Developmental effects of endocrine-disrupting chemicals in wildlife and humans

Estrogenic potential of certain pyrethroid compounds in the MCF-7 human breast carcinoma cell line

Estrogens, whether natural or synthetic, clearly influence reproductive development, senescence, and carcinogenesis. Pyrethroid insecticides are now the most widely used agents for indoor pest control, providing potential for human exposure. Using the MCF-7 human breast carcinoma cell line, we studied the estrogenic potential of several synthetic pyrethroid compounds in vitro using pS2 mRNA levels as the end point. We tested sumithrin, fenvalerate, d-trans allethrin, and permethrin. Nanomolar concentrations of either sumithrin or fenvalerate were sufficient to increase pS2 expression slightly above basal levels. At micromolar concentrations, these two pyrethroid compounds induced pS2 expression to levels comparable to those elicited by 10 nM 17ss-estradiol (fivefold). The estrogenic activity of sumithrin was abolished with co-treatment with an antiestrogen (ICI 164,384), whereas estrogenic activity of fenvalerate was not significantly diminished with antiestrogen co-treatment. In addition, both sumithrin and fenvalerate were able to induce cell proliferation of MCF-7 cells in a dose-response fashion. Neither permethrin nor d-trans allethrin affected pS2 expression. Permethrin had a noticeable effect on cell proliferation at 100 microM, whereas d-trans allethrin slightly induced MCF-7 cell proliferation at 10 microM, but was toxic at higher concentrations. Overall, our studies imply that each pyrethroid compound is unique in its ability to influence several cellular pathways. These findings suggest that pyrethroids should be considered to be hormone disruptors, and their potential to affect endocrine function in humans and wildlife should be investigated.

Cancer mortality in agricultural regions of Minnesota

Because of its unique geology, Minnesota can be divided into four agricultural regions: south-central region one (corn, soybeans); west-central region two (wheat, corn, soybeans); northwest region three (wheat, sugar beets, potatoes); and northeast region four (forested and urban in character). Cancer mortality (1980-1989) in agricultural regions one, two, and three was compared to region four. Using data compiled by the National Center for Health Statistics, cancer mortality was summarized by 5-year age groups, sex, race, and county. Age-standardized mortality rate ratios were calculated for white males and females for all ages combined, and for children aged 0-14. Increased mortality rate ratios and 95% confidence intervals (CIs) were observed for the following cancer sites: region one--lip (men), standardized rate ratio (SRR) = 2.70 (CI, 1.08-6.71); nasopharynx (women), SRR = 3.35 (CI, 1.20-9.31); region two--non-Hodgkin's lymphoma (women), SRR = 1.35 (CI, 1.09-1.66); and region three--prostate (men), SRR = 1.12 (CI, 1.00-1.26); thyroid (men), SRR = 2.95 (CI, 1.35-6.44); bone (men), SRR = 2.09 (CI, 1. 00-4.34); eye (women), SRR = 5.77 (CI, 1.90-17.50). Deficits of smoking-related cancers were noted. Excess cancers reported are consistent with earlier reports of agriculturally related cancers in the midwestern United States. However, reports on thyroid and bone cancer in association with agricultural pesticides are few in number. The highest use of fungicides occurs in region three. Ethylenebisdithiocarbamates, whose metabolite is a known cause of thyroid cancer in rats, are frequently applied. This report provides a rationale for evaluation of the carcinogenic potential of this suspect agent in humans.

Assays to measure estrogen and androgen agonists and antagonists

Substantial evidence has surfaced on the hormone-like effects of many xenobiotics in fish, wildlife and humans (Colborn et al., 1993). The endocrine and reproductive effects of xenobiotics are believed to be due to their 1) mimicking the effects of endogenous hormones such as estrogens and androgens, 2) antagonizing the effects of normal, endogenous hormones, 3) altering the pattern of synthesis and metabolism of natural hormones, and 4) modifying the hormone receptor levels. Estrogen mimics (xenoestrogens) are among the environmental chemicals found to cause reproductive impairment in wildlife and humans. All of these compounds were found to be estrogenic long after they had been released into the environment. A single causal agent can be identified in cases in which humans have had occupational exposures, whereas in cases where wildlife have shown signs of reproductive damage the exposure is usually a combination of endocrine disruptors that may have acted cumulatively. It has been hypothesized that environmental estrogens may play a role in the decrease of human semen quantity and quality of human semen during the last 50 years. They may also be partly responsible for the increased incidence of testicular cancer and cryptorchidism in males and breast cancer incidence in both females and males in the industrialized word. Testing this hypothesis will require: 1) the identification of xenoestrogens among the chemicals present in the environment, 2) the development of a methodology to assess the interactions among mixtures of xenoestrogens to which humans are exposed, and 3) the discovery of markers of estrogen exposure. The development of fast and sensitive bioassays is central to the achievement of these three goals.

Suppression of calcium oscillation by tri-n-butyltin chloride in cultured rat hepatocytes

The effects of tri-n-butyltin chloride (TBT), an environmental pollutant, on cytoplasmic free calcium ion concentration ([Ca2+]i) were investigated in primary cultured rat hepatocytes. A high concentration (4.0 microM) of TBT increased resting levels of [Ca2+]i and then induced cell blebs resulting in cell death within 2 h. The increase in [Ca2+]i, but not the cell death, depended on the presence of extracellular Ca2+, suggesting that the increase in [Ca2+]i is not critical for the cytotoxicity of TBT. A low concentration (0.1 microM) of TBT did not have any toxic effect (decrease in ATP content, decrease in viability, and shape change) on cultured hepatocytes and did not change [Ca2+]i. However, the calcium responses induced by phenylephrine, [Arg8]-vasopressin, and ATP were suppressed in the cells pretreated with 0.1 microM TBT for 30 min. The suppression was not observed in the cells pretreated with 0.1 microM TBT for only 1 min. Pretreatment with 0.1 microM TBT for 30 min had no effect on the inositol 1,4,5-triphosphate content or its increase in response to hormonal stimulation. These results suggest that TBT suppresses hormone-induced calcium responses at nontoxic low concentrations.

Effects of waterborne exposure to 4-nonylphenol and nonylphenol ethoxylate on secondary sex characteristics and gonads of fathead minnows (Pimephales promelas)

Fathead minnows were exposed to 4-nonylphenol (NP) or nonylphenol ethoxylate (NPEO) to determine the effects of these weak estrogen agonists on secondary sex characteristics and gonads of sexually mature males and females during 42-day continuous-flow exposures. Neither NP nor NPEO caused statistically significant effects on tubercles or fatpad size at the concentrations tested. Exposure to 1. 1 or 3.4 micrograms NP/L caused changes in the number and size of Sertoli cells and germ cell syncytia. Necrotic aggregates of various stages of germ cells in the spermatogenic sequence were observed in the testes of males exposed to NP. Electron microscopy of the testes of NP-exposed males revealed the presence of phagocytic cells in the lumina of seminiferous tubules. The cytoplasm of some Sertoli cells was distended with myelin figures and necrotic spermatozoa. No significant effects on the stages of follicular development were observed in females exposed to NP. There were no differences in the gonads or secondary sex characteristics of males or females exposed to 5.5 micrograms NPEO/L, the greatest concentration studied. The histologic responses observed are sensitive indicators of waterborne exposure to NP at environmentally relevant concentrations, but not as sensitive as induction of plasma vitellogenin. The secondary sex characteristics were not affected by concentrations of NP or NPEO as great as 3.4 or 5.5 micrograms/L, respectively. Histologic responses occurred at concentrations that were less than the final chronic value based on survival and approximately the same as those required to cause effects on egg production. The histologic effects caused by NP were similar to, but not exactly the same as those caused by exposure of fathead minnows to 17 beta-estradiol.

Effects of waterborne exposure to 4-nonylphenol and nonylphenol ethoxylate on secondary sex characteristics and gonads of fathead minnows (Pimephales promelas)

Fathead minnows were exposed to 4-nonylphenol (NP) or nonylphenol ethoxylate (NPEO) to determine the effects of these weak estrogen agonists on secondary sex characteristics and gonads of sexually mature males and females during 42-day continuous-flow exposures. Neither NP nor NPEO caused statistically significant effects on tubercles or fatpad size at the concentrations tested. Exposure to 1. 1 or 3.4 micrograms NP/L caused changes in the number and size of Sertoli cells and germ cell syncytia. Necrotic aggregates of various stages of germ cells in the spermatogenic sequence were observed in the testes of males exposed to NP. Electron microscopy of the testes of NP-exposed males revealed the presence of phagocytic cells in the lumina of seminiferous tubules. The cytoplasm of some Sertoli cells was distended with myelin figures and necrotic spermatozoa. No significant effects on the stages of follicular development were observed in females exposed to NP. There were no differences in the gonads or secondary sex characteristics of males or females exposed to 5.5 micrograms NPEO/L, the greatest concentration studied. The histologic responses observed are sensitive indicators of waterborne exposure to NP at environmentally relevant concentrations, but not as sensitive as induction of plasma vitellogenin. The secondary sex characteristics were not affected by concentrations of NP or NPEO as great as 3.4 or 5.5 micrograms/L, respectively. Histologic responses occurred at concentrations that were less than the final chronic value based on survival and approximately the same as those required to cause effects on egg production. The histologic effects caused by NP were similar to, but not exactly the same as those caused by exposure of fathead minnows to 17 beta-estradiol.

