Association between circulating levels of adiponectin and indices of bone mass and bone metabolism in middle-aged post-menopausal women

Effect of adipokine and ghrelin levels on BMD and fracture risk: an updated systematic review and meta-analysis

Context

Circulating adipokines and ghrelin affect bone remodeling by regulating the activation and differentiation of osteoblasts and osteoclasts. Although the correlation between adipokines, ghrelin, and bone mineral density (BMD) has been studied over the decades, its correlations are still controversial. Accordingly, an updated meta-analysis with new findings is needed.

Objective

This study aimed to explore the impact of serum adipokine and ghrelin levels on BMD and osteoporotic fractures through a meta-analysis.

Data sources

Studies published till October 2020 in Medline, Embase, and the Cochrane Library were reviewed.

Study selection

We included studies that measured at least one serum adipokine level and BMD or fracture risk in healthy individuals. We excluded studies with one or more of the following: patients less than 18 years old, patients with comorbidities, who had undergone metabolic treatment, obese patients, patients with high physical activities, and a study that did not distinguish sex or menopausal status.

Data extraction

We extracted the data that include the correlation coefficient between adipokines (leptin, adiponectin, and resistin) and ghrelin and BMD, fracture risk by osteoporotic status from eligible studies.

Data synthesis

A meta-analysis of the pooled correlations between adipokines and BMD was performed, demonstrating that the correlation between leptin and BMD was prominent in postmenopausal women. In most cases, adiponectin levels were inversely correlated with BMD. A meta-analysis was conducted by pooling the mean differences in adipokine levels according to the osteoporotic status. In postmenopausal women, significantly lower leptin (SMD = -0.88) and higher adiponectin (SMD = 0.94) levels were seen in the osteoporosis group than in the control group. By predicting fracture risk, higher leptin levels were associated with lower fracture risk (HR = 0.68), whereas higher adiponectin levels were associated with an increased fracture risk in men (HR = 1.94) and incident vertebral fracture in postmenopausal women (HR = 1.18).

Conclusions

Serum adipokines levels can utilize to predict osteoporotic status and fracture risk of patients.

Systematic review registration

https://www.crd.york.ac.uk/prospero/display_record.php?ID=CRD42021224855, identifier CRD42021224855.

The Unique Metabolic Characteristics of Bone Marrow Adipose Tissue

Bone marrow adipose tissue (MAT) is distinct from white adipose tissue (WAT) or brown adipose tissue (BAT) for its location, feature and function. As a largely ignored adipose depot, it is situated in bone marrow space and resided with bone tissue side-by-side. MAT is considered not only as a regulator of bone metabolism through paracrine, but also as a functionally particular adipose tissue that may contribute to global metabolism. Adipokines, inflammatory factors and other molecules derived from bone marrow adipocytes may exert systematic effects. In this review, we summary the evidence from several aspects including development, distribution, histological features and phenotype to elaborate the basic characteristics of MAT. We discuss the association between bone metabolism and MAT, and highlight our current understanding of this special adipose tissue. We further demonstrate the probable relationship between MAT and energy metabolism, as well as glucose metabolism. On the basis of preliminary results from animal model and clinical studies, we propose that MAT has its unique secretory and metabolic function, although there is no in-depth study at present.

Novel insights into the relationship between nonalcoholic fatty liver disease and osteoporosis

Excess fat deposition and insulin resistance are considered the main risk factors for nonalcoholic fatty liver disease (NAFLD), and therefore, not surprisingly, the global prevalence of NAFLD increases in parallel with both obesity and type 2 diabetes. Although deterioration of bone homeostasis in patients with NAFLD is commonly observed, its etiology has not been fully elucidated yet. It was shown in several studies that bone tissue seems to be independently associated with NAFLD. A mechanistic perspective puts the liver at the center of mutual interdependencies obviously involving adipose tissue and muscles and also the bone matrix and bone cells, which are relatively novel. In this review, various pathophysiological mechanisms and possible mediating molecules that may interplay between NAFLD and bone tissue are described. Chronic inflammation, vitamin D3, growth hormone, insulin-like growth factor 1, osteopontin, fetuin-A, irisin, osteocalcin, and osteoprotegerin from osteoblasts have been proposed as mediators of mutual interactions among the skeleton, fatty tissue, and liver. Although to date there are still many issues that have not been elucidated, growing evidence suggests that screening and surveillance of bone mineral density in patients with NAFLD should be considered in future strategies and guidelines for NAFLD management.

