Association between urinary polycyclic aromatic hydrocarbon metabolites and sperm DNA damage: a population study in Chongqing, China

Prenatal exposure to environmentally relevant levels of PAHs inhibits spermatogenesis in adult mice and the mechanism involved

Polycyclic aromatic hydrocarbons (PAHs) are a class of contaminants that cannot be banned. Exposure to PAHs has been reported to alter spermatogenesis in mammals, but little is known about prenatal exposure to a mixture of PAHs on the reproductive toxicity of adult offspring. In this study, we investigated the associations between prenatal exposure to environmentally relevant levels of PAHs in mice and testicular dysfunction, including impaired spermatogenesis and steroid hormone dysfunction in male offspring on postnatal day 180. The percentage of testicular apoptotic cells was significantly increased, which was further verified by the up-regulated BAX protein. The expression of Ar and the Leydig cell marker Cyp11a1 was down-regulated, suggesting an impairment in the synthesis of steroid hormones. DNA hypermethylation of the Tnp1 and Sohlh2 promoters suppresses transcriptional expression, consequently altering the sperm production process. This study shows that prenatal exposure to PAHs may induce long-term reproductive toxicity.

Reduction in polycyclic aromatic hydrocarbon exposure in Beijing following China's clean air actions

Exposure to polycyclic aromatic hydrocarbons (PAHs) in the Chinese population was among the highest globally and associated with various adverse effects. This study examines the impact of China's two-phase clean air initiatives, namely the Air Pollution Prevention and Control Action Plan (APPCAP) in 2013-2017 and the Blue-Sky Defense War (BSDW) in 2018-2020, on PAH levels and human exposures in Beijing. To evaluate the effects of APPCAP, we measured 16 PAHs in 287 PM2.5 samples collected in Beijing and 9 PAH metabolites in 358 urine samples obtained from 54 individuals who traveled from Los Angeles to Beijing between 2014 and 2018. The concentration of PM2.5-bound benzo[a]pyrene equivalents (BaPeq) decreased by 88.5% in 2014-2018 due to reduced traffic, coal, and biomass emissions. PAH metabolite concentrations in travelers' urine decreased by 52.3% in Beijing, correlated with changes in PM2.5 and NO2 levels. In contrast, no significant changes were observed in Los Angeles. To evaluate BSDW's effects, we collected 123 additional PM2.5 samples for PAH measurements in 2019-2021. We observed sustained reductions in BaPeq concentrations attributable to reductions in coal and biomass emissions during the BSDW phase, but those from traffic sources remained unchanged. After accounting for meteorological factors, China's two-phase clean air initiatives jointly reduced Beijing's PM2.5-bound BaPeq concentrations by 96.6% from 2014 to 2021. These findings provide compelling evidence for the effectiveness of China's clean air actions in mitigating population exposure to PAHs in Beijing.

Urinary Metabolites of Polycyclic Aromatic Hydrocarbons of Rural Population in Northwestern China: Oxidative Stress and Health Risk Assessment

Polycyclic aromatic hydrocarbon (PAH) exposure is suspected to be linked to oxidative damage. Herein, ten PAH human exposure biomarkers [hydroxylated PAH metabolites (OH-PAHs)] and five oxidative stress biomarkers (OSBs) were detected in urine samples collected from participants living in a rural area (n = 181) in Northwestern China. The median molar concentration of ΣOH-PAHs in urine was 47.0 pmol mL-1. The 2-hydroxynaphthalene (2-OHNap; median: 2.21 ng mL-1) was the dominant OH-PAH. The risk assessment of PAH exposure found that hazard index (HI) values were <1, indicating that the PAH exposure of rural people in Jingyuan would not generate significant cumulative risks. Smokers (median: 0.033) obtained higher HI values than nonsmokers (median: 0.015, p < 0.01), suggesting that smokers face a higher health risk from PAH exposure than nonsmokers. Pearson correlation and multivariate linear regression analysis revealed that ΣOH-PAH concentrations were significant factors in increasing the oxidative damage to deoxyribonucleic acid (DNA) (8-hydroxy-2'-deoxyguanosine, 8-OHdG), ribonucleic acid (RNA) (8-oxo-7,8-dihydroguanine, 8-oxoGua), and protein (o, o'-dityrosine, diY) (p < 0.05). Among all PAH metabolites, only 1-hydroxypyrene (1-OHPyr) could positively affect the expression of all five OSBs (p < 0.05), suggesting that urinary 1-OHPyr might be a reliable biomarker for PAH exposure and a useful indicator for assessing the impacts of PAH exposure on oxidative stress. This study is focused on the relation between PAH exposure and oxidative damage and lays a foundation for the study of the health effect mechanism of PAHs.

The Comet Assay as a Tool in Human Biomonitoring Studies of Environmental and Occupational Exposure to Chemicals-A Systematic Scoping Review

Biomonitoring of human populations exposed to chemical substances that can act as potential mutagens or carcinogens, may enable the detection of damage and early disease prevention. In recent years, the comet assay has become an important tool for assessing DNA damage, both in environmental and occupational exposure contexts. To evidence the role of the comet assay in human biomonitoring, we have analysed original research studies of environmental or occupational exposure that used the comet assay in their assessments, following the PRISMA-ScR method (preferred reporting items for systematic reviews and meta-analyses extension for scoping reviews). Groups of chemicals were designated according to a broad classification, and the results obtained from over 300 original studies (n = 123 on air pollutants, n = 14 on anaesthetics, n = 18 on antineoplastic drugs, n = 57 on heavy metals, n = 59 on pesticides, and n = 49 on solvents) showed overall higher values of DNA strand breaks in the exposed subjects in comparison with the unexposed. In summary, our systematic scoping review strengthens the relevance of the use of the comet assay in assessing DNA damage in human biomonitoring studies.

Association between polycyclic aromatic hydrocarbons and infertility in U.S. women: National Health and Nutrition Examination Survey 2013-2016

Although there is a body of research indicating the potential impact of polycyclic aromatic hydrocarbons (PAHs) exposure on male infertility, the understanding of how PAH might affect female infertility is still limited. This study aimed to evaluate associations of PAHs, both individually and as a mixture, with female infertility using multiple logistic regression, Bayesian kernel machine regression (BKMR), and quantile g-computation (QGC) models based on data from the National Health and Nutrition Examination Survey (NHANES) 2013-2016. The study included 729 female participants. Multiple logistic regression results indicated that there was a significant association between the third tertile of 2-hydroxy fluorene (2-OHFLU) and female infertility, and the OR was 2.84 (95% CI: 1.24-6.53, P value = 0.015) compared with the first tertile after adjusting for the potential covariates. The BKMR model revealed a positive overall trend between mixed PAH exposure and female infertility, particularly when the mixture was at or above the 55th percentile, where 2-hydroxynaphthalene (2-OHNAP) and 1-hydroxypyrene (1-OHPYR) were the primary influences of the mixture. The univariate exposure-response function indicated positive associations between individual PAH exposure, specifically 2-OHNAP, 2-OHFLU, and 1-OHPYR, and female infertility. The QGC model also indicated a positive trend between exposure to a mixture of PAHs and female infertility, although it did not reach statistical significance (OR = 1.33, 95%CI: 0.86-2.07), with 1-OHPYR having the greatest positive effect on the outcome. This study suggested that exposure to PAHs may be associated with female infertility and further research is needed to consolidate and confirm these findings.

Nano-composite rGO-Ag-Cu-Ni mediated photocatalytic degradation of anthracene and benzene

Polycyclic aromatic hydrocarbons (PAHs) are omnipresent, persistent, and carcinogenic pollutants continuously released in the atmosphere due to the rapid increase in population and industrialization worldwide. Hence, there is an ultimate rise in concern about eliminating the toxic PAHs and their related aromatic hydrocarbons from the air, water, and soil environment by employing efficient removal technologies using nanoparticles as a catalyst. Here, the degradation of selective PAHs viz., anthracene and benzene using laboratory synthesized rGO-Ag-Cu-Ni nanocomposite (catalyst) was studied. Characterization studies revealed the nanocomposites exhibited surface plasma resonance at 350 - 450 nm, confirming the presence of Ag, Cu, and Ni metal ions embedded on the reduced graphene substrate. It was found that the nanocomposites synthesized were spherical, amorphous in nature, and aggregated together with measurements ranging from 423 to 477 nm. An SEM-EDX analysis of the nanocomposite demonstrated that it contained 25.13% O, 14.24% Ni, 27.79% Cu, and 32.84% Ag, which confirms the synthesis of the nanocomposite. Crystalline, sharp nanocomposites of average size 17-41 nm with an average diameter of 118.5 nm (X-ray diffraction and DLS) were observed. FTIR spectra showed that the nanocomposites had the functional groups alkanes, alkenes, alkynes, carboxylic acids, and halogen derivatives. Batch adsorption studies revealed that the maximum degradation achieved at optimum nano-composite concentration of 10 μg/mL, pH value of 5, PAHs concentration of 2 μg/mL and effective irradiation source being UV radiations in the case of both benzene and anthracene pollutants. The degradation of benzene and anthracene followed Freundlich & Langmuir isotherm with the highest R2 value of 0.9894 & 0.9885, respectively. Adsorption kinetic studies under optimum conditions revealed that the adsorption of both benzene and anthracene followed Pseudo-second order kinetics. Antimicrobial studies revealed that the synthesized nano-composite exhibited potential antimicrobial activity against Gram positive bacterium (Bacillus subtilis, Staphylococcus aureus), Gram negative bacterium (Klebsiella pneumonia, Escherichia coli) and fungal strain (Aspergillus niger) respectively. Thus, the synthesized rGO-Ag-Cu-Ni nano-composite acts as an effective antimicrobial agent as well as a PAHs degrading agent, helping to overcome antibiotics resistance and to mitigate the overgrowing PAHs pollution in the environment.

