Effect of short-term fasting on urinary excretion of primary lipid peroxidation
products and on markers of oxidative DNA damage in healthy women
Kyoung-Ho Lee
1, Helmut Bartsch
2, Jagadeesan Nair
2,
Dong-Ho Yoo
1, Yun-Chul Hong
1, Soo-Hun Cho
1and
Daehee Kang
1,1Department of Preventive Medicine, Seoul National University College
of Medicine, Institute for Environmental Medicine, SNUMRC, Seoul 110-799, Korea and2German Cancer Research Center (DKFZ),
Division of Toxicology and Cancer Risk Factors, Im Neuenheimer Feld 280, 69120 Heidelberg, Germany
To whom correspondence should be addressed at: Department of
Preventive Medicine, Seoul National University College of Medicine, Institute of Environmental Medicine, SNUMRC, 28 Yongon-Dong Chongno-Gu, Seoul 110-799, Korea. Tel:+82 2 740 8326; Fax:+82 2 747 4830;
E-mail: dhkang@snu.ac.kr
The goal of this study was to determine whether
short-term fasting changes in urinary biomarkers
related to oxidative stress: malondialdehyde (MDA),
8-isoprostaglandin
F
2a(8-isoPGF),
8-hydroxydeoxy-guanosine (8-OHdG) and 1,N
6-ethenodeoxyadenosine
(edA) among female volunteers participating in the
short-term fasting program in South Korea. The study
subjects were 52 healthy women (mean age 28, range
15–48 years old) who provided urine samples both
before and after the fasting program (average 7.2,
range: 3–11 days). Urinary MDA was measured by
HPLC-UV and
edA levels were measured by
immuno-affinity purification followed by HPLC-fluorescence
detection. Urinary 8-OHdG and 8-isoPGF concentrations
were determined by ELISA. Plasma leptin levels were
also measured by radioimmunoassay. Information on
demographic characteristics, personal habits (smoking
and alcohol consumption) and previous medical history
were collected by a self-administered questionnaire.
Percent loss of body weight (average 6.3%, 4.28 ± 0.25
kg) was significantly correlated with fasting duration (r
¼
0.70, n
¼ 52, P < 0.01). The plasma leptin levels after
fasting (5.89 ± 1.10 ng/ml) were significantly lower than
before fasting (6.91 ± 1.13 ng/ml) (n
¼ 27, P ¼ 0.05).
Urinary MDA levels after fasting (0.18 ± 1.10 mg/g
creatinine) were significantly lower than before fasting
(0.37 ± 1.11) (n
¼ 51, P < 0.01). Urinary 8-isoPGF also
were significantly reduced after fasting (n
¼ 47, P < 0.01).
However, there was no significant difference in 8-OHdG
or
edA. There was a statistically significant correlation
between % change of urinary MDA level with % change
of
8-isoPGF
level
(partial
correlation
coefficient
r
¼ 0.57, n ¼ 46, P ¼ 0.01). The correlations between
% change of 8-OHdG and plasma leptin was also
signi-ficant (partial correlation coefficient r
¼ 0.51, n ¼ 27, P ¼
0.02). Our results demonstrate that the short-term fasting
reduces lipid peroxidation products but does not affect
oxidative stress-induced DNA damage.
Introduction
Obesity is related to increased morbidity and mortality of
cancer and cardiovascular disease which are two major
causes of deaths in the USA (1,2). Dietary restriction has
been shown to have several health benefits including
increased insulin sensitivity, stress resistance, reduced
morbidity and increased life span (3,4).
Fasting has been suggested to have beneficial effects on
glucose regulation and neuronal resistance to injury (4).
Short-term fasting has been shown to prolong the life
span of autoimmune-prone mice (5) and to reduce plasma
leptin concentration in dairy cattle, non-obese healthy
humans and sympathectomized men (6–9). A moderate
degree of short-term weight reduction significantly decreases
leptin levels in otherwise healthy overweight adults (10).
