In utero and lactational exposure of the male rat to 2,3,7,8-tetrachlorodibenzo-p-dioxin: impaired prostate growth and development without inhibited androgen production

Animal Toxicology Studies on the Male Reproductive Effects of 2,3,7,8-Tetrachlorodibenzo-p-Dioxin: Data Analysis and Health Effects Evaluation

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is a well-known environmental poison that exist in the environment for many years. However, its effect on the male reproductive system has not been clearly stated. We conducted a meta-analysis of the effect of TCDD on the male reproductive system of rodents about TCDD. Results showed that that TCDD exposure reduced the testis weight (weighted mean difference [WMD]: -0.035, 95% confidence interval [CI]: -0.046 to -0.025), sperm count (WMD: -35, 95% CI: -42.980 to -27.019), and blood testosterone concentration (WMD: -0.171, 95% CI: -0.269 to -0.073). According to our research results, TCDD can cause damage to the male reproductive system of rodents through direct or indirect exposure. In order to further explore the potential hazards of TCDD to humans, more human-related research needs to be carried out.

An androgen-independent mechanism underlying the androgenic effects of 3-methylcholanthrene, a potent aryl hydrocarbon receptor agonist

Aryl hydrocarbon receptor (AhR) and androgen receptor (AR) are ligand-activated transcription factors with profound cross-talk between their signal transduction pathways. Previous studies have shown that AhR agonists activate the transcription of AR-regulated genes in an androgen-independent manner; however, the underlying mechanism remains unclear. To decipher this mechanism, we evaluated the effects of 3-methylcholanthrene (3MC), a potent AhR agonist, on the transcription of AR-regulated genes in three AR-expressing cell lines. 3MC induced the expression of not only three representative AR-regulated chromosomal genes but also the exogenous AR-responsive luciferase reporter gene. No significant difference in the 3MC-induced luciferase activity was detected in the presence of SKF-525A, a non-specific inhibitor of CYP enzymes. The androgenic effects of 3MC were diminished by AhR and AR knockdown. Following 3MC treatment, the amount of nuclear AhR and AR increased synchronously. Co-immunoprecipitation revealed that AhR and AR formed a complex in the nucleus of cells treated with 3MC. AR was recruited to the proximal promoter and distal enhancer regions of the PSA gene upon the addition of 3MC. We propose that AhR activated by 3MC forms a complex with unliganded AR which translocates from the cytoplasm to the nucleus. Nuclear AR now binds the transcriptional regulatory region of AR-regulated genes and activates the transcription.

Protective effect of resveratrol on urogenital sinus and prostate development in rats exposed in utero to TCDD (2,3,7,8-tetrachlorodibenzo-p-dioxin)

This study evaluated the protective effects of resveratrol on the prostate development of rats exposed to TCDD. Pregnant rats received TCDD (1 μg/kg) at GD15 and/or RES (20 mg/kg/day) from GD10 to PND21. Newborn and adult males from Control, TCDD, TCDD + RES and RES groups were euthanized and the prostate was excised. On PND1, there was a reduction in the number of prostatic buds, AR-positive mesenchymal cells and proliferation index in epithelial and mesenchymal cells in TCDD group, but restored by RES. AhR immunoreactivity was greater in TCDD group than the other groups. On PND90, there was higher frequency of functional hyperplasia in the distal area of the prostate acini in TCDD group, but restored by RES. AhRR expression was higher in the TCDD while NRF2 was higher in the TCDD + RES compared to the other groups. Resveratrol was able to reduce the adverse effects of TCDD on prostate development and its long-term repercussions.

Prenatal dioxin exposure estimated from dioxins in breast milk and sex hormone levels in umbilical cord blood in Vietnamese newborn infants

Dioxin concentrations remain elevated in the environment and humans residing near the former US Air Force base in Bien Hoa city, South Vietnam. We recruited 210 mother-infant pairs for whom breast milk dioxin levels were reported in our previous study. Cord blood samples were collected from 162 mother-infant pairs. We selected 16 cord blood samples with a volume over 20mL and fat content of ≥0.03g. Toxic equivalent levels of polychlorinated dibenzodioxins and polychlorinated dibenzofurans (TEQ-PCDD/Fs) and concentrations of 17 congeners, including 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD), in cord blood were measured and compared with levels in breast milk (Study 1). Levels of 2,3,7,8-TCDD and TEQ-PCDD/Fs in cord blood samples were highly and significantly correlated with those in breast milk samples in the same pairs. This suggests dioxins in breast milk reflect prenatal dioxin exposure. Estradiol (E2) and testosterone (TS) were measured in cord blood serum from 162 samples. Associations between dioxins in breast milk and cord blood sex hormones were analyzed by infant sex, after adjusting for confounding factors (Study 2). Increased levels of TEQ-PCDD/Fs in breast milk were associated with decreased cord blood TS in girls. In boys, a significant reduction of cord blood TS was observed in those exposed to 2,3,7,8-TCDD at high levels (≥5.5pg/g lipid). There was no significant association between E2 and dioxins in breast milk in either sex. These results suggest increased prenatal dioxin exposure is associated with decreased cord TS, but in boys, only high level of 2,3,7,8-TCDD influence cord blood TS.

Effects of vitamin E on reproductive hormones and testis structure in chronic dioxin-treated mice

The purpose of this study was to investigate the effects of vitamin E on reproductive hormones and testis structure in mice treated with 2,3,7,8-tetrachlorodibenzo- p-dioxin (TCDD). Five experimental groups of a combination of TCDD and vitamin E were designed as follows: 0 ng/kg/d and 0 mg/kg/d (control group), 100 ng/kg/d and 0 mg/kg/d (Group I), 100 ng/kg/d and 20 mg/kg/d (Group II), 100 ng/kg/d and 100 mg/kg/d (Group III), and 100 ng/kg/d and 500 mg/kg/d (Group IV) respectively. Vitamin E and TCDD were given by oral gavage for 7 weeks. The results demonstrated that TCDD decreased the levels of brain gonadotropin releasing hormone (GnRH), testis luteinizing hormone (LH) and follicle stimulating hormone (FSH), serum testosterone and testis spermatozoa number, and damaged testis structure. Vitamin E at 20 mg/kg alleviated the decrease of GnRH; vitamin E at 20, 100, and 500 mg/kg antagonized the decline of LH and FSH; vitamin E at 20 and 100 mg/kg reversed the decrease of testosterone and spermatozoa number; and vitamin E at 100 mg/kg decreased the damage of the testis structure caused by TCDD. The results indicate that vitamin E antagonizes the reproductive endocrine toxicity and alleviates the changes in testicular structure caused by TCDD.