ADIPONECTIN AS A POTENTIAL BIOMARKER OF LOW BONE MINERAL DENSITY IN POSTMENOPAUSAL WOMEN WITH METABOLIC SYNDROME

CONTEXT

Adiponectin is an abundant adipokine, which has antiinflammatory, anti-atherosclerotic and vasoprotective actions, and potential antiresorptive effects on bone metabolism. It seems to be directly involved in the improvement and control of energy homeostasis, protecting bone health and predicting osteoporotic fracture risk.

OBJECTIVE

To examine the relationship between adiponectin level and bone mineral density (BMD) in post-menopausal women with metabolic syndrome (MetS) and low BMD, and to estimate the prognostic significance of adiponectin in osteoporosis.

DESIGN

Clinical-laboratory cross-sectional study including 120 middle-aged and elder women (average 69.18±7.56 years).

SUBJECTS AND METHODS

The anthropometric parameters were measured for all examinees. Lumbar spine and hip BMD, as well as body fat percentage, were measured using a Hologic DEXA scanner. In all subjects serum adiponectin concentration was measured by ELISA method.

RESULTS

The level of adiponectin was significantly positively correlated with BMD-total, BMD of the lumbar spine and BMD of the femoral neck (r=0.618, r=0.521, r=0.567; p<0.01). Levels of adiponectin and BMD are significantly lower in post-menopausal women with MetS and osteoporosis compared to patients with osteopenia (856.87±453.43 vs. 1287.32±405.21 pg/mL, p<0.01; BMD, p<0.05), and the highest values in healthy examinees. A cut-off value of adiponectin level for osteoporosis/osteopenia was 1076.22/1392.74 pg/mL.

CONCLUSIONS

Post-menopausal women with MetS have significantly lower adiponectin level and low BMD compared to healthy examinees. Adiponectin may be an early, significant and independent predictor of developing osteoporosis in women with MetS, especially in post-menopausal period.

Association between omentin-1, adiponectin and bone health under consideration of osteoprotegerin as possible mediator

PURPOSE

Several studies implicated a crosstalk between bone and fat in the pathogenesis of osteoporosis. Few studies indicated an association between adiponectin and omentin-1 on the bone remodeling process and bone mineral density, and suggested osteoprotegerin (OPG) as a mediator of this relationship. However, only limited evidence on this relationship is available in humans. Therefore, this study aimed to investigate the association between omentin-1, adiponectin and broadband ultrasound attenuation (BUA) in peri-/premenopausal and postmenopausal women, and to assess the role of OPG as a possible mediator.

METHODS

Data from the German population-based EPIC-Potsdam cohort comprising 637 women were analyzed. Multivariable-adjusted ANCOVA including age, BMI, waist circumference, smoking status, education, physical activity, adiponectin or omentin-1 and hormone use was used to investigate potential relationships between the adipokines and BUA levels. A mediation analysis assessed the mediating effect of OPG on the association of BUA and omentin-1 levels.

RESULTS

Peri-/premenopausal women had higher BUA levels (112.5 ± 10.1 dB/MHz), compared to postmenopausal women (106.3 ± 10.0 dB/MHz). In peri-/premenopausal women neither adiponectin nor omentin-1 was significantly associated with BUA. In postmenopausal women, adiponectin was not associated with BUA, but 10 % increase in the omentin-1 concentration was significantly associated with 0.44 dB/MHz lower BUA levels (p = 0.01). Omentin-1 was positively associated with OPG (p = 0.02); however, OPG was not significantly related to BUA (p = 0.62).

CONCLUSION

Our study provides evidence for an inverse association between circulating omentin-1 and BUA levels in postmenopausal women. However, the present findings do not support a mediating effect of OPG in the adipose tissue-bone pathway.

