Endocrine modulation of reproduction

Mate choice, sexual selection, and endocrine-disrupting chemicals

Humans have disproportionately affected the habitat and survival of species through environmental contamination. Important among these anthropogenic influences is the proliferation of organic chemicals, some of which perturb hormone systems, the latter referred to as endocrine-disrupting chemicals (EDCs). EDCs are widespread in the environment and affect all levels of reproduction, including development of reproductive organs, hormone release and regulation through the life cycle, the development of secondary sexual characteristics, and the maturation and maintenance of adult physiology and behavior. However, what is not well-known is how the confluence of EDC actions on the manifestation of morphological and behavioral sexual traits influences mate choice, a process that requires the reciprocal evaluation of and/or acceptance of a sexual partner. Moreover, the outcomes of EDC-induced perturbations are likely to influence sexual selection; yet this has rarely been directly tested. Here, we provide background on the development and manifestation of sexual traits, reproductive competence, and the neurobiology of sexual behavior, and evidence for their perturbation by EDCs. Selection acts on individuals, with the consequences manifest in populations, and we discuss the implications for EDC contamination of these processes, and the future of species.

Co-Administration of Vitamin E and Testosterone Attenuates The Atrazine-Induced Toxic Effects on Sperm Quality and Testes in Rats

OBJECTIVE

Atrazine (ATZ) as a widely used herbicide is considered as a potent endocrine disrupter which adversely affects reproductive systems in both genders. This study aimed to assess the effects of testosterone (T)- and vitamin E (VitE)- alone and their coadministration on testicular function and sperm parameters after exposure to ATZ in rats.

MATERIALS AND METHODS

In this experimental study, the rats (n=30) are assigned into the following 5 groups: control-sham group (n=6) receiving corn oil, ATZ group (n=6) receiving 200 mg/kg ATZ alone, ATZ+VitE group (n=6) receiving 150 mg/kg ATZ+VitE, ATZ+T group (n=6) receiving 400 µg/kg ATZ+T, and ATZ+VitE+T group (n=6) receiving ATZ+VitE+T for 48 consecutive days. Total antioxidant capacity (TAC), total thiol molecules (TTM), and malondialdehyde (MDA) were analyzed. Serum levels of T, luteinizing hormone (LH), and inhibin-B (IN-B) were also determined. Histological examination and sperm analysis were performed. The data were analyzed using Graph-Pad Prism software version 2.01.

RESULTS

Co-administration of VitE and T significantly (P<0.05) increased ATZ-decreased TAC and TTM levels and reduced ATZ-increased MDA content. T and VitE significantly (P<0.05) increased serum levels of ATZ-reduced T (1.94 ± 0.96), IN-B (122.10 ± 24.33) and LH (0.40 ± 0.10). The T+VitE animals showed a reduction in apoptotic cells and an increase in Leydig cells steroidogenesis. Co-administration of T and VitE significantly (P<0.05) reduced the ATZ-induced DNA disintegrity and chromatin de-condensation. VitE and T protected germinal cells RNA and protein contents against ATZ-induced damages.

CONCLUSION

T and VitE in simultaneous form of administration were able to normalize the ATZ-induced derangements through promoting antioxidant capacity and endocrine function.

Changes in equol and major soybean isoflavone contents during processing and storage of yogurts made from control or isoflavone-enriched bovine milk determined using LC-MS (TOF) analysis

The effect of supplementing a basal diet for dairy cows with "Soybean extract 40" (Biomedica, Prague, Czech Republic), containing 40% soybean isoflavones, on the contents of daidzein, glycitein, genistein, and equol in milk as well as fresh and mature yogurts was estimated. To determine the contents of these isoflavonoids, an efficient analytical LC-MS (TOF) technique was used. The "Soybean extract 40" used in our study contained an especially high proportion of daidzein (307gkg-1). In both milk and yogurt samples, the amounts of daidzein and its metabolite equol were significantly higher in samples obtained from cows that received the isoflavone extract-supplemented diet than from those that received the basal diet, as the precursor daidzein contributed to the increased equol concentrations. Fermentation caused significant changes in the daidzein and glycitein concentrations. With maturation, the concentrations of daidzein and equol were unaffected, while the glycitein concentration decreased significantly.

Interactions of triazine herbicides with biochar: Steric and electronic effects

We studied the adsorption of triazine herbicides and several reference heteroaromatic amines from water onto a temperature series of hardwood biochars (300-700 °C, labeled B300-B700). Adsorption on biochars correlated poorly with pyrolysis temperature, H/C, O/C, mean minimum fused ring size, surface area (N2 or CO2), microporosity, and mesoporosity, but correlated well with a weighted sum of microporosity and mesoporosity. Steric effects were evident by the negative influence of solute molecular volume on adsorption rate. For a given compound, adsorption rate maximized for the biochar with the greatest mesoporosity-to-total-porosity ratio, suggesting that mesopores are important for facilitating diffusion into pore networks. The cationic forms of amines adsorb more slowly than the neutral forms. To further probe steric and electronic effects, adsorption on a biochar (B400) was compared to adsorption on graphite-a nonporous reference material with an unhindered, unfunctionalized graphene surface-and in comparison with reference compounds (benzene, naphthalene, pyridine, quinoline and 1,3-triazine). Relative to benzene, the surface area-normalized adsorption of the triazine herbicides was disfavored on B400 (favored on graphite) by 11-19 kJ/mol, depending on concentration. It is estimated that steric suppression of B400 adsorption comprises 6.2 kJ/mol of this difference, the remainder being the difference in polar electronic effects. Based on the behavior of the reference amines, the difference in polar effects is dominated by π-π electron donor-acceptor (EDA) interactions with sites on polyaromatic surfaces, which are more electropositive and/or more abundant on graphite. Overall, our results show that mesoporosity is critical, that adsorption rate is a function of solute molecular size and charge, that steric bulk in the solute suppresses equilibrium adsorption, and that π-π EDA forces play a role in triazine polar interactions with biochar.