Dioxin-induced changes in epididymal sperm count and spermatogenesis

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

Interpretation of studies on the developmental reproductive toxicology of 2,3,7,8-tetrachlorodibenzo-p-dioxin in male offspring

There have been several studies on the maternal administration of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and effects in the reproductive tract of male offspring, subsequent to risk assessments undertaken in 2001. This review compares the methodology and results to examine key methodological features, and consistency in reported outcomes. Maternal dosing at >0.8 microg TCDD/kg causes lethality and weight loss, and it is difficult to distinguish between direct and indirect effects of TCDD at these dose levels. Statistically significant effects of maternal doses of <1 microg TCDD/kg (i.e. the dose levels relevant for risk assessment) on prostate weight or epididymal sperm counts in offspring were reported in the minority of studies. The pharmacokinetics of TCDD differs considerably between acute and chronic dosing, and with dose level of TCDD. On the basis of body burden, TCDD had different potency at inducing adverse effects in the only comparison study between acute and chronic dosing. Understanding of the pharmacokinetics of TCDD and relationship to adverse effects in offspring is required. These analyses identify key features of TCDD developmental toxicity in male offspring, and identify data needs for future risk assessment.

Dioxin-induced changes in epididymal sperm count and spermatogenesis

BACKGROUND

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

DATA SOURCES

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

DATA SYNTHESIS

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

CONCLUSIONS

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

Toxic effects of lactational exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on development of male reproductive system: involvement of antioxidants, oxidants, and p53 protein

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is a potent endocrine disruptor compound and induces multiple organ dysfunctions. The effect of TCDD exposure both in adults and in utero has been well established. However, little is known about the effects of TCDD acquired through mother's milk on the development of the male reproductive system. The aim of this study was to investigate the effects and mechanisms of TCDD from lactational exposure. TCDD (1 microg/kg) was administered to C57BL/6 mouse mothers for 4 days from the day of delivery. On postnatal day 30 (PND 30) and postnatal day 60 (PND 60), body weight, body length, and anogenital distance (AGD) of male offspring were measured. The weights of the testes and epididymides were also measured. Epididymides were used for sperm counts, and testes were used to measure the activity of antioxidant enzymes (SOD, CAT, GPX, GR), the parameters of oxidative stress (hydrogen peroxide, MDA), and testosterone. In addition, expression of p53 and the proapoptotic protein, Bax, were analyzed by Western blot. TCDD exposure decreased body weight, body length, and AGD in both PND 30 and PND 60 groups compared with the control group. The activity of all antioxidant enzymes at PND 60 was decreased after TCDD treatment. TCDD treatment decreased testicular testosterone levels in both the PND 30 and PND 60 groups. The expression of p53 and Bax were also upregulated by TCDD and did not return to normal levels by PND 60. These data suggest that TCDD affects development of male offspring when the mother is exposed to TCDD during lactation. In addition, oxidative stress is a major mediator of TCDD-induced adverse effects, and p53 may play an important role in this mechanism.

Comparative contribution of the aryl hydrocarbon receptor gene to perinatal stage development and dioxin-induced toxicity between the urogenital complex and testis in the mouse

TCDD (2,3,7,8-tetrachlorodebenzo-p-dioxin) requires the presence of the aryl hydrocarbon receptor (Ahr) gene for its toxic effects, such as reproductive disorders in male offspring of maternally exposed rats and mice. To study the involvement of the Ahr gene in producing the toxic phenotype with respect to testicular development, we administered a relatively high dose of TCDD to mice with three different maternally derived Ahr genotypic traits, and then compared several Ahr-dependent alterations among male reproductive systems on Postnatal Day 14. Reduction in anogenital distance and expression of prostatic epithelial genes in the urogenital complex (UGC) were detected in Ahr(+/+) and Ahr(+/-) mice exposed to TCDD, whereas no difference was observed in Ahr(-/-) mice. In situ hybridization revealed the absence of probasin mRNA expression in the prostate epithelium, despite the obvious development of prostatic lobes in TCDD-exposed mice. In contrast to obvious prostatic dysfunction and induction of cytochrome P450 (CYP) family genes in the UGC by TCDD, no alterations in testicular functions were observed in germ cell/Sertoli cell/interstitial cell marker gene expression or CYP family induction. No histopathological changes were observed among the three genotypes and between control and TCDD-exposed mice. Therefore, mouse external genitalia and prostatic development are much more sensitive to TCDD treatment than testis. Further, the Ahr gene, analyzed in this study, does not significantly contribute to testicular function during perinatal and immature stages, and the developing mouse testis appears to be quite resistant to TCDD exposure.

The effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin on foetal male rat steroidogenesis

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is the most toxic and widely investigated dioxin congener. In utero and lactational exposure to TCDD results in developmental and reproductive defects that are the most sensitive endpoints for TCDD toxicity. TCDD has a potential to interfere with steroid metabolism, but the mechanisms by which this occurs are not well understood. In this study, we investigated the effects of TCDD on prenatal rat steroidogenesis. Pregnant Sprague-Dawley female rats were treated once with TCDD (0, 0.3 or 1 microg/kg) by gavage on embryonic day (ED) 11 and the expression levels of androgen (AR) and estrogen receptors (ER), steroidogenic enzymes (P450scc and 3beta-HSD) and four regulatory factors (StAR, SF-1, GATA-4 and Insl-3) involved in foetal Leydig cell and adrenal function were analysed on ED 19.5. Hormonal status of male foetuses was determined by measuring testicular testosterone (T) levels, plasma luteinizing hormone (LH) and corticosterone concentrations. In utero exposure to TCDD reduced intratesticular T of foetal males (significant at 0.3 microg/kg TCDD) and tended to reduce the protein expression of ERalpha and AR of foetal male rat testis. Foetal male rat plasma LH levels were significantly reduced at the dose of 1 microg/kg TCDD, while corticosterone levels tended to be increased possibly because of the TCDD-induced stress. Only minor alterations in steroidogenesis were observed in rat adrenal. mRNA expression of developmental regulatory factors was not influenced by foetal TCDD exposure, except for significantly reduced adrenal SF-1. The results demonstrate that maternal exposure to TCDD suppressed testicular steroidogenesis of 19.5-day-old foetal male Sprague-Dawley rat. The highest dose of TCDD (1 microg/kg) had also an effect on pituitary LH secretion. Our data implicate that TCDD has direct testicular and pituitary effects on foetal male rat but with different dose-responses. These changes can lead to impaired steroidogenesis and it may result in the maldevelopment of the testis and weaken masculinization.

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.

Serum dioxin, testosterone, and subsequent risk of benign prostatic hyperplasia: a prospective cohort study of Air Force veterans

BACKGROUND

Operation Ranch Hand veterans were involved in spraying herbicides, including Agent Orange, during the Vietnam War in 1962-1971; Agent Orange was contaminated with 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). It has been hypothesized that dioxins may be partially responsible for an increase of male reproductive tract disorders such as testicular cancer, cryptorchidism, and hypospadias.

