Protective Effects of Probiotics on Chronic Stress-Induced Intestinal Permeability in Rats are mediated via Mast Cells and PPARγ

• BACKGROUND: Chronic stress, which may affect in the clinical course of inflammatory and functional bowel diseases, disrupts intestinal barrier function by routes involving mast cells. Probiotics have been shown to ameliorate the deleterious effects of stress on intestinal function, but mechanisms remain to be elucidated. Peroxisome proliferator-activated receptor (PPAR)-γ signaling is activated as an endogenous defense mechanism during chronic stress and evidence suggests that probiotics reduce the degradation of PPAR-γ. As a source of the endogenous agonist for PPAR-γ, 15d-PGJ2, and as an important mediator of the stress response, mast cells may have both a beneficial and a deleterious role in the effects on intestinal function by probiotics.AIM: Our aim was to study if mast cells contribute to the positive effects of probiotic therapy on intestinal function in a rat model of chronic stress.METHODS: 32 Mast cell deficient (Ws/Ws) and 32 wild-type (+/+) rats were subjected to water avoidance stress (WAS) or sham stress (SS) 1hr/day for 10 days. Seven days prior to the onset of stress, probiotics (PB, multispecies combination of 10 different lactic acid bacteria) were added to the standard diet (St) in half of the animals. To determine dependence of PPAR-γ, 8 probiotic-fed wild-type rats subjected to WAS were injected daily with the specific PPAR-γ antagonist T0070907. The colonic mucosa was exposed to E. coli HB101 incorporated with green fluorescent protein and permeability was assessed in Ussing chambers. Mesenteric lymph nodes (MLN) were cultured to determine bacterial translocation.RESULTS: Chronic stress induced a marked increase in ileal permeability to E.coli HB101 in +/+ rats (0.17±0.1 x106CFU/hr in SS/St/++ vs. 2.13±0.4 in WAS/St/++; P<0.001). This breach in barrier integrity was less pronounced in Ws/Ws rats (2.13±0.4 in WAS/St/++ vs. 1.19±0.3 in WAS/St/WsWs; P<0.01). Probiotics prevented stress-induced effects in E.coli HB101 passage only in wild-type rats (82% decrease in +/+ vs. 0% in Ws/Ws rats). Furthermore, only in the presence of mast cells did probiotics reduce the enhanced bacterial translocation to MLNs during chronic stress. In wild-type rats treated with a PPAR-γ antagonist, the barrier protective effects of probiotics were diminished.CONCLUSIONS: Mast cells acting via a PPAR-γ dependent pathway contribute to the beneficial effects of probiotics on chronic stress-induced mucosal dysfunction in rats.

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