Effect of Barley Endoprotease EP-B2 on Gluten Digestion in the Intact Rat

Potential therapeutic options for celiac Disease: An update on Current evidence from Gluten-Free diet to cell therapy

Celiac disease (CD) is a chronic autoimmune enteropathy and multifactorial disease caused by inappropriate immune responses to gluten in the small intestine. Weight loss, anemia, osteoporosis, arthritis, and hepatitis are among the extraintestinal manifestations of active CD. Currently, a strict lifelong gluten-free diet (GFD) is the only safe, effective, and available treatment. Despite the social burden, high expenses, and challenges of following a GFD, 2 to 5 percent of patients do not demonstrate clinical or pathophysiological improvement. Therefore, we need novel and alternative therapeutic approaches for patients. Innovative approaches encompass a broad spectrum of strategies, including enzymatic degradation of gluten, inhibition of intestinal permeability, modulation of the immune response, inhibition of the transglutaminase 2 (TG2) enzyme, blocking antigen presentation by HLA-DQ2/8, and induction of tolerance. Hence, this review is focused on comprehensive therapeutic strategies ranging from dietary approaches to novel methods such as antigen-based immunotherapy, cell and gene therapy, and the usage of nanoparticles for CD treatment.

Specificity Enhancement of Glutenase Bga1903 toward Celiac Disease-Eliciting Pro-Immunogenic Peptides via Active-Site Modification

Celiac disease is an autoimmune disease triggered by oral ingestion of gluten, with certain gluten residues resistant to digestive tract enzymes. Within the duodenum, the remaining peptides incite immunogenic responses, including the generation of autoantibodies and inflammation, leading to irreversible damage. Our previous exploration unveiled a glutenase called Bga1903 derived from the Gram-negative bacterium Burkholderia gladioli. The cleavage pattern of Bga1903 indicates its moderate ability to mitigate the toxicity of pro-immunogenic peptides. The crystal structure of Bga1903, along with the identification of subsites within its active site, was determined. To improve its substrate specificity toward prevalent motifs like QPQ within gluten peptides, the active site of Bga1903 underwent site-directed mutagenesis according to structural insights and enzymatic kinetics. Among the double-site mutants, E380Q/S387L exhibits an approximately 34-fold increase in its specificity constant toward the QPQ sequence, favoring glutamines at the P1 and P3 positions compared to the wild type. The increased specificity of E380Q/S387L not only enhances its ability to break down pro-immunogenic peptides but also positions this enzyme variant as a promising candidate for oral therapy for celiac disease.

New Developments in Celiac Disease Treatment

Celiac disease (CD) is a common autoimmune disease affecting around 1% of the population. It consists of an immune-mediated enteropathy, triggered by gluten exposure in susceptible patients. All patients with CD, irrespective of the presence of symptoms, must endure a lifelong gluten-free diet (GFD). This is not an easy task due to a lack of awareness of the gluten content in foods and the extensive incorporation of gluten in processed foods. Furthermore, a GFD imposes a sense of limitation and might be associated with decreased quality of life in CD patients. This results in gluten contamination in the diet of four out of five celiac patients adhering to a GFD. Furthermore, one in three adult patients will report persistent symptoms and two in three will not achieve full histological recovery when on a GFD. In recent years, there has been extensive research conducted in the quest to find the holy grail of pharmacological treatment for CD. This review will present a concise description of the current rationale and main clinical trials related to CD drug therapy.

Complex of Proline-Specific Peptidases in the Genome and Gut Transcriptomes of Tenebrionidae Insects and Their Role in Gliadin Hydrolysis

A detailed analysis of the complexes of proline-specific peptidases (PSPs) in the midgut transcriptomes of the larvae of agricultural pests Tenebrio molitor and Tribolium castaneum and in the genome of T. castaneum is presented. Analysis of the T. castaneum genome revealed 13 PSP sequences from the clans of serine and metal-dependent peptidases, of which 11 sequences were also found in the gut transcriptomes of both tenebrionid species' larvae. Studies of the localization of PSPs, evaluation of the expression level of their genes in gut transcriptomes, and prediction of the presence of signal peptides determining secretory pathways made it possible to propose a set of peptidases that can directly participate in the hydrolysis of food proteins in the larvae guts. The discovered digestive PSPs of tenebrionids in combination with the post-glutamine cleaving cysteine cathepsins of these insects effectively hydrolyzed gliadins, which are the natural food substrates of the studied pests. Based on the data obtained, a hypothetical scheme for the complete hydrolysis of immunogenic gliadin peptides by T. molitor and T. castaneum digestive peptidases was proposed. These results show promise regarding the development of a drug based on tenebrionid digestive enzymes for the enzymatic therapy of celiac disease and gluten intolerance.

A Mouse Model of Celiac Disease

The design and use of mouse models that reproduce key features of human diseases are critical to advance our understanding of the pathogenesis of autoimmune diseases and to test new therapeutic strategies. Celiac disease is a unique organ-specific autoimmune-like disorder occurring in genetically susceptible individuals carrying HLA-DQ2 or HLA-DQ8 molecules who consume gluten. The key histological characteristic of the disease in humans is the destruction of the lining of the small intestine, a feature that has been difficult to reproduce in immunocompetent animal models. This unit describes the DQ8-D^d -villin-IL-15 transgenic mouse model of CeD, which was engineered based on the knowledge acquired from studying CeD patients' intestinal samples, and which represents the first animal model that develops villous atrophy in an HLA- and gluten-dependent manner without administration of any adjuvant. We provide detailed protocols for inducing and monitoring intestinal tissue damage, evaluating the cytotoxic properties of intraepithelial lymphocytes that mediate enterocyte lysis, and assessing the activation of the enzyme transglutaminase 2, which contributes to the generation of highly immunogenic gluten peptides. Detailed protocols to prepare pepsin-trypsin digested gliadin (PT-gliadin) or chymotrypsin-digested gliadin (CT-gliadin), which allow antibody detection against native or deamidated gluten peptides, are also provided in this unit. © 2022 The Authors. Current Protocols published by Wiley Periodicals LLC. Basic Protocol 1: Induction of celiac-like disease in DQ8-D^d -villin-IL-15tg mice Basic Protocol 2: Histological assessment of villous atrophy Support Protocol 1: Morphometric assessment of villous/crypt ratio Support Protocol 2: Evaluation of epithelial cells renewal Support Protocol 3: Evaluation of the density of intraepithelial lymphocytes Basic Protocol 3: Analysis of cytotoxic intraepithelial lymphocytes Basic Protocol 4: Transglutaminase 2 activation and measurement of antibodies against native and deamidated gluten peptides Support Protocol 4: Preparation of CT-gliadin Support Protocol 5: Preparation of PT-gliadin.

