Proposed Mode of Action for In Utero Effects of Some Phthalate Esters on the Developing Male Reproductive Tract

What is driving the global decline of human fertility? Need for a multidisciplinary approach to the underlying mechanisms

An intense period of human population expansion over the past 250 years is about to cease. Total fertility rates are falling dramatically all over the world such that highly industrialized nations, including China and the tiger economies of SE Asia, will see their populations decline significantly in the coming decades. The socioeconomic, geopolitical and environmental ramifications of this change are considerable and invite a multidisciplinary consideration of the underlying mechanisms. In the short-term, socioeconomic factors, particularly urbanization and delayed childbearing are powerful drivers of reduced fertility. In parallel, lifestyle factors such as obesity and the presence of numerous reproductive toxicants in the environment, including air-borne pollutants, nanoplastics and electromagnetic radiation, are seriously compromising reproductive health. In the longer term, it is hypothesized that the reduction in family size that accompanies the demographic transition will decrease selection pressure on high fertility genes leading to a progressive loss of human fecundity. Paradoxically, the uptake of assisted reproductive technologies at scale, may also contribute to such fecundity loss by encouraging the retention of poor fertility genotypes within the population. Since the decline in fertility rate that accompanies the demographic transition appears to be ubiquitous, the public health implications for our species are potentially devastating.

Exposure to di-2-ethylhexyl phthalate (DEHP) increases the risk of cancer

Cancer is a major socioeconomic burden that seriously affects the life and spirit of patients. However, little is known about the role of environmental toxicant exposure in diseases, especially ubiquitous di-(2-ethylhexyl) phthalate (DEHP) which is one of the most widely used plasticizers. Hence, the objective of this study was to assess the potential association between cancer and DEHP. The data were collected using the 2011-2018 National Health and Nutrition Examination Survey (NHANES) data (n = 6147), and multiple logistic regression was conducted to evaluate the association. The concentrations of DEHP were calculated by each metabolite and split into quartiles for analysis. After adjusting for confounding factors, DEHP was significantly associated with an increased risk of cancer prevalence, and the metabolites of DEHP showed similar results (OR > 1.0, p < 0.05). Simultaneously, the association remained when the analyses were stratified by age and sex, and the risk of cancer appeared to be higher in male patients. In addition, further analysis suggested that DEHP exposure obviously increased the risk of female reproductive system cancer, male reproductive system cancer, and other cancers (OR > 1.0, p < 0.05) but not skin and soft tissue cancer. DEHP exposure is associated with the risk of cancer, especially female reproductive system cancer, male reproductive system cancer and other cancers.

Environmentally relevant DEHP exposure during gestational and lactational period inhibits filamin a testicular expression

Toxicological studies have revealed that DEHP exposure during pregnancy may induce developmental disorders, especially in male offspring, leading to morphological and functional alterations in the reproductive system by mechanisms that should be investigated. Thus, the aim of this work was to analyze the testicular toxicity induced by an environmentally relevant DEHP dose during development and its impact on FLNA, a protein that participates in the blood-testis barrier assembly. We used male Wistar rats exposed to DEHP during pregnancy and lactation. The results showed that DEHP exposure during development and lactation increased body weight, decreased gonadal weight and shortened anogenital distance. This phthalate induced morphological changes in the testis, suggestive of hypospermatogenesis. DEHP exposure decreased the number of FLNA positive cells and the expression of FLNA and claudin-1 in prepubertal testes. Furthermore, DEHP inhibited FLNA and claudin-1 protein expression in adult male rats. These results indicated that exposure to DEHP during gestation and lactation perturbed testis development and suggested that FLNA is a target protein of DEHP, possibly contributing to the phthalate-induced damage on BTB.

Reproductive toxicity of emerging plasticizers, flame retardants, and bisphenols, using culture of the rat fetal testis†

The use of bis (2-ethylhexyl) phthalate (DEHP), 2,2'4,4'-tetrabromodiphenyl ether (BDE47), and bisphenol A (BPA), as plasticizers, flame retardants, and epoxy resins, respectively, has been regulated due to their endocrine disrupting activities. Replacements for these chemicals are found in human matrices, yet the endocrine disrupting potential of these emerging contaminants is poorly characterized. We compared the effects of legacy chemicals with those of their replacements using fetal rat testis organ culture. Fetal testes sampled at gestation day 15 were grown ex vivo, and the impact was evaluated after a 3-day exposure to 10 μM of each legacy chemical; two BPA analogs (bisphenol M and bisphenol TMC); three replacements for DEHP/MEHP (2,2,4-trimethyl-1,3-pentanediol diisobutyrate, diisononyl-phthalate, and diisodecyl adipate); or two replacements for BDE47 (tributoxyethyl phosphate and isopropylated triphenyl phosphate). We showed that only BPA and MEHP significantly decrease testosterone secretions after 24 h, while BPM and BPTMC have the opposite effect. Luteinizing hormone-stimulated testosterone was reduced by BPA and MEHP but was increased by BPTMC. After exposure, testes were used for immunofluorescent staining of germ cells, Sertoli cells, and Leydig cells. Interestingly, exposures to BPM or BPTMC induced a significant increase in the Leydig cell density and surface area. A decrease in germ cell density was observed only after treatment with MEHP or BDE47. MEHP also significantly decreased Sertoli cell proliferation. These studies show that some replacement chemicals can affect testicular function, while others appear to show little toxicity in this model. These findings provide essential information regarding the need for their regulation.

Impact of mold growth on di(2-ethylhexyl) phthalate emission from moist wallpaper

Flood damage can increase indoor concentrations of di(2-ethylhexyl) phthalate (DEHP) and molds in households with wallpaper. Wallpaper water content can affect its DEHP emission into indoor environments; however, the influence of mold growth on this DEHP emission remains unclear. Here, we evaluated whether mold growth affects DEHP emission from moist wallpaper (moist WP). Experiments were conducted in glass chambers with wallpaper containing 12.7% (w/w) DEHP and a dust tray sample system at approximately 28 °C and 100% relative humidity (RH). The experimental groups were (1) moist WP, (2) moist WP + Aspergillus versicolor (AV), (3) moist WP + Cladosporium cladosporioides, (4) moist WP + Penicillium chrysogenum, and (5) moist WP + mold mixture. Mold growth on the wallpaper and DEHP emission into air and onto dust were analyzed at nine time-points over 30 days. Initially, the moist WP group emitted relatively high concentrations of DEHP into air, but after at least 8 days, the concentration of DEHP emitted by the mold-added groups exceeded that of the moist WP group. DEHP emission onto dust, especially from the moist WP group, increased considerably at day 15. During the experimental period, the moist WP (13.63 ± 4.67 μg) and moist WP + AV (13.93 ± 0.49 μg) groups emitted higher cumulative amounts of DEHP onto dust. During the 30-day experimental period, obvious mold growth occurred over days 15–30. Moreover, the moist WP group exhibited relatively higher and lower cumulative DEHP emission into air than the mold-added groups during days 2–10 (2.71 vs. 1.94–2.94 μg) and 15–30 (1.16 vs. 1.61–2.12), respectively; a contrasting trend was observed for cumulative DEHP emission onto dust. In conclusion, mold growth affects DEHP emission from water-damaged wallpaper, and the removal or cleaning of wet wallpaper, particularly those with visible mold growth, is critical from a public health perspective.

