Cytokines and Hormones That Contribute to the Positive Association between Fat and Bone

Understanding the Consequences of Fatty Bone and Fatty Muscle: How the Osteosarcopenic Adiposity Phenotype Uncovers the Deterioration of Body Composition

Adiposity is central to aging and several chronic diseases. Adiposity encompasses not just the excess adipose tissue but also body fat redistribution, fat infiltration, hypertrophy of adipocytes, and the shifting of mesenchymal stem cell commitment to adipogenesis. Bone marrow adipose tissue expansion, inflammatory adipokines, and adipocyte-derived extracellular vesicles are central to the development of osteopenic adiposity. Adipose tissue infiltration and local adipogenesis within the muscle are critical in developing sarcopenic adiposity and subsequent poorer functional outcomes. Ultimately, osteosarcopenic adiposity syndrome is the result of all the processes noted above: fat infiltration and adipocyte expansion and redistribution within the bone, muscle, and adipose tissues, resulting in bone loss, muscle mass/strength loss, deteriorated adipose tissue, and subsequent functional decline. Increased fat tissue, typically referred to as obesity and expressed by body mass index (the latter often used inadequately), is now occurring in younger age groups, suggesting people will live longer with the negative effects of adiposity. This review discusses the role of adiposity in the deterioration of bone and muscle, as well as adipose tissue itself. It reveals how considering and including adiposity in the definition and diagnosis of osteopenic adiposity, sarcopenic adiposity, and osteosarcopenic adiposity will help in better understanding the pathophysiology of each and accelerate possible therapies and prevention approaches for both relatively healthy individuals or those with chronic disease.

Preptin: A New Bone Metabolic Parameter?

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

Age, body composition parameters and glycaemic control contribute to trabecular bone score deterioration in acromegaly more than disease activity

Introduction

Impairment of bone structure in patients with acromegaly (AP) varies independently of bone mineral density (BMD). Body composition parameters, which are altered in patients with acromegaly, are important determinants of bone strength.

Purpose

The aim of this study was to examine BMD and lumbar trabecular bone score (TBS) by dual-energy X-ray absorptiometry (DXA) and to assess its relationship with disease activity, age, glucose metabolism, and body composition parameters.

Methods

This cross-sectional prospective study involved 115 patients with acromegaly (70 F, 45 M) and 78 healthy controls (CON) (53 F, 25 M) matched for age, gender, and BMI. Bone mineral density, TBS and body composition parameters were measured using DXA.

Results

AP presented with lower TBS compared to CON (1.2 ± 0.1 v 1.31 ± 0.1, P< 0.001). No significant correlation was observed between IGF-1/GH levels and TBS. Age, glycated haemoglobin, BMI, waist circumference, fat mass, and lean mass negatively correlated with TBS in both sexes. Multiple linear regression analysis of all these parameters revealed age and waist circumference as independent significant predictors of TBS in AP. We did not find difference in BMD (lumbar and femoral sites) between AP and CON nor between active and controlled AP. We observed negative correlation between age and BMD of the femoral neck and total hip (P < 0.001). Testosterone levels in males, BMI, waist circumference, fat mass, and lean mass positively correlated with BMD in AP, with stronger correlation between lean mass and BMD compared to fat mass.

Conclusion

Patients with acromegaly have lower TBS than controls, confirming impaired bone microarchitecture in acromegaly regardless of BMD. Age, body composition parameters and glucose metabolism contribute to TBS deterioration in AP more than disease activity itself.

Bone Mineral Density and Fractures In Postmenopausal Women Of Mayan-Mestizo Ethnic Origin With Different Body Mass Indices

BACKGROUND

Obesity protects against bone loss, but it increases the risk of fragility fractures.

AIM

To determine if bone mineral density (BMD) and the prevalence of fractures are different in postmenopausal Mayan-mestizo women grouped according to their body mass index.

SUBJECTS AND METHODS

We studied 600 postmenopausal Maya-Mestizo women. A structured questionnaire for risk factors was applied. Body mass index (BMI) was determined. BMD was assessed at the lumbar spine and total hip by dual-energy X-ray absorptiometry. History of low trauma fracture was determined from medical records. ANOVA was used to compare mean BMD between women with different BMI. To compare the frequency of fractures according to BMI group, we used χ².

RESULTS

According to WHO classification of BMI, 16.3% of women had normal BMI, 35.3% were overweight, and 48.4% had obesity. We found that women with obesity had a higher BMD versus women with normal BMI or overweight in all the anatomical sites analysed. The prevalence of history of fractures was 18.2%. We did not find differences between the women of different BMI; the wrist was the most frequent skeletal site of the fracture.

CONCLUSIONS

Obesity in postmenopausal Maya-Mestizo women is not a risk factor for developing fragility fractures.

