The human digestive tract has proteases capable of gluten hydrolysis

OBJECTIVE

To identify, purify, and characterize the proteins responsible for glutenase activity in the feces of healthy subjects and patients with celiac disease (CD).

METHODS

Sixteen subjects were included in this study; 8 were healthy with no known food intolerances, and 8 were treated CD patients on a gluten-free diet. Fecal samples were homogenized, and precipitated proteins were purified by chromatography. Glutenase activity was evaluated by bioassays, zymography, and high-performance liquid chromatography with immunogenic 33-mer, 19-mer, and 13-mer gliadin peptides.

RESULTS

The gastrointestinal elastase 3B (CEL3B), elastase 2A (CEL2A), and carboxypeptidase A1 (CBPA1) enzymes degraded human gluten. These proteins fully hydrolyzed 13-mer and 19-mer gliadin peptides that trigger immune-mediated enteropathy in individuals genetically predisposed to CD and partially digested a 33-mer. Feces from patients with CD showed more glutenase activity than feces from individuals without CD (171-466% higher). Peptidase activity against the gliadin peptides also increased in patients with CD.

CONCLUSION

The digestive tracts of patients with CD and healthy subjects have enzymatic machinery needed for gluten degradation. Patients with CD showed more gluten hydrolysis than did healthy individuals, although, in both cases, a fraction of 33-mer peptide remained intact. Gliadin peptides derived from gastrointestinal digestion, especially the 33-mer, can potentially be used by commensal microbiota from both CD-positive and CD-negative individuals, and differences in bacterial hydrolysis can modify its immunogenic capacity.