Ivabradine acutely improves cardiac Ca handling and function in a rat model of Duchenne muscular dystrophy.

The muscular dystrophies caused by dystrophin deficiency, the so-called dystrophinopathies, are associated with impaired cardiac contractility and arrhythmias, which considerably contribute to disease morbidity and mortality. Impaired Ca handling in ventricular cardiomyocytes has been identified as a causative factor for complications in the dystrophic heart, and restoration of normal Ca handling in myocytes has emerged as a promising new therapeutic strategy. In the present study, we explored the hypothesis that ivabradine, a drug clinically approved for the treatment of heart failure and stable angina pectoris, improves Ca handling in dystrophic cardiomyocytes and thereby enhances contractile performance in the dystrophic heart. Therefore, ventricular cardiomyocytes were isolated from the hearts of adult dystrophin-deficient DMDmdx rats, and the effects of acutely applied ivabradine on intracellular Ca transients were tested. In addition, the drug's acute impact on cardiac function in DMDmdx rats was assessed by transthoracic echocardiography. We found that administration of ivabradine to DMDmdx rats significantly improved cardiac function. Moreover, the amplitude of electrically induced intracellular Ca transients in ventricular cardiomyocytes isolated from DMDmdx rats was increased by the drug. We conclude that ivabradine enhances Ca release from the sarcoplasmic reticulum in dystrophic cardiomyocytes and thereby improves contractile performance in the dystrophic heart.

Evidence for a Physiological Role of T-Type Ca Channels in Ventricular Cardiomyocytes of Adult Mice.

T-type Ca channels are strongly expressed and important in the developing heart. In the adult heart, these channels play a significant role in pacemaker tissues, but there is uncertainty about their presence and physiological relevance in the working myocardium. Here, we show that the T-type Ca channel isoforms Cav3.1 and Cav3.2 are expressed at a protein level in ventricular cardiomyocytes from healthy adult C57/BL6 mice. Myocytes isolated from adult wild-type and Cav3.2 KO mice showed considerable whole cell T-type Ca currents under beta-adrenergic stimulation with isoprenaline. We further show that the detectability of basal T-type Ca currents in murine wild-type cardiomyocytes depends on the applied experimental conditions. Together, these findings reveal the presence of functional T-type Ca channels in the membrane of ventricular myocytes. In addition, electrically evoked Ca release from the sarcoplasmic reticulum was significantly impaired in Cav3.2 KO compared to wild-type cardiomyocytes. Our work implies a physiological role of T-type Ca channels in the healthy adult murine ventricular working myocardium.

The Bradycardic Agent Ivabradine Acts as an Atypical Inhibitor of Voltage-Gated Sodium Channels.

Background and purpose: Ivabradine is clinically administered to lower the heart rate, proposedly by inhibiting hyperpolarization-activated cyclic nucleotide-gated cation channels in the sinoatrial node. Recent evidence suggests that voltage-gated sodium channels (VGSC) are inhibited within the same concentration range. VGSCs are expressed within the sinoatrial node and throughout the conduction system of the heart. A block of these channels thus likely contributes to the established and newly raised clinical indications of ivabradine. We, therefore, investigated the pharmacological action of ivabradine on VGSCs in sufficient detail in order to gain a better understanding of the pro- and anti-arrhythmic effects associated with the administration of this drug. Experimental Approach: Ivabradine was tested on VGSCs in native cardiomyocytes isolated from mouse ventricles and the His-Purkinje system and on human Nav1.5 in a heterologous expression system. We investigated the mechanism of channel inhibition by determining its voltage-, frequency-, state-, and temperature-dependence, complemented by a molecular drug docking to the recent Nav1.5 cryoEM structure. Automated patch-clamp experiments were used to investigate ivabradine-mediated changes in Nav1.5 inactivation parameters and inhibition of different VGSC isoforms. Key results: Ivabradine inhibited VGSCs in a voltage- and frequency-dependent manner, but did not alter voltage-dependence of activation and fast inactivation, nor recovery from fast inactivation. Cardiac (Nav1.5), neuronal (Nav1.2), and skeletal muscle (Nav1.4) VGSC isoforms were inhibited by ivabradine within the same concentration range, as were sodium currents in native cardiomyocytes isolated from the ventricles and the His-Purkinje system. Molecular drug docking suggested an interaction of ivabradine with the classical local anesthetic binding site. Conclusion and Implications: Ivabradine acts as an atypical inhibitor of VGSCs. Inhibition of VGSCs likely contributes to the heart rate lowering effect of ivabradine, in particular at higher stimulation frequencies and depolarized membrane potentials, and to the observed slowing of intra-cardiac conduction. Inhibition of VGSCs in native cardiomyocytes and across channel isoforms may provide a potential basis for the anti-arrhythmic potential as observed upon administration of ivabradine.

