Benedetta Tosi

Late Sodium Current Inhibition Reverses Electromechanical Dysfunction in Human Hypertrophic Cardiomyopathy

Background— Hypertrophic cardiomyopathy (HCM), the most common mendelian heart disorder, remains an orphan of disease-specific pharmacological treatment because of the limited understanding of cellular mechanisms underlying arrhythmogenicity and diastolic dysfunction. Methods and Results— We assessed the electromechanical profile of cardiomyocytes from 26 HCM patients undergoing myectomy compared with those from nonfailing nonhypertrophic surgical patients by performing patch-clamp and intracellular Ca2+ (Ca2+i) studies. Compared with controls, HCM cardiomyocytes showed prolonged action potential related to increased late Na+ (INaL) and Ca2+ (ICaL) currents and decreased repolarizing K+ currents, increased occurrence of cellular arrhythmias, prolonged Ca2+i transients, and higher diastolic Ca2+i. Such changes were related to enhanced Ca2+/calmodulin kinase II (CaMKII) activity and increased phosphorylation of its targets. Ranolazine at therapeutic concentrations partially reversed the HCM-related cellular abnormalities via INaL inhibition, with negligible effects in controls. By shortening the action potential duration in HCM cardiomyocytes, ranolazine reduced the occurrence of early and delayed afterdepolarizations. Finally, as a result of the faster kinetics of Ca2+i transients and the lower diastolic Ca2+i, ranolazine accelerated the contraction-relaxation cycle of HCM trabeculae, ameliorating diastolic function. Conclusions— We highlighted a specific set of functional changes in human HCM myocardium that stem from a complex remodeling process involving alterations of CaMKII-dependent signaling, rather than being a direct consequence of the causal sarcomeric mutations. Among the several ion channel and Ca2+i handling proteins changes identified, an enhanced INaL seems to be a major contributor to the electrophysiological and Ca2+i dynamic abnormalities of ventricular myocytes and trabeculae from patients with HCM, suggesting potential therapeutic implications of INaL inhibition.

Impact of detubulation on force and kinetics of cardiac muscle contraction

T-tubule uncoupling from the plasma membrane leads to myocardial contractile abnormalities.

Pathogenesis of Hypertrophic Cardiomyopathy is Mutation Rather Than Disease Specific: A Comparison of the Cardiac Troponin T E163R and R92Q Mouse Models

Background In cardiomyocytes from patients with hypertrophic cardiomyopathy, mechanical dysfunction and arrhythmogenicity are caused by mutation‐driven changes in myofilament function combined with excitation‐contraction (E‐C) coupling abnormalities related to adverse remodeling. Whether myofilament or E‐C coupling alterations are more relevant in disease development is unknown. Here, we aim to investigate whether the relative roles of myofilament dysfunction and E‐C coupling remodeling in determining the hypertrophic cardiomyopathy phenotype are mutation specific. Methods and Results Two hypertrophic cardiomyopathy mouse models carrying the R92Q and the E163R TNNT2 mutations were investigated. Echocardiography showed left ventricular hypertrophy, enhanced contractility, and diastolic dysfunction in both models; however, these phenotypes were more pronounced in the R92Q mice. Both E163R and R92Q trabeculae showed prolonged twitch relaxation and increased occurrence of premature beats. In E163R ventricular myofibrils or skinned trabeculae, relaxation following Ca2+ removal was prolonged; resting tension and resting ATPase were higher; and isometric ATPase at maximal Ca2+ activation, the energy cost of tension generation, and myofilament Ca2+ sensitivity were increased compared with that in wild‐type mice. No sarcomeric changes were observed in R92Q versus wild‐type mice, except for a large increase in myofilament Ca2+ sensitivity. In R92Q myocardium, we found a blunted response to inotropic interventions, slower decay of Ca2+ transients, reduced SERCA function, and increased Ca2+/calmodulin kinase II activity. Contrarily, secondary alterations of E‐C coupling and signaling were minimal in E163R myocardium. Conclusions In E163R models, mutation‐driven myofilament abnormalities directly cause myocardial dysfunction. In R92Q, diastolic dysfunction and arrhythmogenicity are mediated by profound cardiomyocyte signaling and E‐C coupling changes. Similar hypertrophic cardiomyopathy phenotypes can be generated through different pathways, implying different strategies for a precision medicine approach to treatment.

