Redox control of cardiac excitability

Mitochondrial Dysfunction in Cardiac Arrhythmias

Electrophysiological and structural disruptions in cardiac arrhythmias are closely related to mitochondrial dysfunction. Mitochondria are an organelle generating ATP, thereby satisfying the energy demand of the incessant electrical activity in the heart. In arrhythmias, the homeostatic supply-demand relationship is impaired, which is often accompanied by progressive mitochondrial dysfunction leading to reduced ATP production and elevated reactive oxidative species generation. Furthermore, ion homeostasis, membrane excitability, and cardiac structure can be disrupted through pathological changes in gap junctions and inflammatory signaling, which results in impaired cardiac electrical homeostasis. Herein, we review the electrical and molecular mechanisms of cardiac arrhythmias, with a particular focus on mitochondrial dysfunction in ionic regulation and gap junction action. We provide an update on inherited and acquired mitochondrial dysfunction to explore the pathophysiology of different types of arrhythmias. In addition, we highlight the role of mitochondria in bradyarrhythmia, including sinus node dysfunction and atrioventricular node dysfunction. Finally, we discuss how confounding factors, such as aging, gut microbiome, cardiac reperfusion injury, and electrical stimulation, modulate mitochondrial function and cause tachyarrhythmia.

Altered heart cytokine profile and action potential modulation in cardiomyocytes from Mas-deficient mice

The renin-angiotensin system (RAS) is a key hormonal system. In recent years, the functional analysis of the novel axis of the RAS (ACE2/Ang-(1-7)/Mas receptor) revealed that its activation can become protective against several pathologies, including cardiovascular diseases. Mas knockout mice (Mas-KO) represent an important tool for new investigations. Indeed, extensive biological research has focused on investigating the functional implications of Mas receptor deletion. However, although the Mas receptor was identified in neonatal cardiomyocytes and also in adult ventricular myocytes, only few reports have explored the Ang-(1-7)/Mas signaling directly in cardiomyocytes to date. This study investigated the implication of Mas receptor knockout to the cytokine profile, energy metabolism, and electrical properties of mice-isolated cardiomyocytes. Here, we demonstrated that Mas-KO mice have modulation in some cytokines, such as G-CSF, IL-6, IL-10, and VEGF in the left ventricle. This model also presents increased mitochondrial number in cardiomyocytes and a reduction in the myocyte diameter. Finally, Mas-KO cardiomyocytes have altered action potential modulation after diazoxide challenge. Such electrical finding was different from the data showed for the TGR(A1-7)3292 (TGR) model, which overexpresses Ang-(1-7) in the plasma by 4.5, used by us as a control. Collectively, our findings exemplify the importance of understanding the ACE2/Ang-(1-7)/Mas pathway in cardiomyocytes and heart tissue. The Mas-KO mice model can be considered an important tool for new RAS investigations.

Computational Approaches and Tools as Applied to the Study of Rhythms and Chaos in Biology

The temporal dynamics in biological systems displays a wide range of behaviors, from periodic oscillations, as in rhythms, bursts, long-range (fractal) correlations, chaotic dynamics up to brown and white noise. Herein, we propose a comprehensive analytical strategy for identifying, representing, and analyzing biological time series, focusing on two strongly linked dynamics: periodic (oscillatory) rhythms and chaos. Understanding the underlying temporal dynamics of a system is of fundamental importance; however, it presents methodological challenges due to intrinsic characteristics, among them the presence of noise or trends, and distinct dynamics at different time scales given by molecular, dcellular, organ, and organism levels of organization. For example, in locomotion circadian and ultradian rhythms coexist with fractal dynamics at faster time scales. We propose and describe the use of a combined approach employing different analytical methodologies to synergize their strengths and mitigate their weaknesses. Specifically, we describe advantages and caveats to consider for applying probability distribution, autocorrelation analysis, phase space reconstruction, Lyapunov exponent estimation as well as different analyses such as harmonic, namely, power spectrum; continuous wavelet transforms; synchrosqueezing transform; and wavelet coherence. Computational harmonic analysis is proposed as an analytical framework for using different types of wavelet analyses. We show that when the correct wavelet analysis is applied, the complexity in the statistical properties, including temporal scales, present in time series of signals, can be unveiled and modeled. Our chapter showcase two specific examples where an in-depth analysis of rhythms and chaos is performed: (1) locomotor and food intake rhythms over a 42-day period of mice subjected to different feeding regimes; and (2) chaotic calcium dynamics in a computational model of mitochondrial function.

Melatonin to Rescue the Aged Heart: Antiarrhythmic and Antioxidant Benefits

Aging comes with gradual loss of functions that increase the vulnerability to disease, senescence, and death. The mechanisms underlying these processes are linked to a prolonged imbalance between damage and repair. Damaging mechanisms include oxidative stress, mitochondrial dysfunction, chronodisruption, inflammation, and telomere attrition, as well as genetic and epigenetic alterations. Several endogenous tissue repairing mechanisms also decrease. These alterations associated with aging affect the entire organism. The most devastating manifestations involve the cardiovascular system and may lead to lethal cardiac arrhythmias. Together with structural remodeling, electrophysiological and intercellular communication alterations during aging predispose to arrhythmic events. Despite the knowledge on repairing mechanisms in the cardiovascular system, effective antiaging strategies able to reduce the risk of arrhythmias are still missing. Melatonin is a promising therapeutic candidate due to its pleiotropic actions. This indoleamine regulates chronobiology and endocrine physiology. Of relevance, melatonin is an antiaging, antioxidant, antiapoptotic, antiarrhythmic, immunomodulatory, and antiproliferative molecule. This review focuses on the protective effects of melatonin on age-induced cardiac functional and structural alterations, potentially becoming a new fountain of youth for the heart.

Mitochondrial Dysfunction Increases Arrhythmic Triggers and Substrates; Potential Anti-arrhythmic Pharmacological Targets

Incidence of cardiac arrhythmias increases significantly with age. In order to effectively stratify arrhythmic risk in the aging population it is crucial to elucidate the relevant underlying molecular mechanisms. The changes underlying age-related electrophysiological disruption appear to be closely associated with mitochondrial dysfunction. Thus, the present review examines the mechanisms by which age-related mitochondrial dysfunction promotes arrhythmic triggers and substrate. Namely, via alterations in plasmalemmal ionic currents (both sodium and potassium), gap junctions, cellular Ca²⁺ homeostasis, and cardiac fibrosis. Stratification of patients' mitochondrial function status permits application of appropriate anti-arrhythmic therapies. Here, we discuss novel potential anti-arrhythmic pharmacological interventions that specifically target upstream mitochondrial function and hence ameliorates the need for therapies targeting downstream changes which have constituted traditional antiarrhythmic therapy.

