Weight-loss drugs may harm developing brain: study (Reuters)

CHICAGO (Reuters) - A drug from a new class of weight-losstreatments disrupted wiring needed for brain development inyoung mice, U.S. researchers said on Wednesday, raisingconcerns about using such medications in children.

Mark Bear and colleagues at the Massachusetts Institute ofTechnology studied the effects of a chemical that suppressesappetite by blocking cannabinoid receptors in the brain, thesame brain mechanisms that make people hungry when they smokemarijuana.

"I think that the cautionary note is that these mechanismsplay an important role in ... brain development," said Bear,whose study appears in the journal Neuron.

Sanofi-Aventis' weight-loss pill rimonabant, also known asZimulti and sold under the brand name Acomplia in Europe, isthe first in this new class of drugs. A U.S. expert panelrejected it last June because of fears it might triggersuicidal thoughts.

Other drugmakers, including Merck & Co Inc, are working onsimilar drugs.

Bear's team at MIT was hoping to gain insight into how thebrain adapts and rewires itself through learned experiences.This so-called plasticity is central to the development ofneurons in the brain of children and young animals.

Bear said these cannabinoid receptors are known to regulatesignals between neurons, and his team wanted to see if theywould have an effect on plasticity in these young mice.

They were specifically testing learning in the visualcortex of the mouse, a part of the brain that processesinformation gathered from what they see.

ADAPTING TO CHANGE

Their experiments tested how well the animals adapted ifone eye was closed.

The researchers did not use rimonabant in the study.Instead, they used a chemical analog or copy -- in this case adrug available for laboratory use known as AM 251.

When they gave the mice AM 251 to block their cannabinoidreceptors, the animals still behaved as if both eyes were open.This suggested the visual cortex was not adapting as it should.

"Our finding of a profound disruption of corticalplasticity in juvenile mice treated with AM 251 suggestscaution is advised in the use of such compounds in children,"the researchers wrote.

Bear said the finding is similar to the situation with manydrugs.

"You have to weigh the benefits against the risks. If thebenefit is related more to vanity than morbidity, I don't thinkthe risks are tolerable," he said.

Sanofi-Aventis spokeswoman Julissa Viana said rimonabant isnot approved for use in children.

"At this point in time it is approved for use in adults whoare overweight and obese with cardiovascular risk factors," shesaid. "We don't encourage its use in children and it has notbeen studied nor is it indicated for use in children."

The finding is the latest blow for rimonabant, which oncewas predicted to be a multibillion-dollar seller.

A study last month of the drug in obese heart patientsfound more than 40 percent of patients who took the drugdeveloped psychiatric problems.

But last month the drugmaker Sanofi said it still believesAcomplia can be a winner and reiterated plans to submit thedrug worldwide as a treatment for type 2 diabetes in 2009.

(Editing by Maggie Fox and Xavier Briand)