Adiponectin and bone mass density: The InCHIANTI study

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.

The 40-min HIIT acutely induced bone formation which was likely through the increases in muscle derived interleukin 6 and adiponectin activation: The 16 weeks of HIIT intervention, longitudinal randomized controlled trial

PURPOSE

There is some controversy regarding cytokines released from adipocytes, particularly adiponectin, leptin, and IL6 that regulate bone remodeling. In addition, IL6 is released from muscle contraction, which might have a distinct role in bone remodeling. Hence, this study investigated whether muscle contraction during a session of 40 min of high intensity interval training (40-min HIIT) and after 16 weeks of HIIT (16-wk HIIT) altered the release of those cytokines and bone remodeling in overweight women.

METHODS

In total, 22 overweight, premenopausal women were randomly assigned to either the exercise or the control group. The exercise participants engaged in the 40-min HIIT session at 80-90 % of their heart rate reserve (HRR) three times weekly for 16 weeks, while the control participants performed their routine daily activities. Blood was drawn after overnight fasting and immediately after completing the 40-min HIIT sessions to investigate the association of adiponectin, leptin, IL6, CTX, and P1NP through the acute effect of the 40-min HIIT sessions. This process was repeated after the 16-wk intervention program to observe the training effect of HIIT on cytokines linkage. The bone mineral density (BMD) levels of the distal tibia, femur, and lumbar spine were determined prior to and after the 16-wk intervention using dual-energy X-ray absorptiometry.

RESULTS

The P1NP level increased by 8.29-20.52 % (95 % CI) and by 2.91-15.54 % after completing the first and last bouts of the 40-min HIIT sessions, respectively. In addition, IL6 increased by 13.39-28.03 % (95 % CI), while serum CTX and adiponectin were unaltered from the acute effect of the 40-min HIIT sessions. There was an association between the increases in P1NP and adiponectin (r = 0.682, p = 0.015); however, the increase in P1NP was mostly associated with the increase in IL6 (r = 0.572, p = 0.054) after completing a 40-min HIIT session. After the 16-wk HIIT program, the resting adiponectin level of the exercise participants increased; however, this was associated with neither bone biomarkers nor BMD. The BMDs of the exercise participants were maintained; however, the tibial BMD of the control participants decreased with an increase in the resting CTX level after 16 weeks.

CONCLUSION

Muscle contraction during the 40-min HIIT session elevated the IL6 level, which might have subsequently enhanced bone formation. Furthermore, the association between acute changes in adiponectin and P1NP suggested the possibility of an increase in the sensitivity of the adiponectin receptor in osteoblasts.

Celastrol attenuates HFD-induced obesity and improves metabolic function independent of adiponectin signaling

Backgound: Celastrol, a leptin sensitiser, has been shown to inhibit food intake and reduce body weight in diet-induced obese mice, making it a potential treatment for obesity and metabolic diseases. Adiponectin signalling has been reported to play an important role in the treatment of obesity, inflammation, and non-alcoholic fatty liver disease.Materials and methods: Wild-type (WT) and AdipoR1 knockout (AdipoR1-/-) mice were placed on a chow diet or a high-fat diet (HFD) and several metabolic parameters were measured. Celastrol was then administered to the HFD-induced mice and the response of WT and AdipoR1-/- mice to celastrol in terms of body weight, blood glucose, and food intake was also recorded.Results: AdipoR1 knockout caused elevated blood glucose and lipids, impaired glucose tolerance and insulin resistance in mice, as well as increased susceptibility to HFD-induced obesity. After 14 days of treatment, WT and AdipoR1-/- mice showed significant reductions in body weight and blood glucose and improvements in glucose tolerance.Conclusion: The present study demonstrated that AdipoR1 plays a critical role in metabolic regulation and that the improvement of weight and metabolic function by celastrol is independent of the AdipoR1-mediated signalling pathway.

A potential correlation between adipokines, skeletal muscle function and bone mineral density in middle-aged and elderly individuals

BACKGROUND

Evidence exists of a strong association between inflammation and a decrease in skeletal muscle function and bone mineral density (BMD); however, the specific mechanisms of these associations remain unclear. Adipokines, as key regulators of the inflammatory response, may be implicated in these processes. The objective of this study was to explore the potential correlation between adipokines, skeletal muscle function and BMD in middle-aged and elderly individuals.

METHODS

A comparative cross-sectional study was carried out at the Huadong Hospital Affiliated with Fudan University (Shanghai, China). A total of 460 middle-aged and elderly individuals were recruited, and 125 were enrolled in the analysis. Their biochemical indices, body composition, skeletal muscle function and BMD were measured. Bioinformatic analysis was also employed to identify potential adipokine targets linked to skeletal muscle function and BMD. To validate these targets, plasma and peripheral blood mononuclear cells (PBMCs) were harvested from these individuals and subjected to western blotting (WB) and enzyme-linked immunosorbent assay (ELISA).

RESULTS

Individuals in this cross-sectional study were categorized into 2 groups according to their median skeletal muscle mass (SMM) (28.8 kg for males and 20.6 kg for females). Individuals with lower SMM exhibited poorer grip strength (P = 0.017), longer 5-Times-Sit-to-Stand Test (FTSST) duration (P = 0.029), lower total hip BMD (P = 0.043), lower femoral neck BMD (P = 0.011) and higher levels of inflammatory markers in comparison with individuals with higher SMM. Bioinformatics analysis identified LEP, ADIPOQ, RBP4, and DPP4 as potential adipokine targets associated with skeletal muscle function and BMD. In vitro experiments demonstrated that individuals with decreased skeletal muscle function and BMD expressed higher levels of these adipokines.

CONCLUSIONS

Skeletal muscle function is positively correlated with BMD and negatively correlated with levels of inflammatory markers among middle-aged and elderly individuals. Those with lower skeletal muscle function and BMD tend to have a higher expression of LEP, ADIPOQ, RBP4 and DPP4.

Obesity and Bone Health: A Complex Relationship

Recent scientific evidence has shown an increased risk of fractures in patients with obesity, especially in those with a higher visceral adipose tissue content. This contradicts the old paradigm that obese patients were more protected than those with normal weight. Specifically, in older subjects in whom there is a redistribution of fat from subcutaneous adipose tissue to visceral adipose tissue and an infiltration of other tissues such as muscle with the consequent sarcopenia, obesity can accentuate the changes characteristic of this age group that predisposes to a greater risk of falls and fractures. Other factors that determine a greater risk in older subjects with obesity are chronic proinflammatory status, altered adipokine secretion, vitamin D deficiency, insulin resistance and reduced mobility. On the other hand, diagnostic tests may be influenced by obesity and its comorbidities as well as by body composition, and risk scales may underestimate the risk of fractures in these patients. Weight loss with physical activity programs and cessation of high-fat diets may reduce the risk. Finally, more research is needed on the efficacy of anti-osteoporotic treatments in obese patients.

