Molecular pathogenesis of nodular goiter

Association between thyroid disorders and extra-thyroidal cancers, a review

Thyroid hormone has been shown to have both tumor-promoting and tumor-suppressing actions, which has led to significant debate over its involvement in the development of cancer. Proliferation, apoptosis, invasiveness, and angiogenesis are all aspects of cancer that are affected by the thyroid hormones T3 and T4, according to research conducted in animal models and in vitro experiments. The effects of thyroid hormones on cancer cells are mediated by many non-genomic mechanisms, one of which involves the activation of the plasma membrane receptor integrin αvβ3. Typically, abnormal amounts of thyroid hormones are linked to a higher occurrence of cancer. Both benign and malignant thyroid disorders were found to be associated with an increased risk of extra-thyroidal malignancies, specifically colon, breast, prostate, melanoma, and lung cancers. The purpose of this review was to shed light on this link to define which types of cancer are sensitive to thyroid hormones and, as a result, are anticipated to respond favorably to treatment of the thyroid hormone axis.

Oxidative stress mediates the associations between phthalate exposures and thyroid cancer/benign nodule risk

Epidemiological studies have suggested that phthalate exposures are associated with increased risks of thyroid cancer and benign nodule, while the underlying mechanisms are largely unknown. Here, we explored the mediation effects of oxidative stress (OS) biomarkers in the associations between phthalate exposures and the risks of thyroid cancer and benign nodule. Urine samples collected from 143 thyroid cancer, 136 nodule patients, and 141 healthy controls were analyzed for 8 phthalate metabolites and 3 OS biomarkers [8-hydroxy-2-deoxyguanosine (8-OHdG), 4-hydroxy-2-nonenal-mercapturic acid (HNE-MA), and 8-iso-prostaglandin F_2α (8-isoPGF_2α)]. Multivariable linear or logistic regression models were used to explore the associations of OS biomarkers with phthalate metabolite concentrations and the risks of thyroid cancer and nodule. The mediation role of OS biomarkers was also investigated. Urinary monoethyl phthalate (MEP), monomethyl phthalate (MMP), mono (2-ethyl-5-oxohexyl) phthalate (MEOHP), mono (2-ethylhexyl) phthalate (MEHP), and mono (2-ethyl-5-hydroxyhexyl) phthalate (MEHHP) were positively associated with at least 2 OS biomarkers (all P-values<0.01), and part of these positive associations varied in different subgroups. All 3 OS biomarkers were positively associated with the risks of thyroid nodule and cancer (P-values<0.001). The mediation analysis showed that OS biomarkers significantly mediated the associations between urinary MEHOP concentration and nodule, as well as between urinary MMP, MEHP, and MEHHP concentrations and cancer and nodule, with the estimated proportions of mediation ranging from 15.8% to 85.6%. Our results suggest that OS is a potential mediating mechanism through which phthalate exposures induce thyroid carcinogenesis and nodular formation.

Follicular Neoplasm of Thyroid Revisited: Current Differential Diagnosis and the Impact of Molecular Testing

The diagnosis of "follicular neoplasm" (FN) in thyroid cytopathology has a long history that originated not long after the practice of fine-needle aspiration (FNA) of thyroid nodules. From the outset, this interpretive category was intended to convey a set of differential diagnoses rather than a precise diagnosis, as key diagnostic features, such as capsular and vascular invasion, were not detectable on cytology preparations. Cytologic-histologic correlation studies over the past several decades have shown that FN interpretation can be applied to the spectrum of nonneoplastic tumors to carcinomas. Most tumors classified as FN include follicular adenoma, follicular carcinoma, noninvasive follicular thyroid tumor with papillary-like nuclear features, and follicular variant of papillary thyroid carcinoma. Less common entities that may be classified as FN on FNA include hyalinizing trabecular tumor (HTT), poorly differentiated thyroid carcinoma, medullary carcinoma, and nonthyroidal lesions such as parathyroid tissue, paraganglioma, and metastatic tumors. Advances in our ability to detect characteristic molecular alterations (eg, GLIS gene rearrangements for hyalinizing trabecular tumor) in FNA samples may assist in the identification of some of these entities. In this review, we summarize the pathophysiology, history, and evolution of the terminology and the current differential diagnosis according to the recently published 2022 World Health Organization classification, molecular testing, and management of nodules classified as FN.

