Reproductive toxicity and tissue concentrations of low doses of 2,3,7,8-tetrachlorodibenzo-p-dioxin in male offspring rats exposed throughout pregnancy and lactation

The effects of an in utero exposure to 2,3,7,8-tetrachloro-dibenzo-p-dioxin on male reproductive function: identification of Ccl5 as a potential marker

2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and dioxin-like compounds are widely encountered toxic substances suspected of interfering with the endocrine systems of humans and wildlife, and of contributing to the loss of fertility. In this study, we determined the changes in testicular gene expression caused by in utero exposure to TCDD along with the intra-testicular testosterone levels, epididymal sperm reserves, daily sperm production (DSP) and testis histology. To this purpose, female pregnant Sprague-Dawley rats orally received TCDD (10, 100 or 200 ng/kg body weight) or vehicle at embryonic day 15, and the offspring was killed throughout development. Hepatic Cyp1a1 gene expression was measured in the offspring to confirm the exposure to TCDD. The gross histology of the testes and intra-testicular testosterone levels were normal among the studied groups. Sperm reserves were altered in 67-day-old rats of the TCDD-200 group, but not in 145-day-old animals or in the other TCDD-exposed groups. Nonetheless, fertility was not altered in males of the TCDD-200 group, and the F2 males generated had normal sperm reserves and DSP. Microarray analysis permitted the identification of eight differentially expressed genes in the 4-week-old testes of the TCDD-200 compared with that of the control group (cut-off value +/- 1.40), including the down-regulated chemokine Ccl5/Rantes. Inhibition of Ccl5/Rantes gene expression was observed throughout development in the TCDD-200 group, and at 67 and 145 days in the TCDD-100 group (animals of younger ages were not examined). Ccl5/Rantes gene expression was mostly confined in Leydig cells. F2 males generated from males of the TCDD-200 group had normal levels of Ccl5/Rantes in testis and Cyp1a1 in liver, which might indicate that Ccl5/Rantes is a marker of TCDD exposure in testis such as Cyp1a1 in liver. In conclusion, we demonstrated a decrease in Ccl5/Rantes RNA levels and a transitory decline in sperm reserves in the testes of rats of TCDD-dosed dams.

In utero exposure to 2,3,7,8-Tetrachlorodibenzo-p-Dioxin affects the development of reproductive system in mouse

PURPOSE

Exposure of male reproductive organs to 2,3,7,8-Tetrachlorodibenzo-p-Dioxin (TCDD) has been reported to cause developmental changes. In this study, we evaluated the effects of in utero TCDD exposure on male reproductive development.

MATERIALS AND METHODS

Pregnant C57BL/6 mice were administered a single intraperitoneal injection of TCDD (1 microg/kg) on gestation day (GD) 15. The offspring were examined in the immature stage on postnatal day (PND) 30 and in the mature stage on PND 60. The testes were examined for histological changes, androgen receptor (AR), proliferating cell nuclear antigen (PCNA) and apoptosis following the measurement of morphological changes.

RESULTS

Anogenital distance (AGD) and testis weights were reduced by TCDD exposure both on PND 30 and PND 60 while body weights and length of male offspring were not affected by TCDD. The regular sperm developmental stage was impaired with TCDD treatment on PND 30. However, no difference was found between the control group and TCDD groups on PND 60. Simultaneously, the expression of AR was also reduced on PND 30, while it was increased on PND 60 compared with the control group. The expression of PCNA was decreased whereas apoptosis was not affected by TCDD both on PND 30 and PND 60.

CONCLUSION

These results suggest that in utero exposure to TCDD influences the development of testes by inhibiting the expression of AR and PCNA. Moreover, the adverse effects of TCDD on male offspring reduced over time.

A margin-of-exposure approach to assessment of noncancer risks of dioxins based on human exposure and response data

BACKGROUND

Risk assessment of human environmental exposure to polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/PCDFs) and other dioxin-like compounds is complicated by several factors, including limitations in measuring intakes because of the low concentrations of these compounds in foods and the environment and interspecies differences in pharmacokinetics and responses.

OBJECTIVES

We examined the feasibility of relying directly on human studies of exposure and potential responses to PCDD/PCDFs and related compounds in terms of measured lipid-adjusted concentrations to assess margin of exposure (MOE) in a quantitative, benchmark dose (BMD)-based framework using representative exposure and selected response data sets.

METHODS

We characterize estimated central tendency and upper-bound general U.S. population lipid-adjusted concentrations of PCDD/PCDFs from the 1970s and early 2000s based on available data sets. Estimates of benchmark concentrations for three example responses of interest (induction of cytochrome P4501A2 activity, dental anomalies, and neonatal thyroid hormone alterations) were derived based on selected human studies.

RESULTS

The exposure data sets indicate that current serum lipid concentrations in young adults are approximately 6- to 7-fold lower than 1970s-era concentrations. Estimated MOEs for each end point based on current serum lipid concentrations range from < 10 for neonatal thyroid hormone concentrations to > 100 for dental anomalies-approximately 6-fold greater than would have existed during the 1970s.

CONCLUSIONS

Human studies of dioxin exposure and outcomes can be used in a BMD framework for quantitative assessments of MOE. Incomplete exposure characterization can complicate the use of such studies in a BMD framework.

Exposure to dioxin-like pollutants via different food commodities in Swedish children and young adults

The dietary intake of polychlorinated dibenzo-p-dioxins (PCDDs), dibenzofurans (PCDFs) and biphenyls (PCBs) in terms of toxic equivalents (TEQs) was investigated in Swedish children and young adults. Exposure was estimated from concentration data of six groups of individual food commodities (meat, fish, dairy products, egg, edible fats and other foodstuff) combined with food intake data from a 7-day record book obtained from 670 individuals aged 1-24 years. The results showed that Swedish boys and girls, up to the age of ten, had a median TEQ intake that exceeded the tolerable daily intake (TDI) of 2 pg TEQ/kg body weight. Children exceeding the TDI varied from almost all individuals among the youngest children to about 20% among young men and women. Dairy and fish products were the main sources of exposure for the average child, accounting for 59% of the total TEQ intake. The individuals most highly exposed were, on the other hand, characterized by a high consumption of fish. Since children constitute a vulnerable group, results obtained from the present study show that it is essential to perform age specific dietary intake assessments of pollutants and more carefully consider sensitive and/or highly exposed groups in the population in the risk management processes.

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

BACKGROUND

Environmental toxicants are allegedly involved in decreasing semen quality in recent decades; however, definitive proof is not yet available. In 1976 an accident exposed residents in Seveso, Italy, to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD).

OBJECTIVE

The purpose of this study was to investigate reproductive hormones and sperm quality in exposed males.

METHODS

We studied 135 males exposed to TCDD at three age groups, infancy/prepuberty (1-9 years), puberty (10-17 years), and adulthood (18-26 years), and 184 healthy male comparisons using 1976 serum TCDD levels and semen quality and reproductive hormones from samples collected 22 years later.

RESULTS

Relative to comparisons, 71 men (mean age at exposure, 6.2 years; median serum TCDD, 210 ppt) at 22-31 years of age showed reductions in sperm concentration (53.6 vs. 72.5 million/mL; p = 0.025); percent progressive motility (33.2% vs. 40.8%; p < 0.001); total motile sperm count (44.2 vs. 77.5 x 10(6); p = 0.018); estradiol (76.2 vs. 95.9 pmol/L; p = 0.001); and an increase in follicle-stimulating hormone (FSH; 3.58 vs. 2.98 IU/L; p = 0.055). Forty-four men (mean age at exposure, 13.2 years; median serum TCDD, 164 ppt) at 32-39 years of age showed increased total sperm count (272 vs. 191.9 x 10(6); p = 0.042), total motile sperm count (105 vs. 64.9 x10(6); p = 0.036), FSH (4.1 vs. 3.2 UI/L; p = 0.038), and reduced estradiol (74.4 vs. 92.9 pmol/L; p < 0.001). No effects were observed in 20 men, 40-47 years of age, who were exposed to TCDD (median, 123 ppt) as adults (mean age at exposure, 21.5 years).

CONCLUSIONS

Exposure to TCDD in infancy reduces sperm concentration and motility, and an opposite effect is seen with exposure during puberty. Exposure in either period leads to permanent reduction of estradiol and increased FSH. These effects are permanent and occur at TCDD concentrations < 68 ppt, which is within one order of magnitude of those in the industrialized world in the 1970s and 1980s and may be responsible at least in part for the reported decrease in sperm quality, especially in younger men.