Key environmental human health issues in the Great Lakes and St. Lawrence River basins

In May 1997, Health Conference '97-Great Lakes/St. Lawrence, an international conference on the effects of the environment on human health in the Great Lakes and St. Lawrence River basins, was held in Montreal, Québec, Canada. This was the third international conference on this topic sponsored by agencies in the United States and Canada. More than 120 platform and poster presentations were given by scientists of different disciplines from the Great Lakes region and elsewhere. The presentations represented the most current research findings on the effects of the Great Lakes environment on human health. The reports covered environmental contaminant levels of persistent toxic substances (PTSs), routes and pathways of exposure, exposure assessment and human tissue levels of PTSs, human health outcomes, risk communication and assessment, and approaches to scientific collaboration. Reports indicate that levels of contaminants in the Great Lakes and St. Lawrence River basins have generally declined since the 1970s, although certain contaminants have plateaued or slightly increased. The findings include elevated body burden levels of contaminants in persons who consume large amounts of some Great Lakes sport fish, developmental deficits and neurologic problems in children of some fish-consuming parents, nervous system dysfunction in adults, and disturbances in reproductive parameters. The findings underscore the need for better public health intervention strategies.

Developmental synergism of steroidal estrogens in sex determination

Gonadal sex in the red-eared slider turtle, Trachemys scripta, is determined by incubation temperature during embryonic development. Evidence suggests that temperature determines sex by influencing steroid hormone metabolism and/or sensitivity: steroidogenic enzyme inhibitors or exogenous sex steroid hormones and their man-made analogs override (or enhance) temperature effects on sex determination. Specifically, nonaromatizable androgens and aromatase inhibitors induce testis differentiation at female-producing temperatures, whereas aromatizable androgens and estrogens induce ovary differentiation at male-producing temperatures. Moreover, natural estrogens and temperature synergize to produce more females than would be expected if estrogens and temperature had purely additive effects on sex determination. In this study, we use sex reversal of turtle embryos incubated at a male-producing temperature to examine synergism among steroidal estrogens: estrone, 17ss-estradiol, and estriol. A low dose of 17ss-estradiol (200 ng) showed significant synergism when administered with a single low dose of estriol (10 ng). Likewise, a single low dose of estrone (250 ng) had a synergistic effect when combined with the same low dose of estriol (10 ng). We conclude that the weak natural estrogens estrone and 17ss-estradiol synergize with a low dose of the more potent estriol to reverse gonadal sex during the critical period of sexual differentiation. These results suggest that weak environmental estrogens may also synergize with stronger natural estrogens.

Binding characteristics of dialkyl phthalates for the estrogen receptor

Dialkyl phthalates have been suggested to function as xenoestrogen. To explore the structural essentials, a series of ring and alkyl-chain isomers of dialkyl phthalates C6H4(COOCnHm)2 were examined for their ability to displace [3H]17beta-estradiol in the recombinant human estrogen receptor expressed on Sf9 vaculovirus. Compounds with an alkyl chain of more than C3 (n = 3) exhibited a distinct full receptor binding in a dose-dependent manner. When the ring isomers of C3-diallyl (-CH2-CH=CH2) derivatives, namely diallyl phthalate, diallyl isophthalate, and diallyl terephthalate, were examined, the ortho isomer of diallyl phthalate was most potent to bind to the estrogen receptor. The interaction with the estrogen receptor was optimized with dibutyl phthalates of C4. The conformational studies by 1H-NMR measurements and ab initio molecular orbital calculations have suggested that the structure mimics the interface of steroid A and B/C rings of 17beta-estradiol. Dicyclohexyl phthalate bound to the estrogen receptor with a biphasic binding curve, suggesting the compound discriminates two different receptor conformations.

Amphibians as a model to study endocrine disruptors: II. Estrogenic activity of environmental chemicals in vitro and in vivo

Several environmental chemicals are known to have estrogenic activity by interacting with development and functions of endocrine systems in nearly all classes of vertebrates. In order to get a better insight of potential estrogenic effects on amphibians caused by environmental pollution this study aims to develop a model for investigating endocrine disruptors using the amphibian Xenopus laevis. In that model the potential estrogenic activity of endocrine disruptors is determined at several levels of investigation: (I) binding to liver estrogen receptor; (II) estrogenicity in vitro by inducing vitellogenin synthesis in primary cultured hepatocytes; and (III) in vivo effects on sexual development. Here we deal with establishing methods to assay estrogenic activity of environmental chemicals in vitro and in vivo. In vitro we used a semiquantitative reverse transcriptase-polymerase chain reaction (RT-PCR) technique to determine mRNA-induction of the estrogenic biomarker vitellogenin in primary cultured hepatocytes of male Xenopus laevis. Time courses of vitellogenin-mRNA in the presence and absence of 10(-6) M 17 beta-estradiol (E2) resulted in a marked loss of mRNA from controls after 2 days while E2 treatment kept vitellogenin-mRNA at a relatively stable level. After 36 h of incubation estrogenic activities of E2, 4-nonylphenol (NP), and 2,2-bis-(4-hydroxyphenyl)-propan (bisphenol A) at concentrations ranging from 10(-10) to 10(-5) M were assayed by RT-PCR of vitellogenin-mRNA and showed the following ranking of dose-dependent potency: E2 > NP > bisphenol A. These in vitro results were confirmed further by in vivo experiments determining sexual differentiation of Xenopus laevis after exposure to E2 and environmental chemicals during larval development. Concentrations of 10(-7) and 10(-8) M E2 as well as 10(-7) M of NP or bisphenol A caused a significant higher number of female phenotypes compared to controls indicating a similar ranking of estrogenic potencies in vivo as in vitro. In addition, butylhydroxyanisol and octylphenol, both showed feminization at 10(-7) M while octylphenol was also effective at 10(-8) M. In summary these results demonstrate for the first time the use of a semiquantitative RT-PCR technique for screening estrogenicity by assaying mRNA induction of the estrogenic biomarker vitellogenin in vitro. The combination of this newly developed method with classical exposure experiments is necessary for determination of the biological significance of estrogenic chemicals.

Development of a sensitive E-screen assay for quantitative analysis of estrogenic activity in municipal sewage plant effluents

A simplified proliferation test with human estrogen receptor-positive MCF-7 breast cancer cells (E-screen assay) was optimized and validated for the sensitive quantitative determination of total estrogenic activity in effluent samples from municipal sewage plants. After solid phase extraction of 1 l sewage on either 0.2 g polystyrene copolymer (ENV+) or 1 g RP-C18 material and removal of the solvent, analysis of the extracts in the E-screen assay could be performed without any clean-up step. This was even possible with untreated sewage. Parallel extraction of four sewage samples on both different solid phase materials gave comparable quantitative results in the E-screen. A blank sample did not induce cell proliferation. As additive behaviour of the estrogenic response of single compounds was proven for two different mixtures each containing three xenoestrogens, total estrogenic activity in the sewage samples, expressed as 17 beta-estradiol equivalent concentration (EEQ), could be calculated comparing the EC50 values of the samples with those of the positive control 17 beta-estradiol. The detection limit of the E-screen method was 0.05 pmol EEQ/l (0.014 ng EEQ/l), the limit of quantification 0.25-0.5 pmol EEQ/l (0.07-0.14 ng EEQ/l). In total, extracts of nine effluent and one influent sample from five different municipal sewage plants in South Germany were analyzed in the E-screen. All samples strongly induced cell proliferation in a dose-dependent manner which was completely inhibited by coincubation with 5 nM of the estrogen receptor-antagonist ICI 182,780. The proliferative effect relative to the positive control 17 beta-estradiol (RPE) was between 30 and 101%. 17 beta-Estradiol equivalent concentrations were between 2.5 and 25 ng/l indicating a significant input of estrogenic substances via sewage treatment plants into rivers.