Feeding soybean meal increases the blood level of isoflavones and reduces the steroidogenic capacity in bovine corpora lutea, without affecting peripheral progesterone concentrations

Thirty-three Holstein-Friesian cows were followed from 14 days pre partum until the fourth ovulation post partum. Housing conditions and basic ration were identical for all animals. Concentrates were individually supplemented according to the daily milk production level, using two different types of protein rich concentrates: soybean meal and rapeseed meal. Soybean and rapeseed meal are known to be respectively high and low in isoflavones. Cows were randomly divided into three groups and blocked for parity. Group I (n=11) was supplemented with soybean meal and acted as control group. Groups II (n=11) and III (n=11) were respectively supplemented with soybean and rapeseed meal and were subjected to a biopsy sampling of the corpus luteum at day 9 of the first three postpartal estrous cycles. Soybean meal supplementation to lactating dairy cows (1.72 kg on average) induced an increase in the blood concentration of equol, dihydrodaidzein, o-desmethylangolensin in both soy groups and resulted in a reduced area occupied by steroidogenic (P=0.012) and endothelial cells (P=0.0007) in the luteal biopsies. Blood concentrations of equol and glycitein were negatively correlated with the areas occupied by steroidogenic (r=-0.410 with P=0.0002, respectively r=-0.351 with P=0.008) and endothelial cells (r=-0.337 with P=0.01, respectively r=-0.233 with P=0.085) in the 3 first estrous cycles. The latter however did not affect the diestrous peripheral blood progesterone concentration.

Hypothyroidism in adult male rats alters posttranscriptional mechanisms of luteinizing hormone biosynthesis

BACKGROUND

Studies in men are not consistent regarding the effects of thyroid hormone on the production of gonadotropins. In hypothyroidism consequent to diverse causes, an increase or no change in serum luteinizing hormone (LH) have been reported. The attempt to explain the mechanisms involved in this pathology using rats as an experimental model also seems to repeat this divergence, since hypothyroidism has been shown to induce hypogonadotropic hypogonadism, a hypergonadotropic state, or not to affect the basal levels of LH. Notably, the promoter region of the gene encoding the Lh beta subunit and GnRH (gonadotropin-releasing factor) does not contain a thyroid responsive element. Therefore, we investigated the hypothesis that, in male rats, posttranscriptional mechanisms of LH synthesis are altered in hypothyroidism. We also attempted to determine if hypothyroidism directly affects testicular function in male rats.

METHODS

Male Wistar rats, 60 days old, were thyroidectomized or sham-operated. After 20 days, they were decapitated, and the pituitaries were collected and analyzed for Lh mRNA, LH content, poly(A) tail length, and polysome profile. The testes were collected and analyzed for Lh receptor mRNA, LH receptor content, and histology using morphometric analyses. The testis, epididymis, seminal vesicle, and ventral prostate were weighed, and serum concentrations of LH, testosterone, thyrotropin (TSH), and triiodothyronine (T3) were measured.

RESULTS

Hypothyroidism was associated, in the pituitary, with an increase in Lh mRNA expression, a reduction in Lh mRNA poly(A) tail length, a reduction in the number of LH transcripts associated with polysomes. Pituitary LH was decreased but serum LH was increased from 102 to 543 pg/mL. Despite this, serum testosterone concentrations were decreased from 1.8 to 0.25 ng/mL. A decreased germinative epithelium height of the testes and a reduced weight of androgen-responsive tissues were observed (ventral prostrate: 74 vs. 23 mg/100 g body weight [BW]; seminal vesicle undrained: 280 vs. 70 mg/100 g BW; and seminal vesicle drained: 190 vs. 60 mg/100 g BW).

CONCLUSIONS

Hypothyroidism in adult male rats has dual effects on the pituitary testicular axis. It alters posttranscriptional mechanisms of LH synthesis and probably has a direct effect on testicular function. However, these data suggest the possibility that reduced LH bioactivity may account in part for impaired testicular function.

Atrazine and breast cancer: a framework assessment of the toxicological and epidemiological evidence

The causal relationship between atrazine exposure and the occurrence of breast cancer in women was evaluated using the framework developed by Adami et al. (2011) wherein biological plausibility and epidemiological evidence were combined to conclude that a causal relationship between atrazine exposure and breast cancer is “unlikely”. Carcinogenicity studies in female Sprague-Dawley (SD) but not Fischer-344 rats indicate that high doses of atrazine caused a decreased latency and an increased incidence of combined adenocarcinoma and fibroadenoma mammary tumors. There were no effects of atrazine on any other tumor type in male or female SD or Fischer-344 rats or in three strains of mice. Seven key events that precede tumor expression in female SD rats were identified. Atrazine induces mammary tumors in aging female SD rats by suppressing the luteinizing hormone surge, thereby supporting a state of persistent estrus and prolonged exposure to endogenous estrogen and prolactin. This endocrine mode of action has low biological plausibility for women because women who undergo reproductive senescence have low rather than elevated levels of estrogen and prolactin. Four alternative modes of action (genotoxicity, estrogenicity, upregulation of aromatase gene expression or delayed mammary gland development) were considered and none could account for the tumor response in SD rats. Epidemiological studies provide no support for a causal relationship between atrazine exposure and breast cancer. This conclusion is consistent with International Agency for Research on Cancer’s classification of atrazine as “unclassifiable as to carcinogenicity” and the United States Environmental Protection Agency's classification of atrazine as “not likely to be carcinogenic.”

Triazine Herbicides and Epithelial Ovarian Cancer Risk in Central California

OBJECTIVE

We sought to determine whether women with ovarian cancer have increased occupational exposure to triazine herbicides.

METHODS

A population-based case-control study of incident cases (n=256) and random digit-dialed control subjects (n=1122) was conducted. Participants were administered telephone interviews to obtain agricultural work history. These histories were used with the statewide pesticide usage database to calculate cumulative exposure estimates. The data were analyzed by stratified analysis and unconditional logistic regression techniques.

RESULTS

The analysis of ever versus never occupational exposure to triazines demonstrated that cases were slightly but not significantly more likely to be exposed than control subjects (adjusted odds=1.34; 95% confidence interval=0.77-2.33). There was no evidence of a dose-response relationship between triazines and ovarian cancer (P=0.22).

