Is Diabetic Skeletal Fragility Associated with Microvascular Complications in Bone?

Microvascular permeability and texture analysis of bone marrow in diabetic rabbits with critical limb ischemia based on dynamic contrast-enhanced magnetic resonance imaging

BACKGROUND

Early on in the development of diabetes, skeletal muscles can exhibit microarchitectural changes that can be detected using texture analysis (TA) based on volume transfer constant (Ktrans) maps. Nevertheless, there have been few studies and thus we evaluated microvascular permeability and the TA of the bone marrow in diabetics with critical limb ischemia (CLI).

METHODS

Eighteen male rabbits were randomly assigned equally into an operation group with hindlimb ischemia and diabetes, a sham-operated group with diabetes only, and a control group. Dynamic contrast enhanced magnetic resonance imaging (DCE-MRI) was performed on all rabbits at predetermined intervals (1, 5, 10, 15, 20, and 25 days post-surgery). The pharmacokinetic model was used to generate the permeability parameters, while the textural parameters were derived from the Ktrans map. Data analysis methods included the independent sample t-test, Mann-Whitney U test, repeated-measures analysis of variance, and Pearson correlation tests.

RESULTS

The Ktrans values reached a minimum on day 1 after ischemia induction, then gradually recovered, but remained lower than those of the sham-operated group. The volume fraction only showed a significant difference between the operation group and the sham-operated group on day 5 post-surgery, but not in the extravascular extracellular space volume fraction at all time points. A significantly reduced Ktrans on day 1, a decreased number of bone trabeculae (Tb.N), and the area of bone trabeculae (Tb.Ar), and an increased microvessel density on day 25 in the operation group compared with the sham-operated group were observed. At each time point, there was a discernible difference between the two groups in the mean value, mean of positive pixels, and sumAverage.

CONCLUSIONS

The early stages of diabetic bone marrow with CLI can be evaluated by DCE-MRI for microvascular permeability. Texture analysis based on DCE-MRI could act as an imaging discriminator and new radiological analysis tool for critical limb ischemia in diabetes mellitus.

LOX-1 regulation of H-type vascular endothelial cell regeneration in hyperglycemia

AIMS

Diabetic osteoporosis (DOP) is the most common secondary form of osteoporosis. Diabetes mellitus affects bone metabolism; however, the underlying pathophysiological mechanisms remain unclear. Lectin-like oxidized low-density lipoprotein receptor-1 (LOX-1) expression is upregulated in conditions characterized by vascular injury, such as atherosclerosis, hypertension, and diabetes. Additionally, Notch, HIF-1α, and VEGF are involved in angiogenesis and bone formation. Therefore, we aimed to investigate the expression of Notch, HIF-1α, and VEGF in the LOX-1 silencing state.

METHODS

Rat bone H-type vascular endothelial cells (THVECs) were isolated and cultured in vitro. Cell identification was performed using immunofluorescent co-expression of CD31 and Emcn. Lentiviral silencing vector (LV-LOX-1) targeting LOX-1 was constructed using genetic recombination technology and transfected into the cells. The experimental groups included the following: NC group, HG group, LV-LOX-1 group, LV-CON group, HG + LV-LOX-1 group, HG + LV-CON group, HG + LV-LOX-1 + FLI-06 group, HG + LV-CON + FLI-06 group, HG + LV-LOX-1 + LW6 group, and HG + LV-CON + LW6 group. The levels of LOX-1, Notch, Hif-1α, and VEGF were detected using PCR and WB techniques to investigate whether the expression of LOX-1 under high glucose conditions has a regulatory effect on downstream molecules at the gene and protein levels, as well as the specific molecular mechanisms involved.

RESULTS

High glucose (HG) conditions led to a significant increase in LOX-1 expression, leading to inhibition of angiogenesis, whereas silencing LOX-1 can reverse this phenomenon. Further analysis reveals that changes in LOX-1 will promote changes in Notch/HIF-1α and VEGF. Moreover, Notch mediates the activation of HIF-1α and VEGF.

CONCLUSIONS

The activation of LOX-1 and the inhibition of Notch/HIF-1α/VEGF in THVECs are the main causes of DOP. These findings contribute to our understanding of the pathogenesis of DOP and offer a novel approach for preventing and treating osteoporosis.

Diabetes and the Microvasculature of the Bone and Marrow

PURPOSE OF REVIEW

The purpose of this review is to highlight the evidence of microvascular dysfunction in bone and marrow and its relation to poor skeletal outcomes in diabetes mellitus.

RECENT FINDINGS

Diabetes mellitus is characterized by chronic hyperglycemia, which may lead to microangiopathy and macroangiopathy. Micro- and macroangiopathy have been diagnosed in Type 1 and Type 2 diabetes, coinciding with osteopenia, osteoporosis, enhanced fracture risk and delayed fracture healing. Microangiopathy has been reported in the skeleton, correlating with reduced blood flow and perfusion, vasomotor dysfunction, microvascular rarefaction, reduced angiogenic capabilities, and augmented vascular permeability. Microangiopathy within the skeleton may be detrimental to bone and manifest as, among other clinical abnormalities, reduced mass, enhanced fracture risk, and delayed fracture healing. More investigations are required to elucidate the various mechanisms by which diabetic microvascular dysfunction impacts the skeleton.

