Regulation of calcitonin receptor by glucocorticoid in human osteoclast-like cells prepared in vitro using receptor activator of nuclear factor-kappaB ligand and macrophage colony-stimulating factor

Stimulation of osteoclast formation and bone resorption by glucocorticoids: Synergistic interactions with the calcium regulating hormones parathyroid hormone and 1,25(OH)2-vitamin D3

Osteoporosis is a significant health problem, with skeletal fractures increasing morbidity and mortality. Excess glucocorticoids (GC) represents the leading cause of secondary osteoporosis. The first phase of glucocorticoid-induced osteoporosis is increased bone resorption. In this Chapter, in vitro studies of the direct glucocorticoid receptor (GR) mediated cellular effects of GC on osteoclasts to affect bone resorption and indirect effects on osteoblast lineage cells to increase the RANKL/OPG ratio and stimulate osteoclastogenesis and bone resorption are reviewed in detail, together with detailed descriptions of in vivo effects of GC in different portions of the skeleton in research animals and humans. Brief sections are devoted to contrasting functions of GC in osteonecrosis, vitamin D formation, in vitro and in vivo bone resorptive actions dependent on vitamin D receptor and vitamin D toxicity, as well as the molecular basis of GR action. Included are also more detailed assessments of the interactions of GC with the major calcium regulating hormones, 1,25(OH)₂-vitamin D3 and parathyroid hormone, describing the in vitro increases in RANKL/OPG ratios, osteoclastogenesis and synergistic bone resorption that occurs when GC is combined with either 1,25(OH)₂-vitamin D3 or parathyroid hormone. Additionally, a molecular basic for the synergistic interaction of GC with 1,25(OH)₂-vitamin D3 is provided along with a suggested molecular basic for the interaction between GC and parathyroid hormone.

What the Intensivists Need to Know About Critically Ill Myeloma Patients

Multiple myeloma (MM) is a hematological malignancy characterized by an increase in aberrant plasma cells in the bone marrow leading to rising monoclonal protein in serum and urine. With the introduction of novel therapies with manageable side effects, this incurable disease has evolved into a chronic disease with an acceptable quality of life for the majority of patients. Accordingly, management of acute complications is fundamental in reducing the morbidity and mortality in MM. MM emergencies include symptoms and signs related directly to the disease and/or to the treatment; many organs may be involved including, but not limited to, renal, cardiovascular, neurologic, hematologic, and infectious complications. This review will focus on the numerous approaches that are aimed at managing these complications.

Hypercalcemia and cancer: Differential diagnosis and treatment

Incidentally detected hypercalcemia usually presents in an indolent manner and is most likely caused by primary hyperparathyroidism. In contrast, hypercalcemia in the patient with a history of cancer presents in a wide range of clinical settings and may be severe enough to warrant hospitalization. This form of hypercalcemia is usually secondary to hypercalcemia of malignancy and can be fatal. Hypercalcemia of malignancy is most commonly mediated by tumoral production of parathyroid hormone-related protein or by cytokines activating osteoclast degradation of bone. The initial workup, differential diagnoses, confirmatory laboratory testing, imaging, and medical and surgical management of hypercalcemia are described in the patient with cancer.

Cancer-Related Hypercalcemia

Hypercalcemia has been reported to occur in up to 30% of patients who have a malignancy. Hypercalcemia is most common in those who have later-stage malignancies and predicts a poor prognosis for those with it. The most common causes include humoral hypercalcemia of malignancy mediated by parathyroid hormone–related peptide, osteolytic cytokine production, and excess 1,25-dihydroxy vitamin D production. However, the etiology is not always mediated by malignancy. Hypercalcemia can occur in those with malignancy and an additional etiology for hypercalcemia such as primary hyperparathyroidism or granulomatous diseases. This paper reviews the cancers associated with hypercalcemia and their proposed mechanisms, nontumor-mediated hypercalcemia, as well as diagnosis and treatment strategies for each condition.

Glucocorticoids mediate circadian timing in peripheral osteoclasts resulting in the circadian expression rhythm of osteoclast-related genes

