Bone remodeling rate and remodeling balance are not co-regulated in adulthood: implications for the use of activation frequency as an index of remodeling rate

Adenovirus mediated gene delivery of α-calcitonin gene-related peptide facilitates osseointegration of implant in ovariectomized rat

Background

Osteoporosis, which adversely affected osseointegration of dental implants, became prevalent with the entry of ageing era. Recent studies indicated that α-calcitonin gene-related peptide (α-CGRP) played a role in modulating osteoporosis. However, due to the plasma half-life of α-CGRP being estimated at merely 7-10 min, it was difficult to utilize a conventional method that administered sufficient α-CGRP to the implant site. This present study aimed to investigate the efficacy of an α-CGRP transgene in promoting implant osseointegration in ovariectomized (OVX) rats.

Method

The osteoporosis rat model was established through bilateral ovariectomy, following which the subjects were categorized into three distinct groups: the α-CGRP transgene group, the empty virus vector group, and the blank control group. Ad-CGRP-EGFP was locally administered into the bone defect site prior to implant placement in the OVX rats. 7 and 28 days after implantation, the femurs were isolated for molecular and histological analyses, micro-CT analysis and biomechanical test.

Result

Bone marrow stromal cells (BMSCs) transduced with Ad-CGRP-EGFP could continuously express α-CGRP more than 28 days in vitro. Successful transgene expression was confirmed through cryosectioning and Western blot analysis 7 days after implantation in vivo. The results indicated a substantial decrease in the quantity of TRAP + cells in the α-CGRP transgene group. Additionally, quantitative real-time RT-PCR and Western blot analysis revealed a significant elevation in the expression levels of Runx2 and ALP, coupled with a notable reduction in the expression of cathepsin K and RANKL (P<0.05). Moreover, the α-CGRP transgene group exhibited a significant enhancement in osteointegration and restoration of implant stability in OVX rats (P<0.01) 28 days after implantation.

Conclusion

This study implied a great therapeutic potential of α-CGRP in osseointegration of titanium implants in OVX-relative osteoporosis rats, offering valuable insights for guiding bone regeneration strategies under osteoporotic conditions.

High bone fracture risk in a large modern cohort of liver transplant recipients

Liver transplantation (LT) has historically been associated with a high prevalence of osteoporosis, but most of the available data date back to late 1990s-early 2000s with limited sample size. Our aim was to assess the prevalence of bone fragility fractures and contributing factors in a large modern cohort of liver transplant recipients. Retrospective study of 429 consecutive patients receiving liver transplantation from 1/1/2010 to 31/12/2015. Final cohort included 366 patients. Electronic radiological images (lateral views of spine X-rays or Scout CT abdominal scans) performed within 6 months from LT, were blinded reviewed to screen for morphometric vertebral fractures. Symptomatic clinical fragility fractures were recorded from the medical records. Patients with fragility fractures in the cohort were 155/366 (42.3%), with no significant differences between sexes. Most sustained vertebral fractures (145/155, 93.5%), mild or moderate wedges, with severe fractures more frequently observed in women. Multiple vertebral fractures were common (41.3%). Fracture rates were similar across different etiologies of cirrhosis and independent of diabetes or glucocorticoids exposure. Kidney function was significantly worse in women with fractures. Independently of age, sex, alcohol use, eGFR, and etiology of liver disease, low BMI was significantly associated with an increased risk for fractures (adjusted OR 1.058, 95%CI 1.001-1.118, P = 0.046). Our study shows a considerable fracture burden in a large and modern cohort of liver transplant recipients. Given the very high prevalence of bone fractures, a metabolic bone disease screening should be implemented in patients awaiting liver transplantation.