Focusing on testosterone levels in male: A half-longitudinal study of polycyclic aromatic hydrocarbon exposure and diastolic blood pressure in coke oven workers

Polycyclic aromatic hydrocarbons (PAHs) can interfere with testosterone levels, and low levels of testosterone are associated with increased cardiovascular events. To explore the role of testosterone in PAHs exposure and cardiovascular health, we used data from the 2011-2016 National Health and Nutrition Examination Survey (NHANES) and a longitudinal database of 332 male coke oven workers from China. The urine PAHs, tobacco metabolites and plasma testosterone levels of coke oven workers were measured. There were inverse associations between serum (plasma) testosterone concentrations and the risk of dysarteriotony and dyslipidemia among the NHANES participants and coke oven workers. The results of the cross-lagged panel analysis among workers showed that the decrease in testosterone preceded the increase in diastolic blood pressure (DBP), and the absolute value of the path coefficient from baseline testosterone to follow-up DBP (β₂ = -8.162, P = 0.077) was significantly larger than the absolute value of the path coefficient from baseline DBP to follow-up testosterone (β₁ = -0.001, P = 0.781). Results from the half-longitudinal mediation analysis showed that baseline hydroxyfluorene predicted significant decreases in plasma testosterone from baseline to follow-up (path a: 0.71, 95% CI: 1.26, -0.16), whereas plasma testosterone at baseline also predicted significant increments in DBP from baseline to follow-up (path b: 9.22, 95% CI: 17.24, -1.19). The indirect effect of PAHs on DBP via plasma testosterone level was marginally significant (test for indirect effects a*b (P = 0.08)). In conclusion, testosterone level is a longitudinal precursor to increased DBP and plays an essential role in the association between PAHs exposure and damage to the cardiovascular system. Coke oven workers with low plasma testosterone levels are more likely to experience adverse changes in blood pressure and lipid levels after exposure to PAHs.

Establishing the relationship between Polycyclic Aromatic Hydrocarbons (PAHs) exposure and male infertility: A systematic review

It has been demonstrated that human exposure to environmental chemicals may have sperm genotoxic potentiality. Among the different classes, Polycyclic Aromatic Hydrocarbons (PAHs) have been receiving attention in recent years due to reports of sperm geno-toxicity, a series of reproductive defects and male infertility. This review aims to substantiate the effects of PAHs exposure on male infertility, with focus on the sperm characteristics (count, concentration, volume, motility, DNA damage, and morphology). To this end, international databases such as Cochrane Library, PubMed, Web of Science, Embase Ovid, Scopus, and Google Scholar were used to conduct a systematic search for papers on the subject, based on PRISMA guidelines, published up to 24 March 2022. The Newcastle-Ottawa Scale was subsequently used to assess the quality of the studies. The results showed that there is a significant negative relationship between PAHs metabolites and sperm volume, concentration, motility, morphology, as well as an observed DNA degeneration. Also, the CYP1A1 genotype polymorphisms were considered as a representative of PAHs exposure to infertility; the review highlights that polymorphisms of this genotype were more common in the infertile people. In overall, this work provides a solid summary of the existing works correlating PAHs exposure and male infertility, which could impulse further protective measures and informative campaigns on users, workers, and general population.

Associations between repeated measurements of urinary polycyclic aromatic hydrocarbon metabolites and thyroid hormones among reproductive-aged men

BACKGROUND

Polycyclic aromatic hydrocarbons (PAHs) have been shown to disrupt thyroid function in toxicological studies, but epidemiological evidence is inconsistent. Furthermore, little is known on potential effects of mixtures of PAHs.

OBJECTIVE

This study aimed to examine the associations of exposure to PAHs as individual chemicals and mixtures with thyroid hormones.

METHODS

We included 378 men from a Reproductive Medicine Center in Wuhan, China. Ten monohydroxylated PAH (OH-PAH) metabolites in repeated urine specimens collected at two-time points and three thyroid hormones [thyroid-stimulating hormone (TSH), free thyroxine (FT4), and free triiodothyronine (FT3)] in one serum sample were measured. Multivariable linear regression models were applied to assess the associations between individual OH-PAH metabolites and thyroid hormones, and the associations with mixtures of OH-PAH metabolites were assessed by Bayesian kernel machine regression (BKMR) models.

RESULTS

Multivariable linear regression models showed inverse associations between urinary 1-OHNa and TSH, between urinary 1-OHPh and 9-OHPh and FT3, as well as between urinary 2-OHPh, 3-OHPh, 9-OHPh and ∑OHPh and FT4, regardless of these individual OH-PAH metabolites modeled as continuous or tertile variables (e.g., -21.57 % in TSH; 95 % CI: -35.33 %, -4.88 % for the third vs first tertiles of 1-OHNa; p for trend = 0.014). BKMR models showed negative overall effects of all urinary OH-PAH metabolite mixtures on TSH, FT3, and FT4, and 1-OHNa, 9-OHPh, and 2-OHPh as the most important contributors, respectively, with linear inverse exposure-response associations when holding other OH-PAH metabolites at their median concentrations.

CONCLUSION

Urinary OH-PAH metabolites as individual chemicals and mixtures were adversely associated with thyroid hormones among reproductive-aged men.

Impacts of traffic-related particulate matter pollution on semen quality: A retrospective cohort study relying on the random forest model in a megacity of South China

BACKGROUND

Emerging evidence shows the detrimental impacts of particulate matter (PM) on poor semen quality. High-resolution estimates of PM concentrations are conducive to evaluating accurate associations between traffic-related PM exposure and semen quality.

METHODS

In this study, we firstly developed a random forest model incorporating meteorological factors, land-use information, traffic-related variables, and other spatiotemporal predictors to estimate daily traffic-related PM concentrations, including PM_2.5, PM₁₀, and PM₁. Then we enrolled 1310 semen donors corresponding to 4912 semen samples during the study period from January 1, 2019, and December 31, 2019 in Guangzhou city, China. Linear mixed models were employed to associate individual exposures to traffic-related PM during the entire (0-90 lag days) and key periods (0-37 and 34-77 lag days) with semen quality parameters, including sperm concentration, sperm count, progressive motility and total motility.

RESULTS

The results showed that decreased sperm concentration was associated with PM₁₀ exposures (β: -0.21, 95 % CI: -0.35, -0.07), sperm count was inversely related to both PM_2.5 (β: -0.19, 95 % CI: -0.35, -0.02) and PM₁₀ (β: -0.19, 95 % CI: -0.33, -0.05) during the 0-90 days lag exposure window. Besides, PM_2.5 and PM₁₀ might diminish sperm concentration by mainly affecting the late phase of sperm development (0-37 lag days). Stratified analyses suggested that PBF and drinking seemed to modify the associations between PM exposure and sperm motility. We did not observe any significant associations of PM₁ exposures with semen parameters.

CONCLUSION

Our results indicate that exposure to traffic-related PM_2.5 and PM₁₀ pollution throughout spermatogenesis may adversely affect semen quality, especially sperm concentration and count. The findings provided more evidence for the negative associations between traffic-related PM exposure and semen quality, highlighting the necessity to reduce ambient air pollution through environmental policy.

In vitro testicular toxicity of environmentally relevant endocrine-disrupting chemicals: 2D vs. 3D models of prepubertal Leydig TM3 cells

The testis is a priority organ for developing alternative models to assess male reproductive health hazards of chemicals. This study characterized a 3D in vitro model of murine prepubertal Leydig TM3 cells with improved expression of steroidogenesis markers suitable for image-based screening of testicular toxicity. This 3D scaffold-free spheroid model was applied to explore the impact of prototypical endocrine-disrupting chemicals (EDCs) and environmental reprotoxicants (benzo[a]pyrene, 2- and 9-methylanthracenes, fluoranthene, triclosan, triclocarban, methoxychlor) on male reproductive health. The results were compared to the male reprotoxicity potential of EDCs assessed in a traditional monolayer (2D) culture. The testicular toxicity was dependent not only on the type of culture (2D vs. 3D models) but also on the duration of exposure. Benzo[a]pyrene and triclocarban were the most active compounds, eliciting cytotoxic effects in prepubertal Leydig cells at low micromolar concentrations, which might be a mechanism contributing to their male reprotoxicity.

Mixture analysis on associations between semen quality and sperm DNA integrity and occupational exposure to polycyclic aromatic hydrocarbons

The objective of this study was to assess relationships between exposure to PAHs at occupational levels and outcomes of human semen quality and sperm DNA integrity. Personal breathing zone air samples were collected to quantify exposure of 16 targeted PAHs to coke-oven workers at a steel company in southern Taiwan. Semen quality, including concentration, motility, morphology, and viability, were assessed. Sperm DNA fragmentation, 8-oxodGuo, bulky PAH adducts, and benzo[a]pyrene diol epoxide-DNA adducts served as biomarkers for assessment of sperm DNA integrity. The Bayesian Kernel Machine Regression modeling was employed to estimate mixture effects of the PAH mixture on the outcomes of semen quality and sperm DNA integrity and to identify individual compounds of PAH mixtures associated with the mixture effects. Exposure to the PAH mixture was inversely associated with sperm viability, while benzo(b)fluoranthene (B[b]F) was identified as the main predictor for sperm viability. Exposure to the PAH mixture also exhibited a positive trend with sperm DNA fragmentation. B[b]F and benzo(a)anthracene (B[a]A) were identified as individual PAH compounds associated with increased sperm DNA fragmentation.