Diabetic microvascular disease in non-classical beds: the hidden impact beyond the retina, the kidney, and the peripheral nerves

Diabetes microangiopathy, a hallmark complication of diabetes, is characterised by structural and functional abnormalities within the intricate network of microvessels beyond well-known and documented target organs, i.e., the retina, kidney, and peripheral nerves. Indeed, an intact microvascular bed is crucial for preserving each organ's specific functions and achieving physiological balance to meet their respective metabolic demands. Therefore, diabetes-related microvascular dysfunction leads to widespread multiorgan consequences in still-overlooked non-traditional target organs such as the brain, the lung, the bone tissue, the skin, the arterial wall, the heart, or the musculoskeletal system. All these organs are vulnerable to the physiopathological mechanisms that cause microvascular damage in diabetes (i.e., hyperglycaemia-induced oxidative stress, inflammation, and endothelial dysfunction) and collectively contribute to abnormalities in the microvessels' structure and function, compromising blood flow and tissue perfusion. However, the microcirculatory networks differ between organs due to variations in haemodynamic, vascular architecture, and affected cells, resulting in a spectrum of clinical presentations. The aim of this review is to focus on the multifaceted nature of microvascular impairment in diabetes through available evidence of specific consequences in often overlooked organs. A better understanding of diabetes microangiopathy in non-target organs provides a broader perspective on the systemic nature of the disease, underscoring the importance of recognising the comprehensive range of complications beyond the classic target sites.

Vascular deficits contributing to skeletal fragility in type 1 diabetes

Over 1 million Americans are currently living with T1D and improvements in diabetes management have increased the number of adults with T1D living into later decades of life. This growing population of older adults with diabetes is more susceptible to aging comorbidities, including both vascular disease and osteoporosis. Indeed, adults with T1D have a 2- to 3- fold higher risk of any fracture and up to 7-fold higher risk of hip fracture compared to those without diabetes. Recently, diabetes-related vascular deficits have emerged as potential risks factors for impaired bone blood flow and poor bone health and it has been hypothesized that there is a direct pathophysiologic link between vascular disease and skeletal outcomes in T1D. Indeed, microvascular disease (MVD), one of the most serious consequences of diabetes, has been linked to worse bone microarchitecture in older adults with T1D compared to their counterparts without MVD. The association between the presence of microvascular complications and compromised bone microarchitecture indicates the potential direct deleterious effect of vascular compromise, leading to abnormal skeletal blood flow, altered bone remodeling, and deficits in bone structure. In addition, vascular diabetic complications are characterized by increased vascular calcification, decreased arterial distensibility, and vascular remodeling with increased arterial stiffness and thickness of the vessel walls. These extensive alterations in vascular structure lead to impaired myogenic control and reduced nitric-oxide mediated vasodilation, compromising regulation of blood flow across almost all vascular beds and significantly restricting skeletal muscle blood flow seen in those with T1D. Vascular deficits in T1D may very well extend to bone, compromising skeletal blood flow control, and resulting in reduced blood flow to bone, thus negatively impacting bone health. Indeed, several animal and ex vivo human studies report that diabetes induces microvascular damage within bone are strongly correlated with diabetes disease severity and duration. In this review article, we will discuss the contribution of diabetes-induced vascular deficits to bone density, bone microarchitecture, and bone blood flow regulation, and review the potential contribution of vascular disease to skeletal fragility in T1D.

Bone Mineral Density Evaluation Among Type 2 Diabetic Patients in Rural Haryana, India: An Analytical Cross-Sectional Study

Background and objective Diabetes is one of the most prevalent diseases globally, affecting almost all organ systems. The relationship between type 2 diabetes mellitus (T2DM) and bone mineral density (BMD) has been a matter of controversy, and data from developing countries in this regard is highly scarce. Early detection of low BMD in diabetic patients will help prevent further bone loss and risk of fragility fracture. In this study, we aimed to assess the effect of T2DM on BMD among the rural population of Haryana, India. Materials and methods This was a cross-sectional study involving 850 patients between 25 and 60 years of age, including 425 diabetic and 425 non-diabetic subjects (as controls). Calcaneus BMD was measured by using quantitative ultrasound (QUS), and the data were compared against matched parameters in both groups. Results The mean age of diabetics was 42.21 ± 10.5 years and that of non-diabetics was 42.18 ± 10.4 years. The mean BMI was 27.8 ± 4.17 kg/m2 in diabetics and 21.6 ± 3.32 kg/m2 in the non-diabetic control group. BMD values significantly differed between the groups: -4.3 ± 1.23 vs. -2.6 ± 0.34 in diabetics and non-diabetics, respectively (p=0.002). Conclusion A significant difference in BMD was observed between the diabetic and non-diabetic groups. Based on our findings, We recommend that all type 2 diabetics be screened for osteoporosis so that this silent bone loss can be detected in the early phase itself and appropriate preventive measures can be promptly initiated.

