Two-generation reproduction toxicity study in rats with 1,1,1-trichloro-2,2-bis(4-chlorophenyl)ethane (p,p'-DDT)

Endocrine disruptors: Unravelling the link between chemical exposure and Women's reproductive health

An Endocrine Disrupting Chemical (EDC) is any compound that disrupts the function of the endocrine system in humans and is ubiquitous in the environment either as a result of natural events or through anthropogenic activities. Bisphenol A, phthalates, parabens, pesticides, triclosan, polychlorinated biphenyls, and heavy metals, which are frequently found in the pharmaceutical, cosmetic, and packaging sectors, are some of the major sources of EDC pollutants. EDCs have been identified to have a deteriorating effect on the female reproductive system, as evidenced by the increasing number of reproductive disorders such as endometriosis, uterine fibroids, polycystic ovary syndrome, premature ovarian failure, menstrual irregularity, menarche, and infertility. Studying EDCs in relation to women's health is essential for understanding the complex interactions between environmental factors and health outcomes. It enables the development of strategies to mitigate risks, protect reproductive and overall health, and inform public policy decisions to safeguard women's well-being. Healthcare professionals must know the possible dangers of EDC exposure and ask about environmental exposures while evaluating patients. This may result in more precise diagnosis and personalized treatment regimens. This review summarises the existing understanding of prevalent EDCs that impact women's health and involvement in female reproductive dysfunction and underscores the need for more research. Further insights on potential mechanisms of action of EDCs on female has been emphasized in the article. We also discuss the role of nutritional intervention in reducing the effect of EDCs on women's reproductive health. EDC pollution can be further reduced by adhering to strict regulations prohibiting the release of estrogenic substances into the environment.

Endocrine disrupting chemicals impact on ovarian aging: Evidence from epidemiological and experimental evidence

Endocrine-disrupting chemicals (EDCs) are ubiquitous in daily life, but their harmful effects on the human body have not been fully explored. Recent studies have shown that EDCs exposure could lead to infertility, menstrual disorder and menopause, resulting in subsequent effects on female health. Therefore, it is of great significance to clarify and summarize the impacts of EDCs on ovarian aging for explaining the etiology of ovarian aging and maintaining female reproductive health. Here in this review, we focused on the impacts of ten typical environmental contaminants on the progression of ovarian aging during adult exposure, including epidemiological data in humans and experimental models in rodents, with their clinical phenotypes and underlying mechanisms. We found that both persistent (polychlorinated biphenyls, perfluoroalkyl and polyfluoroalkyl substances) and non-persistent (phthalates) EDCs exposure could increase an overall risk of ovarian aging, leading to the diminish of ovarian reserve, decline of fertility or fecundity, irregularity of the menstrual cycle and an earlier age at menopause, and/or premature ovarian insufficiency/failure in epidemiological studies. Among these, the loss of follicles can also be validated in experimental studies of some EDCs, such as BPA, phthalates, parabens and PCBs. The underlying mechanisms may involve the impaired ovarian follicular development by altering receptor-mediated pro-apoptotic pathways, inducing signal transduction and cell cycle arrest and epigenetic modification. However, there were inconsistent results in the impacts on fertility/fecundity, menstrual/estrous cycle and hormone changes response to different EDCs, and differences between human and animal studies. Our review summarizes the current state of knowledge on ovarian disrupters, highlights their risks to ovarian aging and identifies knowledge gaps in humans and animals. We therefore propose that females adopt healthy lifestyle changes to minimize their exposure to both persistent and non-persistent chemicals, that have the potential damage to their reproductive function.

Effects of glyphosate-based herbicide-contaminated diets on reproductive organ toxicity and hypothalamic-pituitary-ovarian axis hormones in weaned piglets

At present, glyphosate (GLP) is the most produced and used herbicide in the world. With the large-scale use of glyphosate-based herbicides (GBHs), their toxic effects on animals and plants have increasingly become a concern. Based on the Codex Alimentarius Commission (CODEX) dose (20 mg kg-1) and the dose set by the government (40 mg kg-1), four experimental groups in which Roundup® (R) herbicide was added to the feed of weaned piglets at GLP concentrations of 0, 10, 20, and 40 mg kg-1 were designed. The results showed that R had no significant effect on the vulvar size or index of reproductive organs but that it could affect the tissue morphology and ultrastructure of the uterus and ovary. With the increase in GLP concentration, the activities of antioxidant enzymes [SOD (P < 0.05) and GPx (P = 0.002)] in the uterus showed significant increases. Compared with the control group, the content of hydrogen peroxide (H2O2) in the treatment groups increased significantly (P < 0.05), the malondialdehyde (MDA) content in the 10 mg kg-1 treatment group was significantly higher than that in the control group. We measured hypothalamic-pituitary-ovarian axis (HPOA) hormones and also found that GLP significantly increased luteinizing hormone-releasing hormone (LHRH), gonadotropin-releasing hormone (GnRH) and testosterone (T) content (P < 0.05) and decreased follicle-stimulating hormone (FSH) content (P < 0.05). In summary, although R does not affect the vulvar size or reproductive organ index of weaned piglets, it changes the morphology and ultrastructure of the uterus and ovaries, interferes with the synthesis and secretion of HPOA hormones, and causes changes in the balance of the antioxidant system of uterus. This study provided a theoretical basis for preventing reproductive system harm caused by GBHs.