Oncocytic nodular hyperplasia of the thyroid

Nodular hyperplasia of the thyroid is a process whereby the gland experiences growth by nodular expansion of thyroid parenchyma. We have encountered 45 patients in whom the process was caused by the growth of well-defined and sharply circumscribed but unencapsulated nodules composed of oncocytic thyroid follicular cells. The lesions arose in 39 women and 6 men, aged 25-69 years (mean = 50.3 years). The surrounding thyroid parenchyma showed features of chronic lymphocytic thyroiditis. The nodules varied from microscopic to 5 cm and appeared to compress the surrounding thyroid parenchyma. Most of the lesions lacked a well-defined capsule. In 26 tumors, the nodules displayed a predominantly follicular pattern of growth; in 8 cases there were admixtures of follicular and trabecular patterns with focal solid areas devoid of follicles. Clinical follow-up in 39 patients ranging from 7 to 22 years (median = 16 years) showed no evidence of recurrence, metastasis, or malignant transformation. One patient died of unknown causes 15 years after the diagnosis, and another patient died 4 years after diagnosis from metastatic colonic adenocarcinoma. Oncocytic nodular hyperplasia is a benign process associated with chronic lymphocytic thyroiditis that should be distinguished from benign and malignant oncocytic (Hurthle cell) tumors of the thyroid.

Is Melanoma Progression Affected by Thyroid Diseases?

Clinical and epidemiological evidence indicate a relationship between thyroid diseases and melanoma. In particular, the hypothyroidism condition appears to promote melanoma spread, which suggests a protective role of thyroid hormones against disease progression. In addition, experimental data suggest that, in addition to thyroid hormones, other hormonal players of the hypothalamic–pituitary–thyroid (HPT) axis, namely the thyrotropin releasing hormone and the thyrotropin, are likely to affect melanoma cells behavior. This information warrants further clinical and experimental studies in order to build a precise pattern of action of the HPT hormones on melanoma cells. An improved knowledge of the involved molecular mechanism(s) could lead to a better and possibly personalized clinical management of these patients.

Emerging Role of Oxidative Stress on EGFR and OGG1-BER Cross-Regulation: Implications in Thyroid Physiopathology

Thyroid diseases have a complex and multifactorial aetiology. Despite the numerous studies on the signals referable to the malignant transition, the molecular mechanisms concerning the role of oxidative stress remain elusive. Based on its strong oxidative power, H2O2 could be responsible for the high level of oxidative DNA damage observed in cancerous thyroid tissue and hyperactivation of mitogen-activated protein kinase (MAPK) and PI3K/Akt, which mediate ErbB signaling. Increased levels of 8-oxoG DNA adducts have been detected in the early stages of thyroid cancer. These DNA lesions are efficiently recognized and removed by the base excision repair (BER) pathway initiated by 8-oxoG glycosylase1 (OGG1). This study investigated the relationships between the EGFR and OGG1-BER pathways and their mutual regulation following oxidative stress stimulus by H2O2 in human thyrocytes. We clarified the modulation of ErbB receptors and their downstream pathways (PI3K/Akt and MAPK/ERK) under oxidative stress (from H2O2) at the level of gene and protein expression, according to the mechanism defined in a human non-pathological cell system, Nthy-ori 3-1. Later, on the basis of the results obtained by gene expression cluster analysis in normal cells, we assessed the dysregulation of the relationships in a model of papillary thyroid cancer with RET/PTC rearrangement (TPC-1). Our observations demonstrated that a H2O2 stress may induce a physiological cross-regulation between ErbB and OGG1-BER pathways in normal thyroid cells (while this is dysregulated in the TPC-1 cells). Gene expression data also delineated that MUTYH gene could play a physiological role in crosstalk between ErbB and BER pathways and this function is instead lost in cancer cells. Overall, our data on OGG1 protein expression suggest that it was physiologically regulated in response to oxidative modulation of ErbB, and that these might be dysregulated in the signaling pathway involving AKT in the progression of thyroid malignancies with RET/PTC rearrangements.

