Hibernating Bears Offer Clues to Osteoporosis
BY LAUREN UZDIENSKI, MARCH 24, 2008
Ever wonder how bears can hibernate without suffering from the softened, weakened bones that affect humans following periods of inactivity? Neither did we, until the Wall Street Journal (subscription required) brought it to our attention. The question occurred to nature-lover and biomedical engingeer Dr. Seth Donahue on a hike almost a decade ago, when he hypothesized that bears had a substance in their bones to help keep them strong during hibernation.
Rather more ornery than a lab rat, bears proved a challenge to study. Hibernating bears have to be anesthetized before a blood sample can be drawn, as the consequences of an awakened bear are potentially dire for both the company present and data itself. Thus Dr. Donahue began his work with only a few blood samples provided by a colleague at Virginia Tech. Later he collaborated with a researcher at Washington State University who was keeping a group of black bears for his own work on hibernation. This gave Dr. Donahue access to bears that had been raised in captivity, were comfortable around humans and were accustomed to lab tests.
Dr. Donahue found that bears did, in fact, experience bone deterioration during hibernation. But he also discovered that due to a unique ursine form of parathyroid hormone, bears replace bone faster than they would otherwise. Bear bone grows even faster when bears wake up in the spring.
Rebuilding bone lost to osteoporosis represents a unmet clinical need, as most drugs only slow bone deteroriation, not rebuild the bone. Eli Lilly does market the daily-injection treatment Forteo, a shortened version of the human parathyroid hormone, though it carries a black-box warning over cancer risks identified in rats. Dr. Donahue's research is a long way from human clinical applications, though he is working with Apjohn Group to commercialize the technology and animal-model studies are ongoing.
The Journal makes one point that surely came as a relief to Dr. Donahue and his team: the ursine parathyroid hormone gene has been sequenced and the substance can be produced synthetically, reducing the need for further bear-human interaction.