Cardiovascular phenotype of the Dmdmdx rat - a suitable animal model for Duchenne muscular dystrophy.

Besides skeletal muscle abnormalities, Duchenne muscular dystrophy (DMD) patients present with dilated cardiomyopathy development, which considerably contributes to morbidity and mortality. Because the mechanisms responsible for the cardiac complications in the context of DMD are largely unknown, evidence-based therapy approaches are still lacking. This has increased the need for basic research efforts into animal models for DMD. Here, we characterized in detail the cardiovascular abnormalities of Dmdmdx rats, with the aim of determining the suitability of this recently established dystrophin-deficient small animal as a model for DMD.Various methods were applied to compare cardiovascular properties between wild-type and Dmdmdx rats, and to characterize the Dmdmdx cardiomyopathy. These methods comprised echocardiography, invasive assessment of left ventricular hemodynamics, examination of adverse remodeling and endothelial cell inflammation, and evaluation of vascular function, employing wire myography. Finally, intracellular Ca2+ transient measurements, and recordings of currents through L-type Ca2+ channels were performed in isolated single ventricular cardiomyocytes. We found that, similar to respective observations in DMD patients, the hearts of Dmdmdx rats show significantly impaired cardiac function, fibrosis and inflammation, consistent with the development of a dilated cardiomyopathy. Moreover, in Dmdmdx rats, vascular endothelial function is impaired, which may relate to inflammation and oxidative stress, and Ca2+ handling in Dmdmdx cardiomyocytes is abnormal.These findings indicate that Dmdmdx rats represent a promising small-animal model to elucidate mechanisms of cardiomyopathy development in the dystrophic heart, and to test mechanism-based therapies aiming to combat cardiovascular complications in DMD.

The bradycardic agent ivabradine decreases conduction velocity in the AV node and in the ventricles in-vivo.

Ivabradine blocks hyperpolarisation-activated cyclic nucleotide-gated (HCN) channels, thereby lowering the heart rate, an action that is used clinically for the treatment of heart failure and angina pectoris. We and others have shown previously that ivabradine, in addition to its HCN channel blocking activity, also inhibits voltage-gated Na channels in vitro at concentrations that may be clinically relevant. Such action may reduce conduction velocity in cardiac atria and ventricles. Here, we explore the effect of administration of ivabradine on parameters of ventricular conduction and repolarization in the surface ECG of anesthetized mice. We found that 5 min after i.p. administration of 10 mg/kg ivabradine spontaneous heart rate had declined by ~13%, which is within the range observed in human clinical studies. At the same time a significant increase in QRS duration by ~18% was observed, suggesting a reduction in ventricular conduction velocity. During transesophageal pacing at heart rates between 100 and 220 beats/min there was no obvious rate-dependence of ivabradine-induced QRS prolongation. On the other hand, ivabradine produced substantial rate-dependent slowing of AV nodal conduction. We conclude that ivabradine prolongs conduction in the AV-node and in the ventricles in vivo.

Reduced Na+ current in Purkinje fibers explains cardiac conduction defects and arrhythmias in Duchenne muscular dystrophy.

