Undercarboxylated Osteocalcin and Its Associations With Bone Mineral Density, Bone Turnover Markers, and Prevalence of Osteopenia and Osteoporosis in Chinese Population: A Cross-Sectional Study

Association of serum osteocalcin with bone microarchitecture and muscle mass in Beijing community-dwelling postmenopausal women

BACKGROUND

Osteoporosis is a systemic skeletal disease with increasing bone fragility and prone to fracture. Osteocalcin (OC), as the most abundant non collagen in bone matrix, has been extensively used in clinic as a biochemical marker of osteogenesis. Two forms of OC were stated on circulation, including carboxylated osteocalcin (cOC) and undercarboxylated osteocalcin (ucOC). OC was not only involved in bone mineralization, but also in the regulation of muscle function.

OBJECTIVE

This study explored the relationship between serum OC, cOC, ucOC levels and bone mineral density (BMD), bone microarchitecture, muscle mass and physical activity in Chinese postmenopausal women.

METHOD

216 community-dwelling postmenopausal women were randomized enrolled. All subjects completed biochemical measurements, including serum β-isomer of C-terminal telopeptides of type I collagen (β-CTX), N-terminal propeptide of type 1 procollagen (P1NP), alkaline phosphatase (ALP), OC, cOC and ucOC. They completed X-ray absorptiometry (DXA) scan to measure BMD, appendicular lean mass (ALM) and trabecular bone score (TBS). They completed high resolution peripheral quantitative CT (HR-pQCT) to assess peripheral bone microarchitectures.

RESULTS

Serum OC, cOC and ucOC were elevated in osteoporosis postmenopausal women. In bone geometry, serum ucOC was positively related with total bone area (Tt.Ar) and trabecular area(Tb.Ar). In bone volumetric density, serum OC and ucOC were negatively associated with total volume bone mineral density (Tt.vBMD) and trabecular volume bone mineral density (Tb.vBMD). In bone microarchitecture, serum OC and ucOC were negatively correlative with Tb.N and Tb.BV/TV, and were positively correlated with Tb.Sp. Serum OC and ucOC were positively associated with Tb.1/N.SD. Serum OC was negatively related with Tb.Th. Serum ucOC was positively associated with ALM. The high level of serum OC was the risk factor of osteoporosis. ALM was the protective factor for osteoporosis.

CONCLUSION

All forms of serum OC were negatively associated with BMD. Serum OC and ucOC mainly influenced microstructure of trabecular bone in peripheral skeletons. Serum ucOC participated in modulating both bone microstructure and muscle mass.

Current knowledge of bone-derived factor osteocalcin: its role in the management and treatment of diabetes mellitus, osteoporosis, osteopetrosis and inflammatory joint diseases

Osteocalcin (OC) is the most abundant non-collagenous and osteoblast-secreted protein in bone. It consists of two forms such as carboxylated OC (cOC) and undercarboxylated OC (ucOC). While cOC promotes bone mineralization and increases bone strength, ucOC is regarded an endocrinologically active form that may have several functions in multiple end organs and tissues. Total OC (tOC) includes both of these forms (cOC and ucOC) and is considered a marker of bone turnover in clinical settings. Most of the data on OC is limited to preclinical studies and therefore may not accurately reflect the situation in clinical conditions. For the stated reason, the aim of this review was not only to summarize current knowledge of all forms of OC and characterize its role in diabetes mellitus, osteoporosis, osteopetrosis, inflammatory joint diseases, but also to provide new interpretations of its involvement in the management and treatment of aforementioned diseases. In this context, special emphasis was placed on available clinical trials. Significantly lower levels of tOC and ucOC could be associated with the risk of type 2 diabetes mellitus. On the contrary, tOC level does not seem to be a good indicator of high bone turnover status in postmenopausal osteoporosis, osteoarthritis and rheumatoid arthritis. The associations between several pharmacological drugs used to treat all disorders mentioned above and OC levels have also been provided. From this perspective, OC may serve as a medium through which certain medications can influence glucose metabolism, body weight, adiponectin secretion, and synovial inflammation.

