Stimulatory effects of selected PAHs on testosterone production in goldfish and rainbow trout and possible mechanisms of action

Urinary polycyclic aromatic hydrocarbon metabolites are positively related to serum testosterone levels of males and serum estradiol levels of females among U.S. adults

BACKGROUND

It has been reported for several years that polycyclic aromatic hydrocarbons (PAHs) could disturb human endocrine function. However, there is still a short of consistent conclusion about the relationship between PAH exposure and levels of sexual hormones. The aim of our study is to explore whether exposure to PAHs and how PAHs affect the levels of serum testosterone (T) and estradiol (E2) in adults, hoping to fulfill the knowledge gap.

MATERIALS AND METHODS

This study included adults aged 20 and above who participated in the National Health and Nutrition Examination Survey (NHANES) from 2011 to 2016. We included 10 PAH metabolites in this study. The levels of urinary PAH metabolites were log-transformed and divided into quartiles. The associations between PAH metabolites and both serum T levels of males and E2 levels of females were investigated using multivariate regression models. We furtherly calculated PAHs scores by sum of ranks across 10 PAHs metabolites, which represented the exposure levels of PAHs mixtures, and the association between PAHs scores and serum T and E2 levels were analyzed.

RESULTS

A total of 4,654 subjects were included in this study, including 2,460 males and 2,194 females. After adjusting for confounders, 2-hydroxynapthalene and 3-hydroxyfluorene were positively associated with serum T levels of males (p-value for trend=0.047, and p-value for trend=0.006, respectively), while 1-hydroxyphenanthrene was positively associated with serum E2 levels of females (p-value for trend=0.013). In the adjusted models, no significant association was found between PAHs scores and either T levels of males or E2 levels of females (p-value for trend=0.615, and p-value for trend=0.241, respectively).

CONCLUSIONS

This study showed urinary 2-hydroxynapthalene and 3-hydroxyfluorene were associated with increased T levels of males, and urinary 1-hydroxyphenanthrene was associated with increased E2 levels of females. The observed association indicated disrupting effects of PAH exposure on reproductive health.

Use of e-cigarettes associated with lower sperm counts in a cross-sectional study of young men from the general population

STUDY QUESTION

Are use of e-cigarettes and snuff associated with testicular function as previously shown for conventional cigarettes and marijuana?

SUMMARY ANSWER

Use of e-cigarettes is associated with reduced semen quality but not with higher serum testosterone level as observed for conventional cigarette use. Snuff use was not associated with markers of testicular function.

WHAT IS KNOWN ALREADY

Cigarette smoking has previously been associated with higher testosterone levels and impaired semen quality, whereas it is unresolved whether use of e-cigarettes or snuff influence the testicular function.

STUDY DESIGN, SIZE, DURATION

This cross-sectional population-based study included 2008 men with information on cigarette and marijuana use (enrolled between 2012 and 2018), among whom 1221 men also had information on e-cigarette and snuff use (enrolled between 2015 and 2018).

PARTICIPANTS/MATERIALS, SETTING, METHODS

Men (median age 19.0 years) from the general population provided a semen and blood sample and filled out a questionnaire on lifestyle including information on smoking behaviour. Associations between different types of smoking (e-cigarettes, snuff, marijuana and cigarettes) and reproductive hormones (total and free testosterone, sex hormone-binding globulin, LH, oestradiol and ratios of inhibin B/FSH, testosterone/LH and free testosterone/LH) and semen parameters (total sperm count and sperm concentration) were examined using multiple linear regression analyses adjusted for relevant confounders.

MAIN RESULTS AND THE ROLE OF CHANCE

Approximately half of the men (52%) were cigarette smokers, 13% used e-cigarettes, 25% used snuff and 33% used marijuana. Users of e-cigarettes and marijuana were often also cigarette smokers. Compared to non-users, daily e-cigarette users had significantly lower total sperm count (147 million vs 91 million) as did daily cigarette smokers (139 million vs 103 million), in adjusted analyses. Furthermore, significantly higher total and free testosterone levels were seen in cigarette smoking men (6.2% and 4.1% higher total testosterone and 6.2% and 6.2% higher free testosterone in daily smokers and occasional smokers, respectively, compared to non-smoking men), but not among e-cigarette users. Daily users of marijuana had 8.3% higher total testosterone levels compared to non-users. No associations were observed for snuff in relation to markers of testicular function.

LIMITATIONS, REASONS FOR CAUTION

We cannot exclude that our results can be influenced by residual confounding by behavioural factors not adjusted for. The number of daily e-cigarette users was limited and findings should be replicated in other studies.

