Effects of free fatty acids on human salivary gland epithelial cells

Lipid Metabolism: An Emerging Player in Sjögren's Syndrome

Sjögren's syndrome (SS) is a chronic autoimmune disorder that primarily affects the exocrine glands. Due to the intricate nature of the disease progression, the exact mechanisms underlying SS are not completely understood. Recent research has highlighted the complex interplay between immune dysregulation and metabolic abnormalities in inflammatory diseases. Notably, lipid metabolism has emerged as a crucial factor in the modulation of immune function and the progression of autoimmune diseases, including SS. This review explores the prevalence of dyslipidemia in SS, emphasizing its role in the onset, progression, and prognosis of the disease. We specifically described the impact of altered lipid metabolism in exocrine glands and its association with disease-specific features, including inflammation and glandular dysfunction. Additionally, we discussed the potential clinical implications of lipid metabolism regulation, including the role of polyunsaturated fatty acids (PUFAs) and their deficits in SS pathogenesis. By identifying lipid metabolism as a promising therapeutic target, this review highlights the need for further research into lipid-based interventions for the management of SS.

Antox targeting AGE/RAGE cascades to restore submandibular gland viability in rat model of type 1 diabetes

Diabetes mellitus (DM) is a chronic disorder of glucose metabolism that threatens several organs, including the submandibular (SMG) salivary glands. Antox (ANX) is a strong multivitamin with significant antioxidant benefits. The goal of this study was to demonstrate the beneficial roles of ANX supplementation in combination with insulin in alleviating diabetic SMG changes. For four weeks, 30 rats were divided into equal five groups (n = 6): (1) control group; (2) diabetic group (DM), with DM induced by streptozotocin (STZ) injection (50 mg/kg i.p.); (3) DM + ANX group: ANX was administrated (10 mg/kg/day/once daily/orally); (4) DM + insulin group: insulin was administrated 1U once/day/s.c.; and (5) DM + insulin + ANX group: co-administrated insulin. The addition of ANX to insulin in diabetic rats alleviated hyposalivation and histopathological alterations associated with diabetic rats. Remarkably, combined ANX and insulin exerted significant antioxidant effects, suppressing inflammatory and apoptotic pathways associated with increased salivary advanced glycation end-product (AGE) production and receptor for advanced glycation end-product expression (RAGE) activation in diabetic SMG tissues. Combined ANX and insulin administration in diabetic rats was more effective in alleviating SMG changes (functions and structures) than administration of insulin alone, exerting suppressive effects on AGE production and frustrating RAGE downstream pathways.

P2X7R and P2X4R expression of mice submandibular gland in high-fat diet/streptozotocin-induced type 2 diabetes

Type 2 diabetes mellitus (T2DM) is a chronic inflammatory disease that can compromise the functioning of various organs, including the salivary glands (SG). The purinergic system is one of the most important inflammatory pathways in T2DM condition, and P2X7R and P2X4R are the primary purinergic receptors in SG that regulate inflammatory homeostasis. This study aimed to evaluate P2X7R and P2X4R expression, and morphological changes in the submandibular gland (SMG) in T2DM. Twenty-four 5-week-old mice were randomly assigned to control (CON) and diabetes mellitus (DM) groups (n = 12 each). Body weight, diet, and blood glucose levels were monitored weekly. The histomorphology of the SMG and the expression of the P2X7R, and P2X7R was evaluated by immunohistochemistry (IHC) staining and reverse transcription-quantitative polymerase chain reaction (RT-qPCR) at 11 and 13 weeks of age. Our findings indicate a significant increase in food consumption, body weight, and blood glucose levels in the DM group. Although a significant increase in P2X7R and P2X4R expression was observed in the DM groups, the receptor location remained unchanged. We also observed a significant increase in the acinar area in the DM13w group, and a significant decrease in the ductal area in the DM11w and DM13w groups. Targeting purinergic receptors may offer novel therapeutic methods for diabetic complications.

Modes and Mechanisms of Salivary Gland Epithelial Cell Death in Sjogren's Syndrome

Sjogren's syndrome is an autoimmune disease in middle and old-aged women with a dry mucosal surface, which is caused by the dysfunction of secretory glands, such as the oral cavity, eyeballs, and pharynx. Pathologically, Sjogren's syndrome are characterized by lymphocyte infiltration into the exocrine glands and epithelial cell destruction caused by autoantibodies Ro/SSA and La/SSB. At present, the exact pathogenesis of Sjogren's syndrome is unclear. Evidence suggests epithelial cell death and the subsequent dysfunction of salivary glands as the main causes of xerostomia. This review summarizes the modes of salivary gland epithelial cell death and their role in Sjogren's syndrome progression. The molecular mechanisms involved in salivary gland epithelial cell death during Sjogren's syndrome as potential leads to treating the disease are also discussed.