Although the underlying mechanism involved in the
bene-ficial effects of dietary restriction are not known, oxidative
stress has been proposed as an important intermediate event.
Caloric restriction can decrease oxidative DNA damage (11).
Caloric restricted C57BL/6 mice show a lower concentration
of 8-oxo-7,8-dihydro-2
0-deoxyguanosine (8-OHdG), the
most widely studied markers of oxidative DNA damage
(12,13). Caloric restriction also reduces malondialdehyde
(MDA), a product of lipid peroxidation (LPO), in skeletal
muscles of Rhesus monkeys (14) but not in
streptozotocin-induced
diabetic
rats
(15,16).
8-Isoprostaglandin-F
2a(8-isoPGF) is the prostaglandin-like compound produced
by non-enzymatic mechanism of peroxidation of lipoproteins
(17). It is chemically stable and can be measured in human
urine (18–19). Diet and exercise intervention can reduce
8-isoPGF levels and short-term weight loss is also associated
with significant reduction of 8-isoPGF (17,20).
Abbreviations:8-isoPGF, 8-isoprostaglandin-F2a; 8-OHdG,
8-oxo-7,8-dihydro-20-deoxyguanosine; ELISA, enzyme-linked immunosorbent assay;
LPO, lipid peroxidation; MDA, malondialdehyde; TBA, 2-thiobarbituric acid;edA, 1,N6-ethenodeoxyadenosine.
Advance Access publication January 9, 2006
The Author 2006. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oxfordjournals.org The online version of this article has been published under an open access model. Users are entitled to use, reproduce, disseminate, or display the open access version of this article for non-commercial purposes provided that: the original authorship is properly and fully attributed; the Journal and Oxford University Press are attributed as the original place of publication with the correct citation details given; if an article is subsequently reproduced or disseminated not in its entirety but only in part or as a derivative work this must be clearly indicated. For commercial re-use, please contact journals.permissions@oxfordjournals.org
1,N
6-Ethenodeoxyadenosine (edA) is formed as stable DNA
base adducts from reactive aldehydes such as
trans-4-hydroxy-2-nonenal during oxidative stress or LPO (21). Urinary
edA as
a whole body marker for LPO has been reported to be
asso-ciated with salt-induced inflammation and
w-6 polyunsaturated
fatty acid intake in postmenopausal Japanese women (22).
The purpose of this study was to determine whether
short-term fasting changes urinary biomarkers related to
oxidative stress. The markers included in the study were
urinary MDA, 8-isoPGF, 8-OHdG and urinary
edA. The
sub-jects recruited for this study were healthy female volunteers
participating in a short-term fasting program.
Materials and methods
Materials
Methanol and acetonitrile were purchased from HAYMAN (Witham, Essex, UK) with a purity of 99.85%. 2-Thiobarbituric acid (TBA) and MDA standard were purchased from the Sigma–Aldrich Korea (Yongin, Kyunggi, Korea). The enzyme-linked immunosorbent assay (ELISA) kit for 8-isoPGF was obtained from OxisResearch (Portland, OR). The commercial ELISA kit for 8-OHdG was from the Japan Institute for the Control of Aging (Fukuroi, Shizuoka, Japan) designed for quantitative measurement of the oxidative DNA adduct 8-OHdG in urine. All other chemicals were obtained in the greatest purity available from commercial suppliers.
Study subjects
The study subjects consisted of 58 volunteers who participated in a fasting program (7.2 days, range: 3–11 days) and provided first morning void urine samples both before and after the fasting program in South Korea. Four males were excluded because of a small proportion (7%) and gender-specific differ-ences in the formation of certain biomarkers for oxidative stress (e.g. 8-isoPGF, edA) (23). Two females who did not complete the questionnaires were also excluded. Finally, 52 women remained in the study (mean age 28.3, range 15– 48 years old). Of these, only 30 people provided paired blood samples. All participants did not have food during the fasting program; however, water was permitted. Participants were allowed to do light exercise during the fasting program including jogging and yoga but strenuous physical activities (e.g. running, cycling, heavy weight lifting, tennis, soccer, etc.) were avoided. Every volunteer had a baseline physical examination. All participants were screened for diabetes, hypertension and other major systemic illnesses such as gastrointestinal disturbance, liver function and nephropathy. At the end of the fasting period, the volunteers started on liquids first and gradually changed to a regular diet. The study was approved by the institutional review board at the Seoul National University College of Medicine and each subject gave written informed consent. Information on demographic characteristics such as smoking, alcohol consumption, diet, medical history and medicine use was collected using a self-administered questionnaire.
