“The action against diabetes takes place in the pancreas,” explains Alexandre Caron, pharmacy researcher at Laval University. Ozempic mimics the action of a hormone, GLP-1, which is produced in response to a meal to stimulate insulin production. [une autre hormone qui facilite l’entrée des sucres dans nos cellules] in the pancreas.
“It increases insulin in the blood, and it reduces blood sugar [le taux de sucres sanguins, qui est anormalement élevée chez les diabétiques].»
We knew that GLP-1 and molecules that imitate it could slow down the transit of food through the digestive system, possibly also act on the brain, and thus, it was said, suppress hunger. But Mr. Caron and his team discovered that it went well beyond what was suspected. And in the process, they also identified new populations of neurons that were still unknown and which, we did not know, play an important role in the regulation of appetite.
Mr. Caron was interested in leptin, which is a hormone produced by our fat cells. “The more fat mass we have, the more leptin we produce, so it is a hormone that reduces appetite. This is the way of adipocytes [les cellules graisseuses] to say: we are full.
“But people who become obese become resistant to leptin. And the more leptin we produce, the less of it reaches the brain,” he explains, so that the satiety signal is weakened in them.
The drug Ozempic (Rocket Lavoie/The Daily)
This signal from our fat cells is picked up by a part of the brain called arcuate nucleus of the hypothalamus — a region located in the center of the skull. Except that we did not know which groups of neurons in the arcuate nucleus, exactly, were responsible for receiving leptin and suppressing hunger.
“Before the 2000s,” relates Mr. Caron, “we believed we were dealing with a system where there were only two populations of neurons in the arcuate nucleus: one which stimulated the appetite and the other which suppressed it. But from the 2000s, we started to realize that it was a lot more complex than that.” But we still didn't know which neurons were responsible for what.
Mr. Caron's team therefore started from “maps”, so to speak, of the neurons of the arcuate nucleus which had recently been published. These maps roughly listed the receptors on the surface of neurons, a kind of “antenna” that is made to capture specific hormones.
The researchers found that there weren't two different populations of neurons in there, but rather eight (!), three of which expressed a receptor they hadn't seen coming, a sort of surprise guest at their “hormone party”: the poetically named crabp1.
This crabp1 is a protein that plays a role in neuronal development in the embryo and which also seems to be involved in certain cancers, but that was about all we knew about it. “In adults, we didn’t really know its function,” says Mr. Caron.
However, it now seems that it contributes greatly to the regulation of appetite. In their study published last April in the medical journal Neuroendocrinologyin fact, Mr. Caron and his team fasted laboratory rats for an entire night before separating them into four groups: only one of the four was able to eat again in the morning, while the other three received either leptin, either liraglutide (essentially the same molecule that is in Ozempic against diabetes and Wegovy against obesity), or a placebo.
However, these four treatments produced quite different effects in crabp1 neurons. It was in mice that had not been able to eat again and had only received a placebo that these neurons were most active, suggesting that these neuron populations serve to stimulate appetite.
Around 40% of them were activated, according to the tests carried out by Mr. Caron, compared to only 30% in the mice which had been able to feed again.
And it was liraglutide that best imitated the effect of a meal on this group of neurons (around 28-30%, even better than leptin (35% activation).
“The idea was to see if these were neurons that respond to nutritional status. And the results show that when we administer liraglutide, it mimics the effect of a meal in these neurons,” says Mr. Caron.
There is still work to be done to confirm these results and better understand how it all works, but it is very possible that Mr. Caron's team has discovered the (or at least, and) mechanism which explains the appetite suppressant effect of Ozempic. At the very least, they have uncovered a previously unsuspected part of our appetite regulation system.
The year 2024 was rich in discoveries for the capital's scientific community. Each in their own field, researchers from the region have written new chapters in scientific history. The Sun presents to you, one per day, the most significant breakthroughs of the year.
– Dec 23 : Hormone party (with surprise guest)
– Dec. 24 : The DNA packager
– Dec 26 : Glacier “on the rocks”
– Dec 27 : Soon “organic” electrodes?
– Dec 28 : The family will wait…