Relative Rates of Gluten Digestion by Nine Commercial Dietary Digestive Supplements

Endopeptidases containing supplements may digest gluten and reduce the impact on celiac and gluten-sensitive subjects who inadvertently consume gluten. We investigated the relative rate of disappearance of coeliac relevant epitopes in extracts of nine commercial supplements, using two competitive enzyme-linked immunosorbent assays (ELISAs)—Ridascreen (detects QQPFP, QQQFP, LQPFP, and QLPFP) and Gluten-Tec (detects Glia-α20 and PFRPQQPYPQ). All epitopes are destroyed by cleavage after P and Q amino acids. Rates at pH 3.5 and pH 7.0 were measured. These experiments were designed to measure relative rates of epitope digestion not to mimic in vivo digestion. The supplements were: 1 GluteGuard, 2 GlutenBlock, 3 GliadinX, 4 GlutnGo, 5 GlutenRescue, 6 Eat E-Z Gluten+, 7 Glutenease, 8 Glutezyme, and 9 Gluten Digest. The mean initial rate and half-lives of epitope digestion were deduced and extrapolated to rates at the recommended dose of one supplement in a fasting stomach volume. At pH 7, supplement 1 was the fastest acting of the supplements, with Ridascreen ELISA, more than twice as fast as the next fastest supplements, 5, 6, 7, and 8. Supplements 2, 3, and 4 showed little activity at pH 7.0. Supplement 1 was also the fastest acting at pH 7 with Gluten-Tec ELISA, more than three times the rate for supplements 2 and 3, with supplements 4–9 showing minimal activity. At pH 3.5, supplement 1 acted more than five times as fast as the next fastest supplements, 2 and 3, when measured by Ridascreen, but supplements 2 and 3 were over two times faster than supplement 1 when measured by Gluten-Tec. Supplements 4–9 demonstrated minimal activity at pH 3.5 with either ELISA. Supplement 1 most rapidly digested the key immuno-reactive gluten epitopes identified by the R5 antibody in the Codex-approved competitive Ridascreen ELISA method and associated with the pathology of celiac disease.

Effective Degradation of Gluten and Its Fragments by Gluten-Specific Peptidases: A Review on Application for the Treatment of Patients with Gluten Sensitivity

To date, there is no effective treatment for celiac disease (CD, gluten enteropathy), an autoimmune disease caused by gluten-containing food. Celiac patients are supported by a strict gluten-free diet (GFD). However, in some cases GFD does not negate gluten-induced symptoms. Many patients with CD, despite following such a diet, retain symptoms of active disease due to high sensitivity even to traces of gluten. In addition, strict adherence to GFD reduces the quality of life of patients, as often it is difficult to maintain in a professional or social environment. Various pharmacological treatments are being developed to complement GFD. One promising treatment is enzyme therapy, involving the intake of peptidases with food to digest immunogenic gluten peptides that are resistant to hydrolysis due to a high prevalence of proline and glutamine amino acids. This narrative review considers the features of the main proline/glutamine-rich proteins of cereals and the conditions that cause the symptoms of CD. In addition, we evaluate information about peptidases from various sources that can effectively break down these proteins and their immunogenic peptides, and analyze data on their activity and preliminary clinical trials. Thus far, the data suggest that enzyme therapy alone is not sufficient for the treatment of CD but can be used as a pharmacological supplement to GFD.

Gluten Degrading Enzymes for Treatment of Celiac Disease

Celiac disease (CeD) affects about 1% of most world populations. It presents a wide spectrum of clinical manifestations, ranging from minor symptoms to mild or severe malabsorption, and it may be associated with a wide variety of autoimmune diseases. CeD is triggered and maintained by the ingestion of gluten proteins from wheat and related grains. Gluten peptides that resist gastrointestinal digestion are antigenically presented to gluten specific T cells in the intestinal mucosa via HLA-DQ2 or HLA-DQ8, the necessary genetic predisposition for CeD. To date, there is no effective or approved treatment for CeD other than a strict adherence to a gluten-free diet, which is difficult to maintain in professional or social environments. Moreover, many patients with CeD have active disease despite diet adherence due to a high sensitivity to traces of gluten. Therefore, safe pharmacological treatments that complement the gluten-free diet are urgently needed. Oral enzyme therapy, employing gluten-degrading enzymes, is a promising therapeutic approach. A prerequisite is that such enzymes are active under gastro-duodenal conditions, quickly neutralize the T cell activating gluten peptides and are safe for human consumption. Several enzymes including prolyl endopeptidases, cysteine proteases and subtilisins can cleave the human digestion-resistant gluten peptides in vitro and in vivo. Examples are several prolyl endopeptidases from bacterial sources, subtilisins from Rothia bacteria that are natural oral colonizers and synthetic enzymes with optimized gluten-degrading activities. Without exception, these enzymes must cleave the otherwise unusual glutamine and proline-rich domains characteristic of antigenic gluten peptides. Moreover, they should be stable and active in both the acidic environment of the stomach and under near neutral pH in the duodenum. This review focuses on those enzymes that have been characterized and evaluated for the treatment of CeD, discussing their origin and activities, their clinical evaluation and challenges for therapeutic application. Novel developments include strategies like enteric coating and genetic modification to increase enzyme stability in the digestive tract.

Directed-Mutagenesis of Flavobacterium meningosepticum Prolyl-Oligopeptidase and a Glutamine-Specific Endopeptidase From Barley

Wheat gluten proteins are the known cause of celiac disease. The repetitive tracts of proline and glutamine residues in these proteins make them exceptionally resilient to digestion in the gastrointestinal tract. These indigested peptides trigger immune reactions in susceptible individuals, which could be either an allergic reaction or celiac disease. Gluten exclusion diet is the only approved remedy for such disorders. Recently, a combination of a glutamine specific endoprotease from barley (EP-B2), and a prolyl endopeptidase from Flavobacterium meningosepticum (Fm-PEP), when expressed in the wheat endosperm, were shown to reasonably detoxify immunogenic gluten peptides under simulated gastrointestinal conditions. However useful, these "glutenases" are limited in application due to their denaturation at high temperatures, which most of the food processes require. Variants of these enzymes from thermophilic organisms exist, but cannot be applied directly due to their optimum activity at temperatures higher than 37°C. Though, these enzymes can serve as a reference to guide the evolution of peptidases of mesophilic origin toward thermostability. Therefore, a sequence guided site-saturation mutagenesis approach was used here to introduce mutations in the genes encoding Fm-PEP and EP-B2. A thermostable variant of Fm-PEP capable of surviving temperatures up to 90°C and EP-B2 variant with a thermostability of up 60°C were identified using this approach. However, the level of thermostability achieved is not sufficient; the present study has provided evidence that the thermostability of glutenases can be improved. And this pilot study has paved the way for more detailed structural studies in the future to obtain variants of Fm-PEP and EP-B2 that can survive temperatures ~100°C to allow their packing in grains and use of such grains in the food industry.

