Autoimmune mechanisms activating the angiotensin AT1 receptor in 'primary' aldosteronism

Autoimmune Implications in a Patient with Graves' Hyperthyroidism, Pre-eclampsia with Severe Features, and Primary Aldosteronism

Background and Objectives: Graves' disease (GD) and primary aldosteronism (PA) are two pathologies that can cause significant morbidity and mortality. GD is mediated by autoantibodies, and recent studies have shown autoantibody involvement in the pathophysiology behind both PA and pre-eclampsia. The coexistence of GD and PA, however, is reportedly rare. This report describes a unique case of Graves' hyperthyroidism and concomitant PA in a patient with a history of pre-eclampsia with severe features. Case Presentation: The patient presented at 17 weeks pregnancy with mild hyperthyroidism, negative TSH receptor antibodies, and a low level of thyroid-stimulating immunoglobulins (TSI). Her TSH became detectable with normal thyroid hormone levels, and therefore, no anti-thyroid medication was administered. At 34 weeks she developed pre-eclampsia with severe features, and a healthy child was delivered; her TSH returned to normal. Seven months after delivery, she presented emergently with severe hyperthyroidism, hypertensive crisis, and a serum potassium of 2.5 mmol/L. Her hypertension was uncontrolled on multiple anti-hypertensives. Both TSI and TSH receptor antibodies were negative. The aldosterone(ng/dL)/renin(ng/mL/h ratio was (13/0.06) = 216.7, and abdominal CT imaging demonstrated normal adrenal glands; thus, a diagnosis of PA was made. Her blood pressure was subsequently controlled with only spironolactone at 50 mg 2xday. Methimazole was started but discontinued because of an allergic reaction. Consequently, a thyroidectomy was performed, and pathology revealed Graves' disease. The patient remained well on levothyroxine at 125 mcg/day and spironolactone at 50 mg 2xday three months after the thyroidectomy. Conclusions: This patient manifested severe GD with antibodies undetectable by conventional TSI and TSH receptor assays and accelerated hypertension from PA simultaneously. These conditions were successfully treated separately by spironolactone and thyroidectomy. Autoimmune PA was considered likely given the clinical picture. The diagnosis of PA should be considered in hypertension with GD.

Serum levels of autoantibodies against the angiotensin II type I receptor are not associated with serum dicarbonyl or AGE levels in patients with an aldosterone-producing adenoma

Patients with an aldosterone-producing adenoma (APA) carry a higher risk of cardiovascular disease and commonly have high levels of autoantibodies (AT1AA) that may activate the angiotensin II type 1 receptor (AT1R). AT1R activation is linked to an increase of the glucose metabolite methylglyoxal (MGO), a potential precursor of advanced glycation endproducts (AGEs) and driver of vascular inflammation. We investigated whether serum AT1AA levels are associated with serum MGO and AGE levels in APA patients. In a case series of 26 patients with APA we measured levels of dicarbonyls MGO, glyoxal (GO) and 3-deoxyglucosone (3-DG), and dicarbonyl-derived AGEs 5-hydro-5-methylimidazolone (MG-H1), Nε-(carboxyethyl)lysine (CEL) and Nε-(carboxymethyl)lysine (CML) with UPLC-MS/MS. We also measured AT1AA by ELISA. These measurements were repeated 1-month after adrenalectomy in a subset of 14 patients. Panels of inflammation and endothelial function were also measured by immunoassays. Although baseline higher AT1AA levels tended to be correlated with higher baseline serum MGO, GO and 3-DG levels (r = 0.18, p = 0.38; r = 0.20, p = 0.33; r = 0.23, p = 0.26; respectively), these correlations were not statistically significant. We observed no obvious correlations between higher AT1AA levels and protein-bound and free MG-H1, CEL and CML levels, and markers of inflammation and endothelial function. No decrease was observed in any of the dicarbonyls, protein-bound AGE levels and markers of inflammation and endothelial function after adrenalectomy. In patients with APA the serum levels of AT1AA were not significantly correlated with serum dicarbonyls, protein-bound and free AGE levels. Increased signalling of the AT1AA receptor may therefore be unlikely to overtly increase systemic dicarbonyl levels.

Primary aldosteronism in pregnancy

Primary aldosteronism (PA) is the most common form of secondary hypertension. Although hypertensive disorders seem to affect around 5-10% of pregnancies worldwide, literature counts less than 80 cases of PA diagnosed during the peri-partum period. In this review we discuss about current knowledge on pathophysiology, natural history, diagnosis and treatment of PA in pregnancy. Because of the physiologic changes in the renin-angiotensin-aldosterone system (RAAS) and the contraindication to both confirmatory test and subtype differentiation, diagnosis of PA during pregnancy is challenging and relies mostly on detection of low/suppressed renin and high aldosterone levels. The course of pregnancy in patients with PA is highly variable, ranging from progesterone-induced amelioration of blood pressure (BP) control to severe and resistant hypertension with potential maternal and fetal complications. Mineralcorticoid receptor antagonists (MRA) are the recommended and most effective drugs for treatment of PA. As the anti-androgenic effect of spironolactone can potentially interfere with sexual development, their prescription is not recommended during pregnancy. On the other side, eplerenone, has proven to be safe and effective in 6 pregnant women and may be added to conventional first line drug regimen in presence of resistant hypertension or persistent hypokalemia. Ideally, patients with unilateral forms of PA should undergo adrenalectomy prior to conception, however, when PA is diagnosed during pregnancy and medical therapy fails to adequately control hypertension or its complications, adrenalectomy can be considered during the second trimester in case of unilateral adrenal mass at MRI-scan.

[Immunogenetics of primary hyperaldosteronism: fundamental studies and their clinical prospects]

Primary hyperaldosteronism (PHA) is the most common form of endocrine hypertension. Until recently, the reason for the development of this condition was believed to be the presence of genetic mutations, however, many studies declare that the disease can be polyetiologic, be the result of genetic mutations and autoimmune triggers or cell clusters of aldosterone-producing cells diffusely located in the adrenal gland at the zona glonerulosa, zona fasculata, zona reticularis, as well as directly under the adrenal capsule. Recently, the actions of autoantibodies to type 1 angiotensin II receptors have been described in patients with renal transplant rejection, with preeclampsia, and with primary hyperaldosteronism. The diagnostic role of antibodies in both forms of PHA (aldosterone-producing adenoma and bilateral hyperaldosteronism) requires clarification. Diagnosis and confirmation of the focus of aldosterone hypersecretion is a multi-stage procedure that requires a long time and economic costs. The relevance of timely diagnosis of primary hyperaldosteronism is to reduce medical and social losses. This work summarizes the knowledge about genetic mutations and presents all the original studies devoted to autoantibodies in PHA, as well as discusses the diagnostic capabilities and limitations of the available methods of primary and differential diagnosis of the disease and the prospects for therapy.

