Glycoprotein abnormalities in colonic carcinomata, adenomata, and hyperplastic polyps shown by lectin peroxidase histochemistry

Lectins as versatile tools to explore cellular glycosylation

Lectins are naturally occurring carbohydrate-binding proteins that are ubiquitous in nature and highly selective for their, often incompletely characterised, binding partners. From their discovery in the late 1880s to the present day, they have provided a broad palette of versatile tools for exploring the glycosylation of cells and tissues and for uncovering the myriad functions of glycosylation in biological systems. The technique of lectin histochemistry, used to map the glycosylation of tissues, has been instrumental in revealing the changing profile of cellular glycosylation in development, health and disease. It has been especially enlightening in revealing fundamental alterations in cellular glycosylation that accompany cancer development and metastasis, and has facilitated the identification of glycosylated biomarkers that can predict prognosis and may have utility in development of early detection and screening, Moreover, it has led to insights into the functional role of glycosylation in healthy tissues and in the processes underlying disease. Recent advances in biotechnology mean that our understanding of the precise binding partners of lectins is improving and an ever-wider range of lectins are available, including recombinant human lectins and lectins with enhanced, engineered properties. Moreover, use of traditional histochemistry to support a broad range of cutting-edge technologies and the development of high throughout microarray platforms opens the way for ever more sophisticated mapping - and understanding - of the glycome.

Nutrition and gut health: the impact of specific dietary components - it's not just five-a-day

The health benefits of fruit, vegetables and dietary fibre have been promoted for many years. Much of the supporting evidence is circumstantial or even contradictory and mechanisms underlying health benefits of specific foods are poorly understood. Colorectal cancer shows marked geographical differences in incidence, probably linked with diet, and explanations for this require knowledge of the complex interactions between diet, microbiota and the gut epithelium. Dietary fibres can act as prebiotics, encouraging growth of saccharolytic bacteria, but other mechanisms are also important. Some but not all soluble fibres have a 'contrabiotic' effect inhibiting bacterial adherence to the epithelium. This is particularly a property of pectins (galacturonans) whereas dietary fructans, previously regarded as beneficial prebiotics, can have a proinflammatory effect mediated via toxic effects of high butyrate concentrations. This also suggests that ulcerative colitis could in part result from potentially toxic faecal butyrate concentrations in the presence of a damaged mucus layer. Epithelial adherence of lectins, either dietary lectins as found in legumes, or bacterial lectins such as the galactose-binding lectin expressed by colon cancer-associated Fusobacterium nucleatum, may also be important and could be inhibitable by specific dietary glycans. Conversely, emulsifiers in processed foods may increase bacterial translocation and alter the microbiota thus promoting inflammation or cancer. Focusing on one condition is of limited value although in developing public health messages and growing evidence for impacts of dietary components on all-cause mortality is gaining more attention. We are only just starting to understand the complex interactions between food, the microbiota and health.

PNA: A Marker of Neoplastic Progression and Differentiation in the Gastrointestinal Tract

We examined 35 cases of stomach carcinoma and 40 cases of colonic carcinoma with PNA associated with peroxidase (peanut agglutinin, lectin which binds to the terminal disaccharide galactose β (1, 3)-N-acetil-galacto-samine).

In this way evaluation of the functional aspects of the normal-neoplastic sequence was undertaken. This method was carried out for histological and ultrastructural investigations. The results obtained in both cases showed a different reactivity in the evolution of neoplastic disease: in fact, positivity in dysplasia is finely granular intracytoplasmic, whereas in well-differentiated neoplastic transformation such a reactivity is preferentially localized along the cellular membranes, with restoration of gross positivity in the cytoplasm for the poorly-differentiated neoplasm. We therefore believe PNA to be a marker not only of neoplastic progression but of differentiation as well: we also hypothesize it to reveal glycoprotein groups with possible antigenic power, involved in immunologic interactions between tumor and host.

Lectin-functionalized mesoporous silica nanoparticles for endoscopic detection of premalignant colonic lesions

Colorectal cancer (CRC) is one of the leading causes of cancer-deaths worldwide. Methods for the early in situ detection of colorectal adenomatous polyps and their precursors - prior to their malignancy transformation into CRC - are urgently needed. Unfortunately at present, the primary diagnostic method, colonoscopy, can only detect polyps and carcinomas by shape/morphology; with sessile polyps more likely to go unnoticed than polypoid lesions. Here we describe our development of polyp-targeting, fluorescently-labeled mesoporous silica nanoparticles (MSNs) that serve as targeted endoscopic contrast agents for the early detection of colorectal polyps and cancer. In vitro cell studies, ex vivo histopathological analysis, and in vivo colonoscopy and endoscopy of murine colorectal cancer models, demonstrate significant binding specificity of our nanoconstructs to pathological lesions via targeting aberrant α-L-fucose expression. Our findings strongly suggest that lectin-functionalized fluorescent MSNs could serve as a promising endoscopic contrast agent for in situ diagnostic imaging of premalignant colonic lesions.

Multifunctional nanobeacon for imaging Thomsen-Friedenreich antigen-associated colorectal cancer

This research aimed to validate the specificity of the newly developed nanobeacon for imaging the Thomsen-Friedenreich (TF) antigen, a potential biomarker of colorectal cancer. The imaging agent is comprised of a submicron-sized polystyrene nanosphere encapsulated with a Coumarin 6 dye. The surface of the nanosphere was modified with peanut agglutinin (PNA) and poly(N-vinylacetamide (PNVA) moieties. The former binds to Gal-β(1-3)GalNAc with high affinity while the latter enhances the specificity of PNA for the carbohydrates. The specificity of the nanobeacon was evaluated in human colorectal cancer cells and specimens, and the data were compared with immunohistochemical staining and flow cytometric analysis. Additionally, distribution of the nanobeacon in vivo was assessed using an "intestinal loop" mouse model. Quantitative analysis of the data indicated that approximately 2 μg of PNA were detected for each milligram of the nanobeacon. The nanobeacon specifically reported colorectal tumors by recognizing the tumor-specific antigen through the surface-immobilized PNA. Removal of TF from human colorectal cancer cells and tissues resulted in a loss of fluorescence signal, which suggests the specificity of the probe. Most importantly, the probe was not absorbed systematically in the large intestine upon topical application. As a result, no registered toxicity was associated with the probe. These data demonstrate the potential use of this novel nanobeacon for imaging the TF antigen as a biomarker for the early detection and prediction of the progression of colorectal cancer at the molecular level.

