Exercise-induced activation of cardiac sympathetic nerve triggers cardioprotection via redox-sensitive activation of eNOS and upregulation of iNOS

Single and 7-day handgrip and squat exercise prevents endothelial ischemia-reperfusion injury in individuals with cardiovascular disease risk factors

Whole body exercise provides protection against endothelial ischemia-reperfusion (IR) injury. In this crossover study, we examined the effects of 1) single bout of local exercise (handgrip, squats) on endothelial responses to IR, and 2) if 7 days of daily local exercise bolsters these effects in individuals with cardiovascular disease (CVD) risk factors. Fifteen participants (9 women, 58 ± 5 yr, ≥2 CVD risk factors) attended the laboratory for six visits. Subsequent to familiarization (visit 1), during visit 2 (control) brachial artery flow-mediated dilation (FMD) was measured before and after IR (15-min upper-arm ischemia, 15-min reperfusion). One week later, participants were randomized to 4 × 5-min unilateral handgrip (50% maximal voluntary contraction, 25 rpm) or squat exercises (15 rpm), followed by IR plus FMD measurements. Subsequently, home-based exercise was performed (6 days), followed by another visit to the laboratory for the IR protocol plus FMD measurements (18-24 h after the last exercise bout). After a 2-wk washout period, procedures were repeated with the alternative exercise mode. For a single exercise bout, we found a significant IR injury × exercise mode interaction (P < 0.01) but no main effect of injury (P = 0.08) or condition (P = 0.61). A lower post-IR FMD was evident after control (pre-IR: 4.3 ± 2.1% to post-IR: 2.9 ± 1.9%, P < 0.01) but not after handgrip (pre-IR: 3.8 ± 1.6% to post-IR: 3.4 ± 1.5%, P = 0.31) or squats (pre-IR: 3.9 ± 1.8% to post-IR: 4.0 ± 1.9%, P = 0.74). After 7 days of daily exercise, we found no change in FMD post-IR following handgrip (pre-IR: 4.3 ± 1.9% to post-IR: 4.7 ± 3.2%) or squats (pre-IR: 3.7 ± 2.1% to post-IR: 4.7 ± 3.0%, P > 0.05). Single bouts of dynamic, local exercise (handgrip, squats) provide remote protection against endothelial IR-induced injury in individuals with CVD risk factors, with 1-wk daily, home-based exercise preserving these effects for up to 24 h following the last exercise bout.NEW & NOTEWORTHY We show that single bouts of dynamic handgrip and squat exercise provide remote protection against endothelial ischemia-reperfusion (IR)-induced injury in individuals with cardiovascular disease (CVD) risk factors, with 1-wk daily, home-based exercise preserving these effects for up to 24 h following the last exercise bout.

Moderate-Intensity Exercise Maintains Redox Homeostasis for Cardiovascular Health

It is well known that exercise is beneficial for cardiovascular health. Oxidative stress is the common pathological basis of many cardiovascular diseases. The overproduction of free radicals, both reactive oxygen species and reactive nitrogen species, can lead to redox imbalance and exacerbate oxidative damage to the cardiovascular system. Maintaining redox homeostasis and enhancing anti-oxidative capacity are critical mechanisms by which exercise protects against cardiovascular diseases. Moderate-intensity exercise is an effective means to maintain cardiovascular redox homeostasis. Moderate-intensity exercise reduces the risk of cardiovascular disease by improving mitochondrial function and anti-oxidative capacity. It also attenuates adverse cardiac remodeling and enhances cardiac function. This paper reviews the primary mechanisms of moderate-intensity exercise-mediated redox homeostasis in the cardiovascular system. Exploring the role of exercise-mediated redox homeostasis in the cardiovascular system is of great significance to the prevention and treatment of cardiovascular diseases.

Short-term exercise-induced protection of cardiovascular function and health: why and how fast does the heart benefit from exercise?

Regular exercise training has potent and powerful protective effects against the development of cardiovascular disease. These cardioprotective effects of regular exercise training are partly explained through the effects of exercise on traditional cardiovascular risk factors and improvement in cardiac and vascular health, which take several weeks to months to develop. This review focuses on the observation that single bouts of exercise may also possess an underrecognized, clinically useful form of immediate cardioprotection. Studies, performed in both animals and humans, demonstrate that single or short-term exercise-induced protection (SEP) attenuates the magnitude of cardiac and/or vascular damage in response to prolonged ischaemia and reperfusion injury. This review highlights preclinical evidence supporting the hypothesis that SEP activates multiple pathways to confer immediate protection against ischaemic events, reduce the severity of potentially lethal ischaemic myocardial injury, and therefore act as a physiological first line of defence against injury. Given the fact that the extent of SEP could be modulated by exercise-related and subject-related factors, it is important to recognize and consider these factors to optimize future clinical implications of SEP. This review also summarizes potential effector signalling pathways (i.e. communication between exercising muscles to vascular/cardiac tissue) and intracellular pathways (i.e. reducing tissue damage) that ultimately confer protection against cardiac and vascular injury. Finally, we discuss potential future directions for designing adequate human and animal studies that will support developing effective SEP strategies for the (multi-)diseased and aged individual. KEY POINTS: Single or short-term exercise-induced protection (SEP) attenuates the magnitude of cardiac and/or vascular damage in response to prolonged ischaemia and reperfusion injury (IR injury). SEP activates multiple pathways to confer cardiac protection, which develops remotely at the site of the activated muscle by release of circulating molecules, which transfer towards activation of intramyocardial signalling that promotes cell survival during episodes of IR injury. SEP represents an attractive intervention in aged individuals and in those with co-morbidities. The immediate protection, low cost and simplicity to increase the 'dose' of SEP offers unique opportunities in the clinical applications of SEP.

Short term exercise‐induced protection of cardiovascular function and health: Why and how fast does the heart benefit from exercise?

Abstract

Regular exercise training has potent and powerful protective effects against the development of cardiovascular disease. These cardioprotective effects of regular exercise training are partly explained through the effects of exercise on traditional cardiovascular risk factors and improvement in cardiac and vascular health, which take several weeks to months to develop. This review focuses on the observation that single bouts of exercise may also possess an underrecognized, clinically useful form of immediate cardioprotection. Studies, performed in both animals and humans, demonstrate that single or short‐term exercise‐induced protection (SEP) attenuates the magnitude of cardiac and/or vascular damage in response to prolonged ischaemia and reperfusion injury. This review highlights preclinical evidence supporting the hypothesis that SEP activates multiple pathways to confer immediate protection against ischaemic events, reduce the severity of potentially lethal ischaemic myocardial injury, and therefore act as a physiological first line of defence against injury. Given the fact that the extent of SEP could be modulated by exercise‐related and subject‐related factors, it is important to recognize and consider these factors to optimize future clinical implications of SEP. This review also summarizes potential effector signalling pathways (i.e. communication between exercising muscles to vascular/cardiac tissue) and intracellular pathways (i.e. reducing tissue damage) that ultimately confer protection against cardiac and vascular injury. Finally, we discuss potential future directions for designing adequate human and animal studies that will support developing effective SEP strategies for the (multi‐)diseased and aged individual.

Key points

Single or short‐term exercise‐induced protection (SEP) attenuates the magnitude of cardiac and/or vascular damage in response to prolonged ischaemia and reperfusion injury (IR injury).

SEP activates multiple pathways to confer cardiac protection, which develops remotely at the site of the activated muscle by release of circulating molecules, which transfer towards activation of intramyocardial signalling that promotes cell survival during episodes of IR injury.

