Serum concentrations of osteocalcin, procollagen type 1 N-terminal propeptide and beta-CrossLaps in obese subjects with varying degrees of glucose tolerance

Contrasting bone profiles in PCOS are related to BMI: a systematic review and meta-analysis

CONTEXT

Controversial results have emerged regarding whether PCOS is protective or increases the risk of bone frailty.

OBJECTIVE

This study investigated whether the PCOS condition affects bone parameters of premenopausal women. This is an update for a previous meta-analysis published in 2019.

DATA SOURCES

We searched MEDLINE and Embase.

STUDY SELECTION

Studies were considered eligible for the update if published in English between the 1st of October 2018 and the 31st of December 2023. The diagnosis of PCOS should be based on NIH criteria, the Rotterdam Consensus, AE-PCOS society criteria, or ICD codes in women over 18 years old. Only records with the Newcastle-Ottawa Scale > 6 were selected for data extraction.

DATA EXTRACTION

Data were extracted by two independent reviewers.

DATA SYNTHESIS

We identified 31 studies that met the inclusion criteria for qualitative analysis from 3322 studies in the whole period (1990-2023). Overall, cross-sectional studies included 1822 individuals with PCOS and 1374 controls, while cohort studies incorporated 30305 women with PCOS and 101907 controls. Contrasting profiles emerged after stratification using a BMI cutoff of 27 kg/m2. Individuals with PCOS and a BMI <27 kg/m2 exhibited lower vertebral and non-vertebral bone density, reduced bone turnover marker (osteocalcin), and increased bone resorption marker (CTX) levels. Conversely, individuals with PCOS and a BMI >27 kg/m2 exhibited increased vertebral and non-vertebral BMD, with no significant changes in bone formation and resorption markers (except osteocalcin).

CONCLUSIONS

The findings of this study alert for a low bone mass, low bone formation, and increased bone resorption PCOS with a BMI <27 kg/m2.

Preptin: A New Bone Metabolic Parameter?

Preptin is a 34-aminoacid peptide derived from the E-peptide of pro-insulin-like growth factor 2 (pro-IGF2) that is co-secreted with insulin and upregulates glucose-mediated insulin secretion. High serum preptin levels were described in conditions associated with insulin resistance, such as polycystic ovary syndrome and type 2 diabetes mellitus (T2M). Insulin and also IGF2 are known to be anabolic bone hormones. The "sweet bone" in T2M usually associates increased density, but altered microarchitecture. Therefore, preptin was proposed to be one of the energy regulatory hormones that positively impacts bone health. Experimental data demonstrate a beneficial impact of preptin upon the osteoblasts. Preptin also appears to regulate osteocalcin secretion, which in turn regulates insulin sensitivity. Preptin is greatly influenced by the glucose tolerance status and the level of physical exercise, both influencing the bone mass. Clinical studies describe low serum preptin concentrations in osteoporosis in both men and women, therefore opening the way towards considering preptin a potential bone anabolic therapy. The current review addresses the relationship between preptin and bone mass and metabolism in the experimental and clinical setting, also considering the effects of preptin on carbohydrate metabolism and the pancreatic-bone loop.

Association between non-alcoholic fatty liver disease and bone turnover markers in southwest China

INTRODUCTION

Non-alcoholic fatty liver disease (NAFLD) is not considered only a liver disease but also associated with an increased risk of extra-hepatic diseases including bone metabolism disorders. In our study, we aim to explore the changes of several bone turnover markers (BTMs) under different fat deposition and stiffness levels of the liver.

MATERIALS AND METHODS

We analyzed the physical examination data of 3353 subjects from February 2018 to June 2021 in this study. The steatosis and stiffness of liver were quantitatively detected using the fat attenuation parameter (FAP) and liver stiffness measurements (LSM) of transient elastography (TE). Serum 25-hydroxyvitamin D3 (25(OH)D3), osteocalcin, carboxy-terminal collagen crosslinks (CTX), amino terminal elongation peptide of total type 1 procollagen (P1NP) were tested. Clinical and other biochemical data were also collected.

RESULTS

With the increasing of FAP, the levels of 25(OH)D3 and osteocalcin decreased, the difference was statistically significant. No correlation was found between LSM and all the four BTMs. Logistic regression analysis revealed that FAP ≥ 244 dB/m was negatively correlated with 25(OH)D3 (in both males and females) and osteocalcin (only in males). No correlation was found between FAP ≥ 244 dB/m and P1NP or CTX.

CONCLUSION

The degree of liver adipose deposition was found to be negatively associated with the serum levels of 25(OH)D3 (in both males and females) and osteocalcin (only in males) in southwest China.

Osteocalcin is associated with triglyceride glucose index rather than HOMA-IR in men with type 2 diabetes

INTRODUCTION

The involvement of osteocalcin in the regulation of glucose tolerance in humans is controversial. We utilized a novel and practical insulin resistance surrogate, the triglyceride-glucose (TyG) index, to investigate the association between serum osteocalcin and insulin resistance in men with type 2 diabetes (T2D).

METHODS

This was a retrospective cross-sectional study that included 667 male patients suffering from T2D, with measurements of N-terminal mid-fragment of osteocalcin (N-MID), triglycerides (TG), fasting blood glucose (FBG) and C-peptide collected on the same day. We used the TyG index and HOMA-IR as surrogate measures for insulin resistance. Binary logistic regression models that adjust the sociodemographic characteristics and metabolism-related factors were used to assess the associations between osteocalcin and insulin resistance. Restricted cubic spline (RCS) analysis was used to test the potential non-linear relationship between N-MID and the risk of severe insulin resistance. Subgroup analysis evaluated the robustness of the association.

RESULTS

N-MID was correlated with the level of insulin resistance when quantified by the TyG index in unadjusted and adjusted binary logistic regression models (all p < 0.05), but the relationship was not observed when assessed by HOMA-IR (all p > 0.05). RCS model further confirmed that the association between N-MID and the severe insulin resistance measured by the TyG index was non-linear (P = 0.047). Subgroup analysis showed that the association was detected only in younger patients with lower BMI and poorer glycemic control, without hypertension or smoking.

CONCLUSIONS

Osteocalcin was inversely associated with the TyG index in men with T2D.

The Influence of Obesity, Ovariectomy, and Greenshell Mussel Supplementation on Bone Mineral Density in Rats

Obesity is considered to impair long-term health by disturbing multiple physiological functions. However, it remains a controversial issue as to whether obesity has beneficial or detrimental effects on bone health in postmenopausal women. The aims of this study were to investigate the relationships between obesity and bone mineral density (BMD) under conditions of ovarian hormone deficiency in an animal model and to evaluate the potential health benefits of Greenshell mussel (GSM) on bone health. A total of 144 adult female Sprague-Dawley rats were fed from age 12 weeks on one of four diets (normal [ND]; ND + GSM; high fat/high sugar [HF/HS]; HF/HS + GSM; n = 36 per diet). At age 20 weeks, after a dual-energy X-ray absorptiometry (DXA) scan, 12 of the rats on each diet underwent ovariectomy (OVX) and the remaining rats were left intact. Twelve of the intact rats in each diet group were culled at age 26 weeks (short-term cohort). The remaining rats were culled at age 48 weeks (long-term cohort). Rats were DXA scanned before cull, then various fat pads were dissected. The results revealed that HF/HS rats and OVX rats dramatically increased body weight and fat deposition in correlation with leptin. In the long-term cohort, vertebral spine BMD rapidly declined after OVX. At termination, the OVX rats had decreased plasma bone turnover markers of CTX-1 and TRAP when compared with sham rats. Significantly higher BMD was found in OVX rats fed the HF/HS diet compared with ND, but this difference was not recapitulated in intact rats. BMD of right femur was significantly increased 5% to 10% by GSM in the short-term cohort. The data demonstrated that obesity can be beneficial by increasing BMD in OVX rats, and this may extrapolate to postmenopausal women as adipocyte-produced estrogen may slightly compensate for the reduction in ovarian hormones. Finally, the data showed that GSM may be beneficial to bone health by increasing BMD accrual. © 2021 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

Stress Hyperglycemia and Osteocalcin in COVID-19 Critically Ill Patients on Artificial Nutrition