Exposure to DEHP is potential to increase the risk of overactive bladder, evidence from NHANES 2003-2008

Overactive bladder (OAB) is a group of clinical symptoms that are highly bothersome to the life and spirit of patients. However, little is known about the role of ubiquitous di-(2-ethylhexyl) phthalate (DEHP) exposure in the disorder. Hence, the study was conducted. The data were collected using the 2003-2008 National Health and Nutrition Examination Survey (NHANES) data (n = 2121), and multiple logistic regression was adapted. The concentrations of DEHP (∑DEHP) were calculated for each metabolite and split into quartiles for analysis. After adjusting for confounding factors, ∑DEHP was associated with increased odds of OAB for the highest quartile (OR = 1.15, 95% CI [1.06, 1.25], p < 0.05), and the highest quartile of metabolites showed similar results, such as mono-(2-ethyl-5-hydroxyhexyl) phthalate (OR = 1.09, 95% CI [1.01, 1.19], p < 0.05), mono-(2-ethyl-5-oxohexyl) phthalate (OR = 1.21, 95% CI [1.11, 1.32], p < 0.05) and mono-(2-ethyl-5-carboxypentyl) phthalate (OR = 1.22, 95% CI [1.12, 1.33], p < 0.05). The association remained when the analyses were stratified by age and sex. Our study adds evidence for understanding the potential role of environmental factors in OAB, and further research is needed to determine whether the status of OAB can be changed by controlling DEHP exposure.

Toxicological outcome of phthalate exposure on male fertility: Ameliorative impacts of the co-administration of N-acetylcysteine and zinc sulfate in rats

Background

Reports have shown that humans are consistently exposed to environmental toxicants such as phthalate (PHT) during their daily activities. This results in reproductive dysfunction and infertility-related issues as already noted in human and experimental animals. We therefore designed this study to investigate fertility outcome in phthalate-exposed male rats treated with N-acetylcysteine (NAC) and zinc sulfate (ZnSO4) with the view of providing a therapeutic alternative to reproductive toxicity caused by phthalate. The research was done in two phases. In phase 1, thirty-five male Wistar rats were randomly assigned to one of five (n = 7) groups given the following treatments for 21 days: group A was given distilled water as a control, while groups B, C, D, and E were given phthalate (750 mg/kg/day). Animals in groups C to E were also given ZnSO4 (0.5 mg/kg/day), N-acetylcysteine (100 mg/kg/day), and ZnSO4 (0.5 mg/kg/day) + N-acetylcysteine (100 mg/kg/day) in addition to phthalate. In phase 2, animals from groups in phase 1 were mated with females for fecundity testing.

Results

The result shows alteration in testicular and epididymis weight and testis/epididymis ratio, semen parameters, sperm capacitation and acrosome reaction, sperm DNA, serum Zn and Mg, testicular mitochondria apoptosis mechanisms (TNF-α and BCL-2), and testicular Ca2+-ATPase as well as fecundity outcome in the phthalate-treated group. However, ZnSO4 and NAC successfully ameliorated the deleterious effects of phthalate on semen parameters, sperm capacitation and acrosome reaction, serum electrolyte and mitochondria apoptosis mechanisms, and testicular electrogenic Ca2+-ATPase in phthalate-induced male rats with a better outcome in the combined therapy. Pregnancy outcome and litter sizes were also higher in the combined therapy when also compared with the phthalate-treated groups.

Conclusion

According to the result, ZnSO4 and NAC increased fertility outcome in phthalate-treated male rats through enhancement of testicular BCL-2, serum electrolyte, testicular Ca2+ATPase pumps, and cytoprotection.

The novel role of the aquaporin water channel in lycopene preventing DEHP-induced renal ionic homeostasis disturbance in mice

Di-(2-ethylhexyl) phthalate (DEHP), an extensively used plasticizer, can cause environmental pollution and organ injury. Lycopene (LYC) is a natural carotene that has the potential to prevent chronic diseases. To reveal the effect of DEHP and/or LYC on the kidney, male mice were treated with LYC (5 mg/kg) and/or DEHP (500 mg/kg or 1000 mg/kg) by gavage for 28 days. The study indicated that DEHP caused glomerular atrophy, tubular expansion, disappearance of the mitochondrial membrane, and cristae rupture. DEHP exposure can increase the expression of aquaporin (AQP) subunits and the activity of Ca²⁺-Mg²⁺-ATPase and decrease the activity of Na⁺-K⁺-ATPase, which results in ion disorder. However, LYC can relieve kidney injury by regulating the activity of ATPase, the expression of ATPase subunits, and AQP subunit expression. The results indicated that AQP was a target for LYC in antagonizing the disturbance of DEHP-induced renal damage.

Perinatal phthalate exposure increases developmental apoptosis in the rat medial prefrontal cortex

Phthalates are a class of endocrine disruptors found in a variety of consumer goods, and offspring can be exposed to these compounds during gestation and lactation. Our laboratory has found that perinatal exposure to an environmentally relevant mixture of phthalates resulted in a decrease in cognitive flexibility and in neuron number in the adult rat medial prefrontal cortex (mPFC). Here, we examine effects of phthalate treatment on prenatal cellular proliferation and perinatal apoptosis in the mPFC. To examine the phthalate effects on cellular proliferation, dams consumed 0, 1, or 5 mg/kg of the phthalate mixture daily from embryonic day 2 (E2) through the day of birth (P0), and on E16 and E17, they were injected with BrdU. The mPFC of offspring was analyzed on P5 and showed a decrease in labelled cells in the phthalate exposed groups. To examine whether changes in BrdU density observed on P5 were due to altered cell survival, cell death was measured on E18, P0, and P5 using a TUNEL assay in a separate cohort of prenatally exposed offspring. There was an increase in TUNEL labelled cells at E18 in the phthalate exposed groups. In the final experiment, dams consumed the phthalate mixture from E2 through P10, at which time mPFC tissue was stained with TUNEL. Phthalate treated subjects showed a higher density of apoptotic cells at P10. These results indicate both pre- and postnatal phthalate exposure increases apoptosis in the male and female rat mPFC. While the impact of phthalates on proliferation cannot be ruled out, these data do not allow for definitive conclusions.

Di-n-butyl phthalate diminishes testicular steroidogenesis by blocking the hypothalamic-pituitary-testicular axis: relationship with germ cell apoptosis in Japanese quail

Although di-n-butyl phthalate (DBP) induces germ cell apoptosis, the underlying mechanism is not yet clear in quail. In this study, prepubertal quails were given a single dose of 500mg kg-1 DBP by gavage and were then killed 3, 6 and 24h after treatment. There was a significant reduction in intratesticular testosterone (ITT) concentrations and testicular steroidogenic enzyme mRNA expression and a significant increase in germ cell apoptosis in DBP-treated compared with control quails at all time points. Maximum apoptosis was detected 6h after treatment and the maximum reduction in testosterone concentrations was at 3h. To investigate whether DBP suppressed testicular steroidogenesis by affecting the hypothalamic-pituitary-testicular axis, we analysed pituitary LH subunit β (Lhb) mRNA expression and serum LH concentrations. At all time points, pituitary Lhb expression and serum LH concentrations were significantly decreased following DBP treatment. The present observations suggest the possibility that DBP blocked LH secretion from the hypothalamus and/or pituitary, thereby decreasing LH stimulation of Leydig cells and reducing ITT concentrations. DBP-induced decreases in ITT concentrations may cause changes to the physical structure of Sertoli cells, which, in turn, may induce germ cell apoptosis.

