• Similarly, Marcinkeiwicz (Charlottesville, USA) described a significant drop in salivary mucin secretion among patients with 3rd-degree reflux śsophagitis. The reduction resulted in deterioration of the śsophageal mucosa's protective mechanisms, and increased the patient's risks of later complications.

• Tanaka et al. (Los Angeles, USA) made simultaneous measurements of mucus-layer thickness and blood flow in the śsophagus of anaesthetised rats using an in vivo microscopy technique. Following stimulation by intraśsophageal acid (pH 1 vs. 7.4 in controls) superfusion, they observed both parameters to increase, and concluded that the śsophagus was able to auto-regulate its riposte to acid attacks.

• Patients with systemic sclerosis and reduced śsophageal motricity complain relatively little of reflux śsophagitis which, given their condition, is somewhat surprising. Carola et al. (Milan, Italy) compared the intraśsophageal milieu's buffer capacity of healthy subjects with that of patients' with systemic sclerosis.
The initial intraluminal pH was comparable (pH 7) in both populations, but the time required to acidify the śsophagus (HCl 0.01 N; 1 ml/mn) was three times longer in the patients than in the controls. The results showed that the hyposensitivity to the acid could be associated with a greater persistence, probably due to the śsophageal hypomotility observed in the patients, and to milieu components (saliva, mucus, and bicarbonates) with a high buffer capacity.

MUCUS AND THE STOMACH

Mucin synthesis and secretion
• Since preliminary studies on the rabbit gastric mucosa have demonstrated ATP activation of the P2U-type purinergic receptors which stimulate mucin secretion, Wagner et al. (Hanover, Germany) looked at the receptor's expression on the gastric mucosa in man. As in the rabbit, they found an increase in intracellular calcium in response to stimulation of human gastric cells by exogenous UTP or ATP (primary culture of mucosal cells and cancer lines producing HM02 and HS746T mucus). Using RT-PCR (reverse transcriptase polymerisation chain reaction) and Southern blot techniques, they revealed the expression of the P2U receptor on these various human cell types. Via this common receptor, the extracellular nucleotides could thus be regulation factors for the production of gastric mucus in man.

• It is possible that the secretagogic action of these nucleotides involves prostaglandin E2. This is what the same workers (Wagner et al, Hanover, Germany) wanted to ascertain on primary cultures of human gastric epithelial cells. They stimulated the P2U purinoceptors by ATP or UTP (100 µM) and the P1 purinoceptors by adenosine (100 µM). The triggering of PU2 receptors stimulated the release of PGE2 and hence of mucins, whereas that of P1 inhibited it. These results shed new light on the mechanism of gastric cytoprotection by PGE2.

• The same team considered another possible regulation factor for the same cell types. Wagner et al. (Hanover, Germany), hypothesised an apolipoprotein (APO) regulation of mucin and phospholipid synthesis in the gastric epithelium. They demonstrated it was essentially APO E that was produced in large quantities, whereas APO A1 and APO B were little detected. From this, they deduced that APO E was certainly involved in controlling gastric mucin secretion.

• Smith et al. (St Louis and Houston, USA) re-examined the mechanism of prostaglandin E2 cytoprotection. It is known that treatment with PGE2 can protect the gastro-intestinal tract against the effects of irritant substances in vivo. The authors wanted to see whether there was a comparable effect in vitro on primary cultures of gastric epithelial cells. After 4 days of incubation, when all cells had produced large amounts of mucus, either PGE2 alone (2.6 µM), ethanol alone (5%), or PGE2 followed 15 minutes later by ethanol (at the same concentrations), was added to the culture medium. The cells treated with ethanol alone for 5 minutes were 75% damaged; pre-treatment by PGE2 reduced the percentage to 35. From this it may be deduced that PGE2 was indeed able to protect the cells against the aggression of an irritant substance, and that the action was probably independent of and/or complementary to the mucus's cytoprotective properties.

• Nakamura et al. (Kyoto, Japan), examined the effects of interleukin IL-1ß on cell proliferation and mucus synthesis by gastric epithelial cells. IL-1ß had no effect on the two parameters per se, but did inhibit the epithelial cell proliferation stimulated by human EGF (epithelial growth factor). The authors concluded that IL-1ß could modulate cell proliferation without affecting mucus synthesis.