Pathogenesis of Celiac Disease and Other Gluten Related Disorders in Wheat and Strategies for Mitigating Them

Wheat is a major cereal crop providing energy and nutrients to the billions of people around the world. Gluten is a structural protein in wheat, that is necessary for its dough making properties, but it is responsible for imparting certain intolerances among some individuals, which are part of this review. Most important among these intolerances is celiac disease, that is gluten triggered T-cell mediated autoimmune enteropathy and results in villous atrophy, inflammation and damage to intestinal lining in genetically liable individuals containing human leukocyte antigen DQ2/DQ8 molecules on antigen presenting cells. Celiac disease occurs due to presence of celiac disease eliciting epitopes in gluten, particularly highly immunogenic alpha-gliadins. Another gluten related disorder is non-celiac gluten-sensitivity in which innate immune-response occurs in patients along with gastrointestinal and non-gastrointestinal symptoms, that disappear upon removal of gluten from the diet. In wheat allergy, either IgE or non-IgE mediated immune response occurs in individuals after inhalation or ingestion of wheat. Following a life-long gluten-free diet by celiac disease and non-celiac gluten-sensitivity patients is very challenging as none of wheat cultivar or related species stands safe for consumption. Hence, different molecular biology, genetic engineering, breeding, microbial, enzymatic, and chemical strategies have been worked upon to reduce the celiac disease epitopes and the gluten content in wheat. Currently, only 8.4% of total population is affected by wheat-related issues, while rest of population remains safe and should not remove wheat from the diet, based on false media coverage.

Detection and Quantitation of Gluten in Fermented-Hydrolyzed Foods by Antibody-Based Methods: Challenges, Progress, and a Potential Path Forward

Celiac disease (CD) affects ~1 in 141 individuals in the United States, requiring adherence to a strict gluten-free diet. The Codex Standard and the European Commission states that gluten level of gluten-free foods must not exceed 20 ppm. The FDA requires food bearing the labeling claim “gluten-free” to contain <20 ppm gluten. Accurate quantitation of gluten in fermented-hydrolyzed foods by antibody-based methods is a challenge due to the lack of appropriate reference materials and variable proteolysis. The recent uses of proteases (e.g., proline endopeptidases or PEP) to hydrolyze immunopathogenic sequences of gluten proteins further complicates the quantitation of immunopathogenic gluten. The commercially available antibody-based methods routinely used to detect and quantitate gluten are not able to distinguish between different hydrolytic patterns arising from differences in fermentation processes. This is a severe limitation that makes accurate quantitation and, ultimately, a detailed evaluation of any potential health risk associated with consuming the food difficult. Utilizing gluten-specific antibodies, a recently developed multiplex-competitive ELISA along with western blot analysis provides a potential path forward in this direction. These complimentary antibody-based technologies provide insight into the extent of proteolysis resulting from various fermentation processes and have the potential to aid in the selection of appropriate hydrolytic calibration standards, leading to accurate gluten quantitation in fermented-hydrolyzed foods.

Evolving Therapy for Celiac Disease

Gluten is known to be the main triggering factor for celiac disease (CeD), an immune-mediated disorder. CeD is therefore managed using a strict and lifelong gluten-free diet (GFD), the only effective treatment available currently. However, the GFD is restrictive. Hence, efforts are being made to explore alternative therapies. Based on their mechanisms of action on various molecular targets involved in the pathogenesis of CeD, these therapies may be classified into one of the following five broad approaches. The first approach focuses on decreasing the immunogenic content of gluten, using strategies like genetically modified wheat, intra-intestinal gluten digestion using glutenases, microwave thermal treatment of hydrated wheat kernels, and gluten pretreatment with either bacterial/ fungal derived endopeptidases or microbial transglutaminase. The second approach involves sequestering gluten in the gut lumen before it is digested into immunogenic peptides and absorbed, using binder drugs like polymer p(HEMA-co-SS), single chain fragment variable (scFv), and anti- gluten antibody AGY. The third approach aims to prevent uptake of digested gluten through intestinal epithelial tight junctions, using a zonulin antagonist. The fourth approach involves tissue transglutaminase (tTG) inhibitors to prevent the enhancement of immunogenicity of digested gluten by the intestinal tTG enzyme. The fifth approach seeks to prevent downstream immune activation after uptake of gluten immunogenic peptides through the intestinal mucosal epithelial layer. Examples include HLA-DQ2 blockers that prevent presentation of gluten derived- antigens by dendritic cells to T cells, immune- tolerizing therapies like the vaccine Nexvax2 and TIMP-Glia, cathepsin inhibitors, immunosuppressants like corticosteroids, azathioprine etc., and anti-cytokine agents targeting TNF-α and interleukin-15. Apart from these approaches, research is being done to evaluate the effectiveness of probiotics/prebiotics, helminth therapy using Necator americanus, low FODMAP diet, and pancreatic enzyme supplementation in CeD symptom control; however, the mechanisms by which they play a beneficial role in CeD are yet to be clearly established. Overall, although many therapies being explored are still in the pre-clinical phase, some like the zonulin antagonist, immune tolerizing therapies and glutenases have reached phase II/III clinical trials. While these potential options appear exciting, currently they may at best be used to supplement rather than supplant the GFD.

Development of wheat genotypes expressing a glutamine-specific endoprotease from barley and a prolyl endopeptidase from Flavobacterium meningosepticum or Pyrococcus furiosus as a potential remedy to celiac disease

Ubiquitous nature of prolamin proteins dubbed gluten from wheat and allied cereals imposes a major challenge in the treatment of celiac disease, an autoimmune disorder with no known treatment other than abstinence diet. Administration of hydrolytic glutenases as food supplement is an alternative to deliver the therapeutic agents directly to the small intestine, where sensitization of immune system and downstream reactions take place. The aim of the present research was to evaluate the capacity of wheat grain to express and store hydrolytic enzymes capable of gluten detoxification. For this purpose, wheat scutellar calli were biolistically transformed to generate plants expressing a combination of glutenase genes for prolamin detoxification. Digestion of prolamins with barley endoprotease B2 (EP-HvB2) combined with Flavobacterium meningosepticum prolyl endopeptidase (PE-FmPep) or Pyrococcus furiosus prolyl endopeptidase (PE-PfuPep) significantly reduced (up to 67%) the amount of the indigestible gluten peptides of all prolamin families tested. Seven of the 168 generated lines showed inheritance of transgene to the T₂ generation. Reversed phase high-performance liquid chromatography of gluten extracts under simulated gastrointestinal conditions allowed the identification of five T₂ lines that contained significantly reduced amounts of immunogenic, celiac disease-provoking gliadin peptides. These findings were complemented by the R5 ELISA test results where up to 72% reduction was observed in the content of immunogenic peptides. The developed wheat genotypes open new horizons for treating celiac disease by an intraluminal enzyme therapy without compromising their agronomical performance.

Impact of food processing and simulated gastrointestinal digestion on gliadin immunoreactivity in rolls

BACKGROUND

The enzymatic modification of wheat proteins during dough fermentation and its digestion as supported by peptidases of microbiological origin can result in the degradation of important peptides in the pathogenesis of coeliac disease. However, baking bread and the high temperature associated with this could change the physicochemical and immunological properties of proteins. Thermal changes in the spatial structure of proteins and their hydrolysis can lead to a masking or degrading of immunoreactive peptides.

