Cardioselective nitric oxide synthase 3 gene transfer protects against myocardial reperfusion injury

Dysfunctional and Dysregulated Nitric Oxide Synthases in Cardiovascular Disease: Mechanisms and Therapeutic Potential

Nitric oxide (NO) plays an important and diverse signalling role in the cardiovascular system, contributing to the regulation of vascular tone, endothelial function, myocardial function, haemostasis, and thrombosis, amongst many other roles. NO is synthesised through the nitric oxide synthase (NOS)-dependent L-arginine-NO pathway, as well as the nitrate-nitrite-NO pathway. The three isoforms of NOS, namely neuronal (NOS1), inducible (NOS2), and endothelial (NOS3), have different localisation and functions in the human body, and are consequently thought to have differing pathophysiological roles. Furthermore, as we continue to develop a deepened understanding of the different roles of NOS isoforms in disease, the possibility of therapeutically modulating NOS activity has emerged. Indeed, impaired (or dysfunctional), as well as overactive (or dysregulated) NOS activity are attractive therapeutic targets in cardiovascular disease. This review aims to describe recent advances in elucidating the physiological role of NOS isoforms within the cardiovascular system, as well as mechanisms of dysfunctional and dysregulated NOS in cardiovascular disease. We then discuss the modulation of NO and NOS activity as a target in the development of novel cardiovascular therapeutics.

Mechanisms of eccentric contraction-induced muscle damage and nutritional supplementations for mitigating it

Eccentric contraction (ECC) often results in large and long-lasting force deficits accompanied by muscle soreness, primarily due to muscle damage. In this sense, exercises that involve ECC are less desirable. Paradoxically, exercise training that includes a substantial eccentric phase leads to a more powerful activation of the genes responsible for skeletal muscle remodeling (e.g., hypertrophy) than other types of training that emphasize a concentric or isometric phase. Therefore, effective strategies that lessen ECC-induced muscle damage will be of interest and importance to many individuals. The purpose of this brief review is to highlight the published literature on the effects of ECC and/or nutritional supplementations on proteins, lipids, metabolic and ionic changes, and enzyme activities in skeletal muscles subjected to an acute bout of ECC. First, we discuss the potential mechanisms by which ECC causes muscle damage. Previous findings implicate a Ca²⁺ overload-oxidative modification pathway as one possible mechanism contributing to muscle damage. Thereafter, the efficacy of two nutritional supplementations, i.e., L-arginine and antioxidant, is discussed because L-arginine and antioxidant would be expected to ameliorate the adverse effects of Ca²⁺ overload and oxidative modification, respectively. Of these, L-arginine ingestion before ECC seems likely to be the effective strategy for mitigating ECC-related proteolysis. More studies are needed to establish the effectiveness of antioxidant ingestion. The application of effective strategies against muscle damage may contribute to improvements in health and fitness, muscle function, and sports performance.

l-arginine ingestion inhibits eccentric contraction-induced proteolysis and force deficit via S-nitrosylation of calpain

It has been shown that calpains are involved in the proteolysis of muscle proteins that occurs with eccentric contraction (ECC) and that exogenously applied nitric oxide decreases the calpain‐mediated proteolysis. The aim of this study was to examine the effects of ingestion of l‐arginine (ARG), a nitric oxide precursor, on ECC‐related calpain activation. In the first and second experiments, male Wistar rats were given ARG in water for 7 days starting from 3 days before the ECC protocol (average ingestion, ~600 mg kg‐body wt⁻¹ day⁻¹). Tibialis anterior muscles underwent 200 repeated ECCs and, subsequently, were excised 3 days later. Whole muscle analyses (the first experiment) revealed that ARG attenuated ECC‐induced force deficit and autolysis of calpain‐1, and increased the amounts of S‐nitrosylated calpain‐1. Regarding ryanodine receptor (RyR) and dihydropyridine receptor (DHPR), ECC‐induced proteolysis was completely inhibited by ARG, whereas the inhibition was partial for junctophilin‐1 (JP1). Skinned fiber analyses (the second experiment) showed that ARG also inhibited ECC‐elicited reductions in the ratio of depolarization‐induced to maximum Ca²⁺‐activated force. In the third experiment, homogenates of rested muscles were treated with S‐nitrosylating agent, S‐nitrosoglutathione (GSNO), and/or high Ca²⁺ concentration ([Ca²⁺]). Treatment with high [Ca²⁺] and without GSNO produced proteolysis of RyR, DHPR, and JP1. On the other hand, treatment with high [Ca²⁺] and GSNO caused complete inhibition of RyR and DHPR proteolysis and partial inhibition of JP1 proteolysis. These results indicate that ARG ingestion can attenuate ECC‐induced proteolysis of Ca²⁺ regulatory proteins and force deficit by decreasing calpain activation via S‐nitrosylation.