Relationship between urinary metabolites of polycyclic aromatic hydrocarbons and risk of papillary thyroid carcinoma and nodular goiter: A case-control study in non-occupational populations

Exposure to polycyclic aromatic hydrocarbons (PAHs) has been linked to the development of certain diseases. However, the relationship between PAH exposure and thyroid disorders remains unknown. We measured 10 of the most common hydroxylated PAHs (OH-PAHs) in the urine of thyroid nodular goiter (NG) patients, papillary thyroid carcinoma (PTC) patients, and healthy controls by gas chromatography-triple-quadrupole mass spectrometry (GC-MS/MS). We found that the concentrations of 2-hydroxyfluorene (2-OH-FLU), 2-hydroxydibenzofuran (2-OH-DBF), and 1-hydroxyphenanthrene (1-OH-PHE) in the NG group, and of 2-hydroxynaphthalene (2-OH-NAP), 2-OH-DBF, and 1-OH-PHE in the PTC group were significantly higher than those in controls. In addition, participants in the high tertiles of 2-OH-FLU and 1-OH-PHE had higher risk of NG. Besides these two OH-PAHs, elevated risk of NG was observed in women in the high tertiles of 1-hydroxynaphthalene (1-OH-NAP), 2-OH-NAP, 2-OH-DBF, and 3-hydroxyfluorene (3-OH-FLU). Furthermore, participants in the high tertiles of seven OH-PAHs, namely, 1-OH-NAP, 2-OH-NAP, 2-OH-DBF, 2-OH-FLU, 3-OH-FLU, 3/9-hydroxyphenanthrene (3/9-OH-PHE), and 1-OH-PHE, had elevated risk of PTC, and females in these high tertiles had an even higher risk of PTC. Our findings suggest that PAH exposure may increase the risk of NG/PTC, and there may be a gender-specific effect of PAH exposure on the development of NG/PTC.

Thyroid diseases and skin autoimmunity

The skin is the largest organ of the body, at the boundary with the outside environment. Primarily, it provides a physical and chemical barrier against external insults, but it can act also as immune organ because it contains a whole host of immune-competent cells of both the innate and the adaptive immune systems, which cooperate in eliminating invading pathogens following tissue injury. On the other hand, improper skin immune responses lead to autoimmune skin diseases (AISD), such as pemphigus, bullous pemphigoid, vitiligo, and alopecia. Although the interplay among genetic, epigenetic, and environmental factors has been shown to play a major role in AISD etiology and progression, the molecular mechanisms underlying disease development are far from being fully elucidated. In this context, epidemiological studies aimed at defining the association of different AISD with other autoimmune pathologies revealed possible shared molecular mechanism(s) responsible for disease progression. In particular, over the last decades, a number of reports have highlighted a significant association between thyroid diseases (TD), mainly autoimmune ones (AITD), and AISD. Here, we will recapitulate the epidemiology, clinical manifestations, and pathogenesis of the main AISD, and we will summarize the epidemiological evidence showing the associations with TD as well as possible molecular mechanism(s) underlying TD and AISD pathological manifestations.

An investigation into symptoms, diagnosis, treatment, and treatment complications in patients with retrosternal goiter

Introduction:

Retrosternal goiter refers to any thyroid enlargement in which over 50% of the thyroid permanently located under the thoracic inlet or the lower pole of thyroid is not palpable with the neck in hyperextended position. Due to the increasing number of surgical procedures of retrosternal goiter, the present study was carried out to examine the symptoms, diagnosis, treatment, and treatment complications in retrosternal goiter patients.