Prenatal di-(2-ethylhexyl) phthalate maternal exposure impairs the spatial memory of adult mouse offspring in a phase- and gender-dependent manner

DEHP is a wildly used plasticizer. Maternal DEHP exposure induced fetal growth restriction (FGR) and behavioral abnormalities in adolescence and adulthood mouse. The effect of low birth weight induced by DEHP on behaviors after growing up is not certain. In this study, the ICR pregnant mice were exposed to 200 mg/kg DEHP during gestation 6-12 days or 13-17 days, which can create FGR model. The F1 offspring were performed three ethological experiments at puberty (6 weeks postpartum) and adult period (8 weeks postpartum). The open field test was performed to detect the locomotor activity and anxiety, the elevated plus maze to test anxiety-like behavior, and the Morris water maze assay to measure the spatial learning and memory capability of male and female offspring. The results showed that spatial memory ability was dramatically impaired for male rather than female offspring in gestation 13-17 days' group. Other behaviors had no statistically different between groups. These findings suggest that prenatal DEHP exposure disturbed mouse offspring spatial memory ability in a phase- and gender-dependent manner.

Intrauterine exposure to diethylhexyl phthalate disrupts gap junctions in the fetal rat testis

Fetal exposure to certain phthalate esters can disrupt testis development in rodents and lead to male reproductive disorders, but with a causal link less certain in humans. Di(2-ethylhexyl) phthalate (DEHP) is one of the most common phthalates found in the environment and in rodents it is known to induce serious testis toxicity, as well as male reproductive disorders including cryptorchidism, hypospadias, impaired spermatogenesis and reduced fertility. In this study, we show that perinatal DEHP exposure disrupts gap junction localization in fetal and postnatal rat testis and correlate these findings to morphological changes. The protein Connexin 43 (CX43), normally expressed strongly in testicular gap junctions, was markedly downregulated in Leydig cells of DEHP-exposed fetal testes. In the postnatal testes, CX43 expression was recovered in the DEHP-exposed animals, even though Leydig cell clusters and malformed cords with intratubular Leydig cells were still present.

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DEHP disrupts gap junction localization in fetal and postnatal rat testis.

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DEHP exposure reduces Cx43-positive gap junctions in Leydig cell clusters in fetal rat testis.

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Leydig cell gap junctions recover in postnatal testis after early life DEHP exposure.

Taxifolin alleviates apoptotic injury induced by DEHP exposure through cytochrome P450 homeostasis in chicken cardiomyocytes

Di-2-ethylhexyl phthalate (DEHP), widely used as a plasticizer, is a ubiquitous artificial pollutant. DEHP can induce biological toxicity in various organs, with an especially high potential for toxicity to the cardiovascular system. Taxifolin (TAX) is used in the treatment of cardiovascular diseases due to its antioxidative capacities. However, it is not clear whether TAX can alleviate apoptosis induced by DEHP exposure through the cytochrome P450 (CYP) pathway in cardiomyocytes. To understand the role of TAX in attenuating cardiomyocyte toxicity induced by DEHP, primary cardiomyocytes were divided into 4 groups (control group, DEHP group, TAX group and DEHP + TAX group). The results showed that in the cardiomyocytes, DEHP initiated apoptosis by increasing the expression of caspase-3, caspase-9, cyt c, and Bax at both the mRNA and protein levels and by decreasing the Bcl-2 levels compared with that of the control group. In addition, the activities of catalase (CAT), superoxide dismutase (SOD), and total antioxidative capacity (T-AOC) were clearly decreased (P < 0.05), while in the DEHP group, the malondialdehyde (MDA) and hydrogen peroxide (H₂O₂) levels were observably increased (P < 0.05), compared with those in control group. Furthermore, compared with the control group, the DEHP group demonstrated a clear partial decrease in the expression of the mRNA levels of CYP1B1 and CYP2C18 (P < 0.05), and DEHP/TAX cotreatment partially prevented apoptosis and oxidative stress damage (P < 0.05). These results showed that exposure to DEHP induced apoptosis in chicken cardiomyocytes, while TAX could antagonize the toxicity of DEHP on cardiomyocytes by attenuating oxidative stress responses and modulating CYPs.

Investigation of the In-Vivo Cytotoxicity and the In Silico-Prediction of MDM2-p53 Inhibitor Potential of Euphorbia peplus Methanolic Extract in Rats

This study explored the probable in vivo cardiac and renal toxicities together with in silico approaches for predicting the apoptogenic potential of Euphorbia peplus methanolic extract (EPME) in rats. Cardiac and renal injury biomarkers were estimated with histopathological and immunohistochemical evaluations of both kidney and heart. The probable underlying mechanism of E. peplus compounds to potentiate p53 activity is examined using Molecular Operating Environment (MOE) docking software and validated experimentally by immunohistochemical localization of p53 protein in the kidney and heart tissues. The gas chromatography/mass spectrometry analysis of E. peplus revealed the presence of nine different compounds dominated by di-(2-ethylhexyl) phthalate (DEHP). Significant elevations of troponin, creatine phosphokinase, creatine kinase-myocardium bound, lactate dehydrogenase, aspartate transaminase, alkaline phosphatase, urea, creatinine, and uric acid were evident in the EPME treated rats. The EPME treated rats showed strong renal and cardiac p53 expression and moderate cardiac TNF-α expression. Further, our in silico results predicted the higher affinity and good inhibition of DEHP, glyceryl linolenate, and lucenin 2 to the MDM2-p53 interface compared to the standard reference 15 a compound. Conclusively, EPME long-term exposure could adversely affect the cardiac and renal tissues probably due to their inflammatory and apoptotic activity. Moreover, the in silico study hypothesizes that EPME inhibits MDM2-mediated degradation of p53 suggesting possible anticancer potentials which confirmed experimental by strong p53 expression in renal and cardiac tissues.

Use of the Adverse Outcome Pathway (AOP) framework to evaluate species concordance and human relevance of Dibutyl phthalate (DBP)-induced male reproductive toxicity

Dibutyl phthalate (DBP) is a phthalate ester used as a plasticizer, and solvent. Studies using rats consistently report that DBP exposure disrupts normal development of the male reproductive system in part via inhibition of androgen synthesis. However, studies using xenograft models report that in human fetal testis DBP exposure is unlikely to impair testosterone synthesis. These results question the validity of the rat model for assessment of male reproductive effects caused by DBP. The Adverse Outcome Pathway (AOP) framework was used to evaluate the available evidence for DBP-induced toxicity to the male reproductive system. Three relevant biological elements were identified: 1) fetal rats are more sensitive than other rodents and human fetal xenografts to DBP-induced anti-androgenic effects, 2) DBP-induced androgen-independent adverse outcomes are conserved amongst different mammalian models and human fetal testis xenografts, and 3) DBP-induced anti-androgenic effects are conserved in different mammalian species when exposure occurs during postnatal life stages.

Di(n-butyl) phthalate exposure impairs meiotic competence and development of mouse oocyte

Di(n-butyl) phthalate (DBP) is extensively used in industrial applications as plasticizer and stabilizer and its presence in the environment may present health risks for human. Previous studies have demonstrated its mutagenic, teratogenic, and carcinogenic ability. However, its effect on mammalian oocyte maturation remains unknown. In this study, we examined the effect of DBP on oocyte maturation both in vitro and in vivo. Our results showed that DBP could significantly reduce mice oocyte germinal vesicle breakdown (GVBD) and polar body extrusion (PBE) rates. In addition, oocyte cytoskeleton was damaged and cortical granule-free domains (CGFDs) were also disrupted. Finally, DBP induced early apoptosis of oocyte and granulosa cells (GCs). Collectively, these data demonstrate that DBP could reduce meiosis competence and mouse oocyte development.