Nitric oxide signalling in cardiovascular health and disease

Nitric oxide (NO) signalling has pleiotropic roles in biology and a crucial function in cardiovascular homeostasis. Tremendous knowledge has been accumulated on the mechanisms of the nitric oxide synthase (NOS)-NO pathway, but how this highly reactive, free radical gas signals to specific targets for precise regulation of cardiovascular function remains the focus of much intense research. In this Review, we summarize the updated paradigms on NOS regulation, NO interaction with reactive oxidant species in specific subcellular compartments, and downstream effects of NO in target cardiovascular tissues, while emphasizing the latest developments of molecular tools and biomarkers to modulate and monitor NO production and bioavailability.

Circulating NOS3 modulates left ventricular remodeling following reperfused myocardial infarction

Purpose

Nitric oxide (NO) is constitutively produced and released from the endothelium and several blood cell types by the isoform 3 of the NO synthase (NOS3). We have shown that NO protects against myocardial ischemia/reperfusion (I/R) injury and that depletion of circulating NOS3 increases within 24h of ischemia/reperfusion the size of myocardial infarction (MI) in chimeric mice devoid of circulating NOS3. In the current study we hypothesized that circulating NOS3 also affects remodeling of the left ventricle following reperfused MI.

Methods

To analyze the role of circulating NOS3 we transplanted bone marrow of NOS3^−/− and wild type (WT) mice into WT mice, producing chimerae expressing NOS3 only in vascular endothelium (BC−/EC+) or in both, blood cells and vascular endothelium (BC+/EC+). Both groups underwent 60 min of coronary occlusion in a closed-chest model of reperfused MI. During the 3 weeks post MI, structural and functional LV remodeling was serially assessed (24h, 4d, 1w, 2w and 3w) by echocardiography. At 72 hours post MI, gene expression of several extracellular matrix (ECM) modifying molecules was determined by quantitative RT-PCR analysis. At 3 weeks post MI, hemodynamics were obtained by pressure catheter, scar size and collagen content were quantified post mortem by Gomori’s One-step trichrome staining.

Results

Three weeks post MI, LV end-systolic (53.2±5.9μl;***p≤0.001;n = 5) and end-diastolic volumes (82.7±5.6μl;*p<0.05;n = 5) were significantly increased in BC−/EC+, along with decreased LV developed pressure (67.5±1.8mmHg;n = 18;***p≤0.001) and increased scar size/left ventricle (19.5±1.5%;n = 13;**p≤0.01) compared to BC+/EC+ (ESV:35.6±2.2μl; EDV:69.1±2.6μl n = 8; LVDP:83.2±3.2mmHg;n = 24;scar size/LV13.8±0.7%;n = 16). Myocardial scar of BC−/EC+ was characterized by increased total collagen content (20.2±0.8%;n = 13;***p≤0.001) compared to BC+/EC+ (15.9±0.5;n = 16), and increased collagen type I and III subtypes.

Conclusion

Circulating NOS3 ameliorates maladaptive left ventricular remodeling following reperfused myocardial infarction.

Depletion of circulating blood NOS3 increases severity of myocardial infarction and left ventricular dysfunction

