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JEPonline
Racial Differences in the Time-Course Oxidative Stress Responses to Acute Exercise
Deborah L Feairheller1, Keith M Diaz1, Kathleen M Sturgeon1, Sheara T Williamson1, and Michael D Brown1, 2
1Hypertension, Molecular and Applied Physiology Laboratory, Department of Kinesiology, 2Cardiovascular Research Center, School of Medicine, Temple University, Philadelphia, PA. USA
ABSTRACT
Feairheller DL, Diaz KM, Sturgeon KM, Williamson ST, Brown MD. Racial Differences in the Time-Course Oxidative Stress Responses to Acute Exercise. JEPonline 2011;14(1):49-59. African Americans have disproportionate levels of cardiovascular disease and oxidative stress. The purpose of our study was to examine racial differences between African American and Caucasian adults in time-course oxidative stress responses to a treadmill test. After a 12-hr fast, 18 participants (9 of each ethnic group; 21 0.4 yrs) completed a submaximal treadmill test and underwent serial blood draws: Pre, Post (within 2 min), 30, 60, and 120 min after exercise. At each time-point, superoxide dismutase (SOD, U/mL), total antioxidant capacity (TAC, mM), protein carbonyls (PC, nmol/mg), and thiobarbituric acid-reactive substance (TBARs, mol/L) were measured. We found no difference between groups for blood pressure, BMI, or exercise capacity (as measured by volume of oxygen consumed, VO2 max). African Americans had significantly (p < 0.05) higher SOD (Pre: 5.45 0.4 vs. 3.69 0.69; 60 min: 8.99 0.7 vs. 4.23 0.6; 120 min: 9.69 1.6 vs. 3.52 0.7), TAC (Pre: 2.31 0.25 vs. 1.16 0.3; Post: 2.39 0.2 vs. 1.34 0.2; 30 min: 2.29 0.2 vs. 1.09 0.2), and PC (Pre: 1.09 0.1 vs. 0.82 0.1; Post: 1.14 0.1 vs. 0.81 0.1; 30 min: 1.13 0.1 vs. 0.85 0.1; 60 min: 1.06 0.1 vs. 0.81 0.05), but not TBARs. Between groups, only SOD exhibited a different time-course response: levels for African Americans rose steadily throughout the 120 min, while levels for Caucasians peaked at 30 min and by 120 min had returned to pre-exercise levels. Race had a greater effect on oxidative stress responses than submaximal exercise did. African Americans had significantly higher TAC, SOD, and PC levels compared to Caucasians.
Key Words: African Americans, Sub-maximal Exercise, Antioxidants, Nitric Oxide, Superoxide Dismutase, Total Antioxidant Capacity
INTRODUCTION
African Americans exhibit disproportionate levels of hypertension (HT), higher incidence of cardiovascular and renal disease, and elevated levels of oxidative stress when compared to other ethnic groups, in particular Caucasians. Additionally, studies in un-stimulated endothelial cell culture have shown that these racial differences also exist in vitro by reporting heightened oxidative stress in African American cells compared to Caucasian cells ADDIN EN.CITE Kalinowski2004181817Kalinowski, L.Dobrucki, I.T.Malinski, T. Race-specific differences in endothelial function. Predisposition of African Americans to vascular diseasesCirculationCirculation2511-2517109Endothelial function2004(17).
The effects of submaximal acute exercise on the oxidant/antioxidant balance over a post-exercise time period are not well known. Inconsistencies are found in results from one study to the next due to differences in exercise protocol, training status, and gender. It is also not well known whether a disparity exists between races in the oxidative stress response to exercise. Since exercise is often prescribed as a non-pharmacologic treatment of chronic diseases like HT, and given that African Americans tend to have higher levels of oxidative stress, it becomes critical to understand the appropriate exercise intensity that will not elicit an exaggerated oxidative stress response.
Oxidative stress is an imbalance between the production of free radicals and the antioxidant systems ability to buffer the oxidative damage. Exercise causes an increase in oxygen consumption and, therefore, the production of reactive oxygen species (ROS), ultimately leading to increased oxidative stress if the antioxidant systems buffering ability is insufficient. This oxidative stress response to exercise varies by biomarker. It is understood that proteins are expressed in response to exercise, their expression levels peak at different times, and the amount of time that it takes to return to baseline expression levels varies by marker. Classic pre-post exercise protocols collect the post-exercise sample immediately following the exercise bout, and only a few studies exist where more than 2 blood samples have been collected to explore time-course responses to acute exercise. Along these lines, in 2007 Michailidis et al. (22) investigated the time-course responses of several oxidative stress markers during a 24-hour period after one session of 45 minutes of treadmill exercise at 70 to 75% VO2 max. They studied 11 untrained men and found different response times for the oxidative stress markers. However, to the best of our knowledge, this type of study has not been done to examine potential racial differences.
The purpose of the present study was to examine racial differences between African American and Caucasian adults in the time-course oxidative stress responses to an acute exercise bout. Because exhaustive exercise to volitional fatigue is not commonplace for most exercise sessions among the general public, we sought to determine whether responses to a submaximal exercise test differed by race.