[Environmental Chemical Exposure and Its Effects on Infants' Reproductive Hormones]

In recent years, the birthrate has been continuously declining in Japan. The main causes of the decline are social factors. On the other hand, there is increasing evidence that many environmental chemicals show endocrine disrupting properties. Thus, we hypothesized that exposure to these chemicals would also be a causal for the fertility crisis. In this review, we examined current evidence that focused on environmental chemical exposure in utero and its association with reproductive hormones in children. We have included the findings from a prospective birth cohorts, the Hokkaido Study on Environment and Children's Health Sapporo cohort. According to the literature, environmental chemical levels in utero, such as polychlorinated biphenyl, dioxins, perfluorinated chemical substances, phthalates, and bisphenol A were somewhat associated with the levels of reproductive hormones, such as testosterone, estradiol, progesterone, inhibin B, and insulin-like factor-3 in cord blood, in early childhood and adolescence. The literature also suggests the association between exposure to these chemicals and brain-sexual differentiation or the anogenital distance, which suggests the disruption of androgen shower during the developmental stage in the fetal period. There are still knowledge gaps on whether these hormones at an early stage affect the pubertal development and reproductive functions in later life. In addition, alternative chemicals are produced after banning one type. The health effects of alternative chemicals should be evaluated. Effects of exposure to a mixture of the chemicals should also be examined in future studies. In conclusion, the prevention of environmental chemical hazards in relation to human reproductive function is important. It would be one of the countermeasures to the falling birthrate caused by fertility issues.

Perinatal Exposure to an Environmentally Relevant Mixture of Phthalates Results in a Lower Number of Neurons and Synapses in the Medial Prefrontal Cortex and Decreased Cognitive Flexibility in Adult Male and Female Rats

The growth and organization of the developing brain are known to be influenced by hormones, but little is known about whether disruption of hormones affects cortical regions, such as mPFC. This region is particularly important given its involvement in executive functions and implication in the pathology of many neuropsychiatric disorders. Here, we examine the long-term effects of perinatal exposure to endocrine-disrupting compounds, the phthalates, on the mPFC and associated behavior. This investigation is pertinent as humans are ubiquitously exposed to phthalates through a variety of consumer products and phthalates can readily cross the placenta and be delivered to offspring via lactation. Pregnant dams orally consumed an environmentally relevant mixture of phthalates at 0, 200, or 1000 μg/kg/d through pregnancy and for 10 d while lactating. As adults, offspring were tested in an attentional set-shifting task, which assesses cognitive flexibility. Brains were also examined in adulthood for stereological quantification of the number of neurons, glia, and synapses within the mPFC. We found that, independent of sex, perinatal phthalate exposure at either dose resulted in a reduction in neuron number, synapse number, and size of the mPFC and a deficit in cognitive flexibility. Interestingly, the number of synapses was correlated with cognitive flexibility, such that rats with fewer synapses were less cognitively flexible than those with more synapses. These results demonstrate that perinatal phthalate exposure can have long-term effects on the cortex and behavior of both male and female rats.SIGNIFICANCE STATEMENT Humans globally are exposed on a daily basis to a variety of phthalates, which are endocrine-disrupting chemicals. The effects of phthalate exposure on the developing brain, especially on cognitively relevant regions, such as the mPFC, are not known. Here, we use a rat model of human prenatal exposure to an environmentally relevant mixture of phthalates and find that there is an appreciable reduction in neuron number, synapse number, and size of the mPFC and a deficit in cognitive flexibility. These results may have serious implications for humans given that the mPFC is involved in executive functions and is implicated in the pathology of many neuropsychiatric disorders.

[Importance of Two Birth Cohorts (n=20,926 and n=514): 15 Years' Experience of the Hokkaido Study on Environment and Children's Health: Malformation, Development and Allergy]

Since "Our Stolen Future" by Theo Colborn was published in 1996, global interest on the impact of chemical substances, such as the endocrine-disrupting action of chemicals, has increased. In Japan, "The Hokkaido Study on Environment and Children's Health: Malformation, Development and Allergy" was launched in 2001. It was a model of Japan Environment and Children's Study of the Ministry of the Environment. In a large-scale, Hokkaido cohort, we obtained the consent of 20,926 mothers at the organogenesis stage with the cooperation of 37 obstetrics clinics in Hokkaido. We tracked the effects of endocrine disruptors on developmental disorders. In a small-scale Sapporo cohort, we observed in detail the neuropsychiatric development of children with the consent of 514 mothers in their late pregnancy. We examined how prenatal exposure to low concentrations of environmental chemicals affect the development of organs and the postnatal development of children. Maternal exposure to POPs, such as PCB/dioxins and perfluorinated alkyl substances, has affected not only children's birth size, thyroid functions, and sex hormone levels, but also postnatal neurodevelopment, infection, and allergy among others. The associations of short-half-life substances, such as DEHP and BPA, with obesity, ASD, and ADHD have been investigated. Gene-environment interactions have been found for smoking, caffeine, folic acid, and PCB/dioxin. In 2015, our center was officially designated as the WHO Collaborating Centre for Environmental Health and Prevention of Chemical Hazards, and we continue to the contribute to the global perspectives of child health.

Assessing the antiandrogenic properties of propyl paraben using the Hershberger bioassay

Propyl paraben is a widely used preservative in pharmaceuticals, cosmetics, and foods preventing microbial and fungal contamination. This study was designed to investigate antiandrogenic profiles of propyl paraben following oral doses at 10, 250, and 750 mg kg-1 day to immature male rats using the Hershberger Bioassay. Rats were divided into six groups including solvent control, negative control (0.4 mg kg-1 day testosterone propionate = TP), positive control (3 mg kg-1 day flutamide = FLU) and treatment groups (10, 250, and 750 mg kg-1 day testosterone propionate + Propyl paraben). Propyl paraben (PP) significantly decreased all accessory sex organ weights at each dose of 250 and 750 mg kg-1 day compared to control groups. Thus, we found that propyl paraben had antiandrogenic activity within the supported results of increasing LH levels and histopathologic results such atrophy, hyalinization, and anastomosis on androgenic tissues.

Toxic Effects of Di-2-ethylhexyl Phthalate: An Overview

Di-2-ethylhexyl phthalate (DEHP) is extensively used as a plasticizer in many products, especially medical devices, furniture materials, cosmetics, and personal care products. DEHP is noncovalently bound to plastics, and therefore, it will leach out of these products after repeated use, heating, and/or cleaning of the products. Due to the overuse of DEHP in many products, it enters and pollutes the environment through release from industrial settings and plastic waste disposal sites. DEHP can enter the body through inhalation, ingestion, and dermal contact on a daily basis, which has raised some concerns about its safety and its potential effects on human health. The main aim of this review is to give an overview of the endocrine, testicular, ovarian, neural, hepatotoxic, and cardiotoxic effects of DEHP on animal models and humans in vitro and in vivo.

