IL-17 mediates estrogen-deficient osteoporosis in an Act1-dependent manner

Authors

Carl J. DeSelm, Yoshifumi Takahata, Julia Warren, Jean C. Chappel, Taimur Khan, Xiaoxia Li, Caini Liu, Yongwon Choi, Youngmi Faith Kim, Wei Zou, Steven L. Teitelbaum

Abstract

Estrogen-deficient osteoporosis may be an inflammatory disorder and we therefore asked if IL-17 participates in its pathogenesis. Deletion of the principal IL-17 receptor (IL-17RA) protects mice from ovariectomy (OVX)-induced bone loss. Further supporting a central role of IL-17 in its pathogenesis, OVX-induced osteoporosis is prevented by a blocking antibody targeting the cytokine. IL-17 promotes osteoclastogenesis by stimulating RANK ligand (RANKL) expression by osteoblastic cells, mediated by the IL-17RA SEFIR/TILL domain. Estrogen deprivation, however does not enhance IL-17RA mRNA expression by osteoblasts or in bone, but augments that of Act1, an IL17RA-interacting protein and signaling mediator. Similar to IL-17RA-/- mice, those lacking Act1 are protected from OVX-induced bone loss. Also mirroring IL-17RA-deficiency, absence of Act1 in osteoblasts, but not osteoclasts, impairs osteoclastogenesis via dampened RANKL expression. Transduction of WT Act1 into Act1-/- osteoblasts substantially rescues their osteoclastogenic capacity. The same construct, however, lacking its E3 ligase U-box or its SEFIR domain, which interacts with its counterpart in IL-17RA, fails to do so. Estrogen deprivation, therefore, promotes RANKL expression and bone resorption in association with upregualtion of the IL-17 effector, Act1, supporting the concept that post-menopausal osteoporosis is a disorder of innate immunity.

Link to Article

http://dx.doi.org/10.1002/jcb.24165

Oral bone loss induced by mineral deficiency in a rat model: Effect of a synthetic bone mineral (SBM) preparation

Authors

Dindo Mijares, Anupama Kulkarni, Kanthi Lewis, Fang Yao, Qing Xi, Samar Tannous, Renata Dias, Racquel Z. LeGeros

Abstract

Osteoporosis affects the craniofacial and oral structures and has been associated with periodontal bone loss, tooth loss and reduced jaw bone mass. This study aimed to test the therapeutic efficacy of synthetic bone mineral (SBM) in minimizing alveolar bone loss induced by mineral deficiency in a rat model. SBM consists of a calcium carbonate apatite (similar to bone apatite) matrix incorporating magnesium, zinc, and fluoride ions. Thirty female Sprague Dawley rats (2 months old) were randomly distributed into 3 groups (10 rats per group): GA (control), on basic diet; GB, on mineral deficient (MD) diet; and GC, on MD + SBM. The rats were sacrificed after 3 months, the jawbones were isolated and the soft tissues removed. Bone density was determined using X-ray radiography (Faxitron); mandibular cortical width, panoramic mandibular index, and alveolar resorption degree (M/M ratio) using BioquantOsteo; and bone micro-architecture micro-computed tomography and scanning electron microscopy. Compared to control (GA), the rats on MD diet (GB) experienced significant mandibular bone loss while the rats on MD + SBM diet (GC) experienced significantly less bone loss compared to the GB group. SBM, administered orally, may have the potential as an osteoporosis therapeutic agent in minimizing or preventing alveolar bone loss induced by mineral deficiency.

Link to Article

http://dx.doi.org/10.1016/j.archoralbio.2012.02.021

Bisphosphonate Binding Affinity Affects Drug Distribution in Both Intracortical and Trabecular Bone of Rabbits

Authors

John Turek, F. Hal Ebetino, Mark W. Lundy, Shuting Sun, Boris A. Kashemirov, Charles E. McKenna, Maxime A. Gallant, Lilian I. Plotkin, Teresita Bellido and Xuchen Duan, et al.

Abstract

Differences in the binding affinities of bisphosphonates for bone mineral have been proposed to determine their localizations and duration of action within bone. The main objective of this study was to test the hypothesis that mineral binding affinity affects bisphosphonate distribution at the basic multicellular unit (BMU) level within both cortical and cancellous bone. To accomplish this objective, skeletally mature female rabbits (n = 8) were injected simultaneously with both low- and high-affinity bisphosphonate analogs bound to different fluorophores. Skeletal distribution was assessed in the rib, tibia, and vertebra using confocal microscopy. The staining intensity ratio between osteocytes contained within the cement line of newly formed rib osteons or within the reversal line of hemiosteons in vertebral trabeculae compared to osteocytes outside the cement/reversal line was greater for the high-affinity compared to the low-affinity compound. This indicates that the low-affinity compound distributes more equally across the cement/reversal line compared to a high-affinity compound, which concentrates mostly near surfaces. These data, from an animal model that undergoes intracortical remodeling similar to humans, demonstrate that the affinity of bisphosphonates for the bone determines the reach of the drugs in both cortical and cancellous bone.

