Summary
In the occupational environment, workers are inevitably exposed to numerous
potentially harmful pollutants, some of them acting as mutagens/carcinogens. However, not
every worker responds in the same way to these exposures, and as a result, some workers may be
at higher risk for developing cancer. The development of well-validated and sensitive biomarkers
of exposure, effect and individual susceptibility and their simultaneous assessment in the
biomonitoring of occupational exposure, are opening new possibilities for the scientific
community to address this issue and to improve, in the long run, cancer risk prediction in
occupational settings.
The general objective of this thesis was to identify genotypes and cellular phenotypes that
may serve as biomarkers for cancer risk prediction in occupationally exposed populations. Two
single biomonitoring studies and two pooled analyses were performed to address this issue at
population level in different occupational environments.
In the first part of this work, inter-individual differences in genotoxic responses [tail
DNA (TD), 8-hydroxy-2′-deoxyguanosine (8-OH-dG), micronuclei in binucleated (MNCB) and
mononucleated (MNMC) lymphocytes] to cobalt (Co) and hard metal (WC-Co) dust have been
addressed through a single biomonitoring study of occupational exposure. Considering the
importance of DNA repair in cellular responses to Co-containing dust, five single nucleotide
polymorphisms (SNPs) in common DNA repair genes (hOGG1326, XRCC1194, XRCC1280,
XRCC1399 and XRCC3241) have been investigated with respect to genotoxicity induction. Our
results showed that in the exposed and total populations, the variant XRCC1280 genotype was
associated with an increase in DNA breakage, as assessed by the percentage of DNA in the
Comet tail (TD). Moreover, a significant increase in DNA breakage was observed in exposed
smokers carrying the variant XRCC3241 genotype. In addition, the interaction between variant
hOGG1326 and XRCC3241 genotypes led to an increase in MNMC frequency in both the exposed
and total populations.
In the second part of this thesis, we addressed through another single biomonitoring study
the effectiveness of protective measures taken by the Belgian Defence in a particular
occupational setting, where workers wearing special protective equipments were exposed to
arsenic trichloride (AsCl3)-phosgene and AsCl3-hydrogen cyanide (HCN) during the collection
(field) and dismantling (plant) of chemical weapons. In addition, we also wanted to identify the
potential genetic susceptibility factors affecting individual responses to chemical warfare. A
wide range of biomarkers of exposure [urinary As, sister chromatid exchanges (SCE), high
frequency cells (HFC)], effect [chromosomal aberrations (CAs), MNCB, MNMC] and individual
susceptibility (MTHFR222, MS919, GSTM1, GSTT1, GSTP1105, hOGG1326, XRCC1194, XRCC1280,
XRCC1399, XRCC3241) were thus selected. Biomarker choice was based on the modes of action of
arsenic, which unlike phosgene and HCN, was shown to induce genotoxic effects through a wide
range of mechanisms. Although no significant correlations between As exposure and any
genotoxicity biomarker were found, the differences in biomarker levels observed across strata of
occupational exposure suggest that the plant exposed workers were well protected, while the
field exposed group needs a better protection. Concerning the influence of genetic
polymorphisms on biomarker levels, a significant influence of the wild type (Ser/Ser)
hOGG1326genotype on MNCB and SCE induction was observed, while the XRCC3241variant
genotype was associated with an elevated SCE frequency.
Considering the size limitations of the workforce in the above mentioned occupational
settings, the interplay between genotypes and cellular phenotypes was further investigated
through two pooled analyses, which allowed a more thorough investigation of gene-gene and
gene-environment interactions.
The first pooled approach showed that in the context of occupational exposures involving
detoxification by xenobiotic metabolizing enzymes, and in particular by the GSTs, workers
carrying both GSTM1 and GSTT1 deletions had lower MNCB frequencies than their positive
counterparts. Moreover, we observed a protective effect of the GSTT1 null genotype on MNCB
induction in younger workers, while this protective effect was reversed in older-age classes.
Additionally, this analysis revealed that women occupationally exposed to genotoxic agents are
at higher risk for MNCB induction than occupationally exposed males, suggesting that this
category of workers may require the elaboration of specific protective measures.
The second pooled analysis, which included the single biomonitoring studies described
above, focused on occupational exposures potentially able to induce DNA strand breakage, and
therefore MNCB, as a result of BER and DSB repair deficiencies. We aimed at investigating the
interplay between common polymorphisms in BER (hOGG1326 and XRCC1399) genes, DSB
repair (XRCC3241) genes and environmental factors in modulating MNCB induction. We have
shown that in the occupationally exposed population, the interaction between smoking and the
variant (Arg/Gln) XRCC1399 genotype led to an impaired ability to repair DNA damage, as
assessed by increased MNCB values. The hOGG1326 - XRCC3241 interaction modulated MNCB
frequencies in the total and referent populations, but not in the occupationally exposed group.
In conclusion, in this thesis we have been able to identify some gene-gene and geneenvironment interactions which modulate genotoxic responses in several occupational settings.
Our results indicate that combinations of different genes rather than single gene polymorphisms
are likely to have a major impact on cellular phenotypes. However, further studies are required to
illuminate the complex landscape of genotype-phenotype associations in the occupational
environment. To achieve a more comprehensive understanding of the mechanistic basis
underlying genotoxic responses to occupational genotoxins, large scale multi-center studies
should be performed, integrating high-throughput technologies and complementary biomarkers.
Mateuca Raluca