Paternal exposure to drugs and environmental chemicals: effects on progeny outcome

In vitro adverse effects of amitraz on semen quality: Consequences in bovine embryo development

Veterinary drugs are potential environmental pollutants that interfere with male reproductive function. Infertility has increased, and it is known that environmental toxins contribute to declining sperm parameters. Amitraz {N,N-[(methylamino) dimeth-ylidyne] di-2,4-xylidine} (AMZ) is a formamidine pesticide widely used as an insecticide and an acaricide. The aim of this study was to evaluate the toxicity of AMZ in bovine sperm. Three experiments using frozen-thawed bovine semen incubated with AMZ for 2 h were carried out. Negative and solvent (dimethyl sulfoxide) controls were run simultaneously with treatments. In experiment 1, the AMZ concentrations used were 10, 15 and 25 μg AMZ/ml and the sperm parameters evaluated were viability, mitochondrial activity, acrosomal status, functional membrane integrity and apoptosis. In experiments 2 and 3, 25 μg AMZ/ml was used to evaluate fertilizing capacity, embryo development and blastocyst DNA damage. In experiment 1, 25 μg AMZ/ml decreased sperm viability (P = 0.01), reduced mitochondrial activity (P = 0.03) and induced apoptosis (P < 0.01). Also, 15 and 25 μg AMZ/ml affected functional membrane integrity (P < 0.01). In experiment 2, AMZ did not alter sperm-zona binding (P = 0.40) and pronucleus formation (P = 0.36). In experiment 3, 25 μg AMZ/ml decreased the rate of embryo development (P < 0.01) and increased apoptosis (P = 0.03). These results suggest that AMZ induced alterations in bovine sperm, probably affecting male fertility at concentrations that could be present in the environment.

Impact of Heavy Metals on Human Male Fertility-An Overview

Heavy metals are endocrine disruptors which interfere with processes mediated by endogenous hormones of the organism, negatively affecting endocrine functions. Some studies have correlated heavy metal exposure with male infertility. However, the number of studies conducted on humans are limited. Therefore, the aim of this study is to summarize the current knowledge on how heavy metals influence human male fertility. Hence, three distinct databases were consulted—PubMed, Scopus and Web of Science—using single keywords and combinations of them. The total number of identified articles was 636. Nevertheless, by using the inclusion and exclusion criteria, 144 articles were finally included in this work. Results display that the development of adequate instruments for heavy metal assessment may play an important function in human male fertility diagnosis and treatment. Furthermore, clinical trials could be useful to confirm the role of heavy metals in human male fertility diagnosis. Overall, further research is required to fully understand the molecular and cellular basis of the influence of environmental and occupational exposure to heavy metals on human male infertility and reproductive outcomes.

Mapping the past, present and future research landscape of paternal effects

BACKGROUND

Although in all sexually reproducing organisms an individual has a mother and a father, non-genetic inheritance has been predominantly studied in mothers. Paternal effects have been far less frequently studied, until recently. In the last 5 years, research on environmentally induced paternal effects has grown rapidly in the number of publications and diversity of topics. Here, we provide an overview of this field using synthesis of evidence (systematic map) and influence (bibliometric analyses).

RESULTS

We find that motivations for studies into paternal effects are diverse. For example, from the ecological and evolutionary perspective, paternal effects are of interest as facilitators of response to environmental change and mediators of extended heredity. Medical researchers track how paternal pre-fertilization exposures to factors, such as diet or trauma, influence offspring health. Toxicologists look at the effects of toxins. We compare how these three research guilds design experiments in relation to objects of their studies: fathers, mothers and offspring. We highlight examples of research gaps, which, in turn, lead to future avenues of research.

CONCLUSIONS

The literature on paternal effects is large and disparate. Our study helps in fostering connections between areas of knowledge that develop in parallel, but which could benefit from the lateral transfer of concepts and methods.

Evaluation of interactive effects between paternal alcohol consumption and paternal socioeconomic status and environmental exposures on congenital heart defects

BACKGROUND

While the maternal risk factors on congenital heart defects (CHDs) have often been assessed, paternal contribution to CHDs, especially the joint effects of paternal risk factors on CHDs remain unknown. This study examined the major impacts of paternal alcohol consumption and its interaction (on multiplicative and additive scales) with paternal socioeconomic status (SES) and environmental exposures on CHDs in China.

