THE IN VITRO-INFLUENCE OF GLIADIN PEPTIDES ON THE HYDROLASES OF THE DUODENAL BRUSH BORDER MEMBRANE IN COELIAC DISEASE IN REMISSION

Abstract

Aims: The molecular mechanism inducing the mucosal damage in coeliac disease (CD) is still unknown. Gliadin causes villus atrophy in CD, and patients on a gluten-free diet recover completely. On the basis of the organ culture of intestinal biopsies we developed an in vitro-system for CD in remission. We used this model to verify our hypothesis postulating a correlation between the mucosal damage caused by gliadin and the biosynthesis of the intestinal hydrolases. Besides we measured the enzyme activity to prove whether this level is afflicted additionally or alternatively. Methods: Intestinal biopsies from 14 coeliac patients in remission (following a gluten-free diet for at least 2 years) and 23 healthy children (control group) were organ cultured for 24 hours in presence or absence of gliadin peptides. A peptictryptic digest of maize prolamine operated as the non-toxic control. The effect of these additives on the enzyme activity of the disaccharidases was determined by a modificated method of Dahlqvist. The influence on the biosynthesis of several hydrolases (LPH, SI, MGA, ACE, APN, DPP IV) was studied by biosynthetical protein-labelling during organ culture, followed by immunoprecipitation, SDS-PAGE, autoradiography and quantified by densitometric scanning. Results: In our model we demonstrated a rapid and specific gliadin-induced reduction of the biosynthesis of all studied hydrolases in biopsies from coeliac patients on gluten-free diet. This phenomenon was neither seen after incubation with maize prolamine nor in healthy children. We could not show an effect of gliadin on the disaccharidase activities after 24 hours of incubation. Because of beginning necrosis in the biopsies a longer incubation was not possible, so we were not able to examine later effects. Conclusions: Our model is suitable for studying the in vitro-situation of CD in remission. Moreover, our results indicate a fast effect of gliadin peptides on inhibiting the biosynthesis of hydrolases of duodenal brush border membranes. It remains unclear whether the gliadin-induced reduction primarily influences the protein biosynthesis or has to be interpreted as a secondary effect of an impaired mRNA synthesis. We suppose that the effect occurs at the translational or transcriptional level. The early modifications within 24 hours of incubation are hardly to explain by activities of the immune system. More likely the results suggest a toxic effect of gliadin peptides on the intestinal mucosa preceeding immunological changes mediated by cytokines.