Thyroid hormone, gene expression, and Central Nervous System: Where we are

Prenatal phthalate exposure and neurodevelopmental differences in twins at 2 years of age

BACKGROUND

Previous studies of singletons evaluating prenatal phthalate exposure and early neurodevelopment reported mixed results and the associations could be biased by parental, obstetrical, and genetic factors.

METHODS

A co-twin control design was employed to test whether prenatal phthalate exposure was associated with children's neurocognitive development. We collected information from 97 mother-twin pairs enrolled in the Wuhan Twin Birth Cohort between March 2016 and October 2018. Fourteen phthalate metabolites were measured in maternal urine collected at each trimester. Neurodevelopmental differences in twins at the age of two were examined as the outcome of interest. Multiple informant model was used to examine the covariate-adjusted associations of prenatal phthalate exposure with mental development index (MDI) and psychomotor development index (PDI) scores assessed at 2 years of age based on Bayley Scales of Infant Development (Second Edition). This model also helps to identify the exposure window of susceptibility.

RESULTS

Maternal urinary levels of mono-2-ethyl-5-oxohexyl phthalate (MEOHP) (β = 1.91, 95% CI: 0.43, 3.39), mono (2-ethyl-5-hydroxyhexyl) phthalate (MEHHP) (β = 1.56, 95% CI: 0.33, 2.79), and the sum of di-(2-ethylhexyl) phthalate metabolites (∑DEHP) (β = 1.85, 95% CI: 0.39, 3.31) during the first trimester showed the strongest and significant positive associations with intra-twin MDI difference. When stratified with twin chorionicity, the positive associations of monoethyl phthalate (MEP), monoisobutyl phthalate (MiBP), mono-n-butyl phthalate (MBP), monobenzyl phthalate (MBzP), individual DEHP metabolites, and ∑DEHP exposure during pregnancy with intra-twin neurodevelopmental differences were more significant in monochorionic diamniotic (MCDA) twins than those in dichorionic diamniotic (DCDA) twins.

CONCLUSIONS

Neurodevelopmental differences in MCDA twins were strongly associated with prenatal phthalate exposure. Our findings warrant further confirmation in longitudinal studies with larger sample sizes.

Thyroid dysfunction alters gene expression of proteins related to iron homeostasis and metabolomics in male rats

Thyroid hormones (THs) are crucial in bodily functions, while iron is essential for processes like oxygen transport. Specialized proteins maintain iron balance, including ferritin, transferrin, ferroportin, and hepcidin. Research suggests that THs can influence iron homeostasis by affecting mRNA and protein expression, such as ferritin and transferrin. Our study focused on male rats to assess mRNA expression of iron homeostasis-related proteins and metabolomics in thyroid dysfunction. We found altered gene expression across various tissues (liver, duodenum, spleen, and kidney) and identified disrupted metabolite patterns in thyroid dysfunction. These findings highlight tissue-specific effects of thyroid dysfunction on essential iron homeostasis proteins and provide insights into associated metabolic changes. Our research contributes to understanding the intricate interplay between thyroid hormones and iron balance. By unveiling tissue-specific gene expression alterations and metabolic disruptions caused by thyroid dysfunction, our work lays a foundation for future investigations to explore underlying mechanisms and develop targeted strategies for managing iron-related complications in thyroid disorders.

Local modulation of thyroid hormone signaling in the retina affects the development of diabetic retinopathy

Thyroid hormone (TH) dyshomeostasis is associated with poor prognosis in acute and prolonged illness, but its role in diabetic retinopathy (DR) has never been investigated. Here, we characterized the TH system in the retinas of db/db mice and highlighted regulatory processes in MIO-M1 cells. In the db/db retinas, typical functional traits and molecular signatures of DR were paralleled by a tissue-restricted reduction of TH levels. A local condition of low T3 (LT3S) was also demonstrated, which was likely to be induced by deiodinase 3 (DIO3) upregulation, and by decreased expression of DIO2 and of TH receptors. Concurrently, T3-responsive genes, including mitochondrial markers and microRNAs (miR-133-3p, 338-3p and 29c-3p), were downregulated. In MIO-M1 cells, a feedback regulatory circuit was evidenced whereby miR-133-3p triggered the post-transcriptional repression of DIO3 in a T3-dependent manner, while high glucose (HG) led to DIO3 upregulation through a nuclear factor erythroid 2-related factor 2-hypoxia-inducible factor-1 pathway. Finally, an in vitro simulated condition of early LT3S and hyperglycemia correlated with reduced markers of both mitochondrial function and stress response, which was reverted by T3 replacement. Together, the data suggest that, in the early phases of DR, a DIO3-driven LT3S may be protective against retinal stress, while, in the chronic phase, it not only fails to limit HG-induced damage, but also increases cell vulnerability likely due to persistent mitochondrial dysfunction.

