Adaptive Time Step for Cardiac Myocyte Models

AbstractThe modeling of the electrical activity of the heart is of great medical and scientific interest as it provides a way to better understand the underlying biophysical phenomena, supports the development of new techniques for diagnoses and serves as a platform for drug tests. At cellular level, the electrical activity of cardiac myocytes may be simulated by solving a system of ordinary di_erential equations (ODEs) describing the electrical behavior of the cell membrane. Because the biophysical processes underlying this phenomenon are non-linear and change very rapidly, the ODE system is challenging to solve numerically. Furthermore, the implementation of these models is a hard task. This paper presents a tool to describe models using Ordinary Differential Equations. It is based on CellML standard and automatically generates C++ source-code, with numerical methods to solve the model's equations. The aim of this work is to present a numerical method with adaptive time step based on the Euler Method and Second Order Runge-Kutta method. The proposed method accelerated the execution and kept numerical errors under control. Preliminary results suggest this adaptive method is up to 25 times faster than the explicit Euler method with fixed time step

Visions of Cardiomyocyte

In the field of cardiology, some of the most dramatic advances in recent years have come from understanding the molecular and cellular basis of cardiovascular disease. Knowledge of the pathological basis of disease in some cases allows the development of new strategies for prevention and treatment. This book was planned not only to convey new facts on cardiovascular diseases, but also to boost the excitement and challenges of research in the dynamic area of modern molecular and cellular biology of cardiology. The integration of multilevel biological data and the connection with clinical practice reveal the potential of personalized medicine, with future implications for prognosis, diagnosis, and management of cardiovascular diseases

The effects of Trypanosoma brucei and mammalian-derived extracellular cathepsin-L on myocardial function

