Induction of apoptosis in caco-2 cells by wheat gliadin peptides

Peroxiredoxins and Hypoxia-Inducible Factor-1α in Duodenal Tissue: Emerging Factors in the Pathophysiology of Pediatric Celiac Disease Patients

Celiac disease (CD) is an autoimmune enteropathy. Peroxiredoxins (PRDXs) are powerful antioxidant enzymes having an important role in significant cellular pathways including cell survival, apoptosis, and inflammation. This study aimed at investigating the expression levels of all PRDX isoforms (1-6) and their possible relationships with a transcription factor, HIF-1α, in the small intestinal tissue samples of pediatric CD patients. The study groups consisted of first-diagnosed CD patients (n = 7) and non-CD patients with functional gastrointestinal tract disorders as the controls (n = 7). The PRDXs and HIF-1α expression levels were determined by using real-time PCR and Western blotting in duodenal biopsy samples. It was observed that the mRNA and protein expression levels of PRDX 5 were significantly higher in the CD patients, whereas the PRDX 1, -2, and -4 expressions were decreased in each case compared to the control group. No significant differences were detected in the PRDX 3 and PRDX 6 expressions. The expression of HIF-1α was also significantly elevated in CD patients. These findings indicate, for the first time, that PRDXs, particularly PRDX 5, may play a significant role in the pathogenesis of CD. Furthermore, our results suggest that HIF-1α may upregulate PRDX-5 transcription in the duodenal tissue of CD.

Inflammatory and Microbiota-Related Regulation of the Intestinal Epithelial Barrier

The intestinal epithelial barrier (IEB) is one of the largest interfaces between the environment and the internal milieu of the body. It is essential to limit the passage of harmful antigens and microorganisms and, on the other side, to assure the absorption of nutrients and water. The maintenance of this delicate equilibrium is tightly regulated as it is essential for human homeostasis. Luminal solutes and ions can pass across the IEB via two main routes: the transcellular pathway or the paracellular pathway. Tight junctions (TJs) are a multi-protein complex responsible for the regulation of paracellular permeability. TJs control the passage of antigens through the IEB and have a key role in maintaining barrier integrity. Several factors, including cytokines, gut microbiota, and dietary components are known to regulate intestinal TJs. Gut microbiota participates in several human functions including the modulation of epithelial cells and immune system through the release of several metabolites, such as short-chain fatty acids (SCFAs). Mediators released by immune cells can induce epithelial cell damage and TJs dysfunction. The subsequent disruption of the IEB allows the passage of antigens into the mucosa leading to further inflammation. Growing evidence indicates that dysbiosis, immune activation, and IEB dysfunction have a role in several diseases, including irritable bowel syndrome (IBS), inflammatory bowel disease (IBD), and gluten-related conditions. Here we summarize the interplay between the IEB and gut microbiota and mucosal immune system and their involvement in IBS, IBD, and gluten-related disorders.

Gliadin Sequestration as a Novel Therapy for Celiac Disease: A Prospective Application for Polyphenols

Celiac disease is an autoimmune disorder characterized by a heightened immune response to gluten proteins in the diet, leading to gastrointestinal symptoms and mucosal damage localized to the small intestine. Despite its prevalence, the only treatment currently available for celiac disease is complete avoidance of gluten proteins in the diet. Ongoing clinical trials have focused on targeting the immune response or gluten proteins through methods such as immunosuppression, enhanced protein degradation and protein sequestration. Recent studies suggest that polyphenols may elicit protective effects within the celiac disease milieu by disrupting the enzymatic hydrolysis of gluten proteins, sequestering gluten proteins from recognition by critical receptors in pathogenesis and exerting anti-inflammatory effects on the system as a whole. This review highlights mechanisms by which polyphenols can protect against celiac disease, takes a critical look at recent works and outlines future applications for this potential treatment method.

A Gluten Free Diet in the Management of Epilepsy in People with Coeliac Disease or Gluten Sensitivity

The aim of this review was to assess the effects of a gluten free diet (GFD) in the management of epilepsy in people with coeliac disease (CD) or gluten sensitivity (GS). A systematic approach was used to undertake a literature review. Five electronic databases (PubMed; Scopus; Google Scholar; Cochrane Epilepsy Group specialised register; Cochrane Register of Controlled Trails (CENTRAL) via the Cochrane Register of Online Trials) were searched using predetermined relevant search terms. In total, 668 articles were identified. Duplicates were removed and predefined inclusion and exclusion criteria were applied, and a PRISMA flow chart was produced. Data was extracted using Covidence software. Twelve studies on Epilepsy and CD involving a total of 70 participants were selected for analysis; narrative synthesis was used owing to the small sample sizes in the selected studies. None of the 12 studies meeting inclusion criteria investigated gluten sensitivity and epilepsy. All the included studies support a link between epilepsy and CD. GFD was effective in 44 out of 70 participants across the studies in terms of a reduction of seizures, reduction of antiepileptic drugs (AEDs) or normalisation of EEG pattern. A total of 44 participants showed a reduction in seizures (across eight studies) and complete cessation of seizures was reported in 22 participants. In general, the earlier the GFD is implemented after the onset of seizures, the better the likelihood of the GFD being successful in supporting control of seizures. Mechanisms linking gluten with epilepsy are not fully understood; possible hypotheses include gluten mediated toxicity, immune-induced cortical damage and malabsorption. Evidence suggests the effectiveness of a GFD in supporting the management of epilepsy in patients with CD, although the quality of evidence is low. There appears to be a growing number of neurologists who are prepared to advocate the use of a GFD. A multidisciplinary approaches and further research are recommended. It could be argued that when balancing potential treatments such as AEDs or surgery, a GFD has a low likelihood of harm.

Abnormalities in metabolic pathways in celiac disease investigated by the metabolic profiling of small intestinal mucosa, blood plasma and urine by NMR spectroscopy

