Bone structure and turnover in type 2 diabetes mellitus

Associations between FGF21, osteonectin and bone turnover markers in type 2 diabetic patients with albuminuria

AIM

We measured the levels of bone turnover markers (BTMs) in patients with early diabetic nephropathy from type 2 diabetes mellitus (T2DM), and investigated the associations of BTMs with adipokines, serum fibroblast growth factor-21 (FGF21) and osteonectin.

METHODS

We included 159 males and 300 females with T2DM in this cross-sectional study. Clinical characteristics, BTMs and adipokines levels were measured.

RESULTS

One-hundred and ninety-two (41.8%) patients presented with albuminuria. Patients with albuminuria had significantly higher levels of serum osteonectin (P<0.0001) and FGF21 (P=0.0125) than those with normoalbuminuria. Serum levels of P1NP were slightly lower among patients with albuminuria (P=0.031), but the difference disappeared after adjusting for FBG, PBG, and HbA1c. Serum FGF21 levels were independently and negatively related to eGFR (overall β=-0.161, P=0.001; albuminuria group β=-0.240, P=0.001) but not related to uACR. While Osteonectin was independently and positively related to uACR (overall β=0.209, P=0.001; albuminuria group β=0.170, P=0.021). The levels of serum FGF21 were independently inversely related with P1NP (overall β=-0.192, P<0.0001; albuminuria group β=-0.195, P=0.031).

CONCLUSIONS

Our results suggest that persistent hyperglycemia may inhibit bone formation. Both osteonectin and FGF21 were associated with early nephropathy in T2DM patients, albeit with different patterns.

The impact of type 2 diabetes on bone metabolism

Diabetes complications and osteoporotic fractures are two of the most important causes of morbidity and mortality in older patients and share many features including genetic susceptibility, molecular mechanisms, and environmental factors. Type 2 diabetes mellitus (T2DM) compromises bone microarchitecture by inducing abnormal bone cell function and matrix structure, with increased osteoblast apoptosis, diminished osteoblast differentiation, and enhanced osteoclast-mediated bone resorption. The linkage between these two chronic diseases creates a possibility that certain antidiabetic therapies may affect bone quality. Both glycemic and bone homeostasis are under control of common regulatory factors. These factors include insulin, accumulation of advanced glycation end products, peroxisome proliferator-activated receptor gamma, gastrointestinal hormones (such as the glucose-dependent insulinotropic peptide and the glucagon-like peptides 1 and 2), and bone-derived hormone osteocalcin. This background allows individual pharmacological targets for antidiabetic therapies to affect the bone quality due to their indirect effects on bone cell differentiation and bone remodeling process. Moreover, it's important to consider the fragility fractures as another diabetes complication and discuss more deeply about the requirement for adequate screening and preventive measures. This review aims to briefly explore the impact of T2DM on bone metabolic and mechanical proprieties and fracture risk.

Visit-to-visit variation of fasting plasma glucose is a predictor of hip fracture in older persons with type 2 diabetes: the Taiwan Diabetes Study

We investigated the association between fasting plasma glucose variability (FPG-CV) and the risk of hip fracture in elderly diabetic patients. Our finding showed a temporal association between FPG-CV and hip fracture as patients categorized as FPG-CV greater than 25.4 % showed an increased risk in hip fractures.

INTRODUCTION

Hip fracture is a major health burden in the population and is associated with high rates of mortality and morbidity especially in elderly. It is evident that diabetes mellitus is a risk factor of osteoporosis which is a significant risk factor of hip fracture. However, epidemiological studies exploring the risks of hip fracture among type 2 diabetic patients are limited.

METHODS

A retrospective study of 26,501 ethnic Chinese older persons enrolled in the National Diabetes Care Management program in Taiwan was conducted; related factors were analyzed with extended Cox proportional hazards regression models to competing risk data on hip fracture incidence.

RESULTS

The results show a temporal association between FPG-CV and hip fracture as patients categorized as FPG-CV greater than 25.4 % showed an increased risk in hip fractures, confirming a linear relationship between the two. After multivariate adjustment, the risk of hip fracture increased among patients with FPG-CV of 25.4-42.3 % and >42.3 % compared with patients with FPG-CV of ≦ 14.3 % (hazard ratio, 1.35; 95 % confidence interval 1.14-1.60 and 1.27; 1.07-1.52, respectively). Significant linear trends among various FPG-CV were observed.

CONCLUSIONS

Thus, the present study demonstrated the importance of glucose stability for fracture prevention in older persons with type 2 diabetes. Future studies should be conducted to explore whether reduction in glucose oscillation in older adults with diabetes mellitus can reduce the risk of hip fracture.

The effect of hyperglycaemia on osseointegration: a review of animal models of diabetes mellitus and titanium implant placement

Patients with type 2 diabetes mellitus have a higher risk of dental and/or orthopaedic implant failure. However, the mechanism behind this phenomenon is unclear, and animal studies may prove useful in shedding light on the processes involved. This review considers the available literature on rat models of diabetes and titanium implantation.

INTRODUCTION

The process of osseointegration whereby direct contact is achieved between bone and an implant surface depends on healthy bone metabolism. Collective evidence suggests that hyperglycaemia adversely affects bone turnover and the quality of the organic matrix resulting in an overall deterioration in the quality, resilience and structure of the bone tissue. This in turn results in compromised osseointegration in patients receiving dental and orthopaedic implants. The incidence of diabetes mellitus (DM), which is a chronic metabolic disorder resulting in hyperglycaemia, is rising. Of particular significance is the rising incidence of adult onset type 2 diabetes mellitus (T2DM) in an ageing population. Understanding the effects of hyperglycaemia on osseointegration will enable clinicians to manage health outcomes for patients receiving implants. Much of our understanding of how hyperglycaemia affects osseointegration comes from animal studies.

METHODS

In this review, we critically analyse the current animal studies.

RESULTS

Our review has found that most studies used a type 1 diabetes mellitus (T1DM) rodent model and looked at a young male population of rodents. The pathophysiology of T1DM is however very different to that of T2DM and is not representative of T2DM, the incidence of which is rising in the ageing adult population. Genetically modified rats have been used to model T2DM, but none of these studies have included female rats and the metabolic changes in bone for some of these models used are not adequately characterized.

CONCLUSIONS

Therefore, the review suggests that the study population needs to be broadened to include both T1DM and T2DM models, older rats as well as young rats, and importantly animals from both sexes to reflect more accurately clinical practice.

Changes in bone macro- and microstructure in diabetic obese mice revealed by high resolution microfocus X-ray computed tomography

High resolution microfocus X-ray computed tomography (HR-microCT) was employed to characterize the structural alterations of the cortical and trabecular bone in a mouse model of obesity-driven type 2 diabetes (T2DM). C57Bl/6J mice were randomly assigned for 14 weeks to either a control diet-fed (CTRL) or a high fat diet (HFD)-fed group developing obesity, hyperglycaemia and insulin resistance. The HFD group showed an increased trabecular thickness and a decreased trabecular number compared to CTRL animals. Midshaft tibia intracortical porosity was assessed at two spatial image resolutions. At 2 μm scale, no change was observed in the intracortical structure. At 1 μm scale, a decrease in the cortical vascular porosity of the HFD bone was evidenced. The study of a group of 8 week old animals corresponding to animals at the start of the diet challenge revealed that the decreased vascular porosity was T2DM-dependant and not related to the ageing process. Our results offer an unprecedented ultra-characterization of the T2DM compromised skeletal micro-architecture and highlight an unrevealed T2DM-related decrease in the cortical vascular porosity, potentially affecting the bone health and fragility. Additionally, it provides some insights into the technical challenge facing the assessment of the rodent bone structure using HR-microCT imaging.

Insulin receptor substrate-1 time-dependently regulates bone formation by controlling collagen Iα2 expression via miR-342

Insulin promotes bone formation via a well-studied canonical signaling pathway. An adapter in this pathway, insulin-receptor substrate (IRS)-1, has been implicated in the diabetic osteopathy provoked by impaired insulin signaling. To further investigate IRS-1’s role in the bone metabolism, we generated Irs-1-deficient Irs-1^smla/smla mice. These null mice developed a spontaneous mutation that led to an increase in trabecular thickness (Tb.Th) in 12-mo-old, but not in 2-mo-old mice. Analyses of the bone marrow stromal cells (BMSCs) from these mice revealed their differential expression of osteogenesis-related genes and miRNAs. The expression of miR-342, predicted and then proven to target the gene encoding collagen type Iα2 (COL1A2), was reduced in BMSCs derived from Irs-1-null mice. COL1A2 expression was then shown to be age dependent in osteoblasts and BMSCs derived from Irs-1^smla/smla mice. After the induction of osteogenesis in BMSCs, miR-342 expression correlated inversely with that of Col1a2. Further, Col1a2-specific small interfering RNA (siRNA) reduced alkaline phosphatase (ALP) activity and inhibited BMSC differentiation into osteocyte-like cells, both in wild-type (WT) and Irs-1^smla/smla mice. Conversely, in Irs-1^smla/smla osteocytes overexpressing COL1A2, ALP-positive staining was stronger than in WT osteocytes. In summary, we uncovered a temporal regulation of BMSC differentiation/bone formation, controlled via Irs-1/miR-342 mediated regulation of Col1a2 expression.—Guo, Y., Tang, C.-Y., Man, X.-F., Tang, H.-N., Tang, J., Wang, F., Zhou, C.-L., Tan, S.-W., Feng, Y.-Z., Zhou, H.-D. Insulin receptor substrate-1 time-dependently regulates bone formation by controlling collagen Iα2 expression via miR-342.