• Wu et al. (Boston, USA) compared the levels of expression of the SP trefoil peptide in the stomach of transgenic mice deficient in the ITF trefoil peptide gene (ITF-KO [knock-out] mouse), in its constitutive state and after induction of experimental colitis by adding dextran sodium sulphate (DSS) to the drinking water for 7 days.
Compared to their non-deficient congenerics (so-called "wild" mice), the ITF-KO mice expressed less SP mRNA on the gastric level, but did express one 79-KDa glycoprotein very strongly. On the other hand, after inducing the DSS colitis, the SP mRNAs were over-expressed in the ITF-KO compared to the "wild" mice, whereas expression of the 79-KDa mucin increased similarly in both types of animal.
Based on these observations, one may deduce that the ITF plays an active role in the functional regulation of the gastric mucosa by acting on the production of other trefoil peptides and mucins.

• The same team (Mashimo et al, Boston, USA) emphasised the importance of ITF in maintaining the integrity or repairing lesions of the intestinal mucosa. They underlined that in these transgenic mice, in which exon 2 coding for virtually all the protein has been suppressed, the non-expression of ITF resulted in an increased susceptibility to colon lesions and, above all, the complete absence of damaged epithelium regeneration.

• Mucins have two structural domains on their molecule, each with different functions : one highly glycosylated "tandem-repeat" domain, resistant to proteases and involved in hydration; the other, a "non-repeat", rich in cysteine residues, involved in mucus polymerisation. Turner et al. (Boston, USA) concentrated on sequencing the domain of cysteine-rich gastric apomucin in the pig. Working from a porcine cDNA bank, they isolated and sequenced a clone called PGM-2X which codes for the 5' "non-repeat" region of the porcine apomucin molecule, which was 60% homologous with human MUC-5A/C.
The expression of proteins from these clones makes functional studies feasible by providing molecular tools which may be able to act specifically on the aggregation and gelification properties so important for the mucus barrier's cytoprotective function.

• Hanajima et al. (Hamamatsu, Japan) observed that the difficulty in evaluating mucus secretion in real time prevents the kinetics and certain aspects of its regulation from being determined. They thus devised a new microscopy technique (VEC-DIC: video-enhanced contrast - differential interference contrast) which allows the gastric epithelial cells' secretory activity to be studied individually.
The technique allowed them to differentiate two types of cell according to their types of spontaneous exocytosis :
type I cells : infrequent, sporadic movements;
type II, sustained salvoes until depletion of the granules' contents.
Type I responses were eliminated in calcium-free milieux, whereas type II were not. Functional regulation of the two cell types was probably ensured by different pathways.

Mucus and nitrogen monoxide (NO)
• Is NO beneficial or harmful to the gastric mucosa ?
In the news more than ever, the question has generated research into two aspects of the problem and demonstrated that the agents differ in both cases.
The harmful effects of NO "donors", such as SIN-1 (3-morpholino-sydnonimine) seem mainly due to the compound releasing superoxide anions (O₂•) and peroxynitrites (ONOO•), agents of oxidative stress, as the NO is being produced (Sasai et al., and Oinuma et al, Tochigi, Japan).
The beneficial effects - cytoprotective - are apparently related more to NO having an activation effect on mucus production.

• It is thus suggested that NO plays a part in regulating mucin synthesis and/or secretion. Using the rat, Ichikawa et al. (Sagamihara, Japan) wanted to find out whether NO was involved in the probably differing mechanisms of mucus production activation by gastrin and the cholinergics.
They thus incubated gastric antrum and body epithelial cells in the presence of gastrin (0.1 µM) or carbachol (1 µM) in a culture medium with or without NG-nitro-L-arginine (L-NNA; 0.1 mM), a NO synthetase inhibitor. They found that the increased incorporation of [3H]glucosamine, evidence of de novo mucin production, induced by the gastrin was blocked by L-NNA in the body but not in the gastric antrum. On the other hand, L-NNA did not disturb carbachol-stimulated mucus production in either the antrum or the body. It would thus seem that gastrin and the cholinergic system could, via different mechanisms, be involved in regulating gastric mucus production, and that part of the gastrin's action would involve NO.

