Vascular tone control in humans: Insights from studies in Bartter's/Gitelman's syndromes

Mechanisms of Antihypertensive Effect of Chlorthalidone in Advanced Chronic Kidney Disease: A Causal Mediation Analysis

Key Points

Chlorthalidone reduces the amount of fluid and the BP, but fluid volume reduction is not the cause of lowering of BP. It is not volume loss but the response to volume loss such as the synthesis of substances that lower BP is important.

Background

Chlorthalidone (CTD) in a chronic kidney disease randomized trial demonstrated a robust reduction in systolic BP in stage 4 CKD. In this study, we explore the mechanisms underlying the antihypertensive effect of CTD.

Methods

In this prespecified analysis, we analyzed the contributions of baseline levels of 24-hour urinary sodium and aldosterone and the changes from baseline to 4 weeks in the multiple mediators reflecting volume status in a causal mediation analysis framework. Baseline levels of these mediators served as covariates. No power calculation for this analysis was performed.

Results

Of the 160 patients randomized, 140 (87.5%) were included in this analysis. Compared with placebo, CTD within 4 weeks reduced weight −1.5% (95% confidence interval [CI], −2.2 to −0.7) and volume −1.4% (95% CI, −2.2 to −0.6), stimulated plasma renin 40.5% (95% CI, 25.4% to 57.4%) and serum aldosterone 40.2% (95% CI, 11.7% to 76%), and reduced plasma N -terminal pro-B-type natriuretic peptide levels −19.4% (95% CI, −33.8% to −1.9%). Mediation analysis revealed the following results: for weight change, the total effect on systolic BP was −10.8 mm Hg (95% CI, −16 to −5.7), of which weight change (indirect effect) accounted for −0.9 mm Hg (95% CI, −4.2 to 2.5) and BP change independent of weight (direct effect) accounted for −10 mm Hg (−15.7 to −4.2). Thus, the percent mediation was 8.1% (95% CI, −22.4 to 38.5). Baseline excretion of 24-hour sodium or aldosterone or any of the changes in the above mediators examined accounted for <2 mm Hg BP drop and were not significant for any of the mediators.

Conclusions

CTD improved BP control among patients with advanced CKD independent of baseline urinary sodium, aldosterone, weight loss, or changes in the renin-angiotensin system or N -terminal pro-B-type natriuretic peptide.

Clinical Trial registry name and registration number:

CTD in chronic kidney disease ClinicalTrials.gov number: NCT02841280 .

Lymphatic vessels and the renin-angiotensin-system

The lymphatic system is an integral part of the circulatory system and plays an important role in the fluid homeostasis of the human body. Accumulating evidence has recently suggested the involvement of lymphatic dysfunction in the pathogenesis of cardio-reno-vascular (CRV) disease. However, how the sophisticated contractile machinery of lymphatic vessels is modulated and, possibly impaired in CRV disease, remains largely unknown. In particular, little attention has been paid to the effect of the renin-angiotensin-system (RAS) on lymphatics, despite the high concentration of RAS mediators that these tissue-draining vessels are exposed to and the established role of the RAS in the development of classic microvascular dysfunction and overt CRV disease. We herein review recent studies linking RAS to lymphatic function and/or plasticity and further highlight RAS-specific signaling pathways, previously shown to drive adverse arterial remodeling and CRV organ damage that have potential for direct modulation of the lymphatic system.

Beauty and the beast: host microRNA-155 versus SARS-CoV-2

Severe acute respiratory coronavirus 2 (SARS-CoV-2) infection in the young and healthy usually results in an asymptomatic or mild viral syndrome, possibly through an erythropoietin (EPO)-dependent, protective evolutionary landscape. In the old and in the presence of co-morbidities, however, a potentially lethal coronavirus disease 2019 (COVID-19) cytokine storm, through unrestrained renin-angiotensin aldosterone system (RAAS) hyperactivity, has been described. Multifunctional microRNA-155 (miR-155) elevation in malaria, dengue virus (DENV), the thalassemias, and SARS-CoV-1/2, plays critical antiviral and cardiovascular roles through its targeted translational repression of over 140 genes. In the present review, we propose a plausible miR-155-dependent mechanism whereby the translational repression of AGRT1, Arginase-2 and Ets-1, reshapes RAAS towards Angiotensin II (Ang II) type 2 (AT2R)-mediated balanced, tolerable, and SARS-CoV-2-protective cardiovascular phenotypes. In addition, it enhances EPO secretion and endothelial nitric oxide synthase activation and substrate availability, and negates proinflammatory Ang II effects. Disrupted miR-155 repression of AT1R + 1166C-allele, significantly associated with adverse cardiovascular and COVID-19 outcomes, manifests its decisive role in RAAS modulation. BACH1 and SOCS1 repression creates an anti-inflammatory and cytoprotective milieu, robustly inducing antiviral interferons. MiR-155 dysregulation in the elderly, and in comorbidities, allows unimpeded RAAS hyperactivity to progress towards a particularly aggressive COVID-19 course. Elevated miR-155 in thalassemia plausibly engenders a favorable cardiovascular profile and protection against malaria, DENV, and SARS-CoV-2. MiR-155 modulating pharmaceutical approaches could offer novel therapeutic options in COVID-19.

Tracing angiotensin II's yin-yang effects on cardiovascular-renal pathophysiology

Adverse changes in cardiovascular and renal systems are major contributors to overall morbidity and mortality. Human cardiovascular and renal systems exhibit a complex network of positive and negative feedback that is reflected in the control of vascular tone via angiotensin II (Ang II) based signaling. This review will examine in some depth, the multiple components and processes that control the status and reflect the health of these various cardiovascular and renal systems, such as pathways associated to monomeric G proteins, RhoA/Rho kinase system and ERK, oxidative stress and NO balance. It will specifically emphasize the "yin-yang" nature of Ang II signaling by comparing and contrasting the effects and activity of various systems, pathways and components found in hypertension to those found in Gitelman's and Bartter's syndromes (GS/BS), two rare autosomal recessive tubulopathies characterized by electrolytic imbalance, metabolic alkalosis, sodium wasting and prominent activation of the renin-angiotensin-aldosterone system. Notwithstanding the activation of the renin-angiotensin-aldosterone system, GS/BS are normo-hypotensive and protected from cardiovascular-renal remodeling and therefore can be considered the mirror image, the opposite of hypertension.

