Nicotine alters bovine oocyte meiosis and affects subsequent embryonic development

Nicotine as a female reproductive toxicant-A review

The preceding decades have seen an extensive emergence of the harmful effects of tobacco smoke on systemic health. Among the various compounds of tobacco, nicotine is one of the principal, potentially hazardous, and toxic components which is an oxidant agent that can affect both men's and women's fertility. Nicotine exerts its effect by modulating the expression of transmembrane ligand-gated ion channels called nicotinic acetylcholine receptors. The activities of female reproduction might be disrupted by exposure to nicotine at various sites, such as the ovary or reproductive tract. It's been demonstrated that nicotine might cause oxidative stress, apoptosis, hormonal imbalance, abnormalities in chromosomal segregation, impact oocyte development, and disruption in ovarian morphology and functions. This review paper summarizes the findings and provides an updated overview of the evidence on the harmful effects of nicotine use on women's reproductive health and the resulting detrimental impacts on the body. Additionally, it provides the detailed possible mechanisms involved in impairing reproductive processes like folliculogenesis, oocyte maturation, steroidogenesis, and pregnancy in different animal species.

Melatonin prevents oocyte deterioration due to cotinine exposure in mice

Levels of cotinine, a major metabolite of nicotine, have been positively correlated with risks of cigarette smoking-related diseases. Melatonin is synthesized by the pineal gland and has been demonstrated to be beneficial to oocyte maturation due to its antioxidative activity. In this study, we investigated the effects of cotinine on mouse oocyte meiosis and the protective roles of melatonin in vitro and in vivo. The results showed that cotinine exposure caused defects in the first polar body extrusion and reduced parthenogenetic activation in in vitro-matured oocytes. Additionally, cotinine exposure increased the level of oxidative stress, which resulted in aberrant actin distribution, abnormal spindle morphology, chromosome misalignment, and even oocyte aneuploidy. Simultaneously, cotinine exposure decreased the mitochondrial membrane potential and antioxidant gene expression and increased apoptosis-related gene expression. However, all these toxic effects of cotinine could be reversed after the addition of melatonin, and the mechanism may be a decrease in reactive oxygen species production. In conclusion, cotinine causes poor oocyte quality, which could be rescued by melatonin supplementation during meiotic maturation in mouse oocytes.

Does maternal exposure to nicotine affect the oocyte quality and reproductive capacity in adult offspring?

Gonadal development begins in the intrauterine phase and females from most species are born with an established oocyte reserve. Exposure to drugs during gestation can compromise the offspring health, also affecting the gametes quality. Nicotine, the main component of cigarettes, is an oxidant agent capable of altering the fertility in men and women. As female gametes are susceptible to oxidative stress, this drug can damage the oolemma and affect oocyte maturation, induce errors during chromosomal segregation and DNA fragmentation. Oocyte mitochondria are particularly susceptible to injuries, contributing to the oocyte quality loss and embryonic development disruption. Thus, considering the high number of women who smoke during pregnancy, while significant events are occurring in the embryo for future fertility of offspring, we seek to verify the quality of the oocytes from adult rats exposed to nicotine during intrauterine phase and breastfeeding. Pregnant Wistar rats received nicotine by osmotic mini-pumps and the female progenies were evaluated in adulthood for oocyte quality (viability, lipid peroxidation, generation of reactive oxygen species and mitochondrial integrity) and reproductive capacity. Embryos (3dpc) and fetuses (20dpc) generated by these rats were also evaluated. The results showed that the dose of 2 mg/kg/day of nicotine through placenta and breast milk does not affect the number of oocytes and the fertility capacity of adult rats. However, it causes some morphological alterations in oocytes, mitochondrial changes, embryonic fragmentation and disruption of fetal development. The malformations in fetuses generated from these gametes can also indicate the occurrence of epigenetic modifications.

Effects of ethanol and nicotine co-administration on follicular atresia and placental histo-morphology in the first-generation mice pups during intrauterine development and lactation periods

This study is evaluating the effects of ethanol and nicotine exposure during pregnancy and lactation on placenta histology and follicular atresia in the first-generation (f1) mice pups. The experimental groups were 5 groups of NMRI pregnant mice, including: control, vehicle (received normal saline) ethanol (3 g/kg/day, 20 % v/v intraperitoneally), nicotine (1 mg/kg/day, subcutaneously), and ethanol plus nicotine which received both. Pregnant animals in each group were then divided into two groups, one group for examining the placenta that was treated for 18 days and the other group for the ovary of one-day-old (PND1) and fifty-six-day-old (PND56) female offspring who were treated for 42 days (during intrauterine development and lactation). After the autopsy procedure, histopathological and morphometrical observations were done. Data revealed that the exposed mice had a significant change in the placenta morphometry and histology as well as a marked increase in the number of ovarian TUNEL positive cells on postnatal days 1 and 56. Therefore, maternal exposure to alcohol and nicotine during developmental and lactation periods could lead to changes in the placenta properties as well as an increase in the apoptotic ovarian follicles in f1 mice pups.