Association Between Insulin Resistance and Bone Structure in Nondiabetic Postmenopausal Women

CONTEXT

The clinical consequences of insulin resistance and hyperinsulinemia on bone remain largely unknown.

OBJECTIVE

The objective of the study was to evaluate the effect of insulin resistance on peripheral bone geometry, volumetric bone mineral density (vBMD), bone microarchitecture, and estimated bone strength.

DESIGN, SETTING, AND PARTICIPANTS

This cross-sectional study included 146 postmenopausal, nondiabetic Caucasian women (mean age 60.3 ± 2.7 y) who were participating in the Study of Women's Health Across the Nation.

INTERVENTIONS

There were no interventions.

MAIN OUTCOME MEASURES

High-resolution peripheral quantitative computed tomography was used to assess bone density and microstructure at the distal radius and tibia. Fasting insulin and glucose were measured and insulin resistance was estimated using homeostasis model assessment of insulin resistance (HOMA-IR), with higher values indicating greater insulin resistance.

RESULTS

There was a negative association between HOMA-IR and bone size and a positive association between HOMA-IR and total vBMD, trabecular vBMD, trabecular thickness, and cortical thickness at the radius and tibia. These relationships remained, even after adjusting for body weight and other potential covariates (eg, time since menopause, cigarette smoking, physical activity, prior use of osteoporosis medications or glucocorticoids).

CONCLUSIONS

In nondiabetic, postmenopausal women, insulin resistance was associated with smaller bone size, greater volumetric bone mineral density, and generally favorable bone microarchitecture at weight-bearing and nonweight-bearing skeletal sites. These associations were independent of body weight and other potential covariates, suggesting that hyperinsulinemia directly affects bone structure independent of obesity and may explain, in part, the higher trabecular bone density and favorable trabecular microarchitecture seen in individuals with type 2 diabetes mellitus.

In vivo evaluation of bone microstructure in humans: Clinically useful?

In vivo evaluation of bone microstructure with high-resolution peripheral quantitative tomography (HRpQCT) has been used for a decade in research settings. In this review, we examine the value this technique could have in clinical practice. Bone microstructure parameters obtained with HRpQCT are associated with prevalent fracture in men and women. In postmenopausal women, some parameters also predict incident fracture, independently of areal bone mineral density. In specific population groups including patients with diabetes, chronic kidney disease, glucocorticosteroid therapy and rheumatic diseases, abnormal microstructure parameters from HRpQCT have been reported. Findings from HRpQCT studies may also explain ethnic differences in bone fragility. Treatment monitoring has been challenging in the various clinical trials with available HRpQCT data. The improvements were of small magnitude but tended to be proportional to the potency of antiresorptive agents. Microfinite element analysis was a better predictor of treatment efficacy than the microarchitectural parameters. In conclusion, HRpQCT remains a valuable research tool, but more work is needed to be able to use it in clinical practice.

Advanced Glycation Endproducts and Bone Material Strength in Type 2 Diabetes

CONTEXT

Skeletal deterioration, leading to an increased risk of fracture, is a known complication of type 2 diabetes mellitus (T2D). Yet plausible mechanisms to account for skeletal fragility in T2D have not been clearly established.

OBJECTIVE

The objective of the study was to determine whether bone material properties, as measured by reference point indentation, and advanced glycation endproducts (AGEs), as determined by skin autofluorescence (SAF), are related in patients with T2D.

DESIGN

This was a cross-sectional study.

SETTING

The study was conducted at a tertiary medical center.

PATIENTS

Sixteen postmenopausal women with T2D and 19 matched controls participated in the study.

MAIN OUTCOME MEASURES

Bone material strength index (BMSi) by in vivo reference point indentation, AGE accumulation by SAF, and circulating bone turnover markers were measured.

RESULTS

BMSi was reduced by 9.2% in T2D (P = .02) and was inversely associated with the duration of T2D (r = -0.68, P = .004). Increased SAF was associated with reduced BMSi (r = -0.65, P = .006) and lower bone formation marker procollagen type 1 amino-terminal propeptide (r = -0.63, P = .01) in T2D, whereas no associations were seen in controls. SAF accounted for 26% of the age-adjusted variance in BMSi in T2D (P = .03).

CONCLUSIONS

Bone material properties are impaired in postmenopausal women with T2D as determined by reference point indentation. The results suggest a role for the accumulation of AGEs to account for inferior BMSi in T2D.

Bone Microarchitecture in Men and Women with Diabetes: The Importance of Cortical Porosity

High-resolution peripheral quantitative computed tomography (HR-pQCT) captures novel aspects of bone geometry, volumetric bone mineral density and offers the ability to measure bone microarchitecture, but data relating measures obtained from this technique to diabetic status are inconsistent in women and lacking in men. Here, we report an analysis from the Hertfordshire Cohort Study, where we were able to study associations between bone microarchitecture from HR-pQCT of distal radius and distal tibia in 332 participants (177 men and 155 women) aged 72.1-81.4 years with or without diabetes mellitus (DM); n = 29 (18 men and 11 women) and n = 303, respectively. Statistical analyses were performed separately for women and men. The mean (SD) age of participants was 76.4 (2.6) and 76.1 (2.5) years in women and men, respectively. Participants with DM differed significantly in terms of weight in both women (70.4 ± 12.3 vs. 80.3 ± 18.3 kg; p = 0.015) and men (81.7 ± 11.4 vs. 92.8 ± 16.3 kg; p < 0.001) but no differences were found in height, smoking status, alcohol intake, social class and physical activity among women or men. Analyses in women revealed that cortical pore volume (Ct.Po.V) was higher in participants with DM and close to statistical significance for cortical porosity (Ct.Po) (β = 0.76 [0.12, 1.41] z-score, p = 0.020 and β = 0.62 [-0.02, 1.27] z-score, p = 0.059, respectively) at the distal radius. Adjustment for weight did not materially affect the relationship described for Ct.Po.V (β = 0.74 [0.09, 1.39], p = 0.027) and Ct.Po (β = 0.65 [-0.01, 1.30], p = 0.053) at the distal radius. After adjustment for weight, analyses in men revealed that Ct.Po and Ct.Po.V were higher in participants with DM (β = 0.57 [0.09, 1.06] z-score, p = 0.021 and β = 0.48 [0.01, 0.95] z-score, p = 0.044, respectively) at the distal tibia. Analyses of distal radial and tibial trabecular bone parameters according to diabetic status revealed no significant differences among men or women after adjustment for weight. We found higher cortical porosity and cortical pore volume at the distal tibia in men with DM and higher cortical pore volume at the distal radius in women with a non-significant tendency for higher cortical porosity. The results of our study suggest that deficits in cortical bone exist both in older men and women with DM.

Assessment of bone turnover and bone quality in type 2 diabetic bone disease: current concepts and future directions

Substantial evidence exists that in addition to the well-known complications of diabetes, increased fracture risk is an important morbidity. This risk is probably due to altered bone properties in diabetes. Circulating biochemical markers of bone turnover have been found to be decreased in type 2 diabetes (T2D) and may be predictive of fractures independently of bone mineral density (BMD). Serum sclerostin levels have been found to be increased in T2D and appear to be predictive of fracture risk independent of BMD. Bone imaging technologies, including trabecular bone score (TBS) and quantitative CT testing have revealed differences in diabetic bone as compared to non-diabetic individuals. Specifically, high resolution peripheral quantitative CT (HRpQCT) imaging has demonstrated increased cortical porosity in diabetic postmenopausal women. Other factors such as bone marrow fat saturation and advanced glycation endproduct (AGE) accumulation might also relate to bone cell function and fracture risk in diabetes. These data have increased our understanding of how T2D adversely impacts both bone metabolism and fracture risk.

Bone Structure and Predictors of Fracture in Type 1 and Type 2 Diabetes

CONTEXT

Type 1 and type 2 diabetes mellitus are associated with an increased risk of fracture.

