Germ cell mutagens: risk assessment challenges in the 21st century

Maternal smoking during pregnancy and birthweight on the third generation: results from two birth cohort studies

The purpose of this research is to investigate whether grandmother's smoking during pregnancy reduces the grandchildren's birthweight and whether maternal smoking during pregnancy modified this association. We also evaluated the effect of duration and intensity of smoking. This study included data from three generations from two birth cohorts carried out in Pelotas, a southern Brazilian city: women enrolled in the perinatal study in the 1982 and 1993 cohorts (G1); daughters (G2) of those G1 mothers who were followed to adulthood; and first children (G3) born from G2 women. Information on maternal smoking during pregnancy was obtained from women (G1) shortly after delivery of the two cohorts and from G2 in the follow-up in adulthood of the 1993 cohort. Mothers (G2) reported G3 birthweight during the follow-up visit at adulthood. Multiple linear regression was used to obtain effect measures adjusted for confounders. The study included 1602 grandmothers (G1), mothers (G2), and grandchildren (G3). Prevalence of maternal (G1) smoking during pregnancy was 43% and mean G3 birthweight was 3118.9 g (SD: 608.8). Grandmother's smoking in the pregnancy was not associated with grandchild's birthweight. However, offspring of both G1 and G2 smokers had lower mean birthweight than those whose mother and grandmother did not smoke (adjusted β: - 223.05; 95% CI: - 415.16, - 32.76).

CONCLUSION

No significant association was observed between grandmother's smoking in the pregnancy and grandchild's birthweight. But it seems that grandmother's smoking in pregnancy has an effect on grandchild's birthweight when the mother also smoked in the pregnancy. .

WHAT IS KNOWN

• Most studies on the association of maternal tobacco smoking in pregnancy with offspring birthweight have been restricted to two generations, and an inverse association is well known.

WHAT IS NEW

• Besides to investigate whether grandmother's smoking during pregnancy reduces the grandchildren's birthweight, we examined whether this association varied according to maternal smoking during pregnancy.

Assessing testicular germ cell DNA damage in the comet assay; introduction of a proof-of-concept

The in vivo comet assay is widely used to measure genotoxicity; however, the current OECD test guideline (TG 489) does not recommend using the assay to assess testicular germ cells, due to the presence of testicular somatic cells. An adapted approach to specifically assess testicular germ cells within the comet assay is certainly warranted, considering regulatory needs for germ cell-specific genotoxicity data in relation to the increasing global production of and exposure to potentially hazardous chemicals. Here, we provide a proof-of-concept to selectively analyze round spermatids and primary spermatocytes, distinguishing them from other cells of the testicle. Utilizing the comet assay recordings of DNA content (total fluorescence intensity) and DNA damage (% tail intensity) of individual comets, we developed a framework to distinguish testicular cell populations based on differences in DNA content/ploidy and appearance. Haploid round spermatid comets are identified through (1) visual inspection of DNA content distributions, (2) setting DNA content thresholds, and (3) modeling DNA content distributions using a normal mixture distribution function. We also describe an approach to distinguish primary spermatocytes during comet scoring, based on their high DNA content and large physical size. Our concept allows both somatic and germ cells to be analyzed in the same animal, adding a versatile, sensitive, rapid, and resource-efficient assay to the limited genotoxicity assessment toolbox for germ cells. An adaptation of TG 489 facilitates accumulation of valuable information regarding distribution of substances to germ cells and their potential for inducing germ cell gene mutations and structural chromosomal aberrations.

Multiple generation exposure to ZnO nanoparticles induces loss of genomic integrity in Caenorhabditis elegans

Zinc oxide nanoparticles (ZnO NPs) are commonly used in industrial and household applications, prompting the assessment of their associated health risks. Previous studies indicated that ZnO NPs can induce somatic cell mutations, while the aging process appears to increase the mutagenicity of ZnO NPs. However, little is known about the influence of ZnO NPs on genome stability of germ cells, and non-exposed progeny. Here we show that 20 nm ZnO NPs exposure disrupts germ cell development, and elevates the overall mutation frequency of germ cells in Caenorhabditis elegans (C. elegans). We observed that pristine ZnO NPs elicit germ cell apoptosis to a greater extent than the 60-day aged ZnO NPs. By treating parental worms with ZnO NPs for seven successive generations, whole-genome sequencing data revealed that, although the frequency of point mutations is kept unchanged, large deletions are significantly increased in F8 worms. Furthermore, we found that the mutagenicity of ZnO NPs might be partially attributed to the release of Zn²⁺ ions. Together, our results demonstrate the genotoxic effects of ZnO NPs on germ cells, and the possible underlying mechanism. These findings suggest that germ cell mutagenicity is worthy of consideration for the health risk assessment of engineered NPs.

