Serum leptin and adiponectin are positively associated with bone mineral density at the distal radius in patients with type 2 diabetes mellitus

Bone Fragility in Diabetes and its Management: A Narrative Review

Bone fragility is a serious yet under-recognised complication of diabetes mellitus (DM) that is associated with significant morbidity and mortality. Multiple complex pathophysiological mechanisms mediating bone fragility amongst DM patients have been proposed and identified. Fracture risk in both type 1 diabetes (T1D) and type 2 diabetes (T2D) continues to be understated and underestimated by conventional risk assessment tools, posing an additional challenge to the identification of at-risk patients who may benefit from earlier intervention or preventive strategies. Over the years, an increasing body of evidence has demonstrated the efficacy of osteo-pharmacological agents in managing skeletal fragility in DM. This review seeks to elaborate on the risk of bone fragility in DM, the underlying pathogenesis and skeletal alterations, the approach to fracture risk assessment in DM, management strategies and therapeutic options.

Long-term effects of canagliflozin treatment on the skeleton of aged UM-HET3 mice

Sodium glucose cotransporter-2 inhibitors (SGLT2is) promote urinary glucose excretion and decrease plasma glucose levels independent of insulin. Canagliflozin (CANA) is an SGLT2i, which is widely prescribed, to reduce cardiovascular complications, and as a second-line therapy after metformin in the treatment of type 2 diabetes mellitus. Despite the robust metabolic benefits, reductions in bone mineral density (BMD) and cortical fractures were reported for CANA-treated subjects. In collaboration with the National Institute on Aging (NIA)-sponsored Interventions Testing Program (ITP), we tested skeletal integrity of UM-HET3 mice fed control (137 mice) or CANA-containing diet (180 ppm, 156 mice) from 7 to 22 months of age. Micro-computed tomography (micro-CT) revealed that CANA treatment caused significant thinning of the femur mid-diaphyseal cortex in both male and female mice, did not affect trabecular bone architecture in the distal femur or the lumbar vertebra-5 in male mice, but was associated with thinning of the trabeculae at the distal femur in CANA-treated female mice. In male mice, CANA treatment is associated with significant reductions in cortical bone volumetric BMD by micro-CT, and by quantitative backscattered scanning electron microscopy. Raman microspectroscopy, taken at the femur mid-diaphyseal posterior cortex, showed significant reductions in the mineral/matrix ratio and an increased carbonate/phosphate ratio in CANA-treated male mice. These data were supported by thermogravimetric assay (TGA) showing significantly decreased mineral and increased carbonate content in CANA-treated male mice. Finally, the sintered remains of TGA were subjected to X-ray diffraction and showed significantly higher fraction of whitlockite, a calcium orthophosphate mineral, which has higher resorbability than hydroxyapatite. Overall, long-term CANA treatment compromised bone morphology and mineral composition of bones, which likely contribute to increased fracture risk seen with this drug.

The multiple regulatory effects of white adipose tissue on bone homeostasis

White adipose tissue (WAT) is not only an energy storage reservoir that is critical in energy homeostasis but is also a highly metabolically active endocrine organ. WAT can secrete a variety of adipocytokines, including leptin (LEP), adiponectin (APN), resistin, visfatin, tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6), and osteopontin (OPN). It can also synthesize and secrete exosomes, which enhance intercellular communication and participate in various physiological processes in the body. It can also synthesize and secrete exosomes to enhance intercellular communication and participate in a variety of physiological processes in the body. The skeleton is an important organ for protecting internal organs. It forms the scaffolding of the body and gives the body its basic form. It drives muscle contraction to produce movement under the regulation of the nervous system. It is also an important hematopoietic organ; and it is regulated by the cytokines secreted by WAT. As research related to the release of adipocytokines from WAT to affect the skeleton continues to progress, an inextricable link between bone lipid regulation has been identified. In this paper, we review the literature to summarize the structure, function and metabolism of WAT, elaborate the specific molecular mechanisms by which WAT-secreted hormones, cytokines and exosomes regulate skeletal cells, provide a theoretical basis for the in-depth study of WAT cross-organ regulation of bone, and provide new ideas for finding new adipose-secreted targeting factors for the treatment of skeletal diseases.

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

CONTEXT

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

METHODS

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

RESULTS

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

CONCLUSION

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

Leptin to adiponectin ratio in puberty is associated with bone mineral density in 18-year-old males

Introduction

Inconsistent associations of leptin and adiponectin with bone mineral characteristics in puberty and adolescence have been reported. We aimed to examine the associations between leptin to adiponectin ratio (LAR) in puberty and bone mineral characteristics at the age of 18 years in healthy males.

Materials and methods

88 white Caucasian boys were investigated at T1 (mean age 12.1 years), T2 (14.0 years) and T3 (18.0 years). Serum leptin and adiponectin were measured and LAR was calculated at T1, T2 and T3, bone mineral density (BMD) and bone mineral apparent density (BMAD) for total body and lumbar spine (LS) at T1 and T3. Spearman correlation coefficient and partial correlation analyses were used to describe the associations between mean pubertal LAR and BMD at T3.

Results

Mean pubertal LAR was negatively correlated with both LS BMD (r = −0.23; P < 0.05) and LS BMAD at T3 (r = −0.33; P < 0.05). These associations remained significant also in partial correlation analysis after controlling for total body fat percentage, total testosterone, HOMA-IR and physical activity at T1 (r = −0.31; P < 0.05 and r = −0.41; P < 0.05 respectively).

Conclusion

LAR in puberty is negatively associated with lumbar spine BMD and lumbar spine BMAD at the age of 18 years.

Perirenalfat thickness is associated with bone turnover markers and bone mineral density in postmenopausal women with type 2 diabetes mellitus

OBJECTIVES

Emerging evidence demonstrated that perirenal fat may modulate bone metabolism through several pathological pathways. This study was aimed to assess the associations between perirenal fat thickness (PrFT) and bone turnover markers (BTMs) and bone mineral density (BMD) in postmenopausal women with type 2 diabetes mellitus (T2DM) and further explore the correlation between PrFT and osteoporosis.

METHODS

In this cross-sectional study, a total of 626 participants with complete data were enrolled in this study. Demographic and anthropometric information was collected. Biochemical parameters and BTMs were determined. PrFT and BMD were measured by computed tomography and dual-energy x-ray absorptiometry, respectively. Correlation analysis and regression models were used to assess the associations between PrFT and BTMs and BMD. The multiple binomial logistic regression model was used to estimate the independent variables of PrFT for osteoporosis.

RESULTS

Overall, the prevalence of osteoporosis was 38.7%. PrFT was negatively correlated with β-cross-linked C-telopeptide of type I collagen (β-CTX) (r = -0.216,< 0.001), L1-L4 BMD (r = -0.351, < 0.001), and T-score (r = -0.396, < 0.001). PrFT also remained significantly correlated with β-CTX (β = -0.291, P< 0.001), L1-L4 BMD (β = -0.109, P= 0.027), and L1-L4 T-score (β = -0.149, P= 0.001) after adjustment for other confounding factors. Furthermore, PrFT was also independently associated with osteoporosis after adjustment for other confounding factors; the OR (95% CI) was 1.13 (1.04-1.23). PrFT also seems to have a relatively good identifying value for osteoporosis. The area under the curve (AUC) value of PrFT in identifying osteoporosis was 0.766 (95% CI: 0.705-0.826, P < 0.001). The optimal cutoff value of PrFT was 15.2 mm (sensitivity: 72.5%, specificity: 79.8%).

