The synthesis and secretion of gastric mucus glycoprotein by mucosal cells cultured in the presence of ethanol

Rat model of experimentally induced abacterial prostatitis

BACKGROUND

An experimental model in rats was developed to investigate the significance of mucosal integrity in abacterial prostatitis.

METHODS

Ethanol was instilled into the ventral prostates of male rats to reduce mucosal integrity; dinitrobenzenesulfonic acid (DNBS) was added as an irritant to induce inflammation. Controls received no treatment, ethanol only, DNBS only, or a suspension of bacteria. After various time points, rats were sacrificed, and their prostates were assayed for gross morphology, histological appearance, and cytokine levels.

RESULTS

Prostates subjected to ethanol plus DNBS showed significant inflammation, most notably after 12, 24, and 48 hr. Inflammation judged by gross and histological observations and interleukin-1beta levels correlated well at these times. Rats given only ethanol, DNBS, or no treatment, acting as negative controls, displayed little or no inflammation; rats given a bacterial suspension, acting as positive controls, showed inflammation consistent with past studies. Cytokine assays revealed raised interleukin-1beta levels in this model, while tumor necrosis factor-alpha remained at a basal level.

CONCLUSIONS

The loss of an intact mucosal surface in the prostate resulted in inflammation caused by an irritant. Interleukin-1beta appears to play a role in this inflammation, while tumor necrosis factor-alpha does not.

Biological water and its role in the effects of alcohol

Alcohol and water compete with each other on target membrane molecules, specifically, lipids and proteins near the membrane surface. The basis for this competition is the hydrogen bonding capability of both compounds. But alcohol's amphiphilic properties give it the capability to be attracted simultaneously to both hydrophobic and hydrophilic targets. Thus, alcohol could bind certain targets preferentially and displace water, leading to conformational consequences. This article reviews the clustering and organized character of biological water, which modulates the conformation of membrane surface molecules, particularly receptor protein. Any alcohol-induced displacement of biological water on or inside of membrane proteins creates the opportunity for allosteric change in membrane receptors. This interaction may also prevail in organelles, such as the Golgi apparatus, which have relatively low concentrations of bulk water. Target molecules of particular interest in neuronal membrane are zwitteronic phospholipids, gangliosides, and membrane proteins, including glycoproteins. FTIR and NMR spectroscopic evidence from model membrane systems shows that alcohol has a nonstereospecific binding capability for membrane surface molecules and that such binding occurs at sites that are otherwise occupied by hydrogen-bonded water. The significance of these effects seems to lie in the need to learn more about biological water as an active participant in biochemical actions. Proposed herein is a new working hypothesis that the molecular targets of ethanol action most deserving of study are those where water is trapped and there is little bulk water. Proteins (enzymes and receptors) certainly differ in this regard, as do organelles.

Prostaglandin E2 and prostaglandin F2 alpha biosynthesis in human gastric mucosa: effect of chronic alcohol misuse

BACKGROUND AND AIMS

The results of experimental studies support the hypothesis that decreased prostaglandin production might play a part in the gastric mucosal injury induced by alcohol. In this study, it was investigated whether alcohol misuse impairs the synthesis of prostaglandin E2 (PGE2) and prostaglandin F2 alpha (PGF2 alpha) in gastric mucosa.

PATIENTS

Fifty six alcoholic patients and 66 subjects without alcohol misuse were included in the study.

METHODS

Mucosal biopsy specimens were obtained from the antrum and body of the stomach. Maximal synthesis rates of PGE2 and PGF2 alpha were determined in the microsomal fraction of the biopsy specimens.

RESULTS

The rates of synthesis of both prostaglandins in biopsy specimens from the antrum were not significantly different from those obtained in the body. Synthesis of both prostaglandins was significantly reduced in alcoholic patients who abstained less than five days compared with the non-alcoholic group with normal mucosa (PGE2-40%, PGF2 alpha-42% respectively). In non-alcoholic patients with severe gastritis PGE2 synthesis was increased (+30%, p < 0.05) and PGF2 alpha synthesis was decreased (-42.5%, p < 0.025). In alcoholic patients with severe gastritis PGE2 synthesis was depressed by almost 60% (p < 0.001) compared with the non-alcoholic group with severe gastritis. Neither colonisation of Helicobacter pylori nor smoking had a significant influence on the prostaglandin synthesis.

CONCLUSIONS

Chronic alcohol misuse is associated with significantly reduced capacity for prostaglandin synthesis in gastric mucosa and this alcohol induced decrease in prostaglandin synthesis is modulated by the presence and degree of gastritis.

