Research Article: Postnatal changes in the development of rat submandibular glands in offspring of diabetic mothers: Biochemical, histological and ultrastructural study

Date Published: October 10, 2018

Publisher: Public Library of Science

Author(s): Abir El Sadik, Enas Mohamed, Ahmed El Zainy, John A. Chiorini.

http://doi.org/10.1371/journal.pone.0205372

Abstract

Development and maturation of submandibular salivary glands are influenced by intrauterine diabetic environment. Several studies investigated the effects of diabetes on the salivary glands. However, the effects of maternal diabetes on the submandibular glands of the offspring was not properly examined. Therefore, the present study was designed to describe the changes in the development of the submandibular glands of the offspring of diabetic mothers. The submandibular glands of the offspring of Streptozotocin (STZ)-induced diabetic female rats were examined at two and four weeks after birth. Detection of mRNA demonstrated that maternal diabetes affects the level of different indicators. The reduction of expression of epidermal growth factor (EGF); a protein mitogen, cytokeratin 5 (CK5); an epithelial cell progenitor, CK7 and aquaporin 5 (AQP5); differentiation markers and B cell lymphoma 2 (Bcl2); an antiapoptotic marker were found. Increase in Bcl2-associated X protein (Bax); an apoptotic marker was detected. These changes indicate their effects on saliva secretion, glands tumorigenesis, growth of normal oral flora and oral microbes, with decreased protein synthesis and production of xerostomia and dental caries. Loss of normal glandular architecture, significant increase in fibrosis, by the detection of collagen fibers, and stagnation of secretory granules were found with atrophic changes in the acinar cells. Marked defect of polysaccharides in the acinar cells, denoting functional changes, was manifested by significant reduction of the intensity of periodic acid-Schiff (PAS) reaction. The positive immunoreactivity of caspase-3, denoting cellular apoptosis, and minimal reaction of alpha-smooth muscle actin (α SMA) and proliferating cell nuclear antigen (PCNA) were evident in the offspring of diabetic mothers. We conclude that maternal diabetes produces degenerative effects in the structure and function of the submandibular salivary glands of the offspring, reflecting possible influences on their secretory activity affecting oral and digestive health.

Partial Text

Development of human salivary glands starts from the fourth week of fetal life and continues after birth [1]. Therefore, maturation of the submandibular salivary glands is influenced by intrauterine and postnatal disturbances. The glands develop in a complex and coordinated dynamic process beginning from the proliferation of solid cord of epithelial cells, then branching, formation of lobules, cords canalization and cytodifferentiation [2]. The submandibular glands produce 65% of the total saliva secreted from all salivary glands. Movement of the saliva is necessary for the removal of bacteria, pH buffering and oral health generally. The high shear rates during eating and swallowing maintain a constant flow of saliva from the ductal openings in the mouth to swallowing into the back of the throat [3]. Secretion of saliva increases above the resting level by taste and mastication and to a lesser degree by olfaction [4]. Carpenter [3] concluded that the principle stimulus for the flow of saliva are chewing and taste. In addition, the antibacterial, antiviral and antifungal components of the saliva help to maintain the normal oral flora [5]. Benn and Thomson [6] reported that submandibular glands secrete viscous saliva composed of 99% water. Other components include sodium, potassium, calcium, magnesium, bicarbonate, phosphates, immunoglobulins, proteins, glycoproteins, mucins, urea, ammonia and sulfated cystatins. Moreover, submandibular salivary secretion contains neuronal and epidermal growth factors which promote lubrication and protection of gums and oral mucosa. Most calcium in saliva is bound to statherin or to other phosphor-containing proteins that prevents excessive precipitation of calcium on the teeth [7].

Loss of normal glandular architecture was found in the present study at the 2nd and 4th weeks old offspring of diabetic mothers. It was manifested by degenerative changes in the acini, atrophy in the striated duct and fibrosis around the ducts and in between the acini. These changes have been suggested to be due to nuclear and cytoplasmic apoptosis, cellular degeneration and failure of growth and development of the glands. Moreover, stagnation of secretory granules in the glandular acini found in the semithin sections could be due to lack of the contractility of myoepithelial cells surrounding the acini, demonstrated by negative reaction of α SMA, leading to accumulation of the secretion of the cells. The inability of these granules to open into the lumen might be due to alterations in the intracellular calcium (Ca2+) balance [16]. It was found that diabetes resulted in increase peroxidation of lipids with subsequent accumulation of Ca2+inside the cells, increase Ca2+ mobilizing ability of muscarinic receptors and reduction of Ca2+stores inside the endoplasmic reticulum. These changes of intracellular Ca2+were suggested to produce reduction of submandibular gland function [34]. These vesicles appeared in the electron microscopic study to be immature secretory vesicles. This criterion clarifies that maternal diabetes affected the submandibular gland functions. From these results, it could be suggested that intrauterine diabetic environment influences the development of the gland and its prenatal and postnatal structure and function. Reports, that studied the effects of diabetes on human submandibular salivary glands, recorded parenchymal atrophy and increase fibrous tissue that affect the gross morphology and produce sialadenosis [35]. Decrease in the number of secretory granules are in consistence with the belief that diabetes reduces the human gland secretory activity [36]. Another study attributed the impairment of rat salivary gland function to the decreased activity of Ca2+ -ATPases and increase Ca2+ influx with accumulation of Ca2+ in the mitochondria [34]. Cell swelling was also a consequence of electrolyte imbalance and changes in aquaporin distribution. Moreover, enlargement of secretory granules could be explained by changes in cell osmolarity and modified electrolyte concentration in the cytoplasm in rats [17]. In addition, diabetes was recorded to produce significant changes in human submandibular glands even with good glycemic control and absence of clinical signs of gland malfunction. The results were detected in ten patients with type two diabetes and mean age of sixty years indicating effects of diabetes on the submandibular glands. These changes were attributed to impaired glucose metabolism [16] and the relationship between intracellular glucose concentration and cell osmolarity producing cell swelling. Lasisi and Fasanmade [37] investigated the salivary flow rate and contents in forty adult human subjects. They found that diabetes significantly increased salivary glucose and potassium levels and reduced salivary flow rate. High salivary glucose level enhanced the possibility of oral infections, dental caries and improper wound healing. In addition, Ladgotra et al. [38], in their study on 120 adult human subjects, reported that diabetes increased glucose, calcium and phosphorus in saliva and reduced total salivary protein levels as result of hyperglycemia which directs protein utilization in other metabolic reactions. They recorded reduction of the level of salivary globulin, due to limited filtration of immunoglobulins down into the saliva compared with increase serum albumin leakage into the saliva, suggesting the possibility of low grade sialadenitis as a complication of diabetes.

From the present work, it could be concluded that maternal diabetes produces degenerative effects in the structure and function of the submandibular salivary glands of the offspring, reflecting possible influences on their secretory activity affecting the oral and digestive health.

 

Source:

http://doi.org/10.1371/journal.pone.0205372

 

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