Altering Calcium Sensitivity in Heart Failure: A Crossroads of Disease Etiology and Therapeutic Innovation.

Heart failure (HF) presents a significant clinical challenge, with current treatments mainly easing symptoms without stopping disease progression. The targeting of calcium (Ca2+) regulation is emerging as a key area for innovative HF treatments that could significantly alter disease outcomes and enhance cardiac function. In this review, we aim to explore the implications of altered Ca2+ sensitivity, a key determinant of cardiac muscle force, in HF, including its roles during systole and diastole and its association with different HF types-HF with preserved and reduced ejection fraction (HFpEF and HFrEF, respectively). We further highlight the role of the two rate constants kon (Ca2+ binding to Troponin C) and koff (its dissociation) to fully comprehend how changes in Ca2+ sensitivity impact heart function. Additionally, we examine how increased Ca2+ sensitivity, while boosting systolic function, also presents diastolic risks, potentially leading to arrhythmias and sudden cardiac death. This suggests that strategies aimed at moderating myofilament Ca2+ sensitivity could revolutionize anti-arrhythmic approaches, reshaping the HF treatment landscape. In conclusion, we emphasize the need for precision in therapeutic approaches targeting Ca2+ sensitivity and call for comprehensive research into the complex interactions between Ca2+ regulation, myofilament sensitivity, and their clinical manifestations in HF.

Impact of etiology on force and kinetics of left ventricular end-stage failing human myocardium.

BACKGROUND: Heart failure (HF) is associated with highly significant morbidity, mortality, and health care costs. Despite the significant advances in therapies and prevention, HF remains associated with poor clinical outcomes. Understanding the contractile force and kinetic changes at the level of cardiac muscle during end-stage HF in consideration of underlying etiology would be beneficial in developing targeted therapies that can help improve cardiac performance. OBJECTIVE: Investigate the impact of the primary etiology of HF (ischemic or non-ischemic) on left ventricular (LV) human myocardium force and kinetics of contraction and relaxation under near-physiological conditions. METHODS AND RESULTS: Contractile and kinetic parameters were assessed in LV intact trabeculae isolated from control non-failing (NF; n = 58) and end-stage failing ischemic (FI; n = 16) and non-ischemic (FNI; n = 38) human myocardium under baseline conditions, length-dependent activation, frequency-dependent activation, and response to the ß-adrenergic stimulation. At baseline, there were no significant differences in contractile force between the three groups; however, kinetics were impaired in failing myocardium with significant slowing down of relaxation kinetics in FNI compared to NF myocardium. Length-dependent activation was preserved and virtually identical in all groups. Frequency-dependent activation was clearly seen in NF myocardium (positive force frequency relationship [FFR]), while significantly impaired in both FI and FNI myocardium (negative FFR). Likewise, ß-adrenergic regulation of contraction was significantly impaired in both HF groups. CONCLUSIONS: End-stage failing myocardium exhibited impaired kinetics under baseline conditions as well as with the three contractile regulatory mechanisms. The pattern of these kinetic impairments in relation to NF myocardium was mainly impacted by etiology with a marked slowing down of kinetics in FNI myocardium. These findings suggest that not only force development, but also kinetics should be considered as a therapeutic target for improving cardiac performance and thus treatment of HF.

Etiology-dependent impairment of relaxation kinetics in right ventricular end-stage failing human myocardium.

