Indian Journal of Biochemistry & Biophysics
Vol. 51, October 2014, pp. 365-371
Energy restriction and impact on indirect calorimetry and oxidative stress in
cardiac tissue in rat
Elisa Ito Kawahara, Nadine Helena Pelegrino Bastos Maués, Klinsmann Carolo dos Santos, Pedro Octávio Barbanera,
Camila Pereira Braga and Ana Angélica Henrique Fernandes1,*
Department of Chemistry and Biochemistry, Institute of Bioscience, São Paulo State University,
UNESP, Botucatu, CEP 18618-970, São Paulo, Brazil
Received 11 October 2013; revised 19 August 2014
Caloric restriction, defined as a reduction in calorie intake below ad libitum, without malnutrition can have beneficial
effects. In this study, we evaluated the impact of caloric restriction of 30 and 60% on calorimetric parameters and oxidative
stress in cardiac tissue in rats. Rats were randomly divided into 3 groups (n = 8): G1 = control; G2 = rats exposed to dietary
restriction of 30%; and G3 = rats exposed to dietary restriction of 60%. Energy restriction decreased final body weight,
oxidation of carbohydrates and lipid, oxygen consumption (VO2), carbon dioxide production (VCO2), resting metabolic rate
(RMR), but elevated respiratory quotient (RQ). G3 animals also displayed an imbalance in the oxidant/antioxidant system,
as revealed by the decrease in the lipid hydroperoxide (LH) level and GSH-Px activity in heart tissue. In conclusion, dietary
restriction decreased oxidative metabolism, as seen by the colorimetric profiles and controlled oxidative stress in cardiac
tissue.
Keywords: Calorimetry, Nutritional parameters, Oxidative stress, Energy restriction, Myocardium.
Dietary restriction can positively influence the
longevity of animals and also decrease the
progression and impact of degenerative chronic
diseases1,2. More specifically, caloric restriction,
defined as a reduction in calorie intake below
ad libitum, without malnutrition and altered normal
levels of macronutrients can provide a nutritional
intervention that extends the life span of a variety of
species, including mammals3.
McCay et al4 first published the effects of caloric
restriction in mice. They noted that caloric restriction
after puberty in the mice led to prolonged life and
mitigation of age-related diseases. In rodents, caloric
reduction of 60% immediately after puberty
(six months) increases longevity by 30 to 60%, while
a reduction of 44% of caloric intake in adulthood
(12 months) extends the maximum life expectancy by
only 10 to 20%5.
——————
*Corresponding author
E-mail: [email protected] or [email protected]
Phone: + 55 (14) 3880-0644
Abbreviations: BW, body weight; CI, carbohydrate intake; VCO2,
carbon dioxide production; EI, energy intake; FE, feed efficiency;
GSH-Px, glutatione peroxidase; LH, lipid hydroperoxide; LI, lipid
intake; VO2, oxygen consumption; PI, protein intake; ROS,
reactive oxygen species, RQ, respiratory quotient; RMR, resting
metabolic rate; SOD, superoxide dismutase.
It has been proposed that food restriction attenuates
the generation of reactive oxygen species (ROS),
consequently decreasing lipoperoxidation, avoiding
structural changes of the cellular membrane and
preventing
the
accumulation
of
oxidized
macromolecules, especially proteins and DNA; these
events prevent cell death and lead to an increase in the
life span6.
Caloric restriction is also reported to elicit an
adaptive reduction in energy expenditure through
mechanisms, such as reduced motor activity, body
weight, basal metabolism, thermogenesis and
fat-increased energy efficiency7,8. Carbohydrate
restriction also results in metabolic adaptations, which
subsequently lead to lipid metabolism. This is caused
by increased secretion of lipolytic hormones
(epinephrine, cortisol and growth hormone) in
response to decreased glucose and insulin levels9.
Lipolysis is stimulated in adipose tissue and,
therefore, increases the availability of circulating free
fatty acids for tissues. In addition, substrates are
available for gluconeogenesis, such as glycerol, which
is derived from tissue adipose, lactate and alanine
formed in the muscle10.
The heart has an essentially aerobic metabolism
with elevated oxidation of carbohydrate and fatty acid
366
INDIAN J. BIOCHEM. BIOPHYS., VOL. 51, OCTOBER 2014
β-oxidation, resulting in reducing equivalents (NADH
and FADH2), which reoxide in the electron transport
chain (ETC) through oxidative phosphorylation11,12.
