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

Female-to-male differential transcription patterns of miRNA-mRNA networks in the livers of dioxin-exposed mice

Non-coding microRNAs (miRNAs) have important roles in regulating the expression of liver mRNAs in response to xenobiotic-exposure, but their roles concerning dioxins such as TCDD (2,3,7,8-Tetrachlorodibenzo-p-dioxin) are less clear. This report concerns the potential implication of liver (class I) and circulating (class II) miRNAs in hepatotoxicity of female and male mice after acute exposure to TCDD. The data show that, of a total of 38 types of miRNAs, the expression of eight miRNAs were upregulated in both female and male mice exposed to TCDD. Inversely, the expression of nine miRNAs were significantly downregulated in both animal genders. Moreover, certain miRNAs were preferentially induced in either females or males. The potential downstream regulatory effects of miRNAs on their target genes was evaluated by determining the expression of three group of genes that are potentially involved in cancer biogenesis, other diseases and in hepatotoxicity. It was found that certain cancer-related genes were more highly expressed females rather than males after exposure to TCDD. Furthermore, a paradoxical female-to-male transcriptional pattern was found for several disease-related and hepatotoxicity-related genes. These results suggest the possibility of developing of new miRNA-specific interfering molecules to address their dysfunctions as caused by TCDD.

Analyze the toxicities of benzalkonium chloride as a COVID-19 disinfectant in physiological goldfish (Carassius auratus)

Background and Aims

Coronavirus disease-2019 (COVID-19) impacts increasing the use of disinfectants (benzalkonium chloride), which indirectly accumulate in water. The disinfectant accumulation in waters has been studied, but there has been no study of its impact on aquatic commodities, especially fish with a high sensitivity, one of which is goldfish (Carassius auratus). Benzalkonium chloride can potentially affect several body proteins, including the cytoskeleton, nervous and endocrine systems, and fish physiology. This study aimed to determine the impact of benzalkonium chloride as a disinfectant on the level of color brightness, growth, gill histopathology, and mortality in goldfish. This investigation provides input into the impact of using disinfectants to prevent COVID-19 on aquatic commodities.

Materials and Methods

This study utilized goldfish specimens sourced from Tulungagung, East Java, Indonesia. The experiment involved different concentration levels of benzalkonium chloride: (T1) 0 mg/L, (T2) 0.03 mg/L, (T3) 0.06 mg/L, (T4) 0.09 mg/L, and (T5) 0.12 mg/L. The research data were subjected to an analysis of variance for analysis. In cases where significant differences were observed, Duncan's test was conducted for color brightness, growth, and mortality data. Furthermore, if the gill histopathological data yielded significant differences, additional tests were applied (Kruskal-Wallis and Mann-Whitney test).

Results

The findings of this study demonstrated significant differences (p < 0.05) in the level of color brightness, growth, gill histopathology, and mortality in goldfish in response to varying concentrations of benzalkonium chloride. The relationship between the length and weight of the goldfish was analyzed using regression coefficients (b values), which were determined as 4.86, -0.04, -0.2, 0.8, and -0.07, respectively. Notably, the brightness level in the T2 group exhibited positive color results with a hue value of 11.55°, while optimal growth was observed in the T4 group, as evidenced by b value of 0.8. The gill histopathological data showed significant differences (p < 0.05). The scoring of histopathological damage in the goldfish gills ranged from 0 to 10, with higher scores indicating more severe damage. The highest total score of 10 was observed in the T5 group exposed to a concentration of 0.12 mg/L, resulting in an 85% mortality rate. This indicates that benzalkonium chloride, with its toxic compounds, can disrupt the respiratory system of fish and lead to death.

Conclusion

The effects of benzalkonium chloride were evident even at a concentration of 0.03 mg/L. With increasing concentration, there was an increase in mortality rate, a decrease in growth, and a rise in histopathological damage to the gills. These findings highlight the negative impact of using conventional disinfectants on water and its organisms, emphasizing the need for further research on environmentally friendly alternatives.