Whole-Genome Sequencing Reveals Germ Cell Mutagenicity of α-Endosulfan in Caenorhabditis elegans

Endosulfan is an extensively used organochlorine pesticide around the world, which was classified as a persistent organic pollutant (POP) in 2009. Although previous studies have documented the reproductive toxicity of endosulfan in a variety of organisms, little is known about the influence of endosulfan on the genome stability of germ cells and nonexposed progeny. Here we applied whole-genome sequencing to explore the germ cell mutagenicity of α-endosulfan in Caenorhabditis elegans (C. elegans). We found that, although low doses of α-endosulfan exhibited a minor effect on the reproductive capacity of C. elegans, chronic exposure to 1 μM α-endosulfan significantly increased the mutation frequencies of nonexposed progeny. Further analysis of genome-wide mutation spectra demonstrated that α-endosulfan preferentially elicited A:T → G:C substitutions and clustered mutations. By using worms deficient in DNA damage response genes, our results suggest the involvement of translesion synthesis polymerase η in modulating α-endosulfan-induced mutations in germ cells. Together, these observations reveal the germ cell mutagenicity of α-endosulfan in C. elegans and the possible underlying mechanism. In addition, our findings implicate that germ cell mutagenicity might be a necessary consideration for the health risk assessment of environmental chemicals such as POPs.

A Return to the Origin of the EMGS: Rejuvenating the Quest for Human Germ Cell Mutagens and Determining the Risk to Future Generations

Fifty years ago, the Environmental Mutagen Society (now Environmental Mutagenesis and Genomics Society) was founded with a laser-focus on germ cell mutagenesis and the protection of "our most vital assets"-the sperm and egg genomes. Yet, five decades on, despite the fact that many agents have been demonstrated to induce inherited changes in the offspring of exposed laboratory rodents, there is no consensus on whether human germ cell mutagens exist. We argue that it is time to reevaluate the available data and conclude that we already have evidence for the existence of environmental exposures that impact human germ cells. What is missing are definite data to demonstrate a significant increase in de novo mutations in the offspring of exposed parents. We believe that with over two decades of research advancing knowledge and technologies in genomics, we are at the cusp of generating data to conclusively show that environmental exposures cause heritable de novo changes in the human offspring. We call on the research community to harness our technologies, synergize our efforts, and return to our Founders' original focus. The next 50 years must involve collaborative work between clinicians, epidemiologists, genetic toxicologists, genomics experts and bioinformaticians to precisely define how environmental exposures impact germ cell genomes. It is time for the research and regulatory communities to prepare to interpret the coming outpouring of data and develop a framework for managing, communicating and mitigating the risk of exposure to human germ cell mutagens. Environ. Mol. Mutagen. 61:42-54, 2020. © 2019 Her Majesty the Queen in Right of Canada.

DNA Copy Number Variations as Markers of Mutagenic Impact

DNA copy number variation (CNV) occurs due to deletion or duplication of DNA segments resulting in a different number of copies of a specific DNA-stretch on homologous chromosomes. Implications of CNVs in evolution and development of different diseases have been demonstrated although contribution of environmental factors, such as mutagens, in the origin of CNVs, is poorly understood. In this review, we summarize current knowledge about mutagen-induced CNVs in human, animal and plant cells. Differences in CNV frequencies induced by radiation and chemical mutagens, distribution of CNVs in the genome, as well as adaptive effects in plants, are discussed. Currently available information concerning impact of mutagens in induction of CNVs in germ cells is presented. Moreover, the potential of CNVs as a new endpoint in mutagenicity test-systems is discussed.

