Periodontal disease-associated compensatory expression of osteoprotegerin is lost in type 1 diabetes mellitus and correlates with alveolar bone destruction by regulating osteoclastogenesis

Recent progress in bone-repair strategies in diabetic conditions

Bone regeneration following trauma, tumor resection, infection, or congenital disease is challenging. Diabetes mellitus (DM) is a metabolic disease characterized by hyperglycemia. It can result in complications affecting multiple systems including the musculoskeletal system. The increased number of diabetes-related fractures poses a great challenge to clinical specialties, particularly orthopedics and dentistry. Various pathological factors underlying DM may directly impair the process of bone regeneration, leading to delayed or even non-union of fractures. This review summarizes the mechanisms by which DM hampers bone regeneration, including immune abnormalities, inflammation, reactive oxygen species (ROS) accumulation, vascular system damage, insulin/insulin-like growth factor (IGF) deficiency, hyperglycemia, and the production of advanced glycation end products (AGEs). Based on published data, it also summarizes bone repair strategies in diabetic conditions, which include immune regulation, inhibition of inflammation, reduction of oxidative stress, promotion of angiogenesis, restoration of stem cell mobilization, and promotion of osteogenic differentiation, in addition to the challenges and future prospects of such approaches.

Type 1 diabetes mellitus leads to gingivitis and an early compensatory increase in bone remodeling

BACKGROUND

Type 1 diabetes mellitus (T1DM) and periodontitis have long been thought to be biologically connected. Indeed, T1DM is a risk factor for periodontal disease. With the population of diabetic individuals growing, it is more important than ever to understand the negative consequences of diabetes on the periodontium and the mechanisms. The aim of this study was to find out the early effects of T1DM on the periodontium without any experimentally induced periodontitis.

METHODS

We established the streptozotocin (STZ)-induced diabetic mouse model and examined the periodontium 8 weeks later by histology, molecular and cellular assays. Microcomputed tomographic (𝜇CT) imaging and in vivo fluorochrome labeling were also used to quantify bone volume and mineral apposition rates (MAR).

RESULTS

The histologic appearance of epithelium tissue, connective tissue, and periodontal ligament in the diabetic condition was comparable with that of control mice. However, immune cell infiltration in the gingiva was dramatically elevated in the diabetic mice, which was accompanied by unmineralized connective tissue degeneration. Bone resorption activity was significantly increased in the diabetic mice, and quantitative 𝜇CT demonstrated the bone volume, the ratio of bone volume over tissue volume, and cemento-enamel junction to alveolar bone crest (CEJ-ABC) in the diabetic condition were equivalent to those in the control group. In vivo fluorochrome labeling revealed increased MAR and bone remodeling in the diabetic mice. Further investigation found the diabetic mice had more osteoprogenitors recruited to the periodontium, allowing more bone formation to balance the enhanced bone resorption.

CONCLUSIONS

STZ-induced T1DM mice, at an early stage, have elevated gingival inflammation and soft tissue degeneration and increased bone resorption; but still the alveolar bone was preserved by recruiting more osteoprogenitor cells and increasing the rate of bone formation. We conclude that inflammation and periodontitis precede alveolar bone deterioration in diabetes.

Diabetes impairs periosteal progenitor regenerative potential

Diabetics are at increased risk for fracture, and experience severely impaired skeletal healing characterized by delayed union or nonunion of the bone. The periosteum harbors osteochondral progenitors that can differentiate into chondrocytes and osteoblasts, and this connective tissue layer is required for efficient fracture healing. While bone marrow-derived stromal cells have been studied extensively in the context of diabetic skeletal repair and osteogenesis, the effect of diabetes on the periosteum and its ability to contribute to bone regeneration has not yet been explicitly evaluated. Within this study, we utilized an established murine model of type I diabetes to evaluate periosteal cell differentiation capacity, proliferation, and availability under the effect of a diabetic environment. Periosteal cells from diabetic mice were deficient in osteogenic differentiation ability in vitro, and diabetic mice had reduced periosteal populations of mesenchymal progenitors with a corresponding reduction in proliferation capacity following injury. Additionally, fracture callus mineralization and mature osteoblast activity during periosteum-mediated healing was impaired in diabetic mice compared to controls. We propose that the effect of diabetes on periosteal progenitors and their ability to aid in skeletal repair directly impairs fracture healing.

