Introduction
Aging is a multifactorial and complex process characterized by a decline in the ability
to respond to stress and to maintain cellular and systemic homeostasis. The free-radical
theory of aging has been the basis of the major anti-aging strategies, although this
theory was not yet been definitely confirmed [31]. In fact, among the various theories that attempt to explain the aging process,
disruption of the whole signaling network involving reactive oxygen species (ROS)
has received increasing recognition over the past two decades [47]. These species play a very important role in the changes induced by aging in various
tissues [14]. ROS accumulation, including superoxide anion, hydrogen peroxide, and the subsequent
oxidative damage to cells can be neutralized to nontoxic forms via elevated antioxidant
defenses, which include superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase
(GPX), and glutathione reductase (GR) [26]
[49]. Non-enzymatic antioxidants include a variety of free radical quenchers, such as
ascorbic acid, alpha-tocopherol, carotenoids, flavonoids, thiols (which include GSH),
ubiquinone Q10, uric acid, bilirubin, ferritin, albumin, transferrin, lactoferrin
and micronutrients, which act as enzymatic cofactors. The aging process causes an
imbalance between ROS production and antioxidant capacity of the tissues, leading
to cell damage [7]. Therefore, further studies should investigate the activation of the host defense
mechanisms in response to oxidative stress in older adults.
Apparently, one of the mechanisms for activating such responses is stress itself [20]. In this context, several studies showed that physical exercise could induce positive
stress [17]
[36]
[37]. In fact, it has been reported that a single bout of exercise induces oxidative
stress while increasing antioxidant enzyme activities in both young and elderly subjects
[39]. Likewise, animal studies have reported that gene expression and protein content
can be upregulated by a single bout of exercise [21]
[32]. These responses to the stimulus of exercise can be attributed to redox signaling
leading to activation of pathways involved in transcription of antioxidant gene enzymes
and increasing resistance to cellular stress [8]
[24]
[43]. The length of time that these effects last from a single bout of exercise is not
well characterized, but it is likely limited unless the stimulus is applied repeatedly
as would occur with chronic exercise. In this sense, recent findings reported a significant
improvement in oxidant/antioxidant balance in response to chronic physical activity
through enhancing the endogenous antioxidant defense system in young and older people
[2]
[30]. In fact, ROS produced during exercise could be harmful to unprepared tissues but
may also activate adaptive responses to oxidative stress, inducing antioxidant defense
systems by upregulation of responsible gene expression [16]. However, it is still unknown whether these adaptive responses differ in elderly
and young subjects. It could be hypothesized that the endogenous antioxidant system
in exercising elderly subjects is not relevant for the same adaptive responses as
compared to exercising young subjects.
On the other hand, significant changes in antioxidant capacity due to regular physical
activity might be more easily detected by examining the effect of exercise on response
to an acute oxidative challenge, which provides a more robust test of an individual’s
antioxidant capacity [46].Previous studies that have measured oxidative stress responses under challenge conditions
have generally used acute exercise as a physiological challenge [12]
[30]
[41]. In response to acute physical exercise, several studies reported better antioxidant
defenses and a lower oxidative stress damage level in the young compared to the elderly.
However, less is known about the effects of regular physical activity on exercise-induced
oxidative stress in elderly and young subjects. In others words, to the best of our
knowledge, data on oxidative stress and acute exercise have mainly focused on parameters
measured immediately before and after an exercise bout. However, it is not well known
whether these responses to chronic exercise provide sustained protection against subsequent
oxidative stressors, especially in older subjects.
Therefore, the aim of this study was to investigate both aging and regular physical
activity effects on blood antioxidant activities and lipid peroxidation levels, as
markers of oxidative stress, in healthy young and older subjects at rest and in response
to acute exercise. We put forward the hypothesis that regular physical activity (i)
could maintain an aging-associated decrease in antioxidant defenses and an increase
in lipid peroxidation damage, and (ii) that beneficial effects on oxidative stress
could be impaired by the aging process.
Methods
Participants
A total of 78 men and women were pre-screened. Twelve were excluded from the study
due to the exclusion criteria [i. e., active coronary artery disease (n=3), hypertension
(n=3), hormonal replacement therapy (n=2), and diabetes (n=4)]. Exercise testing was
completed on 66 participants and 3 of them were excluded because of concerns with
blood draws. Thus, 63 healthy participants were included to the data analysis. Characteristics
of the subjects are presented in [Table 1].