• Yanaka et al. (Tsukuba, Japan) examined the gastroprotective mechanism of tetraprenylacetone (TPA). The created lesions on the luminal surface of guinea pig fundal tissue samples placed in Ussing chambers by exposing them to an NaCl concentration of 1.25 M for 5 minutes at two pH levels: 3 and 7.
They then left the tissue recuperate by perfusing it with 150-mM NaCl for 6 hours, during which they assessed several parameters, amongst which the activity of NO synthetases (cNOS and iNOS) in the presence or absence of TPA (0.1 mM).
Treatment by TPA increased NOS activities no matter what the pH. On the other hand, TPA only promoted restoration of mucosal integrity at pH 3, an effect abolished by L-NAME (NO synthetases inhibitor) or by N-acetyl-L-cysteine (a mucolytic agent).
It may thus be concluded that the mechanism of TPA action involves an increased production of NO and mucus, and requires a highly acid milieu.

• Lastly, Branka et al. (Nantes, France) considered the role of NO in the regulation of epithelial cells' mucin exocytosis process. They stimulated HT29 cell cultures (human colon epithelial carcinoma) by two NO "donors", know for their different redox properties : mahma nonoate, a free radical NO• donor, and sodium nitroprussiate (SNP), a nitrosonium NO+ ion donor.
Mahma nonoate (1 µM) stimulated exocytosis via activation of the intracellular cyclic GMP. SNP also stimulated the secretion of mucins, but did not involve cyclic GMP. It would thus seem that NO, in various redox forms, can stimulate exocytosis along different intracellular pathways.

Mucus and gastroprotection
• Takao et al. (Osaka, Japan) studied the viscosity of neoform mucus following stimulation of the gastric epithelial cells by various active principles. To do so, they used the ELLA (Enzyme-Linked Lectin Assay) method where specific lectins selectively recognise certain side-chain carbohydrate residues responsible for mucin viscosity. In the presence of indometacin (10 µM), ethanol (10%) or ammonium ions (5 mM) in the culture medium for 3 hours, the cells secreted significantly more mucus than in the control medium.
The increased production concerned high-viscosity mucus alone, the one which certainly plays the most effective role in gastroprotection.

• The harmful effects of non-steroid anti-inflammatory drugs (NSAIDs) on the gastric mucosa are well known. To try and determine the mechanism of action, Giraud et al. (Clermont Ferrand, France and Houston, USA) administered hungry rats with indometacin (5 to 50 mg/kg) via the intragastric pathway, and evaluated the mucus gel's physical properties after 2 hours of contact.
Indometacin competitively bound to the hydrophobic domains of the active phospholipid layer on the mucus surface where they acted as stiffening agent by a phenomenon of molecular ordering, resulting in a significant loss of fluidity and hence the phospholipid layer's mucoprotective efficacy.

Mucus, trefoil peptides and Helicobacter pylori (Hp)
• Beil et al. (Hanover, Germany) looked at the role of Hp in functional deteriorations to the gastric mucosa of infected subjects. To a human cell line (HM02), whose mucus-producing properties are well-established, they added a lipid extract of Hp culture medium.
The extract substantially decreased mucin synthesis and secretion, and caused alterations to the nature of the molecules' carbohydrate residues: the number of N-acetyl-galactosamine and fucose residues increased relatively, whereas galactosamine residues did not change. The changes, both quantitative and qualitative, induced by Hp could prove important in the pathogenesis of gastritis and peptic ulcer.

• Hp exhibits a very marked chemotaxis to the gastric mucus. Turner et al. (Nottingham and London, UK) proposed identifying the gastric mucus component responsible. Since the chemotaxin has proved resistant to digestion by trypsin/pronase and heat (100°C), research turned to the trefoil peptides, SP and ITF.
The actual location of the peptides (antrum and ulceration border) could well explain not only the infection topography of H. pylori but also how it manages to get around the host's protective response.

• Rebamipide is an anti-ulcer agent which inhibits the formation of superoxide anions by neutrophils, and scavenges hydroxylated radicals. Saita et al. (Hyogo and Kyoto, Japan) decided to investigate these gastroprotective properties on a model of lesion similar to those caused by Hp. They observed that rats pre-treated with rebamipide (30 or 100 mg/kg, intraperitoneal) were relatively well protected against the conjugated ulcerogenic effects of ammonia and ischemia.
Amongst other parameters, rebamipide prevented the drop in gastric mucus density and hydrophobicity, which very probably contributes towards its anti-ulcer efficacy.

