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Published on: June 8, 2014
A Novel, Direct NO Donor Regulates Osteoblast and Osteoclast Functions and Increases Bone Mass in Ovariectomized Mice
Hema Kalyanaraman1, Ghania Ramdani1, Jisha Joshua1
1Department of Medicine, University of California, San Diego, La Jolla, CA, USA.
Abstract:
Most US Food and Drug Administration (FDA)-approved treatments for osteoporosis target osteoclastic bone resorption. Only PTH derivatives improve bone formation, but they have drawbacks, and novel bone-anabolic agents are needed. Nitrates, which generate NO, improved BMD in estrogen-deficient rats and may improve bone formation markers and BMD in postmenopausal women. However, nitrates are limited by induction of oxidative stress and development of tolerance, and may increase cardiovascular mortality after long-term use. Here we studied nitrosyl-cobinamide (NO-Cbi), a novel, direct NO-releasing agent, in a mouse model of estrogen deficiency-induced osteoporosis. In murine primary osteoblasts, NO-Cbi increased intracellular cGMP, Wnt/β-catenin signaling, proliferation, and osteoblastic gene expression, and protected cells from apoptosis. Correspondingly, in intact and ovariectomized (OVX) female C57Bl/6 mice, NO-Cbi increased serum cGMP concentrations, bone formation, and osteoblastic gene expression, and in OVX mice, it prevented osteocyte apoptosis. NO-Cbi reduced osteoclasts in intact mice and prevented the known increase in osteoclasts in OVX mice, partially through a reduction in the RANKL/osteoprotegerin gene expression ratio, which regulates osteoclast differentiation, and partially through direct inhibition of osteoclast differentiation, observed in vitro in the presence of excess RANKL. The positive NO effects in osteoblasts were mediated by cGMP/protein kinase G (PKG), but some of the osteoclast-inhibitory effects appeared to be cGMP-independent. NO-Cbi increased trabecular bone mass in both intact and OVX mice, consistent with its in vitro effects on osteoblasts and osteoclasts. NO-Cbi is a novel direct NO-releasing agent that, in contrast to nitrates, does not generate oxygen radicals, and combines anabolic and antiresorptive effects in bone, making it an excellent candidate for treating osteoporosis. © 2016 American Society for Bone and Mineral Research.
Insights
Nitrosyl-cobinamide (NO-Cbi) is a novel agent that releases nitric oxide (NO) to treat osteoporosis. It promotes bone formation and reduces bone resorption by targeting osteoblasts and osteoclasts.
Area of Science:
- Bone Biology and Osteoporosis Research
- Pharmacology and Drug Discovery
- Endocrinology
Background:
- Current osteoporosis treatments primarily inhibit bone resorption, with limited options for stimulating bone formation.
- Parathyroid hormone (PTH) derivatives are anabolic but have limitations.
- Nitric oxide (NO) donors show potential for bone health, but traditional nitrates have safety concerns like oxidative stress and cardiovascular risks.
Purpose of the Study:
- To investigate the efficacy of nitrosyl-cobinamide (NO-Cbi), a novel direct NO-releasing agent, in a mouse model of estrogen deficiency-induced osteoporosis.
- To evaluate NO-Cbi's effects on osteoblast and osteoclast function, signaling pathways, and bone mass.
Main Methods:
- Primary murine osteoblasts were treated with NO-Cbi to assess effects on intracellular signaling (cGMP, Wnt/β-catenin), proliferation, gene expression, and apoptosis.
- Intact and ovariectomized (OVX) C57Bl/6 mice received NO-Cbi to measure serum cGMP, bone formation markers, gene expression, and bone microarchitecture.
- In vitro studies examined NO-Cbi's direct effects on osteoclast differentiation in the presence of RANKL.
Main Results:
- NO-Cbi increased osteoblast activity, including cGMP, Wnt/β-catenin signaling, proliferation, and osteoblastic gene expression, while protecting against apoptosis.
- In OVX mice, NO-Cbi prevented osteocyte apoptosis and increased bone formation and osteoblastic gene expression.
- NO-Cbi reduced osteoclast numbers in intact mice and prevented their increase in OVX mice, partly by modulating the RANKL/osteoprotegerin ratio and directly inhibiting osteoclast differentiation.
- NO-Cbi treatment led to increased trabecular bone mass in both intact and OVX mice.
Conclusions:
- NO-Cbi acts as a direct NO-releasing agent with both anabolic and antiresorptive properties for bone.
- Unlike nitrates, NO-Cbi does not generate oxygen radicals, offering a potentially safer profile.
- NO-Cbi's dual action on osteoblasts and osteoclasts makes it a promising therapeutic candidate for osteoporosis.
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