Detoxified flours for CD

Pathogenesis of celiac disease :

Celiac disease (CD), also known as Celiac Sprue or gluten-sensitive enteropathy, is the most common food-sensitive enteropathy in humans. The prevalence is estimated in the range of 1:100-1:300 in North America and Europe.

The mucosal lesion is localised in the proximal part of the small intestine and it is characterised by villous atrophy, crypt cell hyperplasia and lymphocytic infiltration. Environmental, genetic and immunologic factors are involved in the pathogenesis of CD. The environmental factors are very well characterised. CD is the consequence of the absence of oral tolerance to gliadins and glutenins, the two major protein fractions of wheat gluten, together with the prolamin fraction of rye and barley. The toxicity of prolamins from oats remain questionable as only in a small fraction of patients activate CD. The role of genetic factors is also fundamental. CD results strongly associated with HLA class II genes that encode for the DQ2 heterodimer (90-95% of CD patients) and. DQ8 (5-10%). The HLA-DQ2 and –DQ8 alleles are relatively common in white population. So, their presence is a necessary condition, although non sufficient, for the expression of CD. Extensive research for additional genes linked to CD is ongoing.
The HLA association explains the involvement of the immune system in the pathogenesis of the disease. In fact, the inappropriate T-cell activation, commonly observed in CD, is triggered by specific gluten peptides bound to DQ2 and DQ8 heterodimers on the surface of antigen presenting cells. The mucosal intestinal lesion is believed mainly induced by the production of IFN-γ from these gluten-specific T cells.

The toxic proteins are characterised by a high content in glutamine and prolamine residues. This biochemical peculiarity has been demonstrated to play a key role in the disease. To date, most of identified T-cell gliadin epitopes were recognized following deamidation catalysed by tissue transglutaminase (tTG), in which some specific glutamine residues were converted to glutamic acid. In vitro studies showed that the negative charges introduced by this deamidation process increase the binding affinity of gluten peptides to DQ2 and DQ8 molecules. The presence of proline protects against digestive proteolysis and directs tTG-mediated deamidation of glutamines .

Production of serum antibodies to gliadin and tTG, also termed anti-endomysial antibodies, are associated to CD and represent important diagnostic hallmarks of the disease. Interestingly, gluten seems to drive the antibody production, as the presence of tTG antibodies is strictly dependent on dietary gluten exposure.

The central role of T cells for controlling the immune response to gluten that produces the pathology of CD is well established. It has been suggested that the release of IFN-γ by T cells induce macrophages to produce TNF-&alfa;. TNF-&alfa; activates stromal cells to produce KGF, and KGF causes epithelial proliferation and crypt cells hyperplasia. IFN-γ may be also responsible of activation of matrix metalloproteases by subepithelial fibroblasts, that ultimately cause alteration of the extracellular matrix and enterocyte shedding.

A new enzyme treatment for CD. Transamidation of wheat flour blocks the immune response to gliadin

To date, the only available therapy for CD patients is a strict adherence to a gluten-free diet throughout their life. On the other hand, the recognition that CD is an immune mediated injury has stimulated several studies aimed at recovering oral tolerance to gluten. In particular, on the basis of the above described literature data, a new enzymatic approach has been designed to directly treat flours that are toxic to CD patients. This methodology applies a well characterized food-grade microbial transglutaminase (mTGase), previously known for different industrial applications. Biochemical analysis showed the ability of mTGase to catalyze cross-linking of lysine methyl ester, as amino group donor, to gliadin by carrying out the reaction directly in wheat flour. Notably, gliadin extracted from flour treated with mTGase and lysine methyl ester was found ineffective in inducing IFN-γ expression from intestinal T cells isolated from CD patients.

In terms of food safety of the treatment, it must be emphasized that covalent attachment of amino acids by enzymatic procedures is an accepted means of improving the nutritional quality and functional properties of food proteins. In particular, the occurrence of the isopeptide linkage in protein does not impair the digestibility of the gliadin as the metabolic step of products of transglutaminase action occurs largely in kidney, where the ε-(γ-glutamyl)-lysine (as well as –lysine methyl ester) represents a substrate for γ-glutamylamine cyclotransferase.

 

Bibliography

Sollid LM. Coeliac disease: dissecting a complex inflammatory disorder. Nat Rev Immunol 2002;2:647-655. Nilsen E, Jahnsen FL, Lundin KE, Johansen FE, Fausa O, Sollid LM, Jahnsen J, Scott H, Brandtzaeg P. Gluten induces an intestinal cytokine response strongly dominated by interferon gamma in patients with celiac disease. Gastroenterology 1998;115:551-563. Molberg O, McAdam SN, Korner R, Quarsten H, Kristiansen C, Madsen L, Fugger L, Scott H, Noren O, Roepstorff P, Lundin KE, Sjostrom H, Sollid LM. Tissue transglutaminase selectively modifies gliadin peptides that are recognized by gut-derived T cells in celiac disease. Nat Med 1998;4:713-717. Shan L, Molberg O, Parrot I, Hausch F, Filiz F, Gray GM, Sollid LM, Khosla C. Structural basis for gluten intolerance in celiac sprue. Science 2002;297:2275-2279. Costantini S, Rossi M, Colonna G, Facchiano AM. Modelling of HLA-DQ2 and its interaction with gluten peptides to explain molecular recognition in celiac disease. J Mol Graph Model 2005;23:419-431. Rossi M, Maurano F, Luongo D. Immunomodulatory strategies for celiac disease. Int Rev Immunol 2005;24:479-499. Gianfrani C, Siciliano RA, Facchiano AM, Camarca A, Mazzeo MF, Costantini S, Salvati VM, Maurano F, Mozzarella G, Iaquinto G, Rossi M. Transamidation inhibits the intestinal immune response to gliadin in vitro. Gastroenterology 2007;133:780-789. Iwami K, Yasumoto K. Amine-binding capacities of food proteins in transglutaminase reaction and digestibility of wheat gliadin with???-attached lysine. J Sci Food Agric 1986;37:495-503.