Impact of hyperglycemia and treatment with metformin on ligature-induced bone loss, bone repair and expression of bone metabolism transcription factors

This study evaluated the influence of type 2 diabetes mellitus on bone loss, bone repair and cytokine production in hyperglycemic rats, treated or not with metformin. The animals were distributed as follow: Non-Hyperglycemic (NH), Non Hyperglycemic with Ligature (NH-L), Treated Non Hyperglycemic (TNH), Treated Non Hyperglycemic with Ligature Treated (TNH-L), Hyperglycemic (H), Treated Hyperglycemic (TH), Hyperglycemic with Ligature (H-L), Treated Hyperglycemic with Ligature (TH-L). At 40th day after induction of hyperglycemia, the groups NH-L, TNH-L, H-L, TH-L received a ligature to induce periodontitis. On the 69th, the TNH, TNH-L, TH, TH-L groups received metformin until the end of the study. Bone repair was evaluated at histometric and the expression levels of Sox9, RunX2 and Osterix. Analysis of the ex-vivo expression of TNF-α, IFN-γ, IL-12, IL-4, TGF-β, IL-10, IL-6 and IL-17 were also evaluated. Metformin partially reverse induced bone loss in NH and H animals. Lower OPG/RANKL, increased OCN and TRAP expression were observed in hyperglycemic animals, and treatment with metformin partially reversed hyperglycemia on the OPG/RANKL, OPN and TRAP expression in the periodontitis. The expression of SOX9 and RunX2 were also decreased by hyperglycemia and metformin treatment. Increased ex vivo levels of TNF-α, IL-6, IL-4, IL-10 and IL-17 was observed. Hyperglycemia promoted increased IL-10 levels compared to non-hyperglycemic ones. Treatment of NH with metformin was able to mediate increased levels of TNF-α, IL-10 and IL-17, whereas for H an increase of TNF-α and IL-17 was detected in the 24- or 48-hour after stimulation with LPS. Ligature was able to induce increased levels of TNF-α and IL-17 in both NH and H. This study revealed the negative impact of hyperglycemia and/or treatment with metformin in the bone repair via inhibition of transcription factors associated with osteoblastic differentiation.

The Impact of Hyperbaric Oxygen Therapy on Serum C-Reactive Protein Levels, Osteoprotegerin Expression, and Osteoclast Numbers in Induced-Periodontitis Diabetic Rats

Objectives  This study aimed to examine the impact of hyperbaric oxygen therapy (HBOT) on serum C-reactive protein (CRP) levels, osteoclast numbers, and osteoprotegerin (OPG) expression in periodontitis-induced diabetic rats

Materials and Methods  This study constituted an in vivo laboratory-based experiment incorporating a posttest only control group design. Thirty male Wistar rats were divided into three groups of research subjects: a healthy group (K0), periodontitis-induced diabetic group (K1), and periodontitis-induced diabetic group treated with HBOT for 7 days (K2). After treatment, the subjects were sacrificed to determine the level of serum CRP by the ELISA method. Immunohistochemical analysis was conducted to check the level of OPG expression, while a histological analysis was undertaken to quantify the number of osteoclasts.

Statistical Analysis  The data was analyzed using a one-way ANOVA and Least Significant Difference (LSD) test on which a result of p < 0.05 was considered statistically significant.

Results  HBOT appreciably decreased serum CRP levels, significantly enhancing OPG expression in periodontitis-induced diabetic ( p < 0.05) and decreasing the number of osteoclasts in -periodontitis-induced diabetic ( p > 0.05).

Conclusion  HBOT reduced the serum CRP level, increased OPG expression, and decreased osteoclast numbers in periodontitis-induced diabetic rats.