Biochemical Markers of Bone Fragility in Patients with Diabetes. A Narrative Review by the IOF and the ECTS

CONTEXT

The risk of fragility fractures is increased in both type 1 and type 2 diabetes. Numerous biochemical markers reflecting bone and/or glucose metabolism have been evaluated in this context. This review summarizes current data on biochemical markers in relation to bone fragility and fracture risk in diabetes.

METHODS

Literature review by a group of experts from the International Osteoporosis Foundation (IOF) and European Calcified Tissue Society (ECTS) focusing on biochemical markers, diabetes, diabetes treatments and bone in adults.

RESULTS

Although bone resorption and bone formation markers are low and poorly predictive of fracture risk in diabetes, osteoporosis drugs seem to change bone turnover markers in diabetics similarly to non-diabetics, with similar reductions in fracture risk. Several other biochemical markers related to bone and glucose metabolism have been correlated with BMD and/or fracture risk in diabetes, including osteocyte-related markers such as sclerostin, HbA1c and advanced glycation end products (AGEs), inflammatory markers and adipokines, as well as IGF-1 and calciotropic hormones.

CONCLUSION

Several biochemical markers and hormonal levels related to bone and/or glucose metabolism have been associated with skeletal parameters in diabetes. Currently, only HbA1c levels seem to provide a reliable estimate of fracture risk, while bone turnover markers could be used to monitor the effects of anti-osteoporosis therapy.

Ginsenoside Rg1 interferes with the progression of diabetic osteoporosis by promoting type H angiogenesis modulating vasculogenic and osteogenic coupling

Ginsenoside Rg1 (Rg1) has been demonstrated to have antidiabetic and antiosteoporotic activities. The aim of this study was to investigate the protective effect of Rg1 against diabetic osteoporosis and the underlying mechanism. In vitro, we found that Rg1 increased the number of osteoprogenitors and alleviated high glucose (HG) induced apoptosis of osteoprogenitors by MTT assays and flow cytometry. qRT‒PCR and western blot analysis suggested that Rg1 can also promote the secretion of vascular endothelial growth factor (VEGF) by osteoprogenitors and promote the coupling of osteogenesis and angiogenesis. Rg1 can also promote the proliferation of human umbilical vein endothelial cells (HUVECs) cultured in high glucose, enhance the angiogenic ability of endothelial cells, and activate the Notch pathway to promote endothelial cells to secrete the osteogenesis-related factor Noggin to regulate osteogenesis, providing further feedback coupling of angiogenesis and osteogenesis. Therefore, we speculated that Rg1 may have similar effects on type H vessels. We used the Goto-Kakizaki (GK) rat model to perform immunofluorescence staining analysis on two markers of type H vessels, Endomucin (Emcn) and CD31, and the osteoblast-specific transcription factor Osterix, and found that Rg1 stimulates type H angiogenesis and bone formation. In vivo experiments also demonstrated that Rg1 promotes VEGF secretion, activates the Noggin/Notch pathway, increases the level of coupling between type H vessels and osteogenesis, and improves the bone structure of GK rats. All of these data reveal that Rg1 is a promising candidate drug for treating diabetic osteoporosis as a potentially bioactive molecule that promotes angiogenesis and osteointegration coupling.

Secondary Osteoporosis

Osteoporosis is a global public health problem, with fractures contributing to significant morbidity and mortality. Although postmenopausal osteoporosis is most common, up to 30% of postmenopausal women, > 50% of premenopausal women, and between 50% and 80% of men have secondary osteoporosis. Exclusion of secondary causes is important, as treatment of such patients often commences by treating the underlying condition. These are varied but often neglected, ranging from endocrine to chronic inflammatory and genetic conditions. General screening is recommended for all patients with osteoporosis, with advanced investigations reserved for premenopausal women and men aged < 50 years, for older patients in whom classical risk factors for osteoporosis are absent, and for all patients with the lowest bone mass (Z-score ≤ -2). The response of secondary osteoporosis to conventional anti-osteoporosis therapy may be inadequate if the underlying condition is unrecognized and untreated. Bone densitometry, using dual-energy x-ray absorptiometry, may underestimate fracture risk in some chronic diseases, including glucocorticoid-induced osteoporosis, type 2 diabetes, and obesity, and may overestimate fracture risk in others (eg, Turner syndrome). FRAX and trabecular bone score may provide additional information regarding fracture risk in secondary osteoporosis, but their use is limited to adults aged ≥ 40 years and ≥ 50 years, respectively. In addition, FRAX requires adjustment in some chronic conditions, such as glucocorticoid use, type 2 diabetes, and HIV. In most conditions, evidence for antiresorptive or anabolic therapy is limited to increases in bone mass. Current osteoporosis management guidelines also neglect secondary osteoporosis and these existing evidence gaps are discussed.

Marantodes pumilum (blume) Kuntze (Kacip Fatimah) leaves aqueous extract prevents downregulation of Wnt/β-catenin pathway and upregulation of apoptosis in osteoblasts of estrogen-deficient, diabetes-induced rats

ETHNOPHARMACOLOGICAL RELEVANCE

Marantodes pumilum (Blume) Kuntze has been claimed to be beneficial in protecting the bone against loss in post-menopausal women. In view of increased incidence of diabetes mellitus (DM) in post-menopausal period, M. pumilum ability to overcome the detrimental effect of estrogen-deficiency and DM on the bones were identified.

