Cardiac Myocyte Dysfunction Research Articles

Patterns of left ventricular recovery in patients with heart failure with mid-range ejection fraction

Abstract Background Heart failure with mid-range ejection fraction (HFmEF) represents a new classification of heart failure with intermediate clinical characteristics to those with HF with reduced ejection fraction (HFrEF) and HF with preserved ejection fraction (HFpEF). A proportion of HFmEF is attributed to atrio-ventricular dyssynchrony from atrial fibrillation (AF) as opposed to a primary cardiomyopathy with intrinsic cardiac myocyte dysfunction. Purpose We aim to compare the rate of left ventricular ejection fraction (LVEF) recovery in those with AF-mediated cardiomyopathy compared to those with primary myocyte dysfunction. Methods Consecutive patients with stable non-ischaemic cardiomyopathy with LVEF 40–49% on transthoracic echocardiography (TTE) were recruited from our institution's heart failure clinic and followed for 18 months. Patients with ischaemic, valvular or congenital heart disease, incomplete follow-up or poor quality TTE images were excluded. Eligible patients were separated into two groups: AF-mediated (n=44); and primary myocyte dysfunction (n=116). Results A total of 160 patients (62.1±16.4 years, 62% men) were included. There was no significant difference in age (p=0.06) and gender (p=0.59). Comorbid AF was higher in those with AF-mediated HFmEF (100 vs 28.4%; p<0.01), otherwise no significant differences in clinical history was found between groups. AF-mediated HFmEF had lower rates of cardiac-specific beta-blocker use (15.9 vs 47.4%; p<0.01). Baseline TTE showed similar LVEF and LV global longitudinal strain. On log-rank analysis there was no significant difference in all-cause death (p=0.75), or HF-related hospitalisation (p=0.14), however, higher rates of LVEF recovery were observed in the AF-mediated HFmEF group (p<0.01). See figure 1. Conclusion There were higher rates of LVEF recovery in those with AF-mediated HFmEF compared to those with a primary myocardial disorder despite lower rates of cardiac-specific beta-blocker use. This did not translate to improvements in intermediate-term survival or HF related hospitalisation. These findings provide insight into the natural history of the disorder and its clinical phenotype. Funding Acknowledgement Type of funding sources: None. Figure 1. Rate of LVEF Recovery

What's New in Shock, July 2021?

What's New in Shock, July 2021?

Modulations of Cardiac Functions and Pathogenesis by Reactive Oxygen Species and Natural Antioxidants

Homeostasis in the level of reactive oxygen species (ROS) in cardiac myocytes plays a critical role in regulating their physiological functions. Disturbance of balance between generation and removal of ROS is a major cause of cardiac myocyte remodeling, dysfunction, and failure. Cardiac myocytes possess several ROS-producing pathways, such as mitochondrial electron transport chain, NADPH oxidases, and nitric oxide synthases, and have endogenous antioxidation mechanisms. Cardiac Ca2+-signaling toolkit proteins, as well as mitochondrial functions, are largely modulated by ROS under physiological and pathological conditions, thereby producing alterations in contraction, membrane conductivity, cell metabolism and cell growth and death. Mechanical stresses under hypertension, post-myocardial infarction, heart failure, and valve diseases are the main causes for stress-induced cardiac remodeling and functional failure, which are associated with ROS-induced pathogenesis. Experimental evidence demonstrates that many cardioprotective natural antioxidants, enriched in foods or herbs, exert beneficial effects on cardiac functions (Ca2+ signal, contractility and rhythm), myocytes remodeling, inflammation and death in pathological hearts. The review may provide knowledge and insight into the modulation of cardiac pathogenesis by ROS and natural antioxidants.

Pharmacotherapeutic approaches targeting stable angina: simple solutions to complex problems