Rhamnazin ameliorates 2, 3, 7, 8-tetrachlorodibenzo-p-dioxin-evoked testicular toxicity by restoring biochemical, spermatogenic and histological profile in male albino rats

2,3,7,8 tetrachlorodibenzo-p-dioxin (TCDD) is a potential environmental toxin that has the ability to affect male reproductive tract. Rhamnazin is a naturally present flavone that displays multiple medicinal properties. Therefore, the current study was designed to determine the mitigative role of rhamnazin against TCDD induced reproductive damage. 48 adult male albino rats were randomly separated into four groups: control, TCDD (10 µgkg-1), TCDD + rhamnazin (10 µgkg-1 + 5 mgkg-1 respectively) and rhamnazin (5 mgkg-1). The trial was conducted for 56 days. TCDD intoxication notably affected superoxide dismutase (SOD), glutathione peroxidase (GPx), glutathione reductase (GSR) and catalase (CAT) activities, besides reactive oxygen species (ROS) and malondialdehyde (MDA) concentrations were augmented. TCDD administration also lowered sperm motility, viability, sperm number, while it augmented the sperm morphological (tail, neck/midpiece and head) anomalies. Moreover, it decreased the levels of follicle-stimulating hormone (FSH), luteinizing hormone (LH) and plasma testosterone. Moreover, TCDD reduced steroidogenic enzymes i.e., 17-beta hydroxysteroid dehydrogenase (17β-HSD), steroidogenic acute regulatory protein (StAR) and 3-beta hydroxysteroid dehydrogenase (3β-HSD) as well as B-cell lymphoma 2 (Bcl-2) expressions, but increased the expressions of Bcl-2-associated X protein (Bax) and cysteine-aspartic acid protease (Caspase-3). Furthermore, TCDD exposure also induced histopathological anomalies in testicular tissues. However, the supplementation of rhamnazin recovered all the mentioned damages in the testicles. The outcomes revealed that rhamnazin can ameliorate TCDD induced reproductive toxicity due to its anti-oxidant, anti-apoptotic and androgenic nature.

Gestational and lactational exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin in mice: Neurobehavioral effects on female offspring

Emerging evidence suggests that perinatal dioxin exposure affects neurodevelopment and impairs multiple brain functions, including cognitive, language, learning and emotion, in the offspring. However, the impacts of gestational and lactational exposure to dioxin on behavior and related molecular events are still not fully understood. In this study, female C57BL/6J mice were orally administered three doses of 2, 3, 7, 8-tetrachlorodibenzo-p-dioxin (TCDD) (0.1 or 10 μg/kg body weight (bw)) during the pregnancy and lactation periods. The locomotion, exploration and anxiety-related behaviors were examined by an open field test of the young adult female offspring at postnatal day 68. We found that the maternal TCDD exposure, particularly at a low dose, increased movement ability, novelty-exploration and certain anxiety-related behaviors in the offspring. Such hyperactivity-like behaviors were accompanied by the upregulation of certain genes associated with cholinergic neurotransmission or synaptogenesis in the offspring brain. In accordance with the potential enhancement of cholinergic neurotransmission due to the gene upregulations, the enzymatic activity of acetylcholinesterase was decreased, which might lead to excess acetylcholine and consequent hyper-excitation at the synapses. Thus, we found that gestational and lactational TCDD exposure at low dose caused hyperactivity-like behaviors in young adult female offspring and speculated the enhancement of cholinergic neurotransmission and synaptogenesis as potential molecular events underlying the neurobehavioral effects.

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.

Windows of sensitivity to toxic chemicals in the development of reproductive effects: an analysis of ATSDR's toxicological profile database

Development of the fetus is a complex process influenced by many factors including genetics, maternal health, and environmental exposures to toxic chemicals. Adverse developmental effects on the reproductive system have the potential to harm generations beyond those directly exposed. Here, we review the available literature in Agency for Toxic Substances and Disease Registry toxicological profiles related to reproductive-developmental effects in animals following in utero exposure to chemicals. We attempt to identify windows of sensitivity. In the discussion, we correlate the findings with human development. The endpoints noted are fertility, estrus, anogenital distance, sex ratio, spermatogenesis, and mammary gland development. We identified some windows of sensitivity; however, the results were hampered by chronic-exposure studies designed to detect effects occurring throughout developmental, including multi-generational studies. This paper demonstrates the need for more acute studies in animals aimed at understanding time periods of development that are more susceptible to chemically induced adverse effects.

