Systemic sunscreen still in future, despite promise of antioxidants

Vienna, Austria - Although there appears to be potential for developing systemic methods of protecting skin from sun damage, researchers still seem to be a long way from determining how to do that, according to Harald Maier, M.D.

Dr. Maier, of Vienna, spoke here at the 10th World Congress on Cancers of the Skin.

In the past three decades, results of a significant number of investigations have been published showing the efficacy of antioxidants in in vitro and animal experiments.

Direct damage of bio-molecules is the predominant mode of action with UVB.

Reactive oxygen species (ROS) and reactive nitrogen species (RNS) are short-lived intermediate products of photo-oxidative processes that interact with DNA, RNA, proteins and lipids.

Although UVA preferentially causes damage via radical formation and UVB by direct action, neither mode appears to be exclusive to the particular type of UV ray. In healthy organisms, there is equilibrium between pro-oxidative mechanisms and antioxidant activity. An increase of oxidative processes and/or decrease of anti-oxidative protection results in definitive damage.

Dietary protection

The idea behind nutritional/dietary photoprotection, which is synonymous with systemic photoprotection, is to increase anti-oxidative protection via nutritional additives. Carotenoids, tocopherols and flavonoids are all herbal substances that have been subjects of extensive study. They show strong anti-oxidative efficacy in order to protect the light-harvesting enzymes of photosynthesis from oxidative stress by adverse environmental conditions.

Until now, only a few randomized, controlled trials investigated the efficacy in man. For carotenoids, flavonoids and tocopherols, the results have been disappointing. Green tea extract and extract from Polypodium leucotomos, a fern, were more promising, although more large, controlled studies are necessary.

Dr. Maier outlined some of the potential benefits of systemic photo-protectants:

But despite the potential positive contribution of systemic photoprotection, Dr. Maier says there are still some potential shortcomings:

Dr. Maier says it's also undetermined whether that potential SPF of 3 to 4 will be sufficient.

"We always look at the erythema as the endpoint. There are many other endpoints, however, that we have to look at: cancer, immunosuppression, pigmentation.

"At present there is not enough evidence on systemic sun protection to determine whether SPF 3 to 4 would be enough if it comes from within.

"Sunscreens screen the skin, whereas antioxidants protect bio-molecules from deleterious effects of free radicals. That means something has already happened to the equilibrium of oxidant and antioxidant mechanisms."

Dr. Maier says investigators are really still at the beginning of this research.

"Although the mode of action seems to be obvious, there is not enough evidence for the efficacy of systemic protection in man at present. More and bigger studies are urgently needed," he says.