Neale Weitzmann and George Beck have been publishing a series of papers describingÂ how silica nanoparticles can increase bone mineral density in animals. Their findings could someday form the basis for a treatment for osteoporosis.
In 2012, we posted an article and video on this topic. We wanted to call attention to a few of theÂ team’sÂ recent papers, one of which probes the mechanism for aÂ remarkable phenomenon: how can very fine silica particles stimulate bone formation?
The particlesâ€™ properties seem to depend on their size: 50 nanometers wide â€“ smaller than a HIV or influenza vision.Â In a 2014 ACS Nano paper, Beck, Weitzmann and postdoc Shin-Woo Ha show that the particles interact with particular proteins involved in the process of autophagy, a process of â€œself digestionâ€ induced by stress.
â€œThese studies suggest that it is not the material per se that stimulates autophagy but rather size or shape,â€ they write. Read more
In the laboratory, the nanoparticles stimulate the generation of bone-forming osteoblasts and inhibit the maturation of bone-remodeling osteoclasts. Beck says that the particlesâ€™ properties seem to depend on their size (50 nanometers wide) and shape, because larger particles donâ€™t have the same effects.Â The nanoparticles appear to work by being taken up by the cells and then by inhibiting NF-kB, a molecule that controls inflammation.
Silicon is a trace element in the diet of most people. Scientists have known for several years that dietary silicon is linked to strong bones, but how silicon influences bone growth has remained unclear: it could become physically incorporated into bone, or it could provide signals to the cells that make up bone. To be sure, silica nanoparticles may be acting in a way that is different than dietary silicon.
The particlesâ€™ ability to stimulate osteoblasts distinguish them from bisphosphonates, the most common drugs now used to treat osteoporosis, Beck says. Bisphosphonates only inhibit bone breakdown and do not stimulate bone formation.
The Emory team has found that injecting silica nanoparticles can increase the bone density of young mice by roughly 15 percent over six weeks, augmenting the increases coming from adolescent growth.
To test the particlesâ€™ potential for use with humans, the researchers are examining whether injection is the best way to deliver the nanoparticles, and whether long-term toxicity is an issue.Â Inhalation of larger particles of silica dust, an occupational hazard for miners and construction workers, can result in the lung disease silicosis. However, silicosis arises because the lungs can’t absorb and remove the larger dust particles. Since cells clearly can take up the nanoparticles (see video), it is possible that they will not induce the body to respond similarly.
Emory has applied for patents on this technology. A presentation by Emoryâ€™s Office of Technology Transfer is available here.