Dose-response mutation and spectrum analyses reveal similar responses at two microsatellite loci in benzo(a)pyrene-exposed mouse spermatogonia

Identifying chemical exposures that can cause germline mutations is important as these mutations can be inherited, impacting both individual and population health. However, germline mutations are extremely rare and difficult to detect. Chemically induced germline mutations can be detected through analysis of highly unstable tandem repeat DNA. We recently developed a single-molecule PCR (SM-PCR) approach to quantify mutations at a mouse microsatellite locus (Mm2.2.1) in sperm for such purposes. In this study, we refine this approach through the combined analysis of mouse microsatellites Mm2.2.1 and Mm19.2.3. Mice were exposed to 0, 25, 50 or 100 mg/kg/day benzo(a)pyrene (BaP) by oral gavage for 28 days and sperm sampled 42 days after the end of exposure to measure effects on dividing spermatogonia. DNA was diluted to a single genome per PCR well for amplification of microsatellites in singleplex and multiplex reactions, and alleles were sized to identify mutations using capillary electrophoresis. Analysis of ~300-500 molecules per animal at both microsatellite loci, when tested individually, showed a ~2-fold increase in mutations relative to the controls at both the 50 and 100 mg/kg/day BaP doses. Multiplex SM-PCR revealed similar increases in mutation frequencies in both microsatellites. Comparison with results from a previous lacZ mutation assay conducted on the same mice revealed that although microsatellite mutations are a sensitive endpoint for detecting changes in mutation frequencies at lower doses, they appear to be saturable and thus have a reduced dynamic range. These results confirm that BaP is a male germ cell mutagen that broadly impacts tandem repeat DNA. Likewise, addition of a second hypervariable microsatellite increases the sensitivity of this assay.

Applying the erythrocyte Pig-a assay concept to rat epididymal sperm for germ cell mutagenicity evaluation

The Pig-a assay, a recently developed in vivo somatic gene mutation assay, is based on the identification of mutant erythrocytes that have an altered repertoire of glycosylphosphatidylinositol (GPI)-anchored cell surface markers. We hypothesized that the erythrocyte Pig-a assay concept could be applied to rat cauda epididymal spermatozoa (sperm) for germ cell mutagenicity evaluation. We used GPI-anchored CD59 as the Pig-a mutation marker and examined the frequency of CD59-negative sperm using flow cytometry. A reconstruction experiment that spiked un-labeled sperm (mutant-mimic) into labeled sperm at specific ratios yielded good agreement between the detected and expected frequencies of mutant-mimic sperm, demonstrating the analytical ability for CD59-negative sperm detection. Furthermore, this methodology was assessed in F344/DuCrl rats administered N-ethyl-N-nitrosourea (ENU), a prototypical mutagen, or clofibrate, a lipid-lowering drug. Rats treated with 1, 10, or 20 mg/kg body weight/day (mkd) ENU via daily oral garage for five consecutive days showed a dose-dependent increase in the frequency of CD59-negative sperm on study day 63 (i.e., 58 days after the last ENU dose). This ENU dosing regimen also increased the frequency of CD59-negative erythrocytes. In rats treated with 300 mkd clofibrate via daily oral garage for consecutive 28 days, no treatment-related changes were detected in the frequency of CD59-negative sperm on study day 85 (i.e., 57 days after the last dose) or in the frequency of CD59-negative erythrocytes on study day 29. In conclusion, these data suggest that the epidiymal sperm Pig-a assay in rats is a promising method for evaluating germ cell mutagenicity. Environ. Mol. Mutagen. 58:485-493, 2017. © 2017 Wiley Periodicals, Inc.

Use of genetic toxicity data in GHS mutagenicity classification and labeling of substances

One of the key outcomes of testing the potential genotoxicity or mutagenicity of a substance is the conclusion on whether the substance should be classified as a germ cell mutagen and the significance of this for other endpoints such as carcinogenicity. The basis for this conclusion are the criteria presented in classification and labelling systems such as the Globally Harmonized System for classification and labeling (GHS). This article reviews the classification criteria for germ cell mutagenicity and carcinogenicity and how they are applied to substances with evidence of mutagenicity. The implications and suitability of such a classification for hazard communication, risk assessment, and risk management are discussed. It is proposed that genotoxicity assessments should not focus on specifically identifying germ cell mutagens, particularly given the challenges associated with communicating this information in a meaningful way. Rather the focus should be on deriving data to characterize the mode of action and for use in the risk assessment of mutagens, which could then feed into a more robust, risk based management of mutagenic substances versus the current more hazard based approaches. Environ. Mol. Mutagen. 58:354-360, 2017. © 2017 Wiley Periodicals, Inc.

