Transcript Laboratory of Microbial Ecology and Technology (LabMET)

Omzetting van polluenten in
maag-darm systeem
Tom Van de Wiele, PhD
LabMET
Laboratory of Microbial Ecology and Technology
Ghent University
Chemicals in People
Studienamiddag TI-KVIV
15 mei 2006
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Human exposure to pollutants
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Dermal contact
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Inhalation
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Isolation foam, pesticides...
Paints, solvents
Smoking, dust...
NOx, ozone, VOC
Ingestion
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Contaminated food / soil
Dust particles
PBDE, PCB, PAH, heavy metals...
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Oral exposure to pollutants
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Food:
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Soy and hop isoflavones
Heterocyclic aromatic
amines from grilled meat
Mycotoxins
...
Environment:
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Soil ingestion
Inhalation of dust and
subsequent ingestion
Flame retardants in house
...
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Human health risk assessment
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Biological availability
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What fraction of the
pollutant reaches the blood
circulation?
Biological activity
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What fraction of the
pollutant causes toxicity in
target organs?
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What happens to ingested pollutants?
1
2
L
I
V
E
R
3
Release from matrix
Complexation to organic matter
BIOACCESSIBILITY
Intestinal absorption
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6
5
Biotransformation
BIOAVAILABILITY
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What happens to absorbed pollutants ?
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Liver and intestinal epithelium cells:
Biotransformation reactions (phase I and II)
 Make compound more hydrophilic
 Removal from body in urine or bile
DETOXIFICATION
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But:
Biotransformation sometimes goes wrong
 Dead-end metabolite may be formed
 Higher toxicity than parent compound
TOXIFICATION
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What happens to non-absorbed pollutants ?
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Colon ascendens, colon transversum, colon descendens
Non-absorbed pollutants, detoxified pollutants...
enter the large intestine
Vast microbial community
500 species, 1014 CFU/mL
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Colon microbiota and health
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Further digestion
Useful fatty acids
Vitamin K, B12
Immunostimulation
Health-promoting
metabolic conversions
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Pathogens
Formation of toxins
Fat uptake and
synthesis
Production of (geno)toxic metabolites
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How to study intestinal microbiota?
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In vivo studies: animals, humans (if possible)
 Most relevant
 Physiological factors taken into account
But:
 Black box
 No mechanistic studies
 Ethical constraints
 Costly !
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How to study intestinal microbiota?
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In vitro studies: simulation of the gut
 Not physiologically accurate
 Validation in vivo needed
But:
 Mechanistic studies
 Reproducible
 Microbial community from entire gut
 Metabolism of chemicals can be monitored
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SHIME-Tec: gastrointestinal in vitro technology
Simulator of the Human Intestinal
Microbial Ecosystem
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Twin SHIME : parallel treatment and control
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Case study. Oral exposure to PAH
Polycyclic Aromatic Hydrocarbons
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Ingestion of contaminated soil
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Industrial and urban areas
Atmospheric deposition of PAH: 50 g.ha-1.yr-1
Oral uptake
 Adults: 50 mg.d-1
 Children: 200 mg.d-1
 Occasionally: 1-20 g.d-1
Recreation area Zelzate: 49.1 mg PAH/kg DW
Human health risk assessment
Focus on intestinal absorption
and bioactivation by human enzymes
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Colon microbiota contribute to toxicity?
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If so: incorporate in risk assessment !
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Experimental set-up
Incubate in SHIME:
• pure PAH compounds
• PAH contaminated soil
Stomach
Small
Colon
intestine
• Check PAH release from soil matrix along the gut
•If higher release > higher risk ?
• Check biological activation of PAHs
•Screening for hydroxylated PAH metabolites
•Chemical analysis: LC-ESI-MS
•Biological analysis: yeast estrogen bioassay
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SHIME: colon microbiota activate PAHs
Stomach
Small intestine
Colon
Inactivated colon
3,00
nM EE2 equivalence
2,50
2,00
1,50
1,00
0,50
0,00
naphthalene
phenanthrene
pyrene
benzo(a)pyrene
PAH as such are not estrogenic !!!
Hydroxylated PAH metabolites have estrogenic properties
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Chemical analysis
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LC-ESI-MS: hydroxylation of PAHs
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1-OH pyrene: 4.3 µg/L
7-OH B(a)P: 1.9 µg/L
OH
EE2
7-OH B(a)P
Colon microbiota produce hydroxylated PAHs !!!
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Urban playground soil: 49.1 ppm PAH
PAH release
estrogenicity
% EE2 equivalence
µg PAH/L released
25
20
15
10
5
0
stomach
small intestine
colon
Lower release gives higher biological activity !!!
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Biological activity assessment
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PAH exposure from contaminated soil ingestion
Adult: 5 g PAH/d
Child:50 g PAH/d
Released PAHs lowest in colon, but highest
bioactivity
Colon microbiota convert PAH to pseudoestrogenic metabolites
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Relevant biological activity in vivo ?
Contributes to general PAH toxicity?
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Van de Wiele et al. (2005) Environmental Health Perspectives
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Other examples:
Heterocyclic aromatic amines
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Intestinal bacteria convert
procarcinogen PHIP in nonactive metabolite
Detoxification mechanism
Lower risk than expected
3'
4'
2'
1'
5'
6
7
CH3
8
N
6'
5
N
9
2
NH 2
N
3'
4'
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Vanhaecke et al. (2006) Journal of
Agricultural and Food Chemistry
2'
1' 6
5'
7
CH 3
8
N
2
6'
5
N
9
N
10
NH
12
OH
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Other examples: mycotoxins
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Conversion of
zearalenone to zearalenol
Increase in estrogenic
properties
Relationship with
aetiology of cancer
development
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Other examples: phytoestrogens
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Gut bacteria convert
isoxanthohumol to hoppein
Most powerful phytoestrogen
Food supplements
Hormone substitution therapy
Prevention of hormone related
cancers (breast/prostate)
Possemiers et al. (2005) Journal of Nutrition
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Take home messages
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Metabolic potency from gut microbiota
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Identification of responsible bacteria and
process conditions needed
Interindividual variability !
Modulation of biological activation through
dietary factors, microbial community
composition...
Higher than currently anticipated
Consider this process for risk assessment
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Contact information
LabMET – Ghent University
Coupure Links 653
B-9000 Gent
[email protected]
http://labMET.ugent.be/
www.shimetec.be
www.food2know.be
+32 9 264.59.76
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