METHODS

A population-based case-control study involving 4,726 singleton CHDs cases and 4,726 controls (without any malformation and matched on hospital, gender, and gestational age) was conducted in Guangdong, China, 2004-2014. Information on parental demographics, behavioral patterns, disease/medication, and environmental exposures (3 months before pregnancy) was collected through face-to-face interviews. Conditional logistic regression was used to estimate odds ratios (ORs) and 95% confidence intervals (CIs) while controlling for all parental factors.

RESULTS

Paternal alcohol consumption was associated with an increased OR of CHDs (adjusted OR = 2.87, 95% CI: 2.25-3.65). Additionally, paternal smoking, industry occupation, organic solvent contact, virus infection and antibiotic use, living in rural areas, low household income, and migrant status were significantly associated with CHDs (ORs ranged: 1.42-4.44). Significant additive or multiplicative interactions were observed between paternal alcohol consumption and paternal smoking, industrial occupation, and low income on any CHDs (interaction contrast ratio [ICR] = 4.72, 95% CI: 0.96-8.47] and septal defects (ICRs ranged from 2.04 to 2.79, p < .05).

CONCLUSIONS

Paternal alcohol consumption and multiple paternal factors were significantly associated with CHDs in China. Paternal smoking and low SES factors modified paternal alcohol consumption-CHDs relationships. Further studies are needed to confirm these findings.

The Female Response to Seminal Fluid

Seminal fluid is often assumed to have just one function in mammalian reproduction, delivering sperm to fertilize oocytes. But seminal fluid also transmits signaling agents that interact with female reproductive tissues to facilitate conception and .pregnancy. Upon seminal fluid contact, female tissues initiate a controlled inflammatory response that affects several aspects of reproductive function to ultimately maximize the chances of a male producing healthy offspring. This effect is best characterized in mice, where the female response involves several steps. Initially, seminal fluid factors cause leukocytes to infiltrate the female reproductive tract, and to selectively target and eliminate excess sperm. Other signals stimulate ovulation, induce an altered transcriptional program in female tract tissues that modulates embryo developmental programming, and initiate immune adaptations to promote receptivity to implantation and placental development. A key result is expansion of the pool of regulatory T cells that assist implantation by suppressing inflammation, mediating tolerance to male transplantation antigens, and promoting uterine vascular adaptation and placental development. Principal signaling agents in seminal fluid include prostaglandins and transforming growth factor-β. The balance of male signals affects the nature of the female response, providing a mechanism of ‟cryptic female choiceˮ that influences female reproductive investment. Male-female seminal fluid signaling is evident in all mammalian species investigated including human, and effects of seminal fluid in invertebrates indicate evolutionarily conserved mechanisms. Understanding the female response to seminal fluid will shed new light on infertility and pregnancy disorders and is critical to defining how events at conception influence offspring health.

The Long-Term Effects of the Periconceptional Period on Embryo Epigenetic Profile and Phenotype; The Paternal Role and His Contribution, and How Males Can Affect Offspring's Phenotype/Epigenetic Profile

The number of adults afflicted with heart disease, obesity and diabetes, central components of metabolic disorder, has grown rapidly in recent decades, affecting up to one quarter of the world's population. Typically, these diseases are attributed to lifestyle factors such as poor diet, lack of exercise and smoking. However, studies have now identified strong associations between patterns of growth during foetal and neonatal life and an increase predisposition towards developing heart disease, obesity and diabetes in adult life. While the connection between a mother's diet and the long-term health of her offspring has been studied in great detail, our understanding of whether offspring health might be affected by a father's diet remains limited. Greater insight into the impact that paternal nutrition has on sperm quality, epigenetic status and potential offspring programming mechanisms is needed to redress this parental-programming knowledge imbalance. Disturbances in paternal reproductive epigenetic status represents one key mechanism linking paternal diet with the programing of offspring development and adult health, as many enzymatic processes involved in epigenetic regulation use metabolic intermediates to modify DNA and histones. Here, poor paternal nutrition could result in perturbed sperm and testicular epigenetic status, impacting on post-fertilisation gene transcriptional regulation and protein expression in offspring tissues, resulting in increased incidences of metabolic disorder in adult life.