Nitric oxide (NO) derived from endothelial NO synthase (NOS3) plays a central role in myocardial ischemia/reperfusion (I/R)-injury. Subsets of circulating blood cells, including red blood cells (RBCs), carry a NOS3 and contribute to blood pressure regulation and RBC nitrite/nitrate formation. We hypothesized that the circulating blood born NOS3 also modulates the severity of myocardial infarction in disease models. We cross-transplanted bone marrow in wild-type and NOS3^−/− mice with wild-type mice, producing chimeras expressing NOS3 only in vascular endothelium (BC−/EC+) or in both blood cells and vascular endothelium (BC+/EC+). After 60-min closed-chest coronary occlusion followed by 24 h reperfusion, cardiac function, infarct size (IS), NO_x levels, RBCs NO formation, RBC deformability, and vascular reactivity were assessed. At baseline, BC−/EC+ chimera had lower nitrite levels in blood plasma (BC−/EC+: 2.13 ± 0.27 μM vs. BC+/EC+ 3.17 ± 0.29 μM; *p < 0.05), reduced DAF FM associated fluorescence within RBCs (BC−/EC+: 538.4 ± 12.8 mean fluorescence intensity (MFI) vs. BC+/EC+: 619.6 ± 6.9 MFI; ***p < 0.001) and impaired erythrocyte deformability (BC−/EC+: 0.33 ± 0.01 elongation index (EI) vs. BC+/EC+: 0.36 ± 0.06 EI; *p < 0.05), while vascular reactivity remained unaffected. Area at risk did not differ, but infarct size was higher in BC−/EC+ (BC−/EC+: 26 ± 3 %; BC+/EC+: 14 ± 2 %; **p < 0.01), resulting in decreased ejection fraction (BC−/EC+ 46 ± 2 % vs. BC+/EC+: 52 ± 2 %; *p < 0.05) and increased end-systolic volume. Application of the NOS inhibitor S-ethylisothiourea hydrobromide was associated with larger infarct size in BC+/EC+, whereas infarct size in BC−/EC+ mice remained unaffected. Reduced infarct size, preserved cardiac function, NO levels in RBC and RBC deformability suggest a modulating role of circulating NOS3 in an acute model of myocardial I/R in chimeric mice.

Exercise-induced cardioprotection: a role for eNOS uncoupling and NO metabolites

Exercise is an efficient strategy for myocardial protection against ischemia-reperfusion (IR) injury. Although endothelial nitric oxide synthase (eNOS) is phosphorylated and activated during exercise, its role in exercise-induced cardioprotection remains unknown. This study investigated whether modulation of eNOS activation during IR could participate in the exercise-induced cardioprotection against IR injury. Hearts isolated from sedentary or exercised rats (5 weeks training) were perfused with a Langendorff apparatus and IR performed in the presence or absence of NOS inhibitors [N-nitro-L-arginine methyl ester, L-NAME or N5-(1-iminoethyl)-L-ornithine, L-NIO] or tetrahydrobiopterin (BH₄). Exercise training protected hearts against IR injury and this effect was abolished by L-NAME or by L-NIO treatment, indicating that exercise-induced cardioprotection is eNOS dependent. However, a strong reduction of eNOS phosphorylation at Ser1177 (eNOS-PSer1177) and of eNOS coupling during early reperfusion was observed in hearts from exercised rats (which showed higher eNOS-PSer1177 and eNOS dimerization at baseline) in comparison to sedentary rats. Despite eNOS uncoupling, exercised hearts had more S-nitrosylated proteins after early reperfusion and also less nitro-oxidative stress, indexed by lower malondialdehyde content and protein nitrotyrosination compared to sedentary hearts. Moreover, in exercised hearts, stabilization of eNOS dimers by BH4 treatment increased nitro-oxidative stress and then abolished the exercise-induced cardioprotection, indicating that eNOS uncoupling during IR is required for exercise-induced myocardial cardioprotection. Based on these results, we hypothesize that in the hearts of exercised animals, eNOS uncoupling associated with the improved myocardial antioxidant capacity prevents excessive NO synthesis and limits the reaction between NO and O₂·- to form peroxynitrite (ONOO⁻), which is cytotoxic.

Impairment of endothelial-myocardial interaction increases the susceptibility of cardiomyocytes to ischemia/reperfusion injury

Endothelial-myocardial interactions may be critically important for ischemia/reperfusion injury. Tetrahydrobiopterin (BH4) is a required cofactor for nitric oxide (NO) production by endothelial NO synthase (eNOS). Hyperglycemia (HG) leads to significant increases in oxidative stress, oxidizing BH4 to enzymatically incompetent dihydrobiopterin. How alterations in endothelial BH4 content impact myocardial ischemia/reperfusion injury remains elusive. The aim of this study was to examine the effect of endothelial-myocardial interaction on ischemia/reperfusion injury, with an emphasis on the role of endothelial BH4 content. Langendorff-perfused mouse hearts were treated by triton X-100 to produce endothelial dysfunction and subsequently subjected to 30 min of ischemia followed by 2 h of reperfusion. The recovery of left ventricular systolic and diastolic function during reperfusion was impaired in triton X-100 treated hearts compared with vehicle-treated hearts. Cardiomyocytes (CMs) were co-cultured with endothelial cells (ECs) and subsequently subjected to 2 h of hypoxia followed by 2 h of reoxygenation. Addition of ECs to CMs at a ratio of 1∶3 significantly increased NO production and decreased lactate dehydrogenase activity compared with CMs alone. This EC-derived protection was abolished by HG. The addition of 100 µM sepiapterin (a BH4 precursor) or overexpression of GTP cyclohydrolase 1 (the rate-limiting enzyme for BH4 biosynthesis) in ECs by gene trasfer enhanced endothelial BH4 levels, the ratio of eNOS dimer/monomer, eNOS phosphorylation, and NO production and decreased lactate dehydrogenase activity in the presence of HG. These results demonstrate that increased BH4 content in ECs by either pharmacological or genetic approaches reduces myocardial damage during hypoxia/reoxygenation in the presence of HG. Maintaining sufficient endothelial BH4 is crucial for cardioprotection against hypoxia/reoxygenation injury.