Celiac disease (CeD) is an autoimmune enteropathy caused by gluten intake in genetically predisposed individuals. We investigated the metabolism of CeD by metabolic profiling of intestinal mucosa, blood plasma and urine using NMR spectroscopy and multivariate analysis. The metabolic profile of the small intestinal mucosa was compared between patients with CeD (n = 64) and disease controls (DCs, n = 30). The blood plasma and urinary metabolomes of CeD patients were compared with healthy controls (HCs, n = 39). Twelve metabolites (proline (Pro), arginine (Arg), glycine (Gly), histidine (His), glutamate (Glu), aspartate, tryptophan (Trp), fumarate, formate, succinate (Succ), glycerophosphocholine (GPC) and allantoin (Alln)) of intestinal mucosa differentiated CeD from controls. The metabolome of blood plasma with 18 metabolites (Pro, Arg, Gly, alanine, Glu, glutamine, glucose (Glc), lactate (Lac), acetate (Ace), acetoacetate (AcAc), β-hydroxybutyrate (β-OHB), pyruvate (Pyr), Succ, citrate (Cit), choline (Cho), creatine (Cr), phosphocreatine (PCr) and creatinine) and 9 metabolites of urine (Pro, Trp, β-OHB, Pyr, Succ, N-methylnicotinamide (NMN), aminohippurate (AHA), indoxyl sulfate (IS) and Alln) distinguished CeD from HCs. Our data demonstrated changes in nine metabolic pathways. The altered metabolites were associated with increased oxidative stress (Alln), impaired healing and repair mechanisms (Pro, Arg), compromised anti-inflammatory and cytoprotective processes (Gly, His, NMN), altered energy metabolism (Glc, Lac, β-OHB, Ace, AcAc, Pyr, Succ, Cit, Cho, Cr and PCr), impaired membrane metabolism (GPC and Cho) and intestinal dysbiosis (AHA and IS). An orthogonal partial least square discriminant analysis model provided clear differentiation between patients with CeD and controls in all three specimens. A classification model built by combining the distinguishing metabolites of blood plasma and urine samples gave an AUC of 0.99 with 97.7% sensitivity, 93.3% specificity and a predictive accuracy of 95.1%, which was higher than for the models built separately using small intestinal mucosa, blood plasma and urine. In conclusion, a panel of metabolic biomarkers in intestinal biopsies, plasma and urine samples has potential to differentiate CeD from controls and may complement traditional tests to improve the diagnosis of CeD.

Digestion of Intact Gluten Proteins by Bifidobacterium Species: Reduction of Cytotoxicity and Proinflammatory Responses

Celiac disease (CD) is a chronic illness characterized by an inflammatory process triggered by gluten protein intake. Recent evidence has suggested that the lower relative abundance of bifidobacteria in the intestinal lumen may be associated with CD. Herein, we assessed the effect of the Bifidobacterium species Bifidobacterium bifidum, Bifidobacterium longum, Bembidion breve, Bifidobacterium animalis alone, and also a Bifidobacterium consortium on the digestion of intact gluten proteins (gliadins and glutenins) and the associated immunomodulatory responses elicited by the resulting peptides. The cytotoxicity and proinflammatory responses were evaluated through the activation of NF-kB p65 and the expression of cytokines TNF-α and IL-1β in Caco-2 cell cultures exposed to gluten-derived peptides. The peptides induced a clear reduction in cytotoxic responses and proinflammatory marker levels compared to the gluten fragments generated during noninoculated gastrointestinal digestion. These results highlight the possible use of probiotics based on bifidobacteria as a prospective treatment for CD.

Translational Chemistry Meets Gluten-Related Disorders

Gluten‐related disorders are a complex group of diseases that involve the activation of the immune system triggered by the ingestion of gluten. Among these, celiac disease, with a prevalence of 1 %, is the most investigated, but recently, a new pathology, named nonceliac gluten sensitivity, was reported with a general prevalence of 7 %. Finally, there other less‐prevalent gluten‐related diseases such as wheat allergy, gluten ataxia, and dermatitis herpetiformis (with an overall prevalence of less than 0.1 %). As mentioned, the common molecular trigger is gluten, a complex mixture of storage proteins present in wheat, barley, and a variety of oats that are not fully degraded by humans. The most‐studied protein related to disease is gliadin, present in wheat, which possesses in its sequence many pathological fragments. Despite a lot of effort to treat these disorders, the only effective method is a long‐life gluten‐free diet. This Review summarizes the actual knowledge of gluten‐related disorders from a translational chemistry point of view. We discuss what is currently known from the literature about the interaction of gluten with the gut and the critical host responses it evokes and, finally, connect them to our current and novel molecular understanding of the supramolecular organization of gliadin and the 33‐mer gliadin peptide fragment under physiological conditions.

Coeliac disease and gastrointestinal symptom screening in adult first-degree relatives

BACKGROUND AND AIM

The first-degree relatives (FDRs) of patients with coeliac disease are the main risk group for disease development. The study aims to evaluate the screening strategy in FDRs with negative coeliac serology based on human leukocyte antigen (HLA) genotyping, followed by duodenal biopsy, and to analyze the prevalence of gastrointestinal symptoms and the influence of gluten intake.

METHODS

Adult FDRs with negative coeliac serology were invited to participate (n = 205), and a total of 139 completed the study protocol. HLA genotyping, transglutaminase antibody assessment, and duodenal biopsy were performed. Symptomatology was assessed using questionnaires during the various phases of dietary modification (baseline diet, gluten-free diet, and gluten overload).

RESULTS

The study included 139 participants (mean age, 42 years; 53.2% women). HLA-DQ2/8 was positive in 78.4% of the participants (homozygous, 15.1%; heterozygous, 63.3%). Histopathological alterations were noted in 37.1% of participants who underwent duodenal biopsy (Marsh I, 32.7%; Marsh IIIa, 4.4%). At baseline, symptoms were observed in 45.7% of the participants, and the proportion decreased to 24.5% after the gluten-free diet (P < 0.001). Symptoms were not associated with the presence of histological alterations or genetic risk. However, younger age (odds ratio [OR] = 0.91), female sex (OR = 2.9), and the presence of autoimmune disorders (OR = 2.8) were independently associated with a significant symptom response to the gluten-free diet.

CONCLUSIONS

Duodenal lymphocytosis and atrophy are frequently noted in FDRs, despite negative serological markers. In addition, gastrointestinal symptoms are commonly present and associated with gluten intake regardless of the histological pathology.

In vitro toxicity assessment of oral nanocarriers

The fascinating properties of nanomaterials opened new frontiers in medicine. Nanocarriers are useful systems in transporting drugs to site-specific targets. The unique physico-chemical characteristics making nanocarriers promising devices to treat diseases may also be responsible for potential adverse effects. In order to develop functional nano-based drug delivery systems, efficacy and safety should be carefully evaluated. To date, no common testing strategy to address nanomaterial toxicological challenges has been generated. Different cell culture models are currently used to evaluate nanocarrier safety using conventional in vitro assays, but overall they have generated a huge amount of conflicting data. In this review we describe state-of-the-art approaches for in vitro testing of orally administered nanocarriers, highlighting the importance of developing harmonized and validated standard operating procedures. These procedures should be applied in a safe-by-design context with the aim to reduce and/or eliminate the uncertainties and risks associated with nanomedicine development.

Effect of anti-gliadin IgY antibody on epithelial intestinal integrity and inflammatory response induced by gliadin

BACKGROUND

Pepsin-trypsin resistant gliadin (PT-gliadin) promotes intestinal tissue inflammation and increases paracellular permeability of immunogenic gliadin peptides into the lamina propria. This leads to the complications seen in the pathogenesis of celiac disease (CD). In this study, specific anti-gliadin IgY antibody was produced and evaluated for its efficacy on gliadin induced intestinal integrity impairment and proinflammatory effects on intestinal epithelial (Caco-2) cell culture model for CD.