Sample collection
Urine and blood samples were collected before and after the fasting. First morning urine samples were collected before the fasting program started and after the program ended. Urine samples were collected in 50 ml polypro-pylene tubes and stored at20C until analysis. Blood samples (5 ml) were
collected in EDTA vacutainer tubes and kept at80C until analysis.
Analysis of urinary MDA
MDA was measured using a method previously described (24) with minor modifications. The most common method of measuring MDA is based on the reaction with TBA. A 10 mmol/l stock standard of MDA was prepared by dissolving 123.5ml of 1,1,3,3-tetraethoxypropane in 50 ml of ethanol (40% ethanol by volume). TBA–MDA adducts were prepared in glass tubes with a polypropylene stopper. In each tube, 300ml of phosphoric acid (0.5 M) was mixed with 50ml of urine and 150 ml of TBA reagent. The mixtures were incubated at 95C for 1 h and methanol (500ml) was added in each tube.
Following a 5 min centrifugation (5000 g), the samples were analyzed using HPLC on a 4· 150 mm Xtera C18 column with UV (wavelengths, 532 nm). The mobile phase was potassium phosphate (0.05 mol/l; pH 6.8) and methanol (58:42, v/v). The flow rate was 0.8 ml/min.
Analysis of urinary 8-isoPGF
The urine samples were analyzed for 8-isoPGF levels by a competitive enzyme-linked immunoassay (ELISA) (25). This ELISA kit can be used for the quantitation of free 8-isoPGF in urine samples without the need for prior
purification or extraction. In brief, the samples were mixed with an enhancing reagent that essentially eliminates interference due to non-specific binding. Following substrate addition, the intensity of the color was noted to be inversely proportional to the amount of unconjugated 8-isoPGF in the sample or standard.
Analysis of urinary 8-OHdG
The level of urinary 8-OHdG was determined by a competitive enzyme-linked immunosorbent assay (ELISA) kit (JAICA, Fukuroi, Japan). In brief, 50ml of primary monoclonal antibody and a 50ml of sample or standard were added to microtiter plates, which were pre-coated with 8-OHdG, incubated at 37C
for 1 h and washed with 250ml of phosphate-buffered saline (PBS). One hundred microliters of HRP-conjugated secondary antibody was then added to each well, incubated at 37C for 1 h and washed with 250ml of PBS. One
hundred microliters of enzyme substrate was then added to each well, incub-ated at 37C for 1 h and the reaction was terminated with 100ml of 1 N
phosphoric acid. Absorbance of each well was read at 450 nm by a microplate reader (ELx808, Bio-Tek, Winooski, VT).
Analysis of urinaryedA
Urinary edA was analyzed according to a method published earlier (22). Two milliliters urine samples were spiked with an internal standard (1,N6
-ethenoadenosine-[2,8-3H]) and purified on preparative HPLC. Two fractions (internal standard andedA) were collected; the earlier eluted I.S. fraction was counted for recovery by liquid scintillation counter and theedA fraction was concentrated (overnight) in a speed-vac and then used for immuno-precipita-tion.