Functionally Active Antibodies to the Angiotensin II Type 1-Receptor Measured by a Luminometric Bioassay Do Not Correlate With Clinical Manifestations in Systemic Sclerosis: A Comparison With Antibodies to Vascular Receptors and Topoisomerase I Detected by ELISA

Objectives

1) To detect functionally active antibodies(abs) to the angiotensin II type-1-receptor (AT₁R) by a novel luminometric assay. 2) To assess their prevalence in systemic sclerosis (SSc), other collagen disorders, as well as in further chronic inflammatory disorders including autoimmune, toxic and chronic viral diseases. 3) To compare these abs with anti-AT1R antibodies by ELISA as well as with antibodies to endothelin-type-A receptors (ET_A1) and to topoisomerase I (topo-I) with respect to their specificity and clinical relevance.

Methods

Sera from 98 SSc-patients, 110 patients with other chronic inflammatory rheumatic disorders, 97 patients with autoimmune liver diseases, 57 patients with toxic or chronic viral liver diseases and 36 healthy controls were analyzed. A luminometric bioassay was established with Huh-7-cells constitutively expressing the AT₁R. Patients’ sera were also tested by commercially available ELISA for anti-AT₁R, -ET_A1- and by an in-house ELISA for anti–topo-I-abs.

Results

Fifty-two percent of the SSc-patients had functionally active anti-AT₁R-abs with stimulatory (34%) or inhibitory capacity (18%). They were present also in up to 59% of patients with other rheumatic diseases but only 22% of healthy individuals (sensitivity 52%, specificity 53%). The functionally active antibodies detected by the luminometric assay did not correlate with anti-AT₁R-, -ET_A1- or -topo-I-abs measured by ELISA, but there was a strong correlation between anti-topo-I-, AT₁R-, and -ET_A1-ab reactivity measured by ELISA. Sensitivities of 55%, 28% and 47% and specificities of 66%, 87%, and 99% were calculated for these anti-AT₁R-, -ET_A1-, and anti-topo-I-abs, respectively. Functionally active abs did not correlate with disease severity or any organ manifestation. In contrast, abs to topo-I, AT₁R, and ET_A1 were associated with digital ulcers, pulmonary- and esophageal manifestation.

Conclusions

Functionally active anti-AT₁R-abs can be detected in SSc-patients but do not correlate with disease activity. They are not specific for this disease and occur also in other autoimmune disorders and even viral or toxic diseases. Also, the vascular antibodies detected by ELISA are not SSc-specific but correlated with disease manifestations. In contrast, anti-topo-I-abs were confirmed to be a highly specific biomarker for both, diagnosis and organ manifestations of SSc.

The emerging field of non-human leukocyte antigen antibodies in transplant medicine and beyond

The major medical advances in our knowledge of the human leukocyte antigen (HLA) system have allowed us to uncover several gaps in our understanding of alloimmunity. Although the non-HLA system has long sparked the interest of the transplant community, recognition of the role of immunity to non-HLA antigenic targets has only emerged recently. In this review, we will provide a comprehensive summary of the paradigm-changing concept of immunity to the non-HLA angiotensin II type 1 receptor (AT1R), discovered by Duška Dragun et al., that began from careful bedside clinical observations, to validated detection of anti-AT1R antibodies and lead to clinical intervention. This scientific approach has also allowed the recognition of broader pathogenicity of anti-AT1R antibodies across multiple organ transplants and in other human diseases, the integration of both non-HLA and HLA systems to understand their immunologic effects on organ allografts, and the identification of future directions for therapeutic intervention to modulate immunity to AT1R. Rationally designed successful interventions to target AT1R system provide an exemplar for other non-HLA antibodies to cross borders between medical specialties, will generate new avenues in translational research beyond transplantation, and will foster the development of new and reliable tools to improve our understanding of non-HLA immunity and ultimately allow us to improve patient care.

Histologic Antibody-Mediated Kidney Allograft Rejection in the Absence of Donor Specific HLA Antibodies

Histologic antibody-mediated rejection (hAMR) is defined as a kidney allograft biopsy satisfying the first 2 Banff criteria for diagnosing antibody-mediated rejection (AMR): tissue injury and evidence of current/recent antibody interaction with the endothelium. In approximately one-half of such cases, circulating HLA donor specific antibodies (DSA) are not detectable by current methodology at the time of biopsy. Some studies indicated a better prognosis for HLA-DSA-negative cases of hAMR compared to those with detectable HLA-DSA, whereas others found equally poor survival compared to hAMR-negative cases. We reviewed the literature regarding the pathophysiology of HLA-DSA-negative hAMR. We find 3 nonmutually exclusive possibilities: 1) HLA-DSA are involved, but just not detected; 2) non-HLA DSA (allo- or autoantibodies) are pathogenically involved; and/or 3) antibody-independent NK cell activation is mediating the process through "missing self" or other activating mechanisms. These possibilities are discussed in detail. Recommendations regarding the approach to such patients are made. Clearly, more research is necessary regarding the measurement of non-HLA antibodies, recipient/donor NK cell genotyping, and the use of antibody reduction therapy or other immunosuppression in any subset of patients with HLA-DSA-negative hAMR.

Risk of new-onset autoimmune diseases in primary aldosteronism: a nation-wide population-based study

OBJECTIVE

The association between hyperaldosteronism and autoimmune disorders has been postulated. However, long-term incidence of a variety of new-onset autoimmune diseases (NOAD) among patients with primary aldosteronism has not been well investigated.

METHODS

From Taiwan's National Health Insurance Research Database with a 23-million population insurance registry, the identification of primary aldosteronism, essential hypertension and NOAD as well as all-cause mortality were ascertained by a validated algorithm.