Study on Influencing Factors of Semen Quality in Fertile Men

Objective

To establish a system for evaluation of semen quality in fertile men by factor analysis (FA).

Methods

The FA method was used to analyze five sperm test indicators for fertile men (sperm pH, sperm motility, sperm progressive motility, semen density, and total sperm number) to determine the evaluation standard of semen quality. Pearson analysis was adopted for correlation testing.

Results

The comprehensive score formula for semen quality of normal fertile men was as follows: comprehensive score of semen quality = (0.38272 F₁ + 0.36359 F₂ + 0.20018 F₃)/94.699. Across the whole fertile population, semen quality was found to be correlated with abstinence period, age of first spermatorrhea, and frequency of intercourse. Smoking, drinking, and place of residence were correlated with semen quality in the high semen quality population. In the population with medium semen quality, only the abstinence period was associated with semen quality.

Conclusion

It is feasible to evaluate the semen quality of fertile men using the FA method. The comprehensive indicators of semen volume, sperm motility, and semen pH can be used as evaluative measures. Across the whole fertile population, the abstinence period and age of first spermatorrhea were correlated with semen quality. In the high semen quality population, smoking and drinking were negatively correlated with semen quality, and participants living in rural areas had better semen quality.

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.

A Factor Analysis Model for Rapid Evaluation of the Semen Quality of Fertile Men in China

Objective

The objective of this study is to reduce the dimension of several indicators with a strong correlation when conducting semen quality analysis in a small number of comprehensive variables that could retain most of the information in the original variables.

Methods

A total of 1132 subjects were recruited from the Maternal and Child Health Institutions of seven provinces in mainland China. They completed the questionnaire and provided semen samples. Visualization of the correlation between variables was realized by using a function chart and correlation in the PerformanceAnalytics package of the R programming language (version 3.6.3 [2020-02-29]). Factor analysis was conducted using the principal function in the psych package of R. Principal component analysis, combined with varimax rotation, was used in the operation of the model, and two common factors were selected and measured to provide values for the common factor. The score coefficient was estimated using the regression method.

Results

The contribution rates of the two common factors to variable X were 43.7% and 33.98%, respectively. When the two common factors were selected, approximately 78% of the information of the original variables could be explained. The correlation coefficients between the first common factor (the quantitative factor) and sperm density, total sperm count, and semen volume were 0.824, 0.984, and 0.544, respectively. The correlation coefficients between the second common factor (the quality factor) and sperm motility and the percentage of forward-moving (progressive spermatozoa) sperm were 0.978 and 0.976, respectively.

Conclusion

The correlation between the original variables of a semen quality analysis was strong and suitable for dimensionality reduction by factor analysis. Factor analysis and dimensionality reduction provide a fast and accurate assessment of semen quality. Patients with low fertility or infertility can be identified and provided with corresponding treatments.

Mixture Analysis of Associations between Occupational Exposure to Polycyclic Aromatic Hydrocarbons and Sperm Oxidative DNA Damage

OBJECTIVE

This study aimed to determine (i) associations between levels of the polycyclic aromatic hydrocarbon (PAH) mixture with 16 targeted PAH compounds in the personal breathing zone area and sperm oxidative DNA damage, (ii) associations between levels of individual PAH compounds and sperm oxidative DNA damage, (iii) oxidative stress as the mode of action for the genotoxic effects on sperm, and (iv) any dose-response relationship between exposure to the PAH mixture and/or individual PAH compounds and sperm oxidative DNA damage.

METHODS

Sixteen targeted PAH compounds in the personal breathing zone area of 38 coke-oven workers and 24 control subjects were quantified using gas chromatography-mass spectrometry. Sperm oxidative damage and status were evaluated by measuring levels of sperm 7,8-dihydro-8-oxoguanie (8-oxodGuo), seminal malondialdehyde (MDA) and seminal reactive oxygen species (ROS). Bayesian kernel machine regression with hierarchical variable selection process was employed to determine associations of the PAH mixture and the biomarkers of sperm oxidative damage. A novel grouping approach needed for the hierarchical variable selection process was developed based on PAH bay region and molecular weight.

RESULTS

The PAH mixture exhibited a positive trend with increased sperm 8-oxodGuo levels at their lower percentiles (25th-50th). The exposure of the PAH mixture was associated with increased MDA levels in sperm. Bay and bay-like regions of the PAH mixture were the most important group for estimating the associations between the PAH mixture and sperm oxidative stress status. Benzo[a]anthracene was the main individual PAH compound that was associated with increased MDA levels.

CONCLUSION

Sperm oxidative DNA damage induced by occupational exposure to the PAH mixture had a suggestive association with increased MDA levels in coke-oven workers. Finally, the study identified that the individual PAH compound, benzo[a]anthracene, was the primary driver for the suggestive association between the PAH mixture and sperm oxidative damage.

Long-term exposure to environmental levels of phenanthrene disrupts spermatogenesis in male mice

Phenanthrene (Phe) is a tricyclic polycyclic aromatic hydrocarbon with high bioavailability under natural exposure. However, there are few studies on the reproductive toxicity of Phe in mammals. In this study, male Kunming mice were gavaged once every two days with Phe (5, 50, and 500 ng/kg) for 28 weeks. The accumulation levels of Phe in the testis were dose-dependently increased. Histopathological staining showed that Phe exposure reduced the number of spermatogonia, sperm and Sertoli cells. The percentage of testicular apoptotic cells was significantly increased, which was further verified by the upregulated BAX protein. The expression of the GDNF/PI3K/AKT signaling pathway was downregulated, which might suppress the self-renewal and differentiation of spermatogonial stem cells. Meanwhile, Phe exposure inhibited the expression of Sertoli cell markers (Fshr, WT1, Sox9) and the Leydig cell marker Cyp11a1, indicating damage to the function of Sertoli cells and Leydig cells. Serum estrogen and testicular estrogen receptor alpha were significantly upregulated, while androgen receptor expression was downregulated. These alterations might be responsible for impaired spermatogenesis. This study provides new insights for evaluating the reproductive toxicity and potential mechanisms of Phe in mammals.

Application of the comet assay for the evaluation of DNA damage in mature sperm

DNA integrity is considered an important parameter of semen quality and is of significant value as a predictor of male fertility. Currently, there are several methods that can assess sperm DNA integrity. One such assay is the comet assay, or single-cell gel electrophoresis, which is a simple, sensitive, reliable, quick and low-cost technique that is used for measuring DNA strand breaks and repair at the level of individual cells. Although the comet assay is usually performed with somatic cells from different organs, the assay has the ability to detect genotoxicity in germ cells at different stages of spermatogenesis. Since the ability of sperm to remove DNA damage differs between the stages, interpretation of the results is dependent on the cells used. In this paper we give an overview on the use and applications of the comet assay on mature sperm and its ability to detect sperm DNA damage in both animals and humans. Overall, it can be concluded that the presence in sperm of significantly damaged DNA, assessed by the comet assay, is related to male infertility and seems to reduce live births. Although there is some evidence that sperm DNA damage also has a long-term impact on offspring's health, this aspect of DNA damage in sperm is understudied and deserves further attention. In summary, the comet assay can be applied as a useful tool to study effects of genotoxic exposures on sperm DNA integrity in animals and humans.

Exposure to fine particulate matter-bound polycyclic aromatic hydrocarbons, male semen quality, and reproductive hormones: The MARCHS study

Exposure to outdoor fine particulate matter (PM_2.5)-bound polycyclic aromatic hydrocarbons (PAHs) is linked to reproductive dysfunction. However, it is unclear which component of PAHs is responsible for the adverse outcomes. In the Male Reproductive Health in Chongqing College Students (MARHCS) cohort study, we measured the exposure levels of 16 PAHs by collecting air PM_2.5 particles and assessed eight PAHs metabolites from four parent PAHs, including naphthalene, fluorene, phenanthrene, and pyrene in urine samples. We investigated compositional profiles and variation characteristics for 16 PAHs in PM_2.5, and then assessed the association between PAHs exposure and semen routine parameters, sperm chromatin structure, and serum hormone levels in 1452 samples. The results showed that naphthalene (95% CI: -17.989, -8.101), chrysene (95% CI: -64.894, -47.575), benzo[a]anthracene (95% CI: -63.227, -45.936) and all the high molecular weight (HMW) PAHs in PM_2.5 were negatively associated with sperm normal morphology. Most of the low molecular weight (LMW) PAHs, such as acenaphthylene, fluorene, phenanthrene, fluoranthene, pyrene, chrysene, benzo[a]anthracene, ∑LMW PAHs and ∑16 PAHs, were correlated with increased sperm motility (all corrected P < 0.05). On the other hand, sperm normal morphology was all negatively associated with urinary metabolites of ∑OH-Nap (95% CI: -5.611, -0.536), ∑OH-Phe (95% CI: -5.741, -0.957), and ∑OH-PAHs (95% CI: -5.274, -0.361). Urinary concentrations of ∑OH-PAHs were found to be negatively associated with sperm high DNA stainability (HDS) (P = 0.023), while ∑OH-Phe were negatively associated with serum testosterone level and sperm HDS (P = 0.004). Spearman correlation analysis showed that except for the urinary OH-Nap metabolites, the rest of the urinary OH-PAHs metabolites were negatively correlated with their parent PAHs in air. The results of this study suggest that various PAHs' components may affect reproductive parameters differently. Inhalation of PAHs in air, especially HMW PAHs, may be a potential risk factor for male reproductive health.

