Participação de mastócitos e mediadores pró-inflamatórios na patogênese das enterotoxinas do Vibrio cholerae e Bacteroides fragilis

Abstract

This work deals with Vibrio cholerae and Bacteroides fragilis toxins, aiming to investigate the pharmacodynamics of their enterotoxic and proinflammatory activities. Cholera toxin caused dose-dependent secretory response in ligated loops of rat intestine. Rats treated with 48/80 compound or ketotifen showed a significant decrease in intestinal secretory response evoked by cholera toxin (blocking: 45% and 52%, respectively to 48/80 and ketotifen). Such secretory response was also significantly reduced by histamine/serotonine receptors antagonists (cyproheptadine: 48%), histamine (diphenhydramine: 45%), phospholipase Â2 inhibitors (dexamethasone: 43% and quinacrine: 35%), cyclooxygenase blockers (celocoxib: 60% and meloxican: 71%), PAF receptors antagonists (BN 52021: 32% and WEB 2086: 32%) and TNF-a synthesis inhibitors (pentoxifyline: 62% and thatidomide: 44%). On the other hand, the previous treatment with serotonine receptor specific antagonist and lipooxygenase inhibitors failed to inhibit this effect. ELISA trials of intestinal fluid derived from rats submitted to cholera toxin demonstrated that this toxin induced IL-1p and TNF-a release at intestinal fluid. Histopathology examination of intestinal tissue, 18h after toxin injection of loop, revealed hemodynamic disturbances such as congestion and edema of mucosal/submucosal layers, besides a severe infiltration of mast ceils at the intestinal corion. Intraluminal injection of culture supernatants from non toxigenic and toxigenic strains, as well as from purified toxin of 6. fragilis, was not able to induce significant intestinal secretion. However, structural changes were seen in the shape of villi and crypts, plus submucosal and mucosal layers modifications, including the occurrence of severe mast cell infiltration. In addition, some other vital organs exhibited morphological changes such as liver, heart, kidneys and brain. Cell migration, which was induced by B. fragilis purified toxin, was associated with a significant increase in number of mast cells (TBFspg/mi: 0,450 ± 0,050 vs. PBS: 0,200 ± 0,037; 4 h) and eosinophils (TBFspg/mi: 0,750 ±0,157 vs. PBS: 0,367 ± 0,126; 4h; and TBF3pg/mi: 0,800 ± 0,115 vs. PBS: 0,433 ± 0,084; 8h). xxiii On the contrary, B. fragilis purified toxin was not able to induce neutrophil or mononuclear cell migration. Our results suggest that the secretory response to cholera toxin involves an inflammatory reaction orchestrated by mast cells, histamine, prostaglandins, PAF, IL-1p and TNF-a. B. fragilistoxïn promoted mast cells and eosinophils migration, in vivo. This seems to reveal an efficient pro inflammatory participation on biological activities of \/. cholerae and B. fragilis toxins.