RESULTS

The addition of prolyl endopeptidase (PEP), comprising peptidases isolated from Lactobacillus acidophilus 5e2 (LA) or transglutaminase (TG) in the course of fermentation, decreases its immunoreactivity by 83.9%, 51.9% and 18.5%, respectively. An analysis of the fractional composition of gliadins revealed that γ- and ω-gliadins are the proteins most susceptible to enzymatic modification. Hydrolysis of wheat storage proteins with PEP and LA reduces the content of αβ-, γ- and ω-gliadins by 13.7%, 60.2% and 41.9% for PEP and by 22.1%, 43.5% and 36.9% for LA, respectively. Cross-linking of proteins with TG or their hydrolysis by PEP and LA peptidases during the process of forming wheat dough, followed by digesting bread samples with PEP and LA peptidases, decreases the immunoreactivity of bread hydrolysates from 2.4% to 0.02%. The content of peptide detected in polypeptide sequences is 263.4 ± 3.3, 30.9 ± 1.5 and 7.9 ± 0.4 mg kg^-1 in samples of hydrolysates of bread digested with PEP, as produced from dough modified by TG, PEP and LA, respectively.

CONCLUSION

Enzymatic pre-modification of proteins during the process of dough fermentation decreases their immunoreactive potential, such that fewer peptides recognised by R5 antibodies are released during the digestion process from the bread matrix. Immunoreactive peptides are degraded more effectively when digestive enzymes are supported by the addition of PEP. © 2017 Society of Chemical Industry.

Proteomic profiling of barley spent grains guides enzymatic solubilization of the remaining proteins

Within the brewing industry, malted barley is being increasingly replaced by raw barley supplemented with exogenous enzymes to lessen reliance on the time-consuming, high water and energy cost of malting. Regardless of the initial grain of choice, malted or raw, the resultant bulk spent grains are rich in proteins (up to 25% dry weight). Efficient enzymatic solubilization of these proteins requires knowledge of the protein composition within the spent grains. Therefore, a comprehensive proteomic profiling was performed on spent grains derived from (i) malted barley (spent grain A, SGA) and (ii) enzymatically treated raw barley (spent grain B, SGB); data are available via ProteomeXchange with identifier PXD008090. Results from complementary shotgun proteomics and 2D gel electrophoresis showed that the most abundant proteins in both spent grains were storage proteins (hordeins and embryo globulins); these were present at an average of two fold higher in spent grain B. Quantities of other major proteins were generally consistent in both spent grains A and B. Subsequent in silico protein sequence analysis of the predominant proteins facilitated knowledge-based protease selection to enhance spent grain solubilization. Among tested proteases, Alcalase 2.4 L digestion resulted in the highest remaining protein solubilization with 9.2 and 11.7% net dry weight loss in SGA and SGB respectively within 2 h. Thus, Alcalase alone can significantly reduce spent grain side stream, which makes it a possible solution to increase the value of this low-value side stream from the brewing and malt extract beverage manufacturing industry.

Effects of a Proline Endopeptidase on the Detection and Quantitation of Gluten by Antibody-Based Methods during the Fermentation of a Model Sorghum Beer

The effectiveness of a proline endopeptidase (PEP) in hydrolyzing gluten and its putative immunopathogenic sequences was examined using antibody-based methods and mass spectrometry (MS). Based on the results of the antibody-based methods, fermentation of wheat gluten containing sorghum beer resulted in a reduction in the detectable gluten concentration. The addition of PEP further reduced the gluten concentration. Only one sandwich ELISA was able to detect the apparent low levels of gluten present in the beers. A competitive ELISA using a pepsin-trypsin hydrolysate calibrant was unreliable because the peptide profiles of the beers were inconsistent with that of the hydrolysate calibrant. Analysis by MS indicated that PEP enhanced the loss of a fragment of an immunopathogenic 33-mer peptide in the beer. However, Western blot results indicated partial resistance of the high molecular weight (HMW) glutenins to the action of PEP, questioning the ability of PEP in digesting all immunopathogenic sequences present in gluten.

Celiac disease: a disorder emerging from antiquity, its evolving classification and risk, and potential new treatment paradigms

Celiac disease is a chronic genetically based gluten-sensitive immune-mediated enteropathic process primarily affecting the small intestinal mucosa. The disorder classically presents with diarrhea and weight loss; however, more recently, it has been characterized by subclinical occult or latent disease associated with few or no intestinal symptoms. Diagnosis depends on the detection of typical histopathological biopsy changes followed by a gluten-free diet response. A broad range of clinical disorders may mimic celiac disease, along with a wide range of drugs and other therapeutic agents. Recent and intriguing archeological data, largely from the Gobleki Tepe region of the Fertile Crescent, indicate that celiac disease probably emerged as humans transitioned from hunter-gatherer groups to societies dependent on agriculture to secure a stable food supply. Longitudinal studies performed over several decades have suggested that changes in the prevalence of the disease, even apparent epidemic disease, may be due to superimposed or novel environmental factors that may precipitate its appearance. Recent therapeutic approaches are being explored that may supplement, rather than replace, gluten-free diet therapy and permit more nutritional options for future management.

Randomised clinical study: Aspergillus niger-derived enzyme digests gluten in the stomach of healthy volunteers

BACKGROUND

Aspergillus niger prolyl endoprotease (AN-PEP) efficiently degrades gluten molecules into non-immunogenic peptides in vitro.

AIM

To assess the efficacy of AN-PEP on gluten degradation in a low and high calorie meal in healthy subjects.

METHODS

In this randomised, double-blind, placebo-controlled, cross-over study 12 healthy volunteers attended to four test days. A liquid low or high calorie meal (4 g gluten) with AN-PEP or placebo was administered into the stomach. Via a triple-lumen catheter gastric and duodenal aspirates were sampled, and polyethylene glycol (PEG)-3350 was continuously infused. Acetaminophen in the meals tracked gastric emptying time. Gastric and duodenal samples were used to calculate 240-min area under the curve (AUC0-240 min ) of ?-gliadin concentrations. Absolute ?-gliadin AUC0-240 min was calculated using duodenal PEG-3350 concentrations.

RESULTS

AN-PEP lowered α-gliadin concentration AUC0-240 min, compared to placebo, from low and high calorie meals in stomach (low: 35 vs. 389 μg × min/mL; high: 53 vs. 386 μg × min/mL; P < 0.001) and duodenum (low: 7 vs. 168 μg × min/mL; high: 4 vs. 32 μg × min/mL; P < 0.001) and absolute α-gliadin AUC0-240 min in the duodenum from low (2813 vs. 31 952 μg × min; P < 0.001) and high (2553 vs. 13 095 μg × min; P = 0.013) calorie meals. In the placebo group, the high compared to low calorie meal slowed gastric emptying and lowered the duodenal α-gliadin concentration AUC0-240 min (32 vs. 168 μg × min/mL; P = 0.001).

CONCLUSIONS

AN-PEP significantly enhanced gluten digestion in the stomach of healthy volunteers. Increasing caloric density prolonged gastric residence time of the meal. Since AN-PEP already degraded most gluten from low calorie meals, no incremental effect was observed by increasing meal caloric density. ClinicalTrials.gov, Number: NCT01335503; www.trialregister.nl, Number: NTR2780.