SEP represents an attractive intervention in aged individuals and in those with co‐morbidities. The immediate protection, low cost and simplicity to increase the ‘dose’ of SEP offers unique opportunities in the clinical applications of SEP.

Exercise-induced late preconditioning in mice is triggered by eNOS-dependent generation of nitric oxide and activation of PKCε and is mediated by increased iNOS activity

The purpose of this study was to assess whether short-term, mild exercise induces protection against myocardial infarction and, if so, what role the eNOS-PKCε-iNOS axis plays. Mice were subjected to 2 bouts/day of treadmill exercise (60 min at 15 m/min) for 2 consecutive days. At 24 h after the last bout of exercise, mice were subjected to a 30-min coronary artery occlusion and 24 h of reperfusion. In the exercise group (group III, wild-type mice), infarct size (25.5 ± 8.8% of risk region) was significantly (P < 0.05) reduced compared with the control groups (sham exercise, group II [63.4 ± 7.8%] and acute myocardial infarction, group I [58.6 ± 7.0%]). This effect was abolished by pretreatment with the NOS inhibitor L-NA (group VI, 56.1 ± 16.2%) and the PKC inhibitor chelerythrine (group VIII, 57.9 ± 12.5%). Moreover, the late PC effect of exercise was completely abrogated in eNOS^-/- mice (group XIII, 61.0 ± 11.2%). The myocardial phosphorylated eNOS at Ser-1177 was significantly increased at 30 min after treadmill training (exercise group) compared with sham-exercised hearts. PKCε translocation was significantly increased at 30 min after exercise in WT mice but not in eNOS^-/- mice. At 24 h after exercise, iNOS protein was upregulated compared with sham-exercised hearts. The protection of late PC was abrogated in iNOS^-/- mice (group XVI, 56.4 ± 12.9%) and in wildtype mice given the selective iNOS inhibitor 1400 W prior to ischemia (group X 62.0 ± 8.8% of risk region). We conclude that 1) even short, mild exercise induces a delayed PC effect that affords powerful protection against infarction; 2) this cardioprotective effect is dependent on activation of eNOS, eNOS-derived NO generation, and subsequent PKCε activation during PC; 3) the translocation of PKCε is dependent on eNOS; 4) the protection 24 h later is dependent on iNOS activity. Thus, eNOS is the trigger and iNOS the mediator of PC induced by mild exercise.

Morphine induces physiological, structural, and molecular benefits in the diabetic myocardium

The obesity epidemic has increased type II diabetes mellitus (T2DM) across developed countries. Cardiac T2DM risks include ischemic heart disease, heart failure with preserved ejection fraction, intolerance to ischemia-reperfusion (I-R) injury, and refractoriness to cardioprotection. While opioids are cardioprotective, T2DM causes opioid receptor signaling dysfunction. We tested the hypothesis that sustained opioid receptor stimulus may overcome diabetes mellitus-induced cardiac dysfunction via membrane/mitochondrial-dependent protection. In a murine T2DM model, we investigated effects of morphine on cardiac function, I-R tolerance, ultrastructure, subcellular cholesterol expression, mitochondrial protein abundance, and mitochondrial function. T2DM induced 25% weight gain, hyperglycemia, glucose intolerance, cardiac hypertrophy, moderate cardiac depression, exaggerated postischemic myocardial dysfunction, abnormalities in mitochondrial respiration, ultrastructure and Ca2+ -induced swelling, and cell death were all evident. Morphine administration for 5 days: (1) improved glucose homeostasis; (2) reversed cardiac depression; (3) enhanced I-R tolerance; (4) restored mitochondrial ultrastructure; (5) improved mitochondrial function; (6) upregulated Stat3 protein; and (7) preserved membrane cholesterol homeostasis. These data show that morphine treatment restores contractile function, ischemic tolerance, mitochondrial structure and function, and membrane dynamics in type II diabetic hearts. These findings suggest potential translational value for short-term, but high-dose morphine administration in diabetic patients undergoing or recovering from acute ischemic cardiovascular events.

Mechanisms Involved in Cardioprotection Induced by Physical Exercise

Significance: Regular exercise training can reduce myocardial damage caused by acute ischemia/reperfusion (I/R). Exercise can reproduce the phenomenon of ischemic preconditioning, due to the capacity of brief periods of ischemia to reduce myocardial damage caused by acute I/R. In addition, exercise may also activate the multiple kinase cascade responsible for cardioprotection even in the absence of ischemia. Recent Advances: Animal and human studies highlighted the fact that, besides to reduce risk factors related to cardiovascular disease, the beneficial effects of exercise are also due to its ability to induce conditioning of the heart. Exercise behaves as a physiological stress that triggers beneficial adaptive cellular responses, inducing a protective phenotype in the heart. The factors contributing to the exercise-induced heart preconditioning include stimulation of the anti-radical defense system and nitric oxide production, opioids, myokines, and adenosine-5'-triphosphate (ATP) dependent potassium channels. They appear to be also involved in the protective effect exerted by exercise against cardiotoxicity related to chemotherapy. Critical Issues and Future Directions: Although several experimental evidences on the protective effect of exercise have been obtained, the mechanisms underlying this phenomenon have not yet been fully clarified. Further studies are warranted to define precise exercise prescriptions in patients at risk of myocardial infarction or undergoing chemotherapy.

Physical activity as an adjunct treatment for erectile dysfunction

Increasing data are available to suggest that physical activity and lifestyle modification in general can benefit erectile function, with effect sizes comparable with established treatment options such as testosterone therapy and phosphodiesterase type 5 inhibitors. Despite this evidence, primary-care physicians are rarely afforded critical information on the underlying mechanisms through which physical activity works as a treatment, severely hampering treatment credibility for both physician and patient. Physical activity is associated with psychological and metabolic adaptations that are compatible with the adaptations required for the treatment of erectile dysfunction (ED). These adaptations include increased expression and activity of nitric oxide synthase, strengthened endothelial function, acute rises in testosterone, decreased stress and anxiety, and improved body image. Use of physical activity as a first-line treatment option for ED is limited, and explicit physical activity guidelines for the treatment of ED are required. Such guidelines should include not only a suggested exercise programme but also guidelines for physician-patient communication that might enhance patient receptivity and therapy continuation. An understanding of how physical activity affects erectile function, as well as its effectiveness in treating ED compared with other established treatments, can benefit urologists and primary-care physicians searching for noninvasive treatment options for men presenting with poor erectile function.

Expression Pattern of Angiogenic Factors in Healthy Heart in Response to Physical Exercise Intensity

Recently, many studies showing the regeneration potential of both cardiac and hematopoietic stem cells in adult heart following injury were definitively retracted by the literature. Therefore, stimulating myocardial angiogenesis becomes to be important for preventing cardiovascular diseases. Regular endurance exercise has been reported to induce capillary growth in healthy and diseased myocardium resulting in cardioprotective phenotype. Previously, we demonstrated a significantly increased capillary proliferation in mouse hearts following 30 and 45 days of endurance training. In the present study, we examined the localization and expression pattern of vascular endothelial growth factor receptors (VEGFR-1/Flt-1 and VEGFR-2/Flk-1), hypoxia-inducible factor-1α (HIF-1α), and inducible nitric oxide synthase (iNOS) in heart neocapillarization in response to a mild, moderate, and high intensity of endurance training. Sixty-three Swiss male mice were divided into four untrained control groups and three groups trained for 15 (T15), 30 (T30), and 45 (T45) days with a gradually increasing intensity on a treadmill. We observed the localization of studied proteins with immunostaining and their expression level with Western blot analyses. We found that VEGFR-2/Flk-1 expression progressively increased in trained groups compared with controls, while VEGFR-1/Flt-1 and HIF-1α were higher in T15 than in controls, T30, and T45 animals. Differently, iNOS levels enhanced after 15 and 30 days of exercise. The localization of these factors was not altered by exercise. The results showed that the expression of VEGFR-1/Flt-1, VEGFR-2/Flk-1, HIF-1α, and iNOS is differently regulated in cardiac angiogenesis according to the exercise intensity. VEGFR-1/Flt-1 and HIF-1α are upregulated by a mild intensity exercise, while VEGFR-2/Flk-1 progressively enhances with increasing workload. Differently, iNOS protein is modulated by a moderate intensity exercise. VEGF pathway appears to be involved in exercise-related angiogenesis in heart and VEGF might act in a paracrine and endocrine manner. Understanding this relationship is important for developing exercise strategies to protect the heart by insults.