Hepatoprotective and antioxidant effects of dietary Glycyrrhiza polysaccharide against TCDD-induced hepatic injury and RT-PCR quantification of AHR2, ARNT2, CYP1A mRNA in Jian Carp (Cyprinus carpio var. Jian)

To evaluate the protective effects of Glycyrrhiza polysaccharide (GPS) against 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)-induced hepatotoxicity in Jian carp, the fish were fed diets containing GPS at doses of 0.1, 0.5 and 1.0g/kg for 60days before an intraperitoneal injection of 0.6μg/kg TCDD at a volume of 0.05mL/10g body weight. At 72hr post-injection, blood and liver samples were taken for biochemical analysis and the fish liver samples were used for the preparation of pathological slices. The results showed that increases in alanine aminotransferase (GPT), aspartate aminotransferase (GOT), lactate dehydrogenase (LDH), and alkaline phosphatase (AKP) in serum induced by TCDD were significantly inhibited by pre-treatment with 1.0g/kg GPS. Following the 1.0g/kg GPS pre-treatment, total protein (TP), albumin (Alb), catalase (CAT), glutathione peroxidase (GPx), total antioxidant capacity (T-AOC) and superoxide dismutase (SOD) activities in liver tissue increased significantly, malondialdehyde (MDA) formation (P<0.05 or P<0.01) was significantly inhibited, and the expression of cytochrome P4501A (CYP1A), aryl hydrocarbon receptor 2 (AHR2) and aryl hydrocarbon receptor nuclear translocator 2 (ARNT2) mRNA (P<0.05) was significantly enhanced. Histological observations on fish liver were obtained by preparing paraffin tissue sections via HE staining, and the results showed that histological changes were obviously reduced by 0.5 and 1.0g/kg GPS. GPS significantly reduced liver tissue damage caused by TCDD. Overall, these results proved the hepatoprotective effect of GPS in protecting against fish liver injury induced by TCDD, and supported the use of GPS (1.0g/kg) as a hepatoprotective and antioxidant agent in fish.

A Study of 2,3,7,8-Tetrachlorodibenzo-p-dioxin Induced Liver Injury in Jian Carp (Cyprinus carpio var. Jian) Using Precision-Cut Liver Slices

The aim of this study was to establish a model for the study of liver injury induced by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in Jian carp using precision-cut liver slices (PCLS). PCLS were treated with TCDD at concentrations of 0, 0.05, 0.1, 0.3, and 0.6 μg/L for 6 h, followed by collection of the culture supernatant and PCLS for analysis. Several biochemical indices were analyzed, including glutamic pyruvic transaminase (GPT), glutamic oxaloacetic transaminase (GOT), lactate dehydrogenase (LDH), superoxide dismutase (SOD), glutathione peroxidase (GSH-Px), and malondialdehyde (MDA). Expression of mRNA was also estimated for cytochrome P4501A (CYP1A), aryl hydrocarbon receptor2 (AhR2), and aryl hydrocarbon receptor nuclear translocator2 (ARNT2). Results showed that some significant effects (p < 0.05) in MDA, GSH-Px and PCLS viability were observed at a TCDD concentration as low as 0.05 µg/L, and the observed effects increased with exposure concentration. Following exposure to TCDD for 6 h at a concentration of 0.3 μg/L, significant increases (p < 0.01) in the content of GPT, GOT, MDA, and LDH were observed, while SOD activity, GSH-Px activity, and PCLS viability were decreased (p < 0.01 or p < 0.05). Exposure to 0.3 μg/L TCDD also resulted in increased expression of mRNA for CYP1A, AhR2, and ARNT2. Overall, these results provide evidence of TCDD-induced liver injury and oxidative stress in Jian carp. These results also support the use of PCLS as an in vitro model for the evaluation of hepatotoxicity in Jian carp.

