A repeated 28-day oral dose toxicity study of methoxychlor in rats, based on the 'enhanced OECD test guideline 407' for screening endocrine-disrupting chemicals

Long-Term Changes in Ovarian Follicles of Gilts Exposed Neonatally to Methoxychlor: Effects on Oocyte-Derived Factors, Anti-Müllerian Hormone, Follicle-Stimulating Hormone, and Cognate Receptors

In this paper, we investigated the effects of neonatal exposure to methoxychlor (MXC), a synthetic organochlorine used as an insecticide with estrogenic, antiestrogenic, and antiandrogenic activities on ovarian follicles of adult pigs. Piglets were injected with MXC (20 μg/kg body weight) or corn oil (controls) from postnatal Day 1 to Day 10 (n = 5 per group). Then, mRNA expression, protein abundance and immunolocalization of growth and differentiation factor 9 (GDF9), bone morphogenetic protein 15 (BMP15), anti-Müllerian hormone (AMH) and cognate receptors (ACVR1, BMPR1A, BMPR1B, TGFBR1, BMPR2, and AMHR2), as well as FSH receptor (FSHR) were examined in preantral and small antral ovarian follicles of sexually mature gilts. The plasma AMH and FSH levels were also assessed. In preantral follicles, neonatal exposure to MXC increased GDF9, BMPR1B, TGFBR1, and BMPR2 mRNAs, while the levels of AMH and BMP15 mRNAs decreased. In addition, MXC also decreased BMP15 and BMPR1B protein abundance. Regarding small antral follicles, neonatal exposure to MXC upregulated mRNAs for BMPR1B, BMPR2, and AMHR2 and downregulated mRNAs for AMH, BMPR1A, and FSHR. MXC decreased the protein abundance of AMH, and all examined receptors in small antral follicles. GDF9 and BMP15 were immunolocalized in oocytes and granulosa cells of preantral follicles of control and treated ovaries. All analyzed receptors were detected in the oocytes and granulosa cells of preantral follicles, and in the granulosa and theca cells of small antral follicles. The exception, however, was FSHR, which was detected only in the granulosa cells of small antral follicles. In addition, MXC decreased the plasma AMH and FSH concentrations. In conclusion, the present study may indicate long-term effects of neonatal MXC exposure on GDF9, BMP15, AMH, and FSH signaling in ovaries of adult pigs. However, the MXC effects varied at different stages of follicular development. It seems that neonatal MXC exposure may result in accelerated initial recruitment of ovarian follicles and impaired cyclic recruitment of antral follicles.

Endocrine Disruption of the Follicle-Stimulating Hormone Receptor Signaling During the Human Antral Follicle Growth

An increasing number of pollutants with endocrine disrupting potential are accumulating in the environment, increasing the exposure risk for humans. Several of them are known or suspected to interfere with endocrine signals, impairing reproductive functions. Follicle-stimulating hormone (FSH) is a glycoprotein playing an essential role in supporting antral follicle maturation and may be a target of disrupting chemicals (EDs) likely impacting female fertility. EDs may interfere with FSH-mediated signals at different levels, since they may modulate the mRNA or protein levels of both the hormone and its receptor (FSHR), perturb the functioning of partner membrane molecules, modify intracellular signal transduction pathways and gene expression. In vitro studies and animal models provided results helpful to understand ED modes of action and suggest that they could effectively play a role as molecules interfering with the female reproductive system. However, most of these data are potentially subjected to experimental limitations and need to be confirmed by long-term observations in human.

Exploration of fulvic acid as a functional excipient in line with the regulatory requirement

Fulvic acid, a humic substance often considered as a geopolymer, extracted from different natural resources like Shilajit, Peat, dissolved organic matters, etc. There are several reports of its pharmacological properties and its potential as pharmaceutical excipients. So, we have devised a project to strengthen its claim as a functional excipient. For the given project, lyophilized sample of a dietary supplement product (an aqueous solution of peat derived Fulvic acid) was used. The selected studies were typical for an excipient development like physicochemical properties, flow properties, compatibility with other excipient and stability studies, non-clinical safety studies (acute toxicity in mice whereas sub-acute toxicity in rats) and some functionality tests. We also suggest its ability to form co-crystal with natural phytochemicals. Our group has already reported its ability to enhance solubility and or bioavailability of different BCS class II drugs. Henceforth, we can propose that Fulvic acid appears a good candidate to be further explored as a functional excipient and should be evaluated as per the remaining recommendations of IPEC, USFDA, and USP.

Relationship between agrochemical compounds and mammary gland development and breast cancer

The exposure to agrochemical pesticides has been associated with several chronic diseases, including different types of cancer and reproductive disorders. In addition, because agrochemical pesticides may act as endocrine disrupting chemicals (EDCs) during different windows of susceptibility, they can increase the risk of impairing the normal development of the mammary gland and/or of developing mammary lesions. Therefore, the aim of this review is to summarize how exposure to different agrochemical pesticides suspected of being EDCs can interfere with the normal development of the mammary gland and the possible association with breast cancer. It has been shown that the mammary glands of male and female rats and mice are susceptible to exposure to non-organochlorine (vinclozolin, atrazine, glyphosate, chlorpyrifos) and organochlorine (endosulfan, methoxychlor, hexachlorobenzene) pesticides. Some of the effects of these compounds in experimental models include increased or decreased mammary development, impaired cell proliferation and steroid receptor expression and signaling, increased malignant cellular transformation and tumor development and angiogenesis. Contradictory findings have been found as to whether there is a causal link between the exposure or the pesticide body burden and breast cancer in humans. However, an association has been observed between pesticides (especially organochlorine compounds) and specific subtypes of breast cancer. Further studies are needed in both humans and experimental models to understand how agrochemical pesticides can induce or promote changes in the development, differentiation and/or malignant transformation of the mammary gland.

