Polymer-coating the nanoparticles used in sunscreens would protect DNA against any potential UV damage they might cause.

There has been recent controversy over the potentially adverse effects of using nanoparticles such as titania (TiO₂) in sunscreens. TiO₂ is a major component of photovoltaic cells and it is well-known that it emits a photoelectron when exposed to UV light. It is believed that these electrons go on to catalyse the production of peroxide radicals and other reactive oxygen species (ROS) which are known to react with lipids and DNA, causing damage.

Now, Miriam Rafailovich at Stony Brook University, New York, US, and colleagues have provided clear evidence that titania nanoparticles do in fact catalyse DNA damage. But the researchers also say that they have found a solution that would allow nanoparticles to be used safely in sun lotions and creams.¹ 'We have produced a coated titania particle, which completely protects DNA against UV damage,' said Rafailovich.

The team grafted anti-oxidant molecules, made from a mixture of grape seed extracts, and an anionic polymer onto the titania particles. The multi-component polymer coating absorbs the photoelectron generated when titania nanoparticles are exposed to UV light and blocks the photocatalytic activity that causes DNA damage.

What is not clear, however, is exactly what kind of titania particles sunscreen manufacturers are already using. A spokesperson from cosmetics giant L'Oréal UK confirmed that their suncare products do contain titanium dioxide among other sun filtering ingredients. 'This may be in a microparticle form, sometimes coated, to enhance the light filtering performance,' said the spokesperson. 'We comply with all EU and national laws in ensuring the absolute safety of our products and their ingredients, which are clearly labelled on our products.'

Kerry Hanson, a research scientist at the University of California, Riverside, US, has recently published a report on the enhancement of UV-induced reactive oxygen species (ROS) in the skin due to sunscreen.² The real question, said Hanson, is whether titania particles actually penetrate skin cells. Researchers have shown that the particles can penetrate the hair shaft, but whether or not they penetrate the surface of the skin or can travel through the nuclear membrane remains to be determined.

Even if the particles do get deep into cells, it's not clear that UV light would actually reach them there. 'If the molecules penetrate the skin, but the UV attenuation at the skin surface is great such that it does not reach the penetrated particles, then ROS will not be sensitised,' added Hanson.

Nevertheless, Hanson remained enthusiastic about the findings. '[These researchers] have come up with a clever way to reduce ROS generated by the sunscreen itself, right at the source of the ROS, which would prevent any subsequent damage that the sunscreen would have otherwise caused.'

Kathleen Too

References:

1. W. A.  Lee, N. Pernodet, B. Li, C. H. Lin, E. Hatchwell and M. H. Rafailovich, Chem. Commun., 2007, DOI: 10.1039/b709449c

2. K. M. Hanson, E. Gratton and C. J. Bardeen, Free Radical Biol. Med., 2006, 41, 1205-1212.