Characterization of gastric mucoproteins isolated by equilibrium density-gradient centrifugation in caesium chloride

In Vitro Reconstitution of an Intestinal Mucus Layer Shows That Cations and pH Control the Pore Structure That Regulates Its Permeability and Barrier Function

Dysfunction of the intestinal mucus barrier causes disorders such as ulcerative colitis and Crohn's disease. The function of this essential barrier may be affected by the periodically changing luminal environment. We hypothesized that the pH and ion concentration in mucus control its porosity, molecular permeability, and the penetration of microbes. To test this hypothesis, we developed a scalable method to extract porcine small intestinal mucus (PSIM). The aggregation and porosity of PSIM were determined using rheometry, spectrophotometry, and microscopy. Aggregation of PSIM at low pH increased both the elastic (G') and viscous (G″) moduli, and it slowed the transmigration of pathogenic Salmonella. Molecular transport was dependent on ion concentration. At moderate concentrations, many microscopic aggregates (2-5 μm in diameter) impeded diffusion. At higher concentrations, PSIM formed aggregate islands, increasing both porosity and diffusion. This in vitro model could lead to a better understanding of mucus barrier functions and improve the treatment of intestinal diseases.

Secondary Structure and Glycosylation of Mucus Glycoproteins by Raman Spectroscopies

The major structural components of protective mucus hydrogels on mucosal surfaces are the secreted polymeric gel-forming mucins. The very high molecular weight and extensive O-glycosylation of gel-forming mucins, which are key to their viscoelastic properties, create problems when studying mucins using conventional biochemical/structural techniques. Thus, key structural information, such as the secondary structure of the various mucin subdomains, and glycosylation patterns along individual molecules, remains to be elucidated. Here, we utilized Raman spectroscopy, Raman optical activity (ROA), circular dichroism (CD), and tip-enhanced Raman spectroscopy (TERS) to study the structure of the secreted polymeric gel-forming mucin MUC5B. ROA indicated that the protein backbone of MUC5B is dominated by unordered conformation, which was found to originate from the heavily glycosylated central mucin domain by isolation of MUC5B O-glycan-rich regions. In sharp contrast, recombinant proteins of the N-terminal region of MUC5B (D1-D2-D′-D3 domains, NT5B), C-terminal region of MUC5B (D4-B-C-CK domains, CT5B) and the Cys-domain (within the central mucin domain of MUC5B) were found to be dominated by the β-sheet. Using these findings, we employed TERS, which combines the chemical specificity of Raman spectroscopy with the spatial resolution of atomic force microscopy to study the secondary structure along 90 nm of an individual MUC5B molecule. Interestingly, the molecule was found to contain a large amount of α-helix/unordered structures and many signatures of glycosylation, pointing to a highly O-glycosylated region on the mucin.

More than one disease process in chronic sinusitis based on mucin fragmentation patterns and amino Acid analysis

Objective. To characterise fragmentation patterns and amino acid composition of MUC2 and MUC5AC in chronic sinusitis. Methods. Antigenic identity of purified sinus mucins was determined by ELISA. Fragmentation patterns of a MUC5AC rich sample mucin were analysed by Sepharose CL-2B gel chromatography. Samples, divided into one MUC2 rich and one MUC5AC rich group, were subjected to sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) and their amino acid contents were analysed. Results. Reduction, trypsin digestion, and papain digestion produced progressively smaller mucin species. On SDS-PAGE, digested MUC5AC rich mucin produced four distinct products. Amino acid analysis was characteristic of mucins with high serine, threonine, and proline contents and reduction and proteolysis increased relative proportions of these amino acids. MUC5AC rich mucins contained more protein than MUC2 rich mucins. Conclusion. Sinus mucin fragmentation produced mucin subunits and glycopeptide units of smaller molecular sizes which are likely to have lower viscoelastic properties. Applying this in vivo could alter mucus physical properties and biologic functions. Amino acid contents of MUC2 and MUC5AC mucins are different. This could be contributing to biological properties and functions of sinus mucins. These data suggest that there may be different pathological processes occurring at the cellular level on chronic sinusitis.

Sheep intelectin-2 co-purifies with the mucin Muc5ac from gastric mucus

Secretion of gastric mucins plays an essential role in host protection, and modifications in mucus properties are characteristic of the protective immune responses to pathogens. This study describes the purification and characterisation of sheep gastric mucins, and identification of those proteins that co-purify with mucins, with the potential to modify mucus properties. Gastric mucus was collected and pooled from four abattoir sheep and separated by CsCl density gradient centrifugation. Proteomic analysis of the mucin-containing fraction indicated the presence of gastric mucin (Muc5ac) and several co-purifying proteins, including intelectin-2 (Itln2). Further experimentation indicated that a combination of denaturation and reduction was required to fully release Itln2 from gastric mucin. A putative correlation was found between mucin-bound intelectin concentration and rheological properties in further sheep gastric mucus samples. In conclusion, this study provides the first characterisation of sheep gastric mucins and their purification partners, revealing potentially important mucin-intelectin interactions.

An Immunohistochemical Study of Osteopontin in Pigment Gallstone Formation

Mucin glycoproteins from the gallbladder epithelium are thought to contribute to the matrix or nucleus of gallstones and other biomineralization systems. The involved acidic glycoproteins have been reported in bile and gallstones. In addition, osteopontin (Opn) is a noncollagenous acidic bone matrix glycoprotein that possesses calcium-binding properties. To investigate the role of Opn in pigment gallstone formation, the involvement of Opn in pigment gallstone formation was studied immunohistochemically in the gallbladder wall and in the stones. Staining for Opn was strongly positive in the epithelium of stone-laden gallbladders and in their stones. The stone-laden gallbladders were infiltrated by macrophages, which intensely stained for Opn. Sections of the pigment stones, under low magnification, showed a lamellar pattern of Opn immunolabeling and showed a reticular pattern under high magnification. Our results indicate that Opn, an acidic glycoprotein from the gallbladder epithelium, seems to be involved in lithiasis. Opn from macrophages and/or the epithelium seems to help form the matrix protein.

ICP-MS-based multiplex profiling of glycoproteins using lectins conjugated to lanthanide-chelating polymers

Lectins have been increasingly important in the study of glycoproteins. Here, we report a glycoprofiling method based on the covalent attachment of metal-chelating polymers to lectins for use in an ICP-MS-based assay. The labeled lectins are able to distinguish between glycoproteins covalently attached to a microtiter plate and their binding can be directly quantified by ICP-MS. Since each conjugate contains a different lanthanide, the assays can be conducted in a single or multiplex fashion, and may be readily elaborated to many different assay formats.

An immunohistochemical study of osteopontin in hepatolithiasis

BACKGROUND/PURPOSE

Mucin glycoprotein from the intrahepatic bile ducts, and from the intramural and extramural glandular epithelia, is thought to contribute to the formation of the matrix, or nucleus, in hepatolithiasis and to contribute to biomineralization systems. Osteopontin (OPN), a noncollagenous acidic bone matrix glycoprotein that possesses calcium-binding properties. To investigate the role of OPN in the genesis of hepatolithiasis, OPN was immunohistochemically studied in the intrahepatic bile ducts, intramural and extramural glands, and in stones.