MUCUS AND BILE DUCTS

Cytoprotection of the gallbladder
• What is it that prevents the gallbladder from digesting itself ?
This is the question raised by Moore et al. (Richmond, Chicago, Boston, USA), and reminds us that the decades'-old debate on the respective gastroprotective roles of the "mucus barrier" and mucus layer applies just as much to the gallbladder. The gallbladder must obviously protect itself from the bile salts - which are nothing short of detergents - naturally present at high concentrations (up to 300 mM) in the bile. The authors therefore concentrated on the "toxicity" of bile salts, especially that of tauro-cheno-deoxycholate (TCDC), on monolayer cultures of mucus-free human gallbladder epithelial cells. They observed that in the presence of TCDC concentrations (1 or 10 mM) far lower than those present in the bile, the epithelial cells were destroyed within less than 30 minutes. They concluded that a "bare" mucosa does not have the ability to resist bile-salt aggression, and that the physical presence of a "mucus barrier" was thus vital.

Mucin synthesis by the gallbladder
• Studying the expression of genes coding for mucins in the gallbladder is of particular interest because, apart from their protective function, the gallbladder mucins also play a central role in the development of lithiases. Kates et al. (Boston, USA) decided to identify the products of human gallbladder mucin genes.
They found MUC5 to be very strongly expressed, in terms both of mRNA and protein. They suggest that a better understanding of MUC5 gene-expression regulation mechanisms would be of great value in understanding the pathogenesis of cholelithiases.

• The same team (Offner et al, Boston, USA) compared the levels of MUC1 to MUC6 gene expression on tissues from either normal subjects or patients presenting lithiases. They revealed a highly significant increase in both MUC3 and MUC5B mRNA in patients with lithiases, whereas that of MUC1, 2, 4, 5A and 6 did not change.
They also came to the conclusion that identifying the factors regulating the coordinated expression of MUC3 and MUC5B could allow therapies to be developed for preventing hypersecretion of the mucins, and consequently, the formation of lithiases in high-risk patients.

• The physiopathological mechanisms of mucin hypersecretion by the gallbladder are still poorly understood. Eder et al. (Munich, Germany) put forward the hypothesis that the products of lipid peroxidation (oxidative stress) are behind the epithelial cells' mucus hypersecretion.
After cholecystectomising the dog, they removed the bile under sterile, anaerobic conditions. They then measured the concentration in malondialdehyde (MDA), a quantitative marker of lipid peroxidation, and mucus secretion, by determining the quantity of [3H]glucosamine released into the epithelial cell culture medium.
They observed that bile of high crystallisation capacity had high levels of MDA, and that adding MDA to the culture medium significantly stimulated mucin secretion. It is thus perfectly feasible that oxidative stress induced by inflammation of the mucosa could be behind the peroxidation of lipids and resulting mucus hypersecretion.

• The same team (Strigl et al, Munich, Germany) had already shown that activated polynuclear neutrophils (PNN) could trigger off mucus hypersecretion in the dog gallbladder by an unknown mechanism. They tried to compare this with the results they obtained on lipid peroxidation.
The authors observed that the PNNs activated by phorbol myristate acetate significantly increased the concentration of MDA and mucus secretion in epithelial cell cultures without causing cell deterioration.
From this, they concluded that lipid peroxidation was indeed one of the mechanisms of mucus hypersecretion.

Lithogenesis and inflammation of the gallbladder
• Van den Berg et al. (Amsterdam, Holland) studied the possible synergy between mucins and calcium salts (both of which are major components of cholesterol stones) on the lithogenic capacity of a synthetic bile of standardised composition. They showed that the combined addition of calcium and mucins, at concentrations close to the physiological values found in human bile, stimulated the bile's formation of cholesterol crystals more effectively than when added alone.

• Rege et al. (Chicago and Richmond, USA) examined the possibility of cytokines mediating inflammation of the gallbladder epithelium observed in pigmentary lithiasis. They therefore instilled human cytokines (IL-1ß, IL-2, IL-6, IL-8 and TNFa) for 4 hours into the isolated gallbladder of guinea pigs in vivo, and measured the mucus-layer thickness and net flow of water and sodium. Among the cytokines, IL-1, IL-2 and IL-8 produced a significant thickening of the mucus layer and a drop in water and sodium absorption in the gallbladder.
They could thus be major mechanisms in the pathogenesis and progression of cholecystites.