WIDER IMPLICATIONS OF THE FINDINGS

This is the first human study to indicate that not only cigarette smoking but also use of e-cigarettes is associated with lower sperm counts. This could be important knowledge for men trying to achieve a pregnancy, as e-cigarettes are often considered to be less harmful than conventional cigarette smoking.

STUDY FUNDING/COMPETING INTEREST(S)

Funding was received from the Danish Ministry of Health (1-1010-308/59), the Independent Research Fund Denmark (8020-00218B), ReproUnion (20200407) and the Research Fund of the Capital Region of Denmark (A6176). The authors have nothing to disclose.

TRIAL REGISTRATION NUMBER

NA.

Exploring the endocrine activity of air pollutants associated with unconventional oil and gas extraction

BACKGROUND

In the last decade unconventional oil and gas (UOG) extraction has rapidly proliferated throughout the United States (US) and the world. This occurred largely because of the development of directional drilling and hydraulic fracturing which allows access to fossil fuels from geologic formations that were previously not cost effective to pursue. This process is known to use greater than 1,000 chemicals such as solvents, surfactants, detergents, and biocides. In addition, a complex mixture of chemicals, including heavy metals, naturally-occurring radioactive chemicals, and organic compounds are released from the formations and can enter air and water. Compounds associated with UOG activity have been linked to adverse reproductive and developmental outcomes in humans and laboratory animal models, which is possibly due to the presence of endocrine active chemicals.

METHODS

Using systematic methods, electronic searches of PubMed and Web of Science were conducted to identify studies that measured chemicals in air near sites of UOG activity. Records were screened by title and abstract, relevant articles then underwent full text review, and data were extracted from the studies. A list of chemicals detected near UOG sites was generated. Then, the potential endocrine activity of the most frequently detected chemicals was explored via searches of literature from PubMed.

RESULTS

Evaluation of 48 studies that sampled air near sites of UOG activity identified 106 chemicals detected in two or more studies. Ethane, benzene and n-pentane were the top three most frequently detected. Twenty-one chemicals have been shown to have endocrine activity including estrogenic and androgenic activity and the ability to alter steroidogenesis. Literature also suggested that some of the air pollutants may affect reproduction, development, and neurophysiological function, all endpoints which can be modulated by hormones. These chemicals included aromatics (i.e., benzene, toluene, ethylbenzene, and xylene), several polycyclic aromatic hydrocarbons, and mercury.

CONCLUSION

These results provide a basis for prioritizing future primary studies regarding the endocrine disrupting properties of UOG air pollutants, including exposure research in wildlife and humans. Further, we recommend systematic reviews of the health impacts of exposure to specific chemicals, and comprehensive environmental sampling of a broader array of chemicals.

Associations between urinary polycyclic aromatic hydrocarbon metabolites and serum testosterone in U.S. adult males: National Health and nutrition examination survey 2011-2012

Effects of environmental chemicals on human reproductive health and sex hormone levels have been reported for several years, but compared to other environmental chemicals, such as heavy metals, PCBs, triclosan, Phthalate, the links between polycyclic aromatic hydrocarbons (PAHs) and sex hormone levels have not been studied widely. Therefore, our purpose of research was to study the associations between urinary PAH metabolites and serum total testosterone (T) levels among men. The data was obtained from the independent cross-section wave (2011-2012) of the National Health and Nutrition Examination Survey (NHANES), including demographic, socioeconomic, dietary, health-related questions, examinations and laboratory test. All analyses were performed by R software (version 3.2.3), including one-way analysis of variance, multivariable linear regression, stratified analysis and heterogeneity test. Of 1102 American adults aged 20 and above included in the statistical analysis, we found that urinary 3-hydroxyfluorene and 2-hydroxyfluorene were significantly positively associated with serum T levels (β = 40.62, 95%CI = 21.78-59.46, P = 2.56 × 10^-5; β = 35.17, 95%CI = 13.18-57.15, P = 1.75 × 10^-3, respectively). The associations between urinary PAH metabolites and serum T levels signified a major public health problem over the world. Prospective work is needed to investigate the potential long-term health consequences of these findings.

