Evidence of myocardial dysfunction in Bartter's syndrome

The long-term complications of the inherited tubulopathies: an adult perspective

The inherited tubulopathies are lifelong disorders and their clinical features and complications may present quite different challenges in adulthood from those in childhood. In this review we outline the pathophysiology and documented complications (including the late and unusual) of the monogenic tubulopathies from the perspective of the adult nephrologist.

QT and JT dispersion and cardiac performance in children with neonatal Bartter syndrome: a pilot study

BACKGROUND

QT dispersion and JT dispersion are simple noninvasive arrhythmogenic markers that can be used to assess the homogeneity of cardiac repolarization. The aim of this study was to assess QT and JT dispersion and their relation with left ventricular systolic and diastolic functions in children with Bartter syndrome (BS).

METHODS

Nine neonatal patients with BS (median age 9.7 years) and 20 controls (median age 8 years) were investigated at rest. Both study and control subjects underwent electrocardiography (ECG) in which the interval between two R waves and QT intervals, corrected QT, QT dispersion, corrected QT dispersion, JT, corrected JT, JT dispersion and corrected JT dispersion were measured with 12-lead ECG. Two-dimensional, Doppler echocardiographic examinations were performed.

RESULTS

Patients and controls did not differ for gender and for serum levels of potassium, magnesium, and calcium (p > 0.05). Both study and control subjects had normal echocardiographic examination and baseline myocardial performance indexes. The QT dispersion and JT dispersion were significantly prolonged in patients with BS compared to those of the controls {37.5 ms [interquartile range (IQR) 32.5-40] vs. 25.5 ms (IQR 20-30), respectively, p = 0.014 and 37.5 ms (IQR 27.5-40) vs. 22.5 ms (IQR 20-30), respectively, p = 0.003}.

CONCLUSIONS

Elevated QT and JT dispersion during asymptomatic and normokalemic periods may be risk factors for the development of cardiac complications and arrhythmias in children with BS. In these patients the need for systematic cardiac screening and management protocol is extremely important for effective prevention.

A CLCNKA polymorphism (rs10927887; p.Arg83Gly) previously linked to heart failure is associated with the estimated glomerular filtration rate in the RENASTUR cohort

A total of 569 individuals aged 55-85 and Caucasian were genotyped for SNP rs10927887 in the Ka renal chloride channel gene (CLCNKA). The following variables were significantly associated with an estimated glomerular filtration rate of (eGFR) <60 ml/min./1.73 m(2): age, type 2 diabetes, total cholesterol, LDL-cholesterol, and the CLCNKA GG genotype (p=0.03; OR=1.65, 95% CI=1.04-2.62). This novel finding could partly explain the reported greater risk of heart failure linked to the CLCNKA SNP, but requires confirmation on other populations.

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.

Rho kinase and PAI-1 in Bartter's/Gitelman's syndromes

OBJECTIVE

Angiotensin II (Ang II)-mediated activation of Rho kinase (ROK) is involved in the pathophysiology of hypertension and cardiovascular remodeling. ROK also controls plasminogen activator inhibitor-1 (PAI-1) which promotes vascular fibrosis contributing to atherogenesis. Bartter's and Gitelman's syndromes (BS/GS) are useful models to investigate abnormalities of vascular tone regulation, due to their reduced short- and long-term signaling pathways of Ang II. This study evaluated, using BS/GS as a model, ROK and PAI-1 gene and protein expression and the effect of Ang II co-incubation on ROK and PAI-1 gene and protein expression.

DESIGN, METHODS AND RESULTS

We measured ROK and PAI-1 gene and protein expression [reverse transcription-polymerase chain reaction (RT-PCR) and Western blot] in mononuclear cells (PBM) from one BS and eight GS patients. The effect of Ang II on ROK and PAI-1 gene and protein expression was also evaluated and compared with 10 controls. ROK gene and protein expression was reduced in BS/GS [0.47 +/- 0.11 densitometric units (d.u.) versus 0.70 +/- 0.04 d.u., P = 0.0038 and 0.39 +/- 0.07 d.u. versus 0.55 +/- 0.07 d.u., P = 0.0026, respectively]. The basal level of PAI-1 gene and protein expression did not differ (0.40 +/- 0.03 d.u. versus 0.39 +/- 0.02 d.u. and 0.81 +/- 0.02 d.u. versus 0.83 +/- 0.02 d.u., respectively). Ang II increased ROK and PAI-1 gene and protein expression only in controls: from 0.70 +/- 0.04 to 0.90 +/- 0.06 d.u., P = 0.007 (ROK mRNA); from 0.55 +/- 0.07 to 0.86 +/- 0.07 d.u., P = 0.0005 (ROK protein); from 0.40 +/- 0.02 to 0.63 +/- 0.03 d.u., P = 0.001 (PAI-1 mRNA); and from 0.83 +/- 0.02 to 1.34 +/- 0.16 d.u., P = 0.0023 (PAI-1 protein).

CONCLUSIONS

This study confirms BS/GS as a human model to investigate interrelated systems involved in the pathophysiology of hypertension and throws more light on the cellular mechanisms of BS/GS reduced Ang II short- and long-term signaling pathways.

