Dioxin exposure, from infancy through puberty, produces endocrine disruption and affects human semen quality

Phthalates exposure of Chinese reproductive age couples and its effect on male semen quality, a primary study

Phthalates are suspected of having adverse effects on androgen-regulated reproductive development in animals and may be toxic for human sperm. The purposes of our study were to investigate the general exposure of a Chinese reproductive age cohort to these ubiquitous pollutants and to assess their potential effect on semen quality. Six phthalate metabolites, monomethyl phthalate (MMP), monoethyl phthalate (MEP), monobutyl phthalate (MBP), monobenzyl phthalate (MBzP), mono-2-ethylhexyl phthalate (MEHP), and mono-2-ethyl-5-oxohexyl phthalate (MEOHP) were measured in spot urines of 150 individuals recruited from a Chongqing, China, reproductive institute. The questionnaire and clinical data were evaluated, and the correlations of phthalate exposure and semen qualities like semen volume, sperm concentration, motility and sperm motion parameters, were determined by multiple logistic regression analysis. The creatinine adjusted average concentrations for MMP, MEP, MBP, MBzP, MEHP and MEOHP were 41.3, 300, 41.0, 0.78, 2.99 and 3.90 μg/g, respectively. After adjustment for age, body mass index (BMI), abstinence, smoking, drinking, and education, there was a borderline-significant dose-response relationship between MBP and sperm concentration, with odd ratios (ORs) 1.0, 6.8 and 12.0 for increasing exposure tertiles (p=0.05). Although the dose-response relationships for MMP and MEP versus sperm concentration were not significant, a significant positive correlation between MEP and straight-line velocity of sperm motion was observed. The present data may imply some effects of phthalate exposure on semen. However, due to the small sample size, our finding needs to be confirmed on a larger population.

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.

Dioxin and polychlorinated biphenyl concentrations in mother's serum and the timing of pubertal onset in sons

BACKGROUND

Animal studies have demonstrated that timing of pubertal onset can be altered by prenatal exposure to dioxins or polychlorinated biphenyls (PCBs), but studies of human populations have been quite limited.

METHODS

We assessed the association between maternal serum concentrations of dioxins and PCBs and the sons' age of pubertal onset in a prospective cohort of 489 mother-son pairs from Chapaevsk, Russia, a town contaminated with these chemicals during past industrial activity. The boys were recruited at ages 8 to 9 years, and 4 years of annual follow-up data were included in the analysis. Serum samples were collected at enrollment from both mothers and sons for measurement of dioxin and PCB concentrations using high-resolution mass spectrometry. The sons' pubertal onset--defined as pubertal stage 2 or higher for genitalia (G) or pubic hair (P), or testicular volume >3 mL--was assessed annually by the same physician.

RESULTS

In multivariate Cox models, elevated maternal serum PCBs were associated with earlier pubertal onset defined by stage G2 or higher (4th quartile hazard ratio = 1.7 [95% confidence interval = 1.1- 2.5]), but not for stage P2 or higher or for testicular volume >3 mL. Maternal serum concentrations of dioxin toxic equivalents were not consistently associated with the sons' pubertal onset, although a dose-related delay in pubertal onset (only for G2 or higher) was seen among boys who breast-fed for 6 months or more.

CONCLUSIONS

Maternal PCB serum concentrations measured 8 or 9 years after sons' births--which may reflect sons' prenatal and early-life exposures--were associated with acceleration in some, but not all, measures of pubertal onset.

A rapid method for screening of the Stockholm Convention POPs in small amounts of human plasma using SPE and HRGC/HRMS

A rapid analytical screening method allowing simultaneous analysis of 23 persistent organic pollutants (POPs) in human plasma was developed. Sample preparation based on solid-phase extraction (SPE) with additional clean-up using small multilayer silica gel columns. SPE was performed using a custom made polystyrene-divinylbenzene sorbent for the extraction of chlorinated and brominated POPs. Special efforts to reduce sample volume and improve speed and efficiency of the analytical procedure were made. Determination of 16 polychlorinated biphenyls (PCBs), 5 organochlorine (OC) pesticides, octachlorinated dibenzo-p-dioxin (OCDD) and polybrominated diphenyl ether (BDE #47) in 0.5 mL human plasma was performed by using high resolution gas chromatography coupled to high resolution mass spectrometry (HRGC/HRMS). Recovery of POPs ranged between 46% and 110%, and reproducibility was below 25% relative standard deviation (RSD) for all target compounds, except for trans-nonachlor and OCDD, which were present only at low levels. Limits of detection (LOD) were for the PCBs between 0.8 and 117.7 pg mL(-1) plasma and for the OC pesticides between 5.9 and 89.1 pg mL(-1) plasma. The LOD for OCDD and BDE #47 were 1.4 pg mL(-1) plasma, and 9.2 pg mL(-1) plasma, respectively. The presented method was successfully applied to 1016 human plasma samples from an epidemiological study on cardiovascular disease.

