The association between serum estradiol levels and sperm DNA integrity.

In men from the general population, BMI has been associated with a lower sperm DNA fragmentation index (DFI). We wondered whether this could be due to estradiol, which is associated with BMI and reported important for sperm function. Our objective was to investigate the association between estradiol and DFI. In 2008-2010, we recruited 284 young men from the general population to deliver samples of semen and blood and answer questionnaires. Serum concentrations of reproductive hormones and DFI were analyzed, the latter using the Sperm Chromatin Structure Assay. Associations were studied using general linear models. The first model utilized metric values of estradiol, whereas the second model compared men with high and low levels, dichotomized by the median value. A possible interaction between estradiol and testosterone was also examined. When investigating metric estradiol levels and DFI, an inverse association was seen without adjustments (p = .02), but the statistical significance was lost at adjustments for potential confounders (p = .08). Men with lower estradiol levels (<88 pmol/L, mean 71 pmol/L) had a statistically significantly higher DFI than men with higher levels of estradiol (≥88 pmol/L, mean 110 pmol/L). Mean ratio difference was 1.21 (p = .002) without adjustments and 1.18 (p = .01) with adjustments. A statistically significant difference in DFI was observed in men with testosterone levels below median when comparing high and low estradiol (p < .001). This study supports the idea that serum estradiol levels are protective for sperm DNA integrity, at least at lower testosterone levels.

Decreased sperm counts in Swedish users of oral tobacco.

BACKGROUND: Smoke-free tobacco via moist oral snuff (snus) is used daily in more than 20% of Swedish men. Negative effects of cigarette smoking on sperm parameters are well documented, unlike for snuff, despite relevance also for other smoke-free nicotine products. OBJECTIVES: We wanted to investigate whether reproductive parameters differed between users and non-users of snuff, and whether the amount of snuff and nicotine exposure mattered. MATERIALS AND METHODS: Men (n = 613) from the general population, recruited 2000-2010, were physically examined, answered questions on smoking and snuff use, and delivered urine, blood and semen samples. Sperm concentration, total sperm count, semen volume, percent morphologically normal and progressively motile sperm, and DNA fragmentation index (by the Sperm Chromatin Structure Assay) and reproductive hormones were analysed. Nicotine exposure was measured through urinary levels of cotinine. We used general linear models, with adjustments including cigarette smoking, and for semen parameters also abstinence time. RESULTS: After adjustments, total sperm count was 24% lower (P = 0.03) and testosterone 14% higher (P < 0.001) in 109 users of snuff than in non-users, whereas cotinine was positively associated with testosterone and oestradiol (P < 0.001). Numbers of boxes of snuff used per week were associated with testosterone and FSH (P < 0.001). DISCUSSION: Applied to the general population, the consumption of smoke-free tobacco by the use of snuff was associated with a lower sperm count and a higher testosterone, for which the extent seemed to play a role. CONCLUSIONS: Independent of smoking, consumption of snuff was associated with lower total sperm count and different hormone levels. Applying these results to a reported association between sperm count and the chance of pregnancy, men who used snuff would have about a 10% lower chance of fathering a child.

Exposure to polycyclic aromatic hydrocarbons and nicotine, and associations with sperm DNA fragmentation.

