Gliadin proteolytical resistant peptides: the interplay between structure and self-assembly in gluten-related disorders

In recent years, the evaluation of the structural properties of food has become of crucial importance in the understanding of food-related disorders. One of the most exciting systems is gliadin, a protein in wheat gluten, that plays a protagonist role in gluten-related disorders with a worldwide prevalence of 5%, including autoimmune celiac disease (CeD) (1%) and non-celiac wheat sensitivity (0.5–13%). It is accepted that gliadin is not fully digested by humans, producing large peptides that reach the gut mucosa. The gliadin peptides cross the lamina propria eliciting different immune responses in susceptible patients. Many clinical and biomedical efforts aim to diagnose and understand gluten-related disorders; meanwhile, the early stages of the inflammatory events remain elusive. Interestingly, although the primary sequence of many gliadin peptides is well known, it was only recently revealed the self-assembly capability of two pathogenic gliadin fragments and their connection to the early stage of diseases. This review is dedicated to the most relevant biophysical characterization of the complex gliadin digest and the two most studied gliadin fragments, the immunodominant 33-mer peptide and the toxic p31-43 in connection with inflammation and innate immune response. Here, we want to emphasize that combining different biophysical methods with cellular and in vivo models is of key importance to get an integrative understanding of a complex biological problem, as discussed here.

The Gluten-Free Diet: Use in Digestive Disease Management

PURPOSE OF REVIEW

Gluten is a commonly ingested polymeric protein found in wheat, barley, and rye that has gained recent notoriety because of its relationship to disease and health. Avoidance of gluten is appropriate in patients with a diagnosed gluten-related disorder and may have treatment implications in other diseases of the digestive tract. This review highlights current knowledge of gluten related disorders and the use of a gluten-free diet in gastrointestinal disease management.

RECENT FINDINGS

Gluten-free diets should be used in patients with a diagnosed gluten-related disorder including celiac disease, non-celiac gluten sensitivity, and wheat-sensitive eosinophilic esophagitis. Use of this diet in management of other digestive conditions including gastroesophageal reflux disease, irritable bowel syndrome, and inflammatory bowel disease is controversial and not currently supported by the literature. This review provides a framework for classifying gluten-related disorders in terms of pathogenesis, understanding the literature that supports dietary avoidance in modulation of gastrointestinal disease, and identifies limitations of dietary restriction in patients.

Extra-intestinal manifestations of non-celiac gluten sensitivity: An expanding paradigm

Non celiac gluten sensitivity (NCGS) is a syndrome characterized by a cohort of symptoms related to the ingestion of gluten-containing food in subjects who are not affected by celiac disease (CD) or wheat allergy. The possibility of systemic manifestations in this condition has been suggested by some reports. In most cases they are characterized by vague symptoms such as ‘foggy mind’, headache, fatigue, joint and muscle pain, leg or arm numbness even if more specific complaints have been described. NCGS has an immune-related background. Indeed there is a strong evidence that a selective activation of innate immunity may be the trigger for NCGS inflammatory response. The most commonly autoimmune disorders associated to NCGS are Hashimoto thyroiditis, dermatitis herpetiformis, psoriasis and rheumatologic diseases. The predominance of Hashimoto thyroiditis represents an interesting finding, since it has been indirectly confirmed by an Italian study, showing that autoimmune thyroid disease is a risk factor for the evolution towards NCGS in a group of patients with minimal duodenal inflammation. On these bases, an autoimmune stigma in NCGS is strongly supported; it could be a characteristic feature that could help the diagnosis and be simultaneously managed. A possible neurological involvement has been underlined by NCGS association with gluten ataxia, gluten neuropathy and gluten encephalopathy. NCGS patients may show even psychiatric diseases such as depression, anxiety and psychosis. Finally, a link with functional disorders (irritable bowel syndrome and fibromyalgia) is a topic under discussion. In conclusion, the novelty of this matter has generated an expansion of literature data with the unavoidable consequence that some reports are often based on low levels of evidence. Therefore, only studies performed on large samples with the inclusion of control groups will be able to clearly establish whether the large information from the literature regarding extra-intestinal NCGS manifestations could be supported by evidence-based agreements.

Nomenclature and diagnosis of gluten-related disorders: A position statement by the Italian Association of Hospital Gastroenterologists and Endoscopists (AIGO)

BACKGROUND

"Gluten-related disorders" is a term that encompasses different diseases induced by the ingestion of gluten-containing food. Because of their incidence the scientific community has been intensively studying them.

AIM

To support gastroenterologists with a correct nomenclature and diagnostic approach to gluten-related disorders in adulthood.

METHODS

The Italian Association of Hospital Gastroenterologists and Endoscopists (AIGO) commissioned a panel of experts to prepare a position statement clarifying the nomenclature and diagnosis of gluten-related disorders, focusing on those of gastroenterological interest. Each member was assigned a task and levels of evidence/recommendation have been proposed.

