oxidative stress refers to an imbalance between free radical [ especially reactive oxygen 
 species ( ros ) ] generation and antioxidant defense1 .
the antioxidant system in the human body includes enzymatic [ e.g. 
 superoxide dismutase ( sod ) and glutathione peroxidase ( gpx ) ] and non - enzymatic antioxidants 
 [ e.g. glutathione ( gsh ) ] and it plays an important role in the prevention of oxidative 
 stress .
oxidative stress is involved in the pathogenesis of hypertension , atherosclerosis , 
 diabetes , osteoporosis , and cancer2 .
ros initiates lipid peroxidation through an attack on 
 polyunsaturated fatty acids , and generates products such as mda ( malondialdehyde)4 .
ros also causes oxidative damage to 
 proteins and dnas4 . among these damages , 

oxidative dna damage is the most detrimental one to human health because of its role in the 
 pathogenesis of the various diseases mentioned above .
ros , especially hydroxyl radical 
 ( oh ) , can cause dna base changes , strand breaks , damage to tumor - suppressor genes , and 
 enhanced expression of proto - oncogenes5 . 

in addition to the increase of ros , the decrease of dna repair capacity is the other reason 
 for the accumulation of oxidative dna damage in the human body6 .
physical exercise is an important factor affecting oxidative stress and oxidative dna 
 damage , since a sharp increase in oxygen consumption during exercise results in an increase 
 in ros generation .
however , the effect of exercise - induced oxidative damage is variable 
 depending on several factors such as type , mode , duration , and intensity of exercise7 .
a single bout of exercise induces oxidative 
 stress and dna damage , whereas regular moderate intensity exercise decreases them8 . under the concept of hormesis , 
 low - to - moderate ros generation induced by regular moderate intensity exercise
a previous study demonstrated that long - term high - intensity 
 exercise ( 75%vo2max ) increased 8-hydroxy-2-deoxyguanosine 
 ( 8-ohdg ) , while regular exercise with moderate - intensity 
 ( 50%vo2max ) tended to decrease 8-ohdg10 .
the activity of 8-oxoguanine dna glycosylase ( ogg1 ) , a 
 crucial enzyme for the repair of 8-oxoguanine lesions , is up - regulated after regular 
 exercise in human and animals11 .
tai chi ( tc ) , a traditional chinese exercise , is classified as a moderate intensity 
 exercise , and its intensity is basically similar among different age and gender groups12 .
previous studies have reported the 
 numerous tangible benefits of tc practice , such as improvement of balance and prevention of 
 falls , enhancement of flexibility and strength , as well as amelioration of 
 cardio - respiratory and immune function impairments .
studies of the effects of tc exercise on 
 oxidative stress and oxidative dna damage are limited .
tc exercise reduced the degree of 
 oxidative stress in middle - aged women13 , 
 older adults14 , and obese patients with 
 type 2 diabetes15 , and long - term tc 
 practice reduced the degree of dna damage , measured by the comet assay , in middle - aged13 and older16 adults .
however , the effects of tc intervention on oxidative stress and dna damage have not been 
 investigated in young females who seldom participate in physical exercise .
the efficacy of 
 tc exercise on dna base damage and its repair also remains unclear .
young females are less 
 conscious about physical exercise compared to age - matched males17 .
although tc exercise is suitable for any population18 , only middle - aged and elderly age groups 
 frequently practice tc for health purposes .
tc is becoming popular among chinese college 
 students since it has been designated as a compulsory sport in the physical education 
 curriculum of most colleges .
therefore , the objective of this pilot study was to determine 
 the effects of tc intervention on oxidative stress , dna damage and repair in young females 
 who did not participate in regular physical exercise .
ten sedentary female students from gannan normal university , china , voluntarily 
 participated in this program . they completed inclusion and lifestyle questionnaires . 