Amphibians as a model to study endocrine disruptors: I. Environmental pollution and estrogen receptor binding

Many chemicals released into the environment without toxicological risks have the capacities to disrupt the function of endocrine systems. These endocrine disruptors disturb normal endocrine mechanisms and have been observed in nearly all classes of vertebrates. The aim of this research is to develop a comprehensive model to study endocrine disruption using the amphibian Xenopus laevis. The assessment of estrogenic potencies of endocrine disruptors includes several levels of investigation: (I) binding to liver estrogen receptor, (II) estrogenic activity in vitro by inducing vitellogenin synthesis in primary cultured hepatocytes, and (III) in vivo effects on sexual development caused by exposure of larvae. The present paper is focused on the first part by establishing a radioreceptorassay for [3H]17 beta-estradiol ([3H]E2) binding using liver cytosol fraction. In order to get optimum binding conditions we performed kinetic, saturation, and competitive displacement experiments. Association of [3H]E2 to estrogen receptor revealed that maximum specific binding is achieved between 18 and 48 h of incubation. Scatchard analyses of saturation experiments resulted in a homogenous saturable population of estrogen receptors having no significant differences of binding parameters between both sexes. The values of Kd (dissociation constant) in males and females were 22.4 +/- 6.0 and 15.0 +/- 2.8 nM (mean +/- S.E.M.; n = 5), respectively, while corresponding Bmax (maximum binding capacity) revealed 89 +/- 46 and 136 +/- 46 fmol [3H]E2/mg protein. The specificity of estrogen receptors as shown by competitive displacement experiments demonstrated receptors being highly specific just for estrogens, but not for other endogenous steroids having the following ranking of binding affinities: E2 > estrone > dehydroepiandrosterone > aldosterone > or = testosterone > or = corticosterone > or = progesterone. The affinity ranking of environmental chemicals compared to E2 was: E2 > tetrachlorbiphenyl > diethylphthalate > 2,2-bis-(4-hydroxyphenyl)-propan (bisphenol A) > or = 4-nonylphenol > or = 3-t-butyl-4-hydroxyanisole > or = 4-octylphenol > dichlor-diphenyl-trichlor-ethan (4,4'-DDT). Analyses of five sewage effluents for displacement of [3H]E2 binding resulted in three samples displacing more than 50% of specific binding at their original concentration. Taken together the established radioreceptorassay for [3H]E2 binding in Xenopus laevis liver cytosol is useful to screen estrogen receptor binding of pure compounds or complex mixtures of them, which is the prerequisite for causing either estrogenic or antiestrogenic effects.

Organochlorine residues and elemental contaminants in U.S. freshwater fish, 1976-1986: National Contaminant Biomonitoring Program

As part of the National Contaminant Biomonitoring Program (NCBP, formerly a component of the National Pesticide Monitoring Program), the U.S. Fish and Wildlife Service periodically determined concentrations of organochlorine chemical residues and elemental contaminants in freshwater fish collected from a nationwide network of stations. In late 1986 and early 1987, the last time the network was sampled, a total of 319 composite fish samples were collected from 97 NCBP stations. The samples were analyzed for residues of organochlorine chemicals and the elements As, Cd, Cu, Hg, Pb, Se, and Zn. The mean concentration of total DDT and its homologs (p,p'-constituents) declined from 1984 to 1986, thus continuing a trend that began in 1970. The most persistent DDT homolog (p,p'-DDE) was detected at all stations sampled in 1986, and averaged 74% of total DDT residues, up from 70% in 1974-1979 but essentially unchanged from 1984. Collectively, these findings indicated a low rate of influx and continued weathering of DDT in the environment; nevertheless, DDT concentrations in fish from some stations in the South remained high enough to constitute a threat to piscivorous wildlife. Residues of polychlorinated biphenyls (PCBs) also remained widespread, but a significant downward trend in total PCB concentrations and incidence was evident, and PCB mixtures containing early eluting components were present at fewer stations than in the past. PCB concentrations were generally highest in fish from the industrialized rivers of the Northeast and Midwest and from the Great Lakes. Concentrations of toxaphene also declined, as did its incidence, from 88% of the stations sampled in 1980-1981 to 64% in 1986; however, analytical problems with the 1986 samples may have contributed to the latter. The risks represented by PCBs and toxaphene could not be evaluated on the basis of our data. Among cyclodiene insecticides, dieldrin and chlordane-related residues were the most widespread. Mean concentrations of dieldrin declined through 1986, but remained consistently highest in the Great Lakes. For chlordane-related residues, mean concentrations were lower that reported previously, and trans-nonachlor continued to replace cis-chlordane as the most abundant component. Collectively, these findings suggested a lower rate of chlordane influx to the aquatic environment; however, a point source of cyclodiene insecticides to the Mississippi R. near Memphis, TN, remained evident. Residues of mirex, PCA, BHC isomers, endrin, heptachlor, and HCB were either found at relatively few (< 25%) of the stations sampled in 1986 or were characterized by relatively low concentrations. Concentrations of the herbicide Dacthal (DCPA) were also low, but incidence increased from 46% of the stations sampled in 1984 to 61% in 1986. In general, organochlorine chemical concentrations were lower in 1986 than at any time reported previously. For elemental contaminants, the geometric mean, maximum, and 85th percentile concentrations (respectively, all in microgram/g wet weight) in 1986 samples were as follows: As, 0.083, 1.53, 0.24; Cd, 0.011, 0.32, 0.04; Cu, 0.794, 11.0, 1.7; Hg, 0.087, 0.44, 0.18; Pb, 0.058, 1.90, 0.21; Se, 0.417, 3.41, 0.66; and Zn, 21.191, 94.5, 31.7. Mean concentrations of Cu increased and concentrations of As decreased relative to the 1984 collection, but these changes may reflect subtle differences in the species composition of the 1986 collection relative to other collections; concentrations of both elements differ greatly among fishes. There were no other statistically significant changes from 1984 to 1986; however, mean concentrations of As, Cd, Pb, and Zn declined from 1976, when elemental contaminants in fish were first measured in the NCBP, and 1986. In contrast, mean concentrations of Hg and Se did not change appreciably. Moreover, and in contrast to the other elements measured in 1986, concentrations of Hg and Se were high enough to constitute a threat to pisc

Low-dose bioactivity of xenoestrogens in animals: fetal exposure to low doses of methoxychlor and other xenoestrogens increases adult prostate size in mice

The hormonal activity of natural estrogens is influenced by the degree to which they bind to serum proteins. In the pregnant female and in the fetus, greater than 99% of estradiol may be bound by serum binding proteins. Therefore, even though total serum levels of estradiol appear very high in fetuses, we have found that in rodent fetuses, there is a very low free concentration of estradiol (0.2 pg/ml). Naturally occurring variation in fetal serum estradiol predicts differences in numerous postnatal traits, including prostate size. In addition, when this low level of free estradiol was experimentally increased from 0.2 to 0.3 pg/ml during the last third of fetal life, treated male mice showed an increase in adult prostate weight. Fetal exposure to low doses of xenobiotic estrogens by feeding to pregnant females, including the compounds methoxychlor (20 and 2000 micrograms/kg body weight), DES (0.02 to 2 micrograms/kg body weight) and bisphenol A (2 and 20 micrograms/kg body weight), also led to increased prostate weight in adulthood. In contrast, fetal doses of natural estradiol and DES above the physiological range of estrogenic activity, and within a toxicological dose range, led to the opposite outcome, a reduction in subsequent adult prostate weight. This indicates that it may be impossible to assess endocrine-disrupting activities in response to low doses within a physiological range of activity by using high, toxic doses of xenoestrogens in testing procedures. We have developed approaches in vitro to predict the potential estrogenic bioactivity of compounds in the physiologically relevant range in animals and humans. We address the following factors in predicting the final observed endocrine-disrupting effect in the animal: (1) the intrinsic estrogenic activity of a given molecule, (2) the effective free concentration determined by how the molecule is carried in serum, (3) partitioning between aqueous and lipid compartments in body and cell lipids, and (4) absorption and metabolism relative to the route of exposure. The studies and strategies we describe are important in developing criteria for a tiered testing system for the detection of estrogenic chemicals as well as endocrine-disrupting chemicals with different modes of action.

Endocrine, immune, and behavioral effects of aldicarb (carbamate), atrazine (triazine) and nitrate (fertilizer) mixtures at groundwater concentrations

This paper describes the results of 5 years of research on interactive effects of mixtures of aldicarb, atrazine, and nitrate on endocrine, immune, and nervous system function. The concentrations of chemicals used were the same order of magnitude as current maximum contaminant levels (MCLs) for all three compounds. Such levels occur in groundwater across the United States. Dosing was through voluntary consumption of drinking water. We used fractional and full factorial designs with center replicates to determine multifactor effects. We used chronic doses in experiments that varied in duration from 22 to 103 days. We tested for changes in thyroid hormone levels, ability to make antibodies to foreign proteins, and aggression in wild deer mice, Peromyscus maniculatus, and white outbred Swiss Webster mice, Mus musculus, ND4 strain. Endocrine, immune, and behavior changes occurred due to doses of mixtures, but rarely due to single compounds at the same concentrations. Immune assay data suggest the possibility of seasonal effects at low doses. We present a multiple-level model to help interpret the data in the context of human health and biological conservation concerns. We discuss six testing deficiencies of currently registered pesticides, and suggest areas of human health concerns if present trends in pesticide use continue.

