This Month in Gastroenterology

Article Outline

• Limited Value of Alarm Features in the Diagnosis of Upper Gastrointestinal Malignancy
• Epidemiology and Risk Factors of Diarrhea-Predominant IBS After Bacterial Dysentery
• Paneth Cell Maturation Is Regulated by PPARβ Through Indian Hedgehog Upon Precursor Cells
• Antigen-Specific Regulatory CD4+ T Cells May Suppress CD8+ T cell–Mediated Intestinal Inflammation
• Copyright

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Limited Value of Alarm Features in the Diagnosis of Upper Gastrointestinal Malignancy 

In view of the high prevalence of functional gastrointestinal disorders, clinicians who are confronted with gastrointestinal symptoms in daily practice need to decide whether or not they need to pursue additional testing, or whether empirical therapy can be considered as a first approach. For lower gastrointestinal symptoms, it has now been established that the presence of the Rome criteria for the irritable bowel syndrome, in the absence of alarm features, has a very high predictive value for diagnosing irritable bowel syndrome. These results have helped the design of guidelines proposed in different parts of the world to optimize the use of diagnostic colonoscopy in patients presenting with lower gastrointestinal symptoms.

Upper gastrointestinal symptoms, including dyspepsia and heartburn, are extremely common in the general population. In the majority of the cases, no organic cause can be found, and symptoms can be attributed to functional dyspepsia and non-erosive reflux disease respectively. These disorders, although not always easy to treat, have a benign long-term course and prognosis. However, similar symptoms may also be the presenting features of more severe conditions, including upper gastrointestinal tract malignancy, or biliopancreatic disease. In view of the high prevalence of dyspeptic type symptoms, additional endoscopic examination cannot be recommended for every patient presenting with these symptoms. Hence, similar to the management of lower gastrointestinal symptoms, clinicians have used the presence of alarm features and an age cut-off to decide whether or not patients need referral for prompt endoscopy, and this has been advocated in practice guidelines in different parts of the world.

In their article in this issue, Vakil et al performed a systematic review and meta-analysis of the published literature to assess and evaluate the diagnostic accuracy of alarm features in predicting the presence of an underlying malignancy in patients presenting with dyspeptic-type symptoms. The authors evaluated 15 studies reporting on 57,363 patients, of whom 19% had one or more alarm features like chronic gastrointestinal bleeding, progressive unintentional weight loss, progressive difficulty swallowing, persistent vomiting, iron deficiency anemia, or an epigastric mass. Only 458 patients (0.8%) were diagnosed with an upper gastrointestinal malignancy after diagnostic evaluation.

Based on their meta-analysis, the authors found that the presence of alarm symptoms, clinical opinion (does the clinician suspect malignancy?), and computer modeling based on symptom questionnaires are relatively inaccurate predictors of an underlying malignancy or of serious organic pathology (Figure 1). The sensitivity of alarm symptoms varied from 0%–83% with specificity ranging from 40%–98%. The presence of individual alarm symptoms like weight loss, anemia, or dysphagia, had a low positive predictive value for the detection of an underlying upper gastrointestinal malignancy. A clinical diagnosis made by a physician was highly specific (range, 97%–98%, which reflects the low prevalence of cancer in dyspeptic symptoms) but had low sensitivity (range, 11%–53%).

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• Figure 1. 

  Receiver operator curve for the diagnosis of upper GI malignancy using alarm symptoms, clinical opinion, or computer models applied to symptom questionnaires.

Hence, alarm features seem to have limited value in aiding diagnostic assessment at the present time, and performing endoscopy on the basis of an age threshold seems a logical alternative. The results do not allow abandonment of the concept of alarm features at the present time: it is conceivable, and unassessed in the present study, that combinations of alarm features, or cut-off values for symptoms like weight loss, lead to greater diagnostic value. For the time being, there is a clear need for additional research, and alarm features are likely to remain part of current dyspepsia management strategies until better approaches emerge.

See page 390; CME Quiz on page 659.

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Epidemiology and Risk Factors of Diarrhea-Predominant IBS After Bacterial Dysentery 

The irritable bowel syndrome (IBS) is a highly frequent functional disorder characterized by pain and discomfort associated with a change in stool frequency or stool consistency, in the absence of organic disease that is likely to explain the symptoms. Recent epidemiological studies have identified acute infectious gastroenteritis as the major risk factor for the development of IBS, but its risk factors and especially the long-term clinical course have only been partially elucidated.