The associations between body fat distribution and bone mineral density in the Oxford Biobank: a cross sectional study

BACKGROUND

Body composition is associated with bone mineral density (BMD), but the precise associations between body fat distribution and BMD remain unclear. The regional adipose tissue depots have different metabolic profiles. We hypothesized that they would have independent associations with BMD.

RESEARCH DESIGN AND METHODS

We used data from 4,900 healthy individuals aged 30-50 years old from the Oxford Biobank to analyze associations between regional fat mass, lean mass and total BMD.

RESULTS

Total lean mass was strongly positively associated with BMD. An increase in total BMD was observed with increasing mass of all the fat depots, as measured either by anthropometry or DXA, when accounting for lean mass. However, on adjustment for both total fat mass and lean mass, fat depot specific associations emerged. Increased android and visceral adipose tissue mass in men, and increased visceral adipose tissue mass in women, were associated with lower BMD.

CONCLUSIONS

Fat distribution alters the association between adiposity and BMD.

Bone Response to Weight Loss Following Bariatric Surgery

Obesity is a global health challenge that warrants effective treatments to avoid its multiple comorbidities. Bariatric surgery, a cornerstone treatment to control bodyweight excess and relieve the health-related burdens of obesity, can promote accelerated bone loss and affect skeletal strength, particularly after malabsorptive and mixed surgical procedures, and probably after restrictive surgeries. The increase in bone resorption markers occurs early and persist for up to 12 months or longer after bariatric surgery, while bone formation markers increase but to a lesser extent, suggesting a potential uncoupling process between resorption and formation. The skeletal response to bariatric surgery, as investigated by dual-energy X-ray absorptiometry (DXA), has shown significant loss in bone mineral density (BMD) at the hip with less consistent results for the lumbar spine. Supporting DXA studies, analyses by high-resolution peripheral quantitative computed tomography (HR-pQCT) showed lower cortical density and thickness, higher cortical porosity, and lower trabecular density and number for up to 5 years after bariatric surgery. These alterations translate into an increased risk of fall injury, which contributes to increase the fracture risk in patients who have been subjected to bariatric surgery procedures. As bone deterioration continues for years following bariatric surgery, the fracture risk does not seem to be dependent on acute weight loss but, rather, is a chronic condition with an increasing impact over time. Among the post-bariatric surgery mechanisms that have been claimed to act globally on bone health, there is evidence that micro- and macro-nutrient malabsorptive factors, mechanical unloading and changes in molecules partaking in the crosstalk between adipose tissue, bone and muscle may play a determining role. Given these circumstances, it is conceivable that bone health should be adequately investigated in candidates to bariatric surgery through bone-specific work-up and dedicated postsurgical follow-up. Specific protocols of nutrients supplementation, motor activity, structured rehabilitative programs and, when needed, targeted therapeutic strategies should be deemed as an integral part of post-bariatric surgery clinical support.

Low muscle mass and body composition analysis in a group of postmenopausal women affected by primary Sjögren's syndrome

Objectives

Sarcopenia is the pathological reduction of skeletal muscle mass and strength. This condition is often underestimated in clinical practice, particularly in connective tissue diseases. The purpose of this study is to evaluate the prevalence of low muscle mass in primary Sjögren’s syndrome (pSS) and to explore the relationships linking muscles and bone tissue.

Material and methods

Twenty-eight postmenopausal pSS patients were matched with 30 healthy controls and their body composition analysis was performed by dual-energy X-ray absorptiometry to investigate for sarcopenia considering appendicular lean mass (ALM) and the skeletal muscle mass index (SMI) as references. Bone mineral density analysis of lumbar spine (L1–L4), whole femur, femoral neck and whole body was also performed. Linear regression was used to assess the relationship between body composition and bone mineralization.

Results

Low muscle mass was significantly higher in the pSS group compared to controls whether expressed as ALM, SMI [odds ratio (OR) = 18.40, confidence interval (CI): 4.84–72.08, p < 0.0001] or considering total body lean masses. Lean masses appeared to be the best estimators of bone mineralization: total lean body mass (TLBM) lumbar spine R² = 0.72, p < 0.0001; TLBM femoral neck R² = 0.36, p < 0.004; lean mass of upper limbs lumbar spine R² = 0.70, p < 0.0001; femoral neck R² = 0.66; lean mass of lower limbs lumbar spine R² = 0.66, p < 0.0001; femoral neck R² = 0.44, p = 0.008). Primary Sjögren’s syndrome patients had a significantly higher android/gynoid fat ratio compared to controls.

Conclusions

Female pSS patients have lower muscle mass compared to healthy controls and are exposed to a higher risk of developing sarcopenia than healthy subjects. Our research demonstrates that the amount of lean tissue is the main predictor of bone mineralization in pSS.