Table 1 Descriptive data of the participants (mean±SD).
|
Young sedentary group N=15
|
Young active group N=16
|
Old sedentary group N=15
|
Old active group N=17
|
|
Age (years)
|
20.3±2.8
|
21.4±1.9
|
65.1±3.5**##
|
67.2±4.8**##
|
|
Weight (Kg)
|
66.1±11.7
|
68.9±4.1
|
71.8±7.6
|
72.2±8.5
|
|
Height (m)
|
1.7±0.2
|
1.7±0.3
|
1.6±0.1
|
1.7±0.1
|
|
Physical activity score
|
3.8±1.1**
|
16.9±2.2
|
4.1±2.3††
|
19.4±2.4
|
|
VO
2max
(ml/min/kg)
|
41.2±3.2**
|
58.2±8.1
|
23.2±4.4 **†† ##
|
40.6±3.9 **
|
|
MAP (Watts)
|
220.7±36.4 **
|
296±27.9
|
94.1±32.6 **†† ##
|
195.9±27.2 **
|
|
HR
max
(bpm)
|
185.2±9.1
|
188.3±5.9
|
148 ±19.3*#
|
150.4±16.7 *#
|
|
Time duration of incremental exercise (min)
|
19.2±3.6
|
17.4±2.8
|
16.8±5.4
|
16.4±2.8
|
*: Significantly different from YA (p<0.05), **: Significantly different from YA (p<0.01)
# : Significantly different from YS (p<0.05),
## : Significantly different from YS (p<0.01)
†: Significantly different from OA (p<0.05), ††: Significantly different from OA (p<0.01)
VO2max: maximal oxygen uptake, MAP: maximal aerobic power, HRmax: maximal heart rate
All participants were non-smokers, free of musculoskeletal problems and orthopedic/neuromuscular
limitations, had a resting blood pressure below 140/85 mm Hg, had no sign of cardiovascular/respiratory
complications at rest or during the progressive diagnostic graded exercise test and
did not use hormonal replacement therapy or supplementation with antioxidants within
the 3 months preceding the study.
All the participants were informed about the purpose, nature, and potential risks
related to the study and gave their written informed consent before participation.
The study protocol was approved by the Ethics Committee of CHRU of Lille (N° 07/42)
and met the ethical standards of the International Journal of Sports Medicine [18].
Participants were assigned to one of four groups according to their age and physical
activity level:
a) young sedentary (YS, 20.3±2.8 yrs, N=15),
b) young physically active (YA, 21.4±1.9 yrs, N=16),
c) old sedentary (OS, 65.1±3.5 yrs, N=15), and
d) old physically active (OA, 67.2±4.8yrs, N=17).
To be included in the study, the age range for the young participants was 18–30 years
and at least 60 years for elderly participants.
Participants were assigned to the active or sedentary groups based on the following
criteria: (i) Maximal oxygen uptake (VO2max) had to be below 25 ml/kg/min and 45 ml/kg/min for OS and YS subjects, respectively.
For OA and YA participants, and according to the American College of Sports Medicine
[1], VO2max values had to be over 35 ml/kg/min and over 45 ml/kg/min, respectively.
(ii) Lifetime physical activity history was assessed using the physical activity questionnaire
of Baecke et al. [4] for young subjects and the physical activity questionnaire of Voorrips et al. [48] for elderly participants, both of which were adapted to each age category. Participants
were interviewed about the frequency of the physical activities they performed during
the last 12 months. To be included in the present study, physical activity scores
in the Baecke et al. questionnaire [4] had to be below 6.0 for the YS and over 9.0 for YA. For OS and OA, scores in the
Voorrips et al. physical activity questionnaire [48] had to be below 9.0 and over 16.0, respectively.
YS and OS were recruited from social or cultural clubs in and around the city of Lille,
France. However, YA and OA were recruited from the French Federation of “Cyclotourisme.”
They must have had more than two consecutive years of cycling exercise for at least
10 months per year and no less than 10 h/week. They performed between 60 and 80 km
of cycling per session and three times per week.
