Biomedical subjects

Hannu Norppa

Publications and source records attributed to Hannu Norppa.

At least 19 recordsLinked to original sources

PubMed2006

Chromosomal aberrations and cancer risk: results of a cohort study from Central Europe.

A high level of chromosomal aberrations in peripheral blood lymphocytes may be an early marker of cancer risk, but data on risk of specific cancers and types of chromosomal aberrations (chromosome type and chromatid type) are limited. A total of 6,430 healthy individuals from nine laboratories in Croatia, Hungary, Lithuania, Poland, and Slovakia, included in chromosomal aberration surveys performed during 1978-2002, were followed up for cancer incidence or mortality for an average of 8.5 years; 200 cancer cases were observed. Compared with that for the low-tertile level of chromosomal aberrations, the relative risks of cancer for the medium and high tertiles were 1.78 (95% confidence interval: 1.19, 2.67) and 1.81 (95% confidence interval: 1.20, 2.73), respectively. The relative risk for chromosome-type aberrations above versus below the median was 1.50 (95% confidence interval: 1.12, 2.01), while that for chromatid-type aberrations was 0.97 (95% confidence interval: 0.72, 1.31). The analyses of risk of specific cancers were limited by small numbers, but the association was stronger for stomach cancer. This study confirms the previously reported association between level of chromosomal aberrations and cancer risk and provides novel information on the type of aberrations more strongly predictive of cancer risk and on the types of cancer more strongly predicted by chromosomal aberrations.

Adolescent↗

PubMed2006

An increased micronucleus frequency in peripheral blood lymphocytes predicts the risk of cancer in humans.

The frequency of micronuclei (MN) in peripheral blood lymphocytes (PBL) is extensively used as a biomarker of chromosomal damage and genome stability in human populations. Much theoretical evidence has been accumulated supporting the causal role of MN induction in cancer development, although prospective cohort studies are needed to validate MN as a cancer risk biomarker. A total of 6718 subjects from of 10 countries, screened in 20 laboratories for MN frequency between 1980 and 2002 in ad hoc studies or routine cytogenetic surveillance, were selected from the database of the HUman MicroNucleus (HUMN) international collaborative project and followed up for cancer incidence or mortality. To standardize for the inter-laboratory variability subjects were classified according to the percentiles of MN distribution within each laboratory as low, medium or high frequency. A significant increase of all cancers incidence was found for subjects in the groups with medium (RR=1.84; 95% CI: 1.28-2.66) and high MN frequency (RR=1.53; 1.04-2.25). The same groups also showed a decreased cancer-free survival, i.e. P=0.001 and P=0.025, respectively. This association was present in all national cohorts and for all major cancer sites, especially urogenital (RR=2.80; 1.17-6.73) and gastro-intestinal cancers (RR=1.74; 1.01-4.71). The results from the present study provide preliminary evidence that MN frequency in PBL is a predictive biomarker of cancer risk within a population of healthy subjects. The current wide-spread use of the MN assay provides a valuable opportunity to apply this assay in the planning and validation of cancer surveillance and prevention programs.

Biomarkers↗

PubMed2006

Copy number gains on 5p15, 6p11-q11, 7p12, and 8q24 are rare in sputum cells of individuals at high risk of lung cancer.

