Tibolone is known to increase mineral density, a sign of bone strength, and to alleviate hot flashes and other menopausal symptoms. But doctors have worried that its tendency to reduce high-density lipoprotein, or "good" cholesterol, could result in heart vessel disease. The Wake Forest researchers found that even though tibolone lowered HDL by half, there was no increase in vessel disease. "Our results suggest that tibolone is a cardiovascular-safe treatment for menopausal symptoms as the prevention of osteoporosis," said Thomas Clarkson, D.V.M., professor of comparative medicine at Wake Forest and the study's lead researcher.
The two-year study of 150 postmenopausal monkeys compared two different doses of tribolone, estrogen (Premarin), and estrogen combined with progestin (PremPro). A fifth group of monkeys received no drug treatment. The monkeys received drug doses designed to approximate the levels women are normally prescribed. They were fed a moderately high-fat diet (42 percent of calories from fat) designed to speed up the development of vessel disease.
"We found that both Premarin and PremPro had a robust cardiovascular protective effect, but there was no such protective effect from tibolone," said Clarkson. "On the other hand, we found that tibolone may have advantages over Premarin and PremPro for breast and uterine safety."
Bone mineral density increased by 9.5 percent in the group receiving the high dose of tibolone, 4.5 percent in the PremPro group, and 4.3 percent in the Premarin group. PremPro and Premarin both reduced coronary atherosclerosis by 62 percent, while tiboline had no effect.
The Premarin and PremPro groups both had increased cell growth in the breasts and uterus, which can relate to cancer risk. "Women who are considering treatment for osteoporosis and menopausal symptoms have several options and must work with their doctors to weigh the benefits versus the risks of each," said Clarkson. "Our study is significant because it adds to the current knowledge about these choices."
Tibolone, which is considered an alternative to hormone replacement therapy for women concerned about breast cancer, is approved in 19 European countries for treating postmenopausal symptoms and preventing osteoporosis. It is under consideration by the U.S. Food and Drug Administration for approval.
Media Contacts: Karen Richardson, (336) 716-4453, krchrdsn@wfubmc.edu
The Journal of Clinical Endocrinology & Metabolism