Assessment of DDT contamination in house rat as a possible bioindicator in DDT-sprayed areas from Ethiopia and South Africa

Ethiopia and South Africa are among the few countries to still implement indoor residual spraying with dichloro-diphenyl-trichloroethane (DDT) for malaria vector control. In this study, we investigated the levels and ecological risks of DDT and its metabolites in liver tissues of house rat, as a sentinel animal, for providing an early warning system for public health and wildlife intervention from Ethiopia and South Africa. The results showed that ΣDDT concentration ranged from 127 to 9155 μg/kg wet weight, and the distribution order of DDT and its metabolites in the analyzed liver samples was p,p'-DDD > p,p'-DDE >> p,p'-DDT, o,p'-DDT, and o,p'-DDD. The risk assessment indicated a potential adverse impact on humans, especially for pregnant women and children, because they spend majority of their time in a DDT-sprayed house. The ecological assessment also showed a concern for birds of prey and amphibians like frogs. This study is the first report on DDT contamination in liver tissues of house rats from Ethiopia and South Africa, and henceforth, the data will serve as a reference data for future studies.

Toxicity and Carcinogenicity of Dichlorodiphenyltrichloroethane (DDT)

Dichlorodiphenyltrichloroethane (DDT) is still used in certain areas of tropics and subtropics to control malaria and other insect-transmitted diseases. DDT and its metabolites have been extensively studied for their toxicity and carcinogenicity in animals and humans and shown to have an endocrine disrupting potential affecting reproductive system although the effects may vary among animal species in correlation with exposure levels. Epidemiologic studies revealed either positive or negative associations between exposure to DDT and tumor development, but there has been no clear evidence that DDT causes cancer in humans. In experimental animals, tumor induction by DDT has been shown in the liver, lung, and adrenals. The mechanisms of hepatic tumor development by DDT have been studied in rats and mice. DDT is known as a non-genotoxic hepatocarcinogen and has been shown to induce microsomal enzymes through activation of constitutive androstane receptor (CAR) and to inhibit gap junctional intercellular communication (GJIC) in the rodent liver. The results from our previously conducted 4-week and 2-year feeding studies of p,p'-DDT in F344 rats indicate that DDT may induce hepatocellular eosinophilic foci as a result of oxidative DNA damage and leads them to hepatic neoplasia in combination with its mitogenic activity and inhibitory effect on GJIC. Oxidative stress could be a key factor in hepatocarcinogenesis by DDT.

Polygenic expression of teratozoospermia and normal fertility in B10.MOL-TEN1 mouse strain

Subfertility and infertility are two major reproductive health problems in human and domestic animals. The contribution of the genotype to these conditions is poorly understood. To examine the genetic basis of male subfertility, we analyzed its relationship to sperm morphology in B10.MOL-TEN1 mice, which shows high-frequencies (about 50%) of morphologically abnormal sperm. Drastic histological changes were also found in the testis of the B10.MOL-TEN1. Segregation analysis showed that the abnormal sperm phenotype in B10.MOL-TEN1 was inherited and was predictably controlled by at least three loci. We also found that male fertility of this strain was normal. These findings indicate a complicated relationship between sperm morphology and male subfertility.

Obesogenic effects of endocrine disruptors, what do we know from animal and human studies?

BACKGROUND

Hormonal actions and activation of receptors involved in adipogenesis and brain development during the prenatal period may be affected by exposure to certain chemicals. Experimental studies have shown that amongst others polychlorinated biphenyl (PCB)-153 and dichlorodiphenyltrichloroethane (DDT) may have obesogenic effects in prenatally exposed mice.

OBJECTIVE

To provide an overview of five classes of chemicals which have frequently been indicated as potential obesogens, and to discuss the evidence available regarding early life exposure to these compounds and overweight later in life.

METHODS

Pubmed was systematically searched for publications which related early life exposure to endocrine disrupting chemicals (EDCs) to growth parameters later in life. We included 19 studies, which were published from 1995 and onwards.