Lipid metabolism disorders and bone dysfunction--interrelated and mutually regulated (review)

The association between lipid and bone metabolism has become an increasing focus of interest in recent years, and accumulating evidence has shown that atherosclerosis (AS) and osteoporosis (OP), a disorder of bone metabolism, frequently co-exist. Fat and bone are known to share a common progenitor cell: Multipotent mesenchymal stem cells (MSC) in the bone marrow (BM), which are able to differentiate into various cell phenotypes, including osteoblasts, adipocytes and chondrocytes. Laboratory-based and clinical trials have shown that increasing adipocytes are accompanied by a decrease in bone mineral density (BMD) and bone mass. Statins, lipid-lowering drugs used to treat hyperlipidemia, also provide benefit in the treatment of OP. There is thus evidence that the metabolism of lipids is correlated with that of bone, and that the two are mutually regulated. The present review primarily focuses on the potential association between lipid metabolism disturbance and OP, based on biological metabolism, pathophysiological processes, results from clinical and experimental animal studies, processes involved in the differentiation of adipocytes and osteoblasts, as well as pharmacological treatments of these diseases.

Muscle-bone and fat-bone interactions in regulating bone mass: do PTH and PTHrP play any role?

Metabolic bone disease occurs when there is a net loss in bone density. Osteoporosis, the most common metabolic bone disease, is a devastating problem and an increasingly major public health issue. A substantial body of evidence in the elderly population indicates that a relationship exists between the components of body weight and various measures of bone/mass, density, and function. Both muscle and fat contribute to the body's total weight and the intimate associations of muscle, fat, and bone are known. But the close functional interactions between muscle and bone or fat and bone are largely unidentified and have drawn much attention in recent years. Each of these tissues not only responds to afferent signals from traditional hormone systems and the central nervous systems but also secretes factors with important endocrine functions. Studies suggest that during growth, development, and aging, the relationship of muscle and fat with the skeleton possibly governs bone homeostasis and turnover. A better understanding of the endocrine function and the cellular and molecular mechanisms and pathways linking muscle or adipose tissues with bone anabolism and catabolism is a new avenue for novel pathways for anabolic drug discovery. These in turn will likely lead to more rational therapy toward increasingly prevalent disorders like osteoporosis. In this review, some of the recent works on the interaction of bone with muscle and fat are highlighted, and in so doing the role of parathyroid hormone (PTH), and PTH-related peptide (PTHrP) is surveyed.

The genetic pleiotropy of musculoskeletal aging

Musculoskeletal aging is detrimental to multiple bodily functions and starts early, probably in the fourth decade of an individual's life. Sarcopenia is a health problem that is expected to only increase as a greater portion of the population lives longer; prevalence of the related musculoskeletal diseases is similarly expected to increase. Unraveling the biological and biomechanical associations and molecular mechanisms underlying these diseases represents a formidable challenge. There are two major problems making disentangling the biological complexity of musculoskeletal aging difficult: (a) it is a systemic, rather than "compartmental," problem, which should be approached accordingly, and (b) the aging per se is neither well defined nor reliably measurable. A unique challenge of studying any age-related condition is a need of distinguishing between the "norm" and "pathology," which are interwoven throughout the aging organism. We argue that detecting genes with pleiotropic functions in musculoskeletal aging is needed to provide insights into the potential biological mechanisms underlying inter-individual differences insusceptibility to the musculoskeletal diseases. However, exploring pleiotropic relationships among the system's components is challenging both methodologically and conceptually. We aimed to focus on genetic aspects of the cross-talk between muscle and its "neighboring" tissues and organs (tendon, bone, and cartilage), and to explore the role of genetics to find the new molecular links between skeletal muscle and other parts of the "musculoskeleton." Identification of significant genetic variants underlying the musculoskeletal system's aging is now possible more than ever due to the currently available advanced genomic technologies. In summary, a "holistic" genetic approach is needed to study the systems's normal functioning and the disease predisposition in order to improve musculoskeletal health.