Genetic polymorphism of drug-metabolizing enzymes and styrene-induced DNA damage
A cross-sectional study was carried out on 48 workers exposed to styrene and 14 unexposed healthy controls in order to investigate the genotoxic potential of styrene exposure. DNA damage was assessed in peripheral blood leukocytes (WBCs) by the comet assay. Polymorphisms in glutathione S-transferase genes (GSTM1, GSTT1, GSTP1) and the gene encoding microsomal epoxide hydrolase (EPHX) were characterized to assess their possible modifying role in styrene metabolism and subsequent DNA damage. Exposed workers showed significantly higher levels of DNA damage compared to controls. Among workers, the GSTM1 and GSTT1 polymorphisms significantly affected comet parameters. Subjects bearing a GSTM1pos genotype showed a significantly higher proportion of damaged nuclei compared to people lacking GSTM1-1 expression (GSTM1null), whereas GSTT1pos workers showed significantly lower DNA damage than GSTT1null individuals. Styrene-7,8-oxide (SO)-induced DNA damage was assessed in vitro in WBCs isolated from the healthy controls. A clear dose-response relationship at micromolar doses of SO was found for the whole group. WBCs collected from subjects bearing the homozygous wildtype GSTP1 genotype showed a significant protection compared to cells from subjects bearing at least one GSTP1 variant allele. The field survey confirms that styrene exposure is associated with increased DNA damage and indicates a modulating role for GSTM1 and GSTT1 genotypes. In vitro experiments suggest that the extent of SO-induced DNA strand breaks depends, at least in part, on interindividual differences in GSH-conjugation capabilities.
Available from: Massimo Moretti
- "50th percentile) or the values corresponding to the 75th/95th percentile . This statistical approach in the comet assay was adopted in several researches [47-49]. "
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ABSTRACT: The results of a cross-sectional study aimed to evaluate whether genetic polymorphisms (biomarkers of susceptibility) for CYP1A1, EPHX and GSTM1 genes that affect polycyclic aromatic hydrocarbons (PAH) activation and detoxification might influence the extent of primary DNA damage (biomarker of biologically effective dose) in PAH exposed workers are presented. PAH-exposure of the study populations was assessed by determining the concentration of 1-hydroxypyrene (1OHP) in urine samples (biomarker of exposure dose).
The exposed group consisted of workers (n = 109) at a graphite electrode manufacturing plant, occupationally exposed to PAH. Urinary 1OHP was measured by HPLC. Primary DNA damage was evaluated by the alkaline comet assay in peripheral blood leukocytes. Genetic polymorphisms for CYP1A1, EPHX and GSTM1 were determined by PCR or PCR/RFLP analysis.
1OHP and primary DNA damage were significantly higher in electrode workers compared to reference subjects. Moreover, categorization of subjects as normal or outlier highlighted an increased genotoxic risk OR = 2.59 (CI95% 1.32-5.05) associated to exposure to PAH. Polymorphisms in EPHX exons 3 and 4 was associated to higher urinary concentrations of 1OHP, whereas none of the genotypes analyzed (CYP1A1, EPHX, and GSTM1) had any significant influence on primary DNA damage as evaluated by the comet assay.
The outcomes of the present study show that molecular epidemiology approaches (i.e. cross-sectional studies of genotoxicity biomarkers) can play a role in identifying common genetic risk factors, also attempting to associate the effects with measured exposure data. Moreover, categorization of subjects as normal or outlier allowed the evaluation of the association between occupational exposure to PAH and DNA damage highlighting an increased genotoxic risk.
Available from: onlinelibrary.wiley.com
- "In the test strategy currently applied, in vitro tests are particularly useful for gaining an understanding of the potential genotoxicity of a substance and in most of the cases metabolic pathways that can be simulated adequately in vitro (table 2). However, there are still conditions in which animal tests will be needed, in particular, in cases in which clarification of positive findings of in vitro tests is necessary and in cases where specific metabolic pathways cannot be implemented adequately in in vitro systems such as epoxihydrolase (Haufroid 2002; Buschini et al. 2003). The advent of ''omics'' technology will have impact in the field of genetic toxicology testing since these assays provide a general capability for global assessment of many classes of cellular molecules, providing new approaches to assessing functional cellular alterations including mechanistic insights into the response of cells to DNA damage (Aardema & McGregor 2002; Newton et al. 2003; Hu et al. 2004). "
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ABSTRACT: Describing the toxicological profile of a substance is the first step required for risk assessment. Although a wide range of in vitro methods are widely used to characterise toxicological properties including toxicokinetics, regulatory acceptance is mainly confined to in vitro tests which investigate genotoxic end-points. In vitro tests have been proposed for the endpoints acute toxicity, repeated dose toxicity and toxicity to reproduction which encompass the minimum requirements in the OECD SIDS programme. However, until now, limitations of the proposed tests preclude their application in a regulatory framework. Presently, in vitro tests play a major role in obtaining information on mechanism of toxicity with the perspective to be able to identify pathways of toxic responses by applying toxicogenomics techniques. Physiologically based toxicokinetic modelling is using data from in vitro studies to build up the model for a specific compound. Information from both areas is incorporated into the risk assessment to derive compound-specific safety factors, which account for species differences and for the variability among the human population, including possible sensitive subpopulations. Future developments to further enhance the use of in vitro methods in regulatory toxicology include the development of (Q)SAR approaches supplemented by mechanisms of toxicity, which can be addressed by developing methods of molecular toxicology.
Available from: Antonio Mutti
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ABSTRACT: NEW EFFECT BIOMARKERS. The major research goals for researchers developing biomarkers of effect are the development and validation of biomarkers that permit the prediction of the risk of disease in individuals and groups. One important objective is to prevent human cancer. This article reviews the most recent analytical methodologies, validation studies and field trials together with auditing and quality assessment of the necessary data based on scientific grounds. Consideration is given to new developments in the relatively young field of toxicogenomics, possibly leading to the identification of early changes that may lead to both cancer and non-cancer end points. Although the creation and development of reliable databases integrating information from genomic and proteomic research programmes should offer a contribution to the prediction of risks and prevention of diseases related to chemical exposure, the most promising future application of these technologies lies in the molecular diagnosis of diseases whose nosography will probably be redefined.
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