Single, 14-Day, and 13-Week Repeated Dose Toxicity Studies of Daily Oral Gelidium elegans Extract Administration to Rats

Gelidium elegans extract (GEE) is derived from a red alga from the Asia-Pacific region, which has antioxidant, anti-adipogenic, and anti-hyperglycemic effects. However, detailed studies of the toxicology of GEE have not been performed. We evaluated the single oral dose toxicity of GEE in male and female Sprague-Dawley (CD) rats. GEE did not cause deaths or have toxic effects at dosages of 5000 mg/kg/day, although compound-colored stools and diarrhea were observed in both sexes, which lasted <2 days. Therefore, the LD50 of GEE is likely to be >5000 mg/kg. We next evaluated the repeated oral dose toxicity of GEE in CD rats over 14 days and 13 weeks. GEE did not induce any significant toxicological changes in either sex at 2000 mg/kg/day. Repeated oral dose toxicity studies showed no adverse effects, in terms of clinical signs, mortality, body mass, food consumption, ophthalmic examination, urinalysis, hematology, serum biochemistry, necropsy, organ masses, or histopathology, at dosages of 500, 1000, or 2000 mg/kg/day. The no observed adverse effect level (NOAEL) for GEE is thus likely to be >2000 mg/kg/day, and no pathology was identified in potential target organs. Therefore, this study indicates that repeated oral dosing with GEE is safe in CD rats.

Effects of Endocrine-disrupting Chemicals on Female Reproductive Health

Endocrine-disrupting chemicals (EDCs) are increasingly prevalent in the environment and the evidence demonstrates that they affect reproductive health, has been accumulating for the last few decades. In this review of recent literature, we present evidence of the effects of estrogen-mimicking EDCs on female reproductive health especially the ovaries and uteri. As representative EDCs, data from studies with a pharmaceutical estrogen, diethylstilbestrol (DES), an organochlorine pesticide methoxychlor (MXC), a phytoestrogen (genistein), and a chemical used in plastics, bisphenol a (BPA) have been presented. We also discuss the effects of a commonly found plasticizer in the environment, a phthalate (DEHP), even though it is not a typical estrogenic EDC. Collectively, these studies show that exposures during fetal and neonatal periods cause developmental reprogramming leading to adult reproductive disease. Puberty, estrous cyclicity, ovarian follicular development, and uterine functions are all affected by exposure to these EDCs. Evidence that epigenetic modifications are involved in the progression to adult disease is also presented.

Determination of endocrine disruptors and endogenic androgens and estrogens in rat serum by high-performance liquid chromatography-tandem mass spectrometry

To simultaneously measure some targeted endocrine disruptors and several forms of sex hormones in rat serum, an accurate analytical procedure was developed. First, a comparison between a polymeric-based solid-phase extraction (SPE) and a micro-extraction by packed sorbent was performed to choose the optimal method to extract and concentrate the analytes: bisphenol A, atrazine, vinclozolin metabolite, testosterone, androstenedione, estrone, estradiol, estrone-sulfate and glucuronide and estradiol-sulfate and glucuronide. The analyses were then performed by high-performance liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS) with electrospray ionisation in positive and negative modes. The protocol based on SPE was validated using the ICH/2005 guidelines. The validation demonstrated good performance in terms of linearity (R(2)>0.99), recovery (71-90%) and repeatability (relative standard deviation: 1-18%). The method was sensitive with LOQ comprised between 0.1 and 0.4 ng/ml for androgens and between 0.098 and 10.2 ng/ml for estrogens. The results obtained on the serum of rats exposed to the targeted endocrine disruptors showed the suitability of this analytical strategy.

Interactions of endosulfan and methoxychlor involving CYP3A4 and CYP2B6 in human HepaRG cells

Humans are usually exposed to several pesticides simultaneously; consequently, combined actions between pesticides themselves or between pesticides and other chemicals need to be addressed in the risk assessment. Many pesticides are efficient activators of pregnane X receptor (PXR) and/or constitutive androstane receptor (CAR), two major nuclear receptors that are also activated by other substrates. In the present work, we searched for interactions between endosulfan and methoxychlor, two organochlorine pesticides whose major routes of metabolism involve CAR- and PXR-regulated CYP3A4 and CYP2B6, and whose mechanisms of action in humans remain poorly understood. For this purpose, HepaRG cells were treated with both pesticides separately or in mixture for 24 hours or 2 weeks at concentrations relevant to human exposure levels. In combination they exerted synergistic cytotoxic effects. Whatever the duration of treatment, both compounds increased CYP3A4 and CYP2B6 mRNA levels while differently affecting their corresponding activities. Endosulfan exerted a direct reversible inhibition of CYP3A4 activity that was confirmed in human liver microsomes. By contrast, methoxychlor induced this activity. The effects of the mixture on CYP3A4 activity were equal to the sum of those of each individual compound, suggesting an additive effect of each pesticide. Despite CYP2B6 activity being unchanged and increased with endosulfan and methoxychlor, respectively, no change was observed with their mixture, supporting an antagonistic effect. Altogether, our data suggest that CAR and PXR activators endosulfan and methoxychlor can interact together and with other exogenous substrates in human hepatocytes. Their effects on CYP3A4 and CYP2B6 activities could have important consequences if extrapolated to the in vivo situation.

Epigenetic effects of methoxychlor and vinclozolin on male gametes

Imprinting is an epigenetic form of gene regulation that mediates a parent-of-origin-dependent expression of the alleles of a number of genes. Imprinting, which occurs at specific sites within or surrounding the gene, called differentially methylated domains, consists in a methylation of CpGs. The appropriate transmission of genomics imprints is essential for the control of embryonic development and fetal growth. A number of endocrine disruptors (EDs) affect male reproductive tract development and spermatogenesis. It was postulated that the genetic effects of EDs might be induced by alterations in gene imprinting. We tested two EDs: methoxychlor and vinclozolin. Their administration during gestation induced in the offspring a decrease in sperm counts and significant modifications in the methylation pattern of a selection of paternally and maternally expressed canonical imprinted genes. The observation that imprinting was largely untouched in somatic cells suggests that EDs exert their damaging effects via the process of reprogramming that is unique to gamete development. Interestingly, the effects were transgenerational, although disappearing gradually from F1 to F3. A systematic analysis showed a heterogeneity in the CpG sensitivity to EDs. We propose that the deleterious effects of EDs on the male reproductive system are mediated by imprinting defects in the sperm. The reported effects of EDs on human male spermatogenesis might be mediated by analogous imprinting alterations.