• The same authors (Rege et al, Chicago and Richmond, USA) also looked at the role of prostaglandins in mucus hypersecretion associated with pigmentary lithiases. They had already described prostaglandin involvement in cholelithiases. They thus compared dogs subjected to a lithogenic diet (calculi after 6 weeks) with controls fed in a standard manner.
They measured the tissue and bile concentrations of PGE2, PGF2a and PGF1a, and the thickness of the mucus layer. They demonstrated that the mucus thickness increased significantly in lithiasic dogs without the prostaglandin levels being changed.
From this, they concluded that the prostaglandins were probably not involved in the mucus hypersecretion associated with the presence of pigmentary concretions.

MUCUS, SMALL INTESTINE AND COLON

Synthesis and regulation
• Van Klinken et al. (Amsterdam, Holland and Barcelona, Spain) presented a virtually exhaustive study of the mucins produced by various anatomical portions of the human intestine: the duodenum, jejunum, ascending colon and sigmoid colon. Their study follows and confirms their previous work on the mRNA of intestinal mucins. Using molecular biology techniques, they identified 7 mucins or mucin precursors, differing in molecular mass and location: MUC3 (550 KDa) produced by the small intestine and not by the colon, MUC4 (900 KDa) by the colon, and MUC6 (400 KDa) by the duodenum alone; MUC2 (600 KDa), MUC5A/C (500 KDa) and a new mucin, HGBM (human gallbladder mucin) (470 KDa), were found to be produced by both the small intestine and the colon, but with differences in SDS-PAGE mobility, indicative of the glycoproteins' different levels of glycosylation between the two organs.

• Plaisancie et al. (Lyon, France) described an experimental model of isolated organ (10 cm) under vascular perfusion (Krebs-Henseleit complemented, 2 ml/mn) allowing the neuro-humoral factors regulating colon mucin synthesis to be studied in the rat. The pharmacological agents are introduced into the intra-arterial perfusion flow for 30 mn, then the tissues are fixed and stained in order to quantify the mucins produced.
Doing this allowed them to confirm the secretagogic effects of PGE2 (1.25 and 2.5 µM) and bethanechol (0.1 mM), but, above all, revealed another two potential candidates for the functional regulation of the colon mucosa: peptide YY and neurotensin, both active at nanomolar concentrations.

Trefoil peptides
• "Trefoil peptides", (ITF: intestinal trefoil peptides, and SP: [antral] spasmolytic peptides) are regulatory peptides associated with epithelial mucins. They seem to be involved in repairing gastric ulcers, but their role on the intestinal mucosa is poorly understood.
Poulson et al. (London, UK and New Haven, USA) used in situ hybridisation and immunohistochemical techniques to examine the expression profiles of ITF and SP during restoration of mucosal integrity following intestinal resection in the rat.
They found an increase in ITF expression in the glands close to the anastomosis, whereas SP, which is not expressed in the ileum under normal conditions, was found close to the anastomosis in one case. These experimental data suggest that the trefoil peptides, essentially ITF, may be involved in the process of restoring mucosal integrity by promoting the development of migratory-type phenocells.

• Ogata and Podolsky (Boston, USA) used pharmacological tools to look at the expression regulation mechanisms of ITF (mRNA and protein). The authors tested the effects of various neuropeptides, cytokines and growth factors, on colon epithelial cell line HT29 in culture. Carbachol, VIP (vasoactive intestinal polypeptide) and somatostatin stimulated ITF expression on both the mRNA and protein levels. On the other hand, substance P, the cytokines and growth factors seemed to affect neither the mRNA nor the protein.
Trefoil peptides thus appear to be the actors in a defence mechanism complementing the mucosa's immune processes.

• Playford et al. (Leicester and London, UK) used transgenic mice which, in the jejunum enterocytes, over-express human pS2, a recently described member of the trefoil peptide family often found in intestinal mucosa lesions.
The authors wanted to ascertain whether pS2 played a major role in restoring mucosal integrity in response to aggression caused by the sub-cutaneous injection of indometacin (85 mg/kg). They found that, after indometacin, the transgenic mice presented significantly smaller lesions than the non-transgenic controls at sites where pS2 was expressed (jejunum), but ones very similar to those of the controls in the region of the ileum where pS2 was not expressed.
This provides us with further evidence that trefoil peptides are involved in the process of gastro-intestinal mucosa regeneration.

