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Super-Antioxidant Developed from Catalyst Nanoparticles

Vicki Colvin

Vicki Colvin (Rice University)

Chemists and bioengineers at Rice University in Houston developed an antioxidant from an element used in catalytic converters that they found to be many times more powerful than antioxidants now on the market. The team from the labs of Vicki Colvin and Laura Segatori published their findings earlier this month in the journal ACS Nano (paid subscription required).

Antioxidants are molecules that prevent the chain reaction of highly reactive electrons called free radicals released when oxygen interacts with other molecules causing cell damage. Oxidizing cell damage can result from over-exposure to radiation, and occurs in conditions such as traumatic brain inury, cardiac arrest, and Alzheimer’s disease. As a result, antioxidants can play a role in helping treat or prevent those conditions.

The Rice team tested cerium oxide nanocrystals, a form of the rare earth metal cerium, able to absorb and release oxygen in much the same way cerium absorbs and releases pollutants in a car’s catalytic converter. In nanoscale form — 1 nanometer equals 1 billionth of a meter — the particles are small enough to be injected into the blood stream as a therapy.

The tiny size of the crystals also makes them highly absorbant of oxygen, when introduced even in small quantities. “A gram of these nanoparticles,” says Colvin in a university statement,  “can have the surface area of a football field, and that provides a lot of space to absorb oxygen.” The team’s tests show smaller particles have the most reactive effects.

The cerium oxide nanocrystals, say the researchers, work immediately in absorbing free radicals, and cycle between absorbing the damaging oxygen atoms, then releasing oxygen in less harmful form. At the end of each cycle, cerium oxide slowly reverts back to its original state, ready to absorb more free radicals.

One problem with cerium oxide nanocrystals, however, is their instability in the body. To protect the particles, the researchers gave them a thin coating of oleic acid, a natural and healthy fatty acid found in olive and canola oils. The coating makes it possible for the particles to survive many cycles of free radical absorbtion, while still letting oxygen pass through.

The team tested in their labs cerium oxide particles with a diameter of about 4 nanometers in hydrogen peroxide, a strong oxidizing agent. They found the coated nanoscale cerium oxide particles were 9 times more reactive in absorbing free radicals than the commercial antioxidant Trolox. The cerium oxide nanoparticles were also able to reduce oxidation damage in samples of human skin fibroblast tissue important in healing skin injuries.

Colvin plans to extend the concept of nanoparticles for medical applications in what she calls passive targeting. “For that,” says Colvin, “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.”

Update: Title revised, 16 October 2013

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