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      A Food-Grade Enzyme Preparation with Modest Gluten Detoxification Properties

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          Abstract

          Background and Aims

          Celiac sprue is a life-long disease characterized by an intestinal inflammatory response to dietary gluten. A gluten-free diet is an effective treatment for most patients, but accidental ingestion of gluten is common, leading to incomplete recovery or relapse. Food-grade proteases capable of detoxifying moderate quantities of dietary gluten could mitigate this problem.

          Methods

          We evaluated the gluten detoxification properties of two food-grade enzymes, aspergillopepsin (ASP) from Aspergillus niger and dipeptidyl peptidase IV (DPPIV) from Aspergillus oryzae. The ability of each enzyme to hydrolyze gluten was tested against synthetic gluten peptides, a recombinant gluten protein, and simulated gastric digests of whole gluten and whole-wheat bread. Reaction products were analyzed by mass spectrometry, HPLC, ELISA with a monoclonal antibody that recognizes an immunodominant gluten epitope, and a T cell proliferation assay.

          Results

          ASP markedly enhanced gluten digestion relative to pepsin, and cleaved recombinant α2-gliadin at multiple sites in a non-specific manner. When used alone, neither ASP nor DPPIV efficiently cleaved synthetic immunotoxic gluten peptides. This lack of specificity for gluten was especially evident in the presence of casein, a competing dietary protein. However, supplementation of ASP with DPPIV enabled detoxification of moderate amounts of gluten in the presence of excess casein and in whole-wheat bread. ASP was also effective at enhancing the gluten-detoxifying efficacy of cysteine endoprotease EP-B2 under simulated gastric conditions.

          Conclusions

          Clinical studies are warranted to evaluate whether a fixed dose ratio combination of ASP and DPPIV can provide near-term relief for celiac patients suffering from inadvertent gluten exposure. Due to its markedly greater hydrolytic activity against gluten than endogenous pepsin, food-grade ASP may also augment the activity of therapeutically relevant doses of glutenases such as EP-B2 and certain prolyl endopeptidases.

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          Most cited references 17

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          Identification and analysis of multivalent proteolytically resistant peptides from gluten: implications for celiac sprue.

          Dietary gluten proteins from wheat, rye, and barley are the primary triggers for the immuno-pathogenesis of Celiac Sprue, a widespread immune disease of the small intestine. Recent molecular and structural analyses of representative gluten proteins, most notably alpha- and gamma-gliadin proteins from wheat, have improved our understanding of these pathogenic mechanisms. In particular, based on the properties of a 33-mer peptide, generated from alpha-gliadin under physiological conditions, a link between digestive resistance and inflammatory character of gluten has been proposed. Here, we report three lines of investigation in support of this hypothesis. First, biochemical and immunological analysis of deletion mutants of alpha-2 gliadin confirmed that the DQ2 restricted T cell response to the alpha-2 gliadin are directed toward the epitopes clustered within the 33-mer. Second, proteolytic analysis of a representative gamma-gliadin led to the identification of another multivalent 26-mer peptide that was also resistant to further gastric, pancreatic and intestinal brush border degradation, and was a good substrate of human transglutaminase 2 (TG2). Analogous to the 33-mer, the synthetic 26-mer peptide displayed markedly enhanced T cell antigenicity compared to monovalent control peptides. Finally, in silico analysis of the gluten proteome led to the identification of at least 60 putative peptides that share the common characteristics of the 33-mer and the 26-mer peptides. Together, these results highlight the pivotal role of physiologically generated, proteolytically stable, TG2-reactive, multivalent peptides in the immune response to dietary gluten in Celiac Sprue patients. Prolyl endopeptidase treatment was shown to abolish the antigenicity of both the 33-mer and the 26-mer peptides, and was also predicted to have comparable effects on other proline-rich putatively immunotoxic peptides identified from other polypeptides within the gluten proteome.
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            Etiology of nonresponsive celiac disease: results of a systematic approach.