Effects of Cigarette Smoking on Preimplantation Embryo Development

In this chapter, we first gave a brief introduction to the detriments of cigarette smoking, with an emphasis on its adverse effects on female reproductive health. Then, we outlined recent advances about the impacts of cigarette smoke on preimplantation embryo development. Additionally, toxicities of cadmium and benzo(a)pyrene (BaP) at this specific developmental window were also discussed, to illustrate the potential mechanisms involved in cigarette smoke-associated embryotoxicity. Finally, we provide an overview of the issues to be solved in the future research. Further studies about the molecular mechanism of cigarette smoking-associated female infertility may provide vital insights into developing new interventions for the women smokers and thus improving their reproductive outcomes.

Nicotine Induces Polyspermy in Sea Urchin Eggs through a Non-Cholinergic Pathway Modulating Actin Dynamics

While alkaloids often exert unique pharmacological effects on animal cells, exposure of sea urchin eggs to nicotine causes polyspermy at fertilization in a dose-dependent manner. Here, we studied molecular mechanisms underlying the phenomenon. Although nicotine is an agonist of ionotropic acetylcholine receptors, we found that nicotine-induced polyspermy was neither mimicked by acetylcholine and carbachol nor inhibited by specific antagonists of nicotinic acetylcholine receptors. Unlike acetylcholine and carbachol, nicotine uniquely induced drastic rearrangement of egg cortical microfilaments in a dose-dependent way. Such cytoskeletal changes appeared to render the eggs more receptive to sperm, as judged by the significant alleviation of polyspermy by latrunculin-A and mycalolide-B. In addition, our fluorimetric assay provided the first evidence that nicotine directly accelerates polymerization kinetics of G-actin and attenuates depolymerization of preassembled F-actin. Furthermore, nicotine inhibited cofilin-induced disassembly of F-actin. Unexpectedly, our results suggest that effects of nicotine can also be mediated in some non-cholinergic pathways.

Mode-of-action analysis of the effects induced by nicotine in the in vitro micronucleus assay

Nicotine's genotoxic potential has been extensively studied in vitro. While the results of mammalian cell-based studies have inferred that it can potentially damage chromosomes, in general and with few exceptions, adverse DNA effects have been observed primarily at supraphysiological concentrations in nonregulatory assays that provide little information on its mode-of-action (MoA). In this study, a modern-day regulatory genotoxicity assessment was conducted using a flow cytometry-based in vitro micronucleus (MN) assay, Good Laboratory Practice study conditions, Chinese hamster ovary cells of known provenance, and acceptance/evaluation criteria from the current OECD Test Guideline 487. Nicotine concentrations up to 3.95 mM had no effect on background levels of DNA damage; however, concentrations above the point-of-departure range of 3.94-4.54 mM induced increases in MN and hypodiploid nuclei, indicating a possible aneugenicity hazard. Follow-up experiments designed to elucidate nicotine's MoA revealed cellular vacuolization, accompanying distortions in microtubules, inhibition of tubulin polymerization, centromere-positive DNA, and multinucleate cells at MN-inducing concentrations. Vacuoles likely originated from acidic cellular compartments (e.g., lysosomes). Remarkably, genotoxicity was suppressed by chemicals that raised the luminal pH of these organelles. Other endpoints (e.g., changes in phosphorylated histones) measured in the study cast doubt on the biological relevance of this apparent genotoxicity. In addition, three major nicotine metabolites, including cotinine, had no MN effects but nornicotine induced a nicotine-like profile. It is possible that nicotine's lysosomotropic properties drive the genotoxicity observed in vitro; however, the potency and mechanistic insights revealed here indicate that it is likely of minimal physiological relevance for nicotine consumers. Environ. Mol. Mutagen. 2019. © 2019 The Authors. Environmental and Molecular Mutagenesis published by Wiley Periodicals, Inc. on behalf of Environmental Mutagen Society.

Cigarette smoking and hormones

PURPOSE OF REVIEW

The purpose is to provide a summary of the effects of cigarette smoking on steroid hormone metabolism and how it affects female fertility.

