Subclinical hypothyroidism in pregnant rats impaired learning and memory of their offspring by promoting the p75NTR signal pathway

Ameliorative effects of thiamin on learning behavior and memory dysfunction in a rat model of hypothyroidism: implication of oxidative stress and acetylcholinesterase

Hypothyroidism causes learning and memory impairment. Considering the neuroprotective properties of thiamine (Vitamin B1), this study was conducted to investigate the effects of thiamine on acetylcholinesterase (AChE) activity, oxidative damage, and memory deficits in hypothyroid rats.In this study, 50 rats (21 days old) were randomly divided into 5 groups and treated with propylthiouracil (0.05% in drinking water) and thiamine (50, 100, and 200 mg/kg, oral) for 7 weeks. Following that, Morris water maze (MWM) and passive avoidance (PA) tests were performed. Finally, oxidative stress indicators and AChE activity were measured in brain tissue.Treatment of hypothyroid rats with thiamine, especially at 100 and 200 mg/kg, alleviated the ability to remember the location of the platform as reflected by less time spent and distance to reach the platform, during the MWM test (P < 0.05 to P < 0.001). In the PA test, the latency to enter the dark chamber and light stay time were increased in rats who received thiamine compared to the hypothyroid group (P < 0.05 to P < 0.001). In addition, thiamine increased the levels of total thiol groups and superoxide dismutase while decreasing the levels of malondialdehyde and AChE.Our results suggest that thiamine supplementation could effectively improve memory loss in a rat model of hypothyroidism. The positive effects of thiamin on the learning and memory of hypothyroid rats may be due to amelioration of redox hemostasis and cholinergic disturbance.

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.

Study on the Effect of Different Iodine Intake on Hippocampal Metabolism in Offspring Rats

Iodine is an essential trace element in the human body. Severe maternal iodine deficiency during pregnancy leads to obvious intellectual disability in the offspring. The effects of iodine deficiency on brain development have been demonstrated, but there is no clear evidence of the effects of iodine excess on brain development. To clarify the effects of iodine excess on the brain development of offspring and to provide clues to the mechanisms underlying the effects of iodine deficiency and iodine excess on the brain development of offspring. In this study, animal models with different iodine intakes were constructed using potassium iodate (KIO₃). The models included four experimental groups (low-iodine group one (LI, 0μg/L iodine), low-iodine group two (LII, 5μg/L iodine), high-iodine group one (HI, 3000μg/L iodine), and high-iodine group two (HII, 10000μg/L iodine)) and one control group (NI, 100μg/L iodine). There were 20 female rats in each group, and 8 offspring were chosen from each group following birth to assess metabolic alterations. The metabolites of subsets of brain hippocampal tissue were profiled by ultra-performance liquid chromatography-linked electrospray ionization quadrupole time-of-flight mass spectrometry (UPLC-ESI-QTOFMS) and the results were subjected to multivariate data analysis. Differential substances were screened by t test (p<0.05), principal component analysis (PCA), and partial least squares analysis (PLS-DA, VIP>1). The thyroid function of the female rats in the experimental group was abnormally changed. Metabolic analysis showed that the five groups were separated which revealed significant differences in hippocampal tissue metabolism among the five groups of offspring. A total of 12 potential metabolites were identified, with the majority of them being related to amino acid and energy metabolism. These metabolites are involved in various metabolic pathways, are interrelated, and may play a function in brain development. Our study highlights changes in metabolites and metabolic pathways in the brain hippocampus of offspring rats with different iodine intakes compared to controls, revealing new insights into hippocampal metabolism in offspring rats and new relevant targets.

The effects of curcumin in learning and memory impairment associated with hypothyroidism in juvenile rats: the role of nitric oxide, oxidative stress, and brain-derived neurotrophic factor

