Two compounds found in sunscreens suppressed multiple sclerosis symptoms in mice, a study shows.
The substances, known as salate derivatives, belong to a class of compounds called nonsteroidal anti-inflammatory drugs.
Researchers published their study in the journal Proceedings of the National Academy of Sciences. It was titled “Salate derivatives found in sunscreens block experimental autoimmune encephalomyelitis in mice,” Experimental autoimmune encephalomyelitis is a mouse model of MS.
Evidence from the 1970s suggested that higher vitamin D levels from getting more sunlight could reduce the rate of MS. Subsequent studies indicated this was unlikely, however.
Researchers who noticed that ultraviolet light suppresses MS in mice hypothesized that this could be the reason for the reduced prevalence of the disease in tropical areas.
University of Wisconsin researchers wondered if sunscreen would prevent ultraviolet light from suppressing MS in mice. The team, led by Dr. Hector F. DeLuca, an emeritus professor in the university’s Department of Biochemistry, chose six commercially available sunscreens, then exposed the mice to UV radiation.
Confirming previous findings, they observed that UV radiation decreased the severity of MS.
But, unexpectedly, they discovered that when mice were not receiving ultraviolet light, some of the sunblocks suppressed their MS for up to 30 days anyway.
An analysis revealed that the salate derivatives homosalate and octisalate were the sunscreen components responsible for suppressing MS. The two are esters of salicylic acid, a common medication for acne, psoriasis, warts, and dandruff.
Further analysis showed that homosalate was able to suppress MS by itself, but octisalate needed to be combined with homosalate to achieve significant results.
The team also discovered that the salates’ effectiveness depended on the dose. The more that homosalate was applied, the better the result, they said.
The only adverse effect of homosalate and octisalate was temporary skin irritation.
The study indicated that salate esters’ ability to suppress MS is not due to their sunblocking ability per se, because some of the sunscreen brands that did a good job of blocking sunlight did not suppress the disease.
Salate derivatives are well-known inhibitors of the enzyme cyclooxygenase, or COX. Because COX-2 has been found in MS lesions, salate derivatives might improve MS by suppressing COX, the researchers said.
Overall, “salates may be useful in stopping the progression of MS, and may provide new insight into mechanisms of controlling autoimmune disease,” the researchers concluded.