CONCLUSIONS

Considered with previous studies and animal laboratory data, the current evidence is not persuasive as to the presence or absence of an association between ovarian cancer and triazine exposure.

Environmental xenobiotics and nuclear receptors--interactions, effects and in vitro assessment

A group of intracellular nuclear receptors is a protein superfamily including arylhydrocarbon AhR, estrogen ER, androgen AR, thyroid TR and retinoid receptors RAR/RXR as well as molecules with unknown function known as orphan receptors. These proteins play an important role in a wide range of physiological as well as toxicological processes acting as transcription factors (ligand-dependent signalling macromolecules modulating expression of various genes in a positive or negative manner). A large number of environmental pollutants and other xenobiotics negatively affect signaling pathways, in which nuclear receptors are involved, and these modulations were related to important in vivo toxic effects such as immunosuppression, carcinogenesis, reproduction or developmental toxicity, and embryotoxicity. Presented review summarizes current knowledge on major nuclear receptors (AhR, ER, AR, RAR/RXR, TR) and their relationship to known in vivo toxic effects. Special attention is focused on priority organic environmental contaminants and experimental approaches for determination and studies of specific toxicity mechanisms.

Twenty-week exposures to the drinking water disinfection by-product dibromoacetic acid: reproductive cyclicity and steroid concentrations in the female Sprague–Dawley rat

Elevated gavage exposures to the drinking water disinfection by-product dibromoacetic acid (DBA) have been found to disrupt estrous cyclicity in the rat and induce increases in estradiol concentrations in both cycling (day of estrus) and ovariectomized/estradiol-implanted females. The present study was designed to investigate both effects in Sprague-Dawley rats following an extended 20-week treatment with lower dosages of DBA administered in the drinking water (calculated mean intake concentrations of 5, 16, and 33 mg/kg/d). No treatment-related effects on cyclicity were present, although elevations in serum estradiol on the day of vaginal estrus were noted in regularly cycling rats when assessed at the 3rd and 11th weeks of exposure. By the 19th week, this effect was no longer present in cycling animals, but its absence was attributable to a marked increase in control estradiol concentrations, which may be associated with endocrine alterations that precede a disruption in estrous cyclicity in middle-aged females. In the 20th week, diestrous estrone levels were elevated at all dosages without effects on serum androstenedione or progesterone. Uterine and pituitary weights were unchanged at this time, although there were modest increases in liver weights at the two highest dosages. A small number of rats in persistent estrus (PE) did show a general increase in pituitary weight associated with DBA exposure, possibly reflecting an added layering of treatment on the PE-associated rise in estradiol normally seen in these females. The results indicate that increases in circulating estradiol from drinking water exposures to DBA were not linked to a premature disruption of estrous cyclicity in this moderately estrogen-sensitive rat strain.

Inhibition of 17beta-hydroxysteroid dehydrogenases by phytoestrogens: comparison with other steroid metabolizing enzymes

Effects of phytoestrogens on human health have been reported for decades. These include not only beneficial action in cancer prevention but also endocrine disruption in males. Since then many molecular mechanisms underlying these effects have been identified. Targets of phytoestrogens comprise steroid receptors, steroid metabolising enzymes, elements of signal transduction and apoptosis pathways, and even the DNA processing machinery. Understanding the specific versus pleiotropic effects of selected phytoestrogens will be crucial for their biomedical application. This review will concentrate on the influence of phytoestrogens on 17beta-hydroxysteroid dehydrogenases from a comparative perspective with other steroid metabolizing enzymes.

Environmental and occupational factors affecting fertility and IVF success

Reproductive function has been shown to be sensitive to changes in the physical, psychosocial and chemical environments. Although reproductive effects of occupational exposure to hazardous chemicals have been well documented in the literature, the potential effects of chemical contaminants at levels representative of contemporary exposures in the general population are much less certain. Evidence for adverse effects of exposure to environmental contaminants is more conclusive among the lower animals than for humans where considerable controversy remains. In addition to potential reproductive hazards of exposure to environmental contaminants, there is also evidence for adverse reproductive effects of the physical and psychosocial environments. In this review we focus on the difficulties involved in linking exposure to putative hazardous substances in environmental and occupational settings to adverse reproductive outcomes, especially success of IVF procedures. We highlight the plausibility of adverse events through animal and cell studies and the application of these results to the interpretation of human data. We consider both the male and female partners since it is essentially their combined contributions of gametes which may be affected by chemicals, which lead to successful outcomes.

Toxicological characteristics of endocrine-disrupting chemicals: developmental toxicity, carcinogenicity, and mutagenicity

It is generally accepted that endocrine-disrupting chemicals (EDCs) play a role in a variety of adverse health effects in an intact organism or its progeny as a consequence of changes in the endocrine system. Primary toxic effects of EDCs were reported to be related to infertility, reduction in sperm count, and teratogenicity, but other important toxic effects of EDCs such as carcinogenicity and mutagenicity have also been demonstrated. The aim of the present study was to systematically analyze the toxicological characteristics of EDCs in pesticides, industrial chemicals, and metals. A comprehensive literature survey on the 48 EDCs classified by the Centers for Disease Control and Prevention (CDC) was conducted using a number of databases which included Medline, Toxline, and Toxnet. The survey results revealed that toxicological characteristics of EDCs were shown to produce developmental toxicity (81%), carcinogenicity (79%, when positive in at least one animal species; 48%, when classified based on IARC evaluation), mutagenicity (79%), immunotoxicity (52%), and neurotoxicity (50%). Regarding the hormone-modulating effects of the 48 EDCs, estrogenic effects were the most predominant in pesticides, while effects on thyroid hormone were found for heavy metals. EDCs showing estrogen-modulating effects were closely related to carcinogenicity or mutagenicity with a high degree of sensitivity. Systematic information on the toxicological characteristics of the EDCs will be useful for future research directions on EDCs, the development of new screening methods, legal regulation, and for investigations of their mechanism of action.