METHODS

An immunohistochemical study was performed in 21 human liver specimens with hepatolithiasis, by the EnVision (Dako Japan, Kyoto, Japan) method.

RESULTS

Staining for OPN was strongly positive in the epithelium of stone-laden intrahepatic bile ducts, intramural and extramural glands, and in stones. The stone-laden intrahepatic bile ducts were infiltrated by macrophages showing intense staining for OPN. Sections of the hepatolithiasis, viewed under low magnification, showed a lamellar pattern of OPN immunolabeling, and they showed a reticular pattern under high magnification. In the center of the stones, large nestlike membranous structures were frequently present.

CONCLUSIONS

Our result indicates that OPN, an acidic glycoprotein from intrahepatic bile ducts and from intramural and extramural glandular epithelia, seems to be involved in lithiasis, both as a core protein in the early phase, and in the late phase.

Preparation and Evaluation of Mucin-Gelatin Mucoadhesive Microspheres for Rectal Delivery of Ceftriaxone Sodium

Soluble mucin (S-mucin) processed from the small intestines (ileal region) of freshly slaughtered pigs via homogenization, dialysis, centrifugation and lyophilization and its admixtures with type A gelatin were dispersed in an aqueous medium and used to formulate ceftriaxone sodium-loaded mucoadhesive microspheres by the emulsification cross-linking method using arachis oil as the continuous phase. The release profile of ceftriaxone sodium from the microspheres was evaluated in both simulated gastric fluid (SGF) without pepsin (pH 1.2) and simulated intestinal fluid (SIF) without pancreatin (pH 7.4). The microspheres were further evaluated as possible novel delivery system for rectal delivery of ceftriaxone sodium in rats. Release of ceftriaxone sodium from the microspheres in both release media was found to occur predominantly by diffusion following non-Fickian transport mechanism and was higher and more rapid in SIF than in SGF. The results obtained from this study may indicate that ceftriaxone sodium could be successfully delivered rectally when embedded in microspheres formulated with either type A gelatin alone or its admixtures with porcine mucin; hence providing a therapeutically viable alternative route for the delivery of this acid-labile third generation cephalosporin.

Mucus glycoprotein structure, gel formation and gastrointestinal mucus function

Gastrointestinal mucus occurs as a water-insoluble gel adherent to the mucosal surfaces and as a viscous, mobile solution in the lumen. The adherent gastroduodenal mucus gel is part of the mucosal defence against acid (with HCO3-), pepsin (diffusion barrier) and mechanical damage. Rheological studies show that gastrointestinal mucus is a weak, viscoelastic gel. The size and physical properties of the isolated component glycoproteins depend critically on the methods used to obtain them. A glycoprotein preparation of Mr approximately 2 X 10(6), which possesses the gel-forming properties of the native mucus, is considered to represent the secreted covalent entity in pig gastric and small intestinal mucus. These glycoproteins have a polymeric structure of subunits joined by disulphide bridges between non-glycosylated regions of their protein cores. Glycoprotein polymerization, essential for gel formation, is deficient in gastric mucus in peptic ulcer disease. In vivo, adherent mucus gel forms a thin but continuous cover of variable thickness (rat 5-500 microns) over the gastroduodenal mucosa. Luminal pepsin rapidly dissolves this mucus cover and its continuity is maintained by fresh mucus secretion. Bile, HCl, 2 M-NaCl and ethanol (less than 40%) do not destroy mucus gel structure. Prostaglandins and carbachol increase mucus thickness, affording better protection, but it is thought that continuity of the protective mucus cover is the critical factor in its protective functions.

Site of synthesis, intracellular transport and secretion of glycoprotein in exocrine cells

The site of attachment of the first sugar, N-acetylgalactosamine, to the seryl and threonyl residues of the protein chain is unknown in exocrine cells. The subsequent sugars of the carbohydrate side chains, galactose and N-acetylglucosamine alternately, and the end-group sugars, galactose, N-acetylgalactosamine and fucose, are attached in the Golgi complex. Sulphate too is attached in that structure. In the stomach, sulphate is probably transferred in the most mature cisterna of the Golgi stacks, galactose and fucose in other cisternae, suggesting a gradient in transferase activities along the stack. The possibilities of regulating the amount and relative sugar composition of the glycoproteins are discussed. The secretory product is stored in granules. Their polygonal, large and swollen appearance and complex formation by loss of bordering membranes, as observed in many kinds of glycoprotein-secreting cells ('mucous cells') might be caused by ineffective fixation techniques. Direct vascular perfusion results in a picture no different from what is found in non-mucous cells. Whether secretion is merely exocytotic, as in non-mucous cells, or whether it is accompanied by a loss of membrane and even cytoplasm needs thorough investigation, with the effects of various fixation techniques being compared.

Absence of CFTR is associated with pleiotropic effects on mucins in mouse gallbladder epithelial cells

Mucus of cystic fibrosis patients exhibits altered biochemical composition and biophysical behavior, but the causal relationships between altered cystic fibrosis transmembrane conductance regulator (CFTR) function and the abnormal mucus seen in various organ systems remain unclear. We used cultured gallbladder epithelial cells (GBEC) from wild-type and Cftr((-/-)) mice to investigate mucin gene and protein expression, kinetics of postexocytotic mucous granule content expansion, and biochemical and ionic compositions of secreted mucins. Muc1, Muc3, Muc4, Muc5ac, and Muc5b mRNA levels were significantly lower in Cftr((-/-)) GBEC compared with wild-type cells, whereas Muc2 mRNA levels were higher in Cftr((-/-)) cells. Quantitative immunoblotting demonstrated a trend toward lower MUC1, MUC2, MUC3, MUC5AC, and MUC5B mucin levels in Cftr((-/-)) cells compared with cells from wild-type mice. In contrast, the levels of secreted MUC1, MUC3, MUC5B, and MUC6 mucins were significantly higher from Cftr((-/-)) cells; a trend toward higher levels of secreted MUC2 and MUC5AC was also noted from Cftr((-/-)) cells. Cftr((-/-)) cells demonstrated slower postexocytotic mucous granule content expansion. Calcium concentration was significantly elevated in the mucous gel secreted by Cftr((-/-)) cells compared with wild-type cells. Secreted mucins from Cftr((-/-)) cells contained higher sulfate concentrations. Thus absence of CFTR is associated with pleiotropic effects on mucins in murine GBEC.

THE BLADDER DOES NOT APPEAR TO HAVE A DYNAMIC SECRETED CONTINUOUS MUCOUS GEL LAYER

PURPOSE

We determined whether the nature of any protective barrier in the bladder is composed of a secreted mucous gel layer.