OBJECTIVES

In this study, our objective was to assess the effect of serum TCDD concentration on the risk of development of benign prostatic hyperplasia (BPH) and on serum testosterone levels.

METHODS

This study was a longitudinal, prospective cohort study made up of U.S. Air Force veterans involved in Operation Ranch Hand. Other Air Force veterans who did not spray herbicides were included as comparisons. BPH was determined by medical record review and by medical examinations conducted during the study. Data were available for 971 Ranch Hand and 1,266 comparison veterans. We investigated the relationship between BPH and serum TCDD level using the Cox proportional hazards models adjusted for testosterone levels, body mass index (BMI), and the percentage change in BMI per year.

RESULTS

In univariate and multivariate analyses, the risk of BPH decreased with increasing serum TCDD in the comparison group. The multivariate risk ratio for BPH in the comparison group was 0.84 (95% confidence interval, 0.73-0.98). Excluding men with prostate cancer, inflammatory or other prostatic diseases did not substantially alter the association. Serum testosterone levels were inversely associated with serum TCDD levels in both Ranch Hand and comparison groups.

CONCLUSIONS

TCDD exposure at general population levels is associated with a decreasing risk of BPH with higher exposure levels. TCDD exposure is also negatively associated with serum testosterone levels.

Epigenetic inactivation of the dioxin-responsive cytochrome P4501A1 gene in human prostate cancer

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD; dioxin) is a toxic environmental contaminant that works through dioxin response elements (DRE) to activate gene expression. We tested the hypothesis that cancer-related epigenetic changes suppress dioxin activation of the cytochrome P4501A1 (CYP1A1) gene. 5-Aza-2'-deoxycytidine (5-aza-CdR), an inhibitor of DNA methylation, increases TCDD-inducible CYP1A1 mRNA expression in cancerous LNCaP cells but not in noncancerous PWR-1E and RWPE-1 cells (all human prostate cell lines). Bisulfite DNA sequencing shows that the TCDD-responsive CYP1A1 enhancer is highly methylated in LNCaP cells but not in RWPE-1 cells. In vivo footprinting experiments reveal that unmethylated DRE sites do not bind protein in response to TCDD in LNCaP cells, whereas inducible DRE occupancy occurs in RWPE-1 cells. Pretreatment of LNCaP cells with 5-aza-CdR partially restores TCDD-inducible DRE occupancy, showing that DNA methylation indirectly suppresses DRE occupancy. Chromatin immunoprecipitation experiments reveal that LNCaP cells lack trimethyl histone H3 lysine 4, a mark of active genes, on the CYP1A1 regulatory region, whereas this histone modification is prevalent in PWR-1E and RWPE-1 cells. We also analyzed CYP1A1 enhancer methylation in human prostate tissue DNA. We do not detect CYP1A1 enhancer methylation in 30 DNA samples isolated from noncancerous prostate tissue. In contrast, 11 of 30 prostate tumor DNA samples have detectable CYP1A1 enhancer methylation, indicating that it is hypermethylated in prostate tumors. This is the first report that shows that CYP1A1 is aberrantly hypermethylated in human prostate cancer and has an altered, inaccessible chromatin structure that suppresses its dioxin responsiveness.

Dioxin exposure and benign prostatic hyperplasia

OBJECTIVE

Dioxins decrease prostate weight, reduce androgen responsiveness, and inhibit prostate morphogenesis in rats. We assessed the association of dioxins and benign prostatic hyperplasia (BPH) in participants in the National Health and Nutritional Examination Survey 1999-2000.

METHODS

Forty-two participants were classified as having BPH and 99 were classified as controls. Dioxin exposure was expressed as dioxin toxic equivalents (TEQ). Age, body mass index, waist circumference, race/ethnicity, smoking, physical activity, and education were assessed as potential confounders.

RESULTS

After age adjustment, men without BPH had 20.9% higher TEQs (95% confidence interval [CI] = 5.4-38.7%) as compared with men with BPH. On weighted, multivariate, logistic regression analyses, men with higher dioxin levels had lower odds of having BPH (odds ratio = 0.22, 95% CI = 0.08-0.62).

CONCLUSIONS

Dioxin exposure in the general population may be associated with decreased odds of BPH. Our study findings need to be confirmed.

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.

Prostate cancer in US Air Force veterans of the Vietnam war

US Air Force veterans of Operation Ranch Hand sprayed herbicides contaminated with 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in Vietnam from 1962 to 1971. Comparisons served in Southeast Asia (SEA) during the same time period but did not spray herbicides. Here we investigate a potential association between exposure to TCDD and prostate cancer. Data were available for 2516 veterans (1019 Ranch Hand and 1497 Comparison) who participated in at least one of six physical examinations starting in 1982 and had a measurement of serum TCDD. We assigned Ranch Hands to two exposure categories: Lower and Higher, based on their median 20-year cumulative TCDD level. In total, 81 Comparison and 59 Ranch Hand prostate cancers were identified between 1 January 1982 and 31 December 2003. We found no overall increase in the risk of prostate cancer in Ranch Hand veterans versus the Comparisons. There was a positive association in Ranch Hand veterans in the Higher TCDD category who served in SEA before 1969 (RR=2.27, 95% CI 1.11-4.66) when more contaminated herbicides were used, but the number of cases was small (n=15). A within-group comparison found that in Comparison veterans, time served in SEA was associated with an increased risk of prostate cancer (RR=2.18, 95% CI 1.27-3.76, >789 days versus < or =789 days). No increase in the risk of prostate cancer was observed within the Ranch Hand group in association with TCDD or time served in SEA. These analyses suggest that a longer service in SEA and exposures other than TCDD may have increased the risk of prostate cancer in Comparison veterans.

In utero and lactational exposure to TCDD; steroidogenic outcomes differ in male and female rat pups

TCDD (2,3,7,8-tetrachlorodibenzo-p-dioxin) has a potency to induce decreased fertility and structural reproductive anomalies in male and female mammals. While the activity profile of sex steroid hormone production distinctly differs in developing males and females, we wanted to analyze sex-specific effects of TCDD introduced in utero and via lactation on gonadal steroidogenesis and gonadotropin levels in male and female rat infant pups. One oral dose of TCDD (0, 0.04, 0.2, or 1.0 microg/kg) was given to dams on gestational day (GD) 13. Plasma testosterone, estradiol, progesterone, follicle stimulating hormone (FSH), luteinizing hormone (LH), and gonadal mRNA levels for steroid acute regulatory protein (StAR), cytochrome P-450 cholesterol side-chain cleavage (P450scc), 3beta-hydroxy-steroid-dehydrogenase/Delta(5)-Delta(4) isomerase type I (3beta-HSD1), P-450 17alpha-hydroxylase/17,20-lyase (P450-17alpha), and cytochrome P-450 aromatase (P450arom) were determined on postnatal days (PND) 10-16. TCDD 1.0 mug/kg reduced body weights but did not affect relative testis weight or alter testicular and ovarian histology. Plasma estradiol levels in dams and female pups were reduced on PND 14 and 16. Progesterone levels remained unaltered, and FSH levels were increased in female pups. In males, testosterone levels were elevated on PND 10. Gonadal mRNA levels for StAR and steroidogenic enzymes increased during the postnatal growth. TCDD caused no changes in relatively low testicular mRNA levels. However, significant reductions in StAR and P450arom mRNA levels were seen in PND 14 ovaries, and P450arom activity was decreased in isolated ovarian follicles. We conclude that developing testis and male gonadotropin secretion are resistant to TCDD-induced toxicity. In female pups, reduced estradiol, ovarian P450arom expression and enzyme activity levels, and elevated FSH levels may have a role in the development of ovarian dysfunction reported in TCDD-exposed females.