Cardiovascular diseases, especially coronary heart disease (CHD), are the leading cause of disability; various registry data show that the annual mortality rate of such patients is 2–3%. This explains the interest of practitioners in the pharmacotherapy of stable forms of coronary artery disease using current progress in the understanding of the pathogenesis of this disease and treatment compliance. Features of the pathogenesis of CHD in the form of increased myocardial oxygen demand, increased pre- and afterload on the performance of the heart necessitate the prescription of rhythm-reducing drugs such as beta-blockers, calcium channel blockers, ivabradine or their combinations, as well as nitric-containing drugs; trimetazidine, ranolazine for the purpose of myocardial cytoprotection. However, the use of hemodynamic drugs (beta-blockers, calcium channel blockers) does not always effectively relieve the symptoms of angina pectoris, even when used in combination with other drugs. This dictates the need to improve the drug effect on the ischemic myocardium with due account for the hypoxia-induced metabolic dysfunction of cardiac myocytes. In this regard, the use of trimetazidine at the initial stages of ischemia – at the level of metabolic dysfunction does not allow for the development of delayed complications: contractile disfunction of cardiac myocytes and myocardium in general. A wealth of clinical experience has been gained in the use of trimetazidine to treat stable angina pectoris in elderly patients, left ventricular dysfunction and symptoms of chronic heart failure. Drugs with a patient-friendly dosage regimen have been created to improve treatment compliance in patients with coronary artery disease. One of these drugs is once-daily modified release matrix tablets of myocardial cytoprotector Deprenorm OD, 70 mg. The creation of drugs with a patient-friendly dosage regimen will help boost patient compliance to medication and, as a result, reduce the frequency of angina attacks and improve the quality of life in this category of patients.

Patterns of Left Ventricular Recovery in Patients With Heart Failure With Mid-range Ejection Fraction

Heart failure with mid-range ejection fraction (HFmEF) represents a new classification of heart failure with intermediate clinical characteristics to those with HF with reduced ejection fraction (HFrEF) and HF with preserved ejection fraction (HFpEF). A proportion of HFmEF is attributed to atrio-ventricular dyssynchrony from atrial fibrillation (AF) as opposed to a primary cardiomyopathy with intrinsic cardiac myocyte dysfunction. We compared the rate of left ventricular ejection fraction (LVEF) recovery in those with AF-mediated cardiomyopathy compared to those with primary myocyte dysfunction.

PKCδ causes sepsis-induced cardiomyopathy by inducing mitochondrial dysfunction.

Sepsis-induced cardiomyopathy (SIC) is associated with increased patient mortality. At present, there are no specific therapies for SIC. Previous studies have reported increased reactive oxygen species (ROS) and mitochondrial dysfunction during SIC. However, a unifying mechanism remains to be defined. We hypothesized that PKCδ is required for abnormal calcium handling and cardiac mitochondrial dysfunction during sepsis and that genetic deletion of PKCδ would be protective. Polymicrobial sepsis induced by cecal ligation and puncture (CLP) surgery decreased the ejection fraction of wild-type (WT) mice but not PKCδ knockout (KO) mice. Similarly, WT cardiomyocytes exposed to lipopolysaccharide (LPS) demonstrated decreases in contractility and calcium transient amplitude that were not observed in PKCδ KO cardiomyocytes. LPS treatment decreased sarcoplasmic reticulum calcium stores in WT cardiomyocytes, which correlated with increased ryanodine receptor-2 oxidation in WT hearts but not PKCδ KO hearts after sepsis. LPS exposure increased mitochondrial ROS and decreased mitochondrial inner membrane potential in WT cardiomyocytes. This corresponded to morphologic changes consistent with mitochondrial dysfunction such as decreased overall size and cristae disorganization. Increased cellular ROS and changes in mitochondrial morphology were not observed in PKCδ KO cardiomyocytes. These data show that PKCδ is required in the pathophysiology of SIC by generating ROS and promoting mitochondrial dysfunction. Thus, PKCδ is a potential target for cardiac protection during sepsis.NEW & NOTEWORTHY Sepsis is often complicated by cardiac dysfunction, which is associated with a high mortality rate. Our work shows that the protein PKCδ is required for decreased cardiac contractility during sepsis. Mice with deletion of PKCδ are protected from cardiac dysfunction after sepsis. PKCδ causes mitochondrial dysfunction in cardiac myocytes, and reducing mitochondrial oxidative stress improves contractility in wild-type cardiomyocytes. Thus, PKCδ is a potential target for cardiac protection during sepsis.

Linking metabolic and contractile dysfunction in aged cardiac myocytes.