BACKGROUND: In patients with end-stage heart failure, the primary etiology often originates in the left ventricle, and eventually the contractile function of the right ventricle (RV) also becomes compromised. RV tissue-level deficits in contractile force and/or kinetics need quantification to understand involvement in ischemic and non-ischemic failing human myocardium. METHODS AND RESULTS: The human population suffering from heart failure is diverse, requiring many subjects to be studied in order to perform an adequately powered statistical analysis. From 2009-present we assessed live tissue-level contractile force and kinetics in isolated myocardial RV trabeculae from 44 non-failing and 41 failing human hearts. At 1 Hz stimulation rate (in vivo resting state) the developed active force was not different in non-failing compared to failing ischemic nor non-ischemic failing trabeculae. In sharp contrast, the kinetics of relaxation were significantly impacted by disease, with 50% relaxation time being significantly shorter in non-failing vs. non-ischemic failing, while the latter was still significantly shorter than ischemic failing. Gender did not significantly impact kinetics. Length-dependent activation was not impacted. Although baseline force was not impacted, contractile reserve was critically blunted. The force-frequency relation was positive in non-failing myocardium, but negative in both ischemic and non-ischemic myocardium, while the ß-adrenergic response to isoproterenol was depressed in both pathologies. CONCLUSIONS: Force development at resting heart rate is not impacted by cardiac pathology, but kinetics are impaired and the magnitude of the impairment depends on the underlying etiology. Focusing on restoration of myocardial kinetics will likely have greater therapeutic potential than targeting force of contraction.

Memantine, an NMDA Receptor Antagonist, Prevents Thyroxin-induced Hypertension, but Not Cardiac Remodeling.

Stimulation of glutamatergic tone has been causally linked to myocardial pathogenesis and amplified systemic blood pressure (BP). Memantine, a noncompetitive N-methyl-D-aspartate glutamatergic receptor (NMDA-R) antagonist, has been proposed to be an active cardioprotective drug. However, the efficacy of memantine and subsequently the possible involvement of the NMDA-R in the thyroxin (T4)-induced cardiovascular complications have never been investigated. We examined the effect of memantine (30 mg·kg·d) on the T4 (500 µg·kg·d)-provoked increase in mouse BP, cardiac hypertrophy indicated by enlarged overall myocardial mass, and reformed reactions of the contractile myocardium both in vivo and ex vivo after 2 weeks of treatment. Memantine alone did not result in any cardiovascular pathology in mice. Instead, memantine significantly prevented the T4-triggered systemic hypertension. But, it did not reverse cardiac hypertrophy, coupled in vivo left ventricular dysfunction (LV) or ex vivo right ventricular (RV) papillary muscle contractile alterations of the T4-treated mice. Our results openly direct the cardiovascular safety and tolerability of memantine therapy. Yet, extra research is necessary to endorse these prospective advantageous outcomes. Also, we believe that this is the first study to inspect the possible role of NMDA-R in the T4-stimulated cardiovascular disorders and concluded that NMDA-R could play a key role in the T4-induced hypertension.

Mechanical Dyssynchrony of Isolated Left and Right Ventricular Human Myocardium in End-Stage Heart Failure.

BACKGROUND: The left and right ventricles of the human heart differ in embryology, shape, thickness, and function. Ventricular dyssynchrony often occurs in cases of heart failure. Our objectives were to assess whether differences in contractile properties exist between the left and right ventricles and to evaluate signs of left/right ventricular mechanical synchrony in isolated healthy and diseased human myocardium. METHODS: Myocardial left and right ventricular trabeculae were dissected from nonfailing and end-stage failing human hearts. Baseline contractile force and contraction/relaxation kinetics of the left ventricle were compared to those of the right ventricle in the nonfailing group (n=41) and in the failing group (n=29). Correlation analysis was performed to assess the mechanical synchrony between left and right ventricular myocardium isolated from the same heart, in nonfailing (n=41) and failing hearts (n=29). RESULTS: The failing right ventricular myocardium showed significantly higher developed force (Fdev; P=0.001; d=0.98), prolonged time to peak (P<0.001; d=1.14), and higher rate of force development (P=0.002; d=0.89) and force decline (P=0.003; d=0.82) compared to corresponding left ventricular myocardium. In healthy myocardium, a strong positive relationship was present between the left and right ventricles in time to peak (r=0.58, P<0.001) and maximal kinetic rate of contraction (r=0.63, P<0.001). These coefficients were much weaker, often nearly absent, in failing myocardium. CONCLUSIONS: At the level of isolated cardiac trabeculae, contractile performance, specifically of contractile kinetics, is correlated in the nonfailing myocardium between the left and right ventricles' but this correlation is significantly weaker, or even absent, in end-stage heart failure, suggesting an interventricular mechanical dyssynchrony.