Anesthetic Considerations for Cesarean Delivery in a Parturient With Severe Gitelman Syndrome

Gitelman syndrome is an autosomal recessive inherited disorder that impairs the function of thiazide-sensitive sodium-chloride cotransporters in the distal convoluted tubule of the nephron. During labor and delivery, avoidance of sympathetic overactivity, meticulous hemodynamic monitoring, and expedited repletion of potassium and magnesium are required to avoid adverse outcomes. We present a parturient with severe Gitelman syndrome, requiring continuous electrolyte and fluid infusions, who underwent successful cesarean delivery. Potential severe morbidity was avoided with multidisciplinary planning and management.

Gitelman syndrome, hypomagnesemia, and venous thrombosis: An intriguing association

Among salt-wasting tubulopathies' complications, venous thrombosis is one of the rarest. We report a case of a young woman with Gitelman syndrome (GS). She presented a deep venous thrombosis in her leg and was treated with heparin with favorable outcomes. We retained hypomagnesemia as the cause of the thrombosis.

Mechanism of Thiazide Diuretic Arterial Pressure Reduction: The Search Continues

Thiazide diuretic (TZD)-mediated chronic reduction of arterial pressure is thought to occur through decreased total peripheral vascular resistance. Further, the decreased peripheral vascular resistance is accomplished through TZD activation of an extrarenal target, resulting in inhibition of vascular constriction. However, despite greater than five decades of investigation, little progress has been made into the identification of the TZD extrarenal target. Proposed mechanisms range from direct inhibition of constrictor and activation of relaxant signaling pathways in the vascular smooth muscle to indirect inhibition through decreased neurogenic and hormonal regulatory pathways. Surprisingly, particularly in view of this lack of progress, comprehensive reviews of the subject are absent. Moreover, even though it is well recognized that 1) several types of hypertension are insensitive to TZD reduction of arterial pressure and, further, TZD fail to reduce arterial pressure in normotensive subjects and animals, and 2) different mechanisms underlie acute and chronic TZD, findings derived from these models and parameters remain largely undifferentiated. This review 1) comprehensively describes findings associated with TZD reduction of arterial pressure; 2) differentiates between observations in TZD-sensitive and TZD-insensitive hypertension, normotensive subjects/animals, and acute and chronic effects of TZD; 3) critically evaluates proposed TZD extrarenal targets; 4) proposes guiding parameters for relevant investigations into extrarenal TZD target identification; and 5) proposes a working model for TZD chronic reduction of arterial pressure through vascular dilation.

Magnesium and Cardiovascular Disease

Magnesium is the most abundant intracellular divalent cation and essential for maintaining normal cellular physiology and metabolism, acting as a cofactor of numerous enzymes, regulating ion channels and energy generation. In the heart, magnesium plays a key role in modulating neuronal excitation, intracardiac conduction, and myocardial contraction by regulating a number of ion transporters, including potassium and calcium channels. Magnesium also has a role in regulating vascular tone, atherogenesis and thrombosis, vascular calcification, and proliferation and migration of endothelial and vascular smooth muscle cells. As such, magnesium potentially has a major influence on the pathogenesis of cardiovascular disease. As the kidney is a major regulator of magnesium homeostasis, kidney disorders can potentially lead to both magnesium depletion and overload, and as such increase the risk of cardiovascular disease. Observational data have shown an association between low serum magnesium concentrations or magnesium intake and increased atherosclerosis, coronary artery disease, arrhythmias, and heart failure. However, major trials of supplementation with magnesium have reported inconsistent benefits and also raised potential adverse effects of magnesium overload. As such, there is currently no firm recommendation for routine magnesium supplementation except when hypomagnesemia has been proven or suspected as a cause for cardiac arrhythmias.

Understanding the mechanisms of angiotensin II signaling involved in hypertension and its long-term sequelae: insights from Bartter's and Gitelman's syndromes, human models of endogenous angiotensin II signaling antagonism

Angiotensin II (Ang II) plays a key role in hypertension, renal and cardiovascular pathophysiology via intracellular pathways that involve the activation of a multiplicity of signaling mechanisms. Although experimental and genetic animal models have been developed and used to explore Ang II signaling's role in hypertension, a complete understanding of the processes mediating Ang II signaling in hypertension in humans remains elusive. One impediment is that these animal models do not exhibit all the traits of human hypertension, making it impossible to extrapolate from them to humans. To overcome this issue, we have used patients with Bartter's and Gitelman's syndromes, a human model of endogenously blunted and blocked Ang II signaling that presents a constellation of clinical findings which manifest themselves as the opposite of hypertension. This article reviews the aspects of the pathophysiology of human hypertension and its short and long term sequelae, and uses the results of our studies in Bartter's and Gitelman's syndromes along with those of others to gain better insight and understanding of the role of Ang II signaling in these processes.

Increased rho kinase activity in mononuclear cells of dialysis and stage 3-4 chronic kidney disease patients with left ventricular hypertrophy: Cardiovascular risk implications

AIMS

Cardiovascular disease (CVD) is the leading cause of excess mortality in chronic kidney disease (CKD) and dialysis patients (DP) who have higher prevalence of left ventricular hypertrophy (LVH), the strongest predictor of CV events. Rho kinase (ROCK) activation is linked in hypertensive patients to cardiac remodeling while ROCK inhibition suppresses cardiomyocyte hypertrophy and, in a human clinical condition opposite to hypertension, its downregulation associates with lack of CV remodeling. Information on ROCK activation-LVH link in CKD and DP is lacking.

MATERIALS AND METHODS

Mononuclear cells (PBMCs) MYPT-1 phosphorylation, a marker of ROCK activity, and the effect of fasudil, a ROCK inhibitor, on MYPT-1 phosphorylation were assessed in 23 DPs, 13 stage 3-4 CKD and 36 healthy subjects (HS) by Western blot. LV mass was assessed by M-mode echocardiography.

