Effects of double ligation of Stensen's duct on the rabbit parotid gland

Apoptotic cell death during regressive changes in salivary glands: A morphological perspective

BACKGROUND

Apoptosis was initially identified through transmission electron microscopy. Subsequent advances in morphological techniques for apoptosis detection have revealed its involvement in multiple pathological conditions in various tissues. This review summarizes previous experimental studies on apoptotic cell death during regressive changes in the salivary glands, with a focus on morphological observations.

HIGHLIGHT

Obstructive sialadenitis is histologically characterized by acinar cell loss and increased number of duct cells. Although acinar cells were previously believed to dedifferentiate into duct cells, there is evidence that they are eliminated by apoptosis. Animals fed a soft diet exhibited parotid gland atrophy, in which acinar cells decreased in size and disappeared because of apoptosis. Age-related changes in the salivary glands involved a reduced number of acinar cell through apoptosis. Additionally, apoptotic acinar cell death occurs in other pathological conditions, including the regression of hypertrophic and irradiated salivary glands.

CONCLUSION

Apoptosis often eliminates acinar cells during atrophic alterations in the salivary glands. Unlike necrosis, apoptosis is an active form of cell death, thereby helping prevent the complete destruction of the salivary glands. However, the contribution of apoptosis to regressive changes in the salivary glands remains unclear and warrants further investigation.

Duct ligation/de-ligation model: exploring mechanisms for salivary gland injury and regeneration

Sialadenitis and sialadenitis-induced sialopathy are typically caused by obstruction of the salivary gland ducts. Atrophy of the salivary glands in experimental animals caused by duct ligation exhibits a histopathology similar to that of salivary gland sialadenitis. Therefore, a variety of duct ligation/de-ligation models have been commonly employed to study salivary gland injury and regeneration. Duct ligation is mainly characterised by apoptosis and activation of different signaling pathways in parenchymal cells, which eventually leads to gland atrophy and progressive dysfunction. By contrast, duct de-ligation can initiate the recovery of gland structure and function by regenerating the secretory tissue. This review summarizes the animal duct ligation/de-ligation models that have been used for the examination of pathological fundamentals in salivary disorders, in order to unravel the pathological changes and underlying mechanisms involved in salivary gland injury and regeneration. These experimental models have contributed to developing effective and curative strategies for gland dysfunction and providing plausible solutions for overcoming salivary disorders.

Case report: Sepsis secondary to infected protracted parotid sialocele after maxillofacial oncologic surgery in a dog

An 8-year-old male intact mixed breed dog was treated for a 3.7×3×3.6 cm grade 1 multilobular osteochondrosarcoma (MLO) arising from the dorsal aspect of the right coronoid process with a coronoidectomy, a zygomectomy, and a caudal maxillectomy. Ten months later, the dog presented for a swelling near the right angular process, which was presumed to be a locoregional recurrence. Blood work and initial staging tests (abdominal ultrasound) had mild abnormalities of no clinical concern/significance. The dog was hospitalized with a plan for computed tomographic (CT) scan of skull and chest the following day. Overnight, the swelling rapidly increased, and the dog became laterally recumbent, febrile, and hypotensive. Laboratory evaluation revealed hypoglycemia, elevated lactate, and elevated band neutrophils with moderate toxicity, most consistent with sepsis. The dog was stabilized with fluid resuscitation, intravenous (IV) antibiotics, IV dextrose, and pressor support. Once stabilized, a contrast CT scan was performed, which revealed evidence of an infected parotid gland sialocele. To our knowledge, this is the first veterinary case that describes sepsis secondary to an infected protracted parotid sialocele.

