Antimicrobial peptides in the gastrointestinal tract

Increased lysozyme expression in gastric biopsies with intestinal metaplasia and pseudopyloric metaplasia

Lysozyme is an innate enzyme with potent non-immunological antibacterial properties in the upper intestinal tract. Lysozyme expression (ly-ex) was investigated in 80 consecutive sets of gastric biopsies having normal gastric mucosa (n=20), chronic gastritis (n=20), gastric intestinal metaplasia (IM, n=20), and pseudopyloric metaplasia (PpM, n=20). In biopsies with normal mucosa and with chronic gastritis, the foveolar epithelium and the mucus neck cells of the fundic mucosa as well as the antropyloric glands had moderate (++) to marked (+++) ly-ex whereas the fundic glands proper did not express lysozyme. In IM the goblet and the Paneth cells showed marked (+++) ly-ex. PpM, developing in patients with autoimmune (corpus) gastritis, had moderate ly-ex (++), thus contrasting with the negative ly-ex in the normal or inflamed fundic mucosa. The Helicobacter pylori did not proliferate in areas with IM or with PpM. The lysozyme production in IM and in PpM might be upregulated to eradicate ingested, proliferating bacteria in acid-deficient stomachs.

Microbial biofilms in the human gastrointestinal tract

The human gastrointestinal tract contains rich and diverse microbiotas along its length. However, while extensive studies have been made on lumenal bacterial communities in the gut, less work has been carried out on organisms growing in biofilms, where individual groups of bacteria exist in a multiplicity of different microhabitats and metabolic niches associated with the mucosa, the mucus layer and particulate surfaces in the gut lumen. Bacteria and yeasts also occur in biofilms attached to artificial surfaces and devices implanted in the host, such as in patients being fed via enteral tubes. Although we are just beginning to investigate the composition and metabolic activities of these structures, increasing evidence suggests that they are important to the host in both health and disease. There is mounting interest in mucosal biofilms in the colon, especially with respect to their role in inflammatory bowel disease. Because bacteria growing in biofilms are more resistant to antibiotics than unattached organisms, it is often difficult to modify the structure and composition of these communities, or to eradicate them from the body. However, recent work has shown that there is considerable potential to alter the species composition of mucosal biofilms in a beneficial way using synbiotics.

Two membrane proteins from Bifidobacterium breve UCC2003 constitute an ABC-type multidrug transporter

Intrinsic resistance to drugs is one of the main determining factors in bacterial survival in the intestinal ecosystem. This is mediated by, among others, multidrug resistance (MDR) transporters, membrane proteins which extrude noxious compounds with very different chemical structures and cellular targets. Two genes from Bifidobacterium breve encoding hypothetical membrane proteins with a high homology with members of the ATP-binding cassette (ABC) family of multidrug efflux transporters, were expressed separately and jointly in Lactococcus lactis. Cells co-expressing both proteins exhibited enhanced resistance levels to the antimicrobials nisin and polymyxin B. Furthermore, the drug extrusion activity in membrane vesicles was increased when both proteins were co-expressed, compared to membranes in which the proteins were produced independently. Both proteins were co-purified from the membrane as a stable complex in a 1:1 ratio. This is believed to be the first study of a functional ABC-type multidrug transporter in Bifidobacterium and contributes to our understanding of the molecular mechanisms underlying the capacity of intestinal bacteria to tolerate cytotoxic compounds.

Does small intestinal atresia affect epithelial protein expression in human newborns?

OBJECTIVES

Bowel segments distal to a congenital intestinal obstruction have been suggested to be immature. In other words, luminal components such as amniotic fluid (before birth) and/or enteral nutrition (after birth) may be required to activate intestinal epithelial protein expression, thereby influencing epithelial differentiation. We investigated cell-type-specific protein expression proximal and distal to jejunal and ileal atresias in human newborns.