MATERIALS AND METHODS

We collected 24-hour urine samples for analysis from 8 healthy 22 to 49-year-old volunteers and 5, 19 to 59-year-old patients treated with bladder reconstruction, in addition to scrapings from 100 freshly slaughtered pig bladders. Samples were subjected to homogenization, dialysis, freeze-drying, papain digestion, gel chromatography, equilibrium density gradient centrifugation, periodic acid-Schiff assay and amino acid analysis. Normal human bladder, pig bladder, normal ileum and transposed intestinal segments were studied for the presence of a mucous layer using a new method of histological analysis.

RESULTS

Mucin content in normal urine is 2.7 mg/24 hours, meaning that less than 0.6% of nondialyzable material in normal urine is mucin. The mucin content of urine from reconstructed bladders amounted to 86 mg/24 hours (5.2% of nondialyzable material). We observed that glycosaminoglycans accounted for 41% of the peak total elution volume of PAS positive material in normal urine. Mucin estimation in urine can be grossly overestimated if contaminating glycoconjugates are not removed. Biochemical analysis of material scraped off the pig bladder surface demonstrated that the maximum thickness of a continuous layer that could be achieved was 13.6 mum. While we could visualize an obvious mucous layer on control ileal samples and biopsies of transposed ileal segments from patients with bladder reconstruction, we were unable to note a distinct, measurable mucous layer lining the bladder surface in humans or pigs.

CONCLUSIONS

Mucin levels in normal human and pig urine would be enough for slow turnover of a thin barrier but the large increase in mucin in the urine of patients with transposed intestinal segments demonstrates that any layer in normal bladder is much different than that lining the transposed intestinal segment. The most likely constituents of this barrier are membrane bound rather than secreted mucins along with the proteoglycan components of the glycocalix.

Calcium binding to biliary mucins is dependent on sodium ion concentration: relevance to cystic fibrosis

Because hypersecretion of gallbladder (GB) mucus occurs in gallstone formation and because binding of Ca(2+) to biliary lipids only accounts for 50% of the total Ca(2+) in GB bile, we investigated the binding of Ca(2+) to human biliary mucin. Biliary mucin was purified from GB bile and binding to Ca(2+) studied. Scatchard plot analysis suggested two binding sites. Removal of sialic acid by neuraminidase resulted in 10% reduction of Ca(2+) binding, whereas, sulfatase treatment reduced Ca(2+) binding by 30%. Using a hypotonic NaCl solution, Ca(2+) binding to mucin increased curvilinearly with mucin concentration. However, binding decreased with increasing ionic strength of the NaCl solution. We conclude that binding of Ca(2+) to mucin is effected mainly through sulfate. Binding to Ca(2+) can be displaced by Na(+). Ca(2+) binding to mucins is enhanced in the setting of low Na(+) concentrations. This phenomenon has pathophysiologic implications for the formation of thick mucus in cystic fibrosis epithelia.

Mucin/poly(acrylic acid) interactions: a spectroscopic investigation of mucoadhesion

Studies using infrared, (1)H and (13)C nuclear magnetic resonance, and X-ray photoelectron spectroscopies and differential scanning calorimetry support the hypothesis that hydrogen bonds, formed between the carboxylic acid functionality of the mucoadhesive material poly(acrylic acid) and the glycoprotein component of mucus, play a significant role in the process of mucoadhesion. There are fewer H-bonded interactions between the components than within the bulk of the pure mucoadhesive agent. The pH of the medium influences the structures of both the poly(acrylic acid) and the mucus, which, in turn, determine the nature and the extent of mucoadhesive interactions.

Bile glycoprotein mucin in sludge occluding biliary stent

Endoscopic biliary stenting is a common treatment for the palliation of obstructive jaundice caused by inoperable malignant hepatobiliary tumors and benign strictures. The biliary stent, however, often becomes nonfunctional as a result of occlusion. In this study, we sought to confirm that bile glycoprotein mucin was a factor in stent occlusion and to investigate its possible role in biliary-stent blockage. The high-molecular-weight glycoprotein fraction was isolated from stent sludge with the use of gel filtration and a cesium chloride density gradient. This fraction was analyzed for amino-acid and carbohydrate compositions and was identified by means of immunoblotting with a specific monoclonal antibody against human gallbladder mucin. Furthermore, the distribution of bile glycoprotein mucin in stent sludge was immunologically demonstrated with fluorescent antibody, and the relationship between bile glycoprotein mucin and bacteria (demonstrated with DAPI stain) was observed. The high-molecular-weight glycoprotein extracts isolated from 11 patients' stent sludge showed strongly positive immunoreactivity with the monoclonal antibody against human gallbladder mucin. Immunofluorescence studies showed that very bright fluorescent signals of bile glycoprotein mucin often appeared on the surface of pigmented deposits, at the periphery of clumps of bacteria and along the inner wall of stents. In nonpigmented sludge, we noted fluorescent signals of bile glycoprotein mucin dispersed among clumps of bacteria. Bile glycoprotein mucin is a constituent of stent sludge. It may play a role in stent occlusion by affecting bacterial adherence to the stent surface or by promoting stent-sludge accumulation as one kind of cement among substances such as calcium bilirubinate and clumps of bacteria.

Development of a rapid and convenient method to purify mucins and determine their in vivo synthesis rate in rats

The intestinal mucoprotein synthesis rate was measured in vivo for the first time. For this, a rapid, reproducible, and convenient method to purify mucoproteins from large numbers of intestinal samples at the same time was developed. The method takes advantage of both the high mucin resistance to protease activities due to their extensive glycosylations and the high mucin molecular size. Intestinal homogenates were partially digested with Flavourzyme. Nonprotected proteins partially degraded were easily separated from mucoproteins by small gel filtration chromatography using Sepharose CL-4B. Electrophoretically pure mucins were obtained. Their amino acid composition was typical of purified intestinal epithelial mucins. The mucoprotein synthesis rate was determined in vivo in rats using the flooding dose method with the stable isotope L-[1-13C]valine. Free L-[1-13C]valine enrichments in the intracellular pool were determined by GC-MS. L-[1-13C]valine enrichments into purified mucoproteins or intestinal mucosal proteins were measured by gas chromatography-combustion-isotope ratio mass spectrometry. In rats, we found that the gut mucosa protein synthesis rate (%/day) decreased regularly from duodenum (122%/day) to colon (43%/day). In contrast, mucoprotein fractional synthesis rates were in the same range along the digestive tract, between 112%/day (colon) and 138%/day (ileum).

