Alterations of fecal short-chain fatty acids solely in the course of multiple sclerosis: rethinking the gut-brain axis in the early stages of MS.

Background: The role of gut microbiota in multiple sclerosis (MS) has become increasingly important, intestinal dysbiosis with reduced production of short-chain fatty acids (SCFA) being the prevailing paradigm. However, the direction of causality, that is, whether intestinal changes are cause or consequence of chronic central nervous system inflammation, remains to be elucidated. Previous studies have focused on long-term MS patients. Alteration in fecal SCFA concentrations in early MS, particularly during relapses, remains to be extensively studied. Objectives: To compare fecal SCFA concentrations in patients with a first diagnosis of MS with those in patients with long-term MS and in healthy controls (HCs). Design: Prospective cohort study. Methods: The prospective case-control study was conducted on relapsing-remitting MS (RRMS) patients at the time of first, acute relapse without ongoing immunotherapy (Early-RRMS). Clinical and demographic parameters, as well as fecal SCFA concentrations (measured by gas chromatography) were collected. The parameters were compared with those of matched RRMS patients under different, long-term immunotherapy (Late-RRMS) and HCs. Results: SCFA concentrations of propionate, butyrate, isobutyrate, valerate, and isovalerate were not significantly different between the early-RRMS cohort and HCs, but were lower in the late-RRMS cohort. Conclusion: The findings indicate that reduction in SCFA levels is exclusively observed in patients with RRMS during the further course of the disease and not at the onset. Decrease in SCFA concentration may be rather consequence or related to neurodegeneration than linked to the first demyelinating event. Further investigation related to disease trajectories of immunomodulatory or neuroprotective treatments are required.