A sensitive zonagenetic assay for rapid in vitro assessment of estrogenic potency of xenobiotics and mycotoxins

Mounting evidence confirms that hepatic biosynthetic processes are essential for female sexual maturation in fish, which is directly controlled by estrogens. These oogenetic events (zonagenesis and vitellogenesis) are induced in both sexes by estrogens. In this paper, we report the induction of zona radiata (zr) proteins and vitellogenin in primary hepatocytes from Atlantic salmon (Salmo salar L.) exposed to xenoestrogens and mycotoxins. Cells were treated with doses of 1, 5, and 10 microM 4-nonylphenol (4-NP), o, p'-DDT, lindane ([gamma]-HCH), and bisphenol A (BPA), which all induced zr proteins and vitellogenin in an approximate dose-dependent manner. Hepatocytes were also treated with combinations of xenoestrogens at 1 or 2 microM, resulting in elevated levels of both zr proteins and vitellogenin, compared to single treatment. The estrogenic activity of the mycotoxin zearalenone (ZEA) and its metabolites [alpha]-ZEA) and ss-zearalenol (ss-ZEA)], with regard to zonagenesis and vitellogenesis, was assessed in this assay system. Mycotoxins were used at concentrations of 10, 100, or 1,000 nM. All induced zr proteins and vitellogenin, with [alpha]-ZEA being the strongest inducer. When cells were treated with xenoestrogens or mycotoxins in combination with an estrogen receptor inhibitor (ICI 182,780), the induction of both zr proteins and vitellogenin was inhibited in all cases. Thus, the reported estrogen effects are bonafide estrogen responses. Zona radiata proteins were more responsive than vitellogenin to both xenoestrogens and mycotoxins. The versatility and sensitivity of the hepatocyte assay demonstrates that biosynthesis of zr proteins provides a new supplementary method for estimating xenoestrogenicity and mycotoxin action.

Comparative estrogenic activity of wine extracts and organochlorine pesticide residues in food

The human diet contains industrial-derived, endocrine-active chemicals and higher levels of naturally occurring compounds that modulate multiple endocrine pathways. Hazard and risk assessment of these mixtures is complicated by noadditive interactions between different endocrine-mediated responses. This study focused on estrogenic chemicals in the diet and compared the relative potencies or estrogen equivalents (EQs) of the daily consumption of xenoestrogenic organochlorine pesticides in food (2.44 micrograms/day) with the EQs in a single 200-ml glass of red cabernet wine. The reconstituted organochlorine mixture contained 1,1,1-trichloro-2-(p-chlorophenyl)-2-(o-chlorophenyl)ethane, 1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane, 1,1-dichloro-2,2-bis(p-chlorophenyl)ethylene, endosulfan-1, endosulfan-2, p,p'-methoxychlor, and toxaphene; the relative proportion of each chemical in the mixture resembled the composition reported in a recent U.S. Food and Drug Administration market basket survey. The following battery of in vitro 17 beta-estradiol (E2)-responsive bioassays were utilized in this study: competitive binding to mouse uterine estrogen receptor (ER); proliferation in T47D human breast cancer cells; luciferase (Luc) induction in human HepG2 cells transiently cotransfected with C3-Luc and the human ER, rat ER-alpha, or rat ER-beta; induction of chloramphenicol acetyltransferase (CAT) activity in MCF-7 human breast cancer cells transfected with E2-responsive cathepsin D-CAT or creatine kinase B-CAT plasmids. For these seven in vitro assays, the calculated EQs in extracts from 200 ml of red cabernet wine varied from 0.15 to 3.68 micrograms/day. In contrast, EQs for consumption of organochlorine pesticides (2.44 micrograms/day) varied from nondetectable to 1.24 ng/day. Based on results of the in vitro bioassays, organochlorine pesticides in food contribute minimally to dietary EQ intake.

Human health and chemical mixtures: an overview

Unlike laboratory animals, people are rarely exposed to a single hazardous chemical. However, most of the information documenting adverse human health effects from environmental and occupational contaminants has come from studies focused on exposure to single chemicals, and there is little information available on how two or more contaminants affect humans. Most information on the effects of mixtures comes from animal systems and limited investigations of isolated human cells in culture, even though the study of mixtures in such systems has also been neglected. Two or more compounds may show additive, antagonistic, or synergistic interactions or may act on totally different systems and thus not interact. Furthermore, even a single chemical may have multiple effects and affect more than one organ system. Effects may vary with age, and metabolites may have totally different actions from the parent compound. This paper will review the variety of health effects in humans that may result from environmental contaminants and discuss how such contaminants may interact with each other. We will also present examples on how different contaminants interact from toxicologic studies of polychlorinated biphenyls performed as part of our Albany, New York, Superfund Basic Research Program project.

Rainbow trout cytochrome P450s: purification, molecular aspects, metabolic activity, induction and role in environmental monitoring

Cytochromes P450 (P450s or CYPs) constitute a superfamily of heme-thiolate proteins that play important roles in oxidative metabolism of endogenous and exogenous compounds. This review provides some limited history but addresses mainly the research progress on the cytochrome P450s in rainbow trout (Oncorhynchus mykiss), their purification, structures at the primary level, role in metabolism, responses to chemicals and environmental pollutants, application to biomonitoring and the effect of various factors on their expression or activities. Information obtained to date suggests that the rainbow trout P450 systems are as complex as those seen in mammals. Fourteen P450s have been purified from liver or trunk kidney to relatively high specific content. cDNAs belonging to seven different P450 families have been documented from trout liver, kidney and ovary. Two CYP1A genes, nine cDNAs containing open reading frames, and a cDNA fragment were entered into GenBank. Among them, CYP2K1, CYP2K3, CYP2K4, CYP2M1, CYP3A27 and CYP4T1 are the most recently described forms. CYP2K1, CYP2M1 and CYP4T1 represent newly identified P450 subfamilies first described in the rainbow trout. In many cases, the cloned rainbow trout P450s have subsequently been expressed in heterologous expressions systems such as COS-7 cells, yeast and baculovirus infected insect cells. Some of the overexpressed P450 isoforms have been partially characterized. Potential future research directions are discussed.

Effects of in utero and lactational exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on serum androgens and steroidogenic enzyme activities in the male rat reproductive tract

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) has been shown to impair reproductive function of males in animal models, possibly due to a reduction in serum androgen levels. Thus, TCDD may alter the testosterone biosynthetic pathway in the testis or the conversion of testosterone to 5alpha-dihydrotestosterone (DHT) in androgen target tissues. Pregnant Sprague Dawley rats were gavaged with TCDD (0, 0.2 or 1.0 microg/kg) on day 15 of gestation only. TCDD caused a reduction in the body weight gain of the dams in both dose groups and a significant reduction in litter size in the higher dose group. Litters delivered normally and TCDD exposed male offspring grew at the same rate as controls. Males were sacrificed at 15, 30, 45, 60, 90 and 120 d of age. Steroidogenic enzyme activities were determined in testicular microsomes and androgen target tissue nuclear fractions. Serum androgens were measured by radioimmunoassay (RIA). At 30 d of age, rats exposed to 1.0 microg/kg TCDD exhibited lower 17-hydroxylase activity (P < 0.05) and lower caput-corpus epididymal weights (P < 0.05). At 45 d of age, the same treatment resulted in testicular 3beta-HSD, 17beta-HSD and 5alpha-reductase activities that were significantly greater (P < 0.05) but, conversely, serum androgens were one quarter the values evident in controls (P < 0.05). At the other ages, no differences were observed in serum androgens and, with the exception of lower 17beta-HSD activity at 90 d of age (P < 0.05), no other differences in testicular steroidogenic enzyme activities were found. 5Alpha-reductase activities in the androgen target tissues were also unchanged. Histological examination of testes showed that the spermatogenic profile was identical to controls at all ages.

Development and validation of a fecal testosterone biomarker in Mus musculus and Peromyscus maniculatus

This is a report on the development and validation of an ELISA method to determine fecal testosterone levels, and on their evaluation as a biomarker for adverse effects of endocrine-disrupting chemicals on reproductive health using male rodents of the Peromyscus maniculatus and Mus musculus species as an animal model. The ELISA antibody had the highest specificity for testosterone (100%), followed by dihydrotestosterone (57.4%) and androstenediol (0.27%). Radiolabeled testosterone was injected i.p. into three mice. Fecal samples were collected, extracted, and analyzed by liquid scintillation counting. The ELISA was performed to characterize the excretion kinetics and metabolic fate of circulating testosterone. Solubilization of feces with 10% methanol overnight provided an extraction efficiency of 87% for all metabolites; an ethyl ether extraction was more selective for testosterone. The fecal excretion of the testosterone was a biphasic process with a majority of the radioactivity recovered in the first 24 hours. HPLC analysis revealed at least five testosterone metabolites in feces, with most metabolites being less polar than testosterone. This study forms the initial evaluation of what will become a field monitoring tool.

Estrogen increases the number of plasma cells and enhances their autoantibody production in nonautoimmune C57BL/6 mice

The immunological consequences of chronic estrogen exposure in normal individuals are not known, particularly in relation to B cells. In this study, by employing ELIspot, image cytometry, flow cytometry, cytology, and ELISA, we show that long-term exposure of normal mice to estrogen activates B cells to produce higher numbers of not only immunoglobulin-producing cells, but also autoantibody-producing cells. Estrogen promoted a decrease in B220(+) splenic lymphocytes, but resulted in a 10-fold increase in plasma cells. Further, the output of immunoglobulins including autoantibodies from individual plasma cells from estrogen-exposed mice was markedly increased, suggesting B cell hyperactivity. Importantly, our findings show that treatment of normal mice, solely with estrogen, can override B cell tolerance and promote autoreactive B cells in normal individuals.

