Exenatide and Sitagliptin Decrease Interleukin 1β, Matrix Metalloproteinase 9, and Nitric Oxide Synthase 2 Gene Expression But Does Not Reduce Alveolar Bone Loss in Rats With Periodontitis

Lipotoxicity: The missing link between diabetes and periodontitis?

Lipotoxicity refers to the accumulation of lipids in tissues other than adipose tissue (body fat). It is one of the major pathophysiological mechanisms responsible for the progression of diabetes complications such as non-alcoholic fatty liver disease and diabetic nephropathy. Accumulating evidence indicates that lipotoxicity also contributes significantly to the toxic effects of diabetes on periodontitis. Therefore, we reviewed the current in vivo, in vitro, and clinical evidence of the detrimental effects of lipotoxicity on periodontitis, focusing on its molecular mechanisms, especially oxidative and endoplasmic reticulum stress, inflammation, ceramides, adipokines, and programmed cell death pathways. By elucidating potential therapeutic strategies targeting lipotoxicity and describing their associated mechanisms and clinical outcomes, including metformin, statins, liraglutide, adiponectin, and omega-3 PUFA, this review seeks to provide a more comprehensive and effective treatment framework against diabetes-associated periodontitis. Furthermore, the challenges and future research directions are proposed, aiming to contribute to a more profound understanding of the impact of lipotoxicity on periodontitis.

Dipeptidyl-Peptidase-4 and Glucagon-like-Peptide-1, a Link in the Connection between Periodontitis and Diabetes Mellitus-What Do We Know So Far?-A Scoping Review

Periodontitis is a common condition affecting the tissues surrounding and supporting teeth. In addition to oral health concerns, periodontal disease increases the chance of developing systemic illnesses including type 2 diabetes mellitus. Porphyromonas gingivalis, a key-stone pathogen that has been linked to the pathophysiology of periodontal disease, can generate a series of dipeptide producing exopeptidases, dipeptidyl peptidases (DPP). DPP-4 levels in gingival crevicular fluid have been shown to increase during active periodontal disease, which may lead to their association with the disease's progression. Following oral glucose administration, mice injected with DPP-4 had higher blood glucose than the control group. DPP-4 inhibitors are used to treat patients with type 2 diabetes mellitus in order to extend the half-life of incretins. Elevated glucagon-like peptide-1 (GLP-1) levels following periodontal therapy could be considered new and applicable real-world evidence confirming the experimental findings of a beneficial interaction between oral microbiota and incretin axis. GLP-1 receptor agonist exendin-4 enhanced the osteoblast proliferation and development of these stem cells and inhibited the effects of glucose on the cells. In addition to lowering blood sugar, liraglutide, a GLP-1 receptor agonist, also possesses anti-inflammatory and bone-protective properties. These findings support the use of GLP-1 in the management and prevention of diabetic periodontitis.

DPP4 as a Potential Candidate in Cardiovascular Disease

The rising prevalence of cardiovascular disease has become a global health concern. The occurrence of cardiovascular disease is the result of long-term interaction of many risk factors, one of which is diabetes. As a novel anti-diabetic drug, DPP4 inhibitor has been proven to be cardiovascular safe in five recently completed cardiovascular outcome trials. Accumulating studies suggest that DPP4 inhibitor has potential benefits in a variety of cardiovascular diseases, including hypertension, calcified aortic valve disease, coronary atherosclerosis, and heart failure. On the one hand, in addition to improving blood glucose control, DPP4 inhibitor is involved in controlling cardiovascular risk factors. On the other hand, DPP4 inhibitor directly regulates the occurrence and progression of cardiovascular diseases through a variety of mechanisms. In this review, we summarize the recent advances of DPP4 in cardiovascular disease, aiming to discuss DPP4 inhibitor as a potential option for cardiovascular therapy.

[Sitagliptin inhibits lipopolysaccharide-induced inflammatory response in human gingival fibroblasts by blocking nuclear factor-κB signaling pathway]

OBJECTIVES

This study was performed to clarify the effects of sitagliptin on Porphyromonas gingivalis-lipopolysaccharide (LPS)-induced inflammatory response in human gingival fibroblasts (HGFs), explore the molecular mechanism of its roles, and provide a foundation for clinical therapeutics in periodontitis.