RESULTS

From 1997 to 2009, 2319 primary aldosteronism patients without previously autoimmune disease were identified and propensity score-matched with 9276 patients with essential hypertension. Among those primary aldosteronism patients, 806 patients with aldosterone-producing adenomas (APA) were identified and matched with 3224 essential hypertension controls. NOAD incidence is augmented in primary aldosteronism patients compared with its matched essential hypertension (hazard ratio 3.82, P < 0.001, versus essential hypertension). Furthermore, NOAD incidence is also higher in APA patients compared with its matched essential hypertension (hazard ratio = 2.96, P < 0.001, versus essential hypertension). However, after a mean 8.9 years of follow-up, primary aldosteronism patients who underwent adrenalectomy (hazard ratio = 3.10, P < 0.001, versus essential hypertension) and took mineralocorticoid receptor antagonist (MRA) still had increased NOAD incidence (hazard ratio = 4.04, P < 0.001, versus essential hypertension).

CONCLUSION

Primary aldosteronism patients had an augmented risk for a variety of incident NOAD and all-cause of mortality, compared with matched essential hypertension controls. Notably, the risk of incident NOAD remained increased in patients treated by adrenalectomy or MRA compared with matched essential hypertension controls. This observation supports the theory of primary aldosteronism being associated with a higher risk of multiple autoimmune diseases.

How common is primary aldosteronism?

PURPOSE OF REVIEW

Primary aldosteronism, characterized by renin-independent aldosterone secretion from one or both adrenal glands, is the most common and modifiable form of secondary hypertension. The prevalence of primary aldosteronism is increasingly recognized to be much higher than previously thought with many cases still undetected.

RECENT FINDINGS

Prior prevalence studies on primary aldosteronism have reported a wide range of estimates due to heterogeneity of both disease definitions and study populations such that it is difficult to claim a single point estimate. More recent evidence demonstrates that primary aldosteronism, as defined by conventional biochemical diagnostic criteria, is highly prevalent within populations where it is not typically considered such as mild-to-moderate hypertension, prehypertension, and even normotension. Yet, our current screening approach fails to capture many cases. Furthermore, there is mounting evidence that renin-independent aldosteronism exists as a continuum of disease that extends below the current biochemical diagnostic thresholds used to define primary aldosteronsim and has clinically relevant treatment and outcome implications for a much broader patient population. Indeed, much of what we current label as 'essential hypertension' is, in fact, renin-independent aldosterone-mediated hypertension.

SUMMARY

Primary aldosteronism and milder forms of renin-independent aldosteronism are highly prevalent, yet vastly under-recognized, in the general population.

Future Directions of Therapeutic Vaccines for Chronic Diseases

Vaccines are well-known therapies for infectious disease and cancer; however, recently, we and others have developed vaccines for other chronic diseases, such as hypertension, diabetes and dyslipidemia. Although we have many treatment options for hypertension, including angiotensin II type 1 receptor blockers, calcium-channel blockers, and diuretics, a substantial portion of the hypertensive population has uncontrolled blood pressure due to poor medication adherence. When these vaccines are established in the future as therapeutic options for chronic diseases, their administration regimen, such as several times per year, will replace daily medication use. Thus, therapeutic vaccines might be a novel option to control the progression of cardiovascular diseases. Importantly, regarding the development of vaccines against self-antigens (i.e., angiotensin II), the vaccine should efficiently induce a blocking antibody response against the self-antigen without provoking cytotoxic T cells. Therefore, to address the safety and efficiency of therapeutic vaccines, we have developed an original B-cell vaccine to induce antibody production and used carrier proteins, which include exogenous T-cell epitopes through the major histocompatibility complex. In this review, we will introduce the challenges in developing therapeutic vaccines for chronic diseases and describe the therapeutic potential for cardiovascular diseases.

Prevalence of Angiotensin II Type 1 Receptor Antibodies in Persons With Hypertension and Relation to Blood Pressure and Medication

BACKGROUND

We aimed to determine the prevalence of antibodies against angiotensin II type 1 receptor (AT1RAb) in hypertensive adults and elucidate the relation of antihypertensive medication type to blood pressure (BP) among persons with and without AT1RAb.

METHODS

Sera from participants in the Healthy Aging in Neighborhoods of Diversity across the Life Span (HANDLS) study with hypertension were tested for AT1RAb using a commercial Enzyme-linked immunosorbent assay (ELISA) (One Lambda; positive ≥17 units/ml). BP measurements, uncontrolled BP (systolic BP ≥140 and/or diastolic BP ≥90 mm Hg), and effect of BP medication type were compared for AT1RAb positive (+) vs. negative (-) participants using descriptive statistics and multivariable regression.

RESULTS

One hundred and thirty-two (13.1%) participants were AT1RAb+. Compared with AT1RAb-, AT1RAb+ persons were more likely to be white (47% vs. 36.7%; P = 0.03) but had similar comorbid disease burden. In models adjusting for age, sex, and race, AT1RAb+ persons had higher diastolic BP (β = 2.61 mm Hg; SE = 1.03; P = 0.01) compared with AT1RAb- participants. Rates of uncontrolled BP were similar between the groups. AT1RAb+ persons on an angiotensin receptor blocker (ARB; n = 21) had a mean of 10.5 mm Hg higher systolic BP (SE = 4.56; P = 0.02) compared with AT1RAb+ persons using other BP medications. The odds of uncontrolled BP among AT1RAb+ participants on an ARB was 2.05 times that of those on other medications. AT1RAb- persons prescribed an angiotensin-converting enzyme inhibitor (ACEi) had 1.8 mm Hg lower diastolic BP (SE = 0.81; P = 0.03) than AT1RAb- persons not prescribed an ACEi.

CONCLUSIONS

AT1RAb was prevalent among hypertensive adults and was associated with higher BP among persons on an ARB.

The Role of GnRH Receptor Autoantibodies in Polycystic Ovary Syndrome

Objective

Is polycystic ovary syndrome (PCOS) associated with activating autoantibodies (AAb) to the second extracellular loop (ECL2) of gonadotropin-releasing hormone receptor (GnRHR)?

