Associations between xerostomia, histopathological alterations, and autonomic innervation of labial salivary glands in men in late midlife

Extracellular matrix turnover in salivary gland disorders and regenerative therapies: Obstacles and opportunities

Salivary gland (SG) extracellular matrix (ECM) has a major influence on tissue development, homeostasis, and tissue regeneration after injury. During aging, disease, and physical insult, normal remodeling of the SG microenvironment (i.e. ECM) becomes dysregulated, leading to alterations in matrix composition which disrupt tissue architecture/structure, alter cell activity, and negatively impact gland function. Matrix metalloproteinases (MMPs) are a large and diverse family of metalloendopeptidases which play a major role in matrix degradation and are intimately involved in regulating development and cell function; dysregulation of these enzymes leads to the production of a fibrotic matrix. In the SG this altered fibrotic ECM (or cell microenvironment) negatively impacts normal cell function and the effectiveness of gene and stem cell therapies which serve as a foundation for many SG regenerative therapies. For this reason, prospective regenerative strategies should prioritize the maintenance and/or restoration of a healthy SG ECM. Mesenchymal stem cells (MSCs) have great potential for mitigating damage to the SG microenvironment by ameliorating inflammation, reducing fibrosis, and repairing the damaged milieu of extracellular regulatory cues, including the matrix. This review addresses our current understanding of the impact of aging and disease on the SG microenvironment and suggests critical deficiencies and opportunities in ECM-targeted therapeutic interventions.

Histamine deficiency inhibits lymphocyte infiltration in the submandibular gland of aged mice via increased anti-aging factor Klotho

OBJECTIVES

Histidine decarboxylase (HDC), a histamine synthase, is expressed in various tissues and is induced by proinflammatory cytokines such as TNFα. As they age, C57BL/6 mice show auto-antibody deposition and lymphocyte infiltration into various tissues, including salivary glands. However, the mechanism underlying cell infiltration and the change in HDC expression in salivary glands with aging remain unclear. Thus, we aimed to elucidate the relationship between histamine and inflammaging.

METHODS

We investigated the change in histology and HDC expression in the major salivary glands (parotid, submandibular, and sublingual) of 6-week- and 9-month-old wild-type mice. We also determined the histological changes, cytokine expression, and anti-aging factor Klotho in the salivary glands of 9-month-old wild-type and HDC-deficient (HDC-KO) mice.

RESULTS

Cell infiltration was observed in the submandibular gland of 9-month-old wild-type mice. Although most cells infiltrating the submandibular glands were CD3-positive and B220-positive lymphocytes, CD11c-positive and F4/80-positive monocyte lineages were also detected. HDC, TNFα, and IL-1β mRNA expression increased in the submandibular gland of 9-month-old wild-type mice. The expression of PPARγ, an anti-inflammatory protein, declined in 9-month-old wild-type mice, and Klotho expression increased in 9-month-old HDC-KO mice. Immunohistochemistry showed that Klotho-positive cells disappeared in the submandibular gland of 9-month-old wild-type mice, while Klotho was detected in all salivary glands in HDC-KO mice of the same age.

CONCLUSION

Our findings demonstrate the multifunctionality of histamine and can aid in the development of novel therapeutic methods for inflammatory diseases such as Sjogren's syndrome and age-related dysfunctions.

The Impact of Xerostomia on Food Choices-A Review with Clinical Recommendations

Xerostomia and hyposalivation are highly prevalent conditions in old age, particularly among multimorbid elders, and are often attributed to the use of multiple medications. These conditions negatively affect oral functions, such as chewing, swallowing, speech, and taste. Additionally, the lack of lubrication of the oral mucosa frequently leads to super-infections with candida. Denture retention and comfort may also be compromised. The risk of dental caries and erosion of natural teeth increases since saliva, which is essential for repairing initial lesions in tooth structures, is insufficient. The dry sensation in the mouth also impacts the emotional and social well-being of elderly individuals. Patients experiencing xerostomia often avoid certain foods that are uncomfortable or difficult to consume. However, some foods may alleviate the symptoms or even stimulate salivation. This review discusses the limited available evidence on nutritional advice for patients with xerostomia and aims to provide insight into the patient's perspective while offering clinical recommendations. Future studies should focus on investigating the nutritional intake of individuals suffering from xerostomia or hyposalivation in order to ensure oral health comfort, prevent malnutrition, and minimize the impact on their quality of life.