The immunoprecipitation of edA was performed in Tris–HCl buffer (10 mM Tris, pH 7.5, 140 mM NaCl, 3 mM NaN3) containing 1% BSA
and 0.1% rabbit IgG (Sigma–Aldrich, Schnelldorf, Germany) and a mono-clonal antibody EM-A-1 provided by Dr P. Lorenz and M. Rajewky (Institute for Cell Biology, University of Essen, Germany). The antigen–antibody com-plex was precipitated with saturated ammonium sulfate. The precipitate was washed andedA eluted using 50% methanol/water and later concentrated in a speed-vac. The pellets were analyzed by an HPLC-fluorescence detector (Hewlett Packard, Waldbronn, Germany). Using a linear gradient (NH4)3PO4, 17 mM, pH 5, buffer/methanol 9:1 to 8:2 in 30 min at a flow
rate of 1 ml/min. TheedA peak was detected at l excitation 230/l emission 410 nm and quantified by a standard curve using edA standard (Sigma– Aldrich). The detection limit of edA in this HPLC system was 5 fmol per injection.
Plasma leptin assay
Plasma leptin levels were measured by a radioimmunoassay using a commer-cially available kit for human leptin (catalogue no. HL-81K; Linco Research, St Louis, MO), as described previously (26).
Statistical methods
The paired t-test was used to compare group means (before and after fasting) of biomarkers. Pearson’s correlation coefficient was used to evaluate correla-tions among biomarkers. All statistical analyses were performed with the SPSS statistical package version 10.0 (SPSS, Chicago, IL). Statistical significance was defined as P< 0.05.
Results
Average body weight loss was 4.28 ± 0.25 kg of their initial
body weight (62.18 ± 1.51 kg) (Table I). The percent loss
of body weight (mean 6.3%) was significantly correlated
with fasting duration (days) (Pearson’s correlation r
¼ 0.70,
n
¼ 52, P < 0.01) (Figure 1).
The plasma leptin levels after fasting (5.89 ± 1.10 ng/ml)
were significantly lower than before fasting (6.91 ± 1.13 ng/ml)
(n
¼ 27, P ¼ 0.05 by paired t-test) (Table I and Figure 2).
Urinary MDA levels after fasting (0.18 ± 1.10 mg/g
creat-inine) were significantly lower than before fasting (0.37 ± 1.11)
(n
¼ 51, P < 0.01 by paired t-test) (Table I). Urinary 8-isoPGF
also was significantly reduced after fasting (n
¼ 47, P < 0.01).
However, there was no significant difference in 8-OHdG
or
edA (Table I). Although creatinine levels increased
(16%) after fasting, the results of biomarker levels before
and after creatinine adjustment remained unchanged (Table II).
There was a statistically significant correlation between
percent change of urinary MDA levels and percent change
of 8-isoPGF levels (partial correlation coefficient r
¼ 0.57,
n
¼ 46, P ¼ 0.01) after adjusting for BMI and smoking. There
was also a statistically significant correlation between percent
change of urinary 8-OHdG with percent change of plasma
leptin level (partial correlation coefficient r
¼ 0.51, n ¼ 27,
P
¼ 0.02) (Table III).
Discussion
There was a significant reduction of urinary biomarkers of
oxidative stress related to LPO (e.g. MDA, 8-isoPGF) after
short-term fasting (average 7 days). A plasma leptin level was
also significantly reduced after fasting. Short-term fasting
reduced both non-specific biomarkers of LPO (MDA) and a
marker for in vivo LPO (8-isoPGF) produced from arachidonic
acid by COX-independent non-enzymatic mechanisms.
How-ever, biomarkers that may reflect longer-term oxidative DNA
damage (e.g. 8-OHdG,
edA) were not observed to change after
short-term fasting.
Although obesity is associated with increased oxidative
stress in animal models and an increase in 8-isoPGF in
the obese Zucker rat, limited information in humans is
2 4 6 8 10 12
Duration of fasting (days)
0 2 4 6 8 10 12 Body w e ight c h a nge (% )
Fig. 1.Correlation of body weight change (%) and fasting duration (days) (Pearson’s correlation coefficient r¼ 0.70, n ¼ 52, P < 0.01).
Table III. Partial correlation coefficients among percent change of biomarkers [(before after fasting)/before fasting · 100]
MDA 8-isoPGF 8-OHdG edA Leptin
MDA 0.57a 0.36 0.01 0.10 8-isoPGF 0.34 0.22 0.31 8-OHdG 0.28 0.51b edA 0.09 a P< 0.01.
bP< 0.05, adjusted for percent change BMI and smoking status.
