Cytophysiological Changes in the Follicular Epithelium of the Thyroid Gland after Long-Term Exposure to Low Doses of Dichlorodiphenyltrichloroethane (DDT)

Exposure to pesticides and the risk of hypothyroidism: a systematic review and meta-analysis

BACKGROUND

Knowledge surrounding the association between exposure to pesticides and hypothyroidism is inconsistent and controversial.

METHODS

The aim of present study was, therefore, to review scientific evidence systematically and conduct a meta-analysis into the contribution of exposure to pesticides to hypothyroidism. PubMed, Scopus, Web of Science, and Google Scholar were searched. The findings are presented as OR, HR, PR, IRR, and 95% confidence interval (95%CI). A fixed-effect model using the inverse-variance method and random-effects inverse-variance model with DerSimonian-Laird method were used for estimating the pooled estimates. Cochran Q and I2 tests were used to confirm the heterogeneity of selected studies.

RESULTS

Twelve studies were included in the systematic review, and 9 studies in the meta-analysis. Epidemiological evidence suggested that exposure to insecticides including organochlorines, organophosphates, and pyrethroids increased risk of hypothyroidism (adjusted odds ratio (aOR) = 1.23, 95%CI = 1.14, 1.33 for organochlorines, aOR = 1.12, 95%CI = 1.07, 1.17 for organophosphates, aOR = 1.15, 95%CI = 1.03, 1.28 for pyrethroids). Exposure to herbicides also increased risk of hypothyroidism (aOR = 1.06, 95%CI = 1.02, 1.10). However, exposure to fungicides and fumigants was not found to be associated with hypothyroidism.

CONCLUSION

To increase current knowledge and confirm evidence to date future research needs to center on large-scale longitudinal epidemiological and biological studies, examination of dose-response relationships, the controlling of relevant confounding variables, using standardized and high sensitivity tools, and investigating the effects of environmental exposure.

Persistent organic pollutants in pregnant women potentially affect child development and thyroid hormone status

BACKGROUND

Potentially harmful effects of persistent organic pollutants (POPs) such as polychlorinated biphenyls (PCBs) and dichlorodiphenyltrichloroethane (DDT) on prenatal development and the endocrine system have been controversially discussed.

METHODS

Working with a German cohort of 324 pregnant women, we assessed POP levels and used robust linear regression models to determine potential associations between maternal POP concentrations and pre- and postnatal development in the children, as well as the thyroid hormone status of the mother and child.

RESULTS

Maternal p,p'-dichlorodiphenyldichloroethylene (p,p'-DDE) and most measured PCBs positively correlated with postnatal weight gain. We detected no correlation between newborn birth weight and head circumference, respectively, and maternal PCB and p,p'-DDE serum levels, while body length at birth was negatively associated with the maternal serum concentration of PCB 183. Maternal p,p'-DDE and nearly all PCB serum levels showed a negative correlation with maternal free triiodothyronine (FT3). p,p'-DDE and PCB 74 and 118 were negatively associated with maternal thyroid-stimulating hormone levels. In addition, we identified significant associations between maternal POP levels and thyroid hormone parameters of the child.

CONCLUSIONS

These results indicate that POP exposure likely affects different aspects of pre- and postnatal development and impacts the thyroid hormone status of both mother and child.

IMPACT

Pregnant women in a German cohort display a substantial accumulation of POPs. Body mass index and age influence maternal serum POP levels. Maternal POP levels show correlations with the child's length at birth and weight gain, and FT3 levels in the mother and child. Our data provide additional evidence for the potentially harmful influence of POPs. Our data indicate that POPs influence pre- and postnatal development.