Identification of Sjögren's syndrome patient subgroups by clustering of labial salivary gland DNA methylation profiles

Heterogeneity in Sjögren's syndrome (SS), increasingly called Sjögren's disease, suggests the presence of disease subtypes, which poses a major challenge for the diagnosis, management, and treatment of this autoimmune disorder. Previous work distinguished patient subgroups based on clinical symptoms, but it is not clear to what extent symptoms reflect underlying pathobiology. The purpose of this study was to discover clinical meaningful subtypes of SS based on genome-wide DNA methylation data. We performed a cluster analysis of genome-wide DNA methylation data from labial salivary gland (LSG) tissue collected from 64 SS cases and 67 non-cases. Specifically, hierarchical clustering was performed on low dimensional embeddings of DNA methylation data extracted from a variational autoencoder to uncover unknown heterogeneity. Clustering revealed clinically severe and mild subgroups of SS. Differential methylation analysis revealed that hypomethylation at the MHC and hypermethylation at other genome regions characterize the epigenetic differences between these SS subgroups. Epigenetic profiling of LSGs in SS yields new insights into mechanisms underlying disease heterogeneity. The methylation patterns at differentially methylated CpGs are different in SS subgroups and support the role of epigenetic contributions to the heterogeneity in SS. Biomarker data derived from epigenetic profiling could be explored in future iterations of the classification criteria for defining SS subgroups.

Hypomethylation mediates genetic association with the major histocompatibility complex genes in Sjögren's syndrome

Differential methylation of immune genes has been a consistent theme observed in Sjögren's syndrome (SS) in CD4+ T cells, CD19+ B cells, whole blood, and labial salivary glands (LSGs). Multiple studies have found associations supporting genetic control of DNA methylation in SS, which in the absence of reverse causation, has positive implications for the potential of epigenetic therapy. However, a formal study of the causal relationship between genetic variation, DNA methylation, and disease status is lacking. We performed a causal mediation analysis of DNA methylation as a mediator of nearby genetic association with SS using LSGs and genotype data collected from 131 female members of the Sjögren's International Collaborative Clinical Alliance registry, comprising of 64 SS cases and 67 non-cases. Bumphunter was used to first identify differentially-methylated regions (DMRs), then the causal inference test (CIT) was applied to identify DMRs mediating the association of nearby methylation quantitative trait loci (MeQTL) with SS. Bumphunter discovered 215 DMRs, with the majority located in the major histocompatibility complex (MHC) on chromosome 6p21.3. Consistent with previous findings, regions hypomethylated in SS cases were enriched for gene sets associated with immune processes. Using the CIT, we observed a total of 19 DMR-MeQTL pairs that exhibited strong evidence for a causal mediation relationship. Close to half of these DMRs reside in the MHC and their corresponding meQTLs are in the region spanning the HLA-DQA1, HLA-DQB1, and HLA-DQA2 loci. The risk of SS conferred by these corresponding MeQTLs in the MHC was further substantiated by previous genome-wide association study results, with modest evidence for independent effects. By validating the presence of causal mediation, our findings suggest both genetic and epigenetic factors contribute to disease susceptibility, and inform the development of targeted epigenetic modification as a therapeutic approach for SS.

Aging-related changes in quantity and quality of saliva: Where do we stand in our understanding?

