Enzymes degrading bacterial chemotactic F-met peptides in human ileal and colonic mucosa

Impact of intestinal PepT1 on the kinetics and dynamics of N-formyl-methionyl-leucyl-phenylalanine, a bacterially-produced chemotactic peptide

The primary purpose of this study was to evaluate the intestinal permeability (P(eff)) of N-formyl-methionyl-leucyl-phenylalanine (fMet-Leu-Phe), a bacterially derived chemotactic tripeptide, in the duodenum, jejunum, ileum, and colon of wild-type and PepT1 knockout mice. A secondary purpose was to determine if the presence of intestinal PepT1 translated into fMet-Leu-Phe directed neutrophil migration in these animals. Using an in situ single pass perfusion technique, the P(eff) of [(3)H]fMet-Leu-Phe was substantially reduced in the duodenum, jejunum, and ileum of PepT1 knockout mice as compared to wild-type animals. In contrast, the P(eff) of [(3)H]fMet-Leu-Phe in colon was unchanged between genotypes and about 5% of that in small intestine. Jejunal uptake of [(3)H]fMet-Leu-Phe was specific for PepT1 and saturable with an intrinsic K(0.5) of 1.6 mM. The peptide/histidine transporters PhT1 and PhT2 were not involved in [(3)H]fMet-Leu-Phe uptake. Myeloperoxidase activity (a measure of neutrophil migration) was significantly increased following 4 h perfusions of 10 μM fMet-Leu-Phe in the jejunum of wild-type mice and was abolished by 50 mM glycylglycine; no change was observed in the jejunum of PepT1 knockout mice. Likewise, fMet-Leu-Phe perfusions had no effect on myeloperoxidase activity in the colon of either genotype. In conclusion, these findings demonstrated that PepT1 had a major influence on the permeability of fMet-Leu-Phe in duodenum, jejunum, and ileum in wild-type mice and on inflammatory response in intestinal regions that expressed PepT1.

Deformylase as a novel antibacterial target

Bacterial genomics has revealed a plethora of previously unknown targets of potential use in the discovery of novel antibacterial drugs. However, so far little has emerged from this approach. Peptide deformylase is an interesting target that was discovered more than 30 years ago, but was not exploited until recently. The reawakening of interest in this target resulted from an improved understanding of the enzyme, making it a more tractable and attractive target. Information on the properties of the enzyme, such as its three-dimensional structure, the activity of inhibitors, its resistance and suitability as a target are discussed.

Bacteria and inflammatory bowel disease

The cause of inflammatory bowel disease is unknown, but both environmental and genetic factors are implicated. This review presents evidence from recent studies involving both animal models and inflammatory bowel disease patients, which supports a role for bacteria in the aetiology and pathogenesis of Crohn's disease and ulcerative colitis.

Ileal mucosal response to bacterial toxin challenge

BACKGROUND

The cause of postinjury intestinal mucosal barrier disruption remains obscure. The present study examines the hypothesis that the bacterial toxin formyl-methionyl leucyl phenylalanine (FMLP) plays an initial role in this process.

METHODS

Mucosal permeability to fluorescein isothiocyanate-labeled dextran (4,400 molecular weight) was measured in perfused distal rat ileum with and without FMLP. Dextran and myeloperoxidase appearance in the lumenal perfusate was assessed in response to surrogates of traumatic stress: ischemia/reperfusion, total abdominal irradiation, and total parenteral nutrition. Recovery of FMLP in the effluent of static closed and perfused ileal loops was determined by mass spectrometry. Release of mast cell mediators in the presence of FMLP was determined in ileal everted sacs.

RESULTS

Seventy-five percent of FMLP was recovered in perfusion effluent in contrast to 5% in closed loops. There was a transient increase in ileal permeability in FMLP/perfused, untreated rats, and in ischemia/reperfusion and total parenteral nutrition treated rats that was recorded with a concomitant increment in myeloperoxidase (inflammatory marker) in all experimental models except irradiated rats, which were unresponsive to FMLP. FMLP responsiveness was associ. ated with a significant rise in release of serotonin (mast cell mediator).

CONCLUSION

These results suggest that mast cells and other resident inflammatory cells within the gut wall are involved in FMLP-induced changes in mucosal barrier permeability and raise the possibility that under conditions of traumatic stress, proinflammatory mediators within the gut wall might be activated by toxic factors in the gut lumen.