CONCLUSIONS

PrFT was significantly associated with β-CTX, BMD, and osteoporosis. These findings indicate that perirenal fat may play an important role in bone metabolism.

CLINICAL TRIAL REGISTRATION

http://www.chictr.org.cn/, identifier (ChiCTR2100052032).

The Effects of Diabetic Polyneuropathy and Autonomic Neuropathy on Bone Turnover

Background: The effect of diabetic polyneuropathy (DPN) and autonomic neuropathy (AN) on bone turnover in type 2 diabetes mellitus (DM) is uncertain due to the lack of data. In this study, we tried to determine the effect of DPN and AN on bone metabolism. Materials and Methods: The study included patients with type 2 DM (aged 18-80 years) and age-matched healthy individuals who presented to the Departments of Metabolism and Diabetes, Geriatrics, and General Internal Medicine, Cerrahpaşa Medical School, Istanbul University. The patients were examined to find out whether they had AN, and neuropathy scores were recorded by exploring peripheral neuropathy. Bone mineral density was measured by dual-energy X-ray (DXA). Demographic characteristics, the presence of microvascular complications, and biochemical data were obtained from patients' files. Serum cross-linked C-telopeptide (Ctx), osteocalcin, and bone-specific alkaline phosphatase (B-ALP) were analyzed. Results: The study comprised a total of 64 patients: 23 had type 2 DM and osteoporosis (OP) (duration of diabetes 10.1 ± 7 years; mean age 63 ± 9.1 years; female/male 18/5; Group 1), 41 had type 2 DM and non-OP (duration of diabetes 10.3 ± 7.6 years; mean age 58 ± 7.4 years; female/male 30/11; Group 2), and 26 healthy volunteers made up the control group (mean age 62 ± 11.9 years; female/male 14/12; Group 3). The bone turnover parameters were lower in type 2 DM individuals. The levels of osteocalcin (13.3 ± 5.2 ng/mL) and B-ALP (44.7 ± 10.9 IU/L) in patients with type 2 DM were lower than those of healthy subjects: osteocalcin (20.6 ± 10 ng/mL) and B-ALP (111 ± 31.4 IU/L; P = 0.001 and P = 0.000, respectively). Ctx levels (193.5 ± 49.3; 207.6 ± 40 ng/mL) were recorded to be similar (P = 0.2). AN was also noted as a risk factor for OP. For patients without AN, the likelihood of developing OP (odds ratio) was 0.7. The corresponding ratio for patients with AN was 9.3. Conclusions: Among the independent variables, the neuropathy score was determined to have an impact on bone turnover. AN was identified to be a significant risk factor for OP.

Pathophysiology and Management of Type 2 Diabetes Mellitus Bone Fragility

Individuals with type 2 diabetes mellitus (T2DM) have an increased risk of bone fragility fractures compared to nondiabetic subjects. This increased fracture risk may occur despite normal or even increased values of bone mineral density (BMD), and poor bone quality is suggested to contribute to skeletal fragility in this population. These concepts explain why the only evaluation of BMD could not be considered an adequate tool for evaluating the risk of fracture in the individual T2DM patient. Unfortunately, nowadays, the bone quality could not be reliably evaluated in the routine clinical practice. On the other hand, getting further insight on the pathogenesis of T2DM-related bone fragility could consent to ameliorate both the detection of the patients at risk for fracture and their appropriate treatment. The pathophysiological mechanisms underlying the increased risk of fragility fractures in a T2DM population are complex. Indeed, in T2DM, bone health is negatively affected by several factors, such as inflammatory cytokines, muscle-derived hormones, incretins, hydrogen sulfide (H2S) production and cortisol secretion, peripheral activation, and sensitivity. All these factors may alter bone formation and resorption, collagen formation, and bone marrow adiposity, ultimately leading to reduced bone strength. Additional factors such as hypoglycemia and the consequent increased propensity for falls and the direct effects on bone and mineral metabolism of certain antidiabetic medications may contribute to the increased fracture risk in this population. The purpose of this review is to summarize the literature evidence that faces the pathophysiological mechanisms underlying bone fragility in T2DM patients.

Vitamin K: Double Bonds beyond Coagulation Insights into Differences between Vitamin K1 and K2 in Health and Disease

Vitamin K is an essential bioactive compound required for optimal body function. Vitamin K can be present in various isoforms, distinguishable by two main structures, namely, phylloquinone (K1) and menaquinones (K2). The difference in structure between K1 and K2 is seen in different absorption rates, tissue distribution, and bioavailability. Although differing in structure, both act as cofactor for the enzyme gamma-glutamylcarboxylase, encompassing both hepatic and extrahepatic activity. Only carboxylated proteins are active and promote a health profile like hemostasis. Furthermore, vitamin K2 in the form of MK-7 has been shown to be a bioactive compound in regulating osteoporosis, atherosclerosis, cancer and inflammatory diseases without risk of negative side effects or overdosing. This review is the first to highlight differences between isoforms vitamin K1 and K2 by means of source, function, and extrahepatic activity.

Effect of Sodium-Glucose Co-transporter 2 Inhibitors on Bone Metabolism and Fracture Risk

The effect of anti-diabetic medications on bone metabolism has received increasing attention, considering that type 2 diabetes mellitus is a common metabolic disorder with adverse effects on bone metabolism. Sodium-glucose co-transporter 2 (SGLT2) inhibitors are novel anti-diabetic medications that prevent glucose resorption at the proximal convoluted tubules in the kidney, increasing urinary glucose excretion, and decreasing the blood glucose level. The superiority of SGLT2 inhibitors shows in reducing the glucose level independent of insulin secretion, lowering the risk of hypoglycemia, and improving cardiovascular outcomes. SGLT2 inhibitors have been associated with genital mycotic infections, increased risk of acute kidney injury, dehydration, orthostatic hypotension, and ketoacidosis. Moreover, the effect of SGLT2 inhibitors on bone metabolism and fracture risk has been widely taken into consideration. Our review summarizes the results of current studies investigating the effects of SGLT2 inhibitors on bone metabolism (possibly including increased bone turnover, disrupted bone microarchitecture, and reduced bone mineral density). Several mechanisms are probably involved, such as bone mineral losses due to the disturbed calcium and phosphate homeostasis, as confirmed by an increase in fibroblast growth factor 23 and parathyroid hormone levels and a decrease in 1,25-dihydroxyvitamin D levels. SGLT2 inhibitors might indirectly increase bone turnover by weight loss. Lowering the blood glucose level might ameliorate bone metabolism impairment in diabetes. The effect of SGLT2 inhibitors on bone fractures remains unclear. Evidence indicating the direct effect of SGLT2 inhibitors on fracture risk is lacking and increased falls probably contribute to fractures.

