Pharmacotherapy and management strategies for coeliac disease

In vivo assessment of a delayed release formulation of larazotide acetate indicated for celiac disease using a porcine model

There is no FDA approved therapy for the treatment of celiac disease (CeD), aside from avoidance of dietary gluten. Larazotide acetate (LA) is a first in class oral peptide developed as a tight junction regulator, which is a lead candidate for management of CeD. A delayed release formulation was tested in vitro and predicted release in the mid duodenum and jejunum, the target site of CeD. The aim of this study was to follow the concentration versus time profile of orally administered LA in the small intestine using a porcine model. A sensitive liquid chromatography/tandem mass spectrometry method was developed to quantify LA concentrations in porcine intestinal fluid samples. Oral dosing of LA (1 mg total) in overnight fasted pigs resulted in time dependent appearance of LA in the distal duodenum and proximal jejunum. Peak LA concentrations (0.32–1.76 μM) occurred at 1 hour in the duodenum and in proximal jejunum following oral dosing, with the continued presence of LA (0.02–0.47 μM) in the distal duodenum and in proximal jejunum (0.00–0.43 μM) from 2 to 4 hours following oral dosing. The data shows that LA is available in detectable concentrations at the site of CeD.

Current and emerging therapy for celiac disease

At present, strict and lifelong gluten-free diet is the only effective treatment for celiac disease. Even small amounts of gluten (50 mg/day) can be immunogenic; therefore all food and food items and drugs that contain gluten and its derivatives must be eliminated completely from the diet. While prescribing gluten-free diet is easy; the key to the success is the dietary counseling by a nutrition specialist and maintenance of adherence to GFD by the patient. In recent times, a number of targets to halt the process of immunological injury have been explored to find out alternative treatment for celiac disease. These targets include exploration of ancient wheat if they are less immunogenic, intra-luminal digestion of gluten using prolylendopeptidases, pretreatment of whole gluten with bacterial-derived peptidase before ingestion; prevention of passage of immunogenic peptides through the tight junctions such as zonulin antagonists, Blocking of HLA-DQ2 to prevent binding of immunogenic peptides, inhibition of transglutaminase 2, immune-modulation, and induction of tolerance to gluten using gluten tolerizing vaccines, use of gluten-sequestering polymers, use of anti-inflammatory drugs (glucocorticoids, budesonides) and anti-cytokines such as anti TNF-α, and anti-interleukin-15. While many of these targets are still in the pre-clinical phase, some of them including zonulin antagonist and endopeptidases have already reached phase II and phase III clinical trials. Furthermore, while these targets appear very exciting; they at best are likely to be used as adjunctive therapy rather than a complete replacement for gluten-free diet.

Modern diagnosis of celiac disease and relevant differential diagnoses in the case of cereal intolerance

At an incidence of 1:500, celiac disease (formerly sprue) is an important differential diagnosis in patients with malabsorption, abdominal discomfort, diarrhea and food intolerances. Celiac disease can induce a broad spectrum of both gastrointestinal and extraintestinal symptoms, e.g. dermatitis herpetiformis (Duhring's disease). A variety of oligo- and asymptomatic courses (e.g. anemia, osteoporosis, depression) through to refractory collagenic celiac disease are seen. In HLA-DQ2 and -8 predisposed individuals, celiac disease is provoked by contact with wheat gliadin fractions through a predominantly Th1 immune response and an accompanying Th2 response, which can eventually lead to villous atrophy. Using appropriate serological tests (IgA antibodies against tissue-transglutaminase, endomysium and deamidated gliadin peptides) under sufficient gluten ingestion, the diagnosis can be made more reliably today than previously. The same IgG-based serological tests should be used in the case of IgA deficiency. Diagnosis can either be made in children and adolescents with anti-transglutaminase titers exceeding ten times the standard for two of the above-mentioned serological markers and HLA conformity or it is made by endoscopy and histological Marsh classification in adults and in cases of inconclusive serology. If clinically tolerated, gluten challenges are indicated in patients that already have reduced gluten intake, in borderline serological results, discordance between serological and histological results or in suspected food allergy. The diagnosis of celiac disease needs to be definitive and robust before establishing a gluten-free diet, since lifelong abstention from gluten (gliadin < 20 mg/kg foodstuffs), cereal products (wheat, rye, barley and spelt) as well as from preparations and beverages containing gluten, is necessary. With effective elimination of gluten, the prognosis regarding complete resolution of small bowel inflammation is good. Refractory courses are seen only in rare cases, accompanied by enteropathy-associated T-cell lymphoma.