Attenuation of Oxidative Injury With Targeted Expression of NADPH Oxidase 2 Short Hairpin RNA Prevents Onset and Maintenance of Electrical Remodeling in the Canine Atrium: A Novel Gene Therapy Approach to Atrial Fibrillation

BACKGROUND

Atrial fibrillation (AF) is the most common heart rhythm disorder in adults and a major cause of stroke. Unfortunately, current treatments of AF are suboptimal because they are not targeted to the molecular mechanisms underlying AF. Using a highly novel gene therapy approach in a canine, rapid atrial pacing model of AF, we demonstrate that NADPH oxidase 2 (NOX2) generated oxidative injury causes upregulation of a constitutively active form of acetylcholine-dependent K+ current (IKACh), called IKH; this is an important mechanism underlying not only the genesis, but also the perpetuation of electric remodeling in the intact, fibrillating atrium.

METHODS

To understand the mechanism by which oxidative injury promotes the genesis and maintenance of AF, we performed targeted injection of NOX2 short hairpin RNA (followed by electroporation to facilitate gene delivery) in atria of healthy dogs followed by rapid atrial pacing. We used in vivo high-density electric mapping, isolation of atrial myocytes, whole-cell patch clamping, in vitro tachypacing of atrial myocytes, lucigenin chemiluminescence assay, immunoblotting, real-time polymerase chain reaction, immunohistochemistry, and Masson trichrome staining.

RESULTS

First, we demonstrate that generation of oxidative injury in atrial myocytes is a frequency-dependent process, with rapid pacing in canine atrial myocytes inducing oxidative injury through the induction of NOX2 and the generation of mitochondrial reactive oxygen species. We show that oxidative injury likely contributes to electric remodeling in AF by upregulating IKACh by a mechanism involving frequency-dependent activation of PKCε (protein kinase C epsilon). The time to onset of nonsustained AF increased by >5-fold in NOX2 short hairpin RNA-treated dogs. Furthermore, animals treated with NOX2 short hairpin RNA did not develop sustained AF for up to 12 weeks. The electrophysiological mechanism underlying AF prevention was prolongation of atrial effective refractory periods, at least in part attributable to the attenuation of IKACh. Attenuated membrane translocation of PKCε appeared to be a likely molecular mechanism underlying this beneficial electrophysiological remodeling.

CONCLUSIONS

NOX2 oxidative injury (1) underlies the onset, and the maintenance of electric remodeling in AF, as well, and (2) can be successfully prevented with a novel, gene-based approach. Future optimization of this approach may lead to a novel, mechanism-guided therapy for AF.

Thinking outside the nucleus: Mitochondrial DNA copy number in health and disease

Mitochondrial DNA copy number (mtDNA-CN) is a biomarker of mitochondrial function and levels of mtDNA-CN have been reproducibly associated with overall mortality and a number of age-related diseases, including cardiovascular disease, chronic kidney disease, and cancer. Recent advancements in techniques for estimating mtDNA-CN, in particular the use of DNA microarrays and next-generation sequencing data, have led to the comprehensive assessment of mtDNA-CN across these and other diseases and traits. The importance of mtDNA-CN measures to disease and these advancing technologies suggest the potential for mtDNA-CN to be a useful biomarker in the clinic. While the exact mechanism(s) underlying the association of mtDNA-CN with disease remain to be elucidated, we review the existing literature which supports roles for inflammatory dynamics, immune function and alterations to cell signaling as consequences of variation in mtDNA-CN. We propose that future studies should focus on characterizing longitudinal, cell-type and cross-tissue profiles of mtDNA-CN as well as improving methods for measuring mtDNA-CN which will expand the potential for its use as a clinical biomarker.

Diabetes Increases the Vulnerability of the Cardiac Mitochondrial Network to Criticality

Mitochondrial criticality describes a state in which the mitochondrial cardiac network under intense oxidative stress becomes very sensitive to small perturbations, leading from local to cell-wide depolarization and synchronized oscillations that may escalate to the myocardial syncytium generating arrhythmias. Herein, we describe the occurrence of mitochondrial criticality in the chronic setting of a metabolic disorder, type 1 diabetes (T1DM), using a streptozotocin (STZ)-treated guinea pig (GP) animal model. Using wavelet analysis of mitochondrial networks from two-photon microscopy imaging of cardiac myocytes loaded with a fluorescent probe of the mitochondrial membrane potential, we show that cardiomyocytes from T1DM GPs are closer to criticality, making them more vulnerable to cell-wide mitochondrial oscillations as can be judged by the latency period to trigger oscillations after a laser flash perturbation, and their propensity to oscillate. Insulin treatment of T1DM GPs rescued cardiac myocytes to sham control levels of susceptibility, a protective condition that could also be attained with interventions leading to improvement of the cellular redox environment such as preincubation of diabetic cardiac myocytes with the lipid palmitate or a cell-permeable form of glutathione, in the presence of glucose.

Capsaicin Alleviates the Deteriorative Mitochondrial Function by Upregulating 14-3-3η in Anoxic or Anoxic/Reoxygenated Cardiomyocytes

Reactive oxygen species (ROS) are byproducts of a defective electron transport chain (ETC). The redox couples, GSH/GSSG and NAD⁺/NADH, play an essential role in physiology as internal defenses against excessive ROS generation by facilitating intracellular/mitochondrial (mt) redox homeostasis. Anoxia alone and anoxia/reoxygenation (A/R) are dissimilar pathological processes. In this study, we measured the impact of capsaicin (Cap) on these pathological processes using a primary cultured neonatal rat cardiomyocyte in vitro model. The results showed that overproduction of ROS was tightly associated with disturbed GSH/GSSG and NAD⁺/NADH suppressed mt complex I and III activities, decreased oxygen consumption rates, and elevated extracellular acidification rates. During anoxia or A/R period, these indices interact with each other causing the mitochondrial function to worsen. Cap protected cardiomyocytes against the different stages of A/R injury by rescuing NAD⁺/NADH, GSH/GSSG, and mt complex I/III activities and cellular energy metabolism. Importantly, Cap-mediated upregulation of 14-3-3η, a protective phosphoserine-binding protein in cardiomyocytes, ameliorated mt function caused by a disruptive redox status and an impaired ETC. In conclusion, redox pair, mt complex I/III, and metabolic equilibrium were significantly different in anoxia alone and A/R injury; Cap through upregulating 14-3-3η plays a protection against the above injury in cardiomyocyte.