In May 2000, in Walkerton, Ontario, heavy rainfall washed livestock fecal residue into the drinking water supply, which became contaminated with Escherichia coli 0157:H7, Campylobacter jejuni, and a number of other pathogens. This led to a large outbreak of acute bacterial gastroenteritis which affected at least 2300 residents, with 27 cases of hemolytic uremic syndrome and 7 deaths. These tragic events provided a population that was prospectively followed by investigators from McMaster University to define the prevalence and natural course of postinfectious IBS.

In this issue, Marshall et al report on a prospective follow-up study of 2069 eligible Walkerton inhabitants (44.5% male, mean age 46.6 years). Two to 3 years after the outbreak, 23.6% of the subjects had IBS symptoms according to the Rome I criteria. The prevalence of IBS was only 10% in controls (who did not develop gastroenteritis during the outbreak), while it was significantly elevated to 27.5% in subjects with self-reported gastroenteritis and to 36.2% in subjects with clinically suspected gastroenteritis (Figure 2). These prevalences yield an odds ratio of 4.8 (95% CI, 3.4–6.8) for the development of IBS in those with clinically suspected gastroenteritis over controls.

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• Figure 2. 

  Rate of IBS according to the Rome I criteria, 2 to 3 years after acute gastroenteritis from exposure to contaminated drinking water (between-group comparisons reported; overall 3-way comparison by χ² P < .001).

The features of postinfectious IBS are those of diarrhea-predominant IBS, with a high proportion of increased stool frequency, watery stools, and urgency. A multivariate statistical analysis identified younger age, female gender, and 4 features of the acute enteric illness (duration of diarrhea more than 7 days, presence of blood in the stool, abdominal cramps, and weight loss of more than 10 pounds) as independent predictors of IBS.

This study, which had access to a large, well-defined, at-risk cohort with a simultaneous and well-characterized acute enteric illness, confirms the highly significant association between acute bacterial gastroenteritis and subsequent IBS symptoms. Ongoing follow-up over the next few years will further clarify the natural history and sequelae of postinfectious IBS in this population .

See page 445; CME Quiz on page 660.

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Paneth Cell Maturation Is Regulated by PPARβ Through Indian Hedgehog Upon Precursor Cells 

Paneth cells, in addition to enterocytes, goblet cells, and enteroendocrine cells, are differentiated cells that are derived from the intestinal crypt stem cell. Paneth cells are unique from the other 3 types of cells in that they migrate crypt-ward during differentiation, and secrete several microbial peptides important in innate immunity. However, the mechanisms for determining cell lineage from the intestinal stem cell is incompletely understood. Previous studies using mouse models have implicated that high levels of Notch signaling can lead to enterocyte differentiation, whereas low levels of Notch signaling, as well as Wnt signaling commits the stem cells toward secretory lineages. Additionally, Indian hedgehog deficient mice (Ihh^−/−) have defective intestinal stem cell differentiation that affects enteroendocrine cell number, and hedgehog proteins have been implicated in intestinal crypt genesis. Peroxisome proliferator-activated receptor beta (PPARβ), a nuclear receptor that responds to fatty acids, is expressed at high levels in small intestine, and mice who survive the nearly uniform lethality of PPARβ absence (PPARβ^−/− have problems with epithelial wound healing. The location of PPARβ throughout the intestine suggests that it might play a role in cell lineage determination.

The study by Varnat et al examined PPARβ-null mice for expression pattern, differentiation and function, embryonic maturation, and linkage to signaling pathways for Paneth cell determination. In wild-type mice, highest expression of PPARβ was at the crypt bottoms in adult mice, and in developing mice by postnatal day 21 the number of Paneth cells increased 6-fold. In PPARβ-null mice, the number of Paneth cells by postnatal day 21 was dramatically limited with adult mice having fewer Paneth cells with smaller secretory granules. Indian hedgehog (Ihh) was found elevated in PPARβ-null mice, with corresponding increases in known hedgehog downstream targets. Blockade of hedgehog signaling increased Paneth cell numbers by an additional one-third in both wild-type and PPARβ-null mice, but PPARβ-null mice were insensitive to a PPARβ agonist, compared with wild-type mice that showed decreased Ihh expression and increased mature Paneth cell bactericidal activity. By performing immunofluorescent co-localization, mature Paneth cells were found to produce secreted Ihh, but immature Paneth cells located just above the mature cells in the crypt possessed the targets of secreted hedgehog (Ptch-1 and Hip) (Figure 3).

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• Figure 3. 