Semen quality and windows of susceptibility: A case study during COVID-19 outbreak in China

BACKGROUND

To evaluate the impact of air pollution exposure on semen quality parameters during COVID-19 outbreak in China, and to identify potential windows of susceptibility for semen quality.

METHODS

A retrospective observational study was carried out on 1991 semen samples collected between November 23, 2019 and July 23, 2020 (a period covering COVID-19 lock-down in China) from 781 sperm donor candidates at University-affiliated Sichuan Provincial Human Sperm Bank. Multivariate mixed-effects regression models were constructed to investigate the relationship between pollution exposure, windows of susceptibility, and semen quality, while controlling for biographic and meteorologic confounders.

RESULT(S)

The results indicated multiple windows of susceptibility for semen quality, especially sperm motility, due to ambient pollution exposure. Exposure to particulate matters (PM2.5 and PM10), O3 and NO2 during late stages of spermatogenesis appeared to have weak but positive association with semen quality. Exposure to CO late in sperm development appeared to have inverse relationship with sperm movement parameters. Exposure to SO2 appeared to influence semen quality throughout spermatogenesis.

CONCLUSION(S)

Potential windows of susceptibility for semen quality varied depending on air pollutants. Sperm motility was sensitive to pollution exposure. Findings from current study further elucidate the importance of sensitive periods during spermatogenesis and provide new evidence for the determinants of male fertility.

Adverse effects of circadian desynchrony on the male reproductive system: an epidemiological and experimental study

STUDY QUESTION

Is circadian desynchrony a risk factor of male reproductive damage in semen parameters and/or reproductive hormones?

SUMMARY ANSWER

Circadian desynchrony correlates with decrease of sperm count, which was improved when circadian desynchrony was attenuated.

WHAT IS KNOWN ALREADY

Circadian desynchrony caused by work (shift work) and non-work-related reasons is prevalent worldwide and has been found to be associated with decreased female fertility, but whether it harms male reproductive health is unclear.

STUDY DESIGN, SIZE, DURATION

A hybrid research was conducted. (i) A cross-sectional study of 1346 Chinese men in 2007 was used to analyze the association between semen/hormone biomarkers and work-related circadian desynchrony, which was divided into rotating shift work and permanent shift work against non-shift work. (ii) A cohort of 796 Chinese undergraduates from 2013 to 2014 was used to analyzed the association between semen/hormone biomarkers and non-work-related circadian desynchrony (between school days and days off). (iii) The biomarker identified simultaneously in both populations was further validated in male C57BL/6J mice housed under conditions simulating circadian desynchrony.

PARTICIPANTS/MATERIALS, SETTING, METHODS

A total of 17 semen/hormone biomarkers were compared among rotating shift workers and permanent shift workers against non-shift workers in the 1346 reproductive-age Chinese men. A total of 14 semen/hormone biomarker was analyzed in the undergraduate cohort for correlation with non-work-related circadian desynchrony (measured by Munich Chronotype Questionnaire) in 2013 and 2014 and compared between the 2 years. Photoperiod-shifting method was used to establish the mouse model, in which the biomarker was examined and molecular mechanism was explored by apoptosis analysis, DNA content analysis, transcriptome sequencing, real-time PCR and western blotting.

MAIN RESULTS AND THE ROLE OF CHANCE

Among the semen/hormone biomarkers, sperm count was found to be lower in rotating shift workers, who had a higher risk of low sperm count defined by Chinese Ministry of Health (total sperm/ejaculate < 120 × 10⁶) than non-shift workers (odds ratio = 1.26, 95% CI 1.05–1.52). This biomarker was replicated in the undergraduate cohort, where each hour of circadian desynchrony was associated with 1.16 (95% CI 1.02–1.31) fold odds of low sperm count, and sperm count increased during 2014 in men who reduced circadian desynchrony after 2013. A decrease of sperm count with circadian desynchrony and its recovery after removal of circadian desynchrony was also observed in the mouse model. During asynchrony, increased apoptosis was found in seminiferous tubules and the marker genes of post-spermatocyte stage cells were down-regulated. The most enriched functional pathway was homologous recombination, which happened during meiosis.

LIMITATIONS, REASONS FOR CAUTION

The study of human beings was observational while the animal study has potential difference in circadian desynchrony exposure and species susceptibility. Further researches are needed to clarify the causal relationship in men.

WIDER IMPLICATIONS OF THE FINDINGS

These findings provide novel insight to the effect of circadian desynchrony on male reproductive health and a potential strategy for prevention of reproductive damage.

STUDY FUNDING/COMPETING INTEREST(S)

This study was supported by the National Key R&D Program of China [2017YFC1002001] and National Natural Science Foundation of China [81871208]. There are no conflicts of interest to declare.

TRIAL REGISTRATION NUMBER

NA.

Polycyclic aromatic hydrocarbon exposure, oxidative potential in dust, and their relationships to oxidative stress in human body: A case study in the indoor environment of Guangzhou, South China

A comparative study of internal and external exposure is a good method to comprehensively understand human exposure to environmental contaminants that may trigger oxidative stress in human body. Information is limited regarding the influences of reactive oxygen species (ROS) on human health from the environment. In addition, data on the contribution of polycyclic aromatic hydrocarbons (PAHs) from indoor environments, especially air, to total human exposure are still insufficient. The present study measured PAHs in paired indoor dust (n = 101), gas (polyurethane foams, n = 100), and particle samples (quartz fiber filters, n = 100) and their hydroxy metabolites (OH-PAHs) in 205 urine samples from 101 families in Guangzhou, South China. The oxidative potential (OP) in dust samples was quantified with a dithiothreitol (DTT) assay to reflect the oxidizability of ROSs, and explore the relationship between environmental ROSs and oxidative stress in humans (using urinary 8-hydroxy-2'-deoxyguanosine (8-OHdG) as a biomarker). The estimated daily intakes (EDIs) of Σ₁₆PAH via air inhalation were much higher than those from gas dermal contact, dust dermal contact, and dust ingestion (mean: 19.5 > 4.27 > 3.75 > 1.60 ng/kg_bw/day). Generally, approximately 16% of naphthalene, 28% of fluorene, 9% of phenanthrene, and 3% of pyrene were derived from indoor environments for all residents when compared with the total PAH exposure amount from all sources. Significantly positive relationships were found between OH-PAHs and 8-OHdG (coefficients β: 0.129-0.366, p < 0.05) checked by linear mixed effect models, and males seemed to be more susceptible than females to the DNA oxidative damage related to PAH exposure. The mean OP value in dust was 7.14 ± 6.68 pmol/(min·μg). Individual PAHs in dust gradually intensified the oxidizability of dust particles as their molecular weight increased. A potential but not significant dose-relationship was found between dusty OP and urinary 8-OHdG. Further work should determine the impact of chemical profiles on OP in different environmental media and continuously explore the potential to use OP as a useful indicator to reflect the total oxidizability of several groups of environmental pollutants.

Effects of PM2.5 exposure on reproductive system and its mechanisms

With the development of human society, haze has become an important form of air pollution. Haze is a mixture of fog and haze, and the main component of haze is fine particulate matter (PM_2.5), which is the most important indicator of composite air pollution. Epidemiological studies proved that PM_2.5 can break through the respiratory mucosal barrier and enter the human body, causing pathological effects on multiple systems of the body. In the past, people put more attention to PM_2.5 in the respiratory system, cardiovascular system, nervous system, etc, and relatively paid less attention to the reproductive system. Recent studies have shown that PM_2.5 will accumulate in the reproductive organs through blood-testis barrier, placental barrier, epithelial barrier and other barriers protecting reproductive tissues. In addition, PM_2.5 can disrupt hormone levels, ultimately affecting fertility. Prior studies have shown that oxidative stress, inflammation, apoptosis, and the breakdown of barrier structures are now considered to contribute to reproductive toxicity and may cause damage at the molecular and genetic levels. However, the exact mechanism remains to be elucidated. Our review aims to provide an understanding of the pathological effects of PM_2.5 on reproductive system and the existing injury mechanism.

Association between Urinary Triclosan and Serum Testosterone Levels in U.S. Adult Males from NHANES, 2011-2012

Triclosan was introduced into the market in the 1970s and has since been used as an antimicrobial agent in a diverse array of consumer and personal care products. Although it has been widely used over a number of years, there is growing concern and debate over its safety and efficacy and its potential as an endocrine disruptor. Although prior animal toxicology studies have shown an association between triclosan and decreased testosterone levels, human studies have been limited, particularly for adult men. Using the National Health and Nutrition Examination Survey data (NHANES, 2011-2012), we examined the association of urinary triclosan on testosterone levels in adult men 18-65 years of age. Multivariable linear regression analysis failed to show an association between triclosan and serum testosterone (β = 0.0003, p = 0.98, 95% CI = -0.024, 0.025). The results suggest there is no association or that triclosan concentrations are too low to cause a significant impact on testosterone levels. Additionally, longitudinal studies would provide a more comprehensive understanding of the direction of change and magnitude of causal relationships over time.

Interaction effect of polycyclic aromatic hydrocarbon metabolites and cadmium on semen quality in nonsmokers

Both cadmium (Cd) and polycyclic aromatic hydrocarbons (PAHs) are known reproductive toxicants, but their co-exposure and interaction effect on semen quality particularly in nonsmokers remain unknown. We included 333 nonsmoking men and analyzed their urine and semen samples for heavy metals and PAH metabolites. Restricted cubic spline models were used to explore the dose-response relationship between each OH-PAHs, Cd, and semen quality parameters; the generalized linear model was performed to examine the interaction of each urinary OH-PAH metabolite and Cd concentration on semen quality. Also, stratified analysis was applied to further illustrate the independent effect of PAHs on semen quality parameters in low and high concentration Cd subgroups. The dose-response and interaction effect of PAHs and Cd on male semen quality was observed. Stratified analysis in the high concentration Cd subgroup showed a negative association of 1-OHPyr concentration with semen motility. Our findings indicate that Cd not only modifies the association between PAHs and semen quality but can also exacerbate the toxic effect of pyrene on semen quality parameters. However, further studies with larger samples are needed to confirm the findings.