UNLABELLED: Lung cancer specimens display recurrent copy number aberrations in distinguished chromosomal regions as compared with normal lung cells. Such alterations have been utilized in design of fluorescence in situ hybridization (FISH) probe sets in attempts to improve the cytological diagnosis of lung cancer. One of such probe sets, LAVysion, detects copy number changes in the centromeric region of chromosome 6 (CEP6), and regions 5p15, 8q24, and 7p12, often gained in lung cancer. METHODS: We evaluated the feasibility of the LAVysion multi-color probe set in detection of individuals at high risk of lung cancer by applying the FISH probe set on smears prepared of induced sputa obtained from 20 lung cancer patients, 43 asbestos-exposed workers, 21 heavy tobacco smokers, and 15 healthy never-smokers. The hybridized sputum smears were examined using fluorescence microscopy and the number of signals in epithelial cells was examined throughout the hybridized area. Additionally, we review here the previous studies using LAVysion probe set. RESULTS: The FISH probe set was slightly more sensitive than cytology alone in detecting lung cancer. No significant differences in copy number gain were found between high-risk individuals and healthy never-smokers. The proportions of individuals with copy number gains in sputa among the lung cancer patients, asbestos-exposed workers, tobacco smokers, and never-smokers were 50, 20, 12, and 27%, respectively, when three or more cells with a copy number gain detected by at least two different probes was used as the cut-off point. In comparison, the sensitivity of cytology in detecting lung cancer was 44%. In the lung cancer patients the number of abnormal cells by FISH correlated well with the cytologic atypia class (Spearman rank correlation coefficient 0.77, p<0.01). Using multivariant variance analysis, gains in CEP6, 5p15, 8q24 and 7p12 were not associated with smoking or asbestos exposure. CONCLUSIONS: FISH did not significantly exceed the sensitivity of sputum cytology in finding lung cancers. Significant differences were not found between sputa of asbestos-exposed individuals, heavy-smokers and never-smokers. More sensitive methods are needed for the follow-up of populations at high risk of contracting lung cancer.

Adenocarcinoma↗

PubMed2006

In vivo micronuclei in uncultured T-lymphocytes of male railroad transit workers and referents.

In the biomonitoring of human genotoxic effects, micronuclei (MN) usually are scored in phytohaemagglutinin-stimulated cultured lymphocytes. MN also can be examined in uncultured lymphocytes, which facilitates the analysis of genotoxic damage incurred in vivo. Characterization of MN in cultured lymphocytes by fluorescence in situ hybridization (FISH) has shown a clear over-representation of the X and Y chromosomes in the MN of males. However, it is not known if this phenomenon also occurs in vivo. The purpose of the present study was to assess the frequency and composition of MN formed in vivo from immunomagnetically isolated uncultured T-lymphocytes of men. To evaluate the possible effects of genotoxic exposure on in vivo MN, we examined 17 railroad workers occupationally exposed to complex chemical mixtures and 14 referents, all nonsmokers. The results showed similar total frequencies of micronucleated cells among the exposed workers and the referents. When the MN were characterized by FISH, there were no significant differences between the exposed and referents with regards to the frequency of centromere-positive or centromere-negative MN. Centromeric label was observed in 69% of all MN, indicating that most of the MN contained whole chromosomes (or chromatids). 80% of the centromere-positive MN harbored autosomes, 12% Y chromosomes, and 8% X chromosomes. The occurrence of the Y- and X-chromosomes in MN was, respectively, 5.5- and 3.8-times greater than would be expected assuming an equal contribution by all chromosomes. Thus, sex chromosomes appear to be over-represented in lymphocyte MN of men in vivo, confirming previous results obtained in vitro.

Adult↗

PubMed2006

Cytogenetic biomarkers, urinary metabolites and metabolic gene polymorphisms in workers exposed to styrene.

The present study comprised a biomonitoring study in 95 workers occupationally exposed to styrene and 98 unexposed controls, employing an integrated approach involving biomarkers of exposure, effect, and susceptibility. Airborne styrene was evaluated at workplace, and urinary styrene metabolites, mandelic acid (MA), phenylglyoxylic acid (PGA), vinylphenols (VPTs) and phenylhydroxyethylmercapturic acids (PHEMAs), were measured as biomarkers of internal dose. Cytogenetic alterations were evaluated by analysing the frequency of chromosomal aberrations (CAs) and micronucleated binucleated cells (MNBN) in peripheral blood lymphocytes. The micronucleus assay was coupled with centromeric fluorescence in situ hybridization to distinguish micronuclei (MN) arising from chromosomal breakage (C- MN) from those harboring whole chromosomes (C+ MN). The possible influence of genetic polymorphisms of xenobiotic-metabolizing enzymes involved in styrene biotransformation (EPHX1, GSTT1, GSTM1, GSTP1) and NAT2 on the cytogenetic endpoints was investigated. The exposed workers showed a significantly higher frequency of MNBN (13.8+/-0.5% versus 9.2+/-0.4%; P<0.001) compared to control subjects. The effect appeared to concern both C- and C+ MN. A positive correlation was seen between the frequency of C+ MN and urinary level of MA+PGA (P<0.05) and VPTs (P<0.001). Chromosome-type CAs positively correlated with airborne styrene level and VPTs (P<0.05), whereas chromatid-type CAs correlated with PHEMAs (P<0.05). Workers bearing GSTM1 null genotype showed lowered levels of PHEMAs (P<0.001). The GSTT1 null genotype was associated with increased MNBN frequencies in the exposed workers (P<0.05) and the fast activity EPHX genotype with a moderate decrease in both MNBN and CAs in the controls. Our results suggest that occupational exposure to styrene has genotoxic effects that are potentiated by the GSTT1 gene deletion. These observations may have relevance considering the risk of lymphatic and haematopoietic malignancies tentatively associated with styrene exposure.