Endothelial NOS (NOS3) impairs myocardial function in developing sepsis

Endothelial nitric oxide synthase (NOS)3-derived nitric oxide (NO) modulates inotropic response and diastolic interval for optimal cardiac performance under non-inflammatory conditions. In sepsis, excessive NO production plays a key role in severe hypotension and myocardial dysfunction. We aimed to determine the role of NOS3 on myocardial performance, NO production, and time course of sepsis development. NOS3(-/-) and C57BL/6 wildtype mice were rendered septic by cecum ligation and puncture (CLP). Cardiac function was analyzed by serial echocardiography, in vivo pressure and isolated heart measurements. Cardiac output (CO) increased to 160 % of baseline at 10 h after sepsis induction followed by a decline to 63 % of baseline after 18 h in wildtype mice. CO was unaltered in septic NOS3(-/-) mice. Despite the hyperdynamic state, cardiac function and mean arterial pressure were impaired in septic wildtype as early as 6 h post CLP. At 12 h, cardiac function in septic wildtype was refractory to catecholamines in vivo and respective isolated hearts showed impaired pressure development and limited coronary flow reserve. Hemodynamics remained stable in NOS3(-/-) mice leading to significant survival benefit. Unselective NOS inhibition in septic NOS3(-/-) mice diminished this survival benefit. Plasma NO( x )- and local myocardial NO( x )- and NO levels (via NO spin trapping) demonstrated enhanced NO( x )- and bioactive NO levels in septic wildtype as compared to NOS3(-/-) mice. Significant contribution by inducible NOS (NOS2) during this early phase of sepsis was excluded. Our data suggest that NOS3 relevantly contributes to bioactive NO pool in developing sepsis resulting in impaired cardiac contractility.

Cardiomyocyte-restricted overexpression of extracellular superoxide dismutase increases nitric oxide bioavailability and reduces infarct size after ischemia/reperfusion

Increased levels of extracellular superoxide dismutase (ecSOD) induced by preconditioning or gene therapy protect the heart from ischemia/reperfusion injury. To elucidate the mechanism responsible for this action, we studied the effects of increased superoxide scavenging on nitric oxide (NO) bioavailability in a cardiac myocyte-specific ecSOD transgenic (Tg) mouse. Results indicated that ecSOD overexpression increased cardiac myocyte-specific ecSOD activity 27.5-fold. Transgenic ecSOD was localized to the sarcolemma and, notably, the cytoplasm of cardiac myocytes. Ischemia/reperfusion injury was attenuated in ecSOD Tg hearts, in which infarct size was decreased and LV functional recovery was improved. Using the ROS spin trap, DMPO, electron paramagnetic resonance (EPR) spectroscopy demonstrated a significant decrease in ROS in Tg hearts during the first 20 min of reperfusion. This decrease in ROS was accompanied by an increase in NO production determined by EPR using the NO spin trap, Fe-MGD. Attenuated ROS in ecSOD Tg myocytes was also supported by decreased production of peroxynitrite (ONOO⁻). Increased NO bioavailability was confirmed by attenuated guanylate cyclase-dependent (p-VASP) signaling. In conclusion, attenuation of ROS levels by cardiac-specific ecSOD overexpression increases NO bioavailability in response to ischemia/reperfusion and protects against reperfusion injury. These findings are the first to demonstrate increased NO bioavailability with attenuation of ROS by direct measurement of these reactive species (EPR, reactive fluorescent dyes) with cardiac-specific ecSOD expression. This is also the first indication that the predominantly extracellular SOD isoform is capable of cytosolic localization that affects myocardial intracellular signal transduction and function.