The Role of Osteoclast Energy Metabolism in the Occurrence and Development of Osteoporosis

In recent decades, the mechanism underlying bone metabolic disorders based on energy metabolism has been heavily researched. Bone resorption by osteoclasts plays an important role in the occurrence and development of osteoporosis. However, the mechanism underlying the osteoclast energy metabolism disorder that interferes with bone homeostasis has not been determined. Bone resorption by osteoclasts is a process that consumes large amounts of adenosine triphosphate (ATP) produced by glycolysis and oxidative phosphorylation. In addition to glucose, fatty acids and amino acids can also be used as substrates to produce energy through oxidative phosphorylation. In this review, we summarize and analyze the energy-based phenotypic changes, epigenetic regulation, and coupling with systemic energy metabolism of osteoclasts during the development and progression of osteoporosis. At the same time, we propose a hypothesis, the compensatory recovery mechanism (involving the balance between osteoclast survival and functional activation), which may provide a new approach for the treatment of osteoporosis.

Does the Severity of Obesity Influence Bone Mineral Density Values in Premenopausal Women?

The aim of this study was to compare bone mineral content (BMC), bone mineral density (BMD), and geometric indices of hip bone strength among 3 groups of adult obese premenopausal women (severely obese, morbidly obese, and super morbidly obese). This study included 65 young adult premenopausal women whose body mass index (BMI) > 35 kg/m². They were divided into 3 groups using international cut-offs for BMI. Body composition and bone variables were measured by DXA. DXA measurements were completed for the whole body (WB), lumbar spine, total hip (TH), and femoral neck (FN). Geometric indices of FN strength (cross-sectional area, cross-sectional moment of inertia [CSMI], section modulus [Z], strength index [SI], and buckling ratio) were calculated by DXA. Results showed that age and height were not significantly different among the 3 groups. WB BMC values were higher in super morbidly obese women compared to severely and morbidly obese women. WB BMD, L1-L4 BMD, total hip BMD, FN BMD, cross-sectional area, CSMI, Z, and buckling ratio values were not significantly different among the 3 groups. SI values were lower in super morbidly obese compared to morbidly and severely obese women. In the whole population (n = 65), body weight, BMI, lean mass, fat mass, and trunk fat mass were positively correlated to WB BMC and negatively correlated to SI. Weight and lean mass were positively correlated to WB BMD and CSMI. Our findings suggest that the severity of obesity does not influence BMD values in premenopausal women.

Decreased Expression of the Human Urea Transporter SLC14A1 in Bone is Induced by Cytokines and Stimulates Adipogenesis of Mesenchymal Progenitor Cells

The human urea transporter SLC14A1 (HUT11/UT-B) has been suggested as a marker for the adipogenic differentiation of bone cells with a relevance for bone diseases. We investigated the function of SLC14A1 in different cells models from bone environment. SLC14A1 expression and cytokine production was investigated in bone cells obtained from patients with osteoporosis. Gene and protein expression of SLC14A1 was studied during adipogenic or osteogenic differentiation of human mesenchymal progenitor cells (hMSCs) and of the single-cell-derived hMSC line (SCP-1), as well as in osteoclasts and chondrocytes. Localization was determined by histochemical methods and functionality by urea transport experiments. Expression of SLC14A1 mRNA was lower in cells from patients with osteoporosis that produced high levels of cytokines. Accordingly, when adding a combination of cytokines to SCP-1 SLC14A1 mRNA expression decreased. SLC14A1 mRNA expression decreased after both osteogenic and more pronounced adipogenic stimulation of hMSCs and SCP-1 cells. The highest SLC14A1 expression was determined in undifferentiated cells, lowest in chondrocytes and osteoclasts. Downregulation of SLC14A1 by siRNA resulted in an increased expression of interleukin-6 and interleukin-1 beta as well as adipogenic markers. Urea influx through SLC14A1 increased expression of osteogenic markers, adipogenic markers were suppressed. SLC14A1 protein was localized in the cell membrane and the cytoplasm. Summarizing, the SLC14A1 urea transporter affects early differentiation of hMSCs by diminishing osteogenesis or by favoring adipogenesis, depending on its expression level. Therefore, SLC14A1 is not unequivocally an adipogenic marker in bone. Our findings suggest an involvement of SLC14A1 in bone metabolism and inflammatory processes and disease-dependent influences on its expression.

Sarcopenia negatively affects hip structure analysis variables in a group of Lebanese postmenopausal women

BACKGROUND

The current study's purpose is to compare hip structural analysis variables in a group of postmenopausal women with sarcopenia and another group of postmenopausal women with normal skeletal muscle mass index. To do so, the current study included 8 postmenopausal women (whose ages ranged between 65 and 84 years) with sarcopenia and 60 age-matched controls (with normal skeletal muscle mass index (SMI)). Body composition and bone parameters were evaluated by dual-energy X-ray absorptiometry (DXA).