AIM OF THE STUDY

To identify the mechanisms underlying protective effect of MPLA on the bone in estrogen-deficient, diabetic condition.

METHODS

Adult female, estrogen-deficient, diabetic rats (225 ± 10 g) were divided into untreated group and treated with M. pumilum leaf aqueous extract (MPLA) (50 mg/kg/day and 100 mg/kg/day) and estrogen for 28 days (n = 6 per group). Fasting blood glucose (FBG) levels were weekly monitored and at the end of treatment, rats were sacrificed and femur bones were harvested. Bone collagen distribution was observed by Masson's trichome staining. Levels of bone osteoblastogenesis, apoptosis and proliferative markers were evaluated by Realtime PCR, Western blotting, immunofluorescence and immunohistochemistry.

RESULTS

MPLA treatment was able to ameliorate the increased in FBG levels in estrogen deficient, diabetic rats. In these rats, decreased bone collagen content, expression level of osteoblastogenesis markers (Wnt3a, β-catenin, Frizzled, Dvl and LRP-5) and proliferative markers (PCNA and c-Myc) and increased expression of anti-osteoblastogenesis marker (Gsk-3β) and apoptosis markers (Caspase-3, Caspase-9 and Bax) but not Bcl-2 were ameliorated. Effects of 100 mg/kg/day MPLA were greater than estrogen.

CONCLUSION

MPLA was able to protect against bone loss, thus making it a promising agent for the treatment of osteoporosis in women with estrogen deficient, diabetic condition.

Influence of glycemic control and hypoglycemia on the risk of fracture in patients with diabetes mellitus: a systematic review and meta-analysis of observational studies

Individuals with diabetes mellitus (DM) have an increased risk of fracture. Glycemic control is crucial to the management of DM, but there are concerns pertaining to hypoglycemia development in the course of glycemic control target achievement. The extent to which glycemic control may affect the risk of fracture remains less defined. Hypoglycemia-induced falls have been suggested to contribute to an elevated risk of fracture in DM patients. In this meta-analysis of observational studies, we aimed to investigate the relative contribution of glycemic control, as measured by glycated hemoglobin (HbA1c), and hypoglycemia to the risk of fracture in DM. The PubMed and Web of Science databases were searched for relevant studies. A random-effects model was used to generate summary relative risks (RRs) and 95% confidence intervals (CIs). Both increased HbA1c levels (RR _{per 1% increase} 1.08, 95% CI 1.03, 1.14; n_studies = 10) and hypoglycemia (RR 1.52, 95% CI 1.23, 1.88; n_studies = 8) were associated with an increased risk of fracture. The association between HbA1c levels and the risk of fracture was somewhat nonlinear, with a noticeably increased risk observed at an HbA1c level ≥ 8%. The positive associations of HbA1c levels and hypoglycemia with the risk of fracture did not reach statistical significance in the studies that adjusted for insulin use, hypoglycemia, or falls for the former and in those that adjusted for falls for the latter. In summary, both increased HbA1c levels and hypoglycemia may increase the risk of fracture in patients with DM. The positive association between HbA1c levels and the risk of fracture appears to be, in part, explained by hypoglycemia-induced falls, possibly due to insulin use. The avoidance of hypoglycemia in the course of achieving good glycemic control through the careful selection of glucose-lowering medications may contribute to fracture prevention by reducing the risk of falls related to treatment-induced hypoglycemia.

Bone Marrow Adiposity in Premenopausal Women With Type 2 Diabetes With Observations on Peri-Trabecular Adipocytes

CONTEXT

No study has yet evaluated the relationships among bone marrow adiposity (BMA), bone histomorphometry (BH), and glycemic control in premenopausal women with type 2 diabetes (T2DM).

OBJECTIVE

We aimed to assess the effect of glycemic control on BMA, correlate the parameters of BH with BMA, and correlate BMA with the use of hypoglycemic agents and with bone mineral density (BMD).

METHODS

This was a cross-sectional study that evaluated 26 premenopausal women with T2DM who were divided into groups with HbA1c < 7% (good control [GC], n = 10) and HbA1c > 7% (poor control [PC], n = 16). BMA parameters (adipocyte number [Ad.N], total adipocyte perimeter [Ad.Pm], total adipocyte area [Ad.Ar], percentage adipocyte volume per marrow volume [Ad.V/Ma.V]) and peri-trabecular adipocyte number divided by bone surface (Ad.N/BS) were evaluated. BH static (bone volume fraction [BV/TV], osteoid thickness [O.Th], osteoid surface/bone surface [OS/BS]) and dynamic parameters and serum insulin-like growth factor-1 were measured. BMA data were compared between the GC and PC groups. Correlations were performed.

