Transgenerational effects of maternal exposure to chemicals on the functional development of the brain in the offspring

Effects of glufosinate-ammonium on male reproductive health: Focus on epigenome and transcriptome in mouse sperm

Glufosinate-ammonium (GLA) is a widely used herbicide with emerging concern over its neural and reproductive toxicity. To uncover potential effects of GLA on male reproductive health in mammals, adult male C57BL/6J mice were administered 0.2 mg/kg·d GLA for 5 weeks. After examination on fertility, testis histology and semen quality in the GLA group, we performed deep sequencing to identify repressive epigenetic marks including DNA methylation and histone modifications (H3K27me3 and H3K9me3), together with mRNA transcript levels in sperm. Then, we integrated multi-omics sequencing data to comprehensively explore GLA-induced epigenetic and transcriptomic alterations. We found no significant difference either on fertility, testis histology or semen quality-related indicators. As for epigenome, the protein level of H3K27me3 was significantly increased in GLA sperm. Next generation sequencing showed alterations of these epigenetic marks and extensive transcription inhibition in sperm. These differential repressive marks were mainly distributed at intergenic regions and introns. According to results by Gene Ontology enrichment analysis, both differentially methylated and expressed genes were mainly enriched in pathways related to synapse organization. Subtle differences in genomic imprinting were also observed between the two groups. These results suggested that GLA predominantly impaired sperm epigenome and transcriptome in mice, with little effect on fertility, testis histology or semen quality. Further studies on human sperm using similar strategies need to be conducted for a better understanding of the male reproductive toxicity of GLA.

Intrauterine hyperglycemia exposure results in intergenerational inheritance via DNA methylation reprogramming on F1 PGCs

BACKGROUND

The existing reports about intergenerational or transgenerational effects of intrauterine hyperglycemia have included both intrauterine and postnatal metabolic exposure factors, while the impact of intrauterine hyperglycemia per se has not been assessed alone. A number of studies suggest DNA methylation reprogramming of gametes plays a crucial role in the metabolic inheritance, but it is unclear when and how DNA methylation patterns are altered when exposed to intrauterine hyperglycemia. In this study, we selected nondiabetic F1- and F2-gestational diabetes mellitus (GDM) male mice as founders to examine metabolic changes in the next generation and performed methylome sequencing of day 13.5 primordial germ cells (PGCs) from F1-GDM to explore the underlying epigenetic mechanism.

RESULTS

We found that intrauterine hyperglycemia exposure resulted in obesity, insulin resistance, and/or glucose intolerance in F2 male mice, but no metabolic changes in F3 male mice at 8 weeks. Using reduced representation bisulfite sequencing, we found DNA methylome of day 13.5 PGCs from F1-GDM fetuses revealed differently methylated genes enriched in obesity and diabetes. Methylation validation of the insulin resistance and fat accumulation gene Fyn showed a consistent hypomethylation status in F1 PGCs, F1 fetal testes, sperm from F1/C-GDM mice, and somatic cells from F2-GDM male mice. In contrast, no methylation alteration was observed in F2-GDM male germ cells and F3-GDM somatic cells.

CONCLUSION

We provide evidence that intrauterine hyperglycemia exposure per se contributes to intergenerational metabolic changes in the F2 but not F3 generation. And the aberrant DNA methylation reprogramming occurs as early as day 13.5 in PGCs of the F1 generation. Our findings suggest that intrauterine exposure alone is sufficient to cause the epigenetic inheritance in F2 offspring, and the epigenetic memory carried by DNA methylation pattern could be erased by the second wave of methylation reprogramming in F2 PGCs during fetal development.