Adiponectin Deficiency Triggers Bone Loss by Up-Regulation of Osteoclastogenesis and Down-Regulation of Osteoblastogenesis

Osteoporosis and bone disorders related to the metabolic syndrome are often associated with adipokines secreted by adipocytes in bone. Adiponectin, a type of adipokine, is a regulator of immune responses and metabolic processes, but its role in bone biology remains uncertain. We investigated the role of adiponectin in bone metabolism using adiponectin-deficient mice in vivo and in vitro. Adiponectin-deficient mice exhibited reduced bone mass and increased adiposity. Adiponectin-deficient calvarial cells were prone to differentiate into adipocytes rather than osteoblasts. Although bone marrow macrophages (BMMs) from adiponectin-deficient mice had low osteoclastogenic potential as osteoclast precursors with increasing interferon regulatory factor 5 expression, under co-culture conditions of calvarial cells and BMMs, the enhanced receptor activator of nuclear factor κB ligand/osteoprotegerin (RANKL/OPG) ratio of adiponectin-deficient mesenchymal progenitor cells facilitated osteoclast differentiation. In addition, increased RANKL/OPG ratio was observed in the bone marrow extracellular fluid of adiponectin-deficient mice compared to that of wild-type mice. Notably, recombinant adiponectin treatment enhanced RANKL-induced osteoclast differentiation from BMMs but up-regulated OPG production in recombinant adiponectin-exposed calvarial cells, which inhibited osteoclast differentiation. Taken together, these results suggest that adiponectin plays an inhibitory role in bone metabolism through cross talk between precursor cells of both osteoclasts and osteoblasts by regulating RANKL/OPG ratio in the bone marrow microenvironment.

Serum adiponectin level in osteoporotic postmenopausal women with type 2 diabetes mellitus

BACKGROUND

Diabetes Mellitus (DM) is a major health burden worldwide. Patients with type 2 DM has various complications, including impaired bone health. Adiponectin is novel adipocytokine that could influence bone metabolism.

OBJECTIVE

We investigated the relationships between serum adiponectin versus lumbar bone mineral density (BMD) in type 2 diabetic osteoporotic postmenopausal women.

SUBJECTS AND METHODS

This study is a case control study included 90 postmenopausal women; divided as (group A) composed of 30 type 2 diabetic osteoporotic postmenapausal,(group B) composed of 30 non diabetic osteoporotic postmenopausal and 30 apparently healthy non osteoporotic postmenopausal women as a control group. All participants underwent Dual Energy X-ray Absorptiometry to measure the lumbar Bone Mineral Density (BMD).Serum adiponectin was measured by ELISA Kits. SPSS was used to analyze the data.

RESULTS

Among the studied subjects, group B showed a significant negative correlation between serum adiponectin and lumbar BMD. The diabetic osteoporotic postmenapausal group (group B) showed the lowest concentration of serum adiponectin (μg/mL): 5.14 compared with 11.02 and 8.63 in group A, and the control, respectively. Lumbar BMD of group B was significantly higher than that of group A.

CONCLUSIONS

Serum adiponectin is associated with lumber BMD in diabetic osteoporotic postmenopausal women. These findings suggest that serum adiponectin was involved in bone metabolism in this group.

Adiponectin signaling and its role in bone metabolism

Adiponectin, the most prevalent adipo-cytokine in plasma plays critical metabolic and anti-inflammatory roles is fast emerging as an important molecular target for the treatment of metabolic disorders. Adiponectin action is critical in multiple organs including cardio-vascular system, muscle, liver, adipose tissue, brain and bone. Adiponectin signaling in bone has been a topic of active investigation lately. Human association studies and multiple mice models of gene deletion/modification failed to define a clear cause and effect of adiponectin signaling in bone. The most plausible reason could be the multimeric forms of adiponectin that display differential binding to receptors (adipoR1 and adipoR2) with cell-specific receptor variants in bone. Discovery of small molecule agonist of adipoR1 suggested a salutary role of this receptor in bone metabolism. The downstream signaling of adipoR1 in osteoblasts involves stimulation of oxidative phosphorylation leading to increased differentiation via the likely suppression of wnt inhibitor, sclerostin. On the other hand, the inflammation modulatory effect of adiponectin signaling suppresses the RANKL (receptor activator of nuclear factor κ-B ligand) - to - OPG (osteprotegerin) ratio in osteoblasts leading to the suppression of osteoclastogenic response. This review will discuss the adiponectin signaling and its role in skeletal homeostasis and critically assess whether adipoR1 could be a therapeutic target for the treatment of metabolic bone diseases.

A cross-sectional study of the association between adipokine levels and bone mineral density according to obesity and menopausal status in Korean women

Results regarding the association between adipokine levels and bone mineral density (BMD) have been inconsistent; the effects of sex, menopause, and central obesity remain unknown. We evaluated the association between serum leptin, adiponectin, and high-molecular-weight (HMW) adiponectin levels and BMD according to menopause and central obesity status in Korean women. This cross-sectional study comprised 255 women undergoing examinations at the CHA Bundang Medical Center. Participants were divided according to menopause, and central obesity status. We measured serum adipokine levels and BMD using an enzyme-linked immunosorbent assay and dual-energy X-ray absorptiometry, respectively. After adjusting for age, body mass index, alkaline phosphatase levels and the Homeostasis Model Assessment index, leptin levels were negatively associated with non-vertebral BMD (total hip, β = -0.576, P = 0.006; femoral neck, β = -0.608, P = 0.007) in postmenopausal women without central obesity. Among women without central obesity, HMW adiponectin levels were positively associated with total hip BMD (β = 0.240, P = 0.010) in premenopausal women but negatively associated with BMD (lumbar, β = -0.436, P = 0.012; femoral neck, β = -0.468, P = 0.007) in postmenopausal women. Thus, the association between adipokine levels and BMD varies according to the menopause and central obesity status.

Bone Metabolism and Fracture Risk in Diabetes Mellitus

Individuals with Type 1 diabetes mellitus (T1DM) and type 2 diabetes mellitus (T2DM) are at increased risk for fragility fractures. Bone mineral density (BMD) is decreased in T1DM but often normal or even elevated in T2DM when compared with age-matched non-DM populations. However, bone turnover is decreased in both T1DM and T2DM. The pathophysiologic mechanisms leading to bone fragility is multifactorial, and potentially leads to reduced bone formation, altered bone microstructure and decreased bone strength. Interestingly, different antidiabetic treatments may influence fracture risk due to effects on glycemic control, triggering of hypoglycemic events or osteoblastogenesis.

Fenofibrate decreases the bone quality by down regulating Runx2 in high-fat-diet induced Type 2 diabetes mellitus mouse model

Background

This study is to investigate the effect of fenofibrate on the bone quality of Type 2 diabetes mellitus (T2DM) mouse model.

Methods

T2DM mouse model was induced by high-fat-diet, and the mice were treated with fenofibrate (100 mg/kg) (DIO-FENO) or PBS (DIO-PBS) for 4 weeks. The bone microstructure and biomechanical properties of femora were analyzed by micro-CT and 3-Point bending test. The protein expression was detected by immunohistochemical staining and Western blot. The cell apoptosis was evaluated by TUNEL staining. The Bcl2, caspase 3, and osteoblast marker genes were detected by RT-qPCR.

Results

The biomechanical properties of bones from DIO-FENO group were significantly lower than those in the control and DIO-PBS groups. Besides, the trabecular number was lower than those of the other groups, though the cortical porosity was decreased compared with that of DIO-PBS group because of the increase of apoptotic cells. The expression of osteocalcin and collagen I were decreased after treatment with fenofibrate in T2DM mice. Moreover, the cell viability was decreased after treated with different concentrations of fenofibrate, and the expression of Runx2 decreased after treated with high dose of fenofibrate.

Conclusion

Fenofibrate decreases the bone quality of T2DM mice through decreasing the expression of collagen I and osteocalcin, which may be resulted from the down regulation of Runx2 expression.