Aging is associated with declining cardiac contractile function as well as changes in metabolism and mitochondrial function. The relationship between age‐related changes in cardiac metabolism and declining cardiac contractile function has not been determined. In order to define the role energetics play in changes in contractile function, we measured mitochondrial NADH, [NADH]m, during continuous contractions of isolated left ventricular myocytes from young (Y) and old (O) FBN rats. Second, we explored the role of metabolic disruption with rotenone and increased workload with isoproterenol (ISO) had on age‐related changes in myocytes shortening. Single, intact myocytes were stimulated for 10 min of continuous contraction at either 2 Hz or 4 Hz while being perfused with Ringer's solution. Properties of shortening (peak shortening and rate of shortening) were measured at the onset (T0) and after 10 min (T10) of continuous contraction, and the decline in shortening over time (T10/T0) was determined. Although young and old myocytes had similar contractile function under resting conditions, old myocytes demonstrated decrements in [NADH]m during continuous stimulation, while young myocytes maintained constant [NADH]m over this time. In addition, old myocytes exhibited impaired contractile function to a workload (ISO) and metabolic (rotenone) stress compared to young myocytes. Taken together, these results demonstrated that old myocytes are susceptible to stress‐induced contractile dysfunction which may be related to altered cellular energetics.

Cardiac Protection of Valsartan on Juvenile Rats with Heart Failure by Inhibiting Activity of CaMKII via Attenuating Phosphorylation.

Background. This study was undertaken to determine relative contributions of phosphorylation and oxidation to the increased activity of calcium/calmodulin-stimulated protein kinase II (CaMKII) in juveniles with cardiac myocyte dysfunction due to increased pressure overload. Methods. Juvenile rats underwent abdominal aortic constriction to induce heart failure. Four weeks after surgery, rats were then randomly divided into two groups: one group given valsartan (HF + Val) and the other group given placebo (HF + PBO). Simultaneously, the sham-operated rats were randomly given valsartan (Sham + Val) or placebo (Sham + PBO). After 4 weeks of treatment, Western blot analysis was employed to quantify CaMKII and relative calcium handling proteins (RyR2 and PLN) in all groups. Results. The deteriorated cardiac function was reversed by valsartan treatment. In ventricular muscle cells of group HF + PBO, Thr287 phosphorylation of CaMKII and S2808 phosphorylation of RyR2 and PLN were increased and S16 phosphorylation of PLN was decreased compared to the other groups, while Met281 oxidation was not significantly elevated. In addition, these changes in the expression of calcium handling proteins were ameliorated by valsartan administration. Conclusions. The phosphorylation of Thr286 is associated with the early activation of CaMKII rather than the oxidation of Met281.

Epac activation inhibits IL-6-induced cardiac myocyte dysfunction

Pro-inflammatory cytokines are released in septic shock and impair cardiac function via the Jak-STAT pathway. It is well known that sympathetic and thus catecholamine signaling is activated thereafter to compensate for cardiac dysfunction. The mechanism of such compensation by catecholamine signaling has been traditionally understood to be cyclic AMP-dependent protein kinase (PKA)-mediated enforcement of cardiac contractility. We hypothesized that the exchange protein activated by cAMP (Epac), a newly identified target of cAMP signaling that functions independently of PKA, also plays a key role in this mechanism. In cultured cardiac myocytes, activation of Epac attenuated the inhibitory effect of interleukin-6 on the increase of intracellular Ca2+ concentration and contractility in response to isoproterenol, most likely through inhibition of the Jak-STAT pathway via SOCS3, with subsequent changes in inducible nitric oxide synthase expression. These findings suggest a new role of catecholamine signaling in compensating for cardiac dysfunction in heart failure. Epac and its downstream pathway may be a novel target for treating cardiac dysfunction in endotoxemia.

Abstract 402: Selective Protein Secretion Upon Endoplasmic Reticulum Stress Protects Cardiac Myocytes