Development of the adverse outcome pathway "alkylation of DNA in male premeiotic germ cells leading to heritable mutations" using the OECD's users' handbook supplement

The Organisation for Economic Cooperation and Development's (OECD) Adverse Outcome Pathway (AOP) programme aims to develop a knowledgebase of all known pathways of toxicity that lead to adverse effects in humans and ecosystems. A Users' Handbook was recently released to provide supplementary guidance on AOP development. This article describes one AOP-alkylation of DNA in male premeiotic germ cells leading to heritable mutations. This outcome is an important regulatory endpoint. The AOP describes the biological plausibility and empirical evidence supporting that compounds capable of alkylating DNA cause germ cell mutations and subsequent mutations in the offspring of exposed males. Alkyl adducts are subject to DNA repair; however, at high doses the repair machinery becomes saturated. Lack of repair leads to replication of alkylated DNA and ensuing mutations in male premeiotic germ cells. Mutations that do not impair spermatogenesis persist and eventually are present in mature sperm. Thus, the mutations are transmitted to the offspring. Although there are some gaps in empirical support and evidence for essentiality of the key events for certain aspects of this AOP, the overall AOP is generally accepted as dogma and applies broadly to any species that produces sperm. The AOP was developed and used in an iterative process to test and refine the Users' Handbook, and is one of the first publicly available AOPs. It is our hope that this AOP will be leveraged to develop other AOPs in this field to advance method development, computational models to predict germ cell effects, and integrated testing strategies.

Approaches for identifying germ cell mutagens: Report of the 2013 IWGT workshop on germ cell assays(☆)

This workshop reviewed the current science to inform and recommend the best evidence-based approaches on the use of germ cell genotoxicity tests. The workshop questions and key outcomes were as follows. (1) Do genotoxicity and mutagenicity assays in somatic cells predict germ cell effects? Limited data suggest that somatic cell tests detect most germ cell mutagens, but there are strong concerns that dictate caution in drawing conclusions. (2) Should germ cell tests be done, and when? If there is evidence that a chemical or its metabolite(s) will not reach target germ cells or gonadal tissue, it is not necessary to conduct germ cell tests, notwithstanding somatic outcomes. However, it was recommended that negative somatic cell mutagens with clear evidence for gonadal exposure and evidence of toxicity in germ cells could be considered for germ cell mutagenicity testing. For somatic mutagens that are known to reach the gonadal compartments and expose germ cells, the chemical could be assumed to be a germ cell mutagen without further testing. Nevertheless, germ cell mutagenicity testing would be needed for quantitative risk assessment. (3) What new assays should be implemented and how? There is an immediate need for research on the application of whole genome sequencing in heritable mutation analysis in humans and animals, and integration of germ cell assays with somatic cell genotoxicity tests. Focus should be on environmental exposures that can cause de novo mutations, particularly newly recognized types of genomic changes. Mutational events, which may occur by exposure of germ cells during embryonic development, should also be investigated. Finally, where there are indications of germ cell toxicity in repeat dose or reproductive toxicology tests, consideration should be given to leveraging those studies to inform of possible germ cell genotoxicity.

Transgenic rodent assay for quantifying male germ cell mutant frequency

De novo mutations arise mostly in the male germline and may contribute to adverse health outcomes in subsequent generations. Traditional methods for assessing the induction of germ cell mutations require the use of large numbers of animals, making them impractical. As such, germ cell mutagenicity is rarely assessed during chemical testing and risk assessment. Herein, we describe an in vivo male germ cell mutation assay using a transgenic rodent model that is based on a recently approved Organisation for Economic Co-operation and Development (OECD) test guideline. This method uses an in vitro positive selection assay to measure in vivo mutations induced in a transgenic λgt10 vector bearing a reporter gene directly in the germ cells of exposed males. We further describe how the detection of mutations in the transgene recovered from germ cells can be used to characterize the stage-specific sensitivity of the various spermatogenic cell types to mutagen exposure by controlling three experimental parameters: the duration of exposure (administration time), the time between exposure and sample collection (sampling time), and the cell population collected for analysis. Because a large number of germ cells can be assayed from a single male, this method has superior sensitivity compared with traditional methods, requires fewer animals and therefore much less time and resources.