Mortality among triazine herbicide manufacturing workers

Atrazine produces mammary gland cancer in one strain of rats and has been classified as an endocrine modulator. Epidemiologic studies have reported associations between agricultural use of atrazine and several forms of cancer. This study evaluated mortality patterns among workers at a plant that made atrazine and other triazine herbicides. The study covered the time period 1970-1997 and included 2213 people employed for at least 6 mo in operations related to the manufacture or formulation of atrazine and other triazine herbicides at a plant in Louisiana (LA). Vital status was determined for all but six subjects. Standardized mortality ratios (SMRs) with 95% confidence intervals (CIs) compared employees' mortality rates with those of the LA industrial corridor general population. Subjects had a total of 32,473 person-years of observation and a median of 15.8 yr since hire. There were 84 observed/118 expected deaths from all causes combined (SMR = 72, CI = 57-89) and 22/21 total cancer deaths (SMR = 106, CI = 66-160). Subjects had 4/1.1 deaths from non-Hodgkin's lymphoma (SMR = 372, CI = 101-952); this increase was not concentrated in the subgroup with long duration of employment and many years since hire. There were 6/4.8 (SMR = 124, CI = 46-271) digestive cancer and 7/6.3 (SMR = 112, CI = 45-230) lung cancer deaths. Data on other forms of cancer were sparse. This study was limited by its small size, by the relatively young age and short follow-up of its subjects, and by the lack of exposure data. It did not provide evidence that employment in triazine herbicide manufacturing and formulating operations was associated causally with overall or cause-specific mortality.

Developmental, behavioral, and reproductive effects experienced by Japanese medaka (Oryzias latipes) in response to short-term exposure to endosulfan

Japanese medaka (Oryzias latipes) were exposed to concentrations of 0.01, 0.10, and 1.0 microg/L of the pesticide endosulfan for 24h beginning either 4-6h postfertilization or 4-6h posthatch to determine effects on hatching time, growth, mobility, foraging ability, and reproduction. Eggs exposed to endosulfan took longer to hatch, and the resulting fry were smaller at 1 week of age and had decreased mobility at 2 weeks of age. Upon reaching sexual maturity, these individuals also produced fewer eggs, and these eggs took significantly longer to hatch. Medaka exposed to endosulfan shortly after hatching did not differ in early mobility or foraging ability. Interestingly, upon reaching sexual maturity, these individuals produced more eggs than did unexposed females. The observed effects were not dose-dependent, with medaka exposed to intermediate concentrations of endosulfan (0.10 microg/L) exhibiting the greatest response. These results suggest that short-term exposure to environmentally relevant concentrations of a common pesticide may have long-term effects on growth, behavior, and reproduction in fish.

Phytoestrogens as modulators of steroid action in target cells

Although numerous reports exist on the potential beneficial role of nutritional phytoestrogens in human health, their molecular mechanism in target cells is still not completely understood. Phytoestrogens promote estrogen and antiestrogen effects by interacting with numerous molecules, carrier proteins, enzymes and membrane and nuclear receptors, directly or indirectly involved in the transfer of estrogen signals. The hypothesis that the ER beta subtype plays a key role in antiproliferative effect of phytoestrogens, especially in breast cancer, is examined here. This review focus on the effects of phytoestrogens in developmental processes such as those linked to reproductive function, tumorigenesis and angiogenesis.

Cancer incidence among triazine herbicide manufacturing workers

This study evaluated cancer incidence and prostate specific antigen (PSA) testing among workers at a plant in Louisiana (LA) that made atrazine and other triazine herbicides. The study covered the time period 1985 through 1997 and included 2045 subjects, of whom 757 worked for the company that owned the plant and 1288 were contract employees. Linkage with a population-based cancer registry and review of death certificates and plant medical records identified cancer cases. Standardized incidence ratios (SIRs) with 95% confidence intervals (CIs) compared subjects' cancer incidence rates with those of a regional general population. Plant medical records provided data on the proportion receiving PSA tests among male company employees. Subjects had 46 observed and 40 expected cases of all cancers combined (SIR = 114, CI = 83-152) and had 11/6.3 prostate cancers (SIR = 175, CI = 87-312). The prostate cancer excess was greater in actively working company employees (5/1.3, SIR = 394, CI = 128-920) than in contract employees or inactive company employees (6/5.0, SIR = 119, CI = 44-260) and was limited to men under 60 years of age. Of the 11 prostate cancer cases, nine were diagnosed at an early clinical stage. From 1993 to 1999, the proportion of male company employees who had at least one PSA test was 86% for those who reached 40 years of age while actively working and was 98% for those who reached 45 years of age. The observed prostate cancer increase may have been due to the frequent PSA testing of actively working company employees. There is no epidemiologic or other information that clearly supports a causal relation between atrazine and prostate cancer.

Human reproductive system disturbances and pesticide exposure in Brazil

The observation of reproductive disturbances in humans and in the wildlife has been reported in the last decade in different countries. Exposure to different chemicals possibly acting in the endocrine system or endocrine disruptors, including pesticides, has been a hypothesis raised to explain the observed changes. This paper aimed to present results of an epidemiological ecologic study carried out to explore population data on pesticides exposure in selected Brazilian states in the eighties and human reproductive outcomes in the nineties. Pearson correlation coefficients were ascertained between available data pesticides sales in eleven states in Brazil in 1985 and selected further reproductive outcomes or their surrogates. Moderate to high correlations were observed to infertility, testis, breast, prostate and ovarian cancer mortality. Despite the restrains of ecologic studies to establish cause-effect relationships, the observed results are in agreement with evidence supporting a possible association between pesticides exposure and the analyzed reproductive outcomes.