BACKGROUND: Tobacco smoking has been reported to cause DNA fragmentation and has been suggested to cause mutations in spermatozoa. These effects have been ascribed to the action of polycyclic aromatic hydrocarbons (PAH) present in the smoke. Simultaneously, DNA fragmentation has been associated with mutagenesis. OBJECTIVE: The aim of this study was to investigate whether levels of urinary biomarkers of PAH and nicotine exposure were associated with sperm DNA fragmentation. METHODS: In the urine of 381 men recruited from two cohorts of young men (17-21 years old) from the general Swedish population, the PAH metabolites 1-hydroxypyrene and 2-hydroxyphenanthrene, as well as the nicotine metabolite cotinine, were measured. The sperm DNA fragmentation index (DFI) was analysed using the sperm chromatin structure assay. Associations between the DFI, and PAH metabolite levels as continuous variables as well as in quartiles, were studied by general linear models adjusted for abstinence time. A similar analysis was carried out for cotinine levels, according to which the men were categorised as "non-smoking" (n = 216) and "smoking" (n = 165). RESULTS: No association was found between levels of any of the three biomarkers and DFI, either as a continuous variable (p = 0.87-0.99), or when comparing the lowest and the highest quartiles (p = 0.11-0.61). The same was true for comparison of men categorised as non-smoking or smoking (DFI 11.1% vs. 11.8%, p = 0.31). DISCUSSION: We found no evidence of PAH or nicotine exposure to be associated with DFI, which does not exclude that these exposures may have other effects on sperm DNA. CONCLUSION: In these young men, levels of biomarkers of nicotine and PAH exposure were not associated with DFI.

RUBIC (ReproUnion Biobank and Infertility Cohort): A binational clinical foundation to study risk factors, life course, and treatment of infertility and infertility-related morbidity.

BACKGROUND: Infertility affects 15%-25% of all couples during their reproductive life span. It is a significant societal and public health problem with potential psychological, social, and economic consequences. Furthermore, infertility has been linked to adverse long-term health outcomes. Despite the advanced diagnostic and therapeutic techniques available, approximately 30% of infertile couples do not obtain a live birth after fertility treatment. For these couples, there are no further options to increase their chances of a successful pregnancy and live birth. OBJECTIVES: Three overall questions will be studied: (1) What are the risk factors and natural life courses of infertility, early embryonic loss, and adverse pregnancy outcomes? (2) Can we develop new diagnostic and prognostic biomarkers for fecundity and treatment success? And (3) what are the health characteristics of women and men in infertile couples at the time of fertility treatment and during long-term follow-up? MATERIAL AND METHODS: ReproUnion Biobank and Infertility Cohort (RUBIC) is established as an add-on to the routine fertility management at Copenhagen University Hospital Departments in the Capital Region of Denmark and Reproductive Medicine Centre at Skåne University Hospital in Sweden. The aim is to include a total of 5000 couples equally distributed between Denmark and Sweden. The first patients were enrolled in June 2020. All eligible infertile couples are prospectively asked to participate in the project. Participants complete an extensive questionnaire and undergo a physical examination and collection of biospecimens (blood, urine, hair, saliva, rectal swabs, feces, semen, endometrial biopsies, and vaginal swabs). After the cohort is established, the couples will be linked to the Danish and Swedish national registers to obtain information on parental, perinatal, childhood, and adult life histories, including disease and medication history. This will enable us to understand the causes of infertility and identify novel therapeutic options for this important societal problem.

Exposure to polychlorinated compounds and cryptorchidism; A nested case-control study.

BACKGROUND: Maldescended testes or cryptorchidism is a genital birth defect that affects 2-9% of all male new-borns. Over the last 40 years there have been reports of increased prevalence in countries like the US, the UK and the Scandinavian countries. This possible increase has in some studies been linked to a foetal exposure to chemical pollutants. In this matched case-control study, we analysed maternal serum samples in early pregnancy for three different organochlorine compounds, to investigate whether the levels were associated with the risk of cryptorchidism. METHOD: Maternal serum samples taken during the first trimester of pregnancy from 165 cases (boys born with cryptorchidism) and 165 controls, matched for birth year and maternal age, parity and smoking habits during the pregnancy, were retrieved from the Southern Sweden Maternity Biobank. The samples were analysed for 2,2',4,4',5,5'-hexachlorobiphenyl (PCB-153), dichlorodiphenyltrichloroethane (p,p'-DDE) and hexachlorobenzene (HCB), using gas chromatography mass spectrometry. Associations between exposure and cryptorchidism were evaluated by conditional logistic regression. RESULTS: We found no statistically significantly associations between exposure to these compounds and cryptorchidism, either when the exposure variables were used as a continuous variable, or when the exposure levels were divided in quartiles. CONCLUSION: We found no evidence of an association between maternal levels of PCB-153, p,p'-DDE or HCB during the pregnancy and the risk of having cryptorchidism in the sons.