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.

2,3,7,8-Tetrachlorodibenzo-p-dioxin Blocks Androgen-Dependent Cell Proliferation of LNCaP Cells through Modulation of pRB Phosphorylation

Cell-cycle regulatory events associated with inhibition of androgen-dependent cell proliferation by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) were studied in the human-derived LNCaP cell line. TCDD blocked the G(1) to S transition of LNCaP cells synchronized in G(0)/G(1) when these cells were induced to reinitiate cell-cycle progression by dihydrotestosterone (DHT). Western blot analyses of these cells revealed altered expression levels of G(1) regulatory proteins, including increases in hypophosphorylated retinoblastoma protein and concomitant decreases in cyclin D1. p21(WAF1/CIP1), which is involved in the assembly of cyclin D1/cyclin-dependent kinase-4 complexes, was increased by DHT or TCDD when each compound was administered singly but was reduced to background levels in cells simultaneously treated with DHT and TCDD. Reporter gene assays revealed the presence of several Ah receptor response-element motifs in the promoter and first intron of the p21(WAF1/CIP1) gene that respond to TCDD-mediated Ah receptor activation independently of p53. Transcription studies showed that activation of aryl hydrocarbon receptor blocks androgen-dependent gene induction in LNCaP cells as well as in African green monkey CV-1 cells. These data point to at least two mechanisms whereby TCDD blocks androgen receptor function: 1) by blocking androgen-induced cell proliferation through modulation of the expression and activities of regulatory proteins controlling cell-cycle progression; and 2) by squelching androgen receptor-mediated gene transcription through receptor cross-talk, possibly involving competition for coregulators or by direct protein interaction.

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.

A new luciferase reporter gene assay for the detection of androgenic and antiandrogenic effects based on a human prostate specific antigen promoter and PC3/AR human prostate cancer cells

We developed a new mammalian cell-based luciferase reporter gene assay for androgenic and antiandrogenic activities of chemicals and environmental samples. Environmental samples usually have a complex matrix that may contain the constituents acting as androgen receptor (AR) agonists, AR antagonists or aryl hydrocarbon receptor (AhR) agonists. AhR agonists are known to elicit the antiandrogenic effect through cross-talk between AR and AhR signal transduction pathways. In this study, PC3/AR human prostate carcinoma cells were transiently transfected with a prostate-specific antigen (PSA) promoter-driven luciferase expression plasmid. The cells were treated with a test compound or an environmental sample for 24 h at 37 degrees C and then measured for luciferase activity. The luciferase activity was induced by dihydrotestosterone (DHT) in a concentration-dependent manner in a concentration range from 10 fM to 1 nM. R1881, a synthetic androgen receptor agonist, induced luciferase activity and its inductive effects was additive to that of DHT. The luciferase activity was not induced by cortisol, a glucocorticoid, progesterone, a progestin, and 17beta-estradiol, an estrogen in a concentration range of up to 1 microM. DHT-induced luciferase activity was reduced by bicalutamide and cyproterone acetate, AR antagonists, and also by benzo[a]pyrene, an aryl hydrocarbon receptor agonist, through AhR-mediated pathways. All of these findings indicate that the present assay system correctly responds to AR agonists, AR antagonists and AhR agonist and, therefore, it is a powerful tool for the sensitive and selective screening of chemicals and environmental samples for their androgenic and antiandrogenic activities. We developed the first assay system, in which the expression of luciferase was driven by the promoter of a prostate-specific antigen gene, a typical human androgen-regulated gene.

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.

A role of aryl hydrocarbon receptor in the antiandrogenic effects of polycyclic aromatic hydrocarbons in LNCaP human prostate carcinoma cells

The role of aryl hydrocarbon receptor (AhR) on the antiandrogenic effects of polycyclic aromatic hydrocarbons (PAHs) was studied in LNCaP cells. The PAHs used in this study were chrysene (Chr), benzo[ k]fluoranthene (BkF), benzo[ a]pyrene (BaP), anthracene (Ant) and pyrene (Pyr). Chr, BkF and BaP acted as AhR agonists in LNCaP cells, while Ant and Pyr did not. The antiandrogenic effects of the PAHs were evaluated on the basis of regulation of prostate-specific antigen (PSA) mRNA and protein levels by 5alpha-dihydrotestosterone (DHT). Chr, BkF and BaP exhibited an antiandrogenic effect, but Ant and Pyr did not. alpha-Naphthoflavone (alpha-NF), an AhR antagonist, reversed the antiandrogen action of Chr, BkF and BaP, suggesting a requirement for activated AhR. The antiandrogenic PAHs did not significantly decrease androgen receptor (AR) levels or cellular DHT concentrations. Gel mobility shift assays revealed that Chr, BkF and BaP inhibited the binding of AR in nuclear extracts to oligonucleotide probes containing the AR-responsive element (ARE), whereas Ant and Pyr had no effect. The antiandrogenic PAHs elevated mRNA levels of c-fos and c-jun. Since activator protein-1 (AP-1), a heterodimer of c-jun and c-fos proteins, is known to inhibit binding of AR to ARE by protein-protein interaction with AR, the findings in the present study suggest a possible involvement of AP-1 in the antiandrogenic effects of PAHs acting as AhR agonists. These results suggest that AhR can stimulate AP-1 expression resulting in inhibition of the binding of AR to ARE in the transcription regulatory region of target genes such as PSA.