Lipid Metabolism Profiles in Rheumatic Diseases

Rheumatic diseases are a group of chronic autoimmune disorders that involve multiple organs or systems and have high mortality. The mechanisms of these diseases are still ill-defined, and targeted therapeutic strategies are still challenging for physicians. Recent research indicates that cell metabolism plays important roles in the pathogenesis of rheumatic diseases. In this review, we mainly focus on lipid metabolism profiles (dyslipidaemia, fatty acid metabolism) and mechanisms in rheumatic diseases and discuss potential clinical applications based on lipid metabolism profiles.

Protective effect of nano vitamin D against fatty degeneration in submandibular and sublingual salivary glands: A histological and ultrastructural study

BACKGROUND

Poor nutritional habits and a low level of physical activity are associated with obesity, leading to increased caloric and fat intakes. A high-fat diet can significantly impact oral health through the accumulation of lipids in the salivary glands, which ultimately affect salivary gland function. Recently, an increasing number of supplement nano-formulations, such as nano vitamin D, have become available. However, only few studies have explored the effects of nano vitamin D on the maintenance of oral health.

OBJECTIVE

This study aimed to compare the histological effects of nano vitamin D to those of regular vitamin D on fatty degeneration in submandibular and sublingual salivary glands using a rat model.

METHODS

Twenty-four adult male albino Sprague-Dawley rats were divided into the following groups: untreated group, high-fat diet group, high-fat diet and regular vitamin D group, and high-fat diet and nano vitamin group.Thereafter, samples of the submandibular and sublingual salivary glands were dissected for histological and electron microscopic studies. Morphometric digital image analysis was used to quantitatively measure the changes in the size and number of acini and secretory granules.

RESULTS

Regular vitamin D had a partial protective effect. However, vitamin D could fully restore cellular structures to their normal state, thereby protecting against fatty degeneration of the salivary tissue and immune cell infiltration, particularly in the submandibular serous tissue. Nano vitamin D was more efficacious than regular vitamin D at restoring the number and size of submandibular serous secretory granules.

CONCLUSION

Employing nano vitamin D as a supplement to high-fat diets could protect against high-fat diet-induced salivary gland damage in rats.

Lipid droplets disrupt mechanosensing in human hepatocytes

Hepatocellular carcinoma (HCC) is the fourth-leading cause of cancer death in the world. Although most cases occur in stiff, cirrhotic livers, and stiffness is a significant risk factor, HCC can also arise in noncirrhotic livers in the setting of nonalcoholic fatty liver disease (NAFLD). We hypothesized that lipid droplets in NAFLD might apply mechanical forces to the nucleus, functioning as mechanical stressors akin to stiffness. We investigated the effect of lipid droplets on cellular mechanosensing and found that primary human hepatocytes loaded with the fatty acids oleate and linoleate exhibited decreased stiffness-induced cell spreading and disrupted focal adhesions and stress fibers. The presence of large lipid droplets in hepatocytes resulted in increased nuclear localization of the mechano-sensor Yes-associated protein (YAP). In cirrhotic livers from patients with NAFLD, hepatocytes filled with large lipid droplets showed significantly higher nuclear localization of YAP as compared with cells with small lipid droplets. This work suggests that lipid droplets induce a mechanical signal that disrupts the ability of the hepatocyte to sense its underlying matrix stiffness and that the presence of lipid droplets can induce intracellular mechanical stresses.NEW & NOTEWORTHY This work examines the impact of lipid loading on mechanosensing by human hepatocytes. In cirrhotic livers, the presence of large (although not small) lipid droplets increased nuclear localization of the mechanotransducer YAP. In primary hepatocytes in culture, lipid droplets led to decreased stiffness-induced cell spreading and disrupted focal adhesions and stress fibers; the presence of large lipid droplets resulted in increased YAP nuclear localization. Collectively, the data suggest that lipid droplets induce intracellular mechanical stress.