  PPARβ controls the number of Paneth cells by regulating the differentiation of their precursors. (A) Double immunofluorescence showing the co-localization of hedgehog signaling pathway components (Ihh, Ptch-1, and Hip) with lysozyme protein. Red arrows indicate mature Paneth cells and white arrows indicate Paneth cell precursors. (B) Average number of Ptch-1 positive cells in the crypt epithelium as assessed by immunohistochemistry in the small intestine of wild-type and PPARβ-null mice treated or not with L-165041 (a PPARβ agonist) (grey bars) or with cyclopamine (a specific inhibitor of hedgehog signaling) (black bars) (=5; *P < .05). (C) Schematic representation of the hedgehog signaling pathway between mature and precursor Paneth cells. (D) Model for PPARβ action on the level of Ihh, resulting in the alteration of Paneth cell homeostasis.

This study suggests a hedgehog-dependent regulatory loop between mature Paneth cells (secrete Ihh that is negatively regulated by PPARβ) and immature Paneth cells, which respond to decreased Ihh by differentiating into mature Paneth cells.

See page 538 and cover image.

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Antigen-Specific Regulatory CD4⁺ T Cells May Suppress CD8⁺ T cell–Mediated Intestinal Inflammation 

Idiopathic intestinal inflammation, such as that seen with inflammatory bowel disease, results from inappropriate immune effector mechanisms leading to tissue damage, but may also be due to failure of normal immune suppressive mechanisms that may be normally regulated in the gut. It has been previously shown that adoptive transfer of antigen-specific CD8+ T-cell clones into SCID mice induces severe intestinal pathology that is dependent on the presentation of the antigen by MHC class I, and on TNFα production. However, there is little to no data on the regulation of CD8+ T-cells in inflammatory bowel disease.

The study by Westendorf et al examined whether antigen-specific CD8+ T-cell recognition of a single epithelial self-antigen is sufficient to trigger an inflammatory cascade in the intestine, and assessed whether regulatory mechanisms may actively suppress inflammation. Villin-HA transgenic mice (expressing hemagglutinin (HA) as an antigen under the intestinal-specific villin promoter) were crossed with CL4-TCR transgenic mice (expressing an α/β T-cell receptor recognizing an epitope of the HA peptide presented by MHC class I). Surprisingly, these mice did not develop significant intestinal inflammation despite migration and clonal expansion of CD8+ cells to gut mucosal tissues (including 50% of all intraepithelial lymphocytes), the differential expression of activation and memory marker molecules (increased CD25 and CD69 and decreased CD45RB and CD62L), or a robust proliferative response to HA peptide in vitro. However, the activated antigen-specific CD8+ T cells failed to secrete significant amounts of TNFα or IFNγ, and both CD8+ cells and CD4+ cells demonstrated increase in the regulatory T-cell marker Foxp3 (8-fold and 2-fold, respectively). On the other hand, adoptive transfer of CD8+ cells from CL4-TCR mice into Villin-HA mice allowed clonal expansion in Peyer’s patches and as intraepithelial lymphocytes, demonstrated activated and memory markers, made large amounts of IFNγ, and produced severe small intestinal inflammation by day 4, associated with fecal blood and weight loss. Co-transfer of antigen-specific regulatory CD4+ T cells (from a mouse model of chronic HA exposure) with antigen-specific CD8+ cells from CL4-TCR mice blocked CD8+ cell activation, had reduced IFNγ secretion, and ameliorated the intestinal inflammation (Figure 4).

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• Figure 4. 

  Co-transfer of antigen-specific regulatory CD4⁺ T cells reduces the impact of intestinal inflammation. VILLIN-HA transgenic mice received 3 × 10⁶ transgenic CD8⁺Vβ8⁺ T cells with 3 × 10⁶ antigen-specific regulatory CD4⁺T cells from IG-HA × TCR-HA transgenic mice, 3 × 10⁶ polyclonal regulatory CD4⁺ T cells from BALB/c mice or 3 × 10⁶ antigen-specific naïve CD4⁺ T cells from TCR-HA transgenic mice. (A) At day 4 after transfer, H&E staining of the paraffin-embedded tissues from the small intestine were analyzed. (B) Histological scores from (A). Mean values of 2 independent experiments (each group n = 6 total) are depicted. (ns, not significant; **P < .01).

The study suggests a role for antigen-specific regulatory CD4+ T cells that are induced by chronic antigenic stimulation as potent inhibitors of CD8+ T cell–mediated immunity in the intestinal mucosa.

See page 510.