Dietary Manganese Modulates PCB126 Toxicity, Metal Status, and MnSOD in the Rat

PCB126 (3,3',4,4',5-pentachlorobiphenyl) is a potent aryl hydrocarbon receptor agonist and induces oxidative stress. Because liver manganese (Mn) levels decrease in response to PCB126, a Mn dietary study was designed to investigate the role of Mn in PCB126 toxicity. Male Sprague Dawley rats received diets containing 0, 10, or 150 ppm added Mn for 3 weeks, followed by a single ip injection of corn oil or PCB126 (5 µmol/kg body weight). After 2 weeks, Mn, Cu, Zn, and Fe levels in the heart, liver, and liver mitochondria, and Mn-containing superoxide dismutase (MnSOD) and metallothionein mRNA, MnSOD protein, and MnSOD activity were determined. Mn levels in liver, heart, and liver mitochondria were strongly decreased by the Mn-deficient diet. Small effects on Fe levels and a stepwise increase in MnSOD activity with dietary Mn were also visible. PCB126 caused profound changes in Cu (up), Zn, Fe, and Mn (down) in liver, but not in heart, and differing effects (Cu, Zn, and Fe up, Mn down) in liver mitochondria. Liver MnSOD and metallothionein mRNA levels and MnSOD protein were increased but MnSOD activity was decreased by PCB126. PCB126-induced liver enlargement was dose-dependently reduced with increasing dietary Mn. These changes in metals homeostasis and MnSOD activity in liver but not heart may be a/the mechanism of PCB126 liver-specific toxicity. Specifically, transport of Fenton metals (Cu, Fe) into and Mn out of the mitochondria, a probable mechanism for lower MnSOD activity, may be a/the cause of PCB126-induced oxidative stress. The role of metallothioneins needs further evaluation. Dietary Mn slightly alleviated PCB126-induced toxicities.

Effect of tocopherol and acetylsalicylic acid on the biochemical indices of blood in dioxin-exposed rats

New sources of dioxins and increased dioxin concentrations in the environment, coupled with their increased bioavailability along the food chain and accumulation in adipose tissues, contribute to various adverse long-term biological effects. The purpose of the study was to determine whether tocopherol protects the CNS by decreasing the pro-inflammatory influence of free radicals generated by TCDD; whether acetylsalicylic acid inhibits the production of inflammatory mediators; and whether the combined administration of tocopherol and acetylsalicylic acid to TCDD-exposed rats has a potential CNS-protective effect. The study included 117 rats divided into 8 groups: 75 female and 12 male Buffalo rats aged 8-10 weeks, weighing 140-160 g; as well as 30 female rats aged 6 weeks and weighing 120 g, which were the offspring of females from each study group. In the experiment, the following substances were used: 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), dosed at 5 μg/kg BW and 12.5 μg/kg BW, diluted in a 1% DMSO solution at the concentration of 1 μg/ml; α-tocopherol acetate, dosed at 30 mg/kg BW, in 0.2 ml of oil solution; and acetylsalicylic acid, 50mg/kg BW, suspended in 0.5 ml of starch solution, administered orally using a feeding tube. Pleurisy was induced by an injection of 0.15 ml of 1% carrageenin solution. The use of tocopherol reduces the adverse effects of the inflammatory reaction induced by TCDD. Administering tocopherol improves protein metabolism by reducing protein catabolism, and raises γ-globulin fraction levels. Combined acetylsalicylic acid and tocopherol suppress catabolic processes accompanying inflammation.

Olive oil and its phenolic compounds (hydroxytyrosol and tyrosol) ameliorated TCDD-induced heptotoxicity in rats via inhibition of oxidative stress and apoptosis

CONTEXT

Naturally occurring polyphenols including olive oil (OO) and its constituents hydroxytyrosol (HT) and tyrosol (TY), consumed in the Mediterranean diet, have shown to treat various ailments due to their remarkable antioxidant properties.

OBJECTIVE

The present study investigates the hepatoprotective effects of OO and its phenolic compounds HT and TY against TCDD-induced hepatotoxicity in male Wistar rats.

MATERIALS AND METHODS

TCDD was administered at a dose of 100 ng/kg p.o. for 20 d. Administration of OO (10 ml/kg; oral), HT (0.5 mg/kg; oral), and TY (30 mg/kg; i.p) was started 5 d prior to TCDD administration, and continued for 25 d with or without TCDD administration. At the end of the experiment (25 d), blood was taken for biochemical analyses and liver for the measurement of macromolecular damages, antioxidant status, expressions of CYP1A1, and apoptotic factors.

RESULTS

TCDD administration resulted in significant (p < 0.05) increase in the level of hepatic stress markers ALT (101.6 ± 3.07 IU/l), AST (295.0 ± 3.0 IU/l), and ALP (266.66 ± 3.7 IU/l). Also, biochemical analyses of liver reported elevation in nitrite and protein carbonyl content and depletion of NQO1 and HO. However, OO, HT, and TY restored the antioxidant status. Protein expressions by Western Blot technique showed an increase in the level of CYP1A1 and Bax and a decreased level of Bcl-2 on TCDD treatment, and vice versa on OO, HT, and TY treatment.