RESULTS

Ad.N, Ad.Pm, and Ad.Ar were higher in PC (all, P = 0.04). HbA1c correlated positively with Ad.N/BS (P < 0.01) and Ad.N/BS correlated negatively with O.Th (P < 0.01) and OS/BS (P = 0.02). Positive and negative correlations were observed between insulin and metformin use, respectively, with all adipocyte parameters except Ad.N/BS (P < 0.05). Structural parameters were negatively correlated with the BMA. BMD of the femoral neck (r = -549, P < 0.01) and total femur (r = -0.502, P < 0.01) were negatively correlated with Ad.V/Ma.V.

CONCLUSION

Poor glycemic control is associated with hyperplasia and hypertrophy of BMAs and with lower BV/TV. Ad.N/BS, a new BMA parameter, is correlated with HbA1c and negatively with O.Th. The use of insulin seems to stimulate the expansion of BMA while that of metformin has the opposite effect. These findings suggest that the increase in BMA may play a role in the T2DM bone disease; on the other hand, good glycemic control might help prevent it.

Trabecular bone score and 25-hydroxyvitamin D levels in microvascular complications of type 2 diabetes mellitus

BACKGROUND AND OBJECTIVE

Diabetic microvascular disease (MVD) has been associated with increased bone fragility. The objective was to analyse the relationship between MVD and trabecular microstructure -assessed by the trabecular bone score (TBS)- in type 2 diabetic (T2D) patients. A second aim was to know the relationship between vitamin D and MVD.

PATIENTS AND METHODS

Cross-sectional study, which included men >50 years and postmenopausal women participating in a population-based cohort, diagnosed with T2D. The presence of nephropathy, neuropathy and/or retinopathy was classified as MVD+. Clinical and laboratory variables, TBS, 25(OH)D and BMD by DXA, were evaluated. Bivariate and multivariate analysis were performed.

RESULTS

We evaluated 361 patients (51.1% women), 63.8 (9) years old. Of them, 92 were MVD+ and presented poorer metabolic control, longer duration of T2D, lower TBS [1.235 (.1) vs. 1.287 (.1); p=.007] and lower levels of 25(OH)D [18.3 (7) vs. 21.6 (8) ng/ml; p=.0001). There were no differences between MVD+ and MVD- with regard to BMD or P1NP and β-CTX markers. After adjusting for confounders, including HbA1c and duration of T2D, the TBS value in MVD+ was 1.252 (95% CI 1.230-1.274) vs. 1.281 (95% CI 1.267-1.295) in MVD- (p=.034). MVD was associated with a 25(OH)D level <20 ng ml with an adjusted OR of 1.88 (95% CI 1.06-3.31; p=.028).

CONCLUSIONS

The MVD+ patients presented a significantly lower TBS, after adjusting for confounders. Furthermore, multivariable analysis showed a significant relationship between a low 25(OH)D level and a prevalent MVD.

Impairment of type H vessels by NOX2-mediated endothelial oxidative stress: critical mechanisms and therapeutic targets for bone fragility in streptozotocin-induced type 1 diabetic mice

Rationale: Mechanisms underlying the compromised bone formation in type 1 diabetes mellitus (T1DM), which causes bone fragility and frequent fractures, remain poorly understood. Recent advances in organ-specific vascular endothelial cells (ECs) identify type H blood vessel injury in the bone, which actively direct osteogenesis, as a possible player.

Methods: T1DM was induced in mice by streptozotocin (STZ) injection in two severity degrees. Bony endothelium, the coupling of angiogenesis and osteogenesis, and bone mass quality were evaluated. Insulin, antioxidants, and NADPH oxidase (NOX) inhibitors were administered to diabetic animals to investigate possible mechanisms and design therapeutic strategies.

Results: T1DM in mice led to the holistic abnormality of the vascular system in the bone, especially type H vessels, resulting in the uncoupling of angiogenesis and osteogenesis and inhibition of bone formation. The severity of osteopathy was positively related to glycemic levels. These pathological changes were attenuated by early-started, but not late-started, insulin therapy. ECs in diabetic bones showed significantly higher levels of reactive oxygen species (ROS) and NOX 1 and 2. Impairments of bone vessels and bone mass were effectively ameliorated by treatment with anti-oxidants or NOX2 inhibitors, but not by a NOX1/4 inhibitor. GSK2795039 (GSK), a NOX2 inhibitor, significantly supplemented the insulin effect on the diabetic bone.

Conclusions: Diabetic osteopathy could be a chronic microvascular complication of T1DM. The impairment of type H vessels by NOX2-mediated endothelial oxidative stress might be an important contributor that can serve as a therapeutic target for T1DM-induced osteopathy.

Impact of Type 2 Diabetes Mellitus and Antidiabetic Medications on Bone Metabolism

PURPOSE OF REVIEW

This review focuses on the complex interactions between hyperglycemia and bone fragility and the effects of antidiabetic medications on bone metabolism.

RECENT FINDINGS

Type 2 diabetes (T2D) is associated with increased risk of bone fracture even in those with increased or normal bone mineral density (BMD). The pathophysiology of diabetic bone disease is not completely understood, but it is thought to be multifactorial and associated with complex cross talk among factors such as AGEs, IGF-1, enteric hormones, and pro-inflammatory cytokines. Treatment for T2D may have an impact on bone metabolism. Diabetic bone disease should be considered a serious complication of long-standing T2D.

