Recovery of atrophic parotid glands in rats fed a liquid diet by switching to a pellet diet

Oral biosciences: The annual review 2022

BACKGROUND

The Journal of Oral Biosciences is devoted to advancing and disseminating fundamental knowledge concerning every aspect of oral biosciences.

HIGHLIGHT

This review features review articles in the fields of "Bone Cell Biology," "Tooth Development & Regeneration," "Tooth Bleaching," "Adipokines," "Milk Thistle," "Epithelial-Mesenchymal Transition," "Periodontitis," "Diagnosis," "Salivary Glands," "Tooth Root," "Exosome," "New Perspectives of Tooth Identification," "Dental Pulp," and "Saliva" in addition to the review articles by the winner of the "Lion Dental Research Award" ("Plastic changes in nociceptive pathways contributing to persistent orofacial pain") presented by the Japanese Association for Oral Biology.

CONCLUSION

The review articles in the Journal of Oral Biosciences have inspired its readers to broaden their knowledge about various aspects of oral biosciences. The current editorial review introduces these exciting review articles.

Disease-Induced Changes in Salivary Gland Function and the Composition of Saliva

Although the physiological control of salivary secretion has been well studied, the impact of disease on salivary gland function and how this changes the composition and function of saliva is less well understood and is considered in this review. Secretion of saliva is dependent upon nerve-mediated stimuli, which activate glandular fluid and protein secretory mechanisms. The volume of saliva secreted by salivary glands depends upon the frequency and intensity of nerve-mediated stimuli, which increase dramatically with food intake and are subject to facilitatory or inhibitory influences within the central nervous system. Longer-term changes in saliva secretion have been found to occur in response to dietary change and aging, and these physiological influences can alter the composition and function of saliva in the mouth. Salivary gland dysfunction is associated with different diseases, including Sjögren syndrome, sialadenitis, and iatrogenic disease, due to radiotherapy and medications and is usually reported as a loss of secretory volume, which can range in severity. Defining salivary gland dysfunction by measuring salivary flow rates can be difficult since these vary widely in the healthy population. However, saliva can be sampled noninvasively and repeatedly, which facilitates longitudinal studies of subjects, providing a clearer picture of altered function. The application of omics technologies has revealed changes in saliva composition in many systemic diseases, offering disease biomarkers, but these compositional changes may not be related to salivary gland dysfunction. In Sjögren syndrome, there appears to be a change in the rheology of saliva due to altered mucin glycosylation. Analysis of glandular saliva in diseases or therapeutic interventions causing salivary gland inflammation frequently shows increased electrolyte concentrations and increased presence of innate immune proteins, most notably lactoferrin. Altering nerve-mediated signaling of salivary gland secretion contributes to medication-induced dysfunction and may also contribute to altered saliva composition in neurodegenerative disease.

Hematogenous apoptotic mechanism in salivary glands in chronic periodontitis

OBJECTIVE

The aim of the study is to investigate the apoptotic mechanism in salivary glands in the rat experimental periodontitis model.

DESIGN

A rat periodontitis model was prepared by using a ligature around the second upper molar. In the salivary (parotid and submandibular) glands and blood samples, putative apoptotic factors and pathway molecules were investigated in vivo and in vitro.

RESULTS

Four weeks of ligation (chronic periodontitis) demonstrated significant apoptotic atrophy of the salivary gland, but one week of ligation (initial periodontitis) did not. In the blood plasma, tumor necrosis factor-α (TNF-α) was increased in the periodontitis model, but interleukin-1β and -6 were not. TNF-α receptor type 1, which has an intracellular apoptotic pathway, was expressed in the salivary glands of rats. Western blot analysis of cultured rat primary salivary gland cells demonstrated that TNF-α induced cleavage of poly (ADP-ribose) polymerase (PARP) and caspase-3 in a dose-dependent manner, indicating apoptosis induction. Additionally, we found increment of circulating lymphocytes in the model. Expression of mRNA and immunoreactive cells for the B lymphocyte marker CD19 were increased in the salivary gland in the model. Western blotting showed that coculture with extracted B cells from the periodontitis model increased cleaved PARP in salivary gland cells.

CONCLUSIONS

Chronic periodontitis status leads to an increase in circulating TNF-α and B lymphocyte infiltration, resulting in apoptotic atrophy of the salivary gland as a periodontitis-induced systemic response.