Regulation of free radical outflow from an isolated muscle bed in exercising humans

University of California, San Diego, San Diego, California, United States
AJP Heart and Circulatory Physiology (Impact Factor: 3.84). 11/2004; 287(4):H1689-99. DOI: 10.1152/ajpheart.00148.2004
Source: PubMed


Incremental knee extensor (KE) exercise performed at 25, 70, and 100% of single-leg maximal work rate (WR(MAX)) was combined with ex vivo electron paramagnetic resonance (EPR) spectroscopic detection of alpha-phenyl-tert-butylnitrone (PBN) adducts, lipid hydroperoxides (LH), and associated parameters in five males. Blood samples were taken from the femoral arterial and venous circulation that, when combined with measured changes in femoral venous blood flow, permitted a direct examination of oxidant exchange across a functionally isolated contracting muscle bed. KE exercise progressively increased the net outflow of LH and PBN adducts (100% > 70% > 25% WR(MAX), P < 0.05) consistent with the generation of secondary, lipid-derived oxygen (O(2))-centered alkoxyl and carbon-centered alkyl radicals. Radical outflow appeared to be more intimately associated with predicted decreases in intracellular Po(2) (iPo(2)) as opposed to measured increases in leg O(2) uptake, with greater outflow recorded between 25 and 70% WR(MAX) (P < 0.05 vs. 70-100% WR(MAX)). This bias was confirmed when radical venoarterial concentration differences were expressed relative to changes in the convective components of O(2) extraction and flow (25-70% WR(MAX) P < 0.05 vs. 70-100% WR(MAX), P > 0.05). Exercise also resulted in a net outflow of other potentially related redox-reactive parameters, including hydrogen ions, norepinephrine, myoglobin, lactate dehydrogenase, and uric acid, whereas exchange of lipid/lipoproteins, ascorbic acid, and selected lipid-soluble anti-oxidants was unremarkable. These findings provide direct evidence for an exercise intensity-dependent increase in free radical outflow across an active muscle bed that was associated with an increase in sarcolemmal membrane permeability. In addition to increased mitochondrial electron flux subsequent to an increase in O(2) extraction and flow, exercise-induced free radical generation may also be regulated by changes in iPo(2), hydrogen ion generation, norepinephrine autoxidation, peroxidation of damaged tissue, and xanthine oxidase activation.

