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Mucin Expression in Reactive Gastropathy: An Immunohistochemical Analysis

January 14, 2007

By Mino-Kenudson, Mari; Tomita, Shigeki; Lauwers, Gregory Y

* Context.-Reactive gastropathy is the second most common diagnosis made on gastric biopsies. Increased epithelial proliferation and modifications of epithelial cytokeratin profile, distinct from those of Helicobacter pylori gastritis, have been previously reported. However, the evaluation of mucins, important components of the protective mucosal mucous layer, has not been reported.

Objective.-To investigate alterations of membrane and secreted mucins in reactive gastropathy of various etiologies using antibodies against mucin glycoproteins.

Design.-Thirty-eight gastric biopsies diagnosed as reactive gastropathy, related to nonsteroidal anti-inflammatory drugs (n = 18) or bile reflux (n = 6) or of indeterminate etiology (n = 14), were evaluated using antibodies to MUC1, MUC5AC, MUC6, and MUC2. All cases were confirmed to be negative for H pylori. The biopsies were classified in 3 groups based on the severity of cytoarchitectural changes (mild, moderate, and severe). Mucin expression and its distribution were recorded and the results correlated with the cytoarchitectural alterations and etiologies.

Results.-Loss of MUC1, either patchy or complete, was noted in 67% of the cases. Aberrant expression of MUC5AC in pyloric glands was observed in 81% of the cases, and aberrant expression of MUC6 in the upper foveolar epithelium was diffusely seen in 14% of the cases. Aberrant expression of MUC2 in non-goblet cells was observed in a single case. Aberrant expression of MUC6 was less extensive in the nonsteroidal anti-inflammatory drugs group than in other 2 groups (P = .03). Concurrently, the diffuse distribution of aberrant MUC6 expression was seen only in the cases of severe gastropathy (P = .09). There was no correlation between modifications in expression of other mucins and either the etiologies or the severity of cytoarchitectural changes.

Conclusions.-Expressions of membrane (MUC1) and secreted (MUC5AC, MUC6) mucins are frequently modified in reactive gastropathy. The alteration of MUC1, which is involved in cell adhesion and polarity, may play a role in the development of the serrated profile of reactive gastropathy. Milder modifications of the secreted mucins may be explained by the reactive/regenerative nature of the process. Importantly, theses changes are different from the increase in MUC6 and reduction of MUC5AC expression reported in H pylori gastritis, underlying their mechanistic differences. It is worth noting that similar alterations of mucin expression are shared by various etiologies, that is, nonsteroidal anti-inflammatory drugs and bile reflux, consistent with the nonspecific nature of reactive gastropathy.

(Arch Pathol Lab Med. 2007;131:86-90)

The mucosal surface of the stomach is covered by thick layers of mucus composed of mucins, high molecular weight glycoproteins, that are acting as a protective buffer against the acid luminal environment and various exogenous agents.1 In the normal gastric mucosa, MUC1, MUC5AC, and MUC6 are expressed in a characteristic zonal pattern. MUC1 has an apical/membranous staining pattern observed in the surface and foveolar epithelium as well as mucous neck zone cells. Alternatively, in the oxyntic mucosa, chief and parietal cells show diffuse cytoplasmic staining and canalicular system staining, respectively. In contrast, MUC5AC distribution is limited to cytoplasm of the surface and foveolar epithelium and mucous neck cells throughout the stomach. MUC6 is expressed in the cytoplasm of antral pyloric glands but also in mucous neck cells and chief cells of the gastric body.2,3

The characteristics of the gastric mucous layer reflect its physiologic function and changes in its composition can be noted following various insults. Notably, the development of monoclonal antibodies to various mucins has allowed evaluation of the changes in composition and distribution in diverse pathologies. For example, the alteration of mucin expression in the setting of Helicobacter pylori infection has been extensively evaluated.1,4-6 Helicobacter pylori leads to reversible alteration of mucin glycosylation and particularly inhibition of MUC5AC expression1,4 with increase in MUC6 expression on the surface mucous cells.1,3 With regard to MUC1 expression, controversial results (decreased expression in vitro vs preserved expression in vivo) have been reported.1,4,5

Reactive gastropathy, the second most common histologic diagnosis made on gastric biopsies,7 is characterized by foveolar hyperplasia lined by tall columnar cells with variable mucin depletion and enlarged hyperchromatic nuclei. Other histologic hallmarks include ectatic capillaries and prominence of smooth muscle with minimal edema and inflammation of the lamina propria.8,9 Several etiologies have been implicated in the pathogenesis of this reactive gastropathy. Those include chronic usage of nonsteroidal anti- inflammatory drugs (NSAIDs) and bile reflux among others.8-11

Interestingly, little is known about the pathomechanisms associated with the development of the histologic features of reactive gastropathy. A sole report showing difference in cytoskeletal alterations between reactive gastropathy and H pylori gastritis has been published12 and we are not aware of any studies that investigated the mucin profile of reactive gastropathy. The purpose of this study was to evaluate mucin expression in biopsy specimens with this diagnosis. Interestingly, our results indicate noticeable alteration in the expression of mucins in gastric mucosa with histologic evidence of reactive gastropathy.

