Abstract
Celiac disease (CD) is an autoimmune enteropathy caused by an intolerance to gluten proteins. It has been hypothesized that probiotic bacteria may exert beneficial effects by modulating inflammatory processes and by sustaining peptide hydrolysis at the intestinal level. This study aims at evaluating the capacity of a probiotic mixture (two different strains of lactobacilli and three of bifidobacteria) to hydrolyze gluten peptides following simulated gastrointestinal digestion of gliadin (PT-gliadin). The capacity of bacterial hydrolysates to counteract the toxic effects of gliadin-derived peptides in Caco-2 cells was also assessed. The protein and peptide mixtures, untreated or proteolyzed with the probiotic preparation, were analyzed before and after each proteolytic step with different techniques (SDS-PAGE, reverse phase HPLC, filtration on different molecular cut-off membranes). These experiments demonstrated that PT-gliadin can be further digested by bacteria into lower molecular weight peptides. PT-gliadin, untreated or digested with the probiotics, was then used to evaluate oxidative stress, IL-6 cytokine production and expression of tight junctions’ proteins—such as occludin and zonulin—in Caco-2 cells. PT-gliadin induced IL-6 production and modulation and redistribution of zonulin and occludin, while digestion with the probiotic strains reversed these effects. Our data indicate that this probiotic mixture may exert a protective role in CD.
Highlights
Gliadin, a major component of the gluten, comprises a class of prolamines produced by plants of the Triticum genus
In order to assess whether the probiotic mixture was able to further proteolyze gliadin after a first enzymatic digestion by a combination of pepsin and trypsin (PT) or by chymotrypsin alone, various analytical methods were set up
Our results show that untreated Caco-2 monolayers had the typical ZO-1 and occludin localization at the cell periphery [19], whereas the treatment with PT-gliadin for 3 h induces a marked reduction of ZO-1 fluorescence and a redistribution at the cytosolic level for occludin
Summary
A major component of the gluten, comprises a class of prolamines produced by plants of the Triticum genus. Gliadin is responsible for the intestinal damage in celiac disease (CD), an autoimmune disease mediated by T-cell activation in the gastrointestinal mucosa [1]. This disease arises in genetically predisposed individuals after exposure to digested gluten. The immunogenic part of gluten, are poorly degraded by the enzymes of the gastrointestinal tract. Several gliadin epitopes show different immunogenic and toxic properties. These epitopes present multiple proline and glutamine residues that give rise to resistance to proteolysis by gastric, pancreatic and intestinal proteases.
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