Procedure
On arrival of each participant at the hospital (CHRU of Lille, France), a clinical
interview, a resting electrocardiogram (ECG), and a record of blood pressure were
carried out to verify the exclusion criteria of the protocol. Subsequently, all participants
filled out a questionnaire about their physical activity practices and their daily
food intake. Then, body weight and height were measured. Body mass was recorded to
the nearest 0.1 kg using a portable digital scale (PreciaMolen, I 200B, Precia SA,
Privas, France). Standing height was measured to the nearest 0.1 cm with an anthropometric
plane. After anthropometric measurements, a nurse inserted a venous catheter in the
forearm of the participant to take a resting blood sample. Then, each participant
performed an incremental exercise test until exhaustion, followed by a period of recovery
for 10 min, when post-exercise blood samples were collected again.
Exercise protocol
Participants were asked to avoid strenuous physical activity during 48 h before the
exercise testing session. Each subject performed an incremental exercise test until
exhaustion on an electrically-braked cycle ergometer (Excalibur Sport, Lode B.V, Medical
Technology, Groningen, Netherlands) connected to a computer with diagnostic software
(Ergocard®, Medisoft, Dinant, Belgium). After resting for 3 min on the cycle ergometer,
the participant started exercise at 30 watts (W) and 60–70 revolutions per minute
of pedaling for 3 min as a warm-up period. Then, the exercise was performed with an
increased workload of 20 W for men and 10 W for women every 3 min for the OS group.
For YS and OA subjects, the workload increased by 30 W every 3 min until the end of
the exercise. However, for the YA group, the workload increased by 30 W every 2 min.
For all subjects, the last completed stage was followed by 2 min of active recovery
at 25 W and 3 min of passive recovery. The workload increases were chosen in order
to ensure equality in exercise testing duration between the groups. Gas exchanges
(oxygen consumption: VO2, carbon dioxide production: VCO2, and ventilation: VE) were measured continuously throughout the test and for 5 min
during the post-exercise period using a gas-exchange system analyzer (Medisoft, Belgium).
Blood pressure was measured at rest and every 3 min during and after the exercise
period.
The exercise testing was finished when: (i) exhaustion of the participant or inability
to maintain the required pedaling speed was observed, (ii) the VO2 plateau was reached, and (iii) predicted maximum heart rate (HR max) was reached
(208−0.7×age±10%) [44].
Dietary record
All participants received a detailed verbal explanation and written instructions.
Food intake was recorded one week before the beginning of the study and over 4 days
including one weekend day to account for variations that might occur between weekdays
and weekends [22]. Participants were asked to maintain their usual dietary habits during the recording
period and to be as accurate as possible in registering the amount and type of food
and fluid consumed. They were asked to record brand names of all commercial and ready-to-eat
foods and the methods of preparation. A list of common household measures, such as
cups and tablespoons, and specific information on the quantity in each measurement
(grams, etc.) was given to each participant. Any questions, ambiguities, or omissions
regarding the type and amount of food and beverages consumed were resolved during
individual interviews. Each individual’s diet was assessed using the Nutrilog software
package (2.31), a computerized database (Proform) that calculates food composition
from the French standard reference in relation to age [11].
Blood sampling
A blood sample was drawn at rest and 5 min following the exercise to measure MDA level
and 20 min after the exercise to measure SOD, GPX, GR, ascorbic acid, and α-Tocopherol
levels. We chose to take blood samples at different time points because it has been
reported that post-exercise lipid peroxidation peak is generally obtained before higher
antioxidant enzyme values [29].
In our study, blood was drawn from the antecubital vein into a dry tube for the measurement
of α-Tocopherol, an EDTA tube for the measurement of ascorbic acid and MDA, and a
heparinized tube for the measurement of SOD, GPX, and GR. Whole blood was centrifuged
at 3000 rpm for 10 min at 4°C and plasma was removed. Erythrocytes were washed three
times with 0.9% NaCl solution (normal saline) at 4°C. Thereafter, 2 ml of cold distilled
water was added to the erythrocytes. Then, to achieve complete lysis of erythrocytes,
samples were stored at room temperature for 5–10 min. Finally, the mixture was centrifuged
for 10 min at 4°C. The clear supernatant solution was then divided into equal volumes
of 0.5 ml. Aliquots of the resulting plasma and blood erythrocytes were stored at
−80°C until analyzed. α-Tocopherol, ascorbic acid, and MDA levels were evaluated in
plasma and SOD, GPX, and GR activities were evaluated in blood erythrocytes.