Significance of a galactose specific plant lectin for the differential diagnosis of adenocarcinoma cells in effusion

Background:

Distinguishing adenocarcinoma cells from reactively proliferated mesothelial cells and macrophages is one of the greatest challenges in the cytodiagnosis of effusions. Aberrant glycosylation of cell surface glycoconjugates is emblematic to malignancy, and lectins being an important class of probes to demonstrate these aberrations, lectin cytochemistry is of great interest to differentiate adenocarcinoma cells from reactive mesothelial cells.

Aim:

The present study analyzed the potential of a plant lectin to distinguish malignant cells from reactive mesothelial cells and macrophages.

Materials and Methods:

Snake gourd lectin (SGL) was isolated, purified and conjugated to horse radish peroxidase (HRP) and incubated with the cells of benign (46) as well as malignant (39) effusions using the standard immunocytochemical method with diaminobenzidine as the chromogen. The lectin-bound areas were quantitatively assessed as mild, moderate and intense binding.

Statistical Analysis:

The mean score for benign and malignant effusions were statistically analyzed. Student's ‘t’-test was performed to assess the significance.

Results:

The lectin HRP complex bind to the cytoplasm of benign and malignant cells as well as macrophages. A significantly higher score for intense binding (P = 0.001) was found to differentiate malignant cells from reactive mesothelial cells. Macrophages showed intense irregular binding.

Conclusions:

SGL binding assay can play a role in the differential diagnosis of metastatic adenocarcinoma in effusions.

Lectin-epithelial interactions in the human colon

Similar changes in glycosylation occur in the colonic epithelium in inflammatory conditions such as ulcerative colitis and Crohn's disease and also in colon cancer and precancerous adenomatous polyps. They include reduced length of O-glycans, reduced sulfation, increased sialylation and increased expression of oncofetal carbohydrate antigens, such as sialyl-Tn (sialylalpha2-6GalNAc), and the TF antigen (Thomsen-Friedenreich antigen) Galbeta1-3GalNAcalpha-Ser/Thr. The changes affect cell surface as well as secreted glycoproteins and mediate altered interactions between the epithelium and lectins of dietary, microbial or human origin. Different TF-binding lectins cause diverse effects on epithelial cells, reflecting subtle differences in binding specificities e.g. for sialylated TF; some of these interactions, such as with the TF-binding peanut lectin that resists digestion, may be biologically significant. Increased TF expression by cancer cells also allows interaction with the human galactose-binding lectin, galectin-3. This lectin has increased concentration in the sera of patients with metastatic cancer and binds TF on cancer cell surface MUC1 (mucin 1), causing clustering of MUC1 and revealing underlying adhesion molecules which promote adhesion to endothelium. This is likely to be an important mechanism in cancer metastasis and represents a valid therapeutic target. Tools are now available to allow fast and accurate elucidation of glycosylation changes in epithelial disease, characterization of their potential lectin ligands, whether dietary, microbial or human, and determination of the functional significance of their interactions. This should prove a very fruitful area for future research with relevance to infectious, inflammatory and cancerous diseases of the epithelia.

Altered colonic glycoprotein expression in unaffected monozygotic twins of inflammatory bowel disease patients

BACKGROUND AND AIMS

Previous chromatographic analysis of colonic mucins from monozygotic twins with inflammatory bowel disease (IBD) suggested a genetic mucin alteration in ulcerative colitis (UC). This study explores this further by assessing mucosal expression of the oncofetal carbohydrate antigen TF (galactose beta1, 3 N-acetylgalactosamine alpha-), among the same IBD twins.

MATERIALS AND METHODS

Formalin fixed paraffin embedded rectal biopsies were studied from 22 monozygotic twin pairs with IBD. These included eight UC twin pairs and 14 Crohn's disease (CD) twin pairs, with six pairs concordant for disease and 16 unaffected twin siblings. Closely adjacent sections were assessed by peanut lectin histochemistry for TF expression and immunohistochemically for nuclear factor kappaB (NFkappaB) activation with investigators blinded to the diagnosis.

RESULTS

Unaffected twins were almost all TF positive (15/16) compared with 5/29 histologically normal controls (p<0.0001). Unaffected UC (7/8) and CD twins (8/8) were similarly TF positive. TF positivity was confined mainly to the superficial epithelium and absent from the stem cell compartment of the lower crypts, suggesting that glycosylation changes are acquired rather than genetically determined. Activated NFkappaB was present in the surface epithelium of mucosal biopsies from 13/14 unaffected IBD twins but in only 6/22 histologically normal controls (p=0.0004). All 22 affected IBD twins were TF positive and 18 were positive for activated NFkappaB.

CONCLUSIONS

Altered mucosal glycosylation in unaffected identical twins of IBD patients was confirmed in this study. This occurred in both UC and CD twins. The changes are probably acquired rather than congenital and may reflect "preinflammatory" NFkappaB activation.

Lectins: from basic science to clinical application in cancer prevention

Many physiological functions are attributable to lectin-carbohydrate interactions. Lectins are currently being studied for their ability to destroy tumour growth by binding to specific carbohydrate motifs on cancer cells. Cell-surface molecules, including growth factor receptors are often glycosylated, and lectins may act by binding to these. Certain lectins effect the proliferation of intestinal epithelial cells. This effect is cell-type and lectin specific and occurs in the intestine of intact animals, in human colonic explants and colorectal cancer cell lines. Lectins present in mammalian tissue are involved in cell-matrix adhesion, differentiation, lymphocyte circulation and immunomodulation. Mammalian lectins contribute to detection, diagnosis and prognosis of tumour cells, and can be targeted for therapy. New lectins of plant and mammalian origin that have one or more of these functions are currently being developed as tools that could be used to target tumour cells.

Analysis of lectin receptors in normal nasal mucosa, nasal polyp, inverted papilloma and papillary adenocarcinoma

In order to investigate the changes in glycoprotein structure in the process of cellular differentiation of the nasal mucosa, formalin-fixed, paraffin-embedded biopsy specimens of normal nasal mucosae, nasal polyps, inverted papillomas and papillary adenocarcinomas were analysed by the Avidin Biotin-Peroxidase Complex technique for the demonstration of peanut agglutinin (PNA) receptors, concanavalin ensifomis agglutinin (ConA) receptors, ulex europeaus agglutinin (UEA-I) receptors, wheat germ agglutinin (WGA) receptors, carcino-embryonic antigen (CEA) and keratin. The quantity and distribution of PNA receptors, ConA receptors, UEA-I receptors and CEA were different, in relation to the varying pathological changes. The results suggest that the glycoprotein structure in the cells of the nasal mucosa will change following their differentiation and malignant transformation, which may be helpful in establishing the diagnosis.

