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Biological Chemistry

Sunscreen reduces multiple sclerosis symptoms in mice

Scientists identify salicyclic acid derivatives as responsible for surprising effect

by Emma Hiolski
July 31, 2017 | APPEARED IN VOLUME 95, ISSUE 31

Hector DeLuca and colleagues at the University of Wisconsin, Madison, were testing the hypothesis that some wavelengths of ultraviolet light could reduce multiple sclerosis symptoms in mice. They used sunscreen on some mice to block the UV light, predicting the symptoms would return. Instead, the combination of UV light and sunscreen—and even sunscreen alone—fully eliminated all symptoms for up to 30 days.

“We were totally surprised,”DeLuca says.

The team went on to test a suite of sunscreen brands and found only those containing salicylic acid esters could reduce or eliminate symptoms of the neurological disease. By testing the individual active ingredients on the mice, the team found that homosalate and octisalate were responsible for the effect (Proc. Natl. Acad. Sci. USA 2017, DOI: 10.1073/pnas.1703995114).

The researchers have not identified the mechanism behind the salicylic acid ester phenomenon, but they think it could involve inhibition of cyclooxygenase because molecules in the salicylate family inhibit this enzyme.

DeLuca plans to continue investigating the possible mechanism behind the ability of narrow-band UV-B light (300–315 nm) to reduce MS symptoms in mice. He speculates that the UV light and sunscreen effects may be connected, perhaps through a light-triggered formation of salicylate compounds in the skin.

Even if these findings do not lead to development of a novel drug target, DeLuca thinks they may still shed light on MS disease pathways.



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Richard Kelly (July 31, 2017 6:04 PM)
While certainly interesting, this finding does lead to concerns about the unknown systemic effects of minimally tested sunscreen components.
Lana (August 2, 2017 1:12 PM)
Actually these sunscreen components have been tested, much more than some of the next-gen sunscreen products others are raving about the US missing out on. Furthermore, one cannot concluded that this experimental note means the tox/safety community missed anything with regards to these sunscreen compounds. 1. NSAID activity of these components was known at the time of approval, and 2. NSAID activity does not mean the salates are un-safe. 3. This experiment does not translate to any mechanism of harm in humans. These mice are INDUCED with pertussin toxins to simulate MS like symptomologies. They do not have MS, so their MS wasnt cured. Salicylates are known to have NSAID activity. They inhibit COX (hence you dont feel quite so crappy when you take aspirin). COX inhibitors in sunscreen arent going be more active than COX inhibitors you ingest. The literature suggests moderate temporary COX inhibition alone is not going to cause significant adverse human health affects. The dosing in these experiments (grams/kg) is extremely high. Most people apply between 0.25 and 1.5 mg/cm2 of sunscreen. the average person has sun-exposed skin of <1.5m2 and weighs ~50-70kg. At the conservative end of all these calculations that translates to 0.45 mg(SUNSCREEN)/kg bw day. At 15% w/w for the salates this corresponds to a maximal typical human skin application of 67.5 mg/kg bw day...not including the portion that doesn't penetrate the dermis.
MICHAEL MCHENRY (August 2, 2017 1:57 PM)
Aspirin and analogs have been around a long time. If there was a real effect of Salicylates on MS you would think someone would have discovered it by now.
RW (August 6, 2017 6:41 AM)
Michael McHenry: Two things about aspirin: 1) Aspirin is acetylsalicylic acid and may not be the same exact thing; 2) It is digested and may be affected by stomach acid, perhaps meaning it's not entering the bloodstream in the same fashion as on the skin.
JB (September 14, 2017 8:36 PM)
Question it would be interesting to know the effects on any gut microbiota. It raises my curiosity especially toward the Akkermansia (A.) muciniphila, Acinetobacter (A.) calcoaceticus and Parabacteroides (P.) distasonis..

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