Effects of chronic dietary petroleum exposure on reproductive development in polar cod (Boreogadus saida)

Increasing human activities in the Arctic raise the risk of petroleum pollution, thus posing an elevated risk for Arctic organisms to be chronically exposed to petroleum compounds. The endocrine disrupting properties of some of these compounds (i.e. polycyclic aromatic hydrocarbons [PAHs]) present in crude oil may have negative effects on the long and energy intensive reproductive development of polar cod (Boreogadus saida), an Arctic keystone species. In the present study, selected reproductive parameters were examined in feral polar cod exposed to crude oil via a natural diet (0.11, 0.57 and 1.14μg crude oil/g fish/day [corresponding to low, medium and high treatments, respectively]) for 31 weeks prior to spawning. Fish maturing in the current reproductive period made up 92% of the experimental population while 5% were immature and 3% were identified as resting fish. Phase I metabolism of PAHs, indicated by ethoxyresorufin-O-deethylase (EROD) activity, showed a dose-dependent increase in high and medium crude oil treatments at week 6 and 22, respectively. Decreasing EROD activity and increasing PAH bile metabolite concentrations over the experimental period may be explained by reproductive maturity stage. Significant alterations in sperm motility were observed in crude oil exposed males compared to the controls. The investigated somatic indices (gonad and hepatic), germ cell development and plasma steroid levels (estradiol-17β [females], testosterone [males and females] and 11-ketotestosterone [males]) were not significantly altered by chronic dietary exposure to crude oil. The environmentally realistic doses polar cod were chronically exposed to in this study were likely not high enough to induce adverse effects in this ecologically important fish species. This study elucidated many baseline aspects of polar cod reproductive physiology and emphasized the influence of maturation state on biomarkers of PAH biotransformation (EROD and PAH bile metabolites).

Fish Reproduction Is Disrupted upon Lifelong Exposure to Environmental PAHs Fractions Revealing Different Modes of Action

Polycyclic aromatic hydrocarbons (PAHs) constitute a large family of organic pollutants emitted in the environment as complex mixtures, the compositions of which depend on origin. Among a wide range of physiological defects, PAHs are suspected to be involved in disruption of reproduction. In an aquatic environment, the trophic route is an important source of chronic exposure to PAHs. Here, we performed trophic exposure of zebrafish to three fractions of different origin, one pyrolytic and two petrogenic. Produced diets contained PAHs at environmental concentrations. Reproductive traits were analyzed at individual, tissue and molecular levels. Reproductive success and cumulative eggs number were disrupted after exposure to all three fractions, albeit to various extents depending on the fraction and concentrations. Histological analyses revealed ovary maturation defects after exposure to all three fractions as well as degeneration after exposure to a pyrolytic fraction. In testis, hypoplasia was observed after exposure to petrogenic fractions. Genes expression analysis in gonads has allowed us to establish common pathways such as endocrine disruption or differentiation/maturation defects. Taken altogether, these results indicate that PAHs can indeed disrupt fish reproduction and that different fractions trigger different pathways resulting in different effects.

Alternatives to in vivo tests to detect endocrine disrupting chemicals (EDCs) in fish and amphibians--screening for estrogen, androgen and thyroid hormone disruption

Endocrine disruption is considered a highly relevant hazard for environmental risk assessment of chemicals, plant protection products, biocides and pharmaceuticals. Therefore, screening tests with a focus on interference with estrogen, androgen, and thyroid hormone pathways in fish and amphibians have been developed. However, they use a large number of animals and short-term alternatives to animal tests would be advantageous. Therefore, the status of alternative assays for endocrine disruption in fish and frogs was assessed by a detailed literature analysis. The aim was to (i) determine the strengths and limitations of alternative assays and (ii) present conclusions regarding chemical specificity, sensitivity, and correlation with in vivo data. Data from 1995 to present were collected related to the detection/testing of estrogen-, androgen-, and thyroid-active chemicals in the following test systems: cell lines, primary cells, fish/frog embryos, yeast and cell-free systems. The review shows that the majority of alternative assays measure effects directly mediated by receptor binding or resulting from interference with hormone synthesis. Other mechanisms were rarely analysed. A database was established and used for a quantitative and comparative analysis. For example, a high correlation was observed between cell-free ligand binding and cell-based reporter cell assays, between fish and frog estrogenic data and between fish embryo tests and in vivo reproductive effects. It was concluded that there is a need for a more systematic study of the predictive capacity of alternative tests and ways to reduce inter- and intra-assay variability.