Circadian rhythms are prevalent in bone metabolism. However, the molecular mechanisms involved are poorly understood. Recently, we suggested that output signals from the suprachiasmatic nucleus (SCN) are transmitted from the master circadian rhythm to peripheral osteoblasts through β-adrenergic and glucocorticoid signaling. In this study, we examined how the master circadian rhythm is transmitted to peripheral osteoclasts and the role of clock gene in osteoclast. Mice were maintained under 12-hour light/dark periods and sacrificed at Zeitgeber times 0, 4, 8, 12, 16 and 20. mRNA was extracted from femur (cancellous bone) and analyzed for the expression of osteoclast-related genes and clock genes. Osteoclast-related genes such as cathepsin K (CTSK) and nuclear factor of activated T-cells, cytoplasmic 1 (NFATc1) showed circadian rhythmicity like clock genes such as period 1 (PER1), PER2 and brain and muscle Arnt-like protein 1 (BMAL1). In an in vitro study, not β-agonist but glucocorticoid treatment remarkably synchronized clock and osteoclast-related genes in cultured osteoclasts. Chromatin immunoprecipitation (ChIP) assay showed the interaction between BMAL1 proteins and promoter region of CTSK and NFATc1. To examine whether endogenous glucocorticoids influence the osteoclast circadian rhythms, mice were adrenalectomized (ADX) and maintained under 12-hour light/dark periods at least two weeks before glucocorticoid injection. A glucocorticoid injection restarted the circadian expression of CTSK and NFATc1 in ADX mice. These results suggest that glucocorticoids mediate circadian timing to peripheral osteoclasts and osteoclast clock contributes to the circadian expression of osteoclast-related genes such as CTSK and NFATc1.

Bone marrow adipocytes support dexamethasone-induced osteoclast differentiation

The purpose of this study was to examine the ability of bone marrow adipocytes to support osteoclast differentiation in vitro. The primary bone marrow adipocytes were obtained from bone marrow fluid during prosthesis insertion. NFkappa-B ligand (RANKL), Osteoprotegerin (OPG), and macrophage colony stimulating factor (M-CSF) expressions in bone marrow adipocytes with or without dexamethasone were examined. In a co-culture system with bone marrow adipocytes and osteoclast precursor cells, osteoclast differentiation was assessed by the expression of titrate-resistant acid phosphatase (TRAP) staining. RANKL, OPG, and M-CSF mRNA expressions were confirmed in all individuals. Dexamethasone significantly induced RANKL and OPG expression. The RANKL/OPG ratio was increased by dexamethasone and was significant at 10(-7) M dexamethasone. With 10(-7) M dexamethasone, osteoclast precursor cells differentiated into multinucleated TRAP-positive cells when co-cultured with bone marrow adipocytes. The present study demonstrates for the first time that bone marrow adipocytes can support osteoclast differentiation in vitro.

Calcitonin and prednisolone display antagonistic actions on bone and have synergistic effects in experimental arthritis

We tested here the hypothesis that calcitonin and glucocorticoids, known to modulate bone metabolism, could have opposite actions on bone cells regulating expression of cytokine receptor activator of nuclear factor-kappaBeta ligand (RANKL) and osteoprotegerin (OPG). In the U2OS osteosarcoma cell line, calcitonin (10(-11) to 10(-9) mol/L) reduced RANKL and augmented OPG both at the mRNA and protein levels. Cell incubation with prednisolone (10(-8) to 10(-6) mol/L), the glucocorticoid chosen for this study, produced opposite results. These molecular studies prompted more functional analyses whereby osteoclast bone resorptive activity was determined. Calcitonin (10(-10) mol/L) abrogated the stimulating effect of 10 ng/ml RANKL or 10(-9) mol/L prednisolone; similar results were obtained with OPG. Assessment of calcitonin and prednisolone effects in an in vivo model of rheumatoid arthritis revealed partially surprising results. In fact, calcitonin not only preserved bone morphology (as assessed on day 18) in rats subjected to arthritis and treated with prednisolone (0.8 to 4 mg/kg daily from day 13) but also synergized with the steroid to elicit its antiarthritic effects. These results suggest that calcitonin could be used as a novel cotreatment to augment efficacy and reduce side effects associated with the prolonged use of steroids.

Modulation of osteoclastogenesis induced by nucleoside reverse transcriptase inhibitors

Osteopenia is a common and debilitating side-effect of HAART, yet little is known concerning the effects of HAART on bone metabolism. We reported previously that zidovudine (AZT) stimulates osteoclastogenesis in vitro and causes osteopenia in mice. Here, we confirmed that the AZT-induced osteoclastogenesis is dependent on RANKL in that osteoclastogenesis is blocked by osteoprotegestin. Alendronate, which is used for the treatment of osteopenia and osteoporosis, failed to inhibit AZT-induced osteoclastogenesis in vitro. Osteoclastogenesis in vitro was not affected by tumor necrosis factor-alpha. Two other NRTI drugs, ddl and 3TC, also induced osteoclastogenesis in vitro and induced osteopenia in mice. The osteopenia was associated with an elevation of parameters of osteoclasts, but not with osteoblasts. Combinations of the NRTIs did not result in additive or synergistic effects in vitro or in vivo. Finally, AZT induced osteoclastogenesis of human osteoclast precursors in a RANKL-dependent manner. This in vitro osteoclastogenesis assay using human peripheral blood mononuclear cells could be useful in evaluating bone turnover and the risk of developing osteopenia in AIDS patients on HAART.