The effect of curcumin (Cur) on cognitive impairment and the possible role of brain tissue oxidative stress, nitric oxide (NO) levels, and brain-derived neurotrophic factor (BDNF) were investigated in juvenile hypothyroid rats. The juvenile rats (21 days old) were allocated into the following groups: (1) control; (2) hypothyroid (0.05% propylthiouracil (PTU) in drinking water); (3-5) hypothyroid-Cur 50, 100, and 150, which in these groups 50, 100, or 150 mg/kg, Cur was orally administered by gavage during 6 weeks. In the hypothyroid rats, the time elapsed and the traveled distance to locate the hidden platform in the learning trials of Morris water maze (MWM) increased, and on the probe day, the amount of time spent in the target quadrant and the distance traveled in there was decreased. Hypothyroidism also decreased the latency and increased the time spent in the darkroom of the passive avoidance (PA) test. Compared with the hypothyroid group, Cur enhanced the performance of the rats in both MWM and PA tests. In addition, Cur reduced malondialdehyde concentration and NO metabolites; however, it increased thiol content as well as the activity of catalase (CAT) and superoxide dismutase enzymes in both the cortex and hippocampus. Cur also increased hippocampal synthesis of BDNF in hypothyroid rats. The beneficial effects of Cur cognitive function in juvenile hypothyroid rats might be attributed to its protective effect against oxidative stress and potentiation of BDNF production.

Dimethyl fumarate improves cognitive impairment by enhancing hippocampal brain-derived neurotrophic factor levels in hypothyroid rats

BACKGROUND

Dimethyl fumarate (DMF) is an effective drug for multiple sclerosis and can improve the cognitive dysfunction caused by streptozotocin, but the effect on cognitive dysfunction caused by hypothyroidism is unclear.

METHODS

After the hypothyroidism rat model induced by propylthiouracil, we gave rats 25 mg/kg DMF by gavage. The body weight during model building and administration was recorded. The levels of T4 and T3 in serum were detected by an automatic biochemical analyzer. Morris water maze test was used to detect the effect of DMF on cognitive learning ability. The effect of DMF on Nissl bodies in the brain tissue was evaluated by Nissl staining. The mRNA and protein levels of BDNF in brain tissue were detected by quantitative reverse transcription-polymerase chain reaction and Western blot. The degrees of p-AKT/AKT and p-CREB/CREB in brain tissue were detected by Western blot.

RESULTS

After DMF treatment, the body weight of hypothyroid rats recovered, and the levels of T3 and T4 in the serum were ameliorated. DMF also reduced the escape latency and distance traveled, and increased the swim speed. The number of Nissl bodies and expression of BDNF, p-AKT/AKT, and p-CREB/CREB in the brain tissue were increased after DMF treatment.

CONCLUSION

DMF improved the cognitive dysfunction of hypothyroid rats by increasing the level of BDNF in the brain tissue of hypothyroid rats.

Maternal Subclinical Hypothyroidism in Rats Impairs Spatial Learning and Memory in Offspring by Disrupting Balance of the TrkA/p75NTR Signal Pathway

Maternal subclinical hypothyroidism (SCH) during pregnancy can adversely affect the neurodevelopment of the offspring. The balance of nerve growth factor (NGF)-related tropomyosin receptor kinase A/p75 neurotrophin receptor (TrkA/p75^NTR) signaling in the hippocampus is important in brain development, and whether it affects cognitive function in maternal SCH’s offspring is not clear. In this study, we found that compared with the control (CON) group, expression of proliferation-related proteins [NGF, p-TrkA, phospho-extracellular signal-regulated kinase 1/2 (p-ERK1/2) and phospho-cAMP response element-binding protein (p-CREB)] decreased in the hippocampus of the offspring in the SCH group, overt hypothyroidism (OHT) group, and the group with levothyroxine (L-T₄) treatment for SCH from gestational day 17 (E17). In contrast, expression of apoptosis-related proteins [pro-NGF, p75^NTR, phospho-C-Jun N-terminal kinase (p-JNK), p53, Bax and cleaved caspase-3] was increased. The two groups with treatment with L-T₄ for SCH from E10 and E13, respectively, showed no significant difference compared with the CON group. L-T₄ treatment enhanced relative expression of NGF by increasing NGF/proNGF ratio in offspring from maternal SCH rats. In conclusion, L-T₄ treatment for SCH from early pregnancy dramatically ameliorated cognitive impairment via TrkA/p75^NTR signaling, which involved activation of the neuronal proliferation and inhibition of neuronal apoptosis in SCH rats’ offspring.