Cell type-specific transforming growth factor-β (TGF-β) signaling in the regulation of salivary gland fibrosis and regeneration

Salivary gland damage and hypofunction result from various disorders, including autoimmune Sjögren's disease (SjD) and IgG4-related disease (IgG4-RD), as well as a side effect of radiotherapy for treating head and neck cancers. There are no therapeutic strategies to prevent the loss of salivary gland function in these disorders nor facilitate functional salivary gland regeneration. However, ongoing aquaporin-1 gene therapy trials to restore saliva flow show promise. To identify and develop novel therapeutic targets, we must better understand the cell-specific signaling processes involved in salivary gland regeneration. Transforming growth factor-β (TGF-β) signaling is essential to tissue fibrosis, a major endpoint in salivary gland degeneration, which develops in the salivary glands of patients with SjD, IgG4-RD, and radiation-induced damage. Though the deposition and remodeling of extracellular matrix proteins are essential to repair salivary gland damage, pathological fibrosis results in tissue hardening and chronic salivary gland dysfunction orchestrated by multiple cell types, including fibroblasts, myofibroblasts, endothelial cells, stromal cells, and lymphocytes, macrophages, and other immune cell populations. This review is focused on the role of TGF-β signaling in the development of salivary gland fibrosis and the potential for targeting TGF-β as a novel therapeutic approach to regenerate functional salivary glands. The studies presented highlight the divergent roles of TGF-β signaling in salivary gland development and dysfunction and illuminate specific cell populations in damaged or diseased salivary glands that mediate the effects of TGF-β. Overall, these studies strongly support the premise that blocking TGF-β signaling holds promise for the regeneration of functional salivary glands.

Comparative Study of Cytokeratin Immunostaining of Parotid Gland Parenchyma in Normal, Diabetic, and Excretory Duct Ligation of Mongrel Dogs

OBJECTIVES

 The present study aimed to give a glimpse of the normal distribution of intermediate filaments within the parotid gland parenchyma of mongrel dogs and to reveal the pathological changes that may occur as a result of the effects of diabetes mellitus or atrophy of the gland caused by the ligation of the excretory duct to discover whether there is a similarity in these pathological behaviors.

MATERIALS AND METHODS

 Twelve healthy mongrel dogs were used in the experiment and were divided into three groups: group I (the control group), group II (dogs with alloxan-induced diabetes), and group III (dogs with the right-side duct-ligated parotid gland). The dogs were sacrificed 45 days after the parotid excretory duct were tied. The right parotid gland of all groups was dissected and prepared for histological and immunohistochemical expression of cytokeratin 17 assay.

RESULTS

 Histological findings confirmed that the parotid gland parenchyma of the diabetic group had glandular atrophy characterized by the loss of gland structure, degenerated acini, and dilatation of the duct system. Moreover, there is a predominance of the fibrous component with the presence of fat cells within the gland compartments. On the contrary, the excretory duct-ligated group undergoes severe glandular atrophy of the previous character with the presence of duct-like structure as well as extravasation and vasodilatation. Immunohistochemical expression of cytokeratin 17 in control parotid using an immunoperoxidase technique showed that cytokeratin expression varies from negative to mild in all ducts and some serous acinar cells. The gland parenchyma of the diabetic group showed mild to strong cytokeratin expression of duct cells more concentrated in the apical part with moderate to strong expression of diffuse type in some serous acini. The intensity of cytokeratin 17 in gland compartments of the excretory duct-ligated group revealed a variation in expression that ranged from negative to strong diffuse staining throughout the gland.

CONCLUSION

 The severity and prevalence of cytokeratin 17 in our results are predictive of the pathological influence of both diabetes mellitus and duct ligation on the cytokeratin intracellular filaments of the salivary gland parenchyma in a different way that interferes with saliva production and/or secretion leading to xerostomia.

The NF-κB pathway plays a vital role in rat salivary gland atrophy model

Objective

The aim of this study was to explore the histopathological and genetic changes in the submandibular glands after duct ligation and provide important clues to functional regeneration.

Design

We established a rat salivary gland duct ligation model and observed pathological changes in the rat submandibular gland on day 1 and weeks 1, 2, 3, and 4 using hematoxylin and eosin staining, Alcian blue-periodic acid Schiff staining, Masson staining, terminal deoxynucleotidyl transferase dUTP nick-end labeling (TUNEL), and immunohistochemical staining. RNA sequencing was performed on normal salivary glands and those from the ligation model after 1 week. Significantly differentially expressed genes were selected, and Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analyses were performed.

