PPARγ activation improves the molecular and functional components of I(to) remodeling by angiotensin II

Patients with diabetes exhibit significantly altered renin-angiotensin system (RAS) control. Recently, it has been determined that hyperglycemic conditions induce an increase in angiotensin II (AT II) expression; specifically by cardiomyocytes. Altered RAS has been shown to be associated with an increase in oxidative stress and cardiac dysfunction leading to the development of cardiac hypertrophy. The transient outward potassium current (I(to)) in cardiac myocytes is mainly mediated by members of the Kv subfamily of voltage gated potassium channels and has been shown to be altered in cellular localization and expression during the development of cardiac hypertrophy. However it is not clear as to how AT II affects the pore forming complex at the cell membrane and thus directly affects the I(to) current. In the current study, we explored the protective effect of PPARγ ligands on cardiomyocyte I(to) by preventing NADPH Oxidase activation and the ensuing ROS formation. Furthermore, short term PPARγ activation in diabetic leptin deficient db/db mice displayed improvements in the membrane association of the molecular components of I(to) as well as prolonged QT interval. These findings demonstrate that PPARγ agonists have the potential to attenuate cardiomyocyte dysfunction associated with diabetes.

Exercise-induced oxidative stress and hypoxic exercise recovery

Hypoxia due to altitude diminishes performance and alters exercise oxidative stress responses. While oxidative stress and exercise are well studied, the independent impact of hypoxia on exercise recovery remains unknown. Accordingly, we investigated hypoxic recovery effects on post-exercise oxidative stress. Physically active males (n = 12) performed normoxic cycle ergometer exercise consisting of ten high:low intensity intervals, 20 min at moderate intensity, and 6 h recovery at 975 m (normoxic) or simulated 5,000 m (hypoxic chamber) in a randomized counter-balanced cross-over design. Oxygen saturation was monitored via finger pulse oximetry. Blood plasma obtained pre- (Pre), post- (Post), 2 h post- (2Hr), 4 h post- (4Hr), and 6 h (6Hr) post-exercise was assayed for Ferric Reducing Ability of Plasma (FRAP), Trolox Equivalent Antioxidant Capacity (TEAC), Lipid Hydroperoxides (LOOH), and Protein Carbonyls (PC). Biopsies from the vastus lateralis obtained Pre and 6Hr were analyzed by real-time PCR quantify expression of Heme oxygenase 1 (HMOX1), Superoxide Dismutase 2 (SOD2), and Nuclear factor (euthyroid-derived2)-like factor (NFE2L2). PCs were not altered between trials, but a time effect (13 % Post-2Hr increase, p = 0.044) indicated exercise-induced blood oxidative stress. Plasma LOOH revealed only a time effect (p = 0.041), including a 120 % Post-4Hr increase. TEAC values were elevated in normoxic recovery versus hypoxic recovery. FRAP values were higher 6Hr (p = 0.045) in normoxic versus hypoxic recovery. Exercise elevated gene expression of NFE2L2 (20 % increase, p = 0.001) and SOD2 (42 % increase, p = 0.003), but hypoxic recovery abolished this response. Data indicate that recovery in a hypoxic environment, independent of exercise, may alter exercise adaptations to oxidative stress and metabolism.

Lymphocyte enzymatic antioxidant responses to oxidative stress following high-intensity interval exercise

The purposes of this study were to 1) examine the immune and oxidative stress responses following high-intensity interval training (HIIT); 2) determine changes in antioxidant enzyme gene expression and enzyme activity in lymphocytes following HIIT; and 3) assess pre-HIIT, 3-h post-HIIT, and 24-h post-HIIT lymphocyte cell viability following hydrogen peroxide exposure in vitro. Eight recreationally active males completed three identical HIIT protocols. Blood samples were obtained at preexercise, immediately postexercise, 3 h postexercise, and 24 h postexercise. Total number of circulating leukocytes, lymphocytes, and neutrophils, as well as lymphocyte antioxidant enzyme activities, gene expression, cell viability (CV), and plasma thiobarbituric acid-reactive substance (TBARS) levels, were measured. Analytes were compared using a three (day) × four (time) ANOVA with repeated measures on both day and time. The a priori significance level for all analyses was P < 0.05. Significant increases in superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPX) activities were observed in lymphocytes following HIIT. No significant increases in lymphocyte SOD, CAT, or GPX gene expression were found. A significant increase in TBARS was found immediately post-HIIT on days 1 and 2. Lymphocyte CV in vitro significantly increased on days 2 and 3 compared with day 1. Additionally, there was a significant decrease in CV at 3 h compared with pre- and 24 h postexercise. These findings indicate lymphocytes respond to oxidative stress by increasing antioxidant enzyme activity. Additionally, HIIT causes oxidative stress but did not induce a significant postexercise lymphocytopenia. Analyses in vitro suggest that lymphocytes may become more resistant to subsequent episodes of oxidative stress. Furthermore, the analysis in vitro confirms that lymphocytes are more vulnerable to cytotoxic molecules during recovery from exercise.

