Advanced glycation end products increase expression of S100A8 and A9 via RAGE-MAPK in rat dental pulp cells

Glycation promotes pulp calcification in Type 2 diabetes rat model

OBJECTIVES

Intrapulpal calcifications can occur in the dental pulp of patients with diabetes. We focused on the association between ectopic calcifications in the dental pulp and advanced glycation end products (AGEs) in Spontaneously Diabetic Torii (SDT)-fatty rats, an obese type 2 diabetic rat model, to determine the mechanism of calcification with pulp stone in the dental pulp.

MATERIALS AND METHODS

Pathologic calcification in the dental pulp of SDT-fatty rats was observed using electron microscopy and immunohistochemical analysis. Moreover, mechanical analysis of periapical region of molar tooth against occlusal force was performed.

RESULTS

In SDT-fatty rats, pathogenic pulpal calcifications occurred during blood glucose elevation after 6 weeks, and granular calcification was observed in the dental pulp after 11 weeks. Pentosidine, a major AGE, and the receptor for AGEs were strongly expressed in the dental pulp of SDT-fatty rats. S100A8, TNF-α, and IL-6 also showed positive response in the dental pulp of the SDT-fatty rat, which indicated pulpal inflammation. Blood flow disorder and hypoxic dental pulp cells were also observed. In silico simulation, strain from occlusal force concentrates on the root apex.

CONCLUSIONS

Glycation makes blood vessels fragile, and occlusal forces damage the vessels mechanically. These are factors for intrapulpal calcification of diabetes.

Effects of diabetes mellitus on dental pulp: A systematic review of in vivo and in vitro studies

OBJECTIVES

This systematic review (PROSPERO CRD42021227711) evaluated the influence of diabetes mellitus (DM) on the response of the pulp tissue and in the pulp cells behaviour.

MATERIALS AND METHODS

Searches in PubMed/MEDLINE, Embase, Web of Science and OpenGrey were performed until March 2022. Studies evaluating the effects of DM in the pulp tissue inflammation and in the cell behaviour were included, followed by risk of bias assessment (Methodological Index for Non-Randomized Studies and SYRCLE's RoB tools). The meta-analysis was unfeasible, and a narrative synthesis for each outcome was provided.

RESULTS

Of the 615 studies, 21 were eligible, mainly with in vivo analysis (16 studies). The pulp inflammation (10 studies) was analysed mainly by haematoxylin-eosin stain; DM increased pulp inflammation/degeneration in 9 studies, especially after dental procedures. The cell viability (5 studies) was analysed mostly using MTT assay; DM and glycating agents decreased cellular viability in 3 studies. DM reduced collagen in all of three studies. There were controversial results regarding mineralization; however, increased alkaline phosphatase was reported in three of four studies.

CONCLUSIONS

DM seems to increase inflammation/degeneration and mineralization in the pulp tissue while reducing cell proliferation. Further analyses in human pulp are important to provide stronger evidence.

Impaired pulp healing associated with underlying disorders in the dental pulp of rats with type 2 diabetes

Background/purpose

Type 2 diabetes mellitus (T2DM), characterized by hyperglycemia, is a systematic disease affecting structure and healing ability in various tissues. This study aimed to investigate whether T2DM could impair the dental pulp healing and cause underlying pathological changes in the dental pulp before an injury occurred.

Materials and methods

Goto-Kakizaki rats were used as T2DM model animals and performed with direct pulp capping procedures on the first maxillary molars. The molars at 1, 2, 4 weeks after operation and non-injured molars were examined using hematoxylin and eosin staining, immunohistochemical staining, immunofluorescence staining, and Masson's trichrome staining. The fresh dental pulp of maxillary incisors was collected for transmission electron microscopy and glucose content evaluation.

Results

The T2DM rats showed deficient reparative dentin formation compared with the healthy rats. Before the occurrence of an injury, underlying pathological changes of major components in the pulp tissue were observed in T2DM rats, including vasculopathy; collagen abnormalities; decreased proliferation, decreased odontogenetic differentiation and damaged ultrastructure of dental pulp cells. High glucose content and advanced glycation end products accumulation were further found in the pulp tissue in T2DM rats.