Neonatal low- and high-dose exposure to estradiol benzoate in the male rat: II. Effects on male puberty and the reproductive tract

Environmental contaminants with estrogenic properties have been cause for heightened concern about their possible role in inducing adverse health effects. Brief exposure of rodents to high doses of natural estrogens early in life results in permanent alterations of the male reproductive tissues, but the question of whether environmentally relevant doses can cause the same effects remains controversial. The current project was designed to determine the dose-response relationship between neonatal estradiol exposure and the development of the male reproductive tract in the rat. Neonatal male Sprague-Dawley (SD) and Fisher 344 (F344) rats were exposed to beta-estradiol-3-benzoate (EB) at concentrations ranging from 0.015 microg/kg body weight (BW) to 15.0 mg/kg BW and 0.15 microg/kg BW to 1.5 mg/kg BW, respectively. Results showed an inverted U-shaped dose-response profile for testis and epididymis weights in 35-day-old SD rats, with increased organ sizes at the low-dose end of the treatment. This effect was transient and was not sustained into adulthood. Increased hepatic testosterone hydroxylase activities in low-dose animals suggest an advancement of puberty as the cause for increased reproductive organ weights. On postnatal day (PND) 90, a stimulatory low-dose response to EB was present in SD rat testicular and epididymal weights, however at one order of magnitude lower dose than that seen on PND 35, suggesting a separate effect. All SD male reproductive tract organs and serum hormones showed a permanent inhibitory response to high doses of neonatal EB. F344 rats exhibited greater estrogen sensitivity on PND 90. Despite this heightened responsiveness, F344 rats did not exhibit a low-dose effect for any endpoint. These low-dose responses to estradiol are organ and strain specific.

Reproductive effects in male and female rats of neonatal exposure to genistein

Sprague-Dawley rats were administered genistein orally at doses of 12.5, 25, 50, or 100 mg/kg on postnatal days 1 through 5 to examine its effects on reproductive function after puberty. In addition, preputial separation and vaginal opening as endpoints of sexual maturation, estrous cycling, sperm count, serum testosterone concentration, and histopathologic changes of reproductive organs of male and female rats were examined. Body weights of male and female rats exposed to genistein at any dose level examined were lower than those of controls. Timing of preputial separation in males and timing of vaginal opening were not affected by genistein treatment. The number of females showing estrous cycle irregularities was increased by genistein treatment. The fertility of female rats exposed neonatally to genistein at 100 mg/kg was disrupted, while neonatal exposure to genistein did not affect male fertility. Neither sperm counts nor serum testosterone concentration were changed by neonatal exposure to genistein. Female rats exposed neonatally to genistein at 100 mg/kg showed histopathologic changes in the ovaries and uterus, while male rats showed no histopathologic alterations in the gonads. The results of this study indicate that early neonatal exposure to genistein caused dysfunction of postpubertal reproductive performance as well as abnormal development of gonads in female but not in male rats.

Residential pesticide exposure and neuroblastoma

Neuroblastoma is the most common neoplasm in children under 1 year of age. We examined the relation between residential exposure to pesticides and neuroblastoma, using data from a case-control study of risk factors for neuroblastoma. Incident cases of neuroblastoma (N = 538) were identified through the Pediatric Oncology Group and the Children's Cancer Group. One age-matched control was identified for each case by random digit dialing. Telephone interviews with each parent collected information on residential exposure to pesticides. Pesticide use in both the home and garden were modestly associated with neuroblastoma [odds ratio (OR) = 1.6 (95% confidence interval [95% CI] = 1.0-2.3, and OR = 1.7 (95% CI = 0.9-2.1), respectively]. Compared with infants [OR = 1.0 (95% CI = 0.6-2.0)], stronger associations were found for garden pesticides in children diagnosed after 1 year of age [OR = 2.2 (95% CI = 1.3-3.6)], which suggests that pesticides may act through a mechanism more common for neuroblastomas in older children. There was no evidence of differential pesticide effects in subgroups of neuroblastoma defined by MYCN oncogene amplification or tumor stage.

An introduction to endocrine modulators

Keywords. Endocrine modulation; target sites; endocrine modulating effects; humans; reproduction; marine invertebrates; wildlife

Endocrine modulators in the food chain and environment

Recently, considerable attention has been focused on certain environmental contaminants--"endocrine disruptors"--of industrial origin that may mimic the action of sex hormones. Natural compounds and their effects on other types of hormonal activity (eg, on adrenal or thyroid function) have for some reason not provoked similar attention. As exemplified by tributyltin and certain bioaccumulating chlorinated compounds, available evidence indicates that "endocrine disruption" caused by xenobiotics is primarily an ecotoxicologic problem. In mammals, certain phenylmethyl-substituted siloxanes have been found to be by far the most potent endocrine disrupters among various synthetic xenobiotics. On the other hand, it has not been possible to scientifically substantiate either certain alarming reports of powerful synergistic effects between chlorinated pesticides or the alleged adverse effects on the male reproductive tract in rodents (induced by alkylphenols and plasticizers at extremely low exposures). Whereas there is compelling evidence that estrogens in certain foods and herbal medicines can induce hormonal changes in women as well as overt toxicity in men, existing data are insufficient to support a causal relationship between exposure of the general human population to nonpharmaceutical industrial chemicals and adverse effects operating via the endocrine system. Moreover, in terms of magnitude and extent, all such exposures to so-called endocrine disruptors are dwarfed by the extensive use of oral contraceptives and estrogens for treatment of menopausal and postmenopausal disorders. Also, the exposure to hormonally active xenobiotics is virtually insignificant when compared with the intake of the phytoestrogens that are present in food and beverages, and it is even more insignificant when compared with certain herbal potions used in "alternative medicine." Furthermore, while there has been much concern about negligible exposures to xenobiotics with weak hormonelike activities, the potent endocrine disruptor licorice is freely given to children. Long-term exposure to this substance induces severe toxic symptoms of mineral corticoid hormone imbalance. Although exposures to xenobiotics and many natural compounds occur by identical routes of administration and may contribute to the same toxicological end point, they are, regrettably, judged by completely different standards. As is the case with all other chemicals, rational risk assessment and risk management of man-made and natural endocrine modulators must be based on the mode of action and dose-response relationships. Such end points as the induction of reproductive developmental effects, cancer, etc, relating to actual exposures must also be taken into consideration.