2D size of trabecular bone structure units (BSU) correlate more strongly with 3D architectural parameters than age in human vertebrae

Bone tissue is continuously remodeled. In trabecular bone, each remodeling transaction forms a microscopic bone structural unit (BSU), also known as a hemiosteon or a trabecular packet, which is bonded to existing tissue by osteopontin-rich cement lines. The size and shape of the BSUs are determined by the size and shape of the resorption cavity, and whether the cavity is potentially over- or under-filled by the subsequent bone formation. The present study focuses on the recently formed trabecular BSUs, and how their 2D size and shape changes with age and trabecular microstructure. The study was performed using osteopontin-immunostained frontal sections of L2 vertebrae from 8 young (aged 18.5-37.6 years) and 8 old (aged 69.1-96.4 years) control females, which underwent microcomputed tomography (μCT) imaging prior to sectioning. The contour of 4230 BSU profiles (181-385 per vertebra) within 1024 trabecular profiles were outlined, and their 2D width, length, area, and shape were assessed. Of these BSUs, 22 (0.5%) were generated by modeling-based bone formation (i.e. without prior resorption), while 99.5% were generated by remodeling-based bone formation (i.e. with prior resorption). The distributions of BSU profile width, length, and area were significantly smaller in the old versus young females (p < 0.005), and the median profile width, length, and area were negative correlated with age (p < 0.018). Importantly, these BSU profile size parameters were more strongly correlated with trabecular bone volume (BV/TV, p < 0.002) and structure model index (SMI, p < 0.008) assessed by μCT, than age. Moreover, the 2D BSU size parameters were positively correlated to the area of the individual trabecular profiles (p < 0.0001), which were significantly smaller in the old versus young females (p < 0.024). The BSU shape parameters (aspect ratio, circularity, and solidity) were not correlated with age, BV/TV, or SMI. Collectively, the study supports the notion that not only the BSU profile width, but also its length and area, are more influenced by the age-related bone loss and shift from plates to rods (SMI), than age itself. This implies that BSU profile size is mainly driven by changes in the trabecular microstructure, which affect the size of the resorption cavity that the BSU refills.

Bone Diseases in Patients with Chronic Liver Disease

Osteoporosis is a frequently observed complication in patients with chronic liver disease, particularly liver cirrhosis and cholestatic liver diseases. In addition, osteoporosis is critical in patients receiving a liver transplant. Nevertheless, few studies have evaluated bone diseases in patients with more frequently observed chronic liver disease, such as chronic viral hepatitis, nonalcoholic fatty liver disease and alcoholic liver disease. Osteoporosis is a disease caused by an imbalance in the activities of osteoblasts and osteoclasts. Over the last few decades, many advances have improved our knowledge of the pathogenesis of osteoporosis. Importantly, activated immune cells affect the progression of osteoporosis, and chronic inflammation may exert an additional effect on the existing pathophysiology of osteoporosis. The microbiota of the intestinal tract may also affect the progression of bone loss in patients with chronic liver disease. Recently, studies regarding the effects of chronic inflammation on dysbiosis in bone diseases have been conducted. However, mechanisms underlying osteoporosis in patients with chronic liver disease are complex and precise mechanisms remain unknown. The following special considerations in patients with chronic liver disease are reviewed: bone diseases in patients who underwent a liver transplant, the association between chronic hepatitis B virus infection treatment and bone diseases, the association between sarcopenia and bone diseases in patients with chronic liver disease, and the association between chronic liver disease and avascular necrosis of the hip. Few guidelines are currently available for the management of low bone mineral density or bone diseases in patients with chronic liver disease. Due to increased life expectancy and therapeutic advances in chronic liver disease, the importance of managing osteoporosis and other bone diseases in patients with chronic liver disease is expected to increase. Consequently, specific guidelines need to be established in the near future.

Adenoviral delivery of adiponectin ameliorates osteogenesis around implants in ovariectomized rats

BACKGROUND

Adiponectin (APN) has been reported to promote bone formation. However, it is difficult to utilize a conventional method that administers sufficient APN to the implant site. The present study investigated the efficacy of an APN transgene to accelerate the implant osseointegration in ovariectomized (OVX) rats.

