Human myocardial Na,K-ATPase--quantification, regulation and relation to Ca

Multi-Omics Profiling of Hypertrophic Cardiomyopathy Reveals Altered Mechanisms in Mitochondrial Dynamics and Excitation-Contraction Coupling

Hypertrophic cardiomyopathy is one of the most common inherited cardiomyopathies and a leading cause of sudden cardiac death in young adults. Despite profound insights into the genetics, there is imperfect correlation between mutation and clinical prognosis, suggesting complex molecular cascades driving pathogenesis. To investigate this, we performed an integrated quantitative multi-omics (proteomic, phosphoproteomic, and metabolomic) analysis to illuminate the early and direct consequences of mutations in myosin heavy chain in engineered human induced pluripotent stem-cell-derived cardiomyocytes relative to late-stage disease using patient myectomies. We captured hundreds of differential features, which map to distinct molecular mechanisms modulating mitochondrial homeostasis at the earliest stages of pathobiology, as well as stage-specific metabolic and excitation-coupling maladaptation. Collectively, this study fills in gaps from previous studies by expanding knowledge of the initial responses to mutations that protect cells against the early stress prior to contractile dysfunction and overt disease.

Oxidative and osmoregulatory effects of imidacloprid, cadmium, and their combinations on Daphnia magna

Oxidative stress and osmoregulatory system damage-inducing potential of binary mixtures of neonicotinoid insecticide imidacloprid (IMI) and Cd²⁺ in Daphnia magna were evaluated. Animals were subjected to subchronic (7 days) and acute (48 h) of IMI and Cd²⁺ effects with single and binary mixtures. ATPase and antioxidant enzyme activities with lipid peroxidation were measured. Morphometric characteristics were also evaluated. Response patterns showed variability due to the duration, concentration, and toxicant type. While the enzyme activities mostly showed a decreasing trend upon the subchronic IMI effect, there was an increasing trend after the Cd²⁺. Declined enzyme activities were more pronounced with the acute higher IMI+Cd²⁺ exposure. Ca²⁺-ATPase and CAT were the most sensitive biomarkers in the toxicity response. IMI+Cd²⁺ exposures are appeared to increase their toxic effects due to their oxidative potential. ATPase inhibition and antioxidant enzyme alterations with a decrease in morphometric characteristics in Daphnia even at their low concentrations of IMI and Cd²⁺ show evidence of their toxicities on aquatic life. It was emphasized that investigating the combined effects of toxicants at their environmental level based on the multi-biomarker approach is essential in toxicity evaluation.

Cardiac Dysfunction in a Porcine Model of Pediatric Malnutrition

BACKGROUND

Half a million children die annually of severe acute malnutrition and cardiac dysfunction may contribute to the mortality. However, cardiac function remains poorly examined in cases of severe acute malnutrition.

OBJECTIVE

To determine malnutrition-induced echocardiographic disturbances and longitudinal changes in plasma pro-atrial natriuretic peptide and cardiac troponin-T in a pediatric porcine model.

METHODS AND RESULTS

Five-week old piglets (Duroc-x-Danish Landrace-x-Yorkshire) were fed a nutritionally inadequate maize-flour diet to induce malnutrition (MAIZE, n = 12) or a reference diet (AGE-REF, n = 12) for 7 weeks. Outcomes were compared to a weight-matched reference group (WEIGHT-REF, n = 8). Pro-atrial natriuretic peptide and cardiac troponin-T were measured weekly. Plasma pro-atrial natriuretic peptide decreased in both MAIZE and AGE-REF during the first 3 weeks but increased markedly in MAIZE relative to AGE-REF during week 5-7 (p ≤ 0.001). There was overall no difference in plasma cardiac troponin-T between groups. However, further analysis revealed that release of cardiac troponin-T in plasma was more frequent in AGE-REF compared with MAIZE (OR: 4.8; 95%CI: 1.2-19.7; p = 0.03). However, when release occurred, cardiac troponin-T concentration was 6.9-fold higher (95%CI: 3.0-15.9; p < 0.001) in MAIZE compared to AGE-REF. At week 7, the mean body weight in MAIZE was lower than AGE-REF (8.3 vs 32.4 kg, p < 0.001), whereas heart-weight relative to body-weight was similar across the three groups. The myocardial performance index was 86% higher in MAIZE vs AGE-REF (p < 0.001) and 27% higher in MAIZE vs WEIGHT-REF (p = 0.025).

