“Our results demonstrated that selenomelanin offers superior protection from radiation. We also found that it was easier to synthesize selenomelanin than pheomelanin, and what we created was closer than synthetic pheomelanin to the melanin found in nature.”Nathan Gianneschi
A team led by researchers at Northwestern University have managed to synthesize a new kind of melanin that is enriched with selenium. The biomaterial, called selenomelanin, was shown to exhibit properties that help protect human tissue against harmful radiation from medical X-rays and in spaceflight.
With an increasing need for lightweight, multifunctional and radioprotective biomaterials, the team examined whether selenomelanin could offer better protection than other forms of melanin. Although melanin is present in all kinds of organisms, and some organisms are thought to adapt to extreme circumstances such as radiation through its beneficial effects, it is not well understood compared to other biomaterials despite its many interesting properties. Melanin could act as a repository for selenium, helping ensure that organisms benefit from it.
Although there are five types of melanin in nature, pheomelanin, the pigment in red hair, can absorb X-rays more efficiently than the more common eumelanin, which is present in black and brown pigments in dark hair. While other studies had suggested pheomelanin, which contains sulfur, was an ideal candidate for protecting against radiation exposure, this research, described in the Journal of the American Chemical Society [Cao et al, J. Am. Chem. Soc. (2020) DOI: 10.1021/jacs.0c05573], found that selenomelanin could be biosynthesized, so that live cells given the right nutrients could produce selenomelanin on their own while maintaining its radioprotective properties.
While selenium compounds are also found in normal human proteins, they have not previously been associated with melanin in nature. The team synthesized selenomelanin before treating living cells with selenomelanin nanoparticles to compare the effects against synthetic pheomelanin and eumelanin, as well as cells with no protective melanin. On exposing the cells to radiation levels lethal to humans, only the cells treated with selenomelanin still exhibited a normal cell cycle.
As group leader Nathan Gianneschi said “Our results demonstrated that selenomelanin offers superior protection from radiation. We also found that it was easier to synthesize selenomelanin than pheomelanin, and what we created was closer than synthetic pheomelanin to the melanin found in nature.”
The researchers hope this new lightweight biomaterial can find applications in radiation protective materials as coatings for clothing, or surfaces in spacecraft where radiation protection is useful. There are also possible applications in a melanin-based sunscreen, or as a protective film to shield materials from radiation while in transit, and since melanins generate colors and can act as thermal insulators in some animals, their functions could be incorporated into a multifunctional paint or coating.
Treating living cells with selenomelanin to combat radiation