Cardiac arrhythmias significantly contribute to mortality in Duchenne muscular dystrophy (DMD), a degenerative muscle disease triggered by mutations in the gene encoding for the intracellular protein dystrophin. A major source for the arrhythmias in patients with DMD is impaired ventricular impulse conduction, which predisposes for ventricular asynchrony, decreased cardiac output, and the development of reentrant mechanisms. The reason for ventricular conduction impairments and the associated arrhythmias in the dystrophic heart has remained unidentified. In the present study, we explored the hypothesis that dystrophin-deficient cardiac Purkinje fibers have reduced Na+ currents (INa), which would represent a potential mechanism underlying slowed ventricular conduction in the dystrophic heart. Therefore, by using a Langendorff perfusion system, we isolated Purkinje fibers from the hearts of adult wild-type control and dystrophin-deficient mdx mice. Enhanced green fluorescent protein (eGFP) expression under control of the connexin 40 gene allowed us to discriminate Purkinje fibers from eGFP-negative ventricular working cardiomyocytes after cell isolation. Finally, we recorded INa from wild-type and dystrophic mdx Purkinje fibers for comparison by means of the whole cell patch clamp technique. We found substantially reduced INa densities in mdx compared with wild-type Purkinje fibers, suggesting that dystrophin deficiency diminishes INa. Because Na+ channels in the Purkinje fiber membrane represent key determinants of ventricular conduction velocity, we propose that reduced INa in Purkinje fibers at least partly explains impaired ventricular conduction and the associated arrhythmias in the dystrophic heart.NEW & NOTEWORTHY Dystrophic cardiac Purkinje fibers have abnormally reduced Na+ current densities. This explains impaired ventricular conduction in the dystrophic heart.

Oral batyl alcohol supplementation rescues decreased cardiac conduction in ether phospholipid-deficient mice.

Plasmalogens (Pls) are a class of membrane phospholipids which serve a number of essential biological functions. Deficiency of Pls is associated with common disorders such as Alzheimer's disease or ischemic heart disease. A complete lack of Pls due to genetically determined defective biosynthesis gives rise to rhizomelic chondrodysplasia punctata (RCDP), characterized by a number of severe disabling pathologic features and death in early childhood. Frequent cardiac manifestations of RCDP include septal defects, mitral valve prolapse, and patent ductus arteriosus. In a mouse model of RCDP, reduced nerve conduction velocity was partially rescued by dietary oral supplementation of the Pls precursor batyl alcohol (BA). Here, we examine the impact of Pls deficiency on cardiac impulse conduction in a similar mouse model (Gnpat KO). In-vivo electrocardiographic recordings showed that the duration of the QRS complex was significantly longer in Gnpat KO mice than in age- and sex-matched wild-type animals, indicative of reduced cardiac conduction velocity. Oral supplementation of BA for 2 months resulted in normalization of cardiac Pls levels and of the QRS duration in Gnpat KO mice but not in untreated animals. BA treatment had no effect on the QRS duration in age-matched wild-type mice. These data suggest that Pls deficiency is associated with increased ventricular conduction time which can be rescued by oral BA supplementation.

Data on the power of high betatrophin to predict cardiovascular deaths in coronary patients.

Betatrophin is a protein which is produced by the liver and by adipose tissue. There are no clear data about serum betatrophin's cardiovascular role and it is unknown, whether betatrophin is associated with the risk of cardiovascular death. This article provides additional data on the association of betatrophin with its power to predict cardiovascular death in coronary patients. In addition, this data article demonstrates the performance of betatrophin as a biomarker using c-statistics. Analyzed data was derived from 553 coronary patients. Betatrophin was measured in serum samples and cardiovascular deaths were recorded for a median of 7.1 years. This data article is related to a research article titled "High betatrophin in coronary patients protects from cardiovascular events" [1].

Neuronal nitric oxide synthase regulation of calcium cycling in ventricular cardiomyocytes is independent of Cav1.2 channel modulation under basal conditions.

