Diet hormone makes mice thin, but not humans

Research suggests hopes of obesity cure were premature. Steve Connor reports

The first research on humans into an ''anti-obesity'' hormone that makes mice lose weight indicates that it fails to work on people, contrary to expectations that led to shares in one biotechnology company to soar last week.

A clinical study of obese and slim volunteers found that fat people had more than 70 per cent more anti-obesity or ''ob'' hormone than thin people. This suggests that the hormone could not be working to rid the body of fat, as was shown to be the case in research on mice carrying a specific defect in the ob gene.

The new research, published in the Journal of Clinical Investigation, runs directly counter to claims made by Amgen, a California biotechnology company, that genetically engineered versions of the ob hormone could be used as a treatment for obesity within four years. Last week, when details of three investigations into the ob hormone in mice were leaked to Wall Street, shares in Amgen rose by 10 per cent.

Amgen has a $20m (pounds 12.5m) licence to exploit the technology from Rockefeller University in New York, which last week said that the mice research into the ob hormone showed that it regulated weight by acting as a signal for the amount of body fat.

However, this is not what scientists at the Thomas Jefferson University in Pennsylvania have found. Because obese people have significantly higher levels of the ob hormone in their bodies than slim people, they suggest the ''defect in human obesity lies elsewhere''.

They said it has yet to be proved that the ob protein in humans influences appetite. But even if this were the case, they postulate three possibilities for why it does not seem to work in obese people. They suggest:

t The ob hormone is unable to work in fat people because it fails to bind with its receptor protein, which triggers the anti-obesity measures observed in the mouse, such as lower appetite and higher metabolism.

t The hormone is present in large quantities in fat people but is somehow degraded before it has time to act.

t The hormone is not itself a regulator of body fat but signals the release of another, yet unidentified, hormone which is defective in fat people.

The scientists emphasise that these possibilities rely on the ob protein being involved in controlling the human appetite.

in some way.