Role of bile mucin in bacterial adherence to biliary stents

Biliary stent placement is a well-established method of relieving obstructive jaundice. However, a frequent complication is occlusion of the stent caused by bacterial biofilm formation and sludge accumulation. In this study we investigated the possible effect of bile mucin on bacterial adherence to biliary stents at the initial stage of biofilm formation. By means of an in vitro bile-perfusion system, polyethylene stents were perfused with pig gallbladder bile infected with Escherichia coli. The concentrations of mucin in the pig bile were adjusted with purified mucin. The amount of bacteria adhering to the inner surface of the stents was measured and compared for stents perfused with bile containing various concentrations of mucin. Furthermore, we conditioned the stent inner surface with purified pig bile mucin and observed the effect of the conditioning on subsequent bacterial adherence. In addition, a common method for assaying bacterial adhesion with polystyrene microtiter plates was also used in this study. The results demonstrated that more bacteria adhered to the inner surface of stents perfused with bile containing 5 mg/mL mucin than of those perfused with bile containing 0.5 and 0 mg/mL mucin. Increased bacterial adherence was demonstrated on the stent surfaces conditioned with purified mucin compared with that seen on the nonconditioned stent surfaces. The optical densities indicating bacterial adhesion in the microtiter plate wells precoated with mucin were higher than those in non-coated plate wells. The in vitro results indicate that when a biliary stent is implanted in vivo, mucin in bile may condition the stent inner surface, modulate subsequent bacterial adherence to the surface, and participate in stent occlusion.

Characteristics of rodent intestinal mucin Muc3 and alterations in a mouse model of human cystic fibrosis

Human mucin MUC3 and rodent Muc3 are widely assumed to represent secretory mucins expressed in columnar and goblet cells of the intestine. Using a 3'-oligonucleotide probe and in situ hybridization, we observed expression of rat Muc3 mostly in columnar cells. Two antibodies specific for COOH-terminal epitopes of Muc3 localized to apical membranes and cytoplasm of columnar cells. An antibody to the tandem repeat (TR) sequence (TTTPDV)3, however, localized to both columnar and goblet cells. On CsCl gradients, Muc3 appeared in both light- and heavy-density fractions. The lighter species was immunoreactive with all three antibodies, whereas the heavier species reacted only with anti-TR antibody. Thus Muc3 is expressed in two forms, a full-length membrane-associated form found in columnar cells (light density) and a carboxyl-truncated soluble form present in goblet cells (heavy density). In a mouse model of human cystic fibrosis, both soluble Muc3 and goblet cell Muc2 were increased in amount and hypersecreted. Thus Muc2 and Muc3 contribute to the excess intestinal luminal mucus of cystic fibrosis mice.

Sulphated macromolecules produced by in vivo labelling in the rat gastric mucosa

The aim of this study was to investigate the nature and distribution of sulphated macromolecules of the extracellular matrix in rat gastric mucosa. This was achieved by developing an in vivo labelling system. An intraperitoneal injection of 1 mCi [35S]-sulphate was given for either 4 h (0.01% incorporation into macromolecular fraction) or 8 h (0.13% incorporation). At the end of the labelling period the stomach was removed and the mucosa and submucosa was either taken as a single combined sample or separated into four layers by blunt dissection. Each sample was papain digested and analysed by ion-exchange chromatography. This analysis revealed sulphated species of differing charge existing in differing proportions throughout the mucosa. These sulphated species eluted at NaCl concentrations of approximately 0 (A), 0.19 (B), 0.34 (C) and 0.78 mol/L (D) from a Q-Sepharose ion exchange column. Further analysis by size exclusion chromatography and chemical and enzymatic digestion showed that peaks B and C had molecular weights of 2.4 x 10(5) and 2.8 x 10(5), respectively and were resistant to chondroitinase ABC, heparitinase and nitrous acid digestion. Peak D was found to contain a polydisperse population of molecules with a molecular weight range of approximately 1 x 10(4) to 6 x 10(4). This sample was susceptible to nitrous acid and chondroitinase ABC digestion and was found predominantly in the sample isolated from deeper in the tissue. We have thus developed an in vivo labelling technique for sulphated macromolecules that can be used in the further study of injury to the gastric mucosa.

Analysis of a heterogeneous group of human breast carcinoma associated glycoproteins bearing the Tn determinant

The Tn determinant (GalNAc alpha-O-Ser/Thr) is expressed by about 90% of human carcinomas, but is cryptic in most normal human tissues. A murine monoclonal antibody (MAb) 83D4, developed following immunization with human breast carcinoma cells, reacts with a Tn-related epitope. In the present study we characterized the glycoprotein antigen identified by 83D4 in the human breast carcinoma cell line MCF-7. We further showed that the 83D4 antigenic determinant is masked in human milk fat globule membranes (HMFGM), and can be exposed upon mild m-periodate treatment after desialylation. Western-blot analysis resolved the 83D4 antigen from MCF-7 into two main components of 120-190 kD and > 500 kD respectively. Non equilibrium pH gradient electrophoresis/SDS PAGE revealed the acidic nature of the reactive glycoproteins (pI 4.43-4.70). 83D4 antigenic activity resolved by CsCl gradient ultracentrifugation layered on a wide range of densities (1.30-1.46 g/ml) including typical densities of mucin-like glycoproteins but also lower densities. The amino acid composition of the antigen, relatively rich in serine but poor in threonine and proline, confirmed the divergence from other mucin-like carcinoma-associated glycoproteins. Dicarboxylic amino acids were abundant, accounting in part for the acidic nature of the molecules. ELISA and Western-blot analysis of the subcellular fractions from MCF-7 cells revealed that the 83D4 antigen is mainly contained in plasma membranes (85%) from which it may be resolved into two broad bands (slow and fast migrating components). These results provide information on a group of breast carcinoma associated glycoproteins related to but different from typical mucins, and provide data on alteration of O-glycosylation in tumor cells.

Immunoelectrophoretic pattern of native mucosal intracellular glycoproteins of hog healthy and drug-intoxicated stomachs and of hog body fluids

Naturally occurring glycoproteins have been extracted from fundic and antral mucosal tissue of the hog stomach by means of nondegrading techniques. Major and retarded glycoprotein fractions separated by gel filtration were further dissociated from appreciable amounts of noncovalently bound proteins by CsCl density gradient centrifugation. Antisera to glycoprotein fractions of fundic and antral regions of the stomach were prepared in rabbits. The major fractions from both gastric regions have similar molecular mass (approximately 2 x 10(6)), sedimentation coefficient (approximately 31.5 s), and specific viscosity (approximately 1.6). Purified fractions from each region were further separated into two subfractions by affinity chromatography on wheat germ lectin. Glycoprotein subfractions from antrum and fundus differ appreciably in their carbohydrate and amino acids content, share antigenic determinants, but do not cross-react with anti-hog serum protein antisera. Further diversity in native mucin glycoproteins was observed by the use of one-(D) and two-dimensional (2D) immunoelectrophoresis; subfractions that cross-react with specific anti-hog gastric glycoproteins were found to contain three or more components. D-Immunoelectrophoretic analyses demonstrated (1) in vivo degradation of glycoprotein components of the major fundic fraction isolated from mucosal tissue of alcohol/acetyl salicylate-intoxicated hog stomachs and (2) in vitro catabolism of major fundic glycoproteins by corresponding mitochondrial lysosomal (ML) acid hydrolases. Furthermore, 2D-immunoelectrophoretic analyses showed that (1) hog synovial fluid and plasma proteins have similar prosthetic moieties as either reacted with anti-hog serum proteins antisera. Nonetheless, locations, shapes, and staining intensities of the immunoprecipitate lines differed, which is indicative of different structures of the carbohydrate moieties of components of synovial fluid and plasma proteins, and (2) only a minor fraction of hog cerebrospinal fluid cross-reacted with anti-hog serum protein antisera. This is contrary to the generally accepted deduction based on high-resolution 2D-electrophoresis, indicative of different compositional patterns of plasma and cerebrospinal fluids.