RESULTS

Both positive and negative associations are observed between early life exposure and weight or height at various ages, including as early as 14 months, as well as until 20 years of age. In none of the included studies negative associations between perinatal exposure to EDCs and body mass index (BMI) were found and in several studies a positive association was observed. Dose-response relations appear to be non-monotonic.

CONCLUSION

For certain EDCs, early life exposure may be associated with weight homeostasis later in life, however not necessarily in an obesogenic direction. More sensitive measures of adiposity as well as long-term follow-up are warranted for future studies.

A novel mutation in the thyroglobulin gene that causes goiter and dwarfism in Wistar Hannover GALAS rats

Outbred stocks of rats have been used extensively in biomedical, pharmaceutical and/or toxicological studies as a model of genetically heterogeneous human populations. One of such stocks is the Wistar Hannover GALAS rat. However, the colony of Wistar Hannover GALAS rat has been suspected of keeping a problematic mutation that manifests two distinct spontaneous abnormalities, goiter and dwarfism, which often confuses study results. We have successfully identified the responsible mutation, a guanine to thymine transversion at the acceptor site (3' end) of intron 6 in the thyroglobulin (Tg) gene (Tgc.749-1G>T), that induces a complete missing of exon 7 from the whole Tg transcript by mating experiments and subsequent molecular analyses. The following observations confirmed that Tgc.749-1G>T/Tgc.749-1G>T homozygotes manifested both dwarfism and goiter, while Tgc.749-1G>T/+ heterozygotes had only a goiter with normal appearance, suggesting that the mutant phenotypes inherit as an autosomal semi-dominant trait. The mutant phenotypes, goiter and dwarfism, mimicked those caused by typical endocrine disrupters attacking the thyroid. Hence a simple and reliable diagnostic methodology has been developed for genomic DNA-based genotyping of animals. The diagnostic methodology reported here would allow users of Wistar Hannover GALAS rats to evaluate their study results precisely by carefully interpreting the data obtained from Tgc.749-1G>T/+ heterozygotes having externally undetectable thyroidal lesions.

Two-generation reproduction toxicity study in rats with methoxychlor

A two-generation reproduction toxicity study was conducted in rats with a reference estrogenic pesticide, methoxychlor, to validate the sensitivity and competency of current guidelines recommended by the United States Environmental Protection Agency; Japanese Ministry of Agriculture, Forestry and Fisheries; and Organisation for Economic Co-operation and Development for predicting reproductive toxicity of the test compound based on estrogenic endocrine disrupting effects. Both sexes of SD rats were exposed to methoxychlor in the diet at concentrations of 0, 10, 500 and 1500 ppm for two successive generations. The present study has successfully detected estrogenic activities and reproductive toxicities of methoxychlor, as well as its systemic toxicity. Body weights, body weight gains and food consumption of both sexes of animals were suppressed significantly in the 500 and 1500 ppm groups. Typical reproductive toxicities observed in females of these groups included, but were not limited to, prolonged estrous cycle, reduced fertility, decreased numbers of implantation sites and newborns, decreased ovary weights and/or increased incidences of cystic ovary. Uterine weights of weanlings increased significantly in these groups, suggesting that the sensitivity of this parameter for predicting estrogenic ability of the test compound is comparable to that of the uterotrophic assay. Reproductive toxicities of methoxychlor seemed less potent in males than in females. Methoxychlor delayed preputial separation and significantly reduced sperm counts and reproductive organ weights of males of the 500 and/or 1500 ppm groups; however, most males that failed to impregnate females in the same group showed normal fertility when they were re-mated with untreated females. Neither systemic nor reproductive toxicities appeared in the 10 ppm group.

DDT and Other Chlorinated Insecticides

The use of organochlorine insecticides such as DDT, lindane and cyclodieneshas declined markedly worldwide over the last decades. Most are now banned or not used. At an acute toxicity level they have been relatively safe in use for humans. However, the greatest concerns are their persistence in people, wildlife and the environment due to their slow metabolism. Although their carcinogenicity for humans has not been supported by strong epidemiological evidence, their potential to be modulators of endocrine and immune function at levels remaining in the environment or associated with residual spraying of DDT continue to be of concern. At present, DDT is still allowed by the United Nations for combating malaria, with continual monitoring and assessment where possible. The toxicological consequences of exposure of animals and people to DDT is discussed as well as some analogues and other insecticides such as lindane, dieldrin and chlordecone that, although little used, continue to persist in surroundings and people. Because of circumstances of world health brought about by climate change or human activities that have yet to develop, there may come a time when the importance of some may re-emerge.