Late sodium current inhibitors to treat exercise‐induced obstruction in hypertrophic cardiomyopathy: an in vitro study in human myocardium

In 30–40% of hypertrophic cardiomyopathy (HCM) patients, symptomatic left ventricular (LV) outflow gradients develop only during exercise due to catecholamine‐induced LV hypercontractility (inducible obstruction). Negative inotropic pharmacological options are limited to β‐blockers or disopyramide, with low efficacy and tolerability. We assessed the potential of late sodium current (INaL)‐inhibitors to treat inducible obstruction in HCM.

Response to Letter Regarding Article, “Late Sodium Current Inhibition Reverses Electromechanical Dysfunction in Human Hypertrophic Cardiomyopathy”

We thank Sikkel et al for their appreciative letter, particularly focusing on the statistical approach used in our recent work.1 Indeed, physiological parameters of cells from human subjects exhibit considerable and intrinsic interindividual variability, at variance with inbred rodents. Thus, when working on human data, the use of hierarchical statistical analysis is not only the most valid option, but one could say it is mandatory to perform reliable comparisons between normal and diseased states. Hierarchical statistical analysis has been used previously in biomedical research involving human subjects,2 including a recent study comparing mechanical data from single myofibrils isolated from cardiac samples of patients with hypertrophic cardiomyopathy with donor hearts and secondary hypertrophy.3 …

CARDIOVASCULAR ADAPTATION TO PHYSICAL ACTIVITY IN ETHNICALLY DIFFERENT YOUNG ATHLETES

Objective: Cardiovascular adaptation to intense physical training is determined by many factors including age, gender, body size, load training, ethnicity and blood pressure response to exercise. Our retrospective study aimed to assess secondary left ventricular (LV) remodelling to exercise, in terms of interventricular septum (IVS) and posterior wall (PW) thickness, in young male black soccer players (BP) compared to male white soccer players (WP). Design and method: 77 BP and 53 WP (17.8 years old), trained with the same load and having the same lifestyle, were evaluated with maximal ergometric test, echocardiography and speckle-tracking global longitudinal strain (GLS). 30 younger BP and 27 WP (13.2 years old) were selected and followed up for 4 years. Results: In the older group of athletes blood pressure response to exercise and GLS were comparable in BP and WP, whereas IVS and PW thickness were significantly higher in BP (IVS: 10.04 ± 0.14 and 9.35 ± 0.10 mm, p < 0.001; PW: 9.70 ± 0.20 and 9.19 ± 0.10 mm, p < 0.05; in BP and WP respectively). Considering the younger group of athletes no significant difference was found in blood pressure while a higher LV remodelling was detected (IVS = 9.29 ± 0.3 and 8.53 ± 0.12 mm, p < 0.002; PW = 9.01 ± 0.2 and 8.40 ± 0.20, p = 0.1; in BP and WP respectively). The degree of LV remodelling was proportional with body-size and LV mass during the four years of follow-up (IVS = 10.52 ± 0.17 and 9.03 ± 0.22 mm, p < 0.001; PW: 10.06 ± 0.17 and 8.26 ± 0.19 mm, p < 0.001; in BP and WP respectively). Conclusions: Since no significant difference in blood pressure response to exercise was detected and since all principal determinants of cardiovascular response to exercise were overcome by specific selection of all athletes enrolled, ethnicity seems to remain the principal factor involved in cardiovascular adaptation to physical training.

