Influence of iodide excess and interferon-gamma on human primary thyroid cell proliferation, thyroglobulin secretion, and intracellular adhesion molecule-1 and human leukocyte antigen-DR expression

A mini review of fluoride-induced apoptotic pathways

Fluorine or fluoride can have toxic effects on bone tissue and soft tissue at high concentrations. These negative effects include but not limited to cytotoxicity, immunotoxicity, blood toxicity, and oxidative damage. Apoptosis plays an important role in fluoride-induced toxicity of kidney, liver, spleen, thymus, bursa of Fabricius, cecal tonsil, and cultured cells. Here, apoptosis activated by high level of fluoride has been systematically reviewed, focusing on three pathways: mitochondrion-mediated, endoplasmic reticulum (ER) stress-mediated, and death receptor-mediated pathways. However, very limited reports are focused on the death receptor-mediated apoptosis pathways in the fluoride-induced apoptosis. Therefore, understanding and discovery of more pathways and molecular mechanisms of fluoride-induced apoptosis may contribute to designing measures for preventing fluoride toxicity.

Oxidative stress-mediated autophagic cell death participates in the neurotoxic effect on SH-SY5Y cells induced by excessive iodide

Excessive iodide could induce intellectual damage in children, which has attracted broad attention. To investigate the neurotoxic effect of iodide and its mechanism, a human dopaminergic neuroblastoma cell line (SH-SY5Y) was treated with different concentrations of potassium iodide (KI). The results showed that excessive iodide could decrease cell viability, reduce glutathione (GSH) and superoxide dismutase (SOD), and increase the degree of autophagy (by changing the cellular ultrastructure and raising the autophagy-related mRNA and protein expression of LC3, Beclin1, and p62), which were correlated with the immunofluorescence labeling. Furthermore, treatment with the autophagy inhibitor 3-methyladenine (3MA), antioxidant N-acetylcysteine (NAC) and 30 mM KI for 24 h was conducted in the following research. 3MA significantly decreased autophagy-related mRNA and protein expression and improved cell viability, indicating that excess iodide induced autophagic cell death. In addition, oxidative stress regulated autophagy, reflected by the results that NAC decreased the mRNA and protein expression of LC3, Beclin1, and p62. In summary, autophagic cell death mediated by oxidative stress may participate in excessive iodide-induced SH-SY5Y cell death.

Autophagy regulates high concentrations of iodide-induced apoptosis in SH-SY5Y cells

To date, there are many people residing in areas with high levels of iodide in water. Our previous epidemiological study showed that exposure to high iodine in drinking water significantly reduced the intelligence of children although the mechanisms remain unclear. To explore whether high concentrations of iodide may cause cytotoxic effect and the role of autophagy in the high iodide-induced apoptosis, human neuroblastoma cells (SH-SY5Y cells) were exposed to high concentrations of iodide. Morphological phenotypes, cell viability, Hoechst 33258 staining, the expression levels of apoptosis and autophagy-related proteins were detected. A possible effect of an inhibitor (3-methyladenine, 3-MA) or an inducer (rapamycin) of autophagy on high iodide-induced apoptosis also was examined. Results indicated that high iodide changed cellular morphology, decreased cell viability and increased the protein's expression level of apoptosis and autophagy. In addition, high iodide-induced apoptosis was enhanced by inhibition of autophagy and inhibited by activation of autophagy in SH-SY5Y cells. Collectively, high concentrations of iodide are toxic to SH-SY5Y cells, as well as induce apoptosis and autophagy. Furthermore, autophagy plays a regulatory role in high concentrations of iodide-induced apoptosis in SH-SY5Y cells.

Sodium fluoride (NaF) induces the splenic apoptosis via endoplasmic reticulum (ER) stress pathway in vivo and in vitro

At present, there are no reports on the relationship between fluoride-induced apoptosis and endoplasmic reticulum (ER) stress (ER stress) in the spleen of human and animals in vivo and in vitro. Therefore, the aim of this study was to define sodium fluoride (NaF)-induced apoptosis mediated by ER stress in the spleen of mice in vivo and in vitro. Apoptosis and expression levels of the ER stress-related proteins were detected by flow cytometry and western blot, respectively. The results showed that NaF treatment increased lymphocytes apoptosis, which was consistent with NaF-caused ER Stress. NaF-caused ER stress was characterized by up-regulating protein expression levels of glucose-regulated protein 78 (BiP) and glucose-regulated protein 94 (GRP94), and by activating unfolded protein response (UPR). The signaling pathway of ER stress-associated apoptosis was activated by up-regulating protein expression levels of cleaved cysteine aspartate specific protease-12 (cleaved caspase-12), growth arrest and DNA damage-inducible gene 153 (Gadd153/CHOP) and phosphorylation of JUN N-terminal kinase (p-JNK). Additionally, our in vitro study found that apoptotic rate was decreased with remarkable down-regulation of the cleaved caspase-12, CHOP, p-JNK after ER stress was inhibited by 4-Phenylbutyric acid (4-PBA) treatment. In conclusion, NaF-induced apoptosis may mediated by ER stress in the spleen.