Effects of Perinatal Exposure to Phthalates and a High-Fat Diet on Maternal Behavior and Pup Development and Social Play

Humans are ubiquitously exposed to many phthalates, a class of endocrine-disrupting chemicals commonly used in many consumer goods, and diet, especially fatty food, is presumed to be a major source of exposure. Here, we use a rat model of human prenatal exposure to investigate the potential interactive effects of an environmentally relevant mixture of phthalates and a maternal high-fat diet (HFD). From gestation through postnatal day (P)10, dams consumed the mixture of phthalates (0, 200, or 1000 μg/kg/d) and were fed a control diet or HFD. In males, perinatal exposure to the mixture of phthalates decreased prepubertal body weight and, in a dose-specific manner, periadolescent social play behavior. A dose-specific effect from phthalates with HFD was also seen in increased time alone in females during social play. HFD resulted in dams consuming more calories, having greater gestational weight gain, and licking and nursing their pups more, such that an early postnatal HFD generally increased pup body weight. There also was a tendency for increased oxidative stress markers at P10 within the medial prefrontal cortex of males exposed to the relatively high dose of phthalates and HFD. Effects on gene expression were inconsistent at P10 and P90 in both the medial prefrontal cortex and hypothalamus. Overall, this study demonstrates that phthalates and a maternal HFD only rarely interacted, except in oxidative stress markers in males. Additionally, perinatal exposure to an environmentally relevant mixture of phthalates can have a modest, but lasting, impact on social behaviors in both males and females.

The Possible Impact of Antenatal Exposure to Ubiquitous Phthalates Upon Male Reproductive Function at 20 Years of Age

Phthalates are ubiquitous environmental endocrine-disrupting chemicals suspected to interfere with developmental androgen action leading to adverse effects on male reproductive function. Prenatal exposure studies in rodents show cryptorchidism, hypospadias and reduced testicular volume (TV), testosterone and anogenital distance in males. It is postulated that there is a developmental window in utero when phthalate exposure has the most potent adverse effects. Some human studies show associations between prenatal phthalate exposure and reduced calculated "free" serum testosterone in infant boys and shorter anogenital distance. However, there are no data available yet which link antenatal exposure to long-term effects in men. We aimed to correlate antenatal phthalate exposure with adult TV, semen parameters and serum reproductive hormone concentrations. 913 men from the Western Australian (Raine) Pregnancy Cohort were contacted aged 20-22 years. 423 (56%) agreed to participate; 404 underwent testicular ultrasound examination; 365 provided semen samples, and reproductive hormones were measured in 384. Maternal antenatal serum phthalate metabolite measurements were available for 185 and 111 men, who provided serum and semen, respectively. Maternal serum collected at 18 and 34 weeks gestation, stored at -80°C, was pooled and analyzed for 32 phthalate metabolites by liquid chromatography-tandem mass spectrometry. TV was calculated, semen analysis performed by WHO approved methods, and serum concentrations of gonadotrophins, inhibin B, and testosterone measured. Eleven phthalate metabolites were detected. Primary and secondary metabolites of di-(2-ethyl-hexyl) phthalate (DEHP) and di-iso-nonyl phthalate (DiNP) were positively correlated. After correction for adult height, BMI, presence of a varicocele and exposure to maternal smoking mono-iso-nonyl phthalate (MiNP) (r = -0.22) and sums of DEHP and DiNP metabolites (r = -0.24) and the sum of the metabolites of the high molecular weight phthalates (r = -0.21) were negatively correlated with TV (all p < 0.05). After adjustment for BMI adult serum total testosterone was positively associated with exposure to the following antenatal serum phthalate metabolites: mono-(2-ethylhexyl) phthalate (r = 0.26), MiNP (r = 0.18), the sum of metabolites for DEHP (r = 0.21) and DiNP (r = 0.18), and the sum of high molecular phthalates (r = 0.20) (p = 0.0005 to p = 0.02). Given sample size, storage duration and confounding through postnatal exposures, further studies are required.

Di(2-Ethylhexyl) Phthalate Exposure In Utero Damages Sertoli Cell Differentiation Via Disturbance of Sex Determination Pathway in Fetal and Postnatal Mice

Mice may share similar mechanism with human underlying reproductive toxicity induced by di(2-ethylhexyl) phthalate (DEHP), which is not supposed to be associated with decreased testicular testosterone. Pregnant mice were exposed to DEHP by gavage, with the dosage regime beginning at human relevant exposure level. After in utero DEHP exposure, loss of Sertoli cells and germ cells were observed in the male pups at postnatal days 21. And SRY-related HMG box 9 (SOX9), Fibroblast growth factor-9 (FGF9), and Double-sex and Mab-3 related transcripttion factor 1 (DMRT1) proteins were significantly downregulated by DEHP at 2 mg/kg/d and above, suggesting the depression of Sertoli cell differentiation. The repression of Sox9 genes expression was supported by whole-mount in situ hybridization and real-time real-time-quantitative PCR. The expressions of Cyp11α1 and Star were not significantly affected by in utero DEHP exposure, indicating the absence of effects on testosterone biosynthesis. Furthermore, the testosterone-independent pathway regulating Sertoli cells differentiation was disturbed in fetus by DEHP at 2 mg/kg/d and above during the critical time window of sex determination, involving Gadd45g → Gata4/Fog2 → Sry → Sox9 → Fgf9 The results suggest that in utero DEHP exposure damaged Sertoli cells in the postnatal life of mice offspring via disturbance of the differentiation regulating pathway, potentially inducing declines in spermatogenesis.

Comparison of toxicogenomic responses to phthalate ester exposure in an organotypic testis co-culture model and responses observed in vivo

We have developed a three-dimensional testicular co-culture system (3D-TCS) which mimics in vivo testes. In this study, transcriptomic responses to phthalate esters (PE's) were compared in the 3D-TCS with responses in rat testes in vivo. Microarray data from the 3D-TCS and from in vivo testes were used to compare changes in gene expression patterns after exposure to developmentally toxic (DTPE) or developmentally non-toxic (DNTPE) phthalate esters. DTPE treatments clustered separately from DNTPE treatments based on principle components analysis both in vitro and in vivo. Pathway analysis using GO-Elite software showed that terms relating to steroid metabolism or reproductive development were enriched both in vitro and in vivo after DTPE exposure. Processes such as cell cycle, cell proliferation and apoptosis were enriched for DTPE treatments in vitro, but not in vivo. Based on these analyses we concluded that transcriptomic responses in the 3D-TCS reflect key aspects of in vivo phthalate toxicity.

Obstetrical outcomes and biomarkers to assess exposure to phthalates: A review

Studies of the effects on pregnancy outcomes of in utero exposure to phthalates, contaminants that are widely present in the environment, have yielded conflicting results. In addition, the mode of assessment of exposure varies between studies. The aim of this review was therefore to establish a current state of knowledge of the phthalates and metabolites involved in unfavorable pregnancy outcomes. Extant data were analyzed to determine which biomarker is the best suited to assess the relation between in utero exposure to phthalates and pregnancy outcomes. This review of the literature was conducted using the database of PubMed. A search was made of studies investigating exposure to phthalates and the following birth outcomes: preterm birth (gestational age <37 weeks), change in gestational age, change in body size at birth (birth weight, length, head circumference), anti-androgenic function, decreased anogenital distance, cryptorchidism, hypospadias and congenital malformation. The methodological approach adopted in each study was examined, in particular the methods used for exposure assessment (biomarkers and/or questionnaire). Thirty-five studies were included. Premature birth and decreased anogenital distance were the most commonly reported outcomes resulting from a moderate level of exposure to phthalates. The principal metabolites detected and involved were primary metabolites of di-2(ethylhexyl)-phthalate (DEHP) and di-n-butyl-phthalate (DnBP). No clear conclusion could be drawn with regard to gestational age at birth, body size at birth and congenital malformations. In epidemiological studies, maternal urine is the most suitable matrix to assess the association between in utero exposure to phthalates and pregnancy outcomes: in contrast to other matrices (cord blood, amniotic fluid, meconium and milk), sampling is easy, non-invasive and, can be repeated to assess exposure throughout pregnancy. Oxidative metabolites are the most relevant biomarkers since they are not prone to external contamination. Further epidemiological studies are required during pregnancy to i) determine the role of phthalates other than DEHP [currently replaced by various substitution products, in particular diisononyl-phthalate (DiNP)]; ii) establish the effect of phthalates on other outcomes (body size adjusted for gestational age, and congenital malformations); iii) determine the pathophysiological pathways; and iv) identify the most suitable time for biomarker determination of in utero exposure to phthalates.