Materials and Methods:

Data related to demographic data (age and gender), clinical symptoms (dyspnea, dysphagia, dysphonia, lumps in neck, and hoarseness), methods of diagnosis (computed tomography [CT], chest X-ray [CXR], ultrasonography, and magnetic resonance imaging), and postoperative complications (bleeding, early and late dysphonia, early and late dyspnea, transient and permanent hypocalcemia, transient, and permanent recurrent laryngeal nerve paralysis) were collected.

Results:

According to the results 71.4% of patients were women and most of the participants (67.1%) aged 45–60 years. Mass in the neck was the most frequent symptoms before surgery (88.6%). The most common incision for thyroidectomy (95/7%) was neck Collar incision. Diagnosis method in 82.9% and 17.1% of cases was, respectively, based on CT scans with CXR and CT scans with CXR and ultrasound. According to the postoperative pathologic findings, 58.5% of the cases were multinodular goiter, 22.9% were papillary cell carcinoma, 7.1% were medullary carcinoma, 5.7% were anaplastic carcinoma, 5.7% were thyroid lymphoma, and only 1.4% were thyroid adenoma. Postoperative complications occurred in 47.14% of patients. Most common complication was early transient dysphonia.

Conclusion:

This study recommends that retrosternal goiter should be operated early under suitable conditions, and the best diagnosis tool and best surgery methods are CT scan and surgery with collar incision, respectively.

Temporal Changes in Thyroid Nodule Volume: Lack of Effect on Paranodular Thyroid Tissue Volume

BACKGROUND

The term "nodular goiter" has long been used to refer to a nodular thyroid gland, based on the assumption that nodule growth may be associated with hyperplasia of the surrounding non-nodular tissue. The aim of this prospective, multicenter, observational study was to determine whether nodule growth is accompanied by growth in the non-nodular tissue.

METHODS

Eight Italian thyroid-disease referral centers enrolled 992 consecutive patients with one to four benign nodules. Nodular and non-nodular thyroid tissue volumes were assessed for five years with annual ultrasound examinations.

RESULTS

In participants whose nodules remained stable (n = 839), thyroid volumes did not change (baseline 15.0 mL [confidence interval (CI) 14.5-15.6]; five-year evaluation 15.1 mL [CI 14.5-15.7]). In participants with significant growth of one or more nodule (n = 153), thyroid volumes increased and by year 5 were significantly greater than those of the former group (17.4 mL [CI 16-18.7]). In 76 individuals with unilateral nodules that grew, the mean nodular lobe volume significantly exceeded that of the contralateral lobe (8.6 mL [CI 7.4-9.8] vs. 6.7 mL [CI 6-7.4]). The unaffected lobe volumes remained stable over time, while nodular lobes grew steadily and were significantly greater at the end of follow-up (10.1 mL [CI 8.9-11.3]). Excluding the volume of the largest growing nodule in these cases, the remaining volume of the affected lobe remained virtually unchanged with respect to its baseline value. Furthermore, there was no significant difference in the non-nodular tissue volume between the unaffected lobe and the affected lobe (with the largest growing nodule volume subtracted), both at baseline and at the end of follow-up.

CONCLUSIONS

The growth of thyroid nodules is a local process, not associated with growth of the surrounding non-nodular tissue. Therefore, a normal-sized thyroid containing nodules should be referred to as a "uni- or multinodular thyroid gland" and considered a distinct entity from "uni- or multinodular goiter."