Emblica officinalis Garten fruits extract ameliorates reproductive injury and oxidative testicular toxicity induced by chlorpyrifos in male rats

Organophosphate pesticides have destroying properties on male reproduction and chlorpyrifos adversely affects the male reproductive system. Emblica offcinalis Garten plays a vital role to challenge many diseases in human body. We investigated the induction of oxidative stress in the male reproductive system of adult rats (Wistar Strain) exposed to widely used organophosphate pesticide, Chlorpyrifos, and tried to establish the ameliorative properties of Emblica officinalis Garten with respect to reproductive reconstruction in them. Rats were divided into 2 groups, control group and experimental group, and the experimental group was divided into 3 groups (G1-G3). All the groups had 5 rats each. Control group received water, experimental group, G1, received 20 mg/kg bw/day Emblica officinalis Garten, G2 received 12 mg/kg bw/day chlorpyrifos and G3 received 12 mg chlorpyrifos with 20 mg Emblica officinalis Garten /kg bw/day. Treatment was done orally from 30 days. Thereafter body weight, male reproductive organs weight, sperm count, sperm morphology, ACP, ALP, total protein, uric acid and testis and serum testosterone level were determined using standard methods. The changes recorded are indicative of infertility in male rats because of chlorpyrifos exposure. When the subjects were treated with Emblica officinalis Garten in conjunction with chlorpyrifos, these parameters exhibited recovery and when treated with Emblica officinalis Garten alone, these parameters were more or less near to the control group. This highlights the debilitating effect of chlorpyrifos and scavenging property of Emblica officinalis Garten.

Maternal exposure to the mixture of organophosphorus pesticides induces reproductive dysfunction in the offspring

Organophosphorus pesticide residues are found in many food samples due to increasing use of multiple organophosphorus pesticides (OPs) in agriculture. Toxicity of individual organophosphorus has been well-studied in previous epidemiological and laboratory investigations. This study focused on reproductive toxicity of perinatal exposure to the mixture of organophosphorus pesticides (MOPs). The MOPs consists of three most commonly used pesticides, i.e., Dichlorovos, Dimethoate, and Malathion which individually does not cause significant effects on the reproductive system at the similar concentration levels based on previous studies. Using the Sprague-Dawley rats, we established a perinatal exposure model by oral gavage and observed significant endometrial hyperplasia and thickened uterine walls in the F0 rats after administration of high doses of the MOPs. We further monitored several key developmental and behavioral indices in the F1 generation after maternal exposure to the MOPs, and observed significantly delayed physical development and weakened mental development. Moreover, we found increased weights of the reproductive organs (the uterus and the testis) and abnormal levels of key sex hormones (progestin and testosterone) in the MOPs groups. It is more important that we observed a significantly lower pregnancy rate and live birth rate in the high-dose MOPs group. These results indicate that the MOPs may be more detrimental to the maternal endometria and the reproductive functions in the offspring than individual organophosphorus.

Methoxychlor induced biochemical alterations and disruption of spermatogenesis in adult rats

Adult male albino rats were treated orally with methoxychlor at doses of 0, 50, 100 or 200 mg/kg/day for 15 consecutive days. Testicular weight, sperm count and motility were significantly decreased. Methoxychlor at doses of 100 and 200 mg/kg significantly inhibited α-glucosidase activity, while plasma testosterone was significantly decrease by the three dose levels in a dose-related pattern. Testicular activities of 3β-HSD, 17β-HSD, SDH were significantly decreased, while ACP, ALP (except for 50 mg/kg), and LDH were significantly increased. H2O2 production and LPO were significantly increased while the enzymic (SOD, CAT and GPx) and non-enzymic antioxidants (thiol content) were significantly decreased. Caspase-3 activity was significantly increased in a dose related manner. The findings of this study indicate that methoxychlor induces oxidative stress associated with impairment of spermatogenesis, in addition to apoptosis. These data provide insight into the mode of action of methoxychlor-induced toxicity in the rat testis.

Endocrine-Disrupting Chemicals: Some Actions of POPs on Female Reproduction

Persistent organic pollutants (POPs), such as polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs), polychlorinated biphenyls (PCBs), and polybrominated ethers (PBDEs), chloronaftalens (PCNs), and bisphenol A (BPA), are stable, lipophilic pollutants that affect fertility and cause serious reproductive problems, including ovotoxic action, lack of ovulation, premature ovarian failure (POF), or polycystic ovarian syndrome (PCOS). Most of the representatives of POPs influence the activation of transcription factors, not only activation of aromatic hydrocarbon receptor (AhR), but also the steroid hormone receptors. This minireview will focus on a variety of PAH activities in oocyte, ovary, placenta, and mammary gland. The complexity and diversity of factors belonging to POPs and disorders of the reproductive function of women indicate that the impact of environmental pollution as an important determinant factor in fertility should not be minimize.

Environmental exposures and mammary gland development: state of the science, public health implications, and research recommendations

OBJECTIVES

Perturbations in mammary gland (MG) development may increase risk for later adverse effects, including lactation impairment, gynecomastia (in males), and breast cancer. Animal studies indicate that exposure to hormonally active agents leads to this type of developmental effect and related later life susceptibilities. In this review we describe current science, public health issues, and research recommendations for evaluating MG development.

DATA SOURCES

The Mammary Gland Evaluation and Risk Assessment Workshop was convened in Oakland, California, USA, 16-17 November 2009, to integrate the expertise and perspectives of scientists, risk assessors, and public health advocates. Interviews were conducted with 18 experts, and seven laboratories conducted an MG slide evaluation exercise. Workshop participants discussed effects of gestational and early life exposures to hormonally active agents on MG development, the relationship of these developmental effects to lactation and cancer, the relative sensitivity of MG and other developmental end points, the relevance of animal models to humans, and methods for evaluating MG effects.

SYNTHESIS

Normal MG development and MG carcinogenesis demonstrate temporal, morphological, and mechanistic similarities among test animal species and humans. Diverse chemicals, including many not considered primarily estrogenic, alter MG development in rodents. Inconsistent reporting methods hinder comparison across studies, and relationships between altered development and effects on lactation or carcinogenesis are still being defined. In some studies, altered MG development is the most sensitive endocrine end point.

CONCLUSIONS

Early life environmental exposures can alter MG development, disrupt lactation, and increase susceptibility to breast cancer. Assessment of MG development should be incorporated in chemical test guidelines and risk assessment.