MATERIALS AND METHODS

Thirty-six well-oriented consecutive biopsies that were interpreted as reactive gastropathy by 2 of us (M.M.-K. and G.Y.L.) formed our study group. They were obtained from the antrum of 25 women and 11 men with an average age of 57.9 years (range, 20-85 years).

The diagnosis of reactive gastropathy was established by following criteria put forth previously.8,9 In addition, all biopsies were negative for H pylori by Diff-Quick stain and did not demonstrate evidence of chronic active gastritis based on themodified Sydney classification.13 The biopsies were classified in 3 groups based on the severity of cytoarchitectural changes (mild, moderate, and severe; Figure 1, A through C). In addition, the biopsies were categorized as those related to either NSAID (n = 18) or bile reflux (n = 4) or of indeterminate etiology (n = 14), based on the review of medical charts and endoscopy reports. The reactive gastropathy was attributed to NSAID use when patients had been chronically on NSAIDs for more than 6 months. The mucosal changes were attributed to bile reflux when bile was endoscopically noted in an intact stomach.

Immunohistochemical Evaluation

Commercially available monoclonal antibodies against MUC1, MUC5AC, MUC6, and MUC2 were used (Table 1). After antigen retrieval by heating with a pressure cooker (249F, 3 minutes in citrate, pH 6.0), staining was performed with labeled streptavidin-biotin method (Dako, Glostrup, Denmark) followed by visualization with diaminobenzidine as a chromogen and light counterstain with hematoxylin. Normal gastric antrum was used as positive controls for MUC1, MUC5AC, and MUC6 staining and duodenum for MUC2. Sections that were subjected to the aforementioned antigen retrieval and stained with nonimmune serum without primary antibodies served as negative controls.

After staining, the slides were reviewed by 3 of us at a multiheaded microscope and the consensus was captured for the analysis. Mucin expression (present/absent) and topographic distribution were recorded for each of the 4 antibodies. The pattern of staining (patchy or diffuse) was also recorded. The results were correlated with the cytoarchitectural alterations and etiologies. The statistical analysis was performed using the Fisher exact probability test for a 3 rows by 3 columns contingency table and a P value of

RESULTS

Tables 2 and 3 show mucin expression in reactive gastropathy according to etiology and severity.

Five of the biopsy cases showed mild cytoarchitectural changes, 16 moderate changes, and 15 severe changes (Figure 1, A through C).

Loss of membrane mucin MUC1, either complete or patchy, was observed in 24 (67%) of the 36 cases (Figure 2, A). In contrast, aberrant expression of MUC5AC deep in the pyloric glands, which also stained with MUC6, was observed in a patchy distribution in 24 (67%) of the cases, and diffuse aberrant expression was noted in 5 cases (14%) (Figure 2, B). Abnormal expression of MUC6 in the upper foveolar epithelium, which also expressed MUC5AC, was diffusely seen in 5 (14%) of the 36 cases (Figure 2, C). Focal cytoplasmic expression of MUC2 in non-goblet cells was present in a single case. MUC2 also decorated the goblet cells of 2 cases with intestinal metaplasia.

Aberrant expression of MUC6 was less extensive in the NSAID group than in the other 2 groups (P = .03). Concurrently, the diffuse distribution of aberrant MUC6 expression in the upper foveolar epithelium was seen only in severe gastropathy (P = .09). There was no correlation between the changes in expression of other mucins and either the etiologies or the severity of cytoarchitectural changes.

COMMENT

We have demonstrated that alterations of expression of membrane (\MUC1) and secreted (MUC5AC and MUC6) mucins are frequently observed in reactive gastropathy. The changes are different from those reported for H pylori gastritis. In H pylori gastritis, MUC5AC expression on the surface epithelium is decreased and MUC6 expression extends to the surface mucous cells.1,3 With regard to MUC1 expression, controversial results have been reported.1,4,5 The difference in alterations of mucin expression between these 2 common gastropathies is not surprising because their pathogeneses are different. This is also consistent with a previous report revealing a divergence in various cytoskeleton modifications, especially cytokeratins 7 and 20 between the 2 entities.12 However, the precise mechanisms at play in the changes remain to be elucidated.