Protein secretion is important for proper cardiac myocyte function. Many secreted proteins are synthesized and folded in the sarco- endo-plasmic reticulum (SR/ER). A number of diseases, including heart disease, alter the ER in ways that impair ER protein folding, causing ER stress, which can result in cardiac myocyte dysfunction and decreased viability. In studies aimed at assessing the effects of ER stress on cardiac myocyte viability, heart disease-related ER stress was mimicked by treating neonatal rat ventricular myocytes (NRVM) with either tunicamycin (TM) or thapsigargin (TG), which inhibit SR/ER protein glycosylation or decrease SR/ER calcium, respectively. When treated in high culture media volumes, both TM and TG caused cardiac myocyte death; however, in low culture media volumes, while TM still caused death, remarkably, TG was protective, suggesting that potentially protective factors were secreted in response to TG but not TM. To characterize these factors, the identities of proteins in control-, TM-, and TG-conditioned medium from NRVM were determined by proteomic approaches using high performance liquid chromatography and mass spectrometry. Twenty-four different proteins, known to be synthesized in the ER, were identified in control-conditioned medium. The levels of eighteen of these proteins, including extracellular matrix proteins, hormones, and growth factors were decreased in TM- and TG-conditioned medium. However, the levels of three SR/ER-resident, calcium-binding chaperones, glucose regulated protein 78 (GRP78), glucose regulated protein 94 (GRP94), and calreticulin were increased in TG-conditioned medium but not in TM-conditioned medium. Furthermore, we found that ischemia/reperfusion, which decreases SR/ER calcium, upregulated secretion of the proteins selectively secreted in response to TG. Thus, while ER stress mediated by TM or TG decreases the movement of most proteins through the secretory pathway, TG, which mimics the effects of heart disease on SR/ER calcium in cardiac myocytes, selectively enhances the secretion of a subset of proteins, which confer protection. Therefore, proteins once thought to be permanent residents of the SR/ER may have novel, extracellular, protective roles in the diseased heart.

Cardiac myocyte dysfunction induced by streptolysin O is membrane pore and calcium dependent.

Septic cardiomyopathy is a severe complication among some patients who develop group A streptococcal toxic shock syndrome. Despite the importance of cardiac dysfunction in determining prognosis, very little is known about mechanisms that reduce cardiac output in association with streptococcal infection. Here, we investigated the effects of streptococcal extracellular toxins on mechanical contractility of electrically paced primary murine cardiomyocytes. Our data demonstrate that streptolysin O (SLO) is the major streptococcal toxin responsible for cardiomyocyte contractile dysfunction. Streptolysin O dose-dependently affected cardiac myocyte function in discrete stages. Exposure to SLO caused a failure of cardiac cells to respond to electrical pacing, followed by spontaneous dysregulated contractions and augmented strength of contraction. Central to these SLO-mediated effects is a marked influx of calcium into the cytosol through SLO-mediated pores in the cytoplasmic membrane. Such calcium mobilization in response to SLO correlated temporally with hypercontractility and unpaced contractions. During continued exposure to SLO, cardiomyocytes exhibited periods of reversion to normal electrical pacing suggestive of membrane lesion repair and restoration of calcium handling. Together, these observations are consistent with the clinical observation that septic cardiomyopathy is a reversible condition in patients who survive streptococcal toxic shock syndrome. These data provide strong evidence that streptococcal exotoxins, specifically SLO, can directly impact cardiac mechanical function.

Effects of adding intravenous nicorandil to standard therapy on cardiac sympathetic nerve activity and myocyte dysfunction in patients with acute decompensated heart failure.

Nicorandil, an adenosine triphosphate-sensitive potassium channel opener, improves cardiac sympathetic nerve activity (CSNA) in ischemic heart disease or chronic heart failure. However, its effects on CSNA and myocyte dysfunction in acute heart failure (AHF) remain unclear. We investigated the effects of adding intravenous nicorandil to standard therapy on CSNA and myocyte dysfunction in AHF. We selected 70 patients with mild to moderate nonischemic AHF who were treated with standard conventional therapy soon after admission. Thirty-five patients were assigned to additionally receive intravenous nicorandil (4-12mg/h; group A), whereas the remaining patients continued their current drug regimen (group B). Delayed total defect score (TDS), delayed heart to mediastinum count (H/M) ratio, and washout rate (WR) were determined by (123)I-metaiodobenzylguanidine (MIBG) scintigraphy within 3days of admission and 4weeks later. High sensitivity troponin T (hs-TnT) level was also measured at the same time points. After treatment, MIBG scintigraphic parameters significantly improved in both groups. However, the extent of the changes in these parameters in group A significantly exceeded the extent of the changes in group B [TDS -11.3 ± 4.3 in group A vs -4.0 ± 6.0 in group B (p < 0.01); H/M ratio 0.31 ± 0.16 vs 0.14 ± 0.16 (p < 0.01); WR -13.8 ± 7.8% vs -6.1 ± 8.9% (p < 0.01)]. The hs-TnT level decreased significantly from 0.052 ± 0.043 to 0.041 ± 0.033ng/ml (p < 0.05) in group A, but showed no significant change in group B. Moreover, in both groups, no relationships between the extent of changes in MIBG parameters and hs-TnT level were observed. Adding intravenous nicorandil to standard therapy provides additional benefits for CSNA and myocyte dysfunction over conventional therapy alone in AHF patients. Furthermore, the mechanisms of improvement in CSNA and myocyte dysfunction after nicorandil treatment in AHF patients were distinct.