PATIENTS AND METHODS

We immunohistochemically studied intestinal tissue specimens of 16 newborns who had undergone surgery for jejunal or ileal atresia. Sections were taken from both the proximal and distal sides of the atresias.

RESULTS

For all patients, the enterocyte-specific markers lactase, sucrase-isomaltase, sodium glucose cotransporter 1, glucose transporters 2 and 5, intestinal fatty acid-binding protein and alkaline phosphatase were expressed at a mean 3 +/- 1 days after birth, both proximal and distal to jejunal and ileal atresias. Expression of goblet cell-specific markers mucin 2 and trefoil factor 3 and that of the Paneth cell marker lysozyme was maintained at either side of the atretic segment.

CONCLUSIONS

With respect to the markers used, the human small intestinal epithelium is already differentiated shortly after birth. The absence of intestinal continuity in case of a jejunal or ileal atresia does not affect epithelial protein expression. This would seem to indicate that the developing small intestinal epithelium matures independently of luminal components.

Antagonistic activities of lactobacilli and bifidobacteria against microbial pathogens

The gastrointestinal tract is a complex ecosystem that associates a resident microbiota and cells of various phenotypes lining the epithelial wall expressing complex metabolic activities. The resident microbiota in the digestive tract is a heterogeneous microbial ecosystem containing up to 1 x 10(14) colony-forming units (CFUs) of bacteria. The intestinal microbiota plays an important role in normal gut function and maintaining host health. The host is protected from attack by potentially harmful microbial microorganisms by the physical and chemical barriers created by the gastrointestinal epithelium. The cells lining the gastrointestinal epithelium and the resident microbiota are two partners that properly and/or synergistically function to promote an efficient host system of defence. The gastrointestinal cells that make up the epithelium, provide a physical barrier that protects the host against the unwanted intrusion of microorganisms into the gastrointestinal microbiota, and against the penetration of harmful microorganisms which usurp the cellular molecules and signalling pathways of the host to become pathogenic. One of the basic physiological functions of the resident microbiota is that it functions as a microbial barrier against microbial pathogens. The mechanisms by which the species of the microbiota exert this barrier effect remain largely to be determined. There is increasing evidence that lactobacilli and bifidobacteria, which inhabit the gastrointestinal microbiota, develop antimicrobial activities that participate in the host's gastrointestinal system of defence. The objective of this review is to analyze the in vitro and in vivo experimental and clinical studies in which the antimicrobial activities of selected lactobacilli and bifidobacteria strains have been documented.

Paneth cell granule depletion in the human small intestine under infective and nutritional stress

Paneth cells are important contributors to the intestinal antimicrobial barrier through synthesis and release of antimicrobial peptides and proteins. Animal studies indicate that Paneth cell numbers, location and granule morphology are altered by infection and zinc status. We examined human tissue to determine whether Paneth cell numbers, distribution or granule morphology are altered in infective, inflammatory and nutritional disorders. Archival sections from infective disorders (giardiasis, cryptosporidiosis, HIV, helminth infection) were compared with active inflammatory conditions (coeliac, Crohn's and graft-versus-host diseases) and histologically normal tissues. A subset of tissues was studied by electron microscopy and TUNEL staining for apoptosis. Human defensin-5 (HD5) peptide and mRNA was analysed by immunohistochemistry, in situ hybridization and quantitative reverse transcription polymerase chain reaction. Sections from a tropical population cohort study were then analysed to determine the relationship of granule depletion to infection, nutritional status and plasma zinc concentration. In HIV-related cryptosporidiosis, but not other disorders, Paneth cells were reduced in number and markedly depleted of granules. Paneth cell granule depletion was associated with reduced HD5 immunoreactivity, but this was not due to apoptosis and there was no reduction in mRNA transcripts. In the tropical population studied, depletion of granules was associated with reduced body mass index, reduced plasma zinc levels and HIV infection. Paneth cell granules in human small intestine may be depleted in response to infective and nutritional stress. We postulate that this is one mechanism through which zinc status influences host susceptibility to intestinal infection.