Estrogenic and antiprogestagenic activities of pyrethroid insecticides

Many pesticides possess hormonal activity and have thus been classified as endocrine disruptors. Pyrethroids are commonly used insecticides worldwide, but little has been done to characterize their hormone agonist/antagonist potential. We tested four frequently encountered pyrethroids, fenvalerate, sumithrin, d-trans allethrin, and permethrin, for estrogen and progesterone agonist/antagonist activities using the Ishikawa Var-I human endometrial cancer cell line and the T47D human breast cancer cell line. Both cell lines produce alkaline phosphatase as an indicator of hormonal activity. Fenvalerate and sumithrin demonstrated significant estrogenicity; at concentrations of 10 microM, these compounds achieved maximal activities comparable to that of 10 nM 17alpha-ethynylestradiol in Ishikawa Var-I cells. None of the four compounds showed statistically significant estrogen antagonist activity or acted as progestins. However, fenvalerate and d-trans allethrin significantly antagonized the action of progesterone in T47D cells. Through these hormonal pathways, exposure to certain pyrethroids may contribute to reproductive dysfunction, developmental impairment, and cancer.

Metabolism of nonylphenol by rat and human microsomes

The in vitro metabolism of [14C]-nonylphenols (NPs) by rat hepatic microsomes in vitro was examined. Product formation was NADPH dependent and inhibited by the cytochrome P450 inhibitors, piperonyl butoxide and SKF525. Hepatic microsomes isolated from various inducer-treated rats (including beta naphthoflavone, phenobarbital, ethanol, dexamethasone, and clofibrate which selectively induce CYP1A, 2B, 2E, 3A and 4A, respectively) all metabolized NPs. Only microsomes from phenobarbital-treated rats exhibited a significantly higher activity towards NPs and showed a different profile of NP metabolites compared to control, untreated rats. Microsomes from human CYP2B6 transfected cells with endogenous NADPH-P450 reductase activity but not microsomes from the non-transfected parent cells metabolized NPs. The metabolism of NPs using microsomes from phenobarbital-treated rats was inhibited by 4-amino-2, 6-dinitro-1-t-butylxylene, a specific CYP2B enzyme inhibitor. Addition of a general anti-CYP2B sera to the reaction mixture attenuated the enzyme activity of microsomes from phenobarbital-treated rats to metabolize NPs. This metabolic reaction was, however, insensitive to a specific anti-CYP2B1 sera that had been shown to inhibit enzyme activities attributed only to CYP2BI suggesting that the CYP2B2 pathway is predominant in NP metabolism. The results indicate that hepatic cytochrome P450 enzyme(s) can metabolize NPs and that CYP2B isozymes are probably involved.

Validation and application of a rapid in vitro assay for assessing the estrogenic potency of halogenated phenolic chemicals

The E-Screen assay serves as an in vitro tool for the detection of estrogenic activity of chemicals and extracts of environmental samples. Based on the induction of proliferation in human estrogen receptor-positive MCF-7 breast cancer cells we could substantially simplify the assay. As one important step of validation we applied the modified assay for testing nine known xenoestrogens. We could confirm the results of other groups assuring the reproducibility of the E-Screen assay. The results provide evidence that the E-Screen assay is suitable for determination of estradiol equivalency factors (EEFs) for environmental estrogens to rank their estrogenic potency relative to the natural estrogen 17 beta-estradiol. Further, we used the optimized proliferation test to screen nine halogenated phenolic compounds for their possible estrogenic potency. Three widely applied chemicals expressed a weak receptor-mediated estrogenic activity: the flame retardant Tetrabromo-Bisphenol-A, the disinfectant 4-chloro-3-methylphenol, and the herbicide educt 4-chloro-2-methylphenol. Their estrogenic potencies were five to six orders of magnitude lower than that of 17 beta-estradiol.

Human exposure assessment and the National Toxicology Program

The National Institute of Environmental Health Sciences/National Toxicology Program (NIEHS/NTP) is developing a new interagency initiative in exposure assessment. This initiative involves the NIEHS, the Centers for Disease Control and Prevention through its National Center for Environmental Health, the National Institute for Occupational Safety and Health, the EPA, and other participating institutes and agencies of the NTP. This initiative will benefit public health and priority setting in a number of ways. First, as discussed above, it will strengthen the scientific foundation for risk assessments by the development of more credible exposure/response relationships in people by improving cross-species extrapolation, the development of biologically based dose-response models, and the identification of sensitive subpopulations and for "margin of exposure" based estimates of risk. Second, it will provide the kind of information necessary for deciding which chemicals should be studied with the limited resources available for toxicological testing. For example, there are 85,000 chemicals in commerce today, and the NTP can only provide toxicological evaluations on 10-20 per year. Third, we would use the information obtained from the exposure initiative to focus our research on mixtures that are actually present in people's bodies. Fourth, we would obtain information on the kinds and amount of chemicals in children and other potentially sensitive subpopulations. Determinations of whether additional safety factors need to be applied to children must rest, in part, upon comparative exposure analyses between children and adults. Fifth, this initiative, taken together with the environmental genome initiative, will provide the science base essential for meaningful studies on gene/environment interactions, particularly for strengthening the evaluation of epidemiology studies. Sixth, efficacy of public health policies aimed at reducing human exposure to chemical agents could be evaluated in a more meaningful way if body burden data were available over time, including remediation around Superfund sites and efforts to achieve environmental justice. The exposure assessment initiative is needed to address public health needs. It is feasible because of recent advances in analytical technology and molecular biology, and it is an example of how different agencies can work together to better fulfill their respective missions.

Human exposure assessment and the National Toxicology Program

The National Institute of Environmental Health Sciences/National Toxicology Program (NIEHS/NTP) is developing a new interagency initiative in exposure assessment. This initiative involves the NIEHS, the Centers for Disease Control and Prevention through its National Center for Environmental Health, the National Institute for Occupational Safety and Health, the EPA, and other participating institutes and agencies of the NTP. This initiative will benefit public health and priority setting in a number of ways. First, as discussed above, it will strengthen the scientific foundation for risk assessments by the development of more credible exposure/response relationships in people by improving cross-species extrapolation, the development of biologically based dose-response models, and the identification of sensitive subpopulations and for "margin of exposure" based estimates of risk. Second, it will provide the kind of information necessary for deciding which chemicals should be studied with the limited resources available for toxicological testing. For example, there are 85,000 chemicals in commerce today, and the NTP can only provide toxicological evaluations on 10-20 per year. Third, we would use the information obtained from the exposure initiative to focus our research on mixtures that are actually present in people's bodies. Fourth, we would obtain information on the kinds and amount of chemicals in children and other potentially sensitive subpopulations. Determinations of whether additional safety factors need to be applied to children must rest, in part, upon comparative exposure analyses between children and adults. Fifth, this initiative, taken together with the environmental genome initiative, will provide the science base essential for meaningful studies on gene/environment interactions, particularly for strengthening the evaluation of epidemiology studies. Sixth, efficacy of public health policies aimed at reducing human exposure to chemical agents could be evaluated in a more meaningful way if body burden data were available over time, including remediation around Superfund sites and efforts to achieve environmental justice. The exposure assessment initiative is needed to address public health needs. It is feasible because of recent advances in analytical technology and molecular biology, and it is an example of how different agencies can work together to better fulfill their respective missions.

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.

Rapid screening of environmental chemicals for estrogen receptor binding capacity

Over the last few years, an increased awareness of endocrine disrupting chemicals (EDCs) and their potential to affect wildlife and humans has produced a demand for practical screening methods to identify endocrine activity in a wide range of environmental and industrial chemicals. While it is clear that in vivo methods will be required to identify adverse effects produced by these chemicals, in vitro assays can define particular mechanisms of action and have the potential to be employed as rapid and low-cost screens for use in large scale EDC screening programs. Traditional estrogen receptor (ER) binding assays are useful for characterizing a chemical's potential to be an estrogen-acting EDC, but they involve displacement of a radioactive ligand from crude receptor preparations at low temperatures. The usefulness of these assays for realistically determining the ER binding interactions of weakly estrogenic environmental and industrial compounds that have low aqueous solubility is unclear. In this report, we present a novel fluorescence polarization (FP) method that measures the capacity of a competitor chemical to displace a high affinity fluorescent ligand from purified, recombinant human ER-[alpha] at room temperature. The ER-[alpha] binding interactions generated for 15 natural and synthetic compounds were found to be similar to those determined with traditional receptor binding assays. We also discuss the potential to employ this FP technology to binding studies involving ER-ss and other receptors. Thus, the assay introduced in this study is a nonradioactive receptor binding method that shows promise as a high throughput screening method for large-scale testing of environmental and industrial chemicals for ER binding interactions.