Neurotoxic Effects of Platinum Compounds: Studies in vivo on Intracellular Calcium Homeostasis in the Immature Central Nervous System

Platinum compounds cause significant clinical neurotoxicity. Several studies highlight neurological complications especially in paediatric oncology patients with Central Nervous System (CNS) and non-CNS malignancies. To understand the toxicity mechanisms of platinum drugs at cellular and molecular levels in the immature brain, which appears more vulnerable to injury than in the adult one, we compared the effects in vivo of the most used platinum compounds, i.e., cisdichlorodiammineplatinum (cisplatin, cisPt), and the new [Pt(O,O′-acac)(γ-acac)(DMS)] (PtAcacDMS). As models of developing brain areas, we have chosen the cerebellum and hippocampus dentate gyrus. Both areas show the neurogenesis events, from proliferation to differentiation and synaptogenesis, and therefore allow comparing the action of platinum compounds with DNA and non-DNA targets. Here, we focused on the changes in the intracellular calcium homeostasis within CNS architecture, using two immunohistochemical markers, the calcium buffer protein Calbindin and Plasma Membrane Calcium ATPase. From the comparison of the cisPt and PtAcacDMS effects, it emerges how essential the equilibrium and synergy between CB and PMCA1 is or how important the presence of at least one of them is to warrant the morphology and function of nervous tissue and limit neuroarchitecture damages, depending on the peculiar and intrinsic properties of the developing CNS areas.

Cerebellum neurotransmission during postnatal development: [Pt(O,O'-acac)(γ-acac)(DMS)] vs cisplatin and neurotoxicity

Several chemotherapeutic drugs are known to cause neurotoxicity. Platinum-based agents in use or in clinical trials display neurotoxic potential accompanied by neurological complications; recent studies have identified a large number of behavioural issues in paediatric oncology patients. To understand the toxicity of platinum drugs at the molecular and cellular levels, this study compares the possible cytotoxic effects of an older platinum compound, cisplatin and a new platinum compound, [Pt(O,O'-acac)(γ-acac)(DMS)], on the CNS of postnatally developing rats, which is much more vulnerable to injury than the CNS of adult rats. Since several drugs interact with neurotransmitters during neuronal maturation, we performed immunostainings with antibodies raised against markers of glutamate and GABA, the major neurotransmitters in the cerebellum. After a single injection of cisplatin at postnatal day 10 (PD10), the labelling of Purkinje cells with the neurotransmitter markers evidenced alterations between PD11 and PD30, i.e. atrophy of the dendrite tree, changes in the distribution of synaptic contacts of parallel and climbing fibres, delay in the elimination of transient synapses on cell soma and severely impaired pinceau formation at the axon hillock. After treatment with [Pt(O,O'-acac)(γ-acac)(DMS)], the sole relevant change concerned the timing of climbing fibres elimination; the transient synapses disappearance on the Purkinje cell soma was delayed in some cells; instead, the growth of Purkinje cell dendrite tree was normal as was the formation of inhibitory synaptic contacts on these neurons. These findings add new evidence not only on the lower neurotoxicity of [Pt(O,O'-acac)(γ-acac)(DMS)] vs cisplatin but also on the involvement of neurotransmitters and relative synaptic connections in the maturation of central nerve tissue.

Prenatal antidepressant exposure: clinical and preclinical findings

Pharmacological treatment of any maternal illness during pregnancy warrants consideration of the consequences of the illness and/or medication for both the mother and unborn child. In the case of major depressive disorder, which affects up to 10-20% of pregnant women, the deleterious effects of untreated depression on the offspring can be profound and long lasting. Progress has been made in our understanding of the mechanism(s) of action of antidepressants, fetal exposure to these medications, and serotonin's role in development. New technologies and careful study designs have enabled the accurate sampling of maternal serum, breast milk, umbilical cord serum, and infant serum psychotropic medication concentrations to characterize the magnitude of placental transfer and exposure through human breast milk. Despite this progress, the extant clinical literature is largely composed of case series, population-based patient registry data that are reliant on nonobjective means and retrospective recall to determine both medication and maternal depression exposure, and limited inclusion of suitable control groups for maternal depression. Conclusions drawn from such studies often fail to incorporate embryology/neurotransmitter ontogeny, appropriate gestational windows, or a critical discussion of statistically versus clinically significant. Similarly, preclinical studies have predominantly relied on dosing models, leading to exposures that may not be clinically relevant. The elucidation of a defined teratological effect or mechanism, if any, has yet to be conclusively demonstrated. The extant literature indicates that, in many cases, the benefits of antidepressant use during pregnancy for a depressed pregnant woman may outweigh potential risks.