Panax ginseng effects on DNA damage, CYP1A1 expression and histopathological changes in testes of rats exposed to 2,3,7,8-tetrachlorodibenzo-p-dioxin

The effects of Panax ginseng extracts on DNA damage, expression of cytochrome P450 (CYP) 1A1 and reproductive toxicity were evaluated in the testis of rats exposed to 2,3,7,8-tetrachlorodibenzo-p-dioxinthe (TCDD). Fifty rats were divided into five groups according to treatment with 2,3,7,8-TCDD and P. ginseng extracts. Single cell gel electrophoresis assays were performed to evaluate DNA damage that occurred in the lymphocytes of rats. Histological changes in the seminiferous tubules of the testis were determined using Johnsen's scoring system and Real Time-PCR was performed to evaluate the mRNA expression of CYP1A1. Significant pathological effects were observed in the 2,3,7,8-TCDD treated rats including a reduced seminiferous tubular diameter, an increased number of damaged tubules (maturation arrest, eosinophilic degeneration and spermatid giant cells) and increased Johnsen's score. DNA damage and the expression of CYP1A1 mRNA were significantly increased in rat testes. There were no significant differences between the control and animals treated with P. ginseng extracts. However, a significantly decreased level of DNA damage, decreased CYP1A1 expression and reduced pathological effects were observed in the 2,3,7,8-TCDD with P. ginseng extracts treated groups when compared with the TCDD treated group. In summary, our study demonstrates that 2,3,7,8-TCDD induces the pathological and genotoxical damage in rat testes, while P. ginseng extract treatment exhibits a therapeutic capacity to reduce these effects via reduction of CYP1A1 mRNA.

Does paternal exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) affect the sex ratio of offspring?

In 1976, men who were exposed to the highest concentrations of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) after an explosion at a chemical plant near Seveso, Italy, produced more girls than boys. However, few studies have examined the possibility that the exposure of laboratory animals to TCDD, especially that of males, could lead to a lower male/female sex ratio. The aim of this study was to investigate whether direct paternal exposure to TCDD affects the sex ratio of offspring using a relatively large-scale experimental design. Male ICR mice (n=120) were randomly assigned to three, one of which served as a vehicle control, the other two were administered TCDD orally with an initial loading dose of 2 or 2,000 ng TCDD/kg, followed by a weekly maintenance dose of 0.4 (T2/0.4 group) or 400 (T2000/400 group) ng/kg prior to mating. The major organs of each mouse were weighed and histopathologically and immunohistologically investigated, and the sex ratio of offspring [males/(males + females) x 100] was calculated in each dam. There were no significant effects on organ weights, or on the structure of the testis and epididymis between the control and TCDD-exposed males, but TCDD administration produced a significantly lower proportion of male offspring from T2000/400-exposed sires despite no alteration in litter size (

CONTROL

53.1 +/- 1.7; T2/0.4: 48.8 +/- 2.5; T2000/400: 46.2 +/- 2.1). In addition, we further divided the T2000/400 group into 3 subgroups based on the proportion of CYP1A1-immunoreactive areas in the liver; there was a significant correlation between sex ratio and CYP1A1 immunoreactivity. Thus, the present study confirms that direct paternal exposure to TCDD might be associated with an alteration in the sex ratio of offspring. Possible mechanisms through which TCDD might decrease the fertility potential of Y-bearing gametes before conception are discussed.

Polychlorinated biphenyls in clams Tapes philippinarum cultured in the Venice Lagoon (Italy): Contamination levels and dietary exposure assessment

Total polychlorinated biphenyl (SigmaPCB) concentrations calculated as the sum of 21 and the toxicity equivalent (TEQ) of dioxin-like PCBs calculated on the basis of the toxic equivalent factors were assessed in Manila clams Tapes philippinarum cultured in the Venice Lagoon. The concentrations showed a predominance of hexa-chlorobiphenyls followed by penta-, hepta-, tetra- and tri-chlorobiphenyls. The highest levels of SigmaPCB detected were 4.01 ng/g, 2.71 ng/g and 2.68 ng/g wet weight at a southern lagoon site and two northern lagoon sites, respectively. There was a significant differentiation in toxicity levels between culture sites. The highest value was 0.239 pg TEQ/g at a southern lagoon site; the lowest was 0.004 pg TEQ/g at a central lagoon site.

Toxicity of 2,3,7,8-Tetrachlorodibenzo-p-dioxin in the Developing Male Wistar(Han) Rat. I: No Decrease in Epididymal Sperm Count after a Single Acute Dose

It has been reported that fetal exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) causes defects in the male reproductive system of the rat. We set out to replicate and extend these effects using a robust experimental design. Groups of 75 (control vehicle) or 55 (50, 200, or 1000 ng of TCDD/kg bodyweight) female Wistar(Han) rats were exposed to TCDD on gestational day (GD)15, then allowed to litter. The high-dose group dams showed no sustained weight loss compared to control, but four animals had total litter loss. Pups in the high-dose group showed reduced body weight up till day 21, and pups in the medium dose group showed reduced body weight in the first week postpartum. Balano-preputial separation was significantly delayed in the high-dose group male offspring. There were no significant effects of treatment when the offspring were subjected to a functional observational battery or mated with females to assess reproductive capability. Twenty-five males per group were killed on postnatal day (PND) 70, and approximately 60 animals per group (approximately 30 for the high-dose group) on PND120 to assess seminology and other end points. At PND120, the two highest dose groups showed a statistically significant elevation of sperm counts, compared to control; however, this effect was small (approximately 30%), within the normal range of sperm counts for this strain of rat, was not reflected in testicular spermatid counts nor PND70 data, and is therefore postulated to have no biological significance. Although there was an increase in the proportion of abnormal sperm at PND70, seminology parameters were otherwise unremarkable. Testis weights in the high-dose group were slightly decreased at PND70 and 120, and at PND120, brain weights were decreased in the high-dose group, liver to body weight ratios were increased for all three dose groups, with an increase in inflammatory cell foci in the epididymis in the high-dose group. These data show that TCDD is a potent developmental toxin after exposure of the developing fetus but that acute developmental exposure to TCDD on GD15 caused no decrease in sperm counts.

Toxicity of 2,3,7,8-Tetrachlorodibenzo-p-dioxin in the Developing Male Wistar(Han) Rat. II: Chronic Dosing Causes Developmental Delay

We have investigated whether fetal exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) causes defects in the male reproductive system of the rat using chronically exposed rats to ensure continuous exposure of the fetus. Five- to six-week-old rats were exposed to control diet, or diet containing TCDD, to attain an average dose of 2.4, 8, and 46 ng TCDD/kg/day for 12 weeks, whereupon the rats were mated and allowed to litter; rats were switched to control diet after parturition. Male offsprings were allowed to develop until kills on PND70 (25 per group) or PND120 (all remaining animals). Offspring from the high-dose group showed an increase in total litter loss, and the number of animals alive on postnatal day (PND)4 in the high-dose group was approximately 26% less than control. The high and medium dose offsprings showed decreased weights at various ages. Balano-preputial separation (BPS) was significantly delayed in all three dose groups compared to control. There were no significant effects of maternal treatment when the offsprings were subjected to a functional observational battery or learning tests, with the exception that the high-dose group showed a deficit in motor activity. Twenty rats per group were mated to females, and there were no significant effects of maternal treatment on the fertility of these rats or on the F1 or F2 sex ratio. Sperm parameters at PND70 and 120 showed no significant effect of maternal treatment, with the exception that there was an increase in the proportion of abnormal sperm in the high-dose group at PND70; this is associated with the developmental delay in puberty in this dose group. There were no remarkable findings of maternal treatment on organ weights, with the exception that testis weights were reduced by approximately 10% at PND70 (but not PND120), and although the experiment was sufficiently powered to detect small changes, ventral prostate weight was not reduced. There were no significant effects of maternal treatment upon histopathological comparison of high-dose and control group organs. These data confirm that developmental exposure to TCDD shows no potent effect on adult sperm parameters or accessory sexual organs, but show that delay in BPS occurs after exposure to low doses of TCDD, and this is dependent upon whether TCDD is administered acutely or chronically.

