COMPARISON OF LEVELS OF TWENTY CHEMICAL ELEMENTS IN NORMAL THYROID TISSUE AND HYPERTROPHIC THYROID TISSUE
Vladimir Zaichick
Radionuclide Diagnostics Department, Medical Radiological Research Centre, Obninsk, 249036, Russia.
Background: Goiter can appear as a palpable or visible enlargement of the thyroid gland at the base of the neck. If the goiter is accompanied by hypothyroidism or hyperthyroidism, it may be accompanied by symptoms of the underlying disorder, and nodular goiter (NG) is a health problem of international importance. The aim of this exploratory study was to assess whether there were significant changes in thyroid tissue levels of twenty chemical elements (ChE) Al, B, Ba, Br, Ca, Cl, Cu, Fe, I, K, Li, Mg, Mn , Na, P, S, Si, Sr, V, and Zn are present in the goitrous transformed thyroid.
Methods: Thyroid tissue level of twenty ChE was prospectively evaluated in 46 patients with NG and 105 healthy populations. The measurements were performed using a combination of non-destructive and destructive methods: instrumental neutron activation analysis and inductively coupled plasma atomic emission spectrometry, respectively. Tissue samples were divided into two parts. One was used for morphological study while the other was for ChE analysis.
Results: It was found that contents of Al, B, Br, Cl, Cu, Fe, Li, Mg, Mn, Na, P, S, Si, V, and Zn are significantly higher while the I levels are lower in NG than in normal tissues.
Conclusion: There are considerable changes in ChE contents in goitrous tissue of thyroid. Thus, it is reasonable to assume that the levels of these ChE in thyroid tissue can be used as NG markers. However, this topic needs additional studies.
Keywords: Biomarkers for goiter diagnosis, chemical elements, inductively coupled plasma atomic emission spectrometry, instrumental neutron activation analysis, intact thyroid thyroid nodular goiter.
INTRODUCTION
At least 10% of the world's population is affected by goiter detected during examination and palpation and most thyroid lesions are nodular goiter (NG)1. However, the use of NG ultrasound can be detected in approximately 70% of the general population2. NG is also known as endemic nodular goitre, simple goitre, nodular hyperplasia, nontoxic uninodular goitre or multinodular goiter3. NG are benign lesions; however, during clinical examination, they can mimic malignancies. NG can be hyper functioning, hypofunctioning, and functioning normality. Euthyroid NG is defined as localized enlargement of the thyroid gland without concomitant disruption of thyroid function3.
For more than twenty centuries, there has been a prevailing view that NG is a minor consequence of iodine (I) deficiency. However, NG has been found to be a frequent disease even in those countries and regions where the population is never exposed to I deficiency4. Moreover, it was shown that I excess has severe consequences on human health and associated with the presence of thyroidal dysfunctions and autoimmunity, NG and diffuse goiter, benign and malignant tumors of gland5-8. It was also demonstrated that besides the iodine deficiency and excess many other dietary, environmental, and occupational factors are associated with the NG incidence9-11. Among them a disturbance of evolutionary stable input of many chemical elements (ChE) in human body after industrial revolution plays a significant role in etiology of thyroidal disorders12. Besides iodine involved in thyroid function, ChE has basic physiological functions such as maintaining and regulating cell function, regulating genes, activating or inhibiting enzymatic reactions, and regulating membrane function13. The essential or toxic (goitogenic, mutagenic, and carcinogenic) properties of ChE depend on the tissue-specific need or tolerance, respectively13. Excessive accumulation or an imbalance of the ChE may disturb the cell functions and may result in cellular degeneration, death, benign or malignant transfor-mation13-15. In our previous studies the complex of in vivo and in vitro nuclear analytical and related methods was developed and used for the investigation of I and other ChE contents in the normal and pathological thyroid16-22. Level of I in the normal thyroid was investigated in relation to age, gender and some non-thyroidal diseases23-24. After that, variations of ChE content with age in the thyroid of males and females were studied and age- and gender-dependence of some ChE was observed25-41. Furthermore, a significant difference between some ChE contents in normal and cancerous thyroid was demonstrated42-47.