The Influence of Dietary Fatty Acids on Immune Responses

Diet-derived fatty acids (FAs) are essential sources of energy and fundamental structural components of cells. They also play important roles in the modulation of immune responses in health and disease. Saturated and unsaturated FAs influence the effector and regulatory functions of innate and adaptive immune cells by changing membrane composition and fluidity and by acting through specific receptors. Impaired balance of saturated/unsaturated FAs, as well as n-6/n-3 polyunsaturated FAs has significant consequences on immune system homeostasis, contributing to the development of many allergic, autoimmune, and metabolic diseases. In this paper, we discuss up-to-date knowledge and the clinical relevance of the influence of dietary FAs on the biology, homeostasis, and functions of epithelial cells, macrophages, dendritic cells, neutrophils, innate lymphoid cells, T cells and B cells. Additionally, we review the effects of dietary FAs on the pathogenesis of many diseases, including asthma, allergic rhinitis, food allergy, atopic dermatitis, rheumatoid arthritis, multiple sclerosis as well as type 1 and 2 diabetes.

Oral biosciences: The annual review 2018

BACKGROUND

The Journal of Oral Biosciences is devoted to the advancement and dissemination of fundamental knowledge regarding every aspect of oral biosciences.

HIGHLIGHT

This editorial review features summaries of review articles in the fields of "Bone Biology," "Epigenomics," "Periodontium," and "Amelogenesis" in addition to review articles by winners of the Lion Dental Research Award ("Role of non-canonical Wnt signaling pathways in bone resorption," "Mechanisms of orofacial sensory processing in the rat insular cortex," and "Analysis of the mechanism in salivary gland development using gene database") and the Rising Members Award ("Synergistic findings from microbiological and evolutional analyses of virulence factors among pathogenic streptococcal species" and "Free fatty acids may be involved in the pathogenesis of oral-related and cardiovascular diseases"), presented by the Japanese Association for Oral Biology.

CONCLUSION

These reviews published in the Journal of Oral Biosciences have inspired the readers of the Journal to broaden their knowledge of various aspects in the oral biosciences. This editorial review summarizes these exciting articles.

Evaluating All Potential Oral Complications of Diabetes Mellitus

Diabetes mellitus (DM) is associated with several microvascular and macrovascular complications, such as retinopathy, nephropathy, neuropathy, and cardiovascular diseases. The pathogenesis of these complications is complex, and involves metabolic and hemodynamic disturbances, including hyperglycemia, insulin resistance, dyslipidemia, hypertension, and immune dysfunction. These disturbances initiate several damaging processes, such as increased reactive oxygen species (ROS) production, inflammation, and ischemia. These processes mainly exert their damaging effect on endothelial and nerve cells, hence the susceptibility of densely vascularized and innervated sites, such as the eyes, kidneys, and nerves. Since the oral cavity is also highly vascularized and innervated, oral complications can be expected as well. The relationship between DM and oral diseases has received considerable attention in the past few decades. However, most studies only focus on periodontitis, and still approach DM from the limited perspective of elevated blood glucose levels only. In this review, we will assess other potential oral complications as well, including: dental caries, dry mouth, oral mucosal lesions, oral cancer, taste disturbances, temporomandibular disorders, burning mouth syndrome, apical periodontitis, and peri-implant diseases. Each oral complication will be briefly introduced, followed by an assessment of the literature studying epidemiological associations with DM. We will also elaborate on pathogenic mechanisms that might explain associations between DM and oral complications. To do so, we aim to expand our perspective of DM by not only considering elevated blood glucose levels, but also including literature about the other important pathogenic mechanisms, such as insulin resistance, dyslipidemia, hypertension, and immune dysfunction.

Dipeptidyl peptidase-4 inhibitor enhances restoration of salivary glands impaired by obese-insulin resistance

OBJECTIVE

Chronic high-fat diet consumption causes not only obese- insulin resistance, but also leads to pathological changes in salivary glands, including increased mitochondrial dysfunction, apoptosis, oxidative stress, and inflammation. Dipeptidyl peptidase-4 inhibitor (vildagliptin) is an oral anti-diabetic drug, using for treatment of type 2 diabetes. Vildagliptin has been shown to exert beneficial effects on several organs in cases of obese-insulin resistant condition. However, the effect of vildagliptin on salivary glands impaired by obese-insulin resistance has not been investigated. The hypothesis in this study is that vildagliptin confers beneficial effects on the salivary gland impaired by obese-insulin resistance via decreasing mitochondrial dysfunction, apoptosis, oxidative stress, and inflammation.

DESIGN

Twenty-four male Wistar rats were divided into two groups. Each group was fed with either a normal (ND; n=8) or a high fat diet (HFD; n=16) for 16 weeks. At week 13, the HFD-fed rats were subdivided into 2 subgroups to receive either a vehicle or vildagliptin (3mg/kg/day) for 28days via gavage feeding. ND-fed rats were treated with the vehicle. At the end of treatment, metabolic parameters were examined, and rats were killed. Submandibular glands were removed to appraise inflammatory markers, apoptosis and mitochondrial function.

