Inhibition of Gliadin Digestion by Green Tea Polyphenols and the Potential Implications for Celiac Disease

Abstract

Green tea has been suggested to have beneficial effects on human health through a variety of biological mechanisms. (−)‐Epigallocatechin‐3‐gallate (EGCG), the major phenolic constituent of green tea, has been reported to mitigate a number of inflammatory and hypersensitivity disorders in laboratory models, and has been shown to moderate pathways related to food allergies in vitro. Previous studies by our group have characterized interactions between EGCG and a2‐gliadin (amino acids 57–89), an immunodominant peptide associated with stimulation of the immune response in celiac disease, and have demonstrated that this polyphenol is able to form complexes with proline‐rich immunostimulatory epitopes on the peptide. Here, we sought to determine the impact of decaffeinated green tea extract (GTE) on the digestion of gliadin protein and production of smaller immunostimulatory peptides in vitro. Complexation of GTE and gliadin was confirmed via an increase in turbidity as a result of co‐precipitation upon titration of GTE into a gliadin solution. Co‐precipitation was observed again during in vitro digestion when gliadin was exposed to digestive proteases pepsin and trypsin. SDS‐PAGE of post‐digestion suspensions and supernatants revealed that GTE not only precipitated gliadin from solution, but also impeded the hydrolytic activity of pepsin and trypsin, resulting in decreased production of low molecular weight gliadin digestion products. An enzyme inhibition assay revealed the GTE dose‐dependently inhibits trypsin (IC50 = 113 mg/ml) in an uncompetitive manner with regard to substrate concentration. Ongoing studies are focused on determining the inhibitory effect of GTE against pepsin, and characterizing the effects of GTE on the immunogenic properties of gliadin using a cell‐culture based model of intestinal permeability and inflammation. We expect that the sequestration of gliadin via GTE complexation will result in decreased permeability and inflammation. Our results to date provide further support for the potential beneficial effects of GTE in the context of celiac disease.Support or Funding InformationThis project was supported by a National Institute of Food and Agriculture Predoctoral Fellowship awarded to C.V. under Grant no. 2016‐67011‐24702, USDA Agriculture and Food Research Initiative.