Dexamethasone inhibits the formation of multinucleated osteoclastsvia down-regulation of β3 integrin expression

Although glucocorticoids are known to affect osteoclast differentiation and function, there have been conflicting reports about the effect of glucocorticoids on osteoclast formation, leading to the assumption that microenvironment and cell type influence their action. We explored the effect of the synthetic glucocorticoid analog dexamethasone on the formation of osteoclasts. Dexamethasone inhibited the formation of tartrate-resistant acid phosphatase (TRAP)-positive multinucleated osteoclasts without affecting the formation of TRAP-positive mononuclear cells in a coculture of mouse osteoblasts and bone marrow cells. Dexamethasone did not inhibit mRNA expression levels of the receptor activator of nuclear factor-kappaB ligand and osteoprotegerin, the essential regulators of osteoclastogenesis. Dexamethasone down-regulated the expression of beta3 integrin mRNA and protein but did not alter expression of other osteoclast differentiation marker genes. Both dexamethasone and echistatin, a beta3 integrin function blocker, inhibited TRAP-positive multinucleated osteoclast formation but not TRAP-positive mononuclear cell formation. These results suggest that dexamethasone inhibits the formation of multinucleated osteoclasts, at least in part, through the down-regulation of beta3 integrin, which plays an important role in the formation of multinucleated osteoclasts.

Calcitonin is involved in cartilage homeostasis: is calcitonin a treatment for OA?

OBJECTIVE

Osteoarthritis (OA) is the most common form of degenerative joint diseases and a major cause of disability and impaired quality of life in the elderly. Recent observations suggest that calcitonin may act on both osteoclasts and chondrocytes. The present review was sought to summarize emerging observations from the molecular level to the preliminary clinical findings of possible chondroprotective effects of calcitonin.

METHOD

This review summarizes peer-reviewed articles found using pre-defined search criteria and published in the PubMed database before January 2006. In addition, abstracts from the OsteoArthritis Research Society International (OARSI) conferences in the time period 2000-2005 have been included in the search.

RESULTS

Ample evidence for the effect of calcitonin on bone resorption was found. Support for direct effects of calcitonin on chondrocytes on matrix synthesis and inhibition of cartilage degradation have been published. In addition, clinical evidence for the effect of calcitonin on cartilage degradation is emerging.

CONCLUSION

Several independent lines of evidence suggest a direct chondroprotective effect of calcitonin in addition to the well-established effect on bone resorption. Given the currently limited availability of chondroprotective agents, much expectation regards the ongoing clinical assessment of calcitonin therapy for the prevention and treatment of OA.

Lactoferrin reduces in vitro osteoclast differentiation and resorbing activity

Lactoferrin (LF) is a key modulator of inflammatory response. Since bone and immune systems are genetically and functionally linked, we were interested to know if LF could influence bone remodeling. Bovine LF (bLF) inhibited in vitro bone resorbing activity (IC50, 200 microg/ml) in a rabbit mixed bone cell culture, consisting of authentic osteoclasts in an environment of osteoblast and stromal cells. Using human CD14 selected cells committed toward osteoclasts, bLF (10 microg/ml) stimulated cell proliferation, however, led to an inhibition of calcitonin receptor mRNA expression, a main marker of osteoclast phenotype, and decreased the global resorbing activity. No modulation of RANK mRNA expression was observed and mRNA for RANKL and OPG were not detected in this culture system, suggesting that bLF inhibits osteoclastogenesis and reduces bone resorption through a mechanism independent of OPG/RANKL/RANK. In conclusion, bLF appears to modulate bone remodeling. Its mechanism of action remains to be elucidated.

A novel zinc finger protein that inhibits osteoclastogenesis and the function of tumor necrosis factor receptor-associated factor 6

A variety of surface receptors eliciting diverse cellular responses have been shown to recruit tumor necrosis factor receptor-associated factor (TRAF) adaptor molecules. However, a few TRAF-interacting intracellular proteins that serve as downstream targets or regulators of TRAF function have been identified. In search of new intracellular molecules that bind TRAF6, we carried out a yeast two-hybrid cDNA library screening with an N-terminal segment of TRAF6 as the bait. A novel human C(2)H(2)-type zinc finger family protein was identified, which when coexpressed with TRAF6 led to a suppression of TRAF6-induced activation of NF-kappa B and c-Jun N-terminal kinase. This novel protein was designated TIZ (for TRAF6-inhibitory zinc finger protein). TIZ expression also inhibited the signaling of RANK (receptor activator of NF-kappa B), which together with TRAF6 has been shown to be essential for osteoclastogenesis. Furthermore, the expression level of TIZ appeared to be regulated during the differentiation of human peripheral blood monocytes into osteoclasts. More significantly, transfection of TIZ into the monocyte/macrophage cell line Raw264.7 reduced the RANK ligand-induced osteoclastogenesis of this cell line. Our findings suggest that the novel zinc finger protein TIZ may play a role during osteoclast differentiation by modulating TRAF6 signaling activity.