Chromosome Aberrations↗

PubMed2006

The effects of GSTM1 and GSTT1 polymorphisms on micronucleus frequencies in human lymphocytes in vivo.

The influence of genetic polymorphisms in GSTM1 and GSTT1 genes on micronucleus frequencies in human peripheral blood lymphocytes was assessed through a pooled analysis of data from seven laboratories that did biomonitoring studies using the in vivo cytokinesis-block micronucleus assay. A total of 301 nonoccupationally exposed individuals (207 males and 94 females) and 343 workers (237 males and 106 females) occupationally exposed to known or suspected genotoxic substances were analyzed by Poisson regression. The results of the pooled analysis indicate that the GSTT1 null subjects had lower micronucleus frequencies than their positive counterparts in the total population (frequency ratio, 0.55; 95% confidence interval, 0.33-0.89). The protective effect of this genotype is reversed with increasing age, with a frequency ratio of 1.33 (95% confidence interval, 1.06-1.68) in subjects aged 60 years. A significant overall increase in micronucleus frequency with age and gender (P < 0.001 and P = 0.024, respectively) was observed, females having higher micronucleus frequencies than males, when occupationally exposed (P = 0.002). Nonoccupationally exposed smokers had lower micronucleus frequencies than nonsmokers (P = 0.001), whereas no significant difference in micronucleus level was observed between smokers and nonsmokers in the occupationally exposed group (P = 0.79). This study confirms that pooled analyses, by increasing the statistical power, are adequate for assessing the involvement of genetic variants on genome stability and for resolving discrepancies among individual studies.

Adolescent↗

PubMed2006

Biomarkers of exposure, effect, and susceptibility in workers exposed to nitrotoluenes.

Nitrotoluenes, such as 2-nitrotoluene, 2,4-dinitrotoluene (24DNT), and 26DNT, are carcinogenic in animal experiments. Humans are exposed to such chemicals in the workplace and in the environment. It is therefore important to develop methods to biomonitor people exposed to nitrotoluenes to prevent the potential harmful effects. For the present study, workers exposed to high levels of these chemicals were investigated. The external dose (air levels), the internal dose (urine metabolites), the biologically effective dose [hemoglobin (Hb) adducts and urine mutagenicity], and biological effects (chromosomal aberrations and health effects) were determined. Individual susceptibility was assessed by determining genetic polymorphisms of enzymes assumed to function in nitrotoluene metabolism, namely glutathione S-transferases (GSTM1, GSTT1, GSTP1), N-acetyltransferases (NAT1, NAT2), and sulfotransferases (SULT1A1, SULT1A2). The levels of urinary metabolites did not correlate with the air levels. The urinary mutagenicity levels determined in a subset of workers correlated with the levels of a benzylalcohol metabolite of DNT. The Hb-adducts correlated with the urine metabolites but not with the air levels. The frequency of chromosomal aberrations (gaps included) was increased (P < 0.05) in the exposed workers in comparison with a group of factory controls and correlated with the level of 24DNT Hb-adducts in young subjects (<31 years). The GSTM1-null genotype was significantly more prevalent in the controls than in the exposed group, which probably reflected an elevated susceptibility of the GSTM1-null genotype to adverse health effects of DNT exposure, such as nausea (odds ratio, 8.8; 95% confidence interval, 2.4-32.2). A statistically significant effect was seen for SULT1A2 genotype on a 24DNT Hb-adduct; GSTP1 genotype on a 2,4,6-trinitrotoluene Hb-adduct; and SULT1A1, SULT1A2, NAT1, GSTT1, and GSTP1 genotypes on chromosomal aberrations in the exposed workers.