METHODS

In vitro, bone marrow stromal cells were transduced with reconstructed adenovirus (Ad-APN-EGFP) and osteoclast precursor RAW264.7 cells were co-cultured with the conditioned medium secreted by transduced bone marrow stromal cells. Tartrate-resistant acid phosphatase staining and bone slice resorption assay were performed to evaluate the activity of osteoclastogenesis. In vivo, Ad-APN-EGFP was administered into the bone defect prior to implant placement in OVX rats. At 7 and 28 days post implantation, the femurs were harvested and prepared for a real-time reverse transcriptase-polymerase chain reaction, hemotoxylin and eosin staining, immunohistochemical staining, micro-computed tomography analysis and biomechanical testing.

RESULTS

The results showed the formation and function of osteoclasts were significantly suppressed in vitro. Successful transgene expression was confirmed, and a significant increase of OCN, Runx2 and ALP expression was detected in the Ad-APN-EGFP group in vivo. Interestingly, we also found that the overexpression of APN decreased the expression level of potent adipogenic transcription factors such as PPARγ2 and C/EBP-α. At 28 days after implantation, the Ad-APN-EGFP group revealed a significantly increased osseointegration and implant stability in OVX rats compared to the control groups (Ad-EGFP and PBS groups).

CONCLUSIONS

APN via direct adenovirus-mediated gene transfer could ameliorate osseointegration surrounding titanium implants in OVX-related osteoporosis rats. Furthermore, it may be an effective strategy for promoting bone regeneration under osteoporotic conditions.

Understanding age-induced cortical porosity in women: Is a negative BMU balance in quiescent osteons a major contributor?

Cortical bone is remodeled by intracortical basic multicellular units (BMUs), whose end result can be observed as quiescent osteons in histological sections. These osteons offer a unique opportunity to investigate the BMU balance between the magnitude of bone resorption and subsequent bone formation at the BMU level. Our main objective was to investigate whether the latter parameters change between defined categories of osteons and with age, and to which extend these changes contribute to age-induced cortical porosity. Cortices of iliac bone specimens from 35 women (aged 16-78 years) with a higher porosity with age were investigated. A total of 3084 quiescent osteons reflecting 75% of the intracortical pores were histological examined. The osteons diameter, pore diameter, wall thickness, prevalence and contribution to the porosity were highly variable, but unchanged with age. Next, the osteons were categorized according to whether they reflected the remodeling of existing canals (type 2Q osteons) or the generation of new canals (type 1Q osteons). Type 2Q osteons versus type 1Q osteons: (i) had more frequently a pore diameter > 75 μm (7.4 vs. 1.3%; p < 0.001); (ii) had a larger mean pore diameter (40 ± 10 vs. 25 ± 4 μm; p < 0.001), osteon diameter (120 ± 21 vs. 94 ± 21 μm; p < 0.001) and wall thickness (40 ± 10 vs. 35 ± 9; p < 0.05); (iii) had a larger contribution to the cortical porosity (29 ± 18 vs. 8 ± 8%; p < 0.001); (iv) were more prevalent (44 ± 10 vs. 31 ± 11%; p < 0.001); and (v) were more prevalent with age. Collectively, this study demonstrates that quiescent osteons with age more frequently result from remodeling of existing canals, which in some cases had a more negative BMU balance. Still, the osteons showed no overall age-related change in their pore diameter i.e. BMU balance. In contrast to conventional wisdom, these data show that non-quiescent pores, not pores of quiescent osteons, were the main contributor to a higher cortical porosity.

