Abstract
Aging causes morphological and functional changes in the thyroid gland. Free radicals play a key role in the pathology of normal aging. Vimentin and cytokeratin are cytoskeletal intermediate filaments that are often used as indirect indices of tissue injury. The aim of the study was to clarify the age-related alterations in the structure and function of the thyroid gland. The relationship between oxidative/antioxidative stress markers and cytoskeletal intermediate filaments (vimentin and cytokeratin) and oxidative/antioxidative stress markers as well as vascular endothelial growth factor (VEGF) during aging were elucidated. Finally, the role of Nigella sativa (NS) oil in ameliorating age-related alterations of the structure and function of the thyroid gland was studied. Thirty Sprague-Dawley albino rats were divided into five groups: young adult control, young adult NS-treated, late adult control, late adult NS-treated, and senile. The age of young adult, late adult, and senile rats was nearly 7, 18 and 22 months, respectively. NS oil was added to food pellets and was administered at a daily dose of 0.1 g/kg body weight for one month. The thyroid gland was dissected and fixed immediately in 10% formalin saline. The assessment of thyroid structure was based on hematoxylin and eosin, and Masson's trichrome stainings, and histomorphometric analysis of the deparaffinized sections. Localization and distribution of vimentin and cytokeratin filaments was assessed by immunohistochemistry. Measurements of VEGF gene expression by qPCR and oxidative/antioxidative markers (malondialdehyde and glutathione content, superoxide dismutase activity) in thyroid gland homogenates were performed. Serum concentration of thyroid hormones (T3, T4) and TSH were assessed by radioimmunoassay. Follicles in the late adult control group were dilated and disrupted. Follicular cells showed cytoplasmic vacuolation. Follicles in the thyroids of senile rats were of irregular shape, often with cellular exfoliations. Many follicles were dilated and lined with flattened cells. A notable amelioration of these morphological alterations was observed in late adult NS-treated rats. Decrease in serum T3 and T4 levels and increase in TSH levels were observed in the late adult control and senile groups. A clear shift of the oxidative/antioxidative markers (MDA/ /GSH, SOD) was observed in the late adult control and senile groups in favor of oxidants. Administration of NS to late adult rats resulted in normalization of these parameters. Increased area of collagen fibers, immunoreactivity of vimentin and cytokeratin filaments and VEGF gene expression were observed in the thyroids of late adult and senile rat groups as compared to young animals. The mean number of follicular cells decreased in the late adult control and senile groups. Administration of NS to the late adult rats returned these parameters to the level of the young adult rats. Aging-related alterations in both structure and function of the rat thyroid gland that are associated with increased indices of oxidative stress might be abrogated by administration of antioxidative agents present in Nigella sativa oil.
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