KEY FINDINGS

DP and CKD had higher MYPT-1 phosphorylation compared to HS (p<0.001 and p=0.003). Fasudil (500 and 1000μM) dose dependently reduced MYPT-1 phosphorylation in DP (p<0.01). DP had higher LV mass than CKD (p<0.001). MYPT-1 phosphorylation was higher in patients with LVH (p=0.009) and correlated with LV mass both in DP and CKD with LVH (p<0.001 and p=0.006).

SIGNIFICANCE

In DP and CKD, ROCK activity tracks with LVH. This ROCK activation-LVH link provided in these CVD high-risk patients along with similar findings in hypertensive patients and added to opposite findings in a human model opposite to hypertension and in type 2 diabetic patients, identify ROCK activation as a potential LVH marker and provide further rationale for ROCK activation inhibition as target of therapy in CVD high-risk patients.

Bartter/Gitelman syndromes as a model to study systemic oxidative stress in humans

Reactive oxygen species (ROS) are intermediates in reduction-oxidation reactions that begin with the addition of one electron to molecular oxygen, generating the primary ROS superoxide, which in turn interacts with other molecules to produce secondary ROS, such as hydrogen peroxide, hydroxyl radical, and peroxynitrite. ROS are continuously produced during metabolic processes and are deemed to play an important role in cardiovascular diseases, namely, myocardial hypertrophy and fibrosis and atherosclerosis, via oxidative damage of lipids, proteins, and deoxyribonucleic acid. Angiotensin II (Ang II) is a potent vasoactive agent that also exerts mitogenic, proinflammatory, and profibrotic effects through several signaling pathways, in part involving ROS, particularly superoxide and hydrogen peroxide. Moreover, Ang II stimulates NADPH oxidases, leading to higher ROS generation and oxidative stress. Bartter/Gitelman syndrome patients, despite elevated plasma renin activity, Ang II, and aldosterone levels, exhibit reduced peripheral resistance, normal/low blood pressure, and blunted pressor effect of vasoconstrictors. In addition, notwithstanding the activation of the renin-angiotensin system and the increased plasma levels of Ang II, these patients display decreased production of ROS, reduced oxidative stress, and increased antioxidant defenses. In fact, Bartter/Gitelman syndrome patients are characterized by reduced levels of p22(phox) gene expression and undetectable plasma peroxynitrite levels, while showing increased plasma antioxidant power and expression of antioxidant enzymes, such as heme oxygenase-1. In conclusion, multifarious data suggest that Bartter and Gitelman syndrome patients are a model of low oxidative stress and high antioxidant defenses. The contribution offered by the study of these syndromes in elucidating the molecular mechanisms underlying this favorable status could offer chances for new therapeutic targets in disease characterized by high levels of reactive oxygen species.

Assessing the Relationship of Angiotensin II Type 1 Receptors with Erythropoietin in a Human Model of Endogenous Angiotensin II Type 1 Receptor Antagonism

HYPOTHESIS/INTRODUCTION

Angiotensin II (Ang II) has been shown to control erythropoietin (EPO) synthesis as Ang II type 1 receptor (AT1R) blockers block Ang-II-induced EPO oversecretion. To further explore the involvement of AT1R in processes controlling EPO levels, plasma EPO and mononuclear cell NADPH oxidase 4 (NOX4) - a NOX family member involved in oxygen sensing, which is a process central to controlling EPO levels - were assessed in Bartter's/Gitelman's syndrome (BS/GS) patients, a human model of endogenous AT1R antagonism and healthy subjects. Heme oxygenase (HO)-1, antioxidant and anti-inflammatory factor related to NOX4 activation, and the relationship of EPO and NOX4 to HO-1 were also assessed.

MATERIALS AND METHODS

EPO was measured by chemiluminescent immunoassay, HO-1 by sandwich immunoassay and NOX4 protein expression by Western blot.

RESULTS

EPO was increased in BS/GS patients compared to healthy subjects (7.64 ± 2.47 vs. 5.23 ± 1.07 U/l; p = 0.025), whereas NOX4 did not differ between BS/GS and healthy subjects (1.76 ± 0.61 vs. 1.65 ± 0.54 densitometric units; p = n.s.), and HO-1 was increased in BS/GS patients compared to healthy subjects (9.58 ± 3.07 vs. 5.49 ± 1.04 ng/ml; p = 0.003). NOX4 positively correlated with HO-1 only in BS/GS patients; no correlation was found between EPO and either NOX4 or HO-1 in those two groups.

CONCLUSIONS

The effect of the renin-angiotensin system on EPO cannot be solely mediated by Ang II via AT1R signaling, but rather, EPO levels are also determined by a complex interrelated set of signals that involve AT2R, nitric oxide levels, NOX4 and HO-1 activity.

Mechanistic approach to the pathophysiology of target organ damage in hypertension from studies in a human model with characteristics opposite to hypertension: Bartter's and Gitelman's syndromes

INTRODUCTION

Extensive studies using Bartter's/Gitelman's syndrome patients have provided insights into the angiotensin II (Ang II) signaling pathways involved in the regulation of vascular tone and cardiovascular-renal remodeling. The renin-angiotensin-aldosterone system is activated in these syndromes, however, patients do not develop hypertension and cardiovascular remodeling and clinically manifest conditions opposite to hypertension. The short- and the long-term signaling of Ang II remains an important matter of investigation to shed light on mechanisms responsible for the pathophysiology of hypertension and its long-term complications. The long-term signaling of Ang II is involved in the pathophysiology of cardiovascular-renal remodeling and inflammatory responses in which the balance between RhoA/Rho kinase pathway and NO system plays a crucial role.

METHODS AND RESULTS

In this brief review, the results of our studies in Bartter's and Gitelman's syndromes are reported on these processes.

CONCLUSIONS

The information obtained from these studies can clarify, confirm or be used to extend the biochemical mechanisms responsible for the pathophysiology of hypertension and its long-term complications and could offer further chances to identify additional potential significant targets of therapy.