Neuroprotection elicited by resveratrol in a rat model of hypothyroidism: Possible involvement of cholinergic signaling and redox status

Both the cholinergic pathway and oxidative stress are important mechanisms involved in the pathogenesis of hypothyroidism, a condition characterized by low levels of thyroid hormone that predispose the patient to brain dysfunction. Phenolic compounds have numerous health benefits, including antioxidant activity. This study evaluates the preventive effects of resveratrol in the cholinergic system and redox status in rats with methimazole-induced hypothyroidism. Hypothyroidism increases acetylcholinesterase (AChE) activity and density in the cerebral cortex and hippocampus and decreases the α7 and M1 receptor densities in the hippocampus. Hypothyroidism also increases cellular levels of reactive oxygen species (ROS) and thiobarbituric acid reactive substances (TBARS), but reduces total thiol content, and catalase and superoxide dismutase activities in the serum. In the cerebral cortex and hippocampus, hypothyroidism increases the levels of ROS and nitrites. In this study, resveratrol (50 mg/kg) treatment prevents the observed increase in AChE in the cerebral cortex, and increases the protein levels of NeuN, a marker of mature neurons. Resveratrol also prevents changes in serum ROS levels and brain structure, as well as the levels of TBARS, total thiol content, and serum catalase enzyme activity. These collective findings suggest that resveratrol has a high antioxidant capacity and can restore hypothyroidism-triggered alterations related to neurotransmission. Thus, it is a promising agent for the prevention of brain damage resulting from hypothyroidism.

Thyroid Diseases During Pregnancy: Bibliometric Analysis of Scientific Publications

BACKGROUND

Bibliometric analysis can analyze development trends and predict research hotspots. We used these analyses to better understand pregnancy-related implications of thyroid diseases.

METHODS

Publications on thyroid diseases during pregnancy from 1926 to hitherto were retrieved based on the Web of Science database. The publications and references, the institutions and countries, the journals, the keywords and citations, were analyzed by utilizing VOSviewer, CiteSpace and CitNetExplorer.

RESULTS

A total of 3310 publications were retrieved and were cited 87913 times. The United States took the dominant position in outputs and collaborations. Harvard University had the most articles 86, which also had the highest h-index 30. Thyroid ranked first with 201 publications and Journal of Clinical Endocrinology Metabolism had the highest h-index 67. Among the 49 burst keywords, "antibody" had the longest burst period from 1991 to 2012, "thyroxine" had the strongest burst strength 16.7026, "hypothyroxinemia" appeared most recently in 2018. The most frequent keyword was "pregnancy" occurred 1324 times. All the top 98 frequent keywords were clustered into 4 clusters. The citation network visualization was grouped into 8 groups.

CONCLUSION

The research focus of thyroid diseases in pregnancy ranged from clinical thyroid dysfunction to milder thyroid dysfunction. Guidelines published by the American Thyroid Association enacted a crucial purpose in the treatment and development of thyroid diseases during pregnancy. Some randomized controlled studies of unresolved problems and long-term follow-up of offspring may be the direction of future research. In the meantime, bibliometric methods can help scholars choose journals, track research hotspots, and identify the direction or focus of future research.

Early L-T4 intervention improves fetal heart development in pregnant rats with subclinical hypothyroidism rats by activating BMP4/Smad4 signaling pathway

BACKGROUND

It is unclear whether the offspring of subclinical hypothyroidism (SCH) pregnant rats still have abnormal cardiac development, and whether early intervention with L-T4 can improve the abnormality of these offspring. Therefore, the aim of this study was to investigate the effect of early L-T4 intervention on the heart development of offspring of SCH pregnant rats and its possible molecular mechanism.

METHODS

Eighty female Wistar rats were randomly divided into Sham group (placebo control), SCH group, LT4-E10 group (L-T4 treatment started on the 10th day of gestation), and LT4-E13 group (L-T4 treatment started on the 13th day of gestation). Each group was further divided into E16 (16th day of gestation), E18 (18th day of gestation), P5 (5th day postnatal day), and P10 (10th day postnatal day) subgroups. The levels of serum TT4 and TSH, the ratio of heart weight to body weight of offspring rats, the expression of metabolic enzymes, and the histopathology of cardiomyocytes were determined. To elucidate the effects of L-T4 on cardiac development of offspring of SCH pregnant rats, the expression levels of GATA4, Nkx2-5 and proteins involved in BMP4/Smad4 signaling pathway were detected by immunohistochemistry, real time quantitative polymerase chain reaction and Western blotting to elucidate the molecular mechanism of L-T4 regulating the heart development of the offspring of SCH pregnant rats.