Obesity/Metabolic Syndrome and Diabetes Mellitus on Peri-implantitis

Literature has reported that up to 50% of dental implants may be affected by peri-implantitis, a bacteria-induced chronic inflammatory process, which promotes osteoclast-mediated bone resorption and inhibits bone formation, leading to progressive bone loss around implants. Current evidence points toward an increased risk for the development of peri-implantitis in both obesity/metabolic syndrome (MetS) and diabetes mellitus (DM) conditions relative to the healthy population. Currently, there is no effective treatment for peri-implantitis and the 50% prevalence in MetS and DM, along with its predicted increase in the worldwide population, presents a major concern in implant dentistry as hyperglycemic conditions are associated with bone-healing impairment; this may be through dysfunction of osteocalcin-induced glucose metabolism. The MetS/DM proinflammatory systemic condition and altered immune/microbiome response affect both catabolic and anabolic events of bone-healing that include increased osteoclastogenesis and compromised osteoblast activity, which could be explained by the dysfunction of insulin receptor that led to activation of signals related with osteoblast differentiation. Furthermore, chronic hyperglycemia along with associated micro- and macro-vascular ailments leads to delayed/impaired wound healing due to activation of pathways that are particularly important in initiating events linked to inflammation, oxidative stress, and cell apoptosis; this may be through deactivation of AKT/PKB protein, which possesses a pivotal role in drive survival and eNOS signaling. This review presents an overview of the local and systemic mechanisms synergistically affecting bone-healing impairment in MetS/DM individuals, as well as a rationale for hierarchical animal model selection, in an effort to characterize peri-implantitis disease and treatment.

Is the cortical capillary renamed as the transcortical vessel in diaphyseal vascularity?

A recent article published in Nature Metabolism, "A network of trans-cortical capillaries as a mainstay for blood circulation in long bones," explained the long bone vascularity. In the mouse model, the authors demonstrated hundreds of transcortical vessels (TCVs) commencing from the bone marrow and traversing the whole cortical thickness. They realized that TCVs were the same as bleeding vessels of periosteal bed observed in the human tibia and femoral epiphysis during surgery. TCVs expressed arterial or venous markers and were proposed to be the backbone of bone vascularity as 80% of arterial and 59% of venous blood distributed through them. This new evidence challenged the existence of the "cortical capillaries" stated in previous literature. We conducted a review of the existing literature to compare this model with those in earlier research. The bone vascularity model was explained by many researchers who did their work in animal models like pig, dog, rabbit, and mouse. The TCVs were identified in these animal model studies as cortical capillaries or vessels of cortical canals. Studies are scarce, showing the presence of TCVs in humans. The role of TCVs in human cortical vascularity remains ambiguous until the substantial evidence is collected in future studies.

Bone Histomorphometry in Young Patients With Type 2 Diabetes is Affected by Disease Control and Chronic Complications

CONTEXT

Type 2 diabetes mellitus (T2DM) is associated with an increased risk of fractures. No study has evaluated the correlation of bone histomorphometry (BH) parameters with glycemic control and presence of chronic complications (CCs) in premenopausal women with T2DM.

OBJECTIVES

To evaluate BH and correlate them with the degree of glycemic control and presence of CCs.

DESIGN, SETTINGS, AND PATIENTS

This was a cross-sectional study conducted at a tertiary medical center. Twenty-six premenopausal women with T2DM were divided into groups with glycated hemoglobin HbA1c < 7% (good control, GC; n = 10) and HbA1c > 7% (poor control, PC; n = 16), and further subdivided into groups with (n = 9) and without (n = 17) CCs. BH parameters (bone volume [bone volume per total volume, BV/TV], trabecular thickness [Tb.Th], trabecular number [Tb.N], trabecular separation [Tb.Sp], osteoid thickness [O.Th], osteoid surface [osteoid surface per bone surface, OS/BS]), mineralizing surface [MS/BS], bone formation rate [BFR]), mineral apposition rate [MAR]) as well as serum pentosidine (PEN) and insulin-like growth factor (IGF)-1 were measured. The BH data were compared among the groups and with a BH control group (control group, CG, n = 15) matched by age, sex, and race.

RESULTS

BV/TV was increased in GC (P < .001) and PC (P = .05) groups and O.th (P = .03) was smaller in the PC group than in the CG. A comparison of the groups with and without CCs with the CG showed in the group with CCs, O.Th was smaller(P = .01) and BV/TV similar to the CG (P = .11). HbA1c correlated negatively with O.Th (P = .02) and OS/BS (P = .01). There was no correlation of BH to PEN and IGF-1.

CONCLUSION

BH in premenopausal patients with T2DM is affected by disease control and chronic complications.

Osteoprotegerin in diabetic osteopathy

AIM

The aim of this study is to evaluate the relationship between OPG and the degree of glycaemic control in a population of elderly subjects.