Risk assessment of dioxins and dioxin-like PCBs in food--comments by the German Federal Environmental Agency

Human health risk assessments for dioxins and dioxin-like PCBs (with the exception of the one by US-EPA) recommend health based exposure limits within the range of 1-4 pg WHO-TEQ/kg bw per day. As all humans are exposed to measurable levels of dioxins and related substances, the determination of the tolerated daily intake is a very significant decision and may influence limit values guiding risk reduction measures and target levels. The proposed TDI has to protect all human subpopulations. In the case of dioxin this is particularly important as the exposure of infants through breast-feeding may exceed the exposure of adults by one or two orders of magnitude. An overview of recently recommended limit values (WHO, SCF, JECFA) for PCDDs, PCDFs and dioxin-like PCBs using WHO-TEFs shows the common feature that the values were derived only from non carcinogenic endpoints. In November 2000 the Scientific Committee on Food of the European Commission published an 'Opinion of the SCF on the Risk Assessment of Dioxins and Dioxin-like PCBs in Food' [SCF, Scientific Committee on Food 2000. Opinion of the SCF on the risk assessment of dioxins and dioxin-like PCBs in food. European Commission, Brussels, Adopted on November 2000 http://europa.eu.int/comm/food/fs/sc/scf/out78_en.pdf]. On the basis of this extensive review of data and experimental results the Committee recommended a temporary tolerable weekly intake (t-TWI) of 7 pg WHO-TEQ/kg bw. Only six months later the SCF carried out a re-evaluation of its t-TWI from November 2000. The reconsideration of 'pivotal studies' led to the situation that the re-assessment is now based only on rat studies which investigated only reproductive effects only on male offspring and, in addition, three of these studies are single dose studies at gestational day 15. Applying an overall uncertainty factor of 10 to the LOAEL derived estimated human daily intakes (EHDI) the SCF concluded that 14 pg/kg bw per week should be considered as a tolerable intake for 2,3,7,8-TCDD. The SCF stated that on a body weight basis, the dioxin intake of breast-fed infants has been estimated to be one to two orders of magnitude higher than the average adult intake. Recent German data suggest that the body burden of formerly breast-fed children aged 9-11 is still about 30% higher than those of their formula-fed age-mates. As breast-feeding has measurable benefits for neurological and immunological development, formula feeding cannot be recommended as an alternative to lower dioxin intake. So the only remaining way to lower the dioxin uptake is to drastically reduce the background exposure of the general population. It is acknowledged that any recommendation of a precise number for a TDI is flawed by uncertainties and the possibility of different weight being given to the studies of relevance. The determination of the TDI has influence on all regulatory limit values that are based on the TDI value. A higher TDI lowers the level of protection for humans. It is proposed by the German Federal Environmental Agency that the TDI should be reassessed in a process transparent to the public and on the basis of all relevant endpoints from animal experiments and human epidemiology, including the assessment of cancer risks.

Male reproductive impacts of styrene in rat

To determine the effect of styrene on the male reproductive function of rats, male Wistar rats received a daily intraperitoneal (ip) injection of the xenobiotic at a dose of 600 mg/kg body weight. Serum testosterone (T) level was measured in duplicate by radioimmunoassay (RIA). Blood luteinizing hormone (LH) and follicle stimulating hormone (FSH) concentrations were determined using enzyme-linked immunosorbent assay (ELISA). After 10 days of treatment, an increase of the relative weight of the testis occurred, but that of the seminal vesicles and prostate remained unchanged compared to controls injected with an equivalent volume of the vehicle (corn oil). Serum T concentration dropped, while serum hypophyse hormone levels increased. Testicular histological observations revealed a pronounced morphological alteration, with enlarged intracellular spaces, loosening of tissue, and dramatic loss of gametes in the lumen of the seminiferous tubules. Spermatogenesis damage was also confirmed by the decrease in motility and the number of epididymal spermatozoa of treated rats. According to these results, with regard to the lack of a dose response relationship in this study, we may conclude that the testis, precisely the germinal and Sertoli cells, are the major targets for styrene toxicity.

Maternal Exposure of Low Dose of TCDD Modulates the Expression of Estrogen Receptor Subunits of Male Gonads in Offspring

We have analyzed the effects of low-dose transplacental and lactational exposure of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on gene expression relating to the dioxin and sexual hormone cascade, and demonstrated the effects on testicular growth and sexual maturation in male offspring rats. TCDD (10 ng/kg) was administered to dams on Days 7 and 14 of gestation, and on Days 0, 7 and 14 after delivery. Gene expression of cytochrome P450 family 1 subfamily A polypeptide 1 (CYP1A1) in the liver of 17-day-old rats was significantly increased compared with controls. Furthermore, expression of estrogen receptors (ER)alpha and ERbeta was significantly increased at 17 and 42 days old, respectively in the testis of TCDD-administered rats compared with controls. Although testicular weight and the seminiferous tubule diameter were increased in 17-day-old rats, there was no difference in the number of germ cells between TCDD-treated and control animals. The expressions of androgen receptor and inhibin subunit genes were not significantly changed. These findings suggest that low-dose exposure of TCDD leads to unusual development of the testis by perturbation of steroid hormone homeostasis.

Current dietary exposure to polychlorodibenzo-p-dioxins, polychlorodibenzofurans, and dioxin-like polychlorobiphenyls in Italy

This study deals with an assessment of dietary exposure to polychlorodibenzo-p-dioxins (PCDDs), polychlorodibenzofurans (PCDFs), and dioxin-like polychlorobiphenyls (DL-PCBs) for the Italian general population, obtained by combining data from a national food consumption survey with contamination concentrations of European foodstuffs available on the market. The distribution of PCDD, PCDF, and DL-PCB dietary intake(s) in the Italian population was investigated to assess to what extent the variability in dietary habits may cause higher exposures to the previously mentioned contaminants. Results indicate that the main contributions to total PCDD, PCDF, and DL-PCB intake are due to fish and fish products (44%) and to milk and dairy products (27%). The mean PCDD, PCDF, and DL-PCB intake (total toxic equivalents) via food was estimated 5.34, 3.37, and 2.28 pg World Health Organization (WHO)-TE/kg of body weight (kg-bw) per day for the three age groups 0-6 (breastfeeding excluded), 7-12, and 13-94 years old, respectively. The highest exposures due to variation in dietary habits are in general within a factor of 2-3. From the mean exposure estimated for the general population (adults), it can be inferred that a consistent part of it would exceed the tolerable daily intake of 2 pg WHO-TE/kg-bw adopted by the Scientific Committee on Food of the European Commission in 2001.

Risk assessments of polychlorinated dibenzo-p-dioxins, polychlorinated dibenzofurans, and dioxin-like polychlorinated biphenyls in food

The polychlorinated dibenzo-p-dioxins (PCDD), polychlorinated dibenzofurans (PCDF), and dioxin-like polychlorinated biphenyls (dioxin-like PCB) are ubiquitous in food of animal origin and accumulate in fatty tissues of animals and humans. The most toxic congener is 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). The toxic responses include dermal toxicity, immunotoxicity, carcinogenicity, and reproductive and developmental toxicity. Toxic equivalency factors have been established for the other PCDD, PCDF and dioxin-like PCB relative to TCDD, and the combined toxicity of a sample can be expressed as toxic equivalent (WHO-TEQ). The EC Scientific Committee for Food evaluated these compounds in 2001. The assessment used the most sensitive adverse toxicological end-points of TCDD in experimental animals. These were developmental and reproductive effects in the male offspring of rats administered TCDD during pregnancy. Because of the large difference between rats and humans in the biological half-life of TCDD, the assessment used a body burden approach to compare across species and derived a tolerable weekly intake of 14 pg TCDD/kg of body weight (bw), which was extended to include all the 2,3,7,8-substituted PCDD and PCDF, and the dioxin-like PCB, and expressed as a group tolerable weekly intake of 14 pg WHO-TEQ/kg bw. The FAO/WHO Joint Expert Committee on Food Additives (JECFA) performed a similar assessment whereas the US Environmental Protection Agency (US EPA) has paid more attention to human data on carcinogenicity.