Saliva is crucial to oral processing of food and consequently is also related to the sensory and textural experience. It is often assumed that the secretion and properties of saliva change with age, which can result in dry mouth conditions, taste aberrations. Such changes may result in reduced nutrient intake and malnutrition besides adversely affecting the quality of life. Based on some recent research findings, this article reviews our current understandings on age-dependent changes on quantity (bulk salivary flow rate) as well as quality of saliva (e.g., composition, viscosity, lubrication) in healthy elderly individuals. The review begins with a short introduction to histological changes of salivary glands upon aging. This is followed by covering different aspects of salivary changes with key articles highlighting decreased flow rate, increased ionic concentration, decreased calcium and mucin content in saliva of elderly subjects consequently affecting the oral coating and flavor perception. We also highlight issues in data associated with respect to variance in saliva collection protocols as well as factors influencing such results other than age, such as health conditions and polypharmacy. Clear gaps in literature have been highlighted with respect to lack of quantitative data in viscoelasticity, rheology, and lubrication properties of saliva in healthy elderly population and the potential impact of changes in these material properties on sensory and textural perception of food and consequently food intake. Such insights will not only have clinical implications for maintaining optimal oral health in elderly population but also serve to optimize food for elderly population. PRACTICAL APPLICATIONS: The population has undergone a fundamental change in its age structure globally, with a rapid increase in elderly population. Innovation of tailored foods is still in its early stage to satisfy the needs of growing aging population. One of the biggest challenges in such food product development is lack of adequate understanding and characterization of endogenous factors, that is, age-related changes in saliva, which may influence oral processing of food and subsequently nutrient intake. Aging affects the salivary glands and alters quantity (flow rate) and quality (e.g., ion and protein composition, rheology, tribology) of saliva. Thus, older adults may suffer from dry mouth, taste aberration, and poor oral hygiene, greatly affecting their quality of life. This review provides insights into how age versus other health conditions influence salivary properties. Understanding of age-dependent changes in salivary rheology and tribology will be of paramount importance to optimize food for elderly population.

Peculiar histopathological features in minor salivary gland in lupus erythematosus

Salivary glands (SGs) can be affected by lupus erythematosus (LE). Many authors debate whether this condition is a secondary manifestation of Sjögren syndrome (SS) or a glandular aspect of LE. The present study investigated the histopathological aspects of biopsied minor salivary glands from LE patients to analyze their peculiar features that lead to xerostomia. Twenty-three minor labial salivary gland (MLSG) cases were included in the study; the diagnosis of LE was rendered according to the American College of Rheumatology criteria. Twenty-three healthy MLSGs were used as a control, for comparison. Regarding lupus MLSG, the presence of hyalinization and thickening of ductal basement membrane, perivascular inflammatory infiltrate, epithelial spongiosis with no ductal lymphocytic aggression, vacuolar degeneration of the ductal cells and acinar serous metaplasia were statistically significant compared to the control group. In the LE group, there was a statistically significant correlation between acinar atrophy and acinar fibrosis; acinar atrophy and ductal ectasia; acinar fibrosis and ductal ectasia; ductal atrophy and ductal spongiosis with no lymphocytic focus, interstitial inflammatory infiltrate intensity and vasculitis as well as vascular thrombi and vasculitis. There were no morphological differences between the three subtypes of lupus analyzed. Minor salivary glands from patients diagnosed with LE present peculiar histopathological changes and may be a multisystemic presentation.

Image analysis of fibrosis in labial salivary glands of patients with systemic autoimmune diseases. Close correlation of lobular fibrosis to seropositive rheumatoid arthritis and increased anti-CCP and RF titres in the serum

Lobular fibrosis in labial salivary glands of patients with systemic autoimmune disease is a rarely examined and rather neglected histological change. Its significance and disease association is poorly understood. Our aim was to explore the clinical correlations of fibrosis in labial salivary gland samples using objective methods and laboratory parameters. Labial salivary gland samples from more than 300 patients over a 3-year period were selected from the archives of the pathology department, histologically examined, digitised, image analysed and statistically evaluated to identify the presence and intensity of lobular fibrosis, its relation to age, clinical diagnoses of systemic autoimmune disease and the presence of rheumatoid factor (RF), anti-cyclic citrullinated peptide (CCP), antinuclear antibodies (ANAs), and anti-dsDNA serum markers. Significant correlation was found between lobular fibrosis and the presence of autoimmune disease (p = 0.023), mainly seropositive rheumatoid arthritis (p < 0.001). Also significant association was found between the fibrosis and the presence of serum anti-CCP (p < 0.001) and IgA/IgG/IgM-RF (p < 0.001, p < 0.001 and p = 0.008, respectively). Significant association was explored between the anti-dsDNA positivity and the negative histology groups (p = 0.033) and between the ANA positivity and the inflammation only group (p = 0.021). The results suggest that lobular fibrosis tends to associate to certain systemic autoimmune diseases, mainly seropositive rheumatoid arthritis, and seems to be rare in labial salivary gland biopsies of autoimmune diseases characterised by presence of anti-dsDNA. The close correlation of ANA positivity and the inflammation only histology was not surprising, since the majority of patients (62%) have Sjögren's syndrome, known for its inflammatory infiltrate. These findings emphasise that evaluation of lobular fibrosis and inflammation in histological samples of labial salivary gland biopsies are equally important.