The impact of diabetes on periodontal diseases

The susceptibility and severity of periodontal diseases is made more severe by diabetes, with the impact on the disease process inversely proportional to the level of glycemic control. Although type 1 diabetes mellitus and type 2 diabetes mellitus have different etiologies, and their impact on bone is not identical, they share many of the same complications. Studies in animals and humans agree that both forms of diabetes increase inflammatory events in periodontal tissue, impair new bone formation, and increase expression of RANKL in response to bacterial challenge. High levels of glucose, reactive oxygen species, and advanced glycation end-products are found in the periodontium of diabetic individuals and lead to increased activation of nuclear factor-kappa B and expression of inflammatory cytokines such as tumor necrosis factor and interleukin-1. Studies in animals, moreover, suggest that there are multiple cell types in periodontal tissues that are affected by diabetes, including leukocytes, vascular cells, mesenchymal stem cells, periodontal ligament fibroblasts, osteoblasts, and osteocytes. The etiology of periodontal disease involves the host response to bacterial challenge that is affected by diabetes, which increases the expression of RANKL and reduces coupled bone formation. In addition, the inflammatory response also modifies the oral microbiota to render it more pathogenic, as demonstrated by increased inflammation and bone loss in animals where bacteria are transferred from diabetic donors to germ-free hosts compared with transfer from normoglycemic donors. This approach has the advantage of not relying upon limited knowledge of the specific bacterial taxa to determine pathogenicity, and examines the overall impact of the microbiota rather than the presumed pathogenicity of a few bacterial groups. Thus, animal studies have provided new insights into pathogenic mechanisms that identify cause-and-effect relationships that are difficult to perform in human studies.

Oral supplementation with p-coumaric acid protects mice against diabetes-associated spontaneous destruction of periodontal tissue

OBJECTIVE

Dietary bioactive materials having anti-inflammatory and antioxidant potentials are able to inhibit diabetes-associated periodontal complications. Although numerous studies indicate that administration of p-coumaric acid (p-CA) ameliorates diabetes and diabetes-related complications, the roles of p-CA on periodontal tissue destruction in diabetic mice and the possible mechanisms therein are not completely understood. In this study, we evaluated whether supplementation with p-CA protects mice against diabetes-associated spontaneous periodontal destruction and also explored the associated mechanism therein using in vivo and in vitro experimental systems.

MATERIALS AND METHODS

C57BL/6 male mice were divided into sham, streptozotocin (STZ), and STZ+CA groups (n = 5/group). Sham group was intraperitoneally injected with sodium buffer, whereas other two groups were injected with the buffer containing 160 mg/kg of STZ. STZ-induced diabetic mice received oral gavage with p-CA (50 mg/kg) (STZ+CA group) or with buffer only (STZ group) daily for 6 weeks. The effect of p-CA on diabetes-associated spontaneous periodontal destruction was evaluated using μCT analysis, hematoxylin and eosin staining, tartrate-resistant acid phosphatase staining, and immunohistochemical staining methods. The efficacies of p-CA on cell proliferation, osteoblast differentiation, reactive oxygen species (ROS) accumulation, and antioxidant-related marker expression were examined using human periodontal ligament fibroblasts (hPLFs) cultured under high glucose condition.

RESULTS

Streptozotocin group exhibited periodontal tissue destruction along with increased inflammation, oxidative stress, and osteoclast formation, as well as with decreased osteogenesis. However, oral administration with p-CA protected mice against STZ-induced periodontal destruction by inhibiting inflammation and osteoclastic activation. STZ+CA group also showed higher expression of antioxidant and osteogenic markers in periodontal tissue than did STZ group. Treatment with high glucose concentration (30 mmol/L) impaired proliferation and osteoblast differentiation of hPLFs along with cellular ROS accumulation, whereas these impairments were almost completely disappeared by supplementation with p-CA.

CONCLUSION

These findings demonstrate that supplementation with p-CA inhibits diabetes-associated spontaneous destruction of periodontal tissue by enhancing anti-inflammatory, anti-osteoclastogenic, and antioxidant defense systems in STZ-treated mice.