RECENT FINDINGS

Components of tobacco smoke such as polycyclic aromatic hydrocarbons lead to transcriptional upregulation of a number of genes, including members of the cytochrome P450 (CYP) family, in particular CYP1B1 and CYP1A1. In humans, CYP1A1 and CYP1A2 are the primary enzymes catalyzing the 2-hydroxylation of estradiol. This pathway shunts available estrogen away from the more estrogenically potent 16α-hydroxylation to the production of catechol estrogens, mainly 2 and 4 hydroxyestradiol.

SUMMARY

Smoking has multiple effects on hormone secretion and metabolism. These effects are mainly mediated by the pharmacological action of tobacco alkaloids (nicotine and its metabolite cotinine). A strong body of evidence indicates that the negative effects of cigarette smoking on fertility compromises nearly every system involved in the reproductive process.

Ovotoxicity of cigarette smoke: A systematic review of the literature

This study reviews the scientific literature on the noxious effects of cigarette smoke on the ovarian follicle, and the cumulative data on the impact of smoking on in vitro fertilization (IVF) cycle outcome. There is a close association between tobacco smoke and accelerated follicle loss, abnormal follicle growth and impairment of oocyte morphology and maturation. There is an increasing amount of evidence indicating that smoke can directly derange folliculogenesis. Increased cellular apoptosis or autophagy, DNA damage and abnormal crosstalk between oocyte and granulosa cells have been implicated in the demise of ovarian follicles. It becomes increasingly clear that maternal smoking can exert multigenerational effects on the ovarian function of the progeny. Growing evidence suggests that cigarette smoke is associated with decreased results after IVF. Further research is needed to better define the molecular mechanisms behind smoking-induced ovarian disruption.

A protective role of cumulus cells after short-term exposure of rat cumulus cell-oocyte complexes to lifestyle or environmental contaminants

Ovarian follicular fluid provides a potential reservoir for exogenous compounds that may adversely affect oocyte quality. This study examined the effects of common lifestyle and environmental contaminants, namely bisphenol-A (BPA), caffeine, 3,4-methylenedioxymethamphetamine (MDMA), nicotine and Δ⁹-tetrahydrocannabinol (THC) on gap junction genes (Gja1, Gja4) and proteins (GJA1), glucose metabolism genes (Gfpt1, Pfkp) and oocyte growth factor genes (Bmp15, Gdf9), as well as gap junction transfer rate, in rat cumulus-oocyte complexes (COCs). In vitro exposure to MDMA and THC accelerated the timing of meiotic resumption and all contaminants altered either gap junction gene expression (BPA, caffeine, MDMA and THC) or transfer rate (BPA and nicotine). In vitro exposure of COCs to MDMA also altered glucose metabolism genes. Overall, oocyte-derived genes were largely unaffected following exposure to any contaminant. In summary, the impact of short-term exposure to lifestyle and environmental contaminants on oocyte function may be diminished due to protective properties of cumulus cells.

Prenatal and lactation nicotine exposure affects Sertoli cell and gonadotropin levels in rats

Nicotine is largely consumed in the world as a component of cigarettes. It can cross the placenta and reach the milk of smoking mothers. This drug induces apoptosis, affects sex hormone secretion, and leads to male infertility. To investigate the exposure to nicotine during the whole intrauterine and lactation phases in Sertoli cells, pregnant rats received nicotine (2 mg/kg per day) through osmotic minipumps. Male offsprings (30, 60, and 90 days old) had blood collected for hormonal analysis (FSH and LH) and their testes submitted for histophatological study, analysis of the frequency of the stages of seminiferous epithelium cycle, immunolabeling of apoptotic epithelial cells (TUNEL and Fas/FasL), analysis of the function and structure of Sertoli cells (respectively using transferrin and vimentin immunolabeling), and analysis of Sertoli-germ cell junctional molecule (β-catenin immunolabeling). The exposure to nicotine increased the FSH and LH plasmatic levels in adult rats. Although nicotine had not changed the number of apoptotic cells, neither in Fas nor FasL expression, it provoked an intense sloughing of epithelial cells and also altered the frequency of some stages of the seminiferous epithelium cycle. Transferrin and β-catenin expressions were not changed, but vimentin was significantly reduced in the early stages of the seminiferous cycle of the nicotine-exposed adult rats. Thus, we concluded that nicotine exposure during all gestational and lactation periods affects the structure of Sertoli cells by events causing intense germ cell sloughing observed in the tubular lumen and can compromise the fertility of the offspring.