Alteration of gene expression in human cells treated with the agricultural chemical diazinon: possible interaction in fetal development

Agricultural chemicals frequently alter human health or development, typically because they have endocrine agonist or antagonist activities and alter hormone-regulation of gene expression. The insecticide, diazinon, was evaluated for gene expression disrupting activity using MCF-7 cells, an estrogen-dependent human cell line, to examine the capacity of the insecticide to disrupt gene expression essential for morphological development, immune system development or function, and/or central nervous system development and function. MCF-7 cells were treated with 30, 50 or 67 ppm diazinon, and gene expression was measured in treated cells compared to expression in untreated or estrogen-treated cells. DNA microarray analysis of diazinon-treated cells showed significant up- or down-regulation of a large number of genes compared to untreated cells. Of the 600 human genes on the Phase 1 chip utilized for these studies, two specific genes--calreticulin and TGF-beta3--were selected for corroboration using quantitative real time PCR (qrtPCR). qrtPCR, completed to assess gene expression levels for calreticulin and TGFbeta3, confirmed results showing significant up-regulation of these two genes obtained from the microarray data. These studies were designed to provide baseline data on the gene expression-altering capacity of a specific chemical, diazinon, and allow a partial assessment of the potentially deleterious effects associated with exposure of human cells to this chemical. Currently, it is not known whether results from cells in vitro can be extrapolated to human health consequences of chemical exposure.

The effects of maternal exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin on testicular steroidogenesis in infantile male rats

Exposure of adult male animals to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) decreases serum androgen concentrations. Reduction in androgen levels after maternal exposure has also been reported, but these results have not been reproduced. We have earlier shown that TCDD stimulates rather than inhibits testosterone synthesis in the prenatal rat testis. The aim of the present study was to elucidate in utero-induced effects of TCDD on testicular steroidogenesis in the 14-day-old infant rats. At that time the foetal Leydig cell population is still the prevailing source of androgens. Pregnant Sprague-Dawley dams were given a single oral dose of TCDD (0, 0.04, 0.2, or 1.0 microg/kg) on day 13 of pregnancy. On postnatal day 14, the body weight of male offspring was reduced after exposure to 1.0 microg/kg TCDD (from 33.9 +/- 1.66 g to 31.6 +/- 2.67 g). Relative testis weight, plasma testosterone, luteinizing hormone and follicle-stimulating hormone levels remained unaltered in all exposure groups. Moreover, in ex vivo incubations, testosterone and cAMP production was not affected. StAR protein level in the freshly isolated testes was increased in the 0.2 microg/kg group, and seminiferous cord diameter in the 0.04 microg/kg group. The present study confirms our earlier findings in in utero TCDD-exposed foetal testis indicating that maternal TCDD exposure does not negatively influence the developmental testosterone production of foetal type Leydig cells in rats.

Overview of exposure, toxicity, and risks to children from current levels of 2,3,7,8-tetrachlorodibenzo-p-dioxin and related compounds in the USA

Studies of children indicate that exposure of the general population to low levels of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) does not result in any clinical evidence of disease, although accidental exposure to high levels either before or after birth have led to a number of developmental deficits. Breast-fed infants have higher exposures than formula-fed infants, but studies consistently find that breast-fed infants perform better on developmental neurologic tests than their formula-fed counterparts, supporting the well-recognized benefits of breast feeding. Children receive higher exposures to PCDD/Fs from food than adults on a body-weight basis but those exposures are below the World Health Organization's tolerable daily intake. Laboratory rodents appear to be at least an order of magnitude more sensitive than humans to the aryl hydrocarbon receptor-mediated effects of these substances, which makes them poor surrogates for predicting quantitative risks but makes them good models for establishing safe levels of human exposure by organizations mandated to protect public health. Any exposure limit for PCDD/Fs based on developmental toxicity in sensitive laboratory animals can be expected to be especially protective of human health, including the health of infants and children. Because body burdens and environmental levels continue to decline, it is unlikely that children alive today in the USA will experience exposures to PCDD/Fs that are injurious to their health.

Altered gene expression in human cells treated with the insecticide diazinon: correlation with decreased DNA excision repair capacity

Many industrial and agricultural chemicals have steroid hormone agonist or antagonist activities and disrupt hormone-regulated gene expression. The widely-used agricultural insecticide, diazinon, was evaluated using MCF-7 cells - a breast cancer-derived, estrogen-dependent, human cell line - to examine the capacity of this chemical to alter steroid hormone-regulated gene expression. MCF-7 cells were treated with 30, 50, or 67 ppm of diazinon, and gene expression in treated cells was measured as mRNA levels in the cells compared to mRNA levels in untreated or estrogen-treated cells. DNA microarray analysis showed significant up- or down-regulation of a number of genes in treated cells compared to untreated cells. Of the 600 human genes on the chip utilized, specific genes with related functions were selected for additional consideration. Real time quantitative PCR (qrtPCR) completed to corroborate mRNA levels as a measure of specific gene expression, confirmed results obtained from analysis of the micro-array data. The data show that ERCC5, encoding Xeroderma pigmentosum protein G (XPG), essential for DNA excision repair, and ribonucleotide reductase subunit M1 (RNRM1), encoding a gene necessary for providing the nucleotides needed for DNA repair, were down-regulated in cells treated with diazinon. These studies were designed to provide base-line data on the gene expression-altering capacity of a specific agricultural chemical, diazinon, and allow assessment of some of the potentially deleterious effects associated with exposure of human cells to diazinon.

Identifying soil cleanup criteria for dioxins in urban residential soils: how have 20 years of research and risk assessment experience affected the analysis?

This article reviews the scientific evidence and methodologies that have been used to assess the risks posed by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and presents a probabilistic analysis for identifying virtually safe concentrations of TCDD toxicity equivalents (TEQ) in residential soils. Updated data distributions that consider state-of-the-science cancer and noncancer toxicity criteria, child soil ingestion and dermal uptake, bioavailability in soil, and residential exposure duration are incorporated. The probabilistic analysis shows that the most sensitive determinants of dose and risk are childhood soil ingestion, exposure duration, and the selected TCDD cancer potency factor. It also shows that the cancer risk at 1 per 100,000 predicted more conservative (lower) soil criteria values than did the noncancer hazard (e.g., developmental and reproductive effects). In this analysis, acceptable or tolerable soil dioxin concentrations (TCDD TEQ) ranged from 0.4 to 5.5 ppb at the 95th percentile for cancer potency factors from 9600 to 156,000 (mg/kg/d)(-1) with site-specific adjustments not included. Various possible soil guidelines based on cancer and noncancer risks are presented and discussed. In the main, the current toxicology, epidemiology, and exposure assessment data indicate that the historical 1 ppb TEQ soil guidance value remains a reasonable screening value for most residential sites. This analysis provides risk managers with a thorough and transparent methodology, as well as a comprehensive information base, for making informed decisions about selecting soil cleanup values for PCDD/Fs in urban residential settings.

Effects of Acute and Chronic Exposure to the Aryl Hydrocarbon Receptor Agonist 2,3,7,8-Tetrachlorodibenzo-p-Dioxin on the Transition to Reproductive Senescence in Female Sprague-Dawley Rats1

Activation of the aryl hydrocarbon receptor (AHR) can occur in polluted environments, either from smoking-related toxicants or from endogenous ligands. We tested whether acute or chronic exposure to the AHR agonist 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) alters the transition to reproductive senescence in female Sprague-Dawley rats. In experiment 1, rats (n = 6 per experimental group) received a single dose of 0 or 10 mug/kg of TCDD orally (p.o.) on Postnatal Day 29. Vaginal cytology was monitored for 1 wk each month until rats were killed at 1 yr of age. The single prepubertal exposure to TCDD hastened the transition to reproductive senescence in female rats and was associated with delayed puberty, abnormal cyclicity, and premature reproductive senescence. In a second experiment, rats were exposed to TCDD chronically through weekly dosing (0, 50, or 200 ng kg(-1) wk(-1) p.o., n = 7 each dose) beginning in utero. Lifelong exposure to these lower doses of TCDD induced a dose- and time-dependent loss of normal cyclicity and significantly hastened the onset of the transition to reproductive senescence (P < 0.05). This premature transition to reproductive senescence was associated with prolonged estrous cycles and, at the highest dose of TCDD, persistent estrus or diestrus. The number and size of ovarian follicles were not altered by TCDD. Diestrous concentrations of LH in rats exposed chronically to TCDD were similar to those in controls, whereas progesterone tended to be elevated at both doses of the dioxin (P < 0.08). Serum FSH was elevated in the group exposed to 50 ng/kg of TCDD (P < 0.02), whereas estradiol was decreased at both doses of dioxin (P < 0.01). Data thus far support endocrine disruption rather than depletion of follicular reserves as a primary mechanism of the premature transition to reproductive senescence following activation of the AHR pathway by TCDD in female rats.