Angiotensin II and Cardiovascular-Renal Remodelling in Hypertension: Insights from a Human Model Opposite to Hypertension

Insights into the Angiotensin II (Ang II) signalling pathways have been provided by extensive studies using Bartter's/Gitelman's syndromes patients. These syndromes are characterized by activation of the renin-angiotensin-aldosterone system but do not develop hypertension and cardiovascular remodelling, therefore represent a mirror image of hypertension and clinically manifest themselves as the opposite of hypertension. The short and the long-term signalling of Ang II remain an important matter of investigation to shed light on mechanisms responsible for the pathophysiology of hypertension and its long-term complications, such as cardiovascular remodelling and atherogenesis. In particular the long-term signalling of Ang II is involved in the pathophysiology of cardiovascular-renal remodelling, inflammatory and hypertrophic responses in which the relationship between RhoA/Rho kinase pathway and NO system plays a crucial role. This review reports the results of our studies in Bartter's and Gitelman's syndromes to get better insight these processes and the role of Ang II signaling. The information obtained from the studies in Bartter's/Gitelman's patients can, in fact, clarify, confirm or be used to gather more general data on the biochemical mechanisms responsible for the pathophysiology of hypertension and its long-term complications and could contribute to identify additional potential significant targets of therapy.

Increased level of p63RhoGEF and RhoA/Rho kinase activity in hypertensive patients

OBJECTIVE

p63RhoGEF, a guanine nucleotide exchange factor, has been reported 'in vitro' as key mediator of the angiotensin II-induced RhoA/Rho kinase activation leading to vasoconstriction and cardiovascular remodeling. We assessed p63RhoGEF gene and protein expression and RhoA/Rho kinase activity in essential hypertensive and Bartter's and Gitelman's syndrome patients, a human model opposite to hypertension; the latter have, in fact, increased plasma angiotensin II, activation of the renin-angiotensin system, yet normotension/hypotension, reduced peripheral resistance and lack of cardiovascular remodeling due to an endogenously blunted angiotensin II type 1 receptor signaling.

METHODS

Mononuclear cell p63RhoGEF gene and protein expression and the phosphorylation status of the myosin phosphatase target protein-1 (MYPT-1), marker of Rho kinase activity, were assessed in essential hypertensive patients, Bartter's/Gitelman's patients and healthy individuals by quantitative real-time PCR and western blot.

RESULTS

p63RhoGEF mRNA and protein level and MYPT-1 phosphorylation status were higher in hypertensive patients and lower in Bartter's/Gitelman's patients compared with healthy individuals: p63RhoGEF mRNA level: 0.59 ± 0.17 ΔΔCt vs. 0.37 ± 0.17 vs. 0.20 ± 0.19, analysis of variance (ANOVA): P <0.016; p63RhoGEF protein level 1.35 ± 0.14 vs. 1.09 ± 0.05 vs. 0.90 ± 0.09 densitometric units, ANOVA: P <0.0001; MYPT-1: 1.39 ± 0.34 vs. 1.01 ± 0.12 vs. 0.81 ± 0.06, ANOVA: P < 0.0001. p63RhoGEF mRNA was significantly correlated with both SBP and DBP in both hypertensive patients (R = 0.79, P < 0.02 and R = 0.78, P < 0.02) and in Bartter's syndrome/Gitelman's syndrome patients (R = 0.87, P < 0.001 and R = 0.86, P < 0.001), respectively.

CONCLUSION

Increased p63RhoGEF mRNA and protein level and Rho kinase activity are shown for the first time in essential hypertensive patients, whereas the opposite was found in Bartter's/Gitelman's patients, a human model opposite to hypertension. These results combined with other 'in-vitro' studies strongly support the crucial importance of p63RhoGEF in Ang II-mediated signaling involved in the regulation of blood pressure and its long-term complications in humans.

Effect of olmesartan medoxomil on number and survival of circulating endothelial progenitor cells and calcitonin gene related peptide in hypertensive patients

OBJECTIVE

Injury of vascular endothelium, crucial in vascular disease, is repaired via circulating endothelial progenitor cells (cEPCs). In hypertension, cEPCs number is reduced and function impaired adding further risk for cardiovascular (CV) events. Angiotensin II (Ang II)-induced oxidative stress (OxSt), accelerates cEPCs senescence. Calcitonin gene-related peptide (CGRP), able to prevent and reverse Ang II-induced cEPCs senescence, is reduced in hypertension and stimulated by the antioxidant and anti-inflammatory heme oxygenase (HO)-1. In essential hypertensive patients olmesartan reduced OxSt and markers of CV remodeling and increased HO-1. This study reports in essential hypertensive patients the effect of 6 months treatment with olmesartan on plasma level of CGRP and number and survival of cEPCs.

METHODS AND RESULTS

In 20 essential hypertensive patients treated with olmesartan medoxomil (20  mg per day for 6 months), cEPCs (CD34(+)KDR(+), CD133(+)KDR(+) and CD34(+)CD133(+)KDR(+)) (direct 3-color flow cytometry analysis), apoptosis of cEPCs (CD133(+)KDR(+) cells with Annexin V expression), CGRP determination (ELISA) and HO-1 protein level (western blot) were assessed at baseline and after 3 and 6 months of treatments. Olmesartan normalized blood pressure (P < 0.001), increased cEPCs from baseline (CD34(+)KDR(+): P < 0.003; CD133(+)KDR(+): P < 0.0002; CD34(+)CD133(+)KDR(+): P = 0.0008), reduced cEPCs apoptosis (P < 0.001) and increased CGRP (P < 0.013) and HO-1 (P = 0.039).

CONCLUSION

These results provide a mechanistic rationale for the olmesartan's antioxidant and anti-inflammatory potential translation toward antiatherosclerotic and antiremodeling effects reported on clinical ground.

Increased RBP4 in a human model of activated anti-atherosclerotic and antiremodelling defences

BACKGROUND

Both increased and decreased levels of the adipokine retinol-binding protein 4 (RBP4) have been reported in cardiovascular disease, and levels of RBP4 have been related to diabetes, metabolic syndrome and cardiovascular risk. Recently, clear in vitro and ex vivo vasodilatory and inhibitory of platelet activation effects of RBP4 has been shown and a reduced RBP4 level was found in high cardiovascular risk patients, suggesting a potential cardiovascular protective role for increased levels of RBP4.