DISCUSSION AND CONCLUSION

Our work concludes that dietary supplementation of OO, HT, and TY could serve as a potential preventive drug for TCDD-induced hepatotoxicity.

Histopathological, ultrastructural, and immunohistochemical assessment of hippocampus structures of rats exposed to TCDD and high doses of tocopherol and acetylsalicylic acid

The effect of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on central nervous system consists of changing expression of estrogen receptors, whereas the result of chronic inflammatory reaction caused by dioxin is occurrence of destructive changes in various organs connected with disturbed metabolism of connective tissue and damage of cells. The aim of the study was to determine the effect of dioxins on function, ultrastructure, and cytological and histological structure of hippocampus, particularly on expression of estrogen receptors in central nervous system as well as to define protective influence of tocopherol (TCP) and acetylsalicylic acid (ASA) on the decrease in activity of proinflammatory effects in central nervous system. It was shown that TCDD contributes to destructive and inflammatory changes along with demyelization of myelin sheaths and atrophy of estrogen receptors in hippocampus. Dioxin contributes to atrophy of estrogen receptors in hippocampus, in which also destructive and inflammatory changes were found along with demyelination of myelin sheaths. Histopathological and ultrastructural image of hippocampus areas in rats, in which both TCP and ASA were used, is characterized by poorly expressed degenerative changes and smaller inflammatory reactivity. Using both TCP and ASA has a protective effect on functions of central nervous system.

Genomic and genotoxic responses to controlled weathered-oil exposures confirm and extend field studies on impacts of the Deepwater Horizon oil spill on native killifish

To understand the ecotoxicological impacts of the Deepwater Horizon oil spill, field studies provide a context for ecological realism but laboratory-based studies offer power for connecting biological effects with specific causes. As a complement to field studies, we characterized genome-wide gene expression responses of Gulf killifish (Fundulus grandis) to oil-contaminated waters in controlled laboratory exposures. Transcriptional responses to the highest concentrations of oiled water in the laboratory were predictive of field-observed responses that coincided with the timing and location of major oiling. The transcriptional response to the low concentration (∼10-fold lower than the high concentration) was distinct from the high concentration and was not predictive of major oiling in the field. The high concentration response was characterized by activation of the molecular signaling pathway that facilitates oil metabolism and oil toxicity. The high concentration also induced DNA damage. The low concentration invoked expression of genes that may support a compensatory response, including genes associated with regulation of transcription, cell cycle progression, RNA processing, DNA damage, and apoptosis. We conclude that the gene expression response detected in the field was a robust indicator of exposure to the toxic components of contaminating oil, that animals in the field were exposed to relatively high concentrations that are especially damaging to early life stages, and that such exposures can damage DNA.

Peroxiredoxin I protein, a potential biomarker of hydronephrosis in fetal mice exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin

OBJECTIVE

In previous studies, we established an animal model of human congenital hydronephrosis with exposure of developing mice to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), but the etiopathogenesis is not entirely clear. The present study was to identify the changes that may be involved in the etiology at the protein level.

METHODS

C57BL/6J mice fetuses were treated with TCDD. Comparative proteomic analysis was adopted to identify the proteins associated with hydronephrosis induced by TCDD.

RESULTS

Two-dimensional electrophoresis display revealed that 19 protein spots were differentially expressed in the upper urinary tract tissues in fetal mice after exposure to TCDD. Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) identified 12 up-regulated proteins: peroxiredoxin I (Prx I), cadherin 6, gamma-actin, radixin, desmin, type II transforming growth factor-beta receptor, chromogranin B, serum albumin precursor, transferrin, hypothetical protein LOC70984, lipk protein, and zinc finger protein 336. Histochemical staining indicated that Prx I protein was positively expressed in the ureteric epithelium in the treated group, and not in the control group, which is consistent with MALDI-TOF-MS.

CONCLUSION

Prx I protein may be a potential biomarker or responsive protein of hydronephrosis in fetal mice induced by TCDD.