We aimed to study the possible association of stress hyperglycemia in COVID-19 critically ill patients with prognosis, artificial nutrition, circulating osteocalcin, and other serum markers of inflammation and compare them with non-COVID-19 patients. Fifty-two critical patients at the intensive care unit (ICU), 26 with COVID-19 and 26 non-COVID-19, were included. Glycemic control, delivery of artificial nutrition, serum osteocalcin, total and ICU stays, and mortality were recorded. Patients with COVID-19 had higher ICU stays, were on artificial nutrition for longer (p = 0.004), and needed more frequently insulin infusion therapy (p = 0.022) to control stress hyperglycemia. The need for insulin infusion therapy was associated with higher energy (p = 0.001) and glucose delivered through artificial nutrition (p = 0.040). Those patients with stress hyperglycemia showed higher ICU stays (23 ± 17 vs. 11 ± 13 days, p = 0.007). Serum osteocalcin was a good marker for hyperglycemia, as it inversely correlated with glycemia at admission in the ICU (r = -0.476, p = 0.001) and at days 2 (r = -0.409, p = 0.007) and 3 (r = -0.351, p = 0.049). In conclusion, hyperglycemia in critically ill COVID-19 patients was associated with longer ICU stays. Low circulating osteocalcin was a good marker for stress hyperglycemia.

Osteocalcin Is Independently Associated with C-Reactive Protein during Lifestyle-Induced Weight Loss in Metabolic Syndrome

Bone-derived osteocalcin has been suggested to be a metabolic regulator. To scrutinize the relation between osteocalcin and peripheral insulin sensitivity, we analyzed changes in serum osteocalcin relative to changes in insulin sensitivity, low-grade inflammation, and bone mineral density following lifestyle-induced weight loss in individuals with metabolic syndrome (MetS). Participants with MetS were randomized to a weight loss program or to a control group. Before and after the 6-month intervention period, clinical and laboratory parameters and serum osteocalcin levels were determined. Changes in body composition were analyzed by dual-energy X-ray absorptiometry (DXA). In participants of the intervention group, weight loss resulted in improved insulin sensitivity and amelioration of inflammation. Increased serum levels of osteocalcin correlated inversely with BMI (r = −0.63; p< 0.001), total fat mass (r = −0.58, p < 0.001), total lean mass (r = −0.45, p < 0.001), C-reactive protein (CRP) (r = −0.37; p < 0.01), insulin (r = −0.4; p < 0.001), leptin (r = −0.53; p < 0.001), triglycerides (r = −0.42; p < 0.001), and alanine aminotransferase (ALAT) (r = −0.52; p < 0.001). Regression analysis revealed that osteocalcin was independently associated with changes in CRP but not with changes in insulin concentration, fat mass, or bone mineral density, suggesting that weight loss-induced higher serum osteocalcin is primarily associated with reduced inflammation.

Distinct Effects of a High Fat Diet on Bone in Skeletally Mature and Developing Male C57BL/6J Mice

Increased risks of skeletal fractures are common in patients with impaired glucose handling and type 2 diabetes mellitus (T2DM). The pathogenesis of skeletal fragility in these patients remains ill-defined as patients present with normal to high bone mineral density. With increasing cases of glucose intolerance and T2DM it is imperative that we develop an accurate rodent model for further investigation. We hypothesized that a high fat diet (60%) administered to developing male C57BL/6J mice that had not reached skeletal maturity would over represent bone microarchitectural implications, and that skeletally mature mice would better represent adult-onset glucose intolerance and the pre-diabetes phenotype. Two groups of developing (8 week) and mature (12 week) male C57BL/6J mice were placed onto either a normal chow (NC) or high fat diet (HFD) for 10 weeks. Oral glucose tolerance tests were performed throughout the study period. Long bones were excised and analysed for ex vivo biomechanical testing, micro-computed tomography, 2D histomorphometry and gene/protein expression analyses. The HFD increased fasting blood glucose and significantly reduced glucose tolerance in both age groups by week 7 of the diets. The HFD reduced biomechanical strength, both cortical and trabecular indices in the developing mice, but only affected cortical outcomes in the mature mice. Similar results were reflected in the 2D histomorphometry. Tibial gene expression revealed decreased bone formation in the HFD mice of both age groups, i.e., decreased osteocalcin expression and increased sclerostin RNA expression. In the mature mice only, while the HFD led to a non-significant reduction in runt-related transcription factor 2 (Runx2) RNA expression, this decrease became significant at the protein level in the femora. Our mature HFD mouse model more accurately represents late-onset impaired glucose tolerance/pre-T2DM cases in humans and can be used to uncover potential insights into reduced bone formation as a mechanism of skeletal fragility in these patients.

Associations between Osteocalcin, Calciotropic Hormones, and Energy Metabolism in a Cohort of Chinese Postmenopausal Women: Peking Vertebral Fracture Study

OBJECTIVE

The endocrine function of bone in energy metabolism may be mediated by the osteocalcin (OC). We examined the association between OC and energy metabolism among Chinese postmenopausal women. Design and Setting. A cross-sectional cohort study enrolling 1635 participants was conducted using data from the Peking Vertebral Fracture study. Partial correlation analysis was performed to explore the correlation of OC, parathyroid hormone (PTH), or 25-hydroxyvitamin D (25(OH)D) with glycemic and lipid metabolic parameters. A logistic regression model was used to investigate the association of OC, PTH, or 25(OH)D with the prevalence of diabetes and dyslipidemia.

RESULTS

Serum levels of OC, PTH, and 25(OH)D were all positively correlated with serum cholesterol levels, whereas only OC was negatively associated with serum glucose level. In the logistic regression model, both OC and PTH were negatively associated with the prevalence of diabetes (odds ratio [OR], 95% confidence interval [95% CI]: 0.967, 0.948-0.986 for OC and 0.986, 0.978-0.994 for PTH). No significant association was found between 25(OH)D and diabetes. Both OC and 25(OH)D, rather than PTH, were associated with abnormalities of high cholesterol levels, such as hypercholesterolemia and high LDL-C levels. Further classifying the population based on the median value of OC and PTH, low OC and low PTH subgroup had the highest OR, 95% CI for diabetes (1.873, 1.287-2.737) and the lowest OR, 95% CI for hypercholesterolemia (0.472, 0.324-0.688) and for high LDL-C (0.538, 0.376-0.771).

CONCLUSION

Among Chinese postmenopausal women, a lower serum level of OC was associated with a higher prevalence of diabetes and lower serum cholesterol levels, and a low PTH concentration could magnify these associations.

Low Bone Turnover Markers in Young and Middle-Aged Male Patients with Type 2 Diabetes Mellitus

Accumulating evidence has supported an increased risk of osteoporotic fracture in postmenopausal women and elderly men diagnosed with diabetes mellitus. However, it is not uncommon for young and middle-aged male patients diagnosed with type 2 diabetes mellitus (T2DM) to suffer from osteopenia or osteoporosis. Few studies focused on this population group are available. The aim of this study is to evaluate bone metabolic status and investigate the influence of T2DM on bone metabolism in 30-50-year-old men. Anthropometric assessment and blood samples were obtained from 160 patients with T2DM and 69 nondiabetic volunteers. Serum parathyroid hormone (PTH) and bone turnover markers (BTMs), including serum procollagen type I N-terminal peptide (PINP), osteocalcin (OC), and β-cross-linked C-telopeptide of type I collagen (β-CTX), were analysed. No significant differences were observed based on age, body mass index, systolic blood pressure, serum calcium, phosphorus, creatinine, total protein, and albumin levels when comparing T2DM and control groups. Fasting blood glucose, HbA1c, triglyceride (TG), total cholesterol, and low-density lipoprotein cholesterol were significantly increased, while high-density lipoprotein cholesterol was significantly decreased in the T2DM group. Compared with controls, diabetic patients showed lower serum PINP, OC, and PTH levels, whereas serum β-CTX levels were similar between the two groups. Moreover, HbA1c levels were positively correlated with PINP and inversely associated with PTH levels. TG levels were negatively correlated with OC or β-CTX levels. Furthermore, multiple linear regression revealed a positive correlation between HbA1c and PINP levels. These results also revealed a negative association between HbA1c and PTH, and between TG and OC levels, even after adjusting for expected confounder factors. Collectively, these findings indicated that young and middle-aged male patients with T2DM showed a lower turnover state resulting from bone formation inhibition. Glucose and lipid metabolic disorders may affect bone formation through different pathways.