Chemical and biological work-related risks across occupations in Europe: a review

BACKGROUND

Work-related health inequalities are determined to some extent by an unequal exposure to chemical and biological risk factors of disease. Although their potential economic burden in the European Union (EU-25) might be substantial, comprehensive reviews focusing on the distribution of these risks across occupational groups are limited. Thus, the main objective of this review is to provide a synopsis of the exposure to chemical and biological hazards across occupational groups. In addition, main industrial applications of hazardous substances are identified and some epidemiological evidence is discussed regarding societal costs and incidence rates of work-related diseases.

METHODS

Available lists of carcinogens, sensitisers, mutagens, reprotoxic substances and biological hazards were consulted. For each work-related hazard the main industrial application was identified in order to assess which ISCO occupational groups may be associated with direct exposure. Where available, information on annual tonnage production, risk assessment of the substances and pathogens, and other relevant data were collected and reported.

RESULTS

Altogether 308 chemical and biological hazards were identified which may account to at least 693 direct exposures. These hazards concentrate on the following major occupational groups: technicians (ISCO 3), operators (ISCO 8), agricultural workers (ISCO 6) and workers in elementary occupations (ISCO 9). Common industrial applications associated with increased exposure rates relate among others to: (1) production or application of pigments, resins, cutting fluids, adhesives, pesticides and cleaning products, (2) production of rubber, plastics, textiles, pharmaceuticals and cosmetics, and (3) in agriculture, metallurgy and food processing industry, Societal costs of the unequal distribution of chemical and biological hazards across occupations depend on the corresponding work-related diseases and may range from 2900 EUR to 126000 EUR per case/year.

CONCLUSIONS

Risk of exposure to chemical and biological risks and work-related disease incidence are highly concentrated on four occupational groups. The unequal burden of exposure across occupations is an important contributing factor leading to health inequalities in society. The bulk of societal costs, however, are actually being borne by the workers themselves. There is an urgent need of taking into account the health impact of production processes and services on workers' health.

In utero exposure to nanosized carbon black (Printex90) does not induce tandem repeat mutations in female murine germ cells

Inhalation of particles has been shown to induce mutations in the male germline in mice following both prenatal and adult exposures in several experiments. In contrast, the effects of particles on female germ cell mutagenesis are not well established. Germline mutations are induced during active cell division, which occurs during fetal development in females. We investigated the effects of prenatal exposure to carbon black nanoparticles (CB) on induction of mutations in the female mouse germline during fetal development, spanning the critical developmental stages of oogenesis. Pregnant C57BL/6J mice were exposed four times during gestation by intratracheal instillation of 67μg/animal of nanosized carbon black Printex90 or vehicle (gestation days 7, 10, 15 and 18). Female offspring were raised to maturity and mated with unexposed CBA males. Expanded simple tandem repeat (ESTR) germline mutation rates in the resulting F2 generation were determined from full pedigrees (mother, father, offspring) of F1 female mice (178 CB-exposed and 258 control F2 offspring). ESTR mutation rates in CB-exposed F2 female offspring were not statistically different from those of F2 female control offspring.

Paternal lifestyle as a potential source of germline mutations transmitted to offspring

Paternal exposure to high levels of radioactivity causes heritable germline minisatellite mutations. However, the effect of more general paternal exposures, such as cigarette smoking, on germline mutations remains unexplored. We analyzed two of the most commonly used minisatellite loci (CEB1 and B6.7) to identify germline mutations in blood samples of complete mother-father-child triads from the Norwegian Mother and Child Cohort Study (MoBa). The presence of mutations was subsequently related to general lifestyle factors, including paternal smoking before the partner became pregnant. Paternally derived mutations at the B6.7 locus (mutation frequency 0.07) were not affected by lifestyle. In contrast, high gross yearly income as a general measure of a healthy lifestyle coincided with low-mutation frequencies at the CEB1 locus (P=0.047). Income was inversely related to smoking behavior, and paternally derived CEB1 mutations were dose dependently increased when the father smoked in the 6 mo before pregnancy, 0.21 vs. 0.05 in smoking and nonsmoking fathers, respectively (P=0.061). These results suggest that paternal lifestyle can affect the chance of heritable mutations in unstable repetitive DNA sequences. To our knowledge, this is the first study reporting an effect of lifestyle on germline minisatellite mutation frequencies in a human population with moderate paternal exposures.