Effects of a 12-week aerobic exercise on markers of hypertension in men

Introduction: This study was aimed at determining the effects of a 12-week aerobic exercise program on markers of hypertension in men.

Methods: The study was of a semi-experimental design featuring repeated measurements. A total of 40 men (age range=37.9 ± 2.68) with primary hypertension were divided into two groups, namely, the exercise group (n=20) and the control group (n=20) (systolic blood pressure [SBP]: 140.531 ± 0.23, diastolic blood pressure [DBP]: 90.71 ± 0.05). The exercise group participated in a 12-week aerobic exercise program (55% to 70% of HRmax). Blood samples were taken from both groups at the baseline and at the 4th, 8th, and 12th weeks of the training program for the assessment of adiponectin, paraoxonase-1 (PON-1), and hydrogen peroxide (H2 O2 ) levels as the markers for investigation. A linear mixed model was also used to evaluate the association among the markers.

Results: In the exercise group, exercise reduced the SBP and DBP at week 12 (P=0.031 and 0.023, respectively), and adiponectin increased at weeks 8 and 12 (P=0.014 and 0.001, respectively). The plasma PON-1 level showed a significant increase in all the three stages of measurement (P=0.007, 0.004, and 0.002 at weeks 4, 8, and 12, respectively), whereas the H2 O2 levels showed a significant decrease at weeks 8 and 12 (P=0.013 and 0.011, respectively). The control group exhibited significantly decreased PON-1 (P=0.003) and adiponectin (P=0.025) levels but significantly increased SBP at week 12 (P=0.032).

Conclusion: The exercise-induced reduction of oxidative stress exerts a considerable effect on the reduction of blood pressure in hypertensive patients. According to our results increase in oxidative stress has the great impact on the of blood pressure.

Cardioprotective Exercise and Pharmacologic Interventions as Complementary Antidotes to Cardiovascular Disease

Exercise and pharmacologic therapies to prevent and treat cardiovascular disease have advanced largely through independent efforts. Understanding of first-line drug therapies, findings from preclinical animal studies, and the need for research initiatives related to complementary cardioprotective exercise-pharma interventions are reviewed from the premise that contemporary cardioprotective therapies must include adjunctive exercise and lifestyle interventions in addition to pharmacologic agents.

Myocardial ischemic tolerance in rats subjected to endurance exercise training during adaptation to chronic hypoxia

Chronic hypoxia and exercise are natural stimuli that confer sustainable cardioprotection against ischemia-reperfusion (I/R) injury, but it is unknown whether they can act in synergy to enhance ischemic resistance. Inflammatory response mediated by tumor necrosis factor-α (TNF-α) plays a role in the infarct size limitation by continuous normobaric hypoxia (CNH), whereas exercise is associated with anti-inflammatory effects. This study was conducted to determine if exercise training performed under conditions of CNH (12% O2) affects myocardial ischemic resistance with respect to inflammatory and redox status. Adult male Wistar rats were assigned to one of the following groups: normoxic sedentary, normoxic trained, hypoxic sedentary, and hypoxic trained. ELISA and Western blot analysis, respectively, were used to quantify myocardial cytokines and the expression of TNF-α receptors, nuclear factor-κB (NF-κB), and selected components of related signaling pathways. Infarct size and arrhythmias were assessed in open-chest rats subjected to I/R. CNH increased TNF-α and interleukin-6 levels and the expression of TNF-α type 2 receptor, NF-κB, inducible nitric oxide synthase (iNOS), cytosolic phospholipase A2α, cyclooxygenase-2, manganese superoxide dismutase (MnSOD), and catalase. None of these effects occurred in the normoxic trained group, whereas exercise in hypoxia abolished or significantly attenuated CNH-induced responses, except for NF-κB, iNOS, and MnSOD. Both CNH and exercise reduced infarct size, but their combination provided the same degree of protection as CNH alone. In conclusion, exercise training does not amplify the cardioprotection conferred by CNH. High ischemic tolerance of the CNH hearts persists after exercise, possibly by maintaining the increased antioxidant capacity despite attenuating TNF-α-dependent protective signaling.

NEW & NOTEWORTHY Chronic hypoxia and regular exercise are natural stimuli that confer sustainable myocardial protection against acute ischemia-reperfusion injury. Signaling mediated by TNF-α via its type 2 receptor plays a role in the cardioprotective mechanism of chronic hypoxia. In the present study, we found that exercise training of rats during adaptation to hypoxia does not amplify the infarct size-limiting effect. Ischemia-resistant phenotype is maintained in the combined hypoxia-exercise setting despite exercise-induced attenuation of TNF-α-dependent protective signaling.

Exercise training provides cardioprotection by activating and coupling endothelial nitric oxide synthase via a β3-adrenergic receptor-AMP-activated protein kinase signaling pathway

Exercise training confers sustainable protection against ischemia/reperfusion injury. However, the mechanism by which this process occurs is not fully understood. Previously, it was shown that β₃-adrenergic receptors (β₃-ARs) play a critical role in regulating the activation of endothelial nitric oxide synthase (eNOS) in response to exercise and play a critical role in exercise-mediated cardioprotection. Intriguingly, a deficiency in β₃-ARs led to increased myocardial injury following exercise training. The purpose of the current study was to determine mechanisms by which β₃-ARs are linked to eNOS activation and to determine the mechanism responsible for the exacerbated ischemia/reperfusion injury displayed by β₃-AR deficient (β₃-AR KO) mice after exercise training. Wild-type (n = 37) and β₃-AR KO (n = 40) mice were subjected to voluntary wheel running for 4 weeks. Western blot analysis revealed that neither protein kinase B nor protein kinase A linked β₃-ARs to eNOS following exercise training. However, analysis revealed a role for AMP-activated protein kinase (AMPK). Specifically, exercise training increased the phosphorylation of AMPK in the hearts of wild-type mice, but failed to do so in the hearts of β₃-AR KO mice. Additional studies revealed that exercise training rendered eNOS less coupled and increased NOS-dependent superoxide levels in β₃-AR KO mice. Finally, supplementing β₃-AR KO mice with the eNOS coupler, tetrahydrobiopterin, during the final week of exercise training reduced myocardial infarction. These findings provide important information that exercise training protects the heart in the setting of myocardial ischemia/reperfusion injury by activating and coupling eNOS via the stimulation of a β₃-AR-AMPK signaling pathway.

