Fetal exposure to paternal smoking and semen quality in the adult son

Contribution of the seminal microbiome to paternal programming

The field of Developmental Origins of Health and Disease has primarily focused on maternal programming of offspring health. However, emerging evidence suggests that paternal factors, including the seminal microbiome, could potentially play important roles in shaping the developmental trajectory and long-term offspring health outcomes. Historically, the microbes present in the semen were regarded as inherently pathogenic agents. However, this dogma has recently been challenged by the discovery of a diverse commensal microbial community within the semen of healthy males. In addition, recent studies suggest that the transmission of semen-associated microbes into the female reproductive tract during mating has potentials to not only influence female fertility and embryo development but could also contribute to paternal programming in the offspring. In this review, we summarize the current knowledge on the seminal microbiota in both humans and animals followed by discussing their potential involvement in paternal programming of offspring health. We also propose and discuss potential mechanisms through which paternal influences are transmitted to offspring via the seminal microbiome. Overall, this review provides insights into the seminal microbiome-based paternal programing, which will expand our understanding of the potential paternal programming mechanisms which are currently focused primarily on the epigenetic modifications, oxidative stresses, and cytokines.

Selection bias in a male-offspring cohort investigating fecundity: is there reason for concern?

STUDY QUESTION

Is there risk of selection bias in etiological studies investigating prenatal risk factors of poor male fecundity in a cohort of young men?

SUMMARY ANSWER

The risk of selection bias is considered limited despite a low participation rate.

WHAT IS KNOWN ALREADY

Participation rates in studies relying on volunteers to provide a semen sample are often very low. Many risk factors for poor male fecundity are associated with participation status, and as men with low fecundity may be more inclined to participate in studies of semen quality, a risk of selection bias exists.

STUDY DESIGN, SIZE, DURATION

A population-based follow-up study of 5697 young men invited to the Fetal Programming of Semen Quality (FEPOS) cohort nested within the Danish National Birth Cohort (DNBC), 1998-2019.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Young men (age range: 18 years, 9 months to 21 years, 4 months) born 1998-2000 by mothers included in the DNBC were invited to participate in FEPOS. In total, 1173 men answered a survey in FEPOS (n = 115 participated partly); of those, 1058 men participated fully by also providing a semen and a blood sample at a clinical visit. Differential selection according to parental baseline characteristics in the first trimester, the sons' own characteristics from the FEPOS survey, and urogenital malformations and diseases in reproductive organs from the Danish registers were investigated using logistic regression. The influence of inverse probability of selection weights (IPSWs) to investigate potential selection bias was examined using a predefined exposure-outcome association of maternal smoking in the first trimester (yes, no) and total sperm count analysed using adjusted negative binomial regression. A multidimensional bias analysis on the same association was performed using a variety of bias parameters to assess different scenarios of differential selection.

MAIN RESULTS AND THE ROLE OF CHANCE

Participation differed according to most parental characteristics in first trimester but did not differ according to the prevalence of a urogenital malformation or disease in the reproductive organs. Associations between maternal smoking in the first trimester and male fecundity were similar when the regression models were fitted without and with IPSWs. Adjusting for other potential risk factors for poor male fecundity, maternal smoking was associated with 21% (95% CI: -32% to -9%) lower total sperm count. In the bias analysis, this estimate changed only slightly under realistic scenarios. This may be extrapolated to other exposure-outcome associations.

LIMITATIONS, REASONS FOR CAUTION

We were unable to directly assess markers of male fecundity for non-participants from, for example an external source and therefore relied on potential proxies of fecundity. We did not have sufficient power to analyse associations between prenatal exposures and urogenital malformations.

WIDER IMPLICATIONS OF THE FINDINGS

The results are reassuring when using this cohort to identify causes of poor male fecundity. The results may be generalized to other similar cohorts. As the young men grow older, they can be followed in the Danish registers, as an external source, to examine, whether participation is associated with the risk of having an infertility diagnosis.

STUDY FUNDING/COMPETING INTEREST(S)

The project was funded by the Lundbeck Foundation (R170-2014-855), the Capital Region of Denmark, Medical doctor Sofus Carl Emil Friis and spouse Olga Doris Friis's Grant, Axel Muusfeldt's Foundation (2016-491), AP Møller Foundation (16-37), the Health Foundation, Dagmar Marshall's Fond, Aarhus University and Independent Research Fund Denmark (9039-00128B). The authors declare that they have no conflict of interest.

TRIAL REGISTRATION NUMBER

N/A.

Environmental toxicants and male fertility

Semen quality has declined especially among Western men. Experimental and epidemiological studies have shown potential links between exposure to environmental toxicants and poor male fertility. Some environmental exposures in utero can disrupt fetal testicular function and result in cryptorchidism, low semen quality, low serum testosterone levels, and low fertility. Environmental exposure in childhood and adulthood can also adversely affect germ cells, Sertoli cells, Leydig cells, or the hypothalamic-pituitary-testicular axis, resulting in impaired male fertility. In this review, we report the latest results from human studies that investigated the role of endocrine disrupting chemicals, heavy metals, tobacco smoking, alcohol drinking, and use of marijuana in low semen quality and impaired male fertility. Current evidence suggests the relationship between these environmental factors and low male fertility; however, some factors showed conflicting results which need further investigation.