Conclusion

T2DM can impede pulp healing process in rats, which is associated with underlying pathological changes in the non-injured pulp caused by the advanced glycation end products accumulation under high-glucose conditions.

Effects of glycation end-products on the dental pulp in patients with type 2 diabetes

AIM

This ex vivo study aimed to compare protein expression of advanced glycation end-products (AGE) and receptor (RAGE), and the levels of selected genes associated with inflammation and collagen within dental pulp tissue from patients with type 2 (T2D) diabetes and non-T2D.

METHODOLOGY

Noncarious extracted permanent molar teeth from patients with well-controlled T2D (n = 19) and non-T2D (controls) (n = 19) were collected and compared. The coronal pulp was examined using immunohistochemistry (IHC) (n = 10 per group) for anti-AGE and anti-RAGE. Quantitative PCR (n = 9 per group) was used to analyse the gene expression levels of NFKB, S100A12 and COLIA1. Data analyses were performed between the groups using GraphPad Prism using Pearson correlation, Shapiro-Wilk and Mann-Whitney U-tests, and multiple regression using SPSS.

RESULTS

AGEs were distributed diffusely throughout the pulp extracellular matrix associated with collagen fibres and were present on several cell types. RAGE was expressed at the pulp-dentine interface and was observed on odontoblasts, immune cells, endothelial cells and fibroblasts. Semi-quantitative analysis of IHC samples showed significantly increased expression of AGE (p < .0001) and RAGE (p = .02) in T2D samples compared with controls. The expression of NFKB (p < .0001), S100A12 (p < .0001) and COLIA1 (p = .01) genes were significantly higher in the T2D pulp, and multivariate logistic regression analysis showed that these findings were not affected by age.

CONCLUSION

T2D may exert a similar glycation response in the dental pulp to other body sites. This could occur through activation of NF-κB pathways with a concomitant increase in genes associated with inflammation and collagen.

Identification of S100A8 as a common diagnostic biomarkers and exploring potential pathogenesis for osteoarthritis and metabolic syndrome

Background

Osteoarthritis (OA) is the most frequent musculoskeletal disease and the major contributor to disability worldwide. Metabolic syndrome (MetS) has been recognized as being associated with the pathogenesis of osteoarthritis. However, the exact mechanisms and links between the two are not clear.

Methods

We downloaded clinical information data and gene expression profiles for OA and MetS from the database of Gene Expression Omnibus (GEO), and immune related gene (IRG) from the database of Immunology Database and Analysis Portal (IMMPORT). After screening OA-DEG and MetS-DEG, we identified the common immune hub gene by screening the overlapping genes between OA-DEG, MetS-DEG and IRG. Then we conducted single-gene analysis of S100A8, assessed the correlation of S100A8 with immune cell infiltration, and verified the diagnostic value of S100A8 in OA and MetS database respectively.

Results

323 OA-DEGs,101 MetS-DEGs and an immune-related hub gene, S100A8, were identified. In single gene analysis of S100A8 in OA samples, GSEA suggested that immune-related biological processes were more significantly enriched. The results of immune cell infiltration analysis showed that the enrichment fraction of M2 macrophages was significantly higher in the high S100A8-expressing group, and the level of S100A8 expression was positively correlated with M2 macrophage infiltration. The results of the dataset validation showed that S100A8 expression levels were significantly upregulated in the OA group and performed well in the diagnosis of OA. In single gene analysis of S100A8 in MetS samples, immune cell infiltration analysis showed that monocyte infiltration was higher in the S100A8 high expression samples and that there was a positive correlation between the two. Dataset validation showed that S100A8 is of high value for the diagnosis of MetS. In the validation of the dataset for the four metabolism-related diseases (obesity, diabetes, hypertension and hyperlipidaemia), S100A8 was expressed at higher levels in the disease group and also had a higher diagnostic value for the four metabolism-related diseases.