The effect of in utero exposure to dioxins and polychlorinated biphenyls on reproductive development in eight year-old children

We have previously reported on the effects of in utero exposure to polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) and polychlorinated biphenyls (PCBs) on thyroid function and growth hormone concentrations at birth and in two and five year-old children. Herein, we present our most recent follow-up examination findings for the same cohort of children at eight-years of age. A total of 56 children (23 boys, 33 girls) were examined. Bone age (BA), hormone concentrations, and indicators of reproductive development including Tanner, breast, genital, and armpit stages were assessed. Estradiol concentrations were significantly lower in children exposed to higher levels than median of PCDD/Fs+PCBs TEQ compared to the children exposed to levels lesser than median (P=0.003). Girls exposed to higher levels than median of indicator PCBs had a significantly greater proportion in genital stage 1 and shorter fundi and uteri lengths, as compared to those exposed to low levels (P=0.025 and P<0.05, respectively). There was a significant negative relationship between estradiol concentrations and PCDD/Fs+PCB exposure level (P=0.005). After adjusting for BA, there was a significant association between fundus length and indicator PCB exposure level (P=0.034). Exposure to both high levels of ΣPCDD/Fs+PCBs TEQ and high levels of total PCBs was associated with decreased fundus length (P=0.016) and uterus length (P=0.016). In utero exposure to high levels of PCDD/Fs and PCBs may result in lower estradiol concentrations in eight year-old children and impaired reproductive development in girls.

Effect of maternal coffee, smoking and drinking behavior on adult son's semen quality: prospective evidence from the Child Health and Development Studies

Fetal exposure to caffeine is associated with adverse pregnancy outcomes. Animal and human studies suggest that caffeine may have effects on the developing reproductive system. Here we report on mothers' smoking, coffee and alcohol use, recorded during pregnancy, and semen quality in sons in the age group of 38-47 years. Subjects were a subset of the Child Health and Development Studies, a pregnancy cohort enrolled between 1959 and 1967 in the Kaiser Foundation Health Plan near Oakland, California. In 2005, adult sons participated in a follow-up study (n = 338) and semen samples were donated by 196 participants. Samples were analyzed for sperm concentration, motility and morphology according to the National Cooperative Reproductive Medicine Network (Fertile Male Study) Protocol. Mean sperm concentration was reduced by approximately 16 million sperms for sons with high prenatal exposure (5 cups of maternal coffee use per day) compared with unexposed sons (P-value for decreasing trend = 0.09), which translates to a proportionate reduction of 25%. Mean percent motile sperm decreased by approximately 7 points (P-value = 0.04), a proportionate decline of 13%, and mean percent sperm with normal morphology decreased by approximately 2 points (P-value = 0.01), a proportionate decline of 25%. Maternal cigarette and alcohol use were not associated with son's semen quality. Adjusting for son's contemporary coffee, alcohol and cigarette use did not explain the maternal associations. Findings for son's coffee intake and father's prenatal coffee, cigarette and alcohol use were non-significant and inconclusive. These results contribute to the evidence that maternal coffee use during pregnancy may impair the reproductive development of the male fetus.

Endocrine disrupting chemicals and disease susceptibility

Environmental chemicals have significant impacts on biological systems. Chemical exposures during early stages of development can disrupt normal patterns of development and thus dramatically alter disease susceptibility later in life. Endocrine disrupting chemicals (EDCs) interfere with the body's endocrine system and produce adverse developmental, reproductive, neurological, cardiovascular, metabolic and immune effects in humans. A wide range of substances, both natural and man-made, are thought to cause endocrine disruption, including pharmaceuticals, dioxin and dioxin-like compounds, polychlorinated biphenyls, DDT and other pesticides, and components of plastics such as bisphenol A (BPA) and phthalates. EDCs are found in many everyday products--including plastic bottles, metal food cans, detergents, flame retardants, food additives, toys, cosmetics, and pesticides. EDCs interfere with the synthesis, secretion, transport, activity, or elimination of natural hormones. This interference can block or mimic hormone action, causing a wide range of effects. This review focuses on the mechanisms and modes of action by which EDCs alter hormone signaling. It also includes brief overviews of select disease endpoints associated with endocrine disruption.

Potential protective mechanisms of aryl hydrocarbon receptor (AHR) signaling in benign prostatic hyperplasia

The aryl hydrocarbon receptor (AHR) is an evolutionarily conserved ligand activated transcription factor best known for its role in mediating toxic responses to dioxin-like environmental contaminants. However, AHR signaling has also emerged as an active participant in processes of normal development and disease progression. Here, we review the role of AHR signaling in prostate development and disease processes, with a particular emphasis on benign prostatic hyperplasia (BPH). Inappropriate AHR activation has recently been associated with a decreased risk of symptomatic BPH in humans and has been shown to impair prostate development and disrupt endocrine signaling in rodents. We highlight known physiological responses to AHR activation in prostate and other tissues and discuss potential mechanisms by which it may act in adult human prostate to protect against symptomatic BPH.