Mitochondrial calcium is decreased by high glucose and is improved by reduction of protein O‐GlcNAcylation in cardiac myocytes (1078.2)

Increased nuclear protein O‐linked β‐N‐acetylglucosamine glycosylation (O‐GlcNAcylation) mediated by high glucose treatment or the hyperglycemia of diabetes mellitus contributes to cardiac myocyte dysfunction. Mitochondrial proteins in cardiac myocytes are also submitted to O‐GlcNAcylation, however, whether excessive O‐GlcNAcylation alters mitochondrial function is incompletely studied. We have previously demonstrated decreased mitochondrial calcium concentration in cardiac myocytes exposed to high glucose. We hypothesize that excessive O‐GlcNAcylation may be responsible of this maladaptive phenomenon and that reducing excessive O‐GlcNAcylation may return mitochondrial calcium levels to normal. Our objective was to test this hypothesis, therefore, we incubated cultured neonatal mouse myocytes in high glucose (HG, 25mM) for 72 hours and inhibited O‐GlcNAcylation by adenoviral expression of a dominant negative mutant of the O‐GlcNAc transferase (dnOGT). As expected, mitochondrial calcium levels were reduced by 20% after HG exposure but were returned to control values after dnOGT expression. In addition, mitochondrial calcium uptake decreased by 52% in HG and was improved by expression of dnOGT, however, did not reach control values. We examined the mitochondrial calcium uniporter (MCU) and found that it is susceptible to be O‐GlcNAcylated and HG further increased O‐GlcNAcylation. In conclusion, our results suggest that excessive O‐GlcNAcylation in hyperglycemia alters mitochondrial calcium homeostasis by increasing O‐GlcNAcylated MCU.Grant Funding Source: Supported by UC MEXUS and VA‐5 I01BX001121‐02‐

Ursolic acid prevents endoplasmic reticulum stress-mediated apoptosis induced by heat stress in mouse cardiac myocytes

Heat stress causes serious physiological dysfunction of cardiac myocytes and is associated with several types of cardiovascular diseases. However, the underlying mechanisms and therapeutic strategies to alleviate heat stress-induced myocardial damage are not available. The objective of this study was to (1) investigate the functional role of endoplasmic reticulum (ER) stress-mediated apoptosis in heat exposure-induced myocardial damage, and (2) to evaluate the effects of ursolic acid on the myocardial apoptosis as well as the underlying mechanisms in mouse cardiac myocytes. We show here that heat stress-induced apoptosis is predominantly mediated by the activation of PERK-eIF2α-CHOP unfolded protein response which up-regulates the protein expression of Puma, and by the modulation of cellular redox state. Intriguingly, the myocardial apoptosis is markedly attenuated by ursolic acid treatment. Mechanistically, the protective effects of ursolic acid are mediated, at least partly, by reestablishing the intracellular redox state and inducing the expression of the anti-apoptotic protein Mcl-1, which, in turn, inactivating CHOP-induced Puma up-regulation. The striking finding that ursolic acid has both anti-apoptotic and antioxidative activities against ER stress-associated myocardial damage suggests that supplementation of ursolic acid might be a potential strategy to reduce the detrimental effects of heat stress in cardiomyocytes.