Teriparatide for osteoporosis: importance of the full course

Teriparatide (TPTD) is the only currently available therapeutic agent that increases the formation of new bone tissue and can provide some remediation of the architectural defects in the osteoporotic skeleton. The use of teriparatide clinically is limited to 24 months. We review clinical findings during daily teriparatide treatment over time. Teriparatide appears to increase bone formation more than bone resorption as determined biochemically and histologically. Teriparatide exerts its positive effects on bone formation in two distinct fashions. The first is direct stimulation of bone formation that occurs within active remodeling sites (remodeling-based bone formation) and on surfaces of bone previously inactive (modeling-based bone formation). The second is an increase in the initiation of new remodeling sites. Both processes contribute to the final increase in bone density observed by non-invasive tools such as DXA. Remodeling is the repair process by which skeletal tissue is maintained in a young healthy state, and when stimulated by TPTD is associated with a positive bone balance within each remodeling cavity. It seems likely therefore that this component will contribute to the anti-fracture efficacy of TPTD. Teriparatide reduces the risk of fracture, and this effect appears to increase with longer duration of therapy. The use of novel treatment regimens, including shorter courses, should be held in abeyance until controlled clinical trials are completed to define the relative fracture benefits of such approaches in comparison to the 24-month daily use of the agent. Summary In patients with osteoporosis at high risk for fracture, the full continuous 24-month course with teriparatide results in improved skeletal health and outcomes than shorter time periods.

Bone matrix mineralization is preserved during early perimenopausal stage in healthy women: a paired biopsy study

Bone matrix mineralization based on quantitative backscatter electron imaging remained unchanged during the first year of menopause in paired transiliac biopsy samples from healthy women. This suggests that the reported early perimenopausal reductions in bone mineral density are caused by factors other than decreases in the degree of mineralization.

INTRODUCTION

It is unknown whether perimenopausal loss of bone mass is associated with a drop in bone matrix mineralization.

METHODS

For this purpose, we measured the bone mineralization density distribution (BMDD) by quantitative backscatter electron imaging (qBEI) in n = 17 paired transiliac bone biopsy samples at premenopausal baseline and 12 months after last menses (obtained at average ages of 49 ± 2 and 55 ± 2 years, respectively) in healthy women. For interpretation of BMDD outcomes, previously measured bone mineral density (BMD) and biochemical and histomorphometric markers of bone turnover were revisited for the present biopsy cohort.

RESULTS

Menopause significantly decreased BMD at the lumbar spine (-4.5 %) and femoral neck (-3.8 %), increased the fasting urinary hydroxyproline/creatinine ratio (+60 %, all p < 0.01) and histomorphometric bone formation rate (+25 %, p < 0.05), but affected neither cancellous nor cortical BMDD variables (paired comparison p > 0.05). Mean calcium concentrations of cancellous (Cn.CaMean) and cortical bone (Ct.CaMean) were within normal range (p > 0.05 compared to established reference data). Ct.CaMean was significantly correlated with Cn.CaMean before (R = 0.81, p < 0.001) and after menopause (R = 0.80, p < 0.001) and to cortical porosity of mineralized tissue (Ct.Po.) after menopause (R = -0.57, p = 0.02).

CONCLUSIONS

Surprisingly, the BMDD was found not affected by the changes in bone turnover rates in this cohort. This suggests that the substantial increase in bone formation rates took place shortly before the second biopsy, and the bone mineralization changes lag behind. We conclude that during the first year after the last menses, the degree of bone matrix mineralization is preserved and does not contribute to the observed reductions in BMD.

A 3D vascularized bone remodeling model combining osteoblasts and osteoclasts in a CaP nanoparticle-enriched matrix

AIM

We aimed to establish a 3D vascularized in vitro bone remodeling model.

MATERIALS & METHODS

Human umbilical endothelial cells (HUVECs), bone marrow mesenchymal stem cells (BMSCs), and osteoblast (OBs) and osteoclast (OCs) precursors were embedded in collagen/fibrin hydrogels enriched with calcium phosphate nanoparticles (CaPn). We assessed vasculogenesis in HUVEC-BMSC coculture, osteogenesis with OBs, osteoclastogenesis with OCs, and, ultimately, cell interplay in tetraculture.

RESULTS

HUVECs developed a robust microvascular network and BMSCs differentiated into mural cells. Noteworthy, OB and OC differentiation was increased by their reciprocal coculture and by CaPn, and even more by the combination of the tetraculture and CaPn.