Isolation of mucin from human hepatic bile and its induced effects on precipitation of cholesterol and calcium carbonate in vitro

Biliary mucin was isolated from human hepatic bile, and its induced effects on the appearance time of cholesterol monohydrate crystals (nucleation time) and on the precipitation of calcium carbonate were studied in vitro to examine the possible significance of mucin for ductular gallstone formation. Mucin was isolated by gel filtration on Sepharose CL-4B and a subsequent CsCl density gradient ultracentrifugation. Mucin thus obtained had a high purity as shown by a high-molecular-weight band on SDS-polyacrylamide gel electrophoresis and by the compatible amino acid composition with mucin purified from the gallbladder. The mucin at as low a concentration as 100 micrograms/ml significantly shortened the cholesterol nucleation time in the supersaturated model bile, mimicking human hepatic bile. On the other hand, the addition of mucin inhibited calcium carbonate precipitation in vitro. Taking account of that both cholesterol and calcium salts are major constituents of ductular gallstones, we conclude that biliary mucin is likely to play an important regulating role in the formation of ductular stones.

Culture of human middle ear mucosal explants; mucin production

Middle ear mucosal biopsies could be maintained in culture for up to 7 days, the longest time attempted in this study. Mucin biosynthesis and secretion were measured by incorporation of 14C-glucosamine. Three peaks of radioactivity were present when the dialysed medium was chromatographed. Peak I which accounted for about 10% of the total radioactivity had properties characteristic of mucin. The other two peaks were not characteristic of mucins. Labelled macromolecules excluded on Sepharose 2B were also present in the tissue. Autoradiography of the explants showed that the labelled glucosamine was concentrated in the epithelial layer. Morphometry demonstrated that 1-2% of the epithelial cell volume consisted of goblet cells. The proportionate incorporation of radioactivity into macromolecules increased with increasing epithelial cell volume. This system will allow assessment of factors implicated in the pathogenesis of otitis media with effusion and the study of the action of pharmacological agents on biosynthesis and secretion.

Mucin-like high molecular mass protein fractions from total pig gallbladder bile mucus, pig gallbladder wall mucus, and total human gallbladder bile mucus

Native mucin-like complexes were obtained from both pig gallbladder bile and pig gallbladder wall mucus by precipitation, centrifugation, and gel permeation chromatography. Crude preparations by either dialysis (native mucus from bile, and native gallbladder wall mucus) or by precipitation (crude total bile mucus, and lipomucoid) were purified by gel permeation chromatography on Sephacryl S-300HR and Sephacryl S-500HR (Pharmacia). The elution profiles obtained with a reversibly denaturing and detergent-containing eluent showed the same pattern for all samples, although the amounts of the four main fractions differed somewhat. The excluded fraction with the highest carbohydrate portion had an apparent M(r) > 10(7). This fraction and the following included lipomucoid (in physiological solution tightly bound to fraction I), and an eluent-insoluble mucus portion from all samples were characterized by determination of the protein concentration, carbohydrates, sialic acids, and lipids, using standard methods. Sugar analysis was performed by gas-liquid chromatography. Human gallbladder bile was subjected to the same procedures of mucus precipitation and separation. Human gallbladder bile mucus showed identical behaviour to that of pig gallbladder bile mucus, and showed a very similar elution pattern in gel chromatography.

Role of sulfhydryl-containing agents in the healing of erosive gastritis and chronic gastric ulceration in the rat

One milliliter of 1, 2, or 5% DL-cysteine (cysteine) or DL-methionine methylsulfonium chloride (MMSC) was instilled into the rat stomach 1, 24, and 48 h after giving ethanol (1 mL of 40% solution) by gavage. One hour following the administration of ethanol, gastric mucosal injury was seen in all the animals (22.6 +/- 1.1 mm2, mean +/- SEM; n = 10). Twenty-four hours after giving the ethanol, all the rats treated with cysteine or MMSC still had the mucosal injury. Treatment with 2% cysteine or MMSC significantly (p less than 0.01) reduced the extent of this injury (10.2 +/- 0.6 and 10.1 +/- 0.5 mm2, respectively, versus 20.7 +/- 1.2 mm2, mean +/- SEM; n = 10), an action that was similarly achieved by the 5% solutions (10.1 +/- 0.5 and 9.9 +/- 0.3 mm2, respectively, versus 20.7 +/- 1.2 mm2, mean +/- SEM; n = 10). Forty-eight hours following the administration of ethanol, 30% of the animals given 1% cysteine or MMSC still had gastric mucosal injury, which was significantly (p less than 0.001) less extensive than that seen with ethanol alone (3.8 +/- 0.3 and 4.1 +/- 0.3 mm2, respectively, versus 13.1 +/- 0.8 mm2, mean +/- SEM; n = 10). At this time period, however, none of the animals treated with 2 or 5% solutions of cysteine or MMSC still had any injury. Healing of the ethanol-induced injury was confirmed microscopically and was achieved by regeneration.(ABSTRACT TRUNCATED AT 250 WORDS)

Mucin-type glycoproteins

Considerable advances have been made in recent years in our understanding of the biochemistry of mucin-type glycoproteins. This class of compounds is characterized mainly by a high level of O-linked oligosaccharides. Initially, the glycoproteins were solely known as the major constituents of mucus. Recent studies have shown that mucins from the gastrointestinal tract, lungs, salivary glands, sweat glands, breast, and tumor cells are structurally related to high-molecular-weight glycoproteins, which are produced by epithelial cells as membrane proteins. During mucin synthesis, an orchestrated sequence of events results in giant molecules of Mr 4 to 6 x 10(6), which are stored in mucous granules until secretion. Once secreted, mucin forms a barrier, not only to protect the delicate epithelial cells against the extracellular environment, but also to select substances for binding and uptake by these epithelia. This review is designed to critically examine relations between structure and function of the different compounds categorized as mucin glycoproteins.