Human urinary/seminal phthalates or their metabolite levels and semen quality: A meta-analysis

Health concerns surrounding human exposure to phthalates include diminished semen quality. Epidemiological findings remain inconsistent. We have performed a quality appraisal and meta-analysis to quantitatively summarize evidence for associations between phthalate exposures and human semen quality. Pubmed and Web of Science were searched for pertinent studies through October 2014. Cited references were reviewed to identify secondary studies. Studies that reported quantitative estimates of the association between phthalates or their metabolite levels in humans and semen quality were eligible. Random effects models were used to calculate pooled effects estimates. Overall, 20 studies met our inclusion criteria. Subsequently, 14 studies were included in the meta-analysis. Urinary monobutyl phthalate (MBP) and monobenzyl phthalate (MBzP) were associated with reduced sperm concentration (MBP [7.4-25.3 µg/L], pooled odds ratio [OR]=2.60, 95% confidence interval [CI]=1.32-5.15; MBzP [14.0-540.2 µg/L], pooled OR=2.23, 95% CI=1.16-4.30). Both MBP (24.6-14,459.0 µg/L) and MEHP (3.1-208.1 µg/L) were inversely associated with straight line velocity (VSL; MBP, pooled β=-2.51, 95% CI=-4.44, -0.59; MEHP, pooled β=-1.06, 95% CI=-1.99, -0.12). An IQR increase in MBzP and MEP levels (MBzP, IQR=11.35 µg/L; MEP, IQR=449.4 µg/L) was associated with an increase in comet extent (CE; MBzP, pooled β=3.57, 95% CI=0.89-6.25; MEP, pooled β=4.22, 95% CI=1.66-6.77). No associations were observed between monomethyl phthalate and any semen parameters. Our meta-analysis strengthens the evidence that specific phthalates or their metabolite levels may affect semen quality.

Association between maternal exposure to di(2-ethylhexyl) phthalate and reproductive hormone levels in fetal blood: the Hokkaido study on environment and children's health

Prenatal di(2-ethylhexyl) phthalate (DEHP) exposure can produce reproductive toxicity in animal models. Only limited data exist from human studies on maternal DEHP exposure and its effects on infants. We aimed to examine the associations between DEHP exposure in utero and reproductive hormone levels in cord blood. Between 2002 and 2005, 514 pregnant women agreed to participate in the Hokkaido Study Sapporo Cohort. Maternal blood samples were taken from 23-35 weeks of gestation and the concentration of the primary metabolite of DEHP, mono(2-ethylhexyl) phthalate (MEHP), was measured. Concentrations of infant reproductive hormones including estradiol (E2), total testosterone (T), and progesterone (P4), inhibin B, insulin-like factor 3 (INSL3), steroid hormone binding globulin, follicle-stimulating hormone, and luteinizing hormone were measured from cord blood. Two hundred and two samples with both MEHP and hormones' data were included in statistical analysis. The participants completed a self-administered questionnaire regarding information on maternal characteristics. Gestational age, birth weight and infant sex were obtained from birth records. In an adjusted linear regression analysis fit to all study participants, maternal MEHP levels were found to be associated with reduced levels of T/E2, P4, and inhibin B. For the stratified analyses for sex, inverse associations between maternal MEHP levels T/E2, P4, inhibin B, and INSL3 were statistically significant for males only. In addition, the MEHP quartile model showed a significant p-value trend for P4, inhibin B, and INSL3 decrease in males. Since inhibin B and INSL3 are major secretory products of Sertoli and Leydig cell, respectively, the results of this study suggest that DEHP exposure in utero may have adverse effects on both Sertoli and Leydig cell development in males, which agrees with the results obtained from animal studies. Comprehensive studies investigating phthalates' exposure in humans, as well as their long-term effects on reproductive development are needed.

Impact of butyl benzyl phthalate on development of the reproductive system of European pikeperch, Sander lucioperca (L.)

The effect of butyl benzyl phthalate (BBP) on the sex differentiation process of fish is practically unknown. The experimental material of this study was juvenile European pikeperch [Sander lucioperca (L.)], which is gonochoristic, undergoes immediate sex differentiation, and has a fixed gonad differentiation period. The fish were fed a diet supplemented with BBP (during the sex differentiation phase: age 61-96 days post hatch) in the following quantities: 1.0; 2.0; 4.0; 8.0; 16.0 g BBP kg-1 feed. The control feed was a xenobiotic-free base feed. In the present experiment lasting 10 weeks, the survival and growth of fish, the histopathological changes of the fish gonads and the sex ratio were evaluated. After administration of the two highest doses of BBP, growth inhibition of the fish was observed. BBP also seriously disturbed the gonadal differentiation process of pikeperch. All analysed concentrations of BBP delayed testicular development and, at concentrations of 4.0, 8.0 and 16.0 g BBP kg-1, induction of the feminisation process was observed. The sex ratio was distinctly disrupted in groups receiving 8.0 and 16.0 g BBP kg-1.

Prenatal di-n-butyl phthalate exposure alters reproductive functions at adulthood in male rats

This study was aimed to investigate the reproductive health in adult male rats exposed to di-n-butyl phthalate (DBP) during embryonic development. Pregnant rats were injected with DBP and F1 male rats were weaned and on postnatal day 100, used for mating with normal cycling females to assess reproductive performance. After completion of cohabitation period, rats were analyzed for other reproductive end points. Transplacental exposure to DBP significantly decreased fertility in adult male rats. Prenatal exposure to DBP significantly decreased sperm density, number of motile sperms, viable sperms, and hypoosmotic swelling tail coiled sperms with an increase in morphological abnormalities in sperms. Testicular steroidogenic enzyme activity levels and serum testosterone levels were significantly decreased in rats exposed to DBP during embryonic development. In conclusion, transplacental exposure to DBP impairs male reproductive performance by decreasing steroidogenesis and spermatogenesis.

Di-n-butyl phthalate causes estrogenic effects in adult male Murray rainbowfish (Melanotaenia fluviatilis)

Phthalic acid esters (PAEs) are a class of synthetic industrial chemicals commonly found in the aquatic environment worldwide. PAEs have been recognised as anti-androgens in male mammals but little is known about their endocrine disrupting effects in fish. This study investigated the effects of 7-day exposures to nominal (measured) concentrations of 125 (62), 250 (140), 500 (230) and 1,000 (383) μg/L of di-n-butyl phthalate (DnBP) on the biomarkers of reproduction in adult male Murray River rainbowfish (Melanotaenia fluviatilis) using molecular, biochemical and histological endpoints. None of the tested concentrations of DnBP had any effect on survival or the vital body indices of the fish. The sizes of spermatogonia, Type A and B spermatocytes and spermatids were significantly smaller relative to the controls after treatment with DnBP. This was accompanied by a significant increase in the proportion of spermatogonia in fish treated with 250-1,000 μg/L of DnBP in comparison to the unexposed fish. At the end of the exposure period, the expressions of the transcripts for the androgen receptors α and β were significantly elevated in the livers of the fish treated with 500 and 1,000 μg/L of DnBP. In addition, there was also an increase in the circulating concentrations of vitellogenin in the plasma in the higher treatment groups. An induction in the activity of aromatase was noted in the brains of 1,000 μg/L DnBP-treated fish. This was accompanied by an increase in the hepatic expression of the genes (here and later, whenever the phrase gene expression is used as a synonym for gene transcription although it is acknowledged that it is also regulated, e.g., by translation, mRNA stability and protein stability) encoding for the oestrogen receptors α and β and choriogenin L. Collectively, an increase in the proportion of spermatogonia in the testes, the upregulation of the genes for the oestrogen receptors and choriogenin in the liver, an induction in the brain aromatase activity and the increase in the circulating levels of plasma vitellogenin suggest that continuous exposures for 7 days to sub-acute concentrations of DnBP can adversely affect the reproductive health of the male Murray rainbowfish by an estrogenic mode of action.