Cross-species applicability of an adverse outcome pathway network for thyroid hormone system disruption

Thyroid hormone system disrupting compounds are considered potential threats for human and environmental health. Multiple adverse outcome pathways (AOPs) for thyroid hormone system disruption (THSD) are being developed in different taxa. Combining these AOPs results in a cross-species AOP network for THSD which may provide an evidence-based foundation for extrapolating THSD data across vertebrate species and bridging the gap between human and environmental health. This review aimed to advance the description of the taxonomic domain of applicability (tDOA) in the network to improve its utility for cross-species extrapolation. We focused on the molecular initiating events (MIEs) and adverse outcomes (AOs) and evaluated both their plausible domain of applicability (taxa they are likely applicable to) and empirical domain of applicability (where evidence for applicability to various taxa exists) in a THSD context. The evaluation showed that all MIEs in the AOP network are applicable to mammals. With some exceptions, there was evidence of structural conservation across vertebrate taxa and especially for fish and amphibians, and to a lesser extent for birds, empirical evidence was found. Current evidence supports the applicability of impaired neurodevelopment, neurosensory development (eg, vision) and reproduction across vertebrate taxa. The results of this tDOA evaluation are summarized in a conceptual AOP network that helps prioritize (parts of) AOPs for a more detailed evaluation. In conclusion, this review advances the tDOA description of an existing THSD AOP network and serves as a catalog summarizing plausible and empirical evidence on which future cross-species AOP development and tDOA assessment could build.

Thyroid dysfunction in young, first-episode and drug-naïve patients with major depressive disorder: prevalence and associated clinical factors

Objective

The incidence of thyroid dysfunction (TD) and major depressive disorder (MDD) is increasing year by year in the general population. However, the prevalence and correlates of TD in first-episode drug-naive (FEDN) MDD patients have not been explored. This study sought to fill this gap and examine the association between TD and MDD.

Methods

We recruited 1,289 FEDN MDD patients aged 18 ~ 45 years. A total of 1,289 FEDN MDD outpatients were recruited. Demographical and suicide data were collected for each patient, and lipid profiles, thyroid function, and fasting blood glucose (FBG) levels were measured. The Hamilton Depression Scale 17 (HAMD-17) was assessed for depression.

Results

The prevalence of TD in young FEDN MDD patients was 64.86%. Compared with those without TD, patients with TD had longer duration of illness, greater HAMD score, higher BMI, TG, TC, and LDL-C levels, and higher suicide attempt rates, but lower HDL-C and FBG levels. Further logistic regression indicated that duration of illness, HAMD score, TC, HDL-C, BMI, and FBG levels were significantly associated with TD.

Limitations

No causal relationship can be drawn due to the cross-sectional design.

Conclusion

TD is common in young FEDN MDD patients. So clinicians should monitor thyroid function in patients with MDD.

Microcystin-LR immersion caused sequential endocrine disruption and growth inhibition in zebrafish (Danio rerio) from fertilization to sexual differentiation completion