Hormones and endocrine-disrupting chemicals: low-dose effects and nonmonotonic dose responses

For decades, studies of endocrine-disrupting chemicals (EDCs) have challenged traditional concepts in toxicology, in particular the dogma of "the dose makes the poison," because EDCs can have effects at low doses that are not predicted by effects at higher doses. Here, we review two major concepts in EDC studies: low dose and nonmonotonicity. Low-dose effects were defined by the National Toxicology Program as those that occur in the range of human exposures or effects observed at doses below those used for traditional toxicological studies. We review the mechanistic data for low-dose effects and use a weight-of-evidence approach to analyze five examples from the EDC literature. Additionally, we explore nonmonotonic dose-response curves, defined as a nonlinear relationship between dose and effect where the slope of the curve changes sign somewhere within the range of doses examined. We provide a detailed discussion of the mechanisms responsible for generating these phenomena, plus hundreds of examples from the cell culture, animal, and epidemiology literature. We illustrate that nonmonotonic responses and low-dose effects are remarkably common in studies of natural hormones and EDCs. Whether low doses of EDCs influence certain human disorders is no longer conjecture, because epidemiological studies show that environmental exposures to EDCs are associated with human diseases and disabilities. We conclude that when nonmonotonic dose-response curves occur, the effects of low doses cannot be predicted by the effects observed at high doses. Thus, fundamental changes in chemical testing and safety determination are needed to protect human health.

Integrative environmental genomics of Cod (Gadus morhua): the proteomics approach

Atlantic cod (Gadus morhua) is an essential species in North Atlantic fisheries and increasingly relevant as an aquaculture species. However, potential conflicts with both coastal industry and petroleum industry expanding into northern waters make it important to understand how effluents (produced water, pharmaceuticals, food contaminants, and feed contaminants) affect the growth, reproduction, and health of this species in order to maintain a sustainable cod population and a healthy human food source, and to discover biomarkers for environmental monitoring and risk assessment. The ongoing genome sequencing effort of Atlantic cod has opened the possibility for a systems biology approach to elucidate molecular mechanisms of toxicity. Our study aims to be a first step toward such a systems toxicology understanding of genomic responses to environmental insults. A toxicogenomic approach was initiated that is combining data generated from proteomics analyses and transcriptomics analyses, and the concurrent development of searchable expressed sequence tags (EST) databases and genomic databases. This interdisciplinary study may also open new possibilities of gene annotation and pathway analyses.

Biomarker candidate discovery in Atlantic cod (Gadus morhua) continuously exposed to North Sea produced water from egg to fry

In this study Atlantic cod (Gadus morhua) were exposed to different levels of North Sea produced water (PW) and 17beta-oestradiol (E(2)), a natural oestrogen, from egg to fry stage (90 days). By comparing changes in protein expression following E(2) exposure to changes induced by PW treatment, we were able to compare the induced changes by PW to the mode of action of oestrogens. Changes in the proteome in response to exposure in whole cod fry (approximately 80 days post-hatching, dph) were detected by two-dimensional gel electrophoresis and image analysis and identified by MALDI-ToF-ToF mass spectrometry, using a newly developed cod EST database and the NCBI database. Many of the protein changes occurred at low levels (0.01% and 0.1% PW) of exposure, indicating putative biological responses at lower levels than previously detected. Using discriminant analysis, we identified a set of protein changes that may be useful as biomarker candidates of produced water (PW) and oestradiol exposure in Atlantic cod fry. The biomarker candidates discovered in this study may, following validation, prove effective as diagnostic tools in monitoring exposure and effects of discharges from the petroleum industry offshore, aiding future environmental risk analysis and risk management.

Reproductive hormones in relation to polycyclic aromatic hydrocarbon (PAH) metabolites among non-occupational exposure of males

A limited number of studies have suggested that exposure to PAHs may affect reproductive hormones. Subjects (n=642) in this study were from the affiliated hospitals of Nanjing Medical University. Individual exposures to PAHs were measured as spot urinary concentrations of four PAH metabolites, including 1-naphthol (1-N), 2-naphthol (2-N), 2-hydroxyfluorene (2-OF) and 1-hydroxypyrene (1-OP), which were adjusted by urinary creatinine (CR). Blood samples were collected to measure serum levels of reproductive hormones, including follicle-stimulating hormone (FSH), luteotrophic hormone (LH), estradiol (E2), testosterone (T) and prolactin (PRL). All of the subjects had detectable levels of the four metabolites of PAHs in their urine samples. The median concentrations of 1-N, 2-N, 2-OF and 1-OP were 2.440, 4.176, 2.843 and 1.148 microg/g of CR. There were significant P-values between increased CR-adjusted 1-N tertiles and E2 concentration, 2-OF tertiles and LH, FSH level, 1-OP and E2 level. The multivariate linear regression results also showed significant correlation between the levels of serum LH and 1-OP (the adjusting P-value was 0.048), but no correlations were found between other hormones and the level of PAH metabolites. These observed correlations between levels of hydroxy-PAH and some altered hormones indicated slight endocrine effects on adult men with PAH exposure.