Modulation of embryonic development due to mating with immunised males

The modification of pre- and postnatal development conferred by immunogenic stimulation of mothers provides a population-level adaptation mechanism for non-genetic transfer of maternal experiences to progeny. However little is known about the transmission of paternal immune experiences to offspring. Here, we show that immune priming of males 3–9 days before mating affects the growth and humoral environment of developing embryos of outbred (ICR) and inbred (C57BL and BALB/c) mice. Antigenic stimulation of fathers caused a significant increase in embryonic bodyweight as measured on Day 16 of pregnancy and altered other gestation parameters, such as feto–placental ratio. Pregnant females mated with immunised males were also characterised by changes in humoral conditions as shown by measurements of blood and amniotic progesterone, testosterone and granulocyte–macrophage colony-stimulating factor (GM-CSF) cytokine concentrations. These results emphasise the role of paternal effects of immune priming on the in utero environment and fetal growth.

Models of germ cell development and their application for toxicity studies

Germ cells are unique in their ability to transfer genetic information and traits from generation to generation. As such, the proper development of germ cells and the integrity of their genome are paramount to the health of organisms and the survival of species. Germ cells are also exquisitely sensitive to environmental influences although the testing of germ cell toxicity, especially in females, has proven particularly challenging. In this review, we first describe the remarkable odyssey of germ cells in mammals, with an emphasis on the female germline, from their initial specification early during embryogenesis to the generation of mature gametes in adults. We also describe the current methods used in germ cell toxicity testing and their limitations in examining the complex features of mammalian germ cell development. To bypass these challenges, we propose the use of alternative model systems such as Saccharomyces cerevisiae, Drosophila melanogaster, Caenorhabditis elegans, and in vitro germ cell methods that have distinct advantages over traditional toxicity models. We discuss the benefits and limitations of each approach, their application to germ cell toxicity studies, and the need for computational approaches to maximize the usefulness of these models. Together, the inclusion of these alternative germ cell toxicity models will be invaluable for the examination of stages not easily accessible in mammals as well as the large scale, high-throughput investigation of germ cell toxicity.

Congenital heart disease: the crossroads of genetics, epigenetics and environment

Congenital heart diseases (CHDs) are recognized as the most common type of birth malformations. Although recent advances in pre- and neonatal diagnosis as well as in surgical procedures have reduced the morbidity and mortality for many CHD, the etiology for CHD remains undefined. In non-syndromic and isolated (without a familial history or a Mendelian inheritance) forms of CHDs, a multifactorial pathogenesis with interplay between inherited and non-inherited causes is recognized. In this paper, we discuss the current knowledge of the potential molecular mechanisms, mediating abnormal cardiac development in non-syndromic and isolated CHD, including mutations in cardiac transcription factors, the role of somatic mutations and epigenetic alterations as well as the influence of gene-environment interactions. In the near future, the advent of high-throughput genomic technologies with the integration of system biology will expand our understanding of isolated, non-syndromic CHDs for their prevention, early diagnosis and therapy.

Birth outcomes in newborns fathered by men with multiple sclerosis exposed to disease-modifying drugs

OBJECTIVE

The aim of this study was to determine the incidence of births fathered by men with multiple sclerosis (MS) exposed to a disease-modifying drug (DMD) around the time of conception, and investigate the association between DMD exposure and birth outcomes in newborns of exposed and unexposed MS fathers.

METHODS

Population-based databases in British Columbia (BC), Canada, (the BCMS database, Vital Statistics Birth Registry, Population Data BC Consolidation File/Census GeoData, BC PharmaNet and the BC Perinatal Database Registry) were linked in this retrospective cohort study (1996 to 2010). Multivariate models were used to examine the association between interferon-beta (IFNβ) or glatiramer acetate (GA) exposure (within 64 days prior to or at conception; i.e., the duration of spermatogenesis) with birth weight and gestational age of newborns.