Papillary Thyroid Carcinoma: A Malignant Tumor with Increased Antioxidant Defense Capacity

Papillary thyroid carcinoma (PTC) is the commonest thyroid malignancy worldwide for which the radiation exposure is the most influential risk factor. The levels of oxidative stress in PTC are not well characterized on the tissue level. The objective of this study was to evaluate total oxidant status (TOS) and total antioxidant status (TAS) in PTC and benign goiter (BG) tissues and to examine their association with clinicopathological characteristics. Tumor and normal thyroid tissue samples were collected from 59 PTC patients, and goiter tissues were collected from 50 BG patients. TOS and TAS were quantified in the tissue homogenates by spectrophotometric assays. TOS values in tumor tissues did not differ significantly from normal and goiter tissues; however, PTC tissues have significantly higher TAS values than normal and goiter tissues. TOS values correlated with retrosternal growth in BG patients. The significant correlations were found between TOS and TAS values and thyroid function parameters. In 17 PTC patients with multiple tumor foci (multicentric phenotype), TAS values were significantly lower, compared to 42 patients with unicentric PTC. TAS and TOS are the most useful predictors of thyroid capsular invasion by PTC. The age, sex, body mass index, smoking, familial history of thyroid disease and nodule size did not influence TOS and TAS in PTC or BG patients. In conclusion, we show the profiles of TOS and TAS in PTC and BG tissues. Importantly, PTC tissues possess increased antioxidant capacity. The redox status influences the parameters of the thyroid function and tumor's biological behavior.

Increased Chromosomal and Oxidative DNA Damage in Patients with Multinodular Goiter and Their Association with Cancer

Thyroid nodules are a common clinical problem worldwide. Although thyroid cancer accounts for a small percentage of thyroid nodules, the majority are benign. 8-Hydroxy-2'-deoxyguanosine (8-OHdG) levels are a marker of oxidative stress and play a key role in the initiation and development of a range of diseases and cancer types. This study evaluates cytokinesis-block micronucleus cytome (CBMN-cyt) assay parameters and plasma 8-OHdG levels and their association with thyroid nodule size and thyroid hormones in patients with multinodular goiter. The study included 32 patients with multinodular goiter and 18 age- and sex-matched healthy controls. CBMN-cyt assay parameters in peripheral blood lymphocytes of patients with multinodular goiter and controls were evaluated, and plasma 8-OHdG levels were measured. The micronucleus (MN) frequency (chromosomal DNA damage), apoptotic and necrotic cells (cytotoxicity), and plasma 8-OHdG levels (oxidative DNA damage) were significantly higher among patients with multinodular goiter. Our study is the first report of increased chromosomal and oxidative DNA damage in patients with multinodular goiter, which may predict an increased risk of thyroid cancer in these patients. MN frequency and plasma 8-OHdG levels may be markers of the carcinogenic potential of multinodular goiters and could be used for early detection of different cancer types, including thyroid cancer.

Pathogenesis of Hyperthyroidism

Hyperthyroidism is a form of thyrotoxicosis in which there is excess thyroid hormone synthesis and secretion. Multiple etiologies can lead to a common clinical state of "thyrotoxicosis," which is a consequence of the high thyroid hormone levels and their action on different tissues of the body. The most common cause of thyrotoxicosis is Graves' disease, an autoimmune disorder in which stimulating thyrotropin receptor antibodies bind to thyroid stimulating hormone (TSH) receptors on thyroid cells and cause overproduction of thyroid hormones. Other etiologies include: forms of thyroiditis in which inflammation causes release of preformed hormone, following thyroid gland insult that is autoimmune, infectious, mechanical or medication induced; secretion of human chorionic gonadotropin in the setting of transient gestational thyrotoxicosis and trophoblastic tumors; pituitary thyrotropin release, and exposure to extra-thyroidal sources of thyroid hormone that may be endogenous or exogenous. © 2017 American Physiological Society. Compr Physiol 7:67-79, 2017.

