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.