Alpha-defensins in the gastrointestinal tract

The human intestinal tract is constantly exposed to an enormous indigenous bacterial flora. It has recently been recognised that antimicrobial peptides of the defensin family likely play a role in protection against microbial invasion at a variety of mucosal epithelial surfaces, including that of the intestinal tract. To date, six alpha-defensins have been identified in humans. Four of these, designated Human Neutrophil Peptides (HNP) 1,2,3 and 4, form part of the armoury of neutrophils, where they participate in systemic innate immunity. The remaining two, Human Defensin (HD) 5 and 6, are expressed in intestinal Paneth cells, and probably contribute to innate defense of the GI mucosal surface. Murine intestinal alpha-defensins (the 'cryptdins') have been extensively studied, but less is known about their human counterparts. The putative mature HD-5 was chemically synthesised and used to raise polyclonal antiserum. Using this anti-HD-5 antiserum, the expression of HD-5 in normal and inflamed intestinal mucosal samples was studied using immunohistochemistry. HD-5 is expressed in Paneth cells and also in some villous epithelial cells in normal duodenum, jejunum and ileum. HD-5 is not expressed in the normal stomach or colon. In cases of gastritis, colonic Crohn's disease and ulcerative colitis, HD-5 is expressed in metaplastic Paneth cells. Utilizing the anti-HD-5 antiserum, native HD-5 was isolated and purified from acid extracts of normal terminal ileal mucosal epithelial cells using cation exchange and reverse phase high pressure liquid chromatography. The purified peptide was characterised using N-terminal amino acid sequence and mass spectral analysis. Antimicrobial activity of the peptide was assessed using a sensitive colony forming unit antimicrobial assay. HD-5 is stored in the predicted precursor form in Paneth cells, and this form does not have antimicrobial activity against a defensin sensitive Salmonella. Potential processing of the precursor form of the HD-5 peptide into a mature active form, was studied by stimulating Paneth cell granule secretion in freshly isolated, cultured ileal crypts. A truncated form of the precursor form of HD-5, but not the predicted mature form, was present in the culture supernatant. Recently published studies suggest that further processing of the molecule occurs in vivo. The expression of HNP 1-3 in the normal intestinal mucosa and in cases of inflammatory bowel disease was studied. In the normal intestinal mucosa, HNP are expressed only in sparse lamina propria neutrophils, and not in Paneth cells. In cases of active ulcerative colitis and Crohn's disease, scattered surface epithelial cells, as well as numerous lamina propria neutrophils, were seen to express HNP. In conclusion, HD-5 is stored only in its precursor form in normal ileal Paneth cells, and partial processing of the peptide to a mature form occurs during and/or after secretion. In inflammatory bowel disease, HD-5 is expressed in metaplastic Paneth cells in the colon, and HNP is expressed by some surface epithelial cells. These studies suggest that antimicrobial defensin peptides may be important in protection of the host against microbial invasion in states of intestinal inflammation.

Cell type-specific expression and coregulation of murine resistin and resistin-like molecule-alpha in adipose tissue

Adipocytes are the exclusive or predominant source of several secreted proteins that exert profound effects on systemic carbohydrate and lipid metabolism. Resistin, a 10-kDa adipose tissue specific secretory protein, has recently been implicated in exerting a negative effect on systemic insulin sensitivity. It is, however, not known how resistin mediates this insulin-desensitizing effect or what regulatory mechanisms control resistin expression. Resistin-like molecule-alpha (RELMalpha), a homolog of resistin originally identified by its upregulation in asthmatic lung, is another secreted protein expressed in adipose tissue. The regulation of RELMalpha in adipose tissue and its relationship to resistin expression has not been addressed so far. Here, we demonstrate that the expression of resistin and RELMalpha are similarly regulated in adipose tissue despite the fact that RELMalpha is exclusively expressed in the stromal vascular fraction of adipose tissue and not in adipocytes. Interestingly, this coregulation is limited to adipose tissue as the expression of RELMalpha in lung is independent of metabolic regulation. Additionally, we show that resistin and RELMalpha levels are not subject to regulation by proinflammatory stimuli. Finally, acute hyperglycemia leads to up-regulation of resistin and RELMalpha transcription in various adipose depots.