In utero and lactational treatment with 2,3,7,8-tetrachlorodibenzo-p-dioxin impairs mammary gland differentiation but does not block the response to exogenous estrogen in the postpubertal female rat

These experiments tested whether in utero and lactational exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) alters mammary gland differentiation, estrogen receptor alpha (ERalpha) expression levels, or the response to estrogen in the female postpubertal rat mammary gland. Pregnant Holtzman rats were administered a single oral dose of 1 microg/kg TCDD or vehicle on gestation-day 15. Exposed and non-exposed female offspring were weaned on postnatal day 21 and ovariectomized at 9 weeks of age. Two weeks later, both TCDD and control animals were divided into 3 groups, receiving treatment with placebo, 0.025, or 0.1 mg 17beta-estradiol pellet implants. After 48 h, mammary tissue was removed for analysis following euthanasia. TCDD-exposed mammary glands demonstrated impaired differentiation as measured by the distribution of terminal ductal structures and increased expression levels of ERalpha. The response to exogenous estrogen was tested in TCDD-exposed animals and compared to control non-exposed animals. Estrogen stimulation of the TCDD-exposed glands induced progesterone receptor expression and mammary gland differentiation as measured by a shift in distribution from terminal end buds and terminal ducts to Types I and II lobules. Control glands were better differentiated at baseline and did not exhibit any significant changes in the distribution of terminal ductal structures following estrogen stimulation. The increase in progesterone receptor-expression levels by exogenous estrogen in control glands was similar to the TCDD-exposed glands. These experiments demonstrate that in utero and lactational exposures to TCDD impair mammary gland differentiation but that TCDD-exposed mammary glands retain the ability to differentiate in response to estrogen.

Prenatal testosterone and luteinizing hormone levels in male rats exposed during pregnancy to 2,3,7,8-tetrachlorodibenzo-p-dioxin and diethylstilbestrol

Changes in the perinatal testosterone surge have been related to demasculinization of the central nervous system and androgen-dependent growth of the reproductive organs in male mammals. Earlier reports suggest that 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) interferes with androgen production, but the perinatal effects have remained elusive. In the present study we explored in utero-effects of TCDD (0.05, 0.1, 0.5, and 1.0 microg/kg), introduced on day 13.5 of pregnancy, on prenatal (day 19.5 post-conception [p.c.]) testosterone (T) surge and pituitary luteinizing hormone (LH) production in TCDD-resistant Han/Wistar (H/W) and TCDD-sensitive Long-Evans (L-E) rats. To elucidate estrogenic effects on T and LH production, Sprague-Dawley (S-D) fetuses with previously known DES-sensitivity were exposed in utero to diethylstilbestrol (DES, 100-300 microg/kg) on days 13.5, 15.5, and 17.5 p.c. For comparison, H/W fetuses that responded to TCDD treatments were exposed to DES at concentration of 100 microg/kg. It was found that TCDD has a stimulatory effect on testicular T synthesis in the H/W fetuses and that their circulating T concentrations increased significantly. The effect was not seen in the inbred L-E fetuses, which throughout the study showed considerably low testicular T levels. Pituitary LH concentrations also increased in the H/W fetuses exposed to TCDD. Effects of TCDD (1.0 microg/kg) in the H/W fetuses could be confirmed in vitro by human chorionic gonadotropin (hCG) stimulation assay showing the highest response rate in the TCDD exposed testes. Stimulation of cyclic AMP (adenosine-3', 5'-cyclic monophosphate[cAMP]) production was not considerably altered by in utero TCDD exposure. A significant depression in testicular and plasma T content was seen in the DES-exposed S-D and H/W fetuses, but pituitary LH levels did not alter considerably. In the presence of hCG, DES-exposed testes showed lower in vitro T and cAMP production rates compared to the untreated testes. TCDD (1.0 microg/kg) increased and DES decreased the male body weight gain, but the changes were not sex-dependent. It is concluded that TCDD may increase the amplitude of the prenatal testosterone surge in male rats by stimulating pituitary LH production and enhancing the sensitivity of the fetal testis to LH. DES, on the contrary, apparently impairs testicular steroidogenesis and pituitary function.

Seveso Women's Health Study: does zone of residence predict individual TCDD exposure?

The compound, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), is produced as an unwanted by-product of various chemical reactions and combustion processes, including the manufacture of chlorinated phenols and derivatives. In animals, TCDD exposure is associated with toxic, carcinogenic, developmental, and reproductive effects. In 1976, a chemical plant explosion in Seveso, Italy, exposed the residents in the surrounding community to the highest exposure to TCDD known in humans. Materials from an aerosol cloud of sodium hydroxide, sodium trichlorophenate and TCDD were deposited over an 18.1 km2 area. As evidence of the significant level of TCDD exposure, numerous animals died and 193 cases of chloracne were reported among residents of the area. Initially, the contaminated area was divided into three major exposure Zones (A, B, R) based on the concentration of TCDD in surface soils. To date, the majority of epidemiologic studies conducted in Seveso have used Zone of residence as a proxy measure of exposure. The purpose of the present study is to validate the use of Zone of residence in Seveso as a proxy measure of exposure against individual serum TCDD measurement, and to determine whether questionnaire information can improve the accuracy of the exposure classification. Using data collected from the Seveso Women's Health Study (SWHS), the first comprehensive epidemiologic study of the reproductive health of women in Seveso, we determined that Zone of residence is a good predictor of individual serum TCDD level, explaining 24% of the variance. Using questionnaire information could have improved prediction of individual exposure levels in Seveso, increasing the percent of the variation in serum TCDD levels explained to 42%.

Seveso Women's Health Study: a study of the effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin on reproductive health

Although reproductive effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) exposure have been reported in numerous investigations of animals, studies of this association in humans are limited. In 1976, an explosion in Seveso, Italy exposed the surrounding population to among the highest levels of TCDD recorded in humans. The relatively pure exposure to TCDD and the ability to quantify individual level TCDD exposure from sera collected in 1976 for the Seveso cohort affords a unique opportunity to evaluate the potential dose-response relationship between TCDD exposure and a spectrum of reproductive endpoints. The Seveso Women's Health Study (SWHS) is the first comprehensive study of the reproductive health of a human population exposed to TCDD. The primary objectives of the study are to investigate the relationship of TCDD and the following endpoints: (1) endometriosis; (2) menstrual cycle characteristics; (3) age at menarche; (4) birth outcomes of pregnancies conceived after 1976; (5) time to conception and clinical infertility; and (6) age at menopause. Included in the SWHS cohort are women who were 0-40 yr old in 1976, who have adequate stored sera collected between 1976 and 1980, and who resided in Zones A or B at the time of the accident. All women were interviewed extensively about their reproductive and pregnancy history and had a blood draw. For an eligible subset of women, a pelvic exam and transvaginal ultrasound were conducted and a menstrual diary was completed. More than 95% of the women were located 20 yr after the accident and roughly 80% of the cohort agreed to participate. Data collection was completed in July 1998, serum TCDD analysis of samples for analysis of endometriosis as a nested case-control study was completed in October 1998, and statistical analysis of these data should be completed in early 1999. Serum samples are now being analyzed in order to relate TCDD levels with the remaining reproductive outcomes.