Quantification of Cardiac Adipose Tissue in Failing and Nonfailing Human Myocardium.

Background Because body mass index (BMI) is generally used clinically to define obesity and to estimate body adiposity, BMI likely is positively correlated with epicardial adipose tissue (EAT) level. Based on echocardiography, previous outcomes on this matter have varied from almost absent to rather strong correlations between BMI and EAT. The purpose of our study was to unambiguously examine EAT content and determine if correlations exist between EAT content and BMI, cause of heart failure, or contractile force. Methods and Results We qualitatively scored 150 human hearts ex vivo on EAT distribution. From each heart, multiple photographs of the heart were taken, and both atrial and ventricular adipose tissue levels were semiquantitatively scored. Main findings include a generally higher EAT content on nonfailing hearts compared with end-stage failing hearts (atrial adipose tissue level 5.70±0.13 vs. 5.00±0.12, P<0.001; ventricular adipose tissue level 5.14±0.16 vs. 4.57±0.12, P=0.0048). The results also suggest that EAT quantity is not strongly correlated with BMI in nonfailing (atrial adipose tissue level r=0.069, ventricular adipose tissue level r=0.14) or failing (atrial adipose tissue level r=-0.022, ventricular adipose tissue level r=0.051) hearts. Atrial EAT is closely correlated with ventricular EAT in both nonfailing (r=0.92, P<0.001) and failing (r=0.87, P<0.001) hearts. Conclusions EAT volume appears to be inversely proportional to severity of or length of time with heart failure based on our findings. Based on a lack of correlation with BMI, it is incorrect to assume high EAT volume given high body fat percentage.

Effect of hypothyroidism on contractile performance of isolated end-stage failing human myocardium.

The relationship between hypothyroidism and the occurrence and progression of heart failure (HF) has had increased interest over the past years. The low T3 syndrome, a reduced T3 in the presence of normal thyroid stimulating hormone (TSH), and free T4 concentration, is a strong predictor of all-cause mortality in HF patients. Still, the impact of hypothyroidism on the contractile properties of failing human myocardium is unknown. Our study aimed to investigate that impact using ex-vivo assessment of force and kinetics of contraction/relaxation in left ventricular intact human myocardial muscle preparations. Trabeculae were dissected from non-failing (NF; n = 9), failing with no hypothyroidism (FNH; n = 9), and failing with hypothyroidism (FH; n = 9) hearts. Isolated muscle preparations were transferred into a custom-made setup where baseline conditions as well as the three main physiological modulators that regulate the contractile strength, length-dependent and frequency-dependent activation, as well as ß-adrenergic stimulation, were assessed under near-physiological conditions. Hypothyroidism did not show any additional significant impact on the contractile properties different from the recognized alterations usually detected in such parameters in any end-stage failing heart without thyroid dysfunction. Clinical information for FH patients in our study revealed they were all receiving levothyroxine. Absence of any difference between failing hearts with or without hypothyroidism, may possibly be due to the profound effects of the advanced stage of heart failure that concealed any changes between the groups. Still, we cannot exclude the possibility of differences that may have been present at earlier stages. The effects of THs supplementation such as levothyroxine on contractile force and kinetic parameters of failing human myocardium require further investigation to explore its full potential in improving cardiovascular performance and cardiovascular outcomes of HF associated with hypothyroidism.

Stretching single titin molecules from failing human hearts reveals titin's role in blunting cardiac kinetic reserve.