Specific transgenerational imprinting effects of the endocrine disruptor methoxychlor on male gametes

Endocrine-disrupting chemicals (EDCs), among which methoxychlor (MXC), have been reported to affect the male reproductive system. This study evaluates the possible deleterious effects of MXC on imprinted genes. After administration of the chemical in adult male mice or in pregnant mice we analyzed by pyrosequencing possible methylation defects in two paternally imprinted (H19 and Meg3 (Gtl2)) and three maternally imprinted (Mest (Peg1), Snrpn, and Peg3) genes in the sperm and in the tail, liver, and skeletal muscle DNAs of the adult male mice and of the male offspring. MXC treatment of adult mice decreased the percentages of methylated CpGs of Meg3 and increased those of Mest, Snrpn, and Peg3 in the sperm DNA. MXC treatment of pregnant mice decreased the mean sperm concentrations by 30% and altered the methylation pattern of all the imprinted genes tested in the F1 offspring. In the latter case, MXC effects were transgenerational but disappeared gradually from F1 to F3. MXC did not affect imprinting in the somatic cells, suggesting that it exerts its damaging effects via the process of reprogramming that is unique to gamete development. A systematic analysis at the CpG level showed a heterogeneity in the CpG sensitivity to MXC. This observation suggests that not only DNA methylation but also other epigenetic modifications can explain the transgenerational effects of MXC. The reported effects of EDCs on human male spermatogenesis might be mediated by complex imprinting alterations analogous to those described in this study.

Epigenetic effects of endocrine-disrupting chemicals on female reproduction: an ovarian perspective

The link between in utero and neonatal exposure to environmental toxicants, such as endocrine-disrupting chemicals (EDCs) and adult female reproductive disorders is well established in both epidemiological and animal studies. Recent studies examining the epigenetic mechanisms involved in mediating the effects of EDCs on female reproduction are gathering momentum. In this review, we describe the developmental processes that are susceptible to EDC exposures in female reproductive system, with a special emphasis on the ovary. We discuss studies with select EDCs that have been shown to have physiological and correlated epigenetic effects in the ovary, neuroendocrine system, and uterus. Importantly, EDCs that can directly target the ovary can alter epigenetic mechanisms in the oocyte, leading to transgenerational epigenetic effects. The potential mechanisms involved in such effects are also discussed.

Methoxychlor-induced alteration in the levels of HSP70 and clusterin is accompanied with oxidative stress in adult rat testis

Methoxychlor, an organochlorine pesticide, has been reported to induce abnormalities in male reproductive tract. However, the insight into the mechanisms of gonadal toxicity induced by methoxychlor is not well known. We investigated whether treatment with methoxychlor would alter the levels of stress proteins, heat shock proteins (HSP), and clusterin (CLU), and oxidative stress-related parameters in the testis of adult male rats. Animals were exposed to a single dose of methoxychlor (50 mg/kg body weight) orally and were terminated at various time points (0, 3, 6, 12, 24, and 72 h) using anesthetic ether. The levels of HSP70, CLU, and the activities of superoxide dismutase (SOD), catalase, and lipid peroxidation levels were evaluated in a 10% testis homogenate. A sequential reduction in the activities of catalase and SOD with concomitant increase in the levels of thiobarbituric acid reactive substance (TBARS) was observed. These changes elicited by methoxychlor were very significant between 6-12 h of posttreatment. Immunoblot analysis of HSP revealed the expression of HSP72, an inducible form of HSP, at certain time points (3-24 h) following exposure to methoxychlor. Similarly, the levels of secretory CLU (sCLU) were also found to be elevated between 3-24 h of treatment. The present data demonstrate methoxychlor-elicited increase in the levels of inducible HSP72 and sCLU, which could be a part of protective mechanism mounted to reduce cellular oxidative damage.

Subacute oral toxicity study of bisphenol F based on the draft protocol for the “Enhanced OECD Test Guideline no. 407”

Since bisphenol F (4,4'-dihydroxydiphenylmethane) has been reported to exhibit estrogen agonistic properties in the uterotrophic assay, we performed a 28-day repeated-dose toxicity study (enhanced OECD test guideline No. 407) on bisphenol F based on the OECD draft protocols to determine whether it has endocrine-mediated properties. Bisphenol F was orally administered at doses 0, 20, 100 and 500 mg/kg per day for at least 28 days, but no clear endocrine-mediated changes were detected, and it was concluded to have no endocrine-mediated effects in young adult rats. On the other hand, the main effect of bisphenol F was concluded to be liver toxicity based on clinical biochemical parameters and liver weight, but without histopathological changes. The no-observed-effect level for bisphenol F is concluded to be under 20 mg/kg per day since decreased body weight accompanied by decreased serum total cholesterol, glucose, and albumin values were observed in the female rats given 20 mg/kg per day or higher doses of bisphenol F.

Uterotrophic assay, Hershberger assay, and subacute oral toxicity study of 4,4´-[1-[4-[1-(4-hydroxyphenyl)-1-methylethyl]phenyl]ethylidene]bis[phenol] based on the OECD draft protocols

We performed an uterotrophic assay, the Hershberger assay, and a 28-day repeated-dose toxicity study (enhanced OECD test guideline No. 407) of 4,4 -[1-[4-[1-(4-hydroxyphenyl)-1-methylethyl]phenyl]ethylidene]bis[phenol] based on the OECD draft protocols. In the uterotrophic assay, female SD rats were subcutaneously injected with the chemical at doses of 0, 100, 300, and 1,000 mg/kg on each of 3 days from postnatal day 20 to day 22, and the uterine weight of rats given the 1,000 mg/kg dose of the test chemical plus ethinyl estradiol decreased. In the Hershberger assay, the test chemical was orally administered at doses of 0, 100, 300, and 1,000 mg/kg day to castrated male SD rats for ten consecutive days beginning on postnatal day 56, and no changes were observed. On the other hand, when the test chemical was orally administered at doses 0, 100, 300, and 1,000 mg/kg day for at least 28 days, a decrease in LH values in rats of both sexes and a decrease in FSH and estradiol values in female rats were detected in the 1,000 mg/kg group, and abnormal estrous cycles, uterine glandular atrophy, persistence of ovarian corpora lutea, vaginal epithelial mucification, and mammary glandular hyperplasia were also observed in one female rat in the 1,000 mg/kg group. Therefore, the uterotrophic assay used in this study showed that the chemical has the estrogen-antagonist properties, and some potentially endocrine-mediated effects were detected in growing rats based on the results of the enhanced OECD test guideline No. 407. However, the changes were observed in rats given a high dose of the chemical, 1,000 mg/kg day.