A longitudinal analysis of serum adiponectin levels and bone mineral density in postmenopausal women in Taiwan

Since bone and fat mass are derived from mesenchyme in early development, adipokines secreted by adipose tissue may have an effect on bone metabolism. The relationship between adiponectin and bone mineral density (BMD) has been inconsistent in previous reports, with results being dependent on age, gender, menopausal status and bone sites. We investigated the relationship between serum adiponectin levels and the BMD of proximal femur and vertebrae bones in a 96-week longitudinal study of post-menopausal women with repeated measures of both. Linear regression models were used to determine the relation between adiponectin and BMD at each time point cross-sectionally, and a generalized estimating equation (GEE) model was used to investigate the longitudinal trends. Among 431 subjects, 376 (87%) provided baseline adiponectin measurements and 373 provided more than two measurements for longitudinal analysis. The means of serum adiponectin and BMD decreased with time. In linear regression models, adiponectin at baseline, the 48th week and the 96th week appeared to be inversely associated with BMD of proximal femur bone, but not lumbar spine after adjusting for age and various confounders. However, they all turn insignificant with further adjustment of body mass index. The inverse association between adiponectin and BMD of proximal femur is substantiated by all generalized equation models. Before adding the BMI in the model, the increase of 1 mg/dL of adiponectin can accelerate the decrease of proximal femur BMD by 0.001 (SE = 0.0004, p = 0.008). With BMI in the model, the drop rate was 0.0008 (SE = 0.0004, p = 0.026) and remained similar with further adjustment of two bone turnover markers. In this longitudinal analysis with both adiponectin and BMD measured at three time points, we demonstrate that with the increase of adiponectin level, the decline of proximal femur BMD in postmenopausal women accelerated during a period of 96 weeks.

Anorexia Nervosa and Osteoporosis

Patients with anorexia nervosa (AN) often experience low bone mineral density (BMD) and increased fracture risk, with low body weight and decreased gonadal function being the strongest predictors of the observed bone mineral deficit and fractures. Other metabolic disturbances have also been linked to bone loss in this group of patients, including growth hormone resistance, low insulin-like growth factor-1 (IGF-1) concentrations, low leptin concentrations, and hypercortisolemia. However, these correlations lack definitive evidence of causality. Weight restoration and resumption of menstrual function have the strongest impact on increasing BMD. Other potential treatment options include bisphosphonates and teriparatide, supported by data from small clinical trials, but these agents are not approved for the treatment of low BMD in adolescents or premenopausal women with AN.

Causal roles of circulating adiponectin in osteoporosis and cancers

Circulating adiponectin has some association with the risk of osteoporosis and cancers, but their causal relationships remains elusive. Mendelian randomization (MR) study was used to explore the causal roles of circulating adiponectin in osteoporosis and cancers by using genome-wide association studies (GWASs) associated with circulating adiponectin, osteoporosis and cancers. Fifteen single nucleotide polymorphisms (SNPs) were used as instrumental variables for circulating adiponectin. Genetic predisposition to high circulating adiponectin was strongly associated with low femoral neck bone mineral density (FN-BMD, beta-estimate: -0.015, 95% CI: -0.023 to -0.006, SE: 0.004, P-value = 0.001), low forearm BMD (FA-BMD, beta-estimate: -0.027, 95% CI: -0.050 to -0.004, SE: 0.012, P-value = 0.023) and increased risk of breast cancer (beta-estimate: 0.011, 95% CI: 0.001 to 0.022, SE: 0.005, P-value = 0.031). There was limited evidence of the associations between circulating adiponectin and other outcomes (i.e. lumbar spine BMD [LS-BMD], colorectal cancer, liver cancer, lung cancer, bone cancer and prostate cancer). This study provides robust evidence that high circulating adiponectin is causally associated with low FN-BMD, low FA-BMD and increased risk of breast cancer, which may provide new insight to prevent and treat osteoporosis and breast cancer.

Correlation of ADIPOQ Gene Single Nucleotide Polymorphisms with Bone Strength Index in Middle-Aged and the Elderly of Guangxi Mulam Ethnic Group

BACKGROUND

Osteoporosis (OP) is a common orthopedic disease in the elderly, and Adiponectin (ADIPOQ) is closely related to bone metabolism.

OBJECTIVE

To determine the relationship between five single nucleotide polymorphism (SNP) loci in the ADIPOQ gene and osteoporosis in middle-aged and elderly Mulam subjects in Hechi, Guangxi.

METHODS

This case-control study included 297 middle-aged and elderly Mulam subjects with normal bone mass, 49 subjects with reduced bone mass, and 38 subjects with osteoporosis. Five loci (rs266729, rs1063539, rs2241766, rs3774261, rs710445) of the ADIPOQ in the Mulam subjects were genotyped using SNP with multiple-base extension.

RESULTS

The bone strength index (SI) of middle-aged and elderly Mulam subjects showed an overall decreasing trend when the subjects were older. Age, muscle mass, and subcutaneous fat content were the main factors influencing the SI in Mulam subjects. The GC genotype of rs266729 and the GA and GG genotypes of rs710445 were significantly correlated with risk of bone loss (p < 0.05). rs2241766 and rs1063539 showed strong LD (D' > 0.8, r² > 0.33). rs710445 and rs266729 loci and rs3774261 and rs2241766 loci showed complete LD (D' = 1).

CONCLUSIONS

The GC genotype at rs266729 of the ADIPOQ gene, the GA and GG genotypes at rs710445, and the haplotypes CCGAA and GGTAG correlated with osteoporosis (p < 0.05). The allele C of rs1063539, rs266729 and rs710445 may afford protection for osteoporosis. The allele G may be the genetic susceptibility gene for osteoporosis, increasing the risk of osteoporosis.

Paracrine Effects of Recombinant Human Adiponectin Promote Bone Regeneration

Bone regeneration is a delicate physiological process. Non-union and delayed fracture healing remains a great challenge in clinical practice nowadays. Bone and fat hold a close relationship to remain balanced through hormones and cytokines. Adiponectin is a well-known protein to maintain the hemostasis, which may be an interesting target for fracture healing. Herein, we provided a facile and efficient method to obtain high-purity and high-yield recombinant human adiponectin (ADPN). The biocompatibility and the pharmaceutical behaviors were evaluated in Sprague–Dawley rats. The paracrine effects of adiponectin on bone fracture healing were investigated with a rat tibia fracture model via intrabone injection. Significantly accelerated bone healing was observed in the medulla injection group, indicating the paracrine effects of adiponectin could be potentially utilized for clinical treatments. The underlying mechanism was primarily assessed, and the expression of osteogenic markers, including bone morphogenic protein 2, alkaline phosphatase, and osteocalcin, along with adiponectin receptor 1 (AdipoR1), was markedly increased at the fracture site. The increased bone healing of ADPN treatment may result from both enhanced osteogenic proliferation as well as differentiation. Cell experiments confirmed that the expression of osteogenesis markers increased significantly in ADPN treatment groups, while it decreased when the expression of AdipoR1 was knocked down by siRNA. Our study provided a feasible and efficacious way for bone fracture treatment with local administration of ADPN, which could be rapidly translated into the clinics.

