|Year : 2014 | Volume
| Issue : 3 | Page : 137-150
Histological study of the effect of potassium dichromate on the thyroid follicular cells of adult male albino rat and the possible protective role of ascorbic acid (vitamin C)
Reda H ElBakry, Sadika M Tawfik
Histology Department, Faculty of Medicine, Tanta University, Egypt
|Date of Web Publication||6-Feb-2018|
Sadika M Tawfik
Histology Department, Faculty of Medicine, Tanta University
Source of Support: None, Conflict of Interest: None
Occupational exposure to toxic heavy metals renders the industrial workers with various health problems. Many heavy metals act as endocrine disruptors. Chromium salts are commonly used in industries as asbestos brake lining, cement dust and food additives. Thyroid is a metabolically active important endocrine gland. Little is known about the toxic effects of chromium on thyroid. So, the aim of this study was evaluation of the histological changes induced by chromium on thyrocytes and the possible protective role of vitamin C. Forty adult male albino rats were divided into four equal groups: control group, vitamin C treated group, potassium dichromate treated group and the fourth group co treated with potassium dichromate and vitamin C. Potassium dichromate was given intraperitonially for 2 weeks at a dose 2mg/kg daily. Vitamin C was given at a dose 120mg/kg orally daily for the same period. Specimens were processed for light and electron microscopy. Apoptosis was evaluated immunohistochemically. Specimens of potassium dichromate group showed disturbance of the normal architecture of the gland with coalescence and degeneration of thyroid follicles and desquamated cells in its lumen. Disruption of the apical and basal membranes of some thyrocytes, flattened hyperchromatic nuclei, dilated RER and swollen degenerated mitochondria were also noted. Immunohistochemically, there were changes in the immune expression of Bcl2 in the cytoplasm of thyrocytes. Vitamin C supplemented group showed partial improvement of the previous changes. So, potassium dichromate induced structural changes in the thyroid follicular cells that were partially improved by vitamin C supplementation.
Keywords: Histological changes, Potassium dichromate, Thyroid gland, Rat, Ascorbic acid
|How to cite this article:|
ElBakry RH, Tawfik SM. Histological study of the effect of potassium dichromate on the thyroid follicular cells of adult male albino rat and the possible protective role of ascorbic acid (vitamin C). J Microsc Ultrastruct 2014;2:137-50
|How to cite this URL:|
ElBakry RH, Tawfik SM. Histological study of the effect of potassium dichromate on the thyroid follicular cells of adult male albino rat and the possible protective role of ascorbic acid (vitamin C). J Microsc Ultrastruct [serial online] 2014 [cited 2020 Apr 5];2:137-50. Available from: http://www.jmau.org/text.asp?2014/2/3/137/224878
| 1. Introduction|| |
Chromium (Cr) is a naturally occurring heavy metal found in rocks, volcanic dust and gases, soils as well as plants and animals. Chromium compounds are used in paints, metal finishes, and stainless steel. Increased usage of hexavalent chromium (CrVI) and its improper disposal lead to various health hazards ,. However, chromium in a small amount is considered an important nutrient responsible for carbohydrate metabolism .
Chromium is present in two forms: trivalent Cr(III) which is poorly transported across membranes and hexavalent Cr(VI) can readily cross cellular membranes. Inside the cell, the hexavalent form is reduced to the trivalent form. This biotransformation process reduces the toxicity because the trivalent form does not cross cellular membrane rapidly. The trivalent form complexes with intracellular macromolecules, these toxic compounds are responsible for many toxic and mutagenic effects of chromium, not biodegradable and accumulate in the environment ,.
Hexavalent chromium usually linked with oxygen forming strong oxidizing agent that is widely known to cause allergic dermatitis as well as toxic and carcinogenic effects in humans and animals . The fate of chromium in the environment is dependent on its oxidation state. Hexavalent chromium primarily enters the cells and undergoes metabolic reduction to trivalent chromium, resulting in the formation of reactive oxygen species together with oxidative tissue damage and a cascade of cellular events .