Carcinogenic risks of dioxin: Mechanistic considerations

Dioxins and dioxin-like chemicals demonstrate high affinity binding to the aryl hydrocarbon receptor (AhR), a ligand activated transcription factor, which mediates most, if not all, of the toxic responses of these agents. Since dioxins are not directly genotoxic their carcinogenic effect is likely the result of their tumor promoting activity produced by activation of the AhR. For the purpose of risk assessment extrapolation from effects in the observable high dose range to background dietary exposure is necessary. In the present review, we discuss various aspects of low-dose-response of receptor-mediated processes in general, including threshold phenomena with regard to tumor promotion during multi-stage carcinogenesis. In this connection the reversibility of tumor promotion plays an important role but this may not be valid for dioxins due to their long half life. The relevance of cytochrome P 4501 A-induction as biomarker for prediction of carcinogenic effects of dioxins at low doses is considered. Dioxins may act in concert with endogenous ligands of the AhR, an effect which becomes particularly relevant at low toxicant concentrations. At present, however, the nature and role of these postulated ligands are unknown. Furthermore, it is unclear whether dioxins produce synergistic tumor promotional effects with non-dioxin-like chemicals to which humans are also exposed. Dioxins and, e.g., non-dioxin-like PCBs act through different receptors and there is, albeit yet limited, experimental evidence from experimental studies to suggest that they may act on different target cell populations within the same target organ. From the available data the existence of a (physiological) threshold of effects cannot be proven and may not even exist. For regulatory purposes the application of a so called "practical threshold" for the carcinogenic effect of dioxins is proposed. Further mechanistic studies should be conducted to get insight into the dose-response characteristics of relevant events of dioxin-like and non-dioxin-like agents and into the consequences of potential interactions between both group of compounds during carcinogenesis.

In Utero and Lactational Exposure to an Environmentally Relevant Organochlorine Mixture Disrupts Reproductive Development and Function in Male Rats1

We hypothesized that in utero and lactational exposure of male rats to a mixture of more than 15 organochlorines, resembling that found in blubber from northern Quebec seals, alters reproductive development and function. Female rats were gavaged with either corn oil (controls) or the organochlorine mixture in increasing doses (low, medium, and high) for 5 wk before mating and through gestation. Developmental effects were monitored in the male offspring from Postnatal Day (PND) 2 until PND 90. The high-dose mixture reduced the number of pups per litter, percentage of live offspring, and pup weights (P < 0.05). Because only three rats from the high-dose treatment survived, data from this group beyond PND 2 were not included in the statistical analyses. As assessed by the time of preputial separation, puberty was delayed in the pups from treated dams (P < 0.05). Testes weights in the medium-dose group were greater than those in controls on PND 21 (P < 0.05). Ventral prostate weights were lower for the medium-dose group on PND 60 (P < 0.05). On PND 90, weights of the epididymis, ventral prostate, and seminal vesicle of the medium-dose rats were reduced compared to those of controls (P < 0.05). On PND 90, sperm motility parameters assessed by computer-assisted sperm analysis were altered in the low- and medium-dose groups (P < 0.05). Testicular and epididymal morphology was severely affected in rats exposed to the high dose of the mixture. Serum testosterone, LH, FSH, prolactin, and total thyroxine levels did not differ because of organochlorine treatment. Therefore, in utero and lactational exposure to an environmentally relevant organochlorine mixture adversely affects the reproductive system of male rats, perhaps via antiandrogenic effects during testis development, suggesting a possible reproductive health hazard for humans and other species.

Repeated in utero and lactational 2,3,7,8-tetrachlorodibenzo-p-dioxin exposure affects male gonads in offspring, leading to sex ratio changes in F2 progeny

The effects of in utero and lactational 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on the reproductive system of male rat offspring (F1) and the sex ratio of the subsequent generation (F2) were examined. Female Holtzman rats were gavaged with an initial loading dose of 400 ng/kg TCDD prior to mating, followed by weekly maintenance doses of 80 ng/kg during mating, pregnancy, and the lactation period. Maternal exposure to TCDD had no significant effects on fetus/pup (F1) mortality, litter size, or sex ratio on gestation day (GD) 20 or postnatal day (PND) 2. The TCDD concentration in maternal livers and adipose tissue on GD20 was 1.21 and 1.81 ng/kg, respectively, and decreased at weaning to 0.72 in the liver and 0.84 in the adipose tissue. In contrast, the TCDD concentration in pup livers was 1.32 ng/kg on PND2 and increased to 1.80 ng/kg at weaning. Ventral prostate weight of male offspring was significantly decreased by TCDD exposure on PND28 and 120 compared with that of controls. Weight of the testes, cauda epididymides, and seminal vesicle, and sperm number in the cauda epididymis were not changed by TCDD exposure at PND120. TCDD- or vehicle-exposed male offspring were mated with unexposed females. The sex ratio (percentage of male pups) of F2 offspring was significantly reduced in the TCDD-exposed group compared with controls. These results suggest that in utero and lactational TCDD exposures affect the development of male gonads in offspring (F1), leading to changes in the sex ratio of the subsequent generation (F2).

Effects of maternal exposure to 3,3',4,4',5-pentachlorobiphenyl (PCB126) or 3,3',4,4',5,5'-hexachlorobiphenyl (PCB169) on testicular steroidogenesis and spermatogenesis in male offspring rats

On days 7-21 of gestation, Sprague-Dawley rats were orally administered 3 or 30 mug/kg/d of 3,3',4,4',5-pentachlorobiphenyl (PCB126) or 3,3',4,4',5,5'-hexachlorobiphenyl (PCB169) daily. Their male offspring were autopsied at 3, 6, and 15 weeks after birth to investigate the effects of the 2 polychlorinated biphenyls (PCBs) on spermatogenesis and steroidogenesis in their testes. PCB treatment caused a decrease in the area ratio of 3beta-hydroxysteroid dehydrogenase (HSD)-expressing cells (Leydig cells)/testis at 3 weeks after birth. When PCB126 was administered to pregnant rats, the plasma testosterone levels in their offspring were decreased at 3 weeks. The expression levels of P450scc, 3beta-HSD, and P450(17alpha) mitochondrial RNAs (mRNAs) were unchanged, although the StAR (steroidogenic acute regulatory protein) mRNA expression level was increased at 6 weeks. On the other hand, when PCB169 was administered, plasma testosterone levels were decreased at 3 and 6 weeks and were increased at 15 weeks. Plasma luteinizing hormone (LH) levels were decreased at 6 weeks, and plasma follicle-stimulating hormone (FSH) levels were increased at 15 weeks. The expression levels of 3beta-HSD and P450(17alpha) were increased, and the mRNA level of 5alpha-reductase 1 was decreased at 15 weeks. PCB169 treatment suppressed the conversion of round spermatids between stages VII and VIII. These results indicate that in utero and lactational exposure to PCB126 or PCB169 decreases plasma testosterone levels in 3-week-old rats, with no change in the expression levels of the mRNAs of enzymes, and that PCB169 inhibits testicular steroid synthesis more strongly than PCB126. PCB169 greatly altered the concentration of testosterone, indicating a stronger inhibitory effect on spermatogenesis. Low testosterone and LH levels in prenatally PCB169-exposed rats until 6 weeks after birth presumably retard the functional differentiation of testicular Leydig cells; however, the increased testosterone levels at 15 weeks suggest that Leydig cells in PCB-exposed rats are virtually mature by the 15th week.

Disruption of estrogen-regulated gene expression by dioxin: downregulation of a gene associated with the onset of non-insulin-dependent diabetes mellitus (type 2 diabetes)

Expression of an estrogen-regulated reporter gene, growth of MCF-7 cells in the presence of 17beta-estradiol (E2) or E2 plus TCDD, and DNA microarray plus real time quantitative PCR analyses of gene expression in MCF-7 cells were used to evaluate the effects of TCDD, a known E2 antagonist, on E2-regulated gene expression in human cells. TCDD added simultaneously with E2 exhibited significantly decreased E2-associated upregulation of reporter gene expression compared with cells treated with E2 alone, and decreased E2 enhancement of mitosis in MCF-7 cells. MCF-7 cells treated with E2 or E2 plus TCDD and DNA microarray-evaluated to determine patterns of gene expression, showed substantial differences in gene expression in TCDD-treated cells compared with E2-treated cells. Of the 2400 genes on the Perkin Elmer global array microchip utilized for this analysis, a minimum of 317 were significantly upregulated and 488 were significantly downregulated. Of these, the gene encoding insulin receptor substrate-1 (IRS-1), the protein product of which has been previously reported to be decreased, missing, altered, or defective in persons with type 2 diabetes mellitus, was evaluated by real time quantitative PCR to corroborate the array data. An evaluation of the potential consequences of TCDD-altered IRS-1 downregulation is presented.