METHODS AND RESULTS

Data presented included 172 elderly subjects, of whom 107 were hospitalized for a hip fracture and 65 were non fractured outpatients. All participants received a multidimensional geriatric evaluation and underwent blood sampling. HbA1c, OPG, CTX and OC were measured and DXA scans were performed. Carotid intima-media thickness (IMT) was measured in all outpatients. Diabetic patients had more comorbidities, higher mean values of lumbar spine and femoral neck BMD and T-score, lower circulating levels of OC and CTX, and higher circulating levels of OPG compared to non-diabetic subjects. OPG was directly correlated with HbA1c. This association was most evident in non-fractured elderly subjects. Moreover, diabetic patients with IMT>1.5 mm had greater mean values of OPG than non-diabetic subjects with high IMT and than elderly subjects with IMT < 1.5 mm, with and without T2DM.

CONCLUSIONS

Diabetic patients have reduced circulating levels of OC and CTX, and elevated serum levels of OPG, suggesting a state of low bone turnover. Reduced bone turnover causes an increase of BMD and could lead to a poor bone quality. OPG and HbA1c were directly correlated and OPG mean values were higher in diabetic patients with poor glucose control. Diabetic osteopathy could be considered a late complication of T2DM, directly related with the degree of glucose control and the duration of the disease.

Is Retinal Microvascular Abnormalities an Independent Risk Factor of Vertebral Fractures? A Prospective Study From a Chinese Population

Low bone mineral density (BMD) and microvascular diseases (MVD) share various common risk factors; however, whether MVD is an independent risk factor of vertebral fractures is incompletely understood. The aim of this study is to clarify whether MVD is an independent risk factor of vertebral fractures. In this prospective study, calcaneal BMD and retinal microvascular abnormalities were assessed at baseline from June 2011 to January 2012. A total of 2176 premenopausal women, 2633 postmenopausal women, 2998 men aged <65 years, and 737 men aged ≥65 were included. Then with/without retinal microvascular abnormalities cohorts were followed for an average of 2.93 years to find out the relationship between MVD and vertebral fractures. At the baseline, after full adjustment, retinal microvascular abnormalities were related to risk of low BMD only in men aged ≥65 years (odds ratio [OR] = 2.506; 95% confidence interval [CI] 1.454–4.321; p = 0.001). After follow‐up of 2.93 years, retinal microvascular abnormalities were related to risk of vertebral fractures in men aged ≥65 years (OR = 2.475; 95% CI 1.085–5.646; p = 0.031) when adjustment for confounding factors. However, no associations were found between MVD and vertebral fractures in men aged <65 years, premenopausal women, and postmenopausal women. When stratified by diabetes, in the without‐diabetes group, the men with retinal microvascular abnormalities had higher risk for vertebral fractures than without retinopathy (OR = 2.194; 95% CI 1.097–4.389; p = 0.026); however, the difference was not found in women. In the diabetes group, there were no significant differences of risk for vertebral fractures between those with retinal microvascular abnormalities and those without both in men and women. Stratified by hypertension, the men with retinopathy had higher risk for vertebral fractures than those without among the hypertension group (OR = 2.034; 95% CI 1.163–3.559; p = 0.013), but a difference was not found among women. In the without‐hypertension group, no relation was found between MVD and fracture both in men and women. In conclusion, MVD is an independent risk factor of vertebral fractures in old men. © 2017 The Authors. JBMR Plus is published by Wiley Periodicals, Inc. on behalf of the American Society for Bone and Mineral Research.

Angiogenesis impairment by the NADPH oxidase-triggered oxidative stress at the bone-implant interface: Critical mechanisms and therapeutic targets for implant failure under hyperglycemic conditions in diabetes

Mechanism underlying the diabetes-induced poor osteointegration of implants remains elusive, making it a challenge to develop corresponding solutions. Here, we studied the role of angiogenesis in the diabetes-induced poor bone repair at the bone-implant interface (BII) and the related mechanisms. In vivo, titanium screws were implanted in the femurs of mice, and, in vitro, vascular endothelial cell (VEC) was cultured on titanium surface. Results showed that, compared with normal milieu (NM), diabetic milieu (DM) led to angiogenesis inhibition around implants which resulted in reduced osteoprogenitors and poor bone formation on BII in vivo. In vitro, DM caused significant increase of NADPH oxidases (NOX), dysfunction of mitochondria and overproduction of reactive oxygen species (ROS) in VEC on titanium surface, inducing obvious cell dysfunction. Both Mito-TEMPO (Mito, a mitochondria-targeted ROS antagonist) and apocynin (APO, a NOX inhibitor) effectively attenuated the oxidative stress and dysfunction of VEC, with the beneficial effects of APO significantly better than those of Mito. Further study showed that the diabetes-induced metabolic disturbance of VEC was significantly related to the increase of advanced glycation end products (AGEs) at the BII. Our results suggested that the AGEs-related and NOX-triggered cellular oxidative stress leads to VEC dysfunction and angiogenesis impairment at the BII, which plays a critical role in the compromised implant osteointegration under diabetic conditions. These demonstrated new insights into the BII in pathological states and also provided NOX and AGEs as promising therapeutic targets for developing novel implant materials to accelerate the angiogenesis and osteointegration of implants in diabetic patients with hyperglycemia.