            Nonresponse or relapse of symptoms is common in patients with celiac disease treated with gluten free diet. Refractory sprue (RS) is defined as initial or subsequent failure of a strict gluten-free diet to restore normal intestinal architecture and function in patients who have celiac-like enteropathy. The aims of this study were: 1) to identify causes of persistent symptoms in patients referred with presumed diagnosis of nonresponsive celiac disease (NCD); and 2) to characterize patients with true RS. Patients were identified who had been systematically evaluated for NCD between January 1997, and May 2001. Patient records and small bowel biopsy results were reviewed. A total of 55 patients were referred with a presumed diagnosis of NCD. Six did not have celiac disease and had other diseases responsible for their symptoms. Diarrhea, abdominal pain, and weight loss were the most common reasons for evaluation in cases of NCD, whereas weight loss, steatorrhea, and diarrhea were the most common presenting features of RS (nine patients). Of the 49 patients with celiac disease, 25 were identified as having gluten contamination. Additional diagnoses accounting for persistent symptoms included: pancreatic insufficiency, irritable bowel syndrome, bacterial overgrowth, lymphocytic colitis, collagenous colitis, ulcerative jejunitis, T-cell lymphoma, pancreatic cancer, fructose intolerance, protein losing enteropathy, cavitating lymphadenopathy syndrome, and tropical sprue. Based on this study, we conclude the following: 1) gluten contamination is the leading reason for NCD; 2) of NCD cases, 18% are due to RS; and 3) alternative diseases or those coexistent with celiac disease and gluten contamination should be ruled out before a diagnosis of RS is made.
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              Intestinal digestive resistance of immunodominant gliadin peptides.

              Two recently identified immunodominant epitopes from alpha-gliadin account for most of the stimulatory activity of dietary gluten on intestinal and peripheral T lymphocytes in patients with celiac sprue. The proteolytic kinetics of peptides containing these epitopes were analyzed in vitro using soluble proteases from bovine and porcine pancreas and brush-border membrane vesicles from adult rat intestine. We showed that these proline-glutamine-rich epitopes are exceptionally resistant to enzymatic processing. Moreover, as estimated from the residual peptide structure and confirmed by exogenous peptidase supplementation, dipeptidyl peptidase IV and dipeptidyl carboxypeptidase I were identified as the rate-limiting enzymes in the digestive breakdown of these peptides. A similar conclusion also emerged from analogous studies with brush-border membrane from a human intestinal biopsy. Supplementation of rat brush-border membrane with trace quantities of a bacterial prolyl endopeptidase led to the rapid destruction of the immunodominant epitopes in these peptides. These results suggest a possible enzyme therapy strategy for celiac sprue, for which the only current therapeutic option is strict exclusion of gluten-containing food.
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                Author and article information

                Contributors
                Role: Editor
                Journal
                PLoS One
                plos
                plosone
                PLoS ONE
                Public Library of Science (San Francisco, USA )
                1932-6203
                2009
                21 July 2009
                : 4
                : 7
                Affiliations
                [1 ]Department of Chemical Engineering, Stanford University, Stanford, California, United States of America
                [2 ]Department of Chemistry, Stanford University, Stanford, California, United States of America
                [3 ]Department of Biochemistry, Stanford University, Stanford, California, United States of America
                [4 ]Department of Medicine, Stanford University, Stanford, California, United States of America
                Cairo University, Egypt
                Author notes

                Conceived and designed the experiments: JE BM EM MTB GMG CK. Performed the experiments: JE BM EM. Analyzed the data: JE BM EM MTB GMG CK. Contributed reagents/materials/analysis tools: JE BM EM MTB. Wrote the paper: JE BM MTB GMG CK.

                Article
                09-PONE-RA-09462R1
                10.1371/journal.pone.0006313
                2708912
                19621078
                Ehren et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
                Page count
                Pages: 10
                Categories
                Research Article
                Gastroenterology and Hepatology/Inflammatory Bowel Disease
                Gastroenterology and Hepatology/Small Intestine
                Gastroenterology and Hepatology/Stomach and Duodenum

                Uncategorized

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