RESULTS

Vehicle-treated HFD-fed rats developed obese-insulin resistance with an increase in oxidative stress, inflammation, apoptosis, and mitochondrial dysfunction in the salivary glands. Vildagliptin therapy reduced oxidative stress, inflammation, apoptosis and mitochondrial dysfunction in salivary gland of HFD-fed rats.

CONCLUSION

Vildagliptin prevented salivary gland injury occurring due to obese-insulin resistance.

The biochemical alterations underlying post-burn hypermetabolism

A severe burn can trigger a hypermetabolic state which lasts for years following the injury, to the detriment of the patient. The drastic increase in metabolic demands during this phase renders it difficult to meet the body's nutritional requirements, thus increasing muscle, bone and adipose catabolism and predisposing the patient to a host of disorders such as multi-organ dysfunction and sepsis, or even death. Despite advances in burn care over the last 50 years, due to the multifactorial nature of the hypermetabolic phenomenon it is difficult if not impossible to precisely identify and pharmacologically modulate the biological mediators contributing to this substantial metabolic derangement. Here, we discuss biomarkers and molecules which play a role in the induction and mediation of the hypercatabolic condition post-thermal injury. Furthermore, this thorough review covers the development of the factors released after burns, how they induce cellular and metabolic dysfunction, and how these factors can be targeted for therapeutic interventions to restore a more physiological metabolic phenotype after severe thermal injuries. This article is part of a Special Issue entitled: Immune and Metabolic Alterations in Trauma and Sepsis edited by Dr. Raghavan Raju.

Potential Role of Free Fatty Acids in the Pathogenesis of Periodontitis and Primary Sjögren's Syndrome

Clinical studies have shown that metabolic disorders such as type 2 diabetes and dyslipidemia are associated with increased risk of oral-related diseases, such as periodontitis and Sjögren’s syndrome. Although changes in the immune system are critical in both of these metabolic disorders and oral-related diseases, the mechanism underlying the interaction between these diseases remains largely unknown. Obesity and type 2 diabetes are known to be associated with higher concentrations of free fatty acids in blood. Among free fatty acids, saturated fatty acids such as palmitic acid have been demonstrated to induce inflammatory responses mainly via the innate immune systems, and to be involved in the pathogenesis of type 2 diabetes in tissues such as adipose tissue, liver, pancreas, and skeletal muscle. Here, we highlight recent advances in evidence for the potential involvement of palmitic acid in the pathogenesis of periodontitis and Sjögren’s syndrome, and discuss the possibility that improvement of the lipid profile could be a new strategy for the treatment of these diseases.

Integrating genomic data from high-throughput studies with computational modeling reveals differences in the molecular basis of hyposalivation between type 1 and type 2 diabetes

OBJECTIVES

Both type 1 and type 2 diabetes are accompanied by a high prevalence of hyposalivation (decreased salivary secretion), resulting in oral tissue damage. However, the molecular basis for the hyposalivation is yet unknown. Identifying genes and proteins that account for diabetes-related hyposalivation will help understanding the basis for this condition and identifying disease biomarkers in saliva.

MATERIALS AND METHODS

We integrated genomic data from 110 high-throughput studies with computational modeling, to explore the relationship between diabetes and salivary glands on a genomic scale.

RESULTS

A significant overlap exists between genes that are altered in both types of diabetes and genes that are expressed in salivary glands; 87 type 1 diabetes and 34 type 2 diabetes associated genes are also common to salivary glands. However, the overlap between these genes is not significant.

CONCLUSIONS

Type 1 and type 2 diabetes associated genes are involved in the salivary secretion process, but mostly at different parts of it. This suggests that type 1 and type 2 diabetes impair salivary secretion by affecting different processes in the salivary tissue.

CLINICAL RELEVANCE

The genomic characteristics of Type 1 and type 2 diabetes may explain differences in salivary gland tissues morphology and saliva composition in people with diabetes, and suggest candidate proteins for diabetes salivary biomarkers.