Abnormal glycosylation and altered Golgi structure in colorectal cancer: dependence on intra-Golgi pH

Abnormal glycosylation of cellular glycoconjugates is a common phenotypic change in many human tumors. Here, we explore the possibility that an altered Golgi pH may also be responsible for these cancer-associated glycosylation abnormalities. We show that a mere dissipation of the acidic Golgi pH results both in increased expression of some cancer-associated carbohydrate antigens and in structural disorganization of the Golgi apparatus in otherwise normally glycosylating cells. pH dependence of these alterations was confirmed by showing that an acidification-defective breast cancer cell line (MCF-7) also displayed a fragmented Golgi apparatus, whereas the Golgi apparatus was structurally normal in its acidification-competent subline (MCF-7/AdrR). Acidification competence was also found to rescue normal glycosylation potential in MCF-7/AdrR cells. Finally, we show that abnormal glycosylation is also accompanied by similar structural disorganization and fragmentation of the Golgi apparatus in colorectal cancer cells in vitro and in vivo. These results suggest that an inappropriate Golgi pH may indeed be responsible for the abnormal Golgi structure and lowered glycosylation potential of the Golgi apparatus in malignant cells.

Cell surface-expressed Thomsen-Friedenreich antigen in colon cancer is predominantly carried on high molecular weight splice variants of CD44

Increased mucosal expression of TF, the Thomsen-Friedenreich oncofetal blood group antigen (galactose beta1-3 N-acetylgalactosamine alpha-) occurs in colon cancer and colitis. This allows binding of TF-specific lectins, such as peanut agglutinin (PNA), which is mitogenic to the colorectal epithelium. To identify the cell surface TF-expressing glycoprotein(s), HT29 and Caco2 colon cancer cells were surface-labeled with Na[(125)I] and subjected to PNA-agarose affinity purification and electrophoresis. Proteins, approximately 110-180 kDa, present in HT29 but not Caco2 were identified by Western blotting as high molecular weight splice variants of CD44 (CD44v). Selective removal of TF antigen by Streptococcus pneumoniae endo-alpha-N-acetylgalactosaminidase substantially reduced PNA binding to CD44v. Immunoprecipitated CD44v from HT29 cell extracts also expressed sialyl-Tn (sialyl 2-6 N-acetylgalactosaminealpha-). Incubation of PNA 15 microg/ml with HT29 cells caused no additional proliferative effect in the presence of anti-CD44v6 mAb. In colon cancer tissue extracts (N = 3) PNA bound to CD44v but not to standard CD44. These data show that CD44v is a major PNA-binding glycoprotein in colon cancer cells. Because CD44 high molecular weight splice variants are present in colon cancer and inflammatory bowel disease tissue but are absent from normal mucosa, these results may also explain the increased PNA reactivity in colon cancer and inflammatory bowel disease. The coexpression of oncofetal carbohydrate antigens TF and sialyl-Tn on CD44 splice variants provides a link between cancer-associated changes in glycosylation and CD44 splicing, both of which correlate with increased metastatic potential.

Human intestinal M cells display the sialyl Lewis A antigen

The biochemical features that distinguish human M cells from other intestinal epithelial cell types are important for understanding microbial pathogenesis and for targeting vaccines to the mucosal immune system. We applied a large panel of carbohydrate-specific monoclonal antibodies and lectins to Peyer's patch and cecum biopsy specimens from three normal individuals and a patient with inflammatory bowel disease. The results show that human M-cell glycosylation patterns are distinct from those of other species examined and that human M cells preferentially display the sialyl Lewis A antigen. This carbohydrate epitope is also present in a small subpopulation of enterocytes in the follicle-associated epithelium and in goblet cell mucins.

Coexpression of MUC1 mucin peptide core and the Thomsen-Friedenreich antigen in colorectal neoplasms

BACKGROUND

Controversial findings have been reported regarding the expression of the Thomsen-Friedenreich (TF) antigen in colorectal neoplasms when different monoclonal antibodies (MoAbs) have been used. Moreover, there is no information available regarding the carrier protein(s) of this antigen.

METHODS

Forty-five colorectal adenomas and 48 carcinomas were studied by avidin-biotin complex-peroxidase immunohistochemistry. The immunohistochemistry employed the MoAb BW835, which was reactive to a carrier specific and site specific TF antigen on MUC1 mucin, as well as reference antibodies directed to MUC1 (HMFG2) or MUC2 core peptides (4F1) and directed to TF antigen irrespective of its carrier (A78-G/A7, peanut agglutinin). To evaluate the coexpression of different epitopes by the same antigen, sandwich enzyme-linked immunoadsorbent assays were performed.

RESULTS

Although MUC1 peptide antigen and MUC1-bound TF antigen were not detectable in normal or transitional mucosa surrounding colorectal neoplasms, expression of these antigens in adenomas accompanied the development of high grade dysplasia. By contrast, MUC2 expression detected by the MoAb 4F1 was inversely correlated with the progression of the adenoma-carcinoma sequence. In well- and moderately differentiated colorectal carcinomas, the neo-expressed TF antigen is predominantly bound to MUC1. This feature could be demonstrated by antigen coexpression using peptide and the TF antigen specific MoAbs. However, in mucinous carcinomas exhibiting a weak MUC1 peptide expression in most specimens, the presence of TF antigen on the MUC2 peptide core cannot be ruled out.

CONCLUSIONS

TF antigen is strongly coexpressed with MUC1 mucin peptide core in the colorectal adenoma-carcinoma sequence, resulting in well- and moderately differentiated carcinomas. Only in mucinous carcinomas may it be coexpressed with MUC2 antigen.

Detection of colorectal neoplasia with peanut-agglutinin (PNA)-reactive carbohydrate structures in rectal mucus

In contrast to normal colorectal mucosa, peanut-agglutinin-(PNA)-reactive glycoconjugates are commonly expressed in most colorectal carcinomas and in some pre-malignant conditions such as adenomas and ulcerative colitis. Since enzymatically detectable galactose-beta1-3-N-acetyl-galactosamine residues are found in rectal mucus obtained from patients with carcinoma of the large bowel, it was investigated here whether PNA-reactive carbohydrate structures in rectal mucus can be exploited in the detection of colorectal neoplasia. Samples of rectal mucus obtained from 261 randomly selected patients with colorectal symptoms were applied on nitrocellulose filters. The presence of PNA-reactive glycoconjugates in mucus samples was determined by a peroxidase-conjugated PNA-overlay procedure. The results were correlated to findings from total colonoscopy/surgery and histopathology. PNA-reactive carbohydrate structures were detected in 76% of patients with carcinoma (p < 0.005), in 62% of patients with adenoma (p < 0.005), in 69% of patients with inflammatory bowel disease (p < 0.005), and in 38% of patients with hyperplastic polyps (NS), in contrast to 21% of the control subjects with macroscopically normal colorectal mucosa. These results show that PNA-reactive carbohydrate alterations in rectal mucus correlates with neoplastic and hyperproliferative conditions of the colorectal mucosa. The specificity of the PNA test for colorectal neoplasia was 76%. Therefore the use of more discriminate carbohydrate probes are needed for the pre-symptomatic detection of colorectal neoplasia.