Bone Mineral Density in Congenital Generalized Lipodystrophy: The Role of Bone Marrow Tissue, Adipokines, and Insulin Resistance

Congenital Generalized Lipodystrophy (CGL) is a rare syndrome characterized by the almost total absence of subcutaneous adipose tissue due to the inability of storing lipid in adipocytes. Patients present generalized lack of subcutaneous fat and normal to low weight. They evolve with severe metabolic disorders, non-alcoholic fatty liver disease, early cardiac abnormalities, and infectious complications. Although low body weight is a known risk factor for osteoporosis, it has been reported that type 1 and 2 CGL have a tendency of high bone mineral density (BMD). In this review, we discuss the role of bone marrow tissue, adipokines, and insulin resistance in the setting of the normal to high BMD of CGL patients. Data bases from Pubmed and LILACS were searched, and 113 articles published until 10 April 2021 were obtained. Of these, 76 were excluded for not covering the review topic. A manual search for additional literature was performed using the bibliographies of the studies located. The elucidation of the mechanisms responsible for the increase in BMD in this unique model of insulin resistance may contribute to the understanding of the interrelationships between bone, muscle, and adipose tissue in a pathophysiological and therapeutic perspective.

Immune Markers and Their Association with Bone Density in Children, Adolescents, and Young Adults with Perinatally Acquired HIV

To describe distributions of immune markers in children and young adults by sex and HIV status, and within groups, investigate associations of immune markers with bone density across Tanner stage. Using data and samples from 353 participants in a cross-sectional study in youth with perinatally acquired HIV (PHIV) and matched HIV-negative controls, distributions of inflammation and activation immune markers were described by sex and HIV status. Correlations and structural equation models (SEM) were used to explore marginal and multivariable associations of the immune markers with bone density and to assess whether patterns of association varied by sex and HIV status. Immune marker distributions did not differ by sex, but there were some differences by HIV status. Correlation patterns among bone, body composition, and immune markers were similar across the sex and HIV status groups. Conclusions from SEMs were limited by small sample sizes, but there was some indication that patterns of association between bone density and certain immune markers differed in male PHIV with more advanced Tanner stage compared to the other three groups. In conclusion, distributions of bone density, body composition, and immune markers may vary by sex and HIV status, although associations among these outcomes within sex and HIV status groups appear similar. Bone density of male PHIV appears to be more negatively affected than females, regardless of female HIV status. Larger longitudinal studies across Tanner stages are needed to further explore potential biological relationships between immune markers and bone density in youth living with HIV.

Greater Bone Marrow Adiposity Predicts Bone Loss in Older Women

Bone marrow adiposity (BMA) is associated with aging and osteoporosis, but whether BMA can predict bone loss and fractures remains unknown. Using data from the Age Gene/Environment Susceptibility (AGES)-Reykjavik study, we investigated the associations between ¹ H-MRS-based measures of vertebral bone marrow adipose tissue (BMAT), annualized change in bone density/strength by quantitative computed tomography (QCT) and DXA, and secondarily, with incident clinical fractures and radiographic vertebral fractures among older adults. The associations between BMAT and annualized change in bone density/strength were evaluated using linear regression models, adjusted for age, body mass index (BMI), diabetes, estradiol, and testosterone. Cox proportional hazards models were used to evaluate the associations between baseline BMAT and incident clinical fractures, and logistic regression models for incident vertebral fractures. At baseline, mean ± SD age was 80.9 ± 4.2 and 82.6 ± 4.2 years in women (n = 148) and men (n = 150), respectively. Mean baseline BMAT was 55.4% ± 8.1% in women and 54.1% ± 8.2% in men. Incident clinical fractures occurred in 7.4% of women over 2.8 years and in 6.0% of men over 2.2 years. Incident vertebral fractures occurred in 12% of women over 3.3 years and in 17% of men over 2.7 years. Each 1 SD increase in baseline BMAT was associated with a 3.9 mg² /cm⁴ /year greater loss of spine compressive strength index (p value = .003), a 0.9 mg/cm³ /year greater loss of spine trabecular BMD (p value = .02), and a 1.2 mg/cm³ /year greater loss of femoral neck trabecular BMD (p value = .02) in women. Among men, there were no associations between BMAT and changes in bone density/strength. There were no associations between BMAT and incident fractures in women or men. In conclusion, we found greater BMAT is associated with greater loss of trabecular bone at the spine and femoral neck, and greater loss of spine compressive strength, in older women. © 2019 American Society for Bone and Mineral Research.

AdipoRon Affects Cell Cycle Progression and Inhibits Proliferation in Human Osteosarcoma Cells

AdipoRon (AdipoR) is the first synthetic molecule acting as a selective and potent adiponectin receptor agonist. Recently, the possible pharmacological use of AdipoR in different pathological conditions has been addressed. Interestingly, initial evidence suggests that AdipoR may have anticancer properties in different preclinical models, such as pancreatic and ovarian cancer. To our knowledge, so far no research has been directed at determining the impact of AdipoR on osteosarcoma, the most aggressive and metastatic bone malignancy occurring in childhood and adolescence age. Here, we investigate the possible antitumor effects of AdipoR in osteosarcoma cell lines. MTT and cell growth curve assays clearly indicate that AdipoR inhibits, at different extents, proliferation in both U2OS and Saos-2 osteosarcoma cell lines, the latter being more sensitive. Moreover, flow cytometry-based assays point out a significant G0/G1 phase accumulation and a contemporary S phase decrease in response to AdipoR. Consistent with the different sensitivity, a strong subG1 appearance in Saos-2 after 48 and 72 hours of treatment is also observed. The investigation of the molecular mechanisms highlights a common and initial ERK1/2 activation in response to AdipoR in both Saos-2 and U2OS cells. Interestingly, a simultaneous and dramatic downregulation of p70S6K phosphorylation, one of the main targets of mTORC1 pathway, has also been observed in AdipoR-treated Saos-2, but not in U2OS cells. Importantly, a strengthening of AdipoR-induced effects was reported upon everolimus-mediated mTORC1 perturbation in U2OS cells. In conclusion, our findings provide initial evidence of AdipoR as an anticancer molecule differently affecting various signaling pathways involved in cell cycle and cell death in osteosarcoma cells and encourage the design of future studies to further understand its pattern of activities.

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.

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.

APPL1 negatively regulates bone mass, possibly by controlling the fate of bone marrow mesenchymal progenitor cells

Adiponectin is an adipokine that can exert a regulatory function on bone metabolism. However, there are many contradictions between clinical and pre-clinical studies on adiponectin. APPL1 is an adaptor protein that can interact with adiponectin receptors. In the current study, we found that knockout of the Appl1 gene in male mice was associated with higher bone volume and numbers of trabeculae than in females or controls. The trabecular thickness, cortical thickness, ratio of bone volume/trabecular volume, cross-sectional bone area, and mean polar moment of inertia increased in Appl1 KO mice compared with wild-type mice. The number of osteoblasts increased but the number of adipocytes decreased in Appl1 KO mice. Knockdown of Appl1 impaired adipogenesis in bone marrow-derived mesenchymal stem cells. Mineralization was increased by knockdown of Appl1 during osteoblast differentiation. Data from differentiation-related genes showed results consistent with the in vivo effects. In summary, this study provides further clarification of the effect of the adiponectin signaling pathway on bone metabolism.

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.

Adipokines and bone status in a cohort of anorexic patients

INTRODUCTION

Bone loss in anorexia nervosa (AN) is multifactorial; its mechanisms are not yet clearly understood and may vary depending on disease duration and severity. To determine to what extent adipokines may be involved in the bone alterations found in anorexic patients, we evaluated plasma levels for leptin, adiponectin and Pref-1 against other clinical and biological parameters in a population of anorexic patients split according to weight and bone status.