Bone health in diabetes and prediabetes

Bone fragility has been recognized as a complication of diabetes, both type 1 diabetes (T1D) and type 2 diabetes (T2D), whereas the relationship between prediabetes and fracture risk is less clear. Fractures can deeply impact a diabetic patient's quality of life. However, the mechanisms underlying bone fragility in diabetes are complex and have not been fully elucidated. Patients with T1D generally exhibit low bone mineral density (BMD), although the relatively small reduction in BMD does not entirely explain the increase in fracture risk. On the contrary, patients with T2D or prediabetes have normal or even higher BMD as compared with healthy subjects. These observations suggest that factors other than bone mass may influence fracture risk. Some of these factors have been identified, including disease duration, poor glycemic control, presence of diabetes complications, and certain antidiabetic drugs. Nevertheless, currently available tools for the prediction of risk inadequately capture diabetic patients at increased risk of fracture. Aim of this review is to provide a comprehensive overview of bone health and the mechanisms responsible for increased susceptibility to fracture across the spectrum of glycemic status, spanning from insulin resistance to overt forms of diabetes. The management of bone fragility in diabetic patient is also discussed.

Metformin one in a Million Efficient Medicines for Rheumatoid Arthritis Complications: Inflammation, Osteoblastogenesis, Cardiovascular Disease, Malignancies

BACKGROUND

Rheumatoid arthritis is a widespread autoimmune disease and inflammation and bone destruction are two main issues in rheumatoid arthritis.

OBJECTIVE

To discussing metformin effects on rheumatoid arthritis complications.

METHODS

We conducted a narrative literature search including clinical trials, experimental studies on laboratory animals and cell lines. Our search covered Medline, PubMed and Google Scholar databases from 1999 until 2018. We used the terms" Metformin; Rheumatoid arthritis; Cardiovascular disease; Cancer; Osteoblastogenesis.

DISCUSSION

Inflammatory pro-cytokines such as Interlukin-6 play important roles in T. helper 17 cell lineage differentiation. Interlukin-6 and Tumor Necrosis Factor-α activate Janus kinase receptors signal through signaling transducer and activator of transcription signaling pathway which plays important role in inflammation, bone destruction and cancer in rheumatoid arthritis patients. Interlukin-6 and Tumor Necrosis Factor-α synergistically activate signaling transducer and activator of transcription and Nuclear Factor-kβ pathways and both cytokines increase the chance of cancer development in rheumatoid arthritis patients. Metformin is AMPK activators that can suppress mTOR, STAT3 and HIF-1 so AMPK activation plays important role in suppressing inflammation and osteoclastogenesis and decreasing cancer.

CONCLUSION

Metformin effect on AMPK and mTOR pathways gives the capability to change Treg/Th17 balance and decrease Th17 differentiation and inflammation, osteoclastogenesis and cancers in RA patients. Metformin can be useful in protecting bones especially in first stages of RA and it can decrease inflammation, CVD and cancer in RA patients so Metformin beside DAMARs can be useful in increasing RA patients' life quality with less harm and cost.

Correlation Between Serum miR-154-5p and Osteocalcin in Males and Postmenopausal Females of Type 2 Diabetes With Different Urinary Albumin Creatinine Ratios

Purpose: To investigate the serum levels of miR-154-5p, osteocalcin (OC), and other clinical parameters in male and post-menopausal female type 2 diabetes mellitus (T2DM) patients with different urinary albumin creatinine ratio (UACR) levels and to discuss the relationship between miR-154-5p and glycolipid metabolism, bone metabolism, and different urinary albumin excretion rate in T2DM. Methods: Seven hundred thirty-eight T2DM patients were categorized into six groups, including 374 men and 364 post-menopausal women who were sub-divided into three groups based on albumin excretion that involved normal albuminuria, microalbuminuria, and large amount of albuminuria (138, 127, 109, 135, 125, and 104 cases, UACR<30, 30-300, and >300 mg/g, M1, M2, M3, F1, F2, and F3). Measurement of circulating miR-154-5p, OC, and other biochemical indicators were performed by real-time PCR, ELISA, and chemiluminescence assays in T2DM patients and in 141 M0 and 139 F0 control subjects. Results: There are few differences appeared between groups. Comparing with men, women had higher age, waist-to-hip ratio (WHR), adiponectin (ADPN), connective tissue growth factor (CTGF), UACR, procollagen type 1 N-terminal propeptide (P1NP), β-C-terminal telopeptide of type I collagen (β-CTx), OC, and miR-154-5p, but lower FPG, HOMA-IR, and HbA1c. T2DM patients with albuminuria (micro or macro) had lower bone turnover markers (P1NP, β-CTx, and OC) and adiponectin, but higher HbA1c, CTGF, and miR-154-5p. In addition, after regression analysis, UACR was positively correlated with CTGF, HbA1c, and miR-154-5p, and negatively correlated with ADPN and bone turnover markers (P1NP, β-CTx, and OC). However, OC showed a positive correlation with ADPN and other bone turnover markers (P1NP and β-CTx), but negative correlation with CTGF, UACR, and miR-154-5p in all three groups. Conclusion: These findings suggested that increased serum levels of miR-154-5p and decreased OC levels may influence osteogenesis and proteinuria in T2DM and may identify novel targets for diagnosis and treatment of diabetic kidney disease and osteoporosis.

Relationship between serum osteocalcin/undercarboxylated osteocalcin and type 2 diabetes: a systematic review/meta-analysis study protocol

INTRODUCTION

The global burden of type 2 diabetes (T2DM) is steadily increasing. Experimental studies have demonstrated that a novel hormone secreted by bone cells, osteocalcin (OC), can stimulate beta-cell proliferation and improve insulin sensitivity in mice. Observational studies in humans have investigated the relationship between OC and metabolic parameters, and T2DM. Importantly, few studies have reported on the undercarboxylated form of OC (ucOC), which is the putative active form of OC suggested to affect glucose metabolism.

OBJECTIVES

We will conduct a systematic review and meta-analysis to: (1) compare the levels of serum OC and ucOC between T2DM and normal glucose-tolerant controls (NGC); (2) investigate the risk ratios between serum OC and ucOC, and T2DM; (3) determine the correlation coefficient between OC and ucOC and fasting insulin levels, homeostatic model assessment-insulin resistance, haemoglobin A1c and fasting glucose levels and (4) explore potential sources of between-study heterogeneity. The secondary objective is to compare the serum OC and ucOC between pre-diabetes (PD) and NGC and between T2DM and PD.

HODS AND ANALYSIS

This study will report items in line with the guidelines outlined in preferred reporting items for systematic reviews and meta-analysis of observational studies in epidemiology. We will include observational studies (cohort, case-control and cross-sectional studies) and intervention studies with baseline data. Three databases (MEDLINE, EMBASE and SCOPUS) will be searched from inception until July 2018 without language restrictions. Two reviewers will independently screen the titles and abstracts and conduct a full-text assessment to identify eligible studies. Discrepancies will be resolved by consensus with a third reviewer. The risk of bias assessment will be conducted by two reviewers independently based on the Newcastle-Ottawa Scale. Potential sources of between-study heterogeneity will be tested using meta-regression/subgroup analyses. Contour-enhanced funnel plots and Egger's test will be used to identify potential publication bias.

ETHICS AND DISSEMINATION

Formal ethical approval is not required. We will disseminate the results to a peer-reviewed publication and conference presentation.

PROSPERO REGISTRATION NUMBER

CRD42017073127.

Acute continuous moderate-intensity exercise, but not low-volume high-intensity interval exercise, attenuates postprandial suppression of circulating osteocalcin in young overweight and obese adults

Bone remodeling markers (BRMs) are suppressed following the consumption of a meal. Our findings indicate that a single session of continuous moderate-intensity exercise, but not low-volume high-intensity interval exercise, performed 1 h after a meal attenuates the postprandial suppression of BRMs.

