Relation of human gastrointestinal mucus to disease states

Gut biofilm forming bacteria in inflammatory bowel disease

Inflammatory bowel disease (IBD) symbolizes a group of intestinal disorders in which prolonged inflammation occur in the digestive tract (esophagus, large intestine, small intestine mouth, stomach). Both genetic and environmental factors (infections, stress, diet) are involved in the development of IBD. As we know that bacteria are found in the intestinal mucosa of human and clinical observations revealed bacterial biofilms associated with patients of IBD. Various factors and microbes are found to play an essential role in biofilm formation and mucosal colonization during IBD. Biofilm formation in the digestive tract is dependent on an extracellular matrix synthesized by the bacteria and it has an adverse effect on the immune response of the host. There is no satisfactory and safe treatment option for IBD. Therefore, the current research aims to disrupt biofilm in IBD and concentrates predominantly on improving the drug. Here, we review the literature on bacterial biofilm and IBD to gather new knowledge on the current understanding of biofilm formation in IBD, host immune deregulation and dysbiosis in IBD, molecular mechanism, bacteria involved in biofilm formation, current and future regimen. It is urgently required to plan new ways to control and eradicate bacteria in biofilms that will open up novel diagnostic and therapeutic avenues for IBD. This article includes the mechanism of signaling molecules with respect to the biofilm-related genes as well as the diagnostic methods and new technologies involved in the treatment of IBD.

Human gut endogenous proteins as a potential source of angiotensin-I-converting enzyme (ACE-I)-, renin inhibitory and antioxidant peptides

It is well known that endogenous bioactive proteins and peptides play a substantial role in the body's first line of immunological defence, immune-regulation and normal body functioning. Further, the peptides derived from the luminal digestion of proteins are also important for body function. For example, within the peptide database BIOPEP (http://www.uwm.edu.pl/biochemia/index.php/en/biopep) 12 endogenous antimicrobial and 64 angiotensin-I-converting enzyme (ACE-I) inhibitory peptides derived from human milk and plasma proteins are listed. The antimicrobial peptide database (http://aps.unmc.edu/AP/main.php) lists over 111 human host-defence peptides. Several endogenous proteins are secreted in the gut and are subject to the same gastrointestinal digestion processes as food proteins derived from the diet. The human gut endogenous proteins (GEP) include mucins, serum albumin, digestive enzymes, hormones, and proteins from sloughed off epithelial cells and gut microbiota, and numerous other secreted proteins. To date, much work has been carried out regarding the health altering effects of food-derived bioactive peptides but little attention has been paid to the possibility that GEP may also be a source of bioactive peptides. In this review, we discuss the potential of GEP to constitute a gut cryptome from which bioactive peptides such as ACE-I inhibitory, renin inhibitory and antioxidant peptides may be derived.

Microbial biofilms and gastrointestinal diseases

The majority of bacteria live not planktonically, but as residents of sessile biofilm communities. Such populations have been defined as 'matrix-enclosed microbial accretions, which adhere to both biological and nonbiological surfaces'. Bacterial formation of biofilm is implicated in many chronic disease states. Growth in this mode promotes survival by increasing community recalcitrance to clearance by host immune effectors and therapeutic antimicrobials. The human gastrointestinal (GI) tract encompasses a plethora of nutritional and physicochemical environments, many of which are ideal for biofilm formation and survival. However, little is known of the nature, function, and clinical relevance of these communities. This review summarizes current knowledge of the composition and association with health and disease of biofilm communities in the GI tract.

Six2 activity is required for the formation of the mammalian pyloric sphincter

The functional activity of Six2, a member of the so/Six family of homeodomain-containing transcription factors, is required during mammalian kidney organogenesis. We have now determined that Six2 activity is also necessary for the formation of the pyloric sphincter, the functional gate at the stomach-duodenum junction that inhibits duodenogastric reflux. Our data reveal that several genes known to be important for pyloric sphincter formation in the chick (e.g., Bmp4, Bmpr1b, Nkx2.5, Sox9, and Gremlin) also appear to be required for the formation of this structure in mammals. Thus, we propose that Six2 activity regulates this gene network during the genesis of the pyloric sphincter in the mouse.