Lack of synergy by mixtures of weakly estrogenic hydroxylated polychlorinated biphenyls and pesticides

We examined the estrogenicity of binary mixtures of the hydroxylated polychlorinated biphenyls (OHPCBs) 2,4,6-trichloro-4'-biphenylol (2,4,6-TCB-4'-OH) and 2,3,4,5-tetrachloro-4'-biphenylol and the pesticides endosulfan and dieldrin. The OHPCBs and pesticides were tested in both the MCF-7 focus assay and a competitive estrogen-receptor binding assay. Although the individual OHPCBs were estrogenic in both assays, there was no synergy when they were combined at various concentrations as equimolar mixtures. Of the pesticides, only endosulfan was estrogenic. Its weak estrogenicity was seen only in the MCF-7 focus assay at the highest concentration tested--10 microM. There was no synergy of the equimolar mixture of pesticides. To determine whether OHPCBs might respond synergistically when combined with the natural estrogen 17-beta-estradiol (E2), we tested various concentrations of 2,4,6-TCB-4'-OH in the MCF-7 focus assay in combination with physiologically relevant concentrations of E2. There was no synergy between 2,4,6-TCB-4'-OH and E2. Pretreatment for 3 or 7 days with 2,4,6-TCB-4'-OH had no effect on subsequent foci induced by a concentration of 2,4,6-TCB-4'-OH and E2. Although our results showing no synergy between the pesticides or the OHPCBs are in contrast to a recent report that binary mixtures of these same compounds produce synergistic responses in estrogen-sensitive assays, they are in agreement with the results from other assays showing a lack of synergy. Considering all results, it appears that synergy of these weakly estrogenic compounds acting through the estrogen receptor is unlikely.

Bisphenol A interacts with the estrogen receptor alpha in a distinct manner from estradiol

We investigated the interaction of bisphenol A (BPA, an estrogenic environmental contaminant used in the manufacture of plastics) with the estrogen receptor alpha (ERalpha) transfected into the human HepG2 hepatoma cell line and expanded the study in vivo to examine the effect of BPA on the immature rat uterus. Bisphenol A was 26-fold less potent in activating ER-WT and was a partial agonist with the ERalpha compared to E2. The use of ERalpha mutants in which the AF1 or AF2 regions were inactivated has permitted the classification of ER ligands into mechanistically distinct groups. The pattern of activity of BPA with the ERalpha mutants differed from the activity observed with weak estrogens (estrone and estriol), partial ERalpha agonists (raloxifene or 4-OH-tamoxifen), or a pure antagonist (ICI 182, 780). Intact immature female Sprague-Dawley rats were exposed to BPA alone or with E2 for 3 days. Unlike E2, BPA had no effect on uterine weight; however, like E2, both peroxidase activity and PR levels were elevated, though not to the level induced by E2. Following simultaneous administration, BPA antagonized the E2 stimulatory effects on both peroxidase activity and PR levels but did not inhibit E2-induced increases of uterine weight. These results demonstrate that BPA is not merely a weak estrogen mimic but exhibits a distinct mechanism of action at the ERalpha.

Socioeconomic and environmental covariates of premature mortality in Ontario

This paper contributes to debates on the broad determinants of health and on the policy shift from curative to preventive and protective interventions. It addresses empirically the relative importance of influences on health with a multiple regression analysis of ecologic data from the 49 counties of Ontario. One model achieved high predictive power (that is, Adj R2 > 75%, p < 0.0001). Educational levels were a strong predictor of population health, showing a consistent inverse relationship with premature mortality ratios for both sexes and it was the strongest predictor for females. A low income variable supplied the strongest prediction for male mortality. This variable displayed a positive association with male mortality. Municipal expenditures on environmental protection exerted a negative effect on male mortality. These findings raise questions about the current directions of health policy in Ontario where the provincial government has reduced funding to social and environmental programs, while promising to maintain health care funding.

Differential sensitivity of zonagenesis and vitellogenesis in Atlantic salmon (Salmo salar L) to DDT pesticides

In Atlantic salmon (Salmo salar L) female sexual maturation entails both zonagenesis and vitellogenesis, both of which are controlled by increasing levels of estradiol-17 beta (E2). Antibodies against salmon zona radiata proteins (eggshell zr-proteins) and vitellogenin were used to monitor induction of oogenesis in juvenile salmon. Molecular weights of zr-monomers were estimated to about 66, 61, and 55 kDa, and to about 180 kDa for vitellogenin. Xenobiotics such as the pesticide DDT impair biological reproduction. The o,p'-DDT (1,1,1-trichloro-2[2-chlorophenyl]-2-[4-chlorophenyl]ethane) isomer seems to be a xenoestrogen. Serum levels of zr-proteins and vitellogenin, and hepatocytic biosynthesis of these components, were determined after in vivo treatment of salmon with DDT (technical, p,p'-(1,1,1-trichloro-2,2-bis[4-chlorophenyl]ethane) or o,p'-DDT) or E2. Exposing fish to frequent doses of o,p'-DDT (25 mg/kg b.w. (body weight) twice a week, six times totally) resulted in induction of all three zr-protein monomers, but not of vitellogenin. In contrast, three weekly injection of 10 mg/kg b.w. of either of the three DDT preparations did not induce typical zr-proteins or vitellogenin in serum. In vivo studies with combined DDT + E2 injections showed that none of the DDT preparations influenced E2-induced biosynthesis of zr-proteins or vitellogenin. E2 induction of these oogenetic processes was not blocked even by a high concentration (125 mg/kg b.w.) of o,p'-DDT. Furthermore, pretreatment of salmon with o,p'-DDT for 2 weeks, followed by one injection of E2, did not antagonize biosynthesis of zr-proteins, but serum concentration of vitellogenin was decreased. The data indicate that in juvenile salmon o,p'-DDT may be xenoestrogenic with regard to zonagenesis, but weakly anti-(xeno)estrogenic with regard to vitellogenesis. These findings suggest new complexities in fish reproductive toxicology of xenoestrogens. Compared to vitellogenesis, zonagenesis is a more sensitive parameter for monitoring reproductive effects of xenoestrogens.

Inhibition of androgen receptor-dependent transcriptional activity by DDT isomers and methoxychlor in HepG2 human hepatoma cells

Recent reports have raised new concerns that chemicals in our environment may disrupt normal reproduction and development through inhibition of androgen receptor function. This heightened concern has also increased our need for methods that allow us to characterize chemical interaction with the androgen receptor. In this report we describe an androgen receptor assay that utilizes the HepG2 human hepatoma cell line transiently transfected with the human androgen receptor and an androgen-responsive reporter. We used this assay to characterize the interaction with the androgen receptor of several steroidal and nonsteroidal chemicals, including isomers of DDT and methoxychlor. Chemicals were tested either in the absence (for determining agonist activity) or presence of 10(-7) M dihydrotestosterone (for determining antagonist activity). Testosterone and dihydrotestosterone were equally potent agonists in this assay. Estradiol and progesterone displayed partial agonist/antagonist activity. Flutamide was a complete agonist, whereas its hydroxylated metabolite, hydroxyflutamide, only partially antagonized and displayed some agonist activity at 10(-6) M and above. o,p'-DDT, o,p'-DDE, o,p'-DDD, p,p'-DDT, p,p'-DDE, and p, p'-DDD all behaved as antagonists at concentrations above 10(-6) M. p,p'-DDE also showed some agonist activity at 10(-5) M. Methoxychlor was only weakly antagonistic while its hydroxylated metabolite, HPTE, was approximately 10-fold more potent. Our results demonstrate that the HepG2 assay is a sensitive and specific method for detecting chemical interaction with the androgen receptor. This reporter gene assay, which we have used to characterize interaction with both the estrogen and androgen receptors, coupled with more extensive in vivo studies, should be useful for determining the role of multiple steroid receptors in the mechanism of action of endocrine active chemicals.

An anthropological approach to the evaluation of preschool children exposed to pesticides in Mexico

In this comparative study, we compensated for many of the known variables that influence children's growth and development by selecting two groups of 4-5-year-old Yaqui children who reside in the Yaqui Valley of northwestern Mexico. These children share similar genetic backgrounds, diets, water mineral contents, cultural patterns, and social behaviors. The major difference was their exposure to pesticides. Pesticides have been applied to the agricultural area of the valley since the late 1940s. In 1990, high levels of multiple pesticides were found in the cord blood of newborns and in breast milk. Building on anthropological methods for rapid rural appraisal of problems within the environment, a Rapid Assessment Tool for Preschool Children (RATPC) was developed to measure growth and development. The children of the agrarian region were compared to children living in the foothills, where pesticide use is avoided. The RATPC measured varied aspects of physical growth and abilities to perform, or function in, normal childhood activities. No differences were found in growth patterns. Functionally, the exposed children demonstrated decreases in stamina, gross and fine eye-hand coordination, 30-minute memory, and the ability to draw a person. The RATPC also pointed out areas in which more in-depth research on the toxicology of pesticides would be valuable.