CONCLUSIONS

Malnutrition associates with cardiac dysfunction in a pediatric porcine model by increased myocardial performance index and pro-atrial natriuretic peptide and it associates with cardiac injury by elevated cardiac troponin-T. Clinical studies are needed to see if the same applies for children suffering from malnutrition.

Melatonin protects against ischemic heart failure in rats

Ischemic injury, which occurs as a result of sympathetic hyperactivity, plays an important role in heart failure. Melatonin is thought to have antiatherogenic, antioxidant, and vasodilatory effects. In this study, we investigated whether melatonin protects against ischemic heart failure (HF). In Wistar albino rats, HF was induced by left anterior descending (LAD) coronary artery ligation and rats were treated with either vehicle or melatonin (10 mg/kg) for 4 weeks. At the end of this period, echocardiographic measurements were recorded and the rats were decapitated to obtain plasma and cardiac tissue samples. Lactate dehydrogenase, creatine kinase, aspartate aminotransferase, alanine aminotransferase, and lysosomal enzymes (β-D-glucuronidase, β-galactosidase, β-D-N-acetyl-glucosaminidase, acid phosphatase, and cathepsin-D) were studied in plasma samples, while malondialdehyde and glutathione levels and Na+, K+-ATPase, caspase-3 and myeloperoxidase activities were determined in the cardiac samples. Sarco/endoplasmic reticulum calcium ATPase (SERCA) and caveolin-3 levels in cardiac tissues were evaluated using Western blot analyses. Furthermore, caveolin-3 levels were also determined by histological analyses. In the vehicle-treated HF group, cardiotoxicity resulted in decreased cardiac Na+, K+-ATPase and SERCA activities, GSH contents and caveolin-3 levels, while plasma LDH, CK, and lysosomal enzyme activities and cardiac MDA and Myeloperoxidase (MPO) activities were found to be increased. On the other hand, melatonin treatment reversed all the functional and biochemical changes. The present results demonstrate that Mel ameliorates ischemic heart failure in rats. These observations highlight that melatonin is a promising supplement for improving defense mechanisms in the heart against oxidative stress caused by heart failure.

Increased functional importance of the Na,Ca-exchanger in contracting failing human myocardium but unchanged activity in isolated vesicles

The present study aimed to investigate the hypothesis that the function of the Na,Ca-exchanger (NCX) is of higher importance for contractility and Ca(2+)-homeostasis in left ventricle from terminally failing than from nonfailing human hearts. The effect of decreasing extracellular [Na](e) (140 to 25 mmol/L) on force of contraction in isolated left ventricular papillary muscle strips was studied as a reflection of NCX function in multicellular preparations (terminally failing, DCM, dilated cardiomyopathy, NYHA IV, n = 13; nonfailing, NF, donor hearts, n = 10). Decreasing [Na](e) has previously been shown to increase contractility in vitro secondary to a decreased Ca(2+)-extrusion by the NCX. In addition, the NCX activity was measured as Na(+)-dependent (45)Ca(2+)-uptake into isolated myocardial vesicles as a function of time and Ca(2+)-concentration (DCM n = 8, NF n = 8). Decreasing [Na](e) enhanced the contractility of papillary muscle strips in both DCM and NF, but the contractility of DCM was increased at smaller reductions of [Na](e) than NF. The NCX activity in isolated myocardial vesicles was unchanged as a function of time (T(1/2): DCM 2.4 +/- 0.3 s versus NF 2.5 +/- 0.3 s) and as a function of Ca(2+) (DCM 0.99 +/- 0.08 versus NF 0.96 +/- 0.07 nmol/mg protein x 3 s, K(1/2): DCM 39.2 microM versus NF 38.3 microM). These results demonstrate a higher sensitivity of the failing human myocardium towards Na,Ca-exchanger mediated positive inotropic effects, suggesting a higher significance of the Na,Ca-exchanger for the extrusion of Ca(2+)-ions in intact failing versus nonfailing human myocardium. Since the activity and the Ca (2+)-affinity of the Na,Ca-exchanger in isolated vesicles was unchanged, we propose that alterations in Ca(2+)-and Na(+)-homeostasis (due to impaired function of the sarcoplasmic reticulum and the Na(+), K(+)-ATPase) or the prolonged action potential are the reason for this observation.

