The Role of Gluten in the Pathogenesis of Type 1 Diabetes Mellitus and Crohn Disease

The role of gluten is well known in the pathogenesis of coeliac disase,as its trigger factor. Gluten is characterized by its high content of prolin and glutamin, and after their digestion even by the normal small intestinal mucosa long polypeptides remain, which are able to increase the permeability of even normal intestinal mucosa through their ability to release zonulin. It can be stated, that gluten could have a dose-dependent detrimental effect on the gut barrier, primarily in the small intestine even without coeliac disease. This effect of gluten raises the possibility its pathogenetic role of other diseases in addition to coeliac disease, first of all in type 1 diabetes mellitus (T1DM) and Crohn disease (CD). Our earlier observation that in the jejunal mucosa of children with T1DM signs of immune activation are observed could have been the consequence of increased intestinal permeability. In this study the patients had significantly more α4/β7 integrin positive cells in the lamina propria compared to controls. This observation is highly relevant, because T-cells from humans diabetic pancreas with T1DM express the gut-associated homing receptor α4/β7 integrin. The pathogenetic role of gluten in induction of T1DM is indicated also by the frequent association of T1DM and coeliac disease and it was observed that in the majority of cases the onset of T1DM is earlier than that of coeliac disease, when the patient is not on a gluten free diet. According to several studies it is probable that beside characteristic genetic traits mostly the diet influences the development of CD. The prevalance of CD is on the rise in developed countries exposed to Western diet. This is also indicated by the very efficient therapeutical results of exclusive enteral nutrition (EEN) in CD. Pediatric studies confirmed that 70-90% of children fed an exclusive liquid formula and no exposure to other food, reach a complete remission. The effect of formula is not depend on its composition or the degree of hydrolysis of its protein (elemental or polymer formula). Therefore, the EEN may have its effect principally that it does not contain those compounds which are frequently occur in the normal diet, it is also gluten free. Increased gut permeability caused by gluten may be the primary factor triggering CD. On the base of the above mentioned fact it is probable that gluten may play a decisive role in the pathogenesis of type 1 diabetes mellitus (T1DM) and of Crohn’s disease (CD). Introduction The triggering role of gluten in the development and maintaining the pathological process in coeliac disease was proved more than sixty years ago by Dicke. His discovery made possible the treatment of this disorder with gluten free diet. Gluten is a storage protein with high viscoelastic properties and so it is an essential ingredient for making a high quality dough. Therefore gluten is one of the most commonly used proteins in the food industry. Its toxic component triggering coeliac disease is the ethanol soluble gliadin, which belongs to the prolamins. The related prolamins in rye and barley called secalin and hordein, which are also toxic in patients with coeliac disease (CeD). These prolamins protein are different from other cereals’ storage proteins insofar as they have a higher proportions of glutamine and proline, which make them resistant to enzymatic processing in the intestine. It was showed that even beside prolonged in vitro digestion with gastric, pancreatic and brush border enzymes, a 33-mer peptide survived, which is toxic in coeliac disease. Fasano et al identified a human protein named zonulin which induces tight junction disassembly and consequently an increase in intestinal permeability. They also detected that the concentration of this protein is increased in the intestinal mucosa of patients with active CeD. Later they also proved that gliadin induces a direct increase in small intestinal permeability by binding to the chemokine receptor CXCR3 expressed in the intetinal epithelium, which elicit MyD88dependent zonulin release. When biopsies taken from non-coeliac controls were exposed to gliadin a transient zonulin release was observed with an increase of intestinal permeability, which was less than in biopsy taken from active coeliac patients. It can be stated, that consumption of gluten could have a dose-dependent detrimental effect on the gut barrier, primarily in the small intestine even without coeliac disease. On the base of undermentioned fact it is very probable that gluten may play a decisive role in the pathogenesis of type 1 diabetes mellitus (T1DM) and of Crohn’s disease (CD). JURNALUL PEDIATRULUI – Year XVIII, Vol. XVIII, Supplement 3, 2015 56 T1DM It has been recognised for decades that coeliac disease occurs with a greater than expected frequency in patients with T1DM. According to screening studies the prevalence of CeD ranges between 1,3% and 16,4%. In our previous study we found among 205 diabetic children 17 cases with CeD (8,3%). The increased association of CeD and T1DM is probably due to a common genetic prediposition, approximately 95% ofpatients with CeD express HLA-DQ2, which is also apositive risk factor for T1DM. In our study, patients with T1DM and those with CDand T1DM, the occurrence of HLA-DQ2/8 heterozygosity was significantly higher than in children with CD only and in control children. In the majority of cases in children with T1DM and CeD, CeD starts later than the diabetes. In our series of 51 children with both T1DM and CeD in 45 T1DM started earlier than CeD. The median of elapsed time from the onset of T1DM to CeD was 21 months, when T1DM started under 5 year, while with onset of T1DM over 5 years the median was 3 months. Sapone et al detected that serum zonulin levels was higher in adult patients with T1DM, as compared with agematched controls. It was also observed in their study that the increased zonulin levels correlated with increased intestinal permeability in vivo examined with lactulose/mannitol (L/M) test. In a pilot study it was also recognized that