Evaluation of immuno- and reproductive toxicities and association between immunotoxicological and genotoxicological parameters in waste incineration workers

In this study, we investigated immunotoxicity levels of 2,3,7,8-tetrachlorodibenzo-p-dioxin in 31 waste incineration workers and in 84 control subjects, and evaluated the association between immunological and genotoxicological parameters. DNA damage in mononuclear and polynuclear lymphocytes, and the level of the urinary metabolites, 1-OHP and 2-naphthol, were evaluated in both waste incineration workers and control subjects. Significant differences were detected in these values between exposed and control groups. Number of sperms was lower in the waste incineration workers than in the control subjects, as was the percentage of motile sperms, but a significant difference existed only in the number of sperms (p=0.05). DNA damage in the spermatozoa of waste incineration workers and control subjects measured 1.40+/-0.08 and 1.26+/-0.03, respectively (p=0.001). Specific surface antigens of peripheral lymphocytes, namely, CD3, CD4, CD8, CD19, and CD69 were used to measure immune status in waste incineration workers and control subjects. There was no significant difference in T- and B-cell profiles showed between waste incineration workers and control subjects (p=0.684 and 0.157). In addition, the ratio of T helper cells to T cytotoxic cells was also not remarkably different between groups (p=0.174). However, T-cell activation was found to be significantly higher in the waste incineration workers than in the control subjects (p=0.001), although B-cell activation did not exhibit this trend. The levels of two cytokines (IL-4 an INF-gamma) and four immunoglobulins (IgA, IgE, IgG, and IgM) were also measured in the experimental population. All immunoglobulin types were found in lower amounts in the waste incineration workers, but this diaparity was not significant one. In addition, the levels of two cytokines, IL-4 and INF-gamma, were also found to be lower in the waste incineration workers than in the control subjects, and only in IL-4 was a significant difference determined to exist.

Exposure to persistent organochlorine pollutants and seminal levels of markers of epididymal and accessory sex gland functions in Swedish men

BACKGROUND

A major exposure route for persistent organochlorine pollutants (POPs) in Sweden is through consumption of fatty fish from the Baltic Sea. Endocrine disruptors, such as POPs, may have a negative impact on sperm quality. The present study aimed to investigate whether exposure to 2,2',4,4',5,5'-hexachlorobiphenyl (CB-153) and 1,1-dichloro-2,2-bis (p-chlorophenyl)-ethylene (p,p'-DDE) affects epididymal and accessory sex gland function.

METHODS

157 fishermen from the coastal stretches of Sweden, aged 27-67 years, provided semen samples which were analyzed for prostate-specific antigen (PSA), neutral alpha-glucosidase (NAG), fructose and zinc levels. Serum levels of CB-153 and p'p-DDE were determined.

RESULTS

The median CB-153 serum level was 189 ng/g lipid (range 40-1460) and a median p,p'-DDE serum level 231 ng/g lipid (range 40-2252). There was a significant linear association between CB-153 and total amount of PSA (slope [beta] = -2.5, 95% confidence interval [CI] -4.0, -0.9; P = 0.02). With age, abstinence time and smoking included in the model the association became non-significant (beta = -1.4, 95% CI-3.0, 0.1; P = 0.07). There were no significant associations between CB-153 and zinc, fructose and NAG. As for the exposure variable p,p'-DDE and the outcome variables, no significant associations were found.

CONCLUSIONS

The study gives only very limited support of an association between CB-153 in serum and total PSA, and a random finding cannot be excluded.

Effects of steroids and dioxin (2,3,7,8-TCDD) on the developing wolffian ducts of the tiger salamander (Ambystoma tigrinum)

This study was undertaken to investigate effects of the prototypical dioxin, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on steroid-dependent development of the wolffian ducts of an amphibian, the tiger salamander (Ambystoma tigrinum). Larvae with immature gonads and undeveloped mullerian ducts were injected with the steroid hormones estradiol (E2), dihydrotestosterone (DHT), or vehicle alone. Additionally, steroid-treated and vehicle-control larvae were immersed in sub-lethal solutions of technical grade TCDD (0, 0.0003, 0.003, 0.03, 0.3, and 3.0 microg TCDD/L). Both steroid treatments stimulated hypertrophy of the wolffian duct epithelium and an increase in mean epithelial cell size. Only DHT treatment stimulated epithelial cell proliferation. TCDD stimulated wolffian duct hypertrophy through an increase in mean epithelial cell size. TCDD acted as an androgen agonist on wolffian duct epithelial area and epithelial cell size. TCDD had no effect on wolffian duct epithelium among E2-injected animals. Stimulatory effects on cell size were observed at 0.0003 microg/L TCDD in saline-injected animals and at 0.003 microg/L TCDD in DHT-injected animals. Both E2 and DHT stimulated growth of the wolffian ducts early in development. Technical grade TCDD alone mimics E2 and DHT action but exhibits an androgen-agonistic action in the presence of exogenously administered DHT. Implications of possible interactions between TCDD and xenosteroids are discussed.

A novel spermatogenesis related factor-2 (SRF-2) gene expression affected by TCDD treatment

We have cloned a gene which is specifically expressed at the stage of sexual maturation in the rat testis by means of differential display, and have named it spermatogenesis-related factor-2 (SRF-2). Testicular expression was first detected at 5 weeks of age, and its level of the expression increased up to 7 weeks, and was maintained even at 63 weeks. Its cDNA was 2,789 bp in length and encoded an open reading frame of 718 amino acids. This gene was mainly expressed in the spermatocyte, judging from the result of in situ hybridization. The hypothetical gene product had a motif highly homologous with RabGAP/TBC protein. Taken together, this gene is considered to have some important functions for meiosis. The gene expression was significantly decreased by treatment with TCDD, a candidate endocrine disruptor, when administered to male rats of the nursling period. Body weight and testis weight were decreased by the treatment, but even then the sperm concentration in cauda epididymis was not changed significantly. SRF-2 gene may be a promising biomarker to construct a detection system of uncertain endocrine disruptors.

Exposure to PCBs and p,p'-DDE and human sperm chromatin integrity

Persistent organochlorine pollutants (POPs) such as polychlorinated biphenyls (PCBs) and dichlorodiphenyldichloroethylene (p,p'-DDE), the major metabolite of dichlorodiphenyltrichloroethane (DDT), are stable lipophilic compounds widely found in the environment and in the general population. They can enter the food chain, and their negative impact on male reproduction is currently under active scrutiny. To explore the hypothesis that environmental exposure to these compounds is associated with altered sperm chromatin structure integrity in human sperm, we conducted a study of 176 Swedish fishermen (with low and high consumption of fatty fish, a very important exposure source of POPs). We determined serum levels of 2,2',4,4',5,5'-hexachlorobiphenyl (CB-153) and p,p'-DDE, and we used the sperm chromatin structure assay (SCSA) to assess sperm DNA/chromatin integrity. When CB-153 serum levels (individual dose range, 39-1,460 ng/g lipid) were categorized into equally sized quintiles, we found an association with the DNA fragmentation index (%DFI). A significantly lower %DFI was found in the lowest CB-153 quintile (< 113 ng/g lipid) compared with the other quintiles; there was a similar tendency, although not statistically significant, between %DFI and p,p'-DDE. These results suggest that POP exposure may have a slight negative impact on human sperm chromatin integrity.