RESULTS

Weight, lean mass, body mass index, femoral neck cross-sectional area (FN CSA), FN section modulus (Z), FN cross sectional moment of inertia (CSMI), intertrochanteric (IT) CSA, IT Z, IT CSMI, IT cortical thickness (CT), femoral shaft (FS) CSA, FS Z and FS CSMI were significantly greater (p < 0.05) in women with normal SMI compared to women with sarcopenia. In the whole population, SMI was positively associated with IT CSA, IT Z, IT CSMI, IT CT, FS CSA, FS Z, FS CSMI, FS CT but negatively correlated to IT buckling ratio (BR) and FS BR.

CONCLUSION

The current study suggests that sarcopenia has a negative effect on hip bone strength indices in postmenopausal women.

Greater inflammation and adiposity are associated with lower bone mineral density in youth with type 1 diabetes

AIMS

The objectives of this study were to investigate relationships of inflammation and adiposity with bone mineral density (BMD) in youth with type 1 diabetes followed prospectively for 18 months.

METHODS

Participants were youth with type 1 diabetes (n = 136, 8-16.9 years) enrolled in an 18-month behavioral nutrition intervention trial. BMD of the total body, subtotal, lumbar spine, pelvis leg, arm and rib, percent body fat and percent trunk fat (by dual energy x-ray absorptiometry) and C-reactive protein (CRP), a marker of inflammation, were assessed at baseline, 12 and 18 months. Linear mixed-effects models estimated associations of time-varying BMD with time-varying CRP, and with percent body and trunk fat.

RESULTS

CRP was inversely associated with BMD of the total body, pelvis and leg (n = 136). Percent body fat was inversely associated with BMD of the total body and pelvis; whereas percent trunk fat was related only to total body BMD.

CONCLUSIONS

Greater inflammation and adiposity were related to lower BMD in youth with type 1 diabetes. Investigating the impact of inflammation and adiposity on bone turnover markers could provide insights on mechanisms that contribute to this relationship.

Amylin in Alzheimer's disease: Pathological peptide or potential treatment?

Alzheimer's disease (AD) is a neurodegenerative disease for which we currently lack effective treatments or a cure. The pancreatic peptide hormone amylin has recently garnered interest as a potential pharmacological target for the treatment of AD. A number of studies have demonstrated that amylin and amylin analogs like the FDA-approved diabetes drug pramlintide can reduce amyloid burden in the brain and improve cognitive symptoms of AD. However, other data suggest that amylin may have pathological effects in AD due to its propensity to misfold and aggregate under certain conditions. Here, the literature supporting a beneficial versus harmful role of amylin in AD is reviewed. Additionally, several critical gaps in the literature are discussed, such as our limited understanding of the amylin system during aging and in disease states, as well as complexities of amylin receptor signaling and of changing pathophysiology during AD progression that might underlie the seemingly conflicting or contradictory results in the amylin/AD literature. This article is part of the Special Issue entitled 'Metabolic Impairment as Risk Factors for Neurodegenerative Disorders.'

Bone status and adipokine levels in children on vegetarian and omnivorous diets

BACKGROUND & AIMS

Measurements of bone mineral density (BMD) reflect bone status but not the dynamics of bone turnover. Biochemical markers, which show global skeletal activity, were validated for the assessment of bone formation and resorption processes. Adipokines also play a significant role in the regulation of bone metabolism.

OBJECTIVE

To assess body composition, bone mineral density, bone turnover markers and adipokine levels in relation to vegetarian and omnivorous diets.

METHODS

The study included 53 vegetarian and 53 omnivorous prepubertal healthy children matched for age and sex (median age 7.0 years). Body composition and BMD were assessed by dual-energy X-ray absorptiometry. 25-hydroxyvitamin D and parathormone levels were measured by chemiluminescence method. Serum carboxy-terminal propeptide of type I collagen (CICP), total osteocalcin (OC) and its forms carboxylated (c-OC) and undercarboxylated (uc-OC), C-terminal cross-linking telopeptide of collagen type I (CTX), leptin and adiponectin levels were determined using immunoenzymatic assays.

RESULTS

Both groups of children were comparable in terms of body composition, except for the percentage of fat mass, which was lower (19.24 vs. 21.77%, p = 0.018) in vegetarians. Mean values of total BMD z-score and lumbar spine BMD z-score were lower (-0.583 vs. -0.194, p = 0.009 and -0.877 vs. -0.496, p = 0.019, respectively) in vegetarians compared with omnivores. Serum leptin level was about 2-fold lower (1.39 vs. 2.94 ng/mL, p < 0.001) in vegetarians, however, adiponectin concentration was similar in both groups. Vegetarians had similar concentration of 25-hydroxyvitamin D, but higher parathormone (40.8 vs. 32.1 pg/mL, p = 0.015) and CTX (1.94 vs. 1.76 ng/mL, p = 0.077) levels than omnivores. Total osteocalcin and CICP concentrations were comparable in both groups, however, c-OC/uc-OC ratio was higher (1.43 vs. 1.04 ng/mL, p < 0.05) in vegetarians. We found positive correlation between c-OC and nutritional parameters adjusted for total energy intake (plant protein, phosphorus, magnesium and fiber intakes) in vegetarian children.