Occupational exposure to Cr is found among approximately half a million industrial workers worldwide. Also, water contaminated with hexavalent chromium is a worldwide problem, as it is the major route of chromium exposure for the general population ,. Potassium dichromate (K2Cr2O7) is a soluble hexavalent chromium compound that is widely used in several industries .
Ascorbic acid (vitamin C) is as an essential micronutrient that performs important metabolic function in human . It also acts as a biological antioxidant by donating an electron to free radical species, such as tocopherol radical, thereby interrupting the radical chain reaction in biological membranes .
Vitamin C has been reported to function as a major reductant of Cr(VI) in animals and cell culture systems . From these points it was important to evaluate the effect of potassium dichromate on the thyroid gland of rats and the possible protective effect of vitamin C.
| 2. Materials and methods|| |
The present work was carried out on 40 adult male albino rats that were divided into four groups each, 10 rats. Group one acts as a control group that was subdivided into two subgroups: A positive control which received intra peritoneal injection of 1 ml distilled water, the solvent of the material used in this work. The other subgroup B which was the negative subgroup that did not receive any treatment through the experiment.
The second group received vitamin C in dose of 120mg/kg  orally for 2 weeks. The third group was the treated group received potassium dichromate in a dose of 2mg/kg  intra peritoneal per day for 2 weeks. The fourth group (the protective group) received the same dose of potassium dichromate concomitant with vitamin C in the same dose like the second one. Potassium dichromate (K2Cr2O7) was supplied by El-Nasr pharmaceutical chemicals company ADWIC, Egypt.
At the end of the experiment the rats were anaesthetized (better with carbon dioxide). Mid line incision was done with careful dissection of the neck to identify sternohyoid and sternomastoid muscle. The muscles were then separated to expose the trachea. Trace the trachea upward gently until the thyroid glands were visible. It appeared as two small reddish oval masses on each side of the trachea. Dissect the glands gently to avoid its injury . The thyroid glands were collected and divided into two parts. One part was processed for light microscope study using PAS stain and some sections used for immunohistochemical methods for detection of apoptosis using BCL2 immune expression. The second part was processed for electron microscope study. The blood was drawn directly from the left ventricle through cardiac puncture. It was used for estimation of serum T3, T4 and TSH according to the instructions of their referred methods using Milliplex. Map Rat Thyroid Hormone TSH panel-2 plex (EMD Millipore, Billerica, MA, USA). The biochemical data were expressed as the mean ± standard error using ANOVA test (f test) and unpaired Student’s test (Scheffe test).
2.1. Immunohistochemical staining for detection of Bcl2 protein (antiapoptotic marker) 
Immunohistochemical reaction was performed using avidin biotin peroxidase technique. The primary antibody was a rabbit monoclonal antibody) Sigma Laboratories). The universal kit was avidin biotin peroxidase produced by Nova Castra Laboratories Ltd, UK.
Tissue sections were deparaffinized and rehydrated. Slides were incubated in hydrogen peroxide (10%) for 10-15 min to inhibit the activity of endogenous peroxidase to reduce nonspecific background staining. Antigen retrieval was done by immersing the sections in a preheated citrate buffer solution (pH 6) and maintaining heat in a microwave at 2 W for 10-20 min. Sections were left to cool for 20 min at room temperature. Slides were washed for 2 times in buffer (0.05% sodium azide). Monoclonal antibody Bcl2a Ab-1 (Ms-123-R7) was applied. Slides were washed for 4 times in buffer (0.05% sodium azide). Biotinylated goat anti-polyvalent was applied. Slides were incubated for 10 min at room temperature. Slides were washed for 4 times in buffer (0.05% sodium azide). Chro- mogenic substrate was applied (diaminobenzidine) DAB and incubated until desired reaction was achieved. Mayer’s haematoxylin was used as a counter stain ,.