Conclusion

S100A8 is a common hub gene and diagnostic biomarker for OA and MetS, and the immune regulation involved in S100A8 may play a central role in the pathogenesis of OA and MetS.

The Role of Cellular Metabolism in Maintaining the Function of the Dentine-Pulp Complex: A Narrative Review

The cellular metabolic processes ensure the physiological integrity of the dentine-pulp complex. Odontoblasts and odontoblast-like cells are responsible for the defence mechanisms in the form of tertiary dentine formation. In turn, the main defence reaction of the pulp is the development of inflammation, during which the metabolic and signalling pathways of the cells are significantly altered. The selected dental procedures, such as orthodontic treatment, resin infiltration, resin restorations or dental bleaching, can impact the cellular metabolism in the dental pulp. Among systemic metabolic diseases, diabetes mellitus causes the most consequences for the cellular metabolism of the dentine-pulp complex. Similarly, ageing processes present a proven effect on the metabolic functioning of the odontoblasts and the pulp cells. In the literature, several potential metabolic mediators demonstrating anti-inflammatory properties on inflamed dental pulp are mentioned. Moreover, the pulp stem cells exhibit the regenerative potential essential for maintaining the function of the dentine-pulp complex.

Proinflammatory S100A9 stimulates TLR4/NF-κB signaling pathways causing enhanced phagocytic capacity of microglial cells

Alzheimer's disease (AD) is the main cause of dementia, affecting the increasingly aging population. Growing evidence indicates that neuro-inflammation plays crucial roles, e.g., the association between AD risk genes with innate immune functions. In this study, we demonstrate that moderate concentrations of pro-inflammatory cytokine S100A9 regulate immune response of BV2 microglial cells, i.e., the phagocytic capacity, reflected by elevated number of 1 μm diameter Dsred-stained latex beads in the cytoplasm. In contrast, at high S100A9 concentrations, both the viability and phagocytic capacity of BV2 cells drop substantially. Furthermore, it is uncovered that S100A9 affects phagocytosis of microglia via NF-κB signaling pathways. Application of related target-specific drugs, i.e., IKK and TLR4 inhibitors, effectively suppresses BV2 cells' immune responses. These results suggest that pro-inflammatory S100A9 activates microglial phagocytosis, and possibly contributes to the clearance of amyloidogenic species at the early stage of AD.

Advanced Glycation End-Products and Their Effects on Gut Health

Dietary advanced glycation end-products (AGEs) are a heterogeneous group of compounds formed when reducing sugars are heated with proteins, amino acids, or lipids at high temperatures for a prolonged period. The presence and accumulation of AGEs in numerous cell types and tissues are known to be prevalent in the pathology of many diseases. Modern diets, which contain a high proportion of processed foods and therefore a high level of AGE, cause deleterious effects leading to a multitude of unregulated intracellular and extracellular signalling and inflammatory pathways. Currently, many studies focus on investigating the chemical and structural aspects of AGEs and how they affect the metabolism and the cardiovascular and renal systems. Studies have also shown that AGEs affect the digestive system. However, there is no complete picture of the implication of AGEs in this area. The gastrointestinal tract is not only the first and principal site for the digestion and absorption of dietary AGEs but also one of the most susceptible organs to AGEs, which may exert many local and systemic effects. In this review, we summarise the current evidence of the association between a high-AGE diet and poor health outcomes, with a special focus on the relationship between dietary AGEs and alterations in the gastrointestinal structure, modifications in enteric neurons, and microbiota reshaping.

Altered Prevalence of Pulp Diagnoses in Diabetes Mellitus Patients: A Retrospective Study

INTRODUCTION

Diabetes mellitus (DM) is a complex multisystemic disorder that affects an estimated 21 million Americans. No studies have evaluated the association of DM with the prevalence of each pulpal diagnosis. The objective of this study was to compare the prevalence of each pulp diagnosis including symptomatic irreversible pulpitis (SIP), asymptomatic irreversible pulpitis, reversible pulpitis, normal pulp, and pulp necrosis (PN) in DM patients against a nondiabetic control group.