CONCLUSIONS

Prepubertal children on a vegetarian diet had significantly lower total and lumbar spine BMD z-scores, but absolute values of bone mineral density did not differ. BMD z-scores did not correlate with bone metabolism markers and nutritional variables, but were positively associated with anthropometric parameters. Lower leptin levels in vegetarian children reflect lower body fat. Longitudinal studies are necessary to evaluate the impact of the observed association on bone health at adulthood.

Bone Health following Bariatric Surgery: Implications for Management Strategies to Attenuate Bone Loss

Bariatric surgery (BS) is an effective treatment for morbid obesity and its associated comorbidities. Following such a procedure, however, patients are at risk of developing metabolic bone disease owing to the combination of rapid weight loss, severely restricted dietary intake, and reduced intestinal nutrient absorption. Patients undergoing malabsorptive procedures are at a higher risk of postoperative bone health deterioration than those undergoing restrictive procedures; however, studies have demonstrated negative skeletal consequences of restrictive procedures as well. The clinical practice guidelines of some international associations have previously addressed preoperative evaluation and postoperative clinical care in order to maintain bone health in BS patients. Nevertheless, some issues regarding bone health in BS patients remain unclear owing to the lack of relevant randomized clinical trials, including doses of nutritional supplements pre- and post-BS. This review summarizes the current data regarding the skeletal consequences of BS and its mechanisms, with an emphasis on the preventive strategies and nutritional care that may be warranted in order to attenuate bone deterioration following BS.

Bone metabolism in anorexia nervosa and hypothalamic amenorrhea

Anorexia nervosa (AN) and hypothalamic amenorrhea (HA) are states of chronic energy deprivation associated with severely compromised bone health. Poor bone accrual during adolescence followed by increased bone loss results in lifelong low bone density, degraded bone architecture, and higher risk of fractures, despite recovery from AN/HA. Amenorrhea is only one of several compensatory responses to the negative energy balance. Other hypothalamic-pituitary hormones are affected and contribute to bone deficits, including activation of hypothalamic-pituitary-adrenal axis and growth hormone resistance. Adipokines, particularly leptin, provide information on fat/energy stores, and gut hormones play a role in the regulation of appetite and food intake. Alterations in all these hormones influence bone metabolism. Restricted in scope, current pharmacologic approaches to improve bone health have had overall limited success.

Bariatric Roux-En-Y Gastric Bypass Surgery: Adipocyte Proteins Involved in Increased Bone Remodeling in Humans

PURPOSE

Bariatric surgery has been associated with bone remodeling changes. The action of adipokines on the expression of receptor activator of nuclear factor kappa β ligand (RANKL) and osteoprotegerin (OPG) and on an increase in sclerostin could be related to these changes.

MATERIALS AND METHODS

This study aimed to assess the repercussions of weight loss, fat mass (FM), and fat-free mass (FFM) loss and biochemical and hormonal changes on bone remodeling markers after Roux-en-Y gastric bypass (RYGB). Anthropometric data, parathyroid hormone (PTH), bone-specific alkaline phosphatase (BSAP), collagen type 1 C-telopeptide (CTX), 25-hydroxy vitamin D (25-OH-VitD), leptin, adiponectin, RANKL, OPG, and sclerostin of 30 menstruating women were measured preoperatively (Pre), and 3, 12, and 24 months (m) after RYGB.

RESULTS

Leptin (34.4 (14.7; 51.9) vs. 22.5 (1.9; 52.7) ng/mL) and OPG (3.6 (1.1; 11.5) vs. 3.4 (1.5; 6) pmol/L) decreased, and adiponectin (7.4 (1.7; 18.4) vs. 13.8 (3.0; 34.6) μg/mL), CTX (0.2 (0.1; 2.2) vs. 0.6 (0.4; 6.0) ng/mL), RANKL (0.1 (0.0; 0.5) vs. 0.3 (0.0; 2.0) pmol/L), and sclerostin (21.7 (3.2; 75.1) vs. 34.8 (6.4; 80.5) pmol/L) increased after 3 m. BSAP increased after 12 m (10.1 (5.4; 18.9) vs. 13.9 (6.9; 30.2) μg/mL) (p < 0.005). CTX correlated positively with adiponectin at 24 m and inversely with leptin Pre; OPG at 3 m; weight, FM, FFM, and leptin at 24 m. RANKL correlated directly with weight at 3 m. Sclerostin correlated inversely with weight Pre and FM at 3 m. BSAP correlated negatively with 25-OH-VitD at 12 m, and positively with PTH at 24 m.

CONCLUSIONS

RYGB induced weight loss, and biochemical, hormonal, and body composition changes are associated with higher bone remodeling.

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.