The Bcl2 cytoplasmic site of reaction was stained brown and nuclei stained blue. The same method was applied to prepare negative control sections but the primary antibody was not added. Tonsil was used as positive control tissue .
| 3. Results|| |
3.1. Biochemical results
Potassium dichromate treated rats showed a significant decrease in the serum T3 and T4 and a significant increase in the TSH levels when compared with control group and vitamin C treated group. In the protective group, there was a significant increase in the level of the T3 and T4 and a significant decrease in the serum TSH compared with potassium dichromate treated group [Table 1], [Table 2], [Table 3].
|Table 1: The mean level of serum tri-iodothyronine (T3) in different studied groups.|
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|Table 2: The mean level of serum thyroxine (T4) in different studied groups.|
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|Table 3: The mean level of serum thyroid stimulating hormone (TSH) in different studied groups.|
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3.2. Light microscopic results
3.2.1. Control and vitamin C treated groups
Examination of the semi-thin sections obtained from the thyroid glands of the control group and vitamin C treated showed the normal histological structure. The thyroid gland was formed of follicles of various sizes, each follicle was lined with a single layer of cuboidal epithelial cells and filled with homogenous colloid and separated by capillary beds [Figure 1].
|Figure 1: Photomicrographs of a semi-thin section of the thyroid gland of the control group showing thyroid follicles lined with cuboidal epithelium and filled with homogeneous colloid (F) and separated by capillary beds (C) (Toluidine blue, 1000×).|
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Basal lamina of follicular cells showed moderate PAS reaction while colloid showed marked reaction with peripheral vacuolization [Figure 2].
|Figure 2: Photomicrographs of the thyroid gland of the control group showing strong PAS reaction in the colloid with peripheral vacuolation and moderate reaction in the basal lamina. Notice, in (A) there are follicles with no peripheral vacuolation (PAS, 400×).|
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Immunohistochemically, there was strong cytoplasmic BCL2 expression in follicular cells [Figure 3].
|Figure 3: Photomicrographs of the thyroid gland of the control group showing strong BCL2 immunoexpression in the cytoplasm of the majority of follicular cells (BCL2 immunoexpression, 400×, 1000×).|
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3.2.2. Potassium dichromate treated group
Semi-thin sections of the thyroid gland of the potassium dichromate treated rats showed complete loss of the normal architecture of the thyroid gland. Disruption of the basal laminae of some follicles with their coalescence was detected [Figure 4]. Some follicles appeared distended with colloid lined with squamous epithelium, others were completely collapsed. Some follicles were degenerated and filled with exfoliated cells [Figure 5]. Disruption of the apical membranes of some thyrocytes with desquamated cytoplasm and nuclei inside the follicles was observed. Some thyrocytes appeared tall columnar with apical pseudo- podia [Figure 6]. Vacuolization of the cytoplasm of some thyrocytes, variable densities of colloid staining and widening of the interfollicular space appeared in some sections [Figure 7].
|Figure 4: A photomicrograph of a semi-thin section of the thyroid gland of potassium dichromate treated group showing loss of the normal architecture of the thyroid gland (F), the basal lamina of the follicles are disrupted (arrows) with adherence of the follicles (Toluidine blue, 400×).|
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|Figure 5: Photomicrographs of a semi-thin section of the thyroid gland of potassium dichromate treated group showing: (A) some follicles are distended with colloid (F), others appear collapsed (C). (B) Higher magnification of A, showing some of thyroid follicles appeared collapsed (C), while the others are degenerated (D) with desquamated cells in the lumen (arrows) (Toluidine blue, 400×, 1000×).|
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|Figure 6: Photomicrographs of a semi-thin section of the thyroid gland of the same group showing (A) disruption of the apical membranes of some thyrocytes with the presence of the cytoplasmic content in the lumen (S). Notice vacuolation of the cytoplasm of the other thyrocytes in the same follicle (arrows). (B) Apical pseudopodia (thick arrows) of some thyrocytes while the others have vacuolated cytoplasm (thin arrows) (Toluidine blue, 1000×).|
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|Figure 7: Photomicrographs of a semi-thin section of the thyroid gland of the same group showing (A) widening of the interfollicular space (stars) and variable densities of the colloid staining (v). (B) Mast cells in the interfollicular space (arrows) (Toluidine blue, 1000×).|
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Basal lamina of follicular cells showed a weak PAS reaction while colloid showed a moderate reaction with abnormal pattern of vacuolization and colloid retraction in some follicles [Figure 8].