Using mouse models of autism spectrum disorders to study the neurotoxicology of gene-environment interactions

To better study the role of genetics in autism, mouse models have been developed which mimic the genetics of specific autism spectrum and related disorders. These models have facilitated research on the role genetic susceptibility factors in the pathogenesis of autism in the absence of environmental factors. Inbred mouse strains have been similarly studied to assess the role of environmental agents on neurodevelopment, typically without the complications of genetic heterogeneity of the human population. What has not been as actively pursued, however, is the methodical study of the interaction between these factors (e.g., gene and environmental interactions in neurodevelopment). This review suggests that a genetic predisposition paired with exposure to environmental toxicants plays an important role in the etiology of neurodevelopmental disorders including autism, and may contribute to the largely unexplained rise in the number of children diagnosed with autism worldwide. Specifically, descriptions of the major mouse models of autism and toxic mechanisms of prevalent environmental chemicals are provided followed by a discussion of current and future research strategies to evaluate the role of gene and environment interactions in neurodevelopmental disorders.

Male reprotoxicity and endocrine disruption

Mammalian reproductive tract development is a tightly regulated process that can be disrupted following exposure to drugs, toxicants, endocrine-disrupting chemicals (EDCs), or other compounds via alterations to gene and protein expression or epigenetic regulation. Indeed, the impacts of developmental exposure to certain toxicants may not be fully realized until puberty or adulthood when the reproductive tract becomes sexually mature and altered functionality is manifested. Exposures that occur later in life, once development is complete, can also disrupt the intricate hormonal and paracrine interactions responsible for adult functions, such as spermatogenesis. In this chapter, the biology and toxicology of the male reproductive tract is explored, proceeding through the various life stages including in utero development, puberty, adulthood, and senescence. Special attention is given to the discussion of EDCs, chemical mixtures, low-dose effects, transgenerational effects, and potential exposure-related causes of male reproductive tract cancers.

The human relevant potency threshold: reducing uncertainty by human calibration of cumulative risk assessments

The 2008 National Research Council report "Phthalates and Cumulative Risk Assessment: Tasks Ahead," rejected the underlying premises of TEQ-like approaches - e.g., chemicals are true congeners; are metabolized and detoxified similarly; produce the same biological effects by the same mode of action; exhibit parallel dose response curves - instead asserting that cumulative risk assessment should apply dose addition (DA) to all chemicals that produce "common adverse outcomes" (CAOS). Published mixtures data and a human health risk assessment for phthalates and anti-androgens were evaluated to determine how firmly the DA-CAOS concept is supported and with what level of statistical certainty the results may be extrapolated to lower doses in humans. Underlying assumptions of the DA-CAOS concept were tested for accuracy and consistency against data for two human pharmaceuticals and its logical predictions were compared to human clinical and epidemiological experience. Those analyses revealed that DA-CAOS is scientifically untenable. Therefore, an alternative approach was developed - the Human-Relevant Potency-Threshold (HRPT) - that appears to fit the data better and avoids the contradictions inherent in the DA-CAOS concept. The proposed approach recommends application of independent action for phthalates and other chemicals with potential anti-androgenic properties at current human exposure levels.

Testicular connexin 43, a precocious molecular target for the effect of environmental toxicants on male fertility

Many recent epidemiological, clinical and experimental findings support the hypothesis that environmental toxicants are responsible for the increasing male reproductive disorders (congenital malformations, declining sperm counts and testicular cancer) over the past 20 years. It has also been reported that exposure to these toxicants, during critical periods of development (fetal and neonatal), represents a more considerable risk for animals and humans than exposure during adulthood. However, the molecular targets for these chemicals have not been clearly identified. Recent studies showed that a family of transmembranous proteins, named connexins, regulates numerous physiological processes involved in testicular development and function, such as Sertoli and germ cell proliferation, differentiation, germ cell migration and apoptosis. In the testis, knockout strategy revealed that connexin 43, the predominant connexin in this organ, is essential for spermatogenesis. In addition, there is evidence that many environmental toxicants could alter testicular connexin 43 by dysregulation of numerous mechanisms controlling its function. In the present work, we propose first to give an overview of connexin expression and intercellular gap junction coupling in the developing fetal and neonatal testes. Second, we underline the impact of maternally chemical exposure on connexin 43 expression in the perinatal developing testis. Lastly, we attempt to link this precocious effect to male offspring fertility.

Evaluation of EPA's Tier 1 Endocrine Screening Battery and recommendations for improving the interpretation of screening results

EPA's Endocrine Disruptor Screening Program (EDSP) was implemented in 2009-2010 with the issuance of test orders requiring manufacturers and registrants of 58 pesticide active ingredients and nine pesticide inert/high production volume chemicals to evaluate the potential of these chemicals to interact with the estrogen, androgen and thyroid hormone systems. The required endocrine screening will be conducted over the next 2-3years. Based on estimates of the impacted sectors, costs are at least $750,000-$1,000,000 per substance if all of the Tier 1 assays must be conducted. The screening will entail evaluation of responses in EPA's Tier 1 Endocrine Screening Battery (EDSP ESB), consisting of 11 distinct in vitro and in vivo assays. We reviewed the details of each test method and describe the critical factors integral to the design and conduct of the EDSP ESB assays as well as the limitations related to specificity and sensitivity. We discuss challenges to evaluating each assay, identify significant shortcomings, and make recommendations to enhance interpretation of results. Factors that affect the length of time necessary to complete the EDSP ESB for any particular substance are presented, and based on the overall analysis, we recommend a sequence for running the EDSP ESB assays. It is imperative that a structured, systematic weight of evidence framework is promptly developed, subjected to peer review and adopted. This will help to ensure an objective analysis of the results of the required EDSP screening, consistent integration of results across the EDSP ESB assays, and consistent decision making as to whether subsequent testing for adverse effects is needed. Based upon the limitations of the current EPA EDSP ESB, we concur with the Agency's Scientific Advisory Panel's recommendation that after the initial set of substances has been screened, the EDSP ESB should pause so that the results can be fully analyzed to determine the value of the existing assays. After this analysis, assays that are unnecessarily redundant or that lack endocrine specificity should be eliminated and if necessary, replaced by new or revised screens that are more mechanistically specific, rapid, reliable, and cost effective.