METHODS

Plasma concentrations of leptin, total adiponectin, high molecular weight (HMW) adiponectin, and Pref-1 were measured. The ratio of HMW adiponectin to total adiponectin - HMW (percentage) - was calculated. We divided our population into 5 groups with different phenotypes characterizing the severity of the disease and/or the severity of bone involvement: 1 - Normal BMD and body mass index (BMI): recovery from AN; 2 - Osteopenia (-2<Z-score<-1) and BMI>17kg/m²; 3 - Osteopenia and BMI≤17kg/m²; 4 - Osteoporosis (Z-score≤-2) and BMI>17kg/m²; 5 - Osteoporosis and BMI≤17kg/m².

RESULTS

The study involved 80 anorexia nervosa patients. Mean BMI was 16.8±2.4kg/m². No significant difference was found in total and HMW adiponectin plasma concentrations between the 5 groups. HMW (percentage) was significantly higher in group 5 compared to group 1. Leptin was significantly lower in groups 3 and 5 compared to the other groups. For the whole group femoral neck and hip BMD correlated negatively with total adiponectin and HMW adiponectin. No correlation was found between BMD (whatever the site) and plasma leptin. Multivariate analysis revealed that 2 factors - leptin and BMI - explained 10% of the variance in spine BMD. For femoral neck BMD, the 2 explanatory factors were BMI and total adiponectin which explained 14% of the variance in BMD. For total hip BMD, 27% of the variance in BMD was explained by 3 factors: leptin, BMI, and total adiponectin.

CONCLUSION

Bone status in anorexia nervosa is mainly determined by BMI, leptin and adiponectin.

Adiponectin Reduces Bone Stiffness: Verified in a Three-Dimensional Artificial Human Bone Model In Vitro

Primary human osteoblasts and osteoclasts incubated in a rotating coculture system without any scaffolding material, form bone-like tissue that may be used to evaluate effects of various compounds on mechanical strength. Circulating adiponectin has been found to be negatively associated with BMD and strength and was therefore assessed in this system. Osteospheres of human osteoblasts and osteoclasts were generated with and without adiponectin. The osteospheres were scanned using micro-computed tomography, the mechanical properties were tested by flat punch compression using nanoindentation equipment, and the cellular morphology characterized by microscopy. The association between autologously produced adiponectin and biomechanical properties was further evaluated by quantitation of adiponectin levels using quantitative polymerase chain reaction (qPCR) and immunoassays, and identification of stiffness by bending test of rat femurs. The molecular mechanisms were examined in vitro using human bone cells. Mechanical testing revealed that adiponectin induced a more compliant osteosphere compared with control. The osteospheres had a round, lobulated appearance with morphologically different areas; inner regions containing few cells embedded in a bone-like material surrounded by an external area with a higher cell quantity. The expression of adiponectin was found to correlate positively to ultimate bending moment and ultimate energy absorption and deflection, on the other hand, it correlated negatively to bending stiffness, indicating autocrine and/or paracrine effects of adiponectin in bone. Adiponectin enhanced proliferation and expression of collagen, leptin, and tumor necrosis factor-alpha in osteoblasts and stimulated proliferation, but not the functional activity of osteoclasts. Our results indicate that both administration of adiponectin during osteosphere production and in situ elevated levels of adiponectin in rat femurs, reduced stiffness of the bone tissues. An increase in undifferentiated cells and extracellular matrix proteins, such as collagen, may explain the reduced bone stiffness seen in the osteospheres treated with adiponectin.

The relationship between circulating adiponectin, leptin and vaspin with bone mineral density (BMD), arterial calcification and stiffness: a cross-sectional study in post-menopausal women

OBJECTIVE

To explore the relationship between circulating adiponectin, leptin and vaspin with bone mineral density (BMD), arterial stiffness and vascular calcification in post-menopausal women. We hypothesised that adipokines produced by adipose tissue may be mediators of bone and cardiovascular disease (CVD) and explain, in part, the observed association between osteoporosis and CVD.

DESIGN

We studied 386 ambulant community dwelling postmenopausal women aged (mean [SD] 61 [6.4] years). BMD at the lumbar spine, femoral neck (FN), and total hip (TH), body composition; fat mass (FM) and lean mass (LM) as well as abdominal aortic calcification (AAC) were determined by dual energy X-ray absorptiometry. Pulse wave velocity (PWV) and augmentation index, markers of arterial stiffness were measured. Fasting adiponectin, leptin and vaspin were quantified in serum.

RESULTS

A positive independent association was observed between vaspin and BMD at the FN (p = 0.009), TH (p = 0.037) in the whole study population adjusted for confounders including age, FM, LM and lifestyle variables. Using the same model, a negative association was seen between adiponectin and BMD at the FN in women with osteoporosis (p = 0.043). Serum adiponectin was significantly higher in women with fractures (20.8 [9.3] µg/ml compared to those without (18.5 [8.6] µg/ml, p = 0.018) and associated with a significant increased risk of fracture (HR 1.032, 95% CI 1.003-1.063, p = 0.032). Leptin was not associated with BMD or fracture risk after adjustment. Adiponectin was independently associated with AAC (p = 0.007) and significantly higher in women with AAC scores > 1; (19.2[9.2]) compared to those with no or low AAC scores (<1); 16.8 [8.0], p = 0.018). In adjusted analyses, PWV velocity was positively associated with circulating vaspin (p = 0.039) and AI was negatively associated with serum leptin (p = 0.002).

CONCLUSION

Adiponectin, leptin, vaspin are related to markers of bone and vascular health and may contribute to the observed association between osteoporosis and CVD.

The Activity of Adiponectin in Bone

The adipokine adiponectin affects multiple target tissues and plays important roles in glucose metabolism and whole-body energy homeostasis. Circulating adiponectin levels in obese people are lower than in non-obese, and increased serum adiponectin is associated with weight loss. Numerous clinical studies have established that fat mass is positively related to bone mass, a relationship that is maintained by communication between the two tissues through hormones and cytokines. Since adiponectin levels inversely correspond to fat mass, its bone effects and its potential contribution to the relationship between fat and bone have been investigated. In clinical observational studies, adiponectin was found to be negatively associated with bone mineral density, suggesting it might be a negative regulator of bone metabolism. In order to identify the mechanisms that underlie the activity of adiponectin in bone, a large number of laboratory studies in vitro and in animal models of mice over-expressing or deficient of adiponectin have been carried out. Results of these studies are not entirely congruent, partly due to variation among experimental systems and partly due to the complex nature of adiponectin signaling, which involves a combination of multiple direct and indirect mechanisms.