Design and Methods

We retrospectively screened sera from 40 patients with PCOS and 14 normal controls (NCs) with regular menses using enzyme-linked immunosorbent assay (ELISA) for the presence of GnRHR-ECL2-AAb. We obtained similar data from 40 non-PCOS ovulatory but infertile patients as a control group (OIC) of interest. We analyzed GnRHR-ECL2-AAb activity in purified immunoglobulin (Ig)G using a cell-based GnRHR bioassay.

Results

The mean ELISA value in the PCOS group was markedly higher than the NC (P = .000036) and the OIC (P = .0028) groups. IgG from a sample of 5 PCOS subjects, in contrast to a sample of 5 OIC subjects, demonstrated a dose-dependent increase in GnRHR-stimulating activity qualitatively similar to the acute action of the natural ligand GnRH and the synthetic agonist leuprolide. The GnRHR antagonist cetrorelix significantly suppressed (P < .01) the elevated GnRHR activity induced by IgG from 7 PCOS patients while the IgG activity level from 7 OIC subjects was unchanged. Five other OIC subjects had relatively high ELISA values at or above the 95% confidence limits. On further study, 3 had normal or low activity while 2 had elevated IgG-induced GnRHR activity. One suppressed with cetrorelix while the other did not. The copresence of PCOS IgG increased the responsiveness to GnRH and shifted the dosage response curve to the left (P < .01).

Conclusions

GnRHR-ECL2-AAb are significantly elevated in patients with PCOS compared with NCs. Their presence raises important etiological, diagnostic, and therapeutic implications.

Angiotensin II Type 1 Receptor Autoantibodies in Primary Aldosteronism

Primary aldosteronism (PA) is the most common form of endocrine hypertension. Agonistic autoantibodies against the angiotensin II type 1 receptor (AT₁R-Abs) have been described in transplantation medicine and women with pre-eclampsia and more recently in patients with PA. Any functional role of AT₁R-Abs in either of the two main subtypes of PA (aldosterone-producing adenoma or bilateral adrenal hyperplasia) requires clarification. In this review, we discuss the studies performed to date on AT₁R-Abs in PA.

The Impact of Glucocorticoid Co-Secretion in Primary Aldosteronism on Thyroid Autoantibody Titers During the Course of Disease

Excess aldosterone is associated with the increased risk of cardio-/cerebrovascular events as well as metabolic comorbidities not only due to its hypertensive effect but also due to its proinflammatory action. Autonomous cortisol secretion (ACS) in the setting of primary aldosteronism (PA) is known to worsen cardiovascular outcome and potentially exhibit immunosuppressive effects. The aim of this study was to determine the impact of ACS status in patients with PA on kinetics of thyroid autoantibodies (anti-TPO, anti-TG) pre and post therapy initiation. Ninety-seven PA patients (43 unilateral, 54 with bilateral PA) from the database of the German Conn's Registry were included. Anti-TPO and anti-TG levels were measured pre and 6-12 months post therapeutic intervention. Patients were assessed for ACS according to their 24- hour urinary cortisol excretion, late night salivary cortisol and low-dose dexamethasone suppression test. Abnormal test results in line with ACS were identified in 74.2% of patients with PA. Following adrenalectomy, significant increases in anti-TPO levels were observed in patients with at least one abnormal test (p = 0.049), adrenalectomized patients with at least two pathological ACS tests (p = 0.015) and adrenalectomized patients with pathologic dexamethasone suppression tests (p = 0.018). No antibody increases were observed in unilateral PA patients without ACS and in patients with bilateral PA receiving mineralocorticoid antagonist therapy (MRA). Our data are in line with an immunosuppressive effect of mild glucocorticoid excess in PA on thyroid autoantibody titers. This effect is uncovered by adrenalectomy, but not by MRA treatment.

Aldosterone Stimulates Its Biosynthesis Via a Novel GPER-Mediated Mechanism

CONTEXT

The G protein-coupled estrogen receptor (GPER) mediates an aldosterone secretagogue effect of 17β-estradiol in human HAC15 adrenocortical cells after estrogen receptor β blockade. Because GPER mediates mineralocorticoid receptor-independent aldosterone effects in other cell types, we hypothesized that aldosterone could modulate its own synthesis via GPER activation.

METHODS

HAC15 cells were exposed to aldosterone in the presence or absence of canrenone, a mineralocorticoid receptor antagonist, and/or of the selective GPER antagonist G36. Aldosterone synthase (CYP11B2) mRNA and protein levels changes were the study end points. Similar experiments were repeated in strips obtained ex vivo from aldosterone-producing adenoma (APA) and in GPER-silenced HAC15 cells.

RESULTS

Aldosterone markedly increased CYP11B2 mRNA and protein expression (vs untreated samples, P < 0.001) in both models by acting via GPER, because these effects were abolished by G36 (P < 0.01) and not by canrenone. GPER-silencing (P < 0.01) abolished the aldosterone-induced increase of CYP11B2, thus proving that aldosterone acts via GPER to augment the step-limiting mitochondrial enzyme (CYP11B2) of its synthesis. Angiotensin II potentiated the GPER-mediated effect of aldosterone on CYP11B2. Coimmunoprecipitation studies provided evidence for GPER-angiotensin type-1 receptor heterodimerization.

CONCLUSION

We propose that this autocrine-paracrine mechanism could enhance aldosterone biosynthesis under conditions of immediate physiological need in which the renin-angiotensin-aldosterone system is stimulated as, for example, hypovolemia. Moreover, as APA overexpresses GPER this mechanism could contribute to the aldosterone excess that occurs in primary aldosteronism in a seemingly autonomous fashion from angiotensin II.

AT1AA (Angiotensin II Type-1 Receptor Autoantibodies): Cause or Consequence of Human Primary Aldosteronism?