Cardiac Ischemia/Reperfusion Injury: The Beneficial Effects of Exercise

Cardiac ischemia reperfusion injury (IRI) occurs when the myocardium is revascularized after an episode of limited or absent blood supply. Many changes, including free radical production, calcium overload, protease activation, altered membrane lipids and leukocyte activation, contribute to IRI-induced myocardium damage. Aerobic exercise is the only countermeasure against IRI that can be sustained on a regular basis in clinical practice. Interestingly, both short-term (3-5 days) and long-term (several weeks) exercise increase myocardial tolerance, reduce infarct size area and arrhythmias induced by IRI. Exercise protects the heart against IRI in a biphasic manner. The early phase of cardioprotection occurs between 30 min and 3 h following an acute exercise bout, whilst the late phase is achieved within 24 h after the exercise bout and persists for several days. As for the exercise intensity, although controversial data exists, it is feasible that the amount of cardioprotection is proportional to exercise intensity and only achieved above a critical threshold. It is known that aerobic exercise produces a cardioprotective phenotype, however the mechanisms responsible for this phenomenon remain unclear. Apparently, aerobic exercise-induced preconditioning is dependent on several factors that work together to protect the heart. Altered nitric oxide (NO) signaling, increased levels of heat shock proteins (HSPs), enhanced function of ATP-sensitive potassium channels, increased activation of opioids system, and enhanced antioxidant capacity may contribute to exercise-induced cardioprotection. Much has been discovered from animal models involving exercise-induced cardioprotection against cardiac IRI, however translating these findings to clinical practice still represents the major challenge in this field.

Exercise-induced protection against reperfusion arrhythmia involves stabilization of mitochondrial energetics

Mitochondria influence cardiac electrophysiology through energy- and redox-sensitive ion channels in the sarcolemma, with the collapse of energetics believed to be centrally involved in arrhythmogenesis. This study was conducted to determine if preservation of mitochondrial membrane potential (ΔΨm) contributes to the antiarrhythmic effect of exercise. We utilized perfused hearts, isolated myocytes, and isolated mitochondria exposed to metabolic challenge to determine the effects of exercise on cardiac mitochondria. Hearts from sedentary (Sed) and exercised (Ex; 10 days of treadmill running) Sprague-Dawley rats were perfused on a two-photon microscope stage for simultaneous measurement of ΔΨm and ECG. After ischemia-reperfusion, the collapse of ΔΨm was commensurate with the onset of arrhythmia. Exercise preserved ΔΨm and decreased the incidence of fibrillation/tachycardia (P < 0.05). Our findings in intact hearts were corroborated in isolated myocytes exposed to in vitro hypoxia-reoxygenation, with Ex rats demonstrating enhanced redox control and sustained ΔΨm during reoxygenation. Finally, we induced anoxia-reoxygenation in isolated mitochondria using high-resolution respirometry with simultaneous measurement of respiration and H2O2 Mitochondria from Ex rats sustained respiration with lower rates of H2O2 emission than Sed rats. Exercise helps sustain postischemic mitochondrial bioenergetics and redox homeostasis, which is associated with preserved ΔΨm and protection against reperfusion arrhythmia. The reduction of fatal ventricular arrhythmias through exercise-induced mitochondrial adaptations indicates that mitochondrial therapeutics may be an effective target for the treatment of heart disease.

Sex differences with aging in nutritive skeletal muscle blood flow: impact of exercise training, nitric oxide, and α-adrenergic-mediated mechanisms

The incidence of cardiovascular disease increases progressively with age, but aging may affect men and women differently. Age-associated changes in vascular structure and function may manifest in impaired nutritive blood flow, although the regulation of nutritive blood flow in healthy aging is not well understood. The purpose of this study was to determine if nitric oxide (NO)-mediated or α-adrenergic-mediated regulation of nutritive skeletal muscle blood flow is impaired with advanced age, and if exercise training improves age-related deficiencies. Nutritive blood flow was monitored in the vastus lateralis of healthy young and aged men and women via the microdialysis-ethanol technique prior to and following seven consecutive days of exercise training. NO-mediated and α-adrenergic-mediated regulation of nutritive blood flow was assessed by microdialysis perfusion of acetylcholine, sodium nitroprusside, N(G)-monomethyl-L-arginine, norepinephrine, or phentolamine. Pretraining nutritive blood flow was attenuated in aged compared with young women (7.39 ± 1.5 vs. 15.5 ± 1.9 ml·100 g(−1)·min(−1), P = 0.018), but not aged men (aged 13.5 ± 3.7 vs. young 9.4 ± 1.3 ml·100 g(−1)·min(−1), P = 0.747). There were no age-associated differences in NO-mediated or α-adrenergic-mediated nutritive blood flow. Exercise training increased resting nutritive blood flow only in young men (9.4 ± 1.3 vs. 19.7 ml·100 g(−1)·min(−1), P = 0.005). The vasodilatory effect of phentolamine was significantly reduced following exercise training only in young men (12.3 ± 6.14 vs. −3.68 ± 3.26 ml·100 g(−1)·min(−1), P = 0.048). In conclusion, the age-associated attenuation of resting nutritive skeletal muscle blood flow was specific to women, while the exercise-induced alleviation of α-adrenergic mediated vasoconstriction that was specific to young men suggests an age-associated modulation of the sympathetic response to exercise training.

Mechanisms Involved in Exercise-Induced Cardioprotection: A Systematic Review

BACKGROUND

Acute myocardial infarction is the leading cause of morbidity and mortality worldwide. Furthermore, research has shown that exercise, in addition to reducing cardiovascular risk factors, can also protect the heart against injury due to ischemia and reperfusion through a direct effect on the myocardium. However, the specific mechanism involved in exerciseinduced cardiac preconditioning is still under debate.

OBJECTIVE

To perform a systematic review of the studies that have addressed the mechanisms by which aerobic exercise promotes direct cardioprotection against ischemia and reperfusion injury.

METHODS

A search was conducted using MEDLINE, Literatura Latino-Americana e do Caribe de Informação em Ciências da Saúde, and Scientific Electronic Library Online databases. Data were extracted in a standardized manner by two independent researchers, who were responsible for assessing the methodological quality of the studies.

RESULTS

The search retrieved 78 studies; after evaluating the abstracts, 30 studies were excluded. The manuscripts of the remaining 48 studies were completely read and, of these, 20 were excluded. Finally, 28 studies were included in this systematic review.

CONCLUSION

On the basis of the selected studies, the following are potentially involved in the cardioprotective response to exercise: increased heat shock protein production, nitric oxide pathway involvement, increased cardiac antioxidant capacity, improvement in ATP-dependent potassium channel function, and opioid system activation. Despite all the previous investigations, further research is still necessary to obtain more consistent conclusions.

Why Does Exercise "Trigger" Adaptive Protective Responses in the Heart?

Numerous epidemiological studies suggest that individuals who exercise have decreased cardiac morbidity and mortality. Pre-clinical studies in animal models also find clear cardioprotective phenotypes in animals that exercise, specifically characterized by lower myocardial infarction and arrhythmia. Despite the clear benefits, the underlying cellular and molecular mechanisms that are responsible for exercise preconditioning are not fully understood. In particular, the adaptive signaling events that occur during exercise to "trigger" cardioprotection represent emerging paradigms. In this review, we discuss recent studies that have identified several different factors that appear to initiate exercise preconditioning. We summarize the evidence for and against specific cellular factors in triggering exercise adaptations and identify areas for future study.

