Myoglobin deficiency impairs maximal oxygen uptake and exercise performance: a lesson from Mb-/- mice.

Myoglobin (Mb) plays an important role at rest and during exercise as a reservoir of oxygen and has been suggested to regulate NO• bioavailability under hypoxic/acidic conditions. However, its ultimate role during exercise is still a subject of debate. We aimed to study the effect of Mb deficiency on maximal oxygen uptake ( V ̇ O 2 max ${\dot V_{{{\mathrm{O}}_2}\max }}$ ) and exercise performance in myoglobin knockout mice (Mb-/- ) when compared to control mice (Mb+/+ ). Furthermore, we also studied NO• bioavailability, assessed as nitrite (NO2 - ) and nitrate (NO3 - ) in the heart, locomotory muscle and in plasma, at rest and during exercise at exhaustion both in Mb-/- and in Mb+/+ mice. The mice performed maximal running incremental exercise on a treadmill with whole-body gas exchange measurements. The Mb-/- mice had lower body mass, heart and hind limb muscle mass (P < 0.001). Mb-/- mice had significantly reduced maximal running performance (P < 0.001). V ̇ O 2 max ${\dot V_{{{\mathrm{O}}_2}\max }}$ expressed in ml min-1 in Mb-/ - mice was 37% lower than in Mb+/+ mice (P < 0.001) and 13% lower when expressed in ml min-1  kg body mass-1 (P = 0.001). Additionally, Mb-/- mice had significantly lower plasma, heart and locomotory muscle NO2 - levels at rest. During exercise NO2 - increased significantly in the heart and locomotory muscles of Mb-/- and Mb+/+ mice, whereas no significant changes in NO2 - were found in plasma. Our study showed that, contrary to recent suggestions, Mb deficiency significantly impairs V ̇ O 2 max ${\dot V_{{{\mathrm{O}}_2}\max }}$ and maximal running performance in mice. KEY POINTS: Myoglobin knockout mice (Mb-/- ) possess lower maximal oxygen uptake ( V ̇ O 2 max ${\dot V_{{{\mathrm{O}}_2}\max }}$ ) and poorer maximal running performance than control mice (Mb+/+ ). Respiratory exchange ratio values at high running velocities in Mb-/- mice are higher than in control mice suggesting a shift in substrate utilization towards glucose metabolism in Mb-/- mice at the same running velocities. Lack of myoglobin lowers basal systemic and muscle NO• bioavailability, but does not affect exercise-induced NO2 - changes in plasma, heart and locomotory muscles. The present study demonstrates that myoglobin is of vital importance for V ̇ O 2 max ${\dot V_{{{\mathrm{O}}_2}\max }}$ and maximal running performance as well as explains why previous studies have failed to prove such a role of myoglobin when using the Mb-/- mouse model.

Preclinical models of cardiotoxicity from immune checkpoint inhibitor therapy.

Immune checkpoint inhibitor (ICI) therapy represents a ground-breaking paradigm in cancer treatment, harnessing the immune system to combat malignancies by targeting checkpoints such as cytotoxic T-lymphocyte-associated protein 4 (CTLA-4) and programmed cell death protein 1 (PD-1). The use of ICI therapy generates distinctive immune-related adverse events (irAEs) including cardiovascular toxicity, necessitating targeted research efforts. This comprehensive review explores preclinical models dedicated to ICI-mediated cardiovascular complications including myocarditis. Tailored preclinical models of ICI-mediated myocardial toxicities highlight the key role of CD8+ T cells, emphasizing the profound impact of immune checkpoints on maintaining cardiac integrity. Cytokines and macrophages were identified as possible driving factors in disease progression, and at the same time, initial data on possible cardiac antigens responsible are emerging. The implications of contributing factors including thoracic radiation, autoimmune disorder, and the presence of cancer itself are increasingly understood. Besides myocarditis, mouse models unveiled an accelerated progression of atherosclerosis, adding another layer for a thorough understanding of the diverse processes involving cardiovascular immune checkpoint signalling. This review aims to discuss current preclinical models of ICI cardiotoxicity and their potential for improving enhanced risk assessment and diagnostics, offering potential targets for innovative cardioprotective strategies. Lessons from ICI therapy can drive novel approaches in cardiovascular research, extending insights to areas such as myocardial infarction and heart failure.