AT1AA (Angiotensin II type-1 receptor autoantibodies) were first detected in patients with primary aldosteronism (PA) because of aldosterone-producing adenoma (APA) with an in-house developed assay, but it remained unclear if they can be ascertained also with commercially available assays and if they have a functional role. Aims of our study were to investigate if (1) commercially available kits allow detection of raised AT1AA titer in APA; (2) this titer is normalized by adrenalectomy; and (3) AT1AA display any biological roles in vitro. We measured with 2 ELISA kits the AT1AA titer in serum of APA patients and its changes after adrenalectomy. We also investigated AT1AA bioactivity by using AT1-R (angiotensin type-1 receptor)-transfected Chinese hamster ovary and human adrenocortical carcinoma cells, and by measuring aldosterone synthase (CYP11B2) expression in human adrenocortical carcinoma cells after incubation with IgG. Both kits allowed detection of higher AT1AA levels in APA patients than in healthy subjects; surgical cure of PA did not decrease this titer at 1-month follow-up. Human adrenocortical carcinoma cells stimulation with IgG purified from sera of APA patients increased both CYP11B2 expression and aldosterone release (+40% and +76%, respectively, versus healthy subjects). However, no detectable effect of IgG was seen in Chinese hamster ovary cells expressing AT1-R. These findings support the contentions that (1) the raised AT1AA titer does not seem to be a consequence of hyperaldosteronism as it did not normalize after its cure; (2) AT1AA act as weak stimulators of aldosterone biosynthesis, but this effect can be identified only by using a sensitive in vitro technique.

Diverse Responses of Autoantibodies to the Angiotensin II Type 1 Receptor in Primary Aldosteronism

Primary aldosteronism is a common form of endocrine hypertension mainly caused by a unilateral aldosterone-producing adenoma (APA) or bilateral adrenal hyperplasia (BAH). AT1R-Abs (autoantibodies to the angiotensin II type 1 receptor) have been reported in patients with disorders associated with hypertension. Our objective was to assess AT1R-Ab levels in patients with primary aldosteronism (APA, n=40 and BAH, n=40) relative to patients with primary hypertension (n=40), preeclampsia (n=23), and normotensive individuals (n=25). AT1R-Abs in whole sera were measured using 2 different ELISAs which gave contrasting results. A functional cell-based assay was used to quantify activation of the AT1R (angiotensin II type 1 receptor) using whole sera or affinity-purified antibodies in the absence or presence of losartan (a specific AT1R antagonist). Serum samples from all groups displayed different levels of AT1R activation with different responses to losartan. Patients with BAH displayed higher losartan-independent affinity-isolated agonistic AT1R-Ab levels compared with patients with APA (P<0.01) and with normotensive individuals (P<0.0001). In patients with APA, BAH, and primary hypertension combined, higher aldosterone-to-renin ratios and lower plasma renin concentrations were associated with higher compared with lower agonistic AT1R-Ab levels. In patients with primary aldosteronism, higher AT1R-Ab activity was associated with an increased likelihood of a diagnosis of BAH compared with APA and with the presence of adrenal hyperplasia detected by computed tomography. Taken together, these data suggest that agonistic AT1R-Abs may have a functional role in a subgroup of patients with primary aldosteronism.

Antibodies against Angiotensin II Type 1 and Endothelin A Receptors: Relevance and pathogenicity

Antibodies against two G-protein coupled receptors (GPCRs), angiotensin II type 1 receptor (AT1R) and endothelin A receptor (ETAR) are among a growing number of autoantibodies that are found to be associated with allograft dysfunction. AT1R antibodies (AT1Rabs) and ETAR antibodies (ETARabs) have been shown to activate their target receptors and affect signaling pathways. Multiple single center reports have shown an association between presence of these antibodies and acute or chronic rejection and graft loss in kidney, heart, liver, lung and composite tissue transplantations. However, the characteristics of patients that are most likely to develop adverse outcomes, the phenotypes associated with graft damage solely due to these antibodies, and the antibody titer required to cause dysfunction are areas that remain controversial. This review compiles existing knowledge on the effect of antibodies against GPCRs in other diseases in order to bridge the gap in knowledge within transplantation biology. Future areas for research are highlighted and include the need for functional assays and treatment protocols for transplant patients who present with AT1Rabs and ETARabs. Understanding how antibodies that activate GPCRs influence transplantation outcome will have direct clinical implications for preemptive evaluation of transplant candidates as well as the post-transplant care of organ recipients.

The Biology of Normal Zona Glomerulosa and Aldosterone-Producing Adenoma: Pathological Implications

The identification of several germline and somatic ion channel mutations in aldosterone-producing adenomas (APAs) and detection of cell clusters that can be responsible for excess aldosterone production, as well as the isolation of autoantibodies activating the angiotensin II type 1 receptor, have rapidly advanced the understanding of the biology of primary aldosteronism (PA), particularly that of APA. Hence, the main purpose of this review is to discuss how discoveries of the last decade could affect histopathology analysis and clinical practice. The structural remodeling through development and aging of the human adrenal cortex, particularly of the zona glomerulosa, and the complex regulation of aldosterone, with emphasis on the concepts of zonation and channelopathies, will be addressed. Finally, the diagnostic workup for PA and its subtyping to optimize treatment are reviewed.

Evaluation of angiotensin II type-1 receptor antibodies in primary aldosteronism and further considerations about their possible pathogenetic role

Angiotensin II type-1 receptor autoantibodies (AT1RAb) have been involved in the genesis of primary aldosteronism (PA), both in aldosterone-producing adenoma (APA) and in idiopathic hyperaldosteronism (IHA). In this study, we evaluated the titer of AT1RAb in 44 PA patients (15 with APA and 29 with IHA) compared with 18 normotensive healthy controls who were matched for gender and age. In 17 PA patients (6 APA and 11 IHA) the titer was evaluated under mineralocorticoid receptor (MR) antagonist treatment. We found that PA patients had a significantly higher titer of AT1RAb compared with controls (median values 33 [IQR 15.6] IU/mL vs 17.5 [IQR 10.8] IU/mL, respectively; P < 0.0001). No significant difference of the AT1RAb titer was reported among PA patients, subdivided according to the subtypes and the concomitant MR antagonist therapy. No significant correlation was detected between age, gender, BMI, blood pressure values, baseline aldosterone, ARR, and the AT1RAb titer of all patients enrolled. Our data confirm an increased titer of AT1RAb in both subtypes of PA, independently from the concomitant use of MR antagonists and clinical/biochemical characteristics of PA patients. The small sample of patients and the relatively short time of treatment could have influenced these results. Moreover, the ELISA assay fails to evaluate the bioactivity of AT1RAb. Further studies should evaluate if the subtype, the clinical/biochemical recovery of PA, or both, influence the pathogenetic role of AT1RAb. The possible autoimmune pathogenesis and reversal effect with AT1R blocker treatment in PA patients with AT1RAb positivity is intriguing and requires further study.