Succinate and its G-protein-coupled receptor stimulates osteoclastogenesis

The mechanism underlying bone impairment in patients with diabetes mellitus, a metabolic disorder characterized by chronic hyperglycaemia and dysregulation in metabolism, is unclear. Here we show the difference in the metabolomics of bone marrow stromal cells (BMSCs) derived from hyperglycaemic (type 2 diabetes mellitus, T2D) and normoglycaemic mice. One hundred and forty-two metabolites are substantially regulated in BMSCs from T2D mice, with the tricarboxylic acid (TCA) cycle being one of the primary metabolic pathways impaired by hyperglycaemia. Importantly, succinate, an intermediate metabolite in the TCA cycle, is increased by 24-fold in BMSCs from T2D mice. Succinate functions as an extracellular ligand through binding to its specific receptor on osteoclastic lineage cells and stimulates osteoclastogenesis in vitro and in vivo. Strategies targeting the receptor activation inhibit osteoclastogenesis. This study reveals a metabolite-mediated mechanism of osteoclastogenesis modulation that contributes to bone dysregulation in metabolic disorders.

Bone loss is common in patients with diabetes, but the underlying molecular and cellular mechanisms are unclear. Here the authors show high succinate levels in mice with type 2 diabetes and that succinate can signal through succinate receptor 1 on osteoclasts to induce bone resorption.

Deletion of FoxO1, 3, and 4 in Osteoblast Progenitors Attenuates the Loss of Cancellous Bone Mass in a Mouse Model of Type 1 Diabetes

Type 1 diabetes is associated with osteopenia and increased fragility fractures, attributed to reduced bone formation. However, the molecular mechanisms mediating these effects remain unknown. Insulin promotes osteoblast formation and inhibits the activity of the FoxO transcription factors. FoxOs, on the other hand, inhibit osteoprogenitor proliferation and bone formation. Here, we investigated whether FoxOs play a role in the low bone mass associated with type 1 diabetes, using mice lacking FoxO1, 3, and 4 in osteoprogenitor cells (FoxO1,3,4ΔOsx1-Cre ). Streptozotocin-induced diabetes caused a reduction in bone mass and strength in FoxO-intact mice. In contrast, cancellous bone was unaffected in diabetic FoxO1,3,4ΔOsx1-Cre mice. The low bone mass in the FoxO-intact diabetic mice was associated with decreased osteoblast number and bone formation, as well as decreased expression of the anti-osteoclastogenic cytokine osteoprotegerin (OPG) and increased osteoclast number. FoxO deficiency did not alter the effects of diabetes on bone formation; however, it did prevent the decrease in OPG and the increase in osteoclast number. Addition of high glucose to osteoblastic cell cultures decreased OPG mRNA, indicating that hyperglycemia in and of itself contributes to diabetic bone loss. Taken together, these results suggest that FoxOs exacerbate the loss of cancellous bone mass associated with type 1 diabetes and that inactivation of FoxOs might ameliorate the adverse effects of insulin deficiency. © 2016 American Society for Bone and Mineral Research.

A review of the evidence for pathogenic mechanisms that may link periodontitis and diabetes

AIMS

To review the evidence for the molecular and cellular processes that may potentially link periodontal disease and diabetes. The pathogenic roles of cytokines and metabolic molecules (e.g. glucose, lipids) are explored and the role of periodontal bacteria is also addressed. Paradigms for bidirectional relationships between periodontitis and diabetes are discussed and opportunities for elaborating these models are considered.

METHODS

Database searches were performed using MeSH terms, keywords, and title words. Studies were evaluated and summarized in a narrative review.

RESULTS

Periodontal microbiota appears unaltered by diabetes and there is little evidence that it may influence glycaemic control. Small-scale clinical studies and experiments in animal models suggest that IL-1β, TNF-α, IL-6, OPG and RANKL may mediate periodontitis in diabetes. The AGE-RAGE axis is likely an important pathway of tissue destruction and impaired repair in diabetes-associated periodontitis. A role for locally activated pro-inflammatory factors in the periodontium, which subsequently impact on diabetes, remains speculative.

CONCLUSION

There is substantial information on potential mechanistic pathways which support a close association between diabetes and periodontitis, but there is a real need for longitudinal clinical studies using larger patient groups, integrated with studies of animal models and cells/tissues in vitro.