Developing central nervous system and vulnerability to platinum compounds

Comparative studies on the effects of the platinum complexes in use or in clinical trials are carried out in order to discover differences in the neurotoxic potential and the reversibility of neurotoxicity. In this paper, we summarized the current literature on neurotoxicity and chemoresistance of cisplatin (cisPt) and discussed our recent efforts on the interference of cisPt and a new platinum compound [Pt(O,O′-acac)(γ-acac)(DMS)] (PtAcacDMS), with high specific reactivity with sulphur ligands instead of nucleobases as cisPt, on some crucial events of rat postnatal cerebellum development. The acute effects of drug treatments on cell proliferation and death in the external granular layer and granule cell migration and the late effects on the dendrite growth of Purkinje cells were evaluated. Together with the demonstrated antineoplastic effectiveness in vitro, compared with cisPt, data suggest a lower neurotoxicity of PtAcacDMS, in spite of its presence in the brain that involves considerations on the blood brain barrier permeability.

Effects of glufosinate on antioxidant enzymes, subcellular structure, and gene expression in the unicellular green alga Chlorella vulgaris

Greater exposure to herbicide increases the likelihood of harmful effects in humans and the environment. Glufosinate, a non-selective herbicide, inhibits glutamine synthetase (GS) and thus blocks ammonium assimilation in plants. In the present study, the aquatic unicellular alga Chlorella vulgaris was chosen to assess the effects of acute glufosinate toxicity. We observed physiological changes during 12-96 h of exposure, and gene transcription during 6-48 h of exposure. Exposure to glufosinate increased malondialdehyde content by up to 2.73 times compared with the control, suggesting that there was some oxidative damage. Electron microscopy also showed that there were some chloroplast abnormalities in response to glufosinate. The activities of the antioxidant enzymes superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) also increased markedly in the presence of glufosinate. Maximum activities of SOD, POD, and CAT were 2.90, 2.91, and 2.48 times that of the control, respectively. These elevated activities may help alleviate oxidative damage. A real-time polymerase chain reaction (PCR) assay showed changes in transcript abundances of three photosynthetic genes, psaB, psbC, and rbcL. The results showed that glufosinate reduced the transcript abundances of the three genes after 12h exposure. The lowest abundances of psaB, psbC and rbcL transcripts in response to glufosinate exposure were 38%, 16% and 43% of those of the control, respectively. Our results demonstrate that glufosinate affects the activities of antioxidant enzymes, disrupts chloroplast ultrastructure, and reduces transcription of photosynthesis-related genes in C. vulgaris.

Environmental epigenomics and disease susceptibility

Epidemiological evidence increasingly suggests that environmental exposures early in development have a role in susceptibility to disease in later life. In addition, some of these environmental effects seem to be passed on through subsequent generations. Epigenetic modifications provide a plausible link between the environment and alterations in gene expression that might lead to disease phenotypes. An increasing body of evidence from animal studies supports the role of environmental epigenetics in disease susceptibility. Furthermore, recent studies have demonstrated for the first time that heritable environmentally induced epigenetic modifications underlie reversible transgenerational alterations in phenotype. Methods are now becoming available to investigate the relevance of these phenomena to human disease.