Antioxidant enzyme activity assay
SOD activity was analyzed using a clinical chemical analyzer (Konelab 60, Thermo Fisher
Scientific Society). This method uses xanthine and xanthine oxidase to generate superoxide
radicals that react with 2-(4-iodophenyl-)-3-(4-nitrophenyl)-5-phenyltetrazoluim chloride
to form a red formazan dye. The SOD activity is then quantified by measuring the degree
of inhibition of this reaction.
GPX activity was measured using a reagent set (Ransel, Randox Laboratories) and indirectly
by a coupled reaction with GR. Oxidized glutathione (GSSG), produced upon reduction
of an organic hydroperoxide by GPX, is recycled to its reduced state by GR and nicotinamide
adenine dinucleotide phosphate (NADPH). The oxidation of NADPH to NADP+ is accompanied by a decrease in absorbance at 340 nm. The rate of decrease is directly
proportional to the GPX activity in the sample.
GR activity was measured using a clinical chemical analyzer (Konelab 60). GR is a
flavoprotein that catalyses the reaction, whereby reduced NADPH converts GSSG to reduced
glutathione (GSH). We evaluated this enzymatic activity with a GR, determining the
rate of NADPH oxidation. The oxidation of NADPH to NADP+ results in a decreased absorbance at 340 nm that is directly proportional to the
GR activity.
α-Tocopherol
Plasma α-Tocopherol was measured using the high-performance liquid chromatography
technique with spectrophotometric detection. In this technique, α-Tocopherol is extracted
with heptanes after protein precipitation by ethanol and then injected into the HPLC
system. The selected wavelength was 292 nm.
Ascorbic acid
After deproteinization of plasma with metaphosphoric acid, ascorbic acid was oxidized
to dehydroascorbic acid by ascorbate oxidase (DHAA). The DHAA bound to the o-phenylenediamine
(OPDA), which produced a chromophore whose absorbance was read at 340 nm on a clinical
chemical analyzer (Konelab 60). Thus, the rate of ascorbic acid in plasma was deduced
from the amount of chromophore formed.
Lipid peroxidation
The MDA was measured in plasma by the HPLC technique with fluorimetric detection.
It was determined by modified thiobarbituric acid (TBARS). 100 µl of plasma was precipitated
with trichloroacetic acid (200 µl) and mixed with 450 µl of normal saline solution
(0.9%). The whole mixture was incubated in a 90°C water bath for 30 min then cooled
in water. After centrifugation at 3000 rpm for 5 min at 4°C, the absorbance was read
at 532 nm.
For MDA, ascorbic acid and α-Tocopherol assays, plasma volume was corrected using
the guidelines provided by Dill et al. [10].
Statistical analyses
The statistical analysis was performed using Sigma STAT software. Normal Gaussian
distribution of the data was verified by the Shapiro-Wilk test. Results were expressed
as means±SD and p<0.05 was considered statistically significant. Experimental analysis
for oxidative stress markers was performed with three-way ANOVA (age×physical activity
status×time) to determine differences within and between groups over time. If a significant
interaction was found, a Bonferroni post hoc test was used to determine if and where
there was a difference between groups. To compare cardiorespiratory adaptations to
the exercise, anthropometric values, and dietary intake data between groups, a one-way
ANOVA test was performed.
Results
Physiological exercise data and dietary intake
The physical activity score showed a significant difference between active and sedentary
subjects (p<0.01) ([Table 1]). The assessment of VO2max and maximal aerobic power (MAP) values showed that regular physical activity increased
VO2max and MAP in both groups (young and older) (p<0.01). It should be noted that no difference
in aerobic fitness capacity (VO2max and MAP) were noted between YS and OA groups ([Table 1]).
Concerning the dietary analysis, and in comparison with sedentary subjects, whatever
their age, exercising participants had higher daily total energy and copper intake
(p<0.05). YA subjects had significantly higher protein and vitamin E intake in comparison
with the other groups (p<0.05). The daily energy intake derived from carbohydrates
was higher in OA compared to the other groups (p<0.05). No significant difference
in vitamin C, zinc (Zn), selenium (Se) and lipid intake was shown between the studied
groups ([Table 2]).