Use of genomic data in risk assessment case study: I. Evaluation of the dibutyl phthalate male reproductive development toxicity data set

A case study was conducted, using dibutyl phthalate (DBP), to explore an approach to using toxicogenomic data in risk assessment. The toxicity and toxicogenomic data sets relative to DBP-related male reproductive developmental outcomes were considered conjointly to derive information about mode and mechanism of action. In this manuscript, we describe the case study evaluation of the toxicological database for DBP, focusing on identifying the full spectrum of male reproductive developmental effects. The data were assessed to 1) evaluate low dose and low incidence findings and 2) identify male reproductive toxicity endpoints without well-established modes of action (MOAs). These efforts led to the characterization of data gaps and research needs for the toxicity and toxicogenomic studies in a risk assessment context. Further, the identification of endpoints with unexplained MOAs in the toxicity data set was useful in the subsequent evaluation of the mechanistic information that the toxicogenomic data set evaluation could provide. The extensive analysis of the toxicology data set within the MOA context provided a resource of information for DBP in attempts to hypothesize MOAs (for endpoints without a well-established MOA) and to phenotypically anchor toxicogenomic and other mechanistic data both to toxicity endpoints and to available toxicogenomic data. This case study serves as an example of the steps that can be taken to develop a toxicological data source for a risk assessment, both in general and especially for risk assessments that include toxicogenomic data.

The concordance between serum anti-Mullerian hormone and testosterone concentrations depends on duration of hCG stimulation in boys undergoing investigation of gonadal function

BACKGROUND

In boys undergoing investigation of gonadal function, the relationship between a single measurement of serum anti-Mullerian hormone (AMH) and hCG stimulated serum testosterone is unclear.

AIM

The aim of the study was to assess concordance between serum AMH and testosterone concentrations following hCG stimulation of two different durations.

METHODS

Samples from 284 children (M : F, 154 : 130) with a median age of 8 years (10th, 90th centiles, 0.25, 14) were used to establish an AMH reference range. Clinical data were reviewed in boys undergoing investigation of gonadal function and who had an AMH measurement and a hCG stimulated (3-day or 3-week) (n = 26) testosterone. Of these 26 boys, 11 had combined genital anomalies, whereas the rest had conditions such as isolated hypospadias, undescended testes or microphallus. Normal testosterone response to hCG stimulation was defined as a level greater than 3.5 nmol at day 4 and 9.5 nmol/l at day 22.

RESULTS

In the reference group, the 5th centile AMH for boys below 1 year was 215 pmol/l and between 1 and 8 years 180 pmol/l. The 95th centile for girls for these respective age groups was 30 pmol/l and 25 pmol/l. In those cases where serum testosterone concentrations were available at day 1, day 4 and day 22 of the 3 week-hCG test, five cases had a normal serum testosterone at day 4 and three cases only showed such a response by day 22. In those where serum AMH was less than 180 pmol/l, a poor testosterone response of less than 3.5 nmol was observed in approximately seven of eight (88%) cases with a 3-day hCG stimulation test or the 3-week test. An AMH of greater than 180 pmol/l was associated with a normal testosterone response at day 4 in 10 out of 15 (67%) cases and at day 22 in eight of 11 (73%) cases. However, a low serum testosterone concentration of less than 3.5 nmol after the 3-day hCG test was only associated with a likelihood of a low AMH in three of eight (37%) cases. With the 3-week hCG test, a low day 22 testosterone of 9.5 mmol/l or less was associated with a low AMH of 180 pmol/l or less in four of seven (57%) cases.

CONCLUSION

In boys undergoing investigation of gonadal function, the concordance between AMH and testosterone is better at day 22 than day 4. A normal AMH may provide useful information on overall testicular function but does not exclude the need for an hCG stimulation test.

Gap junctional intercellular communication as a target for liver toxicity and carcinogenicity

Direct communication between hepatocytes, mediated by gap junctions, constitutes a major regulatory platform in the control of liver homeostasis, ranging from hepatocellular proliferation to hepatocyte cell death. Inherent to this pivotal task, gap junction functionality is frequently disrupted upon impairment of the homeostatic balance, as occurs during liver toxicity and carcinogenicity. In the present paper, the deleterious effects of a number of chemical and biological toxic compounds on hepatic gap junctions are discussed, including environmental pollutants, biological toxins, organic solvents, pesticides, pharmaceuticals, peroxides, metals and phthalates. Particular attention is paid to the molecular mechanisms that underlie the abrogation of gap junction functionality. Since hepatic gap junctions are specifically targeted by tumor promoters and epigenetic carcinogens, both in vivo and in vitro, inhibition of gap junction functionality is considered as a suitable indicator for the detection of nongenotoxic hepatocarcinogenicity.

Long-term effects of environmental endocrine disruptors on reproductive physiology and behavior

It is well established that, over the course of development, hormones shape the vertebrate brain such that sex specific physiology and behaviors emerge. Much of this occurs in discrete developmental windows that span gestation through the prenatal period, although it is now becoming clear that at least some of this process continues through puberty. Perturbation of this developmental progression can permanently alter the capacity for reproductive success. Wildlife studies have revealed that exposure to endocrine disrupting compounds (EDCs), either naturally occurring or man made, can profoundly alter reproductive physiology and ultimately impact entire populations. Laboratory studies in rodents and other species have elucidated some of the mechanisms by which this occurs and strongly indicate that humans are also vulnerable to disruption. Use of hormonally active compounds in human medicine has also unfortunately revealed that the developing fetus can be exposed to and affected by endocrine disruptors, and that it might take decades for adverse effects to manifest. Research within the field of environmental endocrine disruption has also contributed to the general understanding of how early life experiences can alter reproductive physiology and behavior through non-genomic, epigenetic mechanisms such as DNA methylation and histone acetylation. These types of effects have the potential to impact future generations if the germ line is affected. This review provides an overview of how exposure to EDCs, particularly those that interfere with estrogen action, impacts reproductive physiology and behaviors in vertebrates.

Reproductive and developmental toxicity of phthalates

The purposes of this review are to (1) evaluate human and experimental evidence for adverse effects on reproduction and development in humans, produced by exposure to phthalates, and (2) identify knowledge gaps as for future studies. The widespread use of phthalates in consumer products leads to ubiquitous and constant exposure of humans to these chemicals. Phthalates were postulated to produce endocrine-disrupting effects in rodents, where fetal exposure to these compounds was found to induce developmental and reproductive toxicity. The adverse effects observed in rodent models raised concerns as to whether exposure to phthalates represents a potential health risk to humans. At present, di(2-ethylhexyl) phthalate (DEHP), di-n-butyl phthalate (DBP), and butyl benzyl phthalate (BBP) have been demonstrated to produce reproductive and developmental toxicity; thus, this review focuses on these chemicals. For the general population, DEHP exposure is predominantly via food. The average concentrations of phthalates are highest in children and decrease with age. At present, DEHP exposures in the general population appear to be close to the tolerable daily intake (TDI), suggesting that at least some individuals exceed the TDI. In addition, specific high-risk groups exist with internal levels that are several orders of magnitude above average. Urinary metabolites used as biomarkers for the internal levels provide additional means to determine more specifically phthalate exposure levels in both general and high-risk populations. However, exposure data are not consistent and there are indications that secondary metabolites may be more accurate indicators of the internal exposure compared to primary metabolites. The present human toxicity data are not sufficient for evaluating the occurrence of reproductive effects following phthalate exposure in humans, based on existing relevant animal data. This is especially the case for data on female reproductive toxicity, which are scarce. Therefore, future research needs to focus on developmental and reproductive endpoints in humans. It should be noted that phthalates occur in mixtures but most toxicological information is based on single compounds. Thus, it is concluded that it is important to improve the knowledge of toxic interactions among the different chemicals and to develop measures for combined exposure to various groups of phthalates.