Reactive oxygen species and nitric oxide imbalances lead to in vivo and in vitro arrhythmogenic phenotype in acute phase of experimental Chagas disease

Chagas Disease (CD) is one of the leading causes of heart failure and sudden death in Latin America. Treatments with antioxidants have provided promising alternatives to ameliorate CD. However, the specific roles of major reactive oxygen species (ROS) sources, including NADPH-oxidase 2 (NOX2), mitochondrial-derived ROS and nitric oxide (NO) in the progression or resolution of CD are yet to be elucidated. We used C57BL/6 (WT) and a gp91PHOX knockout mice (PHOX-/-), lacking functional NOX2, to investigate the effects of ablation of NOX2-derived ROS production on the outcome of acute chagasic cardiomyopathy. Infected PHOX-/- cardiomyocytes displayed an overall pro-arrhythmic phenotype, notably with higher arrhythmia incidence on ECG that was followed by higher number of early afterdepolarizations (EAD) and 2.5-fold increase in action potential (AP) duration alternans, compared to AP from infected WT mice. Furthermore, infected PHOX-/- cardiomyocytes display increased diastolic [Ca2+], aberrant Ca2+ transient and reduced Ca2+ transient amplitude. Cardiomyocyte contraction is reduced in infected WT and PHOX-/- mice, to a similar extent. Nevertheless, only infected PHOX-/- isolated cardiomyocytes displayed significant increase in non-triggered extra contractions (appearing in ~75% of cells). Electro-mechanical remodeling of infected PHOX-/-cardiomyocytes is associated with increase in NO and mitochondria-derived ROS production. Notably, EADs, AP duration alternans and in vivo arrhythmias were reverted by pre-incubation with nitric oxide synthase inhibitor L-NAME. Overall our data show for the first time that lack of NOX2-derived ROS promoted a pro-arrhythmic phenotype in the heart, in which the crosstalk between ROS and NO could play an important role in regulating cardiomyocyte electro-mechanical function during acute CD. Future studies designed to evaluate the potential role of NOX2-derived ROS in the chronic phase of CD could open new and more specific therapeutic strategies to treat CD and prevent deaths due to heart complications.

Thermal tolerance and fish heart integrity: fatty acids profiles as predictors of species resilience

The cardiovascular system is a major limiting system in thermal adaptation, but the exact physiological mechanisms underlying responses to thermal stress are still not completely understood. Recent studies have uncovered the possible role of reactive oxygen species production rates of heart mitochondria in determining species' upper thermal limits. The present study examines the relationship between individual response to a thermal challenge test (CT_max), susceptibility to peroxidation of membrane lipids, heart fatty acid profiles and cardiac antioxidant enzyme activities in two salmonid species from different thermal habitats (Salvelinus alpinus, Salvelinus fontinalis) and their hybrids. The susceptibility to peroxidation of membranes in the heart was negatively correlated with individual thermal tolerance. The same relationship was found for arachidonic and eicosapentaenoic acid. Total H₂O₂ buffering activity of the heart muscle was higher for the group with high thermal resistance. These findings underline a potential general causative relationship between sensitivity to oxidative stress, specific fatty acids, antioxidant activity in the cardiac muscle and thermal tolerance in fish and likely other ectotherms. Heart fatty acid profile could be indicative of species resilience to global change, and more importantly the plasticity of this trait could predict the adaptability of fish species or populations to changes in environmental temperature.

A Spatiotemporal Ventricular Myocyte Model Incorporating Mitochondrial Calcium Cycling

Intracellular calcium (Ca2+) cycling dynamics in cardiac myocytes are spatiotemporally generated by stochastic events arising from a spatially distributed network of coupled Ca2+ release units that interact with an intertwined mitochondrial network. In this study, we developed a spatiotemporal ventricular myocyte model that integrates mitochondria-related Ca2+ cycling components into our previously developed ventricular myocyte model consisting of a three-dimensional Ca2+ release unit network. Mathematical formulations of mitochondrial membrane potential, mitochondrial Ca2+ cycling, mitochondrial permeability transition pore stochastic opening and closing, intracellular reactive oxygen species signaling, and oxidized Ca2+/calmodulin-dependent protein kinase II signaling were incorporated into the model. We then used the model to simulate the effects of mitochondrial depolarization on mitochondrial Ca2+ cycling, Ca2+ spark frequency, and Ca2+ amplitude, which agree well with experimental data. We also simulated the effects of the strength of mitochondrial Ca2+ uniporters and their spatial localization on intracellular Ca2+ cycling properties, which substantially affected diastolic and systolic Ca2+ levels in the mitochondria but exhibited only a small effect on sarcoplasmic reticulum and cytosolic Ca2+ levels under normal conditions. We show that mitochondrial depolarization can cause Ca2+ waves and Ca2+ alternans, which agrees with previous experimental observations. We propose that this new, to our knowledge, spatiotemporal ventricular myocyte model, incorporating properties of mitochondrial Ca2+ cycling and reactive-oxygen-species-dependent signaling, will be useful for investigating the effects of mitochondria on intracellular Ca2+ cycling and action potential dynamics in ventricular myocytes.

Mitochondrial chaotic dynamics: Redox-energetic behavior at the edge of stability

Mitochondria serve multiple key cellular functions, including energy generation, redox balance, and regulation of apoptotic cell death, thus making a major impact on healthy and diseased states. Increasingly recognized is that biological network stability/instability can play critical roles in determining health and disease. We report for the first-time mitochondrial chaotic dynamics, characterizing the conditions leading from stability to chaos in this organelle. Using an experimentally validated computational model of mitochondrial function, we show that complex oscillatory dynamics in key metabolic variables, arising at the “edge” between fully functional and pathological behavior, sets the stage for chaos. Under these conditions, a mild, regular sinusoidal redox forcing perturbation triggers chaotic dynamics with main signature traits such as sensitivity to initial conditions, positive Lyapunov exponents, and strange attractors. At the “edge” mitochondrial chaos is exquisitely sensitive to the antioxidant capacity of matrix Mn superoxide dismutase as well as to the amplitude and frequency of the redox perturbation. These results have potential implications both for mitochondrial signaling determining health maintenance, and pathological transformation, including abnormal cardiac rhythms.

Association between mitochondrial DNA copy number and sudden cardiac death: findings from the Atherosclerosis Risk in Communities study (ARIC)

Aims

Sudden cardiac death (SCD) is a major public health burden. Mitochondrial dysfunction has been implicated in a wide range of cardiovascular diseases including cardiomyopathy, heart failure, and arrhythmias, but it is unknown if it also contributes to SCD risk. We sought to examine the prospective association between mtDNA copy number (mtDNA-CN), a surrogate marker of mitochondrial function, and SCD risk.

