Osteoprotegerin

Serum osteoprotegerin level in hemodialysis patients using low-flux reused dialyzer in relation to atherosclerosis

AIMS

To assess the relation of high serum OPG level and carotid atherosclerosis in maintenance hemodialysis (MHD) patients using low-flux reused dialyzer.

MATERIALS AND METHODS

We examined 209 MHD patients with and without carotid atherosclerosis (83 patients and 126 patients) to establish the relation between OPG and atherosclerosis.

RESULTS

The proportion of carotid atherosclerosis was 39.7%. The median serum OPG level was 45.3 pmol/L. Serum OPG had a good predicting value for atherosclerosis in MHD patients using low-flux reused dialyzer (AUC = 0.934, p < 0.001, cutoff value = 43.35 pmol/L, Se = 81.3%, Sp = 90.9%).

CONCLUSIONS

In this study, serum OPG had a good predicting value for atherosclerosis in MHD patients using low-flux reused dialyzer.

Myeloma Bone Disease: A Comprehensive Review

Multiple myeloma (MM) is a neoplastic clonal proliferation of plasma cells in the bone marrow microenvironment, characterized by overproduction of heavy- and light-chain monoclonal proteins (M-protein). These proteins are mainly found in the serum and/or urine. Reduction in normal gammaglobulins (immunoparesis) leads to an increased risk of infection. The primary site of origin is the bone marrow for nearly all patients affected by MM with disseminated marrow involvement in most cases. MM is known to involve bones and result in myeloma bone disease. Osteolytic lesions are seen in 80% of patients with MM which are complicated frequently by skeletal-related events (SRE) such as hypercalcemia, bone pain, pathological fractures, vertebral collapse, and spinal cord compression. These deteriorate the patient's quality of life and affect the overall survival of the patient. The underlying pathogenesis of myeloma bone disease involves uncoupling of the bone remodeling processes. Interaction of myeloma cells with the bone marrow microenvironment promotes the release of many biochemical markers including osteoclast activating factors and osteoblast inhibitory factors. Elevated levels of osteoclast activating factors such as RANK/RANKL/OPG, MIP-1-α., TNF-α, IL-3, IL-6, and IL-11 increase bone resorption by osteoclast stimulation, differentiation, and maturation, whereas osteoblast inhibitory factors such as the Wnt/DKK1 pathway, secreted frizzle related protein-2, and runt-related transcription factor 2 inhibit osteoblast differentiation and formation leading to decreased bone formation. These biochemical factors also help in development and utilization of appropriate anti-myeloma treatments in myeloma patients. This review article summarizes the pathophysiology and the recent developments of abnormal bone remodeling in MM, while reviewing various approved and potential treatments for myeloma bone disease.

Mesenchymal stem cells expressing osteoprotegerin variants inhibit osteolysis in a murine model of multiple myeloma

The current treatment options for multiple myeloma (MM) osteolytic lesions are mainly combinations of chemotherapy and other small-molecule inhibitors, but toxic side effects still remain a major concern. Studies have shown that osteoclast activity is enhanced in MM patients through increased expression of receptor activator of nuclear factor κB ligand (RANKL), triggering RANK signaling on osteoclast precursors, which results in aggressive bone resorption. Furthermore, osteoprotegerin (OPG), a decoy receptor for RANKL, and the osteogenic potential of mesenchymal stem cells (MSCs) are significantly decreased in myeloma patients with multiple bone lesions. Thus, the use of OPG as a therapeutic molecule would greatly decrease osteolytic damage and reduce morbidity. However, in addition to inhibiting osteoclast activation, OPG binds to tumor necrosis factor-related apoptosis-inducing ligand (TRAIL), thereby rendering the tumor cells resistant to TRAIL-induced apoptosis and limiting the use of OPG for therapy. The present study developed a bone-disseminated myeloma disease model in mouse and successfully tested a cell therapy approach using MSCs, genetically engineered to express OPG variants that retain the capacity to bind RANKL, but do not bind TRAIL. Our results of skeletal remodeling following this regenerative stem cell therapy with OPG variants indicated a significant protection against myeloma-induced osteolytic bone damage in areas of major myeloma skeletal dissemination, suggesting the potential of this therapy for treating osteolytic damage in myeloma patients.

Bone disease in multiple myeloma: pathophysiology and management

Myeloma bone disease (MBD) is a devastating complication of multiple myeloma (MM). More than 80% of MM patients suffer from destructive bony lesions, leading to pain, fractures, mobility issues, and neurological deficits. MBD is not only a main cause of disability and morbidity in MM patients but also increases the cost of management. Bone destruction and lack of bone formation are main factors in the development of MBD. Some novel factors are found to be involved in the pathogenesis of MBD, eg, receptor activator of nuclear factor kappa-B ligand (RANKL), osteoprotegerin (OPG) system (RANKL/OPG), Wingless (Wnt), dickkopf-1 (Wnt/DKK1) pathway. The addition of novel agents in the treatment of MM, use of bisphosphonates and other supportive modalities such as radiotherapy, vertebroplasty/kyphoplasty, and surgical interventions, all have significant roles in the treatment of MBD. This review provides an overview on the pathophysiology and management of MBD.