Impaired mitochondria and intracellular calcium transients in the salivary glands of obese rats

Long-term consumption of a high-fat diet (HFD) causes not only obese-insulin resistance, but is also associated with mitochondrial dysfunction in several organs. However, the effect of obese-insulin resistance on salivary glands has not been investigated. We hypothesized that obese-insulin resistance induced by HFD impaired salivary gland function by reducing salivation, increasing inflammation, and fibrosis, as well as impairing mitochondrial function and calcium transient signaling. Male Wistar rats (200-220 g) were fed either a ND or an HFD (n = 8/group) for 16 weeks. At the end of week 16, salivary flow rates, metabolic parameters, and plasma oxidative stress were determined. Rats were then sacrificed and submandibular glands were removed to determine inflammation, fibrosis, apoptosis, mitochondrial function and dynamics, and intracellular calcium transient signaling. Long-term consumption of an HFD caused obese-insulin resistance and increased oxidative stress, fibrosis, inflammation, and apoptosis in the salivary glands. In addition, impaired mitochondrial function, as indicated by increased mitochondrial reactive oxygen species, mitochondrial membrane depolarization, and mitochondrial swelling in salivary glands and impaired intracellular calcium regulation, as indicated by a reduced intracellular calcium transient rising rate, decay rates, and amplitude of salivary acinar cells, were observed in HFD-fed rats. However, salivary flow rate and level of aquaporin 5 protein were not different between both groups. Although HFD consumption did not affect salivation, it caused obese-insulin resistance, leading to pathophysiological alteration of salivary glands, including impaired intracellular calcium transients, increased oxidative stress and inflammation, and salivary mitochondrial dysfunction.

Possible Involvement of Palmitate in Pathogenesis of Periodontitis

Type 2 diabetes (T2D) is characterized by decreased insulin sensitivity and higher concentrations of free fatty acids (FFAs) in plasma. Among FFAs, saturated fatty acids (SFAs), such as palmitate, have been suggested to promote inflammatory responses. Although many epidemiological studies have shown a link between periodontitis and T2D, little is known about the clinical significance of SFAs in periodontitis. In this study, we showed that gingival fibroblasts have cell-surface expression of CD36, which is also known as FAT/fatty acid translocase. Moreover, CD36 expression was increased in gingival fibroblasts of high-fat diet-induced T2D model mice, compared with gingival fibroblasts of mice fed a normal diet. DNA microarray analysis revealed that palmitate increased mRNA expression of pro-inflammatory cytokines and chemokines in human gingival fibroblasts (HGF). Consistent with these results, we confirmed that palmitate-induced interleukin (IL)-6, IL-8, and CXCL1 secretion in HGF, using a cytokine array and ELISA. SFAs, but not an unsaturated fatty acid, oleate, induced IL-8 production. Docosahexaenoic acid (DHA), which is one of the omega-3 polyunsaturated fatty acids, significantly suppressed palmitate-induced IL-6 and IL-8 production. Treatment of HGF with a CD36 inhibitor also inhibited palmitate-induced pro-inflammatory responses. Finally, we demonstrated that Porphyromonas gingivalis (P.g.) lipopolysaccharide and heat-killed P.g. augmented palmitate-induced chemokine secretion in HGF. These results suggest a potential link between SFAs in plasma and the pathogenesis of periodontitis.

Palmitate-stimulated monocytes induce adhesion molecule expression in endothelial cells via IL-1 signaling pathway

Increased intake of saturated fatty acids (SFAs), such as palmitate (Pal), is linked to a higher risk of type 2 diabetes and cardiovascular disease. Although recent studies have investigated the direct effects of SFAs on inflammatory responses in vascular endothelial cells, it remains unknown whether SFAs also induce these responses mediated by circulating cells. In this study, especially focused on adhesion molecules and monocytes, we investigated the indirect effects of Pal on expression and release of ICAM-1 and E-selectin in vascular endothelial cells. Phorbol 12-myristate 13-acetate (PMA)-treated THP-1 (pTHP-1) cells and human monocytes were stimulated with various free fatty acids (FFAs). SFAs, but not unsaturated fatty acids (UFAs), increased interleukin (IL)-1β secretion and decreased IL-1 receptor antagonist (IL-1Ra) secretion, resulting in an increase in the IL-1β/IL-1Ra secretion ratio. UFAs dose-dependently inhibited the increase in IL-1β secretion and decrease in IL-1Ra secretion induced by Pal. Moreover, in human aortic and vein endothelial cells, expression and release of ICAM-1 and E-selectin were induced by treatment with conditioned medium collected from Pal-stimulated pTHP-1 cells and human monocytes, but not by Pal itself. The up-regulated expression and release of adhesion molecules by the conditioned medium were mostly abolished by recombinant human IL-1Ra supplementation. These results suggest that the Pal-induced increase in the ratio of IL-1β/IL-1Ra secretion in monocytes up-regulates endothelial adhesion molecules, which could enhance leukocyte adhesion to endothelium. This study provides further evidence that IL-1β neutralization through receptor antagonism may be useful for preventing the onset and development of cardiovascular disease.