Weight-loss drugs may harm developing brain: study

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

Mark Bear and colleagues at the Massachusetts Institute of
Technology studied the effects of a chemical that suppresses
appetite by blocking cannabinoid receptors in the brain, the
same brain mechanisms that make people hungry when they smoke
marijuana.

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

Sanofi-Aventis' weight-loss pill rimonabant, also known as
Zimulti and sold under the brand name Acomplia in Europe, is
the first in this new class of drugs. A U.S. expert panel
rejected it last June because of fears it might trigger
suicidal thoughts.

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

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

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

They were specifically testing learning in the visual
cortex of the mouse, a part of the brain that processes
information gathered from what they see.

ADAPTING TO CHANGE

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

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

When they gave the mice AM 251 to block their cannabinoid
receptors, 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 cortical
plasticity in juvenile mice treated with AM 251 suggests
caution is advised in the use of such compounds in children,"
the researchers wrote.

Bear said the finding is similar to the situation with many
drugs.

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

Sanofi-Aventis spokeswoman Julissa Viana said rimonabant is
not approved for use in children.

"At this point in time it is approved for use in adults who
are overweight and obese with cardiovascular risk factors," she
said. "We don't encourage its use in children and it has not
been studied nor is it indicated for use in children."

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

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

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