The "Goldilocks Zone" from a redox perspective-Adaptive vs. deleterious responses to oxidative stress in striated muscle

Consequences of oxidative stress may be beneficial or detrimental in physiological systems. An organ system's position on the “hormetic curve” is governed by the source and temporality of reactive oxygen species (ROS) production, proximity of ROS to moieties most susceptible to damage, and the capacity of the endogenous cellular ROS scavenging mechanisms. Most importantly, the resilience of the tissue (the capacity to recover from damage) is a decisive factor, and this is reflected in the disparate response to ROS in cardiac and skeletal muscle. In myocytes, a high oxidative capacity invariably results in a significant ROS burden which in homeostasis, is rapidly neutralized by the robust antioxidant network. The up-regulation of key pathways in the antioxidant network is a central component of the hormetic response to ROS. Despite such adaptations, persistent oxidative stress over an extended time-frame (e.g., months to years) inevitably leads to cumulative damages, maladaptation and ultimately the pathogenesis of chronic diseases. Indeed, persistent oxidative stress in heart and skeletal muscle has been repeatedly demonstrated to have causal roles in the etiology of heart disease and insulin resistance, respectively. Deciphering the mechanisms that underlie the divergence between adaptive and maladaptive responses to oxidative stress remains an active area of research for basic scientists and clinicians alike, as this would undoubtedly lead to novel therapeutic approaches. Here, we provide an overview of major types of ROS in striated muscle and the divergent adaptations that occur in response to them. Emphasis is placed on highlighting newly uncovered areas of research on this topic, with particular focus on the mitochondria, and the diverging roles that ROS play in muscle health (e.g., exercise or preconditioning) and disease (e.g., cardiomyopathy, ischemia, metabolic syndrome).

Exercise training in adverse cardiac remodeling

Cardiac remodeling in response to a myocardial infarction or chronic pressure-overload is an independent risk factor for the development of heart failure. In contrast, cardiac remodeling produced by regular physical exercise is associated with a decreased risk for heart failure. There is evidence that exercise training has a beneficial effect on disease progression and survival in patients with cardiac remodeling and dysfunction, but concern has also been expressed that exercise training may aggravate pathological remodeling and dysfunction. Here we present studies from our laboratory into the effects of exercise training on pathological cardiac remodeling and dysfunction in mice. The results indicate that even in the presence of a large infarct, exercise training exerts beneficial effects on the heart. These effects were mimicked in part by endothelial nitric oxide synthase (eNOS) overexpression and abrogated by eNOS deficiency, demonstrating the importance of nitric oxide signaling in mediating the cardiac effects of exercise. Exercise prior to a myocardial infarction was also cardioprotective. In contrast, exercise tended to aggravate pathological cardiac remodeling and dysfunction in the setting of pressure-overload produced by an aortic stenosis. These observations emphasize the critical importance of the underlying pathological stimulus for cardiac hypertrophy and remodeling, in determining the effects of exercise training. Future studies are needed to define the influence of exercise type, intensity and duration in different models and severities of pathological cardiac remodeling. Together such studies will aid in optimizing the therapy of exercise training in the setting of cardiovascular disease.

Role of β-adrenergic receptors and nitric oxide signaling in exercise-mediated cardioprotection

Exercise promotes cardioprotection in both humans and animals not only by reducing risk factors associated with cardiovascular disease but by reducing myocardial infarction and improving survival following ischemia. This article will define the role that nitric oxide and β-adrenergic receptors play in mediating the cardioprotective effects of exercise in the setting of ischemia-reperfusion injury.

Skeletal muscle function during exercise-fine-tuning of diverse subsystems by nitric oxide

Skeletal muscle is responsible for altered acute and chronic workload as induced by exercise. Skeletal muscle adaptations range from immediate change of contractility to structural adaptation to adjust the demanded performance capacities. These processes are regulated by mechanically and metabolically induced signaling pathways, which are more or less involved in all of these regulations. Nitric oxide is one of the central signaling molecules involved in functional and structural adaption in different cell types. It is mainly produced by nitric oxide synthases (NOS) and by non-enzymatic pathways also in skeletal muscle. The relevance of a NOS-dependent NO signaling in skeletal muscle is underlined by the differential subcellular expression of NOS1, NOS2, and NOS3, and the alteration of NO production provoked by changes of workload. In skeletal muscle, a variety of highly relevant tasks to maintain skeletal muscle integrity and proper signaling mechanisms during adaptation processes towards mechanical and metabolic stimulations are taken over by NO signaling. The NO signaling can be mediated by cGMP-dependent and -independent signaling, such as S-nitrosylation-dependent modulation of effector molecules involved in contractile and metabolic adaptation to exercise. In this review, we describe the most recent findings of NO signaling in skeletal muscle with a special emphasis on exercise conditions. However, to gain a more detailed understanding of the complex role of NO signaling for functional adaptation of skeletal muscle (during exercise), additional sophisticated studies are needed to provide deeper insights into NO-mediated signaling and the role of non-enzymatic-derived NO in skeletal muscle physiology.

Redox-dependent increases in glutathione reductase and exercise preconditioning: role of NADPH oxidase and mitochondria

AIMS

We have previously shown that exercise leads to sustainable cardioprotection through a mechanism involving improved glutathione replenishment. This study was conducted to determine if redox-dependent modifications in glutathione reductase (GR) were involved in exercise cardioprotection. Furthermore, we sought to determine if reactive oxygen species generated by NADPH oxidase and/or mitochondria during exercise were triggering events for GR modulations.

METHODS AND RESULTS

Rats were exercised for 10 consecutive days, after which isolated hearts were exposed to ischaemia/reperfusion (25 min/120 min). Exercise protected against infarction and arrhythmia, and preserved coronary flow. The GR inhibitor BCNU abolished the beneficial effects. GR activity was increased following exercise in a redox-dependent manner, with no change in GR protein levels. Because fluorescent labelling of GR protein thiols showed lower amounts of reduced thiols after exercise, we sought to determine the source of intracellular reactive oxygen species that may be activating GR. Subsets of animals were exercised immediately after treatment with either NADPH-oxidase inhibitors apocynin or Vas2870, or with mitoTEMPO or Bendavia, which reduce mitochondrial reactive oxygen species levels. The cardioprotective effects of exercise were abolished if animals exercised in the presence of NADPH oxidase inhibitors, in clear contrast to the mitochondrial reagents. These changes correlated with thiol-dependent modifications of GR.

CONCLUSION

Adaptive cardioprotective signalling is triggered by reactive oxygen species from NADPH oxidase, and leads to improved glutathione replenishment through redox-dependent modifications in GR.

Regular treadmill exercise restores cardioprotective signaling pathways in obese mice independently from improvement in associated co-morbidities

Obesity is a major health issue that impedes the ability of preconditioning and postconditioning to protect the myocardium against infarction secondary to dysregulation of kinase signaling pathways. Moreover, exercise decreases cardiovascular mortality in obese patients but the mechanism remains to be established. Wild-type (WT) and obese (ob/ob) mice were assigned to sedentary conditions or regular treadmill exercise (1h/day, 5 days/7, 4 weeks, 4° slope, 10-30 cm/s) and underwent 30 min of coronary artery occlusion followed by 24h of reperfusion for infarct size measurement. In WT, exercise reduced infarct size by 60% and increased phosphorylation of kinases such as Akt, ERK 1/2, p70S6K, AMPK and GSK3β. Importantly, the level of corresponding phosphatases PTEN, MKP-3 and PP2C was decreased. Calcium concentration inducing the opening of mitochondrial permeability transition pore (mPTP) was increased by exercise. In ob/ob, regular exercise induced a robust cardioprotection by reducing infarct size (-67%), increasing kinase phosphorylation, decreasing phosphatase levels and improving the resistance to mPTP opening. However exercise did not modify hyperglycemia, hypercholesterolemia, hyperinsulinemia, fat mass and body weight in obese mice. In conclusion, regular exercise induces cardioprotection against myocardial infarction despite obesity and restores pro-survival signaling pathways with simultaneous increase in kinase phosphorylations, decreased levels of phosphatases and increased resistance of mPTP opening, independently from improvement in associated co-morbidities.