Harnessing genomics to identify environmental determinants of heritable disease

Next-generation sequencing technologies can now be used to directly measure heritable de novo DNA sequence mutations in humans. However, these techniques have not been used to examine environmental factors that induce such mutations and their associated diseases. To address this issue, a working group on environmentally induced germline mutation analysis (ENIGMA) met in October 2011 to propose the necessary foundational studies, which include sequencing of parent-offspring trios from highly exposed human populations, and controlled dose-response experiments in animals. These studies will establish background levels of variability in germline mutation rates and identify environmental agents that influence these rates and heritable disease. Guidance for the types of exposures to examine come from rodent studies that have identified agents such as cancer chemotherapeutic drugs, ionizing radiation, cigarette smoke, and air pollution as germ-cell mutagens. Research is urgently needed to establish the health consequences of parental exposures on subsequent generations.

Investigating the effects of dietary folic acid on sperm count, DNA damage and mutation in Balb/c mice

To date, fewer than 50 mutagens have been studied for their ability to cause heritable mutations. The majority of those studied are classical mutagens like radiation and anti-cancer drugs. Very little is known about the dietary variables influencing germline mutation rates. Folate is essential for DNA synthesis and methylation and can impact chromatin structure. We therefore determined the effects of folic acid-deficient (0mg/kg), control (2mg/kg) and supplemented (6mg/kg) diets in early development and during lactation or post-weaning on mutation rates and chromatin quality in sperm of adult male Balb/c mice. The sperm chromatin structure assay and mutation frequencies at expanded simple tandem repeats (ESTRs) were used to evaluate germline DNA integrity. Treatment of a subset of mice fed the control diet with the mutagen ethylnitrosourea (ENU) at 8 weeks of age was included as a positive control. ENU treated mice exhibited decreased cauda sperm counts, increased DNA fragmentation and increased ESTR mutation frequencies relative to non-ENU treated mice fed the control diet. Male mice weaned to the folic acid deficient diet had decreased cauda sperm numbers, increased DNA fragmentation index, and increased ESTR mutation frequency. Folic acid deficiency in early development did not lead to changes in sperm counts or chromatin integrity in adult mice. Folic acid supplementation in early development or post-weaning did not affect germ cell measures. Therefore, adequate folic acid intake in adulthood is important for preventing chromatin damage and mutation in the male germline. Folic acid supplementation at the level achieved in this study does not improve nor is it detrimental to male germline chromatin integrity.

Cigarette smoke-induced transgenerational alterations in genome stability in cord blood of human F1 offspring

The relevance of preconceptional and prenatal toxicant exposures for genomic stability in offspring is difficult to analyze in human populations, because gestational exposures usually cannot be separated from preconceptional exposures. To analyze the roles of exposures during gestation and conception on genomic stability in the offspring, stability was assessed via the Comet assay and highly sensitive, semiautomated confocal laser scans of γH2AX foci in cord, maternal, and paternal blood as well as spermatozoa from 39 families in Crete, Greece, and the United Kingdom. With use of multivariate linear regression analysis with backward selection, preconceptional paternal smoking (% tail DNA: P>0.032; γH2AX foci: P>0.018) and gestational maternal (% tail DNA: P>0.033) smoking were found to statistically significantly predict DNA damage in the cord blood of F1 offspring. Maternal passive smoke exposure was not identified as a predictor of DNA damage in cord blood, indicating that the effect of paternal smoking may be transmitted via the spermatozoal genome. Taken together, these studies reveal a role for cigarette smoke in the induction of DNA alterations in human F1 offspring via exposures of the fetus in utero or the paternal germline. Moreover, the identification of transgenerational DNA alterations in the unexposed F1 offspring of smoking-exposed fathers supports the claim that cigarette smoke is a human germ cell mutagen.

The epigenome as a target for heritable environmental disruptions of cellular function

The environment is a well-established source of damaging or disrupting influences on cellular function. In the past, studies of the mechanisms by which such disruptions occur have focused largely on either direct toxic effects on cellular function at the protein or cell signaling level, or mutagenic effects that impact the genome. In recent years there has been a growing appreciation for the potential for environmental influences to disrupt the epigenome and mechanisms of epigenetic regulation within the cell. Indeed, because of the inherent lability of the epigenome, this represents a primary target for environmentally induced disruption. This review summarizes the manner in which the epigenome normally regulates cellular function, the effects of disruptions on this function, and the manner in which such disruptions may or may not be corrected within the organism and/or transmitted to subsequent generations.