Anogenital distance and its application in environmental health research

Anogenital distance (AGD), a useful anthropometric measurement for genital development in both animals and humans, was originally found by reproductive toxicologists in rodent experiments. As an easy-to-measure and sensitive marker, AGD has become a bioassay of fetal androgen action and a well-established reproductive toxicity endpoint in animals. It is generally accepted that AGD is sexually dimorphic in many mammals, with males having longer AGD than females. Exposure to proposed endocrine disruptors may result in reduced AGD; thus, it has been used to measure health effects of compounds with endocrine-altering properties or endocrine-disrupting chemicals (EDCs) in environmental toxicology. Moreover, AGD is an important clinical measure to address endocrine-sensitive endpoints in the first year of life and to assess the adverse impact of in utero exposure to environmental EDCs. Recently, AGD has been identified as one of the endpoints in the US Environmental Protection Agency guidelines for reproductive toxicity studies in humans, but use of AGD in human studies is still rare, and the results remain mixed and inconclusive due to many reasons. In order to achieve a breakthrough, researchers are endeavoring to standardize the measurement of AGD, normalize age-specific population data in different ethnic groups, and conduct more in-depth human researches in this field.

Maternal dioxin exposure and pregnancy outcomes over 30 years of follow-up in Seveso

Animal evidence suggests an association between exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and adverse pregnancy outcomes. Epidemiologic studies report inconsistent results, but are limited by narrow range of exposure, small sample size, and lack of a biologic measure of highest lifetime exposure. On July 10, 1976, a chemical explosion in Seveso, Italy resulted in the highest known residential exposure to TCDD. In 1996, we initiated the Seveso Women's Health Study (SWHS), a retrospective cohort of TCDD exposure and reproductive health. Individual-level TCDD was measured in serum collected soon after the explosion. After 20years of follow-up, we found no association between maternal TCDD in 1976 serum or estimated at pregnancy and spontaneous abortion (SAB), fetal growth, or gestational length. Here, we present an updated analysis of TCDD exposure and adverse pregnancy outcomes from a subsequent follow-up of the SWHS cohort in 2008-2009. SWHS women had 1211 post-explosion pregnancies through the 2008-2009 follow-up. We found no association between TCDD estimated at pregnancy and SAB, fetal growth, or gestational length. However, we found a non-significant inverse association between maternal 1976 serum TCDD and birthweight (adjusted β=-22.8, 95% CI: -80.1, 34.6). The association was stronger among first post-explosion births, but remained non-significant (adjusted β=-47.7, 95% CI: -107.3, 11.9). SWHS is the first study to be able to consider two potentially relevant measures of TCDD exposure: highest lifetime dose and in utero. Our results, although non-significant, suggest that highest dose may be more relevant in epidemiologic studies of TCDD and pregnancy outcomes.

Low-dose effects of hormones and endocrine disruptors

Endogenous hormones have effects on tissue morphology, cell physiology, and behaviors at low doses. In fact, hormones are known to circulate in the part-per-trillion and part-per-billion concentrations, making them highly effective and potent signaling molecules. Many endocrine-disrupting chemicals (EDCs) mimic hormones, yet there is strong debate over whether these chemicals can also have effects at low doses. In the 1990s, scientists proposed the "low-dose hypothesis," which postulated that EDCs affect humans and animals at environmentally relevant doses. This chapter focuses on data that support and refute the low-dose hypothesis. A case study examining the highly controversial example of bisphenol A and its low-dose effects on the prostate is examined through the lens of endocrinology. Finally, the chapter concludes with a discussion of factors that can influence the ability of a study to detect and interpret low-dose effects appropriately.

In utero exposure to dioxins and dioxin-like compounds and anogenital distance in newborns and infants

BACKGROUND

Anogenital distance in animals is used as a measure of fetal androgen action. Prenatal exposure to dioxins and dioxin-like compounds in rodents causes reproductive changes in male offspring and decreases anogenital distance.

OBJECTIVE

We assessed whether in utero exposure to dioxins and dioxin-like compounds adversely influences anogenital distance in newborns and young children (median age, 16 months; range, 1-31 months).

METHODS

We measured anogenital distance among participants of the "Rhea" mother-child cohort study in Crete and the Hospital del Mar (HMAR) cohort in Barcelona. Anogenital distance (AGD; anus to upper penis), anoscrotal distance (ASD; anus to scrotum), and penis width (PW) were measured in 119 newborn and 239 young boys; anoclitoral (ACD; anus to clitoris) and anofourchetal distance (AFD; anus to fourchette) were measured in 118 newborn and 223 young girls. We estimated plasma dioxin-like activity in maternal blood samples collected at delivery with the Dioxin-Responsive Chemically Activated LUciferase eXpression (DR CALUX®) bioassay.