A broad-spectrum organophosphate pesticide O,O-dimethyl O-4-nitrophenyl phosphorothioate (methyl parathion) adversely affects the structure and function of male accessory reproductive organs in the rat

Methyl parathion (MP) is an organophosphate pesticide used in agriculture, but also illegally used to spray homes and businesses to control insects. The present study was designed to investigate adverse effects of MP on accessory reproductive organs. Male Wistar rats aged 13-14 weeks were treated and sacrificed as follows. Experiment 1: 0.0 (water vehicle), 1.75, 3.5 or 7mg/kg (i.p.) for 5 days and sacrificed on day 14; experiment 2: 0.0, 0.5 or 1mg/kg (i.p.) for 12 days and sacrificed on day 130; experiment 3: 0.0, 0.5 or 1mg/kg (i.p.) for 12 days and sacrificed on day 77; experiment 4: 0.0, 0.75 or 1.5mg/kg (i.p.) for 25 days and sacrificed on day 17 and experiment 5: 0.0 or 3.5mg/kg (p.o.) for 25 days and sacrificed on day 17, after the last exposure. The accessory reproductive organs were removed, weighed and processed for histopathological analysis. Structural qualitative changes such as epithelial cell morphology and luminal observations were carried out for each organ in all experiments. Epididymis of one side was homogenized and biochemical estimations of acid phosphatase (ACP), cholesterol, total protein, uric acid, and Vitamin C were conducted by calorimetric methods in experiments 4 and 5. In experiment 1 the organ weights did not change; in experiment 2, the epididymal weight increased (P<0.001); in experiment 3, the weights of ductus deferens decreased at 1mg/kg and that of seminal vesicle decreased at both dose-levels (P<0.001). In experiments 4 and 5, weights of epididymis and prostate decreased, whereas in experiment 5, weights of ductus deferens and seminal vesicle increased (P<0.05-0.001). The sperm density was normal in control, moderately decreased in experiment 1 at 3.5 and 7mg/kg; in experiment 2 at 1mg/kg, and in experiment 5 at 3.5mg/kg, and severely decreased in experiment 3 at 1mg/kg and in experiment 4 at both dose-levels. The epithelial necrosis and nuclear pyknosis were seen in experiments 1, 3, 4 and 5, whereas nuclear degeneration was seen in experiment 1 and 4 and germ cells in the lumina of epididymis were seen in experiment 4. The nuclear pyknosis in the ductus deferens was seen in all experiments, except at 1.75mg/kg in experiment 1 and at 0.5mg/kg in experiment 3. Brush border disruption in the ductus deferens was seen in experiments 1 and 4; sperms were seen in the lumen in experiment 1 at 7mg/kg, and in experiments 4 and 5. The vacuoles in the epithelium were seen in experiments 1 and 4 and immature germ cells were seen in the lumen in experiment 4. The ACP and Vitamin C levels decreased in experiment 4 at both dose-levels, and in experiment 5 all biochemical parameters tested found decreased (P<0.01-0.001). The present results indicate that MP affects the structure and function of accessory reproductive organs in the rat.

Subacute oral toxicity study of di(2-ethylhexyl)adipate based on the draft protocol for the "Enhanced OECD Test Guideline no. 407"

We performed a 28-day repeated-dose toxicity study of di(2-ethylhexyl)adipate (DEHA) based on the draft protocol of the "Enhanced OECD Test Guideline 407" to investigate whether it has endocrine-mediated properties according to this assay. DEHA was orally administered to SD rats at doses of 0, 40, 200 and 1,000 mg/kg/day for at least 28 days, and disturbance of the estrous cycle and increased ovarian follicle atresia were detected in the 1,000 mg/kg group.

A repeated 28-day oral dose toxicity study of nonylphenol in rats, based on the 'Enhanced OECD Test Guideline 407' for screening of endocrine-disrupting chemicals

A 28-day repeated oral dose toxicity study of nonylphenol (NP) was performed for an international validation of the 'Enhanced OECD Test Guideline 407' paying particular attention to the sensitivity of individual endocrine-related parameters. Sprague-Dawley rats, each group consisting of ten males and ten females, were administered NP once daily by gavage at doses of 0 (control), 10, 50, or 250 mg/kg body weight. At 250 mg/kg, three females died or became moribund during the experiment. At this dose, hepatic and renal toxicity was evident in both sexes with increase of relative liver and kidney weights as well as histopathological changes, such as centrilobular liver cell hypertrophy and a variety of renal tubular lesions, and alteration of serum biochemical parameters, some of them being evident from 50 mg/kg in females (glucose and inorganic phosphates). Hematologically, development of anemia was evident at 250 mg/kg in both sexes. Regarding endocrine-related effects, increase of thyroid weight in males was detected from 50 mg/kg. At 250 mg/kg, males exhibited reduction of relative weights of the ventral prostate and seminal vesicles, and females developed irregular estrous cyclicity and vaginal mucosal hyperplasia. Although changes in serum hormone levels were detected in both sexes, magnitude of the changes was small to be regarded as a low toxicological significance. In summary, repeated oral doses of NP to rats for 28 days resulted in hepato-renal toxicity from 50 mg/kg and anemia at 250 mg/kg. Effects on the endocrine system were observed from 50 mg/kg, and assessment of weights and histopathology of endocrine-related organs and estrous cyclicity may be valid in a battery for detecting endocrine effects of NP. The no-observed-adverse-effect level of NP was estimated to be 10 mg/kg per day.