Evidence shows that during excessive electron
transport the formation of ROS, such as superoxide
anion occurs11,12. There is association between
increased mitochondrial b-oxidation and ROS
production13,14. It provokes mitochondrial uncoupling,
which is implicated with decrease in the production of
ATP and consequent cellular injury, leading to
cardiac dysfunction15,16.
Thus, restricting the oxidizable substrate uptake could
prevent excessive oxidation of lipid and glucose and
control the amount of electrons from reducing
equivalents NADH and FADH in the ETC and
consequently decrease the ROS generation. This strategy
would avoid cardiac mitochondrial dysfunction,
ensuring adequate supply of ATP to the heart.
Although there are several studies available on
caloric restriction and the aging process, but reports
on the impact of caloric restriction on oxidative stress
and calorimetric parameters in cardiac tissue are
lacking. Therefore, in this study, we have evaluated
the effect of caloric restriction (30 and 60%) on
calorimetric parameters and oxidative stress in the
cardiac tissue in rats.
Materials and Methods
Experimental design
The experimental protocol (No. 479/2013) was
approved by the Ethics Committee on use of animal in
the experimentation of the Bioscience Institute
(UNESP/Botucatu, São Paulo) and all animals were
cared for in accordance with the principles and
guidelines of the Canadian Council on Animal Care.
Male Wistar rats (30-day old) weighing ± 250 g
were maintained under controlled environmental
conditions (22 ± 2°C, 40 to 50% humidity and 12 h
light/dark cycle). Animals were randomly divided into
three groups (n = 8). The control group (G1) received
a standard diet (38.0% fat, 44.5% carbohydrate,
20.0% protein and 3.0 kcal/g of metabolisable energy;
Purina, Campinas, São Paulo, Brazil) ad libitum.
The experimental groups were exposed to dietary
restriction, which was 30% (Group 2 or G2) and 60%
(Group 3 or G3) of the amount of food consumed by
the rats in the control group.
Food consumption was determined daily at the
same time (9:00-10:00 am) and calculated by
subtracting the food offered and that remaining after
consumption in 24 h. At the end of experimental
period (30 days), the animals were fasted overnight
(14), anaesthetised with a mixture (v/v) of xylazine
and ketamine and sacrificed by decapitation. Total
blood was collected and serum was separated by
centrifugation at 6,000 rpm for 15 min. The heart was
retrieved, weighed and stored at -80°C.
Determination of total protein
The protein content was determined with release of
the end product whose intensity of color was
proportional to concentration of the total protein
present in the sample and measured at 540 nm17.
Measurement of oxidative stress
Cardiac tissue (200 mg of left ventricle) was
homogenised (0.1 M phosphate buffer; pH 7.4) and
centrifuged at 10.000 rpm for 15 min. The supernatant
was used to analyze total protein levels, as well as the
activities of lipid hydroperoxide (LH), glutathione
peroxidase (GSH-Px), superoxide dismutase (SOD)
and catalase. The determination of LH was based on
the principle of hydroperoxide-mediated oxidation of
Fe2+ in the presence of xylenol orange, FeSO4, H2SO4
and butylated hydroxytoluene in 90% (v/v) methanol.
The end product was read at 560 nm18.
The activity of GSH-Px was assayed at pH 7.0
(phosphate buffer) in medium containing EDTA,
NADPH, gluthathione reductase, sodium azide and
the reduced form of glutathione. The absorbance of
the reaction was measured at 340 nm19. The sample
containing SOD was mixed with phosphate buffer
(pH 7.4), EDTA, nitroblue tetrazolium (NBT), NADH
and phenazine methosulphate. SOD activity was
proportional to the amount of the reduced form of
NBT. The absorbance was measured at 560 nm20.
Catalase activity was determined with phosphate
buffer (pH 7.0) and hydrogen peroxide. Absorbance
was recorded at 340 nm21.
The values for enzyme activities were obtained
using a microplate reader (µQuant-MQX 200 with
Kcjunior software, Bio-Tec Instruments, Winooski,
VT, USA). All reagents were purchased from Sigma,
St. Louis, MO, USA.
Nutritional parameters
Based on food intake and the amount of calories
(Table 1), the following parameters were calculated:
energy intake (EI; kcal/day) = average daily
consumption of feed ration × metabolisable energy of
the ration in kcal/g; feed efficiency (FE;%) = weight
gain (g)/energy intake (kcal) × 100; protein intake
(PI; g/day) = average daily consumption of feed ration
KAWAHARA et al.: ENERGY RESTRICTION IMPACT IN CARDIAC TISSUE
× percentage of feed protein; lipid intake (LI; g/day) =
average daily consumption of feed ration × percentage
of feed lipids; and carbohydrate intake (CI; g/day) =
average daily consumption of feed ration × percentage
of carbohydrates in the diet22,23. Body weight was
measured once weekly.