PATIENTS AND METHODS

Plasma level of RBP4 (ELISA) was determined in a cohort of Bartter's and Gitelman's syndrome (BS/GS) patients, a human model of endogenous Ang II signalling antagonism and activation of anti-atherosclerotic and antiremodelling defenses, the opposite of cardiovascular risk patients, and in healthy normotensive subjects. Haem Oxygenase (OH)-1 protein level (sandwich immunoassay) as a potential mediator of RBP4 stimulation of PI3K/Akt pathway and flow-mediated dilation (FMD) as a measure of endothelium (NO)-dependent response have also been measured.

RESULTS

RBP4 in BS/GS patients (40·59 ± 15·32 μg/mL vs. 25·05 ± 5·56, P = 0·011) along with HO-1 protein levels (9·44 ± 3·09 ng/mL vs. 5·49 ± 1·04, P = 0·003) and FMD (10·52% ± 2·22 vs. 7·99 ± 1·13 P = 0·006) were significantly increased compared with healthy normotensive subjects.

CONCLUSIONS

The increase of RBP4 in BS/GS, a human model of endogenous Ang II signalling antagonism and activation of anti-atherosclerotic and antiremodelling defenses, the opposite of cardiovascular risk patient, found in concert with an increased NO-mediated vasodilation and HO-1 levels supports a protective role for this adipokine in vascular protection/cardiovascular risk.

Physiology and pathophysiology of SLC12A1/2 transporters

The electroneutral Na(+)-K(+)-Cl(-) cotransporters NKCC1 (encoded by the SLC12A2 gene) and NKCC2 (SLC12A1 gene) belong to the Na(+)-dependent subgroup of solute carrier 12 (SLC12) family of transporters. They mediate the electroneutral movement of Na(+) and K(+), tightly coupled to the movement of Cl(-) across cell membranes. As they use the energy of the ion gradients generated by the Na(+)/K(+)-ATPase to transport Na(+), K(+), and Cl(-) from the outside to the inside of a cell, they are considered secondary active transport mechanisms. NKCC-mediated transport occurs in a 1Na(+), 1K(+), and 2Cl(-) ratio, although NKCC1 has been shown to sometimes mediate partial reactions. Both transporters are blocked by bumetanide and furosemide, drugs which are commonly used in clinical medicine. NKCC2 is the molecular target of loop diuretics as it is expressed on the apical membrane of thick ascending limb of Henle epithelial cells, where it mediates NaCl reabsorption. NKCC1, in contrast, is found on the basolateral membrane of Cl(-) secretory epithelial cells, as well as in a variety of non-epithelial cells, where it mediates cell volume regulation and participates in Cl(-) homeostasis. Following their molecular identification two decades ago, much has been learned about their biophysical properties, their mode of operation, their regulation by kinases and phosphatases, and their physiological relevance. However, despite this tremendous amount of new information, there are still so many gaps in our knowledge. This review summarizes information that constitutes consensus in the field, but it also discusses current points of controversy and highlights many unanswered questions.

Cardiovascular Effects of Aldosterone

Background—

High plasma aldosterone has deleterious cardiovascular effects that are independent of blood pressure, but the role of the mineralocorticoid receptor remains unclear. Renal pseudohypoaldosteronism type 1 is a rare autosomal-dominant disease caused by NR3C2 loss-of-function mutations, which is characterized by renal salt loss and compensatory high renin and aldo secretion. We aimed to assess the cardiovascular outcomes in adults carrying NR3C2 mutations.

Methods and Results—

In this case-control study, 39 NR3C2 mutation carriers were compared with sex- and age-paired noncarriers. Patients underwent cardiac and vascular ultrasound, cardiac MRI with gadolinium injection, measurement of pulse wave velocity, extracellular water, 24-hour ambulatory blood pressure, and autonomous nervous system activity. Mutation carriers showed increased aldo and renin plasma levels (4.5- and 1.6-fold, respectively; P <0.0001), together with increased salt appetite (1.8-fold; P =0.002), with normal extracellular water and blood pressure, and no autonomous nervous system activation. Cardiac and vascular parameters were not significantly different between mutation carriers and noncarriers (no left ventricular remodeling or fibrosis, normal left ventricular systolic function, and aorta stiffness). Tissue Doppler showed better diastolic left ventricular function in mutation carriers (e′, P =0.001; E/e′, P =0.003). Mutation carriers had significantly more frequent history of slow body weight recovery at birth, symptomatic hypotension, and miscarriage in women.

Conclusions—

Despite life-long increase in plasma aldosterone and renin levels, no adverse cardiovascular outcome occurred in pseudohypoaldosteronism type 1, but rather an improved diastolic left ventricular function. This suggests that the cardiovascular consequences of aldosterone excess require full mineralocorticoid receptor signaling.

Clinical Trial Registration—

http://www.clinicaltrials.gov ; unique identifier: NCT00646828.

SIRT1, heme oxygenase-1 and NO-mediated vasodilation in a human model of endogenous angiotensin II type 1 receptor antagonism: implications for hypertension

Reduced NO availability is associated with endothelial dysfunction, hypertension, insulin resistance and cardiovascular remodeling. SIRT1 upregulates eNOS activity and inhibits endothelial cell senescence, and reduced SIRT1 is related to oxidative stress and reduced NO-dependent dilation. Bartter's/Gitelman's syndromes (BS/GS) are rare diseases that feature a picture opposite to that of hypertension in that they present with normo/hypotension, reduced oxidative stress and a lack of cardiovascular remodeling, notwithstanding high levels of angiotensin II and other vasopressors, upregulation of NO system, and increased NO-dependent vasodilation (FMD), as well as increase in both endothelial progenitor cells and insulin sensitivity. To our knowledge, in BS/GS patients SIRT1 has never been evaluated. BS/GS patients' mononuclear cell SIRT1 (western blot), FMD (B-mode scan of the right brachial artery) and heme oxygenase (HO)-1 (sandwich immunoassay), a potent antioxidant protein, were compared with the levels in untreated stage 1 essential hypertensive patients (HPs) and in healthy subjects (C). SIRT1 (1.86 ± 0.29 vs. 1.18 ± 0.18 (HP) vs. 1.45 ± 0.18 (C) densitometric units, P<0.0001) and HO-1 protein (9.44 ± 3.09 vs. 3.70 ± 1.19 (HP) vs. 5.49 ± 1.04 (C) ng ml⁻¹, P<0.0001) levels were higher in BS/GS patients than in the other groups. FMD was also higher in BS/GS patients: 10.52 ± 2.22% vs. 5.99 ± 1 .68% (HP) vs. 7.99 ± 1.13% (C) (ANOVA: P<0.0001). A strong and significant correlation between SIRT1 and FMD was found only in BS/GS patients (r(2)=0.63, P=0.0026). Increased SIRT1 and its direct relationship with increased FMD in BS/GS patients, while strengthening the relationship among SIRT1, NO and vascular function in humans, point toward a role for reduced SIRT1 in the endothelial dysfunction of hypertension.