METHODS

Caco-2 (passages 20-24) monolayers were subjected to 7 experimental conditions (n=3 each): phosphate buffered saline (PBS; control), pancreatic digested-casein (PD-casein; negative control), PT-gliadin (positive control), non-specific IgY with PT-gliadin, and anti-wheat gliadin IgY with PT-gliadin at a ratio of 1:6,000, 1:3,000 and 1:1,500. Caco-2 monolayers were then evaluated for effects of gliadin and/or anti-wheat gliadin IgY after 24 h exposure. Enzyme-linked immunosorbent assay (ELISA) was used to quantify anti-inflammatory markers (TNF-α and IL-1β) 5 days after cells were exposed to PT-gliadin and/or anti-wheat gliadin IgY.

RESULTS

Among other conditions, anti-wheat gliadin IgY at a ratio of 1:3,000 (anti-gliadin IgY: PT-gliadin) significantly prevented gliadin toxicity on Caco-2 by maintaining intestinal integrity, inhibiting phenol red permeation, and inhibiting gliadin absorption and production of proinflammatory cytokines (TNF-α and IL-1β) as compared to PT-gliadin stimulated cultures (P < 0.05).

CONCLUSION

The anti-wheat gliadin IgY antibody produced in this study has proved to inhibit absorption of gliadin and gliadin-induced inflammatory response in Caco2 cell culture model of CD. Anti-gliadin IgY, therefore has potential to be used as an oral passive antibody therapy to treat CD.

MeDiA: Mean Distance Association and Its Applications in Nonlinear Gene Set Analysis

Probabilistic association discovery aims at identifying the association between random vectors, regardless of number of variables involved or linear/nonlinear functional forms. Recently, applications in high-dimensional data have generated rising interest in probabilistic association discovery. We developed a framework based on functions on the observation graph, named MeDiA (Mean Distance Association). We generalize its property to a group of functions on the observation graph. The group of functions encapsulates major existing methods in association discovery, e.g. mutual information and Brownian Covariance, and can be expanded to more complicated forms. We conducted numerical comparison of the statistical power of related methods under multiple scenarios. We further demonstrated the application of MeDiA as a method of gene set analysis that captures a broader range of responses than traditional gene set analysis methods.

Hydrophobicity of whey protein hydrolysates enhances the protective effect against oxidative damage on PC 12 cells

The relationship between hydrophobicity and the protective effect of whey protein hydrolysates (WPHs) against oxidative stress was studied. Whey protein was first hydrolysed by pepsin and trypsin to obtain WPHs. After absorbed by macroporous adsorption resin DA201-C, three fractions named as M20, M40, and M60 were eluted by various concentrations of ethanol. The hydrophobicity showed a trend of increase from M20 to M60. Antioxidant ability test in vitro indicated that all the three components of WPHs displayed reasonably good antioxidant ability. Moreover, with the increase of hydrophobicity, antioxidant ability of WPHs improved significantly. Then rat pheochromocytoma line 12 (PC12) cells oxidative model was built to evaluate the suppression of oxidative stress of three components on PC12 cells induced by H2O2. Morphological alterations, cell viability, apoptosis rate, and intracellular antioxidase system tests all indicated that WPHs exert significant protection on PC cells against H2O2-induced damage. Among them, M60 had the highest protective effect by increasing 19·3% cell survival and reducing 28·6% cell apoptosis. These results suggested hydrophobicity of WPHs was contributing to the antioxidant ability and the protective effect against oxidative damage.

Characterization of Adults With a Self-Diagnosis of Nonceliac Gluten Sensitivity

Background: Nonceliac gluten sensitivity (NCGS), occurring in patients without celiac disease yet whose gastrointestinal symptoms improve on a gluten-free diet (GFD), is largely a self-reported diagnosis and would appear to be very common. The aims of this study were to characterize patients who believe they have NCGS. Materials and Methods: Advertising was directed toward adults who believed they had NCGS and were willing to participate in a clinical trial. Respondents were asked to complete a questionnaire about symptoms, diet, and celiac investigation. Results: Of 248 respondents, 147 completed the survey. Mean age was 43.5 years, and 130 were women. Seventy-two percent did not meet the description of NCGS due to inadequate exclusion of celiac disease (62%), uncontrolled symptoms despite gluten restriction (24%), and not following a GFD (27%), alone or in combination. The GFD was self-initiated in 44% of respondents; in other respondents it was prescribed by alternative health professionals (21%), dietitians (19%), and general practitioners (16%). No celiac investigations had been performed in 15% of respondents. Of 75 respondents who had duodenal biopsies, 29% had no or inadequate gluten intake at the time of endoscopy. Inadequate celiac investigation was common if the GFD was initiated by self (69%), alternative health professionals (70%), general practitioners (46%), or dietitians (43%). In 40 respondents who fulfilled the criteria for NCGS, their knowledge of and adherence to the GFD were excellent, and 65% identified other food intolerances. Conclusions: Just over 1 in 4 respondents self-reporting as NCGS fulfill criteria for its diagnosis. Initiation of a GFD without adequate exclusion of celiac disease is common. In 1 of 4 respondents, symptoms are poorly controlled despite gluten avoidance.

No effects of gluten in patients with self-reported non-celiac gluten sensitivity after dietary reduction of fermentable, poorly absorbed, short-chain carbohydrates

BACKGROUND & AIMS

Patients with non-celiac gluten sensitivity (NCGS) do not have celiac disease but their symptoms improve when they are placed on gluten-free diets. We investigated the specific effects of gluten after dietary reduction of fermentable, poorly absorbed, short-chain carbohydrates (fermentable, oligo-, di-, monosaccharides, and polyols [FODMAPs]) in subjects believed to have NCGS.

METHODS

We performed a double-blind cross-over trial of 37 subjects (aged 24-61 y, 6 men) with NCGS and irritable bowel syndrome (based on Rome III criteria), but not celiac disease. Participants were randomly assigned to groups given a 2-week diet of reduced FODMAPs, and were then placed on high-gluten (16 g gluten/d), low-gluten (2 g gluten/d and 14 g whey protein/d), or control (16 g whey protein/d) diets for 1 week, followed by a washout period of at least 2 weeks. We assessed serum and fecal markers of intestinal inflammation/injury and immune activation, and indices of fatigue. Twenty-two participants then crossed over to groups given gluten (16 g/d), whey (16 g/d), or control (no additional protein) diets for 3 days. Symptoms were evaluated by visual analogue scales.