Table 2 Total daily energy intakes, macronutrient, and antioxidant micronutrient consumption
in all groups (mean±SD).
|
Young sedentary group
|
Young active group
|
Old sedentary group
|
Old active group
|
|
N=15
|
N=16
|
N=15
|
N=17
|
|
Energy intake (Mj/day)
|
9.7±2.3*†
|
13.2±2.1
|
8.9±2.3*†
|
12.4±1.7
|
|
Carbohydrates (g/day)
|
253.2±66†
|
280±32.1†
|
264.7±49.3†
|
348.4±77
|
|
Proteins (g/kg(BW)/j)
|
1.4±0.4*
|
2.7±0.3
|
1.6±0.9*
|
1.46±0.3*
|
|
Lipids (g/day)
|
96.1±33.1
|
109±33.1
|
111.2±24.3
|
108.5±37.5
|
|
Vitamin C (mg/day)
|
90.1±34.7
|
109±20.1
|
101.4±27.1
|
103.2±17.8
|
|
Vitamin E (mg/day)
|
7.5±2.2*
|
12.9±2.1
|
8.5±3.6*
|
9.8±2.1*
|
|
Selenium (µg/day)
|
65.3±12.1
|
75.1±6.6
|
74.1±19.2
|
69.1±19.5
|
|
Zinc (mg/day)
|
8.9±1.8
|
13.4±3.8
|
11.2±4.3
|
13.5±4.7
|
|
Copper (mg/day)
|
1.1±0.3*†
|
1.8±0.7
|
1.2±0.5*†
|
1.7±0.5
|
*: Significantly different from YA (p<0.05), **: Significantly different from YA (p<0.01)
# : Significantly different from YS (p<0.05),
## : Significantly different from YS (p<0.01)
†: Significantly different from OA (p<0.05), ††: Significantly different from OA (p<0.01)
Mj/day: megajoule/day
BW: body weight
Oxidative stress markers
Effects of the aging process
Resting SOD, GR, GPX, ascorbic acid, α-Tocopherol, and MDA levels were not different
between sedentary groups ([Table 3]). Regarding active groups, resting SOD and GR activities were higher in YA compared
to OA (p<0.01 and p<0.05, respectively). However, resting MDA level was higher in
OA compared to YA (p<0.01) ([Table 3]).
Table 3 Blood antioxidant status and malondialdehyde level at rest and during the post-exercise
period in the 4 groups.
|
|
Young sedentary group
|
Young active group
|
Old sedentary group
|
Old active group
|
|
N=15
|
N=16
|
N=15
|
N=17
|
|
Ascorbic acid (µmol/l)
|
Rest
|
50.7±19.1
|
47.2±12.3
|
43.3±20 .9
|
52.2±14.4
|
|
Post-exercise
|
53.7±18.7
|
52.9±8.5
|
48.6±24.2
|
54.7±16.0
|
|
α-Tocopherol (µmol/l)
|
Rest
|
38.7±6.1**
|
44.4±7.8
|
34.4±7.8††
|
43.2±6.6
|
|
Post-exercise
|
38.8±7.4
|
44.2±7.3
|
36.2±7.7
|
43±6.6
|
|
SOD (U/g Hb)
|
Rest
|
1099.1±84.7**
|
1398.8±122.6
|
1029.1±81.3††
|
1209.6±115.9**
|
|
Post-exercise
|
1243.7±84.4αα**
|
1547.4±112αα
|
1080.2±46††
|
1484.6±140.2αα
|
|
GPX (U/g Hb)
|
Rest
|
69.4±11.6**
|
78.6±8.6
|
63±17.2††
|
73.4±9.3
|
|
Post-exercise
|
79.2±15.1αα*
|
91.4±4.2αα
|
71.1±17.2††
|
82.9±12.6αα*
|
|
GR (U/g Hb)
|
Rest
|
6.5±1.3*
|
7.7±0.8
|
6.1±0.6
|
6.4±0.8*
|
|
Post-exercise
|
7.5±1.5*α
|
8.9±1.1αα
|
6.6±0.8
|
6.4±0.9*
|
|
MDA (µmol/l)
|
Rest
|
0.53±0.15*††
|
0.33±0.15
|
0.59±0.13††
|
0.75±0.26**
|
|
Post-exercise
|
0.62±0.19**†
|
1.05±0.18αα
|
0.79±0.25αα†
|
0.98±0.26αα
|
*: Significantly different from YA (p<0.05), **: Significantly different from YA (p<0.01)
#: Significantly different from YS (p<0.05), ##: Significantly different from YS (p<0.01)
†: Significantly different from OA (p<0.05), ††: Significantly different from OA (p<0.01)
α: Significantly different from resting condition (p<0.05), αα: Significantly different from resting condition (p<0.01)
Effects of regular physical activity
The comparisons of YS to YA and OS to OA revealed that active individuals in both
age groups have higher enzymatic and non-enzymatic antioxidant levels ([Table 3]). Thus, YA and OA have higher antioxidant activities (SOD and GPX) and α-Tocopherol
levels in comparison with YS and OS, respectively (p<0.01).