Early ischaemic preconditioning requires Akt- and PKA-mediated activation of eNOS via serine1176 phosphorylation

AIMS

The role of endothelial nitric oxide synthase (eNOS)/NO signalling is well documented in late ischaemic preconditioning (IPC); however, the role of eNOS and its activation in early IPC remains controversial. This study investigates the role of eNOS in early IPC and the signalling pathways and molecular interactions that regulate eNOS activation during early IPC.

METHODS AND RESULTS

Rat hearts were subjected to 30-min global ischaemia and reperfusion (I/R) with or without IPC (three cycles 5-min I and 5-min R) in the presence or absence of the NOS inhibitor l-NAME, phosphatidylinositol 3-kinase (PI3K) inhibitor LY294002 (LY), and protein kinase A (PKA) inhibitor H89 during IPC induction or prior endothelial permeablization. IPC improved post-ischaemic contractile function and reduced infarction compared with I/R with this being abrogated by l-NAME or endothelial permeablization. eNOS(Ser1176), Akt(Ser473), and PKA(Thr197) phosphorylation was increased following IPC. I/R decreased eNOS(Ser1176) phosphorylation, whereas IPC increased it. Mass spectroscopy confirmed eNOS(Ser1176) phosphorylation and quantitative Western blots showed ∼24% modification of eNOS(Ser1176) following IPC. Immunoprecipitation demonstrated eNOS, Akt, and PKA complexation. Immunohistology showed IPC-induced Akt and PKA phosphorylation in cardiomyocytes and endothelium. With eNOS activation, IPC increased NO production as measured by electron paramagnetic resonance spin trapping and fluorescence microscopy. LY or H89 not only decreased Akt(Ser473) or PKA(Thr197) phosphorylation, respectively, but also abolished IPC-induced preservation of eNOS and eNOS(Ser1176) phosphorylation as well as cardioprotection.

CONCLUSION

Thus, Akt- and PKA-mediated eNOS activation, with phosphorylation near the C-terminus, is critical for early IPC-induced cardioprotection, with eNOS-derived NO from the endothelium serving a critical role.

Identification of inducible nitric oxide synthase in peripheral blood cells as a mediator of myocardial ischemia/reperfusion injury

Although the late phase of ischemic preconditioning is known to be mediated by increased inducible nitric oxide synthase (iNOS) activity, controversy persists regarding the role of iNOS in ischemia/reperfusion (I/R) injury and, specifically, whether this protein is protective or detrimental. We hypothesized that iNOS is protective in myocytes but detrimental in inflammatory cells. To test this hypothesis, we created chimeric mice with iNOS-deficient peripheral blood cells by transplanting iNOS knockout (KO) bone marrow in wild-type (WT) mice after lethal irradiation. 2 months later, the mice underwent a 30-min coronary occlusion followed by 24 h of reperfusion. In WT naïve mice (iNOS(+/+) naïve; group I, n = 17), infarct size was 56.9 ± 2.8% of the risk region. In iNOS KO naïve mice with whole-body iNOS deletion (iNOS(-/-) naïve; group II, n = 10), infarct size was comparable to group I (53.4 ± 3.5%). When irradiated WT mice received marrow from WT mice (iNOS(+/+) chimera; group III, n = 10), infarct size was slightly reduced versus group I (44.3 ± 3.2%), indicating that irradiation and/or transplantation slightly decrease I/R injury. However, when WT mice received marrow from iNOS KO mice (iNOS(-/-) chimera; group IV, n = 14), infarct size was profoundly reduced (22.8 ± 2.1%, P < 0.05 vs. group III), indicating that selective deletion of iNOS from peripheral blood cells (with no change in myocardial iNOS content) induces protection against myocardial infarction. Together with our previous work showing the cardioprotective actions of NO donors, iNOS gene therapy, and cardiac-specific overexpression of iNOS, these data support a complex, dual role of iNOS in myocardial infarction (i.e., protective in myocytes but deleterious in blood cells). To our knowledge, this is the first study to identify a critical role of iNOS in peripheral blood cells as a mediator of myocardial I/R injury. The results support heretofore unknown differential actions of iNOS depending on cell source and have important translational implications.