METHODS

Healthy gingival samples were collected from the donors. HGFs were isolated with enzymic digestion method and identified. The effects of LPS and sitagliptin on cell viability were detected by cell-counting kit-8 (CCK8). The mRNA levels of inflammatory cytokines, namely, interleukin (IL)-6, IL-8, C-C motif ligand 2 (CCL2), and superoxide dismutase 2 (SOD2), were evaluated by quantity real-time polymerase chain reaction (qRT-PCR) and enzyme-linked immune sorbent assay (ELISA) was used to measure the secretion protein levels of IL-6, IL-8, and CCL2. Western blot analysis was used to further investigate the activation of nuclear factor (NF)-κB signaling pathway. The effect of NF-κB pathway inhibitor BAY11-7082 on LPS-induced HGF inflammatory cytokines at the gene level was verified by qRT-PCR.

RESULTS

Low concentrations of sitagliptin (0.1, 0.25, and 0.5 µmol·L^-1) did not affect HGF growth in 24 and 48 h, whereas high concentrations of sitagliptin (5-1 000 µmol·L^-1) significantly inhibited cell proliferation. Sitagliptin suppressed 5 µg·mL^-1 of LPS-induced IL-6, IL-8, CCL2, and SOD2 gene expression levels in HGF in a concentration-dependent manner. Furthermore, sitagliptin significantly decreased the elevated secretion of IL-6, IL-8, and CCL2 protein induced by LPS. Western blot analysis showed that 0.5 µmol·L^-1 of sitagliptin significantly inhibited LPS-induced NF-κB signaling pathway activation. Results of qRT-PCR analysis indicated that 0.5 µmol·L^-1 of sitagliptin and 5 µmol·L^-1 of BAY11-7082 significantly inhibited LPS-induced IL-6, IL-8, CCL2, and SOD2 gene expressions.

CONCLUSIONS

Sitagliptin could significantly inhibit LPS-induced HGF inflammatory response by blocking the NF-κB signaling pathway activation.

Hyperhomocysteinemia: an instigating factor for periodontal disease

Hyperhomocysteinemia (HHcy) affects bone remodeling, since a destructive process in cortical alveolar bone has been linked to it; however, the mechanism remains at large. HHcy increases proinflammatory cytokines viz. TNF-α, IL-1b, IL-6, and IL-8 that leads to a cascade that negatively impacts methionine metabolism and homocysteine cycling. Further, chronic inflammation decreases vitamins B12, B6, and folic acid that are required for methionine homocysteine homeostasis. This study aims to investigate a HHcy mouse model (cystathionine β-synthase deficient, CBS^+/-) for studying the potential pathophysiological changes, if any, in the periodontium (gingiva, periodontal ligament, cement, and alveolar bone). We compared the periodontium side-by-side in the CBS^+/- model with that of the wild-type (C57BL/6J) mice. Histology and histomorphometry of the mandibular bone along with gene expression analyses were carried out. Also, proangiogenic proteins and metalloproteinases were studied. To our knowledge, this research shows, for the first time, a direct connection between periodontal disease during CBS deficiency, thereby suggesting the existence of disease drivers during the hyperhomocysteinemic condition. Our findings offer opportunities to develop diagnostics/therapeutics for people who suffer from chronic metabolic disorders like HHcy.