Changes in body composition and metabolic profile during interleukin 6 inhibition in rheumatoid arthritis

BACKGROUND

Rheumatoid arthritis (RA) is a chronic inflammatory disease characterized by increased mortality associated with cardiometabolic disorders including dyslipidaemia, insulin resistance, and cachectic obesity. Tumour necrosis factor inhibitors and interleukin 6 receptor blocker licensed for the treatment of RA decrease inflammation and could thus improve cardiovascular risk, but their effects on body composition and metabolic profile need to be clarified. We investigated the effects of tocilizumab (TCZ), a humanized anti-interleukin 6 receptor antibody, on body composition and metabolic profile in patients treated for RA.

METHODS

Twenty-one active RA patients treated with TCZ were included in a 1 year open follow-up study. Waist circumference, body mass index, blood pressure, lipid profile, fasting glucose, insulin, serum levels of adipokines and pancreatic/gastrointestinal hormones, and body composition (dual-energy X-ray absorptiometry) were measured at baseline and 6 and 12 months of treatment. At baseline, RA patients were compared with 21 non-RA controls matched for age, sex, body mass index, and metabolic syndrome.

RESULTS

Compared with controls, body composition was altered in RA with a decrease in total and appendicular lean mass, whereas fat composition was not modified. Among RA patients, 28.6% had a skeletal muscle mass index below the cut-off point for sarcopaenia (4.8% of controls). After 1 year of treatment with TCZ, there was a significant weight gain without changes for fat mass. In contrast, an increase in lean mass was observed with a significant gain in appendicular lean mass and skeletal muscle mass index between 6 and 12 months. Distribution of the fat was modified with a decrease in trunk/peripheral fat ratio and an increase in subcutaneous adipose tissue. No changes for waist circumference, blood pressure, fasting glucose, and atherogenic index were observed.

CONCLUSIONS

Despite weight gain during treatment with TCZ, no increase in fat but a modification in fat distribution was observed. In contrast, muscle gain suggests that blocking IL-6 might be efficient in treating sarcopaenia associated with RA.

Muscle mass is associated with incident fracture in postmenopausal women: The OFELY study

The relationships between body composition and bone mineral density are well established but the contribution of body composition to the risk of fracture (Fx) has rarely been evaluated prospectively. We analyzed the risk of Fx by body composition in 595 postmenopausal women (mean age 66±8years) from a longitudinal cohort study (Os des Femmes de Lyon). We assessed the risk of the first incident fragility Fx according to body composition obtained from whole-body DXA: abdominal visceral (VFAT) and subcutaneous fat mass (SFAT), total body fat mass (FM), lean mass index (LMI) and appendicular skeletal muscle mass index (ASMI). During a median [IQ] follow-up of 13.1years [1.9], 138 women sustained a first incident Fx, including 85 women with a major osteoporotic Fx (MOP Fx: hip, clinical spine, humerus or wrist). After adjustment for age, women who sustained Fx had lower BMI (-4%, p=0.01), LMI (-6%, p=0.002) and ASMI (-3%, p=0.003), compared with women without Fx. After adjustment for age, prevalent Fx, physical activity, incident falls and FN BMD, each SD increase of baseline values of LMI and ASMI was associated with decreased Fx risk with adjusted hazard ratios of 0.76 for both of p≤0.02. Those associations were similar after accounting for the competing risk of death. VFAT and SFAT were associated with Fx risk in the multivariate model only for MOP Fx and the association did not persist after consideration of competing mortality. We conclude that lean mass and appendicular muscle mass indexes are associated with the risk of fracture in postmenopausal women independently of BMD and clinical risk factors.

Glucagon-like peptide-1(GLP-1) receptor agonists: potential to reduce fracture risk in diabetic patients?

This review summarizes current knowledge about glucagon-like peptide 1 receptor agonists (GLP-1 RA) and their effects on bone metabolism and fracture risk. Recent in vivo and in vitro experiments indicated that GLP-1 RA could improve bone metabolism. GLP-1 could affect the fat-bone axis by promoting osteogenic differentiation and inhibiting adipogenic differentiation of bone mesenchymal precursor cells (BMSCs), which express the GLP-1 receptor. GLP-1 RA may also influence the balance between osteoclasts and osteoblasts, thus leading to more bone formation and less bone resorption. Wnt/β-catenin signalling is involved in this process. Mature osteocytes, which also express the GLP-1 receptor, produce sclerostin which inhibits Wnt/β-catenin signalling by binding to low density lipoprotein receptor-related protein (LRP) 5 and preventing the binding of Wnt. GLP-1 RA also decreases the expression of sclerostin (SOST) and circulating levels of SOST. In addition, GLP-1 receptors are expressed in thyroid C cells, where GLP-1 induces calcitonin release and thus indirectly inhibits bone resorption. Furthermore, GLP-1 RA influences the osteoprotegerin(OPG)/receptor activator of nuclear factor-κB ligand (RANKL)/receptor activator of nuclear factor-κB (RANK) system by increasing OPG gene expression, and thus reverses the decreased bone mass in rats models. However, a recent meta-analysis and a cohort study did not show a significant relationship between GLP-RA use and fracture risk. Future clinical trials will be necessary to investigate thoroughly the relationship between GLP-1 RA use and fracture risk in diabetic patients.