Recent Advances in Cardiac Myocyte Biology and Function

Cardiac myocyte dysfunction is the underlying cause of changes in cardiac contractility associated with several pathological conditions. Hence, the physiology of cardiac myocytes has been the subject of intense investigation and much attention has been paid to important questions such as the following: what maintains and regulates the structural and functional integrity of cardiac myocytes?; how do myocytes respond to stress?; what are the molecular changes that contribute to myocytes dysfunction in cardiac disease?; how can pathological changes in myocytes be prevented or attenuated?; what determines myocyte life and death?; and can adult myocytes be renewed or replenished? Recent advancements in the field continue to address these important issues.1–18 Cardiac myocyte hypertrophy has been an area of intense interest for a long time,19 because it is well-known that maladaptive cardiac myocyte hypertrophy and accompanying cardiac remodeling often lead to heart failure.20,21 Recent studies have uncovered new mechanisms of myocyte hypertrophy. For instance, Matsushima et al22 showed that increased nuclear oxidative stress caused by nicotinamide adenine dinucleotide phosphate oxidase 4 (Nox4) leads to oxidation and nuclear export of histone deacetylase 4 (a class II histone deacetylase), which is a repressor of transcription factors involved in hypertrophic response (eg, nuclear factor of activated T-cells); this suggest that inhibition of Nox4 can be another avenue for dampening maladaptive cardiac hypertrophy. G-protein–coupled receptor kinase-5 (GRK5) is another important regulator/kinase of a class II histone deacetylase 5 and its contribution to cardiac hypertrophy had been implicated previously.23 Recently, Gold et al24 have used both global and cardiac-specific Grk5 knockout mice to test the requirement of this protein for pathological hypertrophy. In response to pressure overload, Grk5 knockout mice showed attenuated hypertrophy, remodeling, and hypertrophy-related gene expression, clearly demonstrating the essential role of this protein in …

GW24-e1806 Atorvastatin attenuates oxygen-glucose deprivation/recovery-induced mitochondrial dysfunction in neonatal rat cardiac myocytes

ObjectivesAtorvastatin (Ator) has been shown to exert protective properties on cardiovascular systems in vivo. However, its mechanism of action remains elusive. Our study aims to assess the potential of Ator...

N-acetylcysteine reverses cardiac myocyte dysfunction in a rodent model of behavioral stress

Compelling clinical reports reveal that behavioral stress alone is sufficient to cause reversible myocardial dysfunction in selected individuals. We developed a rodent stress cardiomyopathy model by a combination of prenatal and postnatal behavioral stresses (Stress). We previously reported a decrease in percent fractional shortening by echo, both systolic and diastolic dysfunction by catheter-based hemodynamics, as well as attenuated hemodynamic and inotropic responses to the β-adrenergic agonist, isoproterenol (ISO) in Stress rats compared with matched controls (Kan H, Birkle D, Jain AC, Failinger C, Xie S, Finkel MS. J Appl Physiol 98: 77-82, 2005). We now report enhanced catecholamine responses to behavioral stress, as evidenced by increased circulating plasma levels of norepinephrine (P < 0.01) and epinephrine (P < 0.01) in Stress rats vs. controls. Cardiac myocytes isolated from Stress rats also reveal evidence of oxidative stress, as indicated by decreased ATP, increased GSSG, and decreased GSH-to-GSSG ratio in the presence of increased GSH peroxidase and catalase activities (P < 0.01, for each). We also report blunted inotropic and intracellular Ca(2+) concentration responses to extracellular Ca(2+) (P < 0.05), as well as altered inotropic responses to the intracellular calcium regulator, caffeine (20 mM; P < 0.01). Treatment of cardiac myocytes with N-acetylcysteine (NAC) (10(-3) M) normalized calcium handling in response to ISO and extracellular Ca(2+) concentration and inotropic response to caffeine (P < 0.01, for each). NAC also attenuated the blunted inotropic response to ISO and Ca(2+) (P < 0.01, for each). Surprisingly, NAC did not reverse the changes in GSH, GSSG, or GSH-to-GSSG ratio. These data support a GSH-independent salutary effect of NAC on intracellular calcium signaling in this rodent model of stress-induced cardiomyopathy.

Protective effects of taurine against oxidative stress in the heart of MsrA knockout mice

Taurine has been shown to have potent anti-oxidant properties under various pathophysiological conditions. We reported previously a cellular dysfunction and mitochondrial damage in cardiac myocytes of methionine sulfoxide reductase A (MsrA) gene knockout mice (MsrA(-/-)). In the present study, we have explored the protective effects of taurine against oxidative stress in the heart of MsrA(-/-) mice with or without taurine treatment. Cardiac cell contractility and Ca(2+) dynamics were measured using cell-based assays and in vivo cardiac function was monitored using high-resolution echocardiography in the tested animals. Our data have shown that MsrA(-/-) mice exhibited a progressive cardiac dysfunction with a significant decrease of ejection fraction (EF) and fraction shortening (FS) at age of 8 months compared to the wild type controls at the same age. However, the dysfunction was corrected in MsrA(-/-) mice treated with taurine supplement in the diet for 5 months. We further investigated the cellular mechanism underlying the protective effect of taurine in the heart. Our data indicated that cardiac myocytes from MsrA(-/-) mice treated with taurine exhibited an improved cell contraction and could tolerate oxidative stress better. Furthermore, taurine treatment reduced significantly the protein oxidation levels in mitochondria of MsrA(-/-) hearts, suggesting an anti-oxidant effect of taurine in cardiac mitochondria. Our study demonstrates that long-term treatment of taurine as a diet supplement is beneficial to a heart that is vulnerable to environmental oxidative stresses.