Biosynthesis of mucin derived from a 60-kDa precursor protein in the human stomach

We studied the biosynthesis of mucin in the human stomach using an anti-mucin core peptide monoclonal antibody, 3G12. Human stomach mucosa was labeled with [35S]methionine, and chased for 3 h. An approximately 60-kDa subunit of human gastric mucin precursor protein was detected in the intracellular product. Under nonreducing conditions, dimer, trimer, and tetramer mucin precursor protein (120, 180, 240 kDa) were detected. Treatment with tunicamycin or endo-beta-N-acetylglucosaminidase H had no effect on the 60-kDa subunit and its oligomers. Extracellular products contained only the high molecular weight mucin, and the secretion was not affected by tunicamycin. By treatment with monensin or brefeldin A, the mature mucin was not secreted extracellularly. These findings suggested that a 60-kDa subunit of the mucin precursor protein was biosynthesized into mature mucin after oligomerization to tetramers, and that neither the oligomerization nor the intracellular transport of the mucin in the human stomach was associated with N-glycosylation.

Enhancement of the protective qualities of gastric mucus by sucralfate: role of phosphoinositides

The effects of intragastric administration of sucralfate on the physicochemical properties of gastric mucus, and the mechanism of its protective action against alcohol-induced mucosal injury were investigated using in vivo and in vitro models. The experiments in vivo were conducted with groups of rats receiving a dose of 100 mg sucralfate twice daily for 5 consecutive days. The animals were sacrificed 16 hours after the last dose, their stomachs dissected, and the mucosa subjected to physicochemical measurements. In the in vitro studies, gastric mucosa was cultured in the presence of sucralfate, ethanol, or both. The in vivo results revealed that sucralfate elicited an 8% increase in mucus gel dimension, while its sulfo- and sialomucin content increased by 63% and 81%, respectively. The changes in mucus gel mucin content with sucralfate were accompanied by a 9.5% increase in mucus hydrogen ion (H+) retardation capacity, 1.9-fold increase in viscosity, and a 60% increase in the gel hydrophobicity. The mucus elaborated in the presence of sucralfate exhibited 14% lower protein content and 62% higher content of carbohydrate than that of control, and contained more neutral lipids. Furthermore, the gastric mucus of the sucralfate group showed a marked increase in mucus glycoprotein polymeric form. The data obtained with gastric mucosal culture demonstrated that sucralfate elicited a significant increase in mucin synthesis, which was reflected in the enhanced metabolism of mucosal phosphoinositides. In contrast, ethanol, which exhibited detrimental effects on mucin synthesis, also caused alterations in the phosphoinositide signal pathway. The changes in mucin and phosphoinositide distribution patterns evoked by ethanol were prevented by sucralfate. Our results suggest that the mucosal strengthening action of sucralfate occurs through the stimulation of the metabolism of phosphoinositide-derived messenger molecules.

Enhancement in gastric mucus gel qualities with colloidal bismuth subcitrate administration

The effects of intragastric administration of an antiulcer drug, colloidal bismuth subcitrate, on the content, composition and physical properties of the mucus component of gastric mucosal barrier were investigated. The experiments were conducted with two groups of rats in which one group received twice daily for three consecutive days a dose of 100 mg/kg colloidal bismuth subcitrate, while the control group received saline. The animals were killed 16 h after the last dose, their stomachs dissected and the mucosa subjected to physicochemical measurements. The results revealed that colloidal bismuth subcitrate elicited a 49% increase in mucus gel dimension, while sulfo- and sialomucin content of the gel increased by 64 and 112%, respectively. The changes in mucus with colloidal bismuth subcitrate were accompanied by a 28% increase in H+ retardation capacity, 2.2-fold increase in viscosity, and a 26% increase in the gel hydrophobicity. The mucus elaborated in the presence of colloidal bismuth subcitrate exhibited 16% lower protein content and 68% higher content of carbohydrate than that of the control, displayed similar levels of total lipids and covalently bound fatty acids, but its phospholipid content was 32% higher. Furthermore, the mucus of the colloidal bismuth subcitrate group showed a marked increase in the proportion of the high molecular weight form of mucin. The results suggest that colloidal bismuth subcitrate is capable of the enhancement of mucus gel qualities associated with the maintenance of gastric mucosal integrity.

