Effect of nicotine on in vitro maturation of bovine oocytes

Impact of Cigarette Smoking on the Expression of Oxidative Stress-Related Genes in Cumulus Cells Retrieved from Healthy Women Undergoing IVF

The female reproductive system represents a sensitive target of the harmful effects of cigarette smoke, with folliculogenesis as one of the ovarian processes most affected by this exposure. The aim of this study was to analyze the impact of tobacco smoking on expression of oxidative stress-related genes in cumulus cells (CCs) from smoking and non-smoking women undergoing IVF techniques. Real time PCR technology was used to analyze the gene expression profile of 88 oxidative stress genes enclosed in a 96-well plate array. Statistical significance was assessed by one-way ANOVA. The biological functions and networks/pathways of modulated genes were evidenced by ingenuity pathway analysis software. Promoter methylation analysis was performed by pyrosequencing. Our results showed a down-regulation of 24 genes and an up-regulation of 2 genes (IL6 and SOD2, respectively) involved in defense against oxidative damage, cell cycle regulation, as well as inflammation in CCs from smoking women. IL-6 lower promoter methylation was found in CCs of the smokers group. In conclusion, the disclosed overall downregulation suggests an oxidant-antioxidant imbalance in CCs triggered by cigarette smoking exposure. This evidence adds a piece to the puzzle of the molecular basis of female reproduction and could help underlay the importance of antioxidant treatments for smoking women undergoing IVF protocols.

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.

Relationships between intensity, duration, cumulative dose, and timing of smoking with age at menopause: A pooled analysis of individual data from 17 observational studies

BACKGROUND

Cigarette smoking is associated with earlier menopause, but the impact of being a former smoker and any dose-response relationships on the degree of smoking and age at menopause have been less clear. If the toxic impact of cigarette smoking on ovarian function is irreversible, we hypothesized that even former smokers might experience earlier menopause, and variations in intensity, duration, cumulative dose, and age at start/quit of smoking might have varying impacts on the risk of experiencing earlier menopause.

METHODS AND FINDINGS

A total of 207,231 and 27,580 postmenopausal women were included in the cross-sectional and prospective analyses, respectively. They were from 17 studies in 7 countries (Australia, Denmark, France, Japan, Sweden, United Kingdom, United States) that contributed data to the International collaboration for a Life course Approach to reproductive health and Chronic disease Events (InterLACE). Information on smoking status, cigarettes smoked per day (intensity), smoking duration, pack-years (cumulative dose), age started, and years since quitting smoking was collected at baseline. We used multinomial logistic regression models to estimate multivariable relative risk ratios (RRRs) and 95% confidence intervals (CIs) for the associations between each smoking measure and categorised age at menopause (<40 (premature), 40-44 (early), 45-49, 50-51 (reference), and ≥52 years). The association with current and former smokers was analysed separately. Sensitivity analyses and two-step meta-analyses were also conducted to test the results. The Bayesian information criterion (BIC) was used to compare the fit of the models of smoking measures. Overall, 1.9% and 7.3% of women experienced premature and early menopause, respectively. Compared with never smokers, current smokers had around twice the risk of experiencing premature (RRR 2.05; 95% CI 1.73-2.44) (p < 0.001) and early menopause (1.80; 1.66-1.95) (p < 0.001). The corresponding RRRs in former smokers were attenuated to 1.13 (1.04-1.23; p = 0.006) and 1.15 (1.05-1.27; p = 0.005). In both current and former smokers, dose-response relationships were observed, i.e., higher intensity, longer duration, higher cumulative dose, earlier age at start smoking, and shorter time since quitting smoking were significantly associated with higher risk of premature and early menopause, as well as earlier menopause at 45-49 years. Duration of smoking was a strong predictor of age at natural menopause. Among current smokers with duration of 15-20 years, the risk was markedly higher for premature (15.58; 11.29-19.86; p < 0.001) and early (6.55; 5.04-8.52; p < 0.001) menopause. Also, current smokers with 11-15 pack-years had over 4-fold (4.35; 2.78-5.92; p < 0.001) and 3-fold (3.01; 2.15-4.21; p < 0.001) risk of premature and early menopause, respectively. Smokers who had quit smoking for more than 10 years had similar risk as never smokers (1.04; 0.98-1.10; p = 0.176). A limitation of the study is the measurement errors that may have arisen due to recall bias.

CONCLUSIONS

The probability of earlier menopause is positively associated with intensity, duration, cumulative dose, and earlier initiation of smoking. Smoking duration is a much stronger predictor of premature and early menopause than others. Our findings highlight the clear benefits for women of early smoking cessation to lower their excess risk of earlier menopause.

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.

Nicotine derived genotoxic effects in human primary parotid gland cells as assessed in vitro by comet assay, cytokinesis-block micronucleus test and chromosome aberrations test

Genotoxic effects of nicotine were described in different human cells including salivary gland cells. Based on the high nicotine concentration in saliva of smokers or patients using therapeutic nicotine patches, the current study was performed to evaluate the genotoxic potential of nicotine in human salivary gland cells. Therefore, primary salivary gland cells from 10 patients undergoing parotid gland surgery were exposed to nicotine concentrations between 1 μM and 1000 μM for 1 h in the absence of exogenous metabolic activation. The acinar phenotype was proven by immunofluorescent staining of alpha-amylase. Genotoxic effects were evaluated using the Comet assay, the micronucleus test and the chromosome aberration test. Cytotoxicity and apoptosis were determined by trypan blue exclusion test and Caspase-3 assay. Nicotine was able to induce genotoxic effects in all three assays. The chromosome aberration test was the most sensitive and increases in numerical and structural (chromatid-type and chromosome-type) aberrations were seen at ≥1 μM, whereas increases in micronuclei frequency were detected at 10 μM and DNA damage as measured in the Comet assay was noted at >100 μM. No cytotoxic damage or influence of apoptosis could be demonstrated. Nicotine as a possible risk factor for tumor initiation in salivary glands is still discussed controversially. Our results demonstrated the potential of nicotine to induce genotoxic effects in salivary gland cells. These results were observed at saliva nicotine levels similar to those found after oral or transdermal exposure to nicotine and suggest the necessity of careful monitoring of the use of nicotine in humans.

[Effects of cigarette smoking on female reproduction: from oocyte to embryo (Part I)]

Cigarette smoking is associated with lower fecundity rate, adverse reproductive outcomes and higher risk of IVF failure. Over the last decades, prevalence of smoking among women of reproductive age has increased. The aim of this work was to focus on the knowledge of the effects of cigarette smoking on all reproductive stages, from oocyte to embryo. For each reproductive functions human clinical and experimental studies were analysed in order to find hypothesis and explanations for effects observed. All reproductive functions are targets of smoke compounds and cigarette smoking impairs ovarian reserve, sexual steroids synthesis, Fallopian tubes functions and embryo development, leading to reduced fecundity. Some of smoke compounds were identified in ovarian tissue, in uterine fluid and in the embryo, suggesting direct toxicity.

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.