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N-acetylcysteine reverses diastolic dysfunction and hypertrophy in familial hypertrophic cardiomyopathy.

ABSTRACT: S-glutathionylation of cardiac myosin-binding protein C (cMyBP-C) induces Ca(2+) sensitization and a slowing of cross-bridge kinetics as a result of increased oxidative signaling. Although there is evidence for a role of oxidative stress in disorders associated with hypertrophic cardiomyopathy (HCM), this mechanism is not well understood. We investigated whether oxidative myofilament modifications may be in part responsible for diastolic dysfunction in HCM. We administered N-acetylcysteine (NAC) for 30 days to 1-mo-old wild-type mice and to transgenic mice expressing a mutant tropomyosin (Tm-E180G) and nontransgenic littermates. Tm-E180G hearts demonstrate a phenotype similar to human HCM. After NAC administration, the morphology and diastolic function of Tm-E180G mice was not significantly different from controls, indicating that NAC had reversed baseline diastolic dysfunction and hypertrophy in our model. NAC administration also increased sarco(endo)plasmic reticulum Ca(2+) ATPase protein expression, reduced extracellular signal-related kinase 1/2 phosphorylation, and normalized phosphorylation of phospholamban, as assessed by Western blot. Detergent-extracted fiber bundles from NAC-administered Tm-E180G mice showed nearly nontransgenic (NTG) myofilament Ca(2+) sensitivity. Additionally, we found that NAC increased tension cost and rate of cross-bridge reattachment. Tm-E180G myofilaments were found to have a significant increase in S-glutathionylation of cMyBP-C, which was returned to NTG levels upon NAC administration. Taken together, our results indicate that oxidative myofilament modifications are an important mediator in diastolic function, and by relieving this modification we were able to reverse established diastolic dysfunction and hypertrophy in HCM.

SUBMITTER: Wilder T

PROVIDER: S-EPMC4666985 | biostudies-literature | 2015 Nov

REPOSITORIES: biostudies-literature

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N-acetylcysteine reverses diastolic dysfunction and hypertrophy in familial hypertrophic cardiomyopathy.

Wilder Tanganyika T Ryba David M DM Wieczorek David F DF Wolska Beata M BM Solaro R John RJ

American journal of physiology. Heart and circulatory physiology 20151002 10

S-glutathionylation of cardiac myosin-binding protein C (cMyBP-C) induces Ca(2+) sensitization and a slowing of cross-bridge kinetics as a result of increased oxidative signaling. Although there is evidence for a role of oxidative stress in disorders associated with hypertrophic cardiomyopathy (HCM), this mechanism is not well understood. We investigated whether oxidative myofilament modifications may be in part responsible for diastolic dysfunction in HCM. We administered N-acetylcysteine (NAC) ...[more]

PMID: 26432840

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Project description:AIMS:Several mutations in the ventricular myosin regulatory light chain (RLC) were identified to cause familial hypertrophic cardiomyopathy (FHC). Based on our previous cellular findings showing delayed calcium transients in electrically stimulated intact papillary muscle fibres from transgenic Tg-R58Q and Tg-N47K mice and, in addition, prolonged force transients in Tg-R58Q fibres, we hypothesized that the malignant FHC phenotype associated with the R58Q mutation is most likely related to diastolic dysfunction. METHODS AND RESULTS:Cardiac morphology and in vivo haemodynamics by echocardiography as well as cardiac function in isolated perfused working hearts were assessed in transgenic (Tg) mutant mice. The ATPase-pCa relationship was determined in myofibrils isolated from Tg mouse hearts. In addition, the effect of both mutations on RLC phosphorylation was examined in rapidly frozen ventricular samples from Tg mice. Significantly, decreased cardiac function was observed in isolated perfused working hearts from both Tg-R58Q and Tg-N47K mice. However, echocardiographic examination showed significant alterations in diastolic transmitral velocities and deceleration time only in Tg-R58Q myocardium. Likewise, changes in Ca(2+) sensitivity, cooperativity, and an elevated level of ATPase activity at low [Ca(2+)] were only observed in myofibrils from Tg-R58Q mice. In addition, the R58Q mutation and not the N47K led to reduced RLC phosphorylation in Tg ventricles. CONCLUSION:Our results suggest that the N47K and R58Q mutations may act through similar mechanisms, leading to compensatory hypertrophy of the functionally compromised myocardium, but the malignant R58Q phenotype is most likely associated with more severe alterations in cardiac performance manifested as impaired relaxation and global diastolic dysfunction. At the molecular level, we suggest that by reducing the phosphorylation of RLC, the R58Q mutation decreases the kinetics of myosin cross-bridges, leading to an increased myofilament calcium sensitivity and to overall changes in intracellular Ca(2+) homeostasis.