Cardiac gene therapy in large animals: bridge from bench to bedside

Several clinical trials are evaluating gene transfer as a therapeutic approach to treat cardiac diseases. Although it has just started on the path to clinical application, recent advances in gene delivery technologies with increasing knowledge of underlying mechanisms raise great expectations for the cardiac gene therapy. Although in vivo experiments using small animals provide the therapeutic potential of gene transfer, there exist many fundamental differences between the small animal and the human hearts. Before applying the therapy to clinical patients, large animal studies are a prerequisite to validate the efficacy in an animal model more relevant to the human heart. Several key factors including vector type, injected dose, delivery method and targeted cardiac disease are all important factors that determine the therapeutic efficacy. Selecting the most optimal combination of these factors is essential for successful gene therapy. In addition to the efficacy, safety profiles need to be addressed as well. In this regard, large animal studies are best suited for comprehensive evaluation at the preclinical stages of therapeutic development to ensure safe and effective gene transfer. As the cardiac gene therapy expands its potential, large animal studies will become more important to bridge the bench side knowledge to the clinical arena.

Nitric oxide synthase in post-ischaemic remodelling: new pathways and mechanisms

The three isoforms of nitric oxide synthase (NOS), spatially confined in specific intracellular compartments in cardiac cells, have distinct roles in the regulation of contractility in pathophysiological situations. Recently, evidence has emerged that implicates NOS in modulating myocardial remodelling during cardiac stress, including after ischaemic insults. As long as they remain in a coupled state the NOS mostly attenuate hypertrophic remodelling through both cGMP-dependent and independent mechanisms. We review the evidence provided from the phenotype of genetic mouse models as well as from in vitro cell experiments dissecting the signalling effectors involved in the NOS-mediated regulation that justify new therapeutic interventions on the NOS-cGMP axis to attenuate the development of heart failure.

Human cardiac-derived adherent proliferating cells reduce murine acute Coxsackievirus B3-induced myocarditis

Background

Under conventional heart failure therapy, inflammatory cardiomyopathy typically has a progressive course, indicating a need for alternative therapeutic strategies to improve long-term outcomes. We recently isolated and identified novel cardiac-derived cells from human cardiac biopsies: cardiac-derived adherent proliferating cells (CAPs). They have similarities with mesenchymal stromal cells, which are known for their anti-apoptotic and immunomodulatory properties. We explored whether CAPs application could be a novel strategy to improve acute Coxsackievirus B3 (CVB3)-induced myocarditis.

Methodology/Principal Findings

To evaluate the safety of our approach, we first analyzed the expression of the coxsackie- and adenovirus receptor (CAR) and the co-receptor CD55 on CAPs, which are both required for effective CVB3 infectivity. We could demonstrate that CAPs only minimally express both receptors, which translates to minimal CVB3 copy numbers, and without viral particle release after CVB3 infection. Co-culture of CAPs with CVB3-infected HL-1 cardiomyocytes resulted in a reduction of CVB3-induced HL-1 apoptosis and viral progeny release. In addition, CAPs reduced CD4 and CD8 T cell proliferation. All CAPs-mediated protective effects were nitric oxide- and interleukin-10-dependent and required interferon-γ. In an acute murine model of CVB3-induced myocarditis, application of CAPs led to a decrease of cardiac apoptosis, cardiac CVB3 viral load and improved left ventricular contractility parameters. This was associated with a decline in cardiac mononuclear cell activity, an increase in T regulatory cells and T cell apoptosis, and an increase in left ventricular interleukin-10 and interferon-γ mRNA expression.

Conclusions

We conclude that CAPs are a unique type of cardiac-derived cells and promising tools to improve acute CVB3-induced myocarditis.

Decreased tetrahydrobiopterin and disrupted association of Hsp90 with eNOS by hyperglycemia impair myocardial ischemic preconditioning