Targeting early stages of cardiotoxicity from anti-PD1 immune checkpoint inhibitor therapy.

AIMS: Cardiac immune-related adverse events (irAEs) from immune checkpoint inhibition (ICI) targeting programmed death 1 (PD1) are of growing concern. Once cardiac irAEs become clinically manifest, fatality rates are high. Cardio-oncology aims to prevent detrimental effects before manifestation of severe complications by targeting early pathological changes. We therefore aimed to investigate early consequences of PD1 inhibition for cardiac integrity to prevent the development of overt cardiac disease. METHODS AND RESULTS: We investigated cardiac-specific consequences from anti-PD1 therapy in a combined biochemical and in vivo phenotyping approach. Mouse hearts showed broad expression of the ligand PDL1 on cardiac endothelial cells as a main mediator of immune-crosstalk. Using a novel melanoma mouse model, we assessed that anti-PD1 therapy promoted myocardial infiltration with CD4+ and CD8+ T cells, the latter being markedly activated. Left ventricular (LV) function was impaired during pharmacological stress, as shown by pressure-volume catheterization. This was associated with a dysregulated myocardial metabolism, including the proteome and the lipidome. Analogous to the experimental approach, in patients with metastatic melanoma (n = 7) receiving anti-PD1 therapy, LV function in response to stress was impaired under therapy. Finally, we identified that blockade of tumour necrosis factor alpha (TNFα) preserved LV function without attenuating the anti-cancer efficacy of anti-PD1 therapy. CONCLUSIONS: Anti-PD1 therapy induces a disruption of cardiac immune homeostasis leading to early impairment of myocardial functional integrity, with potential prognostic effects on the growing number of treated patients. Blockade of TNFα may serve as an approach to prevent the manifestation of ICI-related cardiotoxicity.

Blockade of ß-Adrenergic Receptors by Nebivolol Enables Tumor Control Potential for Uveal Melanoma in 3D Tumor Spheroids and 2D Cultures.

Uveal melanoma (UM) is the most common primary cancer of the eye in adults. A new systemic therapy is needed to reduce the high metastasis and mortality rate. As ß-blockers are known to have anti-tumor effects on various cancer entities, this study focuses on investigating the effect of ß1-selective blockers atenolol, celiprolol, bisoprolol, metoprolol, esmolol, betaxolol, and in particular, nebivolol on UM. The study was performed on 3D tumor spheroids as well as 2D cell cultures, testing tumor viability, morphological changes, long-term survival, and apoptosis. Flow cytometry revealed the presence of all three ß-adrenoceptors with a dominance of ß2-receptors on cell surfaces. Among the blockers tested, solely nebivolol concentration-dependently decreased viability and altered 3D tumor spheroid structure. Nebivolol blocked the repopulation of cells spreading from 3D tumor spheroids, indicating a tumor control potential at a concentration of ≥20 µM. Mechanistically, nebivolol induced ATP depletion and caspase-3/7 activity, indicating that mitochondria-dependent signaling is involved. D-nebivolol or nebivolol combined with the ß2-antagonist ICI 118.551 displayed the highest anti-tumor effects, suggesting a contribution of both ß1- and ß2-receptors. Thus, the present study reveals the tumor control potential of nebivolol in UM, which may offer a perspective for co-adjuvant therapy to reduce recurrence or metastasis.

Anthracycline Therapy Modifies Immune Checkpoint Signaling in the Heart.

Cancer survival rates have increased significantly because of improvements in therapy regimes and novel immunomodulatory drugs. Recently, combination therapies of anthracyclines and immune checkpoint inhibitors (ICIs) have been proposed to maximize neoplastic cell removal. However, it has been speculated that a priori anthracycline exposure may prone the heart vulnerable to increased toxicity from subsequent ICI therapy, such as an anti-programmed cell death protein 1 (PD1) inhibitor. Here, we used a high-dose anthracycline mouse model to characterize the role of the PD1 immune checkpoint signaling pathway in cardiac tissue using flow cytometry and immunostaining. Anthracycline treatment led to decreased heart function, increased concentration of markers of cell death after six days and a change in heart cell population composition with fewer cardiomyocytes. At the same time point, the number of PD1 ligand (PDL1)-positive immune cells and endothelial cells in the heart decreased significantly. The results suggest that PD1/PDL1 signaling is affected after anthracycline treatment, which may contribute to an increased susceptibility to immune-related adverse events of subsequent anti-PD1/PDL1 cancer therapy.