INTRODUCTION

Acute exercise transiently increases BRMs including osteocalcin (tOC) and the undercarboxylated form of osteocalcin (ucOC), a hormone that is implicated in glucose regulation. The effects of acute exercise and exercise-intensity on postprandial levels of tOC and ucOC are unknown.

METHODS

Twenty-seven adults that were overweight or obese (age 30 ± 1 years; BMI 30 ± 1 kg∙m^-2; mean ± SEM) were randomly allocated to perform a single session of low-volume high-intensity interval exercise (LV-HIIE; nine females, five males) or continuous moderate-intensity exercise (CMIE; eightfemales, five males) 1 h after consumption of a standard breakfast. Serum tOC, ucOC, and ucOC/tOC were measured at baseline, 1 h, and 3 h after breakfast consumption on a rest day (no exercise) and the exercise day (exercise 1 h after breakfast).

RESULTS

Compared to baseline, serum tOC and ucOC were suppressed 3 h after breakfast on the rest day (- 10 ± 1% and - 6 ± 2%, respectively; p < 0.05), whereas ucOC/tOC was elevated (2.5 ± 1%; p = 0.08). Compared to the rest day, CMIE attenuated the postprandial-induced suppression of tOC (rest day - 10 ± 2% versus CMIE - 5 ± 2%, p < 0.05) and ucOC (rest day - 6 ± 4% versus CMIE 11 ± 2%, p < 0.05), and increased postprandial ucOC/tOC (rest day 3 ± 2% versus CMIE 15 ± 1%, p < 0.05). In contrast, LV-HIIE did not alter postprandial tOC, ucOC, or ucOC/tOC (all p > 0.1).

CONCLUSIONS

Acute CMIE, but not LV-HIIE, attenuates the postprandial-induced suppression of tOC and ucOC. CMIE may be an effective tool to control the circulating levels of BRMs following meal consumption in overweight/obese adults.

A dual-label time-resolved fluorescence immunoassay for screening of osteoporosis based on simultaneous detection of C-terminal telopeptide (β-CTX) and aminoterminal propeptide (P1NP) of type I procollagen

Osteoporosis is a disease where increased bone weakness increases the risk of a broken bone. Until a broken bone occurs, there are typically no symptoms. Osteoporosis affects more than 75 million people in the United States, Europe and Japan. The diagnosis of osteoporosis is primarily determined by measuring bone mineral density using dual-energy X-ray absorptiometry, but for men under 50 years of age, premenopausal women should not be made on the basis of densitometric criteria alone. Bone biomarkers are a useful tool in detecting osteoporotic. A two-step dual-label time-resolved fluorescence immunoassay (TRFIA) was developed for the simultaneous detection of serum C-terminal telopeptide (β-CTX) and amino-terminal propeptide (P1NP) of Type I procollagen in a single run. The performance of this assay was first evaluated using clinical serum samples, and then compared with commercialized kits. The sensitivity of this assay for β-CTX was 1 ng/L (dynamic range, 0-1000 ng/L), and the sensitivity for P1NP detection was 1 μg/L (dynamic range, 1-1000 μg/L). High correlation coefficients (R) were obtained between the present dual-label TRFIA and commercially available kits (R = 0.99 for β-CTX and P1NP). The present dual-label TRFIA has high sensitivity, specificity and accuracy in clinical sample analysis. It is a good alternative to the single-label diagnostic methods.

High Fat Mixed Meal Tolerance Test Leads to Suppression of Osteocalcin Decrease in Obese Insulin Resistant Subjects Compared to Healthy Adults

Nutrients influence bone turnover. Carboxylated osteocalcin (Gla-OC) participates in bone formation whereas its undercarboxylated form (Glu-OC) acts as a hormone in glucose metabolism. The aim of the study was to determine the responses of Gla-OC, Glu-OC, and total-OC (calculated as the sum of Gla-OC and Glu-OC) to a high fat mixed meal tolerance test (HFMTT) in non-obese (body mass index (BMI) < 30 kg/m², n = 24) and obese subjects (30 < BMI < 40 kg/m², n = 70) (both sexes, aged 25–65 years). Serum Gla-OC and Glu-OC were measured at baseline as well as at 2 and 6 h during a HFMTT by enzyme-linked immunosorbent assay (ELISA). Baseline Gla-OC, Glu-OC, and total-OC levels were lower in obese individuals compared to non-obese participants (p = 0.037, p = 0.016 and p = 0.005, respectively). The decrease in Gla-OC and total-OC, but not in Glu-OC, concentrations during the HFMTT was suppressed in obese, but not in non-obese controls (p < 0.05, p < 0.01, p = 0.08, respectively). Subjects with the highest homeostatic model assessment for insulin resistance (HOMA-IR) index values had a less pronounced decrease in total-OC compared to patients with values of HOMA-IR index in the 1st quartile (p < 0.05). Net incremental area under Gla-OC inversely correlated with adiponectin (rho = −0.35, p = 0.001). Increase in insulin sensitivity and adiponectin level in obese subjects could beneficially influence postprandial bone turnover expressed by osteocalcin concentration.

Association of bone turnover markers with glucose metabolism in Chinese population

The association between type 2 diabetes (T2DM) and bone metabolism has been discussed previously but is controversial. In this study we aimed to evaluate the association of bone turnover markers with glucose metabolism in Chinese population, in which 919 males and 4171 postmenopausal females in a region of Shanghai were recruited. Anthropometric and biochemical traits related to glucose and bone metabolism were analyzed. Participants were classified according to their glucose tolerance as normal glucose tolerance (NGT), impaired glucose regulation (IGR) or T2DM. Males and females were analyzed separately, and then associations between bone turnover markers (BTMs) and glucose metabolism were evaluated. The results showed that in females, the serum levels of N-terminal osteocalcin (N-MID), N-terminal procollagen of type I collagen (PINP) and β-cross-linked C-telopeptide of type I collagen (β-CTX) were significantly decreased in the T2DM group compared to the NGT group (P<0.01). When age, body mass index, serum lipids, fat percentage, visceral fat area, subcutaneous fat area, anti-diabetic medicines, PINP, N-MID and β-CTX were included in one logistic model, N-MID (OR [95% CI]: 0.954 [0.932; 0.976]; P=0.0001) was significantly associated with T2DM in females. In females, N-MID was associated with insulin sensitivity and HOMA-β. PINP was significantly associated with HOMA-β, GUTT-ISI, Stumvoll first-phase insulin secretion index (STU-1) and Stumvoll second-phase insulin secretion index (STU-2), but β-CTX was associated only with HOMA-β (β±SE: 0.1331±0.0311; P=1.95×10^-5) and GUTT-ISI (β±SE: 0.0727±0.0229; P=0.0015). In males, N-MID was significantly correlated with HOMA-β (β±SE: 0.3439±0.0633; P=7.75×10^-8), GUTT-ISI (β±SE: 0.1601±0.0531; P=0.0027) and STU-1 (β±SE: 0.2529±0.1033; P=0.0146). Significant associations were also detected between β-CTX and HOMA-β (β±SE: 0.2736±0.0812; P=0.0009). This study reveals that BTMs are highly associated with T2DM, insulin sensitivity and beta cell function in both Chinese males and postmenopausal females.

Association of Bone Metabolic Markers With Diabetic Retinopathy and Diabetic Macular Edema in Elderly Chinese Individuals With Type 2 Diabetes Mellitus

BACKGROUND

Diabetic retinopathy (DR) is a common and specific microvascular complication of diabetes. The association of bone metabolic markers with the risk of DR and diabetic macular edema (DME) is unclear.

MATERIALS AND METHODS

We investigated the association between bone turnover markers commonly examined in a clinical setting and DR and DME risk in elderly Chinese patients with type 2 diabetes mellitus (T2DM). A total of 408 patients aged 55-70 years with T2DM were included. We first performed univariable logistic regression followed by multivariable logistic regression that included variables selected using purposeful selection.