Intestinal cytoprotection
• Compound U74389 is a 21-aminosteroid which wards off lesions caused by ischemia-reperfusion in the small intestine, at least in part. Stojadinovic et al. (Bethesda and Washington, USA) wanted to determine the mechanism of action in the rat. An experimental ischemia of 30 minutes, followed or not by a 60- or 120-minute phase of reperfusion, was caused in control rats or those treated with U74389 (2.5 mg/kg, 2 mn before ischemia).
The authors assessed certain histological parameters characteristic of mucosal state, the production of mucus by fucose immunoenzyme labelling, the inflammatory tissue infiltration rate by polynuclear neutrophils (PNNs), and the tissue concentrations of LTB4 and PGE2. They observed that U74389 did not protect against the lesions caused by the ischemia, whereas it did satisfactorily prevent the PNN infiltration and LTB4 hypersecretion observed in the controls, and did not modify the PGE2 concentrations.
In rats treated with U74389, on the other hand, they observed an active production of mucus at the apical part of the cells, resulting in the formation of a thick layer on the epithelial surface. In these rats, mucosal restoration was total within 60 mn of reperfusion, whereas the lesions caused by ischemia persisted in the non-treated rats.
The present experimental example illustrates once again the importance of the physical presence of a mucus barrier in protecting the epithelium against oxidative stress.

• The mucus is also the intestine's first defensive barrier against parasites and other pathogenic agents, but not merely because of its physical presence. Research, for example, has shown us that certain mucin carbohydrate residues, such as galactose or N-acetyl-galactosamine, specifically inhibited the fixation of Entamśba histolytica onto the epithelial cells, a necessary stage in pathogenesis. Göttke et al. (Montreal, Canada and Omaha, USA) have thus stated that modifications (genetic or post-transcriptional) to colon mucin glycosylation may affect their efficacy in countering the attack of pathogenic agents.

MUCUS AND CHRONIC INFLAMMATORY DISEASES OF THE INTESTINE

• Deterioration of the mucus layer is very likely to be involved in the pathogenesis of chronic inflammatory diseases of the intestine. Mucin synthesis may be altered quantitatively or qualitatively during physiopathological processes. Van der Wal et al. (Amsterdam, Holland) have already shown that the qualitative biosynthesis of MUC2, a major mucin of the healthy or inflamed colon, remains unchanged in ulcerative colitis. They therefore continued their research to try and highlight the effect of the mucin's quantitative changes on the inflamed colon. They showed that, compared to healthy controls, MUC2 synthesis was significantly reduced during active ulcerative colitis, whereas it increased during periods of remission. In addition, since no difference was observed in the MUC2 mRNA, it would thus seem to be a post-transcriptional regulation and may have implications in the pathogenesis of ulcerative colitis.

• Mucus is a scavenger of oxygenated free radicals released by the cells of the white line in the intestinal mucosa, but may also be a potential "victim". For example, it would appear that the mucus layer is thinner, discontinuous and structurally less resistant in ulcerative colitis than in the healthy intestine. Pearson et al. (Newcastle, UK and Paris, France) evaluated, the mucolytic action of oxygenated free radicals on the one hand, and the possible protective effect of an anti-diarrhśic clay, diosmectite, on the other.
Mucolysis was evaluated by the drop in viscosity of a mucin solution over 24 hours. Generated by two different methods, the free radicals fragmented the mucus and resulted in a significant drop in viscosity. When diosmectite (25 mg/ml) was present in the solution, the free radicals were virtually unable to fragment the mucins.

• Rats immunised against mucins present, from the 8th week after initial immunisation, mucosal lesions similar to those in ulcerative colitis. Ohara et al. (Sagamihara, Japan) determined the antigen recognised by the serum of rats immunised against the colon mucins S or M, and studied the kinetics of mucosal lesion appearance.
They concluded that the colon mucins could be auto-antigens triggering ulcerative colitis.