PD1 Deficiency Modifies Cardiac Immunity during Baseline Conditions and in Reperfused Acute Myocardial Infarction.

The programmed cell death protein 1 (PD1) immune checkpoint prevents inflammatory tissue damage by inhibiting immune reactions. Understanding the relevance of cardiac PD1 signaling may provide new insights into the inflammatory events under baseline conditions and disease. Here, we demonstrate distinct immunological changes upon PD1 deficiency in healthy hearts and during reperfused acute myocardial infarction (repAMI). In PD1-deficient mice, upregulated inflammatory cytokines were identified under baseline conditions including cardiac interleukins and extracellular signal-related kinase 1/2 (ERK1/2). A murine in vivo repAMI model to determine inflammatory changes in the early phase showed downregulation of the ligand PDL1, paralleled by an endothelial injury, indicated by loss of the CD31 signal. Immunofluorescence imaging showed decreased PDL1 expression specifically in the infarct zone, highlighting an involvement in PDL1 in myocardial injury response. Pharmacological depletion of PD1 prior to repAMI did not alter the area of infarction but led to increased numbers of CD8+ T cells in treated mice. We conclude that PD1/PDL1 signaling plays a significant role in healthy hearts and repAMI, emphasizing the relevance of adaptive immunity during myocardial injury. The findings highlight the risk for adverse outcomes from acute myocardial infarction in the growing group of patients receiving immune checkpoint inhibitor therapy.

Nitrite Concentration in the Striated Muscles Is Reversely Related to Myoglobin and Mitochondrial Proteins Content in Rats.

Skeletal muscles are an important reservoir of nitric oxide (NO•) stored in the form of nitrite [NO2-] and nitrate [NO3-] (NOx). Nitrite, which can be reduced to NO• under hypoxic and acidotic conditions, is considered a physiologically relevant, direct source of bioactive NO•. The aim of the present study was to determine the basal levels of NOx in striated muscles (including rat heart and locomotory muscles) with varied contents of tissue nitrite reductases, such as myoglobin and mitochondrial electron transport chain proteins (ETC-proteins). Muscle NOx was determined using a high-performance liquid chromatography-based method. Muscle proteins were evaluated using western-immunoblotting. We found that oxidative muscles with a higher content of ETC-proteins and myoglobin (such as the heart and slow-twitch locomotory muscles) have lower [NO2-] compared to fast-twitch muscles with a lower content of those proteins. The muscle type had no observed effect on the [NO3-]. Our results demonstrated that fast-twitch muscles possess greater potential to generate NO• via nitrite reduction than slow-twitch muscles and the heart. This property might be of special importance for fast skeletal muscles during strenuous exercise and/or hypoxia since it might support muscle blood flow via additional NO• provision (acidic/hypoxic vasodilation) and delay muscle fatigue.

The impact of percutaneous peripheral interventions on endothelial function.

Background: Treatment of symptomatic peripheral artery disease (PAD) through endovascular interventions is the primary revascularization strategy. Interventions restore perfusion but may cause severe injury to the vascular endothelium, which regulates vascular tone. Endothelial dysfunction is involved in the progression of cardiovascular disease, with higher incidences of vascular events. We aimed to determine the impact of percutaneous interventions on change in endothelial function. Patients and methods: Endothelial function was determined using flow-mediated dilation (FMD) before, the day after lower limb intervention with paclitaxel-coated balloons or stent guided interventions and after a six-month follow-up in the target limb, control limb and the systemic circulation in 42 PAD patients aged 70.2±9 years and 66% men. Additionally, macro- and microvascular function were assessed. Results: In PAD patients aged 70.2±9 years and 66% men, we observed an immediate enhancement of macro-, microvascular and endothelial function after endovascular treatment (FMD of superficial femoral artery (SFA) 3.7±0.2% to 4.1±0.1%, n=42, p=0.02), a sustained long-term improvement after 6-months (FMD SFA 3.7±0.2% to 4.2±0.1%, n=42, p=0.01), and moreover an improved systemic endothelial function (FMD brachial artery 4.3±0.1% to 4.7±0.2, n=42, p=0.01) following peripheral interventions. Subgroup analysis however revealed that following paclitaxel-based percutaneous intervention, the paclitaxel dosage applied was inversely related to the chronic improvement in local endothelial function (r=-0.6, n=22, p=0.005) without evidence for systemic effects (r=-0.25, p=0.27). Conclusions: We demonstrate an improved local and systemic endothelial function after treatment of atherosclerotic peripheral disease with a distinguished response after endovascular intervention with higher dosage of applied paclitaxel restraining the benefits. Further studies have to determine the optimal interventional strategy with respect to different treatment modalities to maintain vessel functions.