Methoxychlor induces atresia of antral follicles in ERalpha-overexpressing mice

Methoxychlor (MXC) is a pesticide that is known to bind to estrogen receptor alpha (ERalpha) and to induce atresia of antral ovarian follicles. Although studies have shown that MXC is toxic to the ovary, we hypothesize that perturbation to the estrogen-signaling system (i.e., increase or decrease in estrogen sensitivity) might alter ovarian responsiveness to MXC. Thus, we examined whether ERalpha overexpression alters the ability of MXC to increase follicle atresia. To do so, we employed a transgenic mouse model in which ERalpha can be inducibly overexpressed in animal tissues (ERalpha overexpressors). We dosed female controls and ERalpha overexpressors with sesame oil (vehicle control) or MXC (32 and 64 mg/kg/day) for 20 days. After dosing, the ovaries were collected for histological evaluation of follicle numbers and follicle atresia, while blood was collected for measurements of hormones. Estrous cycles were determined in all animals to ensure that all were terminated during estrus. Although there were no significant effects of MXC on the numbers of primordial, primary, and preantral follicles in both controls and ERalpha overexpressors, there was an effect on antral follicles. Specifically, our data indicate that 32 and 64 mg/kg MXC increased the percentage of atretic follicles compared to vehicle in both control and ERalpha overexpressor groups. Moreover, there was a clear trend toward greater sensitivity to 64 mg/kg MXC in ERalpha-overexpressing mice compared to control animals. Specifically, at the 64-mg/kg MXC dose, ERalpha-overexpressing mice had a significantly higher percentage of atretic follicles compared to control animals (controls = 21.5 +/- 3%, n = 5; ERalpha overexpressors = 37 +/- 23%, n = 9, p < or = 0.05 vs. controls). After 20 days of dosing, there were no differences in estradiol levels between controls and ERalpha-overexpressing mice in all treatment groups. Follicle-stimulating hormone (FSH) levels were similar in sesame oil-treated control mice and control mice treated with 32 mg/kg MXC, while control mice treated with 64 mg/kg MXC had significantly lower levels of FSH compared to sesame oil-treated controls (sesame oil = 4.31 +/- 0.7, MXC [64 mg/kg/day] = 1.89 +/- 0.4, n = 3, p < or = 0.02 vs. sesame oil). ERalpha-overexpressing mice treated with sesame oil, 32 or 64 mg/kg MXC, had similar FSH levels. Thus, we observed an increased percentage of atretic antral follicles in ERalpha-overexpressing mice treated with MXC compared to control mice treated with the same compound, suggesting that the ERalpha-signaling pathway plays an important role in MXC-induced atresia. The trend toward greater sensitivity to MXC in ERalpha-overexpressing mice compared to control animals cannot be explained by alterations in estradiol and/or FSH levels.

Repeated 28-day oral toxicity study of ketoconazole in rats based on the draft protocol for the “Enhanced OECD Test Guideline No. 407” to detect endocrine effects

We performed a 28-day repeated-dose toxicity study of ketoconazole, a widely used an antimycotic drug, based on the draft protocol of the "Enhanced OECD Test Guideline 407" (Enhanced TG407) to investigate whether ketoconazole has endocrine-mediated properties according to this assay. Seven-week-old SD rats were administered with ketoconazole daily by oral gavage at doses of 0, 6.25, 25 or 100 mg kg(-1) day(-1) for at least 28 days. The ketoconazole-treated male rats showed reduction of epididymis and accessory sex organ weights, spermatid retention in the seminiferous tubules, decrease of testosterone and increases of estradiol, luteinizing hormone (LH) and follicular stimulating hormone (FSH). A prolongation of the estrous cycle and increases of estradiol, LH and FSH were observed in the treated female rats. Thyroxin and triiodothyronine were decreased and thyroid-stimulating hormone was increased in both sexes; however, there were no compound-related microscopic lesions in the thyroid gland or changes in the thyroid weight. The endocrine-related effects of ketoconazole could be detected by the parameters examined in the present study based on the Organization for Economic Cooperation and Development (OECD) protocol, suggesting that the Enhanced TG407 protocol should be a suitable screening test for detection of endocrine-mediated effects of chemicals.

Repeated 28-day oral toxicity study of vinclozolin in rats based on the draft protocol for the "Enhanced OECD Test Guideline No. 407" to detect endocrine effects

We performed a 28-day repeated-dose toxicity study of vinclozolin, a widely used fungicide, based on the draft protocol of the "Enhanced OECD Test Guideline 407" (Enhanced TG407) to investigate whether vinclozolin has endocrine-mediated properties according to this assay. Seven-week-old SD rats were administered with vinclozolin daily by oral gavage at dose rates of 0, 3.125, 12.5, 50 and 200 mg/kg/day for at least 28 days. The vinclozolin-treated male rats showed a reduction of epididymis and accessory sex organ weights and an alteration of hormonal patterns. A slight prolongation of the estrous cycle and changes in the estrogen/testosterone ratio and luteinizing hormone level were observed in vinclozolin-treated female rats. Thyroxin concentrations were decreased and thyroid-stimulating hormone concentrations were increased in both sexes; however, there were no compound-related microscopic lesions in the thyroid gland or changes in the thyroid weight. The endocrine-related effects of vinclozolin could be detected by the parameters examined in the present study based on the OECD protocol, suggesting the Enhanced TG407 protocol should be a suitable screening test for the detection of endocrine-mediated effects of chemicals.

In vivo exposure of young adult male rats to methoxychlor reduces serum testosterone levels and ex vivo Leydig cell testosterone formation and cholesterol side-chain cleavage activity

Methoxychlor (MC) was developed as a replacement for the banned pesticide DDT. After in vivo administration, it is metabolized in the liver to 2,2-bis(p-hydroxyphenyl)-1,1,1-trichloroethane (HPTE), which is proposed to be the active agent. Both MC and HPTE have been shown to exhibit weak estrogenic and antiandrogenic activities, and they are thought to exert their effects through estrogen and androgen receptors, respectively. Although in vitro studies using cultured rat Leydig cells have reported that HPTE inhibits both basal and hCG-stimulated testosterone formation, the response of circulating testosterone levels to in vivo MC has been more variable. Therefore, the current studies evaluated whether the daily in vivo administration of MC (0, 5, 40 and 200 mg/kg body weight) for a short duration (days 54-60 of age) by gavage altered serum testosterone levels and ex vivo Leydig cell testosterone formation in young adult male rats. These results demonstrate that both fluid-retained and fluid-expressed seminal vesicle weights declined to 44 and 60% of control, respectively, in the 200 mg/kg MC-exposed animals. Similarly, serum testosterone and dehydroepiandrosterone levels declined to 41 and 45% of control, respectively, in the 200 mg/kg MC-exposed animals; however, serum LH and FSH levels were unaffected. Ex vivo Leydig cell basal testosterone formation over 4h declined to 49% of control in animals exposed to 200 mg/kg MC, and ex vivo Leydig cell P450 cholesterol side-chain cleavage activity declined to 79 and 50% of control in animals exposed to 40 and 200 mg/kg of MC, respectively, supporting previous in vitro studies which demonstrated the sensitivity of this step to MC.