RESULTS

Of 195 births fathered by men with relapsing-onset MS, 80 births (41%) were to fathers treated with a DMD before their child was born, with 53/195 (27%) exposed within 64 days prior to or at the time of conception. Of the 53 exposed births, 37 were to IFNβ and 16 to GA. Mean birth weight of IFNβ-exposed and GA-exposed newborns was similar to that of unexposed newborns (adjusted difference: -107 g for both, p>0.3). IFNβ-exposed and GA-exposed newborns also had comparable mean gestational ages relative to unexposed newborns (adjusted difference: -0.5 and -0.3 weeks, respectively, p>0.2).

CONCLUSIONS

About one in three would-be fathers with MS were exposed to IFNβ or GA around the time of conception; there was no compelling evidence to suggest that exposure was associated with either lower birth weight or gestational age.

Spontaneous abortion in spouses of greenhouse workers exposed to pesticides

OBJECTIVE

The aim of this study was to explore the association between exposure to specific pesticides (including endocrine disrupters) of greenhouse workers and spontaneous abortion in their spouses.

METHODS

A group of exposed workers was compared with a non-exposed group. The risk of spontaneous abortion was evaluated using a logistic regression model.

RESULTS

A significantly higher rate of spontaneous abortion was observed among spouses of workers exposed to specific compounds (atrazine, benomyl-carbendazim, carbaryl and DDT) in comparison with spouses of the unexposed group. The logistic regression model confirmed the increased risk of spontaneous abortion (OR=11.8; 95% CI 2.3-59.6).

CONCLUSIONS

These findings suggest that occupational exposure to pesticides might have an adverse effect on the partner's reproductive health.

Paternal benzo[a]pyrene exposure affects gene expression in the early developing mouse embryo

The health of the offspring depends on the genetic constitution of the parental germ cells. The paternal genome appears to be important; e.g., de novo mutations in some genes seem to arise mostly from the father, whereas epigenetic modifications of DNA and histones are frequent in the paternal gonads. Environmental contaminants which may affect the integrity of the germ cells comprise the polycyclic aromatic hydrocarbon, benzo[a]pyrene (B[a]P). B[a]P has received much attention due to its ubiquitous distribution, its carcinogenic and mutagenic potential, and also effects on reproduction. We conducted an in vitro fertilization (IVF) experiment using sperm cells from B[a]P-exposed male mice to study effects of paternal B[a]P exposure on early gene expression in the developing mouse embryo. Male mice were exposed to a single acute dose of B[a]P (150mg/kg, ip) 4 days prior to isolation of cauda sperm, followed by IVF of oocytes from unexposed superovulated mice. Gene expression in fertilized zygotes/embryos was determined using reverse transcription-qPCR at the 1-, 2-, 4-, 8-, and blastocyst cell stages of embryo development. We found that paternal B[a]P exposure altered the expression of numerous genes in the developing embryo especially at the blastocyst stage. Some genes were also affected at earlier developmental stages. Embryonic gene expression studies seem useful to identify perturbations of signaling pathways resulting from exposure to contaminants, and can be used to address mechanisms of paternal effects on embryo development.

Paternal dietary restriction affects progeny fat content in Caenorhabditis elegans

Epidemiological data from human populations and few reports in rodents suggested that the paternal diet affects offspring adiposity and its related diseases. We tested whether this nongenetic and intergenerational inheritance depends on paternal treatment dose. Using the model organism Caenorhabditis elegans, males undergoing several dietary restriction regimes were crossed with ad libitum fed females. We found an inverted U-shaped relationship between the extent of paternal dietary restriction and the level of fat content of progeny. The relationship was evident in both sexes. Body proportions were not affected in offspring. Overall, our findings extent the concept of developmental and adaptive plasticity to include the extent of paternal food consumption in the origin of phenotypic alterations.