METHODS

A retrospective chart review was approved by Rutgers University Institutional Review Board. The prevalence of the diagnoses SIP, asymptomatic irreversible pulpitis, reversible pulpitis, normal pulp, and PN was calculated from AxiUm (Exan software, Las Vegas, NV) electronic health records at Rutgers School of Dental Medicine. The chi-square test was used to see the relationship between the 2 categoric variables. Second, binary logistic regression analyses were performed for each group.

RESULTS

A total of 2979 teeth were diagnosed with a pulp condition between April 2013 and November 2018. The total tooth number of DM patients was 682, whereas the tooth number of nondiabetic patients was 2297. In the subgroup of patients younger than 40 years old, SIP was notably more prevalent in DM patients. In addition, the prevalence of PN in elderly DM patients (60-69 years old) was significantly higher than in the control group.

CONCLUSIONS

The prevalence of SIP in DM patients was significantly higher compared with the control group (<40 years old), suggesting the possibility that DM could hypersensitize the subgroup of patients younger than 40 years old to pulpitis pain.

Inhibition of LncRNA Vof-16 expression promotes nerve regeneration and functional recovery after spinal cord injury

Our previous RNA sequencing study showed that the long non-coding RNA ischemia-related factor Vof-16 (lncRNA Vof-16) was upregulated after spinal cord injury, but its precise role in spinal cord injury remains unclear. Bioinformatics predictions have indicated that lncRNA Vof-16 may participate in the pathophysiological processes of inflammation and apoptosis. PC12 cells were transfected with a pHBLV-U6-MCS-CMV-ZsGreen-PGK-PURO vector to express an lncRNA Vof-16 knockdown lentivirus and a pHLV-CMVIE-ZsGree-Puro vector to express an lncRNA Vof-16 overexpression lentivirus. The overexpression of lncRNA Vof-16 inhibited PC12 cell survival, proliferation, migration, and neurite extension, whereas lncRNA Vof-16 knockdown lentiviral vector resulted in the opposite effects in PC12 cells. Western blot assay results showed that the overexpression of lncRNA Vof-16 increased the protein expression levels of interleukin 6, tumor necrosis factor-α, and Caspase-3 and decreased Bcl-2 expression levels in PC12 cells. Furthermore, we established rat models of spinal cord injury using the complete transection at T10. Spinal cord injury model rats were injected with the lncRNA Vof-16 knockdown or overexpression lentiviral vectors immediately after injury. At 7 days after spinal cord injury, rats treated with lncRNA Vof-16 knockdown displayed increased neuronal survival and enhanced axonal extension. At 8 weeks after spinal cord injury, rats treated with the lncRNA Vof-16 knockdown lentiviral vector displayed improved neurological function in the hind limb. Notably, lncRNA Vof-16 knockdown injection increased Bcl-2 expression and decreased tumor necrosis factor-α and Caspase-3 expression in treated animals. Rats treated with the lncRNA Vof-16 overexpression lentiviral vector displayed opposite trends. These findings suggested that lncRNA Vof-16 is associated with the regulation of inflammation and apoptosis. The inhibition of lncRNA Vof-16 may be useful for promoting nerve regeneration and functional recovery after spinal cord injury. The experiments were approved by the Institutional Animal Care and Use Committee of Guangdong Medical University, China.

Antidiabetic and protective effects of Scrophularia striata ethanolic extract on diabetic nephropathy via suppression of RAGE and S100A8 expression in kidney tissues of streptozotocin-induced diabetic rats