Developmental exposure to low dose PBDE 99: effects on male fertility and neurobehavior in rat offspring

In utero exposure to a single low dose of 2,2 ,4,4 ,5-pentabromodiphenyl ether (PBDE-99) disrupts neurobehavioral development and causes permanent effects on the rat male reproductive system apparent in adulthood. PBDEs, a class of flame retardants, are widely used in every sector of modern life to prevent fire. They are persistent in the environment, and increasing levels of PBDEs have been found in biota and human breast milk. In the present study we assessed the effects of developmental exposure to one of the most persistent PBDE congeners (PBDE-99) on juvenile basal motor activity levels and adult male reproductive health. Wistar rat dams were treated by gavage on gestation day 6 with a single low dose of 60 or 300 microg PBDE-99/kg body weight (bw). In offspring, basal locomotor activity was evaluated on postnatal days 36 and 71, and reproductive performance was assessed in males at adulthood. The exposure to low-dose PBDE-99 during development caused hyperactivity in the offspring at both time points and permanently impaired spermatogenesis by the means of reduced sperm and spermatid counts. The doses used in this study (60 and 300 microg/kg bw) are relevant to human exposure levels, being approximately 6 and 29 times, respectively, higher than the highest level reported in human breast adipose tissue. This is the lowest dose of PBDE reported to date to have an in vivo toxic effect in rodents and supports the premise that low-dose studies should be encouraged for hazard identification of persistent environmental pollutants.

Dioxin health risk to infants using simulated tissue concentrations

Dioxin concentrations in infant and child were simulated using physiologically based pharmacokinetic (PBPK) models developed for these groups. The infant model was validated by comparing the simulated concentration with the measured concentration from the literature, and they showed good agreement. Simulations with our PBPK model showed temporal patterns in concentrations in various tissues. For risk assessment, estimated concentrations of 29 dioxins in the liver were summed up in a toxic equivalency (TEQ) basis to be compared with actual 2,3,7,8-TCDD concentrations in rat liver associated with toxicity. Maximum liver concentrations in breast-fed and formula-fed infants were 16.8pg TEQ/g and 3.5pg TEQ/g, respectively. The level in breast-fed infant liver was approximately 1/300 of the level associated with hepatocellular carcinoma and 1/5 of the level found in maternal rat liver associated with alterations in reproductive organs in the next generation. Based on our analysis, the present contamination level is not safe enough, but further dose-response data is required for a quantitative risk assessment.

Testicular cytochrome P450scc and LHR as possible targets of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in the mouse

Exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in adult animals has been reported to perturb the regulation of steroidogenesis in the testis, possibly by arylhydrocarbon receptor (AhR). To clarify how AhR is involved in the testicular steroidogenesis, we carried out comparative experiments using wild-type and AhR-null male mice that were intraperitoneally administered TCDD. The TCDD administration to wild-type mice showed significant reduction of P450scc and LHR in the testis, whereas the levels in the AhR-null mouse testis were unchanged. To compare anti-androgenic properties on hypothalamo-pituitary-gonadal (HPG) axis, estradiol-3-benzoate (EB), a synthetic estrogen agonist, was administered to mice, the expression of the LHalpha/FSHalpha, LHbeta, FSHbeta and GnRHR genes was severely impaired in the pituitary gland, in contrast to no observed effects in the TCDD-treated mice. In addition, the expression of the LHR gene was increased in the testis of the EB-treated mice. These observations suggest that the target of TCDD is different from that of EB on HPG axis and that TCDD treatment suppresses the P450scc and LHR genes in the testis in an AhR-dependent manner.

Pattern of Male Reproductive System Effects After in Utero and Lactational 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) Exposure in Three Differentially TCDD-Sensitive Rat Lines

Male reproductive effects induced by in utero and lactational exposure to TCDD were analyzed in three rat lines that are differently sensitive to TCDD. Rats from lines A, B, and C were selectively bred from TCDD-resistant Han/Wistar (Kuopio, H/W) and TCDD-sensitive Long-Evans (Turku/AB, L-E) rats and exhibited very different LD50 values for TCDD: >10,000, 830, and 40 microg/kg in males, respectively. The resistance in line A rats was linked to a mutated H/W-type aryl hydrocarbon receptor (Ahr(hw)) and in line B rats to a H/W-type unknown allele B (B(hw)). Line C rats had no resistance alleles. Influence of the resistance alleles on developmentally induced male reproductive effects of TCDD was studied by exposing pregnant females to TCDD (0.03, 0.1, 0.3, or 1 microg/kg) on gestation day (GD) 15. Male progeny were sacrificed on postnatal day (PND) 70. Next, the dams were given 1 microg/kg TCDD on GD 15 and male progeny were sacrificed on PND 14, 21, 28, 35, or 49. Serum testosterone concentration, male sex organ weights, and testicular and cauda epididymal sperm numbers were analyzed; the most sensitive end point was decreased sperm numbers. The dose of 1 microg/kg TCDD reduced daily sperm production by 9.3, 25, and 36%, and cauda epididymal sperm reserves by 18, 42, and 49% in rat lines A, B, and C when measured on PND 70, respectively. The most consistent and significant effect was decreased weight of prostate lobes. The growth of the male reproductive organs was not markedly affected by the resistance alleles Ahr(hw) and B(hw). In contrast, the effects on sperm parameters appeared to be slightly modified by the resistance alleles. Thus, the intraspecies genetic differences in C-terminal transactivation domain of AHR appear to modify the sensitivity to only certain dioxin-induced male reproductive effects.

Perinatal exposure to low doses of 2,3,7,8-tetrachlorodibenzo-p-dioxin alters sex-dependent expression of hepatic CYP2C11

The cytochrome P450 (CYP) isoform CYP2C11 is specifically expressed in the liver of adult male rats, and 5alpha-reductase is specifically expressed in the liver of the adult female rats. The sexually dimorphic expressions of these hepatic enzymes are regulated by the sex-dependent profiles of the circulating growth hormone (GH). However, it is not well known whether hormonal imprinting or activation factors in the neonatal brain influence the sexually dimorphic expression patterns of hepatic enzymes. We therefore examined the effect of perinatal exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on sex-dependent expressions of hepatic enzymes. Pregnant rats were treated with TCDD at a dose of 0, 200, or 800 ng/kg on gestation day 15, exposing the pups to the chemical. Although the expression of CYP2C11 protein in the livers of male pups on postnatal day (PND) 49 was significantly higher than that of the controls, but the 5alpha-reductase activities in the livers of female pups were not altered by exposure to TCDD. Focusing on perinatal periods, testosterone and estrogen levels significantly increased in the brain of male pups on PND 2. The results suggest that the alteration of testosterone and estrogen levels affect hormonal imprinting in the neonatal brain of male pups, and thus induces a change in the level of male-specific hepatic CYP2C11. We conclude that perinatal exposure to TCDD at low doses may change the sexual differentiation of the neonatal brain in male rats.

Simulation of dioxin accumulation in human tissues and analysis of reproductive risk

Polychlorinated dibenzo-p-dioxin, polychlorinated dibenzofuran and dioxin-like polychlorinated biphenyl concentrations in human liver, kidney, fat, blood, muscle, richly perfused tissue (brain, lung etc.) and skin were simulated to assess the health risk for Japanese fetuses. A 40-year time course of dioxin accumulation via food ingestion was simulated using a physiologically based pharmacokinetic (PBPK) model. In richly perfused tissue, the concentration estimated by the PBPK model showed better agreement with measured concentrations than that calculated by the one-compartment model. Fetal dioxin concentration was simulated based on the assumption that the fetal concentration was almost equal to the concentration in the mother's richly perfused tissue. To assess the reproductive risk, the estimated concentration in human fetus was compared with that in rat fetus in which reproductive function showed signs of alteration by 2,3,7,8-TCDD in previous reports [Toxicol. Appl. Pharmacol. 114 (1992) 118; 146 (1997) 11; Toxicol. Sci. 53 (2000) 411; 57 (2000) 275]. The present daily intake of 2,3,7,8-TCDD is approximately 1/50 of the amount that leads to possible reproductive toxicity in the next generation. However, when 29 kinds of dioxin congeners are considered, the present level is 1/5 of the hazardous levels. For species extrapolation of dioxin risk, further study on tissue concentration versus toxicity is required.

The presence of environmental pollutants in the semen of farm animals (bull, ram, goat, and boar)

Organochlorine pesticides and polychlorinated biphenyls are widely used in agriculture and industry, respectively, and may affect male reproduction function. Although several pollutants have been detected in human semen, similar studies in farm animals have not appeared. In the present study, the semen of bulls, rams, goats, and boars was assayed for the organochlorine pesticides hexachlorobenzene (HCB), hexachlorocyclohexane (HCH, alpha-, beta-, and gamma-isomers), dieldrin, and heptachlor epoxide, for DDT-related chemicals (o,p'-DDE, p,p'-DDE, p,p'-DDD, p,p'-DDT), and for the PCBs congeners (PCB-52, -101, -138, -150, and -180). In all species of farm animals, the most frequently detected pollutants were p,p'-DDE (80-100% of samples), HCB (73.9-100%), and gamma-HCH (69.6-100%). Species differences in the concentrations of HCB, alpha-, beta-, and gamma-HCH, dieldrin, p,p'-DDE, p,p'-DDD, and PCBs were noted as well as differences in the concentrations of some isomers of HCH, DDT-related chemicals, and PCB congeners in the same species.