RESULTS

In all participants, gastrointestinal symptoms consistently and significantly improved during reduced FODMAP intake, but significantly worsened to a similar degree when their diets included gluten or whey protein. Gluten-specific effects were observed in only 8% of participants. There were no diet-specific changes in any biomarker. During the 3-day rechallenge, participants' symptoms increased by similar levels among groups. Gluten-specific gastrointestinal effects were not reproduced. An order effect was observed.

CONCLUSIONS

In a placebo-controlled, cross-over rechallenge study, we found no evidence of specific or dose-dependent effects of gluten in patients with NCGS placed diets low in FODMAPs.

Gene Expression Profiling of Gliadin Effects on Intestinal Epithelial Cells Suggests Novel Non-Enzymatic Functions of Pepsin and Trypsin

Gliadin triggers T-cell mediated immunity in celiac disease, and has cytotoxic effects on enterocytes mediated through obscure mechanisms. In addition, gliadin transport mechanisms, potential cell surface receptors and gliadin-activated downstream signaling pathways are not completely understood. In order to screen for novel downstream gliadin target genes we performed a systematic whole genome expression study on intestinal epithelial cells. Undifferentiated Caco-2 cells were exposed to pepsin- and trypsin- digested gliadin (PT-G), a blank pepsin-trypsin control (PT) and to a synthetic peptide corresponding to gliadin p31-43 peptide for six hours. RNA from four different experiments was used for hybridization on Agilent one color human whole genome DNA microarray chips. The microarray data were analyzed using the Bioconductor package LIMMA. Genes with nominal p<0.01 were considered statistically significant. Compared to the untreated cells 1705, 1755 and 211 probes were affected by PT-G, PT and p31-43 respectively. 46 probes were significantly different between PT and PT-G treated cells. Among the p31-43 peptide affected probes, 10 and 21 probes were affected by PT-G and PT respectively. Only PT-G affected genes could be validated by quantitative real-time polymerase chain reaction. All the genes were, nonetheless, also affected to a comparable level by PT treated negative controls. In conclusion, we could not replicate previously reported direct effects of gliadin peptides on enterocytes. The results rather suggest that certain epitopes derived from pepsin and trypsin may also affect epithelial cell gene transcription. Our study suggests novel non-enzymatic effects of pepsin and trypsin on cells and calls for proper controls in pepsin and trypsin digested gliadin experiments. It is conceivable that gliadin effects on enterocytes are secondary mediated through oxidative stress, NFkB activation and IL-15 up-regulation.

Non-celiac gluten sensitivity

Gluten sensitivity has been best recognized and understood in the context of two conditions, celiac disease and wheat allergy. However, some individuals complain of symptoms in response to ingestion of "gluten," without histologic or serologic evidence of celiac disease or wheat allergy. The term non-celiac gluten sensitivity (NCGS) has been suggested for this condition, although a role for gluten proteins as the sole trigger of the associated symptoms remains to be established. This article reviews the available information regarding symptomatology, epidemiology and genetics, serology and histology, and in vitro and in vivo experimental data on the pathophysiology of NCGS.

Early tissue transglutaminase-mediated response underlies K562(S)-cell gliadin-dependent agglutination

INTRODUCTION

[corrected] K562(S) agglutination has been used as a rapid and economic tool for the in vitro screening of the toxicity of cereal fractions and prolamins in celiac disease (CD). A strict correlation has been reported between the toxicity of cereals and cereal fractions for celiac patients and their ability to agglutinate K562(S) cells. Whether this specificity of K562(S)-cell agglutination is caused by the activation of the same pathogenic events triggered by toxic cereal fractions in CD intestine or simply represents a bystander event of gluten toxicity is, however, unknown.

METHODS

K562(S) cells were incubated in vitro with the peptic-tryptic digest of wheat gliadin.

RESULTS

The agglutination of K562(S) cells by wheat gliadin peptides is orchestrated by a cascade of very early events occurring at the K562(S)-cell surface similar to those occurring at the intestinal epithelial surface. They involve a rapid increase in intracellular calcium levels that activate tissue transglutaminase (TG2), leading to a rapid actin reorganization that is pivotal in driving cell agglutination. These specific effects of toxic cereals are phenocopied by the gliadin-derived peptide p31-43, which orchestrates the activation of innate response to gliadin in CD.

DISCUSSION

Our study provides the rationale for the extensive use of K562(S)-cell agglutination as a valuable tool for screening cereal toxicity.

Celiac disease, inflammation and oxidative damage: a nutrigenetic approach

Celiac disease (CD), a common heritable chronic inflammatory condition of the small intestine caused by permanent intolerance to gluten/gliadin (prolamin), is characterized by a complex interplay between genetic and environmental factors. Developments in proteomics have provided an important contribution to the understanding of the biochemical and immunological aspects of the disease and the mechanisms involved in toxicity of prolamins. It has been demonstrated that some gliadin peptides resistant to complete proteolytic digestion may directly affect intestinal cell structure and functions by modulating gene expression and oxidative stress. In recent years, the creation of the two research fields Nutrigenomics and Nutrigenetics, has enabled the elucidation of some interactions between diet, nutrients and genes. Various dietary components including long chain ω-3 fatty acids, plant flavonoids, and carotenoids have been demonstrated to modulate oxidative stress, gene expression and production of inflammatory mediators. Therefore their adoption could preserve intestinal barrier integrity, play a protective role against toxicity of gliadin peptides and have a role in nutritional therapy of celiac disease.

In vitro models for gluten toxicity: relevance for celiac disease pathogenesis and development of novel treatment options

In genetically predisposed individuals, dietary gluten in wheat, rye and barley triggers celiac disease, a systemic autoimmune disorder hallmarked by an extensive small-bowel mucosal immune response. The current conception of celiac disease pathogenesis is that it involves components of both innate and adaptive immunity whose activation typically leads to small-bowel villous atrophy with crypt hyperplasia. Currently, the only effective treatment for celiac disease is a strict lifelong gluten-free diet excluding all wheat-, rye- and barley-containing food products. During the diet, the clinical symptoms improve and the small-bowel mucosal damage recovers, while re-introduction of gluten into the diet leads to re-appearance of the symptoms and deterioration of the small-bowel mucosal architecture. In view of the restricted nature of the diet, alternative treatment is warranted. Improved understanding of the molecular basis of celiac disease has enabled researchers to suggest other therapeutic approaches. Although there is no animal model reproducing all features of celiac disease, the use of in vitro approaches including a variety of cell lines and the celiac patient small-bowel mucosal biopsy organ culture has generated knowledge about pathogenesis of celiac disease. In these culture systems, gluten induces different effects that can be quantified, thus also enabling studies concerning the efficacy of candidate therapeutic compounds for celiac disease. This review describes the intestinal epithelial cell models, celiac patient T-cell lines and clones, as well as the small-bowel mucosal organ culture methods widely used in studies of celiac disease, and summarizes the major findings obtained with these systems.