AIMS: Heart failure (HF) patients commonly experience symptoms primarily during elevated heart rates, as a result of physical activities or stress. A main determinant of diastolic passive tension, the elastic sarcomeric protein titin, has been shown to be associated with HF, with unresolved involvement regarding its role at different heart rates. To determine whether titin is playing a role in the heart rate (frequency-) dependent acceleration of relaxation (FDAR). W, we studied the FDAR responses in live human left ventricular cardiomyocytes and the corresponding titin-based passive tension (TPT) from failing and non-failing human hearts. METHODS AND RESULTS: Using atomic force, we developed a novel single-molecule force spectroscopy approach to detect TPT based on the frequency-modulated cardiac cycle. Mean TPT reduced upon an increased heart rate in non-failing human hearts, while this reduction was significantly blunted in failing human hearts. These mechanical changes in the titin distal Ig domain significantly correlated with the frequency-dependent relaxation kinetics of human cardiomyocytes obtained from the corresponding hearts. Furthermore, the data suggested that the higher the TPT, the faster the cardiomyocytes relaxed, but the lower the potential of myocytes to speed up relaxation at a higher heart rate. Such poorer FDAR response was also associated with a lesser reduction or a bigger increase in TPT upon elevated heart rate. CONCLUSIONS: Our study established a novel approach in detecting dynamic heart rate relevant tension changes physiologically on native titin domains. Using this approach, the data suggested that the regulation of kinetic reserve in cardiac relaxation and its pathological changes were associated with the intensity and dynamic changes of passive tension by titin.

Protein Kinase A as a Promising Target for Heart Failure Drug Development.

Heart failure (HF) is a clinical syndrome characterized by impaired ability of the heart to fill or eject blood. HF is rather prevalent and it represents the foremost reason of hospitalization in the United States. The costs linked to HF overrun those of all other causes of disabilities, and death in the United States and all over the developed as well as the developing countries which amplify the supreme significance of its prevention. Protein kinase (PK) A plays multiple roles in heart functions including, contraction, metabolism, ion fluxes, and gene transcription. Altered PKA activity is likely to cause the progression to cardiomyopathy and HF. Thus, this review is intended to focus on the roles of PKA and PKA-mediated signal transduction in the healthy heart as well as during the development of HF. Furthermore, the impact of cardiac PKA inhibition/activation will be highlighted to identify PKA as a potential target for the HF drug development.

Assessment of PKA and PKC inhibitors on force and kinetics of non-failing and failing human myocardium.

AIMS: Heart failure (HF) is a prevalent disease that is considered the foremost reason for hospitalization in the United States. Most protein kinases (PK) are activated in heart disease and their inhibition has been shown to improve cardiac function in both animal and human studies. However, little is known about the direct impact of PKA and PKC inhibitors on human cardiac contractile function. MATERIAL AND METHODS: We investigated the ex vivo effect of such inhibitors on force as well as on kinetics of left ventricular (LV) trabeculae dissected from non-failing and failing human hearts. In these experiments, we applied 0.5 µM of H-89 and GF109203X, which are PKA and PKC inhibitors, respectively, in comparison to their vehicle DMSO (0.05%). KEY FINDINGS AND CONCLUSION: Statistical analyses revealed no significant effect for H-89 and GF109203X on either contractile force or kinetics parameters of both non-failing and failing muscles even though they were used at a concentration higher than the reported IC50s and Kis. Therefore, several factors such as selectivity, concentration, and treatment time, which are related to these PK inhibitors according to previous studies require further exploration.

Recovery following Thyroxine Treatment Withdrawal, but Not Propylthiouracil, Averts In Vivo and Ex Vivo Thyroxine-Provoked Cardiac Complications in Adult FVB/N Mice.

Persistent cardiovascular pathology has been described in hyperthyroid patients even with effective antithyroid treatment. Here, we studied the effect of a well-known antithyroid drug, propylthiouracil (PTU; 20 mg/kg/day), on thyroxine (T4; 500 µg/kg/day)-induced increase in blood pressure (BP), cardiac hypertrophy, and altered responses of the contractile myocardium both in vivo and ex vivo after 2 weeks of treatment. Furthermore, the potential recovery through 2 weeks of T4 treatment discontinuation was also investigated. PTU and T4 recovery partially reduced the T4-prompted increase in BP. Alternatively, PTU significantly improved the in vivo left ventricular (LV) function with no considerable effects on cardiac hypertrophy or ex vivo right ventricular (RV) contractile alterations subsequent to T4 treatment. Conversely, T4 recovery considerably enhanced the T4-provoked cardiac changes both in vivo and ex vivo. Altogether, our data is in agreement with the proposal that hyperthyroidism-induced cardiovascular pathology could persevere even with antithyroid treatments, such as PTU. However, this cannot be generalized and further investigation with different antithyroid treatments should be executed. Moreover, we reveal that recovery following experimental hyperthyroidism could potentially ameliorate cardiac function and decrease the risk for additional cardiac complications, yet, this appears to be model-dependent and should be cautiously construed.