Background The present study was conducted to examine the antidiabetic effects of Scrophularia striata ethanolic extract and to evaluate its effects on oxidative stress markers and RAGE and S100A8 gene expressions in the kidney of type 1 diabetic rats. Methods A total of 36 rats (weight 200-250 g) were randomly assigned into six groups as follows: Cnt, Cnt + S. striata 100, and Cnt + S. striata 200 that received normal saline, 100 mg/kg bw, and 200 mg/kg bw of ethanol extract of S. striata, respectively; and group Dibt, Dibt + S. striata 100, and Dibt + S. striata 200 that received normal saline, 100 mg/kg bw, and 200 mg/kg bw of ethanol extract of S. striata, respectively. Type 1 diabetes was induced in rats by a single injection of streptozotocin (55 mg/kg bw). After 60 days of treatment, biochemical factors and oxidative stress markers (superoxide dismutase [SOD] and malondialdehyde [MDA]) were measured using spectrophotometric methods. RAGE and S100A8 gene expressions were analyzed using real-time polymerase chain reaction. Results Diabetes significantly impairs serum and urine fasting blood glucose (FBG), lipid profile, creatinine, urea, and albumin parameters. After the treatment with S. striata extract, these parameters are close to the normal range. It was shown that the S. striata extract significantly decreased the kidney expression levels of RAGE and S100A8 genes and improved oxidative stress markers (SOD and MDA) in the kidney tissues when compared with the diabetic control group. It was also found that the beneficial effects of the S. striata were dose dependent. Conclusions The ethanolic extract of S. striata has beneficial antidiabetic effects. Moreover, by reducing RAGE and S100A8 gene expressions and by improving oxidative stress, S. striata might be used as adjuvant treatment for diabetic complications.

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.

S100A8/A9 in Inflammation

S100A8 and S100A9 (also known as MRP8 and MRP14, respectively) are Ca²⁺ binding proteins belonging to the S100 family. They often exist in the form of heterodimer, while homodimer exists very little because of the stability. S100A8/A9 is constitutively expressed in neutrophils and monocytes as a Ca²⁺ sensor, participating in cytoskeleton rearrangement and arachidonic acid metabolism. During inflammation, S100A8/A9 is released actively and exerts a critical role in modulating the inflammatory response by stimulating leukocyte recruitment and inducing cytokine secretion. S100A8/A9 serves as a candidate biomarker for diagnosis and follow-up as well as a predictive indicator of therapeutic responses to inflammation-associated diseases. As blockade of S100A8/A9 activity using small-molecule inhibitors or antibodies improves pathological conditions in murine models, the heterodimer has potential as a therapeutic target. In this review, we provide a comprehensive and detailed overview of the distribution and biological functions of S100A8/A9 and highlight its application as a diagnostic and therapeutic target in inflammation-associated diseases.

The role of damage- and pathogen-associated molecular patterns in inflammation-mediated vulnerability of atherosclerotic plaques

Atherosclerosis is a chronic inflammatory disease resulting in the formation of the atherosclerotic plaque. Plaque formation starts with the inflammation in fatty streaks and progresses through atheroma, atheromatous plaque, and fibroatheroma leading to development of stable plaque. Hypercholesterolemia, dyslipidemia, and hyperglycemia are the risk factors for atherosclerosis. Inflammation, infection with viruses and bacteria, and dysregulation in the endothelial and vascular smooth muscle cells leads to advanced plaque formation. Death of the cells in the intima due to inflammation results in secretion of damage-associated molecular patterns (DAMPs) such as high mobility group box 1 (HMGB1), receptor for advanced glycation end products (RAGE), alarmins (S100A8, S100A9, S100A12, and oxidized low-density lipoproteins), and infection with pathogens leads to secretion of pathogen-associated molecular patterns (PAMPs) such as lipopolysaccharides, lipoteichoic acids, and peptidoglycans. DAMPs and PAMPs further activate the inflammatory surface receptors such as TREM-1 and toll-like receptors and downstream signaling kinases and transcription factors leading to increased secretion of pro-inflammatory cytokines such as tumor necrosis factor α, interleukin (IL)-1β, IL-6, and interferon-γ and matrix metalloproteinases (MMPs). These mediators and cytokines along with MMPs render the plaque vulnerable for rupture leading to ischemic events. In this review, we have discussed the role of DAMPs and PAMPs in association with inflammation-mediated plaque vulnerability.