Mechanisms of diabetes mellitus-induced bone fragility

The risk of fragility fractures is increased in patients with either type 1 diabetes mellitus (T1DM) or type 2 diabetes mellitus (T2DM). Although BMD is decreased in T1DM, BMD in T2DM is often normal or even slightly elevated compared with an age-matched control population. However, in both T1DM and T2DM, bone turnover is decreased and the bone material properties and microstructure of bone are altered; the latter particularly so when microvascular complications are present. The pathophysiological mechanisms underlying bone fragility in diabetes mellitus are complex, and include hyperglycaemia, oxidative stress and the accumulation of advanced glycation endproducts that compromise collagen properties, increase marrow adiposity, release inflammatory factors and adipokines from visceral fat, and potentially alter the function of osteocytes. Additional factors including treatment-induced hypoglycaemia, certain antidiabetic medications with a direct effect on bone and mineral metabolism (such as thiazolidinediones), as well as an increased propensity for falls, all contribute to the increased fracture risk in patients with diabetes mellitus.

Correlation between serum leptin and bone mineral density in hemodialysis patients

Introduction: For diagnosing of specific types of bone lesions in hemodialysis (HD) patients, it is necessary to conduct a bone biopsy as the gold standard method. However, it is an invasive procedure. While different markers have been suggested as alternative methods, none of them has been selected. The frequency of hip fractures is 80 fold in HD patients who have two-fold mortality as compared with general population.

Objectives: Recently, serum leptin has been suggested as a bone density marker. This study tries to confirm this proposal.

Patients and Methods: In this study about 104 HD patients (53.8% male and 46.2% female) were enrolled. The average age was 38.28±7.89 years. Serum leptin, bone alkaline phosphatase, intact parathyroid hormone (iPTH), 25(OH)D, calcium, phosphorus and bone mineral density (BMD) (at the femoral neck and lumbar spine, as measured by dual-energy x-ray absorptiometry [DXA]) were assessed.

Results: Analysis by polynomial regression revealed no correlation between BMD Z-score at two points and serum leptin level. According to the thresholds of 25 ng/mL and 18-24 ng/mL in some studies, we detected 25 ng/mL as the threshold in our patients. Under this threshold, the leptin effect on bone mass was negative, and above the threshold of 25 ng/mL, we found leptin had positive effect on bone mass.

Conclusion: In this investigation, we found, leptin has a bimodal effect on bone mass. Cortical bones assessment may be a better option for assessment.

BMI and BMD: The Potential Interplay between Obesity and Bone Fragility

Recent evidence demonstrating an increased fracture risk among obese individuals suggests that adipose tissue may negatively impact bone health, challenging the traditional paradigm of fat mass playing a protective role towards bone health. White adipose tissue, far from being a mere energy depot, is a dynamic tissue actively implicated in metabolic reactions, and in fact secretes several hormones called adipokines and inflammatory factors that may in turn promote bone resorption. More specifically, Visceral Adipose Tissue (VAT) may potentially prove detrimental. It is widely acknowledged that obesity is positively associated to many chronic disorders such as metabolic syndrome, dyslipidemia and type 2 diabetes, conditions that could themselves affect bone health. Although aging is largely known to decrease bone strength, little is yet known on the mechanisms via which obesity and its comorbidities may contribute to such damage. Given the exponentially growing obesity rate in recent years and the increased life expectancy of western countries it appears of utmost importance to timely focus on this topic.

Osteocalcin, under-carboxylated osteocalcin and osteopontin are not associated with gestational diabetes mellitus but are inversely associated with leptin in non-diabetic women

OBJECTIVE

To measure serum osteocalcin (OC), under-carboxylated osteocalcin (ucOC), osteopontin (OPN), and leptin in pregnant women with gestational diabetes mellitus (GDM) and in healthy pregnant women during pregnancy and after birth and relate these markers to glucose metabolism.

METHODS

This was a prospective study including 60 women with GDM and 60 subjects with normal gestation who were evaluated at gestational week 30 and 6 weeks postpartum. Serum OC, ucOC, OPN, leptin, insulin and insulin resistance were evaluated during the study.

RESULTS

Bone biomarkers and leptin were similar between GDM and normal pregnancy. After delivery, OC, ucOC and OPN increased in both groups, while leptin decreased only in healthy controls. Bone markers did not correlate with insulin and insulin resistance in the two groups, but leptin was positively correlated with insulin and insulin resistance and negatively correlated with bone biomarkers only in healthy women. Furthermore, the women who developed diabetes postpartum had lower levels of OC than women with normal glucose tolerance.

CONCLUSION

GDM is not associated with OC, ucOC, OPN, and leptin and does not correlate with insulin resistance. At postpartum, women who develop diabetes have lower osteocalcin concentrations. Leptin correlates with insulin resistance and bone biomarkers in non-diabetic women.

Effects of resveratrol treatment on bone and cartilage in obese diabetic mice

Background

Resveratrol is a polyphenolic phytoalexin that has been shown to exhibit osteoprotective and chondroprotective properties. We examine the effects of resveratrol treatment on bone and cartilage tissue of obese, diabetic ob/ob mice.

Methods

Eight-week-old ob/ob and lean control mice were given trans-resveratrol at an oral dose of 25 mg/kg for 3 weeks. Histomorphometric and cross-sectional-geometric variables were analyzed.

Results

Ob/ob mice in our study exhibit significantly reduced femoral length, resistance to loading, and tibial growth plate total area and calcified area than lean controls (P < 0.05). Resveratrol treatment significantly increased cortical area in both ob/ob and control mice, but did not improve cross-sectional indicators of resistance to bending. Resveratrol treatment also reduced tibial length and calcified growth plate cartilage area in comparison to untreated mice (P < 0.05).

Conclusion

Resveratrol treatment of ob/ob mice had mixed effects on bone histomorphometry at the femoral midshaft. Treatment increased cortical area but decreased bone length.

Relationship between leptin and adiponectin concentrations in plasma and femoral and spinal bone mineral density in spinal cord-injured individuals

BACKGROUND CONTEXT

Previously, the associations between leptin and adiponectin levels with bone mineral density (BMD) have been reported in different populations, and occasionally, controversial results have been demonstrated. Until now, these relationships in spinal cord-injured individuals have not yet been described.

PURPOSE

We tried to investigate the correlation between leptin and adiponectin concentrations in plasma and BMD in Iranian patients with spinal cord injury (SCI).

STUDY DESIGN/SETTING

Cross-sectional investigation.

PATIENT SAMPLE

Referred patients with SCI who did not meet our exclusion criteria such as pregnancy, lactation, amputation, history of diabetes, cancer, endocrinology disease, and use of special medications entered the study.

OUTCOME MEASURES

Bone mineral density of femoral neck, trochanter, intertrochanteric zone, total hip, and lumbar vertebrae assessed by dual-energy X-ray absorptiometry and serum leptin and adiponectin levels measured by blood sample analysis using immunoassay techniques.

METHODS

Patient demographic characteristics were measured during face-to-face visits. Injury level and Spinal cord Injury Association (ASIA) score were assessed by clinical examination and were confirmed by imaging aids. Measured levels of leptin and adiponectin and dual-energy X-ray absorptiometry results were analyzed with partial correlation analysis method after adjustment for weight, body mass index (BMI), and age.

RESULTS

Total of 104 patients (19 females and 85 males) entered this investigation. Higher leptin concentration was significantly associated with higher BMD in femoral neck (p=.006, r=0.73), femoral intertrochanteric zone (p=.001, r=0.83), and hip (p=.001, r=0.81) only in female patients, whereas no such association was detected in male participants after adjusting for BMI and age. Leptin and adiponectin levels were not associated with lumbar spine BMD in both genders. Neither injury level nor ASIA score and plegia type (paraplegia or tetraplegia) influenced on leptin and adiponectin concentrations.