Stimulation of proliferation in human colon cancer cells by human monoclonal antibodies against the TF antigen (galactose beta1-3 N-acetyl-galactosamine)

In many tissues, the TF (Thomsen-Friedenreich) blood group antigen (Galbeta1-3GalNAc alpha-) behaves as an onco-foetal carbohydrate antigen, showing increased expression in malignancy and hyperplasia. Dietary lectins which bind the TF antigen have marked effects on proliferation of epithelial cells without cytotoxicity. This led us to speculate that anti-TF antibodies, including those that naturally occur in humans, might have similar effects. Five anti-TF antibodies, TF2 (human), TF5 (human), 5A8 (mouse), 8D8 (mouse) and BM22 (mouse), but not TFI (human) or 49H.9 (mouse), showed marked dose-dependent stimulation (95-192%) of [3H]thymidine incorporation by HT29 human colon cancer cells. Similar stimulation of proliferation of HT29 cells by these monoclonal antibodies (MAbs) was found when cell count assessment was used. Antibody-stimulated proliferation was inhibited by co-incubation with glycoproteins expressing Galbeta1-3GalNAc alpha- (asialo glycophorin or [Galbeta1-3GalNAc alpha-O-p-aminophenyl]n-human serum albumin). A proliferative effect of these antibodies was also demonstrated on human colon cancer cell lines LS174T and HT29-MTX but not on Caco-2 cells. Although immunoblotting showed similar binding patterns of all the antibodies on HT29 cell membrane extracts, there was little correlation between cell surface binding assessed by immunofluorescence and proliferative response, and internalization of the biotinylated antibody TF5 was demonstrated by confocal microscopy. Our results provide further evidence that cell surface glycoproteins which express TF antigen may play an important role in the regulation of cell proliferation and also suggest that human anti-TF antibodies may have proliferative effects on cells which express TF antigen.

In vitro influence of Phaseolus vulgaris, Griffonia simplicifolia, concanavalin A, wheat germ, and peanut agglutinins on HCT-15, LoVo, and SW837 human colorectal cancer cell growth

BACKGROUND/AIMS

Compared with normal colonic mucosa, lectin receptor expression is increased in hyperplastic and neoplastic tissues; some lectins have been shown to influence human colonic epithelial cell proliferation. The aim was to assess further the influence of five lectins (Phaseolus vulgaris (PNA), Griffonia simplicifolia (GSA), concanavalin A (Con A), wheat germ (WGA), and peanut (PHA-L) agglutinins) on cellular growth in three human colorectal cancer cell lines (LoVo, HCT-15 and SW837).

METHODS

Cells were cultured in four lectin concentrations (0.1, 1.0, 10, and 100 micrograms/ml) and growth assessed at days 2, 3, 5, and 7. The experiments were performed in media supplemented with either 1% or 10% fetal calf serum (FCS). Growth was assessed using the MTT (3-(4,5)-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide) colorimetric assay.

RESULTS

Growth in each cell line was greatly affected by at least two of the lectins tested. There was some variation in the effect of a given lectin on different cell lines. Lectin effects showed a dose-response and the greatest effects generally resulted from the highest concentrations at the longest culture time. WGA and Con A induced large effects in all cell lines; the effects of Con A were partly blocked by the higher concentration of FCS. PNA had modest and uniform stimulatory effects overall. The effects of GSA and PHA-L varied between cell lines.

CONCLUSIONS

The lectins studied all have the potential to affect colonic cancer growth in vitro. Many dietary lectins are resistant to digestion and may have important effects in vitro but the definition of their role in human colonic cancer biology must take into account the variability in lectin response.

Differential expression of jackfruit-lectin-specific glycoconjugates in metastatic adenocarcinoma and reactive mesothelial cells-a diagnostic aid in effusion cytology

Distinguishing reactive mesothelial cells from adenocarcinoma cells in serous effusions on the basis of morphological criteria alone is often difficult. Interest has therefore been focused on identifying reliable methods to supplement the conventional cytological techniques. Plant lectins have been reported as diagnostic markers for malignant cells. We studied 51 aspirated samples of benign and malignant effusions using horseradish-peroxidase-conjugated jackfruit lectin. No significant difference was observed between the cells of pleural and peritoneal fluids. The reactively proliferated mesothelial cells of benign effusions showed a predominance of mild staining while moderate and intense staining was predominant in malignant effusions. Intense and irregular lectin binding was observed in macrophages irrespective of the cause of effusion. The lectin staining method therefore appears to have some clinical significance as an additional diagnostic aid for use in effusion cytology.

Prostaglandin E2 alters terminal glycosylation of high molecular weight glycoproteins, released by pig gastric mucous cells in vitro

The gastric mucus layer consists of high molecular weight glycoproteins (HMG). E-Type prostaglandins (PGs) stimulate total HMG release from isolated gastric mucous cells. We determined the effects of PGE2 on HMG glycosylation. Pig gastric mucous cells were cultured for 20 h with 1 mumol/l PGE2. Released HMG were isolated by gel chromatography and periodic acid-Schiff (PAS)-positive sugars and protein-bound [14C]GlcNAc were determined. Monosaccharides terminally linked to HMG oligosaccharide chains were monitored by lectin enzyme linked immunosorbent assay (ELISA): N-acetylglucosamine (GlcNAc) with Datura stramonium agglutinin, N-acetylgalactosamine (GalNAc) with soy bean agglutinin, fucose (Fuc) with Ulex europaeus I agglutinin and sialic acids (Sial) with Sambucus nigra agglutinin. PGE2 stimulated total HMG release, indicated by an increase of PAS-positive sugars to 170% and [14C]GlcNAc to 220% of controls. Terminal GlcNAc increased to 128%, GalNAc to 133%, Fuc to 165% and Sial to 182%. In addition to stimulation of total HMG release, PGE2 caused alterations of HMG glycosylation, which may modulate HMG viscosity and microbiological barrier function.