An anthropological approach to the evaluation of preschool children exposed to pesticides in Mexico

In this comparative study, we compensated for many of the known variables that influence children's growth and development by selecting two groups of 4-5-year-old Yaqui children who reside in the Yaqui Valley of northwestern Mexico. These children share similar genetic backgrounds, diets, water mineral contents, cultural patterns, and social behaviors. The major difference was their exposure to pesticides. Pesticides have been applied to the agricultural area of the valley since the late 1940s. In 1990, high levels of multiple pesticides were found in the cord blood of newborns and in breast milk. Building on anthropological methods for rapid rural appraisal of problems within the environment, a Rapid Assessment Tool for Preschool Children (RATPC) was developed to measure growth and development. The children of the agrarian region were compared to children living in the foothills, where pesticide use is avoided. The RATPC measured varied aspects of physical growth and abilities to perform, or function in, normal childhood activities. No differences were found in growth patterns. Functionally, the exposed children demonstrated decreases in stamina, gross and fine eye-hand coordination, 30-minute memory, and the ability to draw a person. The RATPC also pointed out areas in which more in-depth research on the toxicology of pesticides would be valuable.

Differential spatiotemporal regulation of lactoferrin and progesterone receptor genes in the mouse uterus by primary estrogen, catechol estrogen, and xenoestrogen

Many xenobiotics are considered reproductive toxins because of their ability to interact with the nuclear estrogen receptors (ERalpha and ERbeta). However, there is evidence that these xenobiotics can regulate gene expression in the reproductive targets by mechanisms that do not involve these ERs. To examine this further, we compared the effects of estrogenic (o,p'-DDT [1-(o-chlorophenyl)-1-(p-chlorophenyl)2,2,2-trichloroethane] and Kepone, chlordecone) and nonestrogenic (p,p'-DDD [1,1-dichloro-2,2-bis(p-chlorophenyl)ethane], a metabolite of p,p'-DDT) xenobiotics with those of 17beta-estradiol (E2) and 4-hydroxyestradiol-17beta (4-OH-E2), a catechol metabolite of E2, on uterine expression of lactoferrin (LF) and progesterone receptor (PR). These genes are estrogen responsive in the mouse uterus. Normally, LF is expressed in the uterine epithelium, whereas PR is expressed in both the epithelium and stroma in response to estrogenic stimulation. Ovariectomized mice were injected with xenobiotics (7.5 mg/kg), E2 (10 microg/kg), 4-OH-E2 (10 microg/kg), or the vehicle (oil, 0.1 ml/mouse), and uterine tissues were processed for Northern blot and in situ hybridization. The pure antiestrogen ICI-182780 (ICI; 1 or 20 mg/kg) was used to interfere with estrogenic responses that were associated with the ERs. The results of Northern and in situ hybridization demonstrated increased uterine levels of PR and LF messenger RNAs (mRNAs) by all of these xenobiotics, but quantitatively the responses were much lower than those induced by E2 or 4-OH-E2. The results further showed that the E2-inducible epithelial LF mRNA accumulation was markedly abrogated by pretreatment with ICI (20 mg/kg). In contrast, this treatment retained the epithelial expression of PR mRNA, but down-regulated the stromal expression. In contrast, ICI had negligible effects on LF and PR mRNA responses to 4-OH-E2, indicating that this catechol estrogen exerted its effects primarily via a mechanism(s) other than the ERs. The heightened accumulation of LF mRNA in the epithelium in response to Kepone and o,p'-DDT was also severely compromised by pretreatment with ICI, but this antiestrogen had little effect on responses to p,p'-DDD. Similar to E2, Kepone increased the expression of PR mRNA in both uterine epithelium and stroma. However, pretreatment with ICI decreased stromal cell expression, whereas epithelial cell expression remained unaltered or increased. These responses were not noted in mice treated with o,p'-DDT or p,p'-DDD. Collectively, the results demonstrate that catechol estrogens or xenobiotics can alter uterine expression of estrogen-responsive genes by mechanisms that are not totally mediated by the classical nuclear ERs, and these alterations are cell type specific. We conclude that an interaction of a compound with the nuclear ERalpha and/or ERbeta is not an absolute requirement for producing specific estrogen-like effects in the reproductive target tissues.

Developmental neurotoxicology of endocrine disruptors and pesticides: identification of information gaps and research needs

There is increasing evidence that some environmental chemicals can interrupt neurodevelopmental processes during critical periods of development, resulting in effects on sensory, motor, and cognitive function. It is now generally accepted that developing organisms are differentially sensitive to chemical exposure because of toxicokinetic and/or toxicodynamic factors. Regulatory mechanisms have been implemented to protect humans from over- or inappropriate exposures to environmental chemicals. Current regulatory practices, however, may be insufficient because of the possibility that some environmental chemicals interfere with endocrine function at key periods of neurodevelopment. In addition, a recent National Research Council (NRC) report on pesticide contamination in the diets of infants and children concluded that current regulatory practices may not sufficiently protect infants and children from the risk of pesticide exposure. The NRC report indicates that regulatory agencies might underestimate the actual exposure of infants and children to pesticides and rely too heavily on data from adults in the risk assessment of pesticides. Consideration of endocrine-disrupting chemicals and the differential susceptibility of infants and children has led to identification of a number of information gaps and research needs that should be addressed in order to improve future risk assessments for these chemicals.

Genes and the environment: their impact on children's health

Because the human population is biologically diverse and genetically heterogeneous, it is not surprising that differences in susceptibility to disease among individuals with or without exposure to environmental agents exist. Individuals vary greatly in their susceptibility to disease. This is true of adults and children. The etiologies of many diseases of childhood are due to a combination of factors, including genetic susceptibility and environmental exposures during vulnerable periods of development. Genes regulate cellular growth and development, DNA replication and repair, the metabolism of endogenous agents in the body, and the metabolism and excretion of exogenous agents that the body comes in contact with in the environment. This regulation varies over the life span, contributing to the cellular consequences of the environmental exposures. This paper summarizes the contributions of genetics in understanding the etiology of environmentally induced diseases in children. The use of biomarkers of genetic susceptibility in the study of these diseases will be discussed. Future research needs for expanding our knowledge of the interactions between genetic and environmental components of childhood diseases will be presented.

Treatment of rats during pubertal development with 2,3,7,8-tetrachlorodibenzo-p-dioxin alters both signaling kinase activities and epidermal growth factor receptor binding in the testis and the motility and acrosomal reaction of sperm

Different doses of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) (0.1, 1, 5, and 10 micrograms/kg body wt) were administered i.p. to 21-day-old male Sprague-Dawley rats. Control animals received the same volume of the vehicle (acetone:corn oil, 1:19). Body weight and daily food intake were recorded during the 90-day time course of the study. Random samples of five rats were sacrificed at 34, 49, 62, and 90 days of age. Epidermal growth factor receptor (EGFR) in whole testis was measured, as were the activities of c-Src kinase, protein tyrosine kinase (PTK), mitogen-activated protein 2 kinase (MAP2K also termed as Erk2), protein kinase A (PKA), and protein kinase C (PKC). Testicular tissue from 90-day-old rats was evaluated for histopathology, and sperm numbers in whole testis were counted to estimate daily sperm production. The motility of sperm in the vas deferens and caudal segments of the epididymis of 90-day-old rats was measured by computer assisted sperm analysis (CASA) and the function of the sperm was tested by assessment of acrosome reactions. A dose of 10 micrograms/kg resulted in testicular atrophy and histopathologic examination revealed a decrease in the diameter of the seminiferous tubules. Sertoli cell nuclei were clearly seen, but the spermatogonial population was totally absent. Lower doses of TCDD did not affect testicular histology, but doses as low as 1 microgram/kg significantly decreased testicular sperm numbers and affected some sperm functions (motility parameters and acrosome reactions) in 90-day-old rats. Significant decreases in EGFR were found in 34-day-old rats and this effect on EGFR was sustained until the end of the experiment (90 days). Although TCDD significantly increased c-Src kinase activity in immature and mature rats, opposite effects of TCDD on activities of PTK, PKA, and PKC were found in 34-day-old rats vs 49-, 62-, and 90-day-old rats. When 10 micrograms TCDD/kg was administered to 21-day-old rat, 24-h after c-Src kinase inhibitor geldanamycin, there was no testicular atrophy and no change in the daily sperm production was found. These findings provide evidence for involvement of Src kinase signaling and EGFR in the mechanism by which TCDD disrupts testicular development and subsequently affects testis function.