Interleukin-8 expression by human neutrophils activated by Helicobacter pylori soluble proteins

BACKGROUND

Helicobacter pylori soluble proteins may serve as chemoattractants for neutrophils. Once extravasated and attracted to the gastric mucosa, neutrophils themselves may be a source of interleukin-8 (IL-8), further amplifying the inflammatory response. We evaluated IL-8 expression and the activation of human neutrophils by H. pylori products.

METHODS

After neutrophils had been stimulated with H. pylori culture supernatant, IL-8 mRNA expression was assessed by quantitative reverse transcription polymerase chain reaction, using synthetic standard RNA at 0, 1, 2, 4, and 9 h. The amount of IL-8 protein was measured by enzyme-linked immunosorbent assay (ELISA). Lymphocyte function-associated antigen-1beta (LFA-1beta) (CD18) expression was determined with flow cytometry, and myeloperoxidase secretion was analyzed with ELISA. After acetohydroxamic acid (AHA) and/or N-tert-butoxycarbonyl-methionyl-leucyl-phenylalanine (BOC-MLP) was added to H. pylori culture supernatant, IL-8 ELISA was analyzed for 9 h.

RESULTS

IL-8 mRNA expression by stimulated neutrophils was 16 to 67 times greater than by controls, peaking at 2 h after stimulation. The amount of IL-8 protein was markedly increased at 4 h after stimulation. H. pylori culture supernatant enhanced LFA-1beta expression and myeloperoxidase secretion by neutrophils. AHA and/or BOC-MLP decreased IL-8 production at 2-4 h after stimulation.

CONCLUSIONS

H. pylori-induced neutrophil recruitment may be mediated via IL-8 expressed by neutrophils activated by H. pylori soluble proteins. This may explain the gastric mucosal inflammatory response to the non-invasive organism.

Mucosal factors inducing neutrophil movement in ulcerative colitis: the role of interleukin 8 and leukotriene B4

BACKGROUND

The movement of neutrophils into the colonic mucosa in ulcerative colitis is induced by chemokines including interleukin 8 (IL8) and leukotriene B4 (LTB4).

AIMS

To compare the ability of mucosa from ulcerative colitis patients and controls to stimulate neutrophil movement, to define the contribution of LTB4 to this, and to define the relative biological importance of LTB4 and IL8.

PATIENTS

Resected mucosa was obtained from seven control patients and 10 patients with ulcerative colitis.

METHODS

Mucosal homogenate supernatants were used to stimulate isolated neutrophils and the effect assessed by the neutrophil shape change response. Responses were inhibited with either the LTB4 receptor antagonist SC41930- or neutralising anti-IL8 antibody. LTB4 was extracted and assayed by RIA.

RESULTS

Homogenate supernatants from inflamed mucosa were more bioactive (median 1.2 mg/ml-1 induced 50% response) than those from uninflamed mucosa (4.25 mg/ml-1 induced 50% response; difference 2.8 mg/ml-1 (96.5% CI 0.5 to 6.1, p < 0.05). Maximal inhibition by SC41930 of the response was significantly greater in inflamed mucosa (54% median) than in uninflamed mucosa (34%). This inhibition correlated with the level of immunoreactive LTB4 (r = 0.78). Anti-IL8 reduced bioactivity of homogenate supernatants from inflamed mucosa (at 1:10 dilution) by 11.4% (IQR 1.2 to 51.8, p = 0.021) whereas SC41930 reduced it by 54.8% (35.6 to 77.5, p = 0.008).

CONCLUSIONS

Inflamed colonic mucosa releases more neutrophil movement inducing bioactivity than uninflamed mucosa, and has greater LTB4 dependent activity. It yields both IL8 and LTB4 dependent activity but greater LTB4 dependent activity.

In vivo rectal inflammatory mediator changes with radiotherapy to the pelvis

In vivo changes in the rectal values of eicosanoid inflammatory mediators induced by pelvic radiotherapy were measured to study the pathophysiology of the early radiation bowel reaction. Ten patients having pelvic radiotherapy, aged 57 to 78, had rectal dialysis. Values of the eicosanoids leukotriene B4 (LTB4), thromboxane B2 (TXB2), and prostaglandin E2 (PGE2) were measured before radiotherapy, at the end of radiotherapy, and at least four weeks after radiotherapy. Values of LTB4 rose with radiotherapy from 0.21 ng.ml-1 (median) to 1.14 ng.ml-1 (p = 0.012); PGE2 rose from 0.60 ng.ml-1 to 1.58 ng.ml-1 (p = 0.038), and TXB2 rose from 0.365 ng.ml-1 to 1.6 ng.ml-1 (p = 0.005). The rise in eicosanoid inflammatory mediators may have an important role in the pathophysiology of the early radiation bowel reaction.