RESULTS

Anogenital distances were sexually dimorphic, being longer in males than females. Plasma dioxin-like activity was negatively associated with AGD in male newborns. The estimated change in AGD per 10 pg CALUX®-toxic equivalent/g lipid increase was -0.44 mm (95% CI: -0.80, -0.08) after adjusting for confounders. Negative but smaller and nonsignificant associations were observed for AGD in young boys. No associations were found in girls.

CONCLUSIONS

Male infants may be susceptible to endocrine-disrupting effects of dioxins. Our findings are consistent with the experimental animal evidence used by the Food and Agriculture Organization/World Health Organization to set recommendations for human dioxin intake.

Mono-(2-ethylhexyl) phthalate induces oxidative stress and inhibits growth of mouse ovarian antral follicles

Mono-(2-ethylhexyl) phthalate (MEHP) is the active metabolite of the most commonly used plasticizer, di-(2-ethylhexyl) phthalate, and is considered to be a reproductive toxicant. However, little is known about the effects of MEHP on ovarian antral follicles. Thus, the present study tested the hypothesis that MEHP inhibits follicle growth via oxidative stress pathways. The data indicate that MEHP increases reactive oxygen species (ROS) levels and inhibits follicle growth in antral follicles, whereas N-acetylcysteine (NAC; an antioxidant) restores ROS levels to control levels and rescues follicles from MEHP-induced inhibition of follicle growth. To further analyze the mechanism by which MEHP induces oxidative stress and inhibits follicle growth, the expression and activities of various key antioxidant enzymes (copper/zinc superoxide dismutase [SOD1], glutathione peroxidase [GPX], and catalase [CAT]) and the expression of key cell-cycle regulators (Ccnd2, Ccne1, and Cdk4) and apoptotic regulators (Bcl-2 and Bax) were compared in control and MEHP-treated follicles. The data indicate that MEHP inhibits the expression and activities of SOD1 and GPX; does not inhibit Cat expression; inhibits the expression of Ccnd2, Ccne1, Cdk4, and Bcl-2; but increases the expression of Bax compared to controls. Furthermore, NAC blocks these toxic effects of MEHP. Collectively, these data suggest that MEHP induces oxidative stress by disrupting the activities of antioxidant enzymes. This may lead to decreased expression of cell-cycle regulators and antiapoptotic regulators and increased expression of proapoptotic factors, which then may lead to inhibition of follicle growth.

Induction of Heat Shock Proteins and Antioxidant Enzymes in 2,3,7,8-TCDD-Induced Hepatotoxicity in Rats

2,3,7,8-Tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD) is an environmental toxicant with a polyhalogenated aromatic hydrocarbon structure and is one of the most toxic man-made chemicals. Exposure to 2,3,7,8-TCDD induces reproductive toxicity, immunotoxicity, and hepatotoxicity. In this study, we evaluated how 2,3,7,8-TCDD-induced hepatotoxicity affect the expression of heat shock proteins and antioxidant enzymes using the real-time polymerase chain reaction (PCR) in rat. 2,3,7,8-TCDD increased heat shock protein (Hsp27, α-B-crystallin, Mortalin, Hsp105, and Hsp90s) and antioxidant enzymes (SOD-3, GST and catalase) expression after a 1 day exposure in livers of rats, whereas heat shock protein (α-B-crystallin, Hsp90, and GRP78) and antioxidant enzymes (SOD-1, SOD-3, catalase, GST, and GPXs) expression decreased on day 2 and then slowly recovered back to control levels on day 8. These results suggest that heat shock proteins and antioxidant enzymes were induced as protective mechanisms against 2,3,7,8-TCDD induced hepatotoxicity, and that prolonged exposure depressed their levels, which recovered to control levels due to reduced 2,3,7,8-TCDD induced hepatotoxicity.