Reactive oxygen species are not a required trigger for exercise-induced late preconditioning in the rat heart

Reactive oxygen species (ROS) have been reported to play a primary role in triggering the cardioprotective adaptations by some preconditioning procedures, but whether they are required for exercise-induced preconditioning is unclear. Thus in this study we used the free radical scavenger N-(2-mercaptopropionyl)glycine (MPG) to test the hypothesis that ROS is the trigger for exercise-induced preconditioning of the heart against ischemia-reperfusion injury. Male F344 rats were assigned to four groups: sedentary (SED, n = 7), SED/MPG (100 mg/kg ip daily for 2 days, n = 12), exercised on a treadmill for 2 days at 20 m/min, 6° grade, for 60 min (RUN, n = 7), and RUN/MPG with 100 mg/kg MPG injected 15 min before exercise (n = 10). Preliminary experiments verified that MPG administration maintained myocardial redox status during the exercise bout. Twenty-four hours postexercise or MPG treatment isolated perfused working hearts were subjected to global ischemia for 22.5 min followed by reperfusion for 30 min. Recovery of myocardial external work (percentage of preischemic systolic pressure times cardiac output) for SED (50.4 ± 4.5) and SED/RUN (54.7 ± 6.6) was similar and improved in both exercise groups (P < 0.05) to 77.9 ± 3.0 in RUN and 76.7 ± 4.5 in RUN/MPG. A 2 × 2 ANOVA also revealed that exercise decreased lactate dehydrogenase release from the heart during reperfusion (marker of cell damage) without MPG effects or interactions. Expression of the cytoprotective protein inducible heat shock protein 70 increased by similar amounts in the left ventricles of RUN and RUN/MPG compared with sedentary groups (P < 0.05). We conclude that ROS are not a necessary trigger for exercise-induced preconditioning in rats.

Voluntary running in mice beneficially modulates myocardial ischemic tolerance, signaling kinases, and gene expression patterns

Exercise triggers hormesis, conditioning hearts against damaging consequences of subsequent ischemia-reperfusion (I/R). We test whether “low-stress” voluntary activity modifies I/R tolerance and molecular determinants of cardiac survival. Male C57BL/6 mice were provided 7-day access to locked (7SED) or rotating (7EX) running-wheels before analysis of cardiac prosurvival (Akt, ERK 1/2) and prodeath (GSK3β) kinases, transcriptomic adaptations, and functional tolerance of isolated hearts to 25-min ischemia/45-min reperfusion. Over 7 days, 7EX mice increased running from 2.1 ± 0.2 to 5.3 ± 0.3 km/day (mean speed 38 ± 2 m/min), with activity improving myocardial I/R tolerance: 7SED hearts recovered 43 ± 3% of ventricular force with diastolic contracture of 33 ± 3 mmHg, whereas 7EX hearts recovered 63 ± 5% of force with diastolic dysfunction reduced to 23 ± 2 mmHg ( P < 0.05). Cytosolic expression (total protein) of Akt and GSK3β was unaltered, while ERK 1/2 increased 30% in 7EX vs. 7SED hearts. Phosphorylation of Akt and ERK 1/2 was unaltered, whereas GSK3β phosphorylation increased ∼90%. Microarray interrogation identified significant changes (≥1.3-fold expression change, ≤5% FDR) in 142 known genes, the majority (92%) repressed. Significantly modified paths/networks related to inflammatory/immune function (particularly interferon-dependent), together with cell movement, growth, and death. Of only 14 induced transcripts, 3 encoded interrelated sarcomeric proteins titin, α-actinin, and myomesin-2, while transcripts for protective actin-stabilizing ND1-L and activator of mitochondrial biogenesis ALAS1 were also induced. There was no transcriptional evidence of oxidative heat-shock or other canonical “stress” responses. These data demonstrate that relatively brief voluntary activity substantially improves cardiac ischemic tolerance, an effect independent of shifts in Akt, but associated with increased total ERK 1/2 and phospho-inhibition of GSK3β. Transcriptomic data implicate inflammatory/immune and sarcomeric modulation in activity-dependent protection.

Cardioprotection requires flipping the 'posttranslational modification' switch

Minimizing damage during reperfusion of the heart following an ischemic event is an important part of the recovery process, as is preventing future recurrences; however, restoring blood perfusion to the heart following ischemia can lead to apoptosis, necrosis, and finally, diminished cardiac function. Exercise reduces risk of heart disease and has been shown to improve the recovery of the heart following ischemia and reperfusion. Brief intermittent ischemic events administered prior to or following a myocardial infarction have also been demonstrated to reduce the infarct size and improve cardiac function, thereby providing cardioprotection. Many signaling transduction pathways are known to regulate cardioprotection, including but not limited to calcium regulation, antioxidant scavenging, and kinase activation. Although posttranslational modifications (PTM) such as phosphorylation, O-GlcNAcylation, methylation, and acetylation are essential regulators of these pathways, their contributions are often overlooked in the literature. This review will examine how PTMS are important regulators of cardioprotection and demonstrate why they should be targeted when developing future therapies for the minimization of damage caused by cardiac ischemia and reperfusion.

Ascorbic acid and N-acetyl cysteine prevent uncoupling of nitric oxide synthase and increase tolerance to ischemia/reperfusion injury in diabetic rat heart

Oxidative stress may cause a loss of tetrahydrobiopterin (BH4), a co-factor of nitric oxide synthase (NOS), decrease the bioavailability of NO and aggravate ischemia/reperfusion (I/R) injury in diabetic heart. We hypothesized that ascorbic acid (AA) and N-acetyl cysteine (NAC) protect the diabetic heart from I/R injury by increasing BH4/dihydrobiopterin (BH2) ratio and inhibiting uncoupling of NOS. Diabetes mellitus was induced in rats by streptozotocin treatment, and the hearts were isolated and perfused. BH4 and BH4/BH2 ratio decreased in the diabetic heart associated with increased production of superoxide and nitrotyrosine (NT). Treatment with AA or NAC significantly increased BH4/BH2 ratio in the diabetic heart associated with decreased production of superoxide and NT and increased generation of nitrate plus nitrite (NOx). Pre-treatment with AA or NAC before 30 min ischemia followed by 120 min reperfusion improved left ventricular (LV) function and reduced infarct size in the diabetic but not non-diabetic hearts. The NOS inhibitor, L-NAME, inhibited the increase in the generation of superoxide, NT and NOx, but aggravated LV function and increased infarct size in the diabetic heart. L-NAME also abrogated the increase in NOx and improvement of LV function and the infarct size-limiting effect induced by AA or NAC in the diabetic heart. These results suggest that AA and NAC increase BH4/BH2 ratio and prevent NOS uncoupling in the diabetic heart. Resultant increase in the bioavailability of NO renders the diabetic heart toleratant to I/R injury.