Participation of phosphoinositides in gastric mucosal protection by colloidal bismuth subcitrate against ethanol-induced injury

The mechanism of gastric mucosal protection by an antiulcer agent, colloidal bismuth subcitrate (CBS), against ethanol-induced injury was investigated using in vivo and in vitro systems. The experiments in vivo were conducted with groups of rats with and without indomethacin pretreatment, and the animals received either a dose of CBS (100 mg/kg) or a vehicle (saline), followed 30 min later by ethanol. In the in vitro studies, gastric mucosa segments were cultured in the presence of CBS, ethanol, or both. The results of in vivo experiments revealed that in the absence of CBS, ethanol caused extensive gastric hemorrhagic lesions which were significantly reduced following CBS pretreatment and this effect of CBS was not prevented by indomethacin. The data obtained with gastric mucosal culture established that in comparison to the controls, ethanol caused a 27% decrease in mucin synthesis, while mucin synthesis in the presence of CBS increased by 48%. The increase in mucin synthesis evoked by CBS was accompanied by the enhanced metabolism of mucosal phosphoinositides, as reflected by a decrease in PI (15%) and PIP2 (30%), and an increase in IP1 (26%) and IP3 (67%). In contrast, ethanol, which exhibited detrimental effect on mucin synthesis, caused a decrease in PIP (35%), IP2 (47%) and IP3 (38%), and an increase in PIP2 (80%), and IP1 (51%). However, when the mucosal culture was carried out in the presence of both CBS and ethanol, the detrimental changes evoked by ethanol on mucin synthesis were prevented, and the phosphoinositide and inositide phosphate distribution patterns were quite similar to those in the mucosa cultured in the presence of CBS only.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Carbohydrate-deficient transferrin (CDT) in serum in women with early alcohol addiction

Carbohydrate-deficient transferrin (CDT) in serum was determined by micro anion exchange chromatography and a transferrin radioimmune assay in 58 consecutive women treated for early alcohol dependence compared, with 62 healthy females with an alcohol consumption of 0-15 g of ethanol/day. The upper normal CDT level was 74 mg/l. CDT was elevated above this value in 83% of the alcoholic women with an intake of 60 g of ethanol/day or more for at least 7 days within the preceding two weeks. CDT values were significantly positively correlated with daily alcohol consumption but not with GT, ASAT, ALAT or MCV. During abstinence CDT level declined exponentially with a half-life of 14 +/- 3 days. The results indicated that CDT may be as sensitive and specific a marker in women with early alcohol addiction as in previously studied male alcoholics. The amount of alcohol consumed appeared to be more important than sex or liver function. Determination of CDT may thus offer a means for early objective diagnosis and adequate treatment also of women in early stages of alcoholism.

Prostaglandin effect on the enzymatic sulfation of mucus glycoprotein in gastric mucosa

The effect of 16,16-dimethyl prostaglandin E2 (DMPGE2) on the sulfation of mucus glycoprotein in gastric mucosa was investigated. The enzymatic activity which catalyzes the transfer of the sulfate ester group from 3'-phosphoadenosine-5'-phosphosulfate to gastric mucus glycoprotein was located in the detergent extracts of Golgi-rich membrane fraction of antral and body mucosa of rat stomach. The sulfotransferase activity of this fraction from body mucosa, however, was 35% higher than that from the antrum. The enzyme exhibited optimum activity at pH 6.8 using 0.5% Triton X-100 and 30 mM NaF. The apparent Km of the enzyme for sulfation of mucus glycoprotein was 10.5 microM, and the sulfate ester was found incorporated into the carbohydrate chains of the glycoprotein. Introduction of DMPGE2 to the reaction mixtures led to an enhancement in the rate of mucus glycoprotein sulfation. The rate of enhancement was proportional to the concentration of DMPGE2 up to 1.0 x 10(-4) M and was of the competitive type, with an apparent Km value of 6.7 microM. Since sulfated mucins play an important role in gastric mucosal defense and the increase in their sulfation occurred at levels of prostaglandin present in gastric mucosa, the observed effect may be of significance to gastric mucosal defense in vivo.

Co-translational processing and intracellular transport of rat salivary mucus glycoprotein

A preparation of peptidyl-tRNA from intact microsomes of mucin-synthesizing polysomes of sublingual salivary gland cells contained fatty-acylated galactosamine-free and galactosamine-enriched peptidyl-tRNA fractions, whereas trypsin-chymotrypsin treated microsomes yielded predominantly the acylated galactosamine-enriched peptidyl-tRNA complexes. Radioscanning and chemical analyses revealed that palmitate was substituted on all nascent peptides, except those shorter than 20 amino-acid residues. In contrast, the [35S]-methionine label was detected only on galactosamine-free peptides containing up to 70 amino acids. On SDS-polyacrylamide gel, the peptides released from galactosamine-enriched tRNA complexes separated into a multitude of bands ranging in size from 6000 to 60,000 dalton, whereas the total preparation afforded peptides ranging from 2000 to 60,000 dalton. Pulse-chase experiments, using radiolabelled methionine, palmitic acid and N-acetylgalactosamine, combined with chemical characterization of the radiolabelled fatty acids and carbohydrates from purified peptidyl-tRNA, confirmed that the N-terminal fatty acylation and the initial O-glycosylation with N-acetylgalactosamine are the co-translational processes taking place as soon as peptide is sufficiently large to be acylated, trimmed, and translocated to the luminal site of endoplasmic membrane.