N-acetylcysteine reverses cardiac myocyte dysfunction in HIV-Tat proteinopathy

HIV cardiomyopathy remains highly prevalent among the estimated 33 million HIV-infected individuals worldwide. This is particularly true in developing countries. Potential mechanisms responsible for myocardial dysfunction following HIV infection include direct effects of HIV proteins. We have previously reported that cardiac myocyte-specific expression of HIV-Tat (Tat) results in a murine cardiomyopathy model. We now report that Tat exhibits decreased myocardial ATP [wild type (WT) vs. Tat transgenic (TG), P < 0.01] and myocyte GSH levels (WT vs. TG, P < 0.01), decreased GSH/GSSG ratio (WT vs. TG, P < 0.01), increased H(2)O(2) levels (WT vs. TG, P < 0.05), and increased catalase (TG vs. WT, P < 0.05) and GPX1 (glutathione peroxidase 1) activities (WT vs. TG, P < 0.05), blunted cardiac myocyte positive inotropy (% peak shortening, WT vs. TG, P < 0.01; +dl/dt, WT vs. TG, P < 0.01) and negative inotropy (-dl/dt, WT vs. TG, P < 0.01), and blunted inotropic responses to Ca(2+) (P < 0.01, for each) and shortened anatomical and functional survival in vitro (P < 0.01). The sulfhydryl donor, N-acetylcysteine (NAC; 10(-4) M), completely reversed both the positive and negative inotropic defects in Tat; increased GSH (P < 0.01) and GSH/GSSG (P < 0.01); reversed H(2)O(2) level (P < 0.05) and GPX1 activity (P < 0.05); and normalized the blunted inotropic response to Ca(2+) (P < 0.01). NAC (10(-7)) M normalized duration of contractile function from <40 min to >120 min (P < 0.01), with no effect on GSH and GSH/GSSG. NAC (10(-4) M) reverses cardiac myocyte dysfunction and markers of oxidative stress. NAC (10(-7) M) enhances myocyte function independent of changes in glutathione. Elucidating the molecular mechanisms involved in the GSH-dependent and GSH-independent salutary effects of NAC should identify novel therapeutic targets for myocardial proteinopathies recently appreciated in human cardiomyopathies.

Oxidative stress and aldehyde generation by monoamine oxidase cause mitochondrial dysfunction in cardiac myocytes

Monoamine oxidases (MAO) have been shown to play a major role in cardiac injury following ischemia/reperfusion or pressure overload. Mitochondrial dysfunction occurs in both conditions, yet there is no definitive proof that MAO activity directly jeopardizes mitochondrial function. We stimulated MAO activity with dopamine (DA) in neonatal rat cardiomyocytes, monitoring reactive oxygen species (ROS) production by Mitotracker Red and mitochondrial function with TMRM. DA administration induced a significant increase in mitochondrial ROS production (+50%, p&lt;0.05) and MAO inhibitor pargyline completely prevented it (p&lt;0.05). Mitochondrial membrane potential was unchanged in the same experimental conditions (100±0 in ctrl vs 106±4.5 % in DA‐treated cells). However, when cells were co‐incubated with DA and ATP synthase inhibitor oligomycin, membrane potential dropped by 50%. Pargyline offset this change suggesting that MAO activation induces mitochondrial dysfunction causing mitochondria to hydrolyze ATP. Furthermore, inhibition of aldehyde dehydrogenase (a DA catabolic enzyme downstream of MAO) in the presence of DA, also determined a 50% loss in membrane potential (p&lt;0.05) and pargyline completely prevented this (p&lt;0.005). Here we show that ROS and aldehyde intermediates deriving from MAO activity can directly target mitochondria leading to organelle dysfunction and eventually cell death.