Usefulness of bovine and porcine IVM/IVF models for reproductive toxicology

Women presenting fertility problems are often helped by Assisted Reproductive Techniques (ART), such as in vitro fertilization (IVF) programs. However, in many cases the etiology of the in/subfertility remains unknown even after treatment. Although several aspects should be considered when assisting a woman with problems to conceive, a survey on the patients' exposure to contaminants would help to understand the cause of the fertility problem, as well as to follow the patient properly during IVF. Daily exposure to toxic compounds, mainly environmental and dietary ones, may result in reproductive impairment. For instance, because affects oocyte developmental competence. Many of these compounds, natural or synthetic, are endocrine disruptors or endocrine active substances that may impair reproduction. To understand the risks and the mechanism of action of such chemicals in human cells, the use of proper in vitro models is essential. The present review proposes the bovine and porcine models to evaluate toxic compounds on oocyte maturation, fertilization and embryo production in vitro. Moreover, we discuss here the species-specific differences when mice, bovine and porcine are used as models for human.

SGO1 maintains bovine meiotic and mitotic centromeric cohesions of sister chromatids and directly affects embryo development

Shugoshin (SGO) is a critical factor that enforces cohesion from segregation of paired sister chromatids during mitosis and meiosis. It has been studied mainly in invertebrates. Knowledge of SGO(s) in a mammalian system has only been reported in the mouse and Hela cells. In this study, the functions of SGO1 in bovine oocytes during meiotic maturation, early embryonic development and somatic cell mitosis were investigated. The results showed that SGO1 was expressed from germinal vesicle (GV) to the metaphase II stage. SGO1 accumulated on condensed and scattered chromosomes from pre-metaphase I to metaphase II. The over-expression of SGO1 did not interfere with the process of homologous chromosome separation, although once separated they were unable to move to the opposing spindle poles. This often resulted in the formation of oocytes with 60 replicated chromosomes. Depletion of SGO1 in GV oocytes affected chromosomal separation resulting in abnormal chromosome alignment at a significantly higher proportion than in control oocytes. Knockdown of SGO1 expression significantly decreased the embryonic developmental rate and quality. To further confirm the function(s) of SGO1 during mitosis, bovine embryonic fibroblast cells were transfected with SGO1 siRNAs. SGO1 depletion induced the premature dissociation of chromosomal cohesion at the centromere and along the chromosome arm giving rise to abnormal appearing mitotic patterns. The results of this study infer that SGO1 is involved in the centromeric cohesion of sister chromatids and chromosomal movement towards the spindle poles. Depletion of SGO1 causes arrestment of cell division in meiosis and mitosis.

The bovine oocyte in vitro maturation model: a potential tool for reproductive toxicology screening

Reproductive toxicity testing according to the present guidelines requires a high number of animals. Therefore, the development of alternative in vitro methods is urgently required. The aim of the present study was to investigate the applicability domain of the bovine oocyte in vitro maturation assay (bIVM) to study female reproductive toxicology. Therefore, bovine oocytes were exposed to a broad set of chemicals of two distinct biological function groups: (a) affecting female fertility and (b) affecting embryonic development and having a broad range of physical and chemical properties. The endpoints evaluated were the oocyte nuclear maturation (progression of meiosis) and general cytotoxicity. The oocyte nuclear maturation was negatively affected by all compounds tested and the effect was observed at concentrations lower than the cytotoxic ones. The bIVM assay correctly predicted the classification of compounds between those predefined groups. Additionally, the bIVM model contributes significantly for the 3R principle, since no test animals are used in this assay. In conclusion, the bIVM is a sensitive and valuable alternative assay to identify potential chemical hazard on female fertility.

Diploid oocyte formation and tetraploid embryo development induced by cytochalasin B in bovine

Tetraploid embryos are a useful model for postimplantation development of polyploidy cells, and tetraploid cells are an advantage in studies for chimeras yielding offspring completely derived from embryo stem cells or induced pluripotent cells. This study was designed to investigate the effects of cytochalasin B (CB) on bovine oocyte meiosis, and to induce the formation of diploid oocytes and tetraploid embryos. The results showed that: (1) incubation of oocytes in CB at ≥2.0 μg/mL concentrations for 24 h significantly decreased oocyte maturation and the matured oocytes' haploid composition. Over 50% of the CB-treated oocytes did not expel PB1 (non-PB1), and most of the non-PB1 oocytes contained 2n (60) chromosomes. (2) Pretreatment of oocytes with CB at concentrations of 7.5 and 15 μg/mL for 10 h significantly decreased oocyte maturation. Posttreatment of oocytes with CB resulted in most of the oocytes containing 2n chromosomes. (3) The parthenogenetic blastocysts (25-28%) derived from the non-PB1 oocytes of posttreatment group was significantly higher than that from pretreatment, whole period treatment, and the control oocytes (12-16%). (4) Cytogenetic analysis of the embryos derived from CB-treated non-PB1 oocytes resulted in 74% of the one-cell stage embryos being 4n = 120 chromosomes, 82% of two-cell stage embryos contained 4n chromosomes in each blastomere, and 75% of the blastocysts were tetraploidy (4n = 120). (6) The stopped uncleaved one-cell embryos showed an amazing phenomenon of over 15% of them containing extra chromosomes, which suggested multiple DNA duplication occurred within 40 h after activation. In conclusion, CB inhibits PB1 extrusion, disfigures spindle structure, decreases oocyte maturation, and results in formation of diploid (2n or 4c) oocytes. The diploid oocytes resulted in a higher development of tetraploid embryos, which would be a unique approach for the production of tetraploid embryos in bovine.