Direct demonstration of increased expression of Thomsen-Friedenreich (TF) antigen in colonic adenocarcinoma and ulcerative colitis mucin and its concealment in normal mucin

Increased binding of the lectin peanut agglutinin is a common feature in epithelial malignancy and hyperplasia. This may have considerable functional importance in the intestine by allowing interaction between the epithelium and mitogenic lectins of dietary or microbial origin. Peanut agglutinin binds the disaccharide Thomsen-Friedenreich (TF, T or core 1) blood group antigen, Gal beta (1-3) GalNAc alpha-, but is not totally specific for this site. Consequently, there has been controversy about the presence of this structure in colon cancer; studies with anti-TF monoclonal antibodies have failed to detect it. We have examined the presence of TF antigen in colonic mucus glycoprotein (mucin) using endo-alpha-N-acetylgalactosaminidase (O-Glycanase), which specifically catalyzes the hydrolysis of TF antigen from glycoconjugates. Samples of adenocarcinoma, inflammatory bowel disease (ulcerative colitis), and normal mucin were treated with O-glycanase, the liberated disaccharide was separated from the glycoprotein and analyzed using dual CarboPac PA-100 column high performance anion-exchange chromatography coupled with pulsed amperometric detection. O-Glycanase treatment released increased amounts of TF antigen from both colonic adenocarcinoma (8.0 +/- 3.9 ng/micrograms protein, n = 11; P < 0.0001 ANOVA) and ulcerative colitis mucin (3.3 +/- 0.3 ng/micrograms protein, n = 5; P = 0.04) compared with mucin samples from histologically normal mucosa distant from carcinoma (1.5 +/- 1.1 ng/micrograms protein, n = 9). However, after mild acid treatment to remove sialic acids and fucose, releasable TF antigen was increased in all nine of these histologically normal mucin samples (5.5 +/- 2.6 ng/micrograms protein, P < 0.0002). We conclude that TF antigen is an oncofetal antigen which is expressed in colon cancer, but is concealed by further glycosylation (sialylation and/or fucosylation) in the normal colonic mucosa.

Peanut agglutinin binding to human prolactin-producing pituitary adenomas

Peanut agglutinin (PNA)-binding sites in human prolactin (PRL)-producing pituitary adenomas were examined by light and electron microscopy together with immunoblot analysis. At the light microscopic level, the majority of the PRL-producing adenoma cells stained positively for PNA in 15 of 20 cases. PNA binding observed in the cytoplasm had a granular appearance. PRL-producing cells adjacent to the adenoma tissue showed negative PNA staining. In normal pituitary glands, the PRL-positive glandular cells were negative for PNA staining. By electron microscopy, reaction products showing PNA-binding sites were detected in some of the secretory granules. Immunoblotting analysis revealed that the PRL bands corresponded to PNA-stained ones with the exception of the main 23-kDa band. PNA-binding sites have some relation to the secretory granules containing glycosylated forms of PRL. These observations suggest that PNA staining can be used as a valuable method to analyze human PRL-producing pituitary adenomas.

Jack fruit lectin-specific glycoconjugate expression during the progression of cervical intraepithelial neoplasia: a study on exfoliated cells

The expression of glycoconjugates specific to Jack fruit lectin (JFL) was studied in the exfoliated squamous cells of different grades of intraepithelial and invasive neoplasia of the uterine cervix. It was observed that while normal cells showed almost negative binding, the lectin binding percentage of squamous cells significantly increased with increasing atypia of the epithelium. Correlation analysis between different groups revealed that mild lectin binding in cells had a negative correlation and intense binding had a positive correlation with various stages of tumor progression. These results indicate that the number of cells with aberrant expression of glycoconjugates increases as neoplastic transformation advances. The percentage of labeled and unlabeled cells also shows a continuous transition from low to severe grades of cervical intraepithelial neoplasia and invasive carcinomas. The present study therefore shows that JFL may be used as a probe for further elaboration of detection and grading of precancerous and cancerous lesions of the uterine cervix.

Glycoconjugates of the normal human colorectum: a lectin histochemical study

Previous studies of the normal human colorectum by lectin histochemistry have used a mixture of tissues, including those derived from colons harbouring neoplasia and inflammatory bowel diseases. In the current investigation, tissues from patients without either of these conditions have been examined with a wide panel of lectins, encompassing specificities directed against both N- and O-linked sequences, using an avidin peroxidase revealing system and evaluated with a semiquantitative scoring method. The results of binding of these lectins have been compared with those seen in the resection margins of (at least 5 cm away from) colorectal carcinomas. Consistent regional variations were noted between right- and left-sided colonic tissues, with more diverse glycan structures and a greater sialyl content in the distal colon. There was evidence of graduation of formation of oligosaccharide chains in developing crypts, possibly related to the maturation and expression of glycosyl transferases responsible for the incorporation of mannose residues of N-linked oligosaccharides and of N-acetylgalactosamine and N-acetylglucosamine. Comparison with previous reports has revealed some variations, possibly related to tissue fixation and processing and to lectin concentrations employed, which raises the question of standardization of methodologies in lectin histochemical investigations.

Histocytochemistry of glycoconjugates in nasal inverted papilloma

In order to investigate the changes in cellular distribution of the glycocalyces in nasal inverted papilloma, formalin-fixed, paraffin-embedded biopsy specimens of inverted papilloma were analyzed by the avidin-biotin-peroxidase complex technique for the demonstration of peanut agglutinin (PNA) receptors, concanavalin A (Canavalia ensiformis agglutinin; ConA) receptors, carcinoembryonic antigen (CEA), and keratin, and compared with normal nasal mucosa, nasal polyps, and papillary adenocarcinoma. The inverted papillomas were positive for PNA and CEA, to the same degree as papillary adenocarcinoma. Their PNA binding was related to the degree of dysplasia. The ConA reaction was intermediate between that of normal mucosa and adenocarcinoma. The results suggest that the alteration of cellular glycoprotein structure in inverted papilloma is associated with its biologic characterization.

Peanut lectin stimulates proliferation in colonic explants from patients with inflammatory bowel disease and colon polyps

BACKGROUND/AIMS

The TF antigen (galactose-beta 1,3-N-acetylgalactosamine alpha) is overexpressed in malignant and premalignant colonic epithelium. Previous studies have shown that peanut lectin (PNA), which binds TF, is mitogenic for normal human colonic epithelium. This study aimed to determine its effect on abnormal colonic epithelium.

METHODS

Crypt cell proliferation rate (CCPR) was measured using vincristine arrest and mucus synthesis by incorporation of radiolabeled N-acetyl glucosamine in colonoscopic biopsy specimens cultured with and without PNA.