Post-160-km race illness rates and decreases in granulocyte respiratory burst and salivary IgA output are not countered by quercetin ingestion

This study measured the influence of the flavonoid quercetin on immune changes and incidence rates of upper respiratory tract infections in ultramarathoners competing in the 160-km Western States Endurance Run. Sixty-three runners were randomized to quercetin and placebo groups, and under double-blinded methods ingested 1000 mg/day quercetin for 3 wks before, during, and 2 wks after the race. Thirty-nine of the 63 subjects (n = 18 for quercetin, n = 21 for placebo) finished the race and provided blood and saliva samples the morning before the race and 15 - 30 min postrace. Upper respiratory tract infections were assessed during the week before and the 2-wk period after the race using an illness symptom checklist. Race times did not differ significantly between quercetin and placebo groups. Significant pre- to postrace decreases were measured for natural killer cells (43 %), granulocyte respiratory burst activity (55 %), and salivary IgA output (48 %), and increases for neutrophil (288 %) and monocyte (211 %) cell counts, with no significant group differences. Postrace illness rates did not differ between groups. In conclusion, quercetin supplementation for 3 wks before and 2 wks after the Western States Endurance Run had no effect on illness rates, perturbations in leukocyte subset counts, or decreases in granulocyte respiratory burst activity and salivary IgA.

Intermittent hyperthermia enhances skeletal muscle regrowth and attenuates oxidative damage following reloading

Skeletal muscle reloading following disuse is characterized by profound oxidative damage. This study tested the hypothesis that intermittent hyperthermia during reloading attenuates oxidative damage and augments skeletal muscle regrowth following immobilization. Forty animals were randomly divided into four groups: control (Con), immobilized (Im), reloaded (RC), and reloaded and heated (RH). All groups but Con were immobilized for 7 days. Animals in the RC and RH groups were then reloaded for 7 days with (RH) or without (RC) hyperthermia (41-41.5 degrees C for 30 min on alternating days) during reloading. Heating resulted in approximately 25% elevation in heat shock protein expression (P < 0.05) and an approximately 30% greater soleus regrowth (P < 0.05) in RH compared with RC. Furthermore, oxidant damage was lower in the RH group compared with RC because nitrotyrosine and 4-hydroxy-2-nonenol were returned to near baseline when heating was combined with reloading. Reduced oxidant damage was independent of antioxidant enzymes (manganese superoxide dismutase, copper-zinc superoxide dismutase, catalase, glutathione peroxidase, glutathione reductase). In summary, these data suggest that intermittent hyperthermia during reloading attenuates oxidative stress and improves the rate of skeletal muscle regrowth during reloading after immobilization.

Exercise training provides cardioprotection against ischemia–reperfusion induced apoptosis in young and old animals

Endurance exercise provides cardioprotection against ischemia-reperfusion (IR)-induced necrotic cell death in young animals. However, whether exercise-induced cardioprotection prevents IR-induced apoptosis in young and old animals is unknown. We tested the hypothesis that endurance exercise training will attenuate IR-induced myocardial apoptosis in young (4 months) and old (24 months) male F344 rats. Young and old rats remained sedentary or performed multiple bouts of moderate intensity running exercise. To induce apoptosis, isolated working hearts were exposed to 45 min of ischemia followed by 90 min of reperfusion. Assessment of myocardial levels of caspase-3 cleaved alpha-spectrin and TUNEL labeled nuclei revealed that IR resulted in apoptosis in hearts from both young and old animals. Importantly, independent of age, exercise attenuated the IR-induced apoptosis of cardiac myocytes. Moreover, exercise attenuated IR-induced calpain activation in the hearts of both young and old animals. These experiments for the first time demonstrate that exercise attenuates IR-induced myocardial apoptosis in both young and old animals. Potential mechanisms for this exercise-induced cardioprotection against IR-induced apoptosis include improved myocardial antioxidant capacity and prevention of calpain and caspase-3 activation.

Aging, Exercise, and Cardioprotection

Myocardial ischemia-reperfusion (I-R) injury is a major contributor to the morbidity and mortality associated with coronary artery disease. The incidence of I-R events is greatest in older persons, and studies also indicate that the magnitude of myocardial I-R injury is greater in senescent individuals compared to younger adults. Regular exercise has been confirmed as a pragmatic countermeasure to protect against I-R-induced cardiac injury. Specifically, endurance exercise has been proven to provide cardioprotection against an I-R insult in both young and old animals. Proposed mechanisms to explain the cardioprotective effect of exercise include the induction of myocardial heat shock proteins (HSPs), improved cardiac antioxidant capacity, and/or elevation of other cardioprotective proteins. Of these potential mechanisms, evidence indicates that elevated myocardial levels of heat shock proteins or antioxidants can provide myocardial protection against I-R injury. At present, which of these protective mechanisms is essential for exercise-induced cardioprotection remains unclear. Understanding the molecular basis for exercise-induced cardioprotection is important in developing exercise paradigms to protect the heart during an I-R insult.