Influence of Bifidobacterium longum CECT 7347 and gliadin peptides on intestinal epithelial cell proteome

Celiac disease is an enteropathy caused by an abnormal immune response to cereal gluten proteins (gliadin). To unravel the possible role of the interactions between gliadin peptides and specific intestinal bacteria, the response of intestinal epithelial (Caco-2) cells to gliadin subjected to gastrointestinal digestion in the presence or absence of Bifidobacterium longum CECT 7347 has been studied. Changes in the proteome of Caco-2 cells were determined by 2DE and MALDI-TOF. Gliadins digested without B. longum altered the expression of a higher number of proteins than in the presence of the bacterium (21 versus 9), and these proteins were involved in disorganization of cell cytoskeleton, inflammation, and apoptosis. Gliadins digested in the presence of the bacterium influenced the production of proteins involved in calcium homeostasis and cell survival and function. Therefore, B. longum CECT 7347 might ameliorate gliadin toxicity and modify the responses of intestinal epithelial cells to the gliadin challenge.

Does gluten cause gastrointestinal symptoms in subjects without coeliac disease?

AIM

To determine the evidence for the effect of gluten ingestion on gastrointestinal symptoms, intestinal permeability and other indices of small intestinal injury in non-coeliac, gluten intolerant individuals.

METHODS

A literature review was performed searching for interventional studies that addressed the issue.

RESULTS

One unblinded study that identified symptomatic response to gluten did not effectively exclude patients with coeliac disease, since many had intraepithelial lymphocytosis. A double-blinded, randomised, placebo-controlled rechallenge trial was recently reported in patients in whom coeliac disease had been excluded by either normal duodenal histology on a gluten containing diet, or absence of the HLA DQ2 or DQ8 haplotype (56%). Participants were randomly assigned to receive either 16 g/day carbohydrate-free gluten or placebo for six weeks. Participants were enrolled if they had gastrointestinal symptoms that had improved on a GFD and had been on a gluten free diet for at least 6 weeks prior to enrollment. 19 received gluten and 15 received placebo. Change between baseline and final weeks were greater for patients receiving gluten in overall symptom severity compared with those receiving placebo (p=0.047). and were worse with gluten within one week for pain (p=0.016), bloating (p=0.031), satisfaction with stool consistency (p=0.024), and tiredness (p=0.001). Mechanisms for symptom induction were not identified.

CONCLUSIONS

Non-coeliac gluten intolerance does exist. Future studies need to identify issues of the dose of gluten needed and mechanisms of action.

Gluten causes gastrointestinal symptoms in subjects without celiac disease: a double-blind randomized placebo-controlled trial

OBJECTIVES

Despite increased prescription of a gluten-free diet for gastrointestinal symptoms in individuals who do not have celiac disease, there is minimal evidence that suggests that gluten is a trigger. The aims of this study were to determine whether gluten ingestion can induce symptoms in non-celiac individuals and to examine the mechanism.

METHODS

A double-blind, randomized, placebo-controlled rechallenge trial was undertaken in patients with irritable bowel syndrome in whom celiac disease was excluded and who were symptomatically controlled on a gluten-free diet. Participants received either gluten or placebo in the form of two bread slices plus one muffin per day with a gluten-free diet for up to 6 weeks. Symptoms were evaluated using a visual analog scale and markers of intestinal inflammation, injury, and immune activation were monitored.

RESULTS

A total of 34 patients (aged 29-59 years, 4 men) completed the study as per protocol. Overall, 56% had human leukocyte antigen (HLA)-DQ2 and/or HLA-DQ8. Adherence to diet and supplements was very high. Of 19 patients (68%) in the gluten group, 13 reported that symptoms were not adequately controlled compared with 6 of 15 (40%) on placebo (P=0.0001; generalized estimating equation). On a visual analog scale, patients were significantly worse with gluten within 1 week for overall symptoms (P=0.047), pain (P=0.016), bloating (P=0.031), satisfaction with stool consistency (P=0.024), and tiredness (P=0.001). Anti-gliadin antibodies were not induced. There were no significant changes in fecal lactoferrin, levels of celiac antibodies, highly sensitive C-reactive protein, or intestinal permeability. There were no differences in any end point in individuals with or without DQ2/DQ8.

CONCLUSIONS

"Non-celiac gluten intolerance" may exist, but no clues to the mechanism were elucidated.

Gliadin peptide P31-43 localises to endocytic vesicles and interferes with their maturation

BACKGROUND

Celiac Disease (CD) is both a frequent disease (1:100) and an interesting model of a disease induced by food. It consists in an immunogenic reaction to wheat gluten and glutenins that has been found to arise in a specific genetic background; however, this reaction is still only partially understood. Activation of innate immunity by gliadin peptides is an important component of the early events of the disease. In particular the so-called "toxic" A-gliadin peptide P31-43 induces several pleiotropic effects including Epidermal Growth Factor Receptor (EGFR)-dependent actin remodelling and proliferation in cultured cell lines and in enterocytes from CD patients. These effects are mediated by delayed EGFR degradation and prolonged EGFR activation in endocytic vesicles. In the present study we investigated the effects of gliadin peptides on the trafficking and maturation of endocytic vesicles.

METHODS/PRINCIPAL FINDINGS

Both P31-43 and the control P57-68 peptide labelled with fluorochromes were found to enter CaCo-2 cells and interact with the endocytic compartment in pulse and chase, time-lapse, experiments. P31-43 was localised to vesicles carrying early endocytic markers at time points when P57-68-carrying vesicles mature into late endosomes. In time-lapse experiments the trafficking of P31-43-labelled vesicles was delayed, regardless of the cargo they were carrying. Furthermore in celiac enterocytes, from cultured duodenal biopsies, P31-43 trafficking is delayed in early endocytic vesicles. A sequence similarity search revealed that P31-43 is strikingly similar to Hrs, a key molecule regulating endocytic maturation. A-gliadin peptide P31-43 interfered with Hrs correct localisation to early endosomes as revealed by western blot and immunofluorescence microscopy.

CONCLUSIONS

P31-43 and P57-68 enter cells by endocytosis. Only P31-43 localises at the endocytic membranes and delays vesicle trafficking by interfering with Hrs-mediated maturation to late endosomes in cells and intestinal biopsies. Consequently, in P31-43-treated cells, Receptor Tyrosine Kinase (RTK) activation is extended. This finding may explain the role played by gliadin peptides in inducing proliferation and other effects in enterocytes from CD biopsies.