When in Rome, don’t do as the Romans do

In 2010, the American Heart Association (AHA) established, and made available to the public, an aggregation of 7 targets for health behaviours and factors, “The Simple 7”, to enhance awareness of and promote heart-healthy behaviours to reach the goal of 20% reduction in cardiovascular mortality (Table 1) [1]. All the seven factors are classified in three categories: ideal, intermediate, and poor. To achieve the target of “Ideal Cardiovascular Health,” a single subject has to respect the ideal category for all the seven factors. The definition emphasizes the importance of modifiable risk factors for which patients can take ownership and control, because the basic principles of cardiovascular disease prevention (no smoking, regular physical activity, healthy diet, and keeping hypertension, dyslipidaemia, and diabetes under control) impact the prevalence of cardiovascular risk factors more than any other strategy. At least 50% of the reduction in cardiovascular events observed during the last decades is indeed attributable to preventive efforts, specifically control of blood pressure, treatment of dyslipidaemias, and a reduction in smoking [2]. Nevertheless, epidemiological studies, and large surveys are revealing that we are still far away from desired targets, because the penetration of poor health in the population is alarming. In the US, only 1 of the nearly 2000 participants to the Heart SCORE study (0.1%) embraced all the “Simple 7” factors, where only 1.4 and 2% of the subjects presented all 4 health factors (high blood pressure, high blood glucose, high blood cholesterol, smoking) and all 4 health behaviours (low physical activity, poor diet, high body weight, and smoking), respectively [3]. It is now evident that a multipart strategy is needed, because in addition to the classic risk factors, social determinants and limited access to care also play a crucial role in public health [4–6]. The study by van Nieuwenhuizen [7] sheds light on some of the challenges related to minority populations in Europe [8]. African ancestry early on has emerged as an important determinant of the lack of achievement ideal cardiovascular health in the US [3], whereas no data are available in Europe. According to Nieuwenhuizen et al. [7], only 0.3% of the 3510 Ghanaian adults (aged 25–70 years) residing in rural and urban Ghana and three European cities (Amsterdam, London and Berlin) meet all 7 metrics of the AHA’s definition of ideal Cardiovascular Health (CVH). Although this proportion may appear very low, it is not so different from 0.1% observed among general population in the US [9], where racial/ethnic disparities in overall CVH are still evident among women [10]. Any comparison between African American and European Ghanaians can hardly be made (i.e. differences in migration history, health systems) [11]. A second finding, also expected, is the rural to urban gradient followed by the proportion of Ghanaian who had 6–7 metrics in the ideal category (25% in rural Ghana, 7.5% urban Ghana, 4.4% in Amsterdam, 2.7% in Berlin, and 1.7% in London). However, the real key finding of the study is the observation that the reasons for not fulfilling the status of ideal health may differ between ethnic minority and native EU populations. The Achilles’ heel for Ghanaians seems to reside in health factors, while the main weak point in European natives seems to be in health behaviours. A high proportion of Ghanaians across all sites present with high blood pressure [7], that is consistent with the higher blood pressure values measured among sub-Saharan African descent when compared to native European populations [12–14]. The principle strategies now active in Europe to face hypertension are universal access to healthcare, available in most EU countries, and the promotion of the reduction of salt consumption, now active in about half of the EU member Commentary to: Ideal cardiovascular health among Ghanaian populations in three European countries and rural and urban Ghana: the RODAM study. https ://doi.org/10.1007/s1173 9-0181846-6

Seasonal blood pressure variation: implications for cardiovascular risk stratification

Long-term blood pressure variations contribute to an increased risk of cardiovascular events during cold season, requiring personalized management of antihypertensive medications in a single patient, and can influence the results of clinical trials and epidemiological surveys in population studies. In addition to blood pressure values, which guide the stratification of cardiovascular risk, other cardiovascular risk factor levels also tend to be higher in the winter months and lower in the summer months. The resultant estimation of individual cardiovascular risk may thus vary depending on the season. At the patient level, only a low value in the winter should thus be considered a true measure of low cardiovascular risk, whereas low values measured in the summer do not indicate a low risk in the winter. Likewise, estimations of cardiovascular risk in population studies may vary according to the period of the year. Efforts should thus be directed at considering the potential influence of seasonal variations in establishing “normal” and “high-risk” assessment at both the patient and population levels, integrating such data into clinical practice.