OBJECTIVE

The objective of the study was to compare the bone structure and density between type 1 and type 2 diabetes patients and to investigate fracture associations.

DESIGN

This was a cross-sectional study.

SETTING AND PATIENTS

Physician-diagnosed type 1 and type 2 diabetes patients were included from the outpatient clinics at two university hospitals participated in the study.

MAIN OUTCOME MEASURES

Bone density and structure were assessed by dual-energy x-ray absorptiometry and high-resolution peripheral quantitative computed tomography. Blood samples were collected for bone turnover markers. Prevalent vertebral fractures were assessed by vertebral fracture assessment and x-ray, and incident fractures were collected from The Danish National Hospital Discharge Register.

RESULTS

Bone mineral density (BMD) was higher in type 2 than type 1 diabetes patients at the hip, femur, and spine; however, only the hip differed in multivariate-adjusted models. Bone tissue stiffness at the tibia was increased in type 2 diabetes patients also in adjusted models. Sclerostin levels were inversely associated with fracture in type 1 diabetes patients. The patients with the highest tertile of sclerostin had an 81% decreased risk of a fracture compared with the lowest tertile.

CONCLUSIONS

Type 1 and type 2 diabetes patients differ in BMD of the hip and tissue stiffness at the tibia. Sclerostin may be a marker independent of BMD to predict fractures in type 1 diabetes patients and thus potentially of clinical importance. Studies with longer follow-up are needed.

Femoral bone structure in Otsuka Long-Evans Tokushima Fatty rats

OBJECTIVES

Type 2 diabetes mellitus (T2DM) increases fracture risk despite normal to high levels of bone mineral density. Bone quality is known to affect bone fragility in T2DM. The aim of this study was to clarify the trabecular bone microstructure and cortical bone geometry of the femur in T2DM model rats.

METHODS

Five-week-old Otsuka Long-Evans Tokushima Fatty (OLETF; n = 5) and Long-Evans Tokushima Otsuka (LETO; n = 5) rats were used. At the age of 18 months, femurs were scanned with micro-computed tomography, and trabecular bone microstructure and cortical bone geometry were analyzed.

RESULTS

Trabecular bone microstructure and cortical bone geometry deteriorated in the femur in OLETF rats. Compared with in LETO rats, in OLETF rats, bone volume fraction, trabecular number and connectivity density decreased, and trabecular space significantly increased. Moreover, in OLETF rats, cortical bone volume and section area decreased, and medullary volume significantly increased.

CONCLUSIONS

Long-term T2DM leaded to deterioration in trabecular and cortical bone structure. Therefore, OLETF rats may serve as a useful animal model for investigating the relationship between T2DM and bone quality.

Efficacy and Safety of Risedronate in Osteoporosis Subjects with Comorbid Diabetes, Hypertension, and/or Dyslipidemia: A Post Hoc Analysis of Phase III Trials Conducted in Japan

Many osteoporotics have comorbid diabetes mellitus (DM), hypertension (HT), and dyslipidemia (DL). However, whether such comorbidities alter response to anti-osteoporotic treatment is unknown. We did post hoc analyses of combined data from three risedronate Japanese phase III trials to determine whether the presence of DM, HT, or DL affects its efficacy and safety. Data from 885 subjects who received 48-week treatment with risedronate were collected and combined from the three phase III trials. They were divided into two groups by the presence or absence of comorbidities: DM (n = 53) versus non-DM (n = 832); HT (n = 278) versus non-HT (n = 607); and DL (n = 292) versus non-DL (n = 593). Bone mineral density (BMD), urinary type 1 collagen N-telopeptide (uNTX), and serum bone-specific alkaline phosphatase (BAP) were measured at baseline and sequentially until 48 weeks. BMD or bone markers were not different between any of the two groups. Overall, BMD was increased by 5.52%, and uNTX and BAP were decreased by 35.4 and 33.8%, respectively. Some bone markers were slightly lower in DM and DL subjects, but the responses to risedronate were not significantly different. Statin users had lower uNTX and BAP, but showed no difference in the treatment response. All the other medications had no apparent effect. Adverse event incidence was marginally higher in DL compared with non-DL (Relative risk 1.06; 95% confidence interval 1.01-1.11), but was not related to increase in any specific events. Risedronate shows consistent safety and efficacy in suppressing bone turnover and increasing BMD in osteoporosis patients with comorbid DM, HT, and/or DL.

Bone turnover biomarkers and risk of osteoporotic hip fracture in an Asian population

While epidemiologic studies suggest that bone turnover biomarkers may predict hip fracture risk, findings are inconsistent and Asian data are lacking. We conducted a matched case-control (1:1) study nested in the Singapore Chinese Health Study, a population-based prospective cohort of Chinese men and women (45-74years) recruited from 1993 to 1998 in Singapore. One hundred cases with incident hip fracture and 100 individually matched controls were randomly selected from 63,257 participants. Serum bone turnover biomarkers, namely bone alkaline phosphatase (bone ALP), osteocalcin (OC), procollagen type I N propeptide (PINP), N-terminal and C-terminal crosslinking telopeptide of type I collagen (NTX-I and CTX-I) were measured using immunoassays. Hip fracture cases had significantly higher serum levels of OC, PINP, CTX-I and NTX-I than controls (p<0.05). There was a dose-dependent positive relationship between OC, PINP, CTX-I and NTX-I and risk of hip fracture (all Ps for trend≤0.006), where the risk was significantly increased by 4.32-8.23 folds for the respective BTM [Quartile (Q) 4 vs. Q1]. The odds ratio [OR (95% CI)] at the highest quartile (Q4) was 6.63 (2.02-21.18) for PINP and 4.92 (1.67-14.51) for CTX-I. The joint effect of PINP and CTX-I showed a 7-fold increase in risk (OR: 7.36; 95% CI: 2.53-21.41) comparing participants with higher levels of PINP (Q4) and CTX-I (Q3-Q4) to those with low levels of PINP (Q1-Q3) and CTX-I (Q1-Q2). Our data demonstrated that higher serum levels of bone turnover biomarkers were associated with increased risk of hip fracture in an Asian population.

Compromised cortical bone compartment in type 2 diabetes mellitus patients with microvascular disease

OBJECTIVE AND DESIGN

Patients with type 2 diabetes mellitus (T2D) have an increased fracture risk despite a normal or elevated bone mineral density (BMD). The aim of this cross-sectional in vivo study was to assess parameters of peripheral bone microarchitecture, estimated bone strength and bone remodeling in T2D patients with and without diabetic microvascular disease (MVD+ and MVD- respectively) and to compare them with healthy controls.

METHODS

Fifty-one T2D patients (MVD+ group: n=25) were recruited from Funen Diabetic Database and matched for age, sex and height with 51 healthy subjects. High-resolution peripheral quantitative tomography (HR-pQCT) was used to assess bone structure at the non-dominant distal radius and tibia. Estimated bone strength was calculated using finite element analysis. Biochemical markers of bone turnover were measured in all participants.

RESULTS

After adjusting for BMI, MVD+ patients displayed lower cortical volumetric BMD (P=0.02) and cortical thickness (P=0.02) and higher cortical porosity at the radius (P=0.02) and a trend towards higher cortical porosity at the tibia (P=0.07) compared to controls. HR-pQCT parameters did not differ between MVD- and control subjects. Biochemical markers of bone turnover were significantly lower in MVD+ and MVD- patients compared to controls (all P<0.01). These were no significant correlations between disease duration, glycemic control (average glycated hemoglobin over the previous 3 years) and HR-pQCT parameters.

CONCLUSION

Cortical bone deficits are not a characteristic of all T2D patients but of a subgroup characterized by the presence of microvascular complications. Whether this influences fracture rates in these patients needs further investigation.

[Imaging of diabetic osteopathy]

CLINICAL ISSUE

Diabetic bone diseases are more than just osteoporosis in patients with diabetes mellitus (DM): a relatively high bone mineral density is paired with a paradoxically high risk of fragility fractures. Diabetics exhibit low bone turnover, osteocyte dysfunction, relative hypoparathyroidism and an accumulation of advanced glycation end products in the bone matrix. Besides typical insufficiency fractures, diabetics show a high risk for peripheral fractures of the lower extremities (e.g. metatarsal fractures). The correct interdisciplinary assessment of fracture risks in patients with DM is therefore a clinical challenge.

STANDARD RADIOLOGICAL METHODS

There are two state of the art imaging methods for the quantification of fracture risks: dual energy X-ray absorptiometry (DXA) and quantitative computed tomography (QCT). Radiography, multidetector computed tomography (MDCT) and magnetic resonance imaging (MRI) are suitable for the detection of insufficiency fractures.