Methoxychlor Directly Affects Ovarian Antral Follicle Growth and Atresia through Bcl-2- and Bax-Mediated Pathways

Methoxychlor (MXC) is an organochlorine pesticide and reproductive toxicant. While in vivo studies indicate that MXC exposure increases antral follicle atresia, in part by altering apoptotic regulators (Bcl-2 and Bax), they do not distinguish whether MXC does so via direct or indirect mechanisms. Therefore, we utilized an in vitro follicle culture system to test the hypothesis that MXC is directly toxic to antral follicles, and that overexpression of anti-apoptotic Bcl-2, or deletion of pro-apoptotic Bax, protects antral follicles from MXC-induced toxicity. Antral follicles were isolated from wild-type (WT), Bcl-2 overexpressing (Bcl-2 OE), or Bax deficient (BaxKO) mice, and exposed to dimethylsulfoxide (control) or MXC (1-100 microg/ml) for 96 h. Follicle diameters were measured every 24 h to assess growth. After 96 h, follicles were histologically evaluated for atresia or collected for quantitative PCR analysis of Bcl-2 and Bax mRNA levels. MXC (10-100 microg/ml) significantly inhibited antral follicle growth at 72 and 96 h, and increased atresia (100 microg/ml) compared to controls at 96 h. Furthermore, MXC increased Bax mRNA levels between 48-96 h and decreased Bcl-2 mRNA levels at 96 h. While MXC inhibited growth of WT antral follicles beginning at 72 h, it did not inhibit growth of Bcl-2 OE or BaxKO follicles until 96 h. MXC also increased atresia of small and large WT and BaxKO antral follicles over controls, but it did not increase atresia of large Bcl-2 OE antral follicles over controls. These data suggest that MXC directly inhibits follicle growth partly by Bcl-2 and Bax pathways, and increases atresia partly through Bcl-2 pathways.

Subacute oral toxicity study of diethylphthalate based on the draft protocol for “Enhanced OECD Test Guideline no. 407”

We performed a 28-day repeated-dose toxicity study of diethylphthalate based on the draft protocol of the "Enhanced OECD Test Guideline 407" to investigate whether it has endocrine-mediated properties according to this assay. Diethylphthalate was orally administered to SD rats at doses of 0, 40, 200, and 1,000 mg/kg/day for at least 28 days, but no endocrine-mediated effects were detected based on any of the parameters examined, suggesting that diethylphthalate does not possess endocrine properties according to this assay.

A comparison of in vitro and in vivo EDSTAC test battery results for detecting antiandrogenic activity

The androgen receptor (AR) transactivation, binding, and Hershberger assays are being developed for large-scale screening of chemicals for endocrine activity. The goal of this study was to evaluate the correlation between in vitro and in vivo antiandrogenicity assays using a variety of compounds (p,p'-DDE, flutamide (FLUT), spironolactone, procymidone, RU486, methoxychlor (MXC), benzo(a)pyrene (BAP), and selected metabolites). For the AR transactivation assay, AR(+) LNCaP prostate carcinoma cells were transfected with an inducible luciferase reporter construct (pGudLuc7ARE) and exposed for 24 h to test materials (< or = 10 microM) in the presence and absence of 1 nM of the AR agonist R-1881. Each of these materials, including the hydroxlated metabolites of BAP and MXC, produced significant antiandrogenic activity in vitro as evidenced by their inhibition of the response to R-1881. Similarly, in vitro AR binding experiments using the recombinant ligand-binding domain (LBD) of the human AR and fluorescence polarization (FP) methodology yielded IC50s comparable to that of testosterone for RU486 and 9-OH-BAP. Other parent compounds and metabolites exhibited lesser binding affinity. In vivo antiandrogenic activity was evaluated with the Hershberger assay, wherein castrated male CD rats were dosed by gavage for 10 days with (mg/kg per day): MXC (10, 50, 100, and 200), BAP (1, 10, 50, and 100), RU486 (1, 5, 10, and 25), and FLUT (10) in the presence of 0.4 mg/kg per day (sc) of testosterone propionate (TP). Neither BAP nor MXC produced significant decreases in accessory sex tissue (AST) weights relative to TP control. However, 200 MXC resulted in a significant decrease in body weight and 100 BAP significantly increased absolute and relative liver weights. RU486 (25) produced significant decreases in ventral prostate, seminal vesicle, and Cowper's gland weights without affecting body weight. FLUT (10) decreased all AST weights measured. The antiandrogenic activities of the remaining materials (p,p'-DDE, spironolactone, and procymidone) have been demonstrated in previous Hershberger assays. These data indicate the importance of including in vivo results in assessing the endocrine activity of test materials and further stress the importance of a weight of evidence approach in assessing endocrine activity of test materials.

Methoxychlor-Induced Atresia in the Mouse Involves Bcl-2 Family Members, but Not Gonadotropins or Estradiol1

Methoxychlor (MXC) is an organochlorine pesticide that increases the rate of ovarian atresia. To date, little is known about the mechanism by which MXC induces atresia. Because Bcl-2 (an antiapoptotic factor), Bax (a proapoptotic factor), gonadotropins, and estradiol are important regulators of atresia in the ovary, the purpose of this study was first to examine whether MXC-induced atresia occurred through alterations in Bcl-2 or Bax, and second, to examine the effect of MXC on gonadotropins, estradiol, and their receptors. CD-1 mice were dosed with 8-64 mg kg(-1) day(-1) MXC or vehicle (sesame oil). Ovaries were subjected to analysis of antral follicle numbers, Bcl-2, Bax, estrogen receptor, and follicle-stimulating hormone receptor levels. Blood was used to measure gonadotropins and estradiol. In some experiments, mice that overexpressed Bcl-2 or mice that were deficient in Bax were dosed with MXC or vehicle and their ovaries were analyzed for atresia. MXC caused a dose-dependent increase in the percentage of atretic antral follicles compared with controls at the 32 and 64 mg kg(-1) day(-1) doses of MXC. MXC treatment did not result in changes in Bcl-2 levels, but it did result in an increase in Bax levels in antral follicles. MXC treatment did not affect gonadotropin or estradiol levels, nor did it affect the levels of follicle-stimulating hormone or estrogen receptors. Mice that overexpressed Bcl-2 or mice that were deficient in Bax were protected from MXC-induced atresia. These data suggest that MXC induces atresia through direct effects on the Bax and Bcl-2 signaling pathways in the ovary.