Therapeutic approaches for celiac disease

Celiac disease is a common, lifelong autoimmune disorder for which dietary control is the only accepted form of therapy. A strict gluten-free diet is burdensome to patients and can be limited in efficacy, indicating there is an unmet need for novel therapeutic approaches to supplement or supplant dietary therapy. Many molecular events required for disease pathogenesis have been recently characterized and inspire most current and emerging drug-discovery efforts. Genome-wide association studies (GWAS) confirm the importance of human leukocyte antigen genes in our pathogenic model and identify a number of new risk loci in this complex disease. Here, we review the status of both emerging and potential therapeutic strategies in the context of disease pathophysiology. We conclude with a discussion of how genes identified during GWAS and follow-up studies that enhance susceptibility may offer insight into developing novel therapies.

Identification of Pseudolysin (lasB) as an Aciduric Gluten-Degrading Enzyme with High Therapeutic Potential for Celiac Disease

OBJECTIVES

Immunogenic gluten proteins implicated in celiac disease (CD) largely resist degradation by human digestive enzymes. Here we pursued the isolation of gluten-degrading organisms from human feces, aiming at bacteria that would digest gluten under acidic conditions, as prevails in the stomach.

METHODS

Bacteria with gluten-degrading activities were isolated using selective gluten agar plates at pH 4.0 and 7.0. Proteins in concentrated bacterial cell sonicates were separated by diethylaminoethanol chromatography. Enzyme activity was monitored with chromogenic substrates and gliadin zymography. Elimination of major immunogenic gluten epitopes was studied with R5 and G12 enzyme-linked immunosorbent assays.

RESULTS

Gliadin-degrading enzyme activities were observed for 43 fecal isolates, displaying activities in the ~150-200 and <50 kDa regions. The active strains were identified as Pseudomonas aeruginosa. Gliadin degradation in gel was observed from pH 2.0 to 7.0. Liquid chromatography-electrospray ionization-tandem mass spectrometry analysis identified the enzyme as pseudolysin (lasB), a metalloprotease belonging to the thermolysin (M4) family proteases. Its electrophoretic mobility in SDS-polyacrylamide gel electrophoresis and gliadin zymogram gels was similar to that of a commercial lasB preparation, with tendency of oligomerization. Pseudolysin eliminated epitopes recognized by the R5 antibody, while those detected by the G12 antibody remained intact, despite destruction of the nearby major T-cell epitope QPQLPY.

CONCLUSIONS

Pseudolysin was identified as an enzyme cleaving gluten effectively at extremely low as well as near-neutral pH values. The potential to degrade gluten during gastric transport opens possibilities for its application as a novel therapeutic agent for the treatment of CD.

Novel treatments for celiac disease: glutenases and beyond

Currently, the only effective treatment for celiac disease is a strict lifelong gluten-free diet. However, gluten-free dieting is restrictive, difficult to maintain and nutritionally less than optimal. The improved knowledge on celiac disease pathogenesis has enabled researchers to suggest alternative strategies to treat the disorder. The drug development poses a challenge as any novel drug for celiac disease should be simultaneously effective and as safe as the gluten-free diet. The rationale behind enzyme supplementation therapy as a future treatment option for celiac patients lies in the fact that gluten is only poorly digested by gastrointestinal proteases. Due to incomplete degradation in the gastrointestinal tract, fairly long gluten peptides enter the small-intestinal lumen and come into contact with the mucosal epithelium, and in celiac disease patients this encounter launches deleterious downstream effects. Enzyme supplement therapy using either bacterial or fungal endopeptidases or proteases from germinating cereals has been proposed to promote complete digestion of prolamins and destroy disease-inducing gluten peptides. A major advantage of these glutenases is that they work in the lumen of the small intestine and do not themselves take part in the immunological cascade of events in the lamina propria, thus being unlikely to cause harmful side effects to the host. Studies to test this rationale, e.g. with Aspergillus niger prolyl endoprotease and a combination enzyme product ALV003, are already ongoing. The development of a novel medication for celiac disease is still in its early days, and thus the conventional dietary treatment will hold its place for the time being.

Glutenase and collagenase activities of wheat cysteine protease Triticain-α: feasibility for enzymatic therapy assays

Insufficient and/or improper protein degradation is associated with the development of various human pathologies. Enzymatic therapy with proteolytic enzymes aimed to improve insufficient proteolytic activity was suggested as a treatment of protease deficiency-induced disorders. Since in many cases human degradome is incapable of degrading the entire target protein(s), other organisms can be used as a source of proteases exhibiting activities distinct from human enzymes, and plants are perspective candidates for this source. In this study recombinant wheat cysteine protease Triticain-α was shown to refold in vitro into an autocatalytically activated proteolytic enzyme possessing glutenase and collagenase activities at acidic (or close to neutral) pH levels at the temperature of human body. Mass-spectrometry analysis of the products of Triticain-α-catalyzed gluten hydrolysis revealed multiple cleavage sites within the sequences of gliadin toxic peptides, in particular, in the major toxic 33-mer α-gliadin-derived peptide initiating inflammatory responses to gluten in celiac disease (CD) patients. Triticain-α was found to be relatively stable in the conditions simulating stomach environment. We conclude that Triticain-α can be exploited as a basic compound for development of (i) pharmaceuticals for oral administration aimed at release of the active enzyme into the gastric lumen for CD treatment, and (ii) topically active pharmaceuticals for wound debridement applications.

Emerging drugs for celiac disease

INTRODUCTION

Celiac disease is an immune-mediated gluten-dependent disorder, primarily affecting the small intestine in genetically predisposed individuals. The disorder has a very heterogeneous clinical and histopathological spectrum. Current treatment with a gluten-free diet is very effective, but the diet is difficult to maintain and remains costly.

AREAS COVERED

Alternatives to the gluten-free diet have been proposed to either replace this current treatment, or at least, to supplement use of the gluten-free diet. Studies in the published English language literature relevant to this review were examined for this report.

EXPERT OPINION

Most recent published double-blind, placebo-controlled clinical trials have focused on an orally administered recombinant glutenase (ALV003) showing significant but limited benefit to celiac disease patients already compliant with a gluten-free diet. Other studies have addressed other immune mechanisms that may play a role in its pathogenesis and have not been so positive. Added investigations, particularly over the long-term, in other larger and more heterogeneous populations are needed.

Treatment of both native and deamidated gluten peptides with an endo-peptidase from Aspergillus niger prevents stimulation of gut-derived gluten-reactive T cells from either children or adults with celiac disease

Celiac disease (CD) is characterized by an inappropriate immunological reaction against gluten driven by gluten-specific CD4+ T cells. We screened 25 proteases and tested 10 for their potential to degrade gluten in vitro. Five proteases were further tested for their ability to prevent the proliferative response by a gluten-specific CD4+ T cell clone and seven gluten-reactive T cell lines to protease-digested gluten peptides. A proline-specific endo-peptidase from Aspergillus niger (AnP2) was particularly efficient at diminishing proliferation after stimulation with cleaved antigen, and could completely block the response against both native and deamidated gluten peptides. We found that AnP2 was efficient down to a 1:64 protease:substrate ratio (w:w). When AnP2 was tested in assays using seven gluten-reactive T cell lines from individual CD patients (three adults and four children), the response to gluten was diminished in all cases. Our study indicates a therapeutic benefit of AnP2 to CD patients.

