1. 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

2. Human exposure to pollutants
Dermal contact
Isolation foam, pesticides...
Inhalation
Paints, solvents
Smoking, dust...
NOx, ozone, VOC
Ingestion
Contaminated food / soil
Dust particles
PBDE, PCB, PAH, heavy metals...

3. Oral exposure to pollutants
Food:
Soy and hop isoflavones
Heterocyclic aromatic amines from grilled meat
Mycotoxins
...
Environment:
Soil ingestion
Inhalation of dust and subsequent ingestion
Flame retardants in house

4. Human health risk assessment
Biological availability
What fraction of the pollutant reaches the blood circulation?
Biological activity
What fraction of the pollutant causes toxicity in target organs?

5. What happens to ingested pollutants?6 4 L I V E R 5 2 3 1
Release from matrix
Complexation to organic matter
BIOACCESSIBILITY
Intestinal absorption
Biotransformation
BIOAVAILABILITY

6. What happens to absorbed pollutants ?
Liver and intestinal epithelium cells:
Biotransformation reactions (phase I and II)
Make compound more hydrophilic
Removal from body in urine or bile
DETOXIFICATION
But:
Biotransformation sometimes goes wrong
Dead-end metabolite may be formed
Higher toxicity than parent compound
TOXIFICATION

7. What happens to non-absorbed pollutants ?
Colon ascendens, colon transversum, colon descendens
Non-absorbed pollutants, detoxified pollutants... enter the large intestine
Vast microbial community
500 species, 1014 CFU/mL

8. Colon microbiota and health
Further digestion
Useful fatty acids
Vitamin K, B12
Immunostimulation
Health-promoting metabolic conversions
Pathogens
Formation of toxins
Fat uptake and synthesis
Production of (geno)-toxic metabolites

9. How to study intestinal microbiota?
In vivo studies: animals, humans (if possible)
Most relevant
Physiological factors taken into account
But:
Black box
No mechanistic studies
Ethical constraints
Costly !

10. How to study intestinal microbiota?
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

11. SHIME-Tec: gastrointestinal in vitro technology
Simulator of the Human Intestinal
Microbial Ecosystem

12. Twin SHIME : parallel treatment and control

13. Case study. Oral exposure to PAH Polycyclic Aromatic Hydrocarbons
Ingestion of contaminated soil
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
Colon microbiota contribute to toxicity?
If so: incorporate in risk assessment !

14. Experimental set-up Incubate in SHIME: pure PAH compounds
PAH contaminated soil
Stomach
Small
intestine
Colon
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

15. SHIME: colon microbiota activate PAHs
PAH as such are not estrogenic !!!
Hydroxylated PAH metabolites have estrogenic properties

16. Chemical analysis LC-ESI-MS: hydroxylation of PAHs EE2 7-OH B(a)P
1-OH pyrene: 4.3 µg/L
7-OH B(a)P: 1.9 µg/L OH
EE OH B(a)P
Colon microbiota produce hydroxylated PAHs !!!

17. Urban playground soil: 49.1 ppm PAH
Lower release gives higher biological activity !!!

18. Biological activity assessment
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 pseudo-estrogenic metabolites
Relevant biological activity in vivo ?
Contributes to general PAH toxicity?
Van de Wiele et al. (2005) Environmental Health Perspectives

19. Other examples: Heterocyclic aromatic amines
Intestinal bacteria convert procarcinogen PHIP in non-active metabolite
Detoxification mechanism
Lower risk than expected
Vanhaecke et al. (2006) Journal of Agricultural and Food Chemistry

20. Other examples: mycotoxins
Conversion of zearalenone to zearalenol
Increase in estrogenic properties
Relationship with aetiology of cancer development

21. Other examples: phytoestrogens
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

22. Take home messages Metabolic potency from gut microbiota
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

23. Contact information
LabMET – Ghent University
Coupure Links 653
B-9000 Gent