Microcystin-LR (MC-LR) is a highly toxic congener and is also one of the most commonly found. Recent studies have demonstrated that MC-LR can disrupt growth and endocrine in fish, but how it works at the stage of the sex differentiation period had not been determined to date. In this study, zebrafish (Danio rerio) embryos were exposed to MC-LR (0 and 10μg/L), and sampled at 14, 28, and 42 days post fertilization (dpf), respectively. The results demonstrated that MC-LR caused the growth inhibition of zebrafish at 42 dpf. The expression levels of genes related to the growth hormone/insulin-like growth factor (GH/IGF) and hypothalamic-pituitary-thyroid (HPT) axes, as well as the levels of hormone 3,5,3'- Triiodothyronine (T3) and thyroxine (T4), were significantly decreased at all time points. A Significant decrease in the ratio of testosterone and estradiol (T/E2) were detected at 28 and 42 dpf in MC-LR group along with changes in genes related to the hypothalamic-pituitary-gonadal (HPG) axis. The result of sex ratio showed that the percentage of females was up to 61.84%, indicating a estrogenic effect induced by MC-LR. The significant changes on hormone levels and gene transcripts occurred mainly in the stage of sex differentiation. The correlation analysis further suggested that key cross-talks among three endocrine axes may be the growth hormone releasing hormone (GHRH), Transthyretin (TTR) and gonadotropin releasing hormone (GnRH) signaling molecules. Overall, our findings provide a new insight for understanding the mechanisms by which MC-LR affects fish growth and reproduction during gonadal development.

Neuroprotective effect of thyroid hormones on methamphetamine-induced neurotoxicity via cell surface receptors

Thyroid hormones (THs) have an essential role in normal brain development and function. Methamphetamine (MA) is a widely abused psychostimulant that induces irreversible damages to neuronal cells. In the current study, we used rat primary hippocampal neurons (PHNs) to investigate the neuroprotective effect of THs against MA neurotoxicity. PHNs were prepared from 18-day rat embryos and cell viability was assessed using MTT assay, following treatment with various concentrations of MA, T3, T4 or tetrac, an integrin αvβ3 cell surface receptor antagonist. Our results showed that 7 mM MA induced an approximately 50 % reduction in the PHNs viability. Treatment with 800 nM T3 or 8 μM T4 protected PHNs against MA toxicity, an effect which was blocked in the presence of tetrac. These findings suggest that THs protect PHNs against MA-induced cell death by the activation of integrin αvβ3 cell surface receptors. So, targeting integrin αvβ3 receptors or using THs can be considered as promising therapeutic strategies to overcome MA neurotoxicity.

Persistent Organic Pollutant Exposure and Thyroid Function among 12-Year-Old Children

INTRODUCTION

Polychlorobiphenyls (PCBs), organochlorine pesticides (OCPs), and per- and polyfluoroalkyl substances (PFASs) are persistent organic pollutants (POPs) having numerous toxicological properties, including thyroid endocrine disruption. Our aim was to assess the impact of POPs on thyroid hormones among 12-year-old children, while taking puberty into consideration.

METHODS

Exposure to 7 PCBs, 4 OCPs, and 6 PFASs (in µg/L), and free tri-iodothyronine (fT3, pg/mL), free thyroxine (fT4, ng/dL), and thyroid-stimulating hormones (TSH, mIU/L) were assessed through blood-serum measurements at age 12 years in 249 boys and 227 girls of the PELAGIE mother-child cohort (France). Pubertal status was clinically rated using the Tanner stages. For each POP, associations were estimated using linear regression, adjusted for potential confounders.

RESULTS

Among boys, hexachlorobenzene and perfluorodecanoic acid were associated with decreased fT3 (log-scale; β [95% confidence interval] = -0.07 [-0.12,-0.02] and β = -0.03 [-0.06,-0.00], respectively). Intermediate levels of perfluorohexanesulfonic acid (PFHxS) and PCB180 were associated, respectively, with increased and decreased fT4. After stratification on pubertal status, PCBs and OCPs were associated with decreased TSH only in the more advanced Tanner stages (3-5) and with decreased fT3 among early Tanner stages (1-2). Among girls, PFHxS was associated with decreased TSH (log-scale; β = -0.15 [-0.29,-0.00]), and perfluorooctanoic acid was associated with decreased fT3 (β2nd_tercile = -0.06 [-0.10,-0.03] and β3rd_tercile = -0.04 [-0.08,-0.00], versus. 1st tercile).

DISCUSSION

This cross-sectional study highlights associations between some POPs and thyroid function disruption, which appears consistent with the literature. Considering that the associations were sex-specific and moderated by pubertal status in boys, complex endocrine interactions are likely involved.