Regarding peroxidation level, our results showed a higher resting MDA level in OA
(p<0.01) and lower level in YA (p<0.05) as compared to the two sedentary groups.
Effects of acute exercise
Following the incremental exercise test, and for all participants, exercise has no
effect on non-enzymatic antioxidant levels (ascorbic acid and α-Tocopherol). For the
OS group, no significant changes in antioxidant enzyme activities were observed. A
significant increase in SOD and GPX activities was observed in YS, YA and OA during
the post-exercise period (p<0.01). However, GR activity increased only in YS and YA
(p<0.01 and p<0.05, respectively). In addition, GPX and GR activities were higher
in YA during the recovery period (p<0.05).
Following the incremental exercise test, and except for the YS group, an increase
in MDA level was observed in YA (+236%), OS (+33%) and OA (+30%) (p<0.01). Compared
to the two sedentary groups, YA and OA have a higher post-exercise MDA level (p<0.01
and p<0.05, respectively).
Discussion
To the best of the authors’ knowledge, this is the first study to explore the influence
of aging and physical fitness levels on both antioxidants and lipid peroxidation level.
The present study demonstrates that among healthy older adults, increased physical
fitness could restore the aging-associated decrease in antioxidant defenses. Also,
although regular physical activity improves antioxidant levels in both age groups,
OA subjects have lower antioxidant defense levels than YA participants, which could
indicate that the beneficial effects of regular physical activity could be impaired
by the aging process.
Our study has demonstrated that the α-Tocopherol level at rest was higher in active
groups (YA and OA) as compared to sedentary groups. There are two possibilities to
explain this finding. Firstly, this higher level of α-Tocopherol observed in YA could
be related to their higher vitamin E intake as noted in [Table 2]. In fact, several studies have demonstrated a close connection between plasmatic
α-Tocopherol level and dietary vitamin E intake [15]
[23]. Secondly, regular physical activity may increase the α-Tocopherol level in YA and
OA. However, up to now, the mechanism explaining how physical activity regulates α-Tocopherol
expression is unknown. One possible explanation is that active subjects could maintain
a higher level of α-Tocopherol in order to counteract the lipid peroxidation induced
by the free radical increase during physical activity sessions.
The present study results also showed that aging could modulate antioxidant enzyme
activities according to the physical fitness level of the subjects. In fact, as reported
in [Table 3], aging does not affect resting antioxidant activities in sedentary groups (YS and
OS). However, in physically active groups, YA presented significant higher antioxidant
activities (SOD and GR). In addition, except in OS, we showed an increase in antioxidant
activity during the post-exercise period. However, lipid peroxidation levels increased
in all groups at post-exercise. These data report three major findings.
First, the lack of changes in enzymatic activities (SOD, GPX and GR) in OS during
the recovery period suggests that aging could impair antioxidant enzyme efficiency
to scavenge ROS produced during exercise. An alteration of antioxidant gene transcription
factors (NF-kB and AP-1) [27] and/or a decrease in antioxidant enzyme protein content with aging [33] could explain these results.
Second, similar levels of antioxidant enzymes between YS and OA may indicate that
regular physical activity could restore age-related impairment in antioxidant defenses.
Safdar et al. [40] investigated MnSOD activity and MnSOD protein content in young sedentary and older
active subjects. They did not report a difference in MnSOD activity between the two
groups, although the MnSOD protein content was lower in the older active group. These
data could indicate that regular physical activity may induce post-translational modification
of antioxidant proteins that could maintain better antioxidant enzyme activities in
older active subjects.