Analysis of the associations among Helicobacter pylori infection, adiponectin, leptin, and 10-year fracture risk using the fracture risk assessment tool: A cross-sectional community-based study

Helicobacter pylori (H. pylori) infection may induce inflammatory cytokines or adipokines that influence bone turnover and bone fracture risk. This study aimed to evaluate the association among H. pylori infection, adipokines, and 10-year fracture risk using the Fracture Risk Assessment Tool scale. From August 2013 to February 2016, a community-based cohort was surveyed by Keelung Chang-Gung Memorial Hospital. Subjects were included if they were older than 40 years and not pregnant. All participants underwent a standardized questionnaire survey, physical examination, urea breath test, and blood tests. A total of 2,689 participants (1,792 women) were included in this cross-sectional study. In both sexes, participants with a high fracture risk were older and had higher adiponectin values than participants without a high fracture risk (mean age, female: 72.9 ± 5.6 vs. 55.8 ± 7.3 years, P < 0.0001; male: 78.9 ± 4.7 vs. 58.1 ± 8.9 years, P < 0.001) (adiponectin, female: 10.8 ± 6.3 vs. 8.7 ± 5.2 ng/ml, P < 0.001; male: 9.7 ± 6.1 vs. 5.5 ± 3.8 ng/ml, P < 0.001). Adiponectin was correlated with high fracture risk in both sexes, but H. pylori infection and leptin was not. In logistic regression analysis, adiponectin could not predict high fracture risk when adjusting the factor of body mass index (BMI) in men group. In conclusion, H. pylori infection and leptin could not predict 10-year fracture risk in either sex. Adiponectin was correlated with bone fracture risk in both sexes and the correlation might be from the influence of BMI.

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.

Bone Cell Bioenergetics and Skeletal Energy Homeostasis

The rising incidence of metabolic diseases worldwide has prompted renewed interest in the study of intermediary metabolism and cellular bioenergetics. The application of modern biochemical methods for quantitating fuel substrate metabolism with advanced mouse genetic approaches has greatly increased understanding of the mechanisms that integrate energy metabolism in the whole organism. Examination of the intermediary metabolism of skeletal cells has been sparked by a series of unanticipated observations in genetically modified mice that suggest the existence of novel endocrine pathways through which bone cells communicate their energy status to other centers of metabolic control. The recognition of this expanded role of the skeleton has in turn led to new lines of inquiry directed at defining the fuel requirements and bioenergetic properties of bone cells. This article provides a comprehensive review of historical and contemporary studies on the metabolic properties of bone cells and the mechanisms that control energy substrate utilization and bioenergetics. Special attention is devoted to identifying gaps in our current understanding of this new area of skeletal biology that will require additional research to better define the physiological significance of skeletal cell bioenergetics in human health and disease.

Pathophysiology of Bone Fragility in Patients with Diabetes

It has been well established that bone fragility is one of the chronic complications of diabetes mellitus, and both type 1 and type 2 diabetes are risk factors for fragility fractures. Diabetes may negatively affect bone health by unbalancing several pathways: bone formation, bone resorption, collagen formation, inflammatory cytokine, muscular and incretin system, bone marrow adiposity and calcium metabolism. The purpose of this narrative review is to explore the current understanding of pathophysiological pathways underlying bone fragility in diabetics. In particular, the review will focus on the peculiar cellular and molecular system impairment that may lead to increased risk of fracture in type 1 and type 2 diabetes.

Diabetes and disordered bone metabolism (diabetic osteodystrophy): time for recognition

Diabetes and osteoporosis are rapidly growing diseases. The link between the high fracture incidence in diabetes as compared with the non-diabetic state has recently been recognized. While this review cannot cover every aspect of diabetic osteodystrophy, it attempts to incorporate current information from the First International Symposium on Diabetes and Bone presentations in Rome in 2014. Diabetes and osteoporosis are fast-growing diseases in the western world and are becoming a major problem in the emerging economic nations. Aging of populations worldwide will be responsible for an increased risk in the incidence of osteoporosis and diabetes. Furthermore, the economic burden due to complications of these diseases is enormous and will continue to increase unless public awareness of these diseases, the curbing of obesity, and cost-effective measures are instituted. The link between diabetes and fractures being more common in diabetics than non-diabetics has been widely recognized. At the same time, many questions remain regarding the underlying mechanisms for greater bone fragility in diabetic patients and the best approach to risk assessment and treatment to prevent fractures. Although it cannot cover every aspect of diabetic osteodystrophy, this review will attempt to incorporate current information particularly from the First International Symposium on Diabetes and Bone presentations in Rome in November 2014.

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.

Sequences of Regressions Distinguish Nonmechanical from Mechanical Associations between Metabolic Factors, Body Composition, and Bone in Healthy Postmenopausal Women

BACKGROUND

There is increasing recognition of complex interrelations between the endocrine functions of bone and fat tissues or organs.

OBJECTIVE

The objective was to describe nonmechanical and mechanical links between metabolic factors, body composition, and bone with the use of graphical Markov models.

METHODS

Seventy postmenopausal women with a mean ± SD age of 62.3 ± 3.7 y and body mass index (in kg/m2) of 24.9 ± 3.8 were recruited. Bone outcomes were peripheral quantitative computed tomography measures of the distal and diaphyseal tibia, cross-sectional area (CSA), volumetric bone mineral density (vBMD), and cortical CSA. Biomarkers of osteoblast and adipocyte function were plasma concentrations of leptin, adiponectin, osteocalcin, undercarboxylated osteocalcin (UCOC), and phylloquinone. Body composition measurements were lean and percent fat mass, which were derived with the use of a 4-compartment model. Sequences of Regressions, a subclass of graphical Markov models, were used to describe the direct (nonmechanical) and indirect (mechanical) interrelations between metabolic factors and bone by simultaneously modeling multiple bone outcomes and their relation with biomarker outcomes with lean mass, percent fat mass, and height as intermediate explanatory variables.

RESULTS

The graphical Markov models showed both direct and indirect associations linking plasma leptin and adiponectin concentrations with CSA and vBMD. At the distal tibia, lean mass, height, and adiponectin-UCOC interaction were directly explanatory of CSA (R2 = 0.45); at the diaphysis, lean mass, percent fat mass, leptin, osteocalcin, and age-adiponectin interaction were directly explanatory of CSA (R2 = 0.49). The regression models exploring direct associations for vBMD were much weaker, with R2 = 0.15 and 0.18 at the distal and diaphyseal sites, respectively. Lean mass and UCOC were associated, and the global Markov property of the graph indicated that this association was explained by osteocalcin.

CONCLUSIONS

This study, to our knowledge, offers a novel approach to the description of the complex physiological interrelations between adiponectin, leptin, and osteocalcin and the musculoskeletal system. There may be benefits to jointly targeting both systems to improve bone health.

Serum leptin, adiponectin and ghrelin concentrations in post-menopausal women: Is there an association with bone mineral density?

OBJECTIVE

Adipokines and ghrelin exert well-documented effects on energy expenditure and glucose metabolism. Experimental data also support a role in bone metabolism, although data from clinical studies are conflicting. The purpose of this cross-sectional study was to investigate the association of serum concentrations of leptin, adiponectin and ghrelin with bone mineral density (BMD) in post-menopausal women.

METHODS

BMD in lumbar spine and femoral neck, and circulating leptin, adiponectin and ghrelin concentrations were measured in 110 healthy post-menopausal women. Patients with secondary causes of osteoporosis were excluded.

RESULTS

Osteoporosis was diagnosed in 30 (27%) women and osteopenia in 54 (49%). Serum leptin concentrations were positively correlated with both lumbar spine (r=0.343, p<0.01) and femoral neck BMD (r=0.370, p<0.01). Adiponectin concentrations were negatively associated with BMD at both sites (r=-0.321, p<0.01 and r=-0.448, p<0.01 respectively). No significant correlation between ghrelin concentrations and BMD was found. Osteoporotic women had lower body weight, body mass index (BMI) and leptin concentrations, but higher adiponectin concentrations compared with non-osteoporotic women. In multivariate stepwise regression analysis, the association of adiponectin concentrations with BMD remained significant only for femoral neck, after adjustment for body weight or BMI.