Structure activity relationship study on the peptide hormone preptin, a novel bone-anabolic agent for the treatment of osteoporosis

Preptin is a 34-residue pancreatic hormone shown to be anabolic to bone in vitro and in vivo. The bone activity of preptin resides within the (1-16) N-terminal fragment. Due to its peptidic nature, the truncated fragment of preptin is enzymatically unstable; however it provides an attractive framework for the creation of stable analogues using various peptidomimetic techniques. An alanine scan of preptin (1-16) was undertaken which showed that substitution of Ser at position 3 or Pro at position 14 did not inhibit the proliferative activity of preptin in primary rat osteoblasts (bone-forming cells). Importantly, Ser-3 to Ala substitution also showed a significant activity on osteoblast differentiation in vitro and increased the formation of mineralised bone matrix. Additional modifications with non-proteinogenic amino acids at position 3 improved the stability in liver microsomes, but diminished the osteoblast proliferative activity. In addition, to provide greater structural diversity, a series of macrocyclic preptin (1-16) analogues was synthesised using head-to-tail and head-to-side chain macrolactamisation as well as ring-closing metathesis. However, a detrimental effect on osteoblast activity was observed upon macrocyclisation.

Bone Marrow Adipose Tissue: To Be or Not To Be a Typical Adipose Tissue?

Bone marrow adipose tissue (BMAT) emerges as a distinct fat depot whose importance has been proved in the bone-fat interaction. Indeed, it is well recognized that adipokines and free fatty acids released by adipocytes can directly or indirectly interfere with cells of bone remodeling or hematopoiesis. In pathological states, such as osteoporosis, each of adipose tissues - subcutaneous white adipose tissue (WAT), visceral WAT, brown adipose tissue (BAT), and BMAT - is differently associated with bone mineral density (BMD) variations. However, compared with the other fat depots, BMAT displays striking features that makes it a substantial actor in bone alterations. BMAT quantity is well associated with BMD loss in aging, menopause, and other metabolic conditions, such as anorexia nervosa. Consequently, BMAT is sensed as a relevant marker of a compromised bone integrity. However, analyses of BMAT development in metabolic diseases (obesity and diabetes) are scarce and should be, thus, more systematically addressed to better apprehend the bone modifications in that pathophysiological contexts. Moreover, bone marrow (BM) adipogenesis occurs throughout the whole life at different rates. Following an ordered spatiotemporal expansion, BMAT has turned to be a heterogeneous fat depot whose adipocytes diverge in their phenotype and their response to stimuli according to their location in bone and BM. In vitro, in vivo, and clinical studies point to a detrimental role of BM adipocytes (BMAs) throughout the release of paracrine factors that modulate osteoblast and/or osteoclast formation and function. However, the anatomical dissemination and the difficulties to access BMAs still hamper our understanding of the relative contribution of BMAT secretions compared with those of peripheral adipose tissues. A further characterization of the phenotype and the functional regulation of BMAs are ever more required. Based on currently available data and comparison with other fat tissues, this review addresses the originality of the BMAT with regard to its development, anatomy, metabolic properties, and response to physiological cues.

High bone mass in adult mice with diet-induced obesity results from a combination of initial increase in bone mass followed by attenuation in bone formation; implications for high bone mass and decreased bone quality in obesity

Obesity is generally recognized as a condition which positively influences bone mass and bone mineral density (BMD). Positive effect of high body mass index (BMI) on bone has been recognized as a result of increased mechanical loading exerted on the skeleton. However, epidemiologic studies indicate that obesity is associated with increased incidence of fractures. The results presented here offer a new perspective regarding the mechanisms which may be responsible for the increase of bone mass and concurrent decrease in bone quality. Two groups of 12 week old C57BL/6 males were fed either high fat diet (HFD) or regular diet (RD) for 11 weeks. Metabolic profile, bone parameters and gene expression were assessed in these groups at the end of the experiment. Additionally, bone status was evaluated in a third group of 12 week old animals corresponding to animals at the start of the feeding period. Administration of HFD resulted in development of a diet-induced obesity (DIO), glucose intolerance, alteration in energy metabolism, and impairment in WAT function, as compared to the age-matched control animals fed RD. The expression of adiponectin, FABP4/aP2, DIO2 and FoxC2 were decreased in WAT of DIO animals, as well as transcript levels for IGFBP2, the cytokine regulating both energy metabolism and bone mass. At the end of experiment, DIO mice had higher bone mass than both control groups on RD, however they had decreased bone formation, as assessed by calcein labeling, and increased marrow adipocyte content. This study suggests that the bone mass acquired in obesity is a result of a two-phase process. First phase would consist of either beneficial effect of fat expansion to increase bone mass by increased mechanical loading and/or increased production of bone anabolic adipokines and/or nutritional effect of fatty acids. This is followed by a second phase characterized by decreased bone formation and bone turnover resulting from development of metabolic impairment.