Effect of breastfeeding on serum osteoprotegerin and soluble receptor activator of nuclear factor-kappa B ligand in full term neonates

Background

Human breast milk, the sole source of nutrition during the early neonatal period, is rich in nutrients, hormones, growth factors, and immunoactive molecules, which influence the growth, development, and immune status of the newborn infant. It had long been thought that breast milk is an adequate source of anthracitic activity for the newborns and growing child.

Objective

Human milk is a complex biologic fluid which contains nutritional and protective factors such as Osteoprotegerin (OPG), at levels 1000-fold higher than normal human serum. Since OPG and Receptor activator of nuclear factor-kappa B ligand (RANKL) system are tightly involved in bone remodeling and immune activity, the study was designated to evaluate the effect of breastfeeding on serum soluble receptor activator of nuclear factor-kappa B ligand (sRANKL) /OPG ratio in full term neonates in comparison with those of formula feeding full term neonates.

Materials and Methods

In this cross-sectional study serum levels of OPG and sRANKL in 45 breastfed infants were compared to those of 44 formula-fed full term infants. The levels of serum OPG, sRANKL, and Tumor necrosis factor alpha (TNFα) were determined by standard techniques using enzyme-linked immunosorbent assay kits.

Results

The serum levels of OPG were significantly higher (P < 0.001), and the concentrations of TNFα was markedly lower (P = 0.024) in breastfed infants than those of formula-fed infants. No marked differences were observed between the serum levels of sRANKL in the two study groups (P = 0.8).

Conclusions

High OPG and low TNFα levels in serum of breastfed infants are important factors involved in remodeling of bone, and immune activity may prove superiority of breastfeeding over formula feeding during infancy.

The deep-sea natural products, biogenic polyphosphate (Bio-PolyP) and biogenic silica (Bio-Silica), as biomimetic scaffolds for bone tissue engineering: fabrication of a morphogenetically-active polymer

Bone defects in human, caused by fractures/nonunions or trauma, gain increasing impact and have become a medical challenge in the present-day aging population. Frequently, those fractures require surgical intervention which ideally relies on autografts or suboptimally on allografts. Therefore, it is pressing and likewise challenging to develop bone substitution materials to heal bone defects. During the differentiation of osteoblasts from their mesenchymal progenitor/stem cells and of osteoclasts from their hemopoietic precursor cells, a lineage-specific release of growth factors and a trans-lineage homeostatic cross-talk via signaling molecules take place. Hence, the major hurdle is to fabricate a template that is functioning in a way mimicking the morphogenetic, inductive role(s) of the native extracellular matrix. In the last few years, two naturally occurring polymers that are produced by deep-sea sponges, the biogenic polyphosphate (bio-polyP) and biogenic silica (bio-silica) have also been identified as promoting morphogenetic on both osteoblasts and osteoclasts. These polymers elicit cytokines that affect bone mineralization (hydroxyapatite formation). In this manner, bio-silica and bio-polyP cause an increased release of BMP-2, the key mediator activating the anabolic arm of the hydroxyapatite forming cells, and of RANKL. In addition, bio-polyP inhibits the progression of the pre-osteoclasts to functionally active osteoclasts. Based on these findings, new bioinspired strategies for the fabrication of bone biomimetic templates have been developed applying 3D-printing techniques. Finally, a strategy is outlined by which these two morphogenetically active polymers might be used to develop a novel functionally active polymer.

Role of RANKL-RANK/osteoprotegerin molecular complex in bone remodeling and its immunopathologic implications

Bone remodeling is a cyclic and continuous physiological process, which ensures the conservation and renewal of the bone matrix. Osteosynthesis of the bone matrix is achieved by osteoblasts and coordinated within this complex machinery of bone remodeling with resorption of extracellular bone matrix performed by osteoclasts. The mismatch between the activities of osteoblasts and osteoclasts has immunopathologic implications associated with either a decrease or increase of bone mass mineral density. The balance of the trimolecular control factor complex composed of osteoprotegerin (OPG), RANKL (osteoprotegerin ligand) and RANK maintains physiologic bone remodeling. This trimolecular complex functions as receptors and ligands and belongs to the superfamily of tumor necrosis factor (TNF). This mini review highlights the complex interplay of the RANKL-RANK/OPG axis and their immunopathologic implications in clinical medicine.