Ambient air pollution and male fecundity: A retrospective analysis of longitudinal data from a Chinese human sperm bank (2013-2018)

Ambient air pollution has adverse effects on human health and reproduction. A number of studies have suggested a significant association between ambient air pollution and human fecundity, with most studies focusing on cross-sectional data from the general male population with single semen samples. We conducted a retrospective study in China using longitudinal analysis of repeated semen samples to investigate the association between environmental exposure parameters (e.g., PM_2.5, PM₁₀, SO₂, NO₂, CO, ground temperature, and relative humidity) and sperm quality parameters (e.g., semen volume, sperm concentration, forward motility concentration, and percentage of progressive rate) during different exposure windows (current day, 90-day preceding). Data from 686 males and 4841 semen samples collected between 2013 and 2018 at Sichuan Provincial Sperm Bank were included in a mixed-effects model analysis. The study population was young, healthy, and well-educated. The results indicate that 90-day average concentrations of PM_2.5, PM_10, and CO were negatively associated with sperm concentration and forward motility concentration, whereas 90-day average concentration of O₃ was positively associated with forward motility concentration. Between-subject variability played the dominant role in overall model variance. Our results suggest that chronic exposure to particulate matter and CO may interfere with spermatogenesis.

Influence of polycyclic aromatic hydrocarbon exposure on IVF: now is the time to focus on women

RESEARCH QUESTION

Is polycyclic aromatic hydrocarbon (PAH) exposure associated with the reproductive outcomes of IVF treatment?

DESIGN

A prospective, small-scale monocentric cohort study of couples who underwent IVF treatment between January 2018 and June 2019. Both members of each couple answered a questionnaire on PAH exposure and provided urine samples to measure urinary 1-hydroxypyrene (1-OHP) the day before oocyte retrieval and semen collection for fertilization. To assess the specific PAH exposure of gamete cells, immunostaining was conducted on both spermatozoa and granulosa cells obtained during IVF with an anti-benzo(a)pyrene diol epoxide (BPDE) monoclonal antibody that recognizes BDPE-DNA adducts. To assess DNA damage, a comet assay on spermatozoa was conducted. The PAH exposure was compared between couples who had positive HCG and couples who had negative HCG on day 14 after embryo transfer.

RESULTS

Eighteen couples were included. The mean 1-OHP level in women whose HCG tests were positive (n = 6) was significantly lower than that in women with negative HCG tests (0.098 [0.042-0.170] versus 0.177 [0.067-0.812] μg/g creatinine; P = 0.048). The presence of BPDE-DNA adducts in granulosa cells of women with a negative (29.7 [16.2-57.5] arbitrary units) or positive HCG test (20.3 [9.3-23.3] arbitrary units) were not significantly different (P = 0.092). The urinary 1-OHP levels of men and BPDE-DNA adducts in spermatozoa showed no differences between groups.

CONCLUSIONS

This exploratory research should encourage further studies to determine the effect of women's exposure to PAHs on reproductive outcomes of IVF treatment.

Mediation of association between polycyclic aromatic hydrocarbon exposure and semen quality by spermatogenesis-related microRNAs: A pilot study in an infertility clinic

Spermatogenesis-related microRNAs (miRNAs) are vulnerable to polycyclic aromatic hydrocarbons (PAHs). Changes in spermatogenesis-related miRNAs may be biological intermedia in mechanisms linking PAHs and semen quality. This study aimed to investigate whether spermatogenesis-related microRNAs mediate the associations between PAHs and semen quality. We measured 10 monohydroxylated PAHs (OH-PAHs) in repeated urine samples and three candidate spermatogenesis-related miRNAs (miRNA106a, miRNA21, and miRNA34c) in seminal plasma from men attending an infertility clinic (n = 111). Mediation analysis was applied to determine the mediating role of spermatogenesis-related miRNAs in the association of PAH exposure with semen quality. Urinary 2-OHFlu and 2-OHPh were related to reduced seminal plasma miRNA34c (p for trend = 0.05 and 0.03, respectively). Urinary 9-OHPh was related to reduced seminal plasma miR106a (p for trend = 0.02), which in turn, was positively associated with sperm concentration, sperm count, sperm total motility, and progressive motility (all p for trends<0.05). Up to 43.8% of the eff ;ect of urinary 9-OHPh on decreased sperm concentration was mediated by seminal plasma miR106a. Our results suggested that certain PAH exposure was associated with reduced spermatogenesis-related miRNAs and such alterations might be an intermediate mechanism by which PAHs exert its adverse effects on semen quality.

Urinary metabolites of polycyclic aromatic hydrocarbons in pregnant women and their association with a biomarker of oxidative stress

Exposure to polycyclic aromatic hydrocarbons (PAHs) during pregnancy may pose adverse health risk to both the mothers and babies. In the present study, 188 pregnant women of different trimesters were recruited in Guangzhou, south China, and nine hydroxyl PAHs (OH-PAHs) and a biomarker of DNA oxidative damage, 8-hydroxy-2'-deoxyguanosine (8-OHdG), were determined in their urine samples. All OH-PAHs except for 4-hydroxyphenanthrene and 6-hydroxychrysene were found in > 90% samples, with total concentration in the range of 0.52 to 42.9 μg/g creatinine. In general, concentration levels of OH-PAHs in pregnant women were lower than those in general population in the same research area but with higher levels in working women than in housewives. The mean daily intakes of PAHs from dietary estimated by urinary OH-PAHs were 0.021, 0.004, 0.047, and 0.030 μg/kg_bw/day for naphthalene, fluorene, phenanthrene, and pyrene, respectively, which were much lower than the reference doses (20, 30, and 40 μg/kg_bw/day for naphthalene, pyrene, and fluorene, respectively) derived from chronic oral exposure data by the United States Environmental Protection Agency. The low exposure levels of PAHs may be attributed to the traditional dietary taboo of Chinese pregnant women, which is to minimize the consumption of "toxic" food. The concentrations of 8-OHdG (4.67-49.4 μg/g creatinine) were significantly positively correlated with concentrations of several OH-PAHs, such as metabolites of naphthalene, fluorene, and phenanthrene (r = 0.3-0.6). In addition, the concentrations of 8-OHdG were higher in working women than in housewives when exposed to the same levels of PAHs, partly indicating the possible relation between work-related pressure for working women and the oxidative stress.

Determination of 3-Hydroxybenzo[a]pyrene Glucuronide/Sulfate Conjugates in Human Urine and Their Association with 8-Hydroxydeoxyguanosine

While 3-hydroxybenzo[a]pyrene (3-OHBaP) is a preferable biomarker to assess human exposure to benzo[a]pyrene (BaP), a sensitive and simple method is lacking. In this study, a specific and sensitive method based on liquid chromatography coupled with electrospray tandem mass spectrometry (LC-ESI-MS/MS) was developed for direct analysis of 3-OHBaP glucuronide and sulfate conjugates in human urine samples without enzymatic hydrolysis. The limits of detection (LODs) were 0.06 ng L^-1 for BaP-3-sulfate (BaP-3-S) and 0.16 ng L^-1 for BaP-3-glucuronide (BaP-3-G), which showed high sensitivity. Both compounds showed excellent linearity (r² > 0.99) in the range of 0.01-10 μg L^-1 in the instrumental calibration. The absolute recoveries of the target analytes spiked in human urine for the entire analytical procedure were 68.3 ± 4.96% (mean ± SD) and 63.7 ± 5.47% for BaP-3-S and BaP-3-G, respectively. This method was applied to quantify BaP-3-G and BaP-3-S in 150 urine samples collected from healthy volunteers. The mean concentration of BaP-3-S was 0.67 ng g^-1 creatinine (<LOD to 10.20 ng g^-1 creatinine), about 10-fold lower than that of BaP-3-G (6.73 ng g^-1 creatinine, < LOD to 52.64 ng g^-1 creatinine). For comparison, we also detected the concentration of free 3-OHBaP in 15 randomly selected samples without enzymatic hydrolysis and found at least >98% of 3-OHBaP is excreted mainly in these two conjugated forms in human urine. A statistically significant positive association was observed between urinary 3-OHBaP conjugates and urinary 8-OHdG levels (p < 0.001) in the general population. This study developed a sensitive and simple method to determine urinary glucuronide/sulfate conjugated BaP metabolites and for the first time found that BaP exposure associated with 8-OHdG levels in the general population.