RESULTS

Unstimulated CCPR was greater in patients with ulcerative colitis than in patients with histologically normal colon. PNA (25 micrograms/mL) produced a 25% average increase in CCPR in tissues from patients with ulcerative colitis, Crohn's disease, and colonic polyps. In ulcerative colitic biopsy specimens incubated with PNA, CCPR increased to more than double that of unstimulated normal colonic epithelium. In controls, the response to PNA was greater when adjacent specimens were positive for PNA (avidin-biotin) histochemistry than when they were negative. Mucus synthesis was increased by an average 75% over 24 hours by PNA.

CONCLUSIONS

Increased TF expression by premalignant epithelia may allow stimulation of proliferation by dietary galactose N-acetylgalactosamine-binding lectins. If the hyperplasia-dysplasia cancer hypothesis is correct, this could explain the increased colon cancer risk in ulcerative colitis.

Proliferative responses of HT29 and Caco2 human colorectal cancer cells to a panel of lectins

BACKGROUND/AIMS

Altered lectin binding is common in malignant and premalignant epithelia, but its functional significance is unclear. This study examined the proliferative effects of four lectins on HT29 and Caco2 colon cancer cells.

METHODS

Proliferation was assessed in log growth and confluent culture by thymidine incorporation and cell counts. Peanut agglutinin (PNA) binding was characterized by Scatchard analysis and electrophoresis of lectin affinity-purified cell surface-radiolabeled preparations.

RESULTS

PNA, 5 micrograms/mL, increased thymidine incorporation in HT29 but had no effect on Caco2. Wheat germ agglutinin and concanavalin A stimulated proliferation slightly at 0.5-1.0 microgram/mL but were inhibitory at higher concentrations. Ulex europaeus 1 had no significant effect. Similar results were obtained when proliferation was assessed by cell counts and with confluent cell cultures. Scatchard analysis with both cell lines showed multisite best fit models with similar binding affinities. Three PNA-binding glycoproteins were identified in both cell lines, but two were of lower molecular weight in HT29 than in Caco2. Membrane preparations from a resected colorectal cancer contained a 30-kilodalton PNA-binding glycoprotein similar to that in HT29 cells.

CONCLUSIONS

Lectins are plentiful in the normal diet and often escape digestion. This study suggests that altered expression of lectin receptors, particularly the upregulation of PNA receptor seen in colonic malignancy and hyperplasia, may have an important role in growth modulation.

Expression of glycoconjugates in pancreatic, gastric, and colonic tissue by Bauhinia purpurea, Vicia villosa, and peanut lectins

We have earlier prepared a pancreatic cancer-associated mucin, whose altered carbohydrate structure was recognized by Vicia villosa (VVA), Bauhinia purpurea (BPA), and peanut (PNA) lectins and which was found preferentially in the sera of patients with pancreatic or gastric cancer. Cancer-associated structures of the sugar chain on serum antigen may reflect those occurring in malignant tissues. Accordingly, we investigated the tissue distribution of carbohydrate structures reactive to these lectins by using lectin histochemistry in pancreatic cancer, gastric cancer, and colonic cancer tissue specimens and in their normal counterparts. VVA showed a higher affinity for pancreatic cancer (77.5%), gastric cancer (89%), and colonic cancer (87%) cells than for the cells of their normal counterparts, whose affinity was 0%, 41.7%, and 36.4%, respectively. PNA showed a higher affinity for pancreatic (70%) and colonic cancer cells (86.5%). BPA failed to show significant binding differences between neoplastic and normal cells in any of the pancreatic, gastric, or colonic tissue specimens. It did, however, bind to intraductal contents in most of the pancreatic cancer tissues but bound to intraductal contents in only a few chronic pancreatitis and normal pancreatic tissues. VVA and PNA did not bind to intraductal contents in any of the normal, chronic pancreatitis, or pancreatic cancer tissues. These results imply that, among the lectins used so far, VVA has the highest affinity for neoplastic cells, and it may provide a supplement for use in the pathologic diagnosis of malignant diseases.(ABSTRACT TRUNCATED AT 250 WORDS)

Laryngeal hyperplastic lesions, follow-up study and application of lectins and anticytokeratins for their evaluation

A retrospective study of 878 biopsy specimens from 692 patients with laryngeal hyperplastic aberrations was performed according to the Kambic-Lenart classification. Special attention was focused on 88 patients with persistent or recurring disease. In these carcinoma developed in 17 (2.4%) patients, 12 (1.7%) of whom had had atypical hyperplasia. We therefore propose that the term precancerosis, which so definitely implies cancer, should be replaced with the expression risky epithelium where nothing is determined in advance, but a careful follow-up of the patients is imperative. In particular cases of laryngeal hyperplastic lesions, mainly in abnormal and in atypical hyperplasias when the tissue specimens are cut tangentially, the exact identification and position of individual epithelial cells is essential. In such cases histochemical and immunohistochemical methods yield more precise evaluation. Lectins and cytokeratins provide good markers of epithelial maturation. These results contribute to a more useful evaluation of laryngeal hyperplastic lesions, crucial for the choice of adequate therapy.

Mucin associated Tn and sialosyl-Tn antigen expression in colorectal polyps

Sialosyl-Tn antigen and its immediate precursor, Tn antigen, are carbohydrate structures associated with the earliest steps of mucin O-linked glycosylation. Both antigens have been shown previously to be highly sensitive and specific markers of colorectal cancer. One hundred and three colorectal polyps (79 adenomatous; 24 hyperplastic) were examined for expression of Tn antigen using vicia villosa isolectin B4, and for sialosyl-Tn antigen by monoclonal antibody TKH2. Tn antigen was expressed by all of the polyps studied. Sialosyl-Tn, on the other hand was expressed weakly by a few cells in 7 of 24 (29%) hyperplastic polyps. Among the adenomatous polyps, 56% expressed sialosyl-Tn and expression correlated with larger adenoma size, greater villous component, and more severe grades of dysplasia. In individuals with two or more synchronous adenomas, the level of sialosyl-Tn expression within an adenoma was associated with the severity of cytological atypia. All the adenomas that contained a focus of invasive carcinoma expressed sialosyl-Tn. These results indicate that colorectal polyps manifest incomplete glycosylation, exposing antigens in the innermost region of mucin oligosaccharides. In addition, the correlation of sialosyl-Tn antigen expression with the adenoma-carcinoma sequence may make this a useful marker for studying malignant progression in the colon.