exclusion criteria were as follows : having experience of tc exercise ; having performed 
 physical exercise for more than 1 hr per week in the past 3 months ; smoker or regular 
 alcohol drinker ; consuming supplements or medical products with antioxidant properties ; 
 having a history of cardiovascular and respiratory diseases ; having knee joint pain ; having 
 a history of lower - extremity fracture within the past 1  year .
they were asked to 
 keep their usual lifestyle including dietary behavior and daily activities , and medication 
 ( if any ) throughout the study period . at the time of recruitment ,
their demographic 
 characteristics were as follows : age , 20.400.70 yrs old ; height , 155.486.15  cm ; weight , 
 47.136.11  kg ; body mass index ( bmi ) , 19.421.54  kg / m ; and resting heart rate , 
 79.1012.65 beats / minute .
all of the participants completed the 12-week tc training program . according to this 
 protocol
, they practiced the 24-form simplified tc , 5 times ( sessions ) per week ( monday to 
 friday ) , on campus .
the first 2 weeks involved familiarization with tc through teaching and 
 learning . in the following 10 weeks , the participants practiced 5 rounds of tc ( 1 round 
 refers to practice from the 1st movement to the 24th movement of this tc style ) accompanied 
 by a classic music for this tc style in each session .
an experienced tc instructor led all 
 participants in practice and taught them necessary movement corrections in the intervals 
 between rounds .
thus , each session lasted about 60  min including a 10-minute warm - up for 
 stretching and a 5-minute cool - down for relaxation .
heart rate ( hr ) during tc exercise was monitored in the last session of the 5 rounds of the 
 24-form simplified tc in the last 4th , 8th , and 12th weeks .
the exercise duration of five 
 rounds of tc practice lasted for around 30 minutes .
hr parameters such as average hr , 
 maximum hr , and minimum hr were recorded using a polar watch ( suunto t6d running pack , 
 finland ) and the telemetry hr team system ( suunto team manager , finland ) .
blood samples were collected at baseline , 8 , and 12 weeks . in each session of blood 
 collection , 3  ml of whole blood was taken after overnight fasting between 7:308:30 a.m. 
 from a forearm vein and placed into a heparinized tube .
plasma was separated by 
 centrifugation at 3,000  rpm for 5  min and kept frozen at 80c until assayed for 8-ohdg , 
 ogg1 , sod , gpx , mda , gsh , and hydroxyl radical inhibiting capacity ( oh-ic ) .
sod was measured by the hydroxylamine assay using a spectrophotometer ( unico7200 , usa ) at 
 550  nm .
gpx was detected by the rate method using a spectrophotometer ( unico7200 ) at 412  nm . 

mda was assessed by the thiobarbituric acid ( tba ) assay using a spectrophotometer 
 ( unico7200 ) at 532  nm .
gsh was analyzed by colorimetry using a spectrophotometer ( unico7200 ) 
 at 420  nm .
hydroxyl radical inhibiting capacity was determined by the griess colorimetric 
 method using a spectrophotometer ( unico7200 ) at 550  nm .
the kits for sod , gpx , mda , gsh , and 
 oh-ic measurements were all purchased from nanjing jiancheng bioengineering institute , 
 china .
plasma 8-ohdg and ogg1 levels were measured using commercial elisa ( enzyme - linked 
 immunosorbent assay ) kits according to the manufacturer s instructions ( santa cruz 
 biotechnology , inc .
then , either 10  l of anti-8-ohdg or anti - ogg1 antibody in combination with 50  l of 
 streptavidin - biotin - horseradish peroxidase were added to the sample wells in turn . to the 
 standard sample wells , 50  l of 5 different concentrations of standard samples and 50  l of 
 streptavidin - biotin - horseradish peroxidase were added .
the microtiter plate was then 
 incubated for 1 hour at 37  c . then
, the plate was washed with wash buffer 5 times . during 
 the procedure of washing , before discarding the buffer , each well was filled with wash 
 buffer for 30 seconds .
color reactions were then conducted for 10  min in the dark at 37  c 
 after 50  l of chromogenic agent a and 50  l of chromogenic agent b were added in turn to 
 each well .
finally , 50  l of stop solution was added to terminate the reaction and the blue 
 color changed to yellow .