Results

Apoptosis levels and histological and functional KEGG pathway analyses showed that injury to the salivary gland after ligation gradually increased. The TGF-β pathway was activated and promoted fibrosis. RNA sequencing results and further verification of samples at week 1 showed that the NF-κB pathway plays a vital role in salivary gland atrophy.

Conclusions

Our results detailed the pathological changes in the submandibular gland after ligation and the important functions of the NF-κB pathway.

Identifying stem cells in the main excretory ducts of rat major salivary glands: adventures with commercial antibodies

We investigated the entire length of the main excretory ducts (MED) of the major sublingual, parotid and submandibular salivary glands of mature laboratory rats for mucous (goblet) and luminal ciliated cells, biomarkers of cell proliferation, apoptosis, and five biomarkers of stem cells. Spleen and testis were used as positive controls. We used formalin fixed, paraffin embedded tissues. No mucous cells or cells with luminal cilia were observed in hematoxylin and eosin, alcian blue or periodic acid-Schiff stained sections. Immunohistochemistry using rabbit anti-rat antibodies produced anomalous reactions with cleaved caspase-3 for apoptosis, Ki-67 for proliferative activity and Sox 2. Following antigen retrieval, no primary antibody and all three negative controls, labeled macrophages appeared in the spleen. TUNEL staining revealed a few cells per section undergoing apoptosis. Reactions deemed valid occurred in MED with cytokeratin-5 and c-Kit and stem cell antigen 1 (Sca-1) mostly in the gland and middle segments. Other ducts, but not acini or myoepithelial cells, also were variably stained with c-Kit and Sca-1.

Tissue Engineering of Oral Mucosa and Salivary Gland: Disease Modeling and Clinical Applications

Oral mucosa and salivary gland are composed of complex and dynamic networks of extracellular matrix, multiple cell types, vasculature, and various biochemical agents. Two-dimensional (2D) cell culture is commonly used in testing new drugs and experimental therapies. However, 2D cell culture cannot fully replicate the architecture, physiological, and pathological microenvironment of living human oral mucosa and salivary glands. Recent microengineering techniques offer state of the science cell culture models that can recapitulate human organ structures and functions. This narrative review describes emerging in vitro models of oral and salivary gland tissue such as 3D cell culture models, spheroid and organoid models, tissue-on-a-chip, and functional decellularized scaffolds. Clinical applications of these models are also discussed in this review.

Experimental Animal Model Systems for Understanding Salivary Secretory Disorders

Salivary secretory disorders are life-disrupting pathologic conditions with a high prevalence, especially in the geriatric population. Both patients and clinicians frequently feel helpless and get frustrated by the currently available therapeutic strategies, which consist mainly of palliative managements. Accordingly, to unravel the underlying mechanisms and to develop effective and curative strategies, several animal models have been developed and introduced. Experimental findings from these models have contributed to answer biological and biomedical questions. This review aims to provide various methodological considerations used for the examination of pathological fundamentals in salivary disorders using animal models and to summarize the obtained findings. The information provided in this review could provide plausible solutions for overcoming salivary disorders and also suggest purpose-specific experimental animal systems.

Parotid gland atrophy after conservative treatment of a post-traumatic parotid fistula in a two-year-old boy

A parotid fistula is a rare complication following parotid gland and duct injury. A two-year-old boy with a previous parotid fistula after parotid injury due to a dog bite was successfully treated with pressure-dressing therapy, which is generally non-invasive and tolerable by young children. During follow-up, ultrasonography revealed atrophy of the parotid gland. This finding is consistent with the healing mechanism previously assumed in adult patients with a parotid fistula. Consideration should be paid to the possibility of oral environmental changes associated with reduced saliva secretion from parotid gland atrophy after conservative treatment of parotid fistula.

