Sialic acids of human large bowel mucosa: o-acylated variants in normal and malignant states

Enhancing the receptor affinity of the sialic acid-binding domain of Vibrio cholerae sialidase through multivalency

Many glycoside hydrolases possess carbohydrate-binding modules (CBMs) that help target these enzymes to appropriate substrates and increase their catalytic efficiency. The Vibrio cholerae sialidase contains two CBMs, one of which is designated as a family CBM40 module and has been shown through structural and calorimetry studies to recognize the alpha-anomer of sialic acid with a KD of approximately 30 microM at 37 degrees C. The affinity of this V. cholerae CBM40 module for sialic acid is one of the highest reported for recognition of a monosaccharide by a CBM. As Nature often increases a weak substrate affinity through multivalency, we have explored the potential of developing reagents with an increased affinity for sialic acid receptors through linking CBM40 modules together. The V. cholerae CBM40 was subcloned and crystallized in the presence of sialyllactose confirming its ability to recognize sialic acid. Calorimetry revealed that this CBM40 demonstrated specificity to alpha(2,3)-, alpha(2,6)-, and alpha(2,8)-linked sialosides. Polypeptides containing up to four CBM40 modules in tandem were created to determine if an increase in affinity to sialic acid could be achieved through an avidity effect. Using SPR and a multivalent alpha(2,3)-sialyllactose ligand, we show that increasing the number of linked modules does increase the affinity for sialic acid. The four-CBM40 module protein has a 700- to 1500-fold increase in affinity compared with the single-CBM40 module. Varying the linker length of amino acids between each CBM40 module had little effect on the binding of these polypeptides. Finally, fluorescence-activated cell sorting analysis demonstrated that a green fluorescent protein fused to three CBM40 modules bound to subpopulations of human leukocytes. These studies lay the foundation for creating high affinity, multivalent CBMs that could have broad application in glycobiology.

Monoclonal antibody G47 engineered to be reactive with colorectal tumor mucin

We have previously shown that the normal adult colon produces a sialomucin containing the core trisaccharide 1,3 N-acetylgalactosamine. This structure was shown to be the epitope for a polyclonal antiserum that demonstrated colon "specific" activity. Antiserum binding is dependent upon the presence of O-acetylated sialic acids present at high concentrations in normal adult colon tissue. However, O-acetylation of sialic acids is decreased in colorectal cancer. Indeed, approximately 50% of colorectal carcinomas are nonreactive with this antiserum. In the current work, we used a de-O-acetylated, normal colon mucin as immunogen to generate monoclonal antibody (MAb) G47. Untreated normal colon mucins having a high O-acetylated sialic acid content were essentially nonreactive with G47. Removal of O-acetyl groups by saponification generated a reactive mucin derivative while subsequent treatment with neuraminidase abolished reactivity. By immunoperoxidase procedures MAb-G47 was reactive with approximately 85% of colorectal tumors while exhibiting relatively low reactivity with normal colon tissue. Mucins isolated from normal colon had on average less than 10% of the specific epitope as compared with mucins derived from colorectal tumors (p < 0.01). Initial immunohistochemical studies on tumors of noncolonic origin revealed few positive cases. The potential of MAb-G47 to assist in the diagnosis and/or prognosis of colorectal cancer is now being studied.

Mucinous (colloid) adenocarcinomas secrete distinct O-acylated forms of sialomucins: a histochemical study of gastric, colorectal and breast adenocarcinomas

AIMS

Mucinous (colloid) adenocarcinomas represent a distinct group of tumours defined by the presence of large amounts of extracellular mucins. By using histochemical methods, we analysed mucins secreted by mucinous versus non-mucinous adenocarcinomas and looked for differential secretion profiles.

METHODS AND RESULTS

Sixty-four adenocarcinomas were studied (23 colorectal, 17 gastric, and 24 breast tumours). Thirty-two tumours were of the colloid type. The following methods were applied to paraffin tissue sections: (i) Alcian blue (pH 2.5) and periodic acid-Schiff (PAS); (ii) high iron diamine and Alcian blue (pH 2.5); (iii) periodic acid borohydride, potassium hydroxide, and PAS; (iv) periodic acid-thionine Schiff, potassium hydroxide, and PAS; and (v) periodic acid-borohydride and PAS. Most adenocarcinomas secreted acidic mucins, with sialomucins predominating over sulfomucins, except for non-mucinous adenocarcinomas of the breast which showed predominant neutral mucins. All mucinous adenocarcinomas contained C9-O-acyl sialic acid as mono, di(C8,C9)-, or tri(C7,C8,C9)-O-acyl forms. Acidic mucins secreted by the majority of non-colloid adenocarcinomas consisted of non-O-acylated sialomucins.

CONCLUSIONS

C9-O-acylation of sialic acid is a characteristic feature of mucinous adenocarcinomas and can be readily detected by histochemical methods.

Determination of sialic acids by liquid chromatography–mass spectrometry

Sialic acids are widely found in nature as components of oligosaccharide units in mucins, glycoproteins and other microbial polymers. Existing methods for determining these acids are long, tedious, and not specific. A simple, rapid, and sensitive method for determining the most commonly occurring acids, N-acetylneuraminic and N-glycolylneuraminic acid, using LC-MS is described. Standard solutions of the sialic acids with the internal standard, N-acetylneuraminic acid methyl ester, were quantitatively analyzed by positive ion electrospray ionization. Fetuin was used as a model glycoprotein and the hydrolysate was injected directly onto an ES Industries AquaSep 3 microm 150x4.6 mm column eluted with a 0.1% aqueous formic acid mobile phase at a flow-rate of 0.5 ml/min. Detection was achieved using the Finnigan Navigator MS system in the selected ion monitoring mode for the protonated molecular ions at m/z 310, 324, and 326. The linearity over the dynamic range 10 to 1000 ng of sialic acids on-column had a correlation coefficient greater than 0.999. The amount of sialic acids found in the fetuin hydrolysate was in agreement with values reported in the literature.