CONCLUSIONS

We found no association between leptin concentration and BMD in male individuals, whereas a positive correlation between leptin and BMD of femoral neck, intertrochanter, and hip was observed in female patients that shows a sexual polymorphism in this relationship. However, by considering the low number of female participants, these results should be interpreted cautiously. Lumbar spine BMD was associated with neither leptin nor adiponectin level in both genders.

Effect of weight loss on serum osteocalcin and its association with serum adipokines

Studies have suggested that osteocalcin, a bone formation marker, is related to body metabolism and insulin sensitivity. Whether this relation is mediated through an interaction with adipokines remains unclear. The aim of this study was to assess the effect of weight loss on serum osteocalcin and its relation with three adipokines, adiponectin, chemerin, and resistin. Forty-nine obese nondiabetic males completed a four-month dietary program. Body mass index (BMI) decreased significantly from 39.7 ± 7.6 to 37.8 ± 7.6 (P < 0.001). This was associated with significant reduction in waist circumference, fasting blood glucose, HOMA-IR, total and LDL-cholesterol, bone-specific alkaline phosphatase (BAP), and resistin (P < 0.05). There was significant increase in serum adiponectin and undercarboxylated osteocalcin (uOC) (P < 0.001). The changes in uOC levels were negatively correlated with changes in serum triglycerides (r = -0.51, P < 0.001) and positively correlated with changes in BAP (r = 0.52, P < 0.001). In contrast, the changes in uOC were not correlated with changes in BMI, waist circumference, fasting blood glucose, HOMA-IR, total and LDL-cholesterol, hsCRP, vitamin D, and circulating adipokines. We concluded that the increase in serum uOC following weight loss is not related to the changes in circulating adipokines levels.

The bone and fat connection in inflammatory bowel diseases

Osteopenia and osteoporosis are common manifestations in inflammatory bowel diseases (IBD) but the pathogenetic mechanism of bone loss in IBD is only partially understood. There is evidence that fat mass is an important determinant of the bone mineral density and adipose-derived factors seem to play an important role for the association between fat mass and bone mass. The association between adiposity and low bone density is rather poorly studied in IBD, but emerging data on adipokines in IBD in relation to osteoporosis provide a novel pathophysiological concept that may shed light on the etiology of bone loss in IBD. It could be suggested that adipokines interfere in bone metabolism by altering the sensitive balance between osteoblasts and osteoclasts although further studies in this setting are needed.

Relationships between serum adipocyte hormones (adiponectin, leptin, resistin), bone mineral density and bone metabolic markers in osteoporosis patients

The purpose of this study was to investigate the relationship between fasting serum leptin, adiponectin and resistin levels and bone mineral density (BMD) in osteoporosis patients and a non-osteoporosis control group. We studied 81 non-diabetic osteoporosis patients (92 % female, 8 % male; mean age 54.5 ± 15.5 years and body mass index [BMI] 28.2 ± 4.6) and 120 non-diabetic individuals with normal BMD as controls (86 % female, 14 % male; mean age 39.7 ± 10.4 years and BMI 28.8 ± 4.4). BMD was studied by dual-energy X-ray absorptiometry from the lumbar spine (L1-L4) and femoral neck and fasting blood samples were taken for biochemical measurement of fasting blood glucose, leptin, adiponectin and resistin. Fasting levels of plasma adiponectin had a significant negative correlation with BMD of the femoral neck and lumbar spine in the osteoporosis group (r = -0.478, P = 0.003, r = -0.513, P = 0.023) but not in the non-osteoporosis group (r = -0.158, P = 0.057, r = -0.23, P = 0.465). Fasting plasma levels of resistin were significantly correlated only with femur BMD in the osteoporosis group, and not significantly correlated with lumbar spine BMD (r = -0.244, P = 0.048 vs r = 0.276, P = 0.56). Leptin did not have a significant correlation with BMD in either the osteoporosis or non-osteoporosis groups (P > 0.05). Adiponectin had a significant negative correlation with BMD of the lumbar spine and femoral neck. The correlation between leptin and resistin are not inconclusive.

Bone metabolism in obese rats programmed by early weaning

OBJECTIVE

Obesity and osteoporosis seem to have a common pathogenesis, especially because bone and adipose tissue have common origins. Since early weaning (EW) decreases adipogenesis and osteogenesis in neonate, further programming for obesity and hyperleptinemia, we hypothesized that these changes in adipogenesis could affect bone metabolism.

MATERIALS/METHODS

Lactating rats were separated into 3 groups: control - dams whose pups ate milk throughout lactation; mechanical EW (MEW) - dams were involved with a bandage interrupting suckling in the last 3days of lactation; pharmacological EW (PEW) - dams were bromocriptine-treated (0.5mg/twice a day via intraperitoneal injection) 3days before weaning. The adult offspring was subjected to dual-energy X-ray absorptiometry and bone tissue was also evaluated by computed tomography, microcomputed tomography and biomechanical tests, beyond serum analyses.

RESULTS

MEW and PEW presented higher total bone mineral density (BMD), total bone mineral content, spine BMD and bone area in postnatal day 150 (PN150). In PN180, both groups also presented increase of these parameters and higher femur BMD and fourth lumbar vertebra (LV4) BMD, femoral head radiodensity and LV4 vertebral body radiodensity, trabecular number, stiffness and break load; lower trabecular separation, maximal deformation and break deformation, and also hyperleptinemia and higher visceral fat mass and 25-hydroxivitamin D, whereas parathyroid hormone was unchanged. Serum C-terminal cross-linked telopeptide of type I collagen was lower for both groups.

CONCLUSIONS

Since both models program for obesity and increased bone mass, and leptin increases plasma vitamin D levels, probably leptin is the link between obesity and higher bone mass.

Clinical use of adiponectin as a marker of metabolic dysregulation

Adiponectin concentrations exhibit strong cross-sectional relationships with obesity, inflammation, and diabetes. Adiponectin concentrations have been extensively evaluated as epidemiologic markers of diabetes and cardiovascular disease risk. In the present review we will provide an overview of these epidemiologic relationships as the backdrop for an evaluation of the clinical applications of adiponectin measurements. These include using adiponectin as an indicator of need for preventive or therapeutic intervention, as a predictor of response to therapy, and as a marker of therapeutic effectiveness. These efforts are laying the groundwork for the transition of adiponectin measurements from the laboratory to the clinic.

Adiponectin receptors in energy homeostasis and obesity pathogenesis

Adipokines, that is factors secreted by adipose tissue, act through a network of autocrine, paracrine, and endocrine pathways to regulate several aspects of physiology, including glucose and lipid metabolism, neuroendocrine function, reproduction, and cardiovascular function. In particular, adiponectin, a 30-kDa protein, is associated with the regulation of insulin sensitivity, and its levels in serum are affected by altered metabolic homeostasis. Adiponectin effects are mediated by adiponectin receptors, which occur as two isoforms (AdipoR1 and AdipoR2). Transcriptional regulation of adiponectin is by the peroxisome proliferator-activated receptor-gamma (PPAR-γ). However, acting through AdipoR1 and AdipoR2, adiponectin enhances 5' adenosine monophosphate-activated protein kinase (AMPK) and the PPARα-mediated pathways in the liver and skeletal muscles. Adiponectin receptors mediate a wide spectrum of metabolic reactions, including gluconeogenesis and fatty-acid oxidation. Altogether, adiponectin deficiency and/or decreased adiponectin receptor-mediated activity possibly contribute to insulin resistance in metabolic syndromes, coronary heart disease, and liver disease.