Muscle and bone, two interconnected tissues

As bones are levers for skeletal muscle to exert forces, both are complementary and essential for locomotion and individual autonomy. In the past decades, the idea of a bone-muscle unit has emerged. Numerous studies have confirmed this hypothesis from in utero to aging works. Space flight, bed rest as well as osteoporosis and sarcopenia experimentations have allowed to accumulate considerable evidence. Mechanical loading is a key mechanism linking both tissues with a central promoting role of physical activity. Moreover, the skeletal muscle secretome accounts various molecules that affect bone including insulin-like growth factor-1 (IGF-1), basic fibroblast growth factor (FGF-2), interleukin-6 (IL-6), IL-15, myostatin, osteoglycin (OGN), FAM5C, Tmem119 and osteoactivin. Even though studies on the potential effects of bone on muscle metabolism are sparse, few osteokines have been identified. Prostaglandin E2 (PGE2) and Wnt3a, which are secreted by osteocytes, osteocalcin (OCN) and IGF-1, which are produced by osteoblasts and sclerostin which is secreted by both cell types, might impact skeletal muscle cells. Cartilage and adipose tissue are also likely to participate to this control loop and should not be set aside. Indeed, chondrocytes are known to secrete Dickkopf-1 (DKK-1) and Indian hedgehog (Ihh) and adipocytes produce leptin, adiponectin and IL-6, which potentially modulate bone and muscle metabolisms. The understanding of this system will enable to define new levers to prevent/treat sarcopenia and osteoporosis at the same time. These strategies might include nutritional interventions and physical exercise.

Obstructive sleep apnea and metabolic bone disease: insights into the relationship between bone and sleep

Obstructive sleep apnea (OSA) and low bone mass are two prevalent conditions, particularly among older adults-a section of the U.S. population that is expected to grow dramatically over the coming years. OSA, the most common form of sleep-disordered breathing, has been linked to multiple cardiovascular, metabolic, hormonal, and inflammatory derangements and may have adverse effects on bone. However, little is known about how OSA (including the associated hypoxia and sleep loss) affects bone metabolism. In order to gain insight into the relationship between sleep and bone, we review the growing information on OSA and metabolic bone disease and discuss the pathophysiological mechanisms by which OSA may affect bone metabolism/architecture.

Bone damage in type 2 diabetes mellitus

This review focuses on the mechanisms determining bone fragility in patients with type 2 diabetes mellitus (T2DM). Despite bone mineral density (BMD) is usually normal or more often increased in these patients, fracture incidence is high, probably because of altered bone "quality". The latter seems to depend on several, only partly elucidated, mechanisms, such as the increased skeletal content of advanced glycation end-products causing collagen deterioration, the altered differentiation of bone osteogenic cells, the altered bone turnover and micro-architecture. Disease duration, its severity and metabolic control, the type of therapy, the presence or absence of complications, as like as the other known predictors for falls, are all relevant contributing factors affecting fracture risk in T2DM. In these patients the estimate of fracture risk in the everyday clinical practice may be challenging, due to the lower predictive capacity of both BMD and risk factors-based algorithms (e.g. FRAX).

Subchondral insufficiency fractures and spontaneous osteonecrosis of the knee may not be related to osteoporosis

The term insufficiency fracture implies inadequate bone and is applied to some subchondral knee magnetic resonance images. We reviewed bone mineral density, body mass index, meniscal extrusion, comorbidities, and demographics in 32 knee insufficiency fracture patients. Only five were osteoporotic. Meniscal extrusion was predominant.

PURPOSE

The literature supports systemic osteoporosis as a risk fracture for spontaneous osteonecrosis of the knee (SONK). SONK is also called a subchondral insufficiency fracture. Recognizing that insufficiency fracture and SONK are related, we designed this retrospective study to determine if knee subchondral insufficiency fractures were associated with osteoporosis based on bone mineral density.

METHODS

Based on magnetic resonance imaging findings, 32 patients were diagnosed as having an insufficiency fracture by an orthopaedic surgeon with magnetic resonance imaging confirmation by a musculoskeletal radiologist. We reviewed body mass index, age, sex, comorbidities, demographics, and bone mineral density using both T-scores and Z-scores.

RESULTS

The average age was 70, and only five patients were osteoporotic. Twenty-six of the 32 patients were female. The average age-related Z-score was 1 standard deviation above normal.

CONCLUSIONS

We conclude that osteoporosis is not the underlying cause of this disorder in the majority of patients.