Concentrations and temporal trends in pesticide biomarkers in urine of Swedish adolescents, 2000-2017.

Agricultural pesticides are extensively used for weed- and pest control, resulting in residues of these compounds in food. The general population is mainly exposed through dietary intake. Exposure to certain pesticides has been associated with adverse human health outcomes. Our aim was to assess urinary concentrations and temporal trends in the biomarkers of commonly used pesticides. Samples were collected from adolescents (n = 1060) in Scania, Sweden, from 2000 to 2017. Concentrations of 14 pesticide biomarkers were analyzed in urine using LC-MS/MS. Temporal trends in biomarker concentrations (ln-transformed) were evaluated using linear regression. Biomarkers of pyrethroids (3-PBA and DCCA), chlorpyrifos (TCPy), chlormequat (CCC), thiabendazole (OH-TBZ), and mancozeb (ETU) were detected in >90% of the population all sampling years. The biomarkers CCC and TCPy had the highest median concentrations (>0.8 µg/L), whereas the biomarkers of cyfluthrin (4F-3-PBA) and two pyrethroids (CFCA) had the lowest median concentrations (<0.02 µg/L). Increasing temporal trends were found for the biomarkers 3-PBA (3.7%/year), TCPy (1.7%/year) and biomarkers of pyrimethanil (11.9%/year) and tebuconazole (12.2%/year). Decreasing trends were found for CCC (-5.5%/year), OH-TBZ (-5.5%/year), and ETU (-3.9%/year). Our results suggest that Swedish adolescents are commonly exposed to pesticides in low concentrations (median concentrations <3.88 µg/L).

Association between paternal smoking at the time of pregnancy and the semen quality in sons.

BACKGROUND: Maternal smoking during pregnancy has repeatedly been associated with decreased sperm counts in sons. Nevertheless, our team recently detected a lower total sperm count in the sons of smoking fathers as compared to sons of non-smoking fathers. Since paternal and maternal tobacco smoking often coincide, it is difficult to discriminate whether effects are mediated paternally or maternally when using questionnaire- or register-based studies. Therefore, getting an objective measure of the maternal nicotine exposure level during pregnancy might help disentangling the impact of paternally and maternally derived exposure. OBJECTIVES: Our aim was to study how paternal smoking at the time of the pregnancy was associated with semen quality in the sons after adjusting for the maternal levels of nicotine exposure during pregnancy. METHODS: We recruited 104 men (17-20 years old) from the general Swedish population. The participants answered a questionnaire about paternal smoking. Associations between smoking and semen volume, total sperm count, sperm concentration, morphology and motility were adjusted for levels of the nicotine metabolite cotinine in stored maternal serum samples obtained from rubella screening between the 6th and 35th week of pregnancy. We additionally adjusted for the estimated socioeconomic status. RESULTS: After adjusting for the maternal cotinine, the men of smoking fathers had 41% lower sperm concentration and 51% lower total sperm count than the men of non-smoking fathers (p = 0.02 and 0.003, respectively). This was robust to the additional adjustment. CONCLUSIONS: Our results suggest a negative association between paternal smoking and sperm counts in the sons, independent of the level maternal nicotine exposure during the pregnancy.

Phthalate exposure and reproductive parameters in young men from the general Swedish population.