LEFT VENTRICULAR REMODELING IN YOUNG BLACK ATHLETES

Background EKG analysis investigating the impact of the ethnicity on cardiac adaptation to exercise has shown a higher presence of abnormalities, including marked repolarization changes, and signs of left ventricular (LV) hypertrophy in black compared to white athletes. Despite the wide availability of EKG analysis, echocardiographic studies on young black and white athletes is lacking in literature. Objective Assess the effect in the secondary LV remodelling to load training in young black players compared to matched white players. Design 4 years longitudinal study. Setting Sport Medicine outpatients clinic. Patients 49 young black soccer players (BP) and 50 white matched soccer players (WP) at the first evaluation: BP=13.3±0.58 and WP=13.9±0.50 years. Interventions Echocardiography and EKG. Main Outcome Measurements Interventricular septum (IVS) and posterior wall (PW) thickness. Results No differences in weight, height, blood pressure in maximal ergometry test. Electrocardiographic repolarization changes were significantly more frequent in BP compared to WP (55% in BP vs 7% of WP). In BP we observed higher level of LV remodelling, consisted in higher LV wall thickness, i.e. higher interventricular septum (IVS) and posterior wall (PW) thickness (IVS: BP=9.99±0.17, WP=9.07±0.14, p<0.001. PW: BP=9.61±0.25, WP=8.85±0.3 mm, p<0.001). At the beginning, BP showed a significantly higher left ventricular remodelling (IVS: BP=9.14±0.6, WP=8.54±0.21 mm, p<0.001. PW: BP=8.98±0.6, WP=8.4±0.26, p<0.001). Afterwards we observed an increase in LV wall thickness and chambers diameters proportionally with the increase in body-size and LV mass. (IVS: BP=10.87±0.23, WP=9.09±0.28 mm, p<0.001. PW: BP=11.69±1.32, WP=9.02±0.24 mm, p<0.001). Conclusions Also in young blacks athletes we can find an higher cardiac wall thickness compared to their Caucasian peers. This differences remained after 5 years giving probably reason of the fact that those remodelling events happened in the first years of life by genetic factors.

Impact of E163R cTnT Mutation on Cardiac Mechanics and Energetics in a Murine Model

Introduction: Many of cTnT mutations linked to cardiomyopathies fall the TNT1 domain/N terminal tail region of unresolved high definition structure. This region (∼94-170) of cTnT is critical to Tm binding and contraction regulation. Here, the impact of the E163R mutation in cTnT-TNT1 on contractile function and tension cost was investigated using intact and skinned preparations from WT and transgenic mouse hearts.Methods: Left and right ventricular trabeculae were dissected from non-transgenic wild type (WT) and heterozygous (Δ160E or E163R) mouse hearts and mounted isometrically to record twitch tension or, when skinned, Ca2+ activated force. Myofibrillar ATPase activity was measured by fluorimetric enzyme coupled assay (de Tombe and Stienen, 1995).Results: Myocardium of E163R mice shows: (i) no change of myosin isoform expression (ii) maintained peak isomentric twitch tension at all stimulation frequencies, (iii) prolonged time to peak and time to 50% relaxation, with preserved rate-adaptation of twitch duration, (iv) changes of the short-term interval force relationship and increased occurrence of spontaneous contractions. No significant differences were found in maximum Ca2+ activated tension of E163R and WT skinned trabeculae. However, Ca2+ sensitivity of tension was significantly increased in E163R skinned trabeculae when compared with WT. As to the economy of force maintenance, preliminary experiments suggest an increase of tension cost in trabeculae from E163R hearts. Resting ATPase activity also tended to be higher in E163R preparations. Kinetics of force development and relaxation will be assessed on single myofibrils, isolated from the same hearts.Conclusions: Both primary sarcomeric changes and secondary E-C coupling alterations contribute to mechanical impairment in E163R cTnT mutant myocardium. Supported by: EC Grant n. 241577 (BIG-Heart)