Aflatoxins exposure

Report
Aflatoxin exposure, health impacts,
risk assessment and database
Aflatoxin Stakeholders’ Workshop
3-4 December , 2012
Dar es Salaam , Tanzania
Candida Philip Shirima
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Aflatoxins
• They are toxic and fungal metabolites
• Produced (A. flavus, A. parasiticus and rare A.
nomius)
• Types: aflatoxins B1 (AFB1) and B2 (AFB2),
(AFG1) and G2 (AFG2).
• Aflatoxin B1 occurs most frequently and is most
toxic and carcinogenic
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Human exposure to aflatoxins
Dietary exposure – The main source of human
exposure to aflatoxins
• Exposure is through consumption of aflatoxins
contaminated food.
• Contamination of maize and groundnuts is of
particular concern- dietary staples including
children complementary foods.
• The presence of aflatoxins metabolites in breast
milk (AFM1) provides main source of aflatoxins
exposure for lactating newborn infants and breast
feeding young children
• Exposure from animal food products; poultry
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Toxicokinetics of aflatoxin
Absorption
Metabolism/
Distribution
Kidney
Gastro –
Intestinal
Track
Liver
(metabolism site)
DNA , AF-alb
Adducts)
Blood
Circulation
Excretion
Urine
(metabolites)
AFB1-N7-guanine
Breast milk
(metabolite)
AFM1
(AF-albumin)
Faeces
(un-metabolised)
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Aflatoxins exposure assessment
• Quantitative evaluation of the likely intake of
aflatoxin via food.
• The extent of exposure to aflatoxins depends
on the level of the toxin in different foods
and on the level of consumption of those
foods
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Ways of assessing exposure to aflatoxins-1
Food measurement:
1.Use levels of aflatoxin contamination in food and
quantities of food consumption Probably daily intake
(PDI)
Aflatoxin
Contamination
in food
(ng/gm)
Food
consumption
(gm/day)
Aflatoxins
exposure
(ng/kg-bw/day)
Body weight
(Kg)
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Ways of assessing exposure to aflatoxins-2
Use of biomarkers of aflatoxin exposure
• Biomarkers are a measure of a cellular, biochemical or
molecular change in biological media (human tissues,
cells or fluids), which is informative with respect to
assessing an exposure
• Use of biomarkers requires understanding of the
mechanisms of aflatoxin actions
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Ways of assessing human exposure to
aflatoxins-3
Use of biomarkers of aflatoxin exposure
• Biomarkers of aflatoxin exposure include:• Urinary aflatoxin metabolites, such as AFB1-N7guanine and AFM1
• AF-albumin in blood serum, DNA adducts
• AFM1 in breast milk
• These metabolites are well validated as
biomarkers of aflatoxin exposure.
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Aflatoxin research work by TFDA
Completed study
-Iringa, Kilimanjaro, Tabora and Mtwara:
•Aflatoxin occurance: 18% in maize
Contamination level: range 1 to 158 μg/kg
Ongoing studies:
Iringa, Kilimanjaro and Tabora (TFDA & Leeds University)
-Use of biomarkers in the evaluation of dietary exposure to
aflatoxins and fumonisins among young children.
-Association of children growth and exposure to the
mycotoxins
Hanang, Kilosa and Rungwe (TFDA and Ghent University)
Strategies for reducing mycotoxins contamination and
exposure:-Application of GPHP and dietary approaches /diversification
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Aflatoxins and health effects
• Aflatoxins are toxic in humans and animals
• Carcigonen: AFB1 has been classified as a
group 1 human carcinogen by the IARC (1993).
• Associated with aflatoxicosis: acute poisoning
which results in direct liver damage and
subsequent illness or death (Kenya in 2004)
• The liver: Target organ for both acute and
chronic aflatoxin toxicity
• High aflatoxin exposure is associated with
impairment of child growth, particularly stunting;
the underlying mechanisms are unclear
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Aflatoxins and health effects
• Immune suppression effects
• Hepatopmegaly (liver enlargement) (in
Kenyan school children)
• Nutritional interference effects:
-Aflatoxins bind covalently to DNA resulting
in decreased protein synthesis
-Selenium concentrations were found to be
significantly and inversely correlated to
AF-albumin adducts concentrations
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Why affects child growth?
Hypothesis:
1.Intestine permeability and absorption
impaired
2.liver toxicity inhibit IGFs production which
affect the growth axis
3.Immune function suppression may enhance
infectious disease e.g. diarrhoea
4.Epigenetic changes occurred at early life
exposure may have effect
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Aflatoxin risk analysis
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•
•
•
Develops an estimate of the risks
Identifies appropriate measures
Implement appropriate measures
Communicates with stakeholders about
the risks and measures applied
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Aflatoxin database
• Need for a centralised aflatoxin database
-Food consumption data (AF susceptible foods)
-Aflatoxin contamination data (to be coordinated)
-Exposure assessment (e.g conventional & biomarkers)
-Aflatoxin risk analysis
-Findings from aflatoxin studies
• Useful source of information for status of aflatoxin
contamination, exposure and health effects in Tanzania
• Combine and share findings from various independent
studies
• Good/accessible source of information for formulating sound
strategies for AF control
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