Link to Article

http://dx.doi.org/10.1007/s00223-012-9570-0

Chronic hyponatremia exacerbates multiple manifestations of senescence in male rats

Authors

Julia Barsony, Michaele B. Manigrasso, Qin Xu, Helen Tam and Joseph G. Verbalis

Abstract

The syndrome of inappropriate antidiuretic hormone secretion (SIADH) is frequently responsible for chronic hyponatremia in the elderly due to age-related disruption of the inhibitory component of brain osmoregulatory mechanisms. Recent research has indicated that chronic hyponatremia is associated with gait disturbances, increased falls, and bone fragility in humans, and we have found that chronic hyponatremia causes increased bone resorption and reduced bone mineral density in young rats. In this study, we used a model of SIADH to study multi-organ consequences of chronic hyponatremia in aged rats. Sustained hyponatremia for 18 weeks caused progressive reduction of bone mineral density by DXA and decreased bone ash calcium, phosphate and sodium contents at the tibia and lumbar vertebrae. Administration of 10-fold higher vitamin D during the last 8 weeks of the study compensated for the reduction in bone formation and halted bone loss. Hyponatremic rats developed hypogonadism, as indicated by slightly lower serum testosterone and higher serum FSH and LH concentrations, markedly decreased testicular weight, and abnormal testicular histology. Aged hyponatremic rats also manifested decreased body fat, skeletal muscle sarcopenia by densitometry, and cardiomyopathy manifested as increased heart weight and perivascular and interstitial fibrosis by histology. These findings are consistent with recent results in cultured osteoclastic cells, indicating that low extracellular sodium concentrations increased oxidative stress, thereby potentially exacerbating multiple manifestations of senescence. Future prospective studies in patients with SIADH may indicate whether these multi-organ age-related comorbidities may potentially contribute to the observed increased incidence of fractures and mortality in this population.

Link to Article

http://dx.doi.org/10.1007/s11357-011-9347-9

GSK-3 inhibition by an orally active small molecule increases bone mass in rats

Authors

Richard Marsell, Gregor Sisask, Yvonne Nilsson, Anna K. Sundgren-Andersson, Ulf Andersson, Sune Larsson, Olle Nilsson, Östen Ljunggren, Kenneth B. Jonsson

Abstract

Glycogen synthase kinase 3β (GSK-3β) actions are central in the canonical Wnt pathway, important in many biological processes and a potential drug target for treating several diseases. It is appreciated that a balanced Wnt canonical signaling is crucial for the maintenance of normal bone mass. In this study we investigated the effects of a potent orally active GSK-3 inhibitor, AZD2858, on bone mass in rats. Treatment (1 μM) of human osteoblast cells with AZD2858 in vitro increased β-catenin levels after a short period of time. In rats, oral AZD2858 treatment caused a dose-dependent increase in trabecular bone mass compared to control after a two-week treatment with a maximum effect at a dose of 20 mg/kg once daily (total BMC: 172% of control; p < 0.001). A small but significant effect was also seen at cortical sites (total BMC: 111% of control; p < 0.001). Biomechanical testing demonstrated an increase in both vertebral compression strength at a dose of 20 mg/kg once daily (Load at failure: 370% of control, p < 0.001) and diaphyseal strength of femora subjected to a three point bending test (Load at failure: 115% of control; p < 0.01). Furthermore, histomorphometry showed a dramatic increase in bone formation indices, and serum markers of both bone formation (Osteocalcin, 146% of control; p < 0.001) and resorption (CTX, 189% of control; p < 0.001) were elevated. Our conclusion is that a GSK-3 inhibitor drug may prove effective as an anabolic strategy in the treatment of diseases characterized by low bone mass, since AZD2858 has extensive bone building effects at predominantly trabecular sites.

Link to Article

http://dx.doi.org/10.1016/j.bone.2011.11.007

Odanacatib treatment increases hip bone mass and cortical thickness by preserving endocortical bone formation and stimulating periosteal bone formation in the ovariectomized adult rhesus monkey

Authors

T. Cusick, C.M. Chen, B.L. Pennypacker, M. Pickarski, D. Kimmel, B.B. Scott, L.T. Duong

Abstract

Odanacatib (ODN) is a selective and reversible inhibitor of cathepsin K (CatK). Previously, ODN was shown to increase bone mineral density (BMD) and maintained normal bone strength at the spine in ovariectomized (OVX) rhesus monkey. Here, we further characterize the effects of ODN on BMD, bone strength and dynamic histomorphometric analyses of the hip from the same monkeys. Animals were treated for 21-months with vehicle, 6 or 30mg/kg ODN (p.o., q.d.). ODN increased hip BMD by 11% and 15% (p < 0.01), and ultimate load by 17% (p < 0.05) and 19% (p < 0.01) versus vehicle. Treatment-related increases in ultimate load positively correlated with the increased femoral neck (FN) BMD, BMC and cortical thickness. Histomorphometry of FN and proximal femur (PF) revealed that ODN reduced trabecular and intracortical bone formation rate (BFR), but did not affect long-term endocortical BFR Moreover, ODN stimulated long-term FN and PF periosteal BFR by 3.5- and 6-fold with the 30mg/kg dose versus vehicle, respectively. Osteoclast surfaces were either unaffected or trended higher (∼2-fold) in endocortical and trabecular surfaces in the ODN group. Lastly, ODN increased cortical thickness of FN by 21% (p = 0.08) and PF by 19% (p < 0.05) versus vehicle after 21-months of treatment. Together, both doses of ODN increased bone mass and improved bone strength at the hip. Unlike conventional antiresorptives, ODN displayed site specific effects on trabecular versus cortical bone formation. The drug provided marked increases in periosteal bone formation and cortical thickness in OVX-monkeys, suggesting that CatK inhibition may represent a novel therapeutic approach for the treatment of osteoporosis.

Link to Article

http://dx.doi.org/0.1002/jbmr.1477