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.

Novel adipokines and bone metabolism

Osteoporosis is a serious social issue nowadays. Both the high morbidity and its common complication osteoporotic fracture load a heavy burden on the whole society. The adipose tissue is the biggest endocrinology organ that has a different function on the bone. The adipocytes are differentiated from the same cell lineage with osteoblast, and they can secrete multiple adipokines with various functions on bone remolding. Recently, several novel adipokines have been identified and investigated thoroughly. In this paper, we would like to highlight the complicated relation between the bone metabolism and the novel adipokines, and it may provide us with a new target for prediction and treatment of osteoporosis.

High serum adiponectin predicts incident fractures in elderly men: Osteoporotic fractures in men (MrOS) Sweden

Adipocytes and osteoblasts share a common progenitor, and there is, therefore, potential for both autocrine and endocrine effects of adiponectin on skeletal metabolism. The aim of the present study was to determine whether high serum adiponectin was associated with an increased risk of fracture in elderly men. We studied the relationship between serum adiponectin and the risk of fracture in 999 elderly men drawn from the general population and recruited to the Osteoporotic Fractures in Men (MrOS) study in Gothenburg, Sweden. Baseline data included general health questionnaires, lifestyle questionnaires, body mass index (BMI), bone mineral density (BMD), serum adiponectin, osteocalcin, and leptin. Men were followed for up to 7.4 years (average, 5.2 years). Poisson regression was used to investigate the relationship between serum adiponectin, other risk variables and the time-to-event hazard function of fracture. Median levels of serum adiponectin at baseline were 10.4 µg/mL (interquartile range, 7.7-14.3). During follow-up, 150 men sustained one or more fractures. The risk of fracture increased in parallel with increasing serum adiponectin (hazard ratio [HR]/SD, 1.46; 95% confidence interval [CI], 1.23-1.72) and persisted after multivariate-adjusted analysis (HR/SD, 1.30; 95% CI, 1.09-1.55). Serum adiponectin shows graded stepwise association with a significant excess risk of fracture in elderly men that was independent of several other risk factors for fracture. Its measurement holds promise as a risk factor for fracture in men.

Arthroplasty in veterans: analysis of cartilage, bone, serum, and synovial fluid reveals differences and similarities in osteoarthritis with and without comorbid diabetes

Osteoarthritis patients with diabetes who receive total knee arthroplasty are more vulnerable to complications, including aseptic loosening and need for revision surgery. To elucidate mechanisms related to arthroplasty failure in diabetes, we examined serum and synovial fluid markers as well as collagen crosslinks in bone and cartilage of 20 patients (10 with diabetes, 10 controls without) undergoing this procedure. Hemoglobin A1c, body mass index, bone alkaline phosphatase, leptin, osteocalcin, and pyridinium were analyzed along with tissue content of the crosslinks hydroxylysylpyridinoline, lysylpyridinoline, and pentosidine. Pentosidine levels in tissue specimens from diabetic subjects were higher than in control subjects. Osteocalcin levels negatively correlated with hydroxylysylpyridinoline levels in cartilage. Osteocalcin levels also negatively correlated with pentosidine levels in cartilage, but only in subjects with diabetes. This study suggests potential metabolic mechanisms for arthroplasty failure in patients with diabetes.

Serum adiponectin, bone mineral density and bone turnover markers in post-menopausal women with newly diagnosed Type 2 diabetes: a 12-month follow-up

OBJECTIVE

During a period of 12 months, we evaluated the longitudinal impact of metabolic control of diabetes on selected bone turnover markers, bone mineral density and serum adiponectin concentrations in post-menopausal women with newly diagnosed Type 2 diabetes.

METHODS

Serum total adiponectin, bone alkaline phosphatase, HbA(1c), urinary deoxypyridinoline excretion, bone mineral density of the total body, lumbar spine and total hip were measured in 57 women aged 50-78 years with newly diagnosed Type 2 diabetes.

RESULTS

At baseline, women had normal bone-specific alkaline phosphatase, deoxypyridinoline and bone mineral density, as evaluated by t- and z-scores. After 12 months of treatment, a significant decrease in body weight, waist circumference and HbA(1c) was observed. Bone mineral density of the total body, lumbar spine and total hip decreased by 0.4, 0.2 and 1.0% (P = 0.018) per year, respectively. Adiponectin was inversely correlated with bone mineral density at three sites (R = -0.28, -0.24 and -0.19, respectively). There was a transient increase (P < 0.05) in serum adiponectin within the first 6 months, followed by a slow decrease toward the baseline value during the next 6 months. An improvement in diabetes control had no impact on bone turnover marker levels, which did not change significantly during the entire study period.

CONCLUSIONS

Bone turnover markers, bone mineral density and the rate of bone loss are within normal ranges in post-menopausal women with newly diagnosed Type 2 diabetes. Bone mineral density of the total body, lumbar spine and total hip is inversely correlated with total adiponectin.

Interactions between Serum Adipokines and Osteocalcin in Older Patients with Hip Fracture

Introduction. Experiments on genetically modified animals have discovered a complex cross-regulation between adipokines (leptin, adiponectin) and osteocalcin. The relationships between these molecules in human osteoporosis are still unclear. We evaluated the hypothesis of a bidirectional link between adipokines and osteocalcin. Materials and Methods. In a cross-sectional study of 294 older patients with osteoporotic hip fracture, we estimated serum concentrations of leptin, adiponectin, resistin, osteocalcin, parameters of mineral metabolism, and renal function. Results. After adjustment for multiple potential confounders, serum osteocalcin concentration was inversely associated with resistin and positively with leptin, leptin/resistin ratio, and adiponectin/resistin ratio. In multivariate regression models, osteocalcin was an independent predictor of serum leptin, resistin, leptin/resistin, and adiponectin/resistin ratios. Conclusions. Our data support the bidirectional regulation between osteocalcin and adipokines, but contrary to the genetically modified animal models, in older subjects with osteoporotic hip fracture, serum osteocalcin is positively associated with leptin and inversely with resistin.

Hyperadiponectinemia enhances bone formation in mice

BACKGROUND

There is growing evidence that adiponectin, a physiologically active polypeptide secreted by adipocytes, controls not only adipose tissue but also bone metabolism. However, a role for adiponectin in bone development remains controversial.

METHODS

We therefore investigated the endocrine effects of adiponectin on bone metabolism using 12-week-old male transgenic (Ad-Tg) mice with significant hyperadiponectinemia overexpressing human full-length adiponectin in the liver.

RESULTS

In Ad-Tg mice, the serum level of osteocalcin was significantly increased, but the levels of RANKL, osteoprotegerin, and TRAP5b were not. Bone mass was significantly greater in Ad-Tg mice with increased bone formation. In contrast, bone resorption parameters including the number of osteoclasts and eroded surface area did not differ between Ad-Tg and their littermates.

CONCLUSIONS

These findings demonstrate that hyperadiponectinemia enhances bone formation in mice.

Novel insights into the relationship between diabetes and osteoporosis

Only three decades ago adipose tissue was considered inert, with little relationship to insulin resistance. Similarly, bone has long been thought of purely in its structural context. In the last decade, emerging evidence has revealed important endocrine roles for both bone and adipose tissue. The interaction between these two tissues is remarkable. Bone marrow mesenchymal stem cells give rise to both osteoblasts and adipocytes. Leptin and adiponectin, two adipokines secreted by fat tissue, control energy homeostasis, but also have complex actions on the skeleton. In turn, the activities of bone cells are not limited to their bone remodelling activities but also to modulation of adipose cell sensitivity and insulin secretion. This review will discuss these new insights linking bone remodelling to the control of fat metabolism and the association between diabetes mellitus and osteoporosis.