Maternal cypermethrin exposure during lactation impairs testicular development and spermatogenesis in male mouse offspring

Within the last decade, numerous epidemiological studies have demonstrated that endocrine disruptors are a possible cause for a decline in semen quality. Cypermethrin is a widely used pyrethroid insecticide, but little is known about its potentially adverse effects on male reproduction. In the present study, we investigated the effects of maternal cypermethrin exposure during lactation on testicular development and spermatogenesis in male offspring. Maternal mice were administered with cypermethrin (25 mg/kg) by gavage daily from postnatal day 0 (PND0) to PND21. Results showed that the weight of testes at PND21 was significantly decreased in pups whose mothers were exposed to cypermethrin during lactation. Maternal cypermethrin exposure during lactation markedly decreased the layers of spermatogenic cells, increased the inside diameter of seminiferous tubules, and disturbed the array of spermatogenic cells in testes of pups at PND21. In addition, maternal cypermethrin exposure during lactation markedly reduced mRNA and protein levels of testicular P450scc, a testosterone (T) synthetic enzyme. Correspondingly, the level of serum and testicular T at weaning was significantly decreased in pups whose mothers were exposed to cypermethrin during lactation. Although the expression of testicular T synthetic enzymes and serum and testicular T in adulthood had restored to control level, the decreased testicular weight and histological changes were irreversible. Importantly, the number of spermatozoa was significantly decreased in adult male offspring whose mothers were exposed to cypermethrin during lactation. In conclusion, maternal cypermethrin exposure during lactation permanently impairs testicular development and spermatogenesis in male offspring, whereas cypermethrin-induced endocrine disruption is reversible.

Organochlorine compounds and testicular dysgenesis syndrome: human data

Cryptorchidism, hypospadias, subfertility and testicular germ-cell tumour have been suggested to comprise a testicular dysgenesis syndrome (TDS) based on the premise that each may derive from perturbations of embryonal programming and gonadal development during foetal life. Endocrine-disrupting chemicals have been hypothesized to be associated with these disorders, given the importance of sex steroid hormones in urogenital development and homeostasis. Organochlorines are one such set of compounds which are defined as containing between one and ten covalently bonded chlorine atoms. These compounds are persistent pollutants with long half-lives, accumulate in adipose tissue when ingested, bioaccumulate and biomagnify, and have complex and variable toxicological profiles. Examples of organochlorines include dichloro-diphenyl-trichloroethane and its metabolites, polychlorinated biphenyls, and chlordane. In this comprehensive review of human epidemiologic studies which have tested for associations between organochlorines and facets of TDS, we find evidence for associations between the exposures p,p'-DDE, cis-nonachlor and trans-nonachlor with testicular germ-cell tumour. The sum of the evidence from human epidemiological studies does not indicate any association between specific organochlorines studied and cryptorchidism, hypospadias or fertility. Many other endocrine-disrupting chemicals, including additional organochlorines, have yet to be assessed in relation to disorders associated with TDS, yet study of such chemicals has strong scientific merit given the relevance of such hypotheses to urogenital development.

Dioxin-induced changes in epididymal sperm count and spermatogenesis

A single in utero exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on gestation day 15 decreased epididymal sperm count in adult rats and thus was used to establish a tolerable daily intake for TCDD. However, several laboratories have been unable to replicate these findings. Moreover, conflicting reports of TCDD effects on daily sperm production suggest that spermatogenesis may not be as sensitive to the adverse effects of TCDD as previously thought. We performed a PubMed search using relevant search terms linking dioxin exposure with adverse effects on reproduction and spermatogenesis. Developmental exposure to TCDD is consistently linked with decreased cauda epididymal sperm counts in animal studies, although at higher dose levels than those used in some earlier studies. However, the evidence linking in utero TCDD exposure and spermatogenesis is not convincing. Animal studies provide clear evidence of an adverse effect of in utero TCDD exposure on epididymal sperm count but do not support the conclusion that spermatogenesis is adversely affected. The mechanisms underlying decreased epididymal sperm count are unknown; however, we postulate that epididymal function is the key target for the adverse effects of TCDD.

Perinatal exposure to low doses of dioxin can permanently impair human semen quality

BACKGROUND

In recent decades, young men in some industrialized areas have reportedly experienced a decrease in semen quality.

OBJECTIVE

We examined effects of perinatal dioxin exposure on sperm quality and reproductive hormones.

METHODS

We investigated sperm quality and hormone concentrations in 39 sons (mean age, 22.5 years) born between 1977 and 1984 to mothers exposed to dioxin after the accident in Seveso, Italy (1976), and 58 comparisons (mean age, 24.6 years) born to mothers exposed only to background dioxin. Maternal dioxin levels at conception were extrapolated from the concentrations measured in 1976 serum samples.

RESULTS

The 21 breast-fed sons whose exposed mothers had a median serum dioxin concentration as low as 19 ppt at conception had lower sperm concentration (36.3 vs. 86.3 million/mL; p = 0.002), total count (116.9 vs. 231.1; p = 0.02), progressive motility (35.8 vs. 44.2%; p = 0.03), and total motile count (38.7 vs. 98 million; p = 0.01) than did the 36 breast-fed comparisons. The 18 formula-fed exposed and the 22 formula-fed and 36 breast-fed comparisons (maternal dioxin background 10 ppt at conception) had no sperm-related differences. Follicle-stimulating hormone was higher in the breast-fed exposed group than in the breast-fed comparisons (4.1 vs. 2.63 IU/L; p = 0.03) or the formula-fed exposed (4.1 vs. 2.6 IU/L; p = 0.04), and inhibin B was lower (breast-fed exposed group, 70.2; breast-fed comparisons, 101.8 pg/mL, p = 0.01; formula-fed exposed, 99.9 pg/mL, p = 0.02).