[Impact of lifestyle and environmental factors on male reproductive health]

The identification of potential environmental hazards is of clinical relevance for the diagnosis of male infertility. Knowledge about these factors will improve prevention of fertility disorders. Apart from drugs or factors related to lifestyle such as alcohol and tobacco smoke, various environmental and occupational agents, both chemical and physical, may impair male reproduction. Reproductive toxicity may evolve at the hypothalamic-pituitary, testicular, or posttesticular level; endpoints comprise deterioration of spermatogenesis and sperm function as well as endocrine disorders and sexual dysfunction. However, due to the complex regulation of the male reproductive system, information regarding single exogenous factors and their mechanisms of action in humans is limited. This is also due to the fact that extrapolation of results obtained from experimental animal or in vitro studies remains difficult. Nevertheless, the assessment of relevant exposures to reproductive toxicants should be carefully evaluated during diagnostic procedures of andrological patients.

Beyond Genes: Germline Disruption in the Etiology of Autism Spectrum Disorders

Investigations into the etiology of autism spectrum disorders have been largely confined to two realms: variations in DNA sequence and somatic developmental exposures. Here we suggest a third route-disruption of the germline epigenome induced by exogenous toxicants during a parent's gamete development. Similar to cases of germline mutation, these molecular perturbations may produce dysregulated transcription of brain-related genes during fetal and early development, resulting in abnormal neurobehavioral phenotypes in offspring. Many types of exposures may have these impacts, and here we discuss examples of anesthetic gases, tobacco components, synthetic steroids, and valproic acid. Alterations in parental germline could help explain some unsolved phenomena of autism, including increased prevalence, missing heritability, skewed sex ratio, and heterogeneity of neurobiology and behavior.

Per- and polyfluoroalkyl substances (PFAS) and male reproductive function in young adulthood; a cross-sectional study

BACKGROUND

Per- and polyfluoroalkyl substances (PFAS) are a large family of persistent industrial chemicals with endocrine disrupting properties.

OBJECTIVES

To examine biomarkers of reproductive function in young adult males according to current environmental exposure to single and combined PFAS.

METHODS

The study population consisted of young men (n = 1041, age 18-21) from the Fetal Programming of Semen Quality (FEPOS) cohort. These men were recruited from pregnancies included in the Danish National Birth Cohort (DNBC) between 1996 and 2002. From 2017 to 2019, participants answered an online questionnaire, completed a clinical examination and provided a blood and a semen sample. Exposure to 15 PFAS was measured in plasma. Six compounds were quantified above the limit of detection in at least 80% of the participants. We applied negative binomial regression and weighted quantile sum (WQS) regression models to assess associations between single and combined exposure to PFAS and measures of semen quality, testicular volume and reproductive hormones among the young men.

RESULTS

We found no consistent associations between plasma concentrations of PFAS, semen quality and testicular volume. Higher levels of single and combined PFAS were associated with slightly higher levels of follicle-stimulating hormone (FSH) (WQS 4% difference, 95% confidence interval: 0, 9). Perfluorooctanoic acid (PFOA) was the main contributor to this finding with positive signals also from perfluorodecanoic acid (PFDA) and perfluorohexane sulfonic acid (PFHxS).

DISCUSSION

We examined exposure to a range of common PFAS in relation to biomarkers of male reproductive function and found an association with higher levels of FSH among young men from the general population in Denmark. Further studies on especially combined exposure to PFAS are needed to expand our understanding of potential endocrine disruption from both legacy and emerging compounds in relation to male reproductive function.

Urinary Bisphenol A, F and S Levels and Semen Quality in Young Adult Danish Men

Bisphenol A (BPA) is considered an endocrine disruptor and has been associated with deleterious effects on spermatogenesis and male fertility. Bisphenol F (BPF) and S (BPS) are structurally similar to BPA, but knowledge of their effects on male fertility remains limited. In this cross–sectional study, we investigated the associations between exposure to BPA, BPF, and BPS and semen quality in 556 men 18–20 years of age from the Fetal Programming of Semen Quality (FEPOS) cohort. A urine sample was collected from each participant for determination of BPA, BPF, and BPS concentrations while a semen sample was collected to determine ejaculate volume, sperm concentration, total sperm count, sperm motility, and sperm morphology. Associations between urinary bisphenol levels (continuous and quartile–divided) and semen characteristics were estimated using a negative binomial regression model adjusting for urine creatinine concentration, alcohol intake, smoking status, body mass index (BMI), fever, sexual abstinence time, maternal pre–pregnancy BMI, and first trimester smoking, and highest parental education during first trimester. We found no associations between urinary bisphenol of semen quality in a sample of young men from the general Danish population.

Heritable hazards of smoking: Applying the "clean sheet" framework to further science and policy

All the cells in our bodies are derived from the germ cells of our parents, just as our own germ cells become the bodies of our children. The integrity of the genetic information inherited from these germ cells is of paramount importance in establishing the health of each generation and perpetuating our species into the future. There is a large and growing body of evidence strongly suggesting the existence of substances that may threaten this integrity by acting as human germ cell mutagens. However, there generally are no absolute regulatory requirements to test agents for germ cell effects. In addition, the current regulatory testing paradigms do not evaluate the impacts of epigenetically mediated intergenerational effects, and there is no regulatory framework to apply new and emerging tests in regulatory decision making. At the 50th annual meeting of the Environmental Mutagenesis and Genomics Society held in Washington, DC, in September 2019, a workshop took place that examined the heritable effects of hazardous exposures to germ cells, using tobacco smoke as the example hazard. This synopsis provides a summary of areas of concern regarding heritable hazards from tobacco smoke exposures identified at the workshop and the value of the Clean Sheet framework in organizing information to address knowledge and testing gaps.