High-energy electromagnetic radiation from the sun can damage the DNA of humans and animals. Prolonged exposure to this radiation can increase the risk of cancer or, in high-enough doses, cause radiation poisoning. Earth’s atmosphere protects us from the most dangerous radiation, but for astronauts leaving the planet, additional protection is required. Lead, water, or other heavy materials will do the job, but they are heavy and expensive to blast into space.

Researchers led by Wei Cao, a postdoc at Northwestern University, recently published on a potentially-protective chemical. The chemical is based on melanin, which gives human skin and hair their different colors and helps protect against sun damage. Some kinds of melanins, called pheomelanins have sulfur in them. The researchers replaced this sulfur with selenium, which is larger than sulfur but has similar chemical properties, and formed nanoparticles of the selenium compound about 160 nm wide.

To test the nanoparticles’ ability to protect cells from radiation, researchers injected them into skin cells in a petri dish. The nanoparticles entered cells without causing toxicity and formed umbrella-shaped structures around the DNA-containing nucleus. When the cells were subjected to X-ray radiation, cells that were either not treated by a melanin or that were treated by the natural sulfur-containing melanin were not able to divide into new cells. Cells treated with the selenium melanin compound, however, divided successfully.

Further studies showed that the nanoparticles were protective because they reduced cell-damaging reactive oxygen species (aka “free radicals”) produced by radiation and because the nanoparticles absorbed x-ray radiation directly. Finally, the researchers grew the nanoparticles by feeding a bacteria selenium-containing chemicals and allowing it to produce the melanin nanoparticles, demonstrating that the material can be produced in biological systems. In the future, the authors suggest looking for similar selenium-containing materials in organisms exposed to high levels of radiation in their natural environments as well as incorporating the material into clothing or other materials to provide radiation protection outside earth’s atmosphere.

Wei Cao is a post-doctoral research is Nathan Gianneschi’s lab at Northwestern University, where they focus on an interdisciplinary approach to designing nanoparticles.

Corresponding Author: Emily Kerr

 Popular press source: Super space sunblock made from skin pigment could shield astronauts from radiation

Scientific Article: Selenomelanin: An Abiotic Selenium Analogue of Pheomelanin

Image Credit: Bruce McCandless II during EVA in 1984, NASA, public domain