A review of the endocrine disrupting effects of micro and nano plastic and their associated chemicals in mammals

Over the years, the vaste expansion of plastic manufacturing has dramatically increased the environmental impact of microplastics [MPs] and nanoplastics [NPs], making them a threat to marine and terrestrial biota because they contain endocrine disrupting chemicals [EDCs] and other harmful compounds. MPs and NPs have deleteriouse impacts on mammalian endocrine components such as hypothalamus, pituitary, thyroid, adrenal, testes, and ovaries. MPs and NPs absorb and act as a transport medium for harmful chemicals such as bisphenols, phthalates, polybrominated diphenyl ether, polychlorinated biphenyl ether, organotin, perfluorinated compounds, dioxins, polycyclic aromatic hydrocarbons, organic contaminants, and heavy metals, which are commonly used as additives in plastic production. As the EDCs are not covalently bonded to plastics, they can easily leach into milk, water, and other liquids affecting the endocrine system of mammals upon exposure. The toxicity induced by MPs and NPs is size-dependent, as smaller particles have better absorption capacity and larger surface area, releasing more EDC and toxic chemicals. Various EDCs contained or carried by MPs and NPs share structural similarities with specific hormone receptors; hence they interfere with normal hormone receptors, altering the hormonal action of the endocrine glands. This review demonstrates size-dependent MPs' bioaccumulation, distribution, and translocation with potential hazards to the endocrine gland. We reviewed that MPs and NPs disrupt hypothalamic-pituitary axes, including the hypothalamic-pituitary-thyroid/adrenal/testicular/ovarian axis leading to oxidative stress, reproductive toxicity, neurotoxicity, cytotoxicity, developmental abnormalities, decreased sperm quality, and immunotoxicity. The direct consequences of MPs and NPs on the thyroid, testis, and ovaries are documented. Still, studies need to be carried out to identify the direct effects of MPs and NPs on the hypothalamus, pituitary, and adrenal glands.

In vitro assessment of pesticides capacity to act as agonists/antagonists of the thyroid hormone nuclear receptors

Chemicals acting as thyroid hormone disruptors (THDs) are of a particular concern for public health, considering the importance of this hormone in neurodevelopment and metabolic processes. They might either alter the circulating level of thyroid hormone (TH) or interfere with the cellular response to the hormonal stimulation. In order to assess this later possibility we selected 39 pesticides and combined several in vitro tests. Reporter assays respectively addressed the transactivation capacity of the full-length TH nuclear receptor TRα1, the transactivation capacity of its C-terminal ligand binding domain, or the ability of the hormone to destabilize the interaction between TRα1 and the transcriptional corepressor NcoR. Although some pesticides elicit a cellular response, which sometimes interferes with TH signaling, RNA-seq analysis provided no evidence that they can act as TRα1 agonists or antagonists. Their neurodevelopmental toxicity in mammals cannot be explained by an alteration of the response to TH.

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Pesticides were tested for their capacity to interfere with thyroid hormone receptors

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Three reporter assays were combined to identify possible agonists/antagonists

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The tested pesticides are not major disruptors of thyroid hormone signaling

Endocrine Disruptors as a New Etiologic Factor of Bone Tissue Diseases (Review)

At present, diseases of bones and joints stand third after cardiovascular and oncological pathologies which demands the necessity of searching for new etiological factors and pathogenetical mechanisms of these illnesses. The accumulating data show the association between the impairment of bone tissue development and regeneration and endocrine disruptor impact. Endocrine disruptors are chemical substances, mainly of anthropogenic origin, capable of affecting endocrine system functioning and interfering with organ morphogenesis and physiological functions. The development and regeneration of bone tissues have a complex hormonal regulation and therefore bone tissue cells, osteoblasts, and osteoclasts can be considered as potential targets for endocrine disruptors. Endocrine disruptors have been established to be able to impair calcium metabolism which also contributes to the development of musculoskeletal system pathology. Data on histogenesis of bone tissue and regeneration, calcium metabolism as well as on hormonal regulation of bone growth and remodeling processes are presented in this work. Recent information on the effect of the main endocrine disruptor classes (diethylstilbestrol, organochlorine pesticides, alkylphenols, bisphenol A, dioxins, polychlorinated biphenyls, and phthalic acid esters) on the development and remodeling of bone tissues and calcium metabolism has been summarized. The established physiological and molecular mechanisms of their action have been also considered.