BPDE and B[a]P induce mitochondrial compromise by ROS-mediated suppression of the SIRT1/TERT/PGC-1α pathway in spermatogenic cells both in vitro and in vivo

There is increasing evidence that indicates benzo[a]pyrene (B[a]P) and its active metabolite benzo[a]pyrene-7, 8-dihydrodiol-9, 10-epoxide (BPDE) are endocrine disruptors that can cause reproductive toxicity. Nevertheless, the underlying mechanisms are still obscure. The present study investigates the impacts of B[a]P and BPDE on mitochondria, a sensitive target affected by multiple chemicals, in spermatogenic cells. It showed that BPDE treatment induced mitochondrial dysfunction and the inhibition of mitochondrial biogenesis in mouse spermatocyte-derived cells (GC-2). These effects were efficiently mitigated by pretreatment with ZLN005, an activator of PGC-1α, in GC-2 cells. TERT knockdown and re-expression cell models were established to demonstrate that TERT regulated the BPDE-induced mitochondrial damage via PGC-1α signaling in GC-2 cells. Moreover, upregulating or knockdown SIRT1 expression attenuated or aggravated BPDE-induced mitochondrial compromise by activating or inhibiting, respectively, the TERT and PGC-1α molecules in GC-2 cells. Finally, we observed that BPDE markedly elevated oxidative stress in GC-2 cells. Resveratrol and N-acetylcysteine, as reactive oxygen species (ROS) scavengers, attenuated BPDE-mediated mitochondrial damage by increasing SIRT1 activity and expression in GC-2 cells. The in vitro results were corroborated by in vivo experiments in rats treated with B[a]P for 4 weeks. B[a]P administration caused mitochondrial damage and mitochondria-dependent apoptosis in spermatogenic cells, as well as the decreased expression of SIRT1, TERT, and PGC-1α. In summary, the results of the present study demonstrate that B[a]P and BPDE induce mitochondrial damage through ROS production that suppresses SIRT1/TERT/PGC-1a signaling and mediate B[a]P- and BPDE-mediated reproductive toxicity.

Di-n-butyl phthalate epigenetically induces reproductive toxicity via the PTEN/AKT pathway

Di-n-butyl phthalate (DBP) is a kind of ubiquitous chemical linked to hormonal disruptions that affects male reproductive system. However, the mechanism of DBP-induced germ cells toxicity remains unclear. Here, we demonstrate that DBP induces reduction of proliferation, increase of apoptosis and DNA damage dependent on the PTEN/AKT pathway. Mechanistically, DBP decreases PTEN promoter methylation and increases its transcriptional activity, leading to increased PTEN expression. Notably, DNMT3b is confirmed as a target of miR-29b and miR-29b-mediated status of PTEN methylation is involved in the effects of DBP treatment. Meanwhile, DBP decreases AKT pathway expression via increasing PTEN expression. In addition, the fact that DBP decreases the sperm number and the percentage of motile and progressive sperm is associated with downregulated AKT pathway and sperm flagellum-related genes. Collectively, these findings indicate that DBP induces aberrant PTEN demethylation, leading to inhibition of the AKT pathway, which contributes to the reproductive toxicity.

Polycyclic Aromatic Hydrocarbons and Endocrine Disruption: Role of Testicular Gap Junctional Intercellular Communication and Connexins

Ambient air pollution and smoking are well-documented risk factors for male infertility. Prevalent air pollutants and cigarette smoke components, polycyclic aromatic hydrocarbons (PAHs), are environmental and occupational toxicants that act as chemicals disrupting endocrine regulation and reproductive potential in males. Testicular gap junctional intercellular communication (GJIC) is critical for normal development and function of testicular tissue, thus we assessed GJIC as a process potentially targeted by PAHs in testes. Lower MW PAHs with a bay or bay-like region rapidly dysregulated GJIC in Leydig TM3 cells by relocalization of major testicular gap junctional protein connexin 43 (Cx43) from plasma membrane to cytoplasm. This was associated with colocalization between Cx43 and ubiquitin in intracellular compartments, but without any effect on Cx43 degradation rate or steady-state Cx43 mRNA levels. A longer exposure to active PAHs decreased steady-state levels of full-length Cx43 protein and its 2 N-truncated isoforms. Inhibition of GJIC by PAHs, similarly to a prototypic GJIC-inhibitor TPA, was mediated via the MAP kinase-Erk1/2 and PKC pathways. Polycyclic aromatic hydrocarbon-induced GJIC dysregulation in testes was cell-type-specific because neither PAH dysregulated GJIC in Sertoli TM4 cells, despite PAHs were rapidly taken up by both Leydig TM3 as well as Sertoli TM4 cells. Because TPA effectively dysregulated GJIC in both testicular cell types, a unique regulator of GJIC targeted by PAHs might exist in Leydig TM3 cells. Our results indicate that PAHs could be a potential etiological agent contributing to reproductive dysfunctions in males through an impairment of testicular GJIC and junctional and/or nonjunctional functions of Cx43.

Semen quality and sperm DNA damage associa -revised - final-finalted with oxidative stress in relation to exposure to polycyclic aromatic hydrocarbons

The cross-sectional study aimed to assess whether oxidative stress induced by exposure to polycyclic aromatic hydrocarbons (PAHs) affect semen quality and sperm DNA integrity. A total of 106 who met the inclusion criteria, were recruited from a coke-oven plant during their annual health checkup. The human subjects were grouped into the high exposure group, the low exposure group and the control based on PAH concentrations surrounding their employment locations. Semen quality, oxidative stress status, and sperm DNA damage [DNA fragmentation and 8-hydroxy-2'-deoxyguanosine (8-oxodGuo)] were assessed. Urinary 1-hydroxypyren (1-OHP) was used to assess human subject exposure to PAHs. The high exposure group experienced significantly lower sperm motility and normal morphology than the control (P = 0.046 and 0.049, respectively). The high exposure group also had significantly higher 8-oxoGuo concentrations in sperm than the control (P = 0.027). Urinary 1-OHP concentration was associated with decreased motility and less normal morphology, along with increased sperm oxidative damage and ROS concentrations. Oxidative stress induced by exposure to PAHs was associated with decreased sperm quality.

Air pollution from natural and anthropic sources and male fertility

Exposure to air pollution has been clearly associated with a range of adverse health effects, including reproductive toxicity. However, a limited amount of research has been conducted to examine the association between air pollution and male reproductive outcomes, specially semen quality. We performed a systematic review (up to March 2017) to assess the impact of environmental and occupational exposure to air pollution on semen quality. Epidemiological studies focusing on air pollution exposures and male reproduction were identified by a search of the PUBMED, MEDLINE, EBSCO and TOXNET literature bases. Twenty-two studies were included which assess the impact of air pollutants (PM_2.5, PM₁₀, SO₂, NOx, O₃, PAHs) on main semen parameters (sperm concentration, motility, morphology), CASA parameters, DNA fragmentation, sperm aneuploidy and the level of reproductive hormones. The number of studies found significant results supporting the evidence that air pollution may affect: DNA fragmentation, morphology and motility.In summary, most studies concluded that outdoor air pollution affects at least one of the assessed semen parameters. However the diversity of air pollutants and semen parameters presented in the studies included in the review and different study design caused lack of consistency in results and difficulties in comparison.

Association between fertility rate reduction and pre-gestational exposure to ambient fine particles in the United States, 2003-2011

Ambient pollutants are associated with clinical and sub-clinical indicators of infertility, such as poor sperm quality. However, the link between the ambient fine particle (PM_2.5) concentration and the fertility rate (FR) is unclear. In this epidemiological study, we examined the association between PM_2.5 concentration and childlessness in the United States (US). We conducted a nationwide spatiotemporal study of ~29 million births in 520 US counties from 2003 to 2011. We obtained monthly numbers and demographic data of newborns from the Centers for Disease Control and Prevention, and PM_2.5 estimates from a downscaling model of in situ observations and outputs from the Community Multiscale Air Quality Model. We evaluated the association between the mean PM_2.5 concentration and the FR during the gestational (0-8 months before birth) and pre-gestational (9-11 months before birth) periods using a Poisson model with demographic and socioeconomic covariates. We found a significant association between the FR and PM_2.5 exposure during pre-gestation but not gestation. Each 5 μg/m³ increase in pre-gestational PM_2.5 exposure was associated with a 0.7% (0.0%, 1.4%) reduction in the FR. Nonlinear analysis suggested a sublinear association between the reduction in the FR and PM_2.5 concentration without a safety threshold. Additionally, an annual mean reduction of 1.16 (1.15, 1.17) births per 1000 females aged 15-44 years was attributable to PM_2.5. This study established, for the first time, an association in the US between the FR and PM_2.5 concentration, a finding that adds to the extant epidemiological evidence of the effects of ambient pollutants on fertility, and extends the scope of the impact of low air quality on health.

Increment of ambient exposure to fine particles and the reduced human fertility rate in China, 2000-2010

Epidemiological and toxicological studies suggest that exposure to ambient fine particles (PM_2.5) can reduce human reproductive capacity. We previously reported, based on spatial epidemiology, that higher levels of PM_2.5 exposure were associated with a lower fertility rate (FR) in China. However, that study was limited by a lack of temporal variation. Using first-difference regression, we linked temporal changes in FR and PM_2.5 with adjustment for ecological covariates across 2806 counties in China during 2000-2010. Next, we performed a sensitivity analysis of the variation in the PM_2.5-FR association according to (1) geographic region, (2) indicators of the level of development, and (3) PM_2.5 concentrations. Also, we quantified the reduction in the FR attributable to ambient PM_2.5 in China for the first time. The FR decreased by 3.3% (1.2%, 5.3%) for each 10 μg/m³ increment in PM_2.5. The association varied significantly among the geographic regions, but not with the level of development. Nonlinearity analysis suggested a linear exposure-response function with an effect threshold of ~8 μg/m³. We also found that comparing to the 2000 scenario, increment of PM_2.5 in 2010 might result in a reduction of 2.50 (2.44, 2.60) infants per 1000 women aged 15-44 years per year in China. Our results confirm the statistical association between ambient particles and FR and suggest that poor air quality may contribute to childlessness in China.