Bone and glucose metabolism: a two-way street

Evidence from rodent models indicates that undercarboxylated osteocalcin (ucOC), a product of osteoblasts, is a hormone affecting insulin production by the pancreas and insulin sensitivity in peripheral tissues, at least in part through enhanced secretion of adiponectin from adipocytes. Clinical research to test whether this relationship is found in humans is just beginning to emerge. Cross-sectional studies confirm associations between total osteocalcin (OC), ucOC and glucose metabolism but cannot distinguish causality. To date, longitudinal studies have not provided a consistent picture of the effects of ucOC or OC on fasting glucose and insulin sensitivity. Further exploration into the physiological and mechanistic effects of ucOC and OC, in rodent models and clinical studies, is necessary to determine to what extent the skeleton regulates energy metabolism in humans.

Plasma adipokines, bone mass, and hip geometry in rural Chinese adolescents

CONTEXT

Adipokines have been linked to bone phenotypes recently, but with conflicting results. Few such studies have been conducted in adolescents.

OBJECTIVE

The aim of the study was to examine the associations of adiponectin and leptin with multiple bone phenotypes in Chinese adolescents and estimate the genetic contribution to these associations.

DESIGN AND SETTING

This was a cross-sectional study conducted in rural China.

PARTICIPANTS

A total of 675 males and 575 females aged 13-21 yr were included.

OUTCOME MEASURES

Fat mass (FM), lean mass (LM), bone area (BA), bone mineral content (BMC), cross-sectional area (CSA), and section modulus (SM) were measured by dual-energy x-ray absorptiometry. Plasma adipokine concentration was determined using sandwich immunoassays.

RESULTS

Adiponectin was inversely associated with all BMCs in males (P < 0.01), but not in females, after adjusting for LM, body weight, or BMI singly, or for LM and FM simultaneously. No such relationships were observed for CSA or SM in both genders. Leptin was inversely associated with all BAs, total-hip BMC, CSA, and SM in both genders, when adjusting for body weight or BMI. These associations, except for whole-body BA and lumbar spine BA in females, disappeared when simultaneously adjusting for LM and FM. By Cholesky decomposition models using twin design, significant genetic correlations were detected between adiponectin and total-hip BMC in males and between leptin and total-hip BMC in both genders.

CONCLUSIONS

We demonstrated that adiponectin and leptin were inversely associated with adolescent bone phenotypes but showed differential associations by gender, type of bone phenotypes, and adjustment of FM. This study also suggested that adipokines and bone phenotypes may share a common set of genes.

Gamma-carboxylation of osteocalcin and insulin resistance in older men and women

BACKGROUND

The skeletal protein osteocalcin is gamma-carboxylated by vitamin K. High serum uncarboxylated osteocalcin reflects low vitamin K status. In vitro and animal studies indicate that high uncarboxylated osteocalcin is associated with reduced insulin resistance. However, associations between osteocalcin and measures of insulin resistance in humans are less clear.

OBJECTIVE

Our aim was to examine cross-sectional and longitudinal associations between circulating forms of osteocalcin (total, uncarboxylated, and carboxylated) and insulin resistance in older men and women.

DESIGN

Cross-sectional associations between serum measures of total osteocalcin, carboxylated osteocalcin, and uncarboxylated osteocalcin and insulin resistance were examined in 348 nondiabetic men and women (mean age: 68 y; 58% female) by using the homeostasis model assessment of insulin resistance (HOMA-IR). Associations between each form of osteocalcin at baseline and 3-y change in HOMA-IR were examined in 162 adults (mean age: 69 y; 63% female) who did not receive vitamin K supplementation.

RESULTS

Lower circulating uncarboxylated osteocalcin was not associated with higher HOMA-IR at baseline or at 3-y follow-up. Those in the lowest tertiles of total osteocalcin and carboxylated osteocalcin at baseline had higher baseline HOMA-IR (P = 0.006 and P = 0.02, respectively). The concentration of carboxylated osteocalcin at baseline was inversely associated with a 3-y change in HOMA-IR (P = 0.002).

CONCLUSIONS

In older adults, circulating uncarboxylated osteocalcin was not associated with insulin resistance. In contrast, elevated carboxylated osteocalcin and total osteocalcin were associated with lower insulin resistance, which supports a potential link between skeletal physiology and insulin resistance in humans. The role of vitamin K status in this association remains unclear and merits further investigation. This trial is registered at clinicaltrials.gov as NCT00183001.

A link between bone mineral density and serum adiponectin and visfatin levels in acromegaly

CONTEXT

Two adipokines highly expressed in fat mass, adiponectin with antiinflammatory and antiatherogenic properties and visfatin with an insulin-mimetic effect, are potential contributors to bone metabolism. In acromegaly, data on adiponectin are contradictory, and there are no data on visfatin.

OBJECTIVES

The aim of the study was to evaluate adiponectin and visfatin in acromegaly, compared to control subjects, and to analyze their relationship with body composition and bone markers.

METHODS

Bone markers [osteocalcin, total amino-terminal propeptide of type 1 procollagen (total P1NP), carboxy-terminal telopeptide (beta-Crosslaps)], body composition (by dual-energy x-ray absorptiometry), adiponectin (by ELISA), and visfatin (by immunoanalysis)] were evaluated in 60 acromegalic patients (24 males and 36 females) and in 105 age- and gender-matched healthy controls (33 males and 72 females). Acromegalic patients were classified as controlled, with normal IGF-I and nadir GH no greater than 1 microg/liter (n = 41), or active (n = 19).

RESULTS

Acromegalic patients had lower adiponectin (P < 0.01), more lean body mass (P < 0.01), more total body mass (P < 0.01), higher bone formation markers (osteocalcin and total P1NP, P < 0.05 and P < 0.01, respectively), but less bone resorption markers (beta-Crosslaps, P < 0.001) than controls. No differences in visfatin and BMD were found between patients and controls. Adiponectin correlated negatively with BMD (r = -0.374; P < 0.05) and lean mass (r = -0.301; P < 0.05) and positively with age (r = 0.341; P < 0.001) in acromegaly. Visfatin correlated negatively with BMD (r = -0.359; P < 0.05). BMD was the predictor for adiponectin and visfatin.

CONCLUSIONS

Acromegalic patients present hypoadiponectinemia and a favorable bone marker profile. Adiponectin and visfatin could be a link between fat mass and bone in acromegaly.

APPL1: role in adiponectin signaling and beyond

Adiponectin, an adipokine secreted by the white adipose tissue, plays an important role in regulating glucose and lipid metabolism and controlling energy homeostasis in insulin-sensitive tissues. A decrease in the circulating level of adiponectin has been linked to insulin resistance, type 2 diabetes, atherosclerosis, and metabolic syndrome. Adiponectin exerts its effects through two membrane receptors, AdipoR1 and AdipoR2. APPL1 is the first identified protein that interacts directly with adiponectin receptors. APPL1 is an adaptor protein with multiple functional domains, the Bin1/amphiphysin/rvs167, pleckstrin homology, and phosphotyrosine binding domains. The PTB domain of APPL1 interacts directly with the intracellular region of adiponectin receptors. Through this interaction, APPL1 mediates adiponectin signaling and its effects on metabolism. APPL1 also functions in insulin-signaling pathway and is an important mediator of adiponectin-dependent insulin sensitization in skeletal muscle. Adiponectin signaling through APPL1 is necessary to exert its anti-inflammatory and cytoprotective effects on endothelial cells. APPL1 also acts as a mediator of other signaling pathways by interacting directly with membrane receptors or signaling proteins, thereby playing critical roles in cell proliferation, apoptosis, cell survival, endosomal trafficking, and chromatin remodeling. This review focuses mainly on our current understanding of adiponectin signaling in various tissues, the role of APPL1 in mediating adiponectin signaling, and also its role in the cross-talk between adiponectin/insulin-signaling pathways.

