Propionic Acid Shapes the Course of Multiple Sclerosis by a Distinct Immunomodulatory and Neuroprotective Mechanism

Short chain fatty acids (SCFA) are processed from indigestible dietary fibers by gut bacteria and have immunomodulatory properties. Here we investigate the SCFA propionic acid (PA) in multiple sclerosis (MS) as a model of general autoimmune and neurodegenerative diseases. The serum and feces of MS patients exhibited significantly reduced PA-levels, which were associated with a reduction in diversity and abundance of SCFA-producing bacteria. In a proof-of-concept study, we supplemented PA to MS patients as add-on to immunotherapy. After two weeks of PA intake, we observed a significant and sustained increase of functionally competent Treg, while Th1 and Th17 significantly decreased. Retrospective analyses of up to 3years of PA-intake revealed a reduced annual relapse rate, stabilization of disability and reduced brain atrophy. In primary neurons, differentiated from MS patient-specific induced pluripotent stem cells, PA enhanced neurite regrowth after damage, similar to the Treg key cytokine interleukin-10. Our findings suggest that PA can serve as a potent immunomodulatory and neuroprotective supplement to approved MS drugs.