Analysis of reproductive toxicity and classification of glufosinate-ammonium

CONCLUSION REGARDING CLASSIFICATION OF GLUFOSINATE-AMMONIUM: Science Partners' Evaluation Group (Evaluation Group) has conducted an independent analysis of the herbicide glufosinate-ammonium (GA) relative to its potential to cause reproductive toxicity in humans. Further, the Evaluation Group has evaluated the implementation of Annex 6 of Commission Directive 2001/59/EC (28th ATP of Council Directive 67/548/EEC) and Council Directive 91/414/EEC, with respect to classification of chemicals posing potential reproductive hazards. After consideration of all information available to us relevant to the potential of glufosinate-ammonium (GA) to cause reproductive toxicity, the Science Partners Evaluation Group concludes that no classification of GA is justified. The following form the basis of this conclusion. There are no human data to suggest that GA causes reproductive toxicity in women or in their conceptus. The issue concerning possible reproductive hazard to humans is raised solely on the basis of positive animal test results that show GA to cause preimplantation or implantation losses in rats. SPECIFICALLY: a. Daily treatment with GA had no detectable effect on the earliest stages of the reproductive sequence including gametogenesis, ovulation, mating and conception; b. Treatment with GA interfered with rat gestation before and at the stage when the conceptus implants into the uterus. This effect occurred at doses of 360 ppm in the feed (corresponding to daily doses of 27.8 mg/kg bw) and above; and c. After implantation, no further effect of GA on prenatal and post-natal development was recognized. Previous concerns that GA might be toxic to embryonic stages after implantation were not supported by the data. Abortions and stillbirth seen were associated with, and regarded as secondary to, maternal toxicity. There was no evidence suggesting the induction of malformations in the offspring. The mechanism underlying this adverse effect in experimental laboratory animals is identified-inhibition of glutamine synthetase. Glutamine is essential to the viability of the embryo. The embryo is dependent on a maternal source of the amino acid. For embryo lethality to occur, a significant reduction of maternal glutamine is required. Such reduction in maternal glutamine depends on a significant inhibition of glutamine synthetase by GA. This can only occur when the mother is exposed to very high levels of GA. SPECIFICALLY: a. The reproductive toxicity of GA is confined to very short, early stages of reproduction, during which the conceptus is dependent on maternal glutamine; and b. In order for the effect to occur, significant reduction in maternal blood glutamine level is required, which in turn depends on a significant inhibition of glutamine synthetase, induced by high levels of GA in the maternal system. There is no evidence for accumulation of GA in the mammalian organism beyond a factor of two and no evidence for its metabolic toxification. To raise a concern in humans, women would have to be exposed to GA during the very limited time frame of preimplantation or implantation and the exposure would have to be to the exceedingly high levels necessary to alter the maternal metabolism and, correspondingly, result in glutamine levels in maternal tissue and blood plasma being drastically reduced. There is no basis to suggest that such exposures would occur under conditions of normal handling and use. SPECIFICALLY: a. Under conditions of normal handling and use, operators would never be exposed to GA levels that could potentially inhibit glutamine synthetase to the extent that this inhibition could impair preimplantation or implantation. b. All acceptable exposure measurements and predictive calculations confirm this conclusion, and in fact demonstrate that reasonably foreseeable exposure of workers would be to levels significantly below the AOEL. c. The evidence is also clear that there is no reproductive toxicity hazard to workers upon reentry tosprayed fields, bystanders, consumers or toddlers. The safety margin compared to the NOAEL in animal studies is sufficiently large to assure protection of the health of workers using GA as well as bystanders, consumers, and toddlers. Pursuant to Annex 6 of Commission Directive 2001/59/EC (28th ATP of Council Directive 67/548/EEC), to justify a classification of category 2 there must be sufficient evidence to produce a strong presumption that human exposure to the substance may result in impaired fertility in humans. It is the conclusion of the Science Partners Evaluation Group that there is no reasonable evidence to suggest a strong presumption of impairment. To the contrary, there is clear evidence demonstrating a strong presumption that exposure to GA would not cause the adverse effect demonstrated in rats. Pursuant to Annex 6 of Commission Directive 2001/59/EC (28th ATP of Council Directive 67/548/EEC), to justify a classification of category 3, there must be sufficient evidence to provide a strong suspicion of impaired fertility in humans. There is no basis to conclude that the animal data demonstrating impaired preimplantation or implantation has any relevance to humans in that the effect found in rats only occurs at levels which would never be experienced by workers under conditions of normal handling and use or by bystanders, consumers, or toddlers.

Seminiferous cord formation and germ-cell programming: epigenetic transgenerational actions of endocrine disruptors

