Nanoparticle Super Antioxidant Developed at Rice University

Scientists create a super antioxidant with  nanoparticles

QDOTS imagesCAKXSY1K 8(Nanowerk News) Scientists at Rice University are  enhancing the natural antioxidant properties of an element found in a car’s  catalytic converter to make it useful for medical applications.
Rice chemist Vicki Colvin led a team that created small, uniform  spheres of cerium oxide and gave them a thin coating of fatty oleic acid to make  them biocompatible. The researchers say their discovery has the potential to  help treat traumatic brain injury, cardiac arrest and Alzheimer’s patients and  can guard against radiation-induced side effects suffered by cancer patients.
Their nanoparticles also have potential to protect astronauts  from long-term exposure to radiation in space and perhaps even slow the effects  of aging, they reported.
The research appears this month in the American Chemical Society  journal ACS Nano (“Antioxidant Properties of Cerium Oxide Nanocrystals  as a Function of Nanocrystal Diameter and Surface Coating”).
Oleylamine (red dots) and oleac acid (blue) layers serve to protect a cerium oxide nanosphere
Oleylamine (red dots) and oleac acid (blue) layers serve to protect  a cerium oxide nanosphere that catalyzes reactive oxygen species by absorbing  them and turning them into less-harmful molecules. The finding could help treat  injuries, guard against radiation-induced side effects of cancer therapy and  protect astronauts from space radiation. (Credit: Colvin Group/Rice University)
Cerium oxide nanocrystals have the ability to absorb and release  oxygen ions — a chemical reaction known as reduction oxidation, or redox, for  short. It’s the same process that allows catalytic converters in cars to absorb  and eliminate pollutants.
The particles made at Rice are small enough to be injected into  the bloodstream when organs need protection from oxidation, particularly after  traumatic injuries, when damaging reactive oxygen species (ROS) increase  dramatically.
The cerium particles go to work immediately, absorbing ROS free  radicals, and they continue to work over time as the particles revert to their  initial state, a process that remains a mystery, she said. The oxygen species  released in the process “won’t be super reactive,” she said.
Colvin said cerium oxide, a form of the rare earth metal cerium,  remains relatively stable as it cycles between cerium oxide III and IV. In the  first state, the nanoparticles have gaps in their surface that absorb oxygen  ions like a sponge. When cerium oxide III is mixed with free radicals, it  catalyzes a reaction that effectively defangs the ROS by capturing oxygen atoms  and turning into cerium oxide IV. She said cerium oxide IV particles slowly  release their captured oxygen and revert to cerium oxide III, and can break down  free radicals again and again.
Colvin said the nanoparticles’ tiny size makes them effective  scavengers of oxygen.
“The smaller the particles, the more surface area they have  available to capture free radicals,” Colvin said. “A gram of these nanoparticles  can have the surface area of a football field, and that provides a lot of space  to absorb oxygen.”
None of the cerium oxide particles made before Rice tackled the  problem were stable enough to be used in biological settings, she said. “We  created uniform particles whose surfaces are really well-defined, and we found a  water-free production method to maximize the surface gaps available for oxygen  scavenging.”
Colvin said it’s relatively simple to add a polymer coating to  the 3.8-nanometer spheres. The coating is thin enough to let oxygen pass through  to the particle, but robust enough to protect it through many cycles of ROS  absorption.
In testing with hydrogen peroxide, a strong oxidizing agent, the  researchers found their most effective cerium oxide III nanoparticles performed  nine times better than a common antioxidant, Trolox, at first exposure, and held  up well through 20 redox cycles.
“The next logical step for us is to do some passive targeting,”  Colvin said. “For that, we plan to attach antibodies to the surface of the  nanoparticles so they will be attracted to particular cell types, and we will  evaluate these modified particles in more realistic biological settings.”
Colvin is most excited by the potential to help cancer patients  undergoing radiation therapy.
“Existing radioprotectants have to be given in incredibly high  doses,” she said. “They have their own side effects, and there are not a lot of  great options.”
She said a self-renewing antioxidant that can stay in place to  protect organs would have clear benefits over toxic radioprotectants that must  be eliminated from the body before they damage good tissue.
“Probably the neatest thing about this is that so much of  nanomedicine has been about exploiting the magnetic and optical properties of  nanomaterials, and we have great examples of that at Rice,” Colvin said. “But  the special properties of nanoparticles have rarely been leveraged in medical  applications.
“What I like about this work is that it opens a part of  nanochemistry — namely catalysis — to the medical world. Cerium III and IV are  electron shuttles that have broad applications if we can make the chemistry  accessible in a biological setting.
“And of all things, this humble material comes from a catalytic  converter,” she said.
Source: Rice University

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