RESULTS

The panel identified celiac disease, wheat allergy and non-celiac gluten sensitivity as the gluten-related disorders of gastroenterological interest. Celiac disease has an autoimmune nature, wheat allergy is IgE-mediated while the pathogenesis of non-celiac gluten sensitivity is still unknown as is the case of non-IgE mediated allergy. Diagnosis should start with the serological screening for celiac disease and wheat allergy. In case of normal values, the response to a gluten-free diet should be evaluated and a confirmatory blind food challenge carried out.

CONCLUSIONS

Gluten-related disorders are clinically heterogeneous. Patients should be carefully managed and specific protocols applied for a correct differential diagnosis in gastroenterological setting.

Non-celiac gluten sensitivity: Time for sifting the grain

In the last few years, a new nomenclature has been proposed for the disease induced by the ingestion of gluten, a protein present in wheat, rice, barley and oats. Besides celiac disease and wheat allergy, the most studied forms of gluten-related disorders characterized by an evident immune mechanism (autoimmune in celiac disease and IgE-mediated in wheat allergy), a new entity has been included, apparently not driven by an aberrant immune response: the non-celiac gluten sensitivity (NCGS). NCGS is characterized by a heterogeneous clinical picture with intestinal and extraintestinal symptoms arising after gluten ingestion and rapidly improving after its withdrawal from the diet. The pathogenesis of NCGS is largely unknown, but a mixture of factors such as the stimulation of the innate immune system, the direct cytotoxic effects of gluten, and probably the synergy with other wheat molecules, are clues for the complicated puzzle. In addition, the diagnostic procedures still remain problematic due to the absence of efficient diagnostic markers; thus, diagnosis is based upon the symptomatic response to a gluten-free diet and the recurrence of symptoms after gluten reintroduction with the possibility of an important involvement of a placebo effect. The temporary withdrawal of gluten seems a reasonable therapy, but the timing of gluten reintroduction and the correct patient management approach are have not yet been determined.

Overview of biomarkers for diagnosis and monitoring of celiac disease

Among the adverse reactions caused by wheat, celiac disease (CD) is the longest studied and best-known pathology. The more recently defined non-celiac gluten sensitivity (NCGS) presents with symptoms which are often indistinguishable from CD. Diagnosis of CD is based on serologic, molecular, and bioptic testing. The IgA anti-transglutaminase (tTG) test is considered highly important, as it shows high sensitivity and specificity and its levels correlate to the degree of intestinal damage. Small bowel biopsy can be avoided in symptomatic patients with IgA anti-tTG levels above 10× the manufacturer's cut-off. Recently, tests of anti-deamidated peptides of gliadin (DGP) have replaced classic anti-native gliadin (AGA) tests. DGP assays have a considerably higher diagnostic accuracy than AGA assays, especially in the IgG class, and can replace anti-tTG tests in patients with selective IgA deficiency. The combination of IgG anti-DGP plus IgA anti-tTG assays show greater sensitivity than a single test, with very high specificity. EMA tests have great diagnostic accuracy but are not recommended by all the latest guidelines because they are observer dependent. Biopsy must still be considered the gold standard for CD diagnosis. HLA-DQ genotyping can be used to screen asymptomatic children and in cases of histology/serology disagreement. About half of NCGS patients are DQ2 positive and have IgG AGA. To diagnose NCGS, first CD and wheat allergy must be excluded; then the wheat dependence of symptoms must be verified by a gluten-free diet and subsequent gluten challenge.

Non coeliac gluten sensitivity - A new disease with gluten intolerance

Until recently gluten intolerance has been believed to be typical of celiac disease (CD) and wheat allergy (WA). In the last few years, however, several study results have been published that have proved that gluten intolerance can also affect people who do not suffer from any of the above mentioned diseases. The new syndrome has been named non-celiac gluten sensitivity (NCGS) or gluten sensitivity (GS). It has been included in the new list of gluten-related disorders published in 2012. Researchers believe that NCGS is the most common syndrome of gluten intolerance. This review discusses many aspects of NCGS epidemiology, pathophysiology, clinical spectrum, and treatment and current tools to identify patients suffering from CD, WA, and NCGS.

Advances in research of non-coeliac gluten sensitivity

Non-celiac gluten sensitivity (NCGS) is a newly recognized clinical entity that is characterized by a wide variety of intestinal or extra-intestinal manifestations, and it may be the most common one in the spectrum of gluten-related disorders. The symptoms of NCGS improve or disappear after gluten withdrawal and relapse if gluten is reintroduced. There are no specific serological markers for NCGS although nearly half of patients are positive for antigliadin IgG antibodies. Since small intestinal biopsy is normal, the double-blind, placebo-controlled food challenge (DBPCFC) and an exclusion of wheat allergy or coeliac disease are necessary for diagnosis. The pathogenesis is still unclear although immunology may play a role in its pathogenesis. This review will summarize our current knowledge about non-coeliac gluten sensitivity and outline pathogenic and epidemiological differences between NCGS and coeliac disease.