CONCLUSION

We successfully developed a vascularized 3D bone remodeling model, whereby cells interacted and exerted their specific function.

Progression of bone ingrowth and attachment strength for stability of percutaneous osseointegrated prostheses

BACKGROUND

Percutaneous osseointegrated prosthetic (POP) devices have been used clinically in Europe for decades. Unfortunately, their introduction into the United States has been delayed, in part due to the lack of data documenting the progression of osseointegration and mechanical stability.

QUESTIONS/PURPOSES

We determined the progression of bone ingrowth into porous-coated POP devices and established the interrelationship with mechanical stability.

METHODS

After amputation, 64 skeletally mature sheep received a custom porous-coated POP device and were then randomized into five time groups, with subsequent measurement of percentage of bone ingrowth into the available pore spaces (n = 32) and the mechanical pullout force (n = 32).

RESULTS

Postimplantation, there was an accelerated progression of bone ingrowth (~48% from 0 to 3 months) producing a mean pullout force of 5066 ± 1543 N. Subsequently, there was a slower but continued progression of bone ingrowth (~23% from 3 to 12 months) culminating with a mean pullout force of 13,485 ± 1855 N at 12 months postimplantation. There was a high linear correlation (R = 0.94) between the bone ingrowth and mechanical pullout stability.

CONCLUSIONS

This weightbearing model shows an accelerated progression of bone ingrowth into the porous coating; the amount of ingrowth observed at 3 months after surgery within the porous-coated POP devices was sufficient to generate mechanical stability.

CLINICAL RELEVANCE

The data document progression of bone ingrowth into porous-coated POP devices and establish a strong interrelationship between ingrowth and pullout strength. Further human data are needed to validate these findings.

A model for the change of cancellous bone volume and structure over time

A model is presented for characterizing the process by which cancellous bone changes in volume and structure over time. The model comprises simulations of local changes resulting from individual remodelling events, known as bone multicellular units (BMU), and an ordinary differential equation for connecting the number of remodelling events to real time. The model is validated on micro-CT scans of tibiae of normal rats, estrogen deprived rats and estrogen deprived rats treated with bisphosphonates. The model explains the asymptotic trends seen in changes of bone volume over time resulting from estrogen deprivation as well as trends seen subsequent to treatment. The model demonstrates that both bone volume and structure changes can be explained in terms of resetting remodelling parameters. The model also shows that either current understanding of the effects of bisphosphonates is not correct or that the simplest description of remodelling does not suffice to explain both the change in bone volume and structure of rats treated with bisphosphonates.

Histomorphometric interpretation of bone biopsies for the evaluation of osteoporosis treatment

Bone histomorphometry is a valuable tool in the evaluation of bone safety and the mechanism of action of drugs used in the treatment of osteoporosis. Recent studies in patients treated with anti-resorptive agents have highlighted technical issues, in particular, related to the calculation of dynamic indices of bone turnover using fluorochrome labelling. This review addresses the need for standardised approaches for overcoming these problems in order to enable valid comparison of the effects of different interventions on bone remodelling.

The role and efficacy of denosumab in the treatment of osteoporosis: an update

INTRODUCTION

Bone strength determinants such as bone mineral density and bone quality parameters are determined by life-long remodeling of skeletal tissue. Denosumab is a fully human mAb receptor activator of NF-κB ligand, which selectively inhibits osteoclastogenesis, the end product of a cascade interaction among numerous systemic and local factors and osteoblasts. It has been approved for clinical use by the FDA in the US and by the European Medicines Agency in Europe since June 2010 (trade name Prolia(™), Amgen, Thousand Oaks, CA, USA).

AREAS COVERED

This review establishes the concerns and provides insights in issues concerning the cost-effectiveness and safety profile of this new pharmaceutical agent. There is an effort to clarify the special characteristics and the anti-catabolic role of denosumab in the bone tissue homeostasis and more specifically its potential clinical applications and clinical results in the field of postmenopausal osteoporosis.