Bifidobacteria inhibit the inflammatory response induced by gliadins in intestinal epithelial cells via modifications of toxic peptide generation during digestion

Celiac disease (CD) is a chronic enteropathy triggered by intake of gliadin, the toxic component of gluten. This study aims at evaluating the capacity of different Bifidobacterium strains to counteract the inflammatory effects of gliadin-derived peptides in intestinal epithelial (Caco-2) cells. A commercial extract of several gliadin (Gld) types (alpha, beta, gamma, [symbol: see text] ) was subjected to in vitro gastrointestinal digestion (pepsin at pH 3, pancreatin-bile at pH 6), inoculated or not with cell suspensions (10(8) colony forming units/ml) of either B. animalis IATA-A2, B. longum IATA-ES1, or B. bifidum IATA-ES2, in a bicameral system. The generated gliadin-derived peptides were identified by reverse phase-HPLC-ESI-MS/MS. Caco-2 cell cultures were exposed to the different gliadin peptide digestions (0.25 mg protein/ml), and the mRNA expression of nuclear factor kappa-B (NF-kappaB), tumor necrosis factor alpha (TNF-alpha), and chemokine CXCR3 receptor were analyzed by semi-quantitative reverse transcriptase-polymerase chain reaction (RT-PCR) in stimulated cells. The production of the pro-inflammatory markers NF-kappaB p50, TNF-alpha, and IL-1beta (interleukine 1beta) by Caco-2 cells was also determined by ELISA. The peptides from gliadin digestions inoculated with bifidobacteria did not exhibit the toxic amino acid sequences identified in those noninoculated (alpha/beta-Gld [158-164] and alpha/beta-Gld [122-141]). The RT-PCR analysis evidenced a down-regulation in mRNA expression of pro-inflammatory biomarkers. Consistent with these results the production of NF-kappaB, TNF-alpha, and IL-1beta was reduced (18.2-22.4%, 28.0-64.8%, and abolished, respectively) in cell cultures exposed to gliadin digestions inoculated with bifidobacteria. Therefore, bifidobacteria change the gliadin-derived peptide pattern and, thereby, attenuate their pro-inflammatory effects on Caco-2 cells.

Gliadins induce TNFalpha production through cAMP-dependent protein kinase A activation in intestinal cells (Caco-2)

Celiac disease is an autoimmune enteropathy caused by a permanent intolerance to gliadins. In this study the effects of two gliadin-derived peptides (PA2, PQPQLPYPQPQLP and PA9, QLQPFPQPQLPY) on TNFalpha production by intestinal epithelial cells (Caco-2) and whether these effects were related to protein kinase A (PKA) and/or -C (PKC) activities have been evaluated. Caco-2 cell cultures were challenged with several sets of gliadin peptides solutions (0.25 mg/mL), with/without different activators of PKA or PKC, bradykinin (Brdkn) and pyrrolidine dithiocarbamate (PDTC). The gliadin-derived peptides assayed represent the two major immunodominant epitopes of the peptide 33-mer of alpha-gliadin (56-88) (LQLQPFPQPQLPYPQPQLPYPQPQLPYPQPQPF). Both peptides induced the TNFalpha production triggering the inflammatory cell responses, the PA2 being more effective. The addition of the peptides in the presence of dibutyril cyclic AMP (cAMP), Brdkn or PDTC, inhibited the TNFalpha production. The PKC-activator phorbol 12-myristate 13-diacetate additionally increased the PA2- and PA9-induced TNFalpha production. These results link the gliadin-derived peptides induced TNFalpha production through cAMP-dependent PKA activation, where ion channels controlling calcium influx into cells could play a protective role, and requires NF-kappaB activation.

Celiac disease: from pathogenesis to novel therapies

Celiac disease has become one of the best-understood HLA-linked disorders. Although it shares many immunologic features with inflammatory bowel disease, celiac disease is uniquely characterized by (1) a defined trigger (gluten proteins from wheat and related cereals), (2) the necessary presence of HLA-DQ2 or HLA-DQ8, and (3) the generation of circulating autoantibodies to the enzyme tissue transglutaminase (TG2). TG2 deamidates certain gluten peptides, increasing their affinity to HLA-DQ2 or HLA-DQ8. This generates a more vigorous CD4(+) T-helper 1 T-cell activation, which can result in intestinal mucosal inflammation, malabsorption, and numerous secondary symptoms and autoimmune diseases. Moreover, gluten elicits innate immune responses that act in concert with the adaptive immunity. Exclusion of gluten from the diet reverses many disease manifestations but is usually not or less efficient in patients with refractory celiac disease or associated autoimmune diseases. Based on the advanced understanding of the pathogenesis of celiac disease, targeted nondietary therapies have been devised, and some of these are already in phase 1 or 2 clinical trials. Examples are modified flours that have been depleted of immunogenic gluten epitopes, degradation of immunodominant gliadin peptides that resist intestinal proteases by exogenous endopeptidases, decrease of intestinal permeability by blockage of the epithelial ZOT receptor, inhibition of intestinal TG2 activity by transglutaminase inhibitors, inhibition of gluten peptide presentation by HLA-DQ2 antagonists, modulation or inhibition of proinflammatory cytokines, and induction of oral tolerance to gluten. These and other experimental therapies will be discussed critically.

Chickpea protein hydrolysate as a substitute for serum in cell culture

The growth of mammalian cells in vitro requires the use of rich culture media that are prepared by combining serum with specific nutrient formulations. Serum, the most expensive component of culture media, provides a complex mixture of growth factors and nutrients. Protein hydrolysates that can support in vitro cell growth and eliminate or reduce the need to use serum have been obtained from different sources. Here we describe the use of two food grade proteases to produce a chickpea protein hydrolysate that has been added to cell culture medium in order to determine whether it can be used as a substitute for serum. Medium containing the hydrolysate has been tested using two human cells lines: the monocytic THP-1 cell line which grows in suspension, and the epithelial Caco-2 cell line which grows as a monolayer. The chickpea protein hydrolysate was a good substitute for serum in the first case, but did not allow growth of Caco-2 cells. Supplementation of culture media with this inexpensive and safe hydrolysate would greatly reduce the cost of cell culture.