Insight into Salivary Gland Aquaporins

The main role of salivary glands (SG) is the production and secretion of saliva, in which aquaporins (AQPs) play a key role by ensuring water flow. The AQPs are transmembrane channel proteins permeable to water to allow water transport across cell membranes according to osmotic gradient. This review gives an insight into SG AQPs. Indeed, it gives a summary of the expression and localization of AQPs in adult human, rat and mouse SG, as well as of their physiological role in SG function. Furthermore, the review provides a comprehensive view of the involvement of AQPs in pathological conditions affecting SG, including Sjögren's syndrome, diabetes, agedness, head and neck cancer radiotherapy and SG cancer. These conditions are characterized by salivary hypofunction resulting in xerostomia. A specific focus is given on current and future therapeutic strategies aiming at AQPs to treat xerostomia. A deeper understanding of the AQPs involvement in molecular mechanisms of saliva secretion and diseases offered new avenues for therapeutic approaches, including drugs, gene therapy and tissue engineering. As such, AQP5 represents a potential therapeutic target in different strategies for the treatment of xerostomia.

Pediatric Sialorrhea: Submandibular Duct Rerouting and Intraparotid Botulinum Toxin A Injection With Literature Review

OBJECTIVES:

The aim of this study was to assess the effectiveness of bilateral submandibular duct relocation and bilateral sublingual gland excision in combination with botulinum toxin A injection into the parotid glands in children with sialorrhea. Previously in the literature, either surgery or botulinum toxin injection but not their combination has been reported.

METHODS:

Preoperative and at least 6-month postoperative assessments using the Drooling Severity Scale and Drooling Frequency Scale (Thomas-Stonell and Greenberg classification) and the Teacher Drooling Scale and by interviewing parents and caregivers face to face or via telephone were performed. Also, decreases in the daily number of bib changes and hourly frequency of saliva wiping were recorded as success. Complications were recorded.

RESULTS:

The Drooling Frequency and Severity Scale, the Teacher Drooling Scale, daily number of bib changes, and hourly frequency of saliva wiping decreased significantly in 21 patients (95.5%) and remained unchanged in 1 patient (4.5%). Postoperative bleeding was observed in 1 patient (4.5%).

CONCLUSIONS:

Drooling is a complex problem that benefits from a multidisciplinary approach. Many treatment methods exist, each with advantages and disadvantages. In this study botulinum toxin A injection was applied in conjunction with bilateral submandibular duct relocation and bilateral sublingual gland excision surgery, achieving a success rate of 95.5%. Moreover, minimal complications and no recurrence after at least 6-month follow-up were observed. The authors therefore recommend further use of this combination treatment. Larger and longer term studies may also help clarify its effectiveness.

Proliferative Activity of Myoepithelial Cells in Normal Salivary Glands and Adenoid Cystic Carcinomas Based on Double Immunohistochemical Labeling

Objective: To investigate the proliferative activity of myoepithelial cells (MEC) in normal salivary glands (NSG) and adenoid cystic carcinomas (ACC)) Study design. Twenty -three salivary gland specimens (13 ACC, 10 NSG) were studied using double immunohistochemical labeling for α smooth muscle actin (a-SMA) and proliferative cell nuclear antigen (PCNA)). Results: There was a significant difference in PCNA reactivity in normal samples between myoepithelial cells of the parotid glands and of the submandibular glands, rates being higher in the latter. Neoplastic myoepithelial cells exhibited higher expression than neoplastic epithelial cells. In addition, myoepithelial cells of the cribriform type of ACC showed PCNA reactivity lower than those of the tubular type, whereas there was no statistically significant difference in epithelial cell rates. We could not identify myoepithelial cells in solid pattern due to α-SMA negativity; although high PCNA reactivity was evident. Conclusion: These data suggest that the myoepithelial cell has a key role in ACC oncogenesis, more so than its epithelial cell counterparts. Moreover, the data provide a histopathological interpretation for aggressive clinical features of submandibular ACC, as the myoepithelial cells were less differentiated as compared to those of parotid glands.

Differential immunohistochemical expression of type I collagen and matrix metalloproteinase 2 among major salivary glands of young and geriatric mice

Objective

This study aimed to demonstrate the immunohistochemical changes associated with MMP-2 and type 1 collagen separately for the first time in the major salivary glands (the parotid, submaxillary, and sublingual glands) that occur with aging in mice.