Colonization of mucin by human intestinal bacteria and establishment of biofilm communities in a two-stage continuous culture system

The human large intestine is covered with a protective mucus coating, which is heavily colonized by complex bacterial populations that are distinct from those in the gut lumen. Little is known of the composition and metabolic activities of these biofilms, although they are likely to play an important role in mucus breakdown. The aims of this study were to determine how intestinal bacteria colonize mucus and to study physiologic and enzymatic factors involved in the destruction of this glycoprotein. Colonization of mucin gels by fecal bacteria was studied in vitro, using a two-stage continuous culture system, simulating conditions of nutrient availability and limitation characteristic of the proximal (vessel 1) and distal (vessel 2) colon. The establishment of bacterial communities in mucin gels was investigated by selective culture methods, scanning electron microscopy, and confocal laser scanning microscopy, in association with fluorescently labeled 16S rRNA oligonucleotide probes. Gel samples were also taken for analysis of mucin-degrading enzymes and measurements of residual mucin sugars. Mucin gels were rapidly colonized by heterogeneous bacterial populations, especially members of the Bacteroides fragilis group, enterobacteria, and clostridia. Intestinal bacterial populations growing on mucin surfaces were shown to be phylogenetically and metabolically distinct from their planktonic counterparts.

Aspirin-like drugs cause gastrointestinal injuries by metallic cation chelation

Aspirin-like (nonsteroidal anti-inflammatory) drugs may cause injuries including ulcers to the gastrointestinal tract by chelation of the divalent and/or multivalent metallic cations in the gastrointestinal mucus and mucosa, as suggested by the chemical properties of these drugs and supported by experimental and clinical data.

Isolation and partial characterization of serine- and threonine-rich porcine gastric mucus glycopeptides

1. Two subfractions from purified porcine gastric mucus glycopeptide were found to separate from each other by cesium chloride equilibrium centrifugation. The highest density fraction and two lower density fractions separated were designated VHD, HD and LD, respectively. A comparative study of these components was made. 2. The high and low density fractions, HD and LD, appeared almost the same or identical, while VHD differed completely from either of them in the following respects: (1) VHD exhibited strong alcian blue binding activity. (2) 57% of VHD bound to the DEAE-Toyopearl column equilibrated with 0.2 M NaCl. (3) VHD eluted from the Sephacryl S-400 column as a lower molecular subunit. (4) One third of the sialic acid as a minor component in VHD was constituted by N-glycolylneuraminic acid. (5) Carbohydrate composition showed typical mucus glycoprotein with slightly higher fucose content. (6) Amino acid compositions of the anionic components prepared from VHD showed the highest Ser/Thr ratio, 1.92 compared to 0.46 for LD and 0.62 for HD. (7) Oligosaccharide released from VHD by alkaline-sodium borohydride treatment was larger than that from HD or LD. 3. The above results indicate the minor component, VHD, separated from the major components, to be a quite similar but not identical component to the so-called sulfated mucus glycoprotein reported previously [Slomiany et al. (1972) J. biol. Chem. 247, 5062-5070].

Immunohistochemical study of blood group activities in the alimentary canal in normal and pathologic conditions with reference to the nature of epithelial mucopolysaccharides

ABO(H)- and Lewis-activities in the human alimentary canal were investigated by the avidin-biotin-peroxidase complex method using commercial mouse monoclonal antibodies in order to clarify (1) the changes apparent in these activities in carcinoma of the digestive tract or premalignant intestinal metaplasia of the stomach and (2) the relationship of the activities to the histochemical properties of epithelial mucins examined by Alcian blue (pH 2.5)/periodic acid-Schiff (PAS) double staining. In intestinal metaplasia, ectopic goblet cells showed various degrees of ABO(H)-activities according to the PAS stainability of mucins and revealed Lea-activity even in a Le(a-b+) group. In carcinoma of the alimentary canal, ABO(H)- and Lewis-activities compatible with the donors' blood groups were located mainly at the PAS-positive cell surface, and in the Golgi bodies and secretions. It was thus concluded that quantitative and/or qualitative changes in blood group activities were closely associated with those of epithelial mucopolysaccharides.

A histochemical study of the mucins in the digestive tract of the chicken

Little is known about the distribution of glycoproteins in the digestive tube of birds. In the present study, the localization and distribution of mucins in the digestive tract of the chicken are reported. Sialo- and sulpho-mucins were widely distributed throughout the chicken digestive tube. Some of the mucous cells of the proximal segment of the proventriculus presented neutral glycoproteins; in the medial segment, surface cells containing only sialo-mucins were observed. Surface cells of the gizzard contained both sialo- and sulpho-mucins while PAS-positive material was localized in the lumen of the glands. 2 types of mucous cells were observed in the small intestine; 1 type contained only sialo-mucins and the other contained both sialo- and sulpho-mucins. In the large intestine and caecum, both types of acid mucins were present in the mucous cells. In conclusion, the distribution of glycoproteins in the chicken reported in the present study show marked differences with that reported in other avian species.