Hyposalivation and Poor Dental Health Status Are Potential Correlates of Age-Related Cognitive Decline in Late Midlife in Danish Men

Introduction: Peripheral correlates of age-associated cognitive decline are important tools in the screening for potentially abnormal courses of cognitive aging. Since salivary gland function is controlled by the autonomic and central nervous system, associations between cognitive changes and salivary gland hypofunction were tested in two groups of middle-aged men in late midlife, who differed substantially with respect to their midlife performance in verbal intelligence when compared with their performance in young adulthood.

Materials and Methods: Participants (n = 193) were recruited from the Danish Metropolit Cohort of men born in 1953. Based on their individual change in performance in two previously administered intelligence tests, they were allocated to one group of positive and one group of negative outliers in midlife cognition scores, indicating no decline versus decline in test performance. All participants underwent a clinical oral examination including assessments of their dental, periodontal, and mucosal conditions. Whole and parotid saliva flow rates were measured, and the number of systemic diseases and medication intake as well as daytime and nocturnal xerostomia were registered.

Results: Participants with decline in cognitive test performance in midlife had significantly lower unstimulated whole saliva flow rates, higher prevalence of hyposalivation and daytime xerostomia and a higher caries experience than participants with no decline in midlife performance. Daytime and nocturnal xerostomia were associated with daily intake of medication and alcohol.

Discussion: Overall, hyposalivation, xerostomia and poor dental status distinguished a group of men displaying relative decline in cognitive performance from a group of men without evidence of cognitive decline. Thus, hyposalivation and poor dental health status may represent potential correlates of age-related cognitive decline in late midlife, provided that other causes can be excluded.

Elevated p16ink4a Expression in Human Labial Salivary Glands as a Potential Correlate of Cognitive Aging in Late Midlife

BACKGROUND

The cell-cycle inhibitor and tumor suppressor cyclin dependent kinase inhibitor, p16ink4a, is one of the two gene products of the ink4a/ARF (cdkn2a) locus on chromosome 9q21. Up-regulation of p16ink4a has been linked to cellular senescence, and findings from studies on different mammalian tissues suggest that p16ink4a may be a biomarker of organismal versus chronological age.

OBJECTIVE

The aim of this study was to examine the immunolocalization pattern of p16ink4a in human labial salivary gland (LSG) tissue, and to analyze whether its expression level in LSGs is a peripheral correlate of cognitive decline in late midlife.

METHODS

The present study was a part of a study of causes and predictors of cognitive decline in middle-aged men in a Danish birth cohort. It is based on data from 181 male participants from the Danish Metropolit birth cohort, born in 1953, who were examined for age-associated alterations in cognition, dental health, and morphological and autonomic innervation characteristics of the LSGs. The participants were allocated to two groups based on the relative change in cognitive performance from young adulthood to late midlife. LSG biopsies were analyzed by qRT-PCR for the expression level of p16ink4a. Immunohistochemistry was performed on formalin-fixed, paraffin-embedded sections of LSGs.

RESULTS

p16ink4a immunoreactivity was observed in LSG ductal, myoepithelial, and stromal cells, but not in acinar cells. The mean relative expression of p16ink4a in LSGs was higher in the group of participants with decline in cognitive performance. A logistic regression analysis revealed that the relative p16 expression was predictive of the participant's group assignment. A negative correlation was found between relative p16ink4a expression and the participant's standardized regression residuals from early adulthood to late midlife cognitive performance scores.

CONCLUSIONS

p16ink4a expression in human LSGs may constitute a potential peripheral correlate of cognitive decline. Human labial salivary glands seem suitable for studies on organismal as opposed to chronological age.

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.