Detection of endocrine-modulating effects of the antithyroid acting drug 6-propyl-2-thiouracil in rats, based on the “Enhanced OECD Test Guideline 407”

The antithyroid acting drug propylthiouracil (PTU) was administered to male and female Wistar rats at 0, 0.1, 1, or 10mg/kg body weight for 4 weeks according to the draft protocol of the "Enhanced OECD Test Guideline 407" (enhanced TG 407) in order to investigate its suitability to detect endocrine-mediated effects. The study was conducted with two identical subsets of five animals per sex and dose each to provide data on sensitivity. The modified protocol includes the investigation of additional organ weights, pathology, and histopathology, of thyroid hormones, of spermatozoa, and of estrus cycle. At time of sacrifice, all females were in the diestrus stage as prescribed. Adverse effects were observed in the thyroid gland (hypertrophy/ hyperplasia) and the pituitary gland (hyperplasia of basophilic cells, hypoplasia of acidophilic cells) together with dose-related decreased serum triiodothyronine (T3) and thyroxine (T4) levels and increased thyroid stimulating hormone (TSH) levels. Other effects of PTU included decrease of organ weights, anaemia, impaired blood coagulation, and reduced activity of enzymes. Hence, some of the additional examined endpoints of the enhanced TG 407, e.g., examination of pituitary gland and thyroid hormones, were suitable to detect endocrine-modulating effects of propylthiouracil. Treatment of five animals provides sufficient sensitivity to detect the described adverse effects of propylthiouracil. The enhanced TG is currently under investigation in several laboratories, evaluation of all the results will allow determining its practicability as well as the most suitable additional endpoints.

17α-Methyltestosterone: 28-day oral toxicity study in the rat based on the “Enhanced OECD Test Guideline 407” to detect endocrine effects

A 28-day oral gavage toxicity study in the rat with 17alpha-methyltestosterone was conducted as part of the international validation exercise on the modified Enhanced OECD Test Guideline 407 (Organisation for Economic Co-operation and Development, Paris). Special emphasis was placed on the endocrine mediated effects exerted by 17alpha-methyltestosterone, a potent androgen agonist. The test compound was administered daily by oral gavage for at least 28 days to groups of 7-week-old-Wistar rats. Dose levels were 0, 10, 40 and 200 mg/kg body weight per day for males and 0, 10, 100 and 600 mg/kg body weight per day for females. In addition, and outside the remit of the enhanced protocol, testosterone levels in males, oestradiol levels in females and luteinizing hormone (LH) levels in both sexes were measured, to provide a broader profile on the hormonally mediated effects of 17alpha-methyltestosterone. Furthermore, stage-specific quantification of Terminal deoxynucleotidyl transferase-mediated dUTP Nick-End Labeling (TUNEL)-labeled germ cells (apoptotic germ cells) in the seminiferous tubules was also performed, in an effort to demonstrate the precise stages in the spermatogenic cycle 17alpha-methyltestosterone exerts its effect. In this study, the most critical additional parameters contained in the Enhanced OECD Test Guideline 407 for the detection of endocrine disruption were considered to be the histopathological assessment and organ weight data of endocrine-related tissues. Beyond the scope of this validation exercise, an increase in apoptosis in specific germ cell types was detected using the TUNEL assay in male rats treated at 200 and 40 mg/kg.

Pre-validation study for OECD enhanced test guideline 407 protocol by gavage for 4 weeks using propylthiouracil and tamoxifen

To develop and pre-validate an enhanced protocol for OECD Test Guideline 407, we performed a 28-day repeated-dose toxicity study using the administration of propylthiouracil (PTU) and tamoxifen (TAM) in Sprague-Dawley (SD) rats. Six male and female SD rats were treated orally with PTU in corn oil at the dose of 0, 0.1, 1, or 10 mg/kg per day and TAM at dose of 0, 5, 30 or 200 microg/kg per day for 4 weeks. In the study using PTU, the body weights were reduced from the third week of the study in 10 mg/kg per day group. In clinical biochemistry, the levels of 3,5,3'-triiodothyronine (T3) and thyroxine (T4, 3,5,3',5'-tetraiodothyrosine) were also significantly decreased in 10 mg/kg per day group. Also, thyroid glands in 10 mg/kg per day group were bigger than those in the control group. In the histopathological examination, diffuse hyperplasia and hypertrophy of thyroid follicular cells were observed in all treatment groups, leading to the reduction of lumen size and papillary enfolding of lining epithelium. In the study using TAM, the body weights were reduced from the first week of the study in 200 microg/kg per day group. Relative testes and epididymes weights were increased and relative right ovary and uterus weights were reduced in 200 microg/kg per day group. Also, in the histopathological finding severe endometrial squamous metaplasia and endometrial gland atrophy and severe follicular cystic change were observed in TAM 200 microg/kg per day-treated group. On the basis of the results, the thyroid hormone levels, gross findings, and histopathological findings may be useful parameters for the detection of the endocrine-related effect of PTU and also reproductive organ weight and histopathological findings may be good parameters to detect the effect of TAM. Therefore, it is concluded that enhanced OECD TG407 might be useful for screening and detecting endocrine disrupters.

The multidrug resistance-associated protein 1 transports methoxychlor and protects the seminiferous epithelium from injury

We examined the ability of the multidrug resistance-associated protein 1 (MRP1/ABCC1) to transport pesticides, as this transporter mediates the cellular efflux of a variety of xenobiotics, typically as glucuronide, sulfate, or glutathione conjugates. NIH3T3 cells stably expressing MRP1 were 3.37-fold more resistant to the toxicity of fenitrothion, 3.12-fold more resistant to chlorpropham, and 2.5-fold more resistant to methoxychlor, a pesticide with estrogenic and anti-androgenic metabolites. The cells expressing MRP1 also eliminated methoxychlor two times more rapidly than their mock-transfected counterparts. We then examined whether mrp1 expression could alter the toxicity of methoxychlor in vivo using male FVB/mrp1 knockout mice (FVB/mrp1-/-). Both control and knockout mice were fed 25 mg/kg methoxychlor in honey for 39 days, and its effects on testicular morphology were examined. Methoxychlor treatment did not significantly affect testicular morphology in the FVB mice, but markedly reduced the number of developing spermatocytes in the FVB/mrp1-/- mice. These results suggest that MRPI may play a role in protecting the seminiferous tubules from methoxychlor-induced damage.