Table II. Concentration of urinary creatinine and biomarkers (before creatinine adjustment)
Biomarkers N Arithmetic mean Geometric mean
Before fasting After fasting Pa Before fasting After fasting Pb
Creatinine (mg/dl) 52 150.01 ± 11.00 174.28 ± 12.15 0.13 121.82 ± 1.11 151.46 ± 1.08 0.06 MDA (mmol/litre) 51 2.52 ± 0.28 1.47 ± 0.12 <0.01 2.04 ± 1.09 1.29 ± 1.07 <0.01 8-isoPGF (ng/ml) 47 16.43 ± 3.43 7.73 ± 1.53 <0.01 6.06 ± 1.26 3.06 ± 1.30 <0.01 8-OHdG (ng/ml) 50 26.40 ± 4.21 29.14 ± 4.19 0.76 10.55 ± 1.30 15.32 ± 1.24 0.21 edA (fmol/ml) 48 111.95 ± 18.68 88.32 ± 12.30 0.10 68.86 ± 1.16 60.74 ± 1.14 0.41 a
by Wilcoxon signed rank test.
bby paired t-test.
Table I. Means (±SE) and percent change of urinary biomarkers of oxidative stress (MDA, 8-isoPGF, 8-OHdG andedA) and plasma leptin level before and after fasting
Biomarkers N Arithmetic mean Geometric mean
Before fasting After fasting % Change Pa Before fasting After fasting % Change Pb
Body weight (kg) 52 63.01 ± 1.51 58.69 ± 1.41 6.8 <0.01 62.18 ± 1.02 57.90 ± 1.02 6.3 <0.01 MDA (mg/g Cr) 51c 0.50 ± 0.07 0.24 ± 0.03 52.0 <0.01 0.37 ± 1.11 0.18 ± 1.10 51.5 <0.01 8-isoPGF (mg/g Cr) 47c 9.93 ± 2.00 4.40 ± 0.80 55.7 <0.01 5.26 ± 1.18 2.04 ± 1.26 61.2 <0.01 8-OHdG (mg/g Cr) 50c 16.50 ± 2.26 15.75 ± 1.69 4.5 0.97 8.83 ± 1.22 10.02 ± 1.20 +13.6 0.61 edA (fmol/mmol Cr) 48c 6.39 ± 0.61 7.22 ± 1.13 +13.0 0.59 5.32 ± 1.09 5.24 ± 1.12 1.5 0.91 Leptin (ng/ml) 27 8.03 ± 0.76 6.68 ± 0.66 16.8 0.02 6.91 ± 1.13 5.89 ± 1.10 14.8 0.05
aby Wilcoxon signed rank test. b
by paired t-test.
c
available (27,28). Davi et al. (18) showed that women with
android obesity had higher levels of urinary 8-isoPGF than
non-obese women. They also observed a statistically
signific-ant reduction of urinary 8-isoPGF in 11 women with android
obesity (BMI
>28 and waist-hip ratio >0.86) who successfully
achieved weight loss in a short-term weight loss program (12
weeks) (18). Roberts et al. (20) reported a significant reduction
of serum 8-isoPGF in 11 men on a low-fat, high-fiber diet
combined with daily exercise for 45–60 min for 3 weeks.
Thompson et al. (29) also reported a 35% reduction in urinary
8-isoPGF in 28 women after 14 days of consuming an array of
fruits and vegetables. These findings of a lower level of urinary
8-isoPGF may result from reduced oxidative stress from the
diet and exercise intervention.