Neuronal nitric oxide synthase (nNOS) is considered a regulator of Cav1.2 L-type Ca2+ channels and downstream Ca2+ cycling in the heart. The commonest view is that nitric oxide (NO), generated by nNOS activity in cardiomyocytes, reduces the currents through Cav1.2 channels. This gives rise to a diminished Ca2+ release from the sarcoplasmic reticulum, and finally reduced contractility. Here, we report that nNOS inhibitor substances significantly increase intracellular Ca2+ transients in ventricular cardiomyocytes derived from adult mouse and rat hearts. This is consistent with an inhibitory effect of nNOS/NO activity on Ca2+ cycling and contractility. Whole cell currents through L-type Ca2+ channels in rodent myocytes, on the other hand, were not substantially affected by the application of various NOS inhibitors, or application of a NO donor substance. Moreover, the presence of NO donors had no effect on the single-channel open probability of purified human Cav1.2 channel protein reconstituted in artificial liposomes. These results indicate that nNOS/NO activity does not directly modify Cav1.2 channel function. We conclude that-against the currently prevailing view-basal Cav1.2 channel activity in ventricular cardiomyocytes is not substantially regulated by nNOS activity and NO. Hence, nNOS/NO inhibition of Ca2+ cycling and contractility occurs independently of direct regulation of Cav1.2 channels by NO.

High betatrophin in coronary patients protects from cardiovascular events.

BACKGROUND AND AIMS: Betatrophin, also known as angiopoietin-like protein 8 (ANGPTL8) or lipasin, is a nutritionally-regulated mammalian-specific protein secreted by the liver and adipose tissue. Many conflicting data exist with respect to its association with type 2 diabetes mellitus (T2DM), insulin resistance, and lipid markers, but no data are available on its association with cardiovascular risk. METHODS: We measured betatrophin in 553 coronary patients undergoing coronary angiography for the evaluation of established or suspected stable coronary artery disease (CAD) and prospectively recorded cardiovascular events during a follow-up of up to 8 years. RESULTS: During follow-up, 201 patients suffered a cardiovascular event and 64 died from cardiovascular causes. High betatrophin (upper tertile) was significantly and inversely associated with cardiovascular events both univariately (HR = 0.64 [95%CI 0.47-0.87], p = 0.004) and after full adjustment including the status of CAD and T2DM (adj. HR = 0.55 [95%CI 0.40-0.76], p < 0.001). The inclusion of betatrophin into a basic prediction model for the cardiovascular event risk significantly improved the model performance (NRI = 0.728, p < 0.001). CONCLUSIONS: This study is the first to show that betatrophin predicts cardiovascular events independently of conventional risk factors including the presence of CAD and T2DM.

Data on the association between CTRP1 and future major adverse cardiovascular events in patients undergoing coronary angiography.

This article provides additional data on the association of the new adipokine CTRP1 with the incidence of future major adverse cardiovascular events in a prospective cohort of patients undergoing coronary angiography. In this regard, multivariable Cox proportional hazards models taking into account cardiac risk markers are presented. Additionally, data on the impact of baseline variables including metabolic traits and co-morbidities on the incidence of future major adverse cardiovascular events are shown. This data article is associated to the research article titled 'The Novel Adipokine CTRP1 is Significantly Associated with the Incidence of Major Adverse Cardiovascular Events' Muendlein et al., 2019.

Pharmacological Profile of the Bradycardic Agent Ivabradine on Human Cardiac Ion Channels.