Expression of antimicrobial neutrophil defensins in epithelial cells of active inflammatory bowel disease mucosa

BACKGROUND/AIMS

The normal intestinal epithelium is increasingly being recognised as an important component of the mucosal innate protection against microorganisms. Human neutrophil defensins 1-3 (HNP 1-3) and lysozyme are components of the systemic innate immunity. The aim of this study was to investigate the expression of HNP 1-3 and lysozyme in normal and active inflammatory bowel disease (IBD) mucosa.

METHODS

Mucosal tissue sections were studied by immunohistochemistry using antibodies to neutrophil defensins 1-3 and lysozyme. Extracts of purified intestinal epithelial cells were used for immunoblotting studies and antimicrobial activity against the phoP negative strain of Salmonella typhimurium.

RESULTS

Surface epithelial cells strongly immunoreactive for neutrophil defensins and lysozyme were seen in active ulcerative colitis and Crohn's disease (but not normal or inactive IBD) mucosal samples. Many of these cells coexpressed both of the antimicrobial proteins. Immunoblotting studies confirmed the expression of neutrophil defensins in extracts of purified ulcerative colitis epithelial cells, which also demonstrated antimicrobial activity.

CONCLUSION

HNP 1-3 and lysozyme are expressed in surface enterocytes of mucosa with active IBD and they may play an important role in intestinal host defence against luminal microorganisms.

Is there a role for CEA in innate immunity in the colon?

Carcinoembryonic antigen (CEA) is a well known tumor marker associated with the progression of colorectal tumors. The CEA family of glycoproteins has been fully characterized and the function of some of its members is now beginning to be understood. Here, we advance the hypothesis that, rather than functioning in cell adhesion as has been suggested previously, CEA plays a role in protecting the colonic mucosa from microbial invasion. This hypothesis is based on new microscopic, molecular, phylogenetic and microbiological evidence.

Human defensin 5 is stored in precursor form in normal Paneth cells and is expressed by some villous epithelial cells and by metaplastic Paneth cells in the colon in inflammatory bowel disease

BACKGROUND AND AIMS

Intestinal epithelial cell derived antimicrobial peptides of the defensin family may play a major role in host defence against microorganisms. Our aims were to (i) isolate, characterise, and investigate the processing of human defensin 5 (HD-5) in normal Paneth cells and (ii) investigate expression of HD-5 in active inflammatory bowel disease (IBD).

METHODS

Antiserum raised against chemically synthesised putative mature HD-5 was used for immunohistochemistry and purification of HD-5 from extracts of normal terminal ileal crypts.

RESULTS

In normal and Crohn's disease terminal ileum, HD-5 immunoreactivity was seen in Paneth cells and in some villous epithelial cells. Normal colonic mucosa did not express HD-5 but HD-5 immunoreactivity was seen in cells in the colonic crypt region of many IBD samples. N-terminal amino acid sequence analysis of HD-5 purified from normal terminal ileal Paneth cells consistently showed the predicted sequence of the precursor form of the peptide. Following stimulation of isolated intact normal terminal ileal crypts, a truncated form of HD-5, with the N-terminal sequence GEDNQLAIS, was detected in the supernatant.

CONCLUSIONS

(i) HD-5 is present only in the precursor form in normal terminal ileal Paneth cells and is processed to the mature form during and/or after secretion, (ii) some villous epithelial cells express HD-5, and (iii) HD-5 is expressed by metaplastic Paneth cells in the colon in IBD.

