How a Sunscreen Ingredient Could Thwart Superbugs

Zinc oxide nanopyramids could protect pacemakers, replacement joints and other implantables from MRSA and other pathogens, according to University of Michigan researchers.

Chris Newmarker

University of Michigan researchers are reporting some success when it comes to the antibacterial properties of zinc oxide--a sunscreen and diaper rash cream ingredient.

A  coating of zinc oxide nanopyramids disrupted the growth of methicillin-resistant Staphylococcus aureus (MRSA) on covered pegs, according to results published in the journal Nanomedicine. After 24 hours, the pegs with the coating had 95% fewer viable staphylococcal cells than uncoated pegs--presenting a promising avenue for protecting medical device implants.

Roughly 1 million implanted medical devices are infected annually with MRSA and other bacterial species, according to the University of Michigan. "It is extremely difficult to treat these infections," said J. Scott VanEpps, MD, PhD, a clinical lecturer and research fellow at the university medical school's emergency medicine department who led the biological study of the coating. .

Pneumonia and E. coli species were less affected by the zinc oxide nanoparticle coating. The researchers also need find out how such the coating would affect human cells near the implant and explore how the nanopyramids affect other enzymes in humans and bacteria. They hope to perform in vivo testing in the next year.

Still, there is at least some promise to turn the zinc oxide nanopyramids--engineered from the substance that makes the sunscreen lotion thicker and relatively opaque--into an effective antibacterial coating for implants including pacemakers and replacement joints. By preventing bacterial infections from occurring from the start, the coating could reduce the need for long courses of antibiotics or sometimes extensive surgical replacements when such infections occur, VanEpps said.

"While the coating was unable to completely eradicate all staphylococcal cells, this dramatic reduction could likely enable antibiotic treatments to succeed or simply allow the human immune system to take over without the need for antibiotics," VanEpps said.

When reached by Qmed, VanEpps added: "We envision reduction in the incidence of infection for almost any conceivable device. We feel that this technology could be applied to almost any material even after fabrication of the device."

The shape was an important design consideration for the nanoparticles. The particles each look like a pyramid with a hexagon-shaped base, and appear to be quite effective at preventing the enzyme called beta-galactosidase from breaking down lactose into the sugars glucose and galactose.

Beta-galactosidase needs to be able to twist in order to cut the lactose into the smaller sugars.

"Although more studies need to be carried out, we believe that zinc oxide nanopyramids interfere with this twisting motion," said Michigan chemical engineering professor Nicholas Kotov, whose group made the nanoparticles.

Something about an edge or point on the nanoparticle prevents the beta-galactosidase from doing its work, starving out the bacteria in the process.  "By clogging up just one of the four grooves, the nanoparticles can shut down the whole enzyme by preventing the twisting action," Kotov said.

Staph, including MRSA, could be especially vulnerable to the nanopyramids because its cell wall is a matrix of proteins and sugars. The zinc oxide nanoparticles prevented the maintenance of cell walls, causing the bacteria cells to break down.

The good news is that human cells do not have the same vulnerabilities, though the same goes for E. coli.

"The strong antibacterial activity against MRSA and other pathogens is an exciting finding," Kotov said. "We want to better understand the mechanisms of the antibacterial function to fine tune its inhibitory activity and to identify the structural similarities among enzymes that pyramidal nanoparticles can inhibit."

Chris Newmarker is senior editor of Qmed and MPMN. Follow him on Twitter at @newmarker.

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