shanghai , china ) at 450  nm within 15  min , and 
 the concentrations of 8-ohdg and ogg1 in plasma were read from standard curves .
all data were expressed as the mean  sd . the differences of plasma and hr monitoring 
 parameters among different time points were determined by repeated measures analysis of 
 variance ( anova ) .
post hoc pair - hoc comparisons ( lsd ) were performed to test the differences 
 when significance was shown .
the correlation between plasma 8-ohdg and ogg1 levels at the 
 same time point was determined using pearson s correlation coefficient .
the statistical 
 package for social sciences ( spss ) version 17.0 was used for the analysis and values of 
 p<0.05 were considered significant .
when the participants were performing 5 rounds of tc , the average hr and maximum hr tended 
 to increase at 4 , 8 , and 12 weeks , but they did not show significant differences ( table 1table 1 .
comparison of hr among the different time pointsvariables4 weeks8 weeks12 weekshraverage ( bmp)108.310.5110.0010.7113.918.8hrmax ( bmp)124.212.4126.913.4132.922.5hrmin ( bmp)88.310.987.78.384.810.4hraverage = mean heart rate , hrmin = minimum heart rate , hrmax = maximum heart rate , 
 bmp = beats per minute ) . in contrast , the minimum hr tended to decrease during this study period , 
 although the decreases were not statistically significant ( p>0.05 ) ( table 1 ) .
hraverage = mean heart rate , hrmin = minimum heart rate , hrmax = maximum heart rate , 
 bmp = beats per minute the sod level was significantly increased ( p<0.05 ) at 8 and 12 weeks of tc exercise 
 compared to the baseline value ( table 
 2table 2 .
effects of tai chi exercise on oxidative stress markersvariablesbaseline8 weeks12 weekssod ( u / ml)42.763.0549.815.01 * 49.054.73*gpx ( u / ml)130.3022.88133.5318.77141.6028.55mda ( nmol / ml)2.770.412.120.41 * 2.970.54gsh ( mggsh / l)11.925.0710.483.089.194.56oh-ic ( u / ml)351.9759.02406.1934.76 * 408.4949.86**p<0.05 compared to baseline , sod : superoxide dismutase ; gpx : glutathione 
 peroxidase ; mda : malondialdehyde ; gsh : glutathione ; oh-ic : hydroxyl radical 
 inhibiting capacity ) .
conversely , the 
 plasma mda level was significantly decreased at 8 weeks but not at 12 weeks compared to the 
 baseline ( table 2 ) .
however , gpx and gsh levels 
 did not alter significantly during the study period . *
p<0.05 compared to baseline , sod : superoxide dismutase ; gpx : glutathione 
 peroxidase ; mda : malondialdehyde ; gsh : glutathione ; oh-ic : hydroxyl radical 
 inhibiting capacity although the increases were not statistically significant , the plasma 8-ohdg values in this 
 study showed increases at 8 and 12 weeks compared to the baseline value ( table 3table 3 .
comparison of plasma 8-ohdg and ogg1 , and their relationships at different time 
 pointsvariablesbaseline8 weeks12 weeks8-ohdg ( ng / ml)9.452.5410.932.5110.262.34ogg1 ( ng / ml)6.912.058.171.54 * 8.491.62*r ( p value)0.842 ( 0.003)0.78 ( 0.008)0.545 ( 0.103)*p<0.05 compared to baseline , 8-ohdg : 8-hydroxy-2-deoxyguanosine ; ogg1 : 
 8-oxoguanine dna glycosylase ; r : correlation coefficients of plasma 8-ohdg and ogg1 at 
 the same time point ) .
in contrast , the plasma ogg1 level was significantly increased at 8 and 12 
 weeks compared to the baseline value ( table 3 ) . 