So far, the pathogenesis of NG has to be considered as multifactorial. The present study was performed to clarify the role of twenty ChE in maintaining thyroid growth and goitrogenesis. With this in mind, our aim was to assess the aluminum (Al), boron (B), barium (Ba), bromine (Br), calcium (Ca), chlorine (Cl), coper (Cu), iron (Fe), I, potassium (K), lithium (Li), magnesium (Mg), manganese (Mn), sodium (Na), phosphorus (P), sulfur (S), silicon (Si), strontium (Sr), vanadium (V), and zinc (Zn) mass fraction contents in NG tissue using a combination of non-destructive and destructive methods: instrumental neutron activation analysis with high resolution spectrometry of short-lived radionuclides (INAA-SLR) and inductively coupled plasma atomic emission spectrometry (ICPAES), respectively. A further aim was to compare the levels of these twenty ChE in the goitrous thyroid with those in normal gland of apparently healthy persons.
SUBJECTS AND METHODS
Samples
All patients suffered from NG (n=46, mean age M±SD was 48±12 years, range 30-64) were hospitalized in the Head and Neck Department of the Medical Radiological Research Centre and informed consent was taken from the subjects. Thick-needle puncture biopsy of suspicious nodules of the thyroid was performed for every patient, to permit morphological study of thyroid tissue at these sites and to estimate their ChE contents. For all patients the diagnosis has been confirmed by clinical and morphological results obtained during studies of biopsy and resected materials. Histological conclusion for all thyroidal lesions was the colloid NG. Normal thyroids for the control group samples were removed at necropsy from 105 deceased (mean age 44±21 years, range 2-87), who had died suddenly. Samples were obtained within 48 hours after a sudden death. The majority of deaths were due to trauma. Histological examination was used in the control group to match the age criteria, as well as to confirm the absence of micro-nodules and underlying cancer.
Sample preparation, instrumentation and analytical methods
All tissue samples were divided into two portions using a titanium scalpel48. One was used for morphological study while the other was intended for ChE analysis. After the samples intended for ChE analysis were weighed, they were freeze-dried and homogenized49. The pounded samples weighing about 5-10 mg (for biopsy) and 100 mg (for resected materials) were used for ChE measurement by INAA-SLR. The samples for INAA-SLR were sealed separately in thin polyethylene films washed beforehand with acetone and rectified alcohol. The sealed samples were placed in labeled polyethylene ampoules. The content of Br, Ca, Cl, I, K, Mg, Mn, and Na were determined by INAA-SLR using a horizontal channel equipped with the pneumatic rabbit system of the WWR-c research nuclear reactor (Branch of Karpov Institute, Obninsk).
After INAA-SLR investigation the thyroid samples were taken out from the polyethylene ampoules and used for ICP-AES. The samples were decomposed in autoclaves. Sample aliquots were used to determine the Al, B, Ba, Ca, Cu, Fe, K, Li, Mg, Mn, Na, P, S, Si, Sr, V, and Zn mass fractions by ICP-AES using the Spectrometer ICAP-61 (Thermo Jarrell Ash, USA). The determination of the ChE content in aqueous solutions was made by the quantitative method using calibration solutions (High Purity Standards, USA) of 0.5 and 10 mg/L of each element. The calculations of the ChE content in the probe were carried out using software of a spectrometer (ThermoSPEC, version 4.1).
Information detailing with the NAA-SLR and ICP-AES methods used and other details of the analysis were presented in our earlier publications concerning ChE contents in human thyroid, scalp hair, and prostate33,34,50-55.
Standards and certified reference material
To determine contents of the ChE by comparison with a known standard, biological synthetic standards (BSS) prepared from phenol-formaldehyde resins were used56. In addition to BSS, aliquots of commercial, chemically pure compounds were also used as standards. Ten sub-samples of certified reference material (CRM) IAEA H-4 (animal muscle) and five sub-samples of CRM of the Institute of Nuclear Chemistry and Technology (INCT, Warszawa, Poland) INCT-SBF-4 Soya Bean Flour, INCT-TL-1 Tea Leaves, and INCT-MPH-2Mixed Polish Herbs were treated and analyzed in the same conditions that thyroid samples to estimate the precision and accuracy of results. More details about the quality controls of ChE contents in human thyroid were presented in our earlier publications33,34.