Anti-apoptotic and neurogenic properties in the hippocampus as possible mechanisms for learning and memory improving impacts of vitamin D in hypothyroid rats during the growth period

The current study was designed to investigate the protective effects of Vitamin D (VD) on hippocampal neurogenesis, apoptosis, and subsequent hippocampal-dependent learning and memory performance in hypothyroid juvenile rats. Twenty eight male Wistar rats were randomly divided into four groups as; control, Hypothyroid (Hypo), Hypo-VD100 and Hypo-VD500. Hypothyroidism was induced by giving 0.05 % propylthiouracil (PTU), and VD (100 or 500 IU/kg) treatment was performed daily by gavage. At the end of treatment, Morris water maze (MWM) was carried out and evaluated hippocampal neurogenesis, apoptosis, and dark neurons (DNs). Our results revealed that the escape latency and the traveled distance to find the platform in the Hypo group were significantly longer but the time spent and distance traveled in the target area in probe trial was lower than the control group. Hypothyroidism was accompanied by a marked decrease in hippocampal neurogenesis, and a significant increase in the number of apoptotic neurons and DNs compared to the control group. VD decreased escape latency and the traveled distance to find the platform but increased the time spent and distance traveled in the target area in probe trial than the Hypo group. VD also increased neurogenesis, reduced apoptosis and DNs production compared to the Hypo group. In conclusion, these results support a role for VD in the restoring hippocampal neurogenesis impairment, reducing neuronal apoptosis, and DNs in hypothyroid rats as well as raise the possibility that VD may contribute as a therapeutic approach to improve the learning and memory deficits associated with hypothyroidism.

Iodine as a potential endocrine disruptor-a role of oxidative stress

PURPOSE

Iodine is an essential micronutrient required for thyroid hormone biosynthesis. However, overtreatment with iodine can unfavorably affect thyroid physiology. The aim of this review is to present the evidence that iodine-when in excess-can interfere with thyroid hormone synthesis and, therefore, can act as a potential endocrine-disrupting chemical (EDC), and that this action, as well as other abnormalities in the thyroid, occurs-at least partially-via oxidative stress.

METHODS

We reviewed published studies on iodine as a potential EDC, with particular emphasis on the phenomenon of oxidative stress.

RESULTS

This paper summarizes current knowledge on iodine excess in the context of its properties as an EDC and its effects on oxidative processes.

CONCLUSION

Iodine does fulfill the criteria of an EDC because it is an exogenous chemical that interferes-when in excess-with thyroid hormone synthesis. However, this statement cannot change general rules regarding iodine supply, which means that iodine deficiency should be still eliminated worldwide and, at the same time, iodine excess should be avoided. Universal awareness that iodine is a potential EDC would make consumers more careful regarding their diet and what they supplement in tablets, and-what is of great importance-it would make caregivers choose iodine-containing medications (or other chemicals) more prudently. It should be stressed that compared to iodine deficiency, iodine in excess (acting either as a potential EDC or via other mechanisms) is much less harmful in such a sense that it affects only a small percentage of sensitive individuals, whereas the former affects whole populations; therefore, it causes endemic consequences.

Maternal Thyroid Function and Birth Weight in Twins

CONTEXT

Thyroid hormones are associated with birth weight in singleton pregnancy. Twin pregnancies need more thyroid hormones to maintain the normal growth and development of the fetuses compared with single pregnancy.

OBJECTIVE

We aimed to investigate the association of thyroid hormones and birth weight in twins.

METHODS

This was a retrospective cohort study in a Chinese population. Pregnant women who received regular antenatal health care and delivered live-born twins from 2014 to 2019 were included (n = 1626). Linear mixed model with restricted cubic splines and logistic regression models were used to estimate the association of thyroid hormones with birth weight and birth weight discordance in twins.

RESULTS

We observed that both thyrotropin (TSH) and free thyroxine (FT4) were not associated with birth weight in twins overall, while when stratifying on fetal sex or chorionicity, there were nonlinear association between FT4 levels and birth weight in boys (Pnonlinear < .001) and in dichorionic (DC) twins (Pnonlinear = 0.03). Women with levels of FT4 lower than the 10th percentile had a higher risk of birth weight discordance in their offspring than women with normal FT4 levels (range, 2.5 to 97.5 percentiles) (odds ratio = 1.58; 95% CI, 1.05-2.33).