Changes in the DNA Methylation and Hydroxymethylation Status of the Intercellular Adhesion Molecule 1 Gene Promoter in Thyrocytes from Autoimmune Thyroiditis Patients

BACKGROUND

The intercellular adhesion molecule 1 (ICAM1) gene is not expressed in normal thyroid tissue but was shown to be expressed in the thyroid tissue of autoimmune thyroiditis (AIT) patients.

METHODS

This study aimed to explore whether the DNA methylation and hydroxymethylation status of the ICAM1 promoter are aberrantly altered in the thyroid cells of AIT patients and whether this change is associated with dysfunctional expression of ICAM1. A total of 35 AIT patients and 35 sex- and age-matched controls were studied. After the isolation of thyrocytes via density-gradient centrifugation, ICAM1 mRNA expression was measured using real-time PCR. The DNA methylation and hydroxymethylation status were assessed using quantitative PCR following T4 β-glucosyltransferase treatment and MspI/HpaII cleavage at -937 bp, -701 bp, -226 bp, and -65 bp upstream of the transcription start site (TSS). The DNA methylation level was verified via pyrosequencing.

RESULTS

The AIT group showed increased DNA hydroxymethylation at -937 bp and -226 bp and decreased methylation at -937 bp, -701 bp, and -226 bp upstream of the TSS. Pyrosequencing also revealed DNA hypomethylation at -708 bp, -692 bp, -690 bp, and -688 bp upstream of the TSS. The DNA methylation status at -708 bp, -692 bp, and -226 bp upstream of the TSS was negatively associated with ICAM1 mRNA expression.

CONCLUSION

In summary, we identified aberrant DNA methylation and hydroxymethylation of the ICAM1 gene promoter in the thyrocytes of AIT patients. This aberrant epigenetic modification is associated with increased expression of the ICAM1 gene.

Effects of 2-iodohexadecanal in the physiology of thyroid cells

Iodide has direct effects on thyroid function. Several iodinated lipids are biosynthesized by the thyroid and they were postulated as intermediaries in the action of iodide. Among them, 2-iodohexadecanal (2-IHDA) has been identified and proposed to play a role in thyroid autoregulation. The aim of this study was to compare the effect of iodide and 2-IHDA on thyroid cell physiology. For this purpose, FRTL-5 thyroid cells were incubated with the two compounds during 24 or 48 h and several thyroid parameters were evaluated such as: iodide uptake, intracellular calcium and H₂O₂ levels. To further explore the molecular mechanism involved in 2-IHDA action, transcript and protein levels of genes involved in thyroid hormone biosynthesis, as well as the transcriptional expression of these genes were evaluated in the presence of iodide and 2-IHDA. The results obtained indicate that 2-IHDA reproduces the action of excess iodide on the "Wolff-Chaikoff" effect as well as on thyroid specific genes transcription supporting its role in thyroid autoregulation.

The effects and underlying mechanism of excessive iodide on excessive fluoride-induced thyroid cytotoxicity

In many regions, excessive fluoride and excessive iodide coexist in groundwater, which may lead to biphasic hazards to human thyroid. To explore fluoride-induced thyroid cytotoxicity and the mechanism underlying the effects of excessive iodide on fluoride-induced cytotoxicity, a thyroid cell line (Nthy-ori 3-1) was exposed to excessive fluoride and/or excessive iodide. Cell viability, lactate dehydrogenase (LDH) leakage, reactive oxygen species (ROS) formation, apoptosis, and the expression levels of inositol-requiring enzyme 1 (IRE1) pathway-related molecules were detected. Fluoride and/or iodide decreased cell viability and increased LDH leakage and apoptosis. ROS, the expression levels of glucose-regulated protein 78 (GRP78), IRE1, C/EBP homologous protein (CHOP), and spliced X-box-binding protein-1 (sXBP-1) were enhanced by fluoride or the combination of the two elements. Collectively, excessive fluoride and excessive iodide have detrimental influences on human thyroid cells. Furthermore, an antagonistic interaction between fluoride and excessive iodide exists, and cytotoxicity may be related to IRE1 pathway-induced apoptosis.