Table 1: Some statistical parameters of Al, B, Ba, Br, Ca, Cl, Cu, Fe, I, K, Li, Mg, Mn, Na, P, S, Si, Sr, V, and Zn mass fraction (mg/kg, dry mass basis) in normal and goitrous thyroid.
Computer programs and statistic
A dedicated computer program for INAA mode optimization was used56. All thyroid samples were prepared in duplicate, and mean values of ChE contents were used. Mean values of ChE contents were used in final calculation for the Br, Fe, Rb, and Zn mass fractions measured by two methods. Using Microsoft Office Excel, a summary of the statistics, including, arithmetic mean, standard deviation, standard error of mean, minimum and maximum values, median, percentiles with 0.025 and 0.975 levels was calculated for ChE contents. The difference in the results between two groups (normal and NG) was evaluated by the parametric Student’s t-test and non-parametric Wilcoxon-Mann-Whitney U-test. All studies were approved by the Ethical Committees of the Medical Radiological Research Centre (MRRC), Obninsk (Reference number 115050610007, year2017). All the procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and/or National research committee and with the 1964 Helsinki declaration and its later amendments, or with comparable ethical standards.
Table 2: Median, minimum and maximum value of means Al, B, Ba, Br, Ca, Cl, Cu, Fe, I, K, Li, Mg, Mn, Na,
P, S, Si, Sr, V, and Zn contents in the normal and goitrous thyroid according to data from the literature in
comparison with our results (mg/kg, dry mass basis).
RESULTS
Table 1 presents certain statistical parameters (arithmetic mean, standard deviation, standard error of mean, minimal and maximal values, median, percentiles with 0.025 and 0.975 levels) of the Al, B, Ba, Br, Ca, Cl, Cu, Fe, I, K, Li, Mg, Mn, Na, P, S, Si, Sr, V, and Zn mass fraction in normal and goitrous thyroid. The comparison of our results with published data for Al, B, Ba, Br, Ca, Cl, Cu, Fe, I, K, Li, Mg, Mn, Na, P, S, Si, Sr, V, and Zn mass fraction in normal and goitrous thyroid58-91 is shown in Table 2. The ratios of means and the difference between mean values of Al, B, Ba, Br, Ca, Cl, Cu, Fe, I, K, Li, Mg, Mn, Na, P, S, Si, Sr, V, and Zn mass fractions in normal and goitrous thyroid are presented in Table 3.
DISCUSSION
Precision and accuracy of results
As was shown before33,34, good agreement of our results for the Al, B, Ba, Br, Ca, Cl, Cu, Fe, I, K, Mg, Mn, Na, P, S, Sr, V, and Zn mass fractions with the certified values of CRM IAEA H-4, INCT-SBF-4, INCT-TL-1, and INCT-MPH-2 as well as the similarity of the means of the Ca, K, Mg, Mn, and Na mass fractions in the normal human thyroid determined by both INAA-SLR and ICP-AES methods demonstrates acceptable precision and accuracy of the results obtained in the study and presented in Tables 1, Table 2 and Table 3. The mean values and all selected statistical parameters were calculated for twenty ChE (Al, B, Ba, Br, Ca, Cl, Cu, Fe, I, K, Li, Mg, Mn, Na, P, S, Si, Sr, V, and Zn) mass fractions (Table 1). The mass fraction of Al, B, Ba, Br, Ca, Cl, Cu, Fe, I, K, Li, Mg, Mn, Na, P, S, Si, Sr, V, and Zn were measured in all, or a major portion of normal and goitrous tissue samples.