Maternal and paternal environmental risk factors, metabolizing GSTM1 and GSTT1 polymorphisms, and congenital heart disease

Congenital heart defects (CHDs) are the most prevalent of all birth malformations arising from the complex interplay of environmental exposures and genes. Modifiable environmental risk factors are still largely unknown, especially for paternal exposure. The aim of the present study was to examine the association between the environmental exposures of both parents and CHD risk and to explore the modification effect of metabolizing gene polymorphisms in children who lack the genetic capacity to produce the glutathione S-transferase (GST) GSTM1 and GSTT1 enzymes. A total of 330 parents of a child with CHD and 330 parents of a child without any congenital malformations were compared in terms of lifestyle habits and toxicant exposure. GST gene polymorphisms were investigated in 180 patients with CHD (104 males, age 4.9 ± 5.8 years). Paternal smoking (≥15 cigarettes/day) was significantly associated with CHD risk (odds ratio [OR] 2.1, 95% confidence interval [CI] 1.3 to 3.5, p = 0.002). Both maternal (OR 2.6, 95% CI 1.6 to 4.2, p <0.0001) and paternal (OR 2.5, 95% CI 1.6 to 3.8, p <0.0001) occupational/environmental exposures increased the risk of CHD. Also, a significant additive risk (OR 4.5, 95% CI 2.5 to 8.3, p <0.0001) was found when both parents were exposed to toxicants. Both maternal (OR 3.6, 95% CI 1.1 to 11.2, p = 0.03) and paternal (OR 3.3, 95% CI 1.0 to 10.8, p = 0.03) exposure to toxicants increased the CHD risk in children who carried the combined null GST genotypes. The effect for the combined null GST genotypes was also stronger (OR 6.5, 95% CI 1.5 to 28.0) when both parents were exposed. In conclusion, paternal smoking and exposure to toxicants for both parents affect the risk of children with CHD. Polymorphisms in GST genes can modify a person's risk of toxicant exposure-induced disease.

Epigenetics and the origins of paternal effects

Though there are multiple routes through which parents can influence their offspring, recent studies of environmentally induced epigenetic variation have highlighted the role of non-genomic pathways. In addition to the experience-dependent modification of DNA methylation that can be achieved via mother-infant interactions, there has been increasing interest in the epigenetic mechanisms through which paternal influences on offspring development can be achieved. Epidemiological and laboratory studies suggest that paternal nutritional and toxicological exposures as well as paternal age and phenotypic variation can lead to variations in offspring and, in some cases, grand-offspring development. These findings suggest a potential epigenetic germline inheritance of paternal effects. However, it may be important to consider the interplay between maternal and paternal influences as well as the experimental dissociation between experience-dependent and germline transmission when exploring the role of epigenetic variation within the germline as a mediator of these effects. In this review, we will explore these issues, with a particular focus on the potential role of paternally induced maternal investment, highlight the literature illustrating the transgenerational impact of paternal experiences, and discuss the evidence supporting the role of epigenetic mechanisms in maintaining paternal effects both within and across generations.

Protective effects of garlic extract and vitamin C against in vivo cypermethrin-induced teratogenic effects in rat offspring

Exposure of male (55.1 mg/kg b.wt. orally for 60 days) and/or pregnant female Wistar rats (55.1 mg/kg b.wt. orally at days 6-15 of gestation), to the insecticide cypermethrin (CYP); resulted in the development of a lot of external morphological deformities and visceral malformations in their offspring pubs, which signify the potential of such insecticide to induce reproductive toxicity and teratogenesis. Data cleared that CYP treatment induced significant increase in the percentages of post-implantation deaths, dwarf foeti and subcutaneous oedema beside significant decrease in percentages of live borne foeti and uterine implants. CYP also caused many visceral malformations among different treated groups including nasal, ophthalmic, cerebral, pulmonary, cardiac and renal malformations. Concomitant oral administration of garlic extract or vitamin C (5 days/week) to treated fathers and/or pregnant mothers with CYP provided significant reduction in the percentage of the foetal malformations induced by the insecticide, when compared with the control. The current study proves that garlic and ascorbic acid dampen the reproductive toxicity and/or teratogenicity of cypermethrin toxicity in rats; therefore might prove to be effective dietary supplements in developing countries where pesticide pollution is high.