In utero exposure to antiandrogens alters the responsiveness of the prostate to p,p'-DDE in adult rats and may induce prostatic inflammation

DDE is an environmental pollutant with antiandrogenic properties. Following administration to pregnant rats, DDE was shown to cause feminization in the male offspring at the neonatal stages but did not affect the pubertal growth of accessory sex organs. In this study, we examined the potential of in utero exposure to antiandrogens to alter the responsiveness of the male rats to subsequent DDE challenge. Pregnant Long-Evans rats were dosed by gavage from Gestation Day 14 to 18 at 0, 10 (low dose), or 100 (high dose) mg DDE, or 40 mg flutamide/kg body wt (bw)/day (in utero treatment). At approximately 80 days of age, the male offspring from each of the four in utero treatment groups were divided into two groups. One group received the adult treatment of four daily gavage administrations of DDE at 70 mg/kg bw (adult treatment), while the second group served as the adult treatment control (adult control). The in utero treatment resulted in 18, 31, and 53% reductions of ventral prostate weights at approximately 85 days of age compared to the control for the low- and high-dose DDE and flutamide groups, respectively. These results suggest that the in utero antiandrogen treatments produced a latent effect on prostate growth that became pronounced only in the postpubertal stage. The in utero treatment also altered the responsiveness of the prostate to the adult treatment, indicated by a significant reduction in ventral prostate weight that was seen only in the control group of the in utero treatment but not in the other groups. The in utero treatment was also associated with expression of testosterone-repressed prostatic message-2 in the adult ventral prostate. In addition, a few prostates in the high-dose DDE- and flutamide-treated groups of the in utero treatment were found to have chronic suppurative prostatitis. While other types of hormonal manipulations have been shown to incite similar responses in rat prostate, the possible linkage between in utero antiandrogen treatment and prostatic inflammation needs to be further evaluated.

Effects of an environmental endocrine disruptor on fetal development, estrogen receptor(alpha) and epidermal growth factor receptor expression in the porcine male genital tract

PURPOSE

We studied the effect of a potent reproductive tract toxin, 2,3,7,8-tetrachlorodibenzo-rho-dioxin, on fetal development and expression of estrogen receptor alpha and epidermal growth factor receptor (EGFR) in male swine.

MATERIALS AND METHODS

Fetal domestic swine and miniswine were injected with 1 microg./kg. dioxin on day 50 of gestation and removed near term (114 days). Germ cell counts were performed on sections of formalin fixed testes. Estrogen receptor a protein, and messenger ribonucleic acid (mRNA) and EGFR mRNA expression were analyzed in frozen tissue using Western blotting and semiquantitative reverse transcriptase polymerase chain reaction.

RESULTS

Of 15 dioxin exposed male offspring 8 (53%) had genital anomalies, including cryptorchidism in 4, epididymal detachment in 1, epididymal atresia in 1 and vasal dilatation in 3, while 3 of 17 control male swine (18%) had incompletely descended testes (p = 0.06). High intra-abdominal testes were found in 3 of 4 cryptorchid dioxin exposed but no control male swine. Mean germ cell number per tubule was 4.0+/-1.1 and 2.7+/-0.7 in control and dioxin groups, respectively (p = 0.01). Estrogen receptor a protein and mRNA were identified in fetal uterus, testis, gubernaculum and epididymis. Protein levels were 2 to 3-fold higher in dioxin exposed testis, and mRNA levels were significantly lower in gubernaculum and epididymis. EGFR mRNA expression was similar in treated and control testis and epididymis.

CONCLUSIONS

Preliminary data suggest that dioxin produces cryptorchidism and wolffian duct anomalies in male swine exposed just before mid gestation. Germ cell counts and estrogen receptor alpha mRNA expression in gubernaculum and epididymis were significantly reduced, and estrogen receptor a protein expression in testis appeared to be increased by dioxin exposure. Aberrant regulation of estrogen receptor a expression by dioxin may contribute to reproductive tract anomalies in male fetuses.

Cross-talk between 2,3,7,8-tetrachlorodibenzo-p-dioxin and testosterone signal transduction pathways in LNCaP prostate cancer cells

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) and related compounds modulate various endocrine functions by enhancing ligand metabolism, altering hormone synthesis, down regulating receptor levels, and interfering with gene transcription. In the present study, we investigated the effects of TCDD on testosterone signal transduction pathways and vice versa in the androgen receptor (AR) positive LNCaP prostate cancer cell line. TCDD induced CYP1A1 mRNA and related enzyme activity in these cells, with dose and time-dependence. Both normal and testosterone-stimulated cell growth was inhibited by TCDD. The expression levels of the aryl hydrocarbon receptor (AhR), the aryl hydrocarbon receptor nuclear translocator (ARNT), and AR were not affected by exposure to TCDD at a dose of 10 nM for a 24 hr time period. Testosterone treatment dose-dependently inhibited the TCDD-induced CYP1A1 mRNA accumulation and related enzyme activity. Reciprocally, TCDD also dose-dependently inhibited testosterone-dependent transcriptional activity and testosterone-regulated prostate specific antigen (PSA) expression. Taken together, these results demonstrate antiandrogenic functions of TCDD and a specific ligand-induced bilateral transcriptional interference between TCDD and testosterone mediated signal transduction pathways.

Interactive effects of TCDD and p,p'-DDE on male reproductive tract development in in utero and lactationally exposed rats

The developing male rat reproductive system is highly sensitive to low doses of TCDD and p,p'-DDE (DDE), which exert antiandrogenic effects via different mechanisms. This study investigates the interactive effects of in utero and lactational exposure to a mixture of these compounds. Pregnant Holtzman rats received one of the following: vehicle on gestation day (GD) 14-18, 0.25 microgram/kg TCDD on GD15, 100 mg/kg DDE on GD 14-18, or 0.25 microgram/kg TCDD on GD15 and 100 mg/kg DDE on GD 14-18. Male offspring were euthanized on postnatal day (PND) 21 (weaning), PND 32 (prepuberty), PND 49 (puberty), and PND 63 (postpuberty). Coadministration of these doses of TCDD and DDE appeared to potentiate their individual actions on prostate weight on PND 21, while immunostaining for the prostatic androgen receptor exhibited patterns characteristic of the effects of both compounds individually. Cauda epididymal sperm number was reduced by each compound but was not further reduced by exposure to TCDD and DDE in combination. Anogenital distance, age at onset of puberty, daily sperm production, testicular and accessory sex organ weight (nonprostate), and levels of prostatic androgen-regulated gene transcripts are affected at higher doses of both compounds, but not at the doses used in the present study. Only DDE-treated animals retained nipples on PND 13. Serum androgen levels did not differ between treatment groups. In conclusion, the developing rat prostate is uniquely sensitive to the effects of TCDD and DDE, which may augment one another's effects in this organ.

Expression of the aryl hydrocarbon receptor (AhR) and the aryl hydrocarbon receptor nuclear translocator (ARNT) in fetal, benign hyperplastic, and malignant prostate

BACKGROUND

Androgen-dependent tissue has been reported to be affected by chemical ligands of the aryl hydrocarbon receptor (AhR), a ligand-activated transcription factor, which heterodimerizes with the aryl hydrocarbon receptor nuclear translocator protein (ARNT).