Advanced Glycation End Products and Risks for Chronic Diseases: Intervening Through Lifestyle Modification

Advanced glycation end products (AGEs) are a family of compounds of diverse chemical nature that are the products of nonenzymatic reactions between reducing sugars and proteins, lipids, or nucleic acids. AGEs bind to one or more of their multiple receptors (RAGE) found on a variety of cell types and elicit an array of biologic responses. In this review, we have summarized the data on the nature of AGEs and issues associated with their measurements, their receptors, and changes in their expression under different physiologic and disease states. Last, we have used this information to prescribe lifestyle choices to modulate AGE-RAGE cycle for better health.

Signaling pathways involved in the effects of HMGB1 on mesenchymal stem cell migration and osteoblastic differentiation

High mobility group box 1 (HMGB1) epxression has been found in the inflammatory microenvironment of fractures. It is well known that HMGB1 acts as a chemoattractant for mesenchymal stem cells (MSCs); however, the effects of HMGB1 on MSC migration and osteoblastic differentiation, and the signaling pathways involved in these effects, have not yet been elucidated. In this study, we aimed to investigate these effects, as well as the signaling mechanisms involved, using in vitro models. We found that HMGB1, in varying concentrations, promoted the osteoblastic differentiation of MSCs, the synthesis of receptor for advanced glycation end products (RAGE) and Toll-like receptor (TLR)2/4, and the activation of the p38 mitogen-activated protein kinase (MAPK) and nuclear factor‑κB (NF‑κB) signaling pathways. Subsequently, we cultured the MSCs in the appropriate concentration of HMGB1, and determined the signaling pathways involved in the effects of HMGB1 on MSC migration and differentiation, using receptor neutralizing antibodies and signaling pathway inhibitors. From the results of this study, we concluded that HMGB1 promotes MSC migration through the activation of the p38 MAPK signaling pathway, and also promotes MSC differentiation by binding to TLR2/4 and activating the p38 MAPK signaling pathway. These findings elucidate the mechanisms underlying the effects of HMGB1 in the fracture microenvironment, which may provide a theoretical basis for the development of improved clinical treatments for fractures.

Effects of Prolyl Hydroxylase Inhibitor L-mimosine on Dental Pulp in the Presence of Advanced Glycation End Products

INTRODUCTION

Proangiogenic prolyl hydroxylase (PHD) inhibitors represent a novel approach to stimulate tissue regeneration. Diabetes mellitus involves the accumulation of advanced glycation end products (AGEs). Here we evaluated the impact of AGEs on the response of human pulp tissue to the PHD inhibitor L-mimosine (L-MIM) in monolayer cultures of dental pulp-derived cells (DPCs) and tooth slice organ cultures.

METHODS

In monolayer cultures, DPCs were incubated with L-MIM and AGEs. Viability was assessed based on formazan formation, live-dead staining, annexin V/propidium iodide, and trypan blue exclusion assay. Vascular endothelial growth factor (VEGF), interleukin (IL)-6, and IL-8 production was evaluated by quantitative polymerase chain reaction and immunoassays. Furthermore, expression levels of odontoblast markers were assessed, and alizarin red staining was performed. Tooth slice organ cultures were performed, and VEGF, IL-6, and IL8 levels in their supernatants were measured by immunoassays. Pulp tissue vitality and morphology were assessed by MTT assay and histology.

RESULTS

In monolayer cultures of DPCs, L-MIM at nontoxic concentrations increased the production of VEGF and IL-8 in the presence of AGEs. Stimulation with L-MIM decreased alkaline phosphatase levels and matrix mineralization also in the presence of AGEs, whereas no significant changes in dentin matrix protein 1 and dentin sialophosphoprotein expression were observed. In tooth slice organ cultures, L-MIM increased VEGF but not IL-6 and IL-8 production in the presence of AGEs. The pulp tissue was vital, and no signs of apoptosis or necrosis were observed.

CONCLUSIONS

Overall, in the presence of AGEs, L-MIM increases the proangiogenic capacity, but decreases alkaline phosphatase expression and matrix mineralization.