CONCLUSION

Our study suggests there was an association of FT4, but not TSH, with birth weight and birth weight discordance varied by sex and chorionicity. These findings could have implications for obstetricians to be aware of the importance of FT4 levels in preventing birth weight discordance in twin pregnancy.

Impact of endocrine disrupting chemicals on neurodevelopment: the need for better testing strategies for endocrine disruption-induced developmental neurotoxicity

INTRODUCTION

Brain development is highly dependent on hormonal regulation. Exposure to chemicals disrupting endocrine signaling has been associated with neurodevelopmental impairment. This raises concern about exposure to the suspected thousands of endocrine disruptors, and has resulted in efforts to improve regulation of these chemicals. Yet, the causal links between endocrine disruption and developmental neurotoxicity, which would be required for regulatory action, are still largely missing.

AREAS COVERED

In this review, we illustrate the importance of two endocrine systems, thyroid hormone and retinoic acid pathways, for neurodevelopment. We place special emphasis on TH and RA synthesis, metabolism, and how endocrine disrupting chemicals known or suspected to affect these systems are associated with developmental neurotoxicity.

EXPERT OPINION

While it is clear that neurodevelopment is dependent on proper hormonal functioning, and evidence is increasing for developmental neurotoxicity induced by endocrine disrupting chemicals, this is not grasped by current chemical testing. Thus, there is an urgent need to develop test methods detecting endocrine disruption in the context of neurodevelopment. Key to this development is further mechanistic insights on the involvement of endocrine signaling in neurodevelopment as well as increased support to develop and validate new test methods for the regulatory context.

Involvement of integrin αvβ3 in thyroid hormone-induced dendritogenesis

Activation and/or modulation of the membrane-associated receptors plays a critical role in brain development. Thyroid hormone (TH) acts on both nuclear receptors (thyroid hormone receptor, TR) and membrane-associated receptors, particularly integrin αvβ3 in neurons and glia. Integrin αvβ3-mediated signal transduction mediates various cellular events during development including morphogenesis, migration, synaptogenesis, and intracellular metabolism. However, the involvement of integrin αvβ3-mediated TH action during brain development remains poorly understood. Thus, we examined the integrin αvβ3-mediated effects of TH (T₃, T₄, and rT₃) in the neurons and astrocytes using primary cerebellar culture, astrocyte-enriched culture, Neuro-2A clonal cells, and co-culture of neurons and astrocytes. We found that TH augments dendrite arborization of cerebellar Purkinje cells. This augmentation was suppressed by knockdown of integrin αvβ3, as well as TRα and TRβ. A selective integrin αvβ3 antagonist, LM609, was also found to suppress TH-induced arborization. However, whether this effect was a direct action of TH on Purkinje cells or due to indirect actions of other cells subset such as astrocytes was not clarified. To further study neuron-specific molecular mechanisms, we used Neuro-2A clonal cells and found TH also induces neurite growth. TH-induced neurite growth was reduced by co-exposure with LM609 or knockdown of TRα, but not TRβ. Moreover, co-culture of Neuro-2A and astrocytes also increased TH-induced neurite growth, indicating astrocytes may be involved in neuritogenesis. TH increased the localization of synapsin-1 and F-actin in filopodia tips. TH exposure also increased phosphorylation of FAK, Akt, and ERK1/2. Phosphorylation was suppressed by co-exposure with LM609 and TRα knockdown. These results indicate that TRs and integrin αvβ3 play essential roles in TH-induced dendritogenesis and neuritogenesis. Furthermore, astrocytes-neuron communication via TR-dependent and TR-independent signaling through membrane receptors and F-actin are required for TH-induced neuritogenesis.