CONCLUSIONS

An inverse association between adiponectin and femoral neck BMD was found in post-menopausal women, independently of body weight. The positive association between leptin and BMD was dependent on body weight, whereas no effect of ghrelin on BMD was evident.

Relationship between Serum Inflammatory Marker and Bone Mineral Density in Healthy Adults

Background

Inflammatory markers have been shown to play an important role in bone remodeling. The purpose of this study was to investigate the relationship among serum C-reactive protein (CRP), adiponectin, tumor necrosis factor-alpha (TNF-α) and bone health in healthy adults.

Methods

We measured serum levels of CRP, adiponectin, TNF-α as well as lumbar spine and femoral neck bone mineral density (BMD) in 76 adults. Anthropometric measurements and nutrient intake survey of participants were carried out. The participants were divided into two groups (normal BMD group=40; 52.6%, decreased BMD group=36; 47.4%).

Results

The CRP concentration was significantly higher in the decreased BMD group. The adiponectin concentration was lower in the decreased BMD group but the difference was not significant. The TNF-α concentration was higher in the decreased BMD group, the difference was not significant. The participants in the decreased BMD group were found to have lower calcium intakes. The sodium intake of the decreased BMD group was significantly higher. The BMD in the decreased BMD group showed inverse correlations with CRP and dietary sodium intake.

Conclusions

Serum CRP and dietary sodium intake is associated with BMD. Further research is needed to confirm the potential role of inflammatory marker to modulate the effects on bone.

Negative Skeletal Effects of Locally Produced Adiponectin

Epidemiological studies show that high circulating levels of adiponectin are associated with low bone mineral density. The effect of adiponectin on skeletal homeostasis, on osteoblasts in particular, remains controversial. We investigated this issue using mice with adipocyte-specific over-expression of adiponectin (AdTg). MicroCT and histomorphometric analysis revealed decreases (15%) in fractional bone volume in AdTg mice at the proximal tibia with no changes at the distal femur. Cortical bone thickness at mid-shafts of the tibia and at the tibiofibular junction was reduced (3–4%) in AdTg mice. Dynamic histomorphometry at the proximal tibia in AdTg mice revealed inhibition of bone formation. AdTg mice had increased numbers of adipocytes in close proximity to trabecular bone in the tibia, associated with increased adiponectin levels in tibial marrow. Treatment of BMSCs with adiponectin after initiation of osteoblastic differentiation resulted in reduced mineralized colony formation and reduced expression of mRNA of osteoblastic genes, osterix (70%), Runx2 (52%), alkaline phosphatase (72%), Col1 (74%), and osteocalcin (81%). Adiponectin treatment of differentiating osteoblasts increased expression of the osteoblast genes PPARγ (32%) and C/ebpα (55%) and increased adipocyte colony formation. These data suggest a model in which locally produced adiponectin plays a negative role in regulating skeletal homeostasis through inhibition of bone formation and by promoting an adipogenic phenotype.

Pros and cons of fatty acids in bone biology

Despite the growing interest in deciphering the causes and consequences of obesity-related disorders, the mechanisms linking fat intake to bone behaviour remain unclear. Since bone fractures are widely associated with increased morbidity and mortality, most notably in elderly and obese people, bone health has become a major social and economic issue. Consistently, public health system guidelines have encouraged low-fat diets in order to reduce associated complications. However, from a bone point of view, mechanisms linking fat intake to bone alteration remain quite controversial. Thus, after more than a decade of dedicated studies, this timely review offers a comprehensive overview of the relationships between bone and fatty acids. Using clinical evidences as a starting-point to more complex molecular elucidation, this work highlights the complexity of the system and reveals that bone alteration that cannot be solved simply by taking ω-3 pills. Fatty acid effects on bone metabolism can be both direct and indirect and require integrated investigations. Furthermore, even at the level of a single cell, one fatty acid is able to trigger several different independent pathways (receptors, metabolites…) which may all have a say in the final cellular metabolic response.

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.

Bone health as a function of adipokines and vitamin D pattern in elderly patients

BACKGROUND

Adiponectin, leptin, and resistin are involved in bone metabolism, but the evidence regarding their effects is not conclusive. We analyzed the relationship between these adipokines, vitamin D, and bone health using a cluster analysis approach.

METHODS

We used cross-sectional data coming from the InCHIANTI study, in which bone density and area were estimated using computed tomography. The sample size was 690 (women, 57.5%; mean age, 75.2 years; range, 65-102). Five clusters were generated on the basis of gender, age, adipokines, and vitamin D concentrations. The clusters were characterized, respectively, by higher resistin and older age (hR-O, n=134), higher vitamin D and younger age (hD-Y, n=152), higher adiponectin (hA, n=65), and higher leptin (hL, n=52). The last cluster had intermediate values of all the constituting variables (I, n=287). The clusters were compared with respect to bone parameters and clinical characteristics.

RESULTS

Cluster hR-O had the lowest total and cortical bone density. Cluster hD-Y had the lowest adiponectin (9.29 g/mL) and leptin (7.9 ng/mL) serum concentrations, the highest prevalence of men (71.1%), and total/cortical bone density and area. No statistically significant difference across clusters was observed for age- and sex-standardized measures of bone mineral density and bone area, but leptin was associated with these parameters in a linear model adjusted for age, gender, vitamin D, resistin, and leptin.

CONCLUSIONS

In an elderly population, age and sex almost completely explain the variability in bone status across cluster characterized by different levels of circulating adipokines and vitamin D. The role of leptin, however, seems worthy of consideration.

Associations among endocrine, inflammatory, and bone markers, body composition and weight loss induced bone loss

INTRODUCTION

Weight loss reduces co-morbidities of obesity, but decreases bone mass.

PURPOSE

Our aims were to (1) determine if adequate dairy intake attenuates weight loss-induced bone loss; (2) evaluate the associations of endocrine, inflammatory and bone markers, anthropometric and other parameters to bone mineral density and content (BMD, BMC) pre- and post-weight loss; and (3) model the contribution of these variables to post weight-loss BMD and BMC.

METHODS

Overweight/obese women (BMI: 28-37 kg/m2) were enrolled in an energy reduced (-500 kcal/d; -2092 kJ/d) diet with adequate dairy (AD: 3-4 servings/d; n=25, 32.2±8.8 years) or low dairy (LD: ≤1 serving/d; n=26, 31.7±8.4 years). BMD, BMC and body composition were measured by DXA. Bone markers (CTX, PYD, BAP, OC), endocrine (PTH, vitamin D, leptin, adiponectin, ghrelin, amylin, insulin, GLP-1, PAI-1, HOMA) and inflammatory markers (CRP, IL1-β, IL-6, IL-8, TNF-α, cortisol) were measured in serum or plasma. PA was assessed by accelerometry.

