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BETTER treatments for osteoporosis could become available in a few years.

Many people’s bones become weak as they age and their levels of oestrogen or
testosterone fall. The most common treatment is hormone replacement therapy, but
this can increases the risk of cancer. With some types of HRT, women are eight
times as likely to get womb cancer, for example.

Now Stavros Manolagas and Stavroula Kousteni at the University of Arkansas in
Little Rock have created forms of the sex hormones that will keep bone cells
alive but shouldn’t increase the cancer risk. This was made possible by their
discovery that oestrogen and testosterone can trigger more than one kind of
signal in cells.

It was known that when oestrogen binds to receptors in cells, it activates a
signal that changes the expression of genes. But the team found that in bone
cells, oestrogen can also trigger a signal telling the cells not to commit
suicide, prolonging their lives and keeping bone strong. This signal acts
directly rather than through gene expression and is much faster, taking minutes
rather than hours (Cell, vol 104, p 719).

The different signals come from different parts of the molecule, so the team
were able to develop a class of compounds that produce only the fast signal.
These drugs should not have undesirable side effects on the reproductive
system.

Rats given the new compound show up to a 70 per cent increase in bone
strength. Kousteni says it could even strengthen bones in healthy people. The
work could also lead to treatments for other hormone-related diseases.