Download Prenatal Exposure of Mice to the Human Liver Carcinogen Aflatoxin

Prenatal Exposure of Mice to
Aflatoxin B1 Reveals a Susceptibility
to Genetic Change
Supawadee Chawanthayatham, Ph.D.
Department of Biological Engineering and
Center for Environmental Health Sciences, MIT
October 26-29, 2014
Boston, MA
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Acknowledgements
Essigmann / Wogan Group
MIT
John M. Essigmann
Gerald N. Wogan
Robert G. Croy
Leslie Woo
Crystal R. Belanger
Johns Hopkins
Funding
John D. Groopman
Patricia A. Egner
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Aflatoxins are environmental health problem
• Discovered ~1960 in moldy animal feed – also present in human food
– Secondary metabolites produced by Aspergillus flavus (A. flavus toxin =
Aflatoxin)
• AFB1 is predominant and is the most potently toxic and carcinogenic
• 2.5 billion people in the developing world have chronic exposure
through diet which leads to a high risk of developing liver cancer
– Aflatoxin exposure has also been associated with childhood stunting and
impaired neurological development
AFB1
A. flavus on
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Environmental AFB1 -- Relevance to liver cancer
• Geographically specific -- sub-Saharan Africa, Southeast Asia
and China
• Liver cancer incidence is greatly elevated by concurrent
exposure to both aflatoxin and hepatitis B infection
• Early life exposure to aflatoxin could underlie elevated risk of
liver cancer
Age-specific incidence of HCC in male
45-50 yr
70 yr
International Variation in Age-standardized Liver Cancer
Incidence Rates, Global cancer, 2008
Kensler T W et al. Toxicol. Sci. 2011;120:S28-S48
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Aflatoxin adducts are biomarkers
H
that predict cell death, mutations
AFB1
and cancer
H
Blood
Liver Cell
DNA Adducts
Protein Adducts
AFB1-Lysine
Albumin
AFB1-N7-Gua
H
O
AFB1
Phase II
Enzymes
O2
Phase I
Enzymes
HH
(Dialdehyde)
H
O
AFB1-FAPY
H
Reactive
Intermediates
(Epoxide)
O
*
*
*
*
H
Polar
Species
Cell Replication
AFB1-DNA adducts
are functional biomarkers that predict
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Cellcancer;
Death protein adducts are
Mutations
Cancer
liver
stable and?easier
to measure
Serum albumin adducts reveal significant exposure to AFB1
Clear evidence of early life exposure
Serum, Cord Blood, 2-Year Old
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Groopman et al, Food Chem. Toxicol, 2014
Objective
Quantify the risk of developing liver cancer from in utero
exposure to AFB1 by measuring AFB1-DNA adducts and
characterizing the subsequent frequency and spectrum
of mutations in the gpt transgenic mouse
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Log Total Adducts
(AFB1-N7-Gua + AFB1-FAPY)/106 nts
DNA adduct levels in maternal and fetal (GD14) livers
Snapshot of DNA damage 6 h after dosing with aflatoxin B1
100
10
100 X
1
0.1
Fetus
Mother
• Total adducts (N7-Gua + FAPY) in fetal livers were 100-fold lower
than in maternal livers
Increased mutation frequency in the gpt gene of
10 week old mice after in utero exposure to AFB1
• The predominant mutations found in the liver of AFB1
treatment group were G:C T:A transversions
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A DNA adduct in a fetus is 20 times more likely to
cause mutations than the same adduct in adult
Fetus
Adult
0.62
63.5
10 wk gpt MF (x10 )
6.5
30
gpt MF/ DNA adducts
10
0.5
Relative risk of mutation1
20
1
80
<1
AFB1-DNA adducts
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(adducts/10 bases)
-6
Mitotic Index (liver)
2
1
Mutation risk relative to adult liver = [gpt MF/DNA adducts] / [gpt MF/DNA adducts]adult
2 Determined by Ki67 cell proliferation marker staining
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Summary
• A DNA adduct in the liver of a fetus is 20 time more
likely to cause mutations than the same adduct in
the mother.
• Early life measurement of albumin and DNA adduct
biomarkers can predict the risk of developing
diseases resulting from aflatoxin exposure.
• Young animals have increased sensitivity to aflatoxin
(infant is not like a small adult).
• Reduction of early life exposure can have a major
protective effect on cancer outcomes later in life.
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Thank you
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