expression from the intestinal tight junction proteins claudin-1 was increased, while that of claudin-2 decreased. Zonulin levels were also moderately elevated in a group of individuals with risk of T1DM, who had elevated autoantibodies. In this latter group no change in the expression of tight junction genes was observed, which indicate that zonulin upregulation precedes the onset of T1DM. In our study investigating claudin expression in the duodenal mucosa of patients with active CeD, increased expression of claudin 2 and 3 was observed compared to the controls. Our earlier observation that in the jejunal mucosa of children with T1DM signs of immune activation are observed could have been the consequence of increased intestinal permeability. In this study the patients had significantly more α4/β7 integrin positive cells in the lamina propria compared to controls. This observation is highly relevant, because in T-cells from humans diabetic pancreas with T1DM T-cells express the gut-associated homing receptor α4/β7 integrin. It was also observed that gliadin stimulated peripheral blood blood mononuclear cell of patients with T1DM without coeliac disease showed a mixed proinflammatory Th1 and Th17 activation. It is also known that in non-obese diabetic mice gluten-free diet significantly reduces the incidence of T1DM. Recently it was also observed that the gut microbial flora is also changed on gluten-free diet, Akkermansia species was increased, which suggests that dietary gluten could modulate the incidence of T1DM by changing the gut microbiome. In isolated rat islets it was also detected that gliadin digest and the specific 33-mer protein from the gliadin increase the insulin secretion compared to the controls. Gliadin peptides are closing the KATP channels, hereby inducing insulin secretion and so gliadin may contribute to the beta-cell hyperactivity observed prior to the development of T1DM. A recently reported new observation indicates that gluten may contribute even to the development of diabetic nephropathy in children with T1DM. It was found that children with T1DM and CeD on a strict gluten free diet has slower progression in albuminuria over five years of follow-up than children with T1DM alone. It is possible to speculate that gluten-free diet confers renoprotection in T1DM. Crohn’s disease According to studies up to present it is probable that beside characteristic genetic traits mostly the diet influences the development of CD. It is obvious that the prevalance of CD is on the rise in developed countries exposed to Western diet. This is also indicated by the very efficient therapeutical results of exclusive enteral nutrition (EEN) in CD. Several pediatric studies confirmed that 70-90% of children fed an exclusive liquid formula and no exposure to other food, reach a complete remission. In a recent study Levine et al. prospectively evaluating 150 new-onset, untreated children with CD did not find difference between corticosteroid and EEN in achieving clinical remission and what is more EEN was significantly superior to corticosteroids for achieving mucosal healing (deep remission). The effect of formula is not depend on its composition or the degree of hydrolysis of its protein (elemental or polymer formula). Therefore, this diet may have its effect principally that it does not contain those compounds which are frequently occur in processed foods, which could damage the intestinal mucosa increasing the bacterial translocation. Avoiding such components in the diet may prevent the development of CD. Such components in the regular diet are sodium caprate, carboxymethylcellulose, plysorbate 80 and gliadin. As was mentioned earlier gluten can increase the intestinal permeability and one of the constant features in CD is an increase of intestinal permeability that can precede inflammatory lesions and trigger mucosal inflammation. Impairment in the function of the intestinal barrier leads to increased permeability to luminal antigens and bacterial translocation. Pathogen associated molecular patterns of intestinal bacteria interact with pattern recognition receptors, including toll-like receptors (TLRs), which are important component of innate immunity. In our previous study supported we demonstrated that TLR2 and TLR4 mRNA expression and protein levels were higher in the inflamed colonic mucosa of children with freshly diagnosed and relapsed CD compared to the controls, while in the non inflamed colonic mucosa TLR2 and TLR4 expression and protein levels were similar to controls. TLR ligands promote epithelial regeneration in a lower dose, while in a higher dose they have growth-suppressive effects.TLRs in a higher dose promote also fibrogenesis and wound healing with scarring. Increased fibrosis leads to a faster wound closure which is advantageous in the short run, but it can cause long-term problems. JURNALUL PEDIATRULUI – Year XVIII, Vol. XVIII, Supplement 3, 2015 57 Conclusions Proving the role of gluten in the pathogenesis of T1DM would give the possibility the primary prevention of this disorder especially in the first degree relatives of the patients. Putting of these individuals on a gluten-free diet the development of T1DM could be prevented. As it was previously mentioned in our preliminary study we found that the onset of CeD is much more frequent after the onset of T1DM, as vice versa. This is an indirect evidence that gluten free diet mayprevent the development of T1DM.Establishing the role of gluten also in the development in diabetic nephropathy would give the possibility to preventthis complication with a gluten free diet even with patients with T1DM in whom coeliac disease is not detected.Proving the role of gluten in the increase of intestinal permeability of Crohn disease may help to prevent the development ofovert disease by introduction of a gluten free diet. Proving such an effect of gluten, we would get an explanation of the effectof EEN. As all formula used for EEN are gluten free, its effect could be explain that with this therapy the gluten exposition isavoided. References1. Köning F. 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