|Figure 8: Photomicrographs of the thyroid gland of potassium dichromate treated group showing moderate PAS reaction in the colloid and weak reaction in the basal lamina with (A) absence of peripheral vacuolation and (B) abnormal pattern of vacuolization and colloid retraction (PAS, 400×).|
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Immunohistochemically, there was negative cytoplas- mic BCL2 immunoexpression in the majority of follicular cells [Figure 9].
|Figure 9: A photomicrograph of the thyroid gland of potassium dichromate treated group showing negative immune expression of BCL2 in the cytoplasm of the majority of follicular cells (BCL2 immunoexpression, 1000×).|
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3.2.3. Protective group (potassium dichromate + vitamin C)
Examination of semi-thin sections obtained from the thyroid glands of rats of the protective group revealed improvement in the histological changes detected in the previous group. The thyroid gland started to regain its normal architecture. The densities of colloid staining were also variable. However, some follicles still disrupted with desquamated cells in the lumens. The thyrocytes appeared less vacuolated. The interfollicular spaces appeared narrower than the treated group [Figure 10] and [Figure 11].
|Figure 10: Photomicrographs of a semi-thin section of the thyroid gland of the protective group showing: (A) restoration of the normal architecture of the thyroid gland (F). (B) Disruption of the basal lamina of the thyroid follicles (arrows) (Toluidine blue, 400×).|
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|Figure 11: Photographs of a semi-thin section of the thyroid gland of the same group showing (A) the thyroid follicles appear more or less as the control (F) (Toluidine blue, 400×). (B) Higher magnification of A showing vacuolization (arrows) of the cytoplasm of some thyrocytes (Toluidine blue, 1000×).|
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The basal lamina of the thyroid follicles showed apparent increase in the PAS reaction but less than the control group. The colloid showed variable degrees of PAS reaction and still vacuolated [Figure 12].
|Figure 12: Photomicrographs of the thyroid gland of the protective group showing strong PAS reaction in the colloid and moderate reaction in the basal lamina, some follicles showing peripheral vacuolization, while others appear with central vacuolization, the rest appear inactive (PAS, 400×).|
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Immunohistochemically, there was apparent increase in the BCL2 expression in the cytoplasm of the thyroid fol- licular cells but less than the control group [Figure 13].
|Figure 13: A photomicrograph of the thyroid gland of the protective group showing positive cytoplasmic reaction for BCL2 (BCL2 immunoexpression, 1000×).|
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3.3. Electron microscopic study
3.3.1. Control and vitamin C treated groups
EM examination of ultra-thin sections of the thyroid glands of rats of the control and vitamin C treated groups showing the same ultrastructure picture of normal thyroid follicular cells. The thyrocytes appeared with rounded euchromatic nuclei and numerous short apical microvilli. Their cytoplasm contained RER, abundant mitochondria, prominent Golgi apparatuses, SER, lysosomes, abundant apical vesicles containing colloid and electron dense granules [Figure 14].
|Figure 14: (A) Ultrathin section of the thyroid gland of the control group showing follicular cells with apical microvilli containing euchromatic nuclei (N), RER (r), scattered electron dense vesicles (arrows). (B) Higher magnification of (A) showing parts of two follicular cells, containing RER (r), electron dense vesicles (arrows).|
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3.3.2. Potassium dichromate treated group
EM examination of ultra-thin sections of the thyroid glands of this group confirmed the light microscopic examination. Some of the thyrocytes were squamous with flat hyperchromatic nuclei, others were pyramidal or prism like. Stratification of the lining epithelium of some follicles and desquamated cells appeared in the follicular lumens [Figure 15]. The cytoplasm showed variable sized vacuoles with dilated RER with disruption of the apical membrane of some thyrocytes and exfoliated cells were present inside the lumens [Figure 16]. In some sections there is rarefaction of the cytoplasm with loss of the cytoplasmic organelles swollen degenerated mitochondria, fragmented RER and the presence of large sized vacuole [Figure 17].