Indirect calorimetry
At the end of experimental period, respiratory
quotient (RQ) and energy expenditure, i.e., resting
metabolic rate (RMR), average oxygen consumption
(V02) and carbon dioxide production (VC02) within a
40 min period were evaluated in rats fasted overnight
(12 to 14 hr). The measurements were taken by a
computer-monitored indirect calorimeter (CWE, Inc,
St. Paul, USA) coupled to metabolic chambers (air
flow = 1.01/min), which accommodated the rats
fasting overnight (12 to 14 h). The calorimetric
parameters were measured using a respiratory-based
software program (software MMX, CWE, Inc., USA).
The calorimetric parameters were calculated
through the relative oxidative proportions of the
oxidation and the amount of oxygen consumed per g
of oxidised substrate, carbohydrate and fat oxidation
using the equations: VO2 × (RQ - 0.707)/0.293 ×
0.746 (for carbohydrate oxidation) and VO2 ×
(1 - RQ)/0.293 × 0.746 (for fat oxidation), where VO2
is measured as l/min, 1.00 is the RQ for total
carbohydrate oxidation, 0.707 is the RQ for total fat
Table 1—Body weight final, food consumption, energy intake,
food efficiency, carbohydrate intake, protein and lipid intake in
control (G1), 30% (G2) and 60% (G3) energy restriction groups
[Values expressed as mean ± SD]
Parameters
G1
G2
G3
Body weight
421.68 ± 24.57c 336.36 ± 28.47b 246.69 ± 22.22a
(g)
Food
25.04 ± 1.19c 17.70 ± 0.58b 10.09 ± 0.34a
consumption
(g)
Energy intake
95.44 ± 4.54c 67.45 ± 2.22b 38.46 ± 1.32a
(kcal/day)
Food efficiency
0.97 ± 0.05c
0.88 ± 0.03b
0.57 ± 0.02a
(g/kcal)
Carbohydrate
0.29 ± 0.01c
0.20 ± 0.01b
0.12 ± 0.00a
intake
(g/day)
0.94 ± 0.04c
0.67 ± 0.02b
0.38 ± 0.01a
Protein intake
(g/day)
Lipid intake
21.50 ± 1.02c 15.19 ± 0.50b
8.66 ± 0.30a
(g/day)
a,b,c
Means followed by different letters indicate significant
differences between groups (p <0.05).
367
oxidation, 0.293 is the difference between 1.000 and
0.746 and is the number of litres of oxygen consumed
per g of oxidised glucose24.
Statistical analysis
We used a completely randomised design with
3 treatments and 8 replications of the ANOVA scheme.
The mean values of treatments were compared using
Tukey’s test at 5% probability, according to Zar25.
Results
Significant decrease in body weight and nutritional
parameters was observed in groups G2 and G3 rats,
compared to the control group (Table 1). Animals
undergoing energy restriction of 60% had the lowest
(p<0.05) body weight at the end of the experimental
period. Energy intake and food efficiency (p<0.05)
decreased in the energy-restricted groups (G2 = 30%
and G3 = 60%), compared to the control group (G1).
The animals subjected to energy restriction of 60%
(G3) showed lower values (p<0.05) for energy
consumption, as well as total levels of carbohydrates,
protein and lipids, when compared to the control.
Table 2 shows data on indirect calorimetry.