EXPERT OPINION

Administrated as a subcutaneous injection every 6 months, denosumab has been shown to decrease bone turnover and increase bone mineral density in postmenopausal women with low bone mass or osteoporosis and reduce vertebral, hip and nonvertebral fracture risk in postmenopausal women with osteoporosis. The rapid, sustained and reversible effect in suppressing osteoclastic bone resorption, the return of responsiveness on rechallenge, its good tolerability and ease of administration are features that distinguish it from other antiresorptive therapies.

Osteoporosis primer for the vertebroplasty practitioner: expanding the focus beyond needles and cement

Osteoporosis is a common cause of vertebral compression fractures. Although vertebroplasty is used to treat the pain, the risk of additional compression fractures is very high in these patients. Adequate evaluation and management of the underlying osteoporosis is critical to reducing the risk of subsequent fractures. Such an evaluation involves understanding the underlying physiology of osteoporosis and the role of calcium, vitamin D, prescription medication, and lifestyle changes. This brief review is intended to familiarize neuroradiologists with these aspects so they can advise patients about optimizing fracture risk reduction.

Receptor activator of nuclear factor kappaB ligand and osteoprotegerin regulation of bone remodeling in health and disease

Osteoclasts and osteoblasts dictate skeletal mass, structure, and strength via their respective roles in resorbing and forming bone. Bone remodeling is a spatially coordinated lifelong process whereby old bone is removed by osteoclasts and replaced by bone-forming osteoblasts. The refilling of resorption cavities is incomplete in many pathological states, which leads to a net loss of bone mass with each remodeling cycle. Postmenopausal osteoporosis and other conditions are associated with an increased rate of bone remodeling, which leads to accelerated bone loss and increased risk of fracture. Bone resorption is dependent on a cytokine known as RANKL (receptor activator of nuclear factor kappaB ligand), a TNF family member that is essential for osteoclast formation, activity, and survival in normal and pathological states of bone remodeling. The catabolic effects of RANKL are prevented by osteoprotegerin (OPG), a TNF receptor family member that binds RANKL and thereby prevents activation of its single cognate receptor called RANK. Osteoclast activity is likely to depend, at least in part, on the relative balance of RANKL and OPG. Studies in numerous animal models of bone disease show that RANKL inhibition leads to marked suppression of bone resorption and increases in cortical and cancellous bone volume, density, and strength. RANKL inhibitors also prevent focal bone loss that occurs in animal models of rheumatoid arthritis and bone metastasis. Clinical trials are exploring the effects of denosumab, a fully human anti-RANKL antibody, on bone loss in patients with osteoporosis, bone metastasis, myeloma, and rheumatoid arthritis.

Adynamic bone in patients with chronic kidney disease

Adynamic bone in patients with chronic kidney disease (CKD) is a clinical concern because of its potential increased risk for fracture and cardiovascular disease (CVD). Prevalence rates for adynamic bone are reportedly increased, although the variance for its prevalence and incidence is large. Differences in its prevalence are largely attributed to classification and population differences, the latter of which constitutes divergent groups of elderly patients having diabetes and other comorbidities that are prone to low bone formation. Most patients have vitamin D deficiency and the active form, 1,25-dihydroxyvitamin D, invariably decreases to very low levels during CKD progression. Fortunately, therapy with vitamin D receptor activators (VDRAs) appears to be useful in preventing bone loss, in part, by its effect to stimulate bone formation and in decreasing CVD morbidity, and should be considered as essential therapy regardless of bone turnover status. Future studies will depend on assessing cardiovascular outcomes to determine whether the risk/reward profile for complications related to VDRA and CKD is tolerable.

Over-suppression of bone turnover: does it exist?

Bone-turnover suppression is central to the therapeutic benefit of many interventions used to prevent osteoporotic fractures. There are theoretical concerns that long-term suppression may have adverse effects on bone strength, although at present no direct evidence exists that this happens. Nevertheless, further research is required to establish the optimal duration of treatment with antiresorptive agents.