Adult↗

PubMed2005

Influence of DNA repair gene polymorphisms on the yield of chromosomal aberrations.

We evaluated the influence of several DNA repair gene polymorphisms on the frequency of chromosomal aberrations (CAs) analyzed in peripheral lymphocytes, using the fluorescence in situ hybridization technique. The CA data were obtained from an earlier study of 84 healthy nonsmokers (48 women and 36 men) carefully characterized for indoor radon exposure. The frequency of translocations showed a wide interindividual variability, which was only partly explained by age. To investigate the potential role of DNA repair polymorphisms in this variation, genotypes of DNA repair genes OGG1 (codon 326), XPD (codon 751), XRCC1 (X-ray repair cross-complementing group 1) (codons 194, 280, and 399), and XRCC3 (X-ray repair cross-complementing group 3) (codon 241) were determined from leukocyte DNA using polymerase chain reaction-based methods. Negative binomial regression models were applied to evaluate the effect of the polymorphisms and other factors (age, gender, radon exposure, and medical exposure) on the frequency of CAs. No interactions between genotypes and radon, medical exposure, or gender were found. Carriers of the XRCC1 codon 280His variant allele had a two-fold increase (frequency ratio [FR] = 2.01, 95% confidence interval [CI] = 1.01-3.98; P = 0.046) in unstable exchanges (dicentrics and ring chromosomes). In addition, the XRCC3 codon 241 homozygous variant genotype (Met/Met) was associated with an increase (FR = 1.70, 95% CI = 1.06-2.74; P = 0.028) in two-way translocations when age was taken into account in the analysis. Our data suggest that the XRCC1 280His and XRCC3 241Met alleles affect individual CA levels, most probably via influencing the DNA repair phenotype.

Age Factors↗

PubMed2004

Genetic polymorphisms of DNA repair and xenobiotic-metabolizing enzymes: effects on levels of sister chromatid exchanges and chromosomal aberrations.

Elevated levels of chromosomal aberrations (CAs) in peripheral blood lymphocytes, widely used as a cytogenetic biomarker of genotoxic effects, have been linked to cancer predisposition. However, tobacco smoking, occupational carcinogen exposure, or time since CA analysis do not appear to explain the cancer predictivity of CAs. Alternatively, the observed CA-cancer association could reflect unidentified exposures or individual susceptibility. We assessed the effects of genetic polymorphisms of DNA repair proteins and xenobiotic-metabolizing enzymes (XMEs) on the levels of CAs and sister chromatid exchanges (SCEs) in peripheral lymphocytes of 145 (CAs) and 60 (SCEs) healthy Caucasians. Genotypes of DNA repair genes X-ray repair cross-complementation group 1 (XRCC1 codons 194, 280, 399) and 3 (XRCC3 codon 241 [corrected]), and XME genes glutathione-S-transferase (GST) M1 and T1 and N-acetyl transferase 2 (NAT2) were determined using polymerase chain reaction (PCR) and restriction fragment length polymorphism (RFLP)-based methods. After Poisson regression adjustment for age, sex, smoking, country, and genotypes, a higher frequency of chromosome-type breaks was observed for NAT2 slow acetylators (in nonsmokers) and GSTT1 null subjects (in smokers). Individuals carrying variant alleles for XRCC1 codons 280 and 194 showed a decreased level of chromosome-type breaks. The effect of GSTM1 null and XRCC1 codon 399 genotypes on the frequency of CAs was modified by smoking. In linear regression models adjusting for age, sex, smoking, and genotypes, none of the polymorphisms significantly affected SCE frequency, although GSTT1 null subjects had a slightly elevated SCE level. Our results are in line with earlier findings on the influence of NAT2, GSTT1, and GSTM1 polymorphisms on the level of lymphocyte chromosome damage and suggest that also XRCC1 polymorphism affects CA frequencies, thus apparently influencing DNA repair phenotype. It remains to be examined whether these or other genetic polymorphisms could explain the observed cancer risk predictivity of high CA frequency.