Platinum-Based Drugs Cause Mitochondrial Dysfunction in Cultured Dorsal Root Ganglion Neurons.

Cisplatin and oxaliplatin are treatment options for a variety of cancer types. While highly efficient in killing cancer cells, both chemotherapeutics cause severe side effects, e.g., peripheral neuropathies. Using a cell viability assay, a mitochondrial stress assay, and live-cell imaging, the effects of cis- or oxaliplatin on the mitochondrial function, reactive oxygen species (ROS) production, and mitochondrial and cytosolic calcium concentration of transient receptor potential ankyrin 1 (TRPA1)- or vanilloid 1 (TRPV1)-positive dorsal root ganglion (DRG) neurons of adult Wistar rats were determined. Mitochondrial functions were impaired after exposure to cis- or oxaliplatin by mitochondrial respiratory chain complex I-III inhibition. The basal respiration, spare respiratory capacity, and the adenosine triphosphate (ATP)-linked respiration were decreased after exposure to 10 µM cis- or oxaliplatin. The ROS production showed an immediate increase, and after reaching the peak, ROS production dropped. Calcium imaging showed an increase in the cytosolic calcium concentration during exposure to 10 µM cis- or oxaliplatin in TRPA1- or TRPV1-positive DRG neurons while the mitochondrial calcium concentration continuously decreased. Our data demonstrate a significant effect of cis- and oxaliplatin on mitochondrial function as an early event of platinum-based drug exposure, suggesting mitochondria as a potential target for preventing chemotherapy-induced neuropathy.

9-PAHSA Prevents Mitochondrial Dysfunction and Increases the Viability of Steatotic Hepatocytes.

Nonalcoholic fatty liver disease (NAFLD) is quickly becoming the most common liver disease worldwide. Within the NAFLD spectrum, patients with nonalcoholic steatohepatitis (NASH) are at the highest risk of developing cirrhosis and disease progression to hepatocellular carcinoma. To date, therapeutic options for NASH patients have been ineffective, and therefore, new options are urgently needed. Hence, a model system to develop new therapeutic interventions is needed. Here, we introduce two new in vitro models of steatosis induction in HepG2 cells and primary murine hepatocytes. We used a recently discovered novel class of bioactive anti-inflammatory lipids called branched fatty acid esters of hydroxyl fatty acids. Among these bioactive lipids, palmitic-acid-9-hydroxy-stearic-acid (9-PAHSA) is the most promising as a representative nondrug therapy based on dietary supplements or nutritional modifications. In this study, we show a therapeutic effect of 9-PAHSA on lipotoxicity in steatotic primary hepatocytes and HepG2 cells. This could be shown be increased viability and decreased steatosis. Furthermore, we could demonstrate a preventive effect in HepG2 cells. The outcome of 9-PAHSA administration is both preventative and therapeutically effective for hepatocytes with limited damage. In conclusion, bioactive lipids like 9-PAHSA offer new hope for prevention or treatment in patients with fatty liver and steatosis.

Angiotensin-(1-7)-induced Mas receptor activation attenuates atherosclerosis through a nitric oxide-dependent mechanism in apolipoproteinE-KO mice.