Lectin staining of neoplastic and normal background colorectal mucosa in nonpolyposis and polyposis patients

A lectin histochemistry approach was adopted for comparative assessment of a colon cancer risk. Binding of Ulex europaeus agglutinin-I (UEA-I), peanut agglutinin (PNA), Griffonia simplicifolia agglutinin-II (GSA-II), and Dolichos biflorus agglutinin (DBA) was investigated in tumor and background tissue from a total of 34 adenoma and 44 cancer patients and compared with reaction patterns in control and familial adenomatous polyposis (FAP) patients. Adenoma patients with UEA-I positive rectal mucosa were found to have a 33.3 percent familial history of large bowel cancer, which was significantly higher (P less than 0.05) than the respective 4.0 percent figure for patients with negative rectal mucosa. In the cancer patients, an even stronger correlation was noted, with a 63.2 percent UEA-I positive family history association being recorded, as opposed to 4.0 percent in the negative rectal mucosa patients (P less than 0.01). Thus, the results suggest that, apparently, normal rectal background mucosa of individuals genetically at high risk for colon and rectal cancer demonstrates a specific lectin binding ability similar to that of FAP patients and that the simple method using UEA-I staining of rectal biopsy specimens can be of practical use in identification of high-risk colorectal cancer.

Comprehensive lectin histochemistry of normal and neoplastic human choroid plexus cells: alternation of lectin-binding patterns through neoplastic transformation

Lectin histochemistry of the normal and neoplastic human choroid plexus cells [six choroid plexus papillomas (CPPs) and three choroid plexus carcinomas (CPCs)] was performed using eight representative lectins to study the development of sugar chain structures and also to determine whether lectins were useful for a histopathological diagnosis of choroid plexus neoplasms (CPNs). The normal choroid plexus cells reacted with Ricinus communis (RCA-I). Canavalia ensiformis (Con A), Limax flavus (LFA) and Triticum vulgaris (WGA), while Arachis hypoaea (PNA) stained them only after the removal of sialic acid. Human fetal choroid plexus cells at 8 weeks gestation already showed the same lectin-binding patterns as adult ones. All CPNs were stained by RCA-I and Con A in a similar manner as the normal choroid plexus cells. Although seven CPNs were positive for LFA, two CPCs were not stained by LFA, which bound to sialic acid. Two LFA-positive CPPs were stained by PNA before the removal of sialic acid. Moreover, unlike the normal choroid plexus cells, Ulex europaeus-, Glycine maximus- and Dolichos biflorus-binding sites often appeared, and WGA-binding sites of three CPNs remained even after sialic acid removal. In conclusion, the glycosialylation in normal choroid plexus cells was completed during the early embryonic stage. The lectin-binding patterns of CPNs were heterogenous in each case. The alternation of the glycosialylation and/or acquisition of binding sites for some lectins was sometimes observed through a neoplastic transformation.

Serum diagnostic tests for pancreatic cancer

Serological tests for pancreatic cancer have been criticized too harshly as a result of being tested in inappropriate roles. They are never likely to become sufficiently specific for screening an asymptomatic population unless some way can be found of defining a population with a particularly high risk for the disease. Nor are they appropriate in the investigation of the jaundiced patient. The markers that are carried by secreted mucins seem the most promising and in view of the marked heterogeneity of carbohydrate expression on mucins a combination of tests for two or three carefully selected markers is likely to be better than one. The high cost per test that results from using commercially available radioimmunoassay kits with a short shelf-life can be reduced by using enzyme-linked assays which have a much longer shelf-life. These tests are likely to be of most help in the investigation of non-jaundiced patients with unexplained abdominal pain or weight loss. In this group of patients it seems probable that serological tests will compliment scanning techniques but further studies are needed to assess this.

Expression of histocompatibility antigens and characterization of the lymphocyte infiltrate in hyperplastic polyps of the large bowel

HLA-DR expression, lymphocyte subsets, and the distribution of proliferating cells were studied in hyperplastic polyps from the colorectum. The density of T-cells (CD5+) (mean of cells/mm2 of tissue +/- SEM) was higher in the lamina propria of hyperplastic polyps (64.2 +/- 4.2) than in normal colonic mucosa (36.7 +/- 2.6, P less than .001). The CD4/CD8 ratio was higher in hyperplastic polyps (6.3 +/- 0.9, P less than .0001) and in colonic adenomas (5.9 +/- 0.9, P less than .001) compared with normal mucosa (2.3 +/- 0.2). Lymphocytes of the lamina propria were never Ki-67 positive either in normal mucosa or in hyperplastic polyps or adenomas. The epithelial layer of hyperplastic polyps and of normal mucosa did not express the HLA-DR antigen, whereas pericryptal fibroblasts and most of the leukocytes of the lamina propria were strongly positive for this antigen. In the epithelial layer proliferating cells were localized exclusively in the lower part of epithelial crypts, as was the case in normal mucosa, whereas in adenomas Ki-67-positive cells were present throughout the entire height of the mucosa. Thus, in hyperplastic polyps lymphocytes are increased in the lamina propria, with a predominance of the CD4 subset in close contact with HLA-DR positive pericryptal fibroblasts.

Identification of the peanut-agglutinin binding pancreatic cancer serum marker in pancreatic tissue extracts

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Crypt alterations and collagen deposition in hyperplastic polyps of colorectum

In order to investigate the nature of hyperplastic polyps in the colorectum, 44 longitudinally sectioned crypts from biopsied polyps were analyzed morphometrically and compared with 81 control crypts. Although the crypts in hyperplastic polyps were longer and wider, containing more cells, their cell density was less, particularly in the serrated epithelium. In these crypts, both the tall and short epithelial cells contained cytoplasmic vacuoles, even in the surface epithelium. These cells exhibited increased expression of carcinoembryonic antigen. The subepithelial collagen table was of similar thickness in the polyp and control colonic mucosa, but it extended down along the cryptal wall to a greater depth in the polyp. These and other data indicate an aberrant differentiation of cryptal epithelial cells in the polyp. On upward migration to the surface, these cells appeared to undergo an arrested maturational process. Hence, the hyperplastic polyp may be considered a disease of epithelial cell differentiation.

Significance of venous and lymphatic invasion in malignant polyps of the colon and rectum

Three hundred and sixty seven neoplastic colorectal polyps removed at endoscopy of which 34 were complicated by invasive carcinoma, were reviewed clinically and histologically to assess the prevalence and clinical significance of venous and or lymphatic invasion. Traditional stains for histological assessment were supplemented by immunohistochemical methods. Venous and or lymphatic invasion was present in six cases (17.6%), with a statistically significant association with recurrent carcinoma or Dukes's C carcinoma in polyps otherwise regarded as completely excised. The presence or absence of venous and or lymphatic invasion in malignant polyps should be documented as if present, further treatment is indicated. A combination of haematoxylin and eosin and elastic-van Gieson stains will usually identify the presence of vascular invasion. Where a discrepancy arises, however, additional immunohistochemical stains may be of value.