positive correlations between plasma 8-ohdg and ogg1 were found at baseline ( p=0.003 ) and 8 
 weeks ( p=0.008 ) , but no statistically significant correlation ( p=0.103 ) was found at 12 
 weeks ( table 3 ) . * p<0.05 compared to baseline , 8-ohdg : 8-hydroxy-2-deoxyguanosine ; ogg1 : 
 8-oxoguanine dna glycosylase ; r : correlation coefficients of plasma 8-ohdg and ogg1 at 
 the same time point
several empirical studies using different parameters , including heart rate ( hr ) , oxygen 
 consumption ( vo2 ) , and energy expenditure , have shown that tc is an aerobic 
 exercise of moderate intensity12 . 

however , in those previous studies , the intensity of tc was measured only when participants 
 practiced one round of tc , from the first movement to the last one of the specific tc style . 

it is intuitive that several factors such as the individual variances in age , gender , 
 proficiency levels of tc , and also tc style would affect the intensity . in the present 
 study , we monitored the participants hr when they practiced 5 rounds of the 24-form 
 simplified tc at 4 , 8 , and 12 weeks .
the results of hr monitoring show that the average hr 
 during tc practice corresponded to 54.3% , 55.1% , and 57.1% of the age - predicted maximum 
 heart rate ( = 220-age ) at 4 , 8 , and 12 weeks , respectively .
these results indicate that the 
 intensity of tc practice of the present protocol was moderate for the young female 
 students .
although exercise has numerous benefits for human health , it is also often claimed to 
 induce oxidative stress since exercise increases ros generation .
ros generated during exercise is , however , not always 
 harmful because moderate and gradual exercise helps people to acquire antioxidant 
 defenses19 .
the antioxidant defense system in the human body includes enzymes , such as sod and gpx , and 
 non - enzymatic antioxidants such as gsh . in the enzymatic system ,
sod is the first defense 
 against oxidative stress and is the major defense against o2 , 
 whereas gpx is responsible for scavenging h2o2 and other organic 
 peroxides .
, we observed a significant increase 
 in plasma sod and oh-ic levels after 8 weeks of tc exercise indicating that 8 weeks of tc 
 exercise following our protocol is sufficient enough to improve the scavenging capacities 
 for o2 and oh. in this study , the plasma mda level decreased at 8 
 weeks .
thus , tc exercise can help to reduce the lipid peroxidation products attacked by ros . 
 in the present study , although the increase was not statistically significant , gpx tended to 
 increase with time of tc practice .
since gpx is efficiently induced by high ros 
 concentrations20 , our protocol would 
 have generated low concentrations of ros .
our results are in agreement with those of 
 previous studies concerning the protective effects of tc exercise on oxidative stress in 
 middle - aged and elderly subjects13 , 14 .
we propose there are two possible mechanisms of regular moderate - intensity exercise which 
 reduce the markers of oxidative stress .
first , based on the theory of hormesis , 
 low - to - moderate oxidants would cause up - regulation of antioxidant enzymes9 .
ros generated in this type of exercise are 
 not only toxic , but also play an important role in cell signaling and in the regulation of 
 gene expression9 , 19 . in this sense ,
second , the 
 cumulative effects of repeated exercise bouts and exposure to ros during regular 
 moderate - intensity exercise could be the other mechanism19 .
in addition to the changes of oxidative stress markers , no significant changes in plasma 
 8-ohdg were observed throughout this study . in attack by ros ( especially oh ) ,
8-ohdg is the 
 most ubiquitous product of oxidative dna base modification which occurs in approximately 1 
 in 100,000 guanidine residues in a normal human cell22 .
for example , the plasma 8-ohdg level was increased by 12 weeks of 
 high - intensity exercise , whereas it tended to decrease after moderate - intensity exercise in 
 young men10 .