CONCLUSIONS

In utero and lactational exposure of children to relatively low dioxin doses can permanently reduce sperm quality.

Reproductive health and the industrialized food system: a point of intervention for health policy

What food is produced, and how, can have a critical impact on human nutrition and the environment, which in turn are key drivers of healthy human reproduction and development. The US food production system yields a large volume of food that is relatively low in cost for consumers but is often high in calories and low in nutritional value. In this article we examine the evidence that intensive use of pesticides, chemical fertilizers, hormones, antibiotics, and fossil fuel in food production, as well as chemicals in food packaging, are potentially harmful to human reproductive and developmental health. We conclude that policies to advance a healthy food system are necessary to prevent adverse reproductive health effects and avoid associated health costs among current and future generations. These policies include changes to the Farm Bill and the Toxic Substances Control Act, and greater involvement by the health care sector in supporting and sourcing food from urban agriculture programs, farmers' markets, and local food outlets, as well as increasing understanding by clinicians of the links between reproductive health and industrialized food production.

2,3,7,8-Tetrachlorodibenzo-p-dioxin impairs iron homeostasis by modulating iron-related proteins expression and increasing the labile iron pool in mammalian cells

Cellular iron metabolism is essentially controlled by the binding of cytosolic iron regulatory proteins (IRP1 or IRP2) to iron-responsive elements (IREs) located on mRNAs coding for proteins involved in iron acquisition, utilization and storage. The 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) is one of the most potent toxins of current interest that occurs as poisonous chemical in the environment. TCDD exposure has been reported to induce a broad spectrum of toxic and biological responses, including significant changes in gene expression for heme and iron metabolism associated with liver injury. Here, we have investigated the molecular effects of TCDD on the iron metabolism providing the first evidence that administration of the toxin TCDD to mammalian cells affects the maintenance of iron homeostasis. We found that exposure of Madin-Darby Bovine Kidney cell to TCDD caused a divergent modulation of IRP1 and IRP2 RNA-binding capacity. Interestingly, we observed a concomitant IRP1 down-regulation and IRP2 up-regulation thus determining a marked enhancement of transferrin receptor 1 (TfR-1) expression and a biphasic response in ferritin content. The changed ferritin content coupled to TfR-1 induction after TCDD exposure impairs the cellular iron homeostasis, ultimately leading to significant changes in the labile iron pool (LIP) extent. Since important iron requirement changes occur during the regulation of cell growth, it is not surprising that the dioxin-dependent iron metabolism dysregulation herein described may be linked to cell-fate decision, supporting the hypothesis of a central connection among exposure to dioxins and the regulation of critical cellular processes. This article is part of a Special Issue entitled: 11th European Symposium on Calcium.

Aryl hydrocarbon receptor ligands of widely different toxic equivalency factors induce similar histone marks in target gene chromatin

Posttranslational histone modifications are a critical regulatory mechanism of gene transcription. Previous studies from our laboratory have shown that contingent on binding to its cognate promoter motifs in the Cyp1a1 gene, activation of the aryl hydrocarbon receptor (AHR) by benzo[a]pyrene (BaP) treatment induces histone modifications in the Cyp1a1 promoter that are required for activation of gene transcription. Here, we have studied different AHR ligands, including polychlorinated biphenyls (PCBs) of different toxic equivalency factors (TEF), to determine whether changes in histone modifications are linked to different levels of Cyp1a1 expression or dependent on AHR-ligand affinity. We find that all ligands lead to the same pattern of histone modifications in a relationship that parallels the strength of their AHR-ligand affinity. Thus, whereas PCB126 (TEF 0.1), 3-methylcholanthrene, β-naphthoflavone, and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) initiate a pattern of histone marks similar to those induced by BaP, PCB77 (TEF 0.0001) causes a lower level of change in the same marks and requires a longer activation time than PCB126, BaP, or TCDD. In contrast, the non-dioxin-like PCB153 recruits AHR to the Cyp1a1 enhancer causing a displacement of enhancer-associated histone H3 but does not cause the other observed histone mark changes nor does it induce transcription. These results indicate that AHR recruitment to the promoter is not sufficient to induce the histone modifications needed to activate gene expression and show that there is a good correlation between the regulatory chromatin changes associated with ligand-induced AHR target gene transcription and the resultant toxicity of the ligand.

Neurotoxicity of endocrine disruptors: possible involvement in brain development and neurodegeneration

Environmental chemicals that act as endocrine disruptors do not appear to pose a risk to human reproduction; however, their effects on the central nervous systems are less well understood. Animal studies suggested that maternal exposure to endocrine-disrupting chemicals (EDC) produced changes in rearing behavior, locomotion, anxiety, and learning/memory in offspring, as well as neuronal abnormalities. Some investigations suggested that EDC exert effects on central monoaminergic neurons, especially dopaminergic neurons. Our data demonstrated that EDC attenuate the development of dopaminergic neurons, which might be involved in developmental disorders. Perinatal exposure to EDC might affect neuronal plasticity in the hippocampus, thereby potentially modulating neuronal development, leading to impaired cognitive and memory functions. Endocrine disruptors also attenuate gender differences in brain development. For example, the locus ceruleus is larger in female rats than in males, but treatments with bisphenol-A (BPA) enlarge this region in males. Some reports indicated that EDC induce hypothyroidism, which might be evidenced as abnormal brain development. Endocrine disruptors might also affect mature neurons, resulting in neurodegenerative disorders such as Parkinson's disease. The current review focused on alterations in the brain induced by EDC, specifically on the possible involvement of EDC in brain development and neurodegeneration.