Methods and results

We measured baseline mtDNA-CN in 11 093 participants from the Atherosclerosis Risk in Communities (ARIC) study. mtDNA copy number was calculated from probe intensities of mitochondrial single nucleotide polymorphisms (SNP) on the Affymetrix Genome-Wide Human SNP Array 6.0. Sudden cardiac death was defined as a sudden pulseless condition presumed due to a ventricular tachyarrhythmia in a previously stable individual without evidence of a non-cardiac cause of cardiac arrest. Sudden cardiac death cases were reviewed and adjudicated by an expert committee. During a median follow-up of 20.4 years, we observed 361 SCD cases. After adjusting for age, race, sex, and centre, the hazard ratio for SCD comparing the 1st to the 5th quintiles of mtDNA-CN was 2.24 (95% confidence interval 1.58-3.19; P-trend <0.001). When further adjusting for traditional cardiovascular disease risk factors, prevalent coronary heart disease, heart rate, QT interval, and QRS duration, the association remained statistically significant. Spline regression models showed that the association was approximately linear over the range of mtDNA-CN values. No apparent interaction by race or by sex was detected.

Conclusion

In this community-based prospective study, mtDNA-CN in peripheral blood was inversely associated with the risk of SCD.

Pharmacologic inhibition of the mitochondrial Na+/Ca2+ exchanger protects against ventricular arrhythmias in a porcine model of ischemia-reperfusion

BACKGROUND

The mitochondrial Na+/Ca2+ exchanger (mNCX) has been implicated in the pathogenesis of arrhythmogenicity and myocardial reperfusion injury, rendering its inhibition a potential therapeutic strategy. We examined the effects of CGP-37157, a selective mNCX inhibitor, on arrhythmogenesis, infarct size (IS), and no reflow area (NRA) in a porcine model of ischemia-reperfusion.

METHODS

Forty pigs underwent myocardial ischemia for 60 minutes, followed by 2 hours of reperfusion. Animals were randomized to receive intracoronary infusion of 0.02 mg/kg CGP-37157 or vehicle, either before ischemia (n=17) or before reperfusion (n=17). Animals were monitored for arrhythmias. Myocardial area at risk (AR), IS, and NRA were measured by histopathology.

RESULTS

AR, NRA, and IS were comparable between groups. Administration of CGP-37157 before ischemia resulted in the following: (a) suppression of ventricular tachyarrhythmias (events/pig: 1.5±1.1 vs 3.5±1.9, p=0.014), (b) easier cardioversion of ventricular tachyarrhythmias (defibrillations required for cardioversion of each episode: 2.6±2.3 vs 6.2±2.1, p=0.006), and (c) decreased maximal depression of the J point (0.75±0.27 mm vs 1.75±0.82 mm, p=0.007), compared to controls. Administration of CGP-37157 before reperfusion expedited ST-segment resolution; complete ST-segment resolution within 30 minutes of reperfusion was observed in 7/8 CGP-37157-treated animals versus 1/9 controls (p=0.003).

CONCLUSIONS

In a porcine model of myocardial infarction, intracoronary administration of CGP-37157 did not decrease IS or NRA. However, it suppressed ventricular arrhythmias, decreased depression of the J point during ischemia and expedited ST-segment resolution after reperfusion. These findings motivate further investigation of pharmacologic mNCX inhibition as a potential therapeutic strategy to suppress arrhythmias in the injured heart.

Circadian redox rhythms in the regulation of neuronal excitability

Oxidation-reduction reactions are essential to life as the core mechanisms of energy transfer. A large body of evidence in recent years presents an extensive and complex network of interactions between the circadian and cellular redox systems. Recent advances show that cellular redox state undergoes a ~24-h (circadian) oscillation in most tissues and is conserved across the domains of life. In nucleated cells, the metabolic oscillation is dependent upon the circadian transcription-translation machinery and, vice versa, redox-active proteins and cofactors feed back into the molecular oscillator. In the suprachiasmatic nucleus (SCN), a hypothalamic region of the brain specialized for circadian timekeeping, redox oscillation was found to modulate neuronal membrane excitability. The SCN redox environment is relatively reduced in daytime when neuronal activity is highest and relatively oxidized in nighttime when activity is at its lowest. There is evidence that the redox environment directly modulates SCN K⁺ channels, tightly coupling metabolic rhythms to neuronal activity. Application of reducing or oxidizing agents produces rapid changes in membrane excitability in a time-of-day-dependent manner. We propose that this reciprocal interaction may not be unique to the SCN. In this review, we consider the evidence for circadian redox oscillation and its interdependencies with established circadian timekeeping mechanisms. Furthermore, we will investigate the effects of redox on ion-channel gating dynamics and membrane excitability. The susceptibility of many different ion channels to modulation by changes in the redox environment suggests that circadian redox rhythms may play a role in the regulation of all excitable cells.

Human cardiomyocyte calcium handling and transverse tubules in mid-stage of post-myocardial-infarction heart failure

AIMS

Cellular processes in the heart rely mainly on studies from experimental animal models or explanted hearts from patients with terminal end-stage heart failure (HF). To address this limitation, we provide data on excitation contraction coupling, cardiomyocyte contraction and relaxation, and Ca²⁺ handling in post-myocardial-infarction (MI) patients at mid-stage of HF.

METHODS AND RESULTS

Nine MI patients and eight control patients without MI (non-MI) were included. Biopsies were taken from the left ventricular myocardium and processed for further measurements with epifluorescence and confocal microscopy. Cardiomyocyte function was progressively impaired in MI cardiomyocytes compared with non-MI cardiomyocytes when increasing electrical stimulation towards frequencies that simulate heart rates during physical activity (2 Hz); at 3 Hz, we observed almost total breakdown of function in MI. Concurrently, we observed impaired Ca²⁺ handling with more spontaneous Ca²⁺ release events, increased diastolic Ca²⁺ , lower Ca²⁺ amplitude, and prolonged time to diastolic Ca²⁺ removal in MI (P < 0.01). Significantly reduced transverse-tubule density (-35%, P < 0.01) and sarcoplasmic reticulum Ca²⁺ adenosine triphosphatase 2a (SERCA2a) function (-26%, P < 0.01) in MI cardiomyocytes may explain the findings. Reduced protein phosphorylation of phospholamban (PLB) serine-16 and threonine-17 in MI provides further mechanisms to the reduced function.

CONCLUSIONS

Depressed cardiomyocyte contraction and relaxation were associated with impaired intracellular Ca²⁺ handling due to impaired SERCA2a activity caused by a combination of alteration in the PLB/SERCA2a ratio and chronic dephosphorylation of PLB as well as loss of transverse tubules, which disrupts normal intracellular Ca²⁺ homeostasis and handling. This is the first study that presents these mechanisms from viable and intact cardiomyocytes isolated from the left ventricle of human hearts at mid-stage of post-MI HF.