8-ohdg was significantly 
 lower in a moderate endurance exercise group than in a sedentary group4 .
after 10 months of aerobic exercise , the 8-ohdg level was 
 increased significantly compared to the baseline in a group of elderly subjects23 .
inconsistency among these outcomes may be 
 due to the different age groups , exercise types and modes , as well as the exercise 
 intervention duration .
an 
 animal study also showed that 2 months of regular treadmill running significantly 
 upregulated the activity of ogg1 in hepatocyte nuclei of old rats compared to a sedentary 
 old group11 .
another animal study showed 
 that exercise training increased ogg1 levels / activity in the nucleus of skeletal muscles and 
 specific activity of ogg1 in mitochondrial compartments26 .
similarly , our present study demonstrated that the plasma ogg1 
 level significantly increased after tc practice for 8 and 12 weeks .
increase of this enzyme 
 in plasma is likely to be an adaptive response to the increased oxidative damage induced by 
 elevated ros during tc exercise .
the damaged dna 
 with 8-ohdg may contribute to point mutation during the subsequent replication27 . with normal body repair mechanisms
, 
 8-ohdg can be cleaved by ogg1 through the way of base excision pathway and normal guanine is 
 added to the site24 .
for example , kondo et al . showed a positive 
 association between 8-ohdg levels and ogg1 expression ( r=0.702 , p<0.05)28 . in our study ,
significant positive 
 correlations between plasma 8-ohdg and ogg1 were observed at baseline ( r=0.824 , p<0.01 ) 
 and 8 weeks ( r=0.78 , p<0.01 ) ; however , no significant correlation was found at 12 weeks 
 ( r=0.545 , p>0.05 ) .
these results suggest that the increase of ogg1 activity after 12 
 weeks of tc exercise exceeds the requirements for immediately excising all 8-ohdg in young 
 females .
based on the results of this pilot study , a 12-week tc exercise intervention is effective 
 at increasing the activity of plasma sod and ogg1 and decreasing plasma mda concentration in 
 young sedentary females .
it suggests that tc exercise helps to alleviate the oxidative 
 stress response and dna damage in those who have serious levels of oxidative stress and dna 
 damage , such as older and sick people .
third , the authors only told the participants to keep their daily dietary 
 habits and did not ask them to record their dietary details , especially before each blood 
 sampling .
thus , dietary variation might have affected the data of blood parameters . 
 nevertheless , this pilot study showed tc intervention can improve the response to oxidative 
 stress and the dna damage / repair process in female students .
further studies with a longer 
 intervention duration , larger groups , and a control group are needed to confirm our present 
 results . moreover
, the long - term effects of tai chi on oxidative stress response and 
 dna / repair also need to be studied in the future .
   [ purpose ] this study was to examine the effects of 12 weeks of tai chi ( tc ) exercise on 
 antioxidant capacity , and dna damage / repair in young females who did not perform regular 
 physical exercise . 
 [ subjects and methods ] ten female students from a chinese university 
 voluntarily participated in this program . 
 all of them practiced the 24-form simplified tai 
 chi , 5 times weekly , for 12 weeks . 
 plasma levels of superoxide dismutase ( sod ) , 
 glutathione peroxidase ( gpx ) , malondialdehyde ( mda ) , glutathione ( gsh ) , hydroxyl radical 
 inhibiting capacity ( oh-ic ) , 8-hydroxy-2-deoxyguanosine ( 8-ohdg ) , and 8-oxoguanine dna 
 glycosylase ( ogg1 ) were measured at 0 , 8 , and 12 weeks . heart rate ( hr ) was monitored 
 during the last set of the training session at 4 , 8 , and 12 weeks . [ results ] 
 plasma sod 
 and oh-ic levels were increased at 8 and 12 weeks compared to the baseline ( 0 weeks ) . 
 gpx 
 and gsh levels did not change significantly throughout the study period . 
 the plasma mda 
 level was decreased significantly at 8 weeks but not at 12 weeks compared to the baseline 
 value . 
 while the plasma 8-ohdg level did not change throughout the study period , the 
 plasma ogg1 level was significantly increased at 8 and 12 weeks compared to the baseline 
 value . 
 [ conclusion ] tc practice for 12 weeks efficiently improved the oxidative stress 
 response in young females who did not perform regular physical exercise . 
 the tc exercise 
 also increased the dna repairing capacity . 
INTRODUCTION
SUBJECTS AND METHODS
RESULTS
DISCUSSION