The role of the IRE1 pathway in excessive iodide- and/or fluoride-induced apoptosis in Nthy-ori 3-1 cells in vitro

Excessive iodide and fluoride coexist in the groundwater in many regions, causing a potential risk to the human thyroid. To investigate the mechanism of iodide- and fluoride-induced thyroid cytotoxicity, human thyroid follicular epithelial cells (Nthy-ori 3-1) were treated with different concentrations of potassium iodide (KI), with or without sodium fluoride (NaF). Cell morphology, viability, lactate dehydrogenase (LDH) leakage, apoptosis, and expression of inositol-requiring enzyme 1 (IRE1) pathway-related molecules were assessed. Results showed 50 mM of KI, 1 mM of NaF, and 50 mM of KI +1 mM of NaF changed cellular morphology, decreased viability, and increased LDH leakage and apoptosis. Elevated expression of binding protein (BiP), IRE1, and C/EBP homologous protein (CHOP) mRNA and protein, as well as spliced X-box-binding protein-1 (sXBP-1) mRNA, were observed in the 1 mM NaF and 50 mM KI +1 mM NaF groups. Collectively, excessive iodide and/or fluoride is cytotoxic to the human thyroid. Although these data do not manifest iodide could induce the IRE1 pathway, the cytotoxicity followed by exposure to fluoride alone or in combination with iodide may be related to IRE1 pathway-induced apoptosis. Furthermore, exposure to the combination of excessive iodide and fluoride may cause interactive effects on thyroid cytotoxicity.

Effect of early acute high concentrations of iodide exposure on mitochondrial superoxide production in FRTL cells

Excessive oxidative stress has been suggested as one of the underlying mechanisms in the development of thyroid cytotoxicity. Although the involvement of mitochondria has been hypothesized, the effect of early acute high concentrations of iodide on mitochondrial superoxide production remains largely unknown, especially within a 24 h time frame. By using a novel fluorescent probe, MitoSOX Red, we demonstrated the concentration response and time-course response of KI-induced mitochondrial superoxide production in the Fischer rat thyroid cell line (FRTL). A strong increase of MitoSOX Red fluorescence intensity in FRTL cells can be seen at 2 h following high concentrations of iodide exposure. Besides, we indicated that 6-propyl-2-thiouracil (PTU, 300 μM), thyroid-stimulating hormone (TSH, 10 mU/ml), and perchlorate (KClO(4), 30 μM) can inhibit excessive iodide-induced strong mitochondrial superoxide production; however, diethyldithiocarbamic acid (DETC, 2 mM) can further increase excessive iodide-induced mitochondrial superoxide production. By using transmission electron microscopy (TEM), we noted accumulated myelinoid bodies with lipid droplets and numerous apoptotic nuclear bodies at 24 h in FRTL cells. In addition, we demonstrated a significant decrease in cytochrome c (cyt c) content in the mitochondria by enzyme linked immunosorbent assay (ELISA), and DNA fragments and significant increases in lactate dehydrogenase (LDH) activity were detected. We propose a sequence of events mediated by a strong mitochondrial superoxide production at 2 h, followed by lipid peroxidation, cell membrane damage with significant cyt c release, culminating in DNA fragmentation and apoptotic nuclear formation at 24 h, which may partly contribute to the underlying mechanisms of early acute iodide excess.

Iodide-induced chemokines and genes related to immunological function in cultured human thyroid follicles in the presence of thyrotropin

BACKGROUND

It is well known that iodide exacerbates thyroid function in subclinical hypothyroid patients with autoimmune thyroiditis. To investigate the immunological mechanism of iodine-induced thyroid dysfunction, we studied the effect of iodide in cultured human thyroid follicles, which respond to physiological concentrations of human thyrotropin (TSH) (0.3-10 microU/mL) and maintain the Wolff-Chaikoff effect.

MATERIALS AND METHODS

Thyroid follicles obtained from Graves' patients at subtotal thyroidectomy were precultured in medium containing 0.5% fetal calf serum and 10(-8) M iodide for 5 days, and then cultured with the medium containing bovine TSH (30 microU/mL) and low (10(-8)M) or high (10(-5)M) concentrations of iodide. After 3-72 hours of culture, the effect of iodide on thyroid cell mRNA expression was analyzed by microarray and reverse transcriptase-polymerase chain reaction.

RESULTS

After 48 hours of culture, iodide nearly doubled the mRNA expression levels of the immunity-associated genes (intercellular adhesion molecule-1, transforming growth factor beta 1-induced protein, early growth response gene 1, guanylate-binding protein 1, and annexin A1) and decreased the mRNA expression of sodium-iodide symporter to less than 20%. Further, the mRNA expression levels of chemokines (CCL2, CXCL8, and CXCL14) increased nearly twofold, whereas their receptors did not show any significant response. Real-time polymerase chain reaction analyses confirmed that iodide increased the mRNA expression levels of these genes in a time- and concentration-dependent manner. Immunohistochemical studies revealed that the chemokines were expressed mainly in the thyroid follicular cells in addition to the immune cells. The iodide-induced increase in CCL2 was greater in thyroid follicles obtained from thyroid gland that had been moderately infiltrated with the immunocompetent cells.

CONCLUSION

We have demonstrated that iodide stimulates thyroid follicular cells to produce chemokines, particularly CCL2, CXCL8, and CXCL14. These chemokines and intercellular adhesion molecule-1 would attract immunocompetent cells into thyroid gland. These in vitro findings suggest that iodide at high concentrations may induce thyroid dysfunction through not only biochemical but also immunological mechanisms, particularly in patients with autoimmune thyroid disorders.