African trypanosomiasis is a neglected tropical disease affecting both animals and humans in sub-Saharan Africa. The disease is caused bythe protozoan parasite Trypanosoma brucei, which is transmitted by the tsetse fly (Glossina sp.) vector. In animals, infection leads to severe muscle atrophy and anaemia resulting in significant production and economic losses. In humans, infection leads to both neurological and cardiac dysfunction and can be fatal if untreated. While the neurological-related pathogenesis is well studied, and indeed is responsible for the colloquial name “Sleeping Sickness”, the cardiac pathogenesis remains unknown. Previous studies interpreted cardiac dysfunction as being due to immune/inflammatory responses. However, recent work examining the parasite’s interaction with the blood brain barrier, the traversal of which is important for development of neurological signs, has identified direct immune/inflammatory independent mechanisms involving calcium (Ca2+) signalling. The current study exposed isolated ventricular cardiomyocytes and adult rat hearts to T. brucei to test whether trypanosomes can alter Ca2+ signalling and cardiac function independent of a systemic immune/inflammatory response. Using a high-throughput method of observing spontaneous contractile activity in isolated cardiomyocytes, we were able to determine that the presence of T. b. brucei parasites resulted in more cardiomyocytes exhibiting spontaneous contractile events. Moreover, when the parasites were removed by careful centrifugation, the culture supernatant had the same effect. Confocal Ca2+ imaging identified an increase in the frequency of arrhythmogenic spontaneous diastolic sarcoplasmic reticulum (SR)-mediated Ca2+ release (Ca2+ waves). Studies utilising specific inhibitors, recombinant protein and RNA interference all demonstrated that this altered SR function was due to cathepsin-L; a cysteine protease produced by T. brucei (TbCatL). Experiments utilising a Langendorff perfusion method revealed that trypanosome culture supernatant could induce ventricular premature contractions in 50% of a cohort of ex vivo whole rat hearts. Mechanistic experiments were performed on single isolated cardiomyocytes stimulated at 1.0 Hz and perfused first with control media followed by trypanosome culture supernatant. The protocol utilised triple caffeine applications: (i) prior to stimulation to empty the SR of Ca2+, (ii) after perfusion with control media and after supernatant to determine the SR Ca2+ content and sarcolemmal extrusion of Ca2+ following each solution. Results were normalised to a parallel set of cardiomyocytes perfused with control media only as time controls. These experiments revealed a 10-15% increase in SR Ca2+ reuptake by the SR Ca2+ ATPase (SERCA) but a reduced SR Ca2+ content suggesting a concomitant increase in SR-mediated Ca2+ leak. This conclusion was supported by the data demonstrating that TbCatL increased Ca2+ wave frequency. These effects were abolished by autocamtide-2-related inhibitory peptide (AIP), highlighting a role for Ca2+/calmodulin kinase II (CaMKII) in the TbCatL action on SR function. When cytosolic diastolic Ca2+ was measured in cardiomyocytes with SR function inhibited by ryanodine and thapsigargin, trypanosome supernatant prevented a decline in cytosolic diastolic Ca2+ that was observed in control media. AIP did not abolish this effect suggesting that TbCatL may raise diastolic Ca2+ that could activate CaMKII leading to the observed effects. These data demonstrated for the first time that African trypanosomes alter cardiac function independent of a systemic immune response via a mechanism involving extracellular cathepsin-L-mediated changes in SR function. Utilising the same (culture adapted and monomorphic) strain of T. brucei as the in vitro experiments, Lister 427, in a rat model of infection we found no significant increase in the arrhythmia frequency as measured by a 15 min electrocardiogram (ECG). However, when hearts were removed and Langendorff perfused with the addition of isoproterenol the arrhythmia frequency was increased. When the pleomorphic strain T. b. brucei TREU 927 was used in rats with continuous ECG recording from biopotential telemetry there was a significant increase in arrhythmia frequency in the infected rats. When hearts were removed and Langendorff perfused with isoproterenol there was a similar increase in arrhythmia frequency as observed with the 427 infected hearts. This suggests that a cardiac dysfunction phenotype is present during trypanosome infections in an animal model providing the basis for future therapeutic work. The relationship between arrhythmogenic SR-mediated Ca2+ release and TbCatL has parallels with endogenous extracellular cathepsin-L (CatL). It has been demonstrated that a basal level of CatL is necessary for normal cardiac function. However, in coronary heart disease (CHD) CatL levels are increased in the serum of patients correlating with the severity of disease. The effects of raised CatL on cardiac function remain unknown. Work in our lab has identified that ex vivo Langendorff perfused hearts that have undergone a 30 min period of ischaemia followed by 90 min reperfusion show greater CatL activity in coronary effluent than hearts perfused without ischaemia. In addition, preliminary data collected in this thesis suggest that human patients that have suffered a myocardial infarction and have undergone reperfusion via percutaneous coronary intervention (PCI) showed higher CatL levels in post-reperfusion serum samples compared to pre-reperfusion serum. When severity of heart function in patients (measured as left ventricular volume at systole and diastole, ejection fraction, infarct size and area at risk) was assessed by magnetic resonance imaging (MRI) in a preliminary study, there was a positive correlation with serum CatL levels. Using recombinant CatL on isolated rat ventricular cardiomyocytes it was found that the SR Ca2+ content and the stimulated Ca2+ transient were significantly reduced in a concentration dependent manner. This suggests a CatL dependent SR dysfunction. This conclusion was supported by an increase in Ca2+ wave frequency measured by confocal Ca2+ imaging in isolated cardiomyocytes. The work in this thesis demonstrates a role for both mammalian-derived and exogenous extracellular cathepsin-L proteases in arrhythmogenic SR-mediated Ca2+ release