BACKGROUND: In animals, exposure to certain phthalates negatively affects the male reproductive function. Human results are conflicting and mostly based on subfertile males, in whom the association between exposure and reproductive function may differ from the general population. OBJECTIVES: To study if levels of phthalate metabolites were associated with semen quality and reproductive hormones in general Swedish men. METHODS: We recruited 314 young men delivering semen, urine and blood samples at the same visit. We analyzed reproductive hormones and several semen parameters including progressive motility and high DNA stainability (HDS)-a marker for sperm immaturity. In urine, we analyzed metabolites of phthalates, including diethylhexyl phthalate (DEHP). We studied associations between urinary levels of the metabolites and seminal as well as serum reproductive parameters, accounting for potential confounders. RESULTS: DEHP metabolite levels, particularly urinary mono-(2-ethyl-5-carboxypentyl) phthalate (MECPP), were negatively associated with progressive sperm motility, which was 11 (95% CI: 5.0-17) percentage points lower in the highest quartile of MECPP than in the lowest. Further, men in the highest quartile of the DEHP metabolite monoethylhexyl phthalate had 27% (95% CI: 5.5%-53%) higher HDS than men in the lowest quartile. CONCLUSIONS: DEHP metabolite levels seemed negatively associated with sperm motility and maturation.

Prenatal phthalate exposure and reproductive function in young men.

BACKGROUND: Prenatal exposure to phthalates is suggested to negatively impact male reproductive function, but human data are lacking. OBJECTIVES: To study associations between prenatal exposure to diethylhexyl phthalate (DEHP) and diisononyl phthalate (DiNP), and reproductive parameters of adolescent men. METHODS: Using linear regression models adjusted for potential confounders, we studied associations between levels of DEHP- and DiNP metabolites in maternal sera from mean 12 weeks of pregnancy, and testicular size, semen quality and reproductive hormones in 112 adolescent sons, recruited from the general population. RESULTS: Men in the highest exposure tertile of one DiNP metabolite [mono-(carboxy-iso-octyl) phthalate], compared with men in the lowest tertile had: 4.3mL (95% CI: 0.89, 7.6mL; p<0.001) lower total testicular volume; 30% (95% CI: 3.6, 63%; p=0.02) higher levels of follicle-stimulating hormone; and 0.87mL (95% CI: 0.28, 1.5mL; p=0.004) lower semen volume. Men in the highest exposure tertile of one DEHP metabolite [mono-(2-ethyl-5-hydroxylhexyl) phthalate] had 0.70mL (95% CI: 0.090, 1.3mL; p=0.03) lower semen volume than men in the lowest exposure tertile. The levels of two DiNP metabolites [mono-(hydroxy-iso-nonyl) phthalate and mono-(oxo-iso-nonyl) phthalate] were linearly associated with luteinizing hormone (p<0.01). CONCLUSION: Prenatal levels of some metabolites of DEHP and DiNP seemed negatively associated with reproductive function of adolescent men.

Time trends between 1987 and 2007 for perfluoroalkyl acids in plasma from Swedish women.

Perfluoroalkyl acids (PFAAs) are a large group of chemicals which are highly persistent in both nature and humans. The use of the most prominent ones, perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA), was reduced in the early 21st century, and since then levels in human matrices have decreased. However, these two compounds have been exchanged by other PFAAs, for which time trends have not been as extensively investigated. By the use of 80 plasma samples collected between 1987 and 2007 from healthy women (n=1-9 yearly for 1987-2001, n=15 from 2006, and n=10 from 2007), possible time trends of six PFAAs were assessed. Time trends were evaluated for the entire study period, as well as for three sub-periods. As seen in previous studies, levels of perfluorohexane sulfonate (PFHxS), PFOS, and PFOA peaked during the middle time period (1990-2000), with medians of 0.98 ng mL(-1), 18.06 ng mL(-1), and 3.73 ng mL(-1), respectively. However, levels of perfluorononanic acid (PFNA), perfluorodecanic acid (PFDA), and perfluoroundecanoic acid (PFUnDA) increased over the whole study period and most markedly so after year 2000, with medians of 0.73 ng mL(-1), 0.28 ng mL(-1), and 0.24 ng mL(-1), respectively, during the last study period.

The Impact of Paternal and Maternal Smoking on Semen Quality of Adolescent Men.

