Micronuclei in neonates and children: effects of environmental, genetic, demographic and disease variables.

Children may be more susceptible to the effects of the environmental exposure and medical treatments than adults; however, limited information is available about the differences in genotoxic effects in children by age, sex and health status. Micronucleus (MN) assay is a well established method of monitoring genotoxicity, and this approach is thoroughly validated for adult lymphocytes by the Human Micronucleus Biomonitoring project (HUMN.org). Similar international undertaking is in progress for exfoliated buccal cells. Most of the MN studies in children are focused on analyses of lymphocytes but in the recent years, more investigators are interested in using exfoliated cells from the oral cavity and other cell types that can be collected non-invasively, which is particularly important in paediatric cohorts. The baseline MN frequency is relatively low in newborns and its assessment requires large cohorts and cell sample counts. Available results are mostly consistent in conclusion that environmental pollutants and radiation exposures lead to the increase in the MN frequency in children. Effects of medical treatments are less clear, and more studies are needed to optimise the doses and minimise genotoxicity without compromising therapy outcomes. Despite the recent progress in MN assay in children, more studies are warranted to establish the relationship between MN in lymphocytes and exfoliated cells, to clarify sex, age and genotype differences in baseline MN levels and the changes in response to genotoxicants. One of the most important types of MN studies in children are prospective cohorts that will help to clarify the predictive value of MN and other cytome end points for cancer and other chronic diseases of childhood and adulthood. Emerging 'omic' and other novel molecular technologies may shed light on the molecular mechanisms and biological pathways associated with the MN levels in children.

Chromosomal aberration frequency in lymphocytes predicts the risk of cancer: results from a pooled cohort study of 22 358 subjects in 11 countries.

Mechanistic evidence linking chromosomal aberration (CA) to early stages of cancer has been recently supported by the results of epidemiological studies that associated CA frequency in peripheral lymphocytes of healthy individuals to future cancer incidence. To overcome the limitations of single studies and to evaluate the strength of this association, a pooled analysis was carried out. The pooled database included 11 national cohorts and a total of 22 358 cancer-free individuals who underwent genetic screening with CA for biomonitoring purposes during 1965-2002 and were followed up for cancer incidence and/or mortality for an average of 10.1 years; 368 cancer deaths and 675 incident cancer cases were observed. Subjects were classified within each laboratory according to tertiles of CA frequency. The relative risk (RR) of cancer was increased for subjects in the medium [RR = 1.31, 95% confidence interval (CI) = 1.07-1.60] and in the high (RR = 1.41; 95% CI = 1.16-1.72) tertiles when compared with the low tertile. This increase was mostly driven by chromosome-type aberrations. The presence of ring chromosomes increased the RR to 2.22 (95% CI = 1.34-3.68). The strongest association was found for stomach cancer [RR(medium) = 1.17 (95% CI = 0.37-3.70), RR(high) = 3.13 (95% CI = 1.17-8.39)]. Exposure to carcinogens did not modify the effect of CA levels on overall cancer risk. These results reinforce the evidence of a link between CA frequency and cancer risk and provide novel information on the role of aberration subclass and cancer type.

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.

Children's exposure to environmental pollutants and biomarkers of genetic damage. II. Results of a comprehensive literature search and meta-analysis.

The present review is based on findings from 178 publications retrieved through an extensive search of the MedLine/PubMed database for a 25 years time period (1980-2004) and 10 manually identified papers. Among the cytogenetic biomarkers that are frequently used in field studies, chromosome aberrations (CA) and micronuclei (MN) but not sister chromatid exchanges (SCE) were found consistently increased in children exposed to environmental pollutants. Meta-analysis of the studies reporting SCE in cord blood showed similar levels of SCE in exposed and in non-exposed newborns. Exposure to airborne pollutants, soil and drinking water contaminants, mostly increased CA and, to a lesser extent, MN levels in children. The effect of exposure to airborne urban pollutants was consistently reported by field studies measuring DNA, albumin and hemoglobin adducts. Prenatal (in utero) and postnatal exposure (environmental tobacco smoke, ETS) to tobacco smoke compounds were associated with increased frequencies of DNA and hemoglobin adducts and CA. The limited number of field studies measuring DNA fragmentation (Comet assay), hypoxanthine-guanine phosphoribosyltransferase (HPRT) and the glycophorinA (GPA) mutation frequency in environmentally exposed children precluded a meaningful evaluation of the usefulness of these assays. Meta-analyses performed in children exposed to ETS and in newborns exposed in utero to their mothers' smoke showed 1.3 and 7 times higher levels of hemoglobin adducts compared to referent subjects, respectively. These increases are consistent with the epidemiological evidence of higher lung cancer risks reported in adults who had never smoked and were exposed to ETS during childhood and with 7-15 times higher lung cancer risks reported in smokers than in non-smokers. Higher levels of PAH-DNA adducts were found in fetal than in maternal tissue, suggesting a specific susceptibility of the fetus to this class of ubiquitous environmental pollutants. According to these findings, future research and biomonitoring programs on children would greatly benefit from the inclusion of selected biomarkers that could provide biologically based evidence for the identification of intervention priorities in environmental health.