METHODICAL INNOVATIONS AND PERFORMANCE

Novel research imaging techniques, such as high-resolution peripheral quantitative computed tomography (HR-pQCT) provide non-invasive insights into bone microarchitecture of the peripheral skeleton. Using MR spectroscopy, bone marrow composition can be studied. Both methods have been shown to be capable of discriminating between type 2 diabetic patients with and without prevalent fragility fractures and thus bear the potential of improving the current standard of care. Currently both methods remain limited to clinical research applications.

PRACTICAL RECOMMENDATIONS

DXA and HR-pQCT are valid tools for the quantification of bone mineral density and assessment of fracture risk in patients with DM, especially if interpreted in the context of clinical risk factors. Radiography, CT and MRI are suitable for the detection of insufficiency fractures.

Determinants of bone strength and quality in diabetes mellitus in humans

There is growing evidence that the higher fracture rate observed in patients with type 2 diabetes mellitus (T2DM) is associated with normal, or even increased, areal bone mineral density (aBMD) by DXA. This has led to the hypothesis that patients with T2DM may have abnormalities in bone microarchitecture and/or material composition - i.e., key determinants of bone "quality." Consistent with this hypothesis, several studies using high-resolution peripheral quantitative computed tomography (HRpQCT) have demonstrated preserved indices of trabecular microarchitecture but increased cortical porosity in T2DM patients. In addition, a recent study using a novel in vivo microindentation device found an impairment in a measure of bone material properties (bone material strength index, BMSi) in postmenopausal women with longstanding T2DM; notably, the reduction in BMSi was associated with chronic glycemic control, suggesting that the skeleton should be included as another target organ subject to diabetic complications. The underlying pathogenesis of skeletal fragility in T2DM remains to be defined, although high levels of advanced glycation endproducts (AGEs) may play a role. In addition, T2DM is associated with reduced bone turnover, perhaps with an imbalance between bone resorption and bone formation. Although several studies have found increased serum sclerostin levels in patients with T2DM, the role of these increased levels in mediating the observed increases in cortical porosity or reduction in BMSi remains to be defined. Thus, although bone quality appears to be impaired in T2DM, the pathogenesis of these abnormalities and their relationship to the increased fracture risk observed in these patients needs further study.

Sclerostin antibody treatment improves fracture outcomes in a Type I diabetic mouse model

Type 1 diabetes mellitus (T1DM) patients have osteopenia and impaired fracture healing due to decreased osteoblast activity. Further, no adequate treatments are currently available that can restore impaired healing in T1DM; hence a significant need exists to investigate new therapeutics for treatment of orthopedic complications. Sclerostin (SOST), a WNT antagonist, negatively regulates bone formation, and SostAb is a potent bone anabolic agent. To determine whether SOST antibody (SostAb) treatment improves fracture healing in streptozotocin (STZ) induced T1DM mice, we administered SostAb twice weekly for up to 21days post-fracture, and examined bone quality and callus outcomes at 21days and 42days post-fracture (11 and 14weeks of age, respectively). Here we show that SostAb treatment improves bone parameters; these improvements persist after cessation of antibody treatment. Markers of osteoblast differentiation such as Runx2, collagen I, osteocalcin, and DMP1 were reduced, while an abundant number of SP7/osterix-positive early osteoblasts were observed on the bone surface of STZ calluses. These results suggest that STZ calluses have poor osteogenesis resulting from failure of osteoblasts to fully differentiate and produce mineralized matrix, which produces a less mineralized callus. SostAb treatment enhanced fracture healing in both normal and STZ groups, and in STZ+SostAb mice, also reversed the lower mineralization seen in STZ calluses. Micro-CT analysis of calluses revealed improved bone parameters with SostAb treatment, and the mineralized bone was comparable to Controls. Additionally, we found sclerostin levels to be elevated in STZ mice and β-catenin activity to be reduced. Consistent with its function as a WNT antagonist, SostAb treatment enhanced β-catenin activity, but also increased the levels of SOST in the callus and in circulation. Our results indicate that SostAb treatment rescues the impaired osteogenesis seen in the STZ induced T1DM fracture model by facilitating osteoblast differentiation and mineralization of bone.

The impact of vitamin D levels on glycemic control and bone mineral density in postmenopausal women with type 2 diabetes

OBJECTIVES

Whether glycemic control contributes to a decreased number of fractures or favorably impacts bone density in patients with type 2 diabetes mellitus (T2DM)has not been well established. Vitamin D (25 (OH) D3) deficiency appears to be related to glycemic control in patients with T2DM. The aim of this study was to determine the relationship between 25 (OH) D3 levels, glycemic control, bone mineral density (BMD), and the development of osteoporotic fractures (OPF) in postmenopausal women with T2DM.

METHODS

We reviewed the charts of 110 postmenopausal women diagnosed with T2DM. Glycosylated hemoglobin A1c (HbA1c) values over the previous 5 years were recorded and an average was obtained. Based on these values,the patients were divided into three groups: optimal,suboptimal, and poor control. Bone mineral density and 25(OH) D3 levels were also recorded.

RESULTS

In the group of patients with poorly controlled T2DM, 25 (OH) D3 levels were not significantly lower in comparison with the optimal control group 19.29 ± 7.70 vs 17.26 ± 6.93 (p = 0.53). No statistically significant linear relationship between HbA1c and 25 (OH) D3 levels( r(s) = −0.17, p = 0.06) was established. The frequency of osteoporosis and osteopenia was not significantly different between groups. The group with optimal glycemic control had an increased number of OPF events (p = 0.04).

CONCLUSIONS

We do not appreciate a significant relationship between 25 (OH) D3 levels and glucose control or OPF. Therefore, more studies are needed to identify the specific effect of 25 (OH) D3 in T2DM physiopathology.

Association between basal metabolic function and bone metabolism in postmenopausal women with type 2 diabetes

OBJECTIVE

Diabetes is a risk factor for osteoporosis, and glycemic control is critical during osteoporosis treatment in patients with type 2 diabetes (T2D). However, diabetic therapies have potentially adverse effects on bone metabolism. Additionally, biomarkers for bone metabolism are directly affected by drug therapies for osteoporosis. This study examined resting energy expenditure (REE) and respiratory quotient (RQ) as indices of bone metabolism in postmenopausal Japanese women with T2D.

METHODS

Forty-six postmenopausal Japanese women with T2D were examined. Procollagen type 1 N-terminal propeptide (P1NP, a fasting serum bone formation marker) and carboxy-terminal collagen cross-links-1 (CTX-1, a resorption marker) were evaluated, along with intact parathyroid hormone, 25-hydroxyvitamin D (25[OH]D), urine microalbumin, motor nerve conduction velocity, sensory nerve conduction velocity, R-R interval, body composition, REE, RQ, and bone mineral density at the nondominant distal radius.

RESULTS

The mean T-score was low with high variance (-1.7 ± 1.6), and 18 patients (39%) met the criteria for osteoporosis. REE was positively correlated with body mass index (β = 0.517; r(2) = 0.250), serum calcium (β = 0.624; r(2) = 0.200), glycated hemoglobin A1C for the previous 6 mo (β = 0.395; r(2) = 0.137), and the serum P1NP/CTX-1 ratio (β = 0.380; r(2) = 0.144). RQ was positively correlated with serum 25(OH)D (β = 0.387; r(2) = 0.131).

CONCLUSION

The basal metabolic rate and diabetic pathophysiology are interrelated with bone turnover.

Childhood obesity, bone development, and cardiometabolic risk factors

Osteoporosis and obesity are both major public health concerns. It has long been considered that these are distinct disorders rarely found in the same individual; however, emerging evidence supports an important interaction between adipose tissue and the skeleton. Whereas overweight per se may augment bone strength, animal studies suggest that the metabolic impairment that accompanies obesity is detrimental to bone. Obesity during childhood, a critical time for bone development, likely has profound and lasting effects on bone strength and fracture risk. This notion has received little attention in children and results are mixed, with studies reporting that bone strength development is enhanced or impaired by obesity. Whether obesity is a risk factor for osteoporosis or childhood bone health, in general, remains an important clinical question. Here, we will focus on clarifying the controversial relationships between childhood obesity and bone strength development, and provide insights into potential mechanisms that may regulate the effect of excess adiposity on bone.

Ischemic heart disease is associated with lower cortical volumetric bone mineral density of distal radius

In this study, high-resolution peripheral quantitative computed tomography (HR-pQCT) was used to investigate geometric, volumetric and microstructural parameters at the distal radius and at the distal tibia in participants with ischaemic heart disease. We found that, compared with participants without ischaemic heart disease, they had substantially lower cortical volumetric bone mineral density (BMD) at the distal radius.

INTRODUCTION

HR-pQCT captures novel aspects of bone geometry and volumetric bone mineral density (vBMD) and offers the ability to measure bone microarchitecture, but data relating measures obtained from this technique in patients with ischemic heart disease (IHD) are lacking.