Pubertal and early adult exposure to fenvalerate disrupts steroidogenesis and spermatogenesis in mice at adulthood

Fenvalerate, a pyrethroid insecticide used worldwide, has been shown to have a potentially adverse effect on male reproduction. Our earlier study showed that maternal fenvalerate exposure during lactation impaired testicular development in male offspring. In this study, we investigated the effects of pubertal and early adult exposure to fenvalerate on steroidogenesis and spermatogenesis in mice. Male mice were administered fenvalerate (60 mg/kg) by gavage daily from postnatal day 35 (PND35) to PND63. Results showed that sperm count was significantly decreased in fenvalerate-treated mice. In addition, fenvalerate markedly decreased the layers of spermatogenic cells, disturbed the array of spermatogenic cells and increased the number of apoptotic cells in testes. The adverse effects of fenvalerate on male reproduction seemed to be associated with a decrease in serum and testicular testosterone (T). Although pubertal and early adult exposure to fenvalerate had little effect on the number of Leydig cells in testes, mRNA and protein levels of testicular T biosynthetic enzymes including P450(17alpha) and P450scc were significantly downregulated in fenvalerate-treated mice. In conclusion, pubertal and early adult fenvalerate exposure induces a deleterious effect on steroidogenesis and spermatogenesis in adulthood. The decreased testicular T synthesis partially contributes to fenvalerate-induced impairment on spermatogenesis.

Alcohol, drugs, caffeine, tobacco, and environmental contaminant exposure: reproductive health consequences and clinical implications

Reproductive function and fertility are thought to be compromised by behaviors such as cigarette smoking, substance abuse, and alcohol consumption; however, the strength of these associations are uncertain. Furthermore, the reproductive system is thought to be under attack from exposure to environmental contaminants, particularly those chemicals shown to affect endocrine homeostasis. The relationship between exposure to environmental contaminants and adverse effects on human reproductive health are frequently debated in the scientific literature and these controversies have spread into the lay press drawing increased public and regulatory attention. Therefore, the objective of the present review was to critically evaluate the literature concerning the relationship between lifestyle exposures and adverse effects on fertility as well as examining the evidence for a role of environmental contaminants in the purported decline of semen quality and the pathophysiology of subfertility, polycystic ovarian syndrome, and endometriosis. The authors conclude that whereas cigarette smoking is strongly associated with adverse reproductive outcomes, high-level exposures to other lifestyle factors are only weakly linked with negative fertility impacts. Finally, there is no compelling evidence that environmental contaminants, at concentrations representative of the levels measured in contemporary biomonitoring studies, have any effect, positive or negative, on reproductive health in the general population. Further research using prospective study designs with robust sample sizes are needed to evaluate testable hypotheses that address the relationship between exposure and adverse reproductive health effects.

The impact of environmental and occupational exposures on reproductive health

Environmental exposures during critical periods of susceptibility in utero may result in lifelong or intergenerational adverse health effects. Most chemicals in commercial use in the United States have not been tested for possible developmental toxicity to fetuses, infants, and children. Environmental and occupational exposures can result in adverse effects on female and male reproduction. Nurses can identify at-risk patients, provide education about the impact of chemical toxicants, and empower women to take precautionary action.

Environmental/lifestyle effects on spermatogenesis

The high incidence of low sperm counts in young (European) men and evidence for declining sperm counts in recent decades mean that the environmental/lifestyle impact on spermatogenesis is an important health issue. This review assesses potential causes involving adverse effects on testis development in perinatal life (primarily effects on Sertoli cell number), which are probably irreversible, or effects on the process of spermatogenesis in adulthood, which are probably mainly reversible. Several lifestyle-related (obesity, smoking) and environmental (exposure to traffic exhaust fumes, dioxins, combustion products) factors appear to negatively affect both the perinatal and adult testes, emphasizing the importance of environmental/lifestyle impacts throughout the life course. Apart from this, public concern about adverse effects of environmental chemicals (ECs) (pesticides, food additives, persistent pollutants such as DDT, polychlorinated biphenyls) on spermatogenesis in adult men are, in general, not supported by the available data for humans. Where adverse effects of ECs have been shown, they are usually in an occupational setting rather than applying to the general population. In contrast, a modern Western lifestyle (sedentary work/lifestyle, obesity) is potentially damaging to sperm production. Spermatogenesis in normal men is poorly organized and inefficient so that men are poorly placed to cope with environmental/lifestyle insults.