|Figure 15: (A) Ultrathin section of the thyroid gland of the potassium dichromate treated group showing two thyrocytes one of them is squamous with flat hyperchromatic nucleus (N1) and the other is prism like with irregular hyperchromatic nucleus (N2). (B) Stratification of the lining epithelium (S), vacuolation of the cytoplasm (V) and exfoliated cells in the lumen (curved arrows).|
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|Figure 16: Ultrathin section of the thyroid gland of the potassium dichromate treated group showing (A) dilated RER (R) and exfoliated cells in the lumen (curved arrow). (B) Higher magnification of (A) showing dilated RER (R) with the presence of various sized electron dense bodies (arrows). Notice the complete loss of the microvilli on the apical membrane of the follicular cells (arrow head).|
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|Figure 17: Ultrathin section of the thyroid gland of the potassium dichromate treated group showing (A) a thyrocyte with large sized vacuole (V), rarified cytoplasm (star), swollen degenerated mitochondria (curved arrows), fragmented RER (r) and flat hyperchromatic nucleus (N). (B) Thyrocytes with irregular shaped nucleus (N) rarified cytoplasm (star), fragmented RER (r) as well as partial loss of the apical microvilli (arrows).|
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3.3.3. Protective group (potassium dichromate + vitamin C)
The follicular cells of this group appeared more or less as the control group. However, some thyrocytes still have vac- uolated cytoplasm, dilated RER and hyperchromatic nuclei [Figure 18] and [Figure 19].
|Figure 18: (A) Ultrathin section of the thyroid gland of the protective group showing (A) thyrocytes appear more or less as the control except for disruption of the apical membrane (curved arrows) and small cytoplasmic vacuoles (V). (B) A thyrocyte with intact mitochondria (M), RER (R) appear as the control.|
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|Figure 19: (A) Ultrathin section of the thyroid gland of the protective group showing part of thyroid follicle in which the thyrocytes appear with variable shaped nuclei (N), rarified cytoplasm (white stars). (B) A thyrocyte with dilated RER (R) and irregular hyperchromatic nuclei (N) and electron dense bodies (arrows) with loss of the apical microvilli (curved arrow).|
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| 4. Discussion|| |
Hexavalent chromium (CrVI) has been widely used in industries throughout the world. Increased its usage and atmospheric emission of CrVI from catalytic converters of automobiles, and its improper disposal cause various health hazards .
Today, it is known that there is a close relationship between workers health and the amounts of industrial pollution provoked by industries manufacturing chromium containing materials. So, numerous and different in vitro and/or in vivo studies on chromium have been undertaken either in animals or in human .
The present work studied the effect of potassium dichromate on the thyroid gland structure and the possible protective role of vitamin C. The study revealed the effects of chromium compound on the thyroid gland which appeared in the form of irregularity in size and shape of the follicles. Some of them were lined with squamous epithelium, others lined with cubical and the third group of follicles were lined with tall columnar cells with apical pseudopodia. Interfollicular spaces were widened either as a result of collapse of some follicles or due to necrosis of the others leaving empty spaces. The cytoplasm of some follic- ular cells appeared vacuolated and even desquamation of some cells into the lumens were seen in the majority of sections.
Other work reported that, administration of sodium dichromate in the drinking water to rats and mice resulted in focal ulceration, hyperplasia, and metaplasia in the glandular stomach and hyperplasia of the duodenum . Also, histological analysis of the effect of chromium on male reproductive system revealed pronounced morphological alterations with enlarged intracellular spaces and tissue loosening .
The present work revealed increase in the interfollic- ular spaces and disruption of the basal lamina of follicles and these findings were coincided with other studies . The latter reported decrease in the size of follicles and widening of the interfollicular spaces and attributed this widening to disruption of the connective tissue. At the end they concluded that Cr(VI) is potentially toxic to the thyroid gland. Also, another studies found the same results with irregularity and shrunken of some follicular cells increase in the number of disorganized and collapsed follicles. Hyperplasia of follicular cells and nuclei appeared oval, rounded, irregular and even shrunken. They added that disruption of the apical and basal laminae were seen .