Comparison with published data
The means obtained for Al, B, Ba, Br, Ca, Cl, Cu, Fe, I, K, Mg, Mn, Na, P, S, Si, Sr, V, and Zn mass fraction, as shown in Table 2, agree well with the medians of mean values reported by other researches for the human thyroid, including samples received from persons who died from different non-thyroid diseases. The mean obtained for Li is two orders of magnitude lower than the median of previously reported data. Moreover, it is outside the range of previously reported means. A number of values for ChE mass fractions were not expressed on a dry mass basis by the authors of the cited references. Hence we calculated these values using published data for water 75%92 and ash 4.16% on dry mass basis93 contents in thyroid of adults.
In goitrous tissues our results for Al, Br, Ca, Cu, Fe, I, Mn, Si, and Zn contents were within the range of published means, while means for K and Sr were some higher median of previously reported means and also higher the upper level of the range of these means (Table 2). Only one published article on Ba79, Na59, P88, S88, Si88, and V79 contents in the goitrous tissue samples was found in the literature. The mean obtained in the present study for S content in the goitrous tissue agreed well with early published data, while means for Ba and P were some lower and the mean for Na was some higher. The obtained mean for V content in the goitrous tissue was more than one order of magnitude lower than the only reported result. No published data referring B, Cl, and Li contents of goitrous thyroid tissue were found.
Table 3:Differences between mean values (M±SEM) of Al, B, Ba, Br, Ca, Cl, Cu, Fe, I, K, Li, Mg, Mn, Na, P, S, Si, Sr, V, and Zn mass fraction (mg/kg, dry mass basis) in normal and goitrous thyroid.
The range of means of Al, B, Ba, Br, Ca, Cl, Cu, Fe, I, K, Li, Mg, Mn, Na, P, S, Si, Sr, V, and Zn level reported in the literature for normal and for goitrous thyroid varies widely (Table 2). This can be explained by a dependence of ChE on many factors, including the region of the thyroid, from which the sample was taken, age, gender, ethnicity, gland mass, and the NG stage. Not all these factors were strictly controlled in cited studies. Another and, in our opinion, the main reason for the inter-observer discrepancy can be attributed to the accuracy of the analytical techniques, sample preparation methods, and the inability to take standardized samples from affected tissues. It was insufficient quality control of results in these studies. In many reported papers tissue samples were ashed or dried at high temperature for many hours. In other cases, thyroid samples were treated with solvents (distilled water, ethanol, formalin etc). There is evidence that by use of these sample preparation methods some quantities of certain ChE are lost as a result of this treatment That concern not only such volatile halogen as Br, but also other ChE investigated in the study94-96.
Effect of goitrous transformation on ChE contents
From Table 3, it is observed that in goitrous tissue the mass fraction of Al, B, Br, Cl, and Cu are approximately 2.6, 3.6, 2.4, 2.7, and 2.1 times, respectively, higher and also mass fractions of Fe, Li, Mg, Mn, Na, P, S, Si, V, and Zn are almost in 51%,, 35%, 20%, 38%, 70%, 21%, 33%, 60%, 49%, and 27% respectively, higher than in normal tissues of the thyroid. In contrast, the mass fraction of I is 29% significantly lower. Thus, if we accept the ChE contents in thyroid glands in the control group as a norm, we have to conclude that with a goitrous transformation the levels of Al, B, Br, Cl, Cu, Fe, Li, Mg, Mn, Na, P, S, Si, V, and Zn in thyroid tissue significantly increased, whereas the level of I some decreased.
Role of ChE in goitrous transformation of the thyroid
Characteristically, elevated or reduced levels of ChE observed in goitrous tissues are discussed in terms of their potential role in the initiation and promotion of thyroid goiter. In other words, using the low or high levels of the ChE in goitrous tissues researchers try to determine the goitrogenic role of the deficiency or excess of each ChE in investigated organ. In our opinion, abnormal levels of many ChE in NG could be and cause, and also effect of goitrous transformation. From the results of such kind studies, it is not always possible to decide whether the measured decrease or increase in ChE level in pathologically altered tissue is the reason for alterations or vice versa.
Aluminum
The trace element Al is not described as essential, because there is no biochemical function directly associated with it. At this point in our knowledge, there is no doubt that Al overload negatively affects human health, including thyroid function97.
