Synthetic drug may provide an alternative to HRT treatment

A drug that can reverse the bone-loss caused by osteoporosis with few side-effects is being heralded as a possible substitute for conventional hormone replacement therapy.

Studies on laboratory mice published today show that a synthetic hormone called estren helps to build bone without affecting male or female reproductive organs.

The scientists, led by Stavros Manolagas of the University of Arkansas, said that if the same held true for humans, estren could be used instead of conventional HRT to help prevent osteoporosis.

"For a long time we have been giving hormone replacement to women, based in the evidence that oestrogens [female sex hormones] are effective in preventing osteoporosis," Dr Manolagas said. The "big assumption" was that oestrogens and progesterones – also female hormones – worked the same way in all tissues, he said.

However, evidence has emerged that while they build bone, the hormones may also slightly increase the risk of breast and uterine cancer by interacting with these tissues.

Four months ago, an American trial of HRT was stopped because scientists felt that the risks of cancer and other disorders associated with giving oestrogens outweighed the potential benefits. Yesterday, the Medical Research Council announced that a similar trial in Britain had been cancelled.

However the latest research, published in the journal Science, suggested that the synthetic estren could be a viable and safer alternative to the conventional hormone supplements used in HRT, the scientists said. "Our study shows that you can have the benefits [of oestrogen] on non-reproductive tissues without having the side effects," Dr Manolagas said.

Estren belongs to a class of compounds that mimic oestrogen in the way it triggers bone growth but differs in that it has no apparent effect on the genetic machinery of the reproductive tissues c – unlike the female sex hormones.

Experiments on male and female mice lacking either testes or ovaries – which produce the sex hormones – showed that estren builds bone without affecting the other organs and tissues such as the uterus in females or the male seminal vesicles – two small sacs attached to the prostate gland. Oestrogen, however, built bone as well as triggering the growth of the reproductive tissue, an observation which could signify a role in triggering the growth of cancer cells.