Additional Insights Into the Role of Osteocalcin in Osteoblast Differentiation and in the Early Steps of Developing Alveolar Process of Rat Molars

This study investigated whether osteocalcin (OCN) is present in osteoblast precursors and its relationship with initial phases of alveolar process formation. Samples of maxillae of 16-, 18-, and 20-day-old rat embryos (E16, E18, and E20, respectively), and 05-, 10-, and 15-day-old postnatal rats (P05, P10, and P15, respectively) were fixed and embedded in paraffin or araldite. Immunohistochemistry for osterix (Osx), alkaline phosphatase (ALP), and OCN detection was performed and the number of immunolabelled cells was computed. Non-decalcified sections were subjected to the von Kossa method combined with immunohistochemistry for Osx or OCN detection. For OCN immunolocalization, samples were fixed in 0.5% glutaraldehyde/2% formaldehyde and embedded in LR White resin. The highest number of ALP- and OCN-immunolabelled cells was observed in dental follicle of E16 specimens, mainly in basal portions of dental alveolus. In corresponding regions, osteoblasts in differentiation adjacent to von Kossa-positive bone matrix exhibited Osx and OCN immunoreactivity. Ultrastructural analysis revealed OCN immunoreactive particles inside osteoblast in differentiation, and in bone matrix associated with collagen fibrils and within matrix vesicles, at early stages of alveolar process formation. Our results indicate that OCN plays a role in osteoblast differentiation and may regulate calcium/phosphate precipitation during early mineralization of the alveolar process.

Causal association of NAFLD with osteoporosis, fracture and falling risk: a bidirectional Mendelian randomization study

Introduction

The causal association between non-alcoholic fatty liver disease (NAFLD) and osteoporosis remains controversial in previous epidemiological studies. We employed a bidirectional two-sample Mendelian analysis to explore the causal relationship between NAFLD and osteoporosis.

Method

The NAFLD instrumental variables (IVs) were obtained from a large Genome-wide association study (GWAS) meta-analysis dataset of European descent. Two-sample Mendelian randomization (MR) analyses were used to estimate the causal effect of NAFLD on osteoporosis, fracture, and fall. Reverse Mendelian randomization analysis was conducted to estimate the causal effect of osteoporosis on NAFLD. The inverse-variance weighted (IVW) method was the primary analysis in this analysis. We used the MR-Egger method to determine horizontal pleiotropic. The heterogeneity effect of IVs was detected by MR-Egger and IVW analyses.

Results

Five SNPs (rs2980854, rs429358, rs1040196, rs738409, and rs5764430) were chosen as IVs for NAFLD. In forward MR analysis, the IVW-random effect indicated the causal effect of NAFLD on osteoporosis (OR= 1.0021, 95% CI: 1.0006-1.0037, P= 0.007) but not on fracture (OR= 1.0016, 95% CI: 0.998-1.0053, P= 0.389) and fall (OR= 0.9912, 95% CI: 0.9412-1.0440, P= 0.740). Furthermore, the reverse Mendelian randomization did not support a causal effect of osteoporosis on NAFLD (OR= 1.0002, 95% CI: 0.9997-1.0007, P= 0.231). No horizontal pleiotropic was detected in all MR analyses.

Conclusions

The results of this study indicate a causal association between NAFLD and osteoporosis. NAFLD patients have a higher risk of osteoporosis but not fracture and falling risk. In addition, our results do not support a causal effect of osteoporosis on NAFLD.

Layer-by-layer assembly of procyanidin and collagen promotes mesenchymal stem cell proliferation and osteogenic differentiation in vitro and in vivo

Collagen, commonly used in tissue engineering, is widespread in various tissues. During bone tissue regeneration, collagen can stimulate the cellular response and determine the fate of cells. In this work, we integrated collagen type II with procyanidin (PC) onto an implant coating by applying a layer-by-layer technique to demonstrate that collagen and PC can participate in the construction of new biomaterials and serve as multifunctional components. The effects of PC/collagen multilayers on the viability of cocultured bone marrow mesenchymal stem cells (BMSCs) were analyzed by cell counting kit-8 analysis and phalloidin staining. The reactive oxygen species level of BMSCs was revealed through immunofluorescent staining and flow cytometry. Osteogenesis-related genes were detected, and in vivo experiment was performed to reveal the effect of newly designed material on the osteogenic differentiation of BMSCs. Our data demonstrated that in BMSCs PC/collagen multilayers accelerated the proliferation and osteogenic differentiation through Wnt/β-catenin signaling pathway and enhanced bone generation around the implant in the bone defect model of rabbit femurs. In summary, combination of collagen and PC provided a new sight for the research and development of implant materials or coatings in the future.