Cardioprotection by ischemic preconditioning (IPC) is impaired during hyperglycemia, but the mechanisms underlying this phenomenon are poorly understood. This study investigated the role of hyperglycemia to adversely modulate tetrahydrobiopterin (BH(4)) and heat shock protein 90 (Hsp90) during cardioprotection by IPC. Rabbits or mice underwent 30 min of coronary occlusion followed by reperfusion with or without IPC in the presence or absence of hyperglycemia. IPC significantly (P < 0.05) decreased myocardial infarct size (46 ± 1 to 19 ± 2% of the area at risk in control and IPC rabbits, respectively) and increased BH(4) concentrations (HPLC; 7.6 ± 0.2 to 10.2 ± 0.3 pmol/mg protein, respectively), Hsp90-endothelial nitric oxide synthase (eNOS) association (coimmunoprecipitation and Western blotting in mice; 4.0 ± 0.3 to 5.4 ± 0.1, respectively), and the ratio of phosphorylated eNOS/total eNOS. These beneficial actions of IPC on infarct size, BH(4), Hsp90/eNOS, and phosphorylated eNOS were eliminated by hyperglycemia. Pretreatment of animals with the Hsp90 inhibitor geldanamycin (0.6 mg/kg) or the BH(4) synthesis inhibitor diamino-6-hydroxypyrimidine (1.0 g/kg) also eliminated cardioprotection produced by IPC. In contrast, the BH(4) precursor sepiapterin (2 mg/kg iv) restored the beneficial effects of IPC on myocardial BH(4) concentrations, eNOS dimerization, and infarct size during hyperglycemia. A-23871 increased Hsp90-eNOS association (0.33 ± 0.06 to 0.59 ± 0.3) and nitric oxide production (184 ± 17%) in human coronary artery endothelial cells cultured in normal (5.5 mM) but not high (20 mM) glucose media. These data indicate that hyperglycemia eliminates protection by IPC via decreases in myocardial BH(4) concentration and disruption of the association of Hsp90 with eNOS. The results suggest that eNOS dysregulation may be a central mechanism of impaired cardioprotection during hyperglycemia.

Gene transfer as a strategy to achieve permanent cardioprotection I: rAAV-mediated gene therapy with inducible nitric oxide synthase limits infarct size 1 year later without adverse functional consequences

The ultimate goal of prophylactic gene therapy is to confer permanent protection against ischemia. Although gene therapy with inducible nitric oxide synthase (iNOS) is known to protect against myocardial infarction at 3 days and up to 2 months, the long-term effects on myocardial ischemic injury and function are unknown. To address this issue, we created a recombinant adeno-associated viral vector carrying the iNOS gene (rAAV/iNOS), which enables long-lasting transgene expression. The ability of rAAV/iNOS to direct the expression of functional iNOS protein was confirmed in COS-7 cells before in vivo gene transfer. Mice received injections in the anterior LV wall of rAAV/LacZ or rAAV/iNOS; 1 year later, they underwent a 30-min coronary occlusion (O) and 4 h of reperfusion (R). iNOS gene transfer resulted in elevated iNOS protein expression (+3-fold vs. the LacZ group, n = 6; P < 0.05) and iNOS activity (+4.4-fold vs. the LacZ group, n = 6; P < 0.05) 1 year later. Infarct size (% of risk region) was dramatically reduced at 1 year after iNOS gene transfer (13.5 ± 2.2%, n = 12, vs. 41.7 ± 2.9%, n = 10, in the LacZ group; P < 0.05). The infarct-sparing effect of iNOS gene therapy at 1 year was as powerful as that observed 24 h after ischemic preconditioning (six 4-min O/4-min R cycles) (19.3 ± 2.3%, n = 11; P < 0.05). Importantly, compared with the LacZ group (n = 11), iNOS gene transfer (n = 10) had no effect on LV dimensions or function for up to 1 year (at 1 year: FS 34.5 ± 2.0 vs. 34.6 ± 2.6%, EF 57.0 ± 2.0 vs. 59.7 ± 2.9%, LVEDD 4.3 ± 0.1 vs. 4.2 ± 0.2 mm, LVESD 2.8 ± 0.1 vs. 2.9 ± 0.2 mm) (echocardiography). These data demonstrate, for the first time, that rAAV-mediated iNOS gene transfer affords long-term, probably permanent (1 year), cardioprotection without adverse functional consequences, providing a strong rationale for further preclinical testing of prophylactic gene therapy.

North American ginseng protects the heart from ischemia and reperfusion injury via upregulation of endothelial nitric oxide synthase

Emerging evidence suggests ginseng has therapeutic potential in cardiovascular disease. The aim of this study was to investigate the role of endothelial nitric oxide synthase (eNOS) in the cardioprotective effects of ginseng during myocardial ischemia and reperfusion (I/R). Treatment with ginseng extract significantly increased Akt phosphorylation and eNOS protein levels in cultured neonatal cardiomyocytes. Upregulation of eNOS was blocked by LY294002, a PI3-kinase inhibitor, suggesting a PI3-kinase/Akt-dependent mechanism. To simulate I/R, cultured neonatal cardiomyocytes from eNOS(-/-) and wild-type (WT) mice were subjected to anoxia and reoxygenation (A/R). Ginseng treatment inhibited A/R-induced apoptosis in WT, but not in either eNOS(-/-) cardiomyocytes or WT cardiomyocytes treated with LY294002. To further study the cardioprotective effects of ginseng in vivo, WT and eNOS(-/-) mice were pretreated with ginseng extract (50mg/kg/day, oral gavage) for 7 days before they were subjected to myocardial I/R. Treatment with ginseng significantly increased Akt phosphorylation and eNOS protein levels in the myocardium. Furthermore, ginseng-induced myocardial eNOS expression was inhibited by LY294002. Strikingly, ginseng treatment significantly decreased infarct size and myocardial apoptosis following I/R in WT mice, but not in either eNOS(-/-) mice or WT mice treated with LY294002. We conclude that ginseng treatment protects the heart from I/R injury via upregulation of eNOS expression. Our study suggests that ginseng may serve as a potential therapeutic agent to limit myocardial I/R injury.