BACKGROUND: Maternal smoking during pregnancy has been reported to negatively impact sperm counts of the sons. Sufficient data on the effect of paternal smoking is lacking. OBJECTIVES: We wished to elucidate the impact of maternal and paternal smoking during pregnancy and current own smoking on reproductive function of the male offspring. METHODS: Semen parameters including sperm DNA integrity were analyzed in 295 adolescents from the general population close to Malmö, Sweden, recruited for the study during 2008-2010. Information on maternal smoking was obtained from the Swedish Medical Birth Register, and regarding own and paternal smoking from questionnaires. The impacts of maternal, paternal and own smoking were evaluated in a multivariate regression model and by use of models including interaction terms. Totally, three exposures and five outcomes were evaluated. RESULTS: In maternally unexposed men, paternal smoking was associated with 46% lower total sperm count (95%CI: 21%, 64%) in maternally unexposed men. Both paternal and maternal smoking were associated with a lower sperm concentration (mean differences: 35%; 95%CI: 8.1%, 55% and 36%; 95%CI: 3.9%, 57%, respectively) if the other parent was a non-smoker. No statistically significant impact of own smoking on semen parameters was seen. CONCLUSIONS: Prenatal both maternal and paternal smoking were separately associated with some decrease in sperm count in men of whom the other parent was not reported to smoke.

Association between follicle-stimulating hormone receptor polymorphisms and reproductive parameters in young men from the general population.

OBJECTIVE: Follicle-stimulating hormone (FSH) regulates gametogenesis through binding to its receptor (FSHR). In women, the Thr307Ala and Asn680Ser polymorphisms in the FSHR gene affect reproductive function, but it is not clear whether they have any impact on spermatogenesis and have mainly been investigated in infertile men of varying ages. The aim of the present study was therefore to examine whether these genetic variants of the FSHR influence reproductive parameters in men from the general population. METHODS: Men aged 17-20 years (n=313) were genotyped. All men provided a semen sample and a blood sample for hormonal measurements and DNA extraction. They underwent a medical examination and analyses of possible associations between Thr307Ala and Asn680Ser polymorphisms and hormonal and sperm parameters were subsequently carried out. RESULTS: Men homozygous for Thr307/Asn680 had a lower mean serum FSH concentration (3.07 vs. 3.65 IU/l, P=0.009), and higher mean serum estradiol (94.0 vs. 86.1 pmol/l, P=0.001), sex hormone-binding globulin (33.6 vs. 31.3 nmol/l, P<0.0001), and total testosterone (19.1 vs.17.9 nmol/l, P<0.0001) concentrations compared with men with other genotypes. In addition, sperm concentrations (71.9 × 10 vs. 70.8 × 10/ml, P=0.040) and the total sperm counts were higher (212 × 10 vs. 206 × 10, P<0.0001) and their testes volumes were larger (left: 11.5 vs. 11.0 ml, P<0.0001; right: 12.4 vs. 11.6 ml, P=0.002). CONCLUSION: As in women, the results from the present study indicate that variants of the FSHR influence reproductive parameters in men.

Gene-environment interaction and male reproductive function.

As genetic factors can hardly explain the changes taking place during short time spans, environmental and lifestyle-related factors have been suggested as the causes of time-related deterioration of male reproductive function. However, considering the strong heterogeneity of male fecundity between and within populations, genetic variants might be important determinants of the individual susceptibility to the adverse effects of environment or lifestyle. Although the possible mechanisms of such interplay in relation to the reproductive system are largely unknown, some recent studies have indicated that specific genotypes may confer a larger risk of male reproductive disorders following certain exposures. This paper presents a critical review of animal and human evidence on how genes may modify environmental effects on male reproductive function. Some examples have been found that support this mechanism, but the number of studies is still limited. This type of interaction studies may improve our understanding of normal physiology and help us to identify the risk factors to male reproductive malfunction. We also shortly discuss other aspects of gene-environment interaction specifically associated with the issue of reproduction, namely environmental and lifestyle factors as the cause of sperm DNA damage. It remains to be investigated to what extent such genetic changes, by natural conception or through the use of assisted reproductive techniques, are transmitted to the next generation, thereby causing increased morbidity in the offspring.