Calcitonin gene-related peptide, heme oxygenase-1, endothelial progenitor cells and nitric oxide-dependent vasodilation relationships in a human model of angiotensin II type-1 receptor antagonism

OBJECTIVE

An increased number of endothelial progenitor cells (EPCs), which correlated with heme oxygenase-1 gene expression and nitric oxide-mediated vasodilation [flow-mediated dilation (FMD)], has been recently reported by us in Bartter/Gitelman syndromes, rare diseases that represent a human model of endogenous angiotensin (Ang) II type-1 receptor antagonism and depicting an opposite picture of hypertension. Calcitonin gene-related peptide (CGRP), which prevents circulating EPCs senescence and reverses Ang II-induced EPCs senescence is reduced in hypertensive patients, its level is stimulated by heme oxygenase-1 and is related with stimulation of nitric oxide. This study reports on CGRP concentration and heme oxygenase-1 protein level in Bartter/Gitelman syndrome's patients compared with healthy individuals and analyzes their relationships with EPCs [CD34⁺kinase insert domain receptor (KDR⁺), CD133⁺KDR⁺, CD34⁺CD133⁺KDR⁺) as well as FMD.

METHODS AND RESULTS

CGRP concentration (ELISA) and heme oxygenase-1 protein level (sandwich immunoassay) were higher in Bartter/Gitelman syndrome : 38.20 ± 8.23 pg/ml vs. 25.07 ± 3.51, P < 0.002 and 9.44 ± 3.1 ng/ml vs. 5.52 ± 1.1, P < 0.007, respectively. CD133⁺KDR⁺ and CD34⁺CD133⁺KDR⁺ (direct three-color flow cytometry analysis) and FMD (B-mode echo scan of brachial artery) were confirmed higher in Bartter/Gitelman syndrome. CGRP and heme oxygenase-1 strongly correlated (P < 0.0001) and did not differ by group. In Bartter/Gitelman syndrome, both CGRP and heme oxygenase-1 were strongly correlated with both EPCs and FMD.

CONCLUSIONS

Using a human model opposite to hypertension, this study provides information on the relationships between CGRP, heme oxygenase-1, FMD, major clinical and biochemical factors involved in cardiovascular disease, and EPC-specific populations and may also serve to confirm the utility of Bartter/Gitelman syndrome patients in delineating EPCs and related factors roles in the pathophysiology of cardiovascular remodeling in humans.

Pathogenesis of calcineurin inhibitor-induced hypertension

This article reviews the current understanding of the mechanisms of calcineurin inhibitor-induced hypertension. Already early after the introduction of cyclosporine in the 1980s, vasoconstriction, sympathetic excitation and sodium retention by the kidney had been shown to play a role in this form of hypertension. The vasoconstrictive effects of calcineurin inhibitors are related to interference with the balance of vasoactive substances, including endothelin and nitric oxide. Until recently, the renal site of the sodium-retaining effect of calcineurin inhibitors was unknown. We and others have shown that calcineurin inhibitors increase the activity of the thiazide-sensitive sodium chloride cotransporter through an effect on the kinases WNK and SPAK. Here, we review the pertinent literature on the hypertensinogenic effects of calcineurin inhibitors, including neural, vascular and renal effects, and we propose an integrated model of calcineurin inhibitor-induced hypertension.

Miscellaneous non-inflammatory musculoskeletal conditions. Bartter's and Gitelman's diseases

Bartter's and Gitelman's syndromes are two different genetic renal diseases, but are both characterised by hypokalaemia and metabolic alkalosis. Bartter's syndrome is characterised by multiple gene mutations (Na-K-2Cl cotransporter; K(+) channels renal outer medullary potassium channel (ROMK); Cl channels, chloride channel Kb (ClCNKb); regulatory protein Barttin; and Ca(2+) -sensing receptor, CaSR) at the thick ascending limb of Henle's loop, while Gitelman's syndrome is caused by a mutation in the gene encoding the renal thiazide sensitive Na(+)-Cl(-) cotransporter, located in the apical membrane of the distal convoluted tubule. The co-existence of hypokalaemia with hypomagnesaemia and hypocalciuria represents the biochemical hallmark of Gitelman's syndrome that distinguishes it from Bartter's syndrome. Calcium pyrophosphate deposition (CPPD) including chondrocalcinosis has been frequently reported in association with Bartter's syndrome. Some authors postulate that these cases were probably due to Gitelman's syndrome and not due to Bartter's syndrome as all patients had hypomagnesaemia. This electrolyte disorder seems to induce CCP crystal deposition. To date, no cases of CPPD have been reported in patients who had Bartter's syndrome without hypomagnesaemia. CPPD may be found in other conditions associated with hypomagnesaemia, such as short bowel syndrome or tacrolimus therapy in liver transplantation patients. As acute CPP crystal arthropathy or pseudogout can be the onset presentation of Gitelman's syndrome, CPPD should be considered a major feature of this disease. Rheumatologists should be aware of the association between Gitelman's syndrome and CPPD, and should consider this metabolic disorder when CPPD occurs in younger patients.

PLCβ1-SHP-2 complex, PLCβ1 tyrosine dephosphorylation and SHP-2 phosphatase activity: a new part of Angiotensin II signaling?