METHODS

Here, we report an analysis from the Hertfordshire Cohort Study, where we were able to study associations between measures obtained from HR-pQCT of distal radius and distal tibia in 350 participants (184 men and 166 women) aged 71.5-80.5 years with or without IHD (e.g. heart attack, angina or heart failure; n = 75 and n = 275, respectively).

RESULTS

Analyses for all participants (men and women together) revealed that cortical vBMD (Ct.vBMD) was lower (p < 0.001) and cortical thickness (Ct.th) was not different (p = 0.519), whereas cortical porosity (Ct.Po) was higher (p = 0.016) in participants with IHD at the distal radius. Moreover, trabecular microarchitectural parameters were not significantly different in patients with IHD (p > 0.05 for all). Adjustment for a priori confounders (age, gender, body mass index, smoking status, alcohol consumption, high blood pressure and diabetes mellitus) did not materially affect the relationship described for Ct.vBMD (p = 0.002), but differences in Ct.Po were attenuated. Analyses in men alone revealed that only Ct.vBMD was lower at the distal radius in participants with IHD with and without adjustment for a priori confounders (p = 0.0002 and p = 0.004, respectively), whereas no statistical differences were found in women, although patterns of differences were similar in both sexes. Moreover, no association was found between IHD and bone parameters at the distal tibia either in men or women.

CONCLUSIONS

We have demonstrated that IHD is associated with lower Ct.vBMD of the distal radius.

High insulin levels in KK-Ay diabetic mice cause increased cortical bone mass and impaired trabecular micro-structure

Type 2 diabetes mellitus (T2DM) is a chronic disease characterized by hyperglycemia, hyperinsulinemia and complications, including obesity and osteoporosis. Rodents have been widely used to model human T2DM and investigate its effect on the skeleton. We aimed to investigate skeletal alterations in Yellow Kuo Kondo (KK-Ay) diabetic mice displaying high insulin and glucose levels. Bone mineral density (BMD), micro-architecture and bone metabolism-related genes were analyzed. The total femoral areal BMD (aBMD), cortical volumetric BMD (vBMD) and thickness were significantly increased in KK-Ay mice, while the trabecular vBMD and mineralized bone volume/tissue volume (BV/TV), trabecular thickness and number were decreased compared to C57BL mice. The expression of both osteoblast-related genes, such as osteocalcin (OC), bone sialoprotein, Type I Collagen, osteonectin, RUNX2 and OSX, and osteoclast-related genes, such as TRAP and TCIRG, were up-regulated in KK-Ay mice. Correlation analyses showed that serum insulin levels were positively associated with aBMD, cortical vBMD and thickness and negatively associated with trabecular vBMD and micro-architecture. In addition, serum insulin levels were positively related to osteoblast-related and osteoclast-related gene expression. Our data suggest that high insulin levels in KK-Ay diabetic mice may increase cortical bone mass and impair trabecular micro-structure by up-regulating osteoblast-and osteoclast-related gene expression.

An update on diabetes related skeletal fragility

There are several mechanisms by which diabetes could affect bone mass and strength. These mechanisms include insulin deficiency; hyperglycemia; the accumulation of advanced glycation end products that may influence collagen characteristics; marrow adiposity and bone inflammation. Furthermore, associated diabetic complications and treatment with thaizolidinediones may also increase risk of fracturing. The following article provides its readers with an update on the latest information pertaining to diabetes related bone skeletal fragility. In the authors' opinion, future studies are needed in order to clarify the impact of different aspects of diabetes metabolism, glycemic control, and specific treatments for diabetes on bone. Given that dual energy x-ray absorptiometry is a poor predictor of bone morbidity in this group of patients, there is a need to explore novel approaches for assessing bone quality. It is important that we develop a better understanding of how diabetes affects bone in order to improve our ability to protect bone health and prevent fractures in the growing population of adults with diabetes.

Defects in cortical microarchitecture among African-American women with type 2 diabetes

SUMMARY

Patients with type 2 diabetes mellitus (DM2) have increased fracture risk. We found that African-American women with DM2 have increased cortical porosity and lower cortical bone density at the radius than non-diabetic controls. These cortical deficits are associated with hyperglycemia and may contribute to skeletal fragility associated with DM2.

INTRODUCTION

Fracture risk is increased in patients with type 2 diabetes mellitus (DM2) despite normal areal bone mineral density (aBMD). DM2 is more common in African-Americans than in Caucasians. It is not known whether African-American women with DM2 have deficits in bone microstructure.

METHODS

We measured aBMD at the spine and hip by DXA, and volumetric BMD (vBMD) and microarchitecture at the distal radius and tibia by HR-pQCT in 22 DM2 and 78 non-diabetic African-American women participating in the Study of Women Across the Nation (SWAN). We also measured fasting glucose and HOMA-IR.

RESULTS

Age, weight, and aBMD at all sites were similar in both groups. At the radius, cortical porosity was 26% greater, while cortical vBMD and tissue mineral density were lower in women with DM2 than in controls. There were no differences in radius total vBMD or trabecular vBMD between groups. Despite inferior cortical bone properties at the radius, FEA-estimated failure load was similar between groups. Tibia vBMD and microarchitecture were also similar between groups. There were no significant associations between cortical parameters and duration of DM2 or HOMA-IR. However, among women with DM2, higher fasting glucose levels were associated with lower cortical vBMD (r=-0.54, p=0.018).

CONCLUSIONS

DM2 and higher fasting glucose are associated with unfavorable cortical bone microarchitecture at the distal radius in African-American women. These structural deficits may contribute to the increased fracture risk among women with DM2. Further, our results suggest that hyperglycemia may be involved in mechanisms of skeletal fragility associated with DM2.

[Visualization of local cortical defects in Charcot foot using microcomputed tomography]

BACKGROUND

In the pathogenesis of diabetic neuropathic osteoarthropathy (Charcot's foot) fractures cause chronic destruction of soft tissue and bone structure. To improve an early diagnosis of Charcot foot, modern diagnostic imaging is mainly based on magnetic resonance imaging (MRI), for example in relation to the detection of cortical bone fractures.

OBJECTIVES

In this study we investigated the cortical microstructure in cases of Charcot foot with respect to fractures and porosity in order to visualize local cortical defects. This may substantiate recent efforts in a reclassification based on MRI.

MATERIAL AND METHODS

Using microcomputed tomography (microCT) we investigated bone parameters, such as cortical thickness and porosity in order to quantify the local metatarsal microstructure in cases of Charcot foot.

RESULTS

All bone samples showed a high degree of cortical porosity including pores that perforated the cortical bone. The data suggest that areas with reduced cortical thickness coincide with large cortical pores that may serve as initial points for fractures. Whether the detected microfractures are physiological or artefacts of preparation could not be determined.

CONCLUSION

By means of microCT we were able to visualize and quantify the extent of cortical porosity for the first time in high resolution. The data suggest that both cortical fractures and cortical porosity play an important role in the pathogenesis in cases of Charcot foot.

The Charcot foot as a complication of diabetic neuropathy

Diabetes mellitus is a leading global metabolic disorder accompanied by the overwhelming burden of its associated complications. Hyperglycaemia-induced endothelial damage or endothelial dysfunction serves as the primary instigator for the development of microvascular disease. Diabetic neuropathy represents the majority of microvascular sequelae and is the renowned perpetrator of a variety of foot complications, namely the Charcot foot (CF). CF is a debilitating medical emergency which is often mismanaged either due to a delayed diagnosis or lack of clinical expertise in the management of CF. Often, misdiagnosis during the acute stages of CF leads to irreversible and persistent joint destruction which may be refractory to medical or surgical treatment. Timely intervention with offloading measures is crucial during acute CF in ceasing active bone resorption. Current anti-resorptive agents may be considered as adjunctive therapy in combination with offloading. Novel agents are underway that will enable bone formation and suppress bone resorption.

Type 2 diabetes mellitus and fracture risk

Increased fracture risk, traditionally associated with type 1 diabetes, has lately been of great concern in patients with type 2 diabetes. A variable increase in fracture risk has been reported, ranging from 20% to 3-fold, depending on skeletal site, diabetes duration and study design. Longer disease duration, the presence of diabetic complications, inadequate glycemic control, insulin use and increased risk for falls are all reported to increase fracture risk. Patients with type 2 diabetes display a unique skeletal phenotype with either normal or more frequently increased, bone mineral density and impaired structural and geometric properties. Recently, alterations in bone material properties seem to be the predominant defect leading to increased bone fragility. Accumulation of advanced glycation end-products and changes in collagen cross-linking along with suppression of bone turnover seem to be significant factors impairing bone strength. FRAX score has been reported to underestimate fracture risk and lumbar spine BMD is inadequate in predicting vertebral fractures. Anti-diabetic medications, apart from thiazolidinediones, appear to be safe for the skeleton, although more data are needed. Optimal strategies to reduce skeletal fragility in type 2 diabetic patients are yet to be determined.

