Background/Purpose: Several studies have demonstrated that Magnesium (Mg) has a key role in the immune responses. Our previous studies showed that a short-term low Mg diet was significantly protective in mice with Collagen-Induced Arthritis (CIA) arthritis decreasing disease severity and preserving normal joints’ architecture without any erosive changes. Spleen from these mice had reduced levels of Th17 cells and increased numbers of CD4+FoxP3+ Treg cells. Given the strong relationship between Tregs, Th17 cell and the gut microbiota we examined the effect of different Mg diets on the intestinal microbiota of arthritic mice.

Methods: Mice were placed either on a low (50 ppm), regular (500 ppm) or high Mg diet (2800 ppm) 22 days before the induction of CIA, and discontinued three days after the induction. The diets were then converted into a regular Mg diet that was continued until the end of the arthritis experiment. Fecal samples were collected before starting the Mg diets (day 0), after 22 days of diet and at the end of the arthritis scoring period (day 56); Fecal genomic DNA was extracted and expression of the commensal bacteria Bacteroides fragilis (BFR), Bifidobacterium (Bfd), clostridium cluster IV (sg-Clep), Clostridium coccoides group (g-Ccoc), Clostridium Perfingens (Closp), Lactobacillus (Lact) and Segmented filamentous bacteria (SFB) determined by qPCR by amplifying 16S rRNA genes and normalizing for Eubacteria. Splenocytes were used for flow cytometry quantification of Th17 and CD4+FoxP3+ Tregs.

Results: There were no significant group differences in the baseline levels of microbiota before starting the diets. At the end of the arthritis experiment (day 56) the low and high Mg diet groups had significantly lower levels of SFB (p=0.04 and p=0.05, respectively; unpaired t-test; n=5/group), compared with the regular Mg diet (500ppm) group. These results correlated with decreased numbers of Th17 cells in low Mg treated mice. The low Mg diet group also had significantly increased levels of BFR (p=0.05; unpaired t-test, n=5/group) and increased numbers of CD4+FoxP3+ Treg cells. BRF has been shown to promote differentiation and increased suppressive activity of CD4+FoxP3+ Treg cells.

Conclusion: This study describes for the first time that alterations in dietary Mg may affect the status of the gut microbiome and those changes correlate with numbers of Tregs and Th17 cells. These results suggest that changes in dietary Mg may affect arthritis by inducing changes in the microbiome and in pathogenic and protective T cell subsets.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/dietary-magnesium-modulates-the-intestinal-microbiome-and-t-cell-subsets/