Angiotensin (Ang)-(1-7) ameliorates vascular injury by increasing nitric oxide (NO) bioavailability. Evidence that Ang-(1-7) attenuates the development of atherosclerosis through a NO-dependent mechanism is still missing. Moreover, it has been postulated that Ang-(1-7) may mediate its effects by other mechanisms than Mas receptor activation. To investigate Ang-(1-7)-dependent Mas receptor function, we treated apoE-KO and apoE/Mas-KO mice chronically with Ang-(1-7) (82 µg/kg per hour) or saline for 6 weeks. Flow-mediated dilation (FMD), a measure for NO-dependent vasodilation and the most accepted prognostic marker for the development of atherosclerosis, was measured in vivo. Chronic Ang-(1-7) treatment improved FMD and attenuated the development of atherosclerosis in apolipoproteinE (apoE)-KO but not in apoE/Mas-KO mice. These effects were accompanied by increased aortic nitrite and cGMP levels. To test whether Ang-(1-7) modulates atherosclerosis through a NO-dependent mechanism, apoE-KO mice were treated with the NO synthase inhibitor L-NAME (20 mg/kg/day) in the presence or absence of Ang-(1-7). L-NAME treatment reduced aortic nitrite content and increased blood pressure and exaggerated atherosclerosis compared to untreated apoE-KO mice. In L-NAME-treated apoE-KO mice, chronic Ang-(1-7) treatment did not increase aortic nitrite content and consequently showed no effect on blood pressure and the development of atherosclerosis. The present study proves that Ang-(1-7) mediates its protective vascular effects through Mas receptor activation. Moreover, Ang-(1-7)-mediated NO generation is essential for improving vascular function and prevents atherosclerosis in apoE-KO mice.

S-nitrosation of calpains is associated with cardioprotection in myocardial I/R injury.

BACKGROUND: Myocardial infarction remains the single leading cause of death worldwide. Upon reperfusion of occluded arteries, deleterious cellular mediators particularly located at the mitochondria level can be activated, thus limiting the outcome in patients. This may lead to the so-called ischemia/reperfusion (I/R) injury. Calpains are cysteine proteases and mediators of caspase-independent cell death. Recently, they have emerged as central transmitters of cellular injury in several cardiac pathologies e.g. hypertrophy and acute I/R injury. METHODS: Here we investigated the role of cardiac calpains in acute I/R in relation to mitochondrial integrity and whether calpains can be effectively inhibited by posttranslational modification by S-nitrosation. Taking advantage of the a cardiomyocyte cell line (HL1), we determined S-nitrosation by the Biotin-switch approach, cell viability and intracellular calcium concentration after simulated ischemia and reoxygenation - all in dependence of supplementation with nitrite, which is known as an 'hypoxic nitric oxide (NO) donor'. Likewise, using an in vivo I/R model, calpain S-nitrosation, calpain activity and myocardial I/R injury were characterized in vivo. RESULTS: Nitrite administration resulted in an increased S-nitrosation of calpains, and this was associated with an improved cell-survival. No impact was detected on calcium levels. In line with these in vitro experiments, nitrite initiated calpain S-nitrosation in vivo and caused an infarct sparing effect in an in vivo myocardial I/R model. Using electron microscopy in combination with immuno-gold labeling we determined that calpain 10 increased, while calpain 2 decreased in the course of I/R. Nitrite, in turn, prevented an I/R induced increase of calpains 10 at mitochondria and reduced levels of calpain 1. CONCLUSION: Lethal myocardial injury remains a key aspect of myocardial I/R. We show that calpains, as key players in caspase-independent apoptosis, increasingly locate at mitochondria following I/R. Inhibitory post-translational modification by S-nitrosation of calpains reduces deleterious calpain activity in murine cardiomyocytes and in vivo.

Nitrite-Nitric Oxide Signaling and Cardioprotection.