Current status of drugs in development for celiac disease

INTRODUCTION

Gluten is the main trigger for celiac disease, and the current treatment is based on its elimination from the diet. Although the symptoms usually disappear during the diet, it is restrictive and difficult to maintain. Further, despite a strict treatment the small-bowel mucosal damage does now always heal. Consequently, adherence is often poor and new treatment approaches are needed. With an increased understanding of the disease pathogenesis, several novel treatments have been suggested, and some of them have already entered Phase II clinical trials.

AREAS COVERED

This article reviews the latest status of the drugs in development for celiac disease. The article focuses mainly on synthetic drugs currently entering in clinical trials.

EXPERT OPINION

It is anticipated that some of the treatments under investigation will soon enter Phase III clinical trials, although challenges remain. For instance, histological studies are problematic in wide-scale clinical studies. On the other hand, the existing non-invasive serological methods and clinical outcome measures might be too insensitive for monitoring responses to the possible drug candidates. There is also no animal model which would accurately reflect celiac disease. Well-conducted basic and clinical research is required to develop better non-invasive surrogate markers and patient-related outcomes for future pharmacological studies.

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.

Advances in the treatment of coeliac disease: an immunopathogenic perspective

Coeliac disease is a common and fairly well-characterized systemic disorder that mainly affects the small intestine, but also has extraintestinal manifestations. The environmental trigger (gluten derived from wheat, rye and barley), the genetic predisposition conferred by the HLA-DQ2 and HLA-DQ8 haplotypes and many steps in the disease pathogenesis are known. This knowledge has enabled researchers to suggest novel alternative treatments or adjunctive therapies to the gluten-free diet, which is currently the only available and effective treatment for the condition. This Review focuses on emerging and potential treatment strategies that are based on the current concept of the disease pathophysiology. The search for novel future treatment modes, including nonpharmacological and pharmacological approaches, is also outlined. The potential pitfalls associated with the various research avenues are also discussed.

Computational design of an α-gliadin peptidase

The ability to rationally modify enzymes to perform novel chemical transformations is essential for the rapid production of next-generation protein therapeutics. Here we describe the use of chemical principles to identify a naturally occurring acid-active peptidase, and the subsequent use of computational protein design tools to reengineer its specificity toward immunogenic elements found in gluten that are the proposed cause of celiac disease. The engineered enzyme exhibits a k(cat)/K(M) of 568 M(-1) s(-1), representing a 116-fold greater proteolytic activity for a model gluten tetrapeptide than the native template enzyme, as well as an over 800-fold switch in substrate specificity toward immunogenic portions of gluten peptides. The computationally engineered enzyme is resistant to proteolysis by digestive proteases and degrades over 95% of an immunogenic peptide implicated in celiac disease in under an hour. Thus, through identification of a natural enzyme with the pre-existing qualities relevant to an ultimate goal and redefinition of its substrate specificity using computational modeling, we were able to generate an enzyme with potential as a therapeutic for celiac disease.

Nondietary therapies for celiac disease

Currently, the only available therapy for celiac disease is strict lifelong adherence to a gluten-free diet (GFD). Although safe and effective, the GFD is not ideal. It is frequently expensive, of limited nutritional value, and not readily available in many countries. Consequently, a need exists for novel, nondietary therapies for celiac disease. Based on the current understanding of celiac disease pathogenesis, several potential targets of therapeutic intervention exist. These novel strategies provide promise of alternative, adjunctive treatment options but also raise important questions regarding safety, efficacy, and monitoring of long-term treatment effect.

Animal models to study gluten sensitivity

The initial development and maintenance of tolerance to dietary antigens is a complex process that, when prevented or interrupted, can lead to human disease. Understanding the mechanisms by which tolerance to specific dietary antigens is attained and maintained is crucial to our understanding of the pathogenesis of diseases related to intolerance of specific dietary antigens. Two diseases that are the result of intolerance to a dietary antigen are celiac disease (CD) and dermatitis herpetiformis (DH). Both of these diseases are dependent upon the ingestion of gluten (the protein fraction of wheat, rye, and barley) and manifest in the gastrointestinal tract and skin, respectively. These gluten-sensitive diseases are two examples of how devastating abnormal immune responses to a ubiquitous food can be. The well-recognized risk genotype for both is conferred by either of the HLA class II molecules DQ2 or DQ8. However, only a minority of individuals who carry these molecules will develop either disease. Also of interest is that the age at diagnosis can range from infancy to 70-80 years of age. This would indicate that intolerance to gluten may potentially be the result of two different phenomena. The first would be that, for various reasons, tolerance to gluten never developed in certain individuals, but that for other individuals, prior tolerance to gluten was lost at some point after childhood. Of recent interest is the concept of non-celiac gluten sensitivity, which manifests as chronic digestive or neurologic symptoms due to gluten, but through mechanisms that remain to be elucidated. This review will address how animal models of gluten-sensitive disorders have substantially contributed to a better understanding of how gluten intolerance can arise and cause disease.

Future treatment strategies for celiac disease

INTRODUCTION

Ingestion of dietary gluten in wheat, rye and barley by celiac patients leads to small-bowel mucosal villous atrophy, crypt hyperplasia and massive inflammation, often coupled with clinical symptoms and signs. Currently, the only effective treatment is a strict life-long gluten-free diet excluding all gluten-containing food products. In view of the extremely restricted nature of the diet, new treatment options would clearly be desirable.

AREAS COVERED

The improved understanding of celiac disease pathogenesis has enabled researchers to suggest alternative strategies to treat the disorder. This review covers current approaches toward developing an appropriate drug and discusses the possible problems associated with these approaches.

EXPERT OPINION

Phase II clinical trials are already ongoing to test the efficacy of novel alternative treatments for celiac disease. Before any of the candidates can enter Phase III trials, however, researchers must develop novel reliable non-invasive surrogate markers for intestinal injury and disease activity which also accurately reflect patient-related outcomes. Any novel medication for celiac disease should be as effective and safe as the gluten-free diet, and this constitutes a challenge for drug development. It is thus likely that the first medication entering the market will be supplementary to rather than substitute the gluten-free diet.

Oral enzyme therapy for celiac sprue

Celiac sprue is an inflammatory disease of the small intestine caused by dietary gluten and treated by adherence to a life-long gluten-free diet. The recent identification of immunodominant gluten peptides, the discovery of their cogent properties, and the elucidation of the mechanisms by which they engender immunopathology in genetically susceptible individuals have advanced our understanding of the molecular pathogenesis of this complex disease, enabling the rational design of new therapeutic strategies. The most clinically advanced of these is oral enzyme therapy, in which enzymes capable of proteolyzing gluten (i.e., glutenases) are delivered to the alimentary tract of a celiac sprue patient to detoxify ingested gluten in situ. In this chapter, we discuss the key challenges for discovery and preclinical development of oral enzyme therapies for celiac sprue. Methods for lead identification, assay development, gram-scale production and formulation, and lead optimization for next-generation proteases are described and critically assessed.