Animals subjected to energy restriction (G1 and G2)
Table 2—Calorimetric parameters in control (G1), 30% (G2) and
60% (G3) energy restriction groups
[Values expressed as mean ± SD]
Parameters
VO2/body surface
(mL/h.g0.7)
VO2
(mL/min)
VCO2
(mL/min)
RQ
Oxidation of
carbohydrate
(mg/kg min)
Oxidation of lipid
(mg/kg min)
RMR (kcal/h)
Cardiac protein
(mg/100 mg tissue)
Serum total protein
(g/dL)
Heart weight/Corporal
(g/kg)
a,b,c
G1
G2
6.85 ± 1.95b 4.51 ± 0.54a
G3
3.75 ± 0.9a
3.80 ± 1.08b 2.50 ± 0.30a 2.08 ± 0.52a
2.25 ± 0.26b 2.08 ± 0.26b 1.51 ± 0.41a
0.62 ± 0.13a 0.83 ± 0.07c 0.72 ± 0.06b
1.10 ± 1.60c 0.79 ± 0.43b 0.09 ± 0.35a
3.95 ± 2.38b 1.08 ± 0.50a 1.46 ± 0.48a
1.04 ± 0.26b 0.72 ± 0.08a 0.58 ± 0.14a
23.17 ± 0.8c 17.07 ± 0.5b 14.18 ± 0.6a
9.38 ± 1.23a 9.12 ± 0.50a 9.11 ± 1.09a
2.61 ± 0.18a
2.59 ± 0.2a 2.18 ± 0.16a
Means followed by different letters indicate significant
differences between groups (p <0.05). VO2, oxygen consumption;
VCO2, carbon dioxide production; RQ, respiratory quotient;
RMR, resting metabolic rate.
INDIAN J. BIOCHEM. BIOPHYS., VOL. 51, OCTOBER 2014
368
Table 3—Protein and oxidative stress markers in control (G1),
30% (G2) and 60% (G3) energy restriction groups
[Values expressed as mean ± SD]
Parameters
G1
G2
G3
LH
(nmol/g tissue)
145.97 ± 3.5c
93.41 ± 2.0b
70.18 ± 2.7a
Catalase (µmol/g
tissue)
120.09 ± 4.7b
84.27 ± 2.4a
79.95 ± 2.6a
SOD
(nmol/mg pt)
28.53 ± 1.07c
15.03 ± 1.8a
10.34 ± 1.0a
GSH-Px
(nmol/mg tissue)
59.03 ± 3.17b
57.48 ± 2.9b
21.61 ± 1.08a
a,b,c: Means followed by different letters indicate significant
differences between groups (p <0.05). LH, lipid hydroperoxide;
SOD, superoxide dismutase; GSH-Px, glutathione peroxidase.
showed decreased (p<0.05) VO2/surface body,
oxygen consumption (VO2), CO2 production (VCO2),
resting metabolic rate (RMR) and carbohydrate and
lipid oxidation, compared to those who had free
access to food. Respiratory quotient (RQ) increased in
rats subjected to energy restriction, indicating fat
oxidation.
Data related to oxidative stress markers in cardiac
tissue in control and energy restrictive groups are
shown in Table 3. Animals of the groups G2 and G3
rats showed a decrease (p <0.05) in the activities of
catalase and SOD, as well as a reduction of the total
protein level in heart tissue, when compared to G1
animals. GSH-Px activity decreased only in animals
undergoing 60% energy restriction. No differences
(p > 0.05) were observed in the heart-to-body weight
ratio among the groups.
Discussion
The changes in eating habits are an important
factor in altering the oxidant/antioxidant balance in
the body22,26. In this study, we evaluated the effect of
energy restriction of 30 and 60% on indirect
calorimetry and oxidative stress in cardiac tissue in
rats. Caloric restriction in G2 and G3 rats caused the
lowest weight at the end of the experimental period
and lower values of calorimetric parameters,
compared to control (G1) animals.
The VO2 is the amount of oxygen consumed and
VCO2 the amount of CO2 produced per g of metabolic
substrate oxidised in the body. Using these
parameters, it is possible to compare specific oxygen
consumption and CO2 production in different species
and animal tissues, since they reflect the gas exchange
associated with the oxidation of nutrients in relation
to body weight27. As lipid oxidation requires greater
oxygen consumption, there was an increase in VO2
adjusted for body surface area in the energy restricted
animals.
As the chemical composition of carbohydrates
(C6H12O6) differs from that of lipids [CH3-(CH2)
n-COOH]), which contain more hydrogen and carbon
atoms than oxygen ones per molecule, the use of
oxygen in the oxidation of lipids is higher.
Consequently, lipid oxidation yields more ATP
molecules than carbohydrate oxidation28. Thus, lipid
oxidation requires proportionally higher oxygen
consumption and releases less CO2.
The animals subjected to energy restriction had low
oxygen uptake (VO2), indicating low lipid oxidation.
Moreover, lower CO2 production (VCO2) suggested
lower oxidation of carbohydrates in rats exposed to
energy restriction of 60%, probably due to lower lipid
and carbohydrate uptake. Since carbohydrates are
polyhydroxyl aldehydes or ketones, structurally there
is an oxygen atom for carbon for every three-carbon
atom. Therefore, consumption of just one external
oxygen atom is necessary to form a CO2 molecule
during carbohydrate oxidation.
