Contents lists available at ScienceDirect Tissue and Cell journal homepage: www.elsevier.com/locate/tice Histopathological and biochemical alterations of the parotid gland induced by experimental hypothyroidism in adult male rats and the possible therapeutic effect of Nigella sativa oil Wael Amin Nasr El-Din a,b, *, Islam Omar Abdel Fattah b a Department of Anatomy, College of Medicine and Medical Sciences, Arabian Gulf University, Manama, Bahrain b Department of Human Anatomy and Embryology, Faculty of Medicine, Suez Canal University, Ismailia, Egypt ARTICLE INFO Keywords: Hypothyroidism parotid Bax Bcl-2 Nigella sativa oil ABSTRACT Thyroid hormones are essential for metabolic rate regulation and play a role on the integrity of the salivary glands. Nigella sativa is a widely used plant in medicine. This study aimed to evaluate the effect of Nigella sativa oil (NSO) on the hypothyroidism-induced parotid gland pathological alterations. Rats were divided into four groups: control group, hypothyroid group: received daily oral carbimazole for 3 weeks, hypothyroid-NSO group: NSO was orally given for 4 weeks after hypothyroidism induction and NSO group: administrated NSO only for 4 weeks. After 7 weeks, all rats were sacrificed, serum thyroid hormones were estimated, and parotid glands were assessed by histopathological, immunohistochemical, ultrastructural and morphometric analyses. Hypothyroid group showed a significant decrease in thyroid hormones with increase in thyroid-stimulating hormone (TSH) levels and decrease in body and parotid weights compared to the control rats that were improved with NSO treatment. Sections of the hypothyroid group showed fibrosis, acinar cytoplasmic vacuolations, vascular con- gestion, ductal dilatation, wide intercellular canaliculi, nuclear pyknosis and decreased number of secretory granules. Also, there were decreased B-cell lymphoma 2 (Bcl-2) and increased p53, Bcl-2 Associated X (Bax) and alpha-smooth muscle actin (α-SMA) immune-expressions; with decreased Bax/ Bcl-2 ratio that all were atte- nuated by NSO. NSO ameliorates hypothyroidism-induced parotid changes by altering p53, Bax and Bcl-2 pathway. 1. Introduction Thyroid hormones; thyroxine (T4) and triiodothyronine (T3) are hormones that are produced, stored and released by the thyroid gland (Ali Rajab et al., 2017). They are essential for normal cell differentia- tion, fetal growth, bone formation, and development of the nervous and genital systems (Ross et al., 2017). Consequently, any minor impair- ment in the balance of these hormones can be harmful for human health (Zhang et al., 2018). Moreover, thyroid dysfunction can result in pa- thophysiological changes in the salivary glands, so patients suffering from hyposalivation should be assessed for thyroid functions (Hayat et al., 2016a). Actually, most attention had been paid towards the physiological and biochemical effects of thyroid hormones on salivary glands, however, on the other side, the histological effect of hypothyroidism on the salivary glands had not been extensively studied (Hayat et al., 2016a). Apoptosis is a precise programmed process including cell death in response to various stimuli. Mitochondria-dependent apoptotic pathway is a substantial pathway that involved in apoptosis based on p53, Bcl-2 Associated X (Bax) and B-cell lymphoma 2 (Bcl-2) protein balance (Li et al., 2011). Activation of p53 in cell lines can activate various cellular processes, including cellular senescence, cell cycle ar- rest, metabolic adaptation, harmony of various DNA damage/repair pathways and apoptotic cell death (Aubrey et al., 2018). At the same time, an excess of Bax also can result in cell apoptosis, nevertheless excess Bcl-2 is protective against cell apoptosis. Thus, Bax/Bcl-2 ratio inside the cell is an important determinant factor for cell survival and an increased ratio enhances cell apoptosis (Karagül et al., 2018). https://doi.org/10.1016/j.tice.2020.101366 Received 24 January 2020; Received in revised form 21 March 2020; Accepted 5 April 2020 Abbreviations: ANOVA, analysis of variance; Bax, Bcl-2 Associated X; Bcl-2, B-cell lymphoma 2; DAB, 3,3'-Diaminobenzidine tetrahydrochloride; HRP, horseradish peroxidase; Hx&E, hematoxylin and eosin; LM, light microscope; MECs, myoepithelial cells; NSO, Nigella sativa oil; OD, optical density; PBS, phosphate buffered saline; SD, standard deviation; SPSS, Statistical Package for Social Sciences; T3, triiodothyronine; T4, thyroxine; TEM, transmission electron microscope; TQ, thy- moquinone; TSH, thyroid-stimulating hormone; α-SMA, alpha-smooth muscle actin ⁎ Corresponding author. E-mail address: waelamin2010@yahoo.com (W.A. Nasr El-Din). Tissue and Cell 65 (2020) 101366 Available online 11 April 2020 0040-8166/ © 2020 Elsevier Ltd. All rights reserved. T