Total biliary protein, mucus glycoproteins, cyclic-AMP, and apolipoproteins in the gallbladder bile of patients with cholesterol stones and stone-free controls

The concentrations of total protein, mucus glycoprotein, cyclic-AMP, and apolipoproteins A-I, A-II, and B were determined in the gallbladder bile of patients with cholesterol gallbladder stones and in stone-free controls. The total protein content was significantly increased in gallstone patients (2.03 +/- 0.6 versus 1.31 +/- 0.67 mg/ml; p less than 0.05), as was the mucus glycoprotein concentration (380 +/- 88.5 versus 128 +/- 57.2 micrograms/ml; p less than 0.05). The cyclic-AMP concentration in the gallbladder fluid was increased up to 91 +/- 20 pmol/100 microliters in the gallstone subjects, as compared with 46 +/- 26 pmol/100 microliters (p less than 0.01) in stone-free controls. Cyclic-AMP concentrations correlated positively with the glycoprotein content of the bile in cholesterol gallstone patients (r = 0.66; p less than 0.05). The apolipoprotein concentrations were determined by the radial immundiffusion technique. The corresponding values for patients with stones and controls were 7.5 +/- 0.8 versus 3.0 +/- 0.8 for Apo A-I (p less than 0.025), 10.4 +/- 0.6 versus 6.3 +/- 1.3 for Apo A-II (p less than 0.02), and 1.9 +/- 0.5 versus 1.6 +/- 0.2 mg/dl for Apo B (NS), respectively. Biliary proteins probably play an important role in the nucleation process during the pathogenesis of cholesterol gallbladder stones.

Administration of sulfhydryls to stimulate the healing of ischemia-induced acute gastric mucosal injury in the rat

The sulfhydryl-containing agents DL-cysteine and DL-methionine-methyl sulfonium chloride (1-5%), administered orally by gavage for 4 days, stimulate the healing of acute ischemic injury of the rat gastric mucosa produced by 5 mg/kg of reserpine or 50 mg/kg of serotonin (5-hydroxytryptamine) injected once ip without influencing acid secretion (i.e., by cytoprotective mechanisms).

Characterization of bovine gallbladder mucin. Amino acid sequences of tryptic peptides from the glycosylated domain of the protein core

Gallbladder mucin is a densely glycosylated macro-molecule that promotes cholesterol gallstone formation in experimental animals and in humans. Bovine gallbladder mucin structure was studied after chemical deglycosylation by treatment with anhydrous hydrogen fluoride at 23 degrees C for 3 hours. Deglycosylated mucin contained less than 5% of the amino sugar and neutral hexose content of native mucin. Electrophoretic and molecular sieve chromatographic analyses indicated that significant cleavage of the mucin polypeptide core had occurred during deglycosylation. Deglycosylated mucin was separated into three major fractions by reverse-phase chromatography, one of which was enriched with respect to threonine and proline. Tryptic peptides prepared from this fraction were purified by molecular sieve and reverse-phase chromatography, and the amino acid sequences (8-20 residues) of the four principal tryptic peptides were determined. These peptides contained 65%-75% threonine and proline residues and demonstrated 80%-100% sequence similarity. These data provide the first information on the primary structure of gallbladder mucin and suggest that repeating amino acid sequences occur in this protein. Comparison of gallbladder mucin peptide structure with the consensus repeat sequence of human intestinal mucin showed approximately 60% sequence similarity. It was concluded that mammalian gastrointestinal mucins may be derived from a common ancestral gene.

High-performance size-exclusion chromatography of porcine colonic mucins. Comparison of Bio-Gel TSK 40XL and Sepharose 4B columns

A high-performance size-exclusion chromatography (HPSEC) method was developed for the separation of porcine colonic mucins using a Bio-Gel TSK 40XL HPSEC column (300 mm x 75 mm). In addition, porcine gastric and bovine submaxillary mucin preparations were used to describe more fully the separation characteristics of the HPSEC column. For comparison, the same preparations were also separated using a Sepharose 4B column (100 cm x 2.6 cm). The colonic and gastric mucins eluted in the void volume (V0) of both columns. Bovine submaxillary mucin was in the elution volume (Ve) of both columns. Analytical HPSEC of fractions (V0 and Ve) of the various preparations obtained by Sepharose 4B chromatography exhibited retention times identical to those for fractions obtained by HPSEC. After separation by both methods, purified mucins were obtained by CsCl2 density gradient ultracentrifugation; analytical HPSEC profiles, protein contents, and monosaccharide compositions of both gastric and colonic mucins from either column were similar. The HPSEC method, however, is ideally suited to separate microgram to milligram quantities of colonic mucin preparations quickly: 2 to 4 h, compared with 24 to 30 h for the Sepharose 4B method.

Polymorphic epithelial mucin from the sera of advanced breast cancer patients--isolation and partial characterisation

The anti-breast carcinoma monoclonal antibody (MAb), NCRC-11 defines a polymorphic epithelial mucin (PEM) which is elevated in the circulation of advanced breast carcinoma patients. Here we describe the purification and partial characterisation of this component from patients' sera and its use in the production of a second generation MAb, C568 (IgM). Pooled sera was fractionated by immunoaffinity and size-exclusion chromatography and the purity of preparations assessed by sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE) and immunoblotting. Serum-derived PEM shows a similar pattern of electrophoretic mobility to PEM isolated from primary breast tumour tissue and migrates as several bands in 4% SDS polyacrylamide gels (Mr greater than 400,000). The epitope expression of PEMs isolated from either source is also similar, with both bearing topographically distinct determinants for several anti-mucin MAbs. The immunoreactivities of antibodies C568 and NCRC-11 were unaffected by boiling, reduction and alkylation, or by enzyme desialylation of PEM. Periodate oxidation and proteolytic digestion have suggested that the antigenic determinant for C568 is carbohydrate in nature whilst that of NCRC-11 is peptidic. In accord with the mucinous nature of the molecule, serum-derived PEM is susceptible to reductive beta-elimination, elutes in the void volume of a Sepharose CL-4B column and has a buoyant density of 1.45 g ml-1.

Biochemical and immunological properties of the human carcinoma antigen CAR-5 defined by the monoclonal antibody BD-5

The monoclonal antibody (MAb) BD-5 reacts with an epitope (CAR-5) expressed in 83% of the gastric carcinomas and in 51% of the ductal pancreatic carcinomas. This MAb reacts also with epithelial cells of colorectal mucosa, but does not react at all with normal adult gastric mucosa or normal adult pancreas. We report the biochemical and immunochemical characterization of CAR-5-bearing molecule. The epitope was found to be carried on a mucin of more than 400 kDa with a density of 1.45 g/ml, metabolically labelled with 35S-sulfate, 3H-glucosamine, 3H-mannose and 35S-methionine. Antigenicity survived metaperiodate oxidation and alkalinization, while it was fully destroyed by pronase or papain. Trypsin, although cleaving the molecule, did not affect its antigenic activity. CAR-5 epitope is thus carried on the protein moiety of a sulfo-mucin. On the basis of its biochemical properties, the antigen was purified by a 3-step procedure, consisting of perchloric acid extraction, molecular sieving on Sepharose CL-4B and affinity chromatography on wheat-germ agglutinin coupled to Sepharose 4B. Cross-competition experiments, together with the chemical properties displayed by the different epitopes, clearly indicate that CAR-5 is different from all previously characterized carcinoma-associated determinants. Cross-DDIRMA experiments performed with different "catcher" and "tracer" antibody combinations showed that CAR-5 epitope may be expressed on the same mucin bearing CA 19-9, MOv2, DU-PAN-2, Lewisa and Lewisb epitopes.

