levels [66.6 vs. 56.8 (pg/ml)/(ng/ml per h); P = 0.02] than those who did not.

CONCLUSIONS

Lower PRA and higher ARR were associated with the development of CKD in a general population, suggesting that they are independent predictors of CKD.

Gender-, strain-, and inheritance-dependent variation in aldosterone secretion in mice

Arterial hypertension represents one of the most common diseases in developed countries and the rennin-angiotensin-aldosterone system is among the major factors in the regulation of blood pressure and sodium balance. With the exception of rare monogenetic diseases, however, inheritance of aldosterone secretion is widely unknown. In this study, we investigated the aldosterone levels in male and female mice of two inbred strains, C3HeB/FeJ and C57BL/6J, as well as their offspring of the F1 and F2 generation. In all cases, female animals displayed lower aldosterone levels than males. Furthermore, C57BL/6J animals had significantly higher aldosterone levels than C3HeB/FeJ mice of the same age and gender. Depending on the paternal origin of the animal, the F1 offspring showed a tendency toward higher aldosterone values when the paternal side was from the C57BL/6J strain. This observation was confirmed in the F2 generation and over repeated measurements over three consecutive years. Quantification of the aldosterone to renin ratio in the different mouse groups did not show any significant differences, and, similarly, the determination of plasma potassium and kidney parameters did not provide any differences. On the molecular level, investigation of the expression of the enzymes involved in steroidogenesis displayed the same trend as for the aldosterone values, with animals hosting C57BL/6J background in their paternal origin having also the highest expression levels for StAR, cyp11a1, and cyp11b2 enzymes. Taken together, we could demonstrate that the genetic background of the animals plays a significant role modulating their plasma aldosterone levels without clear interference of other parameters in the renin-angiotensin-aldosterone system.

Demonstration of Blood Pressure-Independent Noninfarct Myocardial Fibrosis in Primary Aldosteronism

Background—

Primary aldosteronism (PA) is common and associates with excess cardiovascular morbidity independent of blood pressure. Exposure to aldosterone and sodium leads to cardiac fibrosis and hypertrophy in humans and animals possibly mediated by inflammation and oxidative stress. We aimed to clarify the effects of aldosterone excess on myocardial structure and composition in human subjects with PA and essential hypertension using contrast-enhanced cardiac magnetic resonance imaging as well as explore the mechanistic basis for any observed differences.

Methods and Results—

Twenty-seven subjects with recently diagnosed PA and 54 essential hypertension controls were recruited. Subjects underwent gadolinium-enhanced cardiac magnetic resonance; noninfarct related myocardial fibrosis was identified by a diffuse pattern of late gadolinium enhancement. Patients also underwent assessment of pulse wave velocity, measurement of circulating superoxide anion and C-reactive protein, as well as blood pressure and biochemical assessment. Subjects were well matched with no difference in severity or duration of hypertension. There was a significant increase in the frequency of noninfarct late gadolinium enhancement in PA (70%) when compared with essential hypertension subjects (13%; P <0.0001) with no difference in left ventricular mass. Pulse wave velocity, superoxide, and C-reactive protein were significantly higher in subjects with PA.

Conclusions—

These data illustrate that patients with PA exhibit frequent myocardial fibrosis as demonstrated by late gadolinium enhancement using cardiac magnetic resonance imaging; this finding is independent of blood pressure. This may be mediated partly through inflammation and oxidative stress. This study highlights the importance of specific targeting of aldosterone excess as well as blood pressure reduction to minimize cardiac morbidity in PA.

APEX1 regulation of aldosterone synthase gene transcription is disrupted by a common polymorphism in humans

RATIONALE

The genetic mechanisms underlying hypertension are unclear, but relative aldosterone excess, present in ≈10% of hypertensive patients, is known to be a heritable trait. This phenotype associates with a T/C single nucleotide polymorphism (SNP) at position -344 of the aldosterone synthase gene (CYP11B2). However, deletion of this SNP has no effect on gene transcription. We have identified another T/C SNP at -1651, in tight linkage disequilibrium with the -344 SNP and here investigate its functional effect on CYP11B2 transcription.

OBJECTIVE

We assessed the effect on transcriptional activity of the -1651 T/C SNP in vivo and in vitro and propose the mechanism by which transcriptional activity is altered.

METHODS AND RESULTS

We demonstrated that the SNP at -1651 exerts significant allele-dependent effects on CYP11B2 transcription. We confirm binding of the transcriptional repressor APEX1 to -1651T, which is associated with reduced transcriptional activity in relation to the less strongly bound -1651C. We show that inhibiting APEX1 by small molecule inhibition or small interfering RNA (SiRNA) leads to increased CYP11B2 transcription. In addition, overexpression of APEX1 is associated with reduced transcriptional activity. Finally, we also show that -1651T associates with lower excretion rates of aldosterone metabolites in human subjects.

CONCLUSIONS

We conclude that APEX1 is a novel transcriptional repressor of CYP11B2 and that differential APEX1 binding at -1651 of CYP11B2 results in altered gene expression. This mechanism may contribute to the observed relationship between CYP11B2 genotype and aldosterone phenotype in a subgroup of hypertensive patients.

