vasoactive-intestinal-peptide and Escherichia-coli-Infections

We previously showed that vasoactive intestinal peptide (VIP) protects against bacterial pathogen-induced epithelial barrier disruption and colitis, although the mechanisms remain poorly defined. The aim of the current study was to identify cellular pathways of VIP-mediated protection with use of pharmacological inhibitors during enteropathogenic Escherichia coli (EPEC) infection of Caco-2 cell monolayers and during Citrobacter rodentium-induced colitis. EPEC-induced epithelial barrier disruption involved the PKC pathway but was independent of functional cAMP, Rho, and NF-κB pathways. VIP mediated its protective effects by inhibiting EPEC-induced PKC activity and increasing expression of the junctional protein claudin-4. Short-term treatment with TPA, which is known to activate PKC, was inhibited by VIP pretreatment, while PKC degradation via long-term treatment with TPA mimicked the protective actions of VIP. Immunostaining for specific PKC isotypes showed upregulated expression of PKCθ and PKCε during EPEC infection. Treatment with specific inhibitors revealed a critical role for PKCε in EPEC-induced barrier disruption. Furthermore, activation of PKCε and loss of barrier integrity correlated with claudin-4 degradation. In contrast, inhibition of PKCε by VIP pretreatment or the PKCε inhibitor maintained membrane-bound claudin-4 levels, along with barrier function. Finally, in vivo treatment with the PKCε inhibitor protected mice from C. rodentium-induced colitis. In conclusion, EPEC infection increases intracellular PKCε levels, leading to decreased claudin-4 levels and compromising epithelial barrier integrity. VIP inhibits PKCε activation, thereby attenuating EPEC-induced barrier disruption.

Topics: Adult; Aged; Animals; Caco-2 Cells; Cells, Cultured; Citrobacter rodentium; Claudin-4; Colitis; Cyclic AMP; Enteropathogenic Escherichia coli; Escherichia coli Infections; Female; HT29 Cells; Humans; Intestinal Mucosa; Male; Mice; Mice, Inbred C57BL; NF-kappa B; Protein Kinase C-epsilon; rho-Associated Kinases; Vasoactive Intestinal Peptide

Toll-like receptors (TLRs) recognize microbial pathogens and trigger immune response, but their regulation by neuropeptide-vasoactive intestinal peptide (VIP) in weaned piglets infected by enterotoxigenic Escherichia coli (ETEC) K88 remains unexplored. Therefore, the study was conducted to investigate its role using a model of early weaned piglets infected by ETEC K88. Male Duroc × Landrace × Yorkshire piglets (n = 24) were randomly divided into control, ETEC K88, VIP, and ETEC K88+VIP groups. On the first three days, ETEC K88 and ETEC K88+VIP groups were orally administrated with ETEC K88, other two groups were given sterile medium. Then each piglet from VIP and ETEC K88+VIP group received 10 nmol VIP intraperitoneally (i.p.) once daily, on day four and six. On the seventh day, the piglets were sacrificed. The results indicated that administration of VIP improved the growth performance, reduced diarrhea incidence of ETEC K88 challenged pigs, and mitigated the histopathological changes of intestine. Serum levels of IL-2, IL-6, IL-12p40, IFN-γ and TNF-α in the ETEC K88+ VIP group were significantly reduced compared with those in the ETEC group. VIP significantly increased IL-4, IL-10, TGF-β and S-IgA production compared with the ETEC K88 group. Besides, VIP could inhibit the expression of TLR2, TLR4, MyD88, NF-κB p65 and the phosphorylation of IκB-α, p-ERK, p-JNK, and p-38 induced by ETEC K88. Moreover, VIP could upregulate the expression of occludin in the ileum mucosa compared with the ETEC K88 group. Colon and caecum content bacterial richness and diversity were lower for pigs in the ETEC group than the unchallenged groups. These results demonstrate that VIP is beneficial for the maturation of the intestinal mucosal immune system and elicited local immunomodulatory activities. The TLR2/4-MyD88 mediated NF-κB and MAPK signaling pathway may be critical to the mechanism underlying the modulatory effect of VIP on intestinal mucosal immune function and bacterial community.