Stem Cell Research on Cardiology

Even today, cardiovascular diseases are the main cause of death worldwide, and therapeutic approaches are very restricted. Due to the limited regenerative capabilities of terminally differentiated cardiomyocytes post injury, new strategies to treat cardiac patients are urgently needed. Post myocardial injury, resident fibroblasts begin to generate the extracellular matrix, resulting in fibrosis, and finally, cardiac failure. Recently, preclinical investigations and clinical trials raised hope in stem cell-based approaches, to be an effective therapy option for these diseases. So far, several types of stem cells have been identified to be promising candidates to be applied for treatment: cardiac progenitor cells, bone marrow derived stem cells, embryonic and induced pluripotent stem cells, as well as their descendants. Furthermore, the innovative techniques of direct cardiac reprogramming of cells offered promising options for cardiovascular research, in vitro and in vivo. Hereby, the investigation of underlying and associated mechanisms triggering the therapeutic effects of stem cell application is of particular importance to improve approaches for heart patients. This Special Issue of Cells provides the latest update in the rapidly developing field of regenerative medicine in cardiology

Characterization of the cardiac pacemaker and pathological responses to cardiac diseases in Atlantic salmon (Salmo salar L.)

Doctoral thesis (PhD) – University of Nordland, 2012The heart is considered the powerhouse of the cardiovascular system. In this thesis, characterization of cardiac pacemaker and potential biomarkers of cardiac diseases of Atlantic salmon (Salmo salar L.) were discussed. The normal performance of the heart requires balance, whether for coronary circulation, the synchrony and effectiveness of myocardial contractions or the influence of its nerves and ganglion cells. Neural control is equally important for the power and complexity of the heart. The pacemaker is the cardiac neural tissue that is responsible for initiation and control of heart beat. This thesis described the location of cardiac pacemaker of Atlantic salmon at the junction of sinus venosus and atrium. Morphologically, the pacemaker tissue was composed of lightly stained plexiform modified cardiomyocytes, wavy appearing nerve bundles with oval, wavy, elongated nuclei with pointed ends and large round to pear–shaped postganglionic nerve cell bodies (ganglion cells). Novel immuno–localization of the natriuretic peptides such as salmon cardiac peptide (sCP) and ventricular natriuretic peptide (VNP) in the postganglionic nerve cell bodies at SA junction was demonstrated, suggesting their neuromodulatory/neurotransmitter roles in teleosts (Atlantic salmon). Besides CD3 as a general T cell marker, novel CD3 immunostaining in the postganglionic nerve cell bodies of cardiac pacemaker of Atlantic salmon was demonstrated, suggesting additional roles of CD3 in teleosts and shared similar patterns to mammals. Atlantic salmon aquaculture industry bears huge losses due to viral diseases including cardiac viral diseases. Heart and skeletal muscle inflammation (HSMI), cardiomyopathy syndrome (CMS) and pancreas disease (PD) are viral diseases of marine farmed Atlantic salmon which mainly affect the heart in addition to other vital organs. The main findings of these diseases are necrosis and mononuclear inflammatory cells infiltrates affecting different regions of the heart. To identify the potential biomarkers of cardiac diseases, blood biochemistry markers were correlated to the CMS– and HSMI–affected Atlantic salmon. Candidate biomarkers included serum enzymes such as creatine kinase (CK) and lactate dehydrogenase (LDH) levels were measured and significantly correlated to the cardiac pathology of HSMI–affected fish, suggesting promising potential biomarkers to predict the disease (HSMI). Non–significant correlations of serum enzymes to CMS–affected fish suggested that serum enzymes could be used to differentiate between the HSMI and CMS. Further, immunohistochemistry was performed to identify potential markers of cardiac pathological changes of Atlantic salmon affected with similar cardiac diseases (CMS, HSMI and PD). The spectrum of inflammatory cells associated with the cardiac pathology consisted of mainly CD3Ɛ+ T lymphocytes and lymphocytic response dominated over granulocytes in the CMS–, PD– and HSMI–affected hearts. Macrophage–like and eosinophilic granular cells were identified by rTNFα antiserum in all three investigated diseased hearts, particularly in areas surrounding lesions. MHC class II antiserum identified strong, moderate and low levels of immunopositive cells in diseased hearts in HSMI, CMS and PD respectively. The CD3, MHC class II, PCNA, TNFα, caspase 3 and TUNEL staining were mostly confined to lesioned areas in the diseased hearts, pointing to pathological changes and suggesting the markers appear promising as a supplementary tool in the identification of lesioned areas in the investigated diseased hearts. Interestingly, the apparently similar diseases exhibited differences in the immunopathological responses in Atlantic salmon

