Multiple sclerosis (MS) is a chronic inflammatory autoimmune disease of the central nervous system, affecting 2.5 million people worldwide. In 1974, Agranoff and Goldberg observed that the incidence of MS is inversely related to sun exposure in both hemispheres. Since vitamin D is synthesized from ultraviolet (UV) radiation on the 7-dehydrocholesterol present in the skin, Goldberg suggested that increased vitamin D production caused by exposure to sunlight could be responsible for reducing the incidence of MS. More recent results have made this hypothesis unlikely, however, and narrowband radiation (NBUVB) at 300-315nm has been shown to suppress the experimental model of MS (EAE). This narrow band produces little vitamin D from 7-dehydrocholesterol because it does not increase the levels of 25-hydroxycholecalciferol in the blood.
During the course of their studies, a team from the Department of Biochemistry of the University of Wisconsin-Madison, Madison, studied commercial sunscreen preparations to prevent the suppression of EAE by narrowband UVB. Quite unexpectedly, some solar filter preparations have completely suppressed the EAE without the aid of UV rays. The local application of Coppertone Spray sunscreen completely suppressed the development of lesions. When the mice were treated with NBUVB, the severity of the average disease had drastically decreased. Surprisingly, topical administration of the same sunscreen completely blocked the EAE. Therefore, the researchers focused on the components of active sunscreen preparations. The suppression of EAE by the sun preparations has been traced back to two esters of salicylate, homosalate and octasalate.
These compounds are not likely to work by blocking or absorbing UV light. Simply maintaining mice in complete absence of light did not affect the development of EAE. In addition, some more powerful sunscreens such as avobenzone and oxybenzone do not suppress EAE. Only the filters containing salicylate esters are effective and the salicylates themselves clearly block the EAE. Salicylates are known non-steroidal anti-inflammatory drugs (NSAIDs). However, a previous study revealed that acetylsalicylic acid had no effect on MS. Since NSAIDs are well known inhibitors of cyclooxygenase, mostly the isoform 2, and COX-2 has been observed in MS lesions, a possible mechanism of action of salicylates is the suppression of COX. COX inhibitors suppress EAE, but if salicylates suppress EAE by inhibiting COX it is not yet known. This is what he intends to discover the team with the upcoming experiments already planned.
- Edited by Dr. Gianfrancesco Cormaci, PhD, specialist in Clinical Biochemistry.
Scientific references
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