Mucosal surface pH of the large intestine of the rat and of normal and inflamed large intestine in man

The surface pH of rat distal colonic mucosa and human rectal mucosa was measured in vitro using first a small pH electrode with a flattened tip. In buffer with pH 7.56 the mean rat colonic surface pH was 6.72. Lowering the buffer pH in steps resulted in a small fall in surface pH, the values being buffer pH 7.06 surface pH 6.64, buffer pH 6.58 surface pH 6.61 and finally buffer pH 6.09 surface pH 6.39. Similar results were obtained with a buffer where butyrate, 30 mmol/l replaced chloride and when a CO2/bicarbonate buffer was used. During the time taken for the study transmural potential difference only changed by 1-2 mV. Serosal surface pH changed with buffer pH, suggesting that the maintained surface pH is a property of the mucosal surface only. The surface pH of human rectal mucosa was similar to that of rat distal colonic mucosa. As buffer pH fell from pH 7.51 to 5.96 mucosal surface pH only fell from pH 6.80 to 6.26. The values obtained in ulcerative proctitis did not differ from normal mucosa. Secondly pH microelectrodes were used to measure the juxta mucosal pH and the pH-microclimate thickness when luminal pH was controlled. The microclimate had a pH 6.63 adjacent to the mucosa with a thickness of 840 micron. The importance of mucus in maintaining the microclimate was shown by n-acetyl cysteine thinning and prostaglandin E2 thickening the layer. These results describe a surface microclimate in the large intestine of appreciable thickness and a constant juxta mucosal pH. Luminal pH changes produce only a small change in microclimate pH.

Histochemical demonstration of desialation and desulphation of normal and inflammatory bowel disease rectal mucus by faecal extracts

Experiments were carried out to assess the susceptibility of normal and inflammatory bowel disease rectal mucus to desulphation and desialation by faecal extracts and by bacterial sialidase. The effects were assessed histochemically using a combined high iron diamine (HID) and alcian blue (AB) stain for sulphomucins and sialomucins. Rectal mucus in biopsies from controls (irritable bowel syndrome) and patients with ulcerative colitis or Crohn's disease was resistant to desialation by Clostridium perfringens sialidase, but susceptible to desialation and desulphation by bacteria-free extracts of normal faeces. Periodic acid-Schiff (PAS) staining of adjacent sections similarly treated showed retention of neutral mucus. One faecal extract selectively desulphated all 42 biopsies, causing the goblet cells to change from HID positive to AB positive, suggesting that most, or all HID positive cells also contain sialomucins. This alters the interpretation of previous histochemical studies. Faecal extracts from patients with active ulcerative colitis (n = 6) had desialating and desulphating effects similar to faecal extracts from normal subjects (n = 6). Ulcerative colitis (n = 21), Crohn's disease (n = 18), and control (irritable bowel syndrome) (n = 17) rectal biopsies all showed similar susceptibility to desulphation by a pooled normal faecal extract, but rectal biopsies from patients with Crohn's disease proved more resistant to desialation than control or ulcerative colitis biopsies (p less than 0.02). These studies imply that colonic mucus undergoes continual desulphation and desialation in vivo as a result of faecal enzyme activity that is probably mainly of bacterial origin. Altered susceptibility of colonic mucus to this may be important in the pathogenesis of colonic disease.

Histochemical and morphologic studies of mucosa bordering rectosigmoid carcinomas: comparisons with normal, diseased, and malignant colonic epithelium

Surgically obtained rectosigmoid mucosa ("transitional" mucosa, TM) adjacent to eight primary carcinomas was compared with diseased mucosa (DM) from eight patients without primary carcinoma and mucosa from two normal control subjects by mucin histochemical and morphologic techniques. No differences were found between TM and DM that might have suggested premalignant changes unique to TM. An excess of sialidase-susceptible sialomucins was found in both TM and DM, as was loss of the sulfomucin-sialomucin gradient usually found between normal crypts and surface cells. Increased sialic acid in TM and DM may represent a nonspecific response to injury or inflammation and has been found in other epithelia under similar circumstances. Sialidase also induced substantial reduction of periodic acid-Schiff (PAS) staining, probably due to loss of sialic acid since no other sugars were released during sialidase digestion, as determined by thin-layer chromatography analysis of post-digestion supernatants. Carcinomas generally showed more staining with PAS than with basic dyes; PAS staining was minimally reduced by diastase and sialidase but markedly reduced by phenylhydrazine interposition, suggesting that some type of neutral glycoprotein was responsible. Finally, it was found that overreliance on the high-iron diamine-Alcian blue technique as a single procedure is unwise; this procedure should be accompanied by the use of singly applied dyes, especially high-iron diamine, together with other enzymatic and staining procedures.