Boron
Trace element B is known to influence the activity of many enzymes98. Numerous studies have demonstrated beneficial effects of B on human health, including anti-inflammatory stimulus-reduces levels of inflammatory biomarkers, such as high-sensitivity C-reactive protein (hs-CRP) and tumor necrosis factor α (TNF-α); as well as raises levels of antioxidant enzymes, such as superoxide dismutase (SOD), catalase, and glutathione peroxidase98. Why B content in goitrous thyroid is higher than normal level and how an excess of B acts on thyroid are still to be cleared.
Bromine
This is one of the most abundant and ubiquitous of the recognized trace elements in the biosphere. The inorganic bromide is the ionic form of Br that exerts therapeutic as well as toxic effects. An enhanced intake of bromide could interfere with the metabolism of I at the whole-body level. In the thyroid gland the biological behavior of bromide is more similar to the biological behavior of iodide99. In our previous studies, we found a significant age-related increase of Br content in human thyroid27,28,0-33. Therefore, a goitrogenic and, probably, carcinogenic effect of excessive Br levels in the thyroid of old females was assumed. On the one hand, elevated levels of Br in NG tissues, observed in the present study, supports this conclusion. But, on the other hand, bromide compounds, especially potassium bromide (KBr), sodium bromide (NaBr), and ammonium bromide (NH4Br), are frequently used as sedatives in Russia101. It may be the reason for elevated levels of Br in specimens of patients with NG.
Chlorine
Cl is a ubiquitous, extracellular electrolyte essential to more than one metabolic pathway. Cl exists in the ionic form (chloride) in the human body. In the body, it is mostly present as sodium chloride. Therefore, as usual, there is a correlation between Na and Cl contents in tissues and fluids of human body. It is well known that Cl mass fractions in samples depend mainly on the extracellular water volume, including the blood volumes, in tissues102. NG tissues are predominantly highly vascularized lesions103. Thus, it is possible to speculate that thyroid goiters are characterized by an increase of the mean value of the Cl mass fraction because the level of goiter vascularization is higher than that in normal thyroid tissue.
Coper
Cu is a ubiquitous element in the human body which plays many roles at different levels. Various Cu-enzymes (such as amine oxidase, ceruloplasmin, cytochrome-c oxidase, dopamine-monooxygenase, extracellular superoxide dismutase, lysyl oxidase, peptidyl glycine amidating monoxygenase, Cu/Zn superoxide dismutase, and tyrosinase) mediate the effects of Cu deficiency or excess. Cu excess can have severe negative impacts. Cu generates oxygen radicals and many investigators have hypothesized that excess copper might cause cellular injury via an oxidative pathway, giving rise to enhanced lipid peroxidation, thiol oxidation, and, ultimately, DNA damage104. Thus, Cu accumulation in thyroid parenchyma with age may be involved in oxidative stress, dwindling gland function, and increasing risk of goiter/cancer25,26,31,34. The significantly elevated level of Cu in goitrous thyroid, observed in the present study, supports this speculation. However, an overall comprehension of Cu homeostasis and physiology, which is not yet acquired, is mandatory to establish Cu exact role in the thyroid goiter etiology and metabolism.
Iron
It is well known that Fe as a trace element is involved in many very important functions and biochemical reactions of human body. Fe metabolism is therefore very carefully regulated at both a systemic and cellular level104. Under the impact of age and multiple environmental factors the Fe metabolism may become dysregulated with attendant accumulation of this metal excess in tissues and organs, including thyroid25,26,29-34. Most experimental and epidemiological data support the hypothesis that Fe overload is a risk factor for benign and malignant tumors106. This goitrogenic and oncogenic effect could be explained by an overproduction of ROS and free radicals107.
Iodine
Compared to other soft tissues, the human thyroid gland has higher levels of I, because this element plays an important role in its normal functions, through the production of thyroid hormones (thyroxin and triiodothyronine) which are essential for cellular oxidation, growth, reproduction, and the activity of the central and autonomic nervous system. Goitrous transformation is accompanied by a partial loss of tissue-specific functional features, which leads to a significant reduction in I content associated with functional characteristics of the human thyroid tissue.