BACKGROUND/AIMS: Ivabradine lowers the heart rate by inhibition of hyperpolarisation-activated cyclic nucleotide-gated (HCN) channels mediating the 'funny' pacemaker current If in the sinoatrial node. It is clinically approved for the treatment of heart failure and angina pectoris. Due to its proposed high selectivity for If administration of ivabradine is not associated with the side effects commonly observed following the application of other heart rate lowering agents. Recent evidence, however, has shown significant affinity of ivabradine towards Kv11.1 (ether-a-go-go related gene, ERG) potassium channels. Despite the inhibition of Kv11.1 channels by ivabradine, cardiac action potential (AP) duration and heart rate corrected QT interval (QTc) of the human electrocardiogram (ECG) were not prolonged. We thus surmised that compensatory mechanisms might counteract the drug's inhibitory action on Kv11.1. METHODS: The effects of ivabradine on human Kv11.1 and Kv7.1 potassium, Cav1.2 calcium, and Nav1.5 sodium channels, heterologously expressed in tsA-201 cells, were studied in the voltage-clamp mode of the whole cell patch clamp technique. In addition, changes in action potential parameters of human induced pluripotent stem cell (iPSC) derived cardiomyocytes upon application of ivabradine were studied with current-clamp experiments. RESULTS: Here we show that ivabradine exhibits significant affinity towards cardiac ion channels other than HCN. We demonstrate for the first time inhibition of human voltage-gated Nav1.5 sodium channels at therapeutically relevant concentrations. Within this study we also confirm recent findings of human Kv11.1 inhibition by low µM concentrations of ivabradine and observed no prolongation of ventricular-like APs in cardiomyocytes derived from iPSCs. CONCLUSION: Our results provide an explanation why ivabradine, despite its affinity for Kv11.1 channels, does not prolong the cardiac AP and QTc interval. Furthermore, our results suggest the inhibition of voltage-gated Nav1.5 sodium channels to underlie the recent observations of slowed atrioventricular conduction by increased atrial-His bundle intervals upon administration of ivabradine.

The novel adipokine CTRP1 is significantly associated with the incidence of major adverse cardiovascular events.

BACKGROUND AND AIMS: The recently identified adiponectin paralogue C1q and tumor necrosis factor-related protein 1 (CTRP1) has been associated with obesity-linked disorders and coronary atherosclerosis. So far, the impact of circulating CTRP1 on the incidence of future cardiovascular events is unclear. Therefore, we aimed at investigating the association between CTRP1 and future cardiovascular risk. METHODS: We measured CTRP1 serum levels in 539 patients undergoing coronary angiography for the evaluation of established or suspected stable coronary artery disease (CAD). Prospectively, we recorded major adverse cardiovascular events (MACE), defined as the incidence of cardiovascular death, non-fatal myocardial infarction and non-fatal stroke over a follow-up period of 8 years. RESULTS: At baseline, obesity, the metabolic syndrome, type 2 diabetes, and non-alcoholic fatty liver disease were significantly associated with increased CTRP1 (all p-values ≤0.001). Prospectively, MACE rates were lowest in the first quartile (15.3%) and increased over the second (23.7%) to the third and fourth quartile (each 29.0%; ptrend = 0.008). Moreover, after multivariable adjustment, CTRP1 was significantly associated with future MACE, with adjusted HRs of 1.83 [1.04-3.23]; p=0.037, 2.16 [1.25-3.75]; p=0.006, and 1.80 [1.03-3.15]; p=0.038, for CTRP1 quartiles two, three and four, respectively, when compared to quartile one. CONCLUSIONS: We conclude that high serum levels of CTRP1 are significantly associated with future MACE.

Voltage-Dependent Sarcolemmal Ion Channel Abnormalities in the Dystrophin-Deficient Heart.

Mutations in the gene encoding for the intracellular protein dystrophin cause severe forms of muscular dystrophy. These so-called dystrophinopathies are characterized by skeletal muscle weakness and degeneration. Dystrophin deficiency also gives rise to considerable complications in the heart, including cardiomyopathy development and arrhythmias. The current understanding of the pathomechanisms in the dystrophic heart is limited, but there is growing evidence that dysfunctional voltage-dependent ion channels in dystrophin-deficient cardiomyocytes play a significant role. Herein, we summarize the current knowledge about abnormalities in voltage-dependent sarcolemmal ion channel properties in the dystrophic heart, and discuss the potentially underlying mechanisms, as well as their pathophysiological relevance.

Data on the power of the creatinine to uromodulin ratio in serum to predict cardiovascular events in coronary patients.

Uromodulin is a protein which is produced by the tubular cells of the thick ascending limb in the kidneys and the creatinine to uromodulin ratio in serum recently has attracted interest as a marker of kidney disease. Whether this ratio also is associated with cardiovascular event risk is unknown. This article provides additional data on the association of the creatinine to uromodulin ratio with its power to predict cardiovascular events and major cardiovascular events in coronary patients. In addition, this data article demonstrates the performance of the creatinine to uromodulin ratio as a biomarker using c-statistics. Analyzed data was derived from 529 coronary patients. Uromodulin and creatinine were measured and cardiovascular events were recorded for up to 8 years. This data article is related to a research article titled "Serum Uromodulin is a predictive biomarker for cardiovascular events and overall mortality in coronary patients" [1].