Subunit interactions and physical properties of bovine gallbladder mucin

In this study the interaction of gallbladder mucin subunits was examined by gel permeation chromatography, quasielastic laser light scattering, and viscometry. Purified mucin eluted primarily in the void volume of a Sepharose 2B-Cl column, indicating a molecular weight above 2 x 10(6). Disaggregation of the mucin polymer resulted in the elution of glycoprotein in the included volume of the Sepharose 2B-Cl column. Gallbladder mucin had a hydrodynamic radius of 630 A that was independent of mucin concentration below 2 mg/ml. At mucin concentrations above 2 mg/ml, a concentration-dependent increase in both hydrodynamic radius and apparent viscosity of gallbladder mucin was observed. Mucin demonstrated a strong pH dependence in hydrodynamic radius and viscosity with the maximum occurring at approximately pH 5.5. These findings suggest that noncovalent interactions participate in bovine gallbladder mucin subunit associations. Furthermore, changes that occur in the physicochemical environment of the gallbladder during periods of stasis may enhance the viscoelastic properties of mucin and promote the accumulation of biliary sludge in the gallbladder.

Sulphation causes heterogeneity of gastric mucins

The synthesis of mucus glycoprotein in rat stomach was studied in stomach segments, which were pulse-labelled with both [3H]galactose and [35S]sulphate and chased for various times. The radioactive glycoproteins were analyzed by CsCl centrifugation and by agarose gel electrophoresis. After a pulse-labelling for 15 min with [3H]galactose, a possible intermediate with an Mr of 200,000 and a buoyant density of 1.60 g/ml could be demonstrated. Following chase periods of 1 and 4 h, [3H]galactose and [35S]sulphate were present in glycoproteins with a mean buoyant density of 1.50 g/ml. This is clearly different from the main density of glycoproteins isolated from mucosal scrapings (1.46 g/ml). Another difference is the high electrophoretic mobility on gel electrophoretic analysis of newly synthesized glycoproteins compared to that of the major portion of the glycoproteins from mucosal scrapings. When sulphation of glycoproteins was inhibited by sodium chlorate, electrophoretic mobility and buoyant density both decreased. Sodium chlorate had no effect on glycoprotein synthesis nor on glycoprotein secretion. We conclude from our data that the heterogeneity in electrophoretic mobility and buoyant density can be attributed to a different degree of sulphation of the same glycoprotein.

Submaxillary mucins. Intermolecular interactions and gel-forming potential of concentrated solutions

The intermolecular interactions in concentrated solutions of pig submaxillary mucin (PSM) and sheep submaxillary mucin (SSM) were studied by mechanical spectroscopy. PSM and SSM were purified from detectable protein and nucleic acid by equilibrium centrifugation in a CsCl density gradient. PSM and SSM isolated in the presence of proteinase inhibitors showed distinct differences from preparations isolated in the presence of 0.2 M-NaCl alone, the latter having a carbohydrate and amino acid analysis similar to other preparations isolated by precipitation or ion-exchange techniques. Gel-filtration studies showed that preparations isolated in the presence of 0.2 M-NaCl alone were dissociated into smaller-sized glycoprotein units by 3.5 M-CsCl or 2.0 M-NaCl (SSM), pH 2.0 (PSM) or heating at 100 degrees C for 10 min (PSM and SSM). Preparations isolated in the presence of proteinase inhibitors were not dissociated by these treatments. Proteolysis fragmented all submaxillary mucin preparations into small glycopeptides of Mr 13,700 for PSM and of Mr 14,000 and 15,000 for SSM. PSM preparations when concentrated formed viscoelastic gels, as determined by mechanical spectroscopy. In contrast, SSM showed characteristics of a weak viscoelastic liquid under comparable conditions (coil overlap). PSM glycoprotein isolated in proteinase inhibitors formed weak viscoelastic gels at concentrations between 5 and 15 mg/ml. Preparations of PSM glycoprotein isolated in the presence of 0.2 M-NaCl (concentration 10-97 mg/ml) had the same overall mechanical gel structure as those preparations extracted in the presence of proteinase inhibitors. This gel structure was seen to collapse following proteolysis of both preparations or after acid treatment of the glycoprotein isolated in the presence of 0.2 M-NaCl, consistent with the breakdown in size of the polymeric glycoprotein. Treatment of PSM gel with 0.2 M-2-mercaptoethanol caused a surprising increase in gel strength, which was further markedly increased on removal of the reducing agent by dialysis. An association of reduced subunits of PSM was observed by gel filtration after removal of 0.2 M-2-mercaptoethanol. These results point to intermolecular disulphide exchange occurring on reduction of these PSM glycoprotein preparations. These results demonstrate that gel formation in PSM glycoprotein is similar to that for other gastrointestinal mucus glycoproteins from stomach to colon. Gel formation in PSM, as in other mucins, depends on polymerization of subunits.(ABSTRACT TRUNCATED AT 400 WORDS)

The complexity of mucins

Mucins represent the main components of gel-like secretions, or mucus, secreted by mucosae or some exocrine glands. These high-molecular-weight glycoproteins are characterized by the large number of carbohydrate chains O-glycosidically linked to the peptide. The determination of mucin molecular weight and conformation has been controversial for several reasons: 1) the methods used to solubilize mucus and to purify mucins are different and 2) the molecules have a strong tendency to aggregate or to bind to other molecules (peptides or lipids). Recently, electron microscopy has shown the filamentous shape of most mucins and their polydisperse character which, in some secretions, might correspond to a polymorphism of the peptide part of these molecules. The recent development of high pressure liquid chromatography and high-resolution proton NMR spectroscopy has allowed major progress in the structural study of mucin carbohydrate chains. These chains may have from 1 to about 20 sugars and bear different antigenic determinants, such as A, B, H, I, i, X, Y or Cad antigens. In some mucins, such as human respiratory mucins, the carbohydrate chain diversity is remarkable, which raises many questions. Mucins are molecules located at the interface between mucosae and the external environment. The carbohydrate chain diversity might allow many interactions between mucins and microorganisms and play a major role in the colonization or the defense of mucosae.

