Short Chain Fatty Acids Lower Inflammation and Restore Intestinal Integrity and Function Markers in Mycobacterium paratuberculosis—Infection In Vitro Model

<b>Background</b>: Infection with <i>Mycobacterium avium paratuberculosis</i> (MAP) is closely associated with Crohn's disease (CD) development, where excessive inflammation and marked intestinal damage are observed. <b>Objectives:</b> In this study, the role of short chain fatty acids, including propionic acid (PPA) and butyric acid (BA), was evaluated in an in vitro model, mimicking CD characteristics. <b>Methods</b>: MAP-infected THP-1 macrophages were treated with 1 mM and 10 mM of PPA or BA, and the conditioned media was co-cultured in Caco-2 cells. <b>Results</b>: Both PPA and BA caused an M2 shift with significant downregulation (<i>p</i>-value < 0.0001) in pro-inflammatory markers at both the RNA and protein levels. The downregulation is most likely due to the antimicrobial properties of PPA and BA. MAP growth was inhibited by several folds in MGIT (Mycobacteria Growth Indicator Tube) culture media supplemented with PPA or BA. Dysfunctional Caco-2 intestinal epithelial cells' integrity and function, due to MAP infection, were restored with PPA and BA treatment. Specifically, <i>NOX1</i> expression was significantly decreased in 10 mM of PPA or BA-treated cells (<i>p</i> < 0.001), as validated by RT-PCR and microscopy. PPA and BA restored tight junction integrity by decreasing <i>Claudin-2</i> expression in the MAP group. <b>Conclusions</b>: The data clearly demonstrated that short chain fatty acids contain anti-inflammatory and antimicrobial properties with downstream beneficial effects on damaged intestinal epithelial cells, suggesting potential benefits as a dietary supplement for CD patients, particularly those who are not pregnant, due to a possible increased risk of autism spectrum disorder (ASD) development in offspring associated with propionic acid exposure.