Lectin cytochemical characterization of the N- and O-linked oligosaccharides in the human rectum

The oligosaccharides of the mucus glycoproteins of the human rectum are important for the lubricant and protective role suggested for the rectal mucus. Changes in oligosaccharide composition are observed in several colon diseases, and some of these changes could be used as diagnostic and prognostic indicators. Thus, a previous knowledge of the normal mucus glycoproteins is necessary. The aim of the present study is the characterization of the oligosaccharides of the goblet cells and enterocytes of the human rectum. For this, a battery of 15 lectins, in combination with chemical and enzymatic deglycosylation procedures, was used. Our results suggest the presence of N-acetylglucosamine (GlcNAc), Man, Glc, N-acetylneuraminic acid (Neu5Ac)(alpha2-6)- and Neu5Ac(alpha2-3)-linked, N-acetylgalactosamine (GalNAc) and Gal(beta1-3)GalNAc in the oligosaccharides of the goblet cells. Moreover, N-linked oligosaccharides specifically contained Gal(beta1-4)GlcNAc, while AAA-positive Fuc was only detected in O-linked oligosaccharides. Some of these carbohydrates were only visualized after removal of N- or O-linked oligosaccharides, suggesting a high level of approximation between the oligosaccharide chains, that render the carbohydrate inaccessible to the lectins. Differences in the labelling pattern between the goblet cells of the surface epithelium and the upper half of the crypts, and those of the lower half of the crypts suggests a maturation process for the goblet cells, which modifies the oligosaccharide composition of the secreted glycoproteins, as they ascend throughout the crypts. This maturation process includes the incorporation of new carbohydrates (GlcNAc), and the masking (Neu5Ac(alpha2-3)-linked) or unmasking (Glc and GalNAc) of others.

Different modes of sialyl-Tn expression during malignant transformation of human colonic mucosa

Monoclonal antibodies TKH2 and B72.3, which react with the mucin-associated sialyl-Tn(STn) antigen, preferentially bind to cancerous but not normal colonic tissues. If O-acetyl groups are removed by saponification of tissues, MAb TKH2 will react with normal colonocytes, whereas MAb B72.3 remains non-reactive. To explain this difference in binding specificity, we tested both MAbs against synthetic constructs of single (monomeric) or clustered (trimeric) STn epitopes by enzyme immunoassay. Both MAb TKH2 and MAb B72.3 reacted with trimeric STn, but MAb TKH2 demonstrated greater binding than MAb B72.3 to monomeric STn. This suggests that normal colonic mucosa expresses monomeric STn epitopes, but that with transformation to malignancy, clustered STn epitopes appear. The appearance of clustered STn epitopes during colonic carcinogenesis represents a novel pattern of carbohydrate antigen expression and implicates alterations at the level of apomucins and/or glycosyltransferases responsible for cluster epitope formation.

Binding specificity of influenza C-virus to variably O-acetylated glycoconjugates and its use for histochemical detection of N-acetyl-9-O-acetylneuraminic acid in mammalian tissues

The specificity of influenza C-virus binding to sialoglycoconjugates was tested with various naturally O-acetylated gangliosides or synthetically O-acetylated sialic acid thioketosides, which revealed binding to 9-O-acetylated N-acetylneuraminic acid. Binding was also observed with a sample of Neu5,7Ac2-GD3, however at a lower degree. Sialic acids with two or three O-acetyl groups in the side chain of synthetic sialic acid derivatives are not recognized by the virus. In these experiments, bound viruses were detected with esterase substrates. Influenza C-virus was also used for the histological identification of mono-O-acetylated sialic acids in combination with an immunological visualization of the virus bound to thin-sections. The occurrence of these sialic acids was demonstrated in bovine submandibular gland, rat liver, human normal adult and fetal colon and diseased colon, as well as in human sweat gland. Submandibular gland and colon also contain significant amounts of glycoconjugates with two or three acetyl esters in the sialic acid side chain, demonstrating the value of the virus in discriminating between mono- and higher O-acetylation at the same site. The patterns of staining showed differences between healthy persons and patients with colon carcinoma, ulcerative colitis or Crohn's disease. Remarkably, some human colon samples did not show O-acetyl sialic acid-specific staining. The histochemical observations were controlled by chemical analysis of tissue sialic acids.

Histochemical alterations of mucin in normal colon, inflammatory bowel disease and colonic adenocarcinoma

Loss of sialic acid o-acyl substitutions in colonic mucus was studied using specific histochemical techniques in individuals with a variety of large-bowel diseases and in a control population. Changes found included a focal or field (diffuse) loss of side-chain substitutions which were qualitatively similar in all groups studied. The results were tested statistically using a variety of assumptions that field and/or focal loss of o-acyl substitution may be either abnormal or a normal variant. No statistically significant differences in the prevalence of substitutions were detected between normal males and females or between normal individuals aged 0-29 years and 30-80 years. Significant differences were found between ascending and descending colon in both normal individuals and in the non-neoplastic mucosa of patients with cancer. There were also significant differences between the normal descending colon and cases with cancer of the descending colon. These differences seem unlikely to be due to non-specific factors, since for most assumptions there were also differences between colons containing cancer and those from patients with inflammatory bowel disease. In agreement with the work of other investigators, it seems likely that focal loss of o-acetylation results from an acquired gene mutation. It is not clear whether or not this plays a role in carcinogenesis.