Dioxin-induced changes in epididymal sperm count and spermatogenesis

BACKGROUND

A single in utero exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on gestation day 15 decreased epididymal sperm count in adult rats and thus was used to establish a tolerable daily intake for TCDD. However, several laboratories have been unable to replicate these findings. Moreover, conflicting reports of TCDD effects on daily sperm production suggest that spermatogenesis may not be as sensitive to the adverse effects of TCDD as previously thought.

DATA SOURCES

We performed a PubMed search using relevant search terms linking dioxin exposure with adverse effects on reproduction and spermatogenesis.

DATA SYNTHESIS

Developmental exposure to TCDD is consistently linked with decreased cauda epididymal sperm counts in animal studies, although at higher dose levels than those used in some earlier studies. However, the evidence linking in utero TCDD exposure and spermatogenesis is not convincing.

CONCLUSIONS

Animal studies provide clear evidence of an adverse effect of in utero TCDD exposure on epididymal sperm count but do not support the conclusion that spermatogenesis is adversely affected. The mechanisms underlying decreased epididymal sperm count are unknown; however, we postulate that epididymal function is the key target for the adverse effects of TCDD.

Serum dioxin concentrations and time to pregnancy

BACKGROUND

Pollution may play a role in population trends of declining semen quality and regional differences in time to pregnancy (TTP) in industrialized societies. Dioxins including 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) have been suspected. In 1976, an explosion near Seveso, Italy resulted in the highest TCDD exposure known in residential populations. Twenty years later, we conducted a retrospective cohort study, the Seveso Women's Health Study.

METHODS

Of 981 participants, 472 women attempted pregnancy after the explosion, and 278 delivered a livebirth not associated with contraceptive failure. Individual serum TCDD levels were measured from samples collected soon after the explosion and extrapolated to the conception attempt. We examined the relation of TCDD levels to time to pregnancy (parameterized as the monthly probability of conception within the first 12 months of trying) and to infertility (defined as conception after at least 12 months of trying). We modeled fecundability with discrete-time Cox proportional hazards regression, and we modeled fertility with logistic regression. We tested the sensitivity of the conclusions to differing definitions of eligibility and outcome.

RESULTS

Median TCDD level was 50 parts per trillion, median time to pregnancy was 2 months, and 17% reported taking 12 or more months to conceive. For every 10-fold increase in serum TCDD, we observed a 25% increase in time to pregnancy (adjusted-fecundability odds ratio = 0.75 [95% confidence interval (CI) = 0.60-0.95]) and about a doubling in odds of infertility (adjusted odds ratio = 1.9 [95% CI = 1.1-3.2]). Results were similar for extrapolated TCDD and sensitivity analyses.

CONCLUSIONS

We found dose-related increases in TTP and infertility associated with individual serum TCDD levels in the women from Seveso, Italy. These findings may have implications for fertility in industrialized areas.

Steroidogenesis in the fetal testis and its susceptibility to disruption by exogenous compounds

Masculinization depends on adequate production of testosterone by the fetal testis within a specific "masculinization programming window." Disorders resulting from subtle deficiencies in this process are common in humans, and environmental exposures/lifestyle could contribute causally because common therapeutic and environmental compounds can affect steroidogenesis. This evidence derives mainly from rodent studies, but because there are major species differences in regulation of steroidogenesis in the fetal testis, this may not always be a guide to potential effects in the human. In addition to direct study of the effects of compounds on steroidogenesis, information also derives from study of masculinization disorders that result from mutations in genes in pathways regulating steroidogenesis. This review addresses this issue by critically reviewing the comparative timing of production and regulation of steroidogenesis in the fetal testis of humans and of rodents and its susceptibility to disruption; where there is limited information for the fetus, evidence from effects on steroidogenesis in the adult testis is considered. There are a number of fundamental regulatory differences between the human and rodent fetal testis, most notably in the importance of paracrine vs. endocrine drives during masculinization such that inactivating LH receptor mutations block masculinization in humans but not in rodents. Other large differences involve the steroidogenic response to estrogens and GnRH analogs and possibly phthalates, whereas for other compounds there may be differences in sensitivity to disruption (ketoconazole). This comparison identifies steroidogenic targets that are either vulnerable (mitochondrial cholesterol transport, CYP11A, CYP17) or not (cholesterol uptake) to chemical interference.

When does the sex ratio of offspring of the paternal 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) exposure decrease: in the spermatozoa stage or at fertilization?

Recent animal experiments confirmed that paternal 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) exposure decreases the sex ratio of offspring at birth without altering litter size. However, the timing of this decrease remained unclear. Male mice were administered TCDD at 7-12 weeks of age and mated with non-treated females. The Y-bearing/X-bearing sperm ratio was examined by real-time PCR and FISH methods, and the sex ratio of the 2-cell embryos collected from non-treated females that had been mated with TCDD-exposed males were investigated by nested PCR. The Y-bearing/X-bearing sperm ratio was not significantly decreased in the TCDD group. However, the sex ratio of the 2-cell embryos of the TCDD group was significantly lower than that of the control group. These results may have resulted from a decrease in fertility of Y-bearing sperm. Thus, the results of this study suggested that the sex ratio of the offspring was decreased at fertilization and not during the spermatozoa stage.