RESULTS

Fasting blood glucose (P = 0.007) and duration of diabetes (P < 0.0001) were significantly associated with DME in multivariable logistic regression; however, the association of beta C-terminal telopeptide of collagen type I (β-CTx) with DME risk was not statistically significant (P = 0.053). Sex-stratified analysis showed that β-CTx was significantly associated with DME only in female subjects (P = 0.011).

CONCLUSIONS

β-CTx had no significant association with DR. It was significantly associated with DME in female patients with T2DM, but not in male patients with T2DM. More prospective studies with larger sample sizes are warranted to validate our findings.

Circulating osteocalcin is unrelated to glucose homoeostasis in adults with type 1 diabetes

AIMS

To assess the relationship between total osteocalcin (tOC), undercarboxylated osteocalcin (ucOC) and a range of markers of glucose homeostasis in type 1 diabetes.

METHODS

One hundred and eight community-based Caucasian adults (53 males, 55 females) without a history of osteoporosis and with a mean±SD age 39.1±15.1years and median [inter-quartile range] type 1 diabetes duration of 14.3 [6.6-20.4] years participated in a cross-sectional study of bone health. Fasting serum glucose and HbA_1c, and serum tOC, ucOC, total adiponectin and procollagen type 1N-terminal propeptide (P1NP) were measured using validated assays, and daily insulin dose and estimated glucose disposal rate (eGDR) were calculated. Multiple linear regression was used to determine independent associates of markers of glucose homoeostasis (HbA_1c, fasting serum glucose, daily insulin dose, eGDR and serum total adiponectin).

RESULTS

In sex-adjusted multivariable regression analyses, ln(serum P1NP) was independently and inversely associated with ln(HbA_1c) and ln(serum adiponectin) (P≤0.013). Other associations included those between ln(serum vitamin D) and ln(HbA_1c) (inversely), daily insulin dose (inversely) and eGDR (positively) (P≤0.035), as well as an inverse relationship between overweight by waist circumference and ln(serum adiponectin) (P<0.001). Ln(serum tOC) and ln(serum ucOC) were not independently associated with any glucose homoeostasis marker.

CONCLUSIONS

These data from well characterized community-based adults with type 1 diabetes do not suggest that there is a role for osteocalcin in the potentially complex interplay between the skeleton and energy homoeostasis in type 1 diabetes.

Women with type 2 diabetes mellitus have lower cortical porosity of the proximal femoral shaft using low-resolution CT than nondiabetic women, and increasing glucose is associated with reduced cortical porosity

Increased cortical porosity has been suggested as a possible factor increasing fracture propensity in patients with type 2 diabetes mellitus (T2DM). This is a paradox because cortical porosity is generally associated with high bone turnover, while bone turnover is reduced in patients with T2DM. We therefore wanted to test the hypothesis that women with T2DM have lower bone turnover markers (BTM) and lower cortical porosity than those without diabetes, and that higher serum glucose and body mass index (BMI) are associated with lower BTM, and with lower cortical porosity. This cross-sectional study is based on a prior nested case-control study including 443 postmenopausal women aged 54-94years from the Tromsø Study, 211 with non-vertebral fracture and 232 fracture-free controls. Of those 443 participants, 22 women exhibited T2DM and 421 women did not have diabetes. All had fasting blood samples assayed for procollagen type I N-terminal propeptide (PINP), C-terminal cross-linking telopeptide of type I collagen (CTX) and glucose, and femoral subtrochanteric architecture was quantified using low-resolution clinical CT and StrAx1.0 software. Women with T2DM had higher serum glucose (7.2 vs. 5.3mmol/L), BMI (29.0 vs. 26.4kg/m²), and higher femoral subtrochanteric total volumetric bone mineral density (vBMD) (783 vs. 715mgHA/cm³), but lower cortical porosity (40.9 vs. 42.8%) than nondiabetic women (all p<0.05). Each standard deviation (SD) increment in glucose was associated with 0.10-0.12 SD lower PINP and CTX, and 0.13 SD lower cortical porosity (all p<0.05). Each SD increment in BMI was associated with 0.10-0.18 SD lower serum PINP and CTX, and 0.19 SD thicker cortices (all p<0.05). Increasing glucose and BMI were associated with lower bone turnover suggesting that reduced intracortical and endocortical remodeling leads to reduced porosity and thicker cortices. Using low-resolution clinical CT, cortical porosity was lower in women with T2DM compared to women without diabetes. This indicates that other changes in bone qualities, not increased cortical porosity, are likely to explain the increased fracture propensity in patients with T2DM.

Marrow adipose tissue spectrum in obesity and type 2 diabetes mellitus

OBJECTIVE

To assess the association of bone mass and marrow adipose tissue (MAT) with other fat depots, insulin resistance, bone remodeling markers, adipokines and glucose control in type 2 diabetes and obesity.

DESIGN AND METHODS

The study groups comprised 24 controls (C), 26 obese (O) and 28 type 2 diabetes. Dual-energy X-ray absorptiometry was used to determine bone mineral density (BMD). Blood samples were collected for biochemical measurements. ¹H Magnetic resonance spectroscopy was used to assess MAT in the L3 vertebra, and abdominal magnetic resonance imaging was used to assess intrahepatic lipids in visceral (VAT) and subcutaneous adipose tissue. Regression analysis models were used to test the association between parameters.

RESULTS

At all sites tested, BMD was higher in type 2 diabetes than in O and C subjects. The C group showed lower VAT values than the type 2 diabetes group and lower IHL than the O and type 2 diabetes groups. However, MAT was similar in the 3 groups. Osteocalcin and C-terminal telopeptide of type 1 collagen were lower in type 2 diabetes than those in C and O subjects. Moreover, at all sites, BMD was negatively associated with osteocalcin. No association was observed between MAT and VAT. No relationship was observed among MAT and HOMA-IR, leptin, adiponectin or Pref-1, but MAT was positively associated with glycated hemoglobin.

CONCLUSIONS

MAT is not a niche for fat accumulation under conditions of energy surplus and type 2 diabetes, also is not associated with VAT or insulin resistance. MAT is associated with glycated hemoglobin.

Suitable bone markers assessing bone status in patients with both coronary artery disease and diabetes

Background

We aimed to investigate the bone turnover markers in coronary artery disease (CAD) patients with and without type 2 diabetes (T2DM) in comparison with control subjects without CAD and T2DM.

Methods

This cross-sectional study was performed on 45 subjects undergoing elective heart surgery; either for coronary artery bypass grafting or for valve surgery. According to angiographic results, participants were grouped in two groups with CAD (n = 33) and without CAD (n = 12).

The serum levels of osteocalcin (OC), procollagen I aminoterminal propeptide (P1NP) and carboxy-terminal collagen crosslinks (CTX), as bone turnover markers, as well as serum levels of 25 (OH) vitamin D3, PTH, and common metabolic factors were analyzed in all participants.

Results

Serum levels of bone markers did not differ in patients with CAD compared to non-CAD subjects. Regarding metabolic factors, serum levels of FBG had invert correlation with OC in CAD patients (p = 0.004). The data of subgroup analysis showed serum levels of OC and CTX were statistically significant lower in CAD-DM than CAD-non DM (p < 0.05). There were not any significant differences in the P1NP levels between groups.

Conclusions

Our data suggest that CTX and OC would be used as suitable bone markers in CAD patients with T2DM. However, further clinical studies need to establish the role of these markers in CAD patients with diabetes.

Molecular Actions of Glucocorticoids in Cartilage and Bone During Health, Disease, and Steroid Therapy

Cartilage and bone are severely affected by glucocorticoids (GCs), steroid hormones that are frequently used to treat inflammatory diseases. Major complications associated with long-term steroid therapy include impairment of cartilaginous bone growth and GC-induced osteoporosis. Particularly in arthritis, GC application can increase joint and bone damage. Contrarily, endogenous GC release supports cartilage and bone integrity. In the last decade, substantial progress in the understanding of the molecular mechanisms of GC action has been gained through genome-wide binding studies of the GC receptor. These genomic approaches have revolutionized our understanding of gene regulation by ligand-induced transcription factors in general. Furthermore, specific inactivation of GC signaling and the GC receptor in bone and cartilage cells of rodent models has enabled the cell-specific effects of GCs in normal tissue homeostasis, inflammatory bone diseases, and GC-induced osteoporosis to be dissected. In this review, we summarize the current view of GC action in cartilage and bone. We further discuss future research directions in the context of new concepts for optimized steroid therapies with less detrimental effects on bone.