Higher constitutive IL15R alpha expression and lower IL-15 response threshold in coeliac disease patients

The IL-15 triggering effect of gliadin is not exclusive to coeliac disease (CD) patients, whereas the secondary response is CD specific. We have studied the expression of the IL-15 receptor, and the IL-15 response upon stimulation, in non-CD and CD patients, and the possible existence of a lower immunological threshold in the latter. Forty-two CD patients (20 on a gluten-containing diet, GCD, and 22 on gluten-free diet, GFD) and 24 non-CD healthy individuals were studied. IL15R alpha mRNA expression, and tissue characterization, were assayed in the duodenum. Biopsies from six CD patients on GFD and 10 non-CD individuals were studied in vitro using organ culture in basal conditions, as well as after IL-15 stimulation discarding basal IL-15 production. Secretion of immune mediators was measured in the culture supernatants. IL15R alpha mRNA expression was increased in CD patients, as compared with non-CD controls (on GFD P = 0.0334, on GCD P = 0.0062, respectively), and confirmed also by immunofluorescence. No differences were found between CD patients on GFD and on GCD. After in vitro IL-15 stimulation, IL15R alpha expression was only triggered in non-CD controls (P = 0.0313), though it remained increased in CD patients. Moreover, IL-15 induced a more intense immunological response in CD patients after triggering the production of both nitrites and IFN gamma (P = 0.0313, P = 0.0313, respectively). Gliadin-induced IL15 has a lower response threshold in CD patients, leading to the production of other immune mediators and the development of the intestinal lesion, and thus magnifying its effects within the CD intestine.

Celiac disease pathogenesis: the proinflammatory cytokine network

In susceptible individuals, the adaptive response, mediated by the activation of antigen-specific T lymphocytes, drives a proinflammatory response, which ends in an immune-mediated enteropathy characterized by villous atrophy, crypt hyperplasia, and recruitment of intraepithelial lymphocytes. In addition, some gluten peptides are able to induce an innate immune response in intestinal mucosa. The molecular mechanisms and the cells involved in the initial stages of the gluten-intestinal mucosa interaction are poorly understood to date. There is evidence of a direct toxic effect of gluten peptides in several biological models. However, the failure to control the inflammatory response may be one of the factors underlying gluten intolerance in these individuals. The cytokine network involved in celiac disease is characterized by abundant interferon-gamma in the intestinal mucosa. In addition, the production of interleukin (IL)-15, IL-18, and IL-21 is linked to gluten intake, which can drive the inflammatory response probably sustained by IL-18, IL-21, and perhaps IL-27 through STAT1 and STAT5 pathways, whereas neither IL-12 nor IL-23 plays a significant role in pathogenic mechanisms. Herein we describe the involvement of these activation pathways in the context of the pathogenesis of celiac disease.

A role for tissue transglutaminase in alpha-gliadin peptide cytotoxicity

In coeliac disease, gliadin peptides p56-88, p57-68 and p31-49 have been demonstrated to be involved in the pathogenic damage of the small intestine via their immunogenicity or toxicity to epithelial cells. To try to understand the mechanism of their toxicity, we investigated the effect of synthetic peptides (p31-49, p56-88, p57-68, p69-82) and of their deamidated analogues on Caco2 and FHs 74 Int cell toxicity and tissue tranglutaminase activity. Apoptosis, necrosis and cell viability were assessed by flow cytometry, and peptide deamidation was determined indirectly by measuring its capacity to inhibit tTG activity. The results showed that p56-88 and p57-68 reduced cell growth and concomitantly inhibited tTG activity in both cell types. This effect was abolished when Caco2 cells were treated with antibodies to tTG. Deamidated peptide p57-68 (E(65)) lost practically all of its inhibitory effect on cell growth and on tTG activity. Cellular toxicity was also observed with p31-49, which was not a substrate for tTG. p69-82 was not cytotoxic but became so when glutamine 72 was substituted by glutamic acid. These findings provide evidence for the existence of three types of toxicity among gliadin peptides: (i) peptides that are intrinsically toxic and are not substrates of tTG; (ii) peptides that are non-toxic but become so when they act as substrates of tTG; and (iii) peptides that are non-toxic and are not substrates of tTG but become so when deamidated. A mechanism other than that involving tTG could be responsible for the deamidation of glutamine residues of gliadin in the intestinal tract.

Adaptive and innate immune responses in celiac disease

Celiac disease (CD) is a complex small intestinal disorder due to a dysregulated immune response to wheat gliadin and related proteins which leads to a small intestinal enteropathy. It is generally accepted that CD is a T-cell mediated disease, in which, gliadin derived peptides, either in native form or deamidated by tissue transglutaminase, activate lamina propria infiltrating T lymphocytes which release proinflammatory cytokines. Recent studies indicate that gliadin contains also peptides able to activate an innate immune response. In particular, they induce a selective expansion of IEL, particularly TCRgamma/delta+ and CD8+TCR alpha/beta+ lymphocytes bearing the CD94 NK receptor, as well as a strong epithelial expression of MICA molecules which interact with NKG2D receptor expressed on TCRgamma/delta+ and NK cells. Most of the events of innate immune activation events are inhibited by antibodies neutralizing IL-15, thus confirming the key role of this cytokine as a mediator of intestinal mucosa damage induced by ingestion of gliadin. It remains to be established to what extent the ability of gliadin peptides to activate innate immunity relates to other biological properties exerted not only on celiac cells and tissues; the specificity of celiac patients is probably related to their genetic make up.

Induction of apoptosis in a human lymphoma cell line by hydrophobic peptide fraction separated from anchovy sauce

Peptide fractions showing anticancer activity were isolated from anchovy sauce, and their abilities to induce apoptosis in a human lymphoma cell (U937) were determined by biochemical and flow cytometric methods. The butanol extract (fraction Aob) from the desalted hydrophobic peptide fraction (Ao) separated from anchovy sauce by HP-20 adsorption chromatography was found to possess strong antiproliferative activity against U937 by inducing apoptosis. Treatment of U937 with Aob resulted in sub-G1 peak representing apoptosis in the cell cycle analysis, and apoptotic DNA fragmentation. Antiproliferative activity of the peptide fraction further purified successively by silica gel chromatography, TLC, and reversed-phase HPLC increased proportionally with the purification fold. The peptide fraction having antiproliferative activity was found to be composed of Ala and Phe, and its molecular weight was estimated to be 440.9 Da.

Proteomics identification of acyl-acceptor and acyl-donor substrates for transglutaminase in a human intestinal epithelial cell line. Implications for celiac disease

Transglutaminase (TG)-catalyzed cross-linking of both intracellular and extracellular proteins is an important biochemical event. However, increased concentrations of cross-linked proteins have been observed in many disorders. Moreover, TG-catalyzed modification of proteins might generate new self-antigens responsible for the autoimmune response, as in celiac disease. The identification of available substrates may offer an understanding of how the TG-catalyzed post-translational modification has an impact on physiology and disease. We used a proteomic approach to identify TG-modified protein targets in human intestinal epithelial cells to determine the extent to which transglutaminase specifically contributes to celiac disease. Two probes were used for endogenous TG activity: 5-(biotinamido)pentylamine, which represents the acyl-acceptor, and a biotinylated glutamine-containing peptide, which represents the acyl-donor. This approach identified >25 proteins, which range from 30,000 to 300,000 Daltons and can serve as acyl-acceptor and/or acyl-donor for transglutaminase. Some of them were known transglutaminase substrates, whereas others had not been previously identified. These targets include proteins involved in cytoskeletal network organization, folding of proteins, transport processes, and miscellaneous metabolic functions.