Angiotensin II Type 1 Receptor Autoantibodies in Postural Tachycardia Syndrome

Background

Both the adrenergic and renin‐angiotensin systems contribute to orthostatic circulatory homeostasis, which is impaired in postural orthostatic tachycardia syndrome (POTS). Activating autoantibodies to the α1‐adrenergic and β1/2‐adrenergic receptors have previously been found in sera from patients with POTS. We hypothesized that patients with POTS might also harbor activating autoantibodies to the angiotensin II type 1 receptor (AT1R) independently of antiadrenergic autoimmunity. This study examines a possible pathophysiological role for AT1R autoantibodies in POTS.

Methods and Results

Serum immunoglobulin G from 17 patients with POTS, 6 patients with recurrent vasovagal syncope, and 10 normal controls was analyzed for the ability to activate AT1R and alter AT1R ligand responsiveness in transfected cells in vitro. Of 17 subjects with POTS, 12 demonstrated significant AT1R antibody activity in immunoglobulin G purified from their serum. No significant AT1R antibody activity was found in the subjects with vasovagal syncope or healthy subjects. AT1R activation by POTS immunoglobulin G was specifically blocked by the AT1R blocker losartan. Moreover, POTS immunoglobulin G significantly shifted the angiotensin II dosage response curve to the right, consistent with an inhibitory effect. All subjects with POTS were positive for one or both autoantibodies to the AT1R and α1‐adrenergic receptor.

Conclusions

Most patients with POTS harbor AT1R antibody activity. This supports the concept that AT1R autoantibodies and antiadrenergic autoantibodies, acting separately or together, may exert a significant impact on the cardiovascular pathophysiological characteristics in POTS.

Coexistence of Primary Hyperaldosteronism and Graves' Disease, a Rare Combination of Endocrine Disorders: Is It beyond a Coincidence-A Case Report and Review of the Literature

BACKGROUND

Primary hyperaldosteronism is a known cause for secondary hypertension. In addition to its effect on blood pressure, aldosterone exhibits proinflammatory actions and plays a role in immunomodulation/development of autoimmunity. Recent researches also suggest significant thyroid dysfunction among patients with hyperaldosteronism, but exact causal relationship is not established. Autoimmune hyperthyroidism (Graves' disease) and primary hyperaldosteronism rarely coexist but underlying mechanisms associating the two are still unclear.

CASE PRESENTATION

A 32-year-old Sri Lankan female was evaluated for new onset hypertension in association with hypokalemia. She also had features of hyperthyroidism together with high TSH receptor antibodies suggestive of Graves' disease. On evaluation of persistent hypokalemia and hypertension, primary hyperaldosteronism due to right-sided adrenal adenoma was diagnosed. She was rendered euthyroid with antithyroid drugs followed by right-sided adrenalectomy. Antithyroid drugs were continued up to 12 months, after which the patient entered remission of Graves' disease.

CONCLUSION

Autoimmune hyperthyroidism and primary hyperaldosteronism rarely coexist and this case report adds to the limited number of cases documented in the literature. Underlying mechanism associating the two is still unclear but possibilities of autoimmune mechanisms and autoantibodies warrant further evaluation and research.

Inflammation, Autoimmunity, and Hypertension: The Essential Role of Tissue Transglutaminase

Inflammatory cytokines cause hypertension when introduced into animals. Additional evidence indicates that cytokines induce the production of autoantibodies that activate the AT1 angiotensin receptor (AT1R). Extensive evidence shows that these autoantibodies, termed AT1-AA, contribute to hypertension. We review here recent studies showing that cytokine-induced hypertension and AT1-AA production require the ubiquitous enzyme, tissue transglutaminase (TG2). We consider 3 mechanisms by which TG2 may contribute to hypertension. (i) One involves the posttranslational modification (PTM) of AT1Rs at a glutamine residue that is present in the epitope sequence (AFHYESQ) recognized by AT1-AA. (ii) Another mechanism by which TG2 may contribute to hypertension is by PTM of AT1Rs at glutamine 315. Modification at this glutamine prevents ubiquitination-dependent proteasome degradation and allows AT1Rs to accumulate. Increased AT1R abundance is likely to account for increased sensitivity to Ang II activation and in this way contribute to hypertension. (iii) The increased TG2 produced as a result of elevated inflammatory cytokines is likely to contribute to vascular stiffness by modification of intracellular contractile proteins or by crosslinking vascular proteins in the extracellular matrix. This process, termed inward remodeling, results in reduced vascular lumen, vascular stiffness, and increased blood pressure. Based on the literature reviewed here, we hypothesize that TG2 is an essential participant in cytokine-induced hypertension. From this perspective, selective TG2 inhibitors have the potential to be pharmacologic weapons in the fight against hypertension.

Primary Aldosteronism: Changing Definitions and New Concepts of Physiology and Pathophysiology Both Inside and Outside the Kidney

In the 60 years that have passed since the discovery of the mineralocorticoid hormone aldosterone, much has been learned about its synthesis (both adrenal and extra-adrenal), regulation (by renin-angiotensin II, potassium, adrenocorticotrophin, and other factors), and effects (on both epithelial and nonepithelial tissues). Once thought to be rare, primary aldosteronism (PA, in which aldosterone secretion by the adrenal is excessive and autonomous of its principal regulator, angiotensin II) is now known to be the most common specifically treatable and potentially curable form of hypertension, with most patients lacking the clinical feature of hypokalemia, the presence of which was previously considered to be necessary to warrant further efforts towards confirming a diagnosis of PA. This, and the appreciation that aldosterone excess leads to adverse cardiovascular, renal, central nervous, and psychological effects, that are at least partly independent of its effects on blood pressure, have had a profound influence on raising clinical and research interest in PA. Such research on patients with PA has, in turn, furthered knowledge regarding aldosterone synthesis, regulation, and effects. This review summarizes current progress in our understanding of the physiology of aldosterone, and towards defining the causes (including genetic bases), epidemiology, outcomes, and clinical approaches to diagnostic workup (including screening, diagnostic confirmation, and subtype differentiation) and treatment of PA.