Blood glucose level correlates positively with
carbohydrate oxidation and negatively with fatty acid
oxidation. In the present study, carbohydrate
oxidation decreased with decreasing carbohydrate
uptake. This was consistent with the results
obtained in as earlier study29, since selection of
metabolic fuel by the cell is controlled by
carbohydrate uptake.
Although fatty acids become the main metabolic
fuel during energy deprivation due to increased
lipolysis, in the present study, neither 30 nor 60%
restriction was sufficient in enhancing lipid oxidation.
As the cardiac and skeletal muscle tissues use a large
part of the lipids consumed from a diet, low lipid
oxidation may be a consequence of reduced lipid
uptake. The amount of oxygen required during
complete oxidation of macronutrients, especially fatty
acids and carbohydrates is compatible with the
produced quantity of CO2. Thus, RQ establishes a
relationship between the CO2 produced and O2
consumed, thereby quantifying the mix of catabolized
substrate to obtain energy. Hence, RQ was employed
to determine the type of substrate being oxidized by
the organism. A reduction in RQ indicates increased
use of lipids as the energy substrate30,31.
KAWAHARA et al.: ENERGY RESTRICTION IMPACT IN CARDIAC TISSUE
The elevated RQ in animals subjected to energy
restriction was due to a higher carbohydrate than lipid
oxidation. This increase was higher in rats subjected
to a 30% energy restriction due to the lower drop in
carbohydrate oxidation, compared to those with 60%
energy restriction, whose lipid oxidation remained
unaltered. Animals that underwent energy restriction
of 60% (G3) showed significantly lower RQ values
than those exposed to a restriction of 30% (G2).
However, there were no differences in oxygen
consumption adjusted for body surface area, resting
metabolic rate and lipid oxidation between these two
groups. The significant reduction of the RQ in G3 rats
compared to G2 animals indicated an increase in lipid
oxidation at the expense of carbohydrate oxidation.
Thus, the RQ was the lowest in G1 animals, while
the values of VO2, VO2/surface body and VCO2 were
the highest in this group, compared to G2 and G3
animals. This indicated that G1 animals used the most
carbohydrates as the energy substrate, correlating with
their final body weight, which was the highest among
the three groups32. Comparing G2 and G3 rats, the
latter group displayed the lowest final body weight,
which also correlated with their lowest utilization of
carbohydrate.
Since the execution of vital functions in the waking
period depends on a certain energy demand, the basal
metabolic rate (RMR) accounts for the sum of cellular
metabolic processes needed to preserve physiological
functions. Thus, knowledge of the RMR allows the
establishment of the energy level needed to develop
body mass control strategies by means of energy
restriction33. A reduced RMR may indicate a higher
energy balance, i.e., low use of the ingested energy
for basal metabolism and consequently higher
availability for storage in adipose tissues, leading to
body weight gain34. However, in our study, a
decreased RMR in animals subjected to energy
restriction did not increase body weight. This might
be due to oxygen uptake allowing an indirect
determination of the RMR. Although there was a
reduction in the RMR in animals subjected to energy
restriction, there was no increase in body weight,
indicating that low quantity of ingested energy also
reflected in low quantity of ingested energy to ensure
that the basal activities and low energy were made
available to be stored in the adipose tissue.
Earlier, a reduced basal metabolic rate has been
observed to be associated with caloric restriction;
however, it is emphasized that the effect being
369
controversial since it could be related to weight loss
and metabolic adaptation, especially of muscle and
adipose tissues35. The weight loss is a major symptom
of caloric restriction that can result from either
excessive oxidative degradation of proteins or high
lipolysis. These are related to the metabolic
conditions in energy restricted animals, which
demonstrate
increased
mobilisation
of
the
triacylglycerols stored in adipose tissue (lipolysis).
Moreover, structural proteins can be degraded,
especially muscle. Thus, the carbon skeleton of amino
acids can either be used to generate power or directed
toward gluconeogenesis36, which maintains metabolic
homeostasis during starvation and is associated with a
broad spectrum of metabolic changes in fasting state.
Thus, the reduction of cardiac proteins observed in G3
rats could be due to the degradation of these proteins,
which supply carbon to maintain gluconeogenesis37.
In addition, the lowest concentration of proteins in the
cardiac tissue may be related to low protein synthesis,
even though the level of serum protein did not change
in animals submitted to energy restriction (Table 2).