Serum uromodulin is a predictive biomarker for cardiovascular events and overall mortality in coronary patients.

BACKGROUND: Uromodulin is a protein produced exclusively by the kidneys and present in urine and blood. In contrast to weak and in part contradictory study data on uromodulin in urine samples, the analysis of serum samples recently proved uromodulin's value as superior biomarker for ongoing kidney disease. Whether serum uromodulin is associated with cardiovascular event risk and whether it has predictive power for overall mortality is still unknown and has been evaluated in the present study. METHODS: We measured uromodulin in a series of 529 patients without acute coronary syndrome undergoing coronary angiography for the evaluation of established or suspected stable coronary artery disease (CAD) and prospectively recorded mortality as well as cardiovascular events in our patients during a follow-up of up to 8years. RESULTS: We recorded 95 deaths and 145 cardiovascular events over 8years. Serum uromodulin proved protective for overall mortality (HR=0.56 [95%CI 0.43-0.72]; p<0.001), even after full adjustment including eGFR, current smoking, diabetes, and CAD status (adj. HR=0.57 [95%CI 0.37-0.89]; p=0.014). Patients in the lowest tertile of serum uromodulin had a significantly higher cardiovascular event risk compared to patients in the medium and highest tertile (HR=of 1.45 (95%CI 1.04-2.02, p=0.027). The ratio between creatinine and uromodulin was significantly associated with kidney function (r=-0.322; p<0.001) and significantly predicted the incidence of cardiovascular events (HR of 1.26 [95%CI 1.12-1.41], p<0.001) and major cardiovascular events (HR of 1.37 [95%CI 1.21-1.56], p<0.001). CONCLUSION: We conclude that serum uromodulin is a valuable biomarker to predict overall mortality and cardiovascular events.

Molecular analysis of Cryptosporidium from cattle from five states of Peninsular Malaysia.

Despite the importance of the cattle industry in Malaysia, there are very few studies of the diversity and public health significance of bovine cryptosporidiosis in this country. In the present study, we used a PCR-based approach to detect and genetically characterize Cryptosporidium DNA in faecal samples from a cohort of 215 asymptomatic cattle (of different ages) from six farms from five states of Peninsular Malaysia. Cattle on four of the six farms were test-positive for Cryptosporidium, with an overall prevalence of 3.2%. Cryptosporidium bovis and Cryptosporidium ryanae were detected in two (0.9%) and five (2.3%) samples tested; this low prevalence likely relates to the age of the cattle tested, as most (73%) of the samples tested originated from cattle that were ≥2 years of age. Future studies should investigate the zoonotic potential of Cryptosporidium in pre-weaned and weaned calves in rural communities of Malaysia.

Genetic analysis of Giardia and Cryptosporidium from people in Northern Australia using PCR-based tools.

To date, there has been limited genetic study of the gastrointestinal pathogens Giardia and Cryptosporidium in northern parts of Australia. Here, PCR-based methods were used for the genetic characterization of Giardia and Cryptosporidium from 695 people with histories of gastrointestinal disorders from the tropical North of Australia. Genomic DNAs from fecal samples were subjected to PCR-based analyses of regions from the triose phosphate isomerase (tpi), small subunit (SSU) of the nuclear ribosomal RNA and/or the glycoprotein (gp60) genes. Giardia and Cryptosporidium were detected in 13 and four of the 695 samples, respectively. Giardia duodenalis assemblages A and B were found in 4 (31%) and 9 (69%) of the 13 samples in persons of <9 years of age. Cryptosporidium hominis (subgenotype IdA18), Cryptosporidium mink genotype (subgenotype IIA16R1) and C. felis were also identified in single patients of 11-21 years of age. Future studies might focus on a comparative study of these and other protists in rural communities in Northern Australia.