Development of Proliferative Response of Thymic Lymphocytes to T-Cell Mitogen in Rats Exposed to Endocrine Disrupter DDT during Ontogeny

We studied the formation of proliferative response of thymic lymphocytes to T-cell mitogen in rats exposed to endocrine disrupter DDT during prenatal and postnatal ontogeny. Developmental exposure to the endocrine disruptor was found to attenuate proliferative response during puberty and adulthood due to maintenance of higher proliferation rate of thymic lymphocytes in comparison with age-matched controls. Insufficient proliferative response to mitogens in rats developmentally exposed to the endocrine disrupter increases the risk of impairment of cell-mediated reactions of adaptive immunity.

Developmental exposure to low doses of dichlorodiphenyltrichloroethane impairs proliferative response of thymic lymphocytes to Concanavalin A in rats

The aim of the research was to study formation of thymic lymphocytes proliferative response to T cell mitogen Concanavalin A in 7, 42, and 70 days-old male Wistar rats developmentally exposed to low doses of endocrine disruptor dichlorodiphenyltrichloroethane (2.90 ± 0.13 μg/kg body weight). The thymus of the exposed rats did not show morphological abnormalities. Exposure to the endocrine disrupter was found to alter age-dependent changes of thymic lymphocyte proliferative activity and attenuate proliferative response to Concanavalin A in puberty and adulthood. Insufficient response to mitogen was mediated by higher content of actively proliferating Ki-67-positive lymphoblasts compared to the control values. Insufficient proliferative response to mitogen in developmentally exposed to the endocrine disruptor rats may provide higher risk of impaired cellular immune reactions.

Morphological and Cytophysiological Changes in the Adult Rat Adrenal Medulla after Prenatal and Postnatal Exposure to Endocrine-Disrupting DDT

The aim of the investigation was to study morphological and cytophysiological changes in the adult rat adrenal medulla after prenatal and postnatal exposure to endocrine-disrupting chemical dichlorodiphenyltrichloroethane (DDT).

Pesticides With Potential Thyroid Hormone-Disrupting Effects: A Review of Recent Data

Plant Protection Products, more commonly referred to as pesticides and biocides, are used to control a wide range of yield-reducing pests including insects, fungi, nematodes, and weeds. Concern has been raised that some pesticides may act as endocrine disrupting chemicals (EDCs) with the potential to interfere with the hormone systems of non-target invertebrates and vertebrates, including humans. EDCs act at low doses and particularly vulnerable periods of exposure include pre- and perinatal development. Of critical concern is the number of pesticides with the potential to interfere with the developing nervous system and brain, notably with thyroid hormone signaling. Across vertebrates, thyroid hormone orchestrates metamorphosis, brain development, and metabolism. Pesticide action on thyroid homeostasis can involve interference with TH production and its control, displacement from distributor proteins and liver metabolism. Here we focused on thyroid endpoints for each of the different classes of pesticides reviewing epidemiological and experimental studies carried out both in in vivo and in vitro. We conclude first, that many pesticides were placed on the market with insufficient testing, other than acute or chronic toxicity, and second, that thyroid-specific endpoints for neurodevelopmental effects and mixture assessment are largely absent from regulatory directives.

Thyroid Disrupting Chemicals

Endocrine disruptor compounds are exogenous agents able to interfere with a gland function, exerting their action across different functional passages, from the synthesis to the metabolism and binding to receptors of the hormone produced. Several issues, such as different levels and time of exposure and different action across different ages as well as gender, make the study of endocrine disruptors still a challenge. The thyroid is very sensitive to the action of disruptors, and considering the importance of a correct thyroid function for physical and cognitive functioning, addressing this topic should be considered a priority. In this review, we examined the most recent studies, many of them concentrating on maternal and child exposure, conducted to assess the impact of industrial chemicals which showed an influence on thyroid function. So far, the number of studies conducted on that topic is not sufficient to provide solid conclusions and lead to homogeneous guidelines. The lack of uniformity is certainly due to differences in areas and populations examined, the different conditions of exposures and the remarkable inter-subject variability. Nonetheless, the European Commission for Health and Food Safety is implementing recommendations to ensure that substances identified as endocrine disruptors will be withdrawn from the market.