Glucagon-Like Peptide-1 Receptor Agonist Liraglutide Ameliorates the Development of Periodontitis

Periodontitis is one of the diabetic complications due to its high morbidity and severity in patients with diabetes. The prevention of periodontitis is especially important in diabetic patients because the relationship between diabetes and periodontitis is bidirectional. Here, we evaluated the impacts of glucagon-like peptide-1 (GLP-1) receptor agonist liraglutide on the amelioration of periodontitis. Five-wk-old Male Sprague-Dawley (SD) rats (n = 30) were divided into 3 groups: normal, periodontitis, and periodontitis with liraglutide treatment groups. Periodontitis was induced by ligature around the maxillary second molar in SD rats. Half of the rats were administered liraglutide for 2 weeks. Periodontitis was evaluated by histological staining, gene expressions of inflammatory cytokines in gingiva, and microcomputed tomography. Periodontitis increased inflammatory cell infiltration, macrophage accumulation, and gene expressions of tumor necrosis factor-α and inducible nitric oxide synthase in the gingiva, all of which were ameliorated by liraglutide. Liraglutide decreased M1 macrophages but did not affect M2 macrophages in periodontitis. Moreover, ligature-induced alveolar bone resorption was ameliorated by liraglutide. Liraglutide treatment also reduced osteoclasts on the alveolar bone surface. These results highlight the beyond glucose-lowering effects of liraglutide on the treatment of periodontitis.

Teneligliptin inhibits lipopolysaccharide-induced cytotoxicity and inflammation in dental pulp cells

Diabetes mellitus is one of the most common health threatening disorders. Patients with chronic diabetes are at high risk of contracting oral diseases, including dental pulp damage. In this study, we reviewed how Teneligliptin, a commonly used anti-diabetic agent, protected dental pulp cells from lipopolysaccharide (LPS)-induced cytotoxicity and improved their viability. The dental pulp cells treated with Teneligliptin were resistant to LPS-induced reactive oxygen species (ROS) and its byproduct 4-hydroxynonenal (4-HNE) generation. The Teneligliptin recovered LPS-induced a reduction of cellular glutathione and produced cytokine including tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), and interleukin-6 (IL-6). Mechanistically, we found that Teneligliptin suppressed LPS- that caused an expression of the cell surface receptor toll like receptor 4 (TLR-4) and the activation of JNK kinase and activator protein 1 (AP1) as well as the nuclear factor-κB (NF-κB) signal pathways. Collectively, our study demonstrates that the molecular mechanism Teneligliptin is a protective anti-diabetic agent in dental pulp cells and it has the potential to treat diabetes-associated dental pulp diseases.

Periodontitis and mechanisms of cardiometabolic risk: Novel insights and future perspectives

Periodontitis is an infectious and inflammatory disease of the tooth-supporting tissues caused by the accumulation of subgingival plaque and the action of specific periodontopathogenic bacteria. Periodontitis has been associated with cardiovascular diseases and considered a cardiovascular risk factor. Several mechanisms have been proposed to explain this association, such as the infection of atherosclerotic plaques by periodontal pathogens, the pro-atherogenic effect on the lipid profile, the systemic dissemination of pro-inflammatory mediators or the contribution to type 2 diabetes mellitus. Periodontal treatment has also been related to improvement in cardiometabolic risk variables, and oral hygiene techniques may be useful in reducing cardiometabolic risk. The aim of this review is to provide new and recent insights on the relationship between periodontitis and cardiometabolic risk, focusing on recent evidence. Comments on shared potential therapeutic targets, such as the role of glucagon-like peptide 1, are also highlighted.

Protective Effects of Vildagliptin against Pioglitazone-Induced Bone Loss in Type 2 Diabetic Rats