Energy restricted animals (30% and 60%) had the
same heart-to-body weight ratio as the control group,
indicating that cardiac mass decreased proportionally
with body weight. This suggested that the impact of
energy restriction on the heart did not involve
substantial anatomical remodeling.
Studies on the effect of caloric restriction on ROS
levels have shown controversial results38. The data
presented in this study showed that energy restriction
decreased oxidative stress in cardiac tissue, as
observed by decreased tissue level of HP, a product of
lipid peroxidation. Previous studies39,40 have
demonstrated low levels of ROS generation in rodents
with a hypoenergetic diet. This was consistent with
our observation of reduced myocardial HP level in
animals subjected to a restrictive diet, since HP acts
as a biomarker of oxidative stress. Furthermore, in
another study, in dietary restriction, anti-aging and
reduction in chronic disease with low formation of
free radicals have been observed41. Moreover, the diet
with caloric restriction is reported to increase the
expression of proteins with cytoprotective properties,
especially in cardiac tissue by increasing the cell
resistance due to oxidative stress caused by free
radicals42.
The antioxidant system comprises SOD, which
converts superoxide radicals into hydrogen peroxide
(H2O2) and is the first line of defence against the
370
INDIAN J. BIOCHEM. BIOPHYS., VOL. 51, OCTOBER 2014
action of ROS and two enzymes — catalase and
glutathione peroxidase (GSH-Px) that convert the
H2O2 formed by SOD into H2O21. Since these
enzymes remove H2O2, there is a compensatory
relationship between the two to prevent the toxic
effects of H2O243. In addition, GSH-Px protects
against oxidative damage more than SOD, whose
catalytic activity leads to an increase in H2O2. The
imbalance in the oxidant/antioxidant system was
clearly seen in the G3 group, since there was a
decrease in the activity of myocardial HP.
Although electron transport and oxidative
phosphorylation are coupled and highly efficient
biochemical processes in which O2 is reduced to H2O
after receiving four electrons and 4H+, there is a
potential that the mitochondrial generation of ROS
may increase44. Recently, it is reported that transport
of mitochondrial electrons acts as an important source
of O2- in cardiac tissue during failure due to
alterations in enzymatic complexes, leading to
obstructed normal electron flow12.
Glutathione (reduced-oxidized) system plays a key
role in maintaining the balance between physiological
pro-oxidants and antioxidants, which are essential for
cell survival and \death45. In the present study, there
was a decrease in myocardial GSH-Px activity in
animals subjected to energy restriction of 60%, while
catalase and SOD activities showed significant
reduction in cardiac tissue in rats with energy
restriction (30 and 60%).
Since the myocardium depends almost exclusively
on the energy released from the mitochondrial
oxidation of fatty acids, oxidative metabolism
contributes to increased mitochondrial ROS
production. Thus, the low activity of antioxidant
enzymes might be due to the lower ROS production,
since energy restricted animals showed decreased
oxidation of fatty acids. Our results agreed with the
earlier reports38,46,47, wherein it is reported that caloric
restriction reduces ROS production, thus maximizing
longevity. It is demonstrated that caloric restriction
with reduces energy metabolism and consequently a
lower flow of electrons in the electron transport
chain35.
The decreased catalase activity as observed in the
current study might be due to low consumption of
oxygen. Several observations suggest that changes in
the catalase activity depend on the consumption of
oxygen48. It is demonstrated that catalase and SOD
activities are linearly associated with VO2max in the
skeletal muscle of individuals with a high aerobic
capacity49. It is also observed that the rate of oxygen
consumption and SOD and catalase activities declines
with age in Musca domestica adults50.
The increase in oxygen consumption might
accelerate mitochondrial electron transport through
the respiratory chain, resulting in leakage, leading to
the formation of superoxide anions51. Since NADH
and FADH2 are sources of electrons for the
mitochondrial electron transport chain, decrease in
both the lipid oxidation and VO2 in our energy
restricted animals could have been due to the lower
formation of O2-, thus regulating oxidative stress.
In conclusion, the study demonstrated that energy
restriction decreased the oxidation of carbohydrate
and lipid and reduced energy expenditure, as revealed
by the changes in the calorimetric parameters. Caloric
restriction acted against oxidative stress in cardiac
tissue, since lipid hydroperoxide levels were
decreased in the tissue.
Acknowledgements
This research was supported by grants from
CAPES (“Coordenação de Aperfeiçoamento de
Pessoal de Nível Superior”). All authors of the
manuscript cooperated throughout the development of
the work (laboratory and experimental).
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