Lithium
The results of lifelong Li-poor nutrition of animals show that Li is essential to the fauna, and thus, to humans as well108. Li-poor nutrition has a negative influence on some enzyme activity, mainly the enzymes of the citrate cycle, glycolysis, and of nitrogen metabolism108. On the other hand, Li is widely used in medicine as a mood-stabilizing drug. Because of the active transport of Na+/I- ions, Li is accumulated in the thyroid gland at a concentration 3-4 times higher than that in the plasma. It can inhibit the formation of colloid in thyrocytes, change the structure of thyroglobulin, weaken the iodination of tyrosines, and disrupt their coupling109. In addition, it reduces the clearance of free thyroxine in the serum, thereby indirectly reducing the activity of 5-deiodinase type 1 and 2 and reducing the deiodination of these hormones in the liver108. All these actions may cause the development of goiter.
Magnesium
Mg is abundant in the human body. This element is essential for the functions of more than 300 enzymes (e.g. alkaline phosphatases, ATP-ases, phosphokinases, the oxidative phosphorylation pathway). It plays a crucial role in many cell functions such as energy metabolism, protein and DNA syntheses, and cytoskeleton activation. Moreover, Mg is involved in the thyroid function and plays a central role in determining the clinical picture associated with thyroid disease110. The higher Mg levels in NG than do normal tissues, possibly is a result of the high Mg requirement of growing cells.
Manganese
Trace element Mn is a cofactor for numerous enzymes, playing many functional roles in living organisms. The Mn containing enzyme, manganese superoxide dismutase (Mn-SOD), is the principal antioxidant enzyme which neutralizes the toxic effects of reactive oxygen species. It has been speculated that Mn interferes with thyroid hormone binding, transport, and activity at the tissue level111. However, an overall comprehension of Mn homeostasis and physiology, which is not yet acquired, is mandatory to establish Mn exact role in the thyroid goiter etiology and metabolism.
Sodium
Knowledge concerning ion regulation in many normal and abnormal cell processes has had a rapid development. It was found, among other regulations, that sodium-calcium exchange is associated with the cytoskeleton and the cell membrane. A hypothesis was eventually established that a wide variety of pathological phenomena ranging from acute cell death to chronic processes, such as neoplasia, all have a common series of cellular reactions112. Furthermore, iodide (I−), an essential constituent of the thyroid hormones, is actively transported into the thyroid via the Na+/I− symporter (NIS), a key plasma membrane glycoprotein113. In addition, Na is mainly an extracellular electrolyte and its elevated level in NG might link with a higher goiter vascularization in comparison with the normal thyroid (see Chlorine).
Phosphorus
P is necessary for several, various biological roles in the signal transduction of cells and energy exchange of human body. About 80–90% of P is founded in teeth and bones in the form of hydroxyapatite. Thyroid hormones play an important role in homeostasis of Ca and P levels by their direct action on bone turnover and, as a consequence, Ca and P metabolism is frequently disturbed in thyroid dysfunction with a significant increase in the P serum levels114. The elevated level of P in serum results the higher content of this element in NG tissue, because the goiter vascularization is higher in comparison with the normal thyroid. Besides, the elevated level of thyroid phospholipids in NG is common115.
Sulfur
Proteins contain between 3 and 6% of sulfur amino acids. Sulfur amino acids contribute substantially to the maintenance and integrity of the cellular systems by influencing the cellular redox state and the capacity to detoxify toxic compounds, free radicals and reactive oxygen species (ROS)115. ROS are generated during normal cellular activity and may exist in excess in some pathophysiological conditions, such as inflammation. Therefore exploring fundamental aspects of sulfur metabolism such as the antioxidant effects of sulfur-containing amino acids116 may help elucidate the mechanism by which the S content increases in NG. Thus, it might be assumed that the elevated S level in goitrous thyroid reflects an increase in concentration of ROS in goiter tissue.