Increased fracture risk in patients with type 2 diabetes mellitus: an overview of the underlying mechanisms and the usefulness of imaging modalities and fracture risk assessment tools

Type 2 diabetes mellitus has recently been linked to an increased fracture risk. Since bone mass seems to be normal to elevated in patient with type 2 diabetes, the increased fracture risk is thought to be due to both an increased falling frequency and decreased bone quality. The increased falling frequency is mainly a result of complications of the disease such as a retinopathy and polyneuropathy. Bone quality is affected through changes in bone shape, bone micro-architecture, and in material properties such as bone mineralization and the quality of collagen. Commonly used methods for predicting fracture risk such as dual energy X-ray absorptiometry and fracture risk assessment tools are helpful in patients with type 2 diabetes mellitus, but underestimate the absolute fracture risk for a given score. New imaging modalities such as high resolution peripheral quantitative computed tomography are promising for giving insight in the complex etiology underlying the fragility of the diabetic bone, as they can give more insight into the microarchitecture and geometry of the bone. We present an overview of the contributing mechanisms to the increased fracture risk and the usefulness of imaging modalities and risk assessment tools in predicting fracture risk in patients with type 2 diabetes.

Suppressed bone turnover was associated with increased osteoporotic fracture risks in non-obese postmenopausal Chinese women with type 2 diabetes mellitus

We found that type 2 diabetes mellitus (T2DM) was associated with increased fracture risks in non-obese postmenopausal Chinese women, and suppressed bone turnover might be the underlying mechanism. This is the first study evaluating and explaining the association of T2DM with osteoporotic fracture in Chinese population with such high homogeneity.

INTRODUCTION

The aim of this study was to investigate the association of T2DM with osteoporotic fracture in postmenopausal Chinese women.

METHODS

One thousand four hundred ten postmenopausal women were included and stratified into non-obese population [body mass index (BMI) < 25 kg/m(2)] and obese population (BMI ≥ 25 kg/m(2)). Each type of population was classified into diabetes group, impaired fasting glucose (IFG) group, and normal glucose group. Bone mineral density (BMD) was measured by dual-energy X-ray absorptiometry. Serum C-terminal telopeptide of type I collagen (β-CTX) and serum N-amino terminal prepeptide of type 1 procollagen (P1NP) were quantified. Vertebral fractures (VFs) and non-VFs were assessed by vertebral X-ray and questionnaire, respectively.

RESULTS

Comparing to normal glucose group, diabetes group and IFG group both had lower levels of P1NP and β-CTX, despite population types. Despite having non-decreased BMD, non-obese diabetic patients had higher risks of total fracture and VF than BMI-matched normal glucose subjects (both P < 0.05). Non-obese population was further classified by a mean value of P1NP or β-CTX. Non-obese diabetic patients with low P1NP or high β-CTX had higher fracture risks (both P < 0.05), comparing to non-obese normal glucose subjects with high P1NP or high β-CTX, respectively.

CONCLUSIONS

Type 2 diabetic patients had suppressed bone turnover, which might explain the increased fracture risks, independent of BMD. IFG patients might also have poor bone quality and need early prevention.

Biochemical markers of bone turnover in diabetes patients--a meta-analysis, and a methodological study on the effects of glucose on bone markers

This study examined whether markers of bone turnover differ between individuals with and without diabetes. Bone markers showed heterogeneity between studies and were discrepant for markers of bone creation and markers of bone degradation. Bone markers may be of lesser value in diabetes due to heterogeneity.

INTRODUCTION

The aim of this meta-analysis was to compare existing literature regarding changes in bone markers among diabetics compared to healthy controls. To exclude that blood glucose levels among diabetes patients could influence the assays used for determining bone turnover markers, a methodological study was performed.

METHODS

Medline at Pubmed Embase, Cinahl, Svemed+, Cochrane library, and Bibliotek.dk was searched in August 2012. The studies should examine biochemical bone turnover among diabetes patients in comparison to controls in an observational design. In the methodological study, fasting blood samples were drawn from two individuals. Glucose was added to the blood samples in different concentrations and OC, CTX, and procollagen type 1 amino terminal propeptide were measured after 0, 1, 2, and 3 h.

RESULTS

Twenty-two papers fulfilled the criteria for the meta-analysis. From the pooled data in the meta-analysis, the bone markers osteocalcin (OC) (-1.15 ng/ml [-1.78,-0.52]) and C-terminal cross-linked telopeptide (CTX) (-0.14 ng/ml [-0.22, -0.05]) were significantly lower among diabetes patients than non-diabetes patients, however other markers did not differ. All markers displayed very high heterogeneity by I2 statistics. In the methodological study, the addition of glucose did not significantly change the bone markers neither by level of glucose nor with increasing incubation time.

CONCLUSION

The dissociative pattern of biochemical bone markers of bone formation and bone resorption present in diabetes patients is thus not caused by glucose per se but may be modulated by unknown factors associated with diabetes mellitus.

Differential pattern for regulating insulin secretion, insulin resistance, and lipid metabolism by osteocalcin in male and female T2DM patients

BACKGROUND

Osteocalcin has been reported to be relevant to glucose and lipid metabolism, indicating it may stimulate insulin secretion and improve insulin resistance. Yet the difference between male and female patients is still not clear. We aimed to investigate the difference in serum osteocalcin, and its association with glucose, lipid metabolism, pancreatic function, insulin sensitivity, and resistance in male and female middle-aged and elderly type 2 diabetic (T2DM) patients.

MATERIAL AND METHODS

739 T2DM patients were included. After measurement of body mass index (BMI), the levels of fasting plasma glucose (FPG), insulin (FINS), C peptide (FC-P), 2-h post-OGTT plasma glucose (2h-PG), HbA1C, and osteocalcin were determined. Homeostasis model assessment of β-cell function (HOMA-%B), homeostasis model assessment of insulin sensitivity (HOMA-%S), and homeostasis model assessment of insulin resistance (HOMA-IR) were calculated.

RESULTS

Females had higher osteocalcin concentration than males (P<0.05). In males, serum osteocalcin was negatively correlated with HbA1C, FPG, and 2-h PG (P<0.05), but positively with 2-h post-OGTT C peptide (2hC-P), 2-h post-OGTT serum insulin (2h-INS), and HOMA-%B (P<0.05). In females, serum osteocalcin was negatively correlated with HbA1C, FPG, triglyceride (TG), and HOMA-IR (P<0.05), but positively with 2-h C-P, 2-h INS, HOMA-%B, HOMA-%S, and high-density lipoprotein (HDL) (P<0.05). In all subjects, serum osteocalcin was inversely correlated with HbA1C, FPG, and 2-h PG (P<0.05), but positively with 2-h C-P, 2-h INS, HDL, and HOMA-%B (P<0.05).

CONCLUSIONS

Osteocalcin might improve glucose metabolism through enhancing insulin secretion in males, and through increasing insulin secretion and improving insulin resistance in females with T2DM. Osteocalcin probably also plays an important role in lipid metabolism.

In vivo assessment of bone quality in postmenopausal women with type 2 diabetes

Although patients with type 2 diabetes (T2D) are at significant risk for well-recognized diabetic complications, including macrovascular disease, retinopathy, nephropathy, and neuropathy, it is also clear that T2D patients are at increased risk for fragility fractures. Furthermore, fragility fractures in patients with T2D occur at higher bone mineral density (BMD) values compared to nondiabetic controls, suggesting abnormalities in bone material strength (BMS) and/or bone microarchitecture (bone "quality"). Thus, we performed in vivo microindentation testing of the tibia to directly measure BMS in 60 postmenopausal women (age range, 50-80 years) including 30 patients diagnosed with T2D for >10 years and 30 age-matched, nondiabetic controls. Regional BMD was measured by dual-energy X-ray absorptiometry (DXA); cortical and trabecular bone microarchitecture was assessed from high-resolution peripheral quantitative computed tomography (HRpQCT) images of the distal radius and tibia. Compared to controls, T2D patients had significantly lower BMS: unadjusted (-11.7%; p<0.001); following adjustment for body mass index (BMI) (-10.5%; p<0.001); and following additional adjustment for age, hypertension, nephropathy, neuropathy, retinopathy, and vascular disease (-9.2%; p=0.022). By contrast, after adjustment for confounding by BMI, T2D patients had bone microarchitecture and BMD that were not significantly different than controls; however, radial cortical porosity tended to be higher in the T2D patients. In addition, patients with T2D had significantly reduced serum markers of bone turnover (all p<0.001) compared to controls. Of note, in patients with T2D, the average glycated hemoglobin level over the previous 10 years was negatively correlated with BMS (r=-0.41; p=0.026). In conclusion, these findings represent the first demonstration of compromised BMS in patients with T2D. Furthermore, our results confirm previous studies demonstrating low bone turnover in patients with T2D and highlight the potential detrimental effects of prolonged hyperglycemia on bone quality. Thus, the skeleton needs to be recognized as another important target tissue subject to diabetic complications. © 2014 American Society for Bone and Mineral Research.