Preterm newborns show slower repair of oxidative damage and paternal smoking associated DNA damage

Newborns have to cope with hypoxia during delivery and a sudden increase in oxygen at birth. Oxygen will partly be released as reactive oxygen species having the potential to cause damage to DNA and proteins. In utero, increase of most (non)-enzymatic antioxidants occurs during last weeks of gestation, making preterm neonates probably more sensitive to oxidative stress. Moreover, it has been hypothesized that oxidative stress might be the common etiological factor for certain neonatal diseases in preterm infants. The aim of this study was to assess background DNA damage; in vitro H(2)O(2) induced oxidative DNA damage and repair capacity (residual DNA damage) in peripheral blood mononucleated cells from 25 preterm newborns and their mothers. In addition, demographic data were taken into account and repair capacity of preterm was compared with full-term newborns. Multivariate linear regression analysis revealed that preterm infants from smoking fathers have higher background DNA damage levels than those from non-smoking fathers, emphasizing the risk of paternal smoking behaviour for the progeny. Significantly higher residual DNA damage found after 15-min repair in preterm children compared to their mothers and higher residual DNA damage after 2 h compared to full-term newborns suggest a slower DNA repair capacity in preterm children. In comparison with preterm infants born by caesarean delivery, preterm infants born by vaginal delivery do repair more slowly the in vitro induced oxidative DNA damage. Final impact of passive smoking and of the slower DNA repair activity of preterm infants need to be confirmed in a larger study population combining transgenerational genetic and/or epigenetic effects, antioxidant levels, genotypes, repair enzyme efficiency/levels and infant morbidity.

Declaring the existence of human germ-cell mutagens

After more than 80 years of searching for human germ-cell mutagens, I think that sufficient evidence already exists for a number of agents to be so considered, and definitive confirmation seems imminent due to the application of recently developed genomic techniques. In preparation for this, an assessment panel of internationally recognized experts in germ-cell biology and genomics is required to consider either the current evidence now, or impending genomic evidence later, to declare whether an agent is a human germ-cell mutagen. I propose that such a panel be organized under the aegis of the World Health Organization and constructed similarly to the working groups assembled by the International Agency for Research on Cancer for the evaluation of human carcinogens. Support from prominent national and international organizations would be important. Many regulatory agencies already have procedures in place for assessing potential human germ-cell mutagens, and the time is approaching when definitive genomic data in humans will obligate such evaluations. In my view, application of an IARC-type of assessment using available evidence leads to the conclusion that ionizing radiation, cancer chemotherapy, cigarette smoking, and air pollution are "Group 1" human germ-cell mutagens. Consideration of the potential adverse health effects to the unexposed offspring of an exposed parent will usher in an entirely new realm of environmental health assessment. I suggest that the long search for human germ-cell mutagens is about to end, and a demonstration of the much-anticipated linkage between heritable disease and environmental factors is poised to begin.

Sidestream tobacco smoke is a male germ cell mutagen

Active cigarette smoking increases oxidative damage, DNA adducts, DNA strand breaks, chromosomal aberrations, and heritable mutations in sperm. However, little is known regarding the effects of second-hand smoke on the male germ line. We show here that short-term exposure to mainstream tobacco smoke or sidestream tobacco smoke (STS), the main component of second-hand smoke, induces mutations at an expanded simple tandem repeat locus (Ms6-hm) in mouse sperm. We further show that the response to STS is not linear and that, for both mainstream tobacco smoke and STS, doses that induced significant increases in expanded simple tandem repeat mutations in sperm did not increase the frequencies of micronucleated reticulocytes and erythrocytes in the bone marrow and blood of exposed mice. These data show that passive exposure to cigarette smoke can cause tandem repeat mutations in sperm under conditions that may not induce genetic damage in somatic cells. Although the relationship between noncoding tandem repeat instability and mutations in functional regions of the genome is unclear, our data suggest that paternal exposure to second-hand smoke may have reproductive consequences that go beyond the passive smoker.