Material and Methods

Fourteen Balb/c white mice (50-80 g) were used in this study. The animals were divided into two equal groups. Group I consisted of young animals (2-month-old) (n=7) and Group II consisted of older animals (18-month-old) (n=7). After routine histological follow-ups, Hematoxylin-eosin (H&E), Masson’s Trichrome staining and immunohistochemical staining was performed for type I collagen and MMP-2.

Results

We observed that there were age-related decreases in the number of acinar cells, increase in eosinophilic zymogen granules in cells, collagen accumulation in fibrotic areas and dilatation in interlobular ducts. Also, while type I collagen and MMP-2 immunoreactivity were moderate in the salivary glands of the young mice, they were high in the salivary glands of the old mice (p=0.001). In the H-score assessment, MMP-2 immunoreactivity was lower at a significant level in young mice than in old mice (p=0.001).

Conclusions

This study showed that anatomical, physiological and morphological abnormalities occur in all three major salivary glands as a natural consequence of aging.

Microcalcifications in stone-obstructed human submandibular gland are associated with apoptosis and cell proliferation

OBJECTIVE

Human submandibular gland (SMG) stones are associated with inflammation, fibrosis and microcalcifications in the surrounding tissues. However, there is little information about the accompanying cell injury-repair process, apoptosis, and cell proliferation. The purpose of this study was to investigate such an association and its clinical significance.

DESIGN OF STUDY

Mid-gland paraffin sections of human SMGs ("stone glands") and normal SMGs ("non-stone glands") were subjected to stains for general histology (hematoxylin and eosin), fibrosis (Masson's trichrome), and calcification (alizarin red) and to immunohistochemistry for proliferative activity (Ki-67), and apoptosis (Caspase-3). Tissues were assessed for areas of inflammation, calcium deposition, and fibrosis, and for cycling and apoptotic cells.

RESULTS

Acini were atrophic and proportionately fewer in lobules with fibrosis in stone glands. Additionally, stone glands had intraluminal calcifications (microliths) in scattered excretory and striated ducts and blood vessel walls. Areas of inflammation and fibrosis were small and uncommon, and calcifications were not seen in non-stone glands. Proliferating and apoptotic cells were common in the main duct of stone glands where ciliated and mucous cell hyperplasia and stratified squamous metaplasia had occurred, uncommon in the main duct of non-stone glands, and uncommon in all other parenchymal elements of both stone and non-stone glands.

CONCLUSION

Stone obstruction in the main excretory ducts of SMG resulted in progressive depletion of acini from proximal to distal lobules via calcification, inflammation, fibrosis, and parenchymal cell atrophy, apoptosis and proliferation. Interlobular duct microliths contributed to this depletion by further provoking intralobular inflammation, fibrosis, and acinar atrophy.

Three-dimensional organotypic culture of human salivary glands: the slice culture model

OBJECTIVE

A challenge in studying human salivary glands is to maintain the cells ex vivo in their three-dimensional (3D) morphology with an intact native extracellular matrix (ECM) environment. This paper established a human salivary 3D organotypic slice culture model that could maintain its physiological functions as well as allowing a direct visualization of the cells.

METHODS

Human salivary biopsies from six patients were embedded in agarose and submerged in cold buffer for thin (50 μm) sectioning using a vibratome. 'Salivary slices' were mechanically supported by a porous membrane insert that allowed an air-liquid interface and cultured in serum-free culture media. Cell viability, proliferation, apoptosis, physiological functions, and gene expression were assessed during 14 days of culture.

RESULTS

Human salivary slices maintained cell survival (70-40%) and proliferation (6-17%) for 14 days ex vivo. The protein secretory (amylase) function decreased, but fluid (intracellular calcium mobilization) function was maintained. Acinar, ductal, and myoepithelial cell populations survived and maintained their 3D organization within the slice culture model.

CONCLUSION

The human salivary slice culture model kept cells alive ex vivo for 14 days as well as maintaining their 3D morphology and physiological functions.

Phenotype and cell proliferation activity of duct-like structures in human sublingual glands: a histological and immunohistochemical study

There are several age-related microscopic changes in the salivary glands, including the increase in the number of duct-like structures (DLS). However, the true origin and the phenotype of the DLS are not known.