METHODS
Subjects
Young college-aged African American and Caucasian students 18 to 25 years of age were recruited through advertisements and word of mouth. Following the completion of an extensive health history form during the initial laboratory visit, all subjects were apparently healthy and free of cardiovascular risk factors. This study was approved by the Institutional Review Board of Temple University, Philadelphia, PA., was conducted under HIPPA guidelines, and all qualified students provided their written, informed consent.
Experimental Design
The subjects were asked to refrain from vitamins for 2 weeks prior to the study, from caffeine, alcohol, and exercise training for 24 hours prior to testing, and they were asked to fast for at least 12 hours the night before the study. Research has suggested that the hormone fluctuations during the menstrual cycle can influence oxidative stress responses to exercise ADDIN EN.CITE Joo200452152117Joo, M. H.Maehata, E.Adachi, T.Ishida, A.Murai, F.Mesaki, N.Tsukuba University Grad, School of Comprehensive Human Sciences, 1-1-1, Tennodai Tsukuba, Ibaraki 305-8574, Japan. joomihyun@med.taiiku.tsukuba.ac.jpThe relationship between exercise-induced oxidative stress and the menstrual cycleEur J Appl PhysiolEur J Appl Physiol82-6931-2AdultEstradiol/*bloodFemaleHumansMenstrual Cycle/*blood/physiologyOxidative Stress/*physiologyPhysical Endurance/*physiologyPhysical Exertion/physiologyProgesterone/bloodReactive Oxygen Species/*bloodStatistics as TopicSuperoxide Dismutase/*bloodThiobarbituric Acid Reactive Substances/*metabolism2004Oct15243748http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&dopt=Citation&list_uids=15243748 (16). Therefore, all females were tested during days 1 through 5 of their menstrual cycle because hormone levels tend to be lowest early in the follicular phase.
On the morning of the study, height and weight were measured, and a pre-exercise blood sample was collected. Blood samples were collected in EDTA and Sodium-Heparin tubes, centrifuged at 2000g for 20 minutes at 4C, and then the plasma was frozen at -80C until assay. Then a modified Bruce submaximal treadmill (TM) exercise test was performed. The TM test was terminated when the subjects reached 75 to 80% of their heart rate reserve, then regression analysis using data collected by indirect calorimetry was used to predict VO2 max levels. Post-exercise blood samples were collected at the following time-points: immediately following exercise termination (within 2 minutes), 30, 60, and 120 minutes. All subjects remained in the lab for 2 hours following the exercise period in order to control for food and water intake. During this time, they were instructed to sit and read, or work on the computer. They were allowed to drink up to 1L of water. At the completion of the test, juice and snacks were provided to replenish glucose levels. Subject data were only included if 80% of the blood samples were collected.
Assays (All assays were done in duplicate)
Plasma Superoxide Dismutase (SOD). Plasma samples were diluted 1:5 in sample buffer (50 mM Tris-HCl, pH 8.0). SOD activity was measured by utilizing a tetrazolium salt radical detector solution, diluted in assay buffer (50 mM Tris-HCl, pH 8.0, containing 0.1 mM diethylenetriaminepentaacetic acid and 0.1 mM hypoxanthine), to detect superoxide radicals generated by hypoxanthine and xanthine oxidase. One unit of SOD activity is defined as the amount of enzyme needed to exhibit a 50% dismutation of the superoxide radical. Absorbance was read at 450 nm using a SpectraMax Microplate Reader (Molecular Devices, Sunnyvale, CA). All reagents were obtained from Cayman Chemical (Ann Arbor, MI). The detection limit was 0.025 U/ml. Inter-assay and intra-assay coefficients of variation were 5.9% and 12.4%, respectively.
Total Antioxidant Capacity (TAC). Plasma samples were diluted 1:20 in Assay buffer (5 mM potassium phosphate, pH 7.4, containing 0.9% sodium chloride and 0.1% glucose). TAC measurement was based on the ability of antioxidants in the plasma to inhibit the oxidation of ABTS (2,2-Azino-di- to ABTS+ by metmyoglobin). The capacity of the antioxidants in plasma to prevent ABTS oxidation is compared with that of a water-soluble vitamin E analogue, Trolox. Absorbance was read at 750 nm using a SpectraMax Microplate Reader (Molecular Devices, Sunnyvale, CA), and TAC activity quantified as millimolar Trolox equivalents. All reagents were obtained from Cayman Chemical (Ann Arbor, MI). The detection limit was 0.044 mM. Inter-assay and intra-assay coefficients of variation were 6.7% and 9.2%, respectively.
Protein Carbonyls (PC). Average plasma protein levels were determined to be 6 g/dL by using the Bradford Protein Assay prior to the measurement of PC. PC formation was d e t e r m i n e d w i t h t h e O x i s e l e c t "! P r o t e i n C a r b o n y l E L I S A K i t ( C e l l B i o l a b s , I n c . , S a n D i e g o , C A ) . T h e m a n u f a c t u r e r s i n s t r u c t i o n s w e r e f o l l o w e d a s d e s c r i b e d p r e v i o u s l y A D D I N E N . C I T E <