However, results of the association between caloric
restric-tion and MDA are limited and inconsistent. Although
Zainal et al. (14) reported that caloric restriction lowered
the concentrations of MDA in skeletal muscle in the Rhesus
monkey, Ugochukwu et al. (15) failed to show the effect of
dietary caloric restriction on reduction of plasma MDA in
streptozotocin-induced diabetic rats. In a human intervention
study, there was no significant change in urinary MDA
levels in 28 women after 14 days of consuming fruits and
vegetables (29). These inconsistencies might be due to
insens-itivity and non-specificity of urinary MDA and/or incomplete
control for other factors (e.g. other diets, physical activity,
etc.) which may affect MDA levels. However, the significant
correlation between the change of urinary 8-isoPGF and the
change of MDA during the fasting periods observed in this
study suggests that short-term fasting significantly reduced
oxidative stress, particularly generated by the short-term
LPO process.
On the contrary to a number of previous animal studies
showing significant reduction of oxidative DNA damage
after short-term caloric restriction (30–32), there was no
sig-nificant change in 8-OHdG or
edA levels in this study. The
Before After Ur in ar y M D A 0.0 0.2 0.4 0.6 0.8 1.0 1. A 2 Ur in ar y 8 -I so P G F 0 5 10 15 20 25 30 Before After U rin ar y 8 -O H d G 0 20 40 60 Before After Urinary εdA 0 5 10 15 Before After B C D
Fig. 2. Urinary biomarkers of oxidative stress before and after fasting (solid bar: the median; dotted bar: mean; whiskers: the minimum and maximum; boxes: the first and third quartiles; dot: outlier). A: Urinary MDA (mg/g creatinine), B: Urinary 8-IsoPGF (mg/g creatinine), C: Urinary 8-OHdG (mg/g creatinine), D: Urinary "dA (f mol/mmol creatinine)
finding of no significant reduction in urinary 8-OHdG levels
observed in this study is consistent with the findings from
28 women in a diet intervention program (29). Although the
finding of a significant correlation between the change in
urinary 8-OHdG with the change of plasma leptin levels
observed in this study may suggest the effect of short-term
fasting on urinary 8-OHdG levels, these results could be
explained by several other factors. First, short-term fasting
or severe caloric restriction may not alter the steady-state
level of oxidative DNA damage which is determined, in
part, by the rate of hydroxyl radical generation and individual
repair capacity.
edA which reflects longer-term oxidative DNA
damage may not be associated with short-term fasting or
severe caloric restriction (23). Second, we could not control
for other factors (e.g. inter-individual variation of
toxicokin-etics and/or repair capacity, hidden inflammatory process, etc.)
possibly related to oxidative DNA damage (8-OHdG,
edA)
levels. The study would have been strengthened by following
out for an additional time period after the restoration of the
normal diet.
Although our results may not have practical implications
because of the artificial nature of study design (fasting a few
days), recent biochemical and microarray results summarized
by Spindler (33) suggest that short-term caloric restriction acts
rapidly and reversibly to extend life span in animal model.
Furthermore, short-term caloric restriction (2 weeks)
signi-ficantly decreased cellular oxygen consumption and reactive
oxygen species production of rat muscle mitochondria (30).
However, the results of this study should be cautiously
interpreted and future studies of the effect of long-term fasting
should be conducted.
In conclusion, although the long-term effects of fasting
remain to be investigated, our results suggest that short-term
fasting exerts beneficial effects and reduces urinary levels
of primary LPO products (MDA, 8-isoPGF) without effecting
biomarkers of oxidative DNA damage (8-OHdG,
edA).
Acknowledgement
This study was supported by a grant of the Korea Health 21 R&D Project, Ministry of Health & Welfare, Republic of Korea (02-PJ1-PG1-CH03-0001). Conflict of Interest Statement: None declared.
References
1. Calle,E.E., Rodriguez,C., Walker-Thurmond,K. and Thun,M.J. (2003) Overweight, obesity, and mortality from cancer in a prospectively studied cohort of U.S. adults. N. Engl. J. Med., 348, 1625–1638.