Adult↗

PubMed2004

Cytogenetic biomarkers and genetic polymorphisms.

Cytogenetic biomarkers have long been applied in surveillance of human genotoxic exposure and early effects of genotoxic carcinogens. Due to their wide use, it has been possible to evaluate, in international collaborative studies, if a high level of these biomarkers in peripheral lymphocytes is predictive of cancer risk. Thus far, such an association has been observed for chromosomal aberrations (CAs), but not for sister chromatid exchanges (SCEs) or micronuclei (MN). The cancer risk predictivity of CAs was not dependent on the time between CA analysis and cancer detection and did not appear to be explained by tobacco smoking or occupational exposure to carcinogens but was seen in unexposed non-smokers as well. This suggests a role for individual susceptibility factors. Genetic polymorphisms of various xenobiotic-metabolising enzymes, influencing the metabolic activation and detoxification of carcinogens, have been associated with cancer risk, and some of them also appear to affect cytogenetic biomarkers. The lack of glutathione S-transferase M1 (GSTM1 null genotype) is associated with increased sensitivity to genotoxicity of tobacco smoke, and GSTM1 null smokers also show an increased frequency of CAs and SCEs. N-Acetyltransferase (NAT2) slow acetylation genotype and glutathione S-transferase T1 (GSTT1) null genotype seem to elevate the baseline level of CAs and SCEs and CAs, respectively--possibly because of reduced capacity to detoxify some wide-spread or endogenous genotoxins. For some chemicals, in vitro cytogenetic studies with lymphocyte donors representing different genotypes have been able to predict a differential in vivo response. For instance, in vitro SCE induction by styrene and by epoxide metabolites of 1,3-butadiene is modified by GSTM1 and GSTT1 genotypes--which also influence the excretion of specific mercapturic acids in humans exposed to butadiene and styrene. Polymorphisms of DNA repair and folate metabolism are expected to be of special importance in modulating genotoxic effects. Some evidence exists for the effects of X-ray cross complementation group 1 (XRCC1) codon 280 and (in smokers) Xeroderma pigmentosum group D (XPD) codon 23 polymorphisms on baseline CAs, for XRCC1 codon 399 polymorphism on SCEs in smokers, and for methylene tetrahydrofolate reductase (MTHFR) codon 677 and methionine synthase reductase (MTRR) polymorphisms on spontaneous MN.

Animals↗

PubMed2004

Impact of types of lymphocyte chromosomal aberrations on human cancer risk: results from Nordic and Italian cohorts.

The frequency of cells with structural chromosomal aberrations (CAs) in peripheral blood lymphocytes is the first genotoxicity biomarker that has shown an association with cancer risk. CAs are usually divided into chromosome-type (CSAs) and chromatid-type aberrations (CTAs), with different mechanisms of formation. From a mechanistic point of view, it is of interest to clarify whether the cancer predictivity of CAs is different with respect to CSAs and CTAs. We report here cancer risk for cytogenetically tested, healthy subjects with respect to frequency of CAs, CSAs, and CTAs in peripheral blood lymphocytes, using Nordic (1981 subjects with CA data, 1871 subjects with CSA/CTA data) and Italian (1573 subjects with CA data, 877 subjects with CTA/CSA data) cohorts, with a median follow-up of 17 years. High levels of CAs at test were clearly associated with increased total cancer incidence in the Nordic cohorts and increased total cancer mortality in the Italian cohort. In the Nordic cohorts, significantly elevated cancer risks were observed for subjects with both high CSAs and high CTAs at test, and these variables showed equally strong cancer predictivity. The results of the Italian cohort did not indicate any clear-cut difference in cancer predictivity between the CSA and CTA biomarkers. There was no significant effect modification by age at test, gender, country, or time since test. The results suggest that both DNA double-strand breaks and other initial DNA lesions responsible for CSAs and CTAs are associated with cancer risk.

Chromatids↗

PubMed2004

Genetic polymorphisms in DNA repair genes and possible links with DNA repair rates, chromosomal aberrations and single-strand breaks in DNA.