Dolichos biflorus agglutinin binding in hereditary bowel cancer

Dolichos biflorus agglutinin (DBA) binds specifically to N-acetylgalactosamine (GalNAc), one of the 5 sugars contributing to the oligosaccharide component of human colorectal goblet cell mucin. DBA binds to goblet cells of the upper crypt and surface epithelium within the proximal colon and to the majority of goblet cells of the distal large bowel. DBA therefore serves as a marker of colorectal goblet cell differentiation with a distinct proximal to distal gradient effect. Previous reports indicate significant loss of DBA reactivity within morphologically normal colorectal mucosa derived from at-risk members of hereditary non-polyposis colorectal cancer (HNPCC) families. This finding could not be confirmed in the present study. Reduced binding was a relatively consistent finding in transitional mucosa, hyperplastic polyps and carcinoma, with adenomas displaying a more varied pattern of loss. Reduced binding by DBA may be explained by several mechanisms and may not necessarily reflect loss of GalNAc. The concept that lectins can be used to identify stepwise changes that occur during neoplastic evolution should not be accepted uncritically.

The roles of enteric bacterial sialidase, sialate O-acetyl esterase and glycosulfatase in the degradation of human colonic mucin

Sialidase activity in normal faecal extracts showed a preference for mucin-related glycoprotein and oligosaccharide substrates, but the presence of two or more O-acetyl esters at positions C7-C9 on the sialic acids retarded the rate of hydrolysis. A specific sialate O-acetyl esterase was detected with a lower total activity relative to sialidase with mucin substrates and having a pH optimum of 7.8 and a KM of approximately 1 mM sialate O-acetyl ester. A specific glycosulfatase activity was found in faecal extracts using the substrate lactit-[3H]ol 6-O-sulfate with a pH optimum of pH 5.0 and a KM of approximately 1 mM. Faecal extracts from ulcerative colitis (UC) patients had higher sialate O-acetyl esterase and glycosulfatase activity, while mucin sialidase activity was unchanged. Metabolically labelled mucin isolated from UC patients contained less sulfate and had lower sialic acid O-acetylation compared with normal mucin. Colonic mucin was degraded more efficiently by faecal extracts from UC patients compared with normal extracts. The UC mucin was degraded more rapidly than the normal mucin by faecal enzyme extracts from both normal and UC subjects.

Mucin histochemistry of virus-induced duodenal adenomas in guinea fowl

The type of mucoproteins in virus-induced duodenal adenomas in guinea fowl were compared with those in the normal duodenal mucosa. The mucin-producing cells in the latter contained a mixture of acid and neutral mucins. Neutral and sulphomucins prevailed in the crypts and in the lower part of the villi, while the amount of the sialomucins increased progressively toward the tip of the villi. In the adenomas, goblet cells were more numerous and were unevenly distributed. In their mucin profile the deeply located tumor glandular structures resembled normal crypts and lower parts of the villi and superficial portions of the adenomas were similar to the upper part of the villi. Qualitative changes in the mucin secretion with deviation from the normal vertical distribution of mucin types were rarely observed. The histochemical study carried out supplemented the histological characterization of the virus-induced duodenal adenomas and contributed to the elucidation of some aspects of their histogenesis.

Regional distribution of glycoconjugates in normal, transitional and neoplastic human colonic mucosa. A histochemical study using lectins

Regional distribution of glycoconjugates in normal and neoplastic colonic mucosa was studied by means of eight lectins: Dolichos biflorus (DBA), Glycine max (SBA), Triticum vulgare (WGA), Arachis hypogaea (PNA), Griffonia simplicifolia-I (GS-I), Canavalia ensiformis (Con A), Limax flavus (LFA), and Ulex europaeus-I (UEA-I). The lectin binding patterns were examined in 40 normal colonic mucosa (NM) (12 proximal (P) and 28 distal (D], 38 carcinomas (15 P and 23 D), and 31 transitional mucosa (TM) (9 P and 22 D). Sections of NM located 5 cm and 10 cm distant from the tumour and sections from the resection margins (more than 10 cm from the tumour) of the surgical specimens were also studied in 19 cases (6 P and 13 D). In NM, regional differences between the proximal and distal colon were detected with most lectins. DBA, SBA and LFA bound mainly to the goblet cell mucin of the distal colon, while GS-I and UEA-I labelling predominated in proximal colonic mucosa. The lectin reactivity in carcinomas was: DBA 26%, SBA 63%, PNA 95%, GS-I 66%, UEA-I 76%, WGA 100%, Con A 92% and LFA 42%. No regional differences were observed in the lectin patterns of proximal and distal colonic carcinomas nor was any relationship detected between lectin reactivities and Dukes stage, size or histological type of tumours. Transitional mucosa of both the proximal and distal colon showed an increase in PNA-binding and loss of DBA and SBA. LFA and UEA-I reactivity in proximal TM was similar to that observed in proximal NM. Distal TM showed a decrease in LFA labelling and the appearance of UEA-I reactivity in goblet cell mucin in 5 cases (23%). The reactivity of the other lectins was as with NM. The only change in normal mucosa distant from tumours was a focal increase in PNA reactivity in 4 cases. These findings suggest that carcinomas from different colonic regions have a more uniform distribution of carbohydrates than the respective NM.

A morphometric assessment of transitional mucosa in the colon

Quantitative morphometric analysis was used in 10 resection specimens to assess so-called transitional mucosa immediately adjacent to colorectal carcinoma. Eleven nuclear and cellular variables were measured from the malignant epithelial area and from zones of increasing distance (1 cm) from the lesion. In addition, mean mucosal height was assessed for each zone. Morphometrical differences between the mucosa immediately adjacent to the malignant epithelium and that taken at some distance from it were determined by Mann-Whitney U tests. Transitional mucosa showed increased mucosal height but no nuclear differences from normal mucosa. Other work has shown that there are nuclear morphometric differences associated with premalignant conditions in the colon. Thus, the suggestion that transitional mucosa represents early neoplastic change cannot be supported.

