Melanin, the pigment that protects our skin from sunlight, is surprisingly difficult to study. But a method developed by researchers at McGill University could unlock its mysteries.
With the summer, many people enjoy the sun and develop a beautiful summer complexion. This color comes from melanin, molecules produced by certain cells in our skin. Melanin protects us from the sun, specifically by absorbing UV rays and converting them into heat.
However, despite being studied for more than a century, our knowledge of melanin remains very superficial. “We know that melanin is made up of different blocks put together one after the other, much like the different cars on a train,” explains Jean-Philip Lumb, a professor in the chemistry department at McGill University. We know what these chains look like, but we don’t know what they are made of. »
The reason the mystery has persisted for so long is because these molecules are very unstable and particularly difficult to study! In our cells, they are isolated in a small vesicle — a small pouch — called a melanosome. Once outside of this structure, they are quickly altered by the outside world. We don’t know exactly what happens when melanin is produced: we only know the beginning and end of the cascade of chemical reactions. And we know little about the properties of the substances involved.
“Furthermore, the interior of the melanosome is an ever-changing mix that responds to the amount of sunlight received and signals from the body,” adds Professor Lumb. Studying the properties of intermediate molecules without access to their interior is an incredible scientific challenge.”
A molecule that has sensitive skin
Professor Lumb and his team have successfully mastered this challenge and published their results in the journal Nature Chemistry last April. “The first step in the chemical cascade that enables our body to produce melanin has one thing in common with a combustion reaction: it needs oxygen,” summarizes Jean-Philip Lumb. Some amino acids react with oxygen to form a first intermediate molecule. This was observed by other researchers as early as the 1990s, but was too unstable for us to study. So we designed a similar but more stable molecule in the lab. Like the original, it is able to react with oxygen for the first time, but its development is subsequently blocked, allowing us to examine it more closely. »
To the team’s surprise, the small molecule that resulted from this one reaction already had many of the properties of melanin. “It absorbs a broad spectrum of sunlight, both visible and ultraviolet, and converts it to heat. This suggests that melanin may not be such a long molecule after all. »
In fact, the team didn’t replicate melanin in the lab. “Melanin is a brown pigment and what we have is kind of greenish. But we’ve taken a first step in the right direction in understanding what’s going on inside the melanosomes, and we might just have to wait for the reaction and add another wagon or two to our train! »
Cream… to the brain!
Could the discovery now enable the development of a 100% natural, highly effective sunscreen? Not so fast, points out Simon-Pierre Gravel, a professor at the University of Montreal’s Faculty of Pharmacy, who was not involved in this work.
“The idea of using melanin in sunscreen has already been tested,” says the researcher. It makes black or brown creams – cosmetically not very interesting [pour une grande partie du marché]. And even if you want to try, it takes many steps to go from an active ingredient found in basic research to a cream that you apply to the skin. At the moment it is difficult to say whether it would be functional or risk-free. However, the researcher believes that with more effort, the molecule discovered in this research could be modified to play a role in such a cream.
In the meantime, progress offers another opportunity: that of contributing to the understanding of other mysterious properties of melanin. “Amazingly, we find this pigment in certain structures of the brain and even in the hair cells of our inner ear,” explains Jean-Philip Lumb. These body parts are never exposed to the sun. So what use can these pigments have? Getting back to basics is the first step in understanding these unknown properties. »
For example, what secrets melanin hides that are far more complex than those of the best post-holiday complexion to post on Instagram!
This article was prepared in collaboration with the Chemical Institute of Canada.