We analysed the associations between genetic polymorphisms in genes coding for DNA repair enzymes XPD (exon 23 A --> C, K751Q), XPG (exon 15 G --> C, D1104H), XPC (exon 15 A --> C, K939Q), XRCC1 (exon 10 G --> A, R399Q) and XRCC3 (exon 7 C --> T, T241 M) and the levels of chromosomal aberrations (CAs) and single-strand breaks (SSBs) in peripheral lymphocytes in a central European population. We also measured the irradiation-specific DNA repair rates and the repair rates of 8-oxoguanines in these individuals. An elevated frequency of CAs was observed in individuals with the XPD exon 23 A allele (AA and AC) genotypes (F = 3.6, P = 0.028, ANOVA). In multifactorial analysis of variance, the XPD exon 23 polymorphism appeared as a major factor influencing CAs (F = 4.2, P = 0.017). SSBs in DNA, on the other hand, were modulated by XPD (F = 4.3, P = 0.023), XPG (F = 4.3, P = 0.024) and XRCC1 genotypes (F = 3.0, P = 0.064). Irradiation-specific DNA repair rates (reflecting mainly base excision repair activity) were affected by XRCC1 (F = 5.9, P = 0.010) and XPC polymorphisms (F = 4.2, P = 0.046, MANOVA). Our results from this study suggest that markers of genotoxicity are associated with polymorphisms in genes encoding DNA repair enzymes.

Adult↗

PubMed2004

Markers of individual susceptibility and DNA repair rate in workers exposed to xenobiotics in a tire plant.

Workers employed in tire plants are exposed to a variety of xenobiotics, such as 1,3-butadiene (BD), soots containing polycyclic aromatic hydrocarbons, and other organic chemicals (e.g., styrene). In the present study, we investigated markers of genotoxicity [chromosomal aberrations (CAs) and single-strand breaks (SSBs)] in a cohort of 110 tire plant workers engaged in jobs with different levels of xenobiotic exposure in relation to various polymorphisms in genes coding for biotransformation enzymes (CYP1A1, CYP2E1, EPHX1, GSTM1, GSTP1, and GSTT1) and in genes involved in DNA repair (XPD exon 23, XPG exon 15, XPC exon 15, XRCC1 exon 10, and XRCC3 exon 7). In addition, the expression of CYP2E1, a gene playing a key role in BD metabolism, was determined by real-time PCR in peripheral blood lymphocytes, and the capacity of lymphocytes to repair gamma-ray-induced SSBs and to convert 8-oxoguanine in HeLa cell DNA into SSBs was assessed using in vitro assays. No positive associations were detected between the CA frequency or SSB induction and levels of workplace exposure; however, a nonsignificant twofold higher irradiation-specific DNA repair rate was found among highly exposed workers. In evaluations conducted with the markers of individual susceptibility, workers with low-EPHX1-activity genotypes exhibited a significantly higher CA frequency as compared to those with medium and high-EPHX1-activity genotypes (P = 0.050). CA frequencies were significantly lower in individuals homozygous for the XPD exon 23 variant allele in comparison to those with the wild-type CC genotype (P = 0.003). Interestingly, CAs were higher in individuals with higher CYP2E1 expression levels, but the association was nonsignificant (P = 0.097). The results from this study suggest the importance of evaluating markers of individual susceptibility, since they may modulate genotoxic effects induced by occupational exposure to xenobiotics.

Adult↗

PubMed2004

DNA damage in bronchial epithelial and mesothelial cells with and without associated crocidolite asbestos fibers.

Mesothelioma is induced almost exclusively by exposure to asbestos fibers. We have investigated whether the induction of DNA damage in human bronchial epithelial BEAS 2B cells and human mesothelial MeT 5A cells by crocidolite asbestos (2 microg/cm2) requires the presence of asbestos fibers in the cells. DNA damage was measured microscopically by the Comet assay, and the presence of fibers in the same cells was assessed using bright-field illumination. After treatment times of 6-72 hr, damage levels were, on the average, two times higher in cells with fibers than in cells without fibers. It was further found that DNA damage decreased with time in BEAS 2B cells both with and without fibers. No decrease in damage with time was seen in MeT 5A cells, suggesting that these mesothelial cells repair the initial damage poorly, lack induction of protective systems, or constantly produce high levels of damaging species. Our results indicate that crocidolite-treated human mesothelial MeT 5A and bronchial epithelial BEAS 2B cells show an elevated level of DNA damage if they contain a fiber. In comparison with epithelial BEAS 2B cells, mesothelial MeT 5A cells have more DNA damage after the crocidolite treatment and the damage is more persistent.