METHODS

Fetal (n = 3), benign hyperplastic (BPH) (n = 10), and carcinomatous (CaP) (n = 19) prostate tissues were analyzed using immunohistochemistry. Western blot analysis was used to confirm the identity of the recognized proteins.

RESULTS

Immunoblotting of enriched prostatic epithelial cells (EC) and stromal cells revealed constitutive expression of bands at around 110 kDa and 90 kDa, using anti-AhR and anti-ARNT, respectively. Immunohistology of the fetal specimens revealed heterogeneous cytoplasmic and nuclear AhR expression of immature EC and mesenchymal cells. Constitutive expression of AhR (primarily cytoplasmic) and ARNT (nuclear and cytoplasmic) by the majority of adult basal and secretory EC, CaP, and smooth muscle cells was confirmed in situ. The most intense anti-AhR/-ARNT reactivity was found on smooth muscle cells, followed by EC and fibrocytes. Secretory BPH-EC revealed significantly decreased AhR expression when compared to normal tissue segments. By contrast, anti-AhR reactivity was frequently increased in the more dedifferentiated tumor areas.

CONCLUSIONS

These findings suggest that an undefined physiologic AhR ligand(s) as well as environmental factors may exert effects on EC and smooth muscle cells in the prostate through binding to these receptors.

In utero and lactational exposure of the male rat to 2,3,7,8-tetrachlorodibenzo-p-dioxin impairs prostate development. 1. Effects on gene expression

In utero and lactational 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) exposure decreases rat prostate weight without decreasing circulating androgen concentrations. Because one mechanism by which TCDD is thought to cause toxicity is by aryl hydrocarbon receptor (AhR)-mediated alterations in gene transcription, the goals of this study were to determine whether the developing prostate expresses the AhR and its dimerization partner, the AhR nuclear translocator (ARNT); to determine whether in utero and lactational TCDD exposure is capable of directly activating gene transcription in the developing prostate; and to identify prostatic mRNAs that exhibit altered abundance in response to in utero and lactational TCDD exposure. Pregnant Holtzman rats were administered TCDD (1.0 microgram/kg po) or vehicle on Gestation Day (GD) 15, and male offspring were euthanized between Postnatal Days (PNDs) 1 and 63. Using reverse transcriptase-polymerase chain reaction (RT-PCR), mRNAs encoding the AhR and ARNT were detected in both ventral and dorsolateral prostates from control animals throughout postnatal development. ARNT protein was expressed in the majority of stromal nuclei early in development, whereas ARNT expression in the prostate epithelium was initially cytoplasmic but became nuclear as development progressed. GD 15 TCDD exposure increased cytochrome P4501A1 (CYP1A1) mRNA and protein in whole prostates between PNDs 7 and 21. In these TCDD-exposed animals, CYP1A1 protein was localized to the epithelium. In order to define other genes in the developing prostate that might be regulated by TCDD at the level of mRNA, RNA samples from PND 21 whole prostates from control and TCDD-exposed animals were compared using mRNA differential display. Although no growth-regulatory candidates were identified using this screening technique, a ventral prostate-specific, androgen-regulated mRNA (20-kDa protein) was identified that seemed to be downregulated by TCDD exposure. Northern blot analysis confirmed this decrease at PND 21 and further showed that the downregulation was transient. Similar results were obtained for four additional androgen-regulated prostatic mRNAs (prostatic binding protein [PBP], Royal Winnipeg Ballet [RWB], probasin, and dorsal protein-1 [DP-1]), all of which are markers of a differentiated ductal epithelium. In contrast, TCDD exposure of adult male rats (25 micrograms TCDD/kg, 24 h) greatly induced CYP1A1 mRNA without affecting the abundance of prostate-specific, androgen-regulated mRNAs. These results suggest that the transient decreases in androgen-regulated prostatic mRNA abundance observed in response to in utero and lactational TCDD exposure were probably not the result of direct action of the activated AhR on these genes but instead were reflective of a TCDD-induced delay in prostate development.

In utero and lactational exposure of the male rat to 2,3,7,8-tetrachlorodibenzo-p-dioxin impairs prostate development. 2. Effects on growth and cytodifferentiation

In the male Holtzman rat, in utero and lactational 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) exposure decreases prostate weight without inhibiting testicular androgen production or decreasing circulating androgen concentrations. Therefore, the present study sought to characterize effects of TCDD exposure on prostate development, from very early outgrowth from the urogenital sinus (Gestation Day [GD] 20) until rapid growth and differentiation are essentially complete (Postnatal Day [PND] 32). Pregnant Holtzman rats were administered a single dose of TCDD (1.0 microgram/kg po) or vehicle on GD 15 and offspring were exposed via placental transfer (GD 20 euthanasia) or placental and subsequent lactational transfer until euthanasia (if before PND 21) or weaning. Results show that the prostatic epithelial budding process was impaired by in utero TCDD exposure, as evidence by significant decreases in the number of buds emerging from dorsal, lateral, and ventral aspects of the GD 20 urogenital sinus. Ventral prostate cell proliferation index was significantly decreased on PND 1 but was similar to or higher than control at later times, whereas apoptosis was an extremely rare event in ventral prostates from both control and TCDD-exposed animals. Delays were noted in the differentiation of pericordal smooth muscle cells and luminal epithelial cells. In addition, ventral prostates from approximately 40% of TCDD-exposed animals examined on PNDs 21 and 32 exhibited alterations in the histological arrangement of cell types that could not be explained by a developmental delay. Compared to controls, these ventral prostates exhibited a disorganized, hyperplastic epithelium containing fewer luminal epithelial cells and an increased density or continuous layer of basal epithelial cells, as well as thicker periductal smooth muscle sheaths. In addition, in ventral prostates from TCDD-exposed animals, the intensity of androgen receptor staining was relatively low in the central and distal epithelium, and the number of androgen receptor-positive cells was relatively high in the periductal stroma. These data suggest that in utero and lactational TCDD exposure interferes with prostate development by decreasing very early epithelial growth, delaying cytodifferentiation, and, in the most severely affected animals, producing alterations in epithelial and stromal cell histological arrangement and the spatial distribution of androgen receptor expression that may be of permanent consequence.