Increased zona pellucida thickness and meiotic spindle disruption in oocytes from cigarette smoking mice

BACKGROUND The precise effects of cigarette smoking on female fertility have not yet been clearly defined. We have used a mouse model that mimics human smoking and is able to control for variables that may confound clinical studies to assess the impact of chronic smoking on the quality of mouse oocytes. METHODS Mice received cigarette smoke directly to their lungs for 12 weeks. Lung tissue was analyzed for emphysematous changes and cumulus enclosed oocytes (CEOs) were recovered to study their quality. CEOs were in vitro matured, fixed and stained for chromatin and tubulin. Meiotic spindles, chromatin and the zona pellucida were all examined using confocal microscopy. RESULTS After 12 weeks of cigarette smoking, mice developed alveolar tissue damage that was determined by an increase in destructive index of the lung parenchyma. The numbers of oocytes recovered and the rates of oocyte maturation were not significantly different from non-smoking mice. However, oocytes from smoking mice had a significantly thicker zona pellucida along with shorter and wider meiotic spindles. Furthermore in total, almost a quarter of oocytes from smoking mice were abnormal as assessed by either errors in chromosomal congression or spindle shape. CONCLUSIONS We have used a novel model of inhalational cigarette smoking to show that chronic smoking has a detrimental effect on oocyte quality, and this can be observed even though oocytes are removed from the ovary and cultured in vitro.

Effects of cigarette smoking on reproduction

BACKGROUND Cigarette smoking is associated with lower fecundity rates, adverse reproductive outcomes and a higher risk of IVF failures. Over the last few decades, prevalence of smoking among women of reproductive age has increased. This review focuses on current knowledge of the potential effects of smoke toxicants on all reproductive stages and the consequences of smoke exposure on reproductive functions. METHODS We conducted a systematic review of the scientific literature on the impact of cigarette smoking and smoke constituents on the different stages of reproductive function, including epidemiological, clinical and experimental studies. We attempted to create hypotheses and find explanations for the deleterious effects of cigarette smoke observed in experimental studies. RESULTS Cigarette smoke contains several thousand components (e.g. nicotine, polycyclic aromatic hydrocarbons and cadmium) with diverse effects. Each stage of reproductive function, folliculogenesis, steroidogenesis, embryo transport, endometrial receptivity, endometrial angiogenesis, uterine blood flow and uterine myometrium is a target for cigarette smoke components. The effects of cigarette smoke are dose-dependent and are influenced by the presence of other toxic substances and hormonal status. Individual sensitivity, dose, time and type of exposure also play a role in the impact of smoke constituents on human fertility. CONCLUSIONS All stages of reproductive functions are targets of cigarette smoke toxicants. Further studies are necessary to better understand the deleterious effects of cigarette smoke compounds on the reproductive system in order to improve health care, help to reduce cigarette smoking and provide a better knowledge of the molecular mechanisms involved in reproductive toxicology.

Cigarette smoking and reproductive function

PURPOSE OF REVIEW

To perform a systematic review of the literature on the relationship between cigarette smoking and reproductive function. Whenever possible, this review is focused on the most recently published studies (mainly the past 2 years). Nevertheless, in many instances older literature was too relevant not to be taken into account.

RECENT FINDINGS

Tobacco compounds exert a deleterious effect on the process of ovarian follicle maturation. This effect is expressed by worse in-vitro fertilization parameters in cycles performed on women with smoking habits. Also, uterine receptiveness is significantly altered by the smoking habit. In men, cigarette smoking reduces sperm production, increases oxidative stress, and DNA damage. Spermatozoa from smokers have reduced fertilizing capacity, and embryos display lower implantation rates. Even in-utero exposition to tobacco constituents leads to reduced sperm count in adult life.

SUMMARY

A strong body of evidence indicates that the negative effect of cigarette smoking on fertility comprises fairly every system involved in the reproductive process. Couples in reproductive age should be strongly discouraged to smoke.