Osteoporosis-associated fracture and diabetes

Osteoporosis and diabetes mellitus are chronic diseases with significant associated morbidity and mortality. Recent evidence suggests that both type 1 and type 2 diabetes are associated with an increased fracture risk. Fracture as a complication of diabetes must be considered when evaluating and treating patients with diabetes.

The alliance of mesenchymal stem cells, bone, and diabetes

Bone fragility has emerged as a new complication of diabetes. Several mechanisms in diabetes may influence bone homeostasis by impairing the action between osteoblasts, osteoclasts, and osteocytes and/or changing the structural properties of the bone tissue. Some of these mechanisms can potentially alter the fate of mesenchymal stem cells, the initial precursor of the osteoblast. In this review, we describe the main factors that impair bone health in diabetic patients and their clinical impact.

A review of rodent models of type 2 diabetic skeletal fragility

Evidence indicating that adult type 2 diabetes (T2D) is associated with increased fracture risk continues to mount. Unlike osteoporosis, diabetic fractures are associated with obesity and normal to high bone mineral density, two factors that are typically associated with reduced fracture risk. Animal models will likely play a critical role in efforts to identify the underlying mechanisms of skeletal fragility in T2D and to develop preventative treatments. In this review we critically examine the ability of current rodent models of T2D to mimic the skeletal characteristics of human T2D. We report that although there are numerous rodent models of T2D, few have undergone thorough assessments of bone metabolism and strength. Further, we find that many of the available rodent models of T2D have limitations for studies of skeletal fragility in T2D because the onset of diabetes is often prior to skeletal maturation and bone mass is low, in contrast to what is seen in adult humans. There is an urgent need to characterize the skeletal phenotype of existing models of T2D, and to develop new models that more closely mimic the skeletal effects seen in adult-onset T2D in humans.

Osteoporosis update from the 2012 Santa Fe Bone Symposium

The core of the 2012 Santa Fe Bone Symposium consisted of plenary presentations on new developments in the fields of osteoporosis and metabolic bone disease, with a focus on current and future implications for patient care. These were complemented by oral abstracts, interactive discussions of challenging cases, a debate on benefits and risks of long-term bisphosphonate therapy, and a panel discussion of controversial issues in the management of osteoporosis. Other topics included a review of the most important scientific publications in the past year, new and emerging therapy for osteoporosis, the benefits and limitations of clinical practice guidelines in the care of individual patients, the effects of metallic elements on skeletal health, clinical applications of bone turnover markers, an engineering perspective of skeletal health and disease, and an update on the role of the International Society for Clinical Densitometry in education, certification, accreditation, and advocacy for high-quality bone density testing. The symposium was highlighted by an inaugural presentation of "2 Million 2 Many," a national campaign of the National Bone Health Alliance to increase awareness of osteoporosis.

Clinical imaging of bone microarchitecture with HR-pQCT

Osteoporosis, a disease characterized by loss of bone mass and structural deterioration, is currently diagnosed by dual-energy x-ray absorptiometry (DXA). However, DXA does not provide information about bone microstructure, which is a key determinant of bone strength. Recent advances in imaging permit the assessment of bone microstructure in vivo using high-resolution peripheral quantitative computed tomography (HR-pQCT). From these data, novel image processing techniques can be applied to characterize bone quality and strength. To date, most HR-pQCT studies are cross-sectional comparing subjects with and without fracture. These studies have shown that HR-pQCT is capable of discriminating fracture status independent of DXA. Recent longitudinal studies present new challenges in terms of analyzing the same region of interest and multisite calibrations. Careful application of analysis techniques and educated clinical interpretation of HR-pQCT results have improved our understanding of various bone-related diseases and will no doubt continue to do so in the future.

Increased cortical porosity in type 2 diabetic postmenopausal women with fragility fractures

The primary goal of this study was to assess peripheral bone microarchitecture and strength in postmenopausal women with type 2 diabetes with fragility fractures (DMFx) and to compare them with postmenopausal women with type 2 diabetics without fractures (DM). Secondary goals were to assess differences in nondiabetic postmenopausal women with fragility fractures (Fx) and nondiabetic postmenopausal women without fragility fractures (Co), and in DM and Co women. Eighty women (mean age 61.3 ± 5.7 years) were recruited into these four groups (DMFx, DM, Fx, and Co; n = 20 per group). Participants underwent dual-energy X-ray absorptiometry (DXA) and high-resolution peripheral quantitative computed tomography (HR-pQCT) of the ultradistal and distal radius and tibia. In the HR-pQCT images volumetric bone mineral density and cortical and trabecular structure measures, including cortical porosity, were calculated. Bone strength was estimated using micro-finite element analysis (µFEA). Differential strength estimates were obtained with and without open cortical pores. At the ultradistal and distal tibia, DMFx had greater intracortical pore volume (+52.6%, p = 0.009; +95.4%, p = 0.020), relative porosity (+58.1%, p = 0.005; +87.9%, p = 0.011) and endocortical bone surface (+10.9%, p = 0.031; +11.5%, p = 0.019) than DM. At the distal radius DMFx had 4.7-fold greater relative porosity (p < 0.0001) than DM. At the ultradistal radius, intracortical pore volume was significantly higher in DMFx than DM (+67.8%, p = 0.018). DMFx also displayed larger trabecular heterogeneity (ultradistal radius: +36.8%, p = 0.035), and lower total and cortical BMD (ultradistal tibia: -12.6%, p = 0.031; -6.8%, p = 0.011) than DM. DMFx exhibited significantly higher pore-related deficits in stiffness, failure load, and cortical load fraction at the ultradistal and distal tibia, and the distal radius than DM. Comparing nondiabetic Fx and Co, we only found a nonsignificant trend with increase in pore volume (+38.9%, p = 0.060) at the ultradistal radius. The results of our study suggest that severe deficits in cortical bone quality are responsible for fragility fractures in postmenopausal diabetic women.

Altered gene expression involved in insulin signaling pathway in type II diabetic osteoporosis rats model

It is well established that both estrogen loss and type II diabetes mellitus (DMII) can impair bone metabolism, but whether estrogen loss exacerbates the effects of DMII is unclear. Therefore, we determined if ovariectomy (OVX) of rats on a long-term high-fat/sugar diet and injection of a low dose of streptozotocin (DMII) decreased bone mineral density (BMD) more than OVX or DMII alone. Bone insulin signaling is known to support bone metabolism; therefore, we also tested the hypothesis that OVX DMII rats (DOVX) would exhibit greater reductions in the expression of proteins important in insulin signaling, including IRS-1, IRS-2, and IGF-1. As hypothesized, BMD and plasma estrogen levels were decreased more in DOVX rats than in rats following OVX (NOVX) or DMII (DS) alone. IGF-1 expression was decreased in the liver, kidney, skeletal muscle, and bone of DOVX, DS, and NOVX rats; however, the decrease was larger and occurred sooner in DOVX rats. While IRS-1 and IRS-2 decreased in most groups in all tissues examined, the expression patterns differed in both a group- and tissue-dependent fashion. In conclusion, these data demonstrate that estrogen loss and DMII induced by a high-fat/sugar diet interact to produce osteoporosis and support the hypothesis that the bone loss may be mediated at least in part by concurrent decreases in the insulin signaling proteins in bone.

Diabetes, biochemical markers of bone turnover, diabetes control, and bone

Diabetes mellitus is known to have late complications including micro vascular and macro vascular disease. This review focuses on another possible area of complication regarding diabetes; bone. Diabetes may affect bone via bone structure, bone density, and biochemical markers of bone turnover. The aim of the present review is to examine in vivo from humans on biochemical markers of bone turnover in diabetics compared to non-diabetics. Furthermore, the effect of glycemic control on bone markers and the similarities and differences of type 1- and type 2-diabetics regarding bone markers will be evaluated. A systematic literature search was conducted using PubMed, Embase, Cinahl, and SveMed+ with the search terms: "Diabetes mellitus," "Diabetes mellitus type 1," "Insulin dependent diabetes mellitus," "Diabetes mellitus type 2," "Non-insulin dependent diabetes mellitus," "Bone," "Bone and Bones," "Bone diseases," "Bone turnover," "Hemoglobin A Glycosylated," and "HbA1C." After removing duplicates from this search 1,188 records were screened by title and abstract and 75 records were assessed by full text for inclusion in the review. In the end 43 records were chosen. Bone formation and resorption markers are investigated as well as bone regulating systems. T1D is found to have lower osteocalcin and CTX, while osteocalcin and tartrate-resistant acid are found to be lower in T2D, and sclerostin is increased and collagen turnover markers altered. Other bone turnover markers do not seem to be altered in T1D or T2D. A major problem is the lack of histomorphometric studies in humans linking changes in turnover markers to actual changes in bone turnover and further research is needed to strengthen this link.