Carbohydrate-deficient transferrin in serum in patients with liver diseases

Carbohydrate-deficient transferrin (CDT) in serum was analyzed by isocratic microanion exchange chromatography at pH 5.65 followed by a transferrin radioimmunoassay in 102 patients with biopsy-verified liver diseases. CDT values were normal in all of the 87 nonalcohol-abusing patients irrespective of type or degree of liver disease. Thirteen of the 15 alcoholic patients (87%) with current abuse showed elevated CDT values while in abstaining alcoholics with remaining liver disease the values were normal. No correlations were found between CDT level and volume density of liver fibrosis or steatosis or values of a number of clinicochemical liver tests. The only significant correlation demonstrated was between CDT concentration and the level of present daily alcohol consumption in the alcoholic patients. These results indicate that CDT can be used as a marker of present but not previous alcohol abuse, even in patients with various liver diseases.

Expression of prostaglandin protective functions in gastric mucosa cells cultured in the presence of ethanol: effects on the synthesis, retention, secretion, and structure of mucus glycoprotein

The magnitude of prostaglandin [16,16-dimethylprostaglandin E2 (DMPGE2)] protection against ethanol action has been evaluated by studying the intracellular events leading to synthesis, modification, intracellular retention, and secretion of mucus glycoprotein in the rat gastric mucosal cell culture. When metabolic activity of the cultured cells was expressed as the amount of radioactive tracer in purified mucus glycoprotein, it was found that ethanol at low concentration (0.1 M) caused an 8- to 9-fold increase in proline and a 5- to 6-fold increase in palmitic acid incorporation into mucus glycoprotein; however, at 1.5 M ethanol, the synthetic processes ceased to function. In the presence of DMPGE2 (10 ng/ml), a 2-fold increase in proline and a 3-fold increase in palmitic acid incorporation into mucus glycoprotein were observed. A simultaneous addition of DMPGE2 (10 ng/ml) and ethanol (0.1-1.5 M), or pretreatment with DMPGE2 (10 ng/ml) for 20 min followed by the addition of ethanol (0.1-1.5 M), resulted in the stabilization of glycoprotein synthesis and secretion, and in restoration of the function at the level observed with DMPGE2 alone. The addition of 10 ng/ml of DMPGE2 caused a 32% increase in mucus glycoprotein secretion and an 11% increase in the intracellular content of the glycoprotein. The amount of mucus apoprotein precursor rose by 18%, and the fatty acylation of the synthesized peptides was up by 38%. Addition of DMPGE2, together with ethanol, prevented depletion of the intracellular glycoprotein stores. As observed with ethanol alone, the secretion was elevated by 16-27%, whereas the intracellular glycoprotein stores remained similar to those of controls. The synthesis of the mucus apoprotein precursor was highly sensitive to ethanol, and addition of DMPGE2 only partially prevented its inhibitory action. Pretreatment with DMPGE2, however, eliminated ethanol toxicity, and the precursor pool level remained elevated (28-30%) at all concentrations of ethanol tested. The fatty acylation, although positively affected by DMPGE2, decreased steadily with increments of ethanol concentration. The results show that DMPGE2 stabilizes the cellular membrane processes and thus imposes control over mucus glycoprotein synthesis, secretion, and its intracellular retention.

Prostaglandin effect on the physical properties of gastric mucus glycoprotein and its susceptibility to pepsin

The effect of 16,16-dimethyl prostaglandin E2 (DMPGE2) on gastric mucus glycoprotein viscosity, permeability to hydrogen ion and degradation by pepsin was investigated. Preincubation with DMPGE2 produced a marked enhancement in the glycoprotein viscosity. The increase was concentration dependent and at 2.6 X 10(-5)M DMPGE2 reached a value of 178%. Permeability measurements revealed that 2.6 X 10(-7)M DMPGE2 increased the retardation ability of the glycoprotein to hydrogen ion by 10%, while 22% increase was obtained with 2.6 X 10(-4)M DMPGE2. The results of peptic activity assay showed that DMPGE2 had no inhibitory effect on the rate of glycoprotein proteolysis, and actually a small stimulatory influence was consistently observed. The results suggest that prostaglandins beneficially affect the physical properties of mucus glycoprotein which are considered to be essential for the protective function of gastric mucus.