Identification of Rothia bacteria as gluten-degrading natural colonizers of the upper gastro-intestinal tract

Background

Gluten proteins, prominent constituents of barley, wheat and rye, cause celiac disease in genetically predisposed subjects. Gluten is notoriously difficult to digest by mammalian proteolytic enzymes and the protease-resistant domains contain multiple immunogenic epitopes. The aim of this study was to identify novel sources of gluten-digesting microbial enzymes from the upper gastro-intestinal tract with the potential to neutralize gluten epitopes.

Methodology/Principal Findings

Oral microorganisms with gluten-degrading capacity were obtained by a selective plating strategy using gluten agar. Microbial speciations were carried out by 16S rDNA gene sequencing. Enzyme activities were assessed using gliadin-derived enzymatic substrates, gliadins in solution, gliadin zymography, and 33-mer α-gliadin and 26-mer γ-gliadin immunogenic peptides. Fragments of the gliadin peptides were separated by RP-HPLC and structurally characterized by mass spectrometry. Strains with high activity towards gluten were typed as Rothia mucilaginosa and Rothia aeria. Gliadins (250 µg/ml) added to Rothia cell suspensions (OD₆₂₀ 1.2) were degraded by 50% after ∼30 min of incubation. Importantly, the 33-mer and 26-mer immunogenic peptides were also cleaved, primarily C-terminal to Xaa-Pro-Gln (XPQ) and Xaa-Pro-Tyr (XPY). The major gliadin-degrading enzymes produced by the Rothia strains were ∼70–75 kDa in size, and the enzyme expressed by Rothia aeria was active over a wide pH range (pH 3–10).

Conclusion/Significance

While the human digestive enzyme system lacks the capacity to cleave immunogenic gluten, such activities are naturally present in the oral microbial enzyme repertoire. The identified bacteria may be exploited for physiologic degradation of harmful gluten peptides.

Novel therapies for coeliac disease

Coeliac disease is a widespread, lifelong disorder for which dietary control represents the only accepted form of therapy. There is an unmet need for nondietary therapies to treat this condition. Most ongoing and emerging drug-discovery programmes are based on the understanding that coeliac disease is caused by an inappropriate T-cell-mediated immune response to dietary gluten proteins. Recent genome-wide association studies lend further support to this pathogenic model. The central role of human leucocyte antigen genes has been validated, and a number of new risk loci have been identified, most of which are related to the biology of T cells and antigen-presenting cells. Here, we review the status of potential nondietary therapies under consideration for coeliac disease. We conclude that future development of novel therapies will be aided considerably by the identification of new, preferably noninvasive, surrogate markers for coeliac disease activity.

Degradation of coeliac disease-inducing rye secalin by germinating cereal enzymes: diminishing toxic effects in intestinal epithelial cells

Currently the only treatment for coeliac disease is a lifelong gluten-free diet excluding food products containing wheat, rye and barley. There is, however, only scarce evidence as to harmful effects of rye in coeliac disease. To confirm the assumption that rye should be excluded from the coeliac patient's diet, we now sought to establish whether rye secalin activates toxic reactions in vitro in intestinal epithelial cell models as extensively as wheat gliadin. Further, we investigated the efficacy of germinating cereal enzymes from oat, wheat and barley to hydrolyse secalin into short fragments and whether secalin-induced harmful effects can be reduced by such pretreatment. In the current study, secalin elicited toxic reactions in intestinal Caco-2 epithelial cells similarly to gliadin: it induced epithelial cell layer permeability, tight junctional protein occludin and ZO-1 distortion and actin reorganization. In high-performance liquid chromatography and mass spectroscopy (HPLC-MS), germinating barley enzymes provided the most efficient degradation of secalin and gliadin peptides and was thus selected for further in vitro analysis. After germinating barley enzyme pretreatment, all toxic reactions induced by secalin were ameliorated. We conclude that germinating enzymes from barley are particularly efficient in the degradation of rye secalin. In future, these enzymes might be utilized as a novel medical treatment for coeliac disease or in food processing in order to develop high-quality coeliac-safe food products.

Visualization of transepithelial passage of the immunogenic 33-residue peptide from alpha-2 gliadin in gluten-sensitive macaques

Background

Based on clinical, histopathological and serological similarities to human celiac disease (CD), we recently established the rhesus macaque model of gluten sensitivity. In this study, we further characterized this condition based on presence of anti-tissue transglutaminase 2 (TG2) antibodies, increased intestinal permeability and transepithelial transport of a proteolytically resistant, immunotoxic, 33-residue peptide from α₂-gliadin in the distal duodenum of gluten-sensitive macaques.

Methodology/Principal Findings

Six rhesus macaques were selected for study from a pool of 500, including two healthy controls and four gluten-sensitive animals with elevated anti-gliadin or anti-TG2 antibodies as well as history of non-infectious chronic diarrhea. Pediatric endoscope-guided pinch biopsies were collected from each animal's distal duodenum following administration of a gluten-containing diet (GD) and again after remission by gluten-free diet (GFD). Control biopsies always showed normal villous architecture, whereas gluten-sensitive animals on GD exhibited histopathology ranging from mild lymphocytic infiltration to villous atrophy, typical of human CD. Immunofluorescent microscopic analysis of biopsies revealed IgG+ and IgA+ plasma-like cells producing antibodies that colocalized with TG2 in gluten-sensitive macaques only. Following instillation in vivo, the Cy-3-labeled 33-residue gluten peptide colocalized with the brush border protein villin in all animals. In a substantially enteropathic macaque with “leaky” duodenum, the peptide penetrated beneath the epithelium into the lamina propria.

Conclusions/Significance

The rhesus macaque model of gluten sensitivity not only resembles the histopathology of CD but it also may provide a model for studying intestinal permeability in states of epithelial integrity and disrepair.

Celiac disease: prevention and treatment

Celiac disease is a common multisystemic disorder that may be diagnosed at any age. Owing to the increasing prevalence, prevention strategies, including encouragement of breastfeeding and introduction of small amounts of gluten whereas still on breastfeeding at fourth to sixth month of age, become more important than before. For avoiding complications of celiac disease, a strict gluten-free diet is essential. A lifelong gluten-free diet may bring about difficulties as avoiding gluten completely is problematic owing to the contamination with gluten of presumably gluten free foods. New therapeutic approaches include enzyme supplementation, correction of the intestinal barrier defect against gluten entry, blocking of gliadin presentation by human leukocyte antigen blockers and tissue transglutaminase inhibitors.