Diabetes and change in bone mineral density at the hip, calcaneus, spine, and radius in older women

Older women with type 2 diabetes mellitus (DM) have higher bone mineral density (BMD) but also have higher rates of fracture compared to those without DM. Limited evidence suggests that DM may also be associated with more rapid bone loss. To determine if bone loss rates differ by DM status in older women, we analyzed BMD data in the Study of Osteoporotic Fractures (SOF) between 1986 and 1998. SOF participants were women ≥65 years at baseline who were recruited from four regions in the U.S. DM was ascertained by self-report. BMD was measured with dual-energy x-ray absorptiometry (DXA) at baseline and at least one follow-up visit at the hip (N = 6624) and calcaneus (N = 6700) and, on a subset of women, at the spine (N = 396) and distal radius (N = 306). Annualized percent change in BMD was compared by DM status, using random effects models. Of 6,867 women with at least one follow-up DXA scan, 409 had DM at baseline. Mean age was 70.8 (SD 4.7) years. Baseline BMD was higher in women with DM at all measured sites. In models adjusted for age and clinic, women with prevalent DM lost bone more rapidly than those without DM at the femoral neck (-0.96 vs. -0.59%/year, p < 0.001), total hip (-0.98 vs. -0.70%/year, p < 0.001), calcaneus (-1.64 vs. -1.40%/year, p = 0.005), and spine (-0.33 vs. +0.33%/year, p = 0.033), but not at the distal radius (-0.97 vs. -0.90%/year, p = 0.91). These findings suggest that despite higher baseline BMD, older women with DM experience more rapid bone loss than those without DM at the hip, spine, and calcaneus, but not the radius. Higher rates of bone loss may partially explain higher fracture rates in older women with DM.

Reduced serum osteocalcin concentrations are associated with type 2 diabetes mellitus and the metabolic syndrome components in postmenopausal women: the crosstalk between bone and energy metabolism

Although it has been shown that osteocalcin functions as a hormone in the regulation of glucose metabolism and fat mass, no population-based study to date has addressed serum osteocalcin levels in relation to energy metabolism concurrent with bone metabolism in postmenopausal women. In a population-based study, cardiovascular risk factors, high-sensitivity C-reactive protein (hs-CRP), osteoprotegerin, receptor activator of nuclear factor-κB ligand, osteocalcin, CrossLaps, alkaline phosphatase, and bone mineral density (BMD) at the lumbar spine (L2-L4) and the proximal femur were measured in 382 Iranian postmenopausal women. In multiple logistic regression analysis, lower osteocalcin and CrossLaps levels were associated with a higher odds ratio (OR) of having type 2 diabetes mellitus when adjustments were made for age, hs-CRP, cardiovascular risk factors, BMD, and markers of bone metabolism [OR 5.17, CI (2.66-10.04), p < 0.0001 and OR 2.51, CI (1.37-4.61), p = 0.003, respectively]. However, lower alkaline phosphatase levels were associated with a lower OR of having type 2 diabetes mellitus [OR 0.28, CI (0.15-0.52), p < 0.0001] in regression analysis. No significant difference was found between serum osteocalcin levels of those with and without metabolic syndrome. Among the metabolic syndrome components, low osteocalcin levels had significant associations with elevated blood glucose [OR 1.89, CI (1.16-3.07), p = 0.010] and elevated waist circumference [OR 2.53, CI (1.13-5.67), p = 0.024] in multivariate analyses. In conclusion, serum osteocalcin was independently associated with glucose intolerance and abdominal obesity as the components of metabolic syndrome and type 2 diabetes mellitus in postmenopausal women. Since CrossLaps and alkaline phosphatase levels were independently associated with the presence of type 2 diabetes mellitus, the unique contribution of osteocalcin in glucose metabolism could not be concluded.

Type 2 diabetes and bone

There is a growing body of research showing that diabetes is an independent risk factor for fracture. Type 2 diabetes (T2D), which predominates in older individuals and is increasing globally as a consequence of the obesity epidemic, is associated with normal or even increased dual-energy x-ray absorptiometry (DXA)-derived areal bone mineral density (BMD). Therefore, the paradoxical increase in fracture risk has led to the hypothesis that there are diabetes-associated alterations in material and structural properties. An overly glycated collagen matrix, confounded by a low turnover state, in the setting of subtle cortical abnormalities, may lead to compromised biomechanical competence. In current clinical practice, because BMD is central to fracture prediction, a consequence of this paradox is a lack of suitable methods, including FRAX, to predict fracture risk in older adults with T2D. The option of adding diabetes to the FRAX algorithm is appealing but requires additional data from large population-based cohorts. The need for improved methods for identification of fracture in older adults with T2D is an important priority for osteoporosis research.

Circulating osteogenic precursor cells in type 2 diabetes mellitus

CONTEXT

Type 2 diabetes mellitus (T2D) is associated with an increased risk of fractures and low bone formation. However, the mechanism for the low bone formation is not well understood. Recently, circulating osteogenic precursor (COP) cells, which contribute to bone formation, have been characterized in the peripheral circulation.

OBJECTIVE

Our objective was to characterize the number and maturity of COP cells in T2D.

PATIENTS, DESIGN, AND SETTING

Eighteen postmenopausal women with T2D and 27 controls participated in this cross-sectional study at a clinical research center.

MAIN OUTCOME MEASURES

COP cells were characterized using flow cytometry and antibodies against osteocalcin (OCN) and early stem cell markers. Histomorphometric (n = 9) and molecular (n=14) indices of bone turnover and oxidative stress were also measured.

RESULTS

The percentage of OCN(+) cells in peripheral blood mononuclear cells was lower in T2D (0.8 ± 0.2 vs. 1.6 ± 0.4%; P < 0.0001), whereas the percentage of OCN(+) cells coexpressing the early marker CD146 was increased (OCN(+)/CD146(+): 33.3 ± 7 vs. 12.0 ± 4%; P < 0.0001). Reduced histomorphometric indices of bone formation were observed in T2D subjects, including mineralizing surface (2.65 ± 1.9 vs. 7.58 ± 2.4%, P = 0.02), bone formation rate (0.01 ± 0.1 vs. 0.05 ±0.2 μm(3)/um(2) · d, P = 0.02), and osteoblast surface (1.23 ±0.9 vs. 4.60 ± 2.5%, P = 0.03). T2D subjects also had reduced molecular expression of the osteoblast regulator gene Runx2 but increased expression of the oxidative stress markers p66(Shc) and SOD2.

CONCLUSIONS

Circulating OCN(+) cells were decreased in T2D, whereas OCN(+)/CD146(+) cells were increased. Histomorphometric indices of bone formation were decreased in T2D, as was molecular expression of osteoblastic activity. Stimulation of bone formation may have beneficial therapeutic skeletal consequences in T2D.

Fracture incidence and risk of osteoporosis in female type 2 diabetic patients in Korea

BACKGROUND

There are no published data regarding fracture risk in type 2 diabetic patients in Korea. In this study, we compared the fracture incidence and risk of osteoporosis of type 2 diabetic female patients with those in a non-diabetic hypertensive cohort.

METHODS

The incidence of fracture in a type 2 diabetic cohort was compared with that in a non-diabetic hypertensive cohort over the course of 7 years. Female type 2 diabetic and non-diabetic hypertensive patients who visited Eulji General Hospital outpatient clinic from January 2004 to April 2004 were assigned to the diabetic cohort and the non-diabetic hypertensive cohort, respectively. Surveys on fracture event, use of anti-osteoporosis medications, and bone mineral density were performed.

RESULTS

The number of fractures was 88 in the female diabetic cohort (n=1,268, 60.6±11.5 years) and 57 in the female non-diabetic hypertensive cohort (n=1,014, 61.4±11.7 years). The RR in the diabetic cohort was 1.38 (P=0.064; 95% confidence interval [CI], 0.98 to 1.94) when adjusted for age. Diabetic patients with microvascular complications (61.0%) showed a higher RR of 1.81 (P=0.014; 95% CI, 1.13 to 2.92) compared with those without these complications. The prevalence of osteoporosis was comparable between the groups, while use of anti-osteoporosis medication was more common in the diabetic cohort (12.8%) than in the hypertensive cohort (4.5%) (P<0.001).

CONCLUSION

In our study, a higher fracture risk was observed in female type 2 diabetics with microvascular complications. Special concern for this risk group is warranted.