Influence of Type 2 Diabetes on Prevalence of Key Periodontal Pathogens, Salivary Matrix Metalloproteinases, and Bone Remodeling Markers in Sudanese Adults with and without Chronic Periodontitis

This study compared the influence of type 2 diabetes on the occurrence of six periodontal pathogens in plaque samples of patients with and without chronic periodontitis. Levels of salivary MMP-8, MMP-9, RANKL, and OPG were also investigated. The study enrolled 31 patients with type 2 diabetes and chronic periodontitis (DM + CP), 29 with chronic periodontitis (CP), and 20 with type 2 diabetes (DM). Questionnaire-guided interviews were conducted and plaque index, bleeding on probing, and pocket depth were recorded. Polymerase chain reaction (PCR) was utilized to determine the prevalence of the bacteria. The levels of salivary molecules were determined by enzyme immunosorbent assay (ELISA). The CP group had the highest prevalence of P. gingivalis (81.5%), followed by the DM + CP (59.3%) and DM (55.0%) groups (P > 0.05). Similar trends were observed for P. intermedia and T. denticola. The prevalence of T. forsythia was 100% in both periodontitis groups compared to 90% in the DM group. There were no significant differences between the groups regarding the concentrations of MMP-8, MMP-9, or OPG. RANKL concentrations were below the detection limit. Our data show that type 2 diabetes has no significant influence on the prevalence of the investigated periodontal pathogens, or the levels of salivary MMP-8, MMP-9, and OPG.

Effects of Melatonin on Oxidative Stress Index and Alveolar Bone Loss in Diabetic Rats With Periodontitis

BACKGROUND

The aim of this study is to evaluate the effects of systemic melatonin treatment on serum oxidative stress index (OSI) and alveolar bone loss (ABL) in rats with diabetes mellitus (DM) and periodontitis.

METHODS

Seventy Sprague Dawley rats were divided into control, experimentally induced periodontitis (EP), DM, EP-DM, EP and melatonin treatment (EP-MEL), DM and melatonin treatment (DMMEL), and EP-DM-MEL groups. DM was induced by alloxan, after which periodontitis was induced by ligature for 4 weeks. After removal of the ligature, the rats in the melatonin groups (EP-MEL, DM-MEL, and EP-DM-MEL) were treated with a single dose of melatonin (10 mg/body weight) every day for 14 consecutive days. At the end of the study, all of the rats were euthanized, and intracardiac blood samples and mandible tissues were obtained for biochemical and histologic analyses. Serum levels of total oxidant status/total antioxidant status and OSI were measured. In addition, neutrophil and osteoclast densities and myeloperoxidase activities were determined in gingival tissue homogenates, and ABL was evaluated with histometric measurements.

RESULTS

Melatonin treatment significantly reduced fasting plasma glucose levels in the rats with DM. In addition, reduced OSI and ABL levels were detected in the EP-MEL and DM-MEL groups; the reductions in the EP-DM-MEL group were found to be more prominent. Melatonin also significantly decreased the increased myeloperoxidase activities and osteoclast and neutrophil densities in the EP, DM, and EP-DM groups.

CONCLUSION

It is revealed in this experimental study that melatonin significantly inhibited hyperglycemia-induced oxidative stress and ABL through antiDM and antioxidant effects in rats with DM and periodontitis.

Diabetes and Its Effect on Bone and Fracture Healing

Diabetes mellitus is a metabolic disorder that increases fracture risk, interferes with bone formation, and impairs fracture healing. Type 1 diabetes mellitus (T1DM) and type 2 diabetes mellitus (T2DM) both increase fracture risk and have several common features that affect the bone including hyperglycemia and increased advanced glycation end product (AGE) formation, reactive oxygen species (ROS) generation, and inflammation. These factors affect both osteoblasts and osteoclasts leading to increased osteoclasts and reduced numbers of osteoblasts and bone formation. In addition to fracture healing, T1DM and T2DM impair bone formation under conditions of perturbation such as bacteria-induced periodontal bone loss by increasing osteoblast apoptosis and reducing expression of factors that stimulate osteoblasts such as BMPs and growth factors.