Glucose-loading reduces bone remodeling in women and osteoblast function in vitro

Aging is associated with a reduction in osteoblast life span and the volume of bone formed by each basic multicellular unit. Each time bone is resorbed, less is deposited producing microstructural deterioration. Aging is also associated with insulin resistance and hyperglycemia, either of which may cause, or be the result of, a decline in undercarboxylated osteocalcin (ucOC), a protein produced by osteoblasts that increases insulin sensitivity. We examined whether glucose‐loading reduces bone remodeling and ucOC in vivo and osteoblast function in vitro, and so compromises bone formation. We administered an oral glucose tolerance test (OGTT) to 18 pre and postmenopausal, nondiabetic women at rest and following exercise and measured serum levels of bone remodeling markers (BRMs) and ucOC. We also assessed whether increasing glucose concentrations with or without insulin reduced survival and activity of cultured human osteoblasts. Glucose‐loading at rest and following exercise reduced BRMs in pre and postmenopausal women and reduced ucOC in postmenopausal women. Higher glucose correlated negatively, whereas insulin correlated positively, with baseline BRMs and ucOC. The increase in serum glucose following resting OGTT was associated with the reduction in bone formation markers. D‐glucose (>10 mmol L⁻¹) increased osteoblast apoptosis, reduced cell activity and osteocalcin expression compared with 5 mmol L⁻¹. Insulin had a protective effect on these parameters. Collagen expression in vitro was not affected in this time course. In conclusion, glucose exposure reduces BRMs in women and exercise failed to attenuate this suppression effect. The suppressive effect of glucose on BRMs may be due to impaired osteoblast work and longevity. Whether glucose influences material composition and microstructure remains to be determined.

The effect of hyperinsulinaemic-euglycaemic clamp and exercise on bone remodeling markers in obese men

Bone remodelling markers (BRMs) are suppressed following a glucose load and during glucose infusion. As exercise increases indices of bone health and improves glucose handling, we hypothesised that, at rest, hyperinsulinaemic-euglycaemic clamp will suppress BRMs in obese men and that exercise prior to the clamp will prevent this suppression. Eleven obese nondiabetic men (age 58.1±2.2 years, body mass index=33.1±1.4 kg m(-2) mean±s.e.m.) had a hyperinsulinaemic-euglycaemic clamp (HEC) at rest (Control) and 60 min post exercise (four bouts × 4 min cycling at 95% of hazard ratiopeak). Blood samples were analysed for serum insulin, glucose, bone formation markers, total osteocalcin (tOC) and procollagen type 1 N-terminal propeptide (P1NP), and the bone resorption marker, β-isomerised C-terminal telopeptides (β-CTx). In the control trial (no exercise), tOC, P1NP and β-CTx decreased with HEC by >10% compared with baseline (P<0.05). Fasting serum glucose, but not insulin, tended to correlate negatively with the BRMs (β range -0.57 to -0.66, p range 0.051-0.087). β-CTx, but not OC or P1NP, increased within 60 min post exercise (∼16%, P<0.01). During the post-exercise HEC, the glucose infusion rate was ∼30% higher compared with the no exercise trial. Despite this, BRMs were only suppressed to a similar extent as in the control session (10%). HEC suppressed BRMs in obese men. Exercise did not prevent this suppression of BRMs by HEC but improved glucose handling during the trial. It remains to be tested whether an exercise intervention of longer duration may be able to prevent the effect of HEC on bone remodelling.

Searching for additional endocrine functions of the skeleton: genetic approaches and implications for therapeutics

Our knowledge of whole organism physiology has greatly advanced in the past decades through mouse genetics. In particular, genetic studies have revealed that most organs interact with one another through hormones in order to maintain normal physiological functions and the homeostasis of the entire organism. Remarkably, through these studies many unexpected novel endocrine means to regulate physiological functions have been uncovered. The skeletal system is one example. In this article, we review a series of studies that over the years have identified bone as an endocrine organ. The mechanism of action, pathological relevance, and therapeutic implications of the functions of the bone-derived hormone osteocalcin are discussed. In the last part of this review we discuss the possibility that additional endocrine functions of the skeleton may exist.

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.

The Relationship between Serum Osteocalcin Concentration and Glucose and Lipid Metabolism in Patients with Type 2 Diabetes Mellitus – The Role of Osteocalcin in Energy Metabolism

BACKGROUND

Recent animal studies have found that the osteocalcin secreted by osteoblasts could participate in glucose and lipid metabolism. Our study aimed to investigate the relationship between serum osteocalcin concentration and glucose and lipid metabolism in patients with type 2 diabetes mellitus.

METHODS

985 patients with type 2 diabetes were divided into the male group (n = 495) and the postmenopausal female group (n = 490). The average ages were 54.42 ± 10.535 and 64.93 ± 9.277, respectively. We collected the parameters of age, duration, fasting plasma glucose, HbA1c, fasting insulin, fasting C peptide, blood lipid, 25 (OH) VD3, parathyroid hormone (PTH), Alkaline phosphatase (ALP), procollagen type 1 N-terminal propeptide (P1NP), β-C-terminal telopeptide of type I collagen (β-CTx), osteocalcin, HOMA-IR, HOMA-β, body mass index (BMI), and waist-to-hip ratio (WHR). The relationship of osteocalcin and these parameters were analyzed by Pearson/Spearman correlation analysis and stepwise multiple regression analysis.

RESULTS

Osteocalcin was negatively correlated with HbA1c (p < 0.05) and it was also an independent relevant factor affecting HbA1c in both groups. Osteocalcin was positively correlated with HOMA-β and it was an independent relevant factor affecting HOMA-β in male group (p < 0.01).

CONCLUSIONS

These findings indicate the association between serum osteocalcin and glucose metabolism and beta cell function. No relationship was found between osteocalcin and insulin resistance and lipid metabolism in type 2 diabetes.

Bone as an endocrine organ relevant to diabetes

There are well-established associations between diabetes and fracture risk and yet the mechanism underlying these associations are controversial. Guided by a series of mouse studies, a specific form of the bone protein, osteocalcin, was proposed to be the mechanistic link between these two chronic diseases. Translation to humans initially appeared elusive in part because serum concentrations of osteocalcin are a biomarker of bone turnover and not necessarily specific to the biology of this protein. The suitability of the mouse model for the study of osteocalcin as a therapeutic target also appears ambiguous. With greater discrimination of the different forms of osteocalcin present in circulation and inclusion of multiple measures of bone turnover, evidence currently does not support osteocalcin as a protein critical to the diabetes and fracture association in humans.

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.

Effects of correction of vitamin D insufficiency on serum osteocalcin and glucose metabolism in obese children

OBJECTIVES

Osteocalcin (OCN) and vitamin D insufficiency (VDI) have been shown to be associated with abnormal glucose metabolism (GluMet). Whether correction of VDI affects serum OCN is unknown. This study evaluated the effects of correction of VDI on OCN and GluMet, and determined the associations of OCN with 25-hydroxyvitamin D (25-OHD) and GluMet.

DESIGN, PATIENTS AND MEASUREMENTS

This study involved 230 obese children in a cross-sectional part and 72 participants in a prospective part in which children with VDI were treated with vitamin D2 at a dose of 20 000 IU daily for 28 days. All 230 children underwent an oral glucose tolerance test and had their serum total and undercarboxylated OCNs and 25-OHD measured. Forty of 72 children were reassessed for the GluMet and serum total and undercarboxylated OCNs and 25-OHD after the vitamin D2 treatment.

RESULTS

In the prospective part, correction of VDI by raising mean (SD) 25-OHD of 51·5 (12·3) to 141·8 (40·8) nmol/l resulted in an improvement of their GluMet and increase in their whole-body insulin sensitivity index with no changes in their OCN measures. In the cross-sectional part, after adjustments for age, sex and puberty, the total (β = 0·322) and undercarboxylated OCNs (β = 0·315) were positively associated with insulinogenic index, which is an index of insulin secretion (P = 0·034 and 0·037, respectively) in the group of prediabetic and diabetic children.