Cardioprotective strategies to prevent damage to mitochondria in acute myocardial infarction are warranted to reduce lethal myocardial ischemia/reperfusion (I/R) injury. Mitochondrial antagonists in I/R are reactive oxygen species (ROS), deteriorated calcium signaling, permeabilization of the mitochondrial outer membrane (MOM) and deranged mitochondrial structural dynamism (fusion and fission). Nitric oxide (NO) related signaling can protect hearts from I/R. Albeit the underlying signaling is incompletely resolved, recent data point to a particular involvement of protective posttranslational modification of mitochondrial elements. We and others have demonstrated that hypoxic NO signaling in cardiomyocytes is associated with a posttranslational mitochondrial complex I modification to reduce the burden of ROS. Induction of cardioprotective NO signaling may occur through several pathways. These include (i) the supplementation with mitochondria unspecific and specific NO-donors, (ii) the administration of the 'hypoxic-NO donors nitrate and nitrite' and (iii) the enhancement of endogenous NO formation, e.g. by remote ischemic preconditioning maneuvers (rIPC). In this chapter, we outline how NO signaling is activated in the cardiomyocyte, characterize the downstream signaling pathways and discuss how this could translate into a tractable therapeutic approach in patients requiring cardioprotection.

Cytosolic BNIP3 Dimer Interacts with Mitochondrial BAX Forming Heterodimers in the Mitochondrial Outer Membrane under Basal Conditions.

The primary function of mitochondria is energy production, a task of particular importance especially for cells with a high energy demand like cardiomyocytes. The B-cell lymphoma (BCL-2) family member BCL-2 adenovirus E1B 19 kDa-interacting protein 3 (BNIP3) is linked to mitochondrial targeting after homodimerization, where it functions in inner membrane depolarization and permeabilization of the mitochondrial outer membrane (MOM) mediating cell death. We investigated the basal distribution of cardiac BNIP3 in vivo and its physical interaction with the pro-death protein BCL2 associated X, apoptosis regulator (BAX) and with mitochondria using immunoblot analysis, co-immunoprecipitation, and continuous wave and pulsed electron paramagnetic resonance spectroscopy techniques. We found that BNIP3 is present as a dimer in the cytosol and in the outer membrane of cardiac mitochondria under basal conditions. It forms disulfide-bridged, but mainly non-covalent dimers in the cytosol. Heterodimers with BAX are formed exclusively in the MOM. Furthermore, our results suggest that BNIP3 interacts with the MOM directly via mitochondrial BAX. However, the physical interactions with BAX and the MOM did not affect the membrane potential and cell viability. These findings suggest that another stimulus other than the mere existence of the BNIP3/BAX dimer in the MOM is required to promote BNIP3 cell-death activity; this could be a potential disturbance of the BNIP3 distribution homeostasis, namely in the direction of the mitochondria.

Circulating nitrite contributes to cardioprotection by remote ischemic preconditioning.

RATIONALE: Remote ischemic preconditioning (rIPC) with short episodes of ischemia/reperfusion (I/R) of an organ remote from the heart is a powerful approach to protect against myocardial I/R injury. The signal transduction pathways for the cross talk between the remote site and the heart remain unclear in detail. OBJECTIVE: To elucidate the role of circulating nitrite in cardioprotection by rIPC. METHODS AND RESULTS: Mice were subjected to 4 cycles of no-flow ischemia with subsequent reactive hyperemia within the femoral region and underwent in vivo myocardial I/R (30 minutes/5 minutes or 24 hours). The mouse experiments were conducted using genetic and pharmacological approaches. Shear stress-dependent stimulation of endothelial nitric oxide synthase within the femoral artery during reactive hyperemia yielded substantial release of nitric oxide, subsequently oxidized to nitrite and transferred humorally to the myocardium. Within the heart, reduction of nitrite to nitric oxide by cardiac myoglobin and subsequent S-nitrosation of mitochondrial membrane proteins reduced mitochondrial respiration, reactive oxygen species formation, and myocardial infarct size. Pharmacological and genetic inhibition of nitric oxide/nitrite generation by endothelial nitric oxide synthase at the remote site or nitrite bioactivation by myoglobin within the target organ abrogated the cardioprotection by rIPC. Transfer experiments of plasma from healthy volunteers subjected to rIPC of the arm identified plasma nitrite as a cardioprotective agent in isolated Langendorff mouse heart preparations exposed to I/R. CONCLUSIONS: Circulating nitrite derived from shear stress-dependent stimulation of endothelial nitric oxide synthase at the remote site of rIPC contributes to cardioprotection during I/R. CLINICAL TRIAL REGISTRATION URL: http://www.clinicaltrials.gov. Unique identifier: NCT01259739.

Nitrite circumvents canonical cGMP signaling to enhance proliferation of myocyte precursor cells.

