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Department of Environmental Health Sciences, School of Hygiene and Public Health, Johns Hopkins University, Baltimore, Maryland 21205 [J-S. W., G. S., X. H., T. W. K., J. D. G.]; Guangxi Cancer Institute, Nanning, Guangxi, Peoples Republic of China [T. H., J. S.]; Fusui Liver Cancer Institute, Fusui, Guangxi, Peoples Republic of China [F. L., Z. W., Y. L.]; and Shanghai Cancer Institute, Shanghai, Peoples Republic of China [H. L., S-Y. K., G-S. Q.].
| Abstract |
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| Introduction |
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Primary prevention, such as vaccination for HBV in infants and food safety procedures to control aflatoxin contamination, offer strategies for lowering HCC rates in the world; however, positive outcomes will require many years. An immediate challenge in cancer prevention and control is to manage those who are already at high risk, such as individuals who are HBsAg carriers and have chronic aflatoxin exposure. The purpose of the following study was to characterize HCC incidence and mortality, status of dietary aflatoxin exposure, and HBV infection in the high-risk region of Fusui County for use in the design of future chemopreventive intervention studies (18 , 19) .
| Materials and Methods |
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3300 residents and is one of the three
townships with the highest incidence and mortality of HCC in Fusui
County. Data for analyses of incidence and mortality of malignant
tumors were collected from village clinics and were confirmed by the
Office of Malignant Tumor Reporting operated by the Fusui Liver Cancer
Institute. The incidence and mortality were standardized according to
the National Population Proportion of China in 1990.
Procedure for Molecular Biomarkers Study.
This collaborative study by the Johns Hopkins University, Guangxi
Cancer Institute, Shanghai Cancer Institute, and Fusui Liver Cancer
Institute used methods and consent forms approved by the Institutional
Review Boards for human studies at Johns Hopkins University and at the
Guangxi Cancer Institute. The consent form in bilingual (Chinese and
English) format was developed, approved, and explained in detail at
village meetings among residents and investigators prior to
recruitment. To be eligible, participants had to meet the following
criteria: adults 2560 years of age in good general health with no
history of chronic illness, no personal history of cancer, no use of
prescribed medications, no pregnancy or lactation for women residents
of different households, agree to stay in the village for the 1-week
study period, and able to provide necessary informed consent. In April
1999, weighed portions of each meal from the participants and 24-h
urine in three cycles (morning, noon, and evening) were collected from
participants for 7 consecutive days. The urine volume was measured and
tested with chemsticks for renal function, and a 200-ml urine aliquot
per day was stored at -20°C. In addition, 10 ml of blood were drawn
into Vacutainers at the beginning and 5 ml at the end of the 7-day
study from each participant. Serum samples were immediately separated
by centrifugation at the village clinic and stored at -20°C until
analysis.
Measurement of HBV Seromarkers and Liver Function.
All serum samples were tested for HBsAg and anti-HBs by RIA using the
AUSRIA II kit (Abbott Laboratories, North Chicago, IL). A test for the
presence of anti-HBc and HBe antigen/anti-HBe was then performed using
a commercially available Corab kit purchased from Abbott Laboratories.
Liver function tests (aspartate aminotransferase, alanine
aminotransferase, and
-fetoprotein) were performed in the clinical
laboratory of Guangxi Tumor Hospital, which is affiliated with Guangxi
Cancer Institute and Guangxi Medical University, according to the
clinical diagnostic procedures.
Measurement of AFB1 in Food, Serum Albumin Biomarkers,
and Urinary Biomarker.
Food analysis for AFB1 was performed using a
previously published immunoaffinity method (20)
. Urinary
aflatoxin biomarkers and serum aflatoxin-albumin adducts were analyzed
according to previously published methods (19
, 21)
.
Statistical Analysis.
All analytical data are expressed as mean ± SE, and levels of
serum aflatoxin-albumin adducts were compared between the beginning and
end of the study and statistically analyzed by Students t
test. Raw data of cases and deaths were adjusted to standardized
incidence and mortality using the National Population Proportion of
China in 1990. Time trends analyses were performed according to the
method described by Parkin et al. (2)
.
| Results |
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4.8:1 (58 cases versus 12
cases). More strikingly, the age distribution of HCC cases revealed
that most cases occurred in early middle age. The median of age of HCC
onset was 34 years in males and 41 years in females.
To characterize AFB1 and HBV exposure in this
village, 15 males and 14 females from different households were
recruited. Two of the study subjects dropped out during the 1-week
period. In total, 56 blood samples, 90 raw food samples, 279 cooked
food samples, which were aggregated by subject, and 567 urine samples
were collected. Additionally, a consecutive 7-day dietary survey for
each participant household was obtained. The daily diet of residents
consisted mainly of corn and rice with side dishes including vegetables
and, occasionally, pork. Almost all of the residents of the village
stored ground corn for their daily food. Ground corn either in corn
rice or corn porridge was consumed by all study participants, and the
average daily corn consumption was 575 g for male subjects and
322 g for female subjects. Rice was consumed only at dinner; the
average daily rice intake was 185 g in men and 117 g in
women. Locally produced peanut oil was the sole source for cooking oil;
daily intake was
18 g per participant.