Identifying reference chemicals for thyroid bioactivity screening

Reference chemicals were selected based on thyroid bioactivity in 'Tier 1' screening assays used by the U.S. EPA's Endocrine Disruptor Screening Program. Active reference chemicals had significant effects on thyroid-responsive endpoints in the amphibian metamorphosis assay, and the male and female pubertal rat assays. In the absence of thyroid weight or histopathological effects, additional published studies providing mechanistic data on thyroid activity were required for active chemicals. Inactive reference chemicals had no significant effects on thyroid-responsive endpoints in Tier 1 assays, or in amphibian or rodent studies from several online databases. The 34 reference chemicals (29 active and five inactive) will be useful for performance-based validation of alternative, high throughput screening assays for thyroid bioactivity.

Vitamin D status in Egyptian euthyroid multinodular non-toxic goiter patients and its correlation with TSH levels

BACKGROUND AND AIM

Although the prevalence of MNG is widespread throughout the world, its pathogenesis is poorly understood, and the complex interactions of both genetic predisposition and the individuals' environment are likely. However, to the best of our knowledge, it remains unknown whether there is a relationship between vitamin D status and prevalence or pathogenesis of euthyroid MNG. Therefore, the goal of the present study was determination of vitamin D status in euthyroid MNG as well as exploration of the correlation between vitamin D status & TSH levels.

METHODS

A total of 77 patients diagnosed with euthyroid MNG and 50 subjects without goiter were matched according to age, weight and BMI as control group in this case control study.

RESULTS

We found that patients with euthyroid MNG had statistically significant lower mean of [25(OH)D] (24.21±8.68ng/mL) in comparison with its mean in control subjects (28.37±10.91ng/mL, P value=0.019). The 28 sufficient vitamin D MNG patients had statistically significant lower level of TSH than 49 insufficient vitamin D MNG patients. Vitamin D and TSH levels correlate with vitamin D levels in MNG patients in Pearson correlation. Also 25 OH vitamin D was a significant independent predictor for TSH levels among euthyroid MNG patients in regression analysis.

CONCLUSIONS

Patients with euthyroid MNG have lower levels of vitamin D and TSH levels correlate with vitamin D levels in euthyroid MNG patients. In addition, 25 OH vitamin D was a significant independent predictor for TSH levels among euthyroid MNG patients. We recommend hypovitaminosis D evaluation and correction in patients with MNG.

Association of thyroid diseases with primary extra-thyroidal malignancies in women: results of a cross-sectional study of 6,386 patients

We here analyzed the prevalence of extra-thyroidal malignancies (EM) in 6,386 female patients affected by different thyroid disease (TD). At first, an age-matched analysis of EM in all patients was performed. We then evaluated EM prevalence in four TD diagnostic categories: non-nodular TD (n = 2,159); solitary nodule (n = 905); multinodular TD (n = 2,871); differentiated thyroid cancers (n = 451). Finally, patients were grouped based on the absence (n = 3,820) or presence of anti-thyroglobulin (TgAb) and/or anti-thyroperoxidase (TPOAb) (n = 2,369), or anti-Thyroid Stmulating Hormone (TSH) receptor autoantibodies (n = 197). A total of 673 EM were recorded. EM prevalence in TD patients was higher compared to the general population (Odds Ratio, OR 3.21) and the most frequent EM was breast cancer (OR 3.94), followed by colorectal (OR 2.18), melanoma (OR 6.71), hematological (OR 8.57), uterus (OR 2.52), kidney (OR 3.40) and ovary (OR 2.62) neoplasms. Age-matched analysis demonstrated that the risk of EM was maximal at age 0-44 yr (OR 11.28), remaining lower, but significantly higher that in the general population, in the 45-59 and 60-74 year age range. Breast and hematological malignancies showed an increased OR in all TD, while other cancers associated with specific TD. An increased OR for melanoma, breast and hematological malignancies was observed in both TPOAb and/or TgAb autoantibody negative and positive patients, while colorectal, uterus, kidney and ovary cancers showed an increased OR only in thyroid autoantibody negative patients. In conclusions, women affected by both benign and malignant TD, especially at a younger age and in absence of thyroid autoimmunity, have an increased risk of developing primary EM, thus requiring a careful follow-up and surveillance.