RESULTS

Following weight loss, AD intake resulted in significantly greater (p=0.004) lumbar spine BMD and serum osteocalcin (p=0.004) concentration compared to LD. Pre- and post-body fat was negatively associated with hip and lumbar spine BMC (r=-0.28, p=0.04 to -0.45, p=0.001). Of note were the significant negative associations among bone markers and IL-1β, TNFα and CRP ranging from r = -0.29 (p=0.04) to r = -0.34 (p=0.01); magnitude of associations did not change with weight loss. Adiponectin was negatively related to change in osteocalcin. Factor analysis resulted in 8 pre- and post-weight loss factors. Pre-weight loss factors accounted for 13.7% of the total variance in pre-weight loss hip BMD; post-weight loss factors explained 19.6% of the total variance in post-weight loss hip BMD. None of the factors contributed to the variance in lumbar spine BMD.

CONCLUSION

AD during weight loss resulted in higher lumbar spine BMD and osteocalcin compared to LD. Significant negative associations were observed between bone and inflammatory markers suggesting that inflammation suppresses bone metabolism. Using factor analysis, 19.6% of total variance in post-weight loss hip BMD could be explained by endocrine, immune, and anthropometric variables, but not lumbar spine BMD.

Relationship of weight, height, and body mass index with fracture risk at different sites in postmenopausal women: the Global Longitudinal study of Osteoporosis in Women (GLOW)

Low body mass index (BMI) is a well-established risk factor for fracture in postmenopausal women. Height and obesity have also been associated with increased fracture risk at some sites. We investigated the relationships of weight, BMI, and height with incident clinical fracture in a practice-based cohort of postmenopausal women participating in the Global Longitudinal study of Osteoporosis in Women (GLOW). Data were collected at baseline and at 1, 2, and 3 years. For hip, spine, wrist, pelvis, rib, upper arm/shoulder, clavicle, ankle, lower leg, and upper leg fractures, we modeled the time to incident self-reported fracture over a 3-year period using the Cox proportional hazards model and fitted the best linear or nonlinear models containing height, weight, and BMI. Of 52,939 women, 3628 (6.9%) reported an incident clinical fracture during the 3-year follow-up period. Linear BMI showed a significant inverse association with hip, clinical spine, and wrist fractures: adjusted hazard ratios (HRs) (95% confidence intervals [CIs]) per increase of 5 kg/m(2) were 0.80 (0.71-0.90), 0.83 (0.76-0.92), and 0.88 (0.83-0.94), respectively (all p < 0.001). For ankle fractures, linear weight showed a significant positive association: adjusted HR per 5-kg increase 1.05 (1.02-1.07) (p < 0.001). For upper arm/shoulder and clavicle fractures, only linear height was significantly associated: adjusted HRs per 10-cm increase were 0.85 (0.75-0.97) (p = 0.02) and 0.73 (0.57-0.92) (p = 0.009), respectively. For pelvic and rib fractures, the best models were for nonlinear BMI or weight (p = 0.05 and 0.03, respectively), with inverse associations at low BMI/body weight and positive associations at high values. These data demonstrate that the relationships between fracture and weight, BMI, and height are site-specific. The different associations may be mediated, at least in part, by effects on bone mineral density, bone structure and geometry, and patterns of falling.

Adiponectin as a biomarker of osteoporosis in postmenopausal women: controversies

The literature reports indicating a link between plasma levels of adiponectin and body fat, bone mineral density, sex hormones, and peri- and postmenopausal changes, draw attention to the possible use of adiponectin as an indicator of osteoporotic changes, suggesting that adiponectin may also modulate bone metabolism. In this study, we attempted to analyze the available in vitro and in vivo results which could verify this hypothesis. Although several studies have shown that adiponectin has an adverse effect on bone mass, mainly by intensifying resorption, this peptide has also been demonstrated to increase the proliferation and differentiation of osteoblasts, inhibit the activity of osteoclasts, and reduce bone resorption. There are still many ambiguities; for example, it can be assumed that concentrations of adiponectin in plasma do not satisfactorily reflect its production by adipose tissue, as well as conflicting in vitro and in vivo results. It seems that the potential benefit in the treatment of patients with osteoporosis associated with the pharmacological regulation of adiponectin is controversial.

The alliance of mesenchymal stem cells, bone, and diabetes

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

Relationship between bone cross-sectional area and indices of peripheral artery disease

Most studies on the relationship between bone mineral density and atherosclerosis have used dual-energy X-ray absorptiometry, but this method is relatively insensitive to bone geometry. The aim of this study was to investigate the relationship between bone area and indices of carotid and peripheral atherosclerosis. We studied 841 persons aged 65 years or older (women = 444, mean age 73.8 years; men = 397, mean age = 75.3 years) enrolled in the InCHIANTI study and free from active malignancies, chronic use of bisphosphonates or steroids, and estrogen replacement therapy. The tibial cortical and total cross-sectional area (CSA) were measured by peripheral quantitative computed tomography and their ratio was calculated (cortical/total cross-sectional area ratio, cCSA/tCSA); carotid plaques were screened by echography, and peripheral artery disease (PAD) was defined as an ankle/brachial index <0.9 or presence of intermittent claudication. No association between cCSA/tCSA and atherosclerosis was observed in men. In women, lower cCSA/tCSA was associated with both carotid plaques [odds ratio (OR) for lowest vs. best quartile = 2.09, 95 % confidence interval (CI) 1.2-3.68] and PAD (OR = 3.43, 95 % CI 1.58-8.12). After correction for potential confounders (age since menopause, body mass index, Parathyroid hormone, vitamin D, leptin, DHEA-S, testosterone, physical activity, chronic obstructive pulmonary disease, and reduced renal function), the association was not confirmed. According to partial logistic regression, the carotid plaque-cCSA/tCSA association, but not the PAD-cCSA/tCSA association, was mostly dependent on years since menopause. In women the association between osteoporosis and carotid plaques likely reflects hormonal deprivation, whereas that between osteoporosis and PAD seems multifactorial in origin.

Serum osteocalcin is associated with improved metabolic state via adiponectin in females versus testosterone in males. Gender specific nature of the bone-energy homeostasis axis

OBJECTIVE

The osteoblast-derived protein osteocalcin (OCN) is known to be involved in glucose metabolism by increasing adiponectin secretion from adipocytes. Recently, OCN was also found to enhance testosterone production in mouse testes, suggesting that OCN effects on energy metabolism may be mediated through testosterone. Our aim was to assess a possible gender difference in the metabolic effect of OCN in humans.

METHODS

We included 135 women and 155 men exhibiting changes in glucose tolerance in our study. Oral and intravenous glucose tolerance tests (OGTT and IVGTT, respectively) and a hyperinsulinemic normoglycemic clamp were performed. For clamp indices, whole body (M1) and muscle (M2) glucose uptake values were used. Leptin, adiponectin serum lipid, lipoprotein, total serum OCN and testosterone levels, and body composition were determined.

RESULTS

Higher OCN values were associated with improving metabolic state in both genders. Adiponectin and OCN correlated significantly only in females (r=+0.254, p=0.0029), while in men, testosterone and OCN values showed a significant positive correlation (r=+0.243, p=0.0023), independent of age, BMI, HbA1c and body composition. In women, adiponectin was confirmed by feature selection analysis as being an independent determinant of OCN, in addition to age and three of the IVGTT glucose values. In men, besides M1, BMI, M2, leptin, body fat percent, and the 90-minute OGTT glucose reading testosterone, but not adiponectin were identified as independent contributors for OCN.

