SAN FRANCISCO (MedscapeWire) Nov 13 — Human parathyroid hormone (1-34) (hPTH), a new drug treatment set to be approved by the US Food and Drug Administration early next year, restored vertebral bone mass — and potentially could reduce the risk of fractures — in postmenopausal women with glucocorticoid-induced osteoporosis, researchers reported here Monday at the 65th annual meeting of the American College of Rheumatology.

"This is the first time we're talking about potentially curing the disease," said lead author Qaiser Rehman, MD, a recent rheumatology fellow at the University of California at San Francisco.

The hormone will initially be approved for use by postmenopausal women suffering from primary osteoporosis. However, the researchers investigated whether hPTH would also restore bone density to women suffering premature bone loss as a result of taking glucocorticoids, such as prednisone, to combat chronic inflammatory disease.

Glucocorticoids are known to cause premature bone loss by suppressing the activity of osteoblasts. While other currently-approved therapies such as estrogen, biphosphonates, and selective estrogen-receptor modulators work by preventing reaborption of bone cells and slowing progression of bone loss, hPTH appears to be able to recreate bone mass by stimulating the osteoblasts.

"hPTH actually acts by acting on the osteoblasts to produce more bone and making the osteoblasts live longer," Rehman said. "We've known for decades that when given intermittently, hPTH actually increases bone mass. So it's interesting for us to look at what structural changes could be responsible for that significant decrease in the risk of fractures."

The researchers studied 51 postmenopausal women (average age, 62 years) with diagnosed osteoporosis who were being treated with glucocorticoids as well as taking estrogen replacement therapy to combat bone loss. The women had been receiving estrogen for an average of 14 years.

Twenty-eight of the women were randomly assigned to receive daily 40-mg injections of hPTH for a year, and the remaining 23 patients continued to receive only estrogen replacement therapy.

The women's spine and hip bone density were measured at baseline using the 2-dimensional dual x-ray absorptiometry (DXA) and a 3-dimensional quantitative computerized tomography (QCT). They were then reevaluated annually after their treatment for up to 2 years.

Rehman reported that women receiving hPTH demonstrated a statistically significant increase in the bone mineral density. After 1 year of treatment, the bone mass density of the spine increased by 11% in women receiving hPTH compared with 1.3% of the women receiving only estrogen.

Rehman noted there was a 5% increase in vertebral cross-sectional area measured by QCT scan and a 2.5% increase as measured by the DXA scan, both of which were statistically significant, he said.

Although previous studies have found that hPTH mainly increased trabecular bone mass, the more osteoblastic-active, inner area of the bone, in this study, hPTH seemed to stimulate corticol bone mass, the protective outer-area of the bone.

"This increase in bone is due to deposition of this new bone on the outside of the veterbrae, right below the periosteal — a thin layer that surrounds the bone," he said. "By showing this phenomenon, we have suggested that the increase in vertebral strength and the fall in risk of vertebral fracture could be ascribed to the increase in corticol bone mass and periosteal deposition."

Rehman said the study was funded by the National Institutes of Health and received no funding from any drug company, although hPTH will likely be tested more extensively for its ability to reduce fractures in populations such as these by its maker, Eli Lilly.

"The excitement about this drug is due to the magnitude of the increase in bone density," Rehman said. For example, the 12% increase in bone mass found with hPTH is higher than what is seen with bisphosphonates, he noted. Similarly, a recent New England Journal of Medicine study recently found that women using hPTH had a 70% reduction in veterbral fractures compared with the 50% reduction found in those using biphosphonates.