The results of the AFB1 analysis in mixed food
samples obtained from study participants are listed in Table 1
. Corn was the major source of dietary aflatoxin exposure. Twenty-three
of the 30 (76.7%) mixed ground corn samples had detectable levels of
AFB1 with an average of 23.7 ± 6.6 ppb
(range, 0.4128.1 ppb). Nine of the 30 ground corn samples had
AFB1 levels >20 ppb, and 5 of these were >50
ppb. Peanut oil was a second major source of dietary aflatoxin
exposure. Twenty of 30 peanut oil samples had detectable levels of
AFB1 with an average of 7.8 ppb (range, 0.152.5
ppb). Four of these 30 samples contained >10 ppb. Rice, when compared
with corn and peanut oil, was a minor source of dietary aflatoxin
exposure. Although 7 of 30 (23.3%) samples had detectable levels of
AFB1, the average level was 1.1 ppb (range,
0.32.0 ppb).
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Pooled urine samples collected from 27 study participants at day 7 were
analyzed for urinary aflatoxin biomarkers, and the results are shown in
Table 2
. AFM1 was detectable in 24 of 27 (88.9%) samples
with an average level of 192.3 ± 65.2 ng/24-h urine (range,
0.91258 ng/24-h urine). AFB-mercapturic acid was also found in 24 of
27 (88.9%) samples with an average level of 103.6 ± 25.3 ng/24-h
urine (range, 6.6494.9 ng/24-h urine).
AFB-N7-guanine was detectable in 11 of
27 (40.7%) samples with an average level of 407.3 ± 158.7
ng/24-h urine (range, 64.91789.8 ng/24-h urine). Aflatoxin
P1 was detectable in 8 of 27 (29.6%)
samples with an average level of 664.9 ± 425.4 ng/24-h urine
(range, 77.33569.7 ng/24-h urine), and aflatoxin
Q1 was detectable in 7 of 27 (25.9%) samples
with an average level of 92.2 ± 8.3 ng/24-h urine (range,
77.3137.5 ng/24-h urine).
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-fetoprotein,
although 4 of 29 (13.8%) were HBsAg positive. Three of these four
people were men, constituting 20% (3 of 15) of the male participants
in the study. Two of these male participants were positive for HBe
antigen. Higher percentages (48.382.8%) of anti-HBs, anti-HBc, and
anti-HBe marker were detected, further demonstrating a high rate of HBV
infection in this population.
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| Discussion |
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1215% of the general population was HBsAg positive. More than
90% of subsequent HCC cases tested HBsAg positive, and incidence of
HCC among HBsAg carriers was close to 1% per year (11
, 16
, 22)
. Studies by Yeh and Shen (8)
in the
early 1980s in Fusui described a strong interaction between HBV
infection and dietary aflatoxin exposure. Furthermore, a nested
case-control study in Shanghai (12
, 13)
revealed a
statistically significant synergistic increase in the relative risk of
HCC with exposure to aflatoxin and HBV. This synergistic interaction
between HBV and AFB1 was further confirmed by
several studies that used similar biomarkers for aflatoxins and HBV in
other populations (14
, 15)
.
Data from the present study showed that dietary
AFB1 exposure is still predominant in this
population as demonstrated by the high positive rate and level of
aflatoxin contamination in corn and peanut oil samples (Table 1)
, which
were consumed daily by the study participants. The absolute
AFB1 daily intake, as calculated by the average
contamination in the diet multiplied by the amount of food consumed,
was
14 µg/day in men and 8 µg/day in women. These levels are
less than that reported for the region 15 years earlier
(23)
, which may reflect a switch from almost 100% corn to
some portions of rice as the primary dietary item within the past
decade. However, this determination may underestimate the real amount
of aflatoxin exposure because the heterogeneity of aflatoxin
contamination of foodstuffs can lead to inter- and intraindividual
variations in the population.
Human urine and serum specimens collected from the Fusui area have been used in the development and validation of molecular dosimetry and biomarkers for aflatoxin exposure. Groopman et al. (23) analyzed urine samples collected from a study group of 42 people in Fusui County in 1984 and found associations between urinary excretion of AFB1-N7-guanine adduct and AFM1 and dietary AFB1 intake. Gan et al. (24) examined formation of aflatoxin-albumin adducts in serum samples from the same group. A significant correlation (r = 0.69) of aflatoxin-albumin adduct level with AFB1 intake was observed. When serum aflatoxin-albumin adduct data were compared with urine AFB-N7-guanine adduct level, a significant correlation was found (r = 0.73). The results of the present study are consistent with these previous findings.
Finally, a recent study showed that 57% (20 of 35) of HCC cases from
Fusui and neighboring areas of Guangxi Region had a G
T transversion
at codon 249 of the p53 tumor suppressor gene
(25)
, a frequency of p53 mutations comparable
to other parts of the world with high levels of aflatoxin contamination
(26
, 27)
. Thus, the high-risk region around Fusui County
is a strong candidate for implementation of primary and chemopreventive
interventions.
| Acknowledgments |
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| Footnotes |
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1 This work was supported financially by Program
Project Grant ES06052 from the National Institute for Environmental
Health Sciences, NIH. ![]()
2 To whom requests for reprints should be
addressed, at The Institute of Environmental and Human Health, Texas
Tech University System, Box 41163, Lubbock, TX 79409-1163. Phone:
(806) 885-0320; Fax: (806) 885-4577; E-mail: js.wang{at}ttu.edu ![]()
3 The abbreviations used are: HCC, hepatocellular
carcinoma; HBV, hepatitis B virus; HBsAg, hepatitis B surface antigen;
HBs, hepatitis B surface protein; HBc, hepatitis B core protein; HBe,
hepatitis B virus envelope; AFB1, aflatoxin B1;
AFM1, aflatoxin M1. ![]()
Received 7/19/00; revised 10/24/00; accepted 11/17/00.
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