Parent-of-origin and trans-generational germline influences on behavioral development: the interacting roles of mothers, fathers, and grandparents

Mothers and fathers do not contribute equally to the development of their offspring. In addition to the differential investment of mothers versus fathers in the rearing of offspring, there are also a number of germline factors that are transmitted unequally from one parent or the other that contribute significantly to offspring development. This article shall review four major sources of such parent-of-origin effects. Firstly, there is increasing evidence that genes inherited on the sex chromosomes including the nonpseudoautosomal part of the Y chromosome that is only inherited from fathers to sons, contribute to brain development and behavior independently of the organizing effects of sex hormones. Secondly, recent work has demonstrated that mitochondrial DNA that is primarily inherited only from mothers may play a much greater than anticipated role in neurobehavioral development. Thirdly, there exists a class of genes known as imprinted genes that are epigenetically silenced when passed on in a parent-of-origin specific manner and have been shown to regulate brain development and a variety of behaviors. Finally, there is converging evidence from several disciplines that environmental variations experienced by mothers and fathers may lead to plasticity in the development and behavior of offspring and that this phenotypic inheritance can be solely transmitted through the germline. Mechanistically, this may be achieved through altered programming within germ cells of the epigenetic status of particular genes such as retrotransposons and imprinted genes or potentially through altered expression of RNAs within gametes.

Shad Garbhakara Bhavas vis-a-vis congenital and genetic disorders

Despite the advancements in diagnostic techniques and therapeutic interventions, medical science has failed to keep the incidence of congenital malformations under control. Ayurveda, the ancient Indian medical system has given due emphasis on this and postulated various measures to minimize the risks. These measures start well before conception. According to Ayurvedic principles, proper preparation of the parents is an essential prerequisite for a healthy progeny. Pre-conception care is a set of interventions that identifies biomedical behavioral and social risks to the health of the mother and the baby. It includes both-prevention and management, emphasizing health issues that require action before conception, very early in pregnancy, for maximal impact. For meeting the objective of healthy progeny, Ayurveda scholars felt the importance of six procreative factors (Shadgarbhkarabhavas) such as Matrija, Pitrija, Aatmaja, Rasaja, Satmyaja, and Sattvaja. The conglomeration of these procreative factors is must for healthy progeny. The physical, mental, social, and spiritual well-being of the person, proper nutrition of the mother during pregnancy, and practice of a wholesome regimen, play a prime role in achieving a healthy offspring, thus structuring a healthy family, society, and nation. Negligence toward any of these factors becomes a cause for unhealthy and defective child birth. The present literary / conceptual study, thus focuses mainly on interpreting these observations, on the basis of modern scientific knowledge.

Air pollution and effects on reproductive-system functions globally with particular emphasis on the Brazilian population

In recent years, numerous studies showed that exposure to environmental air pollutants affected reproductive functions and, in particular, produced adverse effects on pregnancy outcomes, fertility, and fetal health. Epidemiological studies demonstrated that exposure to ambient levels of air pollutants are associated with low birth weight, intrauterine growth retardation, prematurity, neonatal death, and decreased fertility in males. Experimental animal data supported these findings and indicated that female fertility was also disturbed. Although there are various mechanisms of action suggested to show the manner in which air pollutants alter pregnancy and the reproductive systems in both genders, further studies are needed to correlate causal relationships. This information would serve to better understand the underlying physiologic changes in the reproductive system induced by exposure to air pollutants and possibly establish a link between the dose and response of individual or mixture of air pollutants.

A comparative study of Sephadex, glass wool and Percoll separation techniques on sperm quality and IVF results for cryopreserved bovine semen

The aim of this study was to compare the effects of spermatozoa separation techniques on sperm quality and in-vitro fertilization (IVF) results for cryopreserved bovine semen. Sephadex, glass wool and Percoll gradient separation techniques were used for sperm separation and sperm motility, morphology and membrane integrity were evaluated before and after separation. Also, cleavage and blastocyst developmental rate were investigated after IVF with sperm recovered by each separation technique. The motility of samples obtained by the three separation techniques were greater compared to the control samples (p < 0.05). The percentage of spermatozoa with intact plasma-membrane integrity, identified by 6-carboxyfluoresceindiacetate/propidium iodide fluorescent staining and the hypo-osmotic swelling test, was highest in the glass wool filtration samples (p < 0.05). The cleavage and blastocyst rate of total oocytes produced from glass wool filtration samples were also higher than the control and Sephadex filtration samples (p < 0.05), but were not significantly different from Percoll separation samples. However, a significantly greater number of cleaved embryos produced by glass wool filtration developed to blastocyst stage than those produced by Percoll separation (p < 0.05). These results indicate that spermatozoa with good quality can be achieved by these three separation techniques and can be used for bovine IVF. In particular, it suggests that glass wool filtration would be the most effective method of the three for improving sperm quality and embryo production for cryopreserved bovine spermatozoa.