MUCUS AND CANCER

Gastric cancer
• The risks of seeing a gastric intestinal metaplasia (IM) develop into carcinoma are there, although relatively lower than for śsophageal intestinal metaplasias (Barrett's śsophagus). Gastric MIs are easy to diagnose by routine staining of the mucins by alcian blue. Griffel et al. (New Brunswick and Plainfield, USA) have been researching a more specific mucin marker able to predict cancerous progression of gastric MIs. They developed a monoclonal antibody, called 7E12H12 (IgM isotype), which reacts specifically with certain types of mucin found in metaplasias predisposed towards developing into adenocarcinomas.

• Atrophic gastritis is a precursor stage of stomach cancer. Miwa et al. (Tokyo, Japan) investigated the carcinogenetic mechanisms. In rats treated with MNNG (1-methyl-3-nitro-N-nitrosoguanidine; 100 µg/ml; per os), they identified deteriorations to cell parameters leading to the development of atrophic gastritis in less than 8 weeks. Concerning the mucins secreted, their composition changed through the pathologic process, going from a majority of sulphomucins in the controls to a majority of sialomucins in the atrophied mucosa.

Cancer of the pancreas
• Monges et al. (Marseille and Strasbourg, France) studied the expression of MUC1 in the human pancreas. They found that MUC1 was only expressed at the apical part of canalicular an acinar cells of the normal pancreas; in pancreatic adenocarcinoma cells, the mucin was also expressed in the cytoplasm. Histochemical identification of MUC1's cell location in biopsies could prove very useful for diagnosis.

• Taki et al. (Nagoya, Japan), used ultrasonic wave technology to diagnose mucus-producing pancreatic tumours. The carried out studies on 45 patients with tumours of the main pancreatic duct or ramified tumours by means of intracanalicular echography.
Directly viewing infiltration of the canalicular tumour in the parenchyma allowed them to diagnose the existence of a carcinoma. For the ramified tumours, the presence of mural nodules meant the existence of an adenoma or adenocarcinoma.

• Because of their potential malignity, Hammel et al. (Clichy and Paris, France) also propose differentiating mucinous tumours of the pancreas from other cystic lesions. To do so, they used immunohistochemical MUC1 detection in the effluent of pancreatic cystic lesions. They found that the presence of high concentrations of MUC1 in the cystic liquid was a reliable indicator that a pancreatic lesion was of mucinous nature.

Cancer of the colon
• Kim et al. (San Francisco, USA) examined the regulation of mucin secretion in colon carcinomas. To do so, they used colon cell lines, Cla (colloid cancer) and HM3 (adenocarcinoma), labelled with [3H]glucosamine for 18 hours, then stimulated for 1 hour by secretagogues (a muscarinic agonist, carbachol; a calcium ionophore, A23187; a kinase C protein activator, TPA; and a kinase A protein activator, forskolin).
Both cell types responded similarly to the secretagogues, except for carbachol which proved significantly more active on the Cla than on the HM3 cells. It is thus probable that, in vivo, a cholinergic regulation of mucin synthesis operates in a more marked manner on colloid cancers than on colon adenocarcinomas.

• Mucins MUC5 and MUC6 are very strongly expressed on the gastric mucosa, but far less often in the healthy colon. Sanderson et al. (Minneapolis and San Francisco, USA) wanted to check whether MUC5 and MUC6 expression could be correlated to the histopathological criteria of colon cancers. They demonstrated the presence of both types of mucin and their genes in colon adenomas, and a correlation between the mucins' levels of expression and the size of the adenomas.
They concluded that the presence of MUC5 and MUC6 in the colon could be associated with an increased risk of the colon adenomas undergoing malignant transformation.

• One colon cancer marker could well be sialic-a2.6 acid. Murayama et al. (Zurich, Switzerland and Heidelberg, Germany) showed that it was found specifically in colon carcinomas, but not in the healthy colon, and that it was integrated into a membrane or secreted glycoprotein which was neither the sialosyl Tn antigen, nor one of the main mucins expressed in the colon.

• Yeh et al. (San Francisco and Minneapolis, USA) searched among a series of twelve genes of mucins and antigens carbohydrate residues associated with the mucins whose presence in resections could act as markers for the prognosis of colo-rectal cancer.
They found, for example, that the presence of the sialyl LeX antigen in the tissues was associated with a low survival rate at five years. Absence de sialyl Tn and gastro-fundic apomucin, on the other hand, was associated with an excellent prognosis. The antigens could prove reliable markers for the prognosis of colo-rectal cancer.

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