Mucin profiles in ulcerative colitis with dysplasia and carcinoma

Mucin secretion was assessed in Crohn's colitis, in ulcerative colitis with regeneration, dysplasia and carcinoma and in non-colitic adenocarcinoma. The high iron diamine-alcian blue (HID-AB) and periodate borohydride-saponification periodic acid Schiff (PB-KOH-PAS) techniques were used to demonstrate sulphomucins and sialomucins, and O-acylated sialomucins respectively. There was mucosal hyperplasia and increased sialomucin secretion in Crohn's disease, quiescent and active ulcerative colitis. In colitis with carcinoma inflamed mucosa away from the tumour had increased sialomucins as had colitis with dysplasia. They did not differ statistically from each other or from colitic controls without cancer. Dysplastic crypts frequently secreted sulphomucins and the increased sialomucins were in transitional-like glands in the surface fronds or adjacent to the dysplasia. A comparative study of the HID-AB technique gave total correct qualitative allocation of individual quantitatively assessed crypts. Routine HID-AB staining did not aid the recognition of dysplasia in ulcerative colitis. With the PB-KOH-PAS technique colorectal adenocarcinoma showed a significant diminution in O-acylated sialomucins compared with its adjacent mucosa. Mucosal dysplasia in ulcerative colitis displayed a similar trend in O-acylated sialic acid variants, differing with respect to age-and sex-matched colitic controls. The PB-KOH-PAS technique may be of help in assessing mucin secretion in ulcerative colitis as a guide to the evolution of malignancy.

Characterization of mono-, di-, and tri-O-acetylated sialic acids on human cells

The presence of mono-, di-, and tri-O-acetylated sialic acids on human cells was demonstrated by using radiochromatographic and chemical techniques. Human melanoma cells and fresh colon tissue were biosynthetically labeled with 6- (3H) glucosamine. Radiolabeled sialic acids were hydrolytically removed from cellular glycoconjugates, purified by ion-exchange chromatography, and separated by paper chromatography on the basis of the number of O-substitutions on each sialic molecule. This analytical technique characterized radiolabeled sialic acids that migrated with the same Rf as synthetic mono-, di-, and tri-O-acetylated 14C-labeled sialic acids. The mono-O-acetylated sialic acids were characterized by their sensitivity to sodium periodate oxidation and a crude mouse liver esterase preparation. The di- and tri-O-acetylated sialic acids were characterized by their resistance to sodium periodate oxidation and sensitivity to the action of crude mouse liver esterase. Chromatographically separated di- and tri-O-acetylated sialic acids from normal human colon tissue were characterized by their respective ion molecular weights by using fast-atom bombardment-mass spectrometry. Using these methods, we chemically characterized mono, di-, and tri-O-acetylated sialic acids expressed on human cells. Aberrant expression of O-acetylated sialic acids was associated with adenocarcinoma of the colon, leading to a nearly complete loss of di- and tri-O-acetylated sialic acids.

The surface receptor is a major determinant of the cell tropism of influenza C virus

N-Acetyl-9-O-acetylneuraminic acid (Neu5,9Ac2) has been shown to be a high-affinity receptor determinant for attachment of influenza C virus to erythrocytes (G. N. Rogers, G. Herrler, J. C. Paulson, and H-D. Klenk, 1986, J. Biol. Chem. 261, 5947-5951). In this report the nature of the cell surface receptor for influenza C virus on tissue culture cells was analyzed. Pretreatment with either neuraminidase or neuraminate 9-O-acetylesterase was found to render LLC-MK2 cells resistant to infection by influenza C virus as evidenced by the failure to detect virus release into the medium by hemagglutination titration. Susceptibility to infection was fully restored after incubation of neuraminidase-treated cells with bovine brain gangliosides known to contain Neu5,9Ac2. These results indicate that (i) Neu5,9Ac2 is the primary receptor determinant required for influenza C virus to attach to tissue culture cells and to initiate infection and (ii) gangliosides containing this type of sialic acid are potential receptors for influenza C virus. Several cell lines which are resistant to infection by this virus were able to release influenza C virus into the medium provided they were incubated with bovine brain gangliosides prior to virus infection. This result indicates that lack of appropriate receptors on the cell surface is a major reason for the restricted cell tropism of influenza C virus.

Colorectal goblet cell sialomucin heterogeneity: its relation to malignant disease

Mucus secreted by colorectal cancer differs in three respects from that produced normally: an overall reduction, a loss of O-acetyl substituents in sialic acid, and an increase in neutral mucin. Similar changes have been reported in apparently normal mucosa bordering colorectal cancer. "Normal" left sided colorectal mucosa from 32 patients with rectal cancer was studied. Each case was matched by age and sex to a patient with diverticular disease and a patient with irritable bowel syndrome. Twenty five patients with right sided cancer were matched to patients with Crohn's disease. Sections were stained with mild periodic acid Schiff (mPAS) (selectively stains N-acetyl sialic acid lacking in O-acetyl group) and other closely related techniques. Reactions were graded negative, weak, and intense. An intense reaction was found in 9% of cases; there was no difference between the various matched groups. Phenylhydrazine interposition failed to block the mPAS effect, indicating that a positive result was due to a deficiency of sialic acid with O-acetyl substituents rather than neutral mucin. Different staining patterns in left and right colon were probably due to differing ratios of total sialic acid:fucose. These findings indicate a hitherto unsuspected colorectal goblet cell sialomucin heterogeneity within the general population, but no association with neoplastic disease is apparent.