Effects of 3,3',4,4',5-pentachlorobiphenyl, a coplanar polychlorinated biphenyl congener, on cultured neonatal mouse testis

3,3',4,4',5-Pentachlorobiphenyl (PCB126), a congener with a planar configuration, has been established to have relatively strong toxicities similar to those of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) via aryl hydrocarbon receptors. We investigated the effects of this coplanar PCB on mammalian early spermatogenesis and steroidogenesis in a mouse neonatal testicular organ culture system. Testes collected from newborn mice were subjected to organ culture in medium containing 0, 10, 100 or 1000 nM PCB126. Histochemical analysis revealed that the BrdU-labeling indices of both spermatogenic cells and Sertoli cells were unchanged in all testis specimens exposed to the coplanar PCB. CYP1A1 and steroidogenic enzymes (P450scc, P450c17, 3beta-HSD and 17beta-HSD) mRNA levels were determined by semiquantitative RT-PCR. The CYP1A1 mRNA level in cultured testis was significantly increased by PCB126 in a dose-dependent manner. Although mRNA levels of 3beta-HSD and 17beta-HSD were unchanged, the P450scc mRNA level was significantly down-regulated by PCB126 in a dose-dependent manner. In contrast, the P450c17 mRNA level was significantly higher in 1000 nM PCB126-exposed testis than in control testis. These results suggest that the coplanar PCB does not alter the proliferative activity of spermatogenic cells and Sertoli cells in neonatal testis, but that it directly affects the expression of steroidogenic enzyme genes.

Pre and postnatal exposure to endosulfan in Wistar rats

The possible reproductive adverse effects of the pesticide endosulfan on male offspring rats exposed in utero and during lactation were investigated. Dams were treated orally with 0, 0.5 or 1.5 mg of endosulfan/kg 21 days prior to mating, during the mating, pregnancy and lactation. Maternal and reproductive outcome data and male sexual development landmarks (testis descent and preputial separation) were assessed. Reproductive endpoints of the male offspring were examined at adulthood: sex organ weights, daily sperm production, spermatid number, sperm transit, sperm morphology and testosterone level. No signs of maternal toxicity were detected at the dose levels tested. Sexual development landmarks were also unaffected. Moreover, with the exception of a significant increase in the relative epididymis weight seen in the group treated with the lowest dose, we have not found any statistically significant adverse effect in the reproductive endpoints investigated at adulthood. The results of the present study indicate that pre and postnatal exposure to low doses of endosulfan (0.5 and 1.5 mg/kg) do not induce significant adverse effects in the reproductive system of male offspring Wistar rats at adulthood.

Basis for a proposed reference dose (RfD) for dioxin of 1-10 pg/kg-day: a weight of evidence evaluation of the human and animal studies

The dioxins have been perhaps the most studied of all chemicals to which humans are routinely exposed. It has been reported that more than 5,000 scientific papers have been published that have evaluated the toxicology of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Although the cancer hazard posed by this chemical has probably received the bulk of attention over the past 20 years, the U.S. Environmental Protection Agency (EPA) and the recent U.S. EPA Science Advisory Board (SAB) that reviewed the "Reassessment" have suggested that the noncancer hazard may well be more important than the cancer hazard at current background doses to the general public. The World Health Organization (WHO) and U.K. Food Standards Agency (FAO) committee (JECFA) on dioxins has reached similar conclusions. This article reviews the published studies involving laboratory animals and humans that address the noncancer effects. Based on our review, developmental toxicity is the most sensitive effect of TCDD consistently seen in mice and rats. Specifically, of the various studies, a no-observed-adverse-effects level (NOAEL) of 13 ng/kg (maternal body burden) was identified as the most pertinent for deriving a reference dose (RfD) for humans. Although more than a dozen different adverse effects have been reported in various studies of humans over the past 25 years, the most consistent clinically important adverse effect of human exposure appears to be chloracne. Following a review of all published studies, we concluded that the best estimate of a LOAEL for production of chloracne is approximately 160 ng/kg (body burden). Based on our analysis, an RfD of between 1 and 10 pg/kg-d (TCDD TEQ) is consistent with the objectives of this risk criterion. Maintaining a lifetime average daily dose below this concentration, based on what is known today, should prevent noncancer effects in virtually all persons. This value is consistent with the JECFA recommendation of 70 pg/kg-mo.

Infertility and environmental pollutants

While it has long been known that female fertility is impaired by oestrogen exposure, it is unclear whether environmental pollutants with weak oestrogenic effects are sufficiently potent and prevalent to have biological effects in humans. Male fertility, or sperm concentration at least, appears to have deteriorated, and there is substantial spatial variation at both national and global level, as well as a genetic component. Sperm morphology and motility are implicated too. There is good evidence for an increase in testicular cancer, and possibly in other conditions that certain spatial characteristics plus evidence on heritability suggest are linked to impaired spermatogenesis. A candidate agent would need to have started increasing in the early 20th century. Weak environmental oestrogens are not responsible. Candidates include agents affecting endogenous maternal oestrogen levels, environmental anti-androgens (although these cannot explain the epidemiological findings), and dioxin and related compounds. Genetic damage should be considered as a unifying hypothesis, possibly focused on the Y-chromosome.

Possible range of dioxin concentration in human tissues: simulation with a physiologically based model

In risk evaluation of dioxins, monitoring chemical concentrations in human tissues is an important step, and these concentration data can be utilized along with animal toxicity data for extrapolation of human manifestation. However large differences in dioxin concentrations usually exist even among individuals who have never been accidentally exposed to high quantities of dioxin, and this may cause problems in risk analysis. Body size, age, and history of food consumption are factors responsible for these interindividual differences in addition to exposure levels. Using a physiologically based pharmacokinetic (PBPK) model, the influence of differences in body weight, gastrointestinal absorption, and half-life and intake of dioxin were examined on tissue chemical concentration. Dioxin concentrations over a 40-yr time course in human liver, kidneys, fat, blood, muscle and richly perfused tissue were simulated for polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), and coplanar polychlorinated biphenyls (CoPCBs). Model parameters such as tissue-blood partition coefficients for CoPCBs were prepared, and sensitivity analysis was also performed on these parameters. The range of tissue concentrations was approximately 0.17 to 4.1 times the standard concentration, which was calculated using standard model parameters. The simulated ranges included more than 80% of the individual anatomical data for 2,3,7,8-tetrachlorodibenzo-p-dioxin, 1,2,3,7,-pentachlorodibenzo-p-dioxin, and 3,3',4,4',5-pentachlorobiphenyl in liver, fat, and blood. These results suggest that differences in body weight, gastrointestinal absorption, and food intake behavior may partially explain variation in tissue concentrations among individuals, and the possible interindividual uncertainty, which is approximately 24 for the general Japanese population.

Impairment of male rat reproductive function in F1 offspring from dams exposed to 2-bromopropane during gestation and lactation

The toxic effects of 2-bromopropane (2-BP) on the reproductive tracts of male F1 offspring from dams exposed to 2-BP during gestation and lactation were investigated. Ten pregnant (sperm-positive) Sprague-Dawley rats per group were exposed sc to 2-BP at 135, 405, and 1215 mg/kg/day from gestation day (GD) 6 to postnatal day (PND) 20. 2-BP decreased the proportion of dams littering at the two highest doses. At the highest dose, the rate of delivery and surviving pups were significantly lower than in the controls (P < or = 0.05). The relative weights of testes vs. brain were significantly lower than the controls (P < or = 0.05) on PND 33 and 63 at 405 mg/kg/day, and on PND 90 at 1215 mg/kg/day in the F1 rats. Seminiferous tubule atrophy, germ cell loss, and increased Leydig cell proliferation were observed at the highest dose by histopathologic examination. Female offspring has a decrease in all follicle types at the high dose. These results suggest that gestational and lactational exposure to 2-BP at a high maternally toxic dose impairs the development of the reproductive organs of the offspring.