Researchers struggling with the limitations of current medications for osteoporosis may soon be out of the woods. Michigan Technological University biomedical engineer Seth Donohue has been trying to figure out why the bones of bears stay strong despite several months of hibernation each year. This amount of inactivity for humans would make our bones as frail as pretzel sticks.
By studying bear bones, Donohue's work could lead to new treatments for osteoporosis, the loss of bone density that comes with age. It's natural for bone to renew itself constantly — a cycle of bone resorption (decay) and formation. When our bones decay, cells called osteoclasts break down the bone and release the minerals inside. An imbalance in this cycle is the core mechanism for osteoporosis.
Most of today's drugs for this disease aim to prevent bone loss. But Donohue argues that it may be more effective to increase bone formation.
That's what hibernating black bears do. Donohue reported online in the Journal of Experimental Biology that while they do lose bone during hibernation, black bears grow new bone cells at an equal or faster rate. "And in fact their bending strength increases as a function of age, despite these annual periods of immobilization," Donohue says.
Analyzing blood samples from hibernating bears, he reported that levels of a hormone known to promote bone growth, called parathyroid hormone or PTH, actually increase during hibernation. He points to one study in people that found that a synthetic version of PTH increased bone mineral density in postmenopausal women.
Donohue says that since the black bear version of the PTH gene is different from humans, understanding how it works could lead to better ways to treat or prevent osteoporosis in people. "We could develop those hormones or other growth factors synthetically, and then this could be used for drug treatments for osteoporosis in humans," he says.
Donahue has synthesized the hormone in his lab and his next step is to sprinkle it on bone cells and watch for bone-forming activity.