Silicon
Si as a trace element is essential to some specific biological functions in humans118. For example, Si is necessary for the association between cells and one or more macromolecules such as osteonectin, which affects cartilage composition and ultimately cartilage calcification119. However, an association between the disorders of thyroid function and the Si excess in the diets was found120. An increase in the thyrotropin (TSH) level in rats was observed after Si-treatment, without statistically significant differences in thyroid hormones concentrations between the test and control groups of animals121.
Vanadium
V complexes are cofactors for several enzymes that maintaining hemostasis in health and pathology. For example, V compounds normalized blood pressure, ischemia and the metabolism of the thyroid122. However, all V compounds have been considered toxic and a goitrogenic and carcinogenic role of V on the thyroid was proposed123. V compounds promote the induction and perpetuation of an inflammatory reaction in the thyroid123. Thus, the elevated V level in thyroid may be a cause of the gland dysfunctions, NG and cancer.
Zinc
Zn is active in more than 300 proteins and over 100 DNA-binding proteins, including the tumor suppressor protein p53, a Zn-binding transcription factor acting as a key regulator of cell growth and survival upon various forms of cellular stress. p53 is mutated in half of human tumors and its activity is tightly regulated by metals and redox mechanisms. On the other hand, excessive intracellular Zn concentrations may be harmful to normal metabolism of cells124. By now much data has been obtained related both to the direct and indirect action of intracellular Zn on the DNA polymeric organization, replication and lesions, and to its vital role for cell division125,126. Other actions of Zn have been also described. They include its action as a potent anti-apoptotic agent127-131. All these facts allowed us to speculate that age-related overload Zn content in female thyroid, as was found in our previous study25,29,31,33, is probably one of the factors in etiology of thyroid goiter and malignant tumors. Therefore, the elevated Zn level in NG in comparison with normal level, detected in this study, supports our hypothesis.
Our findings show that mass fraction of Al, B, Br, Cl, Cu, Fe, I, Li, Mg, Mn, Na, P, S, Si, V, and Zn are significantly different in NG as compared to normal thyroid tissues (Tables 6). Thus, it is plausible to assume that levels of these ChE in thyroid tissue can be used as NG markers. However, this subjects needs in additional studies.
Limitations
This study has several limitations. Firstly, analytical techniques employed in this study measure only twenty ChE (Al, B, Ba, Br, Ca, Cl, Cu, Fe, I, K, Li, Mg, Mn, Na, P, S, Si, Sr, V, and Zn) mass fractions. Future studies should be directed toward using other analytical methods which will extend the list of ChE investigated in normal and goitrous thyroid. Secondly, the sample size of NG group was relatively small. It was not allow us to carry out the investigations of ChE contents in NG group using differentials like gender, histological types of goiter, stage of disease, and dietary habits of healthy persons and patients with NG. Lastly, generalization of our results may be limited to Russian population. Despite these limitations, this study provides evidence on goiter-specific tissue Al, B, Br, Cl, Cu, Fe, I, Li, Mg, Mn, Na, P, S, Si, V, and Zn level alteration and shows the necessity to continue ChE research of goitrous thyroid.
CONCLUSION
In this work, ChE measurements in tissue samples from normal and NG colloid thyroid were performed using two useful analytical methods: non-destructive neutron activation analysis with high-resolution short-lived radionuclide spectrometry and inductively coupled plasma atomic emission spectrometry. The combination of these methods has been shown to be a suitable analytical tool for the determination of twenty ChEs (Al, B, Ba, Br, Ca, Cl, Cu, Fe, I, K, Li, Mg, Mn, Na, P, S, Si, Sr, and V and Zn) in tissue samples from healthy and affected human thyroid, including needle biopsy samples. It was observed that the content of goitrous tissues of Al, B, Br, Cl, Cu, Fe, Li, Mg, Mn, Na, P, S, Si, V and Zn increased significantly while the level of I decreased in comparison with normal thyroid tissues. In our opinion, the presented study data strongly suggest that ChE plays an important role in thyroid health and the etiology of colloidal NG. It was assumed that the differences in ChE levels in affected thyroid tissue could be used as colloidal NG markers.
CONFLICT OF INTEREST
No conflict of interest associated with this work.
REFERENCES