STATEMENT OF SIGNIFICANCE

The high failure rate of bone implants in diabetic patients causes patients terrible pain and limits the clinical application of implant materials. The mechanism underlying this phenomenon needs elucidation so that it would be possible to develop corresponding solutions. Our study demonstrated that the AGEs-related and NOX-triggered oxidative stress of VEC leads to angiogenesis impairment at the bone-implant interface (BII) in diabetes. These are critical mechanisms underlying the compromised implant osteointegration in diabetic hyperglycemia. These provide new insights into the BII in diseased states and also suggest NOX and AGEs as crucial therapeutic targets for developing novel implant materials which could modulate the oxidative stress on BII to get improved osteointegration and reduced implant failure, especially in diabetic patients.

Novel skeletal effects of glucagon-like peptide-1 (GLP-1) receptor agonists

Type 2 diabetes mellitus (T2DM) leads to bone fragility and predisposes to increased risk of fracture, poor bone healing and other skeletal complications. In addition, some anti-diabetic therapies for T2DM can have notable detrimental skeletal effects. Thus, an appropriate therapeutic strategy for T2DM should not only be effective in re-establishing good glycaemic control but also in minimising skeletal complications. There is increasing evidence that glucagon-like peptide-1 receptor agonists (GLP-1RAs), now greatly prescribed for the treatment of T2DM, have beneficial skeletal effects although the underlying mechanisms are not completely understood. This review provides an overview of the direct and indirect effects of GLP-1RAs on bone physiology, focusing on bone quality and novel mechanisms of action on the vasculature and hormonal regulation. The overall experimental studies indicate significant positive skeletal effects of GLP-1RAs on bone quality and strength although their mechanisms of actions may differ according to various GLP-1RAs and clinical studies supporting their bone protective effects are still lacking. The possibility that GLP-1RAs could improve blood supply to bone, which is essential for skeletal health, is of major interest and suggests that GLP-1 anti-diabetic therapy could benefit the rising number of elderly T2DM patients with osteoporosis and high fracture risk.

Bone disease in diabetes: another manifestation of microvascular disease?

Type 1 and type 2 diabetes are generally accepted to be associated with increased bone fracture risk. However, the pathophysiological mechanisms of diabetic bone disease are poorly understood, and whether the associated increased skeletal fragility is a comorbidity or a complication of diabetes remains under debate. Although there is some indication of a direct deleterious effect of microangiopathy on bone, the evidence is open to question, and whether diabetic osteopathy can be classified as a chronic, microvascular complication of diabetes remains uncertain. Here, we review the current knowledge of potential contributory factors to diabetic bone disease, particularly the association between diabetic microangiopathy and bone mineral density, bone structure, and bone turnover. Additionally, we discuss and propose a pathophysiological model of the effects of diabetic microvascular disease on bone, and examine the progression of bone disease alongside the evolution of diabetes.

Insulin-Stimulated Bone Blood Flow and Bone Biomechanical Properties Are Compromised in Obese, Type 2 Diabetic OLETF Rats

Type 2 diabetes (T2D) increases skeletal fragility and fracture risk; however, the underlying mechanisms remain to be identified. Impaired bone vascular function, in particular insulin‐stimulated vasodilation and blood flow is a potential, yet unexplored mechanism. The purpose of this study was to determine the effects of T2D on femoral biomechanical properties, trabecular microarchitecture, and insulin‐stimulated bone vasodilation by comparison of hyperphagic Otsuka Long‐Evans Tokushima Fatty (OLETF) rats with normoglycemic control OLETF rats. Four‐week old, male OLETF rats were randomized to two groups: type 2 diabetes (O‐T2D) or normoglycemic control (O‐CON). O‐T2D were allowed ad libitum access to a rodent chow diet and O‐CON underwent moderate caloric restriction (30% restriction relative to intake of O‐T2D) to maintain normal body weight (BW) and glycemia until 40 weeks of age. Hyperphagic O‐T2D rats had significantly greater BW, body fat, and blood glucose than O‐CON. Total cross‐sectional area (Tt.Ar), cortical area (Ct.Ar), Ct.Ar/Tt.Ar, and polar moment of inertia of the mid‐diaphyseal femur adjusted for BW were greater in O‐T2D rats versus O‐CON. Whole‐bone biomechanical properties of the femur assessed by torsional loading to failure did not differ between O‐T2D and O‐CON, but tissue‐level strength and stiffness adjusted for BW were reduced in O‐T2D relative to O‐CON. Micro–computed tomography (μCT) of the distal epiphysis showed that O‐T2D rats had reduced percent bone volume, trabecular number, and connectivity density, and greater trabecular spacing compared with O‐CON. Basal tibial blood flow assessed by microsphere infusion was similar in O‐T2D and O‐CON, but the blood flow response to insulin stimulation in both the proximal epiphysis and diaphyseal marrow was lesser in O‐T2D compared to O‐CON. In summary, impaired insulin‐stimulated bone blood flow is associated with deleterious changes in bone trabecular microarchitecture and cortical biomechanical properties in T2D, suggesting that vascular dysfunction might play a causal role in diabetic bone fragility. © 2017 The Authors. JBMR Plus Published by Wiley Periodicals, Inc. on behalf of the American Society for Bone and Mineral Research.