Skeletal muscle tissue has a remarkable high regenerative capacity. The underlying cellular events are governed by complex signaling processes, and the proliferation of skeletal myoblasts is a key initial event. The role of nitric oxide (NO) in cell cycle regulation is well-appreciated. Nitrite, an NO oxidation product, is a stable source for NO-like bioactivity particularly in cases when oxygen shortage compromises NO-synthases activity. Although numerous studies suggest that nitrite effects are largely related to NO-dependent signaling, emerging evidence also implicates that nitrite itself can activate protein pathways albeit under physiological, normoxic conditions. This includes a recently demonstrated cyclic guanosine monophosphate-(cGMP)-independent enhancement of endothelial cell proliferation. Whether nitrite itself has the potential to affect myoblast proliferation and metabolism with or without activation of the canonical NO/cGMP pathway to subsequently support muscle cell regeneration is not known. Here we show that nitrite increases proliferation and metabolic activity of murine cultured myoblasts dose-dependently. This effect is not abolished by the NO scavenger 2-(4-carboxy-phenyl)-4,4,5,5-tetramethylimida-zoline-1-oxyl-3 oxide and does not affect intracellular cGMP levels, implicating a cGMP-independent mechanism. Nitrite circumvents the rapamycin induced attenuation of myoblast proliferation and enhances mTOR activity. Our results provide evidence for a novel potential physiological and therapeutic approach of nitrite in skeletal muscle regeneration processes under normoxia independent of NO and cGMP.

S-nitrosation of mitochondrial connexin 43 regulates mitochondrial function.

S-nitrosation (SNO) of connexin 43 (Cx43)-formed channels modifies dye uptake in astrocytes and gap junctional communication in endothelial cells. Apart from forming channels at the plasma membrane of several cell types, Cx43 is also located at the inner membrane of myocardial subsarcolemmal mitochondria (SSM), but not in interfibrillar mitochondria (IFM). The absence or pharmacological blockade of mitochondrial Cx43 (mtCx43) reduces dye and potassium uptake. Lack of mtCx43 is associated with loss of endogenous cardioprotection by ischemic preconditioning (IPC), which is mediated by formation of reactive oxygen species (ROS). Whether or not mitochondrial Lucifer Yellow (LY), ion uptake, or ROS generation are affected by SNO of mtCx43 and whether or not cardioprotective interventions affect SNO of mtCx43 remains unknown. In SSM from rat hearts, application of NO donors (48 nmol to 1 mmol) increased LY uptake (0.5 mmol SNAP 38.4 ± 7.1 %, p < 0.05; 1 mmol GSNO 28.1 ± 7.4 %, p < 0.05) and the refilling rate of potassium (SNAP 227.9 ± 30.1 %, p < 0.05; GSNO 122.6 ± 28.1 %, p < 0.05). These effects were absent following blockade of Cx43 hemichannels by carbenoxolone as well as in IFM lacking Cx43. Unlike potassium, the sodium permeability was not affected by application of NO. Furthermore, mitochondrial ROS formation was increased following NO application compared to control SSM (0.5 mmol SNAP 22.9 ± 1.8 %, p < 0.05; 1 mmol GSNO 40.6 ± 7.1 %, p < 0.05), but decreased in NO treated IFM compared to control (0.5 mmol SNAP 14.4 ± 4 %, p < 0.05; 1 mmol GSNO 13.8 ± 4 %, p < 0.05). NO donor administration to isolated SSM increased SNO of mtCx43 by 109.2 ± 15.8 %. Nitrite application (48 nmol) to mice was also associated with elevated SNO of mtCx43 by 59.3 ± 18.2 % (p < 0.05). IPC by four cycles of 5 min of ischemia and 5 min of reperfusion increased SNO of mtCx43 by 41.6 ± 1.7 % (p < 0.05) when compared to control perfused rat hearts. These data suggest that SNO of mtCx43 increases mitochondrial permeability, especially for potassium and leads to increased ROS formation. The increased amount of SNO mtCx43 by IPC or nitrite administration may link NO and Cx43 in the signal transduction cascade of cardioprotective interventions.

Implanted Carbon Nanotubes Harvest Electrical Energy from Heartbeat for Medical Implants.