Project description:AimsDiastolic dysfunction (DD) is common among hypertrophic cardiomyopathy (HCM) patients, causing major morbidity and mortality. However, its cellular mechanisms are not fully understood, and presently there is no effective treatment. Patient-specific induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) hold great potential for investigating the mechanisms underlying DD in HCM and as a platform for drug discovery.Methods and resultsIn the present study, beating iPSC-CMs were generated from healthy controls and HCM patients with DD. Micropatterned iPSC-CMs from HCM patients showed impaired diastolic function, as evidenced by prolonged relaxation time, decreased relaxation rate, and shortened diastolic sarcomere length. Ratiometric Ca2+ imaging indicated elevated diastolic [Ca2+]i and abnormal Ca2+ handling in HCM iPSC-CMs, which were exacerbated by β-adrenergic challenge. Combining Ca2+ imaging and traction force microscopy, we observed enhanced myofilament Ca2+ sensitivity (measured as dF/Δ[Ca2+]i) in HCM iPSC-CMs. These results were confirmed with genome-edited isogenic iPSC lines that carry HCM mutations, indicating that cytosolic diastolic Ca2+ overload, slowed [Ca2+]i recycling, and increased myofilament Ca2+ sensitivity, collectively impairing the relaxation of HCM iPSC-CMs. Treatment with partial blockade of Ca2+ or late Na+ current reset diastolic Ca2+ homeostasis, restored diastolic function, and improved long-term survival, suggesting that disturbed Ca2+ signalling is an important cellular pathological mechanism of DD. Further investigation showed increased expression of L-type Ca2+channel (LTCC) and transient receptor potential cation channels (TRPC) in HCM iPSC-CMs compared with control iPSC-CMs, which likely contributed to diastolic [Ca2+]i overload.ConclusionIn summary, this study recapitulated DD in HCM at the single-cell level, and revealed novel cellular mechanisms and potential therapeutic targets of DD using iPSC-CMs.

Project description:RATIONALE:Hypertrophic cardiomyopathy (HCM) is a genetic paradigm of cardiac hypertrophy. Cardiac hypertrophy and interstitial fibrosis are important risk factors for sudden death and morbidity in HCM. Oxidative stress is implicated in the pathogenesis of cardiac hypertrophy and fibrosis. Treatment with antioxidant N-acetylcysteine (NAC) reverses cardiac hypertrophy and fibrosis in animal models of HCM. OBJECTIVE:To determine effect sizes of NAC on indices of cardiac hypertrophy and fibrosis in patients with established HCM. METHODS AND RESULTS:HALT-HCM (Hypertrophy Regression With N-Acetylcysteine in Hypertrophic Cardiomyopathy) is a double-blind, randomized, sex-matched, placebo-controlled single-center pilot study in patients with HCM. Patients with HCM, who had a left ventricular wall thickness of ≥15 mm, were randomized either to a placebo or to NAC (1:2 ratio, respectively). NAC was titrated ≤2.4 g per day. Clinical evaluation, blood chemistry, and 6-minute walk test were performed every 3 months, and electrocardiography, echocardiography, and cardiac magnetic resonance imaging, the latter whenever not contraindicated, before and after 12 months of treatment. Eighty-five of 232 screened patients met the eligibility criteria, 42 agreed to participate; 29 were randomized to NAC and 13 to placebo groups. Demographic, echocardiographic, and cardiac magnetic resonance imaging phenotypes at the baseline between the 2 groups were similar. WSE in 38 patients identified a spectrum of 42 pathogenic variants in genes implicated in HCM in 26 participants. Twenty-four patients in the NAC group and 11 in the placebo group completed the study. Six severe adverse events occurred in the NAC group but were considered unrelated to NAC. The effect sizes of NAC on the clinical phenotype, echocardiographic, and cardiac magnetic resonance imaging indices of cardiac hypertrophy, function, and extent of late gadolinium enhancement-a surrogate for fibrosis-were small. CONCLUSIONS:Treatment with NAC for 12 months had small effect sizes on indices of cardiac hypertrophy or fibrosis. The small sample size of the HALT-HCM study hinders from making firm conclusions about efficacy of NAC in HCM. CLINICAL TRIAL REGISTRATION:URL: http://www.clinicaltrials.gov. Unique identifier: NCT01537926.

Project description:ObjectivesMyocardial strain is reported to be a sensitive indicator of myocardial mechanical changes in patients with hypertrophic cardiomyopathy (HCM). The changes in the mechanics of the myocardium of normal wall thickness (< 12 mm) have yet to be well studied. This study aimed to evaluate the function of myocardial segments of normal thickness in patients with HCM.MethodsSixty-three patients with HCM and 30 controls were retrospectively enrolled in this retrospective study. Cine imaging, native and post-contrast T1 maps, T2 maps, and late gadolinium enhancement were performed. In addition, regional myocardial strain was assessed by cardiac magnetic resonance-tissue tracking. Strain parameters were compared between the controls and HCM patients with segments of the myocardium of normal thickness. Subgroup analysis was conducted in obstructive and non-obstructive HCM. Lastly, p < 0.05 was considered statistically significant.ResultsIn normal-thickness myocardial segments of HCM (n = 716), diastolic peak strain rates (PSRs) were significantly lower than in the control group (n = 480) (radial, - 2.43 [- 3.36, - 1.78] vs. - 2.67 [- 3.58, - 1.96], p = 0.002; circumferential, 1.28 [1.01,1.60] vs. 1.39 [1.14, 1.78], p < 0.001; and longitudinal, 1.16 [0.75,1.51] vs. 1.28 [0.90, 1.71], p < 0.001). The normal-thickness segments showed no significant difference in systolic PSRs between HCM and the controls. In the subgroup analysis, significantly decreased diastolic PSRs were noted in both obstructive and non-obstructive HCM, compared with the controls (p < 0.05).ConclusionsDiastolic changes in myocardial mechanics were observed in normal-thickness segments of HCM, occurring before morphological remodeling and systolic dysfunction developed. This finding contributed to a better understanding of the mechanical pathophysiology of HCM with preserved left ventricular ejection fraction. It may potentially aid in predicting disease progression and risk stratification.

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N-acetylcysteine reverses diastolic dysfunction and hypertrophy in familial hypertrophic cardiomyopathy.

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N-acetylcysteine reverses diastolic dysfunction and hypertrophy in familial hypertrophic cardiomyopathy.

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