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 low doses of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on the reproductive system of male offspring rats were examined. The dams were treated subcutaneously 2 weeks prior to mating and throughout mating, pregnancy, and lactation. They received an initial loading dose of 25, 60, or 300 ng TCDD/kg body wt, followed by a weekly maintenance dose of 5, 12, or 60 ng TCCD/kg body wt (TCDD 25/5, TCDD 60/12, and TCDD 300/60). Three dams per group were killed on Gestation Day 21 and the fetuses were removed. The concentration of TCDD in the maternal liver and fat was measured. After birth, developmental landmarks in male rats were monitored. At weaning, the concentration of TCDD in the offspring liver and testis was determined. Effects on male reproduction were studied on Postnatal Days (PND) 70 and 170. At weaning, the concentration of TCDD in the offspring liver was 0.24, 0.39, and 1.78 ng/g in the TCDD 25/5, TCDD 60/12, and TCDD 300/60 groups, respectively. In the testes, the concentration of TCDD was 0.25 ng/g in the TCDD 25/5 and TCDD 60/12 groups and 0.28 ng/g in the TCDD 300/60 group. The number of sperm per cauda epididymis was reduced in TCDD groups at puberty and at adulthood. Daily sperm production was permanently decreased as was the sperm transit rate in the TCDD-exposed male rats, thus increasing the time required by the sperm to pass through the cauda epididymis. Moreover, the male rats of the TCDD groups showed an increased number of abnormal sperm when investigated at adulthood. Similarly, mounting and intromission latencies were significantly increased in the TCDD 25/5 and TCDD 300/60 groups. In the highest dose group, serum testosterone concentration was decreased at adulthood. Likewise, in this dose group permanent changes including pyknotic nuclei and the occurrence of cell debris in the lumen were revealed. The lowest adverse effect level and the no observed effect level can be estimated to be substantially lower than the estimated daily dose of the lowest dose which is 0.8 ng/kg body wt/day. Sperm parameters were more susceptible than the other end points investigated. However, the question as to whether such doses exposed throughout gestation and lactation induce subtle changes in humans remains to be determined.

Responsiveness of the adult male rat reproductive tract to 2,3,7,8-tetrachlorodibenzo-p-dioxin exposure: Ah receptor and ARNT expression, CYP1A1 induction, and Ah receptor down-regulation

Exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) either in adulthood or during late fetal and early postnatal development causes a variety of adverse effects on the male rat reproductive system. It was therefore of interest to identify male rat reproductive organs and cell types within these organs that might be direct targets of TCDD exposure. Because TCDD toxicity could possibly be the result of alterations in gene transcription mediated by the TCDD/aryl hydrocarbon receptor (AhR)/AhR nuclear translocator (ARNT) complex, the presence of the AhR and ARNT in the various organs of the adult male reproductive tract was examined using Western blotting. Both proteins were detectable in all organs examined (testis, epididymis, vas deferens, ventral prostate, dorsolateral [combined dorsal and lateral] prostate, and seminal vesicle). Although technical difficulties precluded the immunohistochemical evaluation of AhR distribution in these organs, ARNT was localized in all organs in a variety of cell types, including germ cells, epithelial cells, fibroblasts, smooth muscle cells, and endothelial cells. Subcellular localization varied across organs and across cell types within these organs. In order to determine whether TCDD exposure could alter gene expression in these organs, animals were dosed with TCDD (25 micrograms/kg po) or vehicle and euthanized at 24 h, and cytochrome P4501A1 (CYP1A1) expression was evaluated. By Western blotting, only the ventral and dorsolateral prostates exhibited significant induction of CYP1A1. Immunohistochemistry confirmed this induction and localized CYP1A1 expression to epithelial cells of the ventral and lateral lobes of the prostate. Immunohistochemistry also revealed CYP1A1 induction in select epithelial cells in the epididymis and seminal vesicle, as well as endothelial cells in the vas deferens and seminal vesicle. No induction was observed in the testis. Finally, AhR and ARNT expression in TCDD-exposed and control animals was evaluated by Western blotting. Results revealed no effect of TCDD exposure on ARNT protein expression, while AhR expression was decreased to 5-51% of control in all organs examined. In summary, both AhR and ARNT were expressed in all organs of the adult male rat reproductive tract examined, and epithelial and/or endothelial cells within each of these organs (with the exception of the testis) were responsive to TCDD exposure in terms of CYP1A1 induction. In addition, all tissues exhibited marked reductions in AhR protein content after TCDD exposure that did not correlate with the magnitude of the CYP1A1 response.

Vulnerability of the endocrine system to xenobiotic influence

Natural sex hormones are most important factors guaranteeing the homeostasis of male and female sexual functions, including sexual differentiation and reproduction. Main target tissues include bone and skin, cardiovascular system, and possibly central nervous and immune systems. In medicine, synthetic hormonal substances with agonistic and antagonistic properties have been widely used for decades. Therapeutic benefit is the aim, and the many possibilities to interfere with normal or pathological hormonal situations are rather well understood. Synthetic hormonal agonists or (partial) antagonists may exhibit specific affinities to special receptors resulting in a spectrum of organotropies, or they may even induce opposite actions on different targets. Although not a new issue, environmental substances mimicking potentials of sex hormones have recently gained increased attention. There is not need to reinvent the wheel, since most (adverse) effects may be revealed with today's routine procedures used for testing medicinal substances, but some additional testing strategies should be included. Adverse effects of ecohormones may preferentially affect systems other than the human organism (assuming lower exposure and possibly lower susceptibility). Nevertheless, this survey is confined to possible alterations in the mammalian organism, since such effects are best understood from numerous experimental studies and clinical trials.

In utero and lactational exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin: effects on development of the male and female reproductive system of the mouse

To evaluate effects of in utero and lactational 2,3,7,8-tetrachlorodibenzo-rho-dioxin (TCDD) exposure on male and female reproductive system development of the mouse, the offspring of pregnant ICR mice administered 0, 15, 30, or 60 microg TCDD/kg on Gestation Day (GD) 14 were examined at the postweanling, pubertal, young adult, and adult stages of development. Dam and offspring body weights and prenatal and postnatal mortality were unaffected by TCDD exposure. The most sensitive endpoints in male offspring were decreased ventral prostate, coagulating gland, and thymus weights, accelerated eye opening, and hydronephrosis. Decreases in pituitary gland weight and epididymal sperm numbers were also found in TCDD-exposed male offspring. Testis, epididymis, and dorsolateral prostate weights, anogenital distance, latencies to testis descent and to preputial separation, and serum testosterone concentrations were unaffected. At the highest maternal TCDD dose uterus weights were decreased in female offspring evaluated during estrus and diestrus. No morphologic changes in the external genitalia of female offspring were found, nor were there alterations in ovary or pituitary gland weights. Cross-species comparisons showed that the mouse was not as sensitive to TCDD-induced developmental reproductive toxicity as the rat and hamster. Many endpoints affected by TCDD in rat and hamster offspring were either not affected or were less sensitive in mouse offspring. Endpoints of androgenic status were not affected in the mouse, decreases in accessory sex organ weights were restricted to fewer organs in the mouse, and decreases in daily sperm production were not found in the mouse. The only developmental reproductive endpoint observed in all three species was a reduction in epididymal sperm numbers.