Transglutaminase is a Critical Link Between Inflammation and Hypertension

Background

The pathogenesis of essential hypertension is multifactorial with different underlying mechanisms contributing to disease. We have recently shown that TNF superfamily member 14 LIGHT (an acronym for homologous to lymphotoxins, exhibits inducible expression, and competes with herpes simplex virus glycoprotein D for herpes virus entry mediator, a receptor expressed by T lymphocytes, also known as TNFSF14) induces hypertension when injected into mice. Research reported here was undertaken to examine the role of transglutaminase (TGase) in LIGHT‐induced hypertension.

Methods and Results

Initial experiments showed that plasma and kidney TGase activity was induced by LIGHT infusion (13.91±2.92 versus 6.75±1.92 mU/mL and 19.86±3.55 versus 12.00±0.97 mU/10 μg) and was accompanied with hypertension (169±7.16 versus 117.17±11.57 mm Hg at day 14) and renal impairment (proteinuria, 61.33±23.21 versus 20.38±9.01 μg/mg; osmolality, 879.57±93.02 versus 1407.2±308.04 mmol/kg). The increase in renal TGase activity corresponded to an increase in RNA for the tissue TGase isoform, termed TG2. Pharmacologically, we showed that LIGHT‐induced hypertension and renal impairment did not occur in the presence of cystamine, a well‐known competitive inhibitor of TGase activity. Genetically, we showed that LIGHT‐mediated induction of TGase, along with hypertension and renal impairment, was dependent on interleukin‐6 and endothelial hypoxia inducible factor‐1α. We also demonstrated that interleukin‐6, endothelial hypoxia inducible factor‐1α, and TGase are required for LIGHT‐induced production of angiotensin receptor agonistic autoantibodies.

Conclusions

Thus, LIGHT‐induced hypertension, renal impairment, and production of angiotensin receptor agonistic autoantibodies require TGase, most likely the TG2 isoform. Our findings establish TGase as a critical link between inflammation, hypertension, and autoimmunity.

Non-HLA antibodies against endothelial targets bridging allo- and autoimmunity

Detrimental actions of donor-specific antibodies (DSAs) directed against both major histocompatibility antigens (human leukocyte antigen [HLA]) and specific non-HLA antigens expressed on the allograft endothelium are a flourishing research area in kidney transplantation. Newly developed solid-phase assays enabling detection of functional non-HLA antibodies targeting G protein-coupled receptors such as angiotensin type I receptor and endothelin type A receptor were instrumental in providing long-awaited confirmation of their broad clinical relevance. Numerous recent clinical studies implicate angiotensin type I receptor and endothelin type A receptor antibodies as prognostic biomarkers for earlier occurrence and severity of acute and chronic immunologic complications in solid organ transplantation, stem cell transplantation, and systemic autoimmune vascular disease. Angiotensin type 1 receptor and endothelin type A receptor antibodies exert their pathophysiologic effects alone and in synergy with HLA-DSA. Recently identified antiperlecan antibodies are also implicated in accelerated allograft vascular pathology. In parallel, protein array technology platforms enabled recognition of new endothelial surface antigens implicated in endothelial cell activation. Upon target antigen recognition, non-HLA antibodies act as powerful inducers of phenotypic perturbations in endothelial cells via activation of distinct intracellular cell-signaling cascades. Comprehensive diagnostic assessment strategies focusing on both HLA-DSA and non-HLA antibody responses could substantially improve immunologic risk stratification before transplantation, help to better define subphenotypes of antibody-mediated rejection, and lead to timely initiation of targeted therapies. Better understanding of similarities and dissimilarities in HLA-DSA and distinct non-HLA antibody-related mechanisms of endothelial damage should facilitate discovery of common downstream signaling targets and pave the way for the development of endothelium-centered therapeutic strategies to accompany intensified immunosuppression and/or mechanical removal of antibodies.

AT2R autoantibodies block angiotensin II and AT1R autoantibody-induced vasoconstriction

Activating autoantibodies to the angiotensin type 1 receptor (AT1R) are associated with hypertensive disorders. The angiotensin type 2 receptor (AT2R) is known to counter-regulate the actions of AT1R. We investigated whether AT2R autoantibodies produced in immunized rabbits will activate AT2R and suppress the vasopressor responses to angiotensin II and AT1R-activating autoantibodies. Five rabbits immunized with a peptide corresponding to the second extracellular loop of AT2R developed high AT2R antibody titers. Rabbit anti-AT2R sera failed to directly dilate isolated rat cremaster arterioles; however, when co-perfused with angiotensin II or AT1R-activating autoantibodies, the anti-AT2R sera significantly inhibited their contractile effects. Rabbit anti-AT2R sera recognized a predominant sequence near the N-terminus of the AT2R second extracellular loop. A decoy peptide based on this sequence effectively reversed the opposing effect of the anti-AT2R sera on angiotensin II-induced contraction of rat cremaster arterioles. A similar blockade of the anti-AT2R sera effect was observed with the AT2R antagonist PD 123319 and the guanylyl cyclase inhibitor 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one. Rabbit anti-AT2R sera reacted specifically with AT2R. No cross-reactivity with AT1R was observed. Blood pressure did not change in immunized animals. However, the pressor responses to incremental angiotensin II infusions were blunted in immunized animals. Thirteen subjects with primary aldosteronism demonstrated increased AT2R autoantibody levels compared with normal controls. In conclusion, AT2R autoantibodies produced in immunized rabbits have the ability to activate AT2R and counteract the AT1R-mediated vasoconstriction. These autoantibodies provide useful and selective tools for the study of their roles in blood pressure regulation and possible therapeutic intervention.

Issues in the Diagnosis and Treatment of Primary Aldosteronism

Primary aldosteronism (PA) is associated with a high rate of cardio- and cerebrovascular complications and metabolic alterations. PA is also recognized as the most frequent, although often unrecognized, secondary form of hypertension. Guidelines have been released to assist clinicians in the diagnostic work-up and subtype differentiation of PA. In this review we discuss and compare the available guidelines in the context of our professional experience and evaluate diagnostic and therapeutic aspects that are still a matter of debate.

Adrenalectomy is comparable with medical treatment for reduction of left ventricular mass in primary aldosteronism: meta-analysis of long-term studies

BACKGROUND

Primary aldosteronism (PA) is associated with an increase in left ventricular (LV) mass beyond the amount needed to compensate the hypertension-related workload. Available evidence suggests effectiveness of surgical treatment of PA in decreasing LV mass, whereas data on medical treatment are controversial. We have conducted a meta-analysis of long-term follow-up studies on surgical and medical treatment of PA to compare the effects of treatments on LV mass.