Iron overload impact on P-ATPases

Iron is a chemical element that is active in the fundamental physiological processes for human life, but its burden can be toxic to the body, mainly because of the stimulation of membrane lipid peroxidation. For this reason, the action of iron on many ATPases has been studied, especially on P-ATPases, such as the Na⁺,K⁺-ATPase and the Ca²⁺-ATPase. On the Fe²⁺-ATPase activity, the free iron acts as an activator, decreasing the intracellular Fe²⁺ and playing a protection role for the cell. On the Ca²⁺-ATPase activity, the iron overload decreases the enzyme activity, raising the cytoplasmic Ca²⁺ and decreasing the sarco/endoplasmic reticulum and the Golgi apparatus Ca²⁺ concentrations, which could promote an enzyme oxidation, nitration, and fragmentation. However, the iron overload effect on the Na⁺,K⁺-ATPase may change according to the tissue expressions. On the renal cells, as well as on the brain and the heart, iron promotes an enzyme inactivation, whereas its effect on the erythrocytes seems to be the opposite, directly stimulating the ATPase activity, or stimulating it by signaling pathways involving ROS and PKC. Modulations in the ATPase activity may impair the ionic transportation, which is essential for cell viability maintenance, inducing irreversible damage to the cell homeostasis. Here, we will discuss about the iron overload effect on the P-ATPases, such as the Na⁺,K⁺-ATPase, the Ca²⁺-ATPase, and the Fe²⁺-ATPase.

Salinomycin induced ROS results in abortive autophagy and leads to regulated necrosis in glioblastoma

Glioblastoma is the most frequent malignant brain tumor. Even with aggressive treatment, prognosis for patients is poor. One characteristic of glioblastoma cells is its intrinsic resistance to apoptosis. Therefore, drugs that induce alternative cell deaths could be interesting to evaluate as alternative therapeutic candidates for glioblastoma. Salinomycin (SLM) was identified through a chemical screening as a promising anticancer drug, but its mechanism of cell death remains unclear. In the present work we set out to elucidate how SLM causes cell death in glioblastoma cell lines (both established cell lines and brain tumor stem cell lines), aiming to find a potential antitumor candidate. In addition, we sought to determine the mechanism of action of SLM so that this mechanism can be can be exploited in the fight against cancer. Our data showed that SLM induces a potent endoplasmic reticulum (ER) stress followed by the trigger of the unfolded protein response (UPR) and an aberrant autophagic flux that culminated in necrosis due to mitochondria and lysosomal alterations. Of importance, the aberrant autophagic flux was orchestrated by the production of Reactive Oxygen Species (ROS). Alleviation of ROS production restored the autophagic flux. Altogether our data suggest that in our system the oxidative stress blocks the autophagic flux through lipid oxidation. Importantly, oxidative stress could be instructing the type of cell death in SLM-treated cells, suggesting that cell death modality is a dynamic concept which depends on the cellular stresses and the cellular mechanism activated.

Hyperthyroidism, but not hypertension, impairs PITX2 expression leading to Wnt-microRNA-ion channel remodeling

PITX2 is a homeobox transcription factor involved in embryonic left/right signaling and more recently has been associated to cardiac arrhythmias. Genome wide association studies have pinpointed PITX2 as a major player underlying atrial fibrillation (AF). We have previously described that PITX2 expression is impaired in AF patients. Furthermore, distinct studies demonstrate that Pitx2 insufficiency leads to complex gene regulatory network remodeling, i.e. Wnt>microRNAs, leading to ion channel impairment and thus to arrhythmogenic events in mice. Whereas large body of evidences has been provided in recent years on PITX2 downstream signaling pathways, scarce information is available on upstream pathways influencing PITX2 in the context of AF. Multiple risk factors are associated to the onset of AF, such as e.g. hypertension (HTN), hyperthyroidism (HTD) and redox homeostasis impairment. In this study we have analyzed whether HTN, HTD and/or redox homeostasis impact on PITX2 and its downstream signaling pathways. Using rat models for spontaneous HTN (SHR) and experimentally-induced HTD we have observed that both cardiovascular risk factors lead to severe Pitx2 downregulation. Interesting HTD, but not SHR, leads to up-regulation of Wnt signaling as well as deregulation of multiple microRNAs and ion channels as previously described in Pitx2 insufficiency models. In addition, redox signaling is impaired in HTD but not SHR, in line with similar findings in atrial-specific Pitx2 deficient mice. In vitro cell culture analyses using gain- and loss-of-function strategies demonstrate that Pitx2, Zfhx3 and Wnt signaling influence redox homeostasis in cardiomyocytes. Thus, redox homeostasis seems to play a pivotal role in this setting, providing a regulatory feedback loop. Overall these data demonstrate that HTD, but not HTN, can impair Pitx2>>Wnt pathway providing thus a molecular link to AF.

Effect of unconjugated hyperbilirubinemia on neonatal autonomic functions: evaluation by heart rate variability

BACKGROUND

Serum bilirubin levels beyond the physiological limits, may lead to alterations in autonomic regulation in a newborn infant. Heart rate variability (HRV), is a noninvasive and quantitative marker of the activity of the autonomic nervous system (ANS). To date, few studies have demonstrated the undesirable effects of severe unconjugated hyperbilirubinemia (UHB) on autonomic functions, and only one study has used HRV as a marker of the autonomic activity. However, the relationship between altered cardiac autonomic functions and UHB by using the HRV derived from 24-hour Holter electrocardiography (ECG) recording has not been investigated previously.

OBJECTIVE

We aimed to assess whether a relationship exists between severe UHB and cardiac autonomic dysfunction by evaluating HRV via 24-hour Holter ECG recording.

METHODS

This single-center, prospective, case-control study was conducted on 50 full-term newborn infants with severe UHB requiring phototherapy and 50 healthy infants as controls. HRV assessment was performed by using 24-hour Holter ECG recording.

RESULTS

There was no significant difference in terms of mean average heart rate, mean maximum heart rate and mean RR duration between the groups. However, mean minimum heart rate was significantly lower in the study group. When 24-hour time and frequency domain parameters were compared, time and frequency domain parameters rMSDD as well as high frequency (HF), which represent parasymphathetic activity, were significantly higher in the study group. Furthermore, low frequency to high frequency (LF/HF) ratio, that serves as an indicator of sympathovagal balance, was significantly lower in the study group.

CONCLUSION

Severe UHB may cause cardiac autonomic dysfunction in favor of parasympathetic predominance in jaundiced neonates.