Foveolar hyperplasia is a response to excessive cell exfoliation from the surface epithelium.10 It accompanies etiologies with varied noxious mechanisms, that is, NSAIDs abuse, bile reflux, and alcoholic gastropathy.8 NSAIDs injure the gastric mucosal by at least 2 pathways. As weak organic acids, they freely diffuse across cell membranes in the highly acidic gastric environment and insult directly the mucosa lining. NSAIDs also inhibit cyclo-oxygenase enzymes required for conversion of arachidonic acid to prostaglandins.14 It results in alteration in cellular proliferation and repair, blood flow, and growth factor expression.14-16 It also leads to diminished bicarbonate and mucus secretion with decrease in hydrophobicity of the mucous gel layer.14-16 Some investigators have observed that mucosal edema and vascular ectasia of NSAIDs gastropathy may be related to the blockage of gastric microcirculation by neutrophils adherence or by reduced outflow of mucosal blood.16

After partial gastrectomy, bile reflux leads to an increase in gastric pH and bacterial contamination by fecaltype microflora. There is a close relationship between reflux (with bile concentrations at 10%-20% of levels found in hepatic bile), foveolar hyperplasia, and cell proliferation.17 The precise mechanisms of cellular alteration have not been convincingly explained. However, bile acids induce cytolysis and are associated with functional and structural alteration of the gastric mucosa.17

Aberrant expression of MUC5AC and MUC6 may correspond to the reparative metaplasia of mucins as seen in the regenerative epithelium of an animal model.18 Aberrant expression in these mucins is also reminiscent of the increase in mucous neck cells at the periphery of ulcers. In this particular animal model, the transitional phenotype between mucous neck cells and glandular cells is believed to reflect either maturation arrest of mucous neck cells or rejuvenation of glandular cells during repair and explain an extension of MUC5AC expression in the deep glandular region.19 Despite the absence of double immunostaining, it appears that there is aberrant coexpression of MUC5AC and MUC6. Notably, deep pyloric glands highlighted by MUC5AC concomitantly expressed MUC6. Concurrently, the upper foveolar epithelium that demonstrated MUC6 expression was also positive for MUC5AC. The finding may simply represent upward extension of mucous neck cells during mucosal regeneration. Conversely, the diffuse expression of MUC6 in the upper foveolar region, more commonly seen in the bile reflux and indeterminate groups (than in the NSAID group) may be related to the severity of mucosal damage noted in the former (data not shown).

Given its role in cell-cell adhesion and maintenance of cell polarity, alteration of mucin MUC1 expression may be related to the development of the characteristic serrated profile of reactive gastropathy. However, the mechanism(s) behind the loss of MUC1 expression remains to be elucidated. It includes the investigation of STAT (signal transducers and activators of transcription) transcription factors that are involved in the regulation of MUC1 expression20 and that can be controlled by NSAIDs.21

The implications of mucin alterations in reactive gastropathy remain largely to be elucidated. However, distinct differences from those of H pylori gastritis underline different mechanisms. In the latter, driven by an infectious agent, the gastric mucosa display what appears to be specific changes. Alternatively, the mucin alterations noted in reactive gastropathy may represent a common pathway of generic mucosal response shared by several etiologies. It is important, however, to gain some understanding of these changes because it may help heighten our understanding of the physiologic and pathologic alterations of the gastric mucosa when damaged.

We thank Desiree E. Eatherton, MS, and Sven Holder, MS, for their technical support.

References

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Mari Mino-Kenudson, MD; Shigeki Tomita, MD, PhD; Gregory Y. Lauwers, MD

Accepted for publication July 7, 2006.

From the Gastrointestinal Pathology Service, Department of Pathology, Massachusetts General Hospital, Boston.

The authors have no relevant financial interest in the products or companies described in this article.

Reprints: Gregory Y. Lauwers, MD, Massachusetts General Hospital Department of Pathology (WRN2), 55 Fruit St, Warren 2, Boston, MA 02114-2696 (e-mail: glauwers@partners.org).

Copyright College of American Pathologists Jan 2007

(c) 2007 Archives of Pathology & Laboratory Medicine. Provided by ProQuest Information and Learning. All rights Reserved.




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