In women, the reproductive harm of toxins such as tobacco smoke is reversible in 6 months: basis for the "olive tree" hypothesis

Ovarian aging: mechanisms and intervention strategies

Ovarian reserve is essential for fertility and influences healthy aging in women. Advanced maternal age correlates with the progressive loss of both the quantity and quality of oocytes. The molecular mechanisms and various contributing factors underlying ovarian aging have been uncovered. In this review, we highlight some of critical factors that impact oocyte quantity and quality during aging. Germ cell and follicle reserve at birth determines reproductive lifespan and timing the menopause in female mammals. Accelerated diminishing ovarian reserve leads to premature ovarian aging or insufficiency. Poor oocyte quality with increasing age could result from chromosomal cohesion deterioration and misaligned chromosomes, telomere shortening, DNA damage and associated genetic mutations, oxidative stress, mitochondrial dysfunction and epigenetic alteration. We also discuss the intervention strategies to delay ovarian aging. Both the efficacy of senotherapies by antioxidants against reproductive aging and mitochondrial therapy are discussed. Functional oocytes and ovarioids could be rejuvenated from pluripotent stem cells or somatic cells. We propose directions for future interventions. As couples increasingly begin delaying parenthood in life worldwide, understanding the molecular mechanisms during female reproductive aging and potential intervention strategies could benefit women in making earlier choices about their reproductive health.

Mitochondria in Ovarian Aging and Reproductive Longevity

Mitochondrial dysfunction is one of the hallmarks of aging. Consistently mitochondrial DNA (mtDNA) copy number and function decline with age in various tissues. There is increasing evidence to support that mitochondrial dysfunction drives ovarian aging. A decreased mtDNA copy number is also reported during ovarian aging. However, the mitochondrial mechanisms contributing to ovarian aging and infertility are not fully understood. Additionally, investigations into mitochondrial therapies to rejuvenate oocyte quality, select viable embryos and improve mitochondrial function may help enhance fertility or extend reproductive longevity in the future. These therapies include the use of mitochondrial replacement techniques, quantification of mtDNA copy number, and various pharmacologic and lifestyle measures. This review aims to describe the key evidence and current knowledge of the role of mitochondria in ovarian aging and identify the emerging potential options for therapy to extend reproductive longevity and improve fertility.

Tobacco consumption is associated with slow-growing day-6 blastocysts

Objective

To investigate if there are any obvious clinical factors associated with delayed blastulation at day 6 (D6) compared with day 5 (D5).

Design

Monocentric observational cohort study from November 2012 to December 2018.

Setting

Tertiary-care academic medical center.

Patient(s)

A total of 941 women with an entire cohort of exclusively D5 blastocysts compared with 162 patients with a cohort of exclusively D6 blastocysts.

Intervention(s)

None.

Main Outcome Measure(s)

Clinical characteristics and data related to the ovarian stimulation protocols.

Result(s)

After univariate analysis, a significantly higher proportion of women who were active smokers was found in the D6 group compared with the D5 group (n = 22/162 [13.6%] vs. n = 82/941 [8.7%]). In addition, the women in the D6 group had a higher rank number of assisted reproductive technology (ART; total no. of ART cycles performed: 2.1 ± 1.4 vs. 1.6 ± 1.1) and a lower antral follicle count (AFC; 18.7 ± 11.3 vs. 22.2 ± 12.8). Moreover, fertilization with the use of intracytoplasmic sperm injection was used more frequently in the D6 group compared with the D5 group. Logistic regression analysis adjusted for confounders highlighted several independent predictors for reaching blastocyst stage at D6 rather than D5: being an active smoker, previous ART cycles, and a lower AFC.

Conclusion(s)

Obtaining an exclusively D6 blastocyst cohort is independently associated with women who are active smokers, previous ART cycles, and a lower AFC. These findings provide evidence, to be confirmed by further studies, that women who are active smokers could greatly benefit from smoking cessation before undergoing ART.

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.

Impact of smoking on fertility and age of menopause: a population-based assessment

BACKGROUND AND AIMS

Studies in patients seeking medically assisted reproduction have shown that smoking reduces fertility, but little information is available in the general population. We assessed the associations between smoking and the number of children, childbearing planning and age at menopause in a representative sample of the population of Lausanne, Switzerland.