Associations between sperm quality, DNA damage, and CYP1A1, GSTT1 and GSTM1 polymorphisms with 1-hydroxypyrene urinary levels in men occupationally exposed to polycyclic aromatic hydrocarbons

PURPOSE

During recent decades, several reports have suggested a decrease in semen quality and DNA damage due in part to environmental toxicants and industrial chemicals. Among these xenobiotics, polycyclic aromatic hydrocarbons (PAHs) are of particular concern because of their remarkable mutagenic and carcinogenic properties and because several experimental and epidemiological studies have reported adverse effects of PAHs on male reproductive health and DNA structure. The aim of the study was to evaluate the association between 1-hydroxypyrene (1-OHP) urinary levels and sperm quality, DNA damage and the frequency of CYP1A1, GSTT1, and GSTM1 polymorphisms.

METHODS

Semen, urine and blood samples were taken for sperm-quality assessment, 1-OHP urinary level measurement, DNA damage evaluation and polymorphism frequency analysis of three genes implicated in PAH metabolism in a total of 70 Mexican subjects exposed and nonexposed to PAHs.

RESULTS

A significant decrease in sperm quality and increased DNA damage were registered in occupationally exposed volunteers. Polymorphisms modified the 1-OHP urinary levels; however, no associations were found between them. Inverse associations were registered between the sperm concentration/mL and 1-OHP levels and between tail lengths and the GSMT1 null genotype.

CONCLUSIONS

Our data showed an inverse association between 1-OHP urinary levels and both sperm quality and the DNA integrity. Additionally, the heterozygote variants of CYP1A1-m1 and CYP1A1-m2 significantly increased the urinary excretion of 1-OHP, and the GSTM1 null variant was inversely associated with the comet parameters evaluated.

TERT regulates telomere-related senescence and apoptosis through DNA damage response in male germ cells exposed to BPDE in vitro and to B[a]P in vivo

Increasing evidence shows that impaired telomere function is associated with male infertility, and various environmental factors are believed to play a pivotal role in telomerase deficiency and telomere shortening. Benzo[a]pyrene (B[a]P), a ubiquitous pollutant of polycyclic aromatic hydrocarbons (PAHs), can act as a reproductive toxicant; however, the adverse effect of B[a]P on telomeres in male reproductive cells has never been studied, and the related mechanisms remain unclear. In this study, we explored the effects of benzo[a]pyrene-7,8-dihydrodiol-9,10-epoxide (BPDE), the active metabolite of B[a]P, on telomere dysfunction in mouse spermatocyte-derived cells (GC-2) and also the potential role of telomerase in BPDE-induced spermatogenic cell damage. The results showed that BPDE induced cell viability inhibition, senescence, and apoptosis in GC-2 cells in a dose-dependent manner. Shortened telomeres, telomere-associated DNA damage, reduced telomerase activity, and TERT expression were also observed in BPDE-treated cells, accompanied with the activation of DNA damage response pathway (ATM/Chk1/p53/p21). Moreover, by establishing the TERT knockdown and re-expression cell models, we found that TERT regulated telomere length and the expression of DNA damage response-related proteins to influence senescence and apoptosis in GC-2 cells. These in vitro findings were further confirmed in vivo in the testicular cells of rats orally administrated with B[a]P for 7 days. B[a]P treatment resulted in histological lesions, apoptosis, and senescence in the testes of rats, which were accompanied by shortened telomeres, reduced levels of TERT protein, and increased expression of DNA damage response-related proteins. In conclusion, it can be concluded that TERT-mediated telomere dysfunction contributes to B[a]P- and BPDE-induced senescence and apoptosis through DNA damage response in male reproductive cells.

Associating ambient exposure to fine particles and human fertility rates in China

BACKGROUND

Adverse effects of ambient fine particles (PM_2.5) on sperm quality and oocyte fertilization have been identified by previous research. However, insufficient human studies tested associations between PM_2.5 and decreased fertility rates.

METHODS

We associated long-term exposure to PM_2.5 and county-level fertility rates reported by 2010 census across China. Exposure assessments were based on PM_2.5 maps (2009-2010) with a spatial resolution of 0.1° derived from satellite remote sensing data from another published study. We used a Poisson regression to examine the relationship between PM_2.5 and fertility rates with adjustment of potential confounders including county-level socioeconomic factors (e.g. sex ratio) and a spatially smoothed trend.

RESULTS

We found that fertility rates were significantly decreased by 2.0% (95% confidence interval: 1.8%, 2.1%) per 10 μg/m³ increment of PM_2.5. We also found a geographical variation of the associations.

CONCLUSIONS

The study add to epidemiological evidences on adverse effects of PM_2.5 on fertility rates.

Exposures to Atmospheric PM10 and PM10-2.5 Affect Male Semen Quality: Results of MARHCS Study

Studies have shown that the effects of ambient particulate matter (PM) may be related to particle's size. However, results on the relationships between different PM and reproductive health are controversial. To explore the impacts of various PM fractions on male reproductive health, a total of 796 eligible subjects recruited in 2013 baseline investigation. In addition, there were 656 (82.4%) and 568 (71.3%) subjects participated follow-up surveys in 2014 and 2015, respectively. We used multivariable regression analysis and mixed-effect model to investigate the associations between air pollutants PM₁₀, PM_10-2.5, and PM_2.5 exposures and semen quality, sperm DNA fragmentation and serum reproductive hormones of subjects. In the preliminary regression analysis, PM₁₀, PM_10-2.5, and PM_2.5 exposure all associated with sperm concentration, morphology, sperm high DNA stainability (HDS), serum estradiol and testosterone levels. However, in mixed models, we only found that PM₁₀ exposure were negatively associated with sperm normal morphology (95% CI: -14.13, -24.47) but positively associated with sperm progressive motility (95% CI: 23.00, 8.49), and PM_10-2.5 exposure was inversely associated with sperm concentration (95% CI: -9.06, -27.31) after multiplicity adjustment. Our results provide the evidence that air PM₁₀ and PM_10-2.5 exposures, not PM_2.5, are risk factors of semen quality.

Sleep duration is associated with sperm chromatin integrity among young men in Chongqing, China

This study explores whether sleep duration is associated with sperm chromatin integrity. To do so, we conducted a three-phase panel study of 796 male volunteers from colleges in Chongqing (China) from 2013 to 2015. Sleep duration was measured using a modified Munich Chronotype Questionnaire. Sperm DNA integrity was examined via Sperm Chromatin Structure Assay and Comet assay. Setting 7-7.5 h day^-1 of sleep duration as a reference, either longer or shorter sleep duration was associated negatively with high DNA stainability (HDS) (P = 0.009), which reflected the immaturity of sperm chromatin. The volunteers with > 9.0 h day^-1 sleep and those with ≤ 6.5 h day^-1 sleep had 40.7 and 30.3% lower HDS than did volunteers with 7-7.5 h day^-1 sleep. No association was found between sleep duration and DNA fragmentation index or Comet assay parameters. This study suggests that sleep duration is associated with sperm chromatin integrity. Further studies are required to validate these findings and investigate the mechanism underlying this association.

Repeated measures of urinary polycyclic aromatic hydrocarbon metabolites in relation to altered reproductive hormones: A cross-sectional study in China

BACKGROUND

Polycyclic aromatic hydrocarbons (PAHs) are a group of ubiquitous environmental pollutants. In vivo and in vitro studies have demonstrated that PAHs can alter endocrine function, yet evidence from human studies is limited.

OBJECTIVES

The objective of this study was to investigate whether environmental exposure to PAHs was associated with altered reproductive hormone levels, using repeated measures of urinary OH-PAHs as biomarkers.

METHODS

We measured 10 monohydroxylated PAHs (OH-PAHs) in repeated urine samples from 371 men in an infertility clinic in Wuhan, China. Multivariable linear regression models were used to estimate the associations between average urinary OH-PAH levels and serum reproductive hormones, and restricted cubic spline models were further used to examine the shapes of dose-response relationships.

RESULTS

We observed dose-response associations of urinary 2-hydroxynaphthalene (2-OHNa) with decreased serum free testosterone (fT) and urinary 1-hydroxypyrene (1-OHP), 9-hydroxyphenanthrene (9-OHPh), and 9-hydroxyfluorene (9-OHFlu) with decreased serum estradiol (all P for trends <0.05). These associations were linear and significant when these four OH-PAHs were modeled as continuous variables in restricted cubic spline models. Furthermore, a U-shaped association was observed across urinary 4-OHPh levels, with lower levels of serum sex hormone-binding globulin (SHBG) at median concentrations compared with 5th and 95th percentile concentrations.

CONCLUSION

Environmental levels of PAH exposure in our study are associated with altered reproductive hormones. However, further research is needed to confirm our findings.

Association of atmospheric concentrations of polycyclic aromatic hydrocarbons with their urinary metabolites in children and adolescents

This study aims to determine the atmospheric concentrations of particulate matter 2.5 (PM_2.5)-bounded polycyclic aromatic hydrocarbons (PAHs) and their association with their urinary metabolites in children and adolescents. This study was conducted from October 2014 to March 2016 in Isfahan, Iran. We measured 16 species of PAHs bounded to PM_2.5 by gas chromatography mass spectrometry (GC/MS) from 7 parts of the city. Moreover, PAH urinary metabolites were measured in 186 children and adolescents, randomly selected from households. Urinary metabolites consisted of 1-hydroxy naphthalene (1-naphthol), 2-hydroxy naphthalene (2-naphthol), 9-hydroxy phenanthrene (9-phenanthrol), and 1-hydroxy pyrene using GC/MS. Considering the short half-lives of PAHs, we measured the metabolites twice with 4 to 6 months of time interval. We found that the ambient concentrations of PAHs were significantly associated with their urinary metabolites. 1-hydroxy naphthalene and 2-hydroxy naphthalene concentrations showed an increase of 1.049 (95% CI: 1.030, 1.069) and 1.047 (95% CI: 1.025, 1.066) for each unit increase (1 ng/m³) in ambient naphthalene. Similarly, 1-hydroxy pyrene showed an increase of 1.009 (95% CI: 1.006-1.011) for each unit increase (1 ng/m³) in ambient pyrene concentration after adjustment for body mass index, physical activity level, urinary creatinine, age, and sex. The association of urinary 9-hydroxyphenanthrene and ambient phenantherene was significant in the crude model; however after adjustment for the abovementioned covariates, it was no more significant. We found significant correlations between exposure to ambient PM_2.5-bounded PAHs and their urinary excretion. Considering the adverse health effects of PAHs in the pediatric age group, biomonitoring of PAHs should be underscored; preventive measures need to be intensified.