Wheat gliadin induces apoptosis of intestinal cells via an autocrine mechanism involving Fas-Fas ligand pathway

Wheat gliadin and other cereal prolamins have been said to be involved in the pathogenic damage of the small intestine in celiac disease via the apoptosis of epithelial cells. In the present work we investigated the mechanisms underlying the pro-apoptotic activity exerted by gliadin-derived peptides in Caco-2 intestinal cells, a cell line which retains many morphological and enzymatic features typical of normal human enterocytes. We found that digested peptides from wheat gliadins (i) induce apoptosis by the CD95/Fas apoptotic pathway, (ii) induce increased Fas and FasL mRNA levels, (iii) determine increased FasL release in the medium, and (iv) that gliadin digest-induced apoptosis can be blocked by Fas cascade blocking agents, i.e. targeted neutralizing antibodies. This favors the hypothesis that gliadin could activate an autocrine/paracrine Fas-mediated cell death pathway. Finally, we found that (v) a small peptide (1157 Da) from durum wheat, previously proposed for clinical practice, exerted a powerful protective activity against gliadin digest cytotoxicity.

In vitro cytotoxic effect of bread wheat gliadin on the LoVo human adenocarcinoma cell line

The pathogenesis of celiac disease is not completely understood but, although the initial step of the process is still unclear, an altered immune response seems to play a major role. Previous studies of the biological properties of gliadin have highlighted its cytotoxic effects, and the aim of this study was to develop an in vitro technique to study them. The LoVo (human colon adenocarcinoma) cell line grown in two-dimensional cultures was exposed to different concentrations of digested bread wheat gliadin (62, 125, 250, 500 and 750 microg/ml) for 48 h, after which cell growth and oxidative balance (the content of reduced glutathione (GSH), and peroxidase, transferase and reductase activity) was evaluated. Other food proteins were used as controls. Our data revealed a statistically significant inhibition of cell growth in proportion to the gliadin concentration (from 26 to 100%), combined with a decrease in GSH content (-38% at 500 microg/ml) and reduced enzymatic activity (-30% at 500 microg/ml). The controls did not show any noxious effect. Our results confirm the usefulness of LoVo cells in evaluating gliadin cytotoxicity and that they can be used to investigate the biological properties of gliadin.

Nitrogen-containing bisphosphonates induce apoptosis of Caco-2 cells in vitro by inhibiting the mevalonate pathway: a model of bisphosphonate-induced gastrointestinal toxicity

Bisphosphonates have become an important addition to the pharmacological armamentarium against postmenopausal osteoporosis. One of the major side effects of oral therapy with some nitrogen-containing bisphosphonates appears to be gastrointestinal (GI) intolerability, particularly esophageal irritation and ulceration. Because nitrogen-containing bisphosphonates can cause apoptosis in a variety of cell types in vitro, by inhibiting the mevalonate pathway, we hypothesized that the effect of these agents on the GI tract may be due to apoptosis or inhibition of growth of gut epithelial cells. A comparison between clodronate, etidronate, pamidronate, alendronate, and risedronate demonstrated that only the nitrogen-containing bisphosphonates were effective at inducing apoptosis or inhibiting proliferation of Caco-2 human epithelial cells in vitro, at concentrations of between 10 and 1000 micromol/L. The ability of nitrogen-containing bisphosphonates to cause apoptosis and inhibit Caco-2 cell proliferation was due to inhibition of the mevalonate pathway, because the addition of farnesol, oxidized low-density lipoprotein (LDL) cholesterol, or especially geranylgeraniol suppressed the effects. Furthermore, pamidronate, alendronate, and risedronate inhibited protein prenylation in Caco-2 cells, as determined by analysis of the processing of Rap1A, a prenylated small GTPase. These studies suggest that the effects of nitrogen-containing bisphosphonates observed in the GI tract may be due to inhibition of proliferation or apoptosis of gut epithelial cells, following loss of prenylated proteins and sterols.

Permeability of human HT-29/B6 colonic epithelium as a function of apoptosis

1. The barrier function of colonic epithelia is challenged by apoptotic loss of enterocytes. In monolayers of human colonic HT-29/B6 cells, apoptosis induced by camptothecin was assessed by poly-(ADP-ribose)-polymerase (PARP) cleavage, histone ELISA and DNA-specific fluorochrome staining (with 4',6'-diamidino-2'-phenylindoladihydrochloride (DAPI)). Epithelial barrier function was studied in Ussing chambers by measuring transepithelial conductivity and unidirectional tracer fluxes. The ion permeability associated with single cell apoptoses was investigated with the conductance scanning technique. 2. The spontaneous rate of apoptotic cells was 3.5 +/- 0.3 % with an overall epithelial conductivity of 3.2 +/- 0.1 mS cm(-2). Camptothecin induced a time- and dose-dependent increase of apoptosis and permeability. With 20 microg ml(-1) of camptothecin for 48 h, apoptosis increased 4.1-fold to 14.3 +/- 1.5 % and the conductivity doubled to 6.4 +/- 1.0 mS cm(-2). 3. While 3H-mannitol flux increased 3.8-fold and 3H-lactulose flux increased 2.6-fold, the flux of 3H-polyethylene glycol 4000 remained unchanged. Hence, the higher permeability was limited to molecules < 4000 Da. 4. The local epithelial conductivity was higher at the sites of apoptosis than in non-apoptotic areas. With camptothecin the leaks associated with apoptosis became more numerous and more conductive, while in non-apoptotic areas the conductivity remained at control level. Hence, the camptothecin-induced increase in epithelial conductivity reflected the opening of apoptotic leaks and thus the results described, for the first time, epithelial permeability as a function of apoptosis only. 5. The conductivity of apoptotic leaks contributed 5.5 % to the epithelial conductivity of controls and 60 % to the conductivity of monolayers treated with 20 microg ml(-1) of camptothecin. Thus apoptosis increased the contribution of paracellular pathways to the overall epithelial permeability. Under control conditions the paracellular conductivity (G(para)) was smaller than the transcellular (G(trans)), but with 12 % apoptosis, G(para) exceeded G(trans). By definition, the epithelium became 'leaky'.

Molecular and cellular biology of small-bowel mucosa

Study of the molecular and cellular biology of the small-intestinal mucosa is providing insights into the remarkable properties of this unique tissue. With its structured pattern of cell proliferation, differentiation, and apoptosis, and its ability to adapt following exposure to luminal nutrients or injury from surgery or pathogens, it functions in a regulated but responsive manner. We review recent publications on factors affecting development, gene expression, cell turnover, and adaptation.