Diabetes mellitus related bone metabolism and periodontal disease

Diabetes mellitus and periodontal disease are chronic diseases affecting a large number of populations worldwide. Changed bone metabolism is one of the important long-term complications associated with diabetes mellitus. Alveolar bone loss is one of the main outcomes of periodontitis, and diabetes is among the primary risk factors for periodontal disease. In this review, we summarise the adverse effects of diabetes on the periodontium in periodontitis subjects, focusing on alveolar bone loss. Bone remodelling begins with osteoclasts resorbing bone, followed by new bone formation by osteoblasts in the resorption lacunae. Therefore, we discuss the potential mechanism of diabetes-enhanced bone loss in relation to osteoblasts and osteoclasts.

Effect of β-anhydroicaritin on the expression levels of tumor necrosis factor-α and matrix metalloproteinase-3 in periodontal tissue of diabetic rats

The present study aimed to investigate the effect of β-anhydroicaritin on the expression levels of tumor necrosis factor (TNF)-α and matrix metalloproteinase (MMP)-3, and the pathological changes in the periodontal tissue of diabetic rats. Male Wistar rats (n=40; three months old) were randomly divided into four groups: Normal control group, diabetes group, diabetes + β-anhydroicaritin group and diabetes + urate group, (n=10 in each group). Following an overnight fast, diabetes was induced by intraperitoneal injection of streptozocin. The rats were maintained for 12 weeks and the blood sugar, urine sugar and body weight were assessed in week 12. Histological changes of the periodontal tissues were observed by hematoxylin and eosin staining, and the expression levels of TNF-α and MMP-3 were observed by immunohistochemistry. Following 12 weeks, the TNF-α grey value in the diabetes group was significantly lower compared with that in the control group (P<0.05), while no significant difference was observed between TNF-α levels in the diabetes + β-anhydroicaritin group, diabetes + urate group and the control group (P>0.05). However, TNF-α levels in the diabetes + β-anhdroicaritin group and diabetes + urate group were significantly higher compared with those in the diabetes group (P<0.05), and those in the diabetes + β-anhydroicaritin group were lower compared with those in the diabetes + urate group (P<0.05). The MMP-3 grey value in the diabetes group was significantly lower compared with that in the control group (P<0.05), while no significant difference was observed between MMP-3 levels in the diabetes + β-anhydroicaritin group, diabetes + urate group and the control group (P>0.05). However, MMP-3 levels the diabetes + β-anhydroicaritin group and diabetes + urate group were significantly higher compared with those in the diabetes group (P<0.05), and those in the diabetes + β-anhydroicaritin group were lower compared with those in the diabetes + urate group (P<0.01). β-anhydroicaritin normalized the expression levels of TNF-α and MMP-3 in the periodontal tissue of diabetic rats and led to the recovery of the changes in the morphological structure of the periodontal tissue.

Type 1 diabetes and osteoporosis: from molecular pathways to bone phenotype

The link between type 1 diabetes mellitus (DM1) and osteoporosis, identified decades ago, has gained attention in recent years. While a number of cellular mechanisms have been postulated to mediate this association, it is now established that defects in osteoblast differentiation and activity are the main culprits underlying bone fragility in DM1. Other contributing factors include an accumulation of advanced glycation end products (AGEs) and the development of diabetes complications (such as neuropathy and hypoglycemia), which cause further decline in bone mineral density (BMD), worsening geometric properties within bone, and increased fall risk. As a result, patients with DM1 have a 6.9-fold increased incidence of hip fracture compared to controls. Despite this increased fracture risk, bone fragility remains an underappreciated complication of DM1 and is not addressed in most diabetes guidelines. There is also a lack of data regarding the efficacy of therapeutic strategies to treat osteoporosis in this patient population. Together, our current understanding of bone fragility in DM1 calls for an update of diabetes guidelines, better screening tools, and further research into the use of therapeutic strategies in this patient population.

Periodontitis: oral complication of diabetes

Periodontitis is a common, chronic, inflammatory disease in which the supporting apparatus of the teeth is gradually destroyed, resulting in tooth mobility and tooth loss. Susceptibility to periodontitis is increased approximately three-fold in people with diabetes. Hyperglycemia leads to exacerbated tissue destruction and the clinical signs of periodontitis. There is evidence to support a two-way relationship between periodontitis and diabetes; not only does diabetes increase the risk for periodontitis, but periodontitis is associated with compromised glycemic control. Cooperation between health care teams would benefit the treatment of patients with diabetes and periodontitis.