Teriparatide studies underscore bone strengthening power. (Anabolic Therapy for Osteoporosis).

HONOLULU -- New research unveiled at an international symposium sponsored by the National Osteoporosis Foundation emphasized the mechanistic differences between anabolic therapy and currently approved osteoporosis drugs, including bisphosphonates, all of which slow bone turnover and inhibit resorption.

The parathyroid hormone (PTH) teriparatide, which is awaiting Food and Drug Administration approval for the treatment of osteoporosis, actually increases bone turnover, but it does so in a manner that "uncouples" the normal relationship between resorption and bone formation, focusing its power on formation of stronger bone.

Subsequent changes in the microarchitecture of bone are so distinct with teriparatide that some researchers now "dare to dream" that osteoporotic bone may be capable of returning to normal levels of bone mineral density (BMD) and strength. The best hope with most previously available therapies is to stem rapid loss of bone, said Dr. John P. Bilezikian, chief of endocrinology and director of the metabolic bone diseases program at Columbia-Presbyterian Medical Center in New York City.

Specifically, teriparatide acts on cancellous bone, which is why bone density of the lumbar spine is dramatically increased in subjects taking the injected drug, while density in the cortical bone of the radius remains stable or even declines among treated subjects, he said.

The strengthening ability of PTH was highlighted in a separate presentation by David W. Dempster, Ph.D., professor of clinical pathology at Columbia University, New York, and director of the regional bone center at Helen Hayes Hospital in West Haverstraw, N.Y.

Microarchitecture of bone in patients receiving PTH exhibits a sevenfold thickening of trabeculae, which are horizontal struts that Dr. Dempster likened to the flying buttresses providing stability to structures such as Notre Dame Cathedral. Trabecular connectivity also increases with PTH, especially in conjunction with hormone replacement therapy he has shown.

Intriguingly, it now appears that parathyroid hormone's strengthening abilities extend to cortical bone as well as cancellous bone, even when bone mineral density remains unchanged or diminished, he said.