Congener specific PCB and polychlorinated camphene (toxaphene) levels in Svalbard ringed seals (Phoca hispida) in relation to sex, age, condition and cytochrome P450 enzyme activity

Congener specific PCB and toxaphene (polychlorinated camphene, PCC) analyses were performed in seal blubber, collected in Svalbard, Norway. The concentration, body burden and metabolic index (PCB congener concentration in seal relative to their prey) were calculated. Multiple regression analyses were carried out to evaluate the influence of age, sex, blubber (as a percentage of total body weight) and cytochrome P450 activities on PCB and PCC levels. Levels of total PCBs found were five times higher than in ringed seals from the Canadian Arctic, corresponding with the relatively high contaminant levels in the European Arctic. The dominant PCB congeners (> 70% of the total PCBs measured) were 153, 138, 99, 180 and 101. The observed PCB and PCC accumulation patterns were very similar to patterns in seals from other studies, suggesting a large resemblance in contaminant metabolism. A decrease in the relative abundance of the lower chlorinated PCBs, was associated with higher concentrations of PCB 153. Since there was no indication for selective PCB excretion by lactating females, this suggests metabolism of these PCBs in ringed seals due to xenobiotic metabolising enzymes. The metabolic index confirmed the model of persistency of the different PCBs except for congener 128 and 138. These congeners, considered persistent in seals, could to some extent be metabolised in ringed seals. However, co-elution of PCB 138 with PCB 163 and of PCB 128 with TOX 50 possibly has resulted in an underestimation of the metabolic index for these congeners. Multiple regression analyses revealed a significant positive effect of age and a negative effect of the blubber content on the PCB concentrations. Since large fluctuations of body lipids occur between seasons in pinnipeds, PCB measurements should account for the total blubber content to avoid biased results. PCBs with vicinal H-atoms in the o, m or the m, p positions showed in addition a relation with cytochrome P450 enzyme activities. Surprisingly, no effect of sex on the PCB concentrations was observed, probably because female ringed seals, unlike other pinnipeds, continue feeding during lactation. This results in only small amounts of lipid and lipid-associated contaminants being mobilised from the blubber. Consequently, contaminant excretion with the milk will be low. Toxaphene concentrations found were low compared to levels found in the Canadian Arctic. Two congeners, TOX 26 and TOX 50 were predominant (15 and 18%, respectively of total toxaphene). There was no effect of sex, age, total blubber, or cytochrome P450 activities on the toxaphene levels. There was also no correlation between toxaphene and PCB levels, which may indicate differences in exposure and metabolism between these contaminants. Toxaphenes did not bioaccumulate to any substantial extent in ringed seals.

Impact of organochlorine contamination on levels of sex hormones and external morphology of common snapping turtles (Chelydra serpentina serpentina) in Ontario, Canada

Recent research has suggested that contaminants in the environment may influence sex differentiation and reproductive endocrine function in wildlife. Concentrations of organochlorine contaminants (total polychlorinated biphenyls, pesticides) were higher in the blood plasma of snapping turtles from contaminated sites than in those from reference sites. The ratio of the precloacal length to the posterior lobe of the plastron (PPR) is sexually dimorphic in snapping turtles. There were significant reductions in the PPR at three contaminated sites versus two reference sites. The magnitude of the response was such that a significantly higher proportion of PPRs of males from a contaminated site (Cootes Paradise) overlapped with those of females than PPRs of males from a reference site (Lake Sasajewun). Observers can incorrectly identify the sex of turtles at the contaminated site based on secondary sexual characteristics alone. Unlike the changes to the morphology, there were few changes in 17 beta-estradiol or testosterone levels, and where differences occurred, there was more variation among reference sites than between the reference and contaminated sites. Our results suggest that environmental contaminants may affect sexually dimorphic morphology in snapping turtles without affecting circulating testosterone or estrogen levels in the adults.

Environmental estrogenic pollutants induce acute vascular relaxation by inhibiting L-type Ca2+ channels in smooth muscle cells

There is an ongoing scientific debate concerning the potential threat of environmental estrogenic pollutants to animal and human health (1-5). Pollutants including the detergents 4-octylphenol and p-nonylphenol and chlorinated insecticides have recently been reported to modulate sexual differentiation by interacting with nuclear steroid receptors (6-8). So far, the focus has been on reproductive organs, but sex steroids have far more widespread actions. The lower incidence of cardiovascular disease in women has been attributed to estrogens (9-14), yet no information is available on the vascular actions of environmental estrogenic pollutants. In the present study we have investigated the effects of acute exposure to 17beta-estradiol, the antiestrogen ICI 182,780, and estrogenic pollutants on coronary vascular tone as well as on intracellular Ca2+ levels ([Ca2+]i) and Ca2+ and K+ channel activity in vascular smooth muscle cells. We report here that 4-octylphenol, p-nonylphenol, o.p'-DDT, and the antiestrogen ICI 182,780 inhibit L-type Ca2+ channels in vascular smooth muscle cells and evoke a rapid and endothelium-independent relaxation of the coronary vasculature similar to that induced by 17beta-estradiol. Thus, inhibition of Ca2+ influx via L-type Ca2+ channels in vascular smooth muscle cells may explain the acute, nongenomic vasodilator actions of environmental estrogenic pollutants.

An updated review of environmental estrogen and androgen mimics and antagonists

For the last 40 y, substantial evidence has surfaced on the hormone-like effects of environmental chemicals such as pesticides and industrial chemicals in wildlife and humans. The endocrine and reproductive effects of these chemicals are believed to be due to their ability to: (1) mimic the effect of endogenous hormones, (2) antagonize the effect of endogenous hormones, (3) disrupt the synthesis and metabolism of endogenous hormones, and (4) disrupt the synthesis and metabolism of hormone receptors. The discovery of hormone-like activity of these chemicals occurred long after they were released into the environment. Aviation crop dusters handling DDT were found to have reduced sperm counts, and workers at a plant producing the insecticide kepone were reported to have lost their libido, became impotent and had low sperm counts. Subsequently, experiments conducted in lab animals demonstrated unambiguously the estrogenic activity of these pesticides. Man-made compounds used in the manufacture of plastics were accidentally found to be estrogenic because they fouled experiments conducted in laboratories studying natural estrogens. For example, polystyrene tubes released nonylphenol, and polycarbonate flasks released bisphenol-A. Alkylphenols are used in the synthesis of detergents (alkylphenol polyethoxylates) and as antioxidants. These detergents are not estrogenic; however, upon degradation during sewage treatment they may release estrogenic alkylphenols. The surfactant nonoxynol is used as intravaginal spermicide and condom lubricant. When administered to lab animals it is metabolized to free nonylphenol. Bisphenol-A was found to contaminate the contents of canned foods; these tin cans are lined with lacquers such as polycarbonate. Bisphenol-A is also used in dental sealants and composites. We found that this estrogen leaches from the treated teeth into saliva; up to 950 microg of bisphenol-A were retrieved from saliva collected during the first hour after polymerization. Other xenoestrogens recently identified among chemicals used in large volumes are the plastizicers benzylbutylphthalate, dibutylphthalate, the antioxidant butylhydroxyanisole, the rubber additive p-phenylphenol and the disinfectant o-phenylphenol. These compounds act cumulatively. In fact, feminized male fish were found near sewage outlets in several rivers in the U.K.; a mixture of chemicals including alkyl phenols resulting from degradation of detergents during sewage treatment seemed to be the causal agent. Estrogen mimics are just a class of endocrine disruptors. Recent studies identified antiandrogenic activity in environmental chemicals such as vinclozolin, a fungicide, and DDE, and insecticide. Moreover, a single chemical may produce neurotoxic, estrogenic and antiandrogenic effects. It has been hypothesized that endocrine disruptors may play a role in the decrease in the quantity and quality of human semen during the last 50 y, as well as in the increased incidence of testicular cancer and cryptorchidism in males and breast cancer incidence in both females and males in the industrialized word. To explore this hypothesis it is necessary to identify putative causal agents by the systematic screening of environmental chemicals and chemicals present in human foods to assess their ability to disrupt the endocrine system. In addition, it will be necessary to develop methods to measure cumulative exposure to (a) estrogen mimics, (b) antiandrogens, and (c) other disruptors.

Isolation and characterization of an estrogen binding protein which may integrate the plethora of estrogenic actions in non-reproductive organs

A putative estrogen receptor (pER) from mouse liver has been characterized. The heterodimer protein (81-84 kDa) consists of two covalently bound subunits (61-67 and 17-27 kDa) with following characteristics: sedimentation constant--4.9 S; IP--4.8; dissociation constant (Kd) for estradiol-17beta binding--0.7 nmol; binding sites--0.746 pmol/mg protein; relative binding affinity--estradiol-17beta--100, estrone--80 and estriol--30; specificity--does not bind, other natural steroids, synthetic estrogens, antiestrogens and bioflavonoids. Importantly, immunosuppressants, neuroleptic and carcinogens influence 3H-estradiol-17beta binding to pER. Interestingly, pER is a serine phosphatase and this may have relevancy to estrogen action in Alzheimer's disease. The polyclonal anti-pER antibody does not react with estrogen receptors (ER). ER antibody does not react with pER. Remarkably, anti-pER antibody reacts with calcineurin, a brain phosphatase and anti-calcineurin antibody reacts with pER. Immunohistochemical analyses showed that pER is undetectable in reproductive organs (except ovary). It is localized on the plasma or the nuclear membranes in some, in cytoplasm and/or nucleus in other cells of non-reproductive organs (skeletal, neural, vascular, hair and retina), and in tumors (mammary, endometrial and prostate cancers, and prostatic hyperplasia). The information presented justifies the proposition that pER may mediate the estrogenic actions in non-reproductive organs.