Probiotics in infective diarrhoea and inflammatory bowel diseases

Bacteria are present throughout the gastrointestinal tract, but their pattern and concentration vary greatly. Probiotics are living organisms that supply beneficial health effects to the host. So far the beneficial effects of probiotics have been shown, almost exclusively, under poorly defined experimental conditions. There are little convincing data from well-designed, double-blind controlled trials supporting health-promoting effects. The use of probiotics to treat gastrointestinal infections has produced contrasting results. Apart from information on rotavirus infection in children, there is no convincing evidence from controlled studies on the efficacy of probiotics in the prevention or treatment of infective diarrhoea. However, experimental and clinical studies suggest that there are potential therapeutic roles for probiotics in the treatment of inflammatory bowel diseases. This review focuses on the available data concerning the mechanisms of action of probiotics, and on the results from clinical studies using probiotics to treat infective diarrhoea and inflammatory bowel disease.

The key role of macrophages in the immunopathogenesis of inflammatory bowel disease

Macrophages are important in the host's immunological and inflammatory responses. There is a large population of these cells in the normal intestinal mucosa where they represent the major antigen presenting cell population capable of determining the type of T cell responses that develop to luminal antigens. Studies suggest that the normal intestinal macrophages cannot be easily induced to mediate acute inflammatory responses. In active inflammatory bowel disease there is an increase in the mucosal macrophage population, derived from circulating monocytes. These recruited macrophages are phenotypically different from the resident population of cells and play a major role in mediating the chronic mucosal inflammation seen in patients with ulcerative colitis and Crohn's disease. They secrete many cytokines that are important in the proinflammatory responses, such as interleukin (IL)-1, IL-6, IL-8, IL-12, IL-18, and tumor necrosis factor-alpha. They also release reactive metabolites of oxygen and nitrogen and proteases that degrade the extracellular matrix. Macrophages also appear to be important during resolution of inflammation and repair of the intestinal mucosa that occurs during disease remission.

Expression of beta-defensin genes by human salivary glands

This study investigated expression of genes encoding human beta-defensins 1 and 2 by human salivary glands. Tissues from surgical biopsies were collected fresh onto ice and stored in liquid nitrogen. Total RNA was extracted using Trizol reagent and human beta-defensin messenger RNA detected by reverse transcriptase polymerase chain reaction amplification. DNA sequencing of amplified fragments, after ligation into pGEM-T Easy vector and transformation of competent Escherichia coli, confirmed identities of cloned fragments. Human beta-defensin 1 messenger RNA was detected in all 25 samples that generated amplifiable cDNA, as assessed using abl-specific primers. Three of 13 submandibular gland samples (two normal, one chronically inflamed), and 2 of 2 minor salivary gland samples (one normal, one chronically inflamed) expressed human beta-defensin 2 messenger RNA. All six parotid gland samples studied were negative for human beta-defensin 2 messenger RNA. Thus, human beta-defensin 1 gene expression occurred in all human major and minor salivary glands studied, whereas human beta-defensin 2 expression occurred only in a small number of gland samples.

Neutrophil Defensins Induce Histamine Secretion from Mast Cells: Mechanisms of Action

Defensins are endogenous antimicrobial peptides stored in neutrophil granules. Here we report that a panel of defensins from human, rat, guinea pig, and rabbit neutrophils all have histamine-releasing activity, degranulating rat peritoneal mast cells with EC50 ranging from 70 to 2500 nM, and between 45 and 60% of the total histamine released. The EC50 for defensin-induced histamine secretion correlates with their net basic charge at neutral pH. There is no correlation between histamine release and antimicrobial potency. Degranulation induced by defensins has characteristics similar to those of activation by substance P. The maximum percent histamine release is achieved in <10 s, and it can be markedly inhibited by pertussis toxin (100 ng/ml) and by pretreatment of mast cells with neuraminidase. These properties differ from those for degranulation induced by IgE-dependent Ag stimulation and by the calcium ionophore A23187. GTPase activity, a measure of G protein activation, was induced in a membrane fraction from mast cells following treatment with defensin. Thus, neutrophil defensins are potent mast cell secretagogues that act in a manner similar to substance P and 48/80, through a rapid G protein-dependent response that is mechanistically distinct from Ag/IgE-dependent mast cell activation. Defensins may provide important pathways for communication between neutrophils and mast cells in defenses against microbial agents and in acute inflammatory responses.

