A once-a-day pill helped completely rebuild bone in rodents with severe osteoporosis, a finding that could lead to a new class of drugs to treat the brittle-bone disease in humans, US researchers said.

The team tested a compound that blocks the production of serotonin produced in the gut in mice and rats with a severe form of the disease and found they completely recovered their bone density.

'If you break the bone, it looks like a normal bone,' said Dr Gerard Karsenty of Columbia University Medical Center in New York, whose study appears in the journal Nature Medicine.

Using the findings, he said the team is working to develop this type of treatment for human patients with osteoporosis, in which bones become fragile and porous, increasing the risk of fracture.

'There is an urgent need to identify new, safe therapies that can increase bone formation on a long-term basis,' Karsenty said.

The study builds on prior research by the same team that found the chemical messenger serotonin -- when released by the gut -- inhibits bone formation.

Serotonin is most commonly known for its role in the brain as a chemical messenger but 95 percent of the serotonin in the body is produced in the gut as a way to regulate bone formation, Karsenty said in a telephone interview.   

'We thought that if we could inhibit the synthesis of serotonin in the gut, it could be a way to treat osteoporosis,' he said. 'Luckily for us, there are a couple of inhibitors of gut-derived serotonin that do not affect the synthesis of brain-derived serotonin.'    

The team tested a compound that blocks the production of serotonin in the gut in mice and rats with osteoporosis. 'Indeed, when you deprive the system of serotonin in the gut, consistent with the human genetic data, what you see in mice or rats is that you correct completely the osteoporosis,' Karsenty said.

He said the drug had already been tested in people in early safety studies. 'This molecule is given once a day orally. Obviously it is very attractive. There are very few molecules that can induce bone formation,' he said.

Karsenty said the findings were very preliminary and many more tests needed to be done before the drug can be tested in people with osteoporosis. - Reuters