2. Calle,E.E. and Thun,M.J. (2004) Obesity and cancer. Oncogene, 23, 6365–6378.
3. Michels,K.B. and Ekbom,A. (2004) Caloric restriction and incidence of breast cancer. JAMA, 291, 1226–1230.
4. Anson,R.M., Guo,Z., de Cabo,R., Lyun,T., Rios,M., Hagepanos,A., Ingram,D.K., Lane,M.A. and Mattson,M.P. (2003) Intermittent fasting dis-sociates beneficial effects of dietary restriction on glucose metabolism and neuronal resistance to injury from calorie intake. Proc. Natl Acad. Sci. USA, 100, 6216–6220.
5. Sogawa,H. and Kubo,C. (2000) Influence of short-term repeated fasting on the longevity of female (NZB· NZW) F1 mice. Mech. Ageing Dev., 115, 61–71.
6. Chelikani,P.K., Ambrose,J.D., Keisler,D.H. and Kennelly,J.J. (2004) Effect of short-term fasting on plasma concentrations of leptin and other hormones and metabolites in dairy cattle. Domest. Anim. Endocrinol., 26, 33–48.
7. Komaki,G., Matsumoto,Y., Nishikata,H., Kawai,K., Nozaki,T., Takii,M., Sogawa,H. and Kubo,C. (2001) Orexin-A and leptin change inversely in fasting non-obese subjects. Eur. J. Endocrinol., 144, 645–651.
8. Weigle,D.S., Duell,P.B., Connor,W.E., Steiner,R.A., Soules,M.R. and Kuijper,J.L. (1997) Effect of fasting, refeeding, and dietary fat restriction on plasma leptin levels. J. Clin. Endocrinol. Metab., 82, 561–565. 9. Jeon,J.Y., Harber,V.J. and Steadward,R.D. (2003) Leptin response to
short-term fasting in sympathectomized men: role of the SNS. Am. J. Phys-Endo. Meta., 284, 634–640.
10. Brook,R.D., Bard,R.L., Glazewski,L., Kehrer,C., Bodary,P.F., Eitzman,D.L. and Rajagopalan,S. (2004) Effect of short-term weight loss on the metabolic syndrome and conduit vascular endothelial function in overweight adults. Am. J. Cardiol., 93, 1012–1016.
11. Halliwell,B. (2002) Effect of diet on cancer development: is oxidative DNA damage a biomarker? Free Radic. Biol. Med., 32, 968–974. 12. Kasai,H. (1997) Analysis of a form of oxidative DNA damage,
8-hydroxy-20-deoxyguanosine, as a marker of cellular oxidative stress during
carcinogenesis. Mutat. Res., 387, 147–163.
13. Sohal,R.S., Agarwal,S., Candas,M., Forster,M.J. and Lal,H. (1994) Effect of age and caloric restriction on DNA oxidative damage in different tissues of C57BL/6 mice. Mech. Ageing Dev., 76, 215–224.
14. Zainal,T.A., Oberley,T.D., Allison,D.B., Szweda,L.I. and Weindruch,R. (2000) Caloric restriction of rhesus monkeys lowers oxidative damage in skeletal musle. FASEB J., 14, 1825–1836.
15. Ugochukwu,N.H., Bagayoko,N.D. and Antwi,M.E. (2004) The effects of dietary caloric restriction on antioxidant statue and lipid peroxidation in mild and severe streptozotocin-induced diabetic rats. Clin. Chim. Acta, 348, 121–129.
16. Lepage,G., Munoz,G., Champagne,J. and Roy,C.C. (1991) Preparative steps for the accurate measurement of malondialdehyde by high-perfor-mance liquid chromatography. Anal. Biochem., 197, 277–283.
17. Morrow,J.D. and Roberts,L.J. (1997) The isoprostanes: unique bioactive products of lipid peroxidation. Prog. Lipid Res., 36, 1–21.
18. Davi,G., Guagnano,M.T., Ciabattoni,G., Basili,S., Falco,A., Marinopiccoli,M., Nutini,M., Sensi,S. and Patrono,C. (2002) Platelet activation in obese women: role of inflammation and oxidant stress. JAMA, 288, 2008–2014.