Noninflammatory gluten peptide analogs as biomarkers for celiac sprue

New tools are needed for managing celiac sprue, a lifelong immune disease of the small intestine. Ongoing drug trials are also prompting a search for noninvasive biomarkers of gluten-induced intestinal change. We have synthesized and characterized noninflammatory gluten peptide analogs in which key Gln residues are replaced by Asn or His. Like their proinflammatory counterparts, these biomarkers are resistant to gastrointestinal proteases, susceptible to glutenases, and permeable across enterocyte barriers. Unlike gluten peptides, however, they are not appreciably recognized by transglutaminase, HLA-DQ2, or disease-specific T cells. In vitro and animal studies show that the biomarkers can detect intestinal permeability changes as well as glutenase-catalyzed gastric detoxification of gluten. Accordingly, controlled clinical studies are warranted to evaluate the use of these peptides as probes for abnormal intestinal permeability in celiac patients and for glutenase efficacy in clinical trials and practice.

Celiac disease: from pathogenesis to novel therapies

Celiac disease has become one of the best-understood HLA-linked disorders. Although it shares many immunologic features with inflammatory bowel disease, celiac disease is uniquely characterized by (1) a defined trigger (gluten proteins from wheat and related cereals), (2) the necessary presence of HLA-DQ2 or HLA-DQ8, and (3) the generation of circulating autoantibodies to the enzyme tissue transglutaminase (TG2). TG2 deamidates certain gluten peptides, increasing their affinity to HLA-DQ2 or HLA-DQ8. This generates a more vigorous CD4(+) T-helper 1 T-cell activation, which can result in intestinal mucosal inflammation, malabsorption, and numerous secondary symptoms and autoimmune diseases. Moreover, gluten elicits innate immune responses that act in concert with the adaptive immunity. Exclusion of gluten from the diet reverses many disease manifestations but is usually not or less efficient in patients with refractory celiac disease or associated autoimmune diseases. Based on the advanced understanding of the pathogenesis of celiac disease, targeted nondietary therapies have been devised, and some of these are already in phase 1 or 2 clinical trials. Examples are modified flours that have been depleted of immunogenic gluten epitopes, degradation of immunodominant gliadin peptides that resist intestinal proteases by exogenous endopeptidases, decrease of intestinal permeability by blockage of the epithelial ZOT receptor, inhibition of intestinal TG2 activity by transglutaminase inhibitors, inhibition of gluten peptide presentation by HLA-DQ2 antagonists, modulation or inhibition of proinflammatory cytokines, and induction of oral tolerance to gluten. These and other experimental therapies will be discussed critically.

Polymeric binders suppress gliadin-induced toxicity in the intestinal epithelium

BACKGROUND & AIMS

Celiac disease is a prevalent immune disorder caused by the ingestion of gliadin-containing grains. We investigated the ability of a polymeric binder to reverse the toxic effects induced by gliadin in human intestinal cells and gliadin-sensitive HCD4-DQ8 mice.

METHODS

Gliadin was neutralized by complexation to a linear copolymer of hydroxyethylmethacrylate (HEMA) and sodium 4-styrene sulfonate (SS). The ability of the polymeric binder to abrogate the damaging effect of gliadin on cell-cell contact was investigated in IEC-6, Caco-2/15, and primary cultured differentiated enterocytes. The efficacy of the polymeric binder in preventing gliadin-induced intestinal barrier dysfunction was assessed using gliadin-sensitive HLA-HCD4/DQ8 transgenic mice.

RESULTS

Poly(hydroxyethylmethacrylate-co-styrene sulfonate) [P(HEMA-co-SS)] complexed with gliadin in a relatively specific fashion. Intestinal cells exposed to gliadin underwent profound alterations in morphology and cell-cell contacts. These changes were averted by complexing the gliadin with P(HEMA-co-SS). More importantly, the P(HEMA-co-SS) hindered the digestion of gliadin by gastrointestinal enzymes, thus minimizing the formation of immunogenic peptides. Coadministration of P(HEMA-co-SS) with gliadin to HLA-HCD4/DQ8 mice attenuated gliadin-induced changes in the intestinal barrier and reduced intraepithelial lymphocyte and macrophage cell counts.

CONCLUSIONS

Polymeric binders can prevent in vitro gliadin-induced epithelial toxicity and intestinal barrier dysfunction in HCD4/DQ8 mice. They have a potential role in the treatment of patients with gluten-induced disorders.

Toward the assessment of food toxicity for celiac patients: characterization of monoclonal antibodies to a main immunogenic gluten peptide

BACKGROUND AND AIMS

Celiac disease is a permanent intolerance to gluten prolamins from wheat, barley, rye and, in some patients, oats. Partially digested gluten peptides produced in the digestive tract cause inflammation of the small intestine. High throughput, immune-based assays using monoclonal antibodies specific for these immunotoxic peptides would facilitate their detection in food and enable monitoring of their enzymatic detoxification. Two monoclonal antibodies, G12 and A1, were developed against a highly immunotoxic 33-mer peptide. The potential of each antibody for quantifying food toxicity for celiac patients was studied.

METHODS

Epitope preferences of G12 and A1 antibodies were determined by ELISA with gluten-derived peptide variants of recombinant, synthetic or enzymatic origin.

RESULTS

The recognition sequences of G12 and A1 antibodies were hexameric and heptameric epitopes, respectively. Although G12 affinity for the 33-mer was superior to A1, the sensitivity for gluten detection was higher for A1. This observation correlated to the higher number of A1 epitopes found in prolamins than G12 epitopes. Activation of T cell from gluten digested by glutenases decreased equivalently to the detection of intact peptides by A1 antibody. Peptide recognition of A1 included gliadin peptides involved in the both the adaptive and innate immunological response in celiac disease.

CONCLUSIONS

The sensitivity and epitope preferences of the A1 antibody resulted to be useful to detect gluten relevant peptides to infer the potential toxicity of food for celiac patients as well as to monitor peptide modifications by transglutaminase 2 or glutenases.

Parallels between pathogens and gluten peptides in celiac sprue

Pathogens are exogenous agents capable of causing disease in susceptible organisms. In celiac sprue, a disease triggered by partially hydrolyzed gluten peptides in the small intestine, the offending immunotoxins cannot replicate, but otherwise have many hallmarks of classical pathogens. First, dietary gluten and its peptide metabolites are ubiquitous components of the modern diet, yet only a small, genetically susceptible fraction of the human population contracts celiac sprue. Second, immunotoxic gluten peptides have certain unusual structural features that allow them to survive the harsh proteolytic conditions of the gastrointestinal tract and thereby interact extensively with the mucosal lining of the small intestine. Third, they invade across epithelial barriers intact to access the underlying gut-associated lymphoid tissue. Fourth, they possess recognition sequences for selective modification by an endogenous enzyme, transglutaminase 2, allowing for in situ activation to a more immunotoxic form via host subversion. Fifth, they precipitate a T cell–mediated immune reaction comprising both innate and adaptive responses that causes chronic inflammation of the small intestine. Sixth, complete elimination of immunotoxic gluten peptides from the celiac diet results in remission, whereas reintroduction of gluten in the diet causes relapse. Therefore, in analogy with antibiotics, orally administered proteases that reduce the host's exposure to the immunotoxin by accelerating gluten peptide destruction have considerable therapeutic potential. Last but not least, notwithstanding the power of in vitro methods to reconstitute the essence of the immune response to gluten in a celiac patient, animal models for the disease, while elusive, are likely to yield fundamentally new systems-level insights.