Multiple sclerosis (MS) is an autoimmune disease that affects the central nervous system, often in a pattern defined by relapsing and remitting. Previous clinical studies have shown that MS relapses are more likely during spring and summer, and a cause of this seasonality has recently been identified. Mauricio Farez (Raúl Carrea Institute for Neurological Research, Buenos Aires, Argentina) and colleagues have showed that the hormone melatonin underlies seasonal MS relapses (Cell 162, 1338–1352; 2015).
Melatonin is produced by the brain and regulates circadian rhythms and sleep patterns. It is made during darkness, so melatonin levels are higher in fall and winter as daylight diminishes. Farez and colleagues examined MS patients and found that the likelihood of relapse negatively correlated with melatonin levels. Since these human data could only show correlation, they turned to mice with experimental autoimmune encephalitis, which is used to model MS in animals. Treating these mice with melatonin decreased clinical symptoms. “Several melatonin-derived drugs have been used or tested in humans for other conditions such as insomnia,” Farez said in a press release. “These drugs could potentially be repurposed to modulate inflammation in multiple sclerosis and other inflammatory conditions.” BBG
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