Lectin-binding sites in normal, hyperplastic, adenomatous and carcinomatous human colorectal mucosa

The carbohydrate structures of cellular glycoconjugates in normal, hyperplastic, adenomatous and carcinomatous human colorectal mucosa were analysed with six fluorescein isothiocyanate-conjugated lectins. In normal, hyperplastic and adenomatous colorectal mucosa showing mild or moderate dysplasia Concanavalin A (Con A), Lens culinaris (LCA), and wheat germ (WGA) agglutinins stained goblet cell glycoconjugates (actual mucin goblet itself) while peanut (PNA), Vicia villosa (VVA), and Griffonia simplicifolia-II (GSA-II) agglutinins showed a supranuclear staining of goblet cell glycoconjugates. After neuraminidase treatment of tissue sections PNA and VVA stained mucin goblets of mature cells in normal mucosa, while less differentiated cells in the lower crypt displayed a supranuclear staining with VVA. The mucin goblets in adenomatous mucosa with mild or moderate dysplasia did not stain with PNA and VVA, neither before nor after neuraminidase treatment. Areas of in situ cancer in adenomas and carcinomas displayed a strong and direct binding of Con A, LCA, WGA and PNA in an apical linear distribution, while the binding of VVA and GSA-II was heterogeneous. We conclude that there are alterations in the carbohydrate structures of cellular glycoconjugates, which can be related to goblet cell differentiation in normal colorectal mucosa and to the degree of dysplasia in adenomas. Heterogeneous and incompletely glycosylated glycoconjugates appear to be synthesized by the majority of colorectal carcinomas.

Colonic mucosa adjacent to adenomas and hyperplastic polyps--a morphological and histochemical study

The morphological and histochemical features of colonic mucosa adjacent to 142 adenomas and 31 hyperplastic polyps were studied. Three predominant patterns were identified: (1) normal mucosa, showing normal histological architecture and secretion of sulphomucins; (2) N+ type, histologically normal mucosa with predominance of sialomucins; (3) transitional mucosa; hyperplastic mucosa secreting sialomucins. Hyperplastic changes were observed in the immediate neighbourhood or at the base of adenomas and were more frequent and extensive near large adenomas than around smaller lesions. Sialomucins were often predominant in the mucosa adjacent to large adenomas, but N+ type mucosa was also seen near minute adenomas and hyperplastic polyps and remote from polypoid lesions. Moreover, both hyperplastic and secretory changes were more frequent in the left colon than in the right. These findings seem to suggest that mucosal hyperplasia more likely represents a local change, parallel with or secondary to tumour development rather than a pre-adenomatous lesion. Secretory modifications are widespread and may result from the action of various factors among which carcinogens cannot be excluded.

Rat colonic mucosal cell sialic acid metabolism in azoxymethane-induced tumours

Colonic tissue was examined from normal (control) rats and azoxymethane- (carcinogen-) treated animals. Tumour-bearing colons from azoxymethane-treated rats were divided into malignant and non-malignant areas. Mucosal cells were prepared from the three types of colonic tissue and then examined for DNA and protein content and for the activities of ten enzymes involved in sialic acid metabolism. Enzyme activities were related to either the protein or the DNA content of fractions. The DNA content of cell homogenates was significantly different between tumour and non-malignant tissue and between both these tissues and normal mucosa. The protein content of the 100000 X g membrane pellet and supernatant fraction did not vary significantly between normal and non-malignant material but both these tissues differed significantly from tumour tissue. Significant variation between normal control and tumour tissue was detected at all levels of sialic acid metabolism, including N-acetylhexosamine interconversion and phosphorylation, sialic acid formation and activation, CMP-NeuAc breakdown and transfer and sialic acid release from glycoconjugates. The results indicate that major changes at all levels of sialic acid metabolism are associated with malignancy in rat colonic mucosa. Some of these changes are apparent in non-malignant mucosa and may reflect a pre-malignant state.

Chemical and histochemical studies of normal and diseased human gastrointestinal tract. III. Changes in the histochemical and chemical properties of the epithelial glycoproteins in the mucosa close to colonic tumours

Histochemical, chemical and histological studies were performed on 26 specimens of human colonic tumours and 62 specimens of mucosa taken at distances of 0.5-5.0 cm from the tumour. The tumour glycoproteins were divided almost equally between three anionic types, sulphomucin, sialomucin and mixed sialomucin and sulphomucin. All showed a reduction in staining for side chain O-acylated sialic acid. In 56% of the tumours, this was accompanied by loss of glycoprotein while, in 44%, abundant mucin was still present. Histochemical examination of the mucosal specimens indicated that in 24.2% the side chain O-acylated sialic acids did not differ from normal. In 41.9% there was a focal change and in 33.9% there was a generalized field reduction in the proportion of side chain O-acyl sialic acids. The latter were subdivided into moderate and severe. Chemical analyses correlated well with the histochemical classification of the mucosal specimens and showed that, on average, the classifications focal and severe field change were not due to sampling error. Forty-five per cent of the cases showed only focal change and 40% only field change. Mucosal specimens associated with 60% of the moderately differentiated tumours showed only focal change while those associated with 75% of well-differentiated tumours showed only field change. Abnormal patterns of staining for side chain O-acylated sialic acids (a) were largely independent of the distance from the tumour, (b) occurred in the presence of a normal pattern of staining for sialomucins and sulphomucins and (c) were associated with 61.4% of the specimens that showed no discernible evidence of histological abnormality. In contrast, only one specimen showed evidence of histological change without a corresponding change in O-acylated sialic acids. The data suggest that abnormal patterns of staining for O-acylated sialic acids may represent premalignant change but their precise significance and specificity requires further studies of non-neoplastic diseases of the colon.