The Impact of the D727E Polymorphism has no Significant Role in Multi Nodular Goiter

Interactions between individual genetic and environmental factors determine the onset of the multi nodular goiter (MNG). The thyroid-stimulating hormone receptor (TSHR) gene is a convincing candidate gene in the pathogenesis of certain thyroid diseases including MNG. We investigated the codon 727 polymorphism (p.Asp727Glu, p.D727E) of the human TSHR gene using the polymerase chain reaction-restriction fragment length polymorphim (PCR-RFLP) methods in 31 Turkish patients with MNG and in 30 control subjects, aiming to evaluate the relationship between this polymorphism and MNG. After genomic DNA isolation, PCR amplification was performed using a pair of primers in exon 10 of the TSHR gene that contains the p.D727E polymorphism and digested by theNlaIII (Hin1II) restriction enzyme. We found the CC and CG genotype incidence for the patient group to be 0.71 and 0.29, respectively, and for the control group to be 0.8 and 0.2, respectively. No statistically significant difference was found between the genotype and allele distribution of both groups (p = 0.417 and p = 0.449, respectively). However, the polymorphism is significantly correlated with the low serum level of the TSH (p = 0.047). These results suggest that the p.D727E polymorphism of the TSHR gene may not contribute to the pathogenesis of nontoxic MNG diseases.

Oxidative stress and the ageing endocrine system

Ageing is a process characterized by a progressive decline in cellular function, organismal fitness and increased risk of age-related diseases and death. Several hundred theories have attempted to explain this phenomenon. One of the most popular is the 'oxidative stress theory', originally termed the 'free radical theory'. The endocrine system seems to have a role in the modulation of oxidative stress; however, much less is known about the role that oxidative stress might have in the ageing of the endocrine system and the induction of age-related endocrine diseases. This Review outlines the interactions between hormones and oxidative metabolism and the potential effects of oxidative stress on ageing of endocrine organs. Many different mechanisms that link oxidative stress and ageing are discussed, all of which converge on the induction or regulation of inflammation. All these mechanisms, including cell senescence, mitochondrial dysfunction and microRNA dysregulation, as well as inflammation itself, could be targets of future studies aimed at clarifying the effects of oxidative stress on ageing of endocrine glands.

Recent insights into the cell biology of thyroid angiofollicular units

In thyrocytes, cell polarity is of crucial importance for proper thyroid function. Many intrinsic mechanisms of self-regulation control how the key players involved in thyroid hormone (TH) biosynthesis interact in apical microvilli, so that hazardous biochemical processes may occur without detriment to the cell. In some pathological conditions, this enzymatic complex is disrupted, with some components abnormally activated into the cytoplasm, which can lead to further morphological and functional breakdown. When iodine intake is altered, autoregulatory mechanisms outside the thyrocytes are activated. They involve adjacent capillaries that, together with thyrocytes, form the angiofollicular units (AFUs) that can be considered as the functional and morphological units of the thyroid. In response to iodine shortage, a rapid expansion of the microvasculature occurs, which, in addition to nutrients and oxygen, optimizes iodide supply. These changes are triggered by angiogenic signals released from thyrocytes via a reactive oxygen species/hypoxia-inducible factor/vascular endothelial growth factor pathway. When intra- and extrathyrocyte autoregulation fails, other forms of adaptation arise, such as euthyroid goiters. From onset, goiters are morphologically and functionally heterogeneous due to the polyclonal nature of the cells, with nodules distributed around areas of quiescent AFUs containing globules of compact thyroglobulin (Tg) and surrounded by a hypotrophic microvasculature. Upon TSH stimulation, quiescent AFUs are activated with Tg globules undergoing fragmentation into soluble Tg, proteins involved in TH biosynthesis being expressed and the local microvascular network extending. Over time and depending on physiological needs, AFUs may undergo repetitive phases of high, moderate, or low cell and tissue activity, which may ultimately culminate in multinodular goiters.