Candidate biomarker discovery in plasma of juvenile cod (Gadus morhua) exposed to crude North Sea oil, alkyl phenols and polycyclic aromatic hydrocarbons (PAHs)

In this study we have investigated protein changes in plasma of juvenile Atlantic cod (Gadus morhua) induced by crude North Sea oil and North Sea oil spiked with alkyl phenols and polycyclic aromatic hydrocarbons, a surrogate produced water composition. Using a proteomic approach, we identified 137 differentially expressed proteins at different levels of crude oil exposure. Many of the induced protein changes occurred at low levels of exposure. The results obtained with protein expression profiles after exposure to oil and surrogate produced water indicate effects on fibrinolysis and the complement cascade, the immune system, fertility-linked proteins, bone resorption, fatty acid metabolism as well as increased oxidative stress, impaired cell mobility and increased levels of proteins associated with apoptosis. Although the number of individuals and samples in this study is limited within each treatment group, the protein changes observed in this study represent a first screening for potential biomarker candidates in cod plasma reflecting potential effects of crude oil and produced water exposure on fish.

Evaluation of the relationships between biochemical endpoints of PAH exposure and physiological endpoints of reproduction in male California Halibut (Paralichthys californicus) exposed to sediments from a natural oil seep

Coal Oil Point (COP) is a natural oil seep off the coast of Santa Barbara, California. Although most studies examining the fate and effects of petroleum have focused upon urbanized or anthropogenic sources of inputs, few have examined the effects of polyaromatic hydrocarbons (PAHs) derived from natural seeps. In order to evaluate the effects of PAHs derived from COP on marine fish populations, hatchery-reared California Halibut (Platichthys californicus) were exposed for 30 days to seven dilutions of sediments collected from COP. Hepatic cytochrome P450 1A (CYP1A), biliary fluorescent aromatic compounds (FACs), gonadal somatic indices, and plasma steroid concentrations. Sixteen USEPA priority PAHs were targeted for analysis in each sediment dilution. In general, biochemical responses were somewhat recalcitrant to dose-response relationships and were less sensitive than the literature values established for the same indicators following exposure to urbanized PAHs. Trends toward reductions in plasma 17beta-estradiol concentrations were observed, but reductions in gonadal somatic indices were not observed. FAC values for naphthalene, benzo(a)pyrene, phenanthrene-related compounds reached maximums at 33-100% COP sediment. The resulting insensitivity may be unique for exposure to "natural" petroleum due to a higher concentration of lower molecular weight PAHs or uncharacterized inhibitors.

Effect of ‘PC Game Room’ use and polycyclic aromatic hydrocarbon exposure on plasma testosterone concentrations in young male Koreans

BACKGROUND

'PC Game Rooms' were first popularized in Korea, although the concept is now becoming popular worldwide. PC Game Rooms provide users with high-performance PC connected to the high-speed internet, and access to computer games. However, PC Game Room users are exposed to various hazardous agents such as cigarette smoke in a confined environment, and thus it is likely that excessive PC Game Room use involves abnormal exposure to polycyclic aromatic hydrocarbons (PAH) as well as being associated with disturbed sleep or circadian rhythm.

METHODS

In this cross-sectional study, the exposure to PAH was evaluated by measuring urinary 1-hydroxypyrene (1-OHP) and 2-naphthol. The correlations between PC Game Room use and PAH exposure and plasma testosterone and LH levels were analysed in 208 young male Koreans.

RESULTS

Urinary 1-OHP concentrations increased (P = 0.0001) and plasma testosterone levels decreased (P = 0.0153) significantly with increased duration of PC Game Room use. Correlation analysis showed that plasma testosterone concentrations were significantly negatively correlated with urinary 1-OHP (r = -0.22, P = 0.0012) and 2-naphthol (r = -0.15, P = 0.0308) concentrations. Moreover, these associations persisted after adjusting for other independent variables. However, the duration of PC Game Room use itself was not found to be an independent significant determinant of plasma testosterone level. Rather, PC Game Room use increased PAH exposure, which decreased plasma testosterone level. The younger age group (15-19 years) showed a more prominent decrease in plasma testosterone concentrations with increasing duration of PC Game Room use than the older age group (20-24 years) (r2 = 0.355, P = 0.0301 versus r2 = 0.213, P = 0.0001).

CONCLUSIONS

These results imply that the excessive use of PC Game Rooms is related to an adverse impact on sex hormonal status in young male Koreans via PAH exposure. This effect was more prominent in the younger age group.