Third, the comparison of YA to OA revealed that young subjects have higher antioxidant
enzyme activities at rest and during the post-exercise period. These data may indicate
that regular physical activity effects on antioxidant enzymes could be impaired by
the aging process. Two possibilities have to be considered to explain these results:
First, aging could induce an alteration of the redox-sensitive transcription factors
[27]. In fact, transcription factors like NF-Kb and AP-1 are present in the promoter
of the human enzymatic antioxidant gene and therefore play an important role in antioxidant
enzyme activity. Likewise, many studies using animal models have reported an alteration
in antioxidant gene transcription factors (NF-Kb and AP-1) with aging [5]. Second, aging could induce post-transcriptional modifications that may impair antioxidant
enzyme adaptation to regular physical activity. In this context, Lambertucci et al.
[26] investigated the mRNA level and enzyme activity of GPX in young trained and old
trained rats. The authors reported higher GPX enzyme activity in young trained rats,
whereas the mRNA level was higher in the old trained rats. They concluded that the
response of antioxidant enzyme activities in older rats exposed to regular physical
activity is less pronounced than the increases in their mRNA levels. This process
may occur due to a decrease in translational efficiency with aging [19]. Therefore, post-transcriptional inhibition of antioxidant enzymes was possibly
induced by aging. According to these results, these modifications with aging could
impair antioxidant enzyme responses to regular physical activity.
On the other hand, our results showed that the resting MDA level was higher in OA
and lower in YA compared to the two sedentary groups. These results suggest that physical
activity effects on lipid peroxidation level are modulated by the aging process. Thus,
in young subjects, it seems that regular physical activity reduces ROS production
[42] and/or reinforces antioxidant defense [3], which could decrease lipid peroxidation damage [34]. In contrast, our results showed that regular physical activity promotes lipid peroxidation
in older adults. One possible explanation could be that ROS produced during physical
activity sessions in OA exceeds their antioxidant capacity. This hypothesis can be
supported by the fact that aging is associated with a failure of the mitochondrial
respiratory chain in older adults promoting a greater release of free radicals [28]. On the other hand, exercise-induced inflammation reactions were previously demonstrated
[25] and some reports showed that aged individuals presented a considerable inflammatory
status when compared to young adults [45]. Thus, post-exercise inflammatory reactions could also contribute to the elevation
of lipid peroxidation levels in older adults [35]. Lastly, aging is characterized by a decrease in repair/turnover of oxidative damaged
biomolecules [13]
[38], which could also enhance lipid peroxidation damage in active older adults.
Methodological limitations
To the best of the authors’ knowledge, this is the first study to explore the influence
of aging and physical fitness levels on both antioxidant and lipid peroxidation level.
However, some limitations inherent to the experimental protocol of this study warrant
mention. Firstly, we categorized our participants into two groups of physical fitness
based on data collected from the physical activity questionnaire. Although the physical
activity questionnaire method was used in several previous studies [6]
[46], the use of an objective measure of daily physical activity, like accelerometry,
would have allowed a better idea about the lifetime physical activity of our participants.
Secondly, we only measured selected biomarkers of oxidative stress and did not include
an exhaustive list of potential markers (F2-isoprostanes, 8-OHdG, etc.). Although the selection of biomarkers recorded in the
present study is well able to characterize oxidative stress status, the inclusion
of additional biomarkers may have strengthened the conclusions. Thirdly, according
to age and the physical fitness level of each group, the MAP measured during the exhaustive
exercise was different between groups, which can induce a methodological bias. However,
the choice of this model of exercise stems from the fact that all participants could
attain their VO2max, that is to say, their maximal physical capacity. So if the absolute MAP was different,
the relative intensity of exercise of each participant was equal considering that
each participant attained his or her maximum (VO2max). In addition, the standardized incremental levels according to age and physical
fitness of each subject, as recommended by the literature [9], permitted attaining a similar exercise duration between groups. So exhaustive incremental
exercise permits (i) comparing groups of different ages and physical fitness levels
at a relatively similar intensity of exercise (VO2max), and (ii) standardizing exercise duration in spite of different ages and physical
fitness levels.