Regional distribution and alterations of lectin binding to colorectal mucin in mucosal biopsies from controls and subjects with inflammatory bowel diseases

Glycoconjugate composition of colorectal goblet cell mucin was characterized according to the anatomical distribution of lectin-binding sites in mucosal biopsies from 35 control subjects and 55 patients with inflammatory bowel disease. 24 of the controls had mucosal inflammation on biopsy, without clinical evidence of inflammatory bowel disease. These inflamed controls showed a similar rate of presence of lectin-binding sites as the normal noninflamed group. In the controls, the frequency of binding of Ricinus communis agglutinin I to galactosyl residues was consistently higher than that found with either Ulex europaeus agglutinin I to fucosyl or Dolichus biflorus agglutinin to N-acetyl galactosyl groups. A significant proximal to distal gradient for Ulex europaeus agglutinin I binding sites was identified in the controls group. These binding sites were present four times more often in the proximal colon than in the distal colon (P less than 0.025). In the ulcerative and Crohn's colitis groups, this gradient effect was lost, predominantly as a result of decreased availability of fucosyl residues in the proximal colon. In the descending colon of Crohn's colitis tissues, there was a complete absence of Dolichus biflorus agglutinin binding sites compared with the 62.5% incidence in the control group (P less than 0.05). These results demonstrate that the expression of lectin-binding sites in human large intestinal goblet mucin is specifically altered in inflammatory bowel disease, indicating that there are changes in glycosylation of colorectal mucin consistent with alterations in goblet cell differentiation.

Mucin profiles in the mucosa adjacent to large bowel non-adenocarcinoma neoplasias

Morphological features and mucin secretion patterns were investigated in the colonic mucosa adjacent to or overlying mesenchymal or primary epithelial neoplasias, other than adenomas and adenocarcinomas. The material included 15 cases of non-adenocarcinoma tumours examined during 1978-1981. Increased sialomucins and morphological features similar to those described in the so-called 'transitional' mucosa adjacent to primary colorectal adenocarcinomas were observed in only two cases. In contrast our previous studies have demonstrated 'transitional' profiles in 98% of adenocarcinomas.

Histochemical identification of side chain substituted O-acylated sialic acids: the PAT-KOH-Bh-PAS and the PAPT-KOH-Bh-PAS procedures

Two new methods, based on the original periodic acid-Thionin Schiff-saponification-periodic acid-Basic Fuchsin Schiff (PAT-KOH-PAS) technique of Culling et al. (1976), have been devised for the histochemical identification of side-chain O-acylated sialic acids. In the first of these, the periodic acid-Thionin Schiff-saponification-borohydride reduction-periodic acid-Basic Fuchsin Schiff (PAT-KOH-Bh-PAS) procedure, the specificity of the original PAT-KOH-PAS technique was improved by: (a) extending, when necessary, the initial period of periodate oxidation, (b) increasing the period of exposure to Thionin Schiff reagent from 30 min to 4 h, (c) using a Thionin Schiff reagent prepared by a different method, (d) interposing a borohydride reduction step between the saponification and PAS steps and, (e) extending the period of oxidation in the final PAS step from 10 to 30 min. In the second procedure, the periodic acid-phenylhydrazine-Thionin Schiff-borohydride reduction-periodic acid-Basic Fuchsin Schiff (PAPT-KOH-Bh-PAS), based on the periodic acid-phenylhydrazine-Schiff (PAPS) technique of Spicer (1961), blue Thionin Schiff staining was confined to sialic acid residues with oxidizable side chain vicinal diols by interposing a treatment with 0.5% (w/v) aqueous phenylhydrazine hydrochloride for 2 h at room temperature between the initial periodic acid oxidation and the Thionin Schiff steps of the PAT-KOH-Bh-PAS procedure. These procedures are discussed within the general framework of the methods available for the histochemical identification of side-chain O-acylated sialic acids.

Chemical and histochemical studies of normal and diseased human gastrointestinal tract. I. A comparison between histologically normal colon, colonic tumours, ulcerative colitis and diverticular disease of the colon

Chemical and histochemical methods were used to compare the epithelial glycoproteins from formalin-fixed surgical specimens of normal human large intestine, colonic tumours, ulcerative colitis and diverticular disease. All the epithelial glycoproteins contained fucose, galactose, glucosamine, galactosamine and, in addition, sialic acids both with and without O-acyl substituents in the side chain and/or at position C4. The glycoproteins of the normal ascending and descending colons differed significantly with respect to the percentage of the sialic acids released following digestion of the de-O-acylated glycoprotein with Vibrio cholera neuraminidase and to the molar fucose-sialic acid ratio. Statistical analysis of the chemical data showed that (a) compared to normal, the sialic acids of the tumour and ulcerative colitis glycoproteins from the descending colon were significantly less substituted in the side chain and at position C4; (b) the O-acetyl substitution pattern of the sialic acids of the ulcerative colitis glycoproteins from the ascending colon and the quantitative composition of the carbohydrate prosthetic groups of the ulcerative colitis glycoproteins from both ascending and descending colons differed from normal; (c) it was not always possible to distinguish between the ulcerative colitis and tumour glycoproteins on the basis of the O-acetyl substitution pattern of their sialic acids; and (d), there were minor differences between normal glycoproteins and those from cases of diverticular disease.