CONCLUSIONS

Correction of VDI increased insulin sensitivity and improved GluMet, but had no effect on serum OCN measures. OCN was associated with increased insulin secretion in children with abnormal GluMet.

Glucocorticoids and bone: local effects and systemic implications

Glucocorticoids (GCs) are highly effective in the treatment of inflammatory and autoimmune conditions but their therapeutic use is limited by numerous adverse effects. Recent insights into the mechanisms of action of both endogenous and exogenous GCs on bone cells have unlocked new approaches to the development of effective strategies for the prevention and treatment of GC-induced osteoporosis. Furthermore, topical studies in rodents indicate that the osteoblast-derived peptide, osteocalcin, plays a central role in the pathogenesis of GC-induced diabetes and obesity. These exciting findings mechanistically link the detrimental effects of GCs on bone and energy metabolism. In this article we review the physiology and pathophysiology of GC action on bone cells, and discuss current and emerging concepts regarding the molecular mechanisms underlying adverse effects of GCs such as osteoporosis and diabetes.

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.

Autosomal dominant osteopetrosis revisited: lessons from recent studies

Systematic studies of autosomal dominant osteopetrosis (ADO) were followed by the identification of underlying mutations giving unique possibilities to perform translational studies. What was previously designated ADO1 turned out to be a high bone mass phenotype caused by a missense mutation in the first propeller of LRP5, a region of importance for binding inhibitory proteins. Thereby, ADO1 cannot be regarded as a classical form of osteopetrosis but must now be considered a disease of LRP5 activation. ADO (Albers-Schönberg disease, or previously ADO2) is characterized by increased number of osteoclasts and a defect in the chloride transport system (ClC-7) of importance for acidification of the resorption lacuna (a form of Chloride Channel 7 Deficiency Osteopetrosis). Ex vivo studies of osteoclasts from ADO have shown that cells do form normally but have reduced resorption capacity and an expanded life span. Bone formation seems normal despite decreased osteoclast function. Uncoupling of formation from resorption makes ADO of interest for new strategies for treatment of osteoporosis. Recent studies have integrated bone metabolism in whole-body energy homeostasis. Patients with ADO may have decreased insulin levels indicating importance beyond bone metabolism. There seems to be a paradigm shift in the treatment of osteoporosis. Targeting ClC-7 might introduce a new principle of dual action. Drugs affecting ClC-7 could be antiresorptive, still allowing ongoing bone formation. Inversely, drugs affecting the inhibitory site of LRP5 might stimulate bone formation and inhibit resorption. Thereby, these studies have highlighted several intriguing treatment possibilities, employing novel modes of action, which could provide benefits to the treatment of osteoporosis.

Diabetes mellitus and osteoporosis

Diabetes mellitus (particularly type 2) and osteoporosis are two very common disorders, and both are increasing in prevalence. Adolescents with type 1 diabetes mellitus may not reach potential peak bone mass, putting them at greater fracture risk. In adults with type 2 diabetes, fracture risk is increased and is not explained by the bone mineral density measured by dual-energy X-ray absorptiometry, still considered the gold standard predictor of fracture. In this review, we explore potential mechanisms behind the increased fracture risk that occurs in patients with diabetes, even those with increased bone mineral density. One potential link between diabetes and bone is the osteoblast-produced factor, osteocalcin. It remains to be established whether osteocalcin reflects or affects the connection between bone and glucose metabolism. Several other potential mediators of the effects of diabetes on bone are discussed.

Total and carboxylated osteocalcin associate with insulin levels in young adults born with normal or very low birth weight

OBJECTIVE

Osteocalcin (OC), a bone-derived protein, has been implicated in the regulation of glucose and energy metabolism. Young adults born with very low birth weight (VLBW) have altered glucose regulation and lower bone mineral density (BMD) compared with those born at term. The aim of this study was to explore the association between bone and glucose metabolism in healthy young adults born prematurely or at term.

METHODS

The cohort of this cross-sectional study comprised 332 non-diabetic young adults (age 18 to 27 years) born either preterm with VLBW (n = 163) or at term (n = 169). OC, carboxylated osteocalcin (cOC) and markers of glucose metabolism were measured at fasting and after a 75-g oral glucose tolerance test (OGTT).

RESULTS

VLBW adults were shorter, had lower BMD (p<0.001) and higher fasting OC (p = 0.027) and cOC (p = 0.005) than term-born subjects. They also had higher 2-hour insulin (p = 0.001) and glucose (p = 0.037) concentrations. OGTT induced a significant reduction in OC (p<0.001), similar in both groups. OC reduction was not associated with OGTT-induced increases in insulin (p = 0.54). However, fasting total OC and cOC correlated negatively with fasting insulin after adjustment for age, gender, BMD and VLBW status (r = -0.182, p = 0.009 and r = -0.283, p<0.001, respectively).

CONCLUSION

Adults born with VLBW have higher OC and cOC than their peers born at term. This may in part reflect the mechanisms that underlie their lower BMD and decreased insulin sensitivity. Serum OC appears to be negatively associated with long-term glucose regulation whereas acute changes during OGTT may be mediated via other mechanisms.

The role of osteocalcin in human glucose metabolism: marker or mediator?

Increasing evidence supports an association between the skeleton and energy metabolism. These interactions are mediated by a variety of hormones, cytokines and nutrients. Here, the evidence for a role of osteocalcin in the regulation of glucose metabolism in humans is reviewed. Osteocalcin is a bone matrix protein that regulates hydroxyapatite size and shape through its vitamin-K-dependent, γ-carboxylated form. The concentration of osteocalcin in the circulation is a measure of bone formation. The undercarboxylated form of osteocalcin is active in glucose metabolism in mice. Total serum osteocalcin concentrations in humans are inversely associated with measures of glucose metabolism; however, human data are inconclusive with regard to the role of uncarboxylated osteocalcin in glucose metabolism because most studies do not account for the influence of vitamin K on the proportion of undercarboxylated osteocalcin or differentiate between the total and uncarboxylated forms of osteocalcin. Furthermore, most human studies do not concomitantly measure other bone turnover markers to isolate the role of osteocalcin as a measure of bone formation from its effect on glucose metabolism. Carefully designed studies are required to define the role of osteocalcin and its carboxylated or undercarboxylated forms in the regulation of glucose metabolism in humans.

Endocrine actions of osteocalcin

Osteocalcin is the most abundant noncollagenous protein of bone matrix. Once transcribed, this protein undergoes posttranslational modifications within osteoblastic cells before its secretion, including the carboxylation of three glutamic residues in glutamic acid, which is essential for hydroxyapatite binding and deposition in the extracellular matrix of bone. Recent provocative data from experimental observations in mice showed that the circulating undercarboxylated fraction of osteocalcin increases insulin secretion and sensitivity, lowers blood glucose, and decreases visceral fat in both genders, while it enhances testosterone production by the testes in males. Moreover, both total and undercarboxylated osteocalcins increase following physical activity with potential positive effects on glucose tolerance. Despite that these evidences have been only in part confirmed in humans, further prospective investigations are needed to definitively establish the endocrine role of osteocalcin both in the general population and cohorts of patients with diabetes or other metabolic disorders.

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.

Association of osteocalcin with obesity, insulin resistance, and cardiovascular risk factors in young adults

Low levels of osteocalcin (OCN), an osteoblast-specific hormone, have recently been associated with insulin resistance (homeostasis model assessment-insulin resistance (HOMA-IR)) and obesity, particularly in older adults. The aim of this study was to determine whether low levels of OCN would be associated with insulin resistance, obesity, and greater cardiovascular (CV) risk in young adults just emerging from adolescence. Undercarboxylated OCN and carboxylated OCN levels were measured on stored serum samples (total OCN = undercarboxylated OCN + carboxylated OCN) on 137 participants (67 males) at mean age 18.6 years (range 17-22 years). Insulin resistance was measured by hyperinsulinemic-euglycemic clamp (M(lbm)). Multivariable regression analyses with ln(OCN) as the independent variable were adjusted for age, sex, ethnicity, and BMI as indicated. Total OCN was inversely related to BMI, waist circumference, systolic blood pressure (SBP), interleukin (IL)-6, and directly related to M(lbm); only SBP remained significant (with M(lbm) P = 0.0560) after further adjustment for BMI. Carboxylated OCN was inversely related to BMI, waist circumference, SBP, low-density lipoprotein cholesterol (LDL-C), and directly related to adiponectin; SBP and adiponectin remained significant after further adjustment for BMI. There were no significant associations with undercarboxylated OCN. In summary, most associations with OCN were mediated via BMI. However, the significant associations of OCN with SBP, obesity, and adiponectin and borderline with M(lbm), suggest a potential role for OCN in the development of insulin resistance and CV risk that becomes more apparent with aging into older adulthood.

