A Bifidobacterium probiotic strain and its soluble factors alleviate chloride secretion by human intestinal...

Previous studies indicate that certain probiotic bacterial strains or their soluble products can alleviate proinflammatory cytokine secretion by intestinal epithelial cells (IEC), but their impact on epithelial chloride (Cl(-)) secretion remains elusive. To further decipher the mechanisms of the cross-talk between bacteria/soluble factors and epithelial cells, we analyzed the capacity of the probiotic strain Bifidobacterium breve C50 (Bb C50), its conditioned medium, and other commensal Gram (+) bacteria to modulate epithelial Cl(-) secretion. The effect of Bb C50 on carbachol- (CCh) or forskolin (Fsk)-induced Cl(-) secretion was measured in an IEC line in Ussing chambers. The mechanisms involved in the regulation of Cl(-) secretion were assessed by measuring intracellular Ca(2+) concentration, phosphatase activity, protein kinase (PK) C and PKA activation, and cystic fibrosis transmembrane conductance regulator (CFTR) expression. CCh- or Fsk-induced Cl(-) secretion [short-circuit current (Isc): 151 +/- 28 and 98 +/- 14 microA/cm(2), respectively] was inhibited dose-dependently by Bb C50 (Isc 33 +/- 12 and 49 +/- 7 microA/cm(2) at multiplicity of infection 100; P < 0.02). Fsk-induced Cl(-) secretion was also inhibited by Lactobacillus rhamnosus 10893. No other inhibitory effect was recorded with the other Gram (+) bacteria tested. The inhibitory effect of Bb C50 on CCh-induced Cl(-) secretion targeted a step downstream of epithelial Ca(2+) mobilization and was associated with decreased PKC activity. Thus, Bb C50 and secreted soluble factors, by inhibiting phosphorylation processes, may promote intestinal homeostasis by controlling Cl(-) secretion.