BACKGROUND

Angiotensin II (Ang II) signaling occurs via two major receptors which activate non-receptor tyrosin kinases that then interact with protein tyrosin-phosphatases (PTPs) to regulate cell function. SHP-2 is one such important PTP that also functions as an adaptor to promote downstream signaling pathway. Its role in Ang II signaling remains to be clarified.

RESULTS

Using cultured normal human fibroblasts, immunoprecipitation and western blots, we show for the first time that SHP-2 and PLCβ1 are present as a preformed complex. Complex PLCβ1 is tyr-phosphorylated basally and Ang II increased SHP-2-PLCβ1 complexes and caused complex associated PLCβ1 tyr-phosphorylation to decline while complex associated SHP-2's tyr-phosphorylation increased and did so via the Ang II type 1 receptors as shown by Ang II type 1 receptor blocker losartan's effects. Moreover, Ang II induced both increased complex phosphatase activity and decreased complex associated PLCβ1 tyr-phosphorylation, the latter response required regulator of G protein signaling (RGS)-2.

CONCLUSIONS

Ang II signals are shown for the first time to involve a preformed SHP-2-PLCβ1 complex. Changes in the complex's PLCβ1 tyr-phosphorylation and SHP-2's tyr-phosphorylation as well as SHP-2-PLCβ1 complex formation are the result of Ang II type 1 receptor activation with changes in complex associated PLCβ1 tyr-phosphorylation requiring RGS-2. These findings might significantly expand the number and complexity of Ang II signaling pathways. Further studies are needed to delineate the role/s of this complex in the Ang II signaling system.

Endothelial progenitor cells relationships with clinical and biochemical factors in a human model of blunted angiotensin II signaling

Angiotensin II (Ang II) is essential for endothelial progenitor cells (EPCs) function as Ang-II-induced oxidative stress causes senescence of EPCs and endothelial dysfunction and Ang II type 1 receptor blockers increase EPCs. Moreover, EPCs activity is dependent on nitric oxide (NO) and heme oxygenase (HO)-1 as these correlate with EPCs senescence and are reduced in hypertensives. Bartter's/Gitelman's syndrome patients (BS/GS), have increased Ang II yet normo/hypotension along with blunted Ang II signaling, reduced oxidative stress, increased NO and HO-1, thus presenting a unique system to explore EPC biology and its relationship with vascular clinical and biochemical correlates. Circulating EPCs, NO-dependent vasodilation (flow-mediated dilation (FMD)) and HO-1 gene expression were characterized in 10 BS/GS patients and in 10 normotensive subjects. EPCs defined by cell surface antigens CD34+kinase-insert domain receptor (KDR+), CD133+KDR+ and CD133+CD34+KDR+ cells were quantitiated via direct three-color flow-cytometry analysis, HO-1 gene expression by reverse transcription-PCR and FMD by B-mode echo scan of the right brachial artery. Correlation analysis was carried out regarding FMD and EPCs, FMD and HO-1 and EPCs and HO-1. In BS/GS, CD34+KDR+ cell numbers did not differ from controls while CD133+KDR+ and CD133+CD34+KDR+ cell numbers were higher. HO-1 gene expression, as well as FMD, was higher in BS/GS compared with controls. Both CD133+KDR+ and CD133+CD34+KDR+ strongly correlated with both FMD and HO-1. FMD and HO-1 were also strongly correlated. These results document in a human system that EPC numbers and specific populations are related to important clinical and biochemical factors involved in cardiovascular (CV) status and reaffirm the utility of BS/GS patients as a useful system to investigate EPC's role(s) in the pathophysiology of cardiovascular remodeling in humans.

Effect of olmesartan on oxidative stress in hypertensive patients: mechanistic support to clinical trials derived evidence

The role of oxidative stress in the pathophysiology of hypertension and target organ damage is widely recognized. Using a molecular biology approach, we report, in essential hypertensive patients, the effect of the angiotensin II type 1 receptor blocker olmesartan on the mononuclear cell (PBMC) protein expression of major elements in the oxidative stress and vascular remodeling-related pathways, p22(phox) and HO-1, along with the phosphorylation state of ERK1/2 and plasma oxidized low-density lipoproteins (oxLDL). Twenty untreated essential hypertensive patients (range blood pressure: 142?156/94?98 mmHg) were treated with olmesartan medoxomil (20 mg/day for 6 months) and blood samples collected at baseline, 3 and 6 months for PBMC p22(phox) and HO-1 protein expression, phosphorylation state of ERK1/2 (western blot) and oxLDL level (ELISA) evaluations. Olmesartan normalized blood pressure since the third month (149 ? 4.7/94.88 ? 1.9 mmHg vs 137.89 ? 2.08/88.44 ? 2.0 at 3 months and vs 135.44 ? 2.18/85.78 ? 1.2 at 6 months, analysis of variance: p < 0.001). p22(phox) protein level declined at 3 months (7.10 ? 2.61 vs 9.32 ? 2.43 densitometric units (d.u.; p < 0.001), further declining at 6 months (4.55 ? 1.26 d.u., p < 0.001). HO-1 levels increased at 3 months (10.87 ? 1.92 vs 7.70 ? 0.71 d.u., p = 0.001) and remained elevated (11.11 ? 1.89 d.u., p = 0.001), without further increase at 6 months. Phosphorylated ERK1/2 declined at 3 months (3.94 ? 1.44 vs 5.62 ? 1.11 d.u., p = 0.001), further declining at 6 months (1.94 ? 0.87, p < 0.001). oxLDL significantly declined at 3 and 6 months. These results demonstrate that olmesartan inhibits oxidative stress. Given the involvement of oxidative stress and its signaling in atherogenesis, and the available evidence of olmesartan's vasoprotective, anti-inflammatory and antiatherosclerotic effects derived from clinical trials in humans, the results of our study provide a mechanistic rationale for the omelsartan's antioxidant and anti-inflammatory potential translation, in the long term, toward the antiatherosclerotic and antiremodeling effects reported on the clinical ground.

High angiotensin II state without cardiac remodeling (Bartter's and Gitelman's syndromes): are angiotensin II type 2 receptors involved?