Validation of in vitro and in vivo methods for assessing endocrine disrupting chemicals

The concepts that require validation in terms of the subject of endocrine disruption are listed and discussed. The main mechanisms by which endocrine disruption can occur are identified, and the assays required for the detection of adverse endocrine disruption toxicities associated with these mechanisms are discussed. The process of assay validation is considered. The validation of structure-activity relationships, the need for reference chemicals, and the problems recently encountered when attempting to reproduce endocrine disruption data are also explored. The most important conclusions derived from this analysis are that given the immature state of research into endocrine disruption toxicity, testing strategies and the types of assay employed should be kept under constant review; inevitably researchers need to accept the fact that future revision of each assay will be required. Second, given the current absence of any chemical that is universally accepted to be devoid of endocrine toxicity, assay specificity will be difficult to assess, and that imposes the need for alternative objective criteria for assessing the value of individual assays.

Threshold of toxicological concern for chemical substances present in the diet: a practical tool for assessing the need for toxicity testing

The de minimis concept acknowledges a human exposure threshold value for chemicals below which there is no significant risk to human health. It is the underlying principle for the US Food and Drug Administration (FDA) regulation on substances used in food-contact articles. Further to this, the principle of Threshold of Toxicological Concern (TTC) has been developed and is now used by the Joint FAO/WHO Expert Committee on Food Additives (JECFA) in their evaluations. Establishing an accepted TTC would benefit consumers, industry and regulators, since it would preclude extensive toxicity evaluations when human intakes are below such threshold, and direct considerable time and cost resources towards testing substances with the highest potential risk to human health. It was questioned, however, whether specific endpoints that may potentially give rise to low-dose effects would be covered by such threshold. In this review, the possibility of defining a TTC for chemical substances present in the diet was examined for general toxicity endpoints (including carcinogenicity), as well as for specific endpoints, namely neurotoxicity and developmental neurotoxicity, immunotoxicity and developmental toxicity. For each of these endpoints, a database of specific no-observed-effect levels (NOELs) was compiled by screening oral toxicity studies. The substances recorded in each specific database were selected on the basis of their demonstrated adverse effects. For the neurotoxicity and developmental neurotoxicity databases, it was intended to cover all classes of compounds reported to have either a demonstrated neurotoxic or developmentally neurotoxic effect, or at least, on a biochemical or pharmacological basis were considered to have a potential for displaying such effects. For the immunotoxicity endpoint, it was ensured that only immunotoxicants were included in the database by selecting most of the substances from the Luster et al. database, provided that they satisfied the criteria for immunotoxicity defined by Luster. For the developmental toxicity database, substances were selected from the Munro et al. database that contained the lowest NOELs retrieved from the literature for more than 600 compounds. After screening these, substances showing any effect which could point to developmental toxicity as broadly defined by the US were recorded in the database. Additionally, endocrine toxicity and allergenicity were addressed as two separate cases, using different approaches and methodology. The distributions of NOELs for the neurotoxicity, developmental neurotoxicity and developmental toxicity endpoints were compared with the distribution of NOELs for non-specific carcinogenic endpoints. As the immunotoxicity database was too limited to draw such a distribution of immune NOELs, the immunotoxicity endpoint was evaluated by comparing immune NOELs (or LOELs-lowest-observed-effect levels-when NOELs were not available) with non-immune NOELs (or LOELs), in order to compare the sensitivity of this endpoint with non-specific endpoints. A different methodology was adopted for the evaluation of the endocrine toxicity endpoint since data currently available do not permit the establishment of a clear causal link between endocrine active chemicals and adverse effects in humans. Therefore, this endpoint was analysed by estimating the human exposure to oestrogenic environmental chemicals and evaluating their potential impact on human health, based on their contribution to the overall exposure, and their estrogenic potency relative to endogenous hormones. The allergenicity endpoint was not analysed as such. It was addressed in a separate section because this issue is not relevant to the overall population but rather to subsets of susceptible individuals, and allergic risks are usually controlled by other means (i.e. labelling) than the Threshold of Toxicological Concern approach. (ABSTRACT TRUNCATED)

An evaluation of endocrine modulators: implications for human health

The potential health risk of a group of chemicals, popularly known as "endocrine disrupters," has generated considerable scientific debate and media attention. The endocrine disrupter hypothesis asserts that exogenous substances with estrogenic or other hormonally active properties may adversely affect human health. Proponents of this hypothesis have associated endocrine modulators with negative outcomes such as cancer in hormonally sensitive tissues and declining sperm counts in men. However, the available laboratory, wildlife, and epidemiological data do not provide consistent or convincing evidence that industrial chemicals suspected of modulating estrogenic pathways are related to adverse health effects in humans. Both public and private initiatives are investigating chemicals labeled as endocrine disrupters for their relative hormonal activity. Screening assays aimed at assessing the endocrine activity or potential of a variety of substances should not be confused with assessment of risk to humans, however. The latter entails not only hazard identification (the type of information that screening assays are designed to provide), but also critical factors such as exposure analysis, potency assessment, and dose-response for individual chemicals.

Rodent Leydig cell tumorigenesis: a review of the physiology, pathology, mechanisms, and relevance to humans

