Researchers have synthesized a new form of melanin enriched with selenium. Called selenomelanin, the new biomaterial shows promise as a shield for human tissue against harmful radiation.
Melanin is found in most organisms across the plant and animal kingdoms as well as in bacteria and fungi. Though best known for pigmentation, melanin also provides valuable protection from radiation. Five kinds of melanin have been observed in nature, with pheomelanin (the pigment in red hair) shown to absorb X-rays more efficiently than the more common eumelanin (black and brown pigments in dark hair).
Unwanted exposure to radiation occurs during many common activities, from air travel to X-ray diagnosis and clinical radiation therapy. It’s an even greater consideration in extreme cases such as a nuclear reactor malfunction or human space travel.
Compared to the weight and bulk of traditional radioprotective materials like lead, melanin is lighter and more flexible in how it can be used. Melanin samples are currently in orbit at the International Space Station, being studied for the material’s response to radiation exposure. Recent studies have focused on pheomelanin, which contains sulfur, as the best candidate for that purpose.
A new kind of melanin — enriched with selenium instead of sulfur — was found to provide better protection against X-rays. Selenium is an essential micronutrient that plays an important role in cancer prevention and previous research reports that selenium compounds can protect animals against radiation. These compounds are found in normal human proteins but have not been associated with melanin in nature before.
The research team synthesized the new biomaterial, which they called selenomelanin, and used it to treat living cells. For comparison, they also prepared cells treated with synthetic pheomelanin and eumelanin as well as cells with no protective melanin. After receiving a dose of radiation that would be lethal to a human being, only the cells treated with selenomelanin still exhibited a normal cell cycle. Further testing with bacteria showed that selenomelanin can be biosynthesized, meaning that live cells fed with appropriate nutrients can then produce selenomelanin on their own and retain its radioprotective properties. In fact, although the selenomelanin was synthesized in a lab, the researchers believe it may already be present in nature.
The team envisions that this new biomaterial could be applied to a person’s skin like a melanin-based sunscreen. It could also be used as a protective film to shield materials from radiation while in transit.