New mechanisms of glucocorticoid-induced insulin resistance: make no bones about it

Glucocorticoids are a powerful tool used to treat a range of human illnesses, including autoimmune diseases and cancer, and to prevent rejection following organ transplantation. While lifesaving for many, they come with a steep price, often leading to obesity, insulin resistance, diabetes, and osteoporosis. In this issue of the JCI, Brennan-Speranza and colleagues provide evidence that the osteoblast-derived peptide osteocalcin is one of the drivers of the metabolic derangements associated with glucocorticoid therapy. This novel mechanism could open up new avenues for the treatment of these disorders.

Arsenic trioxide affects bone remodeling by effects on osteoblast differentiation and function

Arsenic trioxide (ATO) is widely used in tumor treatment, but excessive arsenic exposure can have adverse health effects. This study was to examine the association between ATO treatment and bone remodeling. The effects of ATO on osteoblast function were investigated in primary cell cultures and in an in vivo study in rats. Sprague-Dawley rats (n=30) were randomly assigned to 3 groups which were injected intraperitoneally with saline or 5 or 10 mg/kg of ATO for 4 weeks. In cell culture, ATO decreased osteoblast mineralization by decreasing alkaline phosphatase (ALP) expression and this effect was prevented by co-addition of inorganic phosphate (Pi). Moreover, levels of mRNAs for the transcription factors runt-related transcription factor 2 (Runx2) and osterix, the osteoblast osteogenic gene osteocalcin, and the adherence molecule vascular cell adhesion molecule-1 (VCAM-1) were decreased by ATO. Levels of mRNAs for the cytokine IL-6 were also decreased, whereas GM-CSF mRNA levels were increased. Similar effects of ATO on osteoblasts were seen in in vivo experiments in the rat. Moreover, decreases of bone turnover markers of osteocalcin, Procollagen type I N-terminal propeptide (PINP), and C-terminal cross-linked telopeptide (CTX) as well as bone mineral density (BMD) and trabecular bone volume of femur were observed in ATO-treated rats. These results suggest that ATO interferes with bone remodeling mostly through changes in osteoblast differentiation and function.

Osteocalcin and vitamin D status are inversely associated with homeostatic model assessment of insulin resistance in Canadian Aboriginal and white women: the First Nations Bone Health Study

OBJECTIVE

Osteocalcin, a protein synthesized by osteoblasts, and vitamin D status have independently been implicated in energy metabolism and glucose regulation. This study was conducted to simultaneously explore the relationships among osteocalcin, vitamin D status and indicators of glucose metabolism and adiposity in a mixed-ethnicity cohort of adult women.

DESIGN

Cross-sectional.

METHODS

Aboriginal and white women (n=368) over 25 years of age (45.3±13.6 years) were studied for measures of osteocalcin and 25-hydroxy vitamin D [25(OH)D] plus glucose metabolism including glucose, insulin, C-peptide, hemoglobin A1c (HbA1c) and homeostatic model assessment of insulin resistance (HOMA-IR). Measures of adiposity included body mass index (BMI) plus total body fat and trunk fat from dual-energy X-ray absorptiometry.

RESULTS

Aboriginal women had higher BMI, fat and markers of dysglycemia. Osteocalcin was not different between groups, but 25(OH)D was lower in Aboriginal women. Osteocalcin was inversely related to all five parameters of glucose metabolism, whereas 25(OH)D was inversely related to insulin, C-peptide and HOMA-IR. After accounting for age, ethnicity or adiposity using regression analyses, glucose, HbA1c and HOMA-IR were inversely related to both osteocalcin and 25(OH)D. However, only 25(OH)D was inversely related to C-peptide, and neither osteocalcin nor 25(OH)D was related to insulin.

CONCLUSIONS

These data from a unique mixed Aboriginal and white population suggest that both vitamin D and osteocalcin are involved in glucose control.

Distinct effects of pioglitazone and metformin on circulating sclerostin and biochemical markers of bone turnover in men with type 2 diabetes mellitus

OBJECTIVE

Patients with type 2 diabetes mellitus (T2DM) have an increased risk of fractures and thiazolidinediones (TZDs) increase this risk. TZDs stimulate the expression of sclerostin, a negative regulator of bone formation, in vitro. Abnormal sclerostin production may, therefore, be involved in the pathogenesis of increased bone fragility in patients with T2DM treated with TZDs.

METHODS

We measured serum sclerostin, procollagen type 1 amino-terminal propeptide (P1NP), and carboxy-terminal cross-linking telopeptide of type I collagen (CTX) in 71 men with T2DM treated with either pioglitazone (PIO) (30 mg once daily) or metformin (MET) (1000 mg twice daily). Baseline values of sclerostin and P1NP were compared with those of 30 healthy male controls.

RESULTS

Compared with healthy controls, patients with T2DM had significantly higher serum sclerostin levels (59.9 vs 45.2 pg/ml, P<0.001) but similar serum P1NP levels (33.6 vs 36.0 ng /ml, P=0.39). After 24 weeks of treatment, serum sclerostin levels increased by 11% in PIO-treated patients and decreased by 1.8% in MET-treated patients (P=0.018). Changes in serum sclerostin were significantly correlated with changes in serum CTX in all patients (r=0.36, P=0.002) and in PIO-treated patients (r=0.39, P=0.020), but not in MET-treated patients (r=0.17, P=0.31).

CONCLUSIONS

Men with T2DM have higher serum sclerostin levels than healthy controls, and these levels further increase after treatment with PIO, which is also associated with increased serum CTX. These findings suggest that increased sclerostin production may be involved in the pathogenesis of increased skeletal fragility in patients with T2DM in general and may specifically contribute to the detrimental effect of TZDs on bone.

The effect of oral glucose tolerance test on serum osteocalcin and bone turnover markers in young adults

Osteocalcin (OC) is an osteoblast-derived protein implicated in the regulation of glucose tolerance and energy metabolism. This endocrine function has been suggested to be exerted via its undercarboxylated form, which has been shown to induce expression of adiponectin, insulin, and islet cell proliferation in mice. Furthermore, insulin has recently been shown to regulate the biological activity of OC in bone. Our aim was to explore the association between glucose and bone metabolism by evaluating the effect of a standard 75 g oral glucose tolerance test (OGTT) on serum OC, carboxylated OC (cOC) and bone-turnover markers (BTMs) C terminal telopeptide (βCTX-I) and N terminal propeptide (PINP) of type I collagen and tartrate-resistant acid phosphatase 5b (TRACP5b). Serum samples collected at 0 and at 120 min were analyzed in a cohort of normoglycemic young adults (n = 23, mean age 23.6 years). During OGTT a significant decrease was observed in all BTMs (P < 0.001 for all variables). The median decreases from 0 to 120 min for OC, cOC, βCTX-I, PINP, and TRACP5b were -32.1% (-37.9 to -19.6), -34.4% (-39.8 to -22.2), -61.4% (-68.5 to -53.0), -26.8% (-33.2 to -19.2), and -44.5% (-48.3 to -40.2), respectively. A strong association between the changes in OC and cOC was observed (r = 0.83, P < 0.001). The decrease in PINP was associated with changes in OC, whereas the changes in βCTX-I and TRACP5b were not associated with decreases in OC or cOC. The observed OGTT-induced changes in bone-derived proteins were partially independent of each other and potentially mediated by different mechanisms.