The molecular and cellular control of embryonic testis development was investigated through an analysis of the embryonic testis transcriptome to identify potential regulatory factors for male sex determination and testis morphogenesis. One critical factor identified is neurotropin 3 (NT3). At the onset of male sex determination, Sertoli cells initiate differentiation and express NT3 to act as a chemotactic factor for mesonephros cells to migrate and associate with Sertoli-germ cell aggregates to promote cord formation. Promoter analysis suggests that NT3 may be an initial downstream gene to SRY and helps promote testis morphogenesis. Endocrine disruptors were used to potentially interfere with embryonic testis development and further investigate this biological process. The estrogenic pesticide methoxychlor and antiandrogenic fungicide vinclozolin were used. Previous studies have shown that methoxychlor and vinclozolin both interfere with embryonic testis cord formation and cause increased spermatogenic cell apoptosis in the adult testis. Interestingly, transient in vivo exposure to endocrine disruptors at the time of male sex determination caused a transgenerational phenotype (F1-F4) of spermatogenic cell apoptosis and subfertility. This apparent epigenetic mechanism involves altered DNA methylation and permanent re-programming of the male germ-line. A series of genes with altered DNA methylation and imprinting are being identified. Observations reviewed demonstrate that a transient embryonic in utero exposure to an endocrine disruptor influences the embryonic testis transcriptome and through epigenetic effects (e.g., DNA methylation) results in abnormal germ-cell differentiation that subsequently influences adult spermatogenic capacity and male fertility, and that this phenotype is transgenerational through the germ-line. The novel observations of transgenerational epigenetic endocrine disruptor actions on male reproduction critically impact the potential hazards of these compounds as environmental toxins. The literature reviewed provides insight into the molecular and cellular control of embryonic testis development, male sex determination, and the programming of the male germ-line.

Cervical neoplasia during pregnancy: Diagnosis, management and prognosis

Pregnancy represents an exceptional opportunity for the early diagnosis of cervical cancer since visual inspection, cytological examination and bimanual palpation are considered to be part of routine antenatal care. An abnormal cervical smear should generally be managed as in the non-pregnant state. However, colposcopy and biopsies are mainly intended to exclude invasive disease because a conservative approach is preferred in cases of pre-invasive disease. The only absolute indication for conization in pregnancy is to rule out (micro-)invasive disease or make the diagnosis of invasive carcinoma when such a diagnosis will alter the timing or mode of delivery. Overall, earlier stages of cervical cancer are encountered during pregnancy compared with the general population. Although stage of disease and gestational age will largely influence the timing of the interventions, treatment of invasive cervical cancer is similar to the non-pregnant state. In strongly desired pregnancies, the use of neo-adjuvant chemotherapy in order to obtain fetal maturity should be considered and discussed with the patient. Although good evidence supports short-term safety, long-term data regarding the in-utero exposure of cytotoxic drugs need to be consolidated. After stratifying for stage, the outcome is similar to the non-pregnant state.

Systems biology: new approaches to old environmental health problems

The environment plays a pivotal role as a human health determinant and presence of hazardous pollutants in the environment is often implicated in human disease. That pollutants cause human diseases however is often controversial because data connecting exposure to environmental hazards and human diseases are not well defined, except for some cancers and syndromes such as asthma. Understanding the complex nature of human-environment interactions and the role they play in determining the state of human health is one of the more compelling problems in public health. We are becoming more aware that the reductionist approach promulgated by current methods has not, and will not yield answers to the broad questions of population health risk analysis. If substantive applications of environment-gene interactions are to be made, it is important to move to a systems level approach, to take advantage of epidemiology and molecular genomic advances. Systems biology is the integration of genomics, transcriptomics, proteomics, and metabolomics together with computer technology approaches to elucidate environmentally caused disease in humans. We discuss the applications of environmental systems biology as a route to solution of environmental health problems.

Effect of the herbicide glyphosate on enzymatic activity in pregnant rats and their fetuses

To prevent health risk from environmental chemicals, particularly for progeny, we have studied the effects of the herbicide glyphosate on several enzymes of pregnant rats. Glyphosate is an organophosphorated nonselective agrochemical widely used in many countries including Argentina and acts after the sprout in a systemic way. We have studied three cytosolic enzymes: isocitrate dehydrogenase-NADP dependent, glucose-6-phosphate dehydrogenase, and malic dehydrogenase in liver, heart, and brain of pregnant Wistar rats. The treatment was administered during the 21 days of pregnancy, with 1 week as an acclimation period. The results suggest that maternal exposure to agrochemicals during pregnancy induces a variety of functional abnormalities in the specific activity of the enzymes in the studied organs of the pregnant rats and their fetuses.