Parathyroid Hormone Stimulates Bone Growth

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Parathyroid Hormone Stimulates Bone Growth

By Schorr

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 those making similar versions of the hormone, such as 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.