Mechanism-based testing strategy using in vitro approaches for identification of thyroid hormone disrupting chemicals

The thyroid hormone (TH) system is involved in several important physiological processes, including regulation of energy metabolism, growth and differentiation, development and maintenance of brain function, thermo-regulation, osmo-regulation, and axis of regulation of other endocrine systems, sexual behaviour and fertility and cardiovascular function. Therefore, concern about TH disruption (THD) has resulted in strategies being developed to identify THD chemicals (THDCs). Information on potential of chemicals causing THD is typically derived from animal studies. For the majority of chemicals, however, this information is either limited or unavailable. It is also unlikely that animal experiments will be performed for all THD relevant chemicals in the near future for ethical, financial and practical reasons. In addition, typical animal experiments often do not provide information on the mechanism of action of THDC, making it harder to extrapolate results across species. Relevant effects may not be identified in animal studies when the effects are delayed, life stage specific, not assessed by the experimental paradigm (e.g., behaviour) or only occur when an organism has to adapt to environmental factors by modulating TH levels. Therefore, in vitro and in silico alternatives to identify THDC and quantify their potency are needed. THDC have many potential mechanisms of action, including altered hormone production, transport, metabolism, receptor activation and disruption of several feed-back mechanisms. In vitro assays are available for many of these endpoints, and the application of modern '-omics' technologies, applicable for in vivo studies can help to reveal relevant and possibly new endpoints for inclusion in a targeted THDC in vitro test battery. Within the framework of the ASAT initiative (Assuring Safety without Animal Testing), an international group consisting of experts in the areas of thyroid endocrinology, toxicology of endocrine disruption, neurotoxicology, high-throughput screening, computational biology, and regulatory affairs has reviewed the state of science for (1) known mechanisms for THD plus examples of THDC; (2) in vitro THD tests currently available or under development related to these mechanisms; and (3) in silico methods for estimating the blood levels of THDC. Based on this scientific review, the panel has recommended a battery of test methods to be able to classify chemicals as of less or high concern for further hazard and risk assessment for THD. In addition, research gaps and needs are identified to be able to optimize and validate the targeted THD in vitro test battery for a mechanism-based strategy for a decision to opt out or to proceed with further testing for THD.

Impact of surgical technique on operative morbidity and its socioeconomic benefit in thyroid surgery

PURPOSE

The aim of this retrospective cohort study was to evaluate the rate of complications in relation to the extent of surgery and some of its consequences.

METHODS

Between 1972 and 2010, a total of 5,277 consecutive thyroid gland surgeries with 7,383 nerves at risk were performed at our teaching institution. Data of all patients undergoing thyroidectomy were collected prospectively. A total of 2,867 subtotal resections (first study period from 1972 to 1990) were compared with 2,410 extended thyroid resections involving at least a hemithyroidectomy (second period from 1991 to 2010).

RESULTS

The incidence of permanent recurrent laryngeal nerve palsy in primary operations was significantly higher in the first period compared to the second period (3.6 vs. 0.9 %; p < 0.001). Permanent hypoparathyroidism decreased from 3.2 % in the first period to 0.8 % in the second period (p < 0.001). The incidence of recurrent goiter surgery decreased from 11.1 % in the first period to 8.1 % in the second period (p < 0.001). No significant difference was found in permanent recurrent laryngeal nerve palsy in recurrent disease between the two periods. The socioeconomic benefits of an extended thyroid resection in our patient population are 360 preventable operations, 90 preventable permanent recurrent laryngeal nerve palsies, and 58 preventable cancers. Furthermore, 37 preventable radioiodine ablations and 15 preventable deaths were associated with more radical thyroid resection.

CONCLUSION

Improvements in surgical technique and change in surgical strategy significantly decreased the prevalence of recurrent laryngeal nerve palsy, hypoparathyroidism, and recurrent disease as well as reduced public health costs associated with recurrent goiter.