Chemical and histochemical studies of normal and diseased human gastrointestinal tract. II. A comparison between histologically normal small intestine and Crohn's disease of the small intestine

Comparative chemical and histochemical studies were performed on formalin-fixed, surgical specimens of human small intestine from cases of Crohn's disease and normal controls. The sialic acids of the crude glycoproteins isolated from normal ileum were significantly less neuraminidase-susceptible and more C4 substituted (P less than 0.01) than those of the glycoproteins isolated either from normal upper small intestine (duodenum and jejunum) or from cases of Crohn's disease of the ileum. Fractionation yielded two major sialic acid-containing fractions, eluting from DEAE-cellulose with 0.2 M or 0.3 M sodium chloride. Both fractions contained fucose, galactose, glucosamine and galactosamine in addition to sialic acids both with and without O-acyl substituents at position C4 and/or in the side-chain (side-chain O-acylated sialic acids were also detected by histochemical procedures). The fractions differed significantly from one another with respect to the neuraminidase susceptibility of their sialic acids (P less than 0.01), the percentage of C4 (P less than 0.01) and side-chain substituted sialic acids (P less than 0.05), and the molar fucose-sialic acid ratio (P less than 0.05). The O-acyl substitution patterns of the sialic acids of both the 0.2 M and 0.3 M fractions of the upper small intestine glycoproteins differed significantly from those of the corresponding fractions from normal ileum, while the sialic acids of the 0.2 M fractions from Crohn's disease of the ileum differed significantly from normal with respect to neuraminidase susceptibility (P less than 0.01) and percentage C4 substitution (P less than 0.01); the 0.3 M fractions differed only in the percentage of sialic acids substituted at C4. The differences between the sialic acids from the normal and Crohn's disease specimens were shown to be independent of either the anatomical origin of the specimen or the histopathological sub-group of the Crohn's disease specimens; no significant differences were noted between the sub-groups but all the sub-groups differed from normal.

A scanning electron microscopy study of changes in the colonic mucus layer during chemical carcinogenesis

Scanning electron microscopy was used to examine the appearances of the colonic mucus layer of rats during chemical carcinogenesis with dimethylhydrazine. The normal colonic mucus layer had a dense homogeneous appearance and provided a complete cover for the mucosal epithelium. At high magnifications tiny fenestrations could be seen in this mucus layer. During carcinogenesis these fenestrations enlarged, increased in number, and coalesced, causing focal defects in the mucus layer, which eventually broke into strands and clumps of mucus. The findings indicate that the colonic mucus layer develops progressive abnormalities during carcinogenesis which result in breakdown of its integrity and exposure of the mucosal epithelium to colonic contents.

Morphological and mucus secretion criteria for differential diagnosis of solitary ulcer syndrome and non-specific proctitis

Over a four-year period 21 cases of solitary ulcer syndrome (SUS) were studied for their clinical, histological, and mucus secretion patterns and compared with histological and mucus secretion patterns of 78 cases of non-specific proctitis collected over the same period. Normal mucus composition was found in non-specific proctitis while abnormalities of mucins with predominance of sialomucins were associated with SUS. Although histology remains the most important investigation in the diagnosis of SUS, mucin changes provide valuable additional evidence.

Clinical aspects of gastrointestinal mucus

In such a bird's eye view of a very complicated and complex literature it is inevitable that significant contributions, particularly from earlier investigators, will have been overlooked. We have tried, however, to provide a reasonable framework for the many presentations and discussions which will take place at this conference. As in the past, it is evident that much needs to be done to reconcile the excellent histochemical studies of gastrointestinal mucus in many diseases with the increasing knowledge of mucin structure and composition. This will only be achieved by extraction of highly pure mucin from diseased bowel. In this regard, post mortem material provides an opportunity for mucin researchers which is not available to workers in other fields because of relative freedom from decomposition. The wedding of mucin technology with immunology is also a major priority. Immunoassay techniques provide the answer to quick and accurate product identification in secretion studies. Specific monoclonal antibodies will provide the route to structural differentiation of antigens in complex mixtures. It is also evident that we must seek to develop a variety of controllable models for the study of functional parameters of mucus in physiological conditions, parasite rejection, neoplasia and inflammatory states. Promising initiatives have been touched upon in this review, but these must only be the beginning. One must conclude, however, by recognizing that advances in knowledge have been truly remarkable since the last conference in 1976. One senses that some of the keys which will one day unlock the gates of this "ill-defined" kingdom are already in hand, while the remainder are at least within reach.

Mucin histochemistry of the anal canal epithelium. Studies of normal anal mucosa and mucosa adjacent to carcinoma

The epithelial lining of the anal canal is of colo-rectal type in the upper part and squamous in the lower part, while the middle zone is called the anal transitional zone (ATZ). This zone is characterized by an epithelium which bears a resemblance to that of the anal glands and shows little mucus secretion. The histochemical properties of the mucins in the epithelium of 39 anal canals, resected for ano-rectal adenocarcinoma, basaloid carcinoma, squamous carcinoma and malignant melanoma were investigated. The study reveals that (1) the mucin composition of the ATZ epithelium corresponds to that of the anal glands, being characterized by a mixture of sulpho- and sialomucins with scarcity or absence of O-acylated sialic acids; and (2) cases with carcinomas located near the dentate line show changes in the mucin composition of the adjoining anal canal epithelium, regardless of tumour type. In colo-rectal type mucosa, these mucins consist of increasing amounts of sialomucins with a predominance of N-acyl derivatives, and in the anal glands of increasing amounts of sulphomucins and O-acyl derivatives of sialomucins. No changes could be detected in the ATZ epithelium. It is concluded that rectal and anal glands in the anal canal are exposed to stimuli which alter the normal process of glycoprotein synthesis and secretion. The changes seem to be secondary to tumour growth and independent of the histological type of tumour.

