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Biochemical, Molecular, and Genetic Mechanisms

A Bifidobacterium Probiotic Strain and Its Soluble Factors Alleviate Chloride Secretion by Human Intestinal Epithelial Cells^1,2

³ INSERM U793, 75730 Paris, France ⁴ Université Paris Descartes, Faculté de Médecine René Descartes, IFR94, Paris, France ⁵ INSERM U845, video-imaging core facility of the Centre de Recherche Necker, 75730 Paris, France

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 Ca²⁺ 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 µA/cm², respectively] was inhibited dose-dependently by Bb C50 (Isc 33 ± 12 and 49 ± 7 µA/cm² 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 Ca²⁺ 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.

^* To whom correspondence should be addressed. E-mail: martine.heyman{at}inserm.fr.

Manuscript received 17 August 2009. Initial review completed 28 August 2009. Revision accepted 16 October 2009.