Mesenchymal stem cells improve murine acute coxsackievirus B3-induced myocarditis

Aims

Coxsackievirus B3 (CVB3)-induced myocarditis, initially considered a sole immune-mediated disease, also results from a direct CVB3-mediated injury of the cardiomyocytes. Mesenchymal stem cells (MSCs) have, besides immunomodulatory, also anti-apoptotic features. In view of clinical translation, we first analysed whether MSCs can be infected by CVB3. Next, we explored whether and how MSCs could reduce the direct CVB3-mediated cardiomyocyte injury and viral progeny release, in vitro, in the absence of immune cells. Finally, we investigated whether MSC application could improve murine acute CVB3-induced myocarditis.

Methods and results

Phase contrast pictures and MTS viability assay demonstrated that MSCs did not suffer from CVB3 infection 4–12–24–48 h after CVB3 infection. Coxsackievirus B3 RNA copy number decreased in this time frame, suggesting that no CVB3 replication took place. Co-culture of MSCs with CVB3-infected HL-1 cardiomyocytes resulted in a reduction of CVB3-induced HL-1 apoptosis, oxidative stress, intracellular viral particle production, and viral progeny release in a nitric oxide (NO)-dependent manner. Moreover, MSCs required priming via interferon-γ (IFN-γ) to exert their protective effects. In vivo, MSC application improved the contractility and relaxation parameters in CVB3-induced myocarditis, which was paralleled with a reduction in cardiac apoptosis, cardiomyocyte damage, left ventricular tumour necrosis factor-α mRNA expression, and cardiac mononuclear cell activation. Mesenchymal stem cells reduced the CVB3-induced CD4− and CD8− T cell activation in an NO-dependent way and required IFN-γ priming.

Conclusion

We conclude that MSCs improve murine acute CVB3-induced myocarditis via their anti-apoptotic and immunomodulatory properties, which occur in an NO-dependent manner and require priming via IFN-γ.

eNOS is required for acute in vivo ischemic preconditioning of the heart: effects of ischemic duration and sex

Ischemic preconditioning (IPC) is a powerful phenomenon that provides potent cardioprotection in mammalian hearts; however, the role of endothelial nitric oxide (NO) synthase (eNOS)-mediated NO in this process remains highly controversial. Questions also remain regarding this pathway as a function of sex and ischemic duration. Therefore, we performed extensive experiments in wild-type (WT) and eNOS knockout (eNOS(-/-)) mice to evaluate whether the infarct-limiting effect of IPC depends on eNOS, ischemic periods, and sex. Classical IPC was induced by three cycles of 5 min of regional coronary ischemia separated by 5 min of reperfusion and was followed by 30 or 60 min of sustained ischemia and 24 h of reperfusion. The control ischemia-reperfusion protocol had 30 or 60 min of ischemia followed by 24 h of reperfusion. Protection was evaluated by measuring the myocardial infarct size as a percentage of the area at risk. The major findings were that regardless of sex, WT mice exhibited robust IPC with significantly smaller myocardial infarction, whereas eNOS(-/-) mice did not. IPC-induced cardiac protection was absent in eNOS(-/-) mice of both Jackson and Harvard origin. In general, female WT mice had smaller infarctions compared with male WT mice. Although prolonged ischemia caused significantly larger infarctions in WT mice of both sexes, they were consistently protected by IPC. Importantly, prolonged myocardial ischemia was associated with increased mortality in eNOS(-/-) mice, and the survival rate was higher in female eNOS(-/-) mice compared with male eNOS(-/-) mice. In conclusion, IPC protects WT mice against in vivo myocardial ischemia-reperfusion injury regardless of sex and ischemic duration, but the deletion of eNOS abolishes the cardioprotective effect of classical IPC.