Disorganization of the thyroid follicles and cytoar- chitecture indicate high level of toxicity caused by the chromium. TSH is responsible for the morphological appearance of thyroid follicles and the synthesis and secretion of thyroid hormones leading to hypertrophy and hyperplasia of the follicular cell. One of the early responses of TSH-stimulated thyroid follicular cells is engulfment of colloid material from the follicular lumen into the apical cytoplasm of thyrocytes, in the form of membrane-bound colloid droplets. Administration of TSH to rats pretreated with thyroxin resulted in the formation of numerous pseu- dopods on the apical surface of thyrocytes, followed by the appearance of colloid droplets, at first in the apical and later on in the deeper parts of the cytoplasm. It was also stated that the percentage of follicular cells containing colloid droplets and the number of droplets in cells gradually increased with the increase of TSH dose ,.
However, irregularity in the size of follicles in some animals may be normal, as the size distribution pattern of thyroid follicles is different between the peripheral and central gland regions. In rats, the larger thyroid gland follicles are mostly located at the periphery of the thyroid lobes stated that the large follicles at periphery mainly serve as a pool of old hormone, whereas the smaller, centrally distributed ones are responsible for thyroid hormone secretion ,.
Variation in the nuclear shape and size was characteristic finding in this work and explained by some authors that increased nuclear area is often observed in compounds that block cell cycle and induce DNA damage .
Bcl-2 is an apoptosis-related molecule that was shown to be down-regulated during the early events leading to programmed cell death and its protein might be as an inhibiting molecule and play an important role in the balance between apoptosis promotion and inhibition ,.
The detection of apoptosis in the follicular cells in this study which was explained in many other studies ,. They stated that CrVI induced DNA fragmentation, increased apoptosis, increased cytochrome c release from the mitochondria to cytosol, down regulated anti-apoptotic Bcl-2 and other mediators; upregulated pro-apoptotic . Also it was documented that potassium dichromate- induced apoptosis and oxidative stress in the hepatocytes of Wistar rats.
Some authors explained in details the mechanism by which the Cr(VI) lead to apoptosis. They hypotheses that soluble Cr(VI) is metabolized within cells by reductive agents including ascorbic acid, glutathione and cysteine and a diverse range of genetic lesions are generated. Some forms of Cr damage present physical barriers to DNA replication/transcription and promote a terminal cell fate such as apoptosis or terminal growth arrest. Other DNA lesions are potentially pre-mutagenic and lead to DNA damage and cell cycle arrest ,,.
The electron microscopic results confirmed the results obtained by the light microscope. Some follicles were lined with low prismatic, cuboidal or flattened epithelium with apparent decrease in epithelial height. That was attributed to hypoactivity of the thyroid gland. This was confirmed by biochemical changes in this work in the form of decrease in T3 and T4 level and increase in the TSH level . Others showed stratification of their lining epithelium. The nuclei of thyrocytes appeared shrunked hyperchromatic nuclei, fragmented and dilated rER, swollen mitochondria with degenerated cristae, accumulation of colloid vesicles inside the thyrocytes, even complete loss of all the cytoplasmic organelles. Similar results observed previously in the form of disrupted basal laminae of the follicles, regressed nuclei and disrupted cell organelles . Also, follicular hyperplasia may be connected with a cascade of cellular events involving oxidative stress, genomic DNA damage, and modulation of apop- totic regulatory gene (P53) after exposure to chromium 
The mechanism of chromium toxicity was reported to be associated with mitochondrial and lysosomal injury by biologically Cr(VI) reactive intermediates and reactive oxygen species . The results demonstrated that potassium dichromate was highly cytotoxic to cells, and its cytotox- icity seems to be mediated by oxidative stress and DNA damage . The results indicated that administration of Cr(VI) had caused a significant increase of reactive oxygen species (ROS) level generated during reduction of Cr(VI) ,.