A scanning electron microscopy study of ultrastructural changes in the colonic mucosa of patients with large bowel tumours

Scanning electron microscopy (SEM) has been used to compare the appearances of the colonic mucosal surface and overlying mucus layer of patients with normal colons, adenomatous polyps and colorectal carcinoma. The normal colonic mucosa had a characteristic orderly arrangement of crypts and was completely covered by an intact mucus layer. Epithelial and cryptal irregularities were seen on the surface of both polyps and carcinomas, and, in addition, the mucus layer was fragmented, leaving areas of the underlying epithelium exposed. These changes were more marked in colorectal cancers than in polyps and were present to a lesser degree in the apparently normal mucosa adjacent to tumours. The findings indicate that SEM can detect minor subtle irregularities on the surface of the colon and so may be useful in detecting pre-neoplastic and early neoplastic changes.

The cytoplasmic mucin in Paget cells of extramammary Paget's disease

The cytoplasmic mucin in the Paget cells of extramammary Paget's disease was examined with a battery of histochemical techniques. The staining methods used were alcian blue, azure A and periodic acid-Schiff. In a further attempt to identify various polyanions, staining was carried out with alcian blue containing various concentrations of electrolyte. Methylation, saponification, borohydride reduction, acid hydrolysis, and digestion with diastase, sialidase, chondroitinase ABC, or nucleases were also employed. The results obtained suggest that the cytoplasmic mucin in the Paget cells is sialomucin without side-chain substituent.

Specific techniques for the identification of O-acylated sialic acids in colonic mucins

The development of methodology for the histochemistry of mucins based upon their PAS reactivity is discussed in terms of mechanism, specificity and application. Two new histochemical methods (PB/KOH/PAS and PAT/KOH/PAS), supplemented by a variety of new and standard histochemical techniques, and correlated by parallel chemical studies, were used to demonstrate and identify C4 and side chain O-acylated sialic acids in colonic epithelial mucins. The application of these methods in the field of histopathology is discussed.

Retrospective histochemical study of mucosubstances in adenocarcinomas of the gastrointestinal tract

Use of the PATS/KOH/PAS and PB/KOH/PAS techniques and the diamine method (Spicer 1965) together with the demonstration of metachromasia with toluidine blue pH 3.0, for the study of carbohydrates in a retrospective study of gastric and colorectal adenocarcinomas, disclosed an increase in the sulphate content and the absence of O-acylated sialomucins in the majority of gastric adenocarcinomas. In the colorectal tumours there is no change in the degree of sulphation normally present in this area, but the degree of acylation of the sialic acid in adenocarcinoma is very different to that of normal mucosa and appears related to the degree of differentiation of the tumour. The mucosa adjacent to tumours from both areas were also studied, as well as gastric intestinal metaplasia.

Failure to demonstrate specificity of the morphological and histochemical changes in mucosa adjacent to colonic carcinoma

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Histochemical characteristics of mucins in the small intestine. A comparative study of normal mucosa, benign epithelial tumours and carcinoma

The histochemical properties of the mucins in seven benign epithelial tumours and 15 carcinomas distributed along the duodenum, jejunum and ileum were investigated and compared with normal controls. This study reveals that (a) goblet cells in normal small intestine contain neutral and sialomucins but no sulphated material; (b) the proportion of the different types of mucins in the goblet cells vary along the crypts and villi with an increasing amount of sialomucins towards the villus top; (c) mucin composition also changes from duodenum to ileum particularly in the proportions of sialic acid types and in the presence of traces of sulphomucins in the ileal mucosa close to the ileo-caecal valve, suggesting a gradual transition through the small intestine to the colon; (d) benign tumours show the same mucin pattern as normal mucosa; (e) the adjacent to carcinoma shows increasing amounts of sialomucins and sulphomucins; (f) carcinomas present a variety of mucin patterns, and thus the study of mucins seems to be of no value in differentiating tumours of the small intestine from those elsewhere in the gastrointestinal tract. A working hypothesis based on the Unitary Theory of the origin of the intestinal epithelial cells is proposed to explain the variations in glycoprotein synthesis with cell differentiation and carcinogenes.

Sialyl transferase activity: a serum enzyme marker in the follow-up of cancer patients

Clinical evaluation of serum sialyl transferase as a diagnostic tool in malignant disease has shown that there is a strong correlation between enzyme activity and extent of tumor tissue. Thus, patients with large tumor masses show higher enzyme activity than patients with small tumors or in remission. Furthermore, the surgical removal of tumor tissue results in a decrease of enzyme activity to the normal range. The values remain low until metastases recur; this is connected with a new increase in enzyme activity. It has also been shown that successful chemotherapy corresponding to tumor reduction is reflected in lower values. We are thus led to believe that sialyl transferase is a relevant diagnostic blood parameter in the follow-up of cancer patients.

Variations in sialomucins in the mucosa of the large intestine in malignancy: a quantimet and statistical analysis

The periodate-borohydride/saponification/PAS (PB/KOH/PAS) method, for the identification of sialic acid derivatives, was used to investigate possible changes in human colonic epithelium associated with carcinogenesis. The material was obtained from specimens of the large intestine resected for carcinoma and compared with normal control mucosa from biopsies of patients with no known gastro-intestinal diseases, using a Quantimet Image Analyser Densitometer to measure these staining reactions. An ordination or segregation analysis of the results revealed a marked discrimination between tumours and the normal control mucosa, with the values for the 'transitional' mucosa and mucosa remote from the tumour graded in between. Paired t-tests also showed statistically significant differences between the various types of mucosa. The fact that changes in the staining densities of the sialic acid derivatives are observed in mucosa which is normal by conventional histological criteria raises the hypothesis that malignancy in the colonic epithelium is accompanied by modifications in the sialic acid composition of the mucus secretion. Thus the PB/KOH/PAS method may be of value in the early detection of cancer in colo-rectal biopsies.