Congenital Hypothyroidism in Preterm Newborns - The Challenges of Diagnostics and Treatment: A Review

Preterm newborns are forced to adapt to harsh extrauterine conditions and endure numerous adversities despite their incomplete growth and maturity. The inadequate thyroid hormones secretion as well as the impaired regulation of hypothalamus-pituitary-thyroid axis may lead to hypothyroxinemia. Two first weeks after birth are pivotal for brain neurons development, synaptogenesis and gliogenesis. The decreased level of thyroxine regardless of cause may lead to delayed mental development. Congenital hypothyroidism (CH) is a disorder highly prevalent in premature neonates and it originates from maternal factors, perinatal and labor complications, genetic abnormalities, thyroid malformations as well as side effects of medications and therapeutic actions. Because of that, the prevention is not fully attainable. CH manifests clinically in a few distinctive forms: primary, permanent or transient, and secondary. Their etiologies and implications bear little resemblance. Therefore, the exact diagnosis and differentiation between the subtypes of CH are crucial in order to plan an effective treatment. Hypothyroxinemia of prematurity indicates dynamic changes in thyroid hormone levels dependent on neonatal postmenstrual age, which directly affects patient's maintenance and wellbeing. The basis of a successful treatment relies on an early and accurate diagnosis. Neonatal screening is a recommended method of detecting CH in preterm newborns. The preferred approach involves testing serum TSH and fT4 concentrations and assessing their levels according to the cut-off values. The possible benefits also include the evaluation of CH subtype. Nevertheless, the reference range of thyroid hormones varies all around the world and impedes the introduction of universal testing recommendations. Unification of the methodology in neonatal screening would be advantageous for prevention and management of CH. Current guidelines recommend levothyroxine treatment of CH in preterm infants only when the diagnose is confirmed. Moreover, they underline the importance of the re-evaluation among preterm born infants due to the frequency of transient forms of hypothyroidism. However, results from multiple clinical trials are mixed and depend on the newborn's gestational age at birth. Some benefits of treatment are seen especially in the preterm infants born <29 weeks' gestation. The discrepancies among trials and guidelines create an urgent need to conduct more large sample size studies that could provide further analyses and consensus. This review summarizes the current state of knowledge on congenital hypothyroidism in preterm infants. We discuss screening and treatment options and demonstrate present challenges and controversies.

Nutrition and Brain Development

All nutrients are essential for brain development, but pre-clinical and clinical studies have revealed sensitive periods of brain development during which key nutrients are critical. An understanding of these nutrient-specific sensitive periods and the accompanying brain regions or processes that are developing can guide effective nutrition interventions as well as the choice of meaningful circuit-specific neurobehavioral tests to best determine outcome. For several nutrients including protein, iron, iodine, and choline, pre-clinical and clinical studies align to identify the same sensitive periods, while for other nutrients, such as long-chain polyunsaturated fatty acids, zinc, and vitamin D, pre-clinical models demonstrate benefit which is not consistently shown in clinical studies. This discordance of pre-clinical and clinical results is potentially due to key differences in the timing, dose, and/or duration of the nutritional intervention as well as the pre-existing nutritional status of the target population. In general, however, the optimal window of success for nutritional intervention to best support brain development is in late fetal and early postnatal life. Lack of essential nutrients during these times can lead to long-lasting dysfunction and significant loss of developmental potential.

Contribution of Hypothyroidism to Cognitive Impairment and Hippocampal Synaptic Plasticity Regulation in an Animal Model of Depression

The role that thyroid hormone deficiency plays in depression and synaptic plasticity in adults has only begun to be elucidated. This paper analyzes the possible link between depression and hypothyroidism in cognitive function alterations, using Wistar–Kyoto (WKY—an animal model of depression) rats and control Wistar rats under standard and thyroid hormone deficiency conditions (propylthiouracil administration—PTU). A weakening of memory processes in the WKY rats is shown behaviorally, and in the reduction of long-term potentiation (LTP) in the dentate gyrus (DG) and CA1 hippocampal regions. PTU administration decreased LTP and increased basal excitatory transmission in the DG in Wistar rats. A decrease in short-term synaptic plasticity is shown by the paired-pulse ratio measurement, occurring during hypothyroidism in DG and CA1 in WKY rats. Differences between the strains may result from decreases in the p-CaMKII, p-AKT, and the level of acetylcholine, while in the case of the co-occurrence of depression and hypothyroidism, an increase in the p-ERK1-MAP seemed to be important. Obtained results show that thyroid hormones are less involved in the inhibition of glutamate release and/or excitability of the postsynaptic neurons in WKY rats, which may indicate a lower sensitivity of the hippocampus to the action of thyroid hormones in depression.