Exercise-induced cardiac preconditioning: how exercise protects your achy-breaky heart

The ability of exercise to protect the heart against ischemia-reperfusion (I/R) injury is well known in both human epidemiological studies and experimental animal models. In this review article, we describe what is currently known about the ability of exercise to precondition the heart against infarction. Just 1 day of exercise can protect the heart against ischemia/reperfusion damage, and this protection is upheld with months of exercise, making exercise one of the few sustainable preconditioning stimuli. Exercise preconditioning depends on the model and intensity of exercise, and appears to involve heightened oxidant buffering capacity, upregulated subunits of sarcolemmal ATP-sensitive potassium channels, and adaptations to cardiac mitochondria. We review the putative mechanisms involved in exercise preconditioning and point out many areas where future research is necessary to advance our understanding of how this stimulus confers resistance against I/R damage.

Effect of N-2-mercaptopropionyl glycine on exercise-induced cardiac adaptations

The purpose of this study was to test the hypothesis that exercise-induced cardiac adaptations would be attenuated by the free radical scavenger N-2-mercaptopropionyl glycine (MPG). Male Sprague-Dawley rats were divided into four groups ( n = 9–13 per group) for 3–4 wk: sedentary (S), S+MPG (100 mg/kg ip daily), exercised on a treadmill (E) (60 min/day, 5 days/wk, at a speed of 20 m/min up a 6° grade in a 6°C room), or E+MPG given 10 min prior to exercise. Additional rats ( n = 55) were used to determine acute exercise effects on myocardial redox state [nonprotein nonglutathione sulfhydryls (NPNGSH)] and PI3K/Akt signaling pathway activation. Compared with S, NPNGSH levels were 48% lower in E ( P < 0.05) and unchanged in E+MPG ( P > 0.05). MPG also attenuated exercise-induced activation of the signaling proteins Akt and S6. Hearts from the 4-wk groups were weighed, and cardiac function was evaluated using an isolated perfused working heart preparation. Similar increases ( P < 0.05) in both exercised groups were observed for heart weight and heart weight-to-body weight ratio. Cardiac function improved in E vs. S, as indicated by greater ( P < 0.05) external work performed (cardiac output × systolic pressure) and efficiency of external work (work/V̇o2). MPG prevented these exercise-induced functional improvements. Skeletal muscle mitochondria content increased to similar levels in E and E+MPG. This study provides evidence that free radicals do not play an essential role in the development of exercise-induced cardiac hypertrophy; however, they appear to be involved in functional cardiac adaptations, which may be mediated through the PI3K/Akt pathway.

Bone marrow cell recruitment mediated by inducible nitric oxide synthase/stromal cell-derived factor-1alpha signaling repairs the acoustically damaged cochlear blood-labyrinth barrier

Using a mouse model with noise-induced cochlear blood-labyrinth-barrier (CBLB) injury, we examined the effects of inducible nitric oxide synthase (iNOS) on the recruitment of bone marrow-derived cells (BMDCs) to the CBLB after acoustic injury. Lethally irradiated C57BL/6J and B6.129P2-Nos2(tm1Lau)/J mice were transplanted with GFP(+)-BMDCs from C57Bl/6-Tg (UBC GFP) mice. Four weeks after transplantation, we assessed the population of GFP(+)-BMDCs in the CBLB. Only small numbers of GFP(+)-BMDCs were found to infiltrate the area of the CBLB in the control recipient mice. However, robust GFP(+)-BMDC migration occurred in the area of the CBLB within the injured cochlea during the first week following acoustic trauma, and further BMDC accumulation was seen by 2 weeks posttrauma. After 4 weeks, the BMDCs were integrated into vessels. Local iNOS from perivascular resident macrophages was found to be important for BMDC infiltration, since mice deficient in iNOS (Inos(-/-)) and mice with iNOS that had been inhibited by 1400W displayed reduced BMDC infiltration. Stromal cell-derived factor-1α (SDF-1α) and its chemokine receptor 4 (CXCR4) were required for the iNOS-triggered recruitment. BMDC recruitment was significantly reduced by the inhibition of SDF-1α activity. Inhibition of the iNOS/SDF-1α signaling pathway reduced vascular repair as observed by reduced vascular density. Our study revealed an intrinsic signaling pathway of iNOS that mediates SDF-1α to promote GFP(+)-BMDC infiltration/targeting in cochlear vascular repair.

Cardioprotective effects of nitrite during exercise

Exercise training has been shown to reduce many risk factors related to cardiovascular disease, including high blood pressure, high cholesterol, obesity, and insulin resistance. More importantly, exercise training has been consistently shown to confer sustainable protection against myocardial infarction in animal models and has been associated with improved survival following a heart attack in humans. It is still unclear how exercise training is able to protect the heart, but some studies have suggested that it increases a number of classical signalling molecules. For instance, exercise can increase components of the endogenous antioxidant defences (i.e. superoxide dismutase and catalase), increase the expression of heat shock proteins, activate ATP-sensitive potassium (K(ATP)) channels, and increase the expression and activity of endothelial nitric oxide (NO) synthase resulting in an increase in NO levels. This review article will provide a brief summary of the role that these signalling molecules play in mediating the cardioprotective effects of exercise. In particular, it will highlight the role that NO plays and introduce the idea that the stable NO metabolite, nitrite, may play a major role in mediating these cardioprotective effects.

Beneficial effects of exercise training after myocardial infarction require full eNOS expression

Exercise training attenuates left ventricular (LV) dysfunction after myocardial infarction (MI). It could be speculated that these effects of exercise are mediated by increased endothelial NO synthase (eNOS) activity. In the present study we tested the hypothesis that eNOS plays a critical role in the exercise-induced amelioration of LV dysfunction after MI. MI or sham was induced in eNOS(-/-), eNOS(+/-) and eNOS(+/+) mice. After 8 weeks of voluntary wheel running (approximately 7 km/day in all groups) or sedentary housing, global cardiac function was determined in vivo and (immuno)histochemistry was performed to assess cardiomyocyte size, fibrosis, capillary density and apoptosis in remote myocardium. At baseline eNOS(-/-) mice had higher mean aortic pressure compared to eNOS(+/-) and eNOS(+/+) mice, but had normal global cardiac function. MI resulted in marked LV remodeling, including cardiomyocyte hypertrophy and a reduction in capillary density, increased fibrosis and apoptosis, as well as LV systolic and diastolic dysfunction to the same extent in all genotypes. In eNOS(+/+) MI mice exercise abolished fibrosis and apoptosis in the remote myocardium, attenuated LV systolic dysfunction and ameliorated pulmonary congestion. These beneficial effects were lost in eNOS(+/-) and eNOS(-/-) mice, while LV systolic dysfunction and pulmonary congestion in eNOS(+/-) mice were exacerbated by exercise. In conclusion, the beneficial effects of exercise after MI on LV remodeling and dysfunction depend critically on endogenous eNOS. The observation that the lack of one eNOS allele is sufficient to negate all beneficial effects of exercise, strongly suggests that exercise depends on full eNOS expression.