The Effect of Sorafenib, Tadalafil and Macitentan Treatments on Thyroxin-Induced Hemodynamic Changes and Cardiac Abnormalities.

Multikinase inhibitors (e.g. Sorafenib), phosphodiesterase-5 inhibitors (e.g. Tadalafil), and endothelin-1 receptor blockers (e.g. Macitentan) exert influential protection in a variety of animal models of cardiomyopathy; however, their effects on thyroxin-induced cardiomyopathy have never been investigated. The goal of the present study was to assess the functional impact of these drugs on thyroxin-induced hemodynamic changes, cardiac hypertrophy and associated altered responses of the contractile myocardium both in-vivo at the whole heart level and ex-vivo at the cardiac tissue level. Control and thyroxin (500 µg/kg/day)-treated mice with or without 2-week treatments of sorafenib (10 mg/kg/day; I.P), tadalafil (1 mg/kg/day; I.P or 4 mg/kg/day; oral), macitentan (30 and 100 mg/kg/day; oral), and their vehicles were studied. Blood pressure, echocardiography and electrocardiogram were non-invasively evaluated, followed by ex-vivo assessments of isolated multicellular cardiac preparations. Thyroxin increased blood pressure, resulted in cardiac hypertrophy and left ventricular dysfunction in-vivo. Also, it caused contractile abnormalities in right ventricular papillary muscles ex-vivo. None of the drug treatments were able to significantly attenuate theses hemodynamic changes or cardiac abnormalities in thyroxin-treated mice. We show here for the first time that multikinase (raf1/b, VEGFR, PDGFR), phosphodiesterase-5, and endothelin-1 pathways have no major role in thyroxin-induced hemodynamic changes and cardiac abnormalities. In particular, our data show that the involvement of endothelin-1 pathway in thyroxine-induced cardiac hypertrophy/dysfunction seems to be model-dependent and should be carefully interpreted.

Differential involvement of various sources of reactive oxygen species in thyroxin-induced hemodynamic changes and contractile dysfunction of the heart and diaphragm muscles.

Thyroid hormones are key regulators of basal metabolic state and oxidative metabolism. Hyperthyroidism has been reported to cause significant alterations in hemodynamics, and in cardiac and diaphragm muscle functions, all of which have been linked to increased oxidative stress. However, the definite source of increased reactive oxygen species (ROS) in each of these phenotypes is still unknown. The goal of the current study was to test the hypothesis that thyroxin (T4) may produce distinct hemodynamic, cardiac, and diaphragm muscle abnormalities by differentially affecting various sources of ROS. Wild-type and T4 mice with and without 2-week treatments with allopurinol (xanthine oxidase inhibitor), apocynin (NADPH oxidase inhibitor), L-NIO (nitric oxide synthase inhibitor), or MitoTEMPO (mitochondria-targeted antioxidant) were studied. Blood pressure and echocardiography were noninvasively evaluated, followed by ex vivo assessments of isolated heart and diaphragm muscle functions. Treatment with L-NIO attenuated the T4-induced hypertension in mice. However, apocynin improved the left-ventricular (LV) dysfunction without preventing the cardiac hypertrophy in these mice. Both allopurinol and MitoTEMPO reduced the T4-induced fatigability of the diaphragm muscles. In conclusion, we show here for the first time that T4 exerts differential effects on various sources of ROS to induce distinct cardiovascular and skeletal muscle phenotypes. Additionally, we find that T4-induced LV dysfunction is independent of cardiac hypertrophy and NADPH oxidase is a key player in this process. Furthermore, we prove the significance of both xanthine oxidase and mitochondrial ROS pathways in T4-induced fatigability of diaphragm muscles. Finally, we confirm the importance of the nitric oxide pathway in T4-induced hypertension.