Apoptosis↗

PubMed2004

Cytogenetic markers, DNA single-strand breaks, urinary metabolites, and DNA repair rates in styrene-exposed lamination workers.

The effect of occupational exposure to styrene on frequencies of chromosomal aberrations and binucleated cells with micronuclei and on single-strand break levels in peripheral blood lymphocytes was studied in 86 reinforced plastic workers and 42 control individuals (including 16 maintenance workers with intermittent, low-dose exposure). In these individuals, the irradiation-specific DNA repair rates and the repair rates of 8-oxoguanines were investigated. We assessed the exposure by measuring the concentrations of styrene in air and in blood and of mandelic acid, phenylglyoxylic acid, 4-vinyl phenol conjugates and regioisomeric phenyl hydroxyethyl mercapturic acids in urine. All these parameters correlated with one another. No clear relationship was found between the styrene exposure and the frequencies of chromosomal aberrations. Binucleated cells with micronuclei were moderately related to the parameters of styrene exposure. We found a negative correlation between all exposure parameters and single-strand breaks. The positive correlation between exposure parameters and DNA repair rates suggests that particular DNA repair pathways may be induced by styrene exposure.

Adult↗

PubMed2004

Cytogenetic biomarkers.

Cytogenetic biomarkers in peripheral blood lymphocytes such as chromosomal aberrations, sister chromatid exchanges and micronuclei have long been applied in surveillance of human genotoxic exposure and early effects of genotoxic carcinogens. The use of these biomarker assays is based on the fact that most established human carcinogens are genotoxic in short-term tests and capable of inducing chromosomal damage. The relevance of chromosomal aberrations as a biomarker has been further emphasized by epidemiological studies suggesting that a high frequency of chromosomal aberrations is predictive of an increased risk of cancer. Structural and numerical chromosomal aberrations are typical of cancer cells, probably as a manifestation of genetic instability of such cells, but may also represent mechanisms leading to such instability. The frequency of all three biomarkers increases with age, and this effect is particularly clear for micronuclei in women. Tobacco smoking is known to increase the level of sister chromatid exchanges and chromosomal aberrations, but its effect on micronuclei is unclear. Several studies have recently examined the influence of genetic polymorphisms of xenobiotic metabolizing enzymes on cytogenetic biomarkers. The lack of glutathione S-transferase M1 (GSTM1 null genotype) appears to be associated with increased sensitivity to genotoxicity of tobacco smoking. N-Acetyltransferase (NAT2) slow acetylation genotypes seem to elevate baseline level of chromosomal aberrations, whereas deletion of glutathione S-transferase T1 gene (GSTT1 null genotype) has been found to yield an increase in baseline sister chromatid exchange frequency. These findings may be explained by reduced detoxification capacity rendered by the altered gene and may be linked with exposure to, for example, heterocyclic amines in the case of NAT2 and endogenously formed ethylene oxide in the case of GSTT1. Recently discovered polymorphisms affecting DNA repair may be expected to be of special importance in modulating genotoxic effects, but, as yet, there is very little information about the significance of these polymorphisms or about their impact on cytogenetic biomarkers.

Biomarkers↗

PubMed2003

Report from the in vitro micronucleus assay working group.