Predicting Risk of Emerging Cardiotoxicity

Smoking, hypercholesterolemia, hyperlipidemia, obesity, diabetes, insulin resistance and family history all are well established general risk factors broadly associated with injury in the cardiovascular system. Similarly, echocardiography, electrocardiography, MRI, PET scans and circulating biomarkers like cardiac Troponin (cTn) provide indications that injury has occurred. Traditionally, cardiovascular injury has been attributed to conditions that exacerbate the potential for ischemia, either by producing excessive metabolic/work demands or by impairing the perfusion necessary to support the metabolic/work demands. This review summarizes additional factors that are underappreciated in contributing to the risk of injury, such as iatrogenic injury secondary to treatment for other conditions, infection, environmental exposures, and autoimmune processes

Towards cardiac cell therapy

Tese de doutoramento em Biologia (Biologia Molecular), apresentada à Universidade de Lisboa através da Faculdade de Ciências, 200

The molecular genetics of familial cardiomyopathy

Introduction The cardiomyopathies are responsible for approximately 5.9 of 100,000 deaths in the general global population and in sub-Saharan Africa (SSA), these myocardial diseases are observed in 21.4% of patients with heart failure. The precise etiology of the cardiomyopathies is currently not well known and through our research we aim to contribute to the genetic landscape and bridge the gaps in knowledge for the different cardiomyopathies as SSA could provide some very important insights into the cardiomyopathies and identify other possible disease mechanisms. Methods Through next generation sequencing techniques such as whole exome sequencing and targeted resequencing we studied three South African families with severe cardiomyopathy. Clinical diagnosis and recruitment of cardiomyopathy patients into the study was done at Groote Schuur Hospital, Cape Town by a panel of experts. Next generation sequencing data was analysed and filtered through various stringent criteria and the final list of variants were validated through Sanger sequencing. Results In the first multi-generational family with severe dilated cardiomyopathy (DCM) (DCM 334), we identified a pathogenic DMPK c.1067C>T(p.P356L) variant in the proband and her affected father. We also screened a cohort of 542 cardiomyopathy probands though Sanger sequencing of the DMPK gene and identified the DMPK c.1477C>T(p.R493C) variant as a variant of unknown significance. We then investigated a three-generation family with four affected family members who were also affected with severe DCM (DCM343). We used whole exome sequencing and identified the pathogenic BAG3 c.925C>T (p.R309Ter) variant as the cause of disease within this family. Viral infection, anti-hypertensive medication and genetic modifiers in RYR1 and NEB contributed to the variable phenotype among the individuals with the BAG3 variant. Through targeted resequencing we also identified the same pathogenic BAG3 variant in 2 of the 634 cardiomyopathy probands screened. In the third family, we investigated a South African family affected with severe arrhythmogenic cardiomyopathy (ACM). We used whole exome sequencing and targeted resequencing in combination and identified the pathogenic PKP2 c.2197_2202InsGdelCACACC (p.H733Afs*8) as the cause of disease in the proband and his father. We also present evidence of the ALPK3 c.2701C>T(p.Q901Ter) variant modifying the phenotypic manifestation which correlates with the variable penetrance that is seen among ACM families. Conclusion Through this project, we have identified many firsts. To the best of our knowledge, we are the first to show that DMPK is associated with primary DCM in severely affected young patients. As a first for South Africa, we not only identified the pathogenic BAG3 variant in a family with severe DCM, but we also identified the same variant in two additional probands, raising the possibility of a founder effect. In the third and final family with ACM, we identified the pathogenic PKP2 variant as the cause of disease within this family with the novel ALPK3 variant acting as a possible modifier. Our research has added to what is currently known about the cardiomyopathies in Africa but there is still much work to be done as we believe we have just scratched the tip of the iceberg