Topics: Animals; Cecum; Colon; Cytokines; Enterotoxigenic Escherichia coli; Escherichia coli Infections; Immunity, Mucosal; Immunologic Factors; Intestines; Male; Microbiota; Occludin; Swine; Vasoactive Intestinal Peptide; Weaning

Nitric oxide and vasoactive intestinal peptide (VIP) are potent vasodilators and postulated as inducers of hypotension. These mediators activate guanylate cyclase and adenylate cyclase, respectively, with subsequent biosynthesis of cyclic guanosine monophosphate (cGMP) and cyclic adenosine monophosphate (cAMP) producing vascular smooth muscle relaxation and vasodilatation. Cyclic nucleotides and VIP were evaluated during Escherichia coli septicemia in two groups of rabbits; 1) sepsis alone and 2) sepsis and a competitive inhibitor of nitric oxide synthase, NG-monomethyl-L-arginine. Arterial blood was obtained for determination of bacteremia, lactic acidemia, nucleotides, nitrites, and VIP levels. Significant bacteremia, endotoxemia, tachycardia, lactic acidosis, and hypotension occurred in all animals (P < 0.005). Circulating blood levels of cGMP, nitrites, cAMP, and VIP (P < 0.005) increased with development of shock. The NG-monomethyl-L-arginine treated animals had less cGMP, nitrites, cAMP, and VIP produced (P < 0.01). Plasma cGMP levels remained stable, suggesting that stimulated phagocytes in whole blood were responsible for increased cGMP levels. Infusion of VIP produced profound hypotension and lactic acidemia. Results of these experiments provide definitive evidence that nitric oxide and VIP are mediators during septic shock and their messengers are cGMP and cAMP, respectively. In addition, phagocytic stimulation with increased production of cGMP may initiate shock, with these mediators acting synergistically to prolong hypotension.

Topics: Amino Acid Oxidoreductases; Animals; Arginine; Bacteremia; Blood Pressure; Cyclic AMP; Cyclic GMP; Disease Models, Animal; Escherichia coli Infections; Heart Rate; Lactates; Nitric Oxide; Nitric Oxide Synthase; omega-N-Methylarginine; Rabbits; Reference Values; Vasoactive Intestinal Peptide

The mechanisms by which bacterial enterotoxins cause secretory diarrheas have been well defined, and the definitions of such mechanisms have been important in developing a consistently successful therapeutic approach. The less common secretory diarrheas, caused by the interaction of hormones of tumor origin with the gut small intestinal mucosa have also been clearly defined, and their pathogenetic mechanisms are similar to those by which the cholera and E. coli enterotoxins cause secretory diarrhea. The mechanisms by which histamine and gastrin of tumor origin cause gastric hypersecretion are less clearly delineated; secretory diarrhea caused by both of these agents can be stopped by total gastrectomy without removal of the responsible tumor. The secretory diarrhea caused by villous adenomas of the colon, which does not appear to be related to a distally produced humoral agent, results in the same picture of hypokalemic acidosis that is characteristic of the nonbacterial secretory diarrheas originating in the small intestine and is cured by resection of the responsible tumor.

Topics: Adenoma; Antigens, Bacterial; Bacterial Toxins; Cholera; Cholera Toxin; Colonic Neoplasms; Diarrhea; Enterotoxins; Escherichia coli; Escherichia coli Infections; Escherichia coli Proteins; Fimbriae Proteins; Hormones, Ectopic; Humans; Hydrogen-Ion Concentration; Intestinal Mucosa; Neoplasms, Hormone-Dependent; Prostaglandins; Vasoactive Intestinal Peptide; Water-Electrolyte Balance; Zollinger-Ellison Syndrome