Amiodarone inhibits the 3,5,3'-triiodothyronine-dependent increase of sodium/potassium adenosine triphosphatase activity and concentration in human atrial myocardial tissue

In animal models the function of the sodium pump (sodium/potassium-adenosine triphosphatase [Na+/K(+)-ATPase]) is enhanced by 3,5,3'-triiodothyronine (T3) and inhibited by the antiarrhythmic agent amio. However, it is still unclear whether the effect of the drug on Na+/K(+)-ATPase depends on the interference with thyroid hormone action. We evaluated the interaction of T3 with amiodarone on Na+/K(+)-ATPase activity and site number in human myocardium. Right atrial slices were cultured with (T3+) and without (T3-) 3 nM T3 in presence and absence of amiodarone at therapeutical dose (1.5 microM). When compared to T3+, T3- preparations showed decreased 3H-ouabain binding (p < 0.004) and lower 20-minute and 45-minute 86Rb-uptake (p < or = 0.004). Amiodarone caused an average 49% reduction of the T3-dependent 3H-ouabain binding and decreased the Western blot signal for the Na+/K(+)-ATPase alpha1 subunit. The drug also inhibited T3-dependent increase in 86Rb-influx at 20 and 45 minutes by 66% and 42%, respectively, without affecting the affinity of the pump for K+. No differences were found in the 3H-ouabain binding and 86Rb-uptake of T3-, T3- amio and T3(+)-amio. In conclusion, T3 stimulates the Na+/K(+)-ATPase in human atrial myocardium by increasing the number of ouabain-binding sites, whereas amiodarone decreases the sodium pump function secondarily to the antagonism with thyroid hormone.

Clinical potential of sodium-calcium exchanger inhibitors as antiarrhythmic agents

The Na(+)/Ca(2+) exchanger (NaCaX) plays an important role in calcium handling in myocytes, but in the setting of calcium overload NaCaX can also contribute to the activation of an arrhythmogenic transient inward current (I(ti)). Therefore, approaches to inhibit NaCaX could have potential antiarrhythmic effects in pathophysiological states such as heart failure (HF) or myocardial ischaemia and reperfusion. NaCaX typically functions in a forward (Ca(2+) extrusion) mode but can also function in a reverse (Ca(2+) influx) mode. The determining factors for the directionality of NaCaX ion movement are the electrochemical gradients of calcium and sodium, and membrane potential (E(m)). In HF, upregulated NaCaX plays a dual role: it decreases sarcoplasmic reticulum (SR) calcium load, which leads to contractile dysfunction, and it underlies the I(ti) responsible for delayed after-depolarisations (DADs) and ventricular arrhythmias. In myocardial ischaemia and reperfusion, increases in [Na(+)](i) (as a result of acidosis and activation of the Na(+)/H(+) exchanger [NHE]) lead to calcium overload via the NaCaX and arrhythmogenesis is probably mediated by I(ti) activation due to NaCaX. As such, inhibition of NaCaX could provide a novel therapeutic approach to the prevention and treatment of arrhythmias. Unfortunately, it is difficult to assess the efficacy of such an approach since there are no specific NaCaX inhibitors. Currently available agents are hampered by their nonspecific effects on other ion channels and carriers. The potential utility of specific inhibition of forward or reverse mode NaCaX as an antiarrhythmic approach in the settings of HF and ischaemia/ reperfusion is discussed within the context of current knowledge of myocyte calcium and sodium handling. NaCaX is a challenging and complex therapeutic target because of the delicate balance of SR calcium load (too little contributes to contractile dysfunction and too much leads to calcium overload and arrhythmogenesis). Further understanding of NaCaX function, [Na(+)](i) and [Ca(2+)](i) in HF and ischaemia/reperfusion, combined with the development and assessment of specific NaCaX inhibitors, will ultimately define the potential role of NaCaX inhibition in the prevention and treatment of ventricular arrhythmias.