Previous studies both in vitro and in vivo have demonstrated that chromium(VI) induces an oxidative stress through enhanced production of reactive oxygen species (ROS) leading to genomic DNA damage and oxidative deterioration of lipids and proteins. A cascade of cellular events occur following chromium (VI)-induced oxidative stress including enhanced production of superoxide anion and hydroxyl radicals, increased lipid peroxidation and genomic DNA fragmentation, modulation of intracellular oxidized states, activation of protein kinase C, apoptotic cell death and altered gene expression ,,.
In a recent study demonstrated that catalase is a classical oxidative biomarker and is the most abundant in peroxisomes, where oxidative stress most frequently occurs ,. The increase in these enzyme activities suggests a response toward increased ROS generation ,. Previously, it was reported that Cr(VI) induced thyroid toxicity through increasing cellular oxidative stress and decreasing the activity of antioxidants .
Some authors explained that Cr(VI) accumulates in the pituitary and hypothalamus resulting in apopto- sis evidenced by nuclear fragmentation and caspase 3 activation. Their results indicate that the anterior pituitary gland can be a target of Cr(VI) toxicity in vivo and in vitro, thus producing a negative impact on the hypothalamic-pituitary-axis and affecting the normal endocrine function ,.
Some researches observed hypertrophic follicular cells contain dilated r-ER and colloid droplets. Follicles were lined by tall columnar cells and vacuolated mitochondria with disrupted cristae. They explained their results due to Goitrogenic effects of a soybean diet which result in increased thyroid stimulating hormone leading to hyper- plasia in thyroid gland .
As regard to the thyroid hormone level there was decrease in the level of free T3 and T4. The protective group revealed more or less normal value near to that of the control group. The same results were documented in other works which showed significantly increased TSH and decreased FT3 and FT4 concentrations in protective group serum TSH, FT3 and FT4 concentrations neared control . It was reported that Cr toxicity led quite possibly to a state of hypothyroidism as indicated by a significant increase in the serum TSH and a decrease in the serum FT3 and FT4 concentrations .
Vitamin C administration in this work showed some improvement in the thyroid gland function and structure. As, the level of the thyroid hormones became near to the control one. Also, the thyroid gland regained its normal cellular architecture and appeared more or less near to the control.
Previous studies detected that early and repeated high intravenous doses of vitamin C was the therapy of choice for Cr(VI) poisoning . Also the results of  showed that vitamin C had antimutagenic effect against chromium compound.
Also it was found that administration of exogenous ascorbic acid has been used in the treatment of systemic chromium poisoning and chromium dermatitis as it enhances the extracellular reduction of chromium(VI) . Ascorbic acid influenced Cr(VI) toxicity either by acting as a reducing agent, decreasing Cr(V) persistence or by acting as an antioxidant, decreasing intracellular superoxide anion and hydrogen peroxide formation and also it acts by reducing free radicals formed during reduction of Cr(VI) to Cr(III) .
Many works concluded that co-administration of vit C and E may, significantly diminish the toxic effects of hexavalent chromium on lung . Simultaneous administration of vitamin C significantly prevented the increase in lipid peroxidation and enhanced the antioxidant status. These results proved the protective effect of vitamin C against the Cr(VI) exposure-induced toxicity and test the significance of antioxidants in diet . The functional changes cannot be completely replenished by the ascorbic acid supplementation in response to chromium exposure . However, other works proved that the ascorbic acid may have the potential to protect thyroid gland from chromium toxicity .
| 5. Conclusion|| |
It could be concluded that potassium dichromate had toxic effects on the thyroid follicular cells, which partially improved with vitamin C co-treatment. So, it is recommended to give vitamin C as a protective agent against chromium toxicity in people who are susceptible for continuous exposure.
Conflict of interest
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7], [Figure 8], [Figure 9], [Figure 10], [Figure 11], [Figure 12], [Figure 13], [Figure 14], [Figure 15], [Figure 16], [Figure 17], [Figure 18], [Figure 19]
[Table 1], [Table 2], [Table 3]