Changes in mucus glycoprotein synthesized in rat gastric mucosa exposed to ethanol

The resistance to proteolysis by pepsin of gastric mucus glycoprotein synthesized by tissue culture in the presence and absence of 0.1 M ethanol was investigated. The glycoprotein product of ethanol-supplemented culture was found to contain 68% less associated lipids and 81% less covalently bound fatty acids, but exhibited unaltered content of carbohydrate and protein. The lipid and fatty acyl deficient glycoprotein was 5-times more rapidly and 2-3-times more extensively degraded by pepsin than the glycoprotein synthesized in the absence of ethanol. Following delipidation with organic solvents and deacylation with hydroxylamine both glycoproteins were digested at the same rate and degraded to the same extent. The lower content of fatty acyl residues markedly affected the overall pattern of the proteolytic fragments identified by SDS gel electrophoresis. The peptides corresponding to the acylated fragments of control were degraded and an increase in the amount of smaller peptides was observed. The in vitro assays of the fatty acyltransferase activity towards the substrates obtained from control and alcohol-containing cultures revealed that the enzyme activity was similar and increased proportionally with increased concentration of both glycoprotein substrates and enzyme. However, addition of 0.1 M ethanol to the assay tubes containing complete incubation mixture decreased the acylation of either glycoprotein by 40%. Based on the results presented here, and on previous studies of mucus glycoprotein synthesis in the presence of ethanol, we conclude that ethanol interferes with the process of acylation of mucus glycoprotein with fatty acids.

Micro anion exchange chromatography of carbohydrate-deficient transferrin in serum in relation to alcohol consumption (Swedish Patent 8400587-5)

A new simplified and rapid method for detection and quantitation of "carbohydrate-deficient transferrin" in serum is described. The method is based on isocratic anion exchange chromatography of isotransferrins in disposable microcolumns followed by a double antibody transferrin radioimmune assay. This technique, which separates all transferrin components isoelectric above pH 5.65, showed a very good reproducibility and accuracy with a coefficient of variation between 5 and 9%. 77 alcoholic patients could be clearly separated from 80 healthy "normal consumers" and 33 total abstainers with a specificity of 100% and a sensitivity of 91%. The values were significantly correlated to the amount of alcohol consumed during the latest month, and declined in abstaining alcoholics with a mean biological half-life of 17 days. Elevated levels occasionally appeared in healthy individuals after daily consumption of 60 g of ethanol during a 10-day period. In a sample of 187 patients with nonalcohol-related conditions only 2% false-positive values were found. This method is suggested as a potential tool for detecting and monitoring alcohol abuse.

Fatty acid acylation of salivary mucin in rat submandibular glands

The acylation of salivary mucin with fatty acids and its biosynthesis was investigated by incubating rat submandibular salivary gland cells with [3H]palmitic acid and [3H]proline. The elaborated extracellular and intracellular mucus glycoproteins following delipidation, Bio-Gel P-100 chromatography, and CsCl equilibrium density gradient centrifugation were analyzed for the distribution of the labeled tracers. Both preparations gave single bands at the CsCl density of 1.48, in which carbohydrate peaks coincided with that of the labels. The [3H]palmitic acid in these glycoproteins was susceptible to cleavage by alkali and hydroxylamine, thus indicating the ester nature of the bond. With both intracellular and extracellular glycoproteins deacylation caused the glycoproteins to band in the CsCl gradient at a density of 1.55. The incorporation of both markers into mucus glycoprotein increased steadily with time up to 4 h, at which time about 65% of [3H]palmitate and [3H]proline were found in the extracellular glycoprotein and 35% in the intracellular glycoprotein. The incorporation ratio of proline/palmitate, while showing an increase with incubation time in the extracellular glycoprotein, remained essentially unchanged with time in the intracellular glycoprotein and at 4 h reached respective values of 0.14 and 1.12. The fact that the proline/palmitate incorporation ratio in the intracellular glycoprotein at 1 h of incubation was 22 times higher than in the extracellular and 8 times higher after 4 h suggests that acylation occurs intracellularly and that fatty acids are added after apomucin polypeptide synthesis. As the incorporation of palmitate within the intracellular mucin was greater in the mucus glycoprotein subunit, it would appear that fatty acid acylation of mucin subunits preceeds their assembly into the mucus glycoprotein polymer.