A naturally occurring hormone that University of Pittsburgh researchers have developed as a treatment for osteoporosis shows promise in building weakened bones with minimal or no side effects.

Endocrinologists at the University of Pittsburgh School of Medicine and UPMC are seeking 105 participants with osteoporosis to test whether the new treatment, known as parathyroid hormone-related protein, or PTHrP, leads to bone formation and improves bone density in patients without bone breakdown known as resorption.

Dr. Mara J. Horwitz -- the principal investigator in the trial and assistant professor of medicine in the medical school's Division of Endocrinology and Metabolism -- said women who qualify to participate in the trial would be randomly assigned to take PTHrP or the approved drug, teriparatide, which builds bone density but also involves some bone breakdown.

The study is seeking post-menopausal, nonsmoking Caucasian, Hispanic and Asian women between 45 and 75 who haven't taken osteoporosis or estrogen-replacement medications for at least a year and have no recent history of bone fractures. For more information, call 412-864-3266.

Teriparatide, (brand name Forteo), is approved by the U.S. Food and Drug Administration as an osteoporosis treatment. The trial will determine whether teriparatide or the still experimental PTHrP can produce greater levels of bone formation in patients with osteoporosis, with minimal side effects.

PTHrP as a treatment was developed by Dr. Andrew F. Stewart, chief of the school of medicine's Division of Endocrinology and Metabolism.

In the early online version of the Journal of Clinical Endocrinology and Metabolism published Friday, Dr. Horwitz, Dr. Stewart and their colleagues determined the maximum tolerable dose levels of PTHrP. A previous Phase I study also showed that PTHrP produced increases in bone density of nearly 5 percent after only three months of treatment.

If the latest study supports those findings without bone breakdown and minimal side effects, PTHrP could emerge as a breakthrough treatment for osteoporosis.

"In looking for the next frontier for osteoporosis therapy, PTHrP, as an apparently pure anabolic agent, appears particularly promising," said Dr. Horwitz, who's also a practicing metabolic bone specialist at UPMC.

"It appears to stimulate bone formation and not bone breakdown," she said. "It is more of an anabolic agent, and when given as an injection, it appears to be protective to the bone."

Jill Ryan, spokeswoman for the National Osteoporosis Foundation, said it will not comment on any drug study until the drug receives full FDA approval. "Of course, NOF welcomes scientific research which improves the lives of all those affected by the disease, including new therapeutic options," Ms. Ryan said.

The foundation said osteoporosis involves "low bone mass and structural deterioration of bone tissue" that leads to "bone fragility and an increased susceptibility to fractures, especially of the hip, spine and wrist, although any bone can be affected."

Its Web site is www.nof.org.

"Osteoporosis is a condition in which the bones become weak and can break from a minor fall, or, in serious cases, from a simple action such as a sneeze," the foundation states.

Osteoporosis is a major health threat for about 44 million Americans, or 50 percent of people 50 years of age or older. While it's thought that 10 million already have the disease, another 34 million are estimated to have low bone mass, placing them at risk. Eighty percent of known cases involve women, the foundation states.

But the science behind osteoporosis and its treatments is complicated.

The parathyroid, an organ in the neck, uses parathyroid hormones directly and indirectly through vitamin D to regulate calcium levels in the blood in a complex process that also affects bone formation and breakdown.

The parathyroid hormone, or PTH, builds bone and breaks it down in what's described as bone turnover. When PTH levels go up in the body, it causes bone loss. But teriparatide, a formulation of PTH, actually stimulates greater bone formation when given in daily small-dose injections.

Other osteoporosis drugs, including alendronate (brand-name Fosamax) and raloxifence, decrease bone breakdown but do not promote bone formation.

African-American women are not included in the current trial because of differences in responses to parathyroid hormones that have yet to be well described, Dr. Horwitz said. While African-American women can get osteoporosis, their incidence rate is much lower than that of women of other races.

Participants in the trial will have a bone-density measurement done to determine whether the candidate has osteoporosis. The study will last three months with all participants receiving either teriparatide or PTHrP.

Dr. Horwitz said she expects results within two years.

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