A functional model for extracellular gastric mucus in the rat

There is no morphologically detectable, continuous layer of extracellular mucus over the undamaged gastric mucosa of the rat. Instead, the mucosa is only partially covered by an interconnected network of mucous strands and sheets. This mucus is strongly acidic (sulphated) and is released by epithelial cells which line the isthmic and lower foveolar regions of the gastric glands of the fundus. A thick layer of gelatinous mucus is, however, released within 5 min after topical application of ulcerogenic agents. This mucus is released as a result of exfoliation and disintegration of interfoveolar surface epithelial cells. The released mucous glycoprotein is neutral or weakly acidic and is readily distinguished from the fibrous mucus produced by the epithelial cells which line the upper regions of the gastric glands. The preexisting network of acidic, fibrous mucus is retained at the luminal surface of the mucous cap which is produced over sites of damage. The layer of fibrous mucus is reinforced during the development of mucosal damage by accelerated release of mucous strands from the gastric glands. We propose that the fibrous mucus acts as an external, restraining layer to maintain the locally released, gelatinous mucus over sites of damage during a period in which epithelial continuity is restored by emigration of cells from the gastric glands.

Peanut lectin and anti-Ii antibodies reveal structural differences among human gastrointestinal glycoproteins

Human gastrointestinal glycoproteins (mucins), isolated by pepsin digestion from foetal stomachs and meconia, and from paired tumour and non-neoplastic mucosal samples of patients with gastric and colorectal carcinomas, were tested for precipitating reactions with peanut lectin (PNL) and four anti-carbohydrate antibodies (two anti-I, Ma and Low, and two anti-i, Den and Galli). There was remarkable correlation between reactivities with PNL and anti-I (Ma): both reagents reacted with non-neoplastic gastric glycoproteins of "non-secretors", but not with those of "secretors", and also with the majority of gastric tumour and meconium extracts regardless of secretor status. Colorectal tissue extracts (with the exception of one tumour extract) reacted with neither reagent. The various precipitating activities, and results of mild acid hydrolysis and affinity chromatography experiments, enable certain inferences to be made regarding the oligosaccharide moieties of gastrointestinal glycoproteins: (a) expression of PNL and anti-I (Ma) determinants in gastric glycoproteins is dependent on secretor status; (b) extracts reacting with PNL and anti-I (Ma) are mixtures of macromolecules: minor populations react with both reagents, or with PNL only; the major population lacks both determinants, or they are masked by other substitutions; (c) determinants reactive with anti-Ii sera other than anti-I (Ma) are less frequently expressed; and (d) colonic glycoproteins in their lack of PNL and Ii determinants. This suggests that there are structural differences in the oligosaccharide backbones of the two types of glycoprotein.

The assessment of mucus substances in gastric juice from duodenal ulcer patients and normal subjects

The carbohydrate and nitrogen content of the gastric juice was assessed in 18 persons whose diagnosis were unknown to the investigators and the data compared by discriminant function analysis with similar measurements from 42 patients with proven duodenal ulceration and 22 normal controls. It was possible to assess correctly 14 of the 18 patients (77.8%) of the unknown group as having a duodenal ulcer. The results of three patients (16.7%) were equivocal, and one person (5.5%) was wrongly classified. The investigation confirms that the carbohydrate and nitrogen content of gastric secretion in duodenal ulcer patients is abnormal.

Glycosaminoglycan content and synthesis in gastric carcinoma

The glycosaminoglycan (GAG) content of stomach carcinoma tissue was compared with that of non-neoplastic mucosa. GAG synthesis was also studied, by an analysis of 35S-labelled material after incubation of tissue segments in medium containing 35SO4. No significant difference was found between the amount of GAG and its components in the medullary carcinoma tissue and in non-neoplastic mucosa, but GAG synthesis of the carcinoma tissue was at a much higher rate than that of the non-neoplastic mucosa. In the autoradiograph, high 35S uptake in the carcinoma cells was observed. The GAG content of the scirrhous-carcinoma tissue was about twice that of medullary carcinoma.

Membrane glycoproteins shed in defence of the cells of the gastrointestinal tract

The cells lining the gastrointestinal tract are exposed to various potentially harmful agents, including plant lectins and microorganisms. It is proposed that glycoproteins within the mucus layer of the gut protect against these agents. A hypothesis is presented that membrane glycoproteins are shed and, within the mucus close to the cell surface, block the binding of lectins or attachment of microorganisms to membrane receptors. A model is presented that demonstrates that such blocking can be achieved by soluble glycoproteins. The implications of this hypothesis in health and disease are discussed.