Mucus glycoprotein gels. Role of glycoprotein polymeric structure and carbohydrate side-chains in gel-formation

The structure of mucus glycoprotein gels from the pig gastrointestinal tract was investigated by mechanical spectroscopy. Gastric, duodenal, and colonic mucus had the same mechanical profile, characteristic of a viscoelastic gel. The gel structure collapsed on destruction of the polymeric structure of the component glycoprotein by reduction with 0.2M mercaptoethanol or after proteolysis with papain. The progressive weakening of mechanical properties and the decrease in polymeric glycoprotein content were measured as functions of time of reduction. A linear correlation was obtained between the gel quality [defined by tan delta, the ratio of the loss modulus (G'') to the storage modulus (G')] and the proportion of polymeric to subunit glycoprotein in the mucus. Purified mucus glycoprotein, at the same concentration as that in native mucus, resulted in a gel with mechanical properties no different from those of the respective native secretion, demonstrating that the glycoprotein alone could reproduce the gel-forming properties of mucus. After proteolytic digestion, all native secretions and reconstituted mucus showed an absence of Newtonian behaviour in the frequency dependence of dynamic viscosity at low frequencies. This provided evidence that the noncovalent interactions, characteristic of the native gel matrix, were still present after proteolytic digestion when the nonglycosylated protein core accessible to proteinases had been removed. These results were interpreted to show (a) a common mechanism for gel-formation in gastric, duodenal, and colonic mucus; (b) that the polymeric structure of mucus glycoproteins confers the three-dimensional structure necessary for formation of the gel network; and (c) that noncovalent interactions which arise between the glycoprotein molecules by relatively stable interdigitation of the carbohydrate side-chains are involved in formation of the gel network.

Characterization of human middle ear mucus glycoprotein in chronic secretory otitis media (CSOM)

Middle ear effusion was obtained from children with chronic secretory otitis media undergoing myringotomy. The effusions contained about 120 mg/ml non-dialysable solids, of which 18-31% was mucus glycoprotein. The purified mucus glycoprotein had a composition characteristic of other mucus glycoproteins. Amino acid analysis of the glycoprotein indicates a protein core consisting of glycosylated regions resistant to proteolysis and non-glycosylated regions susceptible to proteolysis. Analysis of the mucus glycoprotein by gel filtration on Sepharose 2B showed that reduction caused a decrease in hydrodynamic size and proteolysis caused a further decrease. The difference was confirmed by sedimentation coefficient and viscosity measurements. The reduced glycoprotein had an intrinsic viscosity of 0.113 ml/mg and an S0(20) of 15.2S compared to a value of 0.018 ml/mg and 9.6S for the proteolytically digested glycoprotein. These results suggest a model for this middle ear mucus glycoprotein, in which the native glycoprotein is a large molecular mass polymer maintained by disulphide bridges. These disulphide linked glycoprotein units are broken down into smaller units by proteolysis. The mucus glycoprotein could not be purified completely free from low molecular mass components. A glycoprotein, susceptible to proteolysis Mr 28,000-33,000 co-fractionates with the major high molecular mass mucus glycoprotein.

Rat and human colonic mucins bind to and inhibit adherence lectin of Entamoeba histolytica

Establishment of adherence by Entamoeba histolytica is mediated by a 170-kD Gal/GalNAc inhibitable lectin and is required for cytolysis and phagocytosis of mammalian target cells. We studied the biochemical mechanisms of the in vitro interaction between rat and human colonic mucins and axenic E. histolytica trophozoites. Crude mucus prevented amebic adherence to Chinese hamster ovary (CHO) cells by up to 70%. Purification of the colonic mucins by Sepharose 4B chromatography, nuclease digestion, and cesium chloride gradient centrifugation resulted in a 1,000-fold enrichment of the inhibitory mucins. Purified rat mucin inhibited amebic adherence to and cytolysis of homologous rat colonic epithelial cells. Oxidation and enzymatic cleavage of rat mucin Gal and GalNAc residues completely abrogated mucin inhibition of amebic adherence. The binding of rat 125I-mucin to amebae was galactose specific, saturable, reversible, and pH dependent. A monoclonal antibody specific for the 170-kD amebic Gal/GalNAc lectin completely inhibited the binding of rat 125I-mucin. Rat mucin bound to Affigel affinity purified the amebic lectin from conditioned medium. Colonic mucin glycoproteins act as an important host defense by binding to the parasite's adherence lectin, thus preventing amebic attachment to and cytolysis of host epithelial cells.

Biosynthesis of proteins by human gastric mucosa in vitro

Incorporation of L-[U-14C]leucine and of D[U-14C]glucose into proteins of fresh human gastric mucosa in vitro was studied after incubation of homogenized tissue and of intact mucosal pieces. CsCl centrifugation was used to separate high-density mucus glycoproteins from other mucosal proteins, and the macromolecular nature of radioactive mucosal glycoprotein fractions was confirmed by SDS/polyacrylamide-gel electrophoresis and autoradiography of the polyacrylamide gels. In all experiments a substantial proportion of total incorporated radioactivity was associated with gastric-mucosal glycoprotein fractions (CsCl fraction L3), indicating their biosynthesis. Radioactivity of these fractions was shown to co-chromatograph with carbohydrates when fractionated either directly or after reduction and alkylation (1) Sephadex G-200 chromatography in the excluded fractions and (2) by DEAE-cellulose ion-exchange chromatography. On incubation of intact mucosa, the major portion of radioactivity associated with the glycoprotein fractions of both leucine- and glucose-labelled specimens was secreted into the mucosal media during the course of the experiment. It is suggested that biosynthesis of mucus in vivo by gastric mucosa may be associated with rapid secretion of the synthesized macromolecules into the lumen of the stomach and that investigations of the metabolic processes within the mucosa should consider the products of secretion of the tissue. Incorporation of L-[U-14C]leucine implies biosynthesis of the polypeptide components of the macromolecules.

Molecular weight of gastric mucus glycoprotein is a determinant of the degree of subsequent aspirin induced chronic gastric ulceration in the rat

Mucus was sampled from the gastric mucosal surface of anaesthetised rats. Three weeks later these rats were orally dosed each day with aspirin (375 mg/kg) for six months. Then the number and size of the aspirin induced chronic gastric ulcers were assessed. Gel filtration chromatography of the mucus samples showed that mucus glycoprotein was present in both high and low molecular weight forms. There was a natural variation between individual rats in the percentage of glycoprotein in the high molecular weight form (mean = 58.9%; SD = 9.6%; n = 23). This variation correlated strongly with the degree of subsequent aspirin induced chronic gastric ulceration (r = -0.85, p less than 0.001). This is the first time that a pre-existent variability in a mucosal defence factor has been shown to predict susceptibility of the stomach to chronic ulceration.

Effects of trimoprostil, a prostaglandin E2 analogue, on human gastric acid secretion and soluble mucin output

We have studied the effects of Trimoprostil, a prostaglandin E2 analogue, on gastric acid and soluble mucus output using human subjects. This compound caused anti-secretory effects on both basal as well as histamine-stimulated gastric acid secretion in a dose-dependent manner. There was a simultaneous increase in total mucus output. When the secreted mucus was fractionated by Sepharose CL-2B gel chromatography, most of the basal gastric mucin was shown to be in the polymeric form (mol wt 2 X 10(6)), whereas after histamine stimulation the mucin was mostly in the subunit form (mol wt 0.5 X 10(6)). The gastric mucin, after stimulation using low doses of prostaglandin, was mainly in the polymeric form; but after higher doses, the subunit form predominated. These observations are important in the understanding of physiological and pharmacological control of gastric mucus output with regard to its chemical composition and molecular heterogeneity, and provide further insight into the rational clinical use of the prostaglandins for gastroduodenal diseases.