Germ-line mutations, DNA damage, and global hypermethylation in mice exposed to particulate air pollution in an urban/industrial location

Particulate air pollution is widespread, yet we have little understanding of the long-term health implications associated with exposure. We investigated DNA damage, mutation, and methylation in gametes of male mice exposed to particulate air pollution in an industrial/urban environment. C57BL/CBA mice were exposed in situ to ambient air near two integrated steel mills and a major highway, alongside control mice breathing high-efficiency air particulate (HEPA) filtered ambient air. PCR analysis of an expanded simple tandem repeat (ESTR) locus revealed a 1.6-fold increase in sperm mutation frequency in mice exposed to ambient air for 10 wks, followed by a 6-wk break, compared with HEPA-filtered air, indicating that mutations were induced in spermatogonial stem cells. DNA collected after 3 or 10 wks of exposure did not exhibit increased mutation frequency. Bulky DNA adducts were below the detection threshold in testes samples, suggesting that DNA reactive chemicals do not reach the germ line and cause ESTR mutation. In contrast, DNA strand breaks were elevated at 3 and 10 wks, possibly resulting from oxidative stress arising from exposure to particles and associated airborne pollutants. Sperm DNA was hypermethylated in mice breathing ambient relative to HEPA-filtered air and this change persisted following removal from the environmental exposure. Increased germ-line DNA mutation frequencies may cause population-level changes in genetic composition and disease. Changes in methylation can have widespread repercussions for chromatin structure, gene expression and genome stability. Potential health effects warrant extensive further investigation.

DNA damage to spermatozoa has impacts on fertilization and pregnancy

DNA damage in the male germ line has been associated with poor semen quality, low fertilization rates, impaired preimplantation development, increased abortion and an elevated incidence of disease in the offspring, including childhood cancer. The causes of this DNA damage are still uncertain but the major candidates are oxidative stress and aberrant apoptosis. The weight of evidence currently favours the former and, in keeping with this conclusion, positive results have been reported for antioxidant therapy both in vivo and in vitro. Resolving the causes of DNA damage in the male germ line will be essential if we are to prevent the generation of genetically damaged human embryos, particularly in the context of assisted conception therapy.

Environmental exposures, toxicologic mechanisms, and adverse pregnancy outcomes

Environmental risk factors (defined as those agents and stresses that are generally the responsibility of environmental agencies) are often tangible indicators of economic and social disparity in the United States. Many site-specific analyses have reported that communities of color and poverty are exposed more often and more intensively to such environmental hazards as lead, air pollution, agrochemicals, incinerator emissions, and releases from hazardous waste sites. Thus, exposures to these toxicants may explain part of the socioeconomic disparity that is observed in terms of risks of adverse pregnancy outcomes. The purpose of this study was to describe the associations between certain environmental exposures and reproductive outcomes through a discussion of both epidemiologic and animal model studies. In addition, we list potential sources of exposure data and describe physiologic changes in pregnancy that may increase the likelihood of both external exposures and increased internal dose. Several models for further study of environmental risk factors are suggested to increase our understanding of gene-environment interactions toward the goal of indentifying preventable risk factors to improve reproductive outcomes of particular concern to disadvantaged populations.

Spermatozoal nuclear determinants of reproductive outcome: implications for ART

A male factor is implicated in more than 50% of couples treated with IVF. However, neither the routine testing of male fertility potential nor its treatment address the specific mechanisms by which spermatozoal factors may impact upon reproductive outcome. An important function of spermatozoa is to deliver the paternal genome to the oocyte. Recently, a number of acquired spermatozoal nuclear factors that may have implications on reproductive outcome have been described. These include non-specific DNA strand breaks, numerical abnormalities in spermatozoal chromosome content, Y chromosome microdeletions and alterations in the epigenetic regulation of paternal genome. The exact mechanisms by which these factors affect reproduction are unknown and their implications for assisted reproduction technology outcome need to be further investigated. These recent findings point to the need for novel and more personalized approaches to test and treat male factor infertility.