Leydig cells (LCs) are the cells of the testis that have as their primary function the production of testosterone. LCs are a common target of compounds tested in rodent carcinogenicity bioassays. The number of reviews on Leydig cell tumors (LCTs) has increased in recent years because of its common occurrence in rodent bioassays and the importance in assessing the relevance of this tumor type to humans. To date, there have been no comprehensive reviews to identify all the compounds that have been shown to induce LCTs in rodents or has any review systematically evaluated the epidemiology data to determine whether humans were at increased risk for developing LCTs from exposure to these agents. This review attempts to fill these deficiencies in the literature by comparing the cytology and ontogeny of the LC, as well as the endocrine and paracrine regulation of both normal and tumorigenic LCs. In addition, the pathology of LCTs in rodents and humans is compared, compounds that induce LC hyperplasia or tumors are enumerated, and the human relevance of chemical-induced LCTs is discussed. There are plausible mechanisms for the chemical induction of LCTs, as typified by agonists of estrogen, gonadotropin releasing hormone (GnRH), and dopamine receptors, androgen receptor antagonists, and inhibitors of 5alpha-reductase, testosterone biosynthesis, and aromatase. Most of these ultimately involve elevation in serum luteinizing hormone (LH) and/or LC responsiveness to LH as proximate mediators. It is expected that further work will uncover additional mechanisms by which LCTs may arise, especially the role of growth factors in modulating LC tumorigenesis. Regarding human relevance, the pathways for regulation of the hypothalamo-pituitary-testis (HPT) axis of rats and humans are similar, such that compounds that either decrease testosterone or estradiol levels or their recognition will increase LH levels. Hence, compounds that induce LCTs in rats by disruption of the HPT axis pose a risk to human health, except for possibly two classes of compounds (GnRH and dopamine agonists). Because GnRH and prolactin receptors are either not expressed or are expressed at very low levels in the testes in humans, the induction of LCTs in rats by GnRH and dopamine agonists would appear not to be relevant to humans; however, the potential relevance to humans of the remaining five pathways of LCT induction cannot be ruled out. Therefore, the central issue becomes what is the relative sensitivity between rat and human LCs in their response to increased LH levels; specifically, is the proliferative stimulus initiated by increased levels of LH attenuated, similar, or enhanced in human vs. rat LCs? There are several lines of evidence that suggest that human LCs are quantitatively less sensitive than rats in their proliferative response to LH, and hence in their sensitivity to chemically induced LCTs. This evidence includes the following: (1) the human incidence of LCTs is much lower than in rodents even when corrected for detection bias; (2) several comparative differences exist between rat and human LCs that may contribute, at least in part, to the greater susceptibility of the rat to both spontaneous and xenobiotic-induced LCTs; (3) endocrine disease states in man (such as androgen-insensitivity syndrome and familial male precocious puberty) underscore the marked comparative differences that exist between rats and man in the responsiveness of their LC's to proliferative stimuli; and (4) several human epidemiology studies are available on a number of compounds that induce LCTs in rats (1,3-butadiene, cadmium, ethanol, lactose, lead, nicotine) that demonstrate no association between human exposure to these compounds and induction of LC hyperplasia or adenomas. (ABSTRACT TRUNCATED)

Evaluation of the placenta: suggestions for a greater role in developmental toxicology

Both in human and in rat, two types of placenta are present: the yolk sac (YS) and the chorioallantoic placenta. Histiotrophy, alpha-fetoprotein synthesis and blood cell formation occur in YS of both species. Besides, the midgut, primordial germ cells and possibly immunological structures originate from the YS tissue. The specialised cells of the chorioallantoic placenta attach the embryo to the uterus and form the vascular connections necessary for the nutrient transport. The placenta redirects maternal endocrine, immune and metabolic functions to conceptus advantage. These complex activities are sensitive to direct toxicity. Indirect effects on the placental functions might be elicited by immunomodulators and endocrine disrupters. Some experimental models could be utilised to identify possible toxic effects on placenta. Among the in vitro models the rodent giant yolk sac culture may be used to study the transport of materials, morphological and/or biochemical alterations and biotransformation activity of the visceral YS epithelium. Other in vitro approaches utilise human derived trophoblastic cells and tissues to investigate implantation and perimplantation toxicology. Besides specific studies, in vivo reproductive toxicity tests could pay more attention to the evaluation of placental tissues. Nowadays, some physiologically based pharmacokinetic models for developmental toxicity are also available to describe the disposition of toxic substances and their metabolites during pregnancy in rodents. Thus, more detailed studies on the embryo-foetal placenta may provide an important tool to understand developmental toxicity mechanisms, with particular regard to embryolethality and delayed development.

Environmental toxicants and female reproduction

OBJECTIVE

To review current knowledge on the potential effects of environmental toxicants on female reproduction in laboratory animals, wildlife, and humans.

DESIGN

Published literature about the effects of endocrine disruptors, heavy metals, solvents, pesticides, plastics, industrial chemicals, and cigarette smoke on female reproduction.

RESULT(S)

Published data indicate that chemical exposures may cause alterations in reproductive behavior and contribute to subfecundity, infertility, pregnancy loss, growth retardation, intrauterine fetal demise, birth defect, and ovarian failure in laboratory animals and wildlife. Data on the association of chemical exposures and adverse reproductive outcomes in humans are equivocal and often controversial. Some studies indicate that chemical exposures are associated with infertility, spontaneous abortion, or reproductive cancer in women. In contrast, other studies indicate that there is no association between chemical exposures and adverse reproductive outcomes. The reasons for ambiguous findings in human studies are unknown but likely include the fact that many studies are limited by multiple confounders, inadequate methodology, inappropriate endpoints, and small sample size. The mechanism by which chemicals alter reproductive function in all species is complex and may involve hormonal and/or immune disruption, DNA adduct formation, altered cellular proliferation, or inappropriate cellular death.

CONCLUSION(S)

Studies are needed to clarify which toxicants affect human reproduction and by which mechanisms of action. Furthermore, methods should be developed to minimize exposure to known reproductive toxicants such as dioxins and cigarette smoke.

The applicability of the ADI (Acceptable Daily Intake) for food additives to infants and children

Children are not little adults. Children may respond differently from adults because they are in a state of growth and development; or because of differences in toxicokinetics or toxicodynamics. Infants and children are often assumed to be more susceptible to toxic effects, but this generalization is founded on assumptions rather than on facts. Available data are mostly concerned with toxicity and therapeutic effects of pharmaceuticals, while the effects in children of industrial chemicals are less well documented. Childhood is characterized by growth and development. Toxicants may interfere with these processes, and therefore toxic exposure may have more serious consequences for children than for adults, irrespective of sensitivity. Immature physiological functions of the foetus and young child theoretically make these age groups more vulnerable to toxicants, at least up to 1 year of age. The existing data on effects of chemical exposure in children point in the direction that susceptibility depends on the substance and on the exposure situation. For a particular compound children may be more sensitive than adults, or they may be less sensitive. Further, the sensitivity of children to a particular substance varies greatly with age. It is necessary to view premature neonates, neonates, infants, and children of different ages as separate risk groups. The long-term studies used as the basis for establishing ADIs cover lifetime for laboratory animals. Methods which have special emphasis on reproductive cells, on the foetus, and on the immature organism are used. Taken together, these studies cover exposure during all life stages. However, some specific types of effects, and delayed effects of perinatal exposure are not always included in standard toxicity test protocols. Exposure may also differ between children and adults. The food intake of children is qualitatively and quantitatively different form that of adults, and the EU Scientific Committee for Food has recommended that intake assessment of children be considered separately from that of adults because patterns of consumption are different. The ADI should cover the entire population including children. Special considerations regarding the use of food additives do apply to infants below the age of 12 weeks, who depend entirely on infant formula for nutrition.