Mitochondrial respiration and ROS emission during β-oxidation in the heart: An experimental-computational study

Lipids are main fuels for cellular energy and mitochondria their major oxidation site. Yet unknown is to what extent the fuel role of lipids is influenced by their uncoupling effects, and how this affects mitochondrial energetics, redox balance and the emission of reactive oxygen species (ROS). Employing a combined experimental-computational approach, we comparatively analyze β-oxidation of palmitoyl CoA (PCoA) in isolated heart mitochondria from Sham and streptozotocin (STZ)-induced type 1 diabetic (T1DM) guinea pigs (GPs). Parallel high throughput measurements of the rates of oxygen consumption (VO2) and hydrogen peroxide (H2O2) emission as a function of PCoA concentration, in the presence of L-carnitine and malate, were performed. We found that PCoA concentration < 200 nmol/mg mito protein resulted in low H2O2 emission flux, increasing thereafter in Sham and T1DM GPs under both states 4 and 3 respiration with diabetic mitochondria releasing higher amounts of ROS. Respiratory uncoupling and ROS excess occurred at PCoA > 600 nmol/mg mito prot, in both control and diabetic animals. Also, for the first time, we show that an integrated two compartment mitochondrial model of β-oxidation of long-chain fatty acids and main energy-redox processes is able to simulate the relationship between VO2 and H2O2 emission as a function of lipid concentration. Model and experimental results indicate that PCoA oxidation and its concentration-dependent uncoupling effect, together with a partial lipid-dependent decrease in the rate of superoxide generation, modulate H2O2 emission as a function of VO2. Results indicate that keeping low levels of intracellular lipid is crucial for mitochondria and cells to maintain ROS within physiological levels compatible with signaling and reliable energy supply.

Acute exhaustive aerobic exercise training impair cardiomyocyte function and calcium handling in Sprague-Dawley rats

Introduction

Recent data from long-distance endurance participants suggest that cardiac function is impaired after completion. Existing data further indicate that right ventricular function is more affected than left ventricular function. The cellular mechanisms underpinning cardiac deterioration are limited and therefore the aim of this study was to examine cardiomyocyte and molecular responses of the right and left ventricle to an acute bout of exhaustive endurance exercise.

Materials and methods

Male Sprague-Dawley rats were assigned to sedentary controls or acute exhaustive endurance exercise consisting of a 120 minutes long forced treadmill run. The contractile function and Ca²⁺ handling properties in isolated cardiomyocytes, protein expression levels of sarcoplasmic reticulum Ca²⁺-ATPase and phospholamban including two of its phosphorylated states (serine 16 and threonine 17), and the mitochondrial respiration in permeabilized cardiac muscle fibers were analyzed.

Results

The exercise group showed a significant reduction in cardiomyocyte fractional shortening (right ventricle 1 Hz and 3 Hz p<0.001; left ventricle 1 Hz p<0.05), intracellular Ca²⁺ amplitude (right ventricle 1 and 3 Hz p<0.001; left ventricle 1 Hz p<0.01 and 3 Hz p<0.05) and rate of diastolic Ca²⁺ decay (right ventricle 1 Hz p<0.001 and 3 Hz p<0.01; left ventricle 1 and 3 Hz p<0.01). Cardiomyocyte relaxation during diastole was only significantly prolonged at 3 Hz in the right ventricle (p<0.05) compared to sedentary controls. We found an increase in phosphorylation of phospholamban at serine 16 and threonine 17 in the left (p<0.05), but not the right, ventricle from exhaustively exercised animals. The protein expression levels of sarcoplasmic reticulum Ca²⁺-ATPase and phospholamban was not changed. Furthermore, we found a reduction in maximal oxidative phosphorylation and electron transport system capacities of mitochondrial respiration in the right (p<0.01 and p<0.05, respectively), but not the left ventricle from rats subjected to acute exhaustive treadmill exercise.

Conclusion

Acute exhaustive treadmill exercise is associated with impairment of cardiomyocyte Ca²⁺ handling and mitochondrial respiration that causes depression in both contraction and diastolic relaxation of cardiomyocytes.

In Vitro Metabolite Formation in Human Hepatocytes and Cardiomyocytes and Metabolism and Tissue Distribution in Monkeys of the 2'-C-Methylguanosine Prodrug BMS-986094

BMS-986094, a 2'-C-methylguanosine prodrug for the treatment of chronic hepatitis C virus infection, was withdrawn from phase 2 clinical trials because of unexpected cardiac and renal toxicities. To better understand these toxicities, the in vitro metabolism of BMS-986094 in human hepatocytes (HHs) and human cardiomyocytes (HCMs) and the measurement of BMS-986094 and selected metabolites in monkey plasma and tissues were assessed. BMS-986094 was extensively metabolized by HHs and HCMs, resulting in more efficient formation and accumulation of the active triphosphorylated metabolite, INX-09114, and less efficient efflux of metabolites in HCMs. The predominant metabolism pathway (hydrolysis) in HHs and HCMs was not associated with the formation of reactive metabolites or oxidative stress. In cynomolgus monkeys dosed with BMS-986094 of 15 or 30 mg/kg/d for 3 weeks, the nucleoside metabolite M2 was the major plasma analyte (66%-68% of the combined area under the curve). INX-09114 was the highest drug-related species in the heart and kidney (2,610-4,280 ng/mL [males]; ∼2-420× the concentration of other analytes). Other analytes increased dose dependently, with BMS-986094 highest in diaphragm (≤4,400 ng/mL) followed by M2 in liver and kidney (≤1,360 ng/mL), and M7 and M8 in other tissues (≤124 ng/mL). Three weeks after the last dose, INX-09114 remained high in the heart and kidney (≤1,870 ng/mL), with low M2 (≤37 ng/mL) in plasma and tissues. Persistent high concentrations of INX-09114 in the heart and kidney appeared to correlate with toxicities in these tissues in monkeys.

Change in Oxidative Stress of Normotensive Elderly Subjects Following Lifestyle Modifications

INTRODUCTION

Oxidative stress is associated with aging, which ultimately causes deterioration of muscles. Antioxidant defense system deteriorates while enhancing accumulations of Reactive Oxygen Species (ROS) due to lipid peroxidation and altered enzyme activities in old age. Regular practice of yoga can maintain the antioxidants level of the body, even in stressful conditions.

AIM

The present study was designed to assess the effects of lifestyle technique on oxidative stress and lipid profile in normotensive elderly subjects.

MATERIALS AND METHODS

Seventy four healthy elderly subjects (43 males and 31 females) 60 to 80 years of age were selected from the Santosh Medical College, Ghaziabad Uttar Pradesh, India, for three months lifestyle modification program which included morning walk, Nadi shodan pranayama, dietary restrictions and increased intake of water. Blood pressure and oxidative stress markers Glutathione (GSH), Super Oxide Dismutase (SOD) and Malondialdehyde (MDA) were recorded twice, one at baseline and another after three months of lifestyle modifications.