BACKGROUND/AIMS

While Angiotensin II (Ang II) is a major factor in the development of cardiomyocyte hypertrophy and a pivotal role for Ang II signals via ERK1/2 has been identified, mechanism(s) responsible are still unclear. As Bartter's and Gitelman's syndrome patients (BS/GS) have increased Ang II, and yet normo/hypotension, hyporesponsiveness to pressors and blunted Ang II signaling via type 1 receptors (AT1R), this study assesses BS/GS's left ventricular (LV) mass and structure as well as Ang II induced ERK1/2 phosphorylation compared with essential hypertensive patients (EH) and normotensive healthy subjects (C) to gain insight into Ang II mediated processes.

METHODS

Indices of cardiac hypertrophy were determined by M-mode, two-dimensional echo Doppler and ERK phosphorylation by Western blot.

RESULTS

None of BS/GS exhibited LV remodelling; LV mass, LV end-diastolic volume and mass/volume ratio were unchanged vs C (60+/-14 g/m2 vs 64+/-12, 64+/-12 ml/m2 vs 60+/-8 and 0.95+/-0.2 vs 1.0+/-0.2, respectively) and reduced vs EH (119+/-15, p<0.001, 78+/-9, p<0.05 and 1.52+/-0.15, p<0.01). Despite BS/GS's higher plasma renin activity and aldosterone and unchanged level of AT1R, Ang II induced ERK1/2 phosphorylation was reduced vs both C and EH: 0.64 d.u.+/-0.08 vs 0.90+/-0.06 in C, p<0.006, and vs 1.45+/-0.07 in EH, p<0.001.

CONCLUSION

The data point to a direct cardioremodeling role for Ang II and support a role of Ang II type 2 receptor (AT2R) signaling as involved in the lack of cardiovascular remodeling in BS/GS. However, further studies using more direct approaches to demonstrate the effects of AT2R signaling must be pursued.

Myocardial perfusion defects in Bartter and Gitelman syndromes

BACKGROUND

Normotensive hypokalaemic tubulopathies (Bartter and Gitelman syndromes (BS/GS)) are genetic diseases that are considered benign. However, QT prolongation, left ventricular dysfunction and reduction of cardiac index upon exercise leading to arrhythmias and sudden cardiac death have been reported in these patients. Hence, we aimed to verifying whether an isometric exercise could represent a useful tool for the identification of patients at risk for future cardiac events.

PATIENTS AND METHODS

Myocardial function (MF) and perfusion, evaluated as myocardial blood flow (MBF) of 10 BS/GS patients and 10 healthy controls, were investigated at rest and during isometric exercise. MF and MBF were evaluated using quantitative two-dimensional and myocardial contrast echocardiography.

RESULTS

BS/GS patients had normal baseline MF and MBF. During exercise in BS/GS patients, corrected QT (QTc) was prolonged to peak value of 494 +/- 9.1 ms (P < 0.001). In controls, MF increased from resting to peak exercise (left ventricular ejection fraction: 65 +/- 4% to 78 +/- 5%, P < 0.003) while in seven BS/GS patients (Group 1) it declined (64 +/- 5% to 43 +/- 9%, P < 0.001). Myocardial perfusion increased upon exercise in controls as shown by changes of its markers: beta (a measure of myocardial flow velocity; 0.89 +/- 0.12 vs. 0.99 +/- 0.12, P < 0.001) and myocardial blood volume (14.4 +/- 2 vs. 20.2 +/- 0.25, P < 0.001), while in Group 1 BS/GS it decreased (0.87 +/- 0.15 vs. 0.67 +/- 0.15, P < 0.001; and 14.5 +/- 1.9 vs. 8.3 +/- 0.22, P < 0.001, respectively).

CONCLUSIONS

Our results document for the first time that exercise induce coronary microvascular and myocardial defects in BS/GS patients. Therefore, this may challenge the idea that BS/GS are benign diseases. In addition, the diagnostic approach to these syndromes should include an in-depth cardiac assessment in order to identify patients at higher risk.

Absence of vascular remodelling in a high angiotensin-II state (Bartter's and Gitelman's syndromes): implications for angiotensin II signalling pathways

BACKGROUND

Angiotensin II (Ang II) is a powerful proinflammatory cytokine and growth factor that activates NF-kappaB, as well as NAD(P)H oxidase, and thus is a key factor for the induction and progression of cardiovascular diseases. Our previous studies have shown high Ang II and high blood pressure-driven proatherogenic remodelling in an animal model. To further explore Ang II in proatherogenic vascular remodelling independent of blood pressure, we used Bartter's/Gitelman's syndrome (BS/GS) patients given their elevated plasma Ang II, yet normo/hypotension, because extensive mechanistic studies in these patients suggest they are a good model to explore Ang II-mediated signalling.

METHODS

The study evaluated BS/GS patients for nitric oxide-dependent (FMD) and -independent vasodilation and intima-media thickness (IMT) of the carotid arteries compared with healthy subjects and essential hypertensive patients.

RESULTS

The results showed the absence of IMT growth in BS/GS patients as cumulative mean-IMT and mean maximum-IMT levels in BS/GS did not differ from normotensives: 0.58 +/- 0.09 mm versus 0.60 +/- 0.09 and 0.67 +/- 0.09 versus 0.70 +/- 0.13 respectively, P = ns, but were significantly lower compared with hypertensive patients: 0.69 +/- 0.13, P < 0.046 and 0.85 +/- 0.19, P < 0.018, respectively. FMD was increased in BS/GS versus hypertensives or normotensive controls (10.8 +/- 2.7% versus 6.5 +/- 2.3 and 8.7 +/- 1.9, P < 0.002 respectively) while endothelium-independent dilation did not differ (10.2 +/- 3.6% versus 7.2 +/- 1.9 and 8.2 +/- 3.3, P = ns) between groups.

CONCLUSIONS

Our study in BS/GS provides to our knowledge the first clinical data that point to a direct proatherogenic role for Ang II. However, because the data are derived from findings in BS/GS and therefore are indirect, further studies in this and other models using more direct approaches should be pursued to demonstrate a direct proatherogenic effect of Ang II as well as further studies on Ang II type 2 receptor (AT2R) signalling that the spectrum of findings of this and other studies indicate as involved in the lack of vascular remodelling.