Dietary antioxidants and exercise

Muscular exercise promotes the production of radicals and other reactive oxygen species in the working muscle. Growing evidence indicates that reactive oxygen species are responsible for exercise-induced protein oxidation and contribute to muscle fatigue. To protect against exercise-induced oxidative injury, muscle cells contain complex endogenous cellular defence mechanisms (enzymatic and non-enzymatic antioxidants) to eliminate reactive oxygen species. Furthermore, exogenous dietary antioxidants interact with endogenous antioxidants to form a cooperative network of cellular antioxidants. Knowledge that exercise-induced oxidant formation can contribute to muscle fatigue has resulted in numerous investigations examining the effects of antioxidant supplementation on human exercise performance. To date, there is limited evidence that dietary supplementation with antioxidants will improve human performance. Furthermore, it is currently unclear whether regular vigorous exercise increases the need for dietary intake of antioxidants. Clearly, additional research that analyses the antioxidant requirements of individual athletes is needed.

Loss of exercise-induced cardioprotection after cessation of exercise

Endurance exercise provides cardioprotection against ischemia-reperfusion (I/R) injury. Exercise-induced cardioprotection is associated with increases in cytoprotective proteins, including heat shock protein 72 (HSP72) and increases in antioxidant enzyme activity. On the basis of the reported half-life of these putative cardioprotective proteins, we hypothesized that exercise-induced cardioprotection against I/R injury would be lost within days after cessation of exercise. To test this, male rats (4 mo) were randomly assigned to one of five experimental groups: 1). sedentary control, 2). exercise followed by 1 day of rest, 3). exercise followed by 3 days of rest, 4). exercise followed by 9 days of rest, and 5). exercise followed by 18 days of rest. Exercise-induced increases (P < 0.05) in left ventricular catalase activity and HSP72 were evident at 1 and 3 days postexercise. However, at 9 days postexercise, myocardial HSP72 and catalase levels declined to sedentary control values. To evaluate cardioprotection during recovery from I/R, hearts were isolated, placed in working heart mode, and subjected to 20.5 min of global ischemia followed by 30 min of reperfusion. Compared with sedentary controls, exercised animals sustained less I/R injury as evidenced by maintenance of a higher (P < 0.05) percentage of preischemia cardiac work during reperfusion at 1, 3, and 9 days postexercise. The exercise-induced cardioprotection vanished by 18 days after exercise cessation. On the basis of the time course of the loss of cardioprotection and the return of HSP72 and catalase to preexercise levels, we conclude that HSP72 and catalase are not essential for exercise-induced protection during myocardial stunning. Therefore, other cytoprotective molecules are responsible for providing protection during I/R.

The effects of endurance exercise and vitamin E on oxidative stress in the elderly

To examine the effects of exercise and vitamin E supplementation on oxidative stress in older adults, 59 participants, age 76.3 +/- 4.2 years, were randomly assigned to 1 of 4 groups: an exercise group taking placebos (EGP) or vitamin E (EGE) or a sedentary group taking placebos (SGP) or vitamin E (SGE). Measures included weight, VO2max, blood pressure (BP), and serum concentrations of vitamin E and lipid hydroperoxide (LOOH). At the end of the 16-week trial, the EGP and EGE had significant increases in VO2max and significant decreases in resting BP, weight, and LOOH concentrations (P < 0.05). The SGE had significant decreases in LOOH and BP (P < 0.05). There were no significant changes in the SGP (P > 0.05). The results suggest that endurance exercise in combination with vitamin E reduces oxidative stress, improves aerobic fitness, and reduces BP and weight in older adults. Even sedentary participants who take vitamin E may reduce oxidative stress and lower BP.

Exercise and cardioprotection

A wealth of data indicates that performing regular exercise is an important lifestyle modification to prevent cardiovascular disease. Although not fully understood, the cardioprotection by regular exercise may be exerted synergistically through improvement in many risk factors associated with cardiovascular disease. Just as important are the direct effects of exercise on the myocardium, resulting in cardioprotection against ischemia-reperfusion (I-R) injury. Cardioprotective countermeasures against myocardial I-R injury may include the development of collateral coronary arteries, induction of myocardial heat shock proteins, and improved cardiac antioxidant capacity. Improving our understanding of the molecular basis for exercise-induced cardioprotection will play an important role in developing optimal exercise interventions to protect the heart from ischemic injury.