METHODS

Data from 6711 participants (3530 women, age range 35-75 years) collected between 2003 and 2006 and again in 2009 and 2012. Smoking status, number of offsprings and age of menopause were assessed.

RESULTS

Women who currently smoke had significantly less children than former or never smokers: the number of children per women (average±SD) was 1.38±1.05, 1.45±1.07 and 1.576±1.16, respectively (p<0.001). Women who currently smoke had their first child at an earlier age than the others: 26.7±5.2, 27.4±5.4 and 26.9±5.2 years old for current, former and never smokers, respectively, (p=0.01). Similar findings were found for men: number of children per men 1.475±1.16, 1.67±1.13 and 1.55±1.22 for current, former and never smokers, respectively (p<0.001); no difference was found regarding age at the first child. The difference persisted after multivariate adjustment (adjusted for age, body mass index, Caucasian origins, alcohol consumption, caffeinated drinks consumption, educational level, receiving social help and women taking contraceptives) for the age at first child among women. No association was found between Heaviness of Smoking Index and the number of children among current smokers in both genders. Women who smoke had their menopause more than 1 year prior than never-smoking women (48.9±0.2 years compared with 47.8±0.3 years, respectively, p=0.002).

CONCLUSIONS

Smoking is associated with an earlier age of having the first child and of menopause among women.

Aging and the environment affect gamete and embryo potential: can we intervene?

Optimal maturation of the oocyte depends on its environment and determines embryo competence, because the embryonic genome is not active until the cleavage stage and new mitochondria are not produced until blastulation. Adverse environmental factors include aging, andropause, oxidative stress, obesity, smoking, alcohol, and psychologic stress, whereas androgen supplementation, a prudent diet, exercise, nutritional supplements, and psychologic interventions have beneficial effects. Mitochondrial function and energy production deteriorate with age, adversely affecting ovarian reserve, chromosome segregation, and embryo competence. In aging mice, the mitochondrial cofactor coenzyme Q10 reverses most of these changes. Early human experience has been encouraging, although only a small study using a shorter duration of intervention compared with the murine model has been carried out. Mitochondrial metabolic stress can result in an abnormal compensatory increase in mitochondrial DNA, which can be assessed in biopsied blastomeres of trophectoderm as a predictive biomarker of implantation failure. Psychologic stress may reduce oocyte competence by shifting blood flow away from the ovary as part of the classic "fight or flight" physiologic response, and methods to reduce stress or the body's reaction to stress improve pregnancy success. Enhancing oocyte competence is a key intervention that promises to reduce the number of euploid embryos failing to produce viable deliveries.

Active and passive smoking and fecundability in Danish pregnancy planners

OBJECTIVE

To investigate the extent to which fecundability is associated with active smoking, time since smoking cessation, and passive smoking.

DESIGN

Prospective cohort study.

SETTING

Denmark, 2007-2011.

PATIENT(S)

A total of 3,773 female pregnancy planners aged 18-40 years.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

Self-reported pregnancy. Fecundability ratios (FRs) and 95% confidence intervals (CIs) were estimated using a proportional probabilities model that adjusted for menstrual cycle at risk and potential confounders.

RESULT(S)

Among current smokers, smoking duration of ≥10 years was associated with reduced fecundability compared with never smokers (FR, 0.85, 95% CI 0.72-1.00). Former smokers who had smoked ≥10 pack-years had reduced fecundability regardless of when they quit smoking (1-1.9 years FR, 0.83, 95% CI 0.54-1.27; ≥2 years FR, 0.73, 95% CI 0.53-1.02). Among never smokers, the FRs were 1.04 (95% CI 0.89-1.21) for passive smoking in early life and 0.92 (95% CI 0.82-1.03) for passive smoking in adulthood.

CONCLUSION(S)

Among Danish pregnancy planners, cumulative exposure to active cigarette smoking was associated with delayed conception among current and former smokers. Time since smoking cessation and passive smoking were not appreciably associated with fecundability.