RESULTS

Post lifestyle modifications technique values revealed a significant increase in GSH (88.03±9.58 ng/ml vs 93.12±9.17 ng/ml, p < 0.0001) and SOD (78.22±11.97 ng/ml vs 85.22±11.08 ng/ml, p < 0.0001), and a decline in MDA (5.28±0.52 m mol/ml vs 4.48± 0.69 m mol/ml, p < 0.0001) levels. Further, there was significant reduction in the systolic blood pressure (p <0.0001) and diastolic blood pressure (p<0.0002); besides all fasting lipids decreased significantly except High Density Lipids (HDL).

CONCLUSION

The findings of the present study show that lifestyle modification is helpful in reducing cardiovascular disease risk but also assuring for good health by decreasing oxidative stress level along with lipid profile. Further, all these modifications are easy to follow. However, more studies are required to make a generalized lifestyle modification program in normotensive elderly subjects.

SERCA2a upregulation ameliorates cellular alternans induced by metabolic inhibition

Cardiac alternans has been associated with the incidence of ventricular tachyarrhythmias and sudden cardiac death. The aim of this study was to investigate the effect of impaired mitochondrial function in the genesis of cellular alternans and to examine whether modulating the sarcoplasmic reticulum (SR) Ca(2+)ameliorates the level of alternans. Cardiomyocytes isolated from control and doxycyline-induced sarco(endo)plasmic reticulum Ca(2+)-ATPase 2a (SERCA2a)-upregulated mice were loaded with two different Ca(2+)indicators to selectively measure mitochondrial and cytosolic Ca(2+)using a custom-made fluorescence photometry system. The degree of alternans was defined as the alternans ratio (AR) [1 - (small Ca(2+)intensity)/(large Ca(2+)intensity)]. Blocking of complex I and II, cytochrome-coxidase, F0F1synthase, α-ketoglutarate dehydrogenase of the electron transport chain, increased alternans in both control and SERCA2a mice (P< 0.01). Changes in AR in SERCA2a-upregulated mice were significantly less pronounced than those observed in control in seven of nine tested conditions (P< 0.04).N-acetyl-l-cysteine (NAC), rescued alternans in myocytes that were previously exposed to an oxidizing agent (P< 0.001). CGP, an antagonist of the mitochondrial Na(+)-Ca(2+)exchanger, had the most severe effect on AR. Exposure to cyclosporin A, a blocker of the mitochondrial permeability transition pore reduced CGP-induced alternans (P< 0.0001). The major findings of this study are that impairment of mitochondrial Ca(2+)cycling and energy production leads to a higher amplitude of alternans in both control and SERCA2a-upregulated mice, but changes in SERCA2a-upregulated mice are less severe, indicating that SERCA2a mice are more capable of sustaining electrical stability during stress. This suggests a relationship between sarcoplasmic Ca(2+)content and mitochondrial dysfunction during alternans, which may potentially help to understand changes in Ca(2+)signaling in myocytes from diseased hearts, leading to new therapeutic targets.

The Actions of Lyophilized Apple Peel on the Electrical Activity and Organization of the Ventricular Syncytium of the Hearts of Diabetic Rats

This study was designed to examine the effects of lyophilized red delicious apple peel (RDP) on the action potentials (APs) and the input resistance-threshold current relationship. The experiments were performed on isolated papillary heart muscles from healthy male rats, healthy male rats treated with RDP, diabetic male rats, and diabetic male rats treated with RDP. The preparation was superfused with oxygenated Tyrode's solution at 37°C. The stimulation and the recording of the APs, the input resistance, and the threshold current were made using conventional electrophysiological methods. The RDP presented no significant effect in normal rats. Equivalent doses in diabetic rats reduced the APD and ARP. The relationship between input resistance and threshold current established an inverse correlation. The results indicate the following: (1) The functional structure of the cardiac ventricular syncytium in healthy rats is heterogeneous, in terms of input resistance and threshold current. Diabetes further accentuates the heterogeneity. (2) As a consequence, conduction block occurs and increases the possibility of reentrant arrhythmias. (3) These modifications in the ventricular syncytium, coupled with the increase in the ARP, are the adequate substrate so that, with diabetes, the heart becomes more arrhythmogenic. (4) RDP decreases the APD, the ARP, and most syncytium irregularity caused by diabetes.

Ellagic acid reduces L-type Ca2+ current and contractility through modulation of NO-GC-cGMP pathways in rat ventricular myocytes

There is evidence that phenolic structure may have biological functions. Ellagic acid (EA), a phenolic compound, has been suggested to have cardioprotective effects. EA effects were investigated on cardiac Ca currents and contractility in rat ventricular myocytes to elucidate the underlying mechanisms. Freshly isolated ventricular myocytes from rat hearts were used. EA dose-dependently reduced Ca currents (ICaL) with EC50 = 23 nM, whereas it did not affect the inactivation and reactivation parameters. Inhibition of adenylate cyclase by SQ-22536 (10 μM) and probucol (5 μM) had no effect on EA modulation of ICaL. Nitric oxide synthase block by L-NAME (500 μM) and of guanylate cyclase by ODQ (1 μM) abolished EA inhibitory effects on ICaL. Moreover, EA blunted ventricular myocytes' fractional shortening in a concentration-dependent manner. In conclusion, EA affects ionic and mechanical properties of rat ventricular myocytes starting at nanomolar concentrations. EA suppresses ICaL and exerts negative inotropic effects through activation of NOS-GC-cGMP pathways. Thus, EA may be useful in pathophysiological conditions such as hypertension and ischemic heart diseases.

Mechanisms of sudden cardiac death: oxidants and metabolism

Ventricular arrhythmia is the leading cause of sudden cardiac death (SCD). Deranged cardiac metabolism and abnormal redox state during cardiac diseases foment arrhythmogenic substrates through direct or indirect modulation of cardiac ion channel/transporter function. This review presents current evidence on the mechanisms linking metabolic derangement and excessive oxidative stress to ion channel/transporter dysfunction that predisposes to ventricular arrhythmias and SCD. Because conventional antiarrhythmic agents aiming at ion channels have proven challenging to use, targeting arrhythmogenic metabolic changes and redox imbalance may provide novel therapeutics to treat or prevent life-threatening arrhythmias and SCD.