19. Helmersson,J. and Basu,S. (2001) F(2)-isoprostane and prostaglandin F(2 alpha) metabolite excretion rate and day to day variation in healthy humans. Prostaglandins Leukot Essent Fatty Acids, 65, 99–102. 20. Roberts,C.K., Vaziri,N.D. and Barnard,R.J. (2002) Effect of diet and
exer-cise intervention on blood pressure, insulin, oxidative stress, and nitric oxide availability. Circulation, 106, 2530–2532.
21. Nair,J., Barbin,A., Velic,I. and Bartsch,H. (1999) Etheno DNA-base adducts from endogenous reactive species. Mutat. Res., 424, 59–69. 22. Hanaoka,T., Nair,J., Takahashi,Y., Sasaki,S., Bartsch,H. and Tsugane,S.
(2002) Urinary level of 1,N(6) -ethenodeoxyadenosine, a marker of oxid-ative stress, is associated with salt excretion and omega 6-polyunsaturated fatty acid intake in postmenopausal Japanese women. Int. J. Cancer, 100, 71–75.
23. Nair,J., Vaca,C.E., Velic,I., Mutanen,M., Valsta,L.M. and Bartsch,H. (1997) High dietary omega-6 polyunsaturated fatty acids drastically increase the formation of etheno-DNA base adducts in white blood cells of female subjects. Cancer Epidemiol. Biomarkers Prev., 6, 597–601.
24. Hong,Y.C., Lee,K.H., Yi,C.H., Ha,E.H. and Christiani,D.C. (2002) Genetic susceptibility of term pregnant women to oxidative damage. Toxicol Lett., 129, 255–262.
25. Sasaki,D.M., Yuan,Y., Gikas,K., Kanai,K., Taber,D., Morrow,J.D., Roberts,L.J.II and Callewaert,D.M. (2002) Enzyme immunoassays for 15-F2T isoprostane-M, an urinary biomarker for oxidant stress.
Adv. Exp. Med. Biol., 507, 537–541.
26. Ma,Z., Gingerich,R.L., Santiago,J.V., Klein,S., Smith,C.H. and amd Landt,M. (1996) Radioimmunoassay of leptin in human plasma. Clin. Chem., 42, 942–946.
27. Laight,D.W., Desai,K.M., Gopaul,N.K., Anggard,E.E. and Carrier,M.J. (1999) F2-isoprostane evidence of oxidant stress in the insulin resistant, obese Zucker rat: effects of vitamin E. Eur. J. Pharmacol., 377, 89–92.
28. Dobrian,A.D., Davies,M.J., Schriver,S.D., Lauterio,T.J. and Prewitt,R.L. (2001) Oxidative stress in a rat model of obesity-induced hypertension. Hypertension, 37, 554–560.
29. Thompson,H.J., Heimendinger,J., Haegele,A., Sedlacek,S.M., Gillette,C., O’Neill,C., Wolfe,P. and Conry,C. (1999) Effect of increased vegetable and fruit consumption on markers of oxidative cellular damage. Carcinogenesis, 20, 2261–2266.
30. Bevilacqua,L., Ramsey,J.J., Hagopian,K., Weindruch,R. and Harper,M.-E. (2004) Effect of short- and medium caloric restriction on muscle mitochon-drial proton leak and reactive oxygen species production. Am. J. Physiol. Endocrinol. Metab., 286, E852–E861.
31. Gredilla,R., Barja,G. and Lopez-Torres,M. (2001) Effect of short-term caloric restriction on H2O2production and oxidative damage in rat liver
mitochondria and location of the free radical source. J. Bioenerg. Biomembr., 33, 279–287.
32. Chung,M.H., Kasai,H., Nishimura,S. and Yu,B.P. (1992) Protection of DNA damage by dietary restriction. Free Radic. Biol. Med., 12, 523–525. 33. Spindler,S.R. (2005) Rapid and reversible induction of the longevity, anticancer and genomic effects of caloric restriction. Mech. Ageing Dev., 126, 960–966.
Received September 11, 2005; revised November 23, 2005; accepted January 3, 2006