Reliability of power supply for current implantable electronic devices is a critical issue for longevity and for reducing the risk of device failure. Energy harvesting is an emerging technology, representing a strategy for establishing autonomous power supply by utilizing biomechanical movements in human body. Here, a novel "Twistron energy cell harvester" (TECH), consisting of coiled carbon nanotube yarn that converts mechanical energy of the beating heart into electrical energy, is presented. The performance of TECH is evaluated in an in vitro artificial heartbeat system which simulates the deformation pattern of the cardiac surface, reaching a maximum peak power of 1.42 W kg-1 and average power of 0.39 W kg-1 at 60 beats per minute. In vivo implantation of TECH onto the left ventricular surface in a porcine model continuously generates electrical energy from cardiac contraction. The generated electrical energy is used for direct pacing of the heart as documented by extensive electrophysiology mapping. Implanted modified carbon nanotubes are applicable as a source for harvesting biomechanical energy from cardiac motion for power supply or cardiac pacing.

Wolfram-silicone implants as effective radiation shielding for ocular brachytherapy: dosimetric features and in vivo animal study on biocompatibility.

OBJECTIVE: To evaluate wolfram as a photon and beta absorber in the management of uveal melanoma with radiotherapy, examining its potential ocular adverse effects and physiologic tolerance using an in vivo rabbit ocular model. METHODS: A method of manufacturing implants from mixtures of wolfram and silicone was developed. Their shielding effect on the radiation of sources used in ocular brachytherapy was investigated by dosimetric measurement in an eye phantom as well as numerical simulations. Different wolfram implantation techniques, such as extraocular fixation of a wolfram-silicone implant (n = 1), vitrectomy with silicone oil and intravitreal injection of a wolfram-silicone oil suspension (n = 2), and concurrent attachment of a wolfram implant onto the sclera (n = 2), were tested to investigate the long-term effects of wolfram. A vitrectomy with silicone oil without wolfram implantation was carried out in 2 rabbits (n = 2), constituting the control group. The eyes were enucleated after 3 months for histologic analysis. RESULTS: Wolfram-silicone mixtures have been dosimetrically proven to be very effective radiation absorbers for use in ocular brachytherapy. Severe complications, such as endophthalmitis, secondary glaucoma, cornea decompensation, and vessel occlusion, were not documented in the tested rabbit eyes after the application of wolfram. Histologic examination of the bulbi after enucleation showed epiretinal gliosis without further pathologic findings in all eyes after vitrectomy. CONCLUSIONS: The results of this study show that wolfram and wolfram-silicone implants constitute a promising candidate as potential radiation shielding substrates.

Dietary nitrate supplementation improves revascularization in chronic ischemia.

BACKGROUND: Revascularization is an adaptive repair mechanism that restores blood flow to undersupplied ischemic tissue. Nitric oxide plays an important role in this process. Whether dietary nitrate, serially reduced to nitrite by commensal bacteria in the oral cavity and subsequently to nitric oxide and other nitrogen oxides, enhances ischemia-induced remodeling of the vascular network is not known. METHODS AND RESULTS: Mice were treated with either nitrate (1 g/L sodium nitrate in drinking water) or sodium chloride (control) for 14 days. At day 7, unilateral hind-limb surgery with excision of the left femoral artery was conducted. Blood flow was determined by laser Doppler. Capillary density, myoblast apoptosis, mobilization of CD34(+)/Flk-1(+), migration of bone marrow-derived CD31(+)/CD45(-), plasma S-nitrosothiols, nitrite, and skeletal tissue cGMP levels were assessed. Enhanced green fluorescence protein transgenic mice were used for bone marrow transplantation. Dietary nitrate increased plasma S-nitrosothiols and nitrite, enhanced revascularization, increased mobilization of CD34(+)/Flk-1(+) and migration of bone marrow-derived CD31(+)/CD45(-) cells to the site of ischemia, and attenuated apoptosis of potentially regenerative myoblasts in chronically ischemic tissue. The regenerative effects of nitrate treatment were abolished by eradication of the nitrate-reducing bacteria in the oral cavity through the use of an antiseptic mouthwash. CONCLUSIONS: Long-term dietary nitrate supplementation may represent a novel nutrition-based strategy to enhance ischemia-induced revascularization.