Urinary metabolites of polycyclic aromatic hydrocarbons, sperm DNA damage and spermatozoa apoptosis

Inconsistent results between polycyclic aromatic hydrocarbons (PAHs) exposure and adverse male reproductive health have been reported in humans. To assess whether PAH exposure is associated with declined sperm function. Ten monohydroxylated PAHs (OH-PAHs) metabolites were analyzed in repeated urine samples from an infertility clinic. We used multivariable linear models to estimate the associations of urinary OH-PAH metabolites with sperm DNA damage (n=405) and spermatozoa apoptosis (n=366). The shapes of dose-dependent associations of exposure measurements with outcomes were further evaluated by restricted cubic splines. Multiple comparisons were adjusted by false discovery rate (FDR). We found that urinary 9-hydroxyfluorene (9-OHFlu) was associated with increased tail length and comet length (p for trend=0.05 and 0.01, respectively), and that urinary 9-hydroxyphenanthrene (9-OHPh) was associated with decreased percentage of Annexin V^-/PI^- spermatozoa (p for trend=0.04). Also, suggestive associations of urinary 9-OHPh and ∑OHFlu with increased comet length, and urinary 9-OHFlu and 2-OHPh with decreased percentage of Annexin V^-/PI^- spermatozoa were observed (all p for trends <0.10). Further, these dose-dependent associations were confirmed in restricted cubic splines. Our results suggest that environmental exposure to fluorene and phenanthrene are associated with declined sperm function.

Relationships between seminal plasma metals/metalloids and semen quality, sperm apoptosis and DNA integrity

This study aimed to investigate the relationships between environmental exposure to metals/metalloids and semen quality, sperm apoptosis and DNA integrity using the metal/metalloids levels in seminal plasma as biomarkers. We determined 18 metals/metalloids in seminal plasma using an inductively coupled plasma-mass spectrometry among 746 men recruited from a reproductive medicine center. Associations of these metals/metalloids with semen quality (n = 746), sperm apoptosis (n = 331) and DNA integrity (n = 404) were evaluated using multivariate linear and logistic regression models. After accounting for multiple comparisons and confounders, seminal plasma arsenic (As) quartiles were negatively associated with progressive and total sperm motility using multivariable linear regression analysis, which were in accordance with the trends for increased odds ratios (ORs) for below-reference semen quality parameters in the logistic models. We also found inverse correlations between cadmium (Cd) quartiles and progressive and total sperm motility, whereas positive correlations between zinc (Zn) quartiles and sperm concentration, between copper (Cu) and As quartiles and the percentage of tail DNA, between As and selenium (Se) quartiles and tail extent and tail distributed moment, and between tin (Sn) categories and the percentage of necrotic spermatozoa (all P_trend<0.05). These relationships remained after the simultaneous consideration of various elements. Our results indicate that environmental exposure to As, Cd, Cu, Se and Sn may impair male reproductive health, whereas Zn may be beneficial to sperm concentration.

Urinary Polycyclic Aromatic Hydrocarbon Metabolites and Human Semen Quality in China

Toxicological studies have demonstrated that polycyclic aromatic hydrocarbons (PAHs) exposure impairs male reproductive health. However, the epidemiological evidence is limited and discordant. Our goal was to investigate the relationship between PAH exposures and human semen quality. We analyzed 12 urinary metabolites of PAHs from 933 men who sought semen quality analysis in an infertility clinic in Wuhan, China. Associations with semen quality were assessed using a multivariable linear regression. Restricted cubic splines were used to explore the dose-response relationships between urinary metabolites of PAHs and semen quality. We observed inverse associations between urinary 1-hydroxynaphthalene (1-OHNa) and sperm count, sperm concentration, and percentage of normal morphology (all p for trends <0.05) as well as between urinary ∑OHNa (sum of 1-OHNa and 2-OHNa) and sperm concentration (p for trend =0.04). Additionally, we found inverse associations between urinary 9-hydroxyphenanthrene (9-OHPh) and semen volume and sperm straight-line velocity (both p for trends <0.05) as well as between urinary ∑OHPh (sum of 1-, 2-, 3-, 4-, and 9-OHPh) and sperm count (p for trend =0.04). These dose-response relationships were further confirmed in the curves of the restricted cubic splines. Our data suggest that exposure to naphthalene and phenanthrene is related to decreased semen quality. Our results contribute to the growing body of evidence regarding the widespread exposure to PAHs and the detriment to male reproductive function.

Polycyclic aromatic hydrocarbons exposure decreased sperm mitochondrial DNA copy number: A cross-sectional study (MARHCS) in Chongqing, China

Polycyclic aromatic hydrocarbons (PAHs) are widespread environmental pollutants that have adverse effects on the male reproductive function. Many studies have confirmed that PAHs preferentially accumulate in mitochondria DNA relative to nuclear DNA and disrupt mitochondrial functions. However, it is rare whether exposure to PAHs is associated with mitochondrial damage and dysfunction in sperm. To evaluate the effects of PAHs on sperm mitochondria, we measured mitochondrial membrane potential (MMP), mitochondrial DNA copy number (mtDNAcn) and mtDNA integrity in 666 individuals from the Male Reproductive Health in Chongqing College Students (MARHCS) study. PAHs exposure was estimated by measuring eight urinary PAH metabolites (1-OHNap, 2-OHNap, 1-OHPhe, 2-OHPhe, 3-OHPhe, 4-OHPhe, 2-OHFlu and 1-OHPyr). The subjects were divided into low, median and high exposure groups using the tertile levels of urinary PAH metabolites. In univariate analyses, the results showed that increased levels of 2-OHPhe, 3-OHPhe, ∑Phe metabolites and 2-OHFlu were found to be associated with decreased sperm mtDNAcn. After adjusting for potential confounders, significantly negative associations of these metabolites remained (p = 0.039, 0.012, 0.01, 0.035, respectively). Each 1 μg/g creatinine increase in 2-OHPhe, 3-OHPhe, ∑Phe metabolites and 2-OHFlu was associated with a decrease in sperm mtDNAcn of 9.427%, 11.488%, 9.635% and 11.692%, respectively. There were no significant associations between urinary PAH metabolites and sperm MMP or mtDNA integrity. The results indicated that the low exposure levels of PAHs can cause abnormities in sperm mitochondria.

Environmental exposure to human carcinogens in teenagers and the association with DNA damage

BACKGROUND

We investigated whether human environmental exposure to chemicals that are labeled as (potential) carcinogens leads to increased (oxidative) damage to DNA in adolescents.

MATERIAL AND METHODS

Six hundred 14-15-year-old youngsters were recruited all over Flanders (Belgium) and in two areas with important industrial activities. DNA damage was assessed by alkaline and formamidopyrimidine DNA glycosylase (Fpg) modified comet assays in peripheral blood cells and analysis of urinary 8-hydroxydeoxyguanosine (8-OHdG) levels. Personal exposure to potentially carcinogenic compounds was measured in urine, namely: chromium, cadmium, nickel, 1-hydroxypyrene as a proxy for exposure to other carcinogenic polycyclic aromatic hydrocarbons (PAHs), t,t-muconic acid as a metabolite of benzene, 2,5-dichlorophenol (2,5-DCP), organophosphate pesticide metabolites, and di(2-ethylhexyl) phthalate (DEHP) metabolites. In blood, arsenic, polychlorinated biphenyl (PCB) congeners 118 and 156, hexachlorobenzene (HCB), dichlorodiphenyltrichloroethane (DDT) and perfluorooctanoic acid (PFOA) were analyzed. Levels of methylmercury (MeHg) were measured in hair. Multiple linear regression models were used to establish exposure-response relationships.

RESULTS

Biomarkers of exposure to PAHs and urinary chromium were associated with higher levels of both 8-OHdG in urine and DNA damage detected by the alkaline comet assay. Concentrations of 8-OHdG in urine increased in relation with increasing concentrations of urinary t,t-muconic acid, cadmium, nickel, 2,5-DCP, and DEHP metabolites. Increased concentrations of PFOA in blood were associated with higher levels of DNA damage measured by the alkaline comet assay, whereas DDT was associated in the same direction with the Fpg-modified comet assay. Inverse associations were observed between blood arsenic, hair MeHg, PCB 156 and HCB, and urinary 8-OHdG. The latter exposure biomarkers were also associated with higher fish intake. Urinary nickel and t,t-muconic acid were inversely associated with the alkaline comet assay.

CONCLUSION

This cross-sectional study found associations between current environmental exposure to (potential) human carcinogens in 14-15-year-old Flemish adolescents and short-term (oxidative) damage to DNA. Prospective follow-up will be required to investigate whether long-term effects may occur due to complex environmental exposures.