Antimicrobial peptides of the brevinin-2 family isolated from gastric tissue of the frog, Rana esculenta

Four structurally related peptides with potent growth-inhibitory activity towards Escherichia coli were isolated from an extract of the stomach of the European green frog Rana esculenta, and were identified as members of the brevinin-2 family. Two peptides, termed brevinin-2Eg (GIMDTLKNLA10 KTAGKGALQS20 LLNHASCK LS30GQC) and brevinin-2Eh (GIMDTLKNLA10 KTAGKGALQS20 LLNHASCKL S30 KQC) have not been described previously. One peptide is identical to brevinin-2Ec, previously isolated from R. esculenta skin secretions, and one peptide is identical to brevinin-2Ef whose structure has been deduced from a cloned cDNA prepared from a R. esculenta skin cDNA library. The data demonstrate that certain peptides of the brevinin-2 family, like the magainins in the toad, Xenopus laevis, may play an important role in protecting the gastrointestinal tract of Ranid frogs against microbial invasion.

Differential lamina propria cell migration via basement membrane pores of inflammatory bowel disease mucosa

BACKGROUND & AIMS

In active inflammatory bowel disease (IBD), the intestinal mucosa is infiltrated by polymorphonuclear cells (PMNs), lymphocytes, and monocytes from the systemic circulation. Using an ex vivo model, we have investigated luminally directed migration of cells out of the lamina propria.

METHODS

Fresh untreated and deepithelialized mucosal samples were studied by electron microscopy. Cells migrating out of the lamina propria were investigated by immunohistochemistry and fluorescence-activated cell sorter analysis.

RESULTS

In intact IBD mucosal samples, tunnels containing cells were prominent in the lamina propria matrix, and PMNs, but not other cell types, were prominent in the epithelium. In deepithelialized mucosal samples, the basement membrane was either destroyed or contained numerous large pores. During culture of deepithelialized mucosal samples, many cells (3.3 [+/-0.8] x 10(5) . g tissue-1 . h-1) migrated out of the lamina propria via basement membrane pores. PMNs and eosinophils were prominent during the first 3 hours of culture, but T cells predominated thereafter. Macrophages also migrated, but B cells were the minority population (<2%) at all times.

CONCLUSIONS

In active IBD mucosa with an intact epithelium, luminally directed migration of lamina propria cells is restricted mainly to PMNs. After loss of the epithelium, other cell types also migrate into the lumen via numerous, large, basement membrane pores.

Potential role of epithelial cell-derived histone H1 proteins in innate antimicrobial defense in the human gastrointestinal tract

In the human gastrointestinal tract, microorganisms are present in large numbers in the colon but are sparse in the proximal small intestine. In this study, we have shown that acid extracts of fresh human terminal ileal mucosal samples mediate antimicrobial activity. Following cation-exchange chromatography, one of the eluted fractions demonstrated antibacterial activity against bacteria normally resident in the human colonic lumen. This activity was further fractionated by reverse-phase high-performance liquid chromatography and identified as histone H1 and its fragments. We have also shown that in tissue sections, immunoreactive histone H1 is present in the cytoplasm of villus epithelial cells. In vitro culturing of detached (from the basement membrane) villus epithelial cells led to the release of antimicrobial histone H1 proteins, while the cells demonstrated ultrastructural features of programmed cell death. Our studies suggest that cytoplasmic histone H1 may provide protection against penetration by microorganisms into villus epithelial cells. Moreover, intestinal epithelial cells released into the lumen may mediate antimicrobial activity by releasing histone H1 proteins and their fragments.