Calpain is a mediator of myocardial injury in experimental uremia: is it activated by endogenous ouabain?

BACKGROUND

Incidence of cardiovascular disease is more than 20-fold higher in patients with chronic renal failure than in aged-matched individuals with normal renal function. Little is understood about the causes or the mechanism of uremia-induced cardiovascular injury, but the involvement of calpain as a possible mediator has recently been under investigation. Mean calpain activity was found to be 3.4-fold higher in the hearts of uremic rats than in control or spontaneously hypertensive (SHR) rats. In addition, calpain activity was found to be stimulated in myoblasts (Girardi) treated with media enriched with uremic serum compared with cells treated with serum from healthy volunteers. In this study, we assessed the impact of calpain activation in uremia and explored the possibility that calpain might be activated in uremia by endogenous ouabain. Ouabain is known to be elevated in uremia and is strongly associated with left ventricular hypertrophy in essential hypertension.

METHODS

Calpain activity was measured in situ in human-derived myoblasts treated with low doses of ouabain similar to those concentrations found in uremic patients.

RESULTS

Low concentrations of ouabain (10 nmol/L) caused a highly significant increase in calpain activity, which could be completely inhibited by the simultaneous chelation of intracellular and extracellular Ca2+, and by the chelation of extracellular Ca2+ alone.

CONCLUSIONS

Calpain activity can be stimulated by nanomolar concentrations of ouabain due to an influx of extracellular Ca2+. As circulating ouabain is known to be elevated in uremia and strongly associated with LVH remodeling, we hypothesize that endogenous ouabain might be one of the factors that facilitates the remodeling of the left ventricle in patients with renal failure.

Downregulation of cardiac myocyte Na(+)-K(+)-ATPase by adenovirus-mediated expression of an alpha-subunit fragment

Cultured rat cardiac myocytes and A7r5 cells were transfected with an adenoviral vector used earlier for in vivo expression of functional alpha(2)-isoform of the catalytic subunit of rat Na(+)-K(+)-ATPase. Expressions of truncated forms of alpha(2), but little or no intact alpha(2), were detected, suggesting the rapid degradation of alpha(2) in these cultured cells. In neonatal myocytes normally containing the alpha(1)- and the alpha(3)-isoforms, expression of the alpha(2)-fragment led to 1) a significant decrease in the level of endogenous alpha(1)-protein and a modest decrease in alpha(3)-protein, 2) decreases in mRNAs of alpha(1) and alpha(3), 3) decrease in Na(+)-K(+)-ATPase function measured as ouabain-sensitive Rb(+) uptake, 4) increase in intracellular Ca(2+) concentration similar to that induced by ouabain, and 5) eventual loss of cell viability. These findings indicate that the alpha(2)-fragment downregulates endogenous Na(+)-K(+)- ATPase most likely by dominant negative interference either with folding and/or assembly of the predominant housekeeping alpha(1)-isoform or with signal transducing function of the enzyme. Demonstration of rise in intracellular Ca(2+) resulting from alpha(1)-downregulation 1) does not support the previously suggested special roles of less abundant alpha(2)- and alpha(3)-isoforms in the regulation of cardiac Ca(2+), 2) lends indirect support to proposals that observed decrease in total Na(+)-K(+)-ATPase of the failing heart may be a mechanism to compensate for impaired cardiac contractility, and 3) suggests the potential therapeutic utility of dominant negative inhibition of Na(+)-K(+)-ATPase.