Effect of paternal tamoxifen on the expression of insulin-like growth factor 2 and insulin-like growth factor type 1 receptor in the post-implantation rat embryos

Nuclear transplantation studies demonstrated the importance of paternal contribution to embryogenesis. Paternal treatment with agents like cyclophosphamide and 5-azacytidine has been shown to cause an increase in pre-implantation loss (PIL) and post-implantation loss (POL). Studies from our laboratory have shown that paternal tamoxifen treatment increases PIL and POL. It was observed that the PIL occurred at day 2 of gestation (embryo at 2-4 cell stage) and the POL occurred around day 9 of gestation (mid-gestation). The insulin-like growth factor (IGF) system represents one of the major growth-controlling system expressed in the embryo. Several studies suggest that in rodents, insulin-like growth factor 2 (Igf2) signaling through the insulin-like growth factor type 1 receptor (Igf1r) modulates embryo growth at around days 9-11 of gestation (mid-gestation). The present study was undertaken to evaluate the expression of Igf2 and Igf1r transcript by RT-PCR in the post-implantation embryos obtained after paternal tamoxifen treatment. It was observed that both the genes were down regulated in resorbed embryos (POL). Since Igf2 is an imprinted gene and the imprint mark is established during spermatogenesis, the present study suggests that paternal tamoxifen treatment may have affected imprinting of the gene during spermatogenesis thereby decreasing its expression and leading to increase in POL. This is to our knowledge the first study correlating the increase in post-implantation embryo loss obtained after paternal drug treatment with the decrease in the expression of Igf2 in these embryos.

The presence of environmental pollutants in the semen of farm animals (bull, ram, goat, and boar)

Organochlorine pesticides and polychlorinated biphenyls are widely used in agriculture and industry, respectively, and may affect male reproduction function. Although several pollutants have been detected in human semen, similar studies in farm animals have not appeared. In the present study, the semen of bulls, rams, goats, and boars was assayed for the organochlorine pesticides hexachlorobenzene (HCB), hexachlorocyclohexane (HCH, alpha-, beta-, and gamma-isomers), dieldrin, and heptachlor epoxide, for DDT-related chemicals (o,p'-DDE, p,p'-DDE, p,p'-DDD, p,p'-DDT), and for the PCBs congeners (PCB-52, -101, -138, -150, and -180). In all species of farm animals, the most frequently detected pollutants were p,p'-DDE (80-100% of samples), HCB (73.9-100%), and gamma-HCH (69.6-100%). Species differences in the concentrations of HCB, alpha-, beta-, and gamma-HCH, dieldrin, p,p'-DDE, p,p'-DDD, and PCBs were noted as well as differences in the concentrations of some isomers of HCH, DDT-related chemicals, and PCB congeners in the same species.

Sperm DNA damage and cancer treatment

Cancer treatments are well known to adversely affect male fertility. Reduction of sperm output arises from the cytotoxic effects of chemo- or radiotherapy upon the spermatogenic epithelium. However, if the epithelium survives there is a hazard to reproduction as the treatments are also mutagenic. The presence of DNA damage in the male genome is shown in animal experiments where there is transgenerational expression as a variety of effects ranging from miscarriage to carcinogenesis. The application of DNA damage methodology to sperm provides the opportunity for direct assessment. The Comet and Chromatin structure assays (SCSA) measure DNA damage by different principles, however, conclusions arising from the data are similar. DNA damage is present in sperm from fertile and infertile men and there is some association with infertility. Both assays detect sperm DNA damage after in vivo treatment with genotoxic agents. In a man treated with chemotherapy for cancer there was increased and persistent DNA damage in sperm. This information is consistent with the generation of human genetic diseases after conception with sperm carrying high loads of DNA damage. Whilst studies have not supported any association between paternal cytotoxic cancer therapy and genetic disease in their children, it would be unwise to discount these observations. The institution of better surveillance of genetic disease in the offspring of men surviving cytotoxic therapies may provide more robust risk assessment.