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    • "Spin-trapping studies have shown hypoxia to compound exercise-induced lipid-derived alkoxyl radical accumulation (Bailey et al. 2001; Davison et al. 2006) despite a comparatively lower maximal (absolute) power output. We have reasoned that a reduction in mitochondrial P O 2 even in the face of a comparatively lower O 2 flux is potentially one of several as yet unidentified mechanisms, underpinning the synergistic (pro-oxidant) effects of hypoxic exercise (Bailey et al. 2004b). "
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    ABSTRACT: Exercise performance in hypoxia may be limited by a critical reduction in cerebral and skeletal tissue oxygenation though the underlying mechanisms remain unclear. We examined if increased systemic free radical accumulation during hypoxia would be associated with elevated microvascular deoxygenation and reduced maximal aerobic capacity (O2MAX). Eleven healthy males were randomly assigned single-blind to an incremental semi-recumbent cycling test to determine O2MAX in both normoxia (21% O2) and hypoxia (12% O2) separated by a week. Continuous wave near infra-red spectroscopy was employed to monitor concentration changes in oxy and deoxyhaemoglobin in the left vastus lateralis muscle and frontal cerebral cortex. Antecubital venous blood samples were obtained at rest and O2MAX to determine oxidative (ascorbate radical by electron paramagnetic resonance spectroscopy), nitrosative [nitric oxide metabolites by ozone-based chemiluminescence and 3-nitrotyrosine by enzyme-linked immunosorbent assay (ELISA)] and inflammatory (soluble intercellular/vascular cell adhesion 1 molecules by ELISA) stress biomarkers. Hypoxia was associated with increased cerebral and muscle tissue deoxygenation and lower O2MAX (P < 0.05 vs. normoxia). Despite an exercise-induced increase in oxidative-nitrosative-inflammatory stress, hypoxia per se did not have an additive effect (P > 0.05 vs. normoxia). Consequently, we failed to observe any correlations between any metabolic, haemodynamic or cardiorespiratory parameters (P > 0.05). Collectively, these findings suggest that altered free radical metabolism cannot explain the elevated microvascular deoxygenation and corresponding lower O2MAX in hypoxia. Further research is required to determine if free radicals when present in excess do indeed contribute towards the premature termination of exercise in hypoxia.This article is protected by copyright. All rights reserved
    Full-text · Article · Oct 2014 · Experimental physiology
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    • "Exercise has been shown to induce an increased formation of reactive oxygen species (ROS) such as superoxide, hydroxyl radicals, or hydrogen peroxide [1] [2]. Sources of exerciseinduced ROS production are the mitochondrial electron transport chain [3] [4] [5], the xanthine oxidase pathway [6], activated neutrophiles [6], and membrane-bound NAD(P)H oxidases of the skeletal muscle [7] [8]. "
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    ABSTRACT: Background. Analysis of γ-H2AX foci is a promising approach to evaluate exercise-induced DNA damage. However, baseline levels and day-to-day variability of γ-H2AX foci have not been investigated in healthy subjects at rest. Methods. Blood was taken from eight moderately trained healthy males (29 ± 3 yrs, 1.84 ± 0.03 m, and 85 ± 6 kg) at two separate days (M1/M2) after 24-hour exercise cessation. Number of γ-H2AX foci per 100 lymphocytes (N), number of foci per affected lymphocyte (NAL), percentage of affected lymphocytes (PAL), and diameter (D) of γ-H2AX foci were analyzed (mean ± SD). Differences between M1 and M2 were analyzed using paired t-tests (α = 0.05). Day-to-day variability was evaluated by calculating the coefficients of variation (CV%), bias, and limits of agreement (LoA). Results. There were no statistically significant differences between M1 (N: 7.6 ± 4.4, NAL: 1.2 ± 0.2, PAL: 5.9 ± 2.6%, and D: 0.63 ± 0.07) and M2 (N: 8.4 ± 4.6, NAL: 1.3 ± 0.1, PAL: 6.9 ± 4.2%, and D: 0.66 ± 0.06). CV was calculated to be 98.5% (N), 88.9% (PAL), 11.3% (NAL), and 8.0% (D). Bias (LoA) was 0.75 (-15.2/13.7), -0.02 (-0.36/0.33), -1.0 (-11.9/9.9), and -0.04 (-0.16/0.09), respectively. Conclusions. Background level in healthy subjects is approximately 0.07 to 0.09 γ-H2AX foci/cell. NAL and D are reliable measures.
    Full-text · Article · Jul 2014 · Journal of nutrition and metabolism
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    • "sm to energy production ( Maglischo , 2003 ) . The effect of lactate produced during exercise on the redox status is rather unclear , as , on the one hand , it has been found to act as an antioxidant ( Groussard et al . , 2000 ) , while , on the other , the drop in pH accompanying lactate production has been reported to increase oxidative stress ( Bailey et al . , 2004 ) . Oxidative damage after the swimming sessions was evident in DNA and lipids , but not in proteins ."
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    ABSTRACT: Abstract Throughout adolescence, swimmers begin to carry out demanding endurance and high-intensity training sets, the effect of which on redox status is largely unknown. The aim of the present study was to investigate the effects of 2000-m continuous swimming and 6 × 50-m maximal swimming on the redox status of adolescent swimmers. Fifteen male and 15 female swimmers, aged 14-18 years, provided blood samples before, immediately after, 1 h after, and 24 h after each exercise for the determination of redox status parameters. Oxidative damage was short-lived and manifest as increases in 8-hydroxy-2΄-deoxyguanosine (8-OHdG) 1 h after high-intensity exercise (39%, P < 0.001) and in malondialdehyde immediately after both exercises (65%, P < 0.001). Alterations in antioxidant parameters were sustained during recovery: reduced glutathione decreased 24 h post-exercise (11%, P = 0.001), uric acid increased gradually after high-intensity exercise (29%, P < 0.001) and bilirubin peaked 24 h post-exercise (29%, P < 0.001). Males had higher 8-OHdG (49%, P = 0.001) and uric acid (29%, P < 0.001) concentrations than females. However, females showed higher values of malondialdehyde than males immediately post-exercise (30%, P = 0.039), despite lower pre-exercise values. In conclusion, both endurance and high-intensity exercise perturbed the redox balance without inducing prolonged oxidative damage in trained adolescent male and female swimmers. These swimming training trials were not found to be detrimental to the redox homeostasis of adolescents.
    Full-text · Article · Jan 2014 · Journal of Sports Sciences
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