Hormones and endocrine-disrupting chemicals: low-dose effects and nonmonotonic dose responses

For decades, studies of endocrine-disrupting chemicals (EDCs) have challenged traditional concepts in toxicology, in particular the dogma of "the dose makes the poison," because EDCs can have effects at low doses that are not predicted by effects at higher doses. Here, we review two major concepts in EDC studies: low dose and nonmonotonicity. Low-dose effects were defined by the National Toxicology Program as those that occur in the range of human exposures or effects observed at doses below those used for traditional toxicological studies. We review the mechanistic data for low-dose effects and use a weight-of-evidence approach to analyze five examples from the EDC literature. Additionally, we explore nonmonotonic dose-response curves, defined as a nonlinear relationship between dose and effect where the slope of the curve changes sign somewhere within the range of doses examined. We provide a detailed discussion of the mechanisms responsible for generating these phenomena, plus hundreds of examples from the cell culture, animal, and epidemiology literature. We illustrate that nonmonotonic responses and low-dose effects are remarkably common in studies of natural hormones and EDCs. Whether low doses of EDCs influence certain human disorders is no longer conjecture, because epidemiological studies show that environmental exposures to EDCs are associated with human diseases and disabilities. We conclude that when nonmonotonic dose-response curves occur, the effects of low doses cannot be predicted by the effects observed at high doses. Thus, fundamental changes in chemical testing and safety determination are needed to protect human health.

Di (2-ethylhexyl) phthalate inhibits growth of mouse ovarian antral follicles through an oxidative stress pathway

Di (2-ethylhexyl) phthalate (DEHP) is a plasticizer that has been shown to inhibit growth of mouse antral follicles, however, little is known about the mechanisms by which DEHP does so. Oxidative stress has been linked to follicle growth inhibition as well as phthalate-induced toxicity in non-ovarian tissues. Thus, we hypothesized that DEHP causes oxidative stress and that this leads to inhibition of the growth of antral follicles. To test this hypothesis, antral follicles isolated from CD-1 mice (age 31-35days) were cultured with vehicle control (dimethylsulfoxide [DMSO]) or DEHP (1-100μg/ml)±N-acetyl cysteine (NAC, an antioxidant at 0.25-1mM). During culture, follicles were measured daily. At the end of culture, follicles were collected and processed for in vitro reactive oxygen species (ROS) assays to measure the presence of free radicals or for measurement of the expression and activity of various key antioxidant enzymes: Cu/Zn superoxide dismutase (SOD1), glutathione peroxidase (GPX) and catalase (CAT). The results indicate that DEHP inhibits the growth of follicles compared to DMSO control and that NAC (0.25-1mM) blocks the ability of DEHP to inhibit follicle growth. Furthermore, DEHP (10μg/ml) significantly increases ROS levels and reduces the expression and activity of SOD1 compared to DMSO controls, whereas NAC (0.5mM) rescues the effects of DEHP on ROS levels and SOD1. However, the expression and activity of GPX and CAT were not affected by DEHP treatment. Collectively, these data suggest that DEHP inhibits follicle growth by inducing production of ROS and by decreasing the expression and activity of SOD1.

Eicosapentaenoic acid protects against 2,3,7,8-tetrachlorodibenzo-p-dioxin-induced hepatic toxicity in cultured rat hepatocytes

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is a persistent and ubiquitous environmental contaminant. The health impact of TCDD exposure is of great concern to the general public. Recent reports have implied that eicosapentaenoic acid (EPA) might be a potential chemopreventive agent and influence hepatotoxicity. The aim of the current study was to explore the effectiveness of EPA in alleviating the toxicity of TCDD on primary cultured rat hepatocytes. EPA (5, 10 and 20 μM) was added to cultures alone or simultaneously with TCDD (5 and 10 μM). Rat hepatocytes were treated with TCDD and EPA for 48 h, and then cytotoxicity was detected by [3-(4,5-dimethyl-thiazol-2-yl) 2,5-diphenyltetrazolium bromide] (MTT) assay and lactate dehydrogenase (LDH) release, while total antioxidant capacity (TAC) and total oxidative stress (TOS) levels were determined to evaluate the oxidative injury. The DNA damage was also analyzed by liver micronucleus assay (LMN) and 8-oxo-2-deoxyguanosine (8-OH-dG). The results of MTT and LDH assays showed that TCDD but not EPA decreased cell viability. TCDD also increased TOS level and significantly decreased TAC level in rat hepatocytes in a clear dose dependent manner. On the basis of increasing doses, the dioxin caused significant increases of micronucleated hepatocytes (MNHEPs) and 8-OH-dG as compared to control culture. Whereas, in cultures treated with EPA alone, TOS level did not change and the level of TAC significantly increased. The presence of EPA with TCDD minimized the toxic effects of the dioxin on primary hepatocytes cultures. Noteworthy, EPA has a protective effect against TCDD-mediated DNA damages.