A review of epidemiologic studies of triazine herbicides and cancer

We evaluated epidemiologic evidence pertaining to the human carcinogenic potential of triazine herbicides in general and of atrazine, the most common triazine. Cancers for which data are available included non-Hodgkin's lymphoma, Hodgkin's disease, leukemia, multiple myeloma, soft tissue sarcoma, colon cancer, and ovarian cancer. The investigations had methodologic limitations, including lack of in-depth exposure measurements and small numbers of subjects with heavy exposure and/or with many years since starting exposure, possibly required for the induction of cancer. The relation between triazines and non-Hodgkin's lymphoma has been assessed in four independent population-based case-control studies, reporting odds ratios ranging from 1.2 to 2.5. However, chance and/or confounding by other agricultural exposures may have produced these weak statistical associations. Furthermore, a pooled analysis of three of the case-control studies and the combined analysis of two retrospective follow-up studies did not demonstrate the types of dose-response or induction time patterns that would be expected if triazines were causal factors. The epidemiologic data pertaining to Hodgkin's disease, leukemia, multiple myeloma, soft tissue sarcoma, colon cancer, and ovarian cancer were inadequate for determining whether associations with atrazine or triazines exist in humans. For each of these cancers, only one or two studies evaluating the relationship were available, and the results of the studies typically were imprecise.

Considerations in the design of studies of dietary influences on mammary carcinogenesis in rats and mice

Design of diets for the study of dietary influences in mammary gland carcinogenesis requires attention to several questions: (1) Do the diets satisfy the nutritional needs of the animal under the conditions of the experiment, and are they palatable? (2) Does the protocol include determination of feed intake (if indicated) and of achievement of the desired level of nutrient deficiency, adequacy, or excess? (3) Are there potentially confounding nutrient interactions or nutrient effects or physiological or pathological responses that must be considered? The particular sensitivity of mammary gland tumorigenesis to intake of fat and calories and to body weight gain must be considered and controlled for in all experiments.

Regulation of mouse liver flavin-containing monooxygenases 1 and 3 by sex steroids

Based on enzyme activity, protein levels, and mRNA levels, we have previously demonstrated the female-predominant, female-specific, and gender-independent expression in mouse liver of FMO forms 1, 3, and 5, respectively. This study investigated the roles of testosterone, 17 beta-estradiol, and progesterone in the regulation of hepatic FMOs. FMO expression was examined in gonadectomized CD-1 mice, normal CD-1 mice receiving hormonal implants, and gonadectomized mice receiving various hormonal treatments. Following castration of males, hepatic FMO activity levels were significantly increased and serum testosterone levels significantly decreased; however, administration of physiological levels of testosterone to castrated animals returned FMO activity and testosterone concentrations to control levels. When sexually intact and ovariectomized female mice were treated with testosterone, their hepatic FMO activity levels were reduced to those of their male counterparts, concomitant with high serum testosterone levels. In males, castration dramatically increased FMO3 and FMO1 expression, and testosterone replacement to castrated males resulted in ablation of FMO3 expression. In addition, testosterone administration to females (sexually intact and gonadectomized animals) reduced FMO1 expression and obviated FMO3 expression. In females, ovariectomy alone slightly reduced FMO activity, indicative of a possible stimulatory role of female sex steroids; however, female FMO isozyme expression was relatively unchanged, and hormone replacement therapy to ovariectomized females had no discernible effect. In males and females, FMO5 levels were unaffected by gonadectomy or hormone administration, thus indicating a sex hormone-independent mechanism of regulation for this isoform. Interestingly, FMO1 protein levels were increased in sexually intact males following treatment with 17 beta-estradiol; however, only a slight increase in FMO3 protein level was observed. No positive hormone effectors of female FMO expression were identified.

A hierarchical approach to the evaluation of chemicals for estrogenic and other endocrine-disrupting properties

The emergence of estrogenicity/endocrine-disruption as an important endpoint in the toxicological assessment of chemicals presents a series of problems to overcome before regulatory control of such agents can be enacted. A framework is presented by which progress in this endeavour can be expedited. A hierarchial approach to testing is proposed, together with consideration of the types of information required to transform test data into human risk estimations. The approach is based broadly on current methods for defining potential human carcinogens and mutagens, and if found acceptable, would dramatically accelerate regulatory progress on this subject. However, several questions must be answered, using focused data, before the approach can be endorsed or transferred into a regulatory context. The importance of early consideration of all aspects of this complex new toxicity, including the unexpected observation of synergism between synthetic estrogens, is emphasized.

Diet and breast cancer: studies in laboratory animals

Increasing dietary fat content increases mammary gland tumorigenesis in laboratory rodents. The effect can be attributed only in part to increasing energy intake, which itself increases tumorigenesis. Restriction of dietary or energy intake, sufficient to reduce body weight, reduces mammary gland tumorigenesis. Consideration of these effects has led to discussion of the possible need for changes in the feeding of laboratory rodents in carcinogenesis bioassays and other chronic studies. Studies of endocrine or other growth factors for the mammary gland have not identified specific effects of dietary fat or energy. In addition, tumorigenesis in other organs responds similarly to increased fat or decreased energy intake, indicating that the mechanisms are not, or not entirely, specific for the mammary gland. Extrapolations of results between species must always be made with caution, but the marked effects of dietary fat and energy in rodent tumorigenesis models must be considered in designing diet advice for humans.