Long-term use of thiazolidinediones (TZDs) is associated with bone loss and an increased risk of fracture in patients with type 2 diabetes (T2DM). Incretin-based drugs (glucagon-like peptide-1 (GLP-1) agonists and dipeptidylpeptidase-4 (DPP-4) inhibitors) have several benefits in many systems in addition to glycemic control. In a previous study, we reported that exendin-4 might increase bone mineral density (BMD) by decreasing the expression of SOST/sclerostin in osteocytes in a T2DM animal model. In this study, we investigated the effects of a DPP-4 inhibitor on TZD-induced bone loss in a T2DM animal model. We randomly divided 12-week-old male Zucker Diabetic Fatty (ZDF) rats into four groups; control, vildagliptin, pioglitazone, and vildagliptin and pioglitazone combination. Animals in each group received the respective treatments for 5 weeks. We performed an intraperitoneal glucose tolerance test (IPGTT) before and after treatment. BMD and the trabecular micro-architecture were measured by DEXA and micro CT, respectively, at the end of the treatment. The circulating levels of active GLP-1, bone turnover markers, and sclerostin were assayed. Vildagliptin treatment significantly increased BMD and trabecular bone volume. The combination therapy restored BMD, trabecular bone volume, and trabecular bone thickness that were decreased by pioglitazone. The levels of the bone formation marker, osteocalcin, decreased and that of the bone resorption marker, tartrate-resistant acid phosphatase (TRAP) 5b increased in the pioglitazone group. These biomarkers were ameliorated and the pioglitazone-induced increase in sclerostin level was lowered to control values by the addition of vildagliptin. In conclusion, our results indicate that orally administered vildagliptin demonstrated a protective effect on pioglitazone-induced bone loss in a type 2 diabetic rat model.

Boning up on DPP4, DPP4 substrates, and DPP4-adipokine interactions: Logical reasoning and known facts about bone related effects of DPP4 inhibitors

Dipeptidyl peptidase 4 (DPP4) is a conserved exopeptidase with an important function in protein regulation. The activity of DPP4, an enzyme which can either be anchored to the plasma membrane or circulate free in the extracellular compartment, affects the glucose metabolism, cellular signaling, migration and differentiation, oxidative stress and the immune system. DPP4 is also expressed on the surface of osteoblasts, osteoclasts and osteocytes, and was found to play a role in collagen metabolism. Many substrates of DPP4 have an established role in bone metabolism, among which are incretins, gastrointestinal peptides and neuropeptides. In general, their effects favor bone formation, but some effects are complex and have not been completely elucidated. DPP4 and some of its substrates are known to interact with adipokines, playing an essential role in the energy metabolism. The prolongation of the half-life of incretins through DPP4 inhibition led to the development of these inhibitors to improve glucose tolerance in diabetes. Current literature indicates that the inhibition of DPP4 activity might also result in a beneficial effect on the bone metabolism, but the long-term effect of DPP4 inhibition on fracture outcome has not been entirely established. Diabetic as well as postmenopausal osteoporosis is associated with an increased activity of DPP4, as well as a shift in the expression levels of DPP4 substrates, their receptors, and adipokines. The interactions between these factors and their relationship in bone metabolism are therefore an interesting field of study.

Nonsurgical periodontal treatment reduced aortic inflammation in ApoE(-/-) mice with periodontitis

Background

Although the correlation between periodontal infection and atherosclerotic lesions has been well recognized, whether and how the nonsurgical periodontal treatment (NSPT) can improve the vascular inflammation has not been investigated clearly.

Methods

Thirty-two apolipoprotein E^−/− (apoE^−/−) mice were randomly divided into four groups: (1) Con group: no treatment, blank control group; (2) Lig group: ligature-induced-periodontitis group; (3) Lig-N group: ligatures were removed on the 7th day; (4) Lig-SRP group: ligatures were removed on the 7th day, and scaling and root planing (SRP) were performed on the 9th day. All the animals were euthanized on the 30th day. Alveolar bone loss (ABL) was assessed under microcomputed tomography. Systemic inflammatory status and lipid contents in the plasma were detected. Expression of several surrogate markers for vascular inflammation was evaluated by immunohistology and quantitative real time PCR.

Results

NSPT reduced ABL, improved lipid profile, and inhibited systemic inflammation with reduced plasma interleukin-6 (IL-6) level in apoE^−/− mice; in addition, reduced inflammation in arterial wall was observed in NSPT treated mice, showing less vascular cell adhesion molecule-1 expression and less macrophage adhesion; furthermore, NSPT improved elastic fiber fragmentation disorder in the aortic wall, thus preserved elasticity of aortic artery.

Conclusion

Ligature-induced periodontitis can lead to inflammatory response in the vascular wall and NSPT has beneficial effect on the early stage of atherosclerosis process in the articular wall by reducing systemic inflammation and improving lipid profile.