METHODS

Medline and Cochrane searches were performed including the following words: hyperaldosteronism, left ventricular mass, mineralocorticoid receptor antagonists, surgery, adrenalectomy, and follow-up studies. Studies published within 2013 focusing on cardiac effects of treatment and follow-up longer than 6 months were selected. Data extraction was performed independently by 2 authors.

RESULTS

Of 61 retrieved articles, 4 were included in the analysis. These studies enrolled 355 patients with PA who had an average follow-up of 4.0 years after unilateral adrenalectomy (n = 178) or treatment with mineralocorticoid receptor antagonists (n = 177). Despite greater effect of surgery over medical treatment in reducing blood pressure, meta-analysis of the selected studies demonstrated no significant difference in LV mass change between patients with PA who were treated with mineralocorticoid receptor antagonists or adrenalectomy (standard mean difference = 0.130; 95% confidence interval = -0.085 to 0.345; P = 0.24; I2 = 0%).

CONCLUSIONS

Available evidence indicates that reduction of LV mass is not different in PA patients treated with adrenalectomy or mineralocorticoid receptor antagonists.

Novel retro-inverso peptide inhibitor reverses angiotensin receptor autoantibody-induced hypertension in the rabbit

Activating autoantibodies to the angiotensin II type 1 receptor (AT1R) have been implicated in hypertensive disorders. We investigated whether AT1R antibodies produced in immunized rabbits will activate AT1R and contribute to hypertension by a direct contractile effect on the vasculature and whether they can be blocked by a novel decoy peptide. A multiple antigenic peptide containing the AT1R epitope AFHYESQ, which is the receptor-binding epitope of AT1R-activating autoantibodies, was used to immunize 6 rabbits. AT1R antibody activity was analyzed in AT1R-transfected cells, and their contractile effects were assayed using isolated perfused rat cremaster resistance arterioles. A retro-inverso D-amino acid epitope-mimetic peptide was tested for AT1R antibody inhibition in vitro and in vivo. All immunized animals produced high AT1R antibody titers and developed elevated blood pressure. No changes in measured blood chemistry values were observed after immunization. Rabbit anti-AT1R sera induced significant AT1R activation in transfected cells and vasoconstriction in the arteriole assay, both of which were blocked by losartan and the retro-inverso D-amino acid peptide. A single intravenous bolus injection of the retro-inverso d-amino acid peptide (1 mg/kg) into immunized rabbits dropped the mean arterial pressure from 122±11 to 82±6 mm Hg. Rabbit anti-AT1R sera partially suppressed angiotensin II-induced contraction of isolated rat cremaster arterioles, and the pressor response to angiotensin II infusion was attenuated in immunized animals. In conclusion, AT1R-activating autoantibodies and the retro-inverso d-amino acid peptide, respectively, have important etiologic and therapeutic implications in hypertensive subjects who harbor these autoantibodies.

Progress in primary aldosteronism: mineralocorticoid receptor antagonists and management of primary aldosteronism in pregnancy

Primary aldosteronism (PA) is the most common cause of secondary hypertension. In this review, we discuss the diagnosis and management of PA during pregnancy based on the literature. As aldosterone and renin are physiologically increased during pregnancy and confirmation tests are not recommended, the diagnosis of PA during pregnancy relies on a repeatedly suppressed plasma renin level. Mineralocorticoid receptor antagonists (MRAs) are the most effective drugs to treat hypertension and hypokalemia in patients with PA. However, spironolactone (FDA pregnancy category C) might lead to undervirilization of male infants due to the anti-androgenic effects. Although data in the literature are very limited, treatment with spironolactone is not recommended. Eplerenone (FDA pregnancy category B) is a selective MRA without anti-androgenic potential. If MRA treatment is required in pregnancy, eplerenone appears to be a safe and effective alternative, although symptomatic treatment with approved antihypertensive drugs and supplementation with potassium is the first choice. In case of aldosterone-producing adenoma, laparoscopic adrenalectomy is a therapeutic option in the second trimester of pregnancy.

The molecular basis of primary aldosteronism: from chimeric gene to channelopathy

Primary aldosteronism (PA) is the most common endocrine cause of high blood pressure. Only a minority of the PA cases are familial and due to known (CYP11B2/CYP11B1 chimeric gene or mutations in the KCNJ5 gene) or unknown causes. In the most common sporadic cases the mechanisms by which the excess aldosterone production persists in spite of high blood pressure, sodium retention, suppression of the renin angiotensin system and low potassium levels, all factors that by themselves would be expected to shut off aldosterone production, were a puzzle for decades. Only recently the discovery of functional mutations and down-regulation of potassium channels provided some explanations. We herein reviewed these recent findings and their mechanistic implications. We also propose a clinical molecular classification of familial hyperaldosteronism, which can be important from the practical standpoint as it considers besides the molecular features also the responsiveness to treatment and the imaging features.

Prevalence of angiotensin II type 1 receptor (AT1R)-activating autoantibodies in primary aldosteronism

Autoantibodies to the angiotensin II type 1 receptor (AT1R) have been reported in patients with primary aldosteronism, including aldosterone producing adenoma (APA) and idiopathic adrenal hyperplasia (IAH). Sera from 25 primary aldosteronism subjects (12 with IAH and 13 with APA) and 15 normotensive control subjects were assayed for AT1R autoantibodies by enzyme-linked immunosorbent assay and an AT1R-transfected cell-based bioassay. Nine of 12 IAH subjects (75%) and six of 13 APA subjects (46%) were positive for AT1R autoantibodies in the bioactivity assay. The mean AT1R autoantibody activity for the IAH and APA subjects was significantly greater than controls (P < .001 and P < .01, respectively), and this in vitro activity was suppressed by the AT1R blocker losartan. None of the controls had significant AT1R autoantibody activity. Enzyme-linked immunosorbent assay values were less sensitive but were positive in some subjects with IAH and APA. The mean arterial pressure of these primary aldosteronism subjects correlated modestly with AT1R autoantibody activity. These data confirm the presence of active AT1R autoantibodies in a high percentage of subjects with primary aldosteronism irrespective of their underlying etiology. These observations have both pathophysiological and clinical implications.