Adiponectin is a negative regulator of bone mineral and bone strength in growing mice

Obesity is associated with increased bone mineral density (BMD) but the mechanism for this is unclear. Serum levels of the adipokine adiponectin are inversely correlated with obesity, but results from studies on its relationship to bone mass are conflicting. The objective of this study was to compare bone mineral content (BMC), BMD and biomechanical strength properties of femur and lumbar vertebrae in 8- and 16-week old adiponectin transgenic mice (AdTg). These mice exhibit significantly elevated circulating adiponectin but have similar body weights compared to wild-type (WT) littermates that were used as controls. Female AdTg mice displayed significantly lower femur BMC at 8 and 16 weeks of age and femur neck peak load was significantly lower in 8-week old AdTg mice of both genders compared to controls. The peak load from compression testing of an individual lumbar vertebra was significantly lower in female AdTg mice compared to WT at 8 weeks, and this difference persisted at 16 weeks of age. In addition, lumbar vertebrae BMC was significantly lower in 16-week old male AdTg mice compared to WT although vertebra peak load was not different. Serum adiponectin levels were inversely correlated with femur BMC. In summary, elevated circulating adiponectin inhibits the acquisition of bone mass in growing mice and results in decreased biomechanical measures of functional strength that are surrogate measures of susceptibility to fractures. These results support a role for circulating adiponectin as a metabolic link that can explain, at least in part, the positive relationship between obesity and both bone mass and reduced susceptibility to fractures.

Serum adiponectin in elderly men does not correlate with fracture risk

CONTEXT

Recent evidence suggests that adiponectin may play a role in bone metabolism, but studies of the correlation between serum adiponectin and bone mineral density (BMD) have given conflicting results, and the impact on fracture risk is unknown.

OBJECTIVE

Our objective was to investigate the association between serum adiponectin levels and BMD and fracture risk. DESIGN, SETTING, PARTICIPANTS, MAIN OUTCOME MEASURES: We used regression analyses to estimate the relationship between adiponectin and BMD in the Prospective Investigation of the Vasculature in Uppsala Seniors cohort of 441 men and 457 women aged 70 yr. The association was thereafter analyzed in the Uppsala Longitudinal Study of Adult Men (ULSAM), in which adiponectin was analyzed at age 70 yr and BMD at 82 yr in 507 men. Fractures in the ULSAM were documented in 314 men during 15 yr follow-up. Cox regression analysis was used to determine the risk of fracture according to serum adiponectin levels.

RESULTS

In multivariable analysis a negative association between adiponectin and BMD was found in both cohorts. When individuals in the highest quintile of adiponectin were compared with those in the lowest quintile, adjusted BMD was 9.7% lower at the lumbar spine, 7.1% lower at the proximal femur, and 5.2% lower for total body in the Prospective Investigation of the Vasculature in Uppsala Seniors (P < 0.001 for all three), and 8.1, 5.1, and 4.1% (P < 0.003 for all three), respectively, in the ULSAM. However, the hazard ratio for fracture per 1 sd of serum adiponectin was 0.99 (95% confidence interval 0.89-1.11).

CONCLUSION

Although adiponectin was a negative determinant of BMD in two independent cohorts, it was not associated with fracture risk in men.

The bone-adipose axis in obesity and weight loss

Body fat and lean mass are correlated with bone mineral density, with obesity apparently exerting protection against osteoporosis. The pathophysiological relevance of adipose tissue in bone integrity resides in the participation of adipokines in bone remodeling through effects on deposition and resorption. On the other hand, the skeleton has recently emerged as an endocrine organ with effects on body weight control and glucose homeostasis through the actions of bone-derived factors such as osteocalcin and osteopontin. The cross-talk between adipose tissue and the skeleton constitutes a homeostatic feedback system with adipokines and molecules secreted by osteoblasts and osteoclasts representing the links of an active bone-adipose axis. Given the impact of bariatric surgery on absorption and the adipokine secretory pattern, to focus on the changes taking place following surgical-induced weight loss on this dynamic system merits detailed consideration.

Mineral metabolism in obese patients following vertical banded gastroplasty

BACKGROUND

Bone disease has been described in patients after surgical treatment for obesity, but few studies have dealt with the impact of vertical banded gastroplasty on mineral metabolism. We have examined bone mineral metabolism in morbidly obese patients before and after 3 months after vertical banded gastroplasty without vitamin D supplementation.

METHODS

Sixteen morbidly obese patients (14 women, 2 men) with a mean (+/-SD) age of 38 +/- 9 years and a body mass index (BMI) of 47.1 +/- 8.1 kg/m2 were studied. No vitamin D supplementation was given. Body weight, fat mass, calcium, 25OHD, iPTH, bone remodeling markers, and leptin levels were measured at baseline and after weight loss.

RESULTS

Mean weight loss was 28 +/- 11 kg; BMI and body fat mass decreased by 20 and 35%, respectively. Bone resorption markers and albumin-corrected serum calcium increased after operation, whereas iPTH fell. Serum 25OHD levels rose. Leptin levels decreased. Serum iPTH was positively correlated with weight, BMI, and fat mass before operation (p < 0.05), and its decline after weight reduction was negatively associated with the increase in bone resorption markers (p < 0.01). Leptin concentration was correlated with BMI and body fat mass (p < 0.05) both before and after surgery.

CONCLUSIONS

Weight reduction obtained in morbidly obese subjects 3 months after vertical banded gastroplasty increases bone turnover markers and decreases PTH secretion. Serum 25OHD levels rose. Therefore, no reasons for a metabolic bone disease related to hypovitaminosis D were readily apparent. However, an increase in bone turnover, which is generally regarded as a potential risk factor for osteoporosis, was observed. Further work is needed to clarify the importance of this turnover increase in the long run.

Diabetes mellitus, bone mineral density, and fracture risk

PURPOSE OF REVIEW

To review recent research on type 1 and 2 diabetes mellitus, bone mineral density, and fractures and to identify high-priority research areas.

RECENT FINDINGS

Recent meta-analyses and cohort studies confirm that type 1 and 2 diabetes are associated with higher fracture risk. These findings are not completely explained by lower bone mineral density in type 1 diabetes or the higher bone mineral density in type 2 diabetes. Studies provide new information on fracture risk for middle-aged diabetic adults, type 1 diabetic men, type 2 diabetic black women, and multiple sites. Recent case-control studies adjusted for key risk factors, and lower bone mineral density in type 1 diabetic adults remained significant at multiple sites. Prospective studies suggest an increased bone mineral density loss for type 2 diabetic white women and with thiazolidinedione use. Longitudinal cohort studies found that subclinical and clinical alterations in peripheral nerve, vascular, and kidney function were associated with lower bone mineral density, higher bone mineral density loss, or higher fracture rates in type 2 diabetic and nondiabetic older adults.

SUMMARY

Prospective studies of risk factors for diabetic bone loss are needed. A greater elucidation of fracture etiology in diabetes has implications for preventive measures.