Melanin enriched with selenium could prove to be a versatile radioprotective material
Researchers from Northwestern University, Illinois, US, have synthesised a biomaterial which they say shows promise for protecting human tissue again harmful radiation. The melanin enriched with selenium, which is called selenomelanin, is said to be lighter and more versatile than traditional radioprotective materials such as lead. The work has been published in Journal of the American Chemical Society.
While mainly associated with 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).
A research team led by Nathan Gianneschi, the Jacob and Rosalind Cohn Professor of Chemistry in Northwestern’s Weinberg College of Arts and Sciences and associate director of the International Institute of Nanotechnology, have synthesised a new kind of melanin; enriched with selenium instead of the naturally occurring sulphur. Selenium is an essential micronutrient that plays an important role in cancer prevention. Previous research indicates 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.
‘It occurred to our postdoctoral fellow, Wei Cao, that melanin containing selenium would offer better protection than other forms of melanin. That brought up the intriguing possibility that this as-yet undiscovered melanin may very well exist in nature, being used in this way. So we skipped the discovery part and decided to make it ourselves.’ Gianneschi said.
The selenomelanin was used to treat living cells, researchers also prepared cells treated with synthetic pheomelanin and eumelanin along with cells that had no protection. After receiving a dose of radiation that would be lethal to a human, only the cells with selenomelanin continued to exhibit a normal cell cycle. ‘Our results demonstrated that selenomelanin offers superior protection from radiation,’ Professor Gianneschi said.
After further testing with bacteria, the researchers noted that selenomelanin can be biosynthesised, meaning that living cells fed with the appropriate nutrients can then produce selenomelanin on their own, and retain the radioprotective properties. Although selenomelanin was synthesised in the lab, researchers believe it may already be present in nature.
Unwanted exposure to radiation occurs during many common activities from air travel to X-ray diagnosis and clinical radiation therapy. Exposure is greatly amplified in extreme cases such as nuclear reactor malfunction or human space travel. The researchers said that melanin samples are currently in orbit at the International Space Station, which are being studied by another research team for the material’s response to radiation exposure. The researchers believe that this new biomaterial has potential to be applied to skin, like a melanin-based sunscreen.
‘Given the increased interest in space travel and the general need for lightweight, multifunctional and radioprotective biomaterials, we’ve become excited about the potential of melanin’, Professor Gianneschi added.
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