CONCLUSION

We confirmed the 'classic' adiponectin-mediated insulin-sensitising effect of OCN only in females. In men, a testosterone-mediated OCN metabolic effect is more likely.

Association of weight-adjusted body fat and fat distribution with bone mineral density in middle-aged chinese adults: a cross-sectional study

Background

Although it is well established that a higher body weight is protective against osteoporosis, the effects of body fat and fat distribution on bone mineral density (BMD) after adjustment for body weight remains uncertain.

Objective

To examine the relationship between body fat and fat distribution and BMD beyond its weight-bearing effect in middle-aged Chinese adults.

Method

The study had a community-based cross-sectional design and involved 1,767 women and 698 men aged 50–75 years. The BMD of the lumbar spine, total hip, and whole body, and the fat mass (FM) and percentage fat mass (%FM) of the total body and segments of the body were measured by dual-energy X-ray absorptiometry. General information on the participants was collected using structured questionnaire interviews.

Result

After adjusting for potential confounders, an analysis of covariance showed the weight-adjusted (WA-) total FM (or %FM) to be negatively associated with BMD in all of the studied sites (P<0.05) in both women and men. The unfavorable effects of WA-total FM were generally more substantial in men than in women, and the whole body was the most sensitive site related to FM, followed by the total hip and the lumbar spine, in both genders. The mean BMD of the lumbar spine, total hip, and whole body was 3.93%, 3.01%, and 3.65% (in women) and 5.02%, 5.57%, 6.03% (in men) lower in the highest quartile (vs. lowest quartile) according to the WA-total FM (all p<0.05). Similar results were noted among the groups for WA-total FM%. In women, abdominal fat had the most unfavorable association with BMD, whereas in men it was limb fat.

Conclusion

FM (or %FM) is inversely associated with BMD beyond its weight-bearing effect. Abdominal fat in women and limb fat in men seems to have the greatest effect on BMD.

Obesity and bone

Recent studies indicate that fractures in obese postmenopausal women and older men contribute significantly to the overall fracture burden. The effect of obesity is to some extent site-dependent, the risk being increased for some fractures and decreased for others, possibly related to different patterns of falling and the presence or absence of soft tissue padding. Risk factors for fracture in obese individuals appear to be similar to those in the nonobese population, although falls may be particularly important in the obese. There is some evidence that the morbidity associated with fractures in obese individuals is greater than in the nonobese; however, a recent study indicates that the mortality associated with fracture is lower in obese and overweight people than in those of normal weight. The evidence base for strategies to prevent fractures in obese individuals is weak and is an important area for future research.

Hip geometry in diabetic women: implications for fracture risk

OBJECTIVE

Women with type 2 diabetes mellitus (T2DM) have a higher risk of fractures despite increased bone mineral density (BMD) as compared to women without diabetes. We hypothesized that bone strength is diminished in women with T2DM after accounting for lean body mass, which may contribute to their increased fracture risk.

METHODS

Participants from Women's Health Initiative Observational Study were included in this cross-sectional study. These analyses include 3 groups of women: 1) T2DM women on diet or oral hypoglycemic agents (n=299); 2) T2DM women on insulin therapy (with or without oral agents) (n=128); and 3) Non-diabetic control women (n=5497). Hip structural analyses were done using the validated Beck's method on hip scans from dual energy x-ray absorptiometry (DXA). We compared BMD and section modulus (bending strength) at the narrow neck with and without correcting for total body DXA lean body mass.

RESULTS

Women in all three groups were of similar ages (63.7, 64.6 and 64.2 years, respectively) and heights, but those with T2DM were heavier, with greater lean body weight vs controls (P<.001). In both diabetic groups, absolute BMD and section modulus were higher compared with controls. However, after adjusting for total lean body weight, diabetic women on insulin had significantly lower BMD and section modulus.

CONCLUSION

Adjusted for lean body weight, the BMD and bending strength in the femoral neck are significantly lower in insulin-treated diabetic women vs controls. This may represent altered adaptation of bone modeling and explain the higher fracture risk in patients with T2DM.

Omentin-1, visfatin and adiponectin levels in relation to bone mineral density in Iranian postmenopausal women

The bone and fat interface is implicated in the pathogenesis of postmenopausal osteoporosis. The association between circulating omentin-1 levels and bone mineral density (BMD) in postmenopausal women has never been assessed. A total of 382 healthy postmenopausal women were randomly selected. Omentin-1, visfatin, adiponectin, the receptor activator of nuclear factor-κB ligand (RANKL), osteoprotegerin, high sensitivity C-reactive protein, degradation products of C-terminal telopeptides of type I collagen, and osteocalcin were measured by highly specific enzyme-linked immunosorbent assay methods. BMD was determined for the lumbar spine (L2-L4) and the proximal femur using dual-energy X-ray absorptiometry. In multivariable-adjusted linear regression, serum omentin-1 levels were inversely correlated with BMD at the lumbar spine (β=-0.11, p=0.020). In multiple regression analyses, serum visfatin and adiponectin levels were not significantly correlated with BMD at different skeletal sites after controlling for age, body mass index, and bone-related markers. However, the highest quartile of adiponectin compared to the lowest quartile, after adjusting for potential confounders, revealed an inverse association with BMD in the lumbar spine (β=-0.19, p=0.010). In conclusion, circulating omentin-1 levels had an inverse correlation with BMD at the lumbar spine in Iranian postmenopausal women. To further understand the role of omentin-1 in bone and mineral metabolism, large-scale longitudinal studies focusing on BMD and osteoporotic fractures are warranted.

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.

Adiponectin interactions in bone and cartilage biology and disease

The adipokine adiponectin promotes insulin sensitivity and fat β-oxidation. In addition to its metabolic effects, adiponectin is an important local and systemic modulator of bone remodeling and cartilage biology, involving direct and indirect mechanisms and a large set of downstream molecular signals. Moreover, data suggest that changes in adiponectin signaling may be associated with bone and cartilage diseases. Adiponectin seems to exert a negative net effect on bone mass and to be an independent predictor of lower bone mass, whereas available data about actions on cartilage are more controversial, showing both pro- and anti-inflammatory actions. Adiponectin-bone cross talk seems to be reciprocal, as osteocalcin, produced by osteoblasts, has been shown to stimulate adiponectin expression and to improve glucose tolerance. Adiponectin-related signaling in bone and cartilage should be considered within the network of hormonal and nutritional signals that may influence skeleton biology, together with body homeostasis and adipose mass changes.

Adiponectin action: a combination of endocrine and autocrine/paracrine effects

The widespread physiological actions of adiponectin have now been well characterized as clinical studies and works in animal models have established strong correlations between circulating adiponectin level and various disease-related outcomes. Thus, conventional thinking attributes many of adiponectin's beneficial effects to endocrine actions of adipose-derived adiponectin. However, it is now clear that several tissues can themselves produce adiponectin and there is growing evidence that locally produced adiponectin can mediate functionally important autocrine or paracrine effects. In this review article we discuss regulation of adiponectin production, its mechanism of action via receptor isoforms and signaling pathways, and its principal physiological effects (i.e., metabolic and cardiovascular). The role of endocrine actions of adiponectin and changes in local production of adiponectin or its receptors in whole body physiology is discussed.