Cardiac work up in primary renal hypokalaemia-hypomagnesaemia (Gitelman syndrome)

BACKGROUND

Potassium and magnesium depletion prolongs the duration of the action potential of the cardiomyocyte, which predisposes to ventricular arrhythmias. In addition, potassium or magnesium depletion might impair cardiac performance and facilitate coronary artery thrombosis.

METHODS

Continuous 24-h ambulatory electrocardiographic monitoring, treadmill exercise testing and echocardiography were assessed in 21 patients (11 female and 10 male subjects, aged 5.9-39, median 19 years) with primary renal hypokalaemia-hypomagnesaemia.

RESULTS

The QT interval corrected for heart rate was normal (between 379 and 430 ms) in 10 and slightly to moderately prolonged in the remaining 11 patients (between 446 and 509 ms). Plasma potassium, magnesium and bicarbonate were similar in patients with normal and in those with prolonged QT interval. Continuous ambulatory electrocardiography over 24 h and exercise testing did not detect significant abnormalities of cardiac rhythm or features suggestive of myocardial ischaemia. Finally, echocardiographic and Doppler assessment failed to reveal any abnormalities in myocardial morphology and function.

CONCLUSION

The QT interval is often prolonged in primary renal hypokalaemia-hypomagnesaemia, confirming that potassium and magnesium depletion tends to prolong the duration of the action potential of the cardiomyocyte. The results of continuous ambulatory electrocardiography, exercise testing and echocardiography are reassuring. Nonetheless, we assume that dangerous cardiac arrhythmias may occur in patients with very severe hypokalaemia, during medication with drugs that prolong the QT interval or in the context of short-term non-adherence to the recommended regimen of care.

[Genetic hypokalemia]

INTRODUCTION

Hypokalemia is the most frequent electrolytic disturbance in hospitalized patients. It is sometimes familial. Careful clinical and biological evaluation may guide further genetic analysis.

CURRENT KNOWLEDGE AND KEY POINTS

Genetic hypokalemia is linked to disorders of mineralocorticoid hormone synthesis or action (glucocorticoid-remediable hyperaldosteronism, congenital adrenal hyperplasia, apparent excess of mineralocorticoids), to renal tubular disorders (Liddle's syndrome, Bartter's and Gitelmann's syndrome, tubular acidosis) or to disorders of cellular transfer of potassium (hypokalemic periodic paralysis).

FUTURE PROSPECTS AND PROJECTS

Molecular mechanisms of adult Bartter's syndrome are probably different from pediatric syndromes. A better clinical and biological evaluation with longitudinal follow-up could allow significant progress in the knowledge of the natural history and prognosis of these syndromes.

Inhibition of furosemide-sensitive cation transport and activation of sodium-lithium exchange by endogenous circulating factor(s) in Bartter's and Gitelman's syndromes

BACKGROUND

The nature of the cellular abnormality causing hypokalemia, hypotension, and hypovolemia in Bartter's and Gitelman's syndromes is still being debated. In fact, despite the recent descriptions of an array of nonconservative missense or point mutations in some ion transporters and in K+ channel, the lack of detectable defects in some patients suggests that other abnormalities of cell ion homeostasis may be involved in the pathophysiology of these syndromes. The study of the activity of cell ion transporters in patients with these syndromes using red blood cells (RBC) as a cellular model never investigated the role of plasma factor(s) affecting ion transport.

OBJECTIVE

To evaluate the effect of plasma from patients with these syndromes on furosemide-sensitive lithium efflux (FSLE) from lithium (Li+)-loaded RBC of healthy subjects in vitro.

METHODS

RBC of healthy controls were loaded with Li+ in the presence of nystatin and FSLE was evaluated in the presence of various concentrations of plasma from controls and patients with the two syndromes.

RESULTS

Plasma from controls did not affect FSLE (0.08 +/- 0.02 mmol/l cells per h with 1:4 vol:vol and 0.07 +/- 0.02 mmol/l cells per h with 1:2 vol:vol plasma dilution). In contrast, doubling concentrations of plasma from patients with either syndrome in the efflux solution halved FSLE (from 0.10 +/- 0.0 mmol/l cells per h with 1:4 vol:vol to 0.05 +/- 0.01 mmol/l cells per h with 1:2 vol:vol plasma dilution, P < 0.05). Na+/Li+ exchange was significantly greater for RBC from patients with either syndrome than it was for RBC from controls (0.373 +/- 0.06 versus 0.257 +/- 0.01 mmol/l cells per h, P < 0.01), but the kinetic properties of furosemide-sensitive Na+-K+-2Cl- cotransport were similar.

CONCLUSION

These data provide evidence for the hypothesis that plasma factor(s) affect ion transport in patients with these two syndromes. Since FSLE estimates Na+-K+-2Cl- cotransport the data suggest that plasma factor(s) contribute(s) to K+ wasting, hypokalemia, and hypotension by inhibiting cotransport in patients with these syndromes. The increase of Na+/Li+ exchange is most likely a secondary phenomenon associated with the hypermineralocorticoid state.