An overview of the effects of dioxins and dioxin-like compounds on vertebrates, as documented in human and ecological epidemiology

Dioxins and dioxin-like compounds are primary examples of persistent organic pollutants that induce toxicity in both wildlife and humans. Over the past 200 years these compounds have been almost exclusively generated by human activity and have left a string of disasters in the wake of their accidental release. Most recently, the contamination of the Irish pork supply with dioxins resulted in an international recall of all Irish pork products. Epidemiologic data on human and ecological dioxin exposures have revealed a common pattern of biological response among vertebrate species, which is mediated through activation of the Aryl hydrocarbon Receptor (AhR). These AhR-mediated effects include profound consequences on the vertebrate individual exposed in early life with respect to myriad developmental endpoints including neurologic, immunologic, and reproductive parameters. Humans appear to be susceptible to these effects in a manner similar to that of the laboratory and wildlife species, which have demonstrated such outcomes. Furthermore, epidemiologic data suggest that there is little or no margin of exposure for humans with respect to these developmental effects. Given these concerns, prudent public health policy should include the continued reduction of exposures.

Predictors of serum dioxins and PCBs among peripubertal Russian boys

BACKGROUND

Although sources and routes of exposure to dioxins and polychlorinated biphenyls (PCBs) have been studied, information regarding exposure among children is limited. Breast-feeding and diet are two important contributors to early life exposure. To further understand other significant contributors to childhood exposure, we studied a cohort of children from a city with high environmental dioxin levels.

OBJECTIVES

We investigated predictors of serum concentrations of polychlorinated dibenzo-p-dioxins (PCDDs)/polychlorinated dibenzofurans (PCDFs)/co-planar PCBs (C-PCBs), toxic equivalents (TEQs), and PCBs among 8- to 9-year-old boys in Chapaevsk, Russia.

METHODS

We used general linear regression models to explore associations of log(10)-transformed serum concentrations of PCDDs/PCDFs/C-PCBs, TEQs, and PCBs at study entry with anthropometric, demographic, geographic, and dietary factors in 482 boys in Chapaevsk, Russia.

RESULTS

The median (25th, 75th percentile) concentration for total 2005 TEQs was 21.1 pg/g lipid (14.4, 33.2). Boys who were older, consumed local foods, were breast-fed longer, and whose mothers were employed at the Khimprom chemical plant (where chlorinated chemicals were produced) or gardened locally had significantly higher serum dioxins and PCBs, whereas boys with higher body mass index or more educated parents had significantly lower serum dioxins and PCBs. Boys who lived < 2 km from Khimprom had higher total TEQs (picograms per gram lipid) [adjusted mean = 30.6; 95% confidence interval (CI), 26.8-35.0] than boys who lived > 5 km away (adjusted mean = 18.8; 95% CI, 17.2-20.6).

CONCLUSIONS

Our findings suggest that there are specific local sources of dioxin and PCB exposure among children in Chapaevsk including maternal gardening, consumption of locally grown food, and residential proximity to the Khimprom plant.

Components of plastic: experimental studies in animals and relevance for human health

Components used in plastics, such as phthalates, bisphenol A (BPA), polybrominated diphenyl ethers (PBDE) and tetrabromobisphenol A (TBBPA), are detected in humans. In addition to their utility in plastics, an inadvertent characteristic of these chemicals is the ability to alter the endocrine system. Phthalates function as anti-androgens while the main action attributed to BPA is oestrogen-like activity. PBDE and TBBPA have been shown to disrupt thyroid hormone homeostasis while PBDEs also exhibit anti-androgen action. Experimental investigations in animals indicate a wide variety of effects associated with exposure to these compounds, causing concern regarding potential risk to human health. For example, the spectrum of effects following perinatal exposure of male rats to phthalates has remarkable similarities to the testicular dysgenesis syndrome in humans. Concentrations of BPA in the foetal mouse within the range of unconjugated BPA levels observed in human foetal blood have produced effects in animal experiments. Finally, thyroid hormones are essential for normal neurological development and reproductive function. Human body burdens of these chemicals are detected with high prevalence, and concentrations in young children, a group particularly sensitive to exogenous insults, are typically higher, indicating the need to decrease exposure to these compounds.

Lower serum testosterone associated with elevated polychlorinated biphenyl concentrations in Native American men

BACKGROUND

Polychlorinated biphenyls (PCBs) and chlorinated pesticides are endocrine disruptors, altering both thyroid and estrogen hormonal systems. Less is known of action on androgenic systems.

OBJECTIVE

We studied the relationship between serum concentrations of testosterone in relation to levels of PCBs and three chlorinated pesticides in an adult Native American (Mohawk) population.

METHODS

We collected fasting serum samples from 703 adult Mohawks (257 men and 436 women) and analyzed samples for 101 PCB congeners, hexachlorobenzene (HCB), dichlorodiphenyldichloroethylene (DDE), and mirex, as well as testosterone, cholesterol, and triglycerides. The associations between testosterone and tertiles of serum organochlorine levels (both wet weight and lipid adjusted) were assessed using a logistic regression model while controlling for age, body mass index (BMI), and other analytes, with the lowest tertile being considered the referent. Males and females were considered separately.