Celiac disease: prevalence, diagnosis, pathogenesis and treatment

Celiac disease (CD) is one of the most common diseases, resulting from both environmental (gluten) and genetic factors [human leukocyte antigen (HLA) and non-HLA genes]. The prevalence of CD has been estimated to approximate 0.5%-1% in different parts of the world. However, the population with diabetes, autoimmune disorder or relatives of CD individuals have even higher risk for the development of CD, at least in part, because of shared HLA typing. Gliadin gains access to the basal surface of the epithelium, and interact directly with the immune system, via both trans- and para-cellular routes. From a diagnostic perspective, symptoms may be viewed as either "typical" or "atypical". In both positive serological screening results suggestive of CD, should lead to small bowel biopsy followed by a favourable clinical and serological response to the gluten-free diet (GFD) to confirm the diagnosis. Positive anti-tissue transglutaminase antibody or anti-endomysial antibody during the clinical course helps to confirm the diagnosis of CD because of their over 99% specificities when small bowel villous atrophy is present on biopsy. Currently, the only treatment available for CD individuals is a strict life-long GFD. A greater understanding of the pathogenesis of CD allows alternative future CD treatments to hydrolyse toxic gliadin peptide, prevent toxic gliadin peptide absorption, blockage of selective deamidation of specific glutamine residues by tissue, restore immune tolerance towards gluten, modulation of immune response to dietary gliadin, and restoration of intestinal architecture.

Recent advances in the development of new treatments for celiac disease

INTRODUCTION

Celiac disease is a common autoimmune condition induced by dietary gluten in genetically susceptible individuals. So far, the only available treatment for the disorder is a lifelong strict gluten-free diet, because of which small intestinal histological changes recover and symptoms disappear. However, gluten-free dieting is restrictive, and nutritionally less than optimal, and gluten is difficult to avoid.

AREAS COVERED

With improving insight into the pathogenesis of celiac disease, several possible drug targets have been suggested. The new strategies include degradation of gluten intraluminally, reduction of mucosal permeability, inhibition of the transglutaminase 2 enzyme, blocking antigen presentation by HLA-DQ2 or HLA-DQ8, modulation of the immune responses of many cytokines, and vaccination.

EXPERT OPINION

Non-dietary treatment options are warranted either as adjunctive therapy together with dieting or to replace the gluten-free diet. The key question is whether the envisaged novel drug is able to prevent gluten-induced small intestinal mucosal injury as efficiently as a strict gluten-free diet, alleviating symptoms and signs of the disease. Furthermore, the gluten dose that can be detoxified, if at all, must be established. The new drug should also be as safe as dietary treatment. Several novel treatment options are under development.

Non-dietary therapeutic clinical trials in coeliac disease

Coeliac disease is a permanent immunological intolerance to gluten proteins in genetically predisposed individuals. The only management is life-long strict adherence to a gluten-free diet. Unfortunately, compliance with gluten-free diet is very difficult in practice due to the widespread presence of gluten in Western diets. For this reason, about 50% of coeliacs following a gluten-free diet continue to suffer from symptoms and present with autoantibodies and/or villous atrophy while on a gluten-free diet. It is therefore important to explore new therapies to improve the management of coeliac disease. To date, five experimental therapies have been tested in randomized and controlled clinical trials. Larazotide acetate reduces the para-cellular passage of gluten to the lamina propria by preventing the opening of intercellular tight junctions. The endopeptidases ALV003 and AN-PEP break down gluten to produce less or non-toxic peptide fragments. A therapeutic vaccine is being tested with the aim of developing gluten tolerance. Finally, infection with the nematode Necator americanus and treatment with the CCR9 antagonist Traficet-EN have also been reported. While substantial progress has been made in the last few years, it is important to remember that all these investigational therapies are in research stage and are generally being considered as "adjunctive" therapies to the gluten-free diet and not as substitutes of the gluten-free diet at this point in time.