Sulindac confers high level ischemic protection to the heart through late preconditioning mechanisms

We have recently shown that sulindac, an anti-inflammatory drug, enhances the killing of cancer cells, but not normal cells, under conditions of oxidative stress, by mechanisms unrelated to its cyclooxygenase (COX) inhibition. To further study the protective effect of sulindac on cells exposed to oxidative stress, we have investigated the effect of sulindac on rat cardiac myocytes subjected to hypoxia/reoxygenation, as well as in a Langendorff model of myocardial ischemia. Low levels of sulindac could protect cardiac myocytes against cell death due to hypoxia/reoxygenation. In the Langendorff model sulindac provided significant protection against cell death, when the drug was fed to the animals before the removal of the heart for the Langendorff procedure. The results indicate that the primary protective effect of sulindac in these experiments does not involve its role as a COX inhibitor. Numerous signaling pathways have been implicated in myocardial protective mechanisms, many of which involve fluctuations in reactive oxygen species (ROS) levels. The results suggest that low levels of sulindac can induce a preconditioning response, triggered by ROS, to protect cardiac tissues against oxidative damage. Blocking of preconditioning pathways by administration of the PKC blocker chelerythrine abrogated the ischemic protection afforded by sulindac. Secondly, after feeding of sulindac, two end-effectors of preconditioning, inducible nitric oxide synthase and heat shock protein 27, were found to be markedly induced in the heart, dependent on PKC. These results suggest that sulindac may have therapeutic potential as a preconditioning agent.

The role of nitric oxide in myocardial repair and remodeling

Nitric oxide (NO) plays a crucial role in many aspects of the pathophysiology of heart failure. NO is a double-edged sword; NO inhibits ischemia/reperfusion (I/R) injury, represses inflammation, and prevents left ventricular (LV) remodeling, whereas excess NO and co-existence of reactive oxygen species (ROS) with NO are injurious. The failing heart is exposed to not only oxidative stress by a plethora of humoral factors and inflammatory cells but also nitrosative stress. Activation of nitric oxide synthase (NOS) of any isoforms, [i.e., endothelial NOS (eNOS), inducible NOS (iNOS), and neuronal NOS (nNOS)], concomitant with oxidative stress results in NOS uncoupling, leading to further oxidative/nitrosative stress. Indiscriminate removal of oxidative stress is not an effective means to prevent this detrimental process, because oxidative stress is necessary for an adaptive mechanism for cell survival against noxious stimuli. Therefore, removal of ROS in a site-specific manner or inhibition of the source of injurious ROS without affecting redox-sensitive survival signal transduction pathways represents a promising approach to elicit the beneficial effect of NO. Recent emerging pharmacological tools and regular exercise inhibit ROS generation in the proximity of NOSs, thereby increasing bioavailable NO and exerting cardioprotection against I/R injury and LV remodeling.

Blueberry-enriched diet protects rat heart from ischemic damage

OBJECTIVES

to assess the cardioprotective properties of a blueberry enriched diet (BD).

BACKGROUND

Reactive oxygen species (ROS) play a major role in ischemia-related myocardial injury. The attempts to use synthetic antioxidants to block the detrimental effects of ROS have produced mixed or negative results precipitating the interest in natural products. Blueberries are readily available product with the highest antioxidant capacity among fruits and vegetables.

METHODS AND RESULTS

Following 3-mo of BD or a regular control diet (CD), the threshold for mitochondrial permeability transition (t(MPT)) was measured in isolated cardiomyocytes obtained from young male Fischer-344 rats. Compared to CD, BD resulted in a 24% increase (p<0.001) of ROS indexed t(MPT). The remaining animals were subjected to a permanent ligation of the left descending coronary artery. 24 hrs later resulting myocardial infarction (MI) in rats on BD was 22% less than in CD rats (p<0.01). Significantly less TUNEL(+) cardiomyocytes (2% vs 9%) and 40% less inflammation cells were observed in the myocardial area at risk of BD compared to CD rats (p<0.01). In the subgroup of rats, after coronary ligation the original diet was either continued or switched to the opposite one, and cardiac remodeling and MI expansion were followed by serial echocardiography for 10 weeks. Measurements suggested that continuation of BD or its withdrawal after MI attenuated or accelerated rates of post MI cardiac remodeling and MI expansion.

CONCLUSION

A blueberry-enriched diet protected the myocardium from induced ischemic damage and demonstrated the potential to attenuate the development of post MI chronic heart failure.

Clinical cardioprotection and the value of conditioning responses

Adjunctive cardioprotective strategies for ameliorating the reversible and irreversible injuries with ischemia-reperfusion (I/R) are highly desirable. However, after decades of research, the promise of clinical cardioprotection from I/R injury remains poorly realized. This may arise from the challenges of trialing and effectively translating experimental findings from laboratory models to patients. One can additionally consider whether features of the more heavily focused upon candidates could limit or preclude therapeutic utility and thus whether we might shift attention to alternate strategies. The phenomena of preconditioning and postconditioning have proven fertile in identification of experimental means of cardioprotection and are the most intensely interrogated responses in the field. However, there is evidence these processes, which share common molecular signaling elements and end effectors, may be poor choices for clinical exploitation. This includes evidence of age dependence, limiting efficacy in target aged or senescent hearts; refractoriness to conditioning stimuli in diseased myocardium; interference from a variety of relevant pharmaceuticals; inadvertent induction of these responses by prior ischemia or commonly used drugs, precluding further benefit; and sex dependence of protective signaling. This review focuses on these features, raising questions about current research strategies, and the suitability of these widely studied phenomena as rational candidates for clinical translation.

Sustained cardioprotection: exploring unconventional modalities

Since Murry et al. [Murry, C.E., Jennings, R.B., Reimer, K.A., 1986. Preconditioning with ischemia: a delay of lethal cell injury in ischemic myocardium. Circulation. 74, 1124-36.] initially reported on the powerful protective effects of ischemic preconditioning (PC), a plethora of experimental investigations have identified varied preconditioning protocols or mimetics to achieve cardioprotection. These stimuli predominantly act via archetypal mediators identified in associated signalling studies (including PI3-K, Akt, PKC, mitochondrial K(ATP) channels). Despite an intense research effort over the last 20 years, there remains a paucity of evidence that this protective paradigm is clinically exploitable. This may arise due to a number of drawbacks to conventional protection, including effects of age, disease, and interactions with other pharmacological agents. This encourages investigation of alternate strategies that trigger protection via unconventional signalling (distinct from conventional PC) and/or mediate sustained shifts in ischemic tolerance in hearts of varying age and disease status. This review considers briefly drawbacks to conventional PC, and focuses on alternate strategies for generating prolonged states of cardiac protection.

Ischemic preconditioning: from molecular mechanisms to therapeutic opportunities

Ischemia/reperfusion (I/R) injury is a major contributory factor to cardiac dysfunction and infarct size that determines patient prognosis after acute myocardial infarction. Considerable interest exists in harnessing the heart's endogenous capacity to resist I/R injury, known as ischemic preconditioning (IPC). The IPC research has contributed to uncovering the pathophysiology of I/R injury on a molecular and cellular basis and to invent potential therapeutic means to combat such damage. However, the translation of basic research findings learned from IPC into clinical practice has often been inadequate because the majority of basic research findings have stemmed from young and healthy animals. Few if any successful implementations of IPC have occurred in the diseased hearts that are the primary target of viable therapies activating cardioprotective mechanisms to limit cardiac dysfunction and infarct size. Therefore, the first purpose of this review is to facilitate understanding of pathophysiology of I/R injury and the mechanisms of cardioprotection afforded by IPC in the normal heart. Then I focus on the problems and opportunities for successful bench-to-bedside translation of IPC in the diseased hearts.

Perspectives in innate and acquired cardioprotection: cardioprotection acquired through exercise

Emerging evidence indicates that exercise training can provide significant protection against myocardial ischemia-reperfusion injury. In this brief review, we provide a synthesis of current literature in the field and summarize the findings to date. Our intent is to identify the unique elements of cardioprotection acquired by exercise, and to illustrate what distinguishes this physiological acquisition of cardioprotection from all other known types of acquired cardioprotection. Finally, we point to future directions for research in this exciting area.