RESULTS

Testosterone concentrations in males were inversely correlated with total PCB concentration, whether using wet-weight or lipid-adjusted values. The odds ratio (OR) of having a testosterone concentration above the median was 0.17 [95% confidence interval (CI), 0.05-0.69] for total wet-weight PCBs (highest vs. lowest tertile) after adjustment for age, BMI, total serum lipids, and three pesticides. The OR for lipid-adjusted total PCB concentration was 0.23 (95% CI, 0.06-0.78) after adjustment for other analytes. Testosterone levels were significantly and inversely related to concentrations of PCBs 74, 99, 153, and 206, but not PCBs 52, 105, 118, 138, 170, 180, 201, or 203. Testosterone concentrations in females are much lower than in males, and not significantly related to serum PCBs. HCB, DDE, and mirex were not associated with testosterone concentration in either men or women.

CONCLUSIONS

Elevation in serum PCB levels is associated with a lower concentration of serum testosterone in Native American men.

Maternal pregnancy levels of polychlorinated biphenyls and risk of hypospadias and cryptorchidism in male offspring

BACKGROUND

The etiologies of the male urogenital anomalies cryptorchidism and hypospadias are poorly understood. It has been suggested, however, that in utero hormone levels may be related to risk. Endocrine-disrupting chemicals, including polychlorinated biphenyl (PCB) compounds, may alter hormone levels and thereby affect the fetus.

OBJECTIVES

To examine whether in utero PCB exposure is related to cryptorchidism and hypospadias, we examined PCB levels among pregnant women enrolled in the Collaborative Perinatal Project (CPP).

METHODS

The CPP enrolled pregnant women at 12 U.S. medical centers between 1959 and 1965. For the present research, we analyzed third-trimester serum samples from the mothers of 230 sons with cryptorchidism, 201 sons with hypospadias, and 593 sons with neither condition. We estimated adjusted odds ratios (ORs) and 95% confidence intervals (CIs) using logistic regression and examined the associations of each anomaly with individual PCB congener levels, sum of PCBs, and several functional groupings of PCBs.

RESULTS

In general, the ORs for cryptorchidism or hypospadias showed no notable associations with individual PCB congener levels or functional groupings of PCBs. However, the ORs and 95% CIs for the sum of PCBs associated with hypospadias were as follows: 0-1.9 microg/L, reference group; 2-2.9 microg/L, OR = 1.57, 95% CI, 1.05-2.34; 3-3.9 microg/L, OR = 1.45, 95% CI, 0.90-2.34; and > or = 4.0 microg/L, OR = 1.69, 95% CI, 1.06-2.68; p-value for trend = 0.08.

CONCLUSIONS

Given the large number of associations examined, these findings do not strongly support the hypothesis that PCBs are associated with cryptorchidism or hypospadias. Because population serum PCB levels at the time of sample collection were considerably higher than levels at present, it is unlikely that current PCB exposure is related to the development of either anomaly.

Endocrine-disrupting chemicals: an Endocrine Society scientific statement

There is growing interest in the possible health threat posed by endocrine-disrupting chemicals (EDCs), which are substances in our environment, food, and consumer products that interfere with hormone biosynthesis, metabolism, or action resulting in a deviation from normal homeostatic control or reproduction. In this first Scientific Statement of The Endocrine Society, we present the evidence that endocrine disruptors have effects on male and female reproduction, breast development and cancer, prostate cancer, neuroendocrinology, thyroid, metabolism and obesity, and cardiovascular endocrinology. Results from animal models, human clinical observations, and epidemiological studies converge to implicate EDCs as a significant concern to public health. The mechanisms of EDCs involve divergent pathways including (but not limited to) estrogenic, antiandrogenic, thyroid, peroxisome proliferator-activated receptor gamma, retinoid, and actions through other nuclear receptors; steroidogenic enzymes; neurotransmitter receptors and systems; and many other pathways that are highly conserved in wildlife and humans, and which can be modeled in laboratory in vitro and in vivo models. Furthermore, EDCs represent a broad class of molecules such as organochlorinated pesticides and industrial chemicals, plastics and plasticizers, fuels, and many other chemicals that are present in the environment or are in widespread use. We make a number of recommendations to increase understanding of effects of EDCs, including enhancing increased basic and clinical research, invoking the precautionary principle, and advocating involvement of individual and scientific society stakeholders in communicating and implementing changes in public policy and awareness.

The influence of endocrine disruptors on pubertal timing

PURPOSE OF REVIEW

Overview of the effects of endocrine disruptors on pubertal timing.

RECENT FINDINGS

Epidemiologic studies in humans support animal data demonstrating that exposures to endocrine-disrupting compounds have pronounced effects on pubertal timing and that the timing of endocrine-disrupting compound exposure and the specific agent causes different outcomes. Recent studies confirm subtle effects of lead, dioxins, and phytoestrogens on delaying onset of puberty and demonstrate an association of phthalates and polychlorinated biphenyls with earlier breast development and menarche, respectively. These studies, however, are complicated by mixed exposures of compounds which individually may have opposing actions on the reproductive axis.

SUMMARY

Animal and human data confirm perturbations in pubertal onset with exposures to endocrine-disrupting compounds.