Enzyme-linked PNA lectin binding assay compared with CA19-9 and CEA radioimmunoassay as a diagnostic blood test for pancreatic cancer

Previous studies have shown that sera from patients with pancreatic cancer often contain a mucus glycoprotein that expresses the oncofetal antigen galactose 1-3, N-acetyl galactosamine, which is the T blood group antigen and the binding site for the lectin peanut agglutinin (PNA). An enzyme-linked lectin assay has been developed to quantify PNA-binding glycoproteins in serum and has been evaluated as a serological test for pancreatic cancer. Sera were studied from 53 patients with pancreatic cancer and 154 controls, including benign obstructive jaundice, acute and chronic pancreatitis, chronic liver disease and inflammatory bowel disease. The enzyme-linked peanut lectin assay proved highly reproducible and has 77% sensitivity and 83% specificity for pancreatic cancer, results that are very similar to those achieved in the same sera by CA19-9 radioimmunoassay (75% sensitivity, 82% specificity with the upper limit of normal set at 37 u ml-1). CEA assay proved less useful (60% sensitivity, 47% specificity). In this study better results were obtained if an upper limit of normal of 50 u ml-1 was used for CA19-9 (75% sensitivity, 92% specificity). Combination of CA19-9 assay with the upper limit set at 50 u ml-1 and the peanut lectin assay improved the sensitivity to 85% with only a slight fall in specificity (85%). These results compare well with published results for ultrasound and CT scanning.

Studies of lectin binding to the human cervix uteri: II. Cervical intraepithelial neoplasia and invasive squamous carcinoma

The cell surface carbohydrate profile of formalin-fixed paraffin-embedded tissue sections of neoplastic cervical squamous epithelium was evaluated using lectins of Bauhinia purpurea (BPA), Canavalin ensiformis (Con A), Griffonia simplicifolia I (GS I), Griffonia simplicifolia II (GS II), Maclura pomifera (MPA), Archis hypogaea (PNA), Glycine max (SBA), Ulex europaeus I (UEA I) and Triticum vulgaris (WGA). Three lectins (BPA, Con A and PNA) showed a similar pattern of staining in both normal squamous epithelium and in cervical intraepithelial neoplasia (CIN). Variable alterations were seen in lectin-binding patterns in CIN with seven lectins (GS I, GS II, MPA, PNA, SBA, UEA I and WGA). A significant difference was seen between the intensity of staining of normal squamous epithelium and CIN with all lectins except WGA. The alteration in GS II-binding pattern and intensity was significantly related to grade of CIN. No correlation was found between lectin binding and the presence of koilocytes in squamous epithelium. Cases of invasive squamous carcinoma showed a heterogeneous lectin-binding pattern and no significant association was found between lectin binding and tumour differentiation of patient survival. These results indicate that neoplasia in cervical squamous epithelium is associated with alterations in terminal alpha-Man residues, alpha- and beta-GalNAc residues, alpha- and beta-GlcNAc residues, alpha- and beta-Gal residues, and alpha-Fuc-containing residues, present in the outer parts of both N-linked and O-linked glycoconjugates. The implications of these findings are discussed.

Histochemical comparison of specificity of three bowel carcinoma-reactive lectins, Griffonia simplicifolia agglutinin-II, peanut agglutinin and Ulex europaeus agglutinin-I

A comparison of the histochemical affinities of three lectins reputedly specific to human large bowel carcinoma, namely Griffonia simplicifolia agglutinin-II (GSA-II), peanut agglutinin (PNA) and Ulex europaeus agglutinin-I (UEA-I), was done using 28 specimens in which normal mucosa, adenoma and carcinoma tissue were present and in contact with each other. In the normal mucosa, GSA-II and PNA revealed only weak affinity to the Golgi region of epithelial cells, whereas UEA-I showed binding to the apical surface of columnar cells and goblet cell mucins, especially in the right colon. Adenoma was characterized by relatively intense reactivity of the Golgi regions of epithelial cells for GSA-II and PNA as well as reactivity of the apical surface of the columnar cells for UEA-I. In carcinomas the apical surface of columnar cell-type tumor cells was stained most intensely with UEA-I, and then in descending order with GSA-II and PNA. GSA-II- and PNA-reactive carcinoma cells occurred more frequently in invasive carcinoma than in intramucosal carcinoma. Goblet cell-type tumor cells retained the properties of their normal counterparts. Staining with these lectins, especially GSA-II-horseradish peroxidase, might be helpful in the identification of carcinoma cells and for analysis of carcinoma-associated antigens.

Lectin-induced damage to the enterocyte brush border. An electron-microscopic study in rabbits

The ultrastructural effects of 11 lectins on the intestinal brush border were examined by means of an in vitro rabbit ileal mucosal explant culture system. Five of the lectins that bind to oligosaccharides containing either N-acetylglucosamine (phytohaemagglutinin, Euonymus europaeus lectin, pokeweed mitogen, and wheat germ agglutinin) or N-acetylneuraminic acid (Mycoplasma gallisepticum lectin) all had a specific effect on microvilli. The effects varied in accordance with the lectin and included lengthening, distortion, and vesiculation of the microvilli. In contrast, lectins binding specifically to galactose, glucose, mannose, and N-acetylgalactosamine had no effect. Incubation of mucosal fragments with the divalent cation ionophore A23187 did not mimic the effect of the lectins. This apparent relationship between lectin damage and receptor specificity may reflect either accessibility of appropriate binding sites or a differential response to binding.

Altered lectin binding by colonic epithelial glycoconjugates in ulcerative colitis and Crohn's disease

Evidence is accumulating that colonic mucin glycoconjugates are altered in ulcerative colitis. In order to investigate this further, the lectin-binding properties of rectal glycoconjugates have been studied in ulcerative colitis, Crohn's disease, and controls using lectin-peroxidase histochemistry. Ten lectins were used including peanut agglutinin (PNA) which is known to bind to malignant and adenomatous but not normal colonic mucins. Eight of 21 ulcerative colitis rectal biopsies and 10 of 17 Crohn's disease rectal biopsies showed PNA positivity, particularly in the supranuclear region of surface epithelial cells. There was no correlation between PNA positivity and duration of disease or inflammation, and none of the biopsies showed evidence of dysplasia. This abnormality in epithelial cell glycoconjugates seems to be commonly present in nondysplastic mucosa and occurs in both ulcerative colitis and Crohn's disease. It may reflect a fundamental abnormality in mucus glycoprotein synthesis in inflammatory bowel disease.