RESULTS

Compared with Sham group, serum TSH was significantly increased in SCH pregnant rats. Moreover, early L-T4 intervention significantly reduced the levels of serum TSH. Compared with the offspring in the SCH group, early L-T4 intervention significantly increased the heart weight, heart weight to body weight ratio, the activities of succinate dehydrogenase (SDH), Na⁺/K⁺-ATPase and Ca²⁺-ATPase, but reduced myocardial cell shrinkage and nuclear staining, hyperemia/congestion and vacuolar degeneration. In addition, early L-T4 intervention not only significantly increased the mRNA and protein expression of Gata4 and Nkx2-5, but also increased the protein expression involved in BMP4/Smad4 signal pathway in myocardium of the offspring of SCH pregnant rats.

CONCLUSIONS

Early L-T4 intervention can regulate the cardiac development of the offspring of SCH pregnant rats by activating BMP4/Smad4 signaling pathway and increasing the expression of Gata4 and Nkx2-5 proteins.

Inducible nitric oxide synthase inhibitor, aminoguanidine improved Ki67 as a marker of neurogenesis and learning and memory in juvenile hypothyroid rats

INTRODUCTION

In the present study, the effect of inducible nitric oxide (NO) synthase inhibitor, aminoguanidine (AG) on neurogenesis indicators, learning and memory, and oxidative stress status in juvenile hypothyroid (Hypo) rats was evaluated.

METHOD

The studied groups were including: (a) Control, (b) Hypo, (c-e) Hypo-AG 10, Hypo-AG 20, and Hypo-AG 30. Hypothyroidism was induced in the groups 2-5 by adding propylthiouracil in drinking water (0.05%). AG (10, 20, or 30 mg/kg) was daily injected intraperitoneally in the groups 3-5. The rats of the groups 1 and 2 were injected by saline instead of AG. After 6 weeks treatment, Morris water maze (MMW) and passive avoidance (PA) tests were done. Deep anesthesia was then induced and the brain tissue was excised for biochemical parameters measuring.

RESULTS

Ki67 as a maker of neurogenesis and thiol, superoxide dismutase (SOD), and catalase (CAT) as oxidative stress indicators were decreased in the brain of Hypo group, whereas malondialdehyde (MDA) and NO metabolites were enhanced. AG improved Ki67, thiol, CAT, and SOD while decreased MDA and NO metabolites. The escape latency in the MWM test increased in the Hypo group. The spending time in the target quadrant in the probe test of MWM and step-through latency in the PA test in the Hypo group was lower than Control group. AG reversed all the negative behavioral effects of hypothyroidism.

CONCLUSION

These results revealed that AG improved neurogenesis, learning and memory impairments, and oxidative imbalance in the brain juvenile Hypo rats.

Universal screening for thyroid disease during pregnancy should be performed

Thyroid disease can significantly impact the pregnant woman and her child. Human and animal studies have firmly linked overt hypothyroidism and overt hyperthyroidism to miscarriage, preterm delivery and other adverse pregnancy outcomes. Overt hypothyroidism and overt hyperthyroidism affect 1% of all pregnancies. Treatment is widely available, and if detected early, results in decreased rates of adverse outcomes. Universal screening for thyroid disease in pregnancy can identify patients with thyroid disease requiring treatment, and ultimately decrease rates of complications. Universal screening is cost-effective compared to the currently accepted practice of targeted screening and may even be cost-saving in some healthcare systems. Targeted screening, which is recommended by most professional associations, fails to detect a large proportion of pregnant women with thyroid disease. In fact, an increasing number of providers are performing universal screening for thyroid disease in pregnancy, contrary to society guidelines. Limited evidence concerning the impact of untreated and treated subclinical disease and thyroid autoimmunity has distracted from the core rationale for universal screening - the beneficial impact of detecting and treating overt thyroid disease. Evidence supporting universal screening for overt disease stands independently from that of subclinical and autoimmune disease. The time to initiate universal screening is now.