UNLABELLED: At the Washington "2nd International Workshop on Genotoxicity Testing" (25-26 March 1999) current methodologies and data for the in vitro micronucleus test were reviewed. As a result, guidelines for the conduct of specific aspects of the protocol were developed. Agreement was achieved on the following topics: choice of cells, slide preparation, analysis of micronuclei, toxicity, use of cytochalasin-B, number of doses, and treatment/harvest times [Environ. Mol. Mutagen. 35 (2000) 167]. Because there were a number of important in vitro micronucleus validation studies in progress, it was not possible to design a definitive, internationally harmonized protocol at that time. These studies have now been completed and the data were reviewed at the Plymouth "3rd International Workshop on Genotoxicity Testing" (28-29 June 2002). Data from studies coordinated by the French Society of Genetic Toxicology, Japanese collaborative studies, European pharmaceutical industry validation studies, along with data from Lilly Research Laboratories were used to prepare conclusions on the main aspects of the in vitro micronucleus protocol. In this paper, the consensus agreements on the protocol for performing the in vitro micronucleus assay are presented. The major recommendations concern: 1. Demonstration of cell proliferation: both cell lines and lymphocytes can be used, but demonstration of cell proliferation in both control and treated cells is compulsory for the acceptance of the test. 2. Assessment of toxicity and dose range finding: assessment of toxicity should be performed by determining cell proliferation, e.g. increased cell counts (CC) or population doubling (PD) without cytochalasin-B, or e.g. cytokinesis-block proliferation index with cytochalasin-B; and by determining other markers for cytotoxicity (confluency, apoptosis, necrosis) which can provide valuable additional information. 3. Treatment schedules for cell lines and lymphocytes. 4. Choice of positive controls: without S9-mix both a clastogen (e.g. mitomycin C or bleomycin) and an aneugen (e.g. colchicine) should be included as positive controls and a clastogen that requires S9 for activity when S9-mix is used (e.g. dimethylnitrosamine, or cyclophosphamide in those cell types that cannot activate this agent directly). 5. Duplicate cultures and number of cells to be scored. 6. Repeat experiments: in lymphocytes, for each experiment blood from 2 different healthy young and non-smoking donors should be compared. In cell lines, the experiments need only to be repeated if the first one is negative. 7. STATISTICS: statistical significance should not be the sole factor for determining positive results. Biological meaning should serve as a guideline. Examples of statistical analyses are given.

Animals↗

PubMed2003

Genetic susceptibility, biomarker respones, and cancer.

A large number of studies have reported associations between polymorphisms of xenobiotic-metabolizing enzymes (XMEs) and various cancers. However, the carcinogenic exposures behind such findings have usually been unclear. Information on susceptibility to specific carcinogens could better be obtained by examining situations where the exposure and the endpoint studied are nearer in time, i.e., by studying biomarkers of carcinogen exposure and early (genotoxic) effect in exposed humans. For example, analyses of DNA adducts and cytogenetic endpoints have indicated an increased susceptibility of glutathione S-transferase M1 (GSTM1) null genotype to genotoxicity of tobacco smoking, supporting the view that the associations of the GSTM1 null genotype with bladder and lung cancer are partly related to smoking. In vitro genotoxicity studies with human cells offer an experimental tool that can be used, within the limits of the cell systems, to predict individual sensitivity and genotype-carcinogen interactions. In vitro sensitivity to the genotoxicity of 1,2:3,4-diepoxybutane, an epoxide metabolite of 1,3-butadiene has clearly been shown to depend on GSTT1 genotype, which has also been implicated to modify, along with GSTM1 genotype, the in vitro genotoxicity of 1,2-epoxy-3-butene, another epoxide metabolite of 1,3-butadiene. These genotypes appear to modulate the excretion of 1,3-butadiene-specific mercapturic acids, and influence genotoxicity biomarker levels in 1,3-butadiene-exposed workers. The excretion of specific mercapturic acids (PHEMA) in workers exposed to styrene has clearly been shown to depend on GSTM1 genotype, and GSTT1 genotype seems to modulate the excretion of one PHEMA diastereoisomer. These genotypes have also been implicated to modulate the in vitro genotoxicity of styrene. In general, the genetic polymorphisms potentially important for biomarker response largely depend on the exposing agent, biological material examined, and ethnicity of the population under study. Individual exposure level may vary a lot, and a reliable estimate of the exposure is essential for correct interpretation of genotype-exposure interaction. Besides XME polymorphisms, any polymorphisms that affect cellular response to DNA damage could, in principle, modify individual sensitivity to genotoxins. For instance, those concerning DNA repair proteins are presently being studied by many laboratories.

Biomarkers↗