Thioredoxins in cardiovascular disease

Key thioredoxin (Trx) system components are nicotinamide adenine dinucleotide phosphate (NADPH), Trx reductase (TrxR), and Trx. TrxR catalyzes disulfide reduction in Trx with NADPH as cofactor. Because Trx is an antioxidant, oxidative stress results in an increase in Trx, which has a reduced disulfide component. If Trx is suppressed, oxidative stress in higher. In contrast a decrease in oxidative stress is associated with low Trx levels. Trx is involved in inflammation, apoptosis, embryogenesis, and cardiovascular disease (CVD). This review focuses on the Trx system in CVD. Abnormal Trx binding occurs in mouse familial combined hyperlipidemia; however, this has not been confirmed in humans. Congestive heart failure is a manifestation of many CVDs, which may be improved by attenuating oxidative stress through the suppression of Trx and decreased reactive oxygen species. Angiotensin II is associated with hypertension and other CVDs, and its receptor blockade results in decreased oxidative stress with reduced Trx levels. Inflammation is a major causative factor of CVDs, and myocarditis as an example, is associated with increased Trx levels. Vascular endothelial dysfunction has an association with CVD. This dysfunction is alleviated by hormone replacement therapy, which involves decreased oxidative stress and Trx levels. Diabetes mellitus has a major association with CVDs; increase in Trx levels may reflect insulin resistance. Identification of Trx system abnormalities may lead to innovative approaches to treat multiple CVDs and other pathologies.

Mitochondrial and cellular mechanisms for managing lipid excess

Current scientific debates center on the impact of lipids and mitochondrial function on diverse aspects of human health, nutrition and disease, among them the association of lipotoxicity with the onset of insulin resistance in skeletal muscle, and with heart dysfunction in obesity and diabetes. Mitochondria play a fundamental role in aging and in prevalent acute or chronic diseases. Lipids are main mitochondrial fuels however these molecules can also behave as uncouplers and inhibitors of oxidative phosphorylation. Knowledge about the functional composition of these contradictory effects and their impact on mitochondrial-cellular energetics/redox status is incomplete. Cells store fatty acids (FAs) as triacylglycerol and package them into cytoplasmic lipid droplets (LDs). New emerging data shows the LD as a highly dynamic storage pool of FAs that can be used for energy reserve. Lipid excess packaging into LDs can be seen as an adaptive response to fulfilling energy supply without hindering mitochondrial or cellular redox status and keeping low concentration of lipotoxic intermediates. Herein we review the mechanisms of action and utilization of lipids by mitochondria reported in liver, heart and skeletal muscle under relevant physiological situations, e.g., exercise. We report on perilipins, a family of proteins that associate with LDs in response to loading of cells with lipids. Evidence showing that in addition to physical contact, mitochondria and LDs exhibit metabolic interactions is presented and discussed. A hypothetical model of channeled lipid utilization by mitochondria is proposed. Direct delivery and channeled processing of lipids in mitochondria could represent a reliable and efficient way to maintain reactive oxygen species (ROS) within levels compatible with signaling while ensuring robust and reliable energy supply.

Mitochondria and arrhythmias

Mitochondria are essential to providing ATP, thereby satisfying the energy demand of the incessant electrical activity and contractile action of cardiac muscle. Emerging evidence indicates that mitochondrial dysfunction can adversely affect cardiac electrical functioning by impairing the intracellular ion homeostasis and membrane excitability through reduced ATP production and excessive reactive oxygen species (ROS) generation, resulting in increased propensity to cardiac arrhythmias. In this review, the molecular mechanisms linking mitochondrial dysfunction to cardiac arrhythmias are discussed with an emphasis on the impact of increased mitochondrial ROS on the cardiac ion channels and transporters that are critical to maintaining normal electromechanical functioning of the cardiomyocytes. The potential of using mitochondria-targeted antioxidants as a novel antiarrhythmia therapy is highlighted.

SIR-2.1 integrates metabolic homeostasis with the reproductive neuromuscular excitability in early aging male Caenorhabditis elegans

The decline of aging C. elegans male's mating behavior is correlated with the increased excitability of the cholinergic circuitry that executes copulation. In this study, we show that the mating circuits' functional durability depends on the metabolic regulator SIR-2.1, a NAD(+)-dependent histone deacetylase. Aging sir-2.1(0) males display accelerated mating behavior decline due to premature hyperexcitability of cholinergic circuits used for intromission and ejaculation. In sir-2.1(0) males, the hypercontraction of the spicule-associated muscles pinch the vas deferens opening, thus blocking sperm release. The hyperexcitability is aggravated by reactive oxygen species (ROS). Our genetic, pharmacological, and behavioral analyses suggest that in sir-2.1(0) and older wild-type males, enhanced catabolic enzymes expression, coupled with the reduced expression of ROS-scavengers contribute to the behavioral decline. However, as a compensatory response to reduce altered catabolism/ROS production, anabolic enzymes expression levels are also increased, resulting in higher gluconeogenesis and lipid synthesis. DOI: http://dx.doi.org/10.7554/eLife.01730.001.

Glutathione and thioredoxin type 1 cooperatively denitrosate HepG2 cells-derived cytosolic S-nitrosoproteins

In this study, we present experimental evidence that glutathione acts in concert with human thioredoxin type 1 in the denitrosation of cytosolic S-nitrosoproteins (PSNOs) from HepG2 cells.

Thyroid hormones and antioxidant systems: focus on oxidative stress in cardiovascular and pulmonary diseases

In previous works we demonstrated an inverse correlation between plasma Coenzyme Q₁₀ (CoQ₁₀) and thyroid hormones; in fact, CoQ₁₀ levels in hyperthyroid patients were found among the lowest detected in human diseases. On the contrary, CoQ₁₀ is elevated in hypothyroid subjects, also in subclinical conditions, suggesting the usefulness of this index in assessing metabolic status in thyroid disorders. A Low-T3 syndrome is a condition observed in several chronic diseases: it is considered an adaptation mechanism, where there is a reduction in pro-hormone T4 conversion. Low T3-Syndrome is not usually considered to be corrected with replacement therapy. We review the role of thyroid hormones in regulation of antioxidant systems, also presenting data on total antioxidant capacity and Coenzyme Q₁₀. Published studies suggest that oxidative stress could be involved in the clinical course of different heart diseases; our data could support the rationale of replacement therapy in low-T3 conditions.

Mitochondrial targets for arrhythmia suppression: is there a role for pharmacological intervention?

Mitochondrial dysfunction is a hallmark of common cardiovascular disorders, including ischemia-reperfusion injury, hypertrophy, heart failure, and diabetes mellitus. While the role of the mitochondrial network in regulating energy production and cell death pathways is well established, its active control of other critical cellular functions, including excitation-contraction coupling and excitability, is less understood. The purpose of this focused review article is to highlight the growing mechanistic link between mitochondrial dysfunction and arrhythmogenesis. The goal is not to provide a comprehensive listing of all factors by which mitochondrial bioenergetics and altered cellular redox status affect ion channel function but rather to focus on one central mechanism of arrhythmogenesis which arises from a mitochondrial origin. In doing so, we discuss the role of mitochondrial targets for suppressing arrhythmias through this mechanism.