Bones that refuse to heal may one day be set straight by a drug that stimulatesthe growth of new blood vessels, according to new research from the University of California, San Francisco. So far, however, the growth factor drug has been tested only in mice, and it could be years before it is used in hospitals.
These results were presented at this week's annual meeting of the OrthopaedicResearch Society, in Orlando, Florida.
As cancer and cardiology researchers already know, VEGF, or vascularendothelial growth factor, promotes blood vessel growth. Oncologists at a fewbiotech companies are running clinical trials of anti-VEGF drugs to reduce theflow of blood to tumors. Cardiologists are studying whether VEGF can sproutnew blood vessels to bypass blocked arteries in patients with inoperable heartdisease.
Blood vessel growth, known as angiogenesis, is also thought to help deliver thechemicals needed for bone cells to rebuild after a fracture, says Jill Helms,PhD, DDS, assistant professor of orthopedic surgery at UCSF. "Vascularinvasion is one of the critical steps of bone repair," said Helms, whocollaborated with Zena Werb, PhD, a professor of anatomy at UCSF.
While most broken bones will repair to their original strength within a matterof weeks, some breaks stubbornly refuse to heal for months, years, or longer,she said. Scientists have suggested a few factors that may interfere with bonehealing, such as nutrition, illnesses such as diabetes, and damage to softtissue surrounding the bone. Helms and her colleagues suspected that softtissue damage interrupts proper blood flow to the fracture, and that proteinsthat encourage angiogenesis, such as VEGF, might help to heal these stubbornbreaks.
To test VEGF as a possible treatment, Helms' team worked with 20 mice withbroken limbs that were being treated with pain-relieving drugs. Aftersplinting the legs of these mice, the researchers shifted the splint each dayto a different position, a procedure that prevents healing growth of new bone,presumably by destroying the newly forming networks of blood vessels.
Manipulating these tiny splints consistently and accurately was a challengingtechnical feat, Helms said. "It requires people with great hands," she said,such as Diane Hu, MD, the staff specialist who perfected the technique.
After 10 days of this treatment, x-rays showed that only cartilage and otherfibrous cells grew in the gap, or interzone, between the pieces of brokenbone.
Helms and her colleagues then injected doses of VEGF into the interzones of 10broken mouse legs, and made sham injections to 10 others. After ten days ofsplint-shifting, the researchers could see osteoblasts, or bone growth cells,developing in interzones of the mice injected with VEGF. The sham-injectedmice still had only fibrous tissue growth. The VEGF-injected mice also hadmuch higher expression of the gene Cbfa1, which is thought to help stimulateformation of new osteoblasts.
Although more research is necessary, VEGF treatment could help to give a happyending to the tragic stories of patients who suffer from non-bony healing, saidTed Miclau, MD, an orthopedic surgeon who works in Helms' lab. "The fracturesthat tend not to heal are open fractures and those from high energy accidents,such as high speed auto, or pedestrian vs. auto accidents,' he said.
In addition to studying VEGF's role in bone healing, Helms' lab is examiningwhether it might also be important in embryonic bone growth. They have beguninjecting either VEGF or inhibitors of VEGF into the limbs of embryonicchickens as they develop in the egg. They will then examine the effects of toolittle or too much VEGF on skeletal development.
Other researchers collaborating on the project were UCSF orthopaedic surgeryresidents Mark Lee, MD, and Christian Oglivie, MD, post-doctoral fellow CelineColnot, PhD, and Thiennu Vu, MD, PhD, a UCSF assistant professor of medicine.
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