Current diagnosis and treatment of primary aldosteronism

Primary aldosteronism is more common than previously recognized but much less common than most experts in this arena have recently stated. The recognition of autonomous hyperaldosteronism is not difficult but the identification of the source of excess aldosterone requires a costly and difficult procedure. Most patients with hyperaldosteronism turn out to have bilateral adrenal hyperplasia for which medical therapy with an aldosterone blocker is indicated. Many of these patients are not hypokalemic and can safely be treated without the need for a costly and usually negative work-up.

Aldosterone, Plasma Renin Activity, and Aldosterone/Renin Ratio in a Normotensive Healthy Pediatric Population

Primary aldosteronism is an important cause of secondary hypertension and is suspected in adults with an aldosterone/renin ratio ≥25. The normal aldosterone/renin ratio is unknown in children. The aim was to establish serum aldosterone, plasma renin activity, and aldosterone/renin ratio values in a healthy pediatric population. A cross-sectional study was performed in 211 healthy normotensive children (4 to 16 years old). Two subgroups of normotensive children were obtained: with hypertensive parents (NH) (n=113) and normotensive parents (n=98). Blood samples for measuring serum aldosterone, plasma renin activity, aldosterone/renin ratio, and DNA were collected. In subjects with aldosterone/renin ratio ≥25, the chimeric CYP11B1/CYP11B2 gene was investigated by long-extension PCR. Results are expressed as median [Q 1 –Q 3 ]. NH and normotensive parents groups were similar in serum aldosterone (6.5 [3.6 to 9.0] ng/dL versus 6.5 [2.9 to 9.7] ng/dL; P =0.968) and plasma renin activity (2.3 [1.6 to 3.1] versus 2.4 [1.7 to 3.7] ng/mL per hour; P =0.129). The aldosterone/renin ratio was higher in the NH group, but this difference did not reach statistical significance (2.8 [1.9 to 4.1] versus 2.5 [1.4 to 4.0], P =0.104). In one subject of the NH group, the chimeric CYP11B1/CYP11B2 gene was detected. We demonstrated that normal aldosterone/renin ratio values in a healthy pediatric population without NH were lower than those reported for an adult normotensive population.

The role of aldosteronism in causing obesity-related cardiovascular risk

A large body of evidence strongly links aldosterone to development and progression of cardiovascular disease, including vascular stiffness, left ventricular hypertrophy, congestive heart failure, chronic kidney disease, and, especially, hypertension. Emerging data suggest that adipocytes may serve as a source of aldosterone, either directly or indirectly, through the release of aldosterone-stimulating factors. If adipocytes are confirmed to have an important contribution to hyperaldosteronism, it would have significant clinical implications in linking aldosterone to obesity-related increases in cardiovascular risk. Such a cause-and-effect situation would then provide the opportunity to reverse that risk with preferential use of aldosterone antagonists in obese patients.

Primary aldosteronism: an update

Primary aldosteronism (PA) is common with an estimated prevalence rate of 10% in subjects with essential hypertension and higher in those with resistant hypertension. As well as contributing to hypertension, aldosterone has detrimental effects on the heart, vasculature and kidneys as well as adverse metabolic effects leading to an excess of cardiovascular morbidity. Therefore, recognition and appropriate treatment of PA is of increasing importance. However, the diagnosis of PA and determination of subtype can be problematic. The purpose of this review is to provide an overview of the evidence supporting this increased prevalence of PA, explore the metabolic and cardiovascular consequences of aldosterone excess and discuss optimal diagnostic and therapeutic strategies of PA.

A screening procedure for primary aldosteronism based on the Diasorin Liaison® automated chemiluminescent immunoassay for direct renin

Background

Primary aldosteronism (PA), the most common secondary cause of hypertension, can be screened for using the aldosterone/renin ratio. This ratio is raised in PA and its accuracy depends on the ability to measure plasma renin at extremely low concentrations.

Methods

We compared two different procedures for assessing plasma renin. The conventional method, which measures plasma renin activity (PRA), is technically demanding and laborious, and the Diasorin Liaison® method, which measures plasma renin concentration (PRC), is an automated immunoassay. Results from each method were used to calculate the aldosterone/renin ratio (ARR) and the performance of the Diasorin Liaison® method compared with that of the conventional assay using receiver operator characteristic curves.

Results

The analytical and functional sensitivity of the PRC method were 2.1 and 5 μIU/mL, respectively. Intra- and inter-assay precision were <7.2% and 10.4%, respectively. There was significant (9%) prorenin interference. Samples with PRA > 1.0 ng/mL/h showed significant correlation with PRC ( r = 0.93; P < 0.05; n = 146); however, with PRA < 1.0 ng/mL/h, no significant correlation occurred ( r = 0.14; P < 0.05; n = 79). An aldosterone (pmol/L)/PRC(μIU/mL) ratio of >35, in patients with aldosterone >300 pmol/L, resulted in 100% sensitivity and 93% specificity, when compared with the commonly accepted aldosterone (pmol/L)/PRA (ng/mL/h) ratio of >750, in identifying patients who may suffer from PA.

Conclusion

This study indicates the feasibility of using the automated PRC assay as a replacement for the conventional manual PRA assay in calculating the ARR as a first-line screen for PA.