IngredientsGliadin is the collective term for a family of storage proteins found exclusively in the endosperm of wheat (Triticum aestivum and related species). Gliadins belong to the prolamin class of cereal storage proteins — a group recognized as being unique to cereal grains and named for their high contents of proline and amide nitrogen (now known to be derived largely from glutamine). This class is given specific names in different cereal species: gliadin in wheat, hordein in barley, secalin in rye, and zein in maize. Prolamins such as gliadin, zein, and kafirin — which are by-products of the cereal starch isolation process — are insoluble in water but soluble in concentrated aqueous ethanol solutions.
Gluten proteins can be divided into two main fractions according to their solubility in aqueous alcohols: the soluble gliadins and the insoluble glutenins. Approximately 50% of gluten proteins are monomeric gliadins with molecular weights (MWs) from 28,000 to 55,000, while about 15% are present as disulfide-linked oligomeric proteins with MWs between 70,000 and 700,000, called HMW-gliadins. The remaining 35% are disulfide-linked polymeric glutenins with MWs from 700,000 to more than 10 million.
Gliadin, the prolamin from wheat, contains 14 grams of proline and 46 grams of glutamic acid in 100 grams of protein; most of the glutamic acid is in the form of glutamine. Gliadin consists of single-chain polypeptides linked by intramolecular disulfide bonds, with each polypeptide chain having an average MW of 25 to 100 kDa.
Gliadins are mainly monomeric proteins with molecular weights around 28,000–55,000 and can be classified according to their different primary structures into the alpha/beta-, gamma-, and omega-types. Gluten proteins comprise ω5-, ω1,2-, α-, and γ-gliadins as well as high-molecular-weight glutenin subunits (HMW-GS) and low-molecular-weight (LMW) GS.
The carboxy-terminal half of α- and γ-gliadins have α-helix-rich secondary structures stabilized with intramolecular disulfide bonds. The amino-terminal-repeat region of α- and γ-gliadins has poly-L-proline II and β-reverse-turn structures. ω-Gliadins also have poly-L-proline II and β-reverse-turn structures, but no α-helix structure. The amino acid compositions of the α/β-, γ-, and ω-gliadins are similar to each other, although the ω-gliadins contain little or no cysteine or methionine and only small amounts of basic amino acids.
The Osborne fractionation system classifies proteins by extraction in a series of solvents; prolamins such as gliadin are soluble in 60–70% alcohol. Gliadin is one of the main proteins in wheat gluten and is extracted using 70% ethanol. Gliadin, or the gliadin fraction of gluten, has a low ionic strength and excellent film-forming properties. Gliadin is insoluble in water; however, its solubility may be modified with the addition of a surfactant and/or adjustment of the pH by acidification. Typical acids suitable for solubilizing gliadin include citric acid, malic acid, lactic acid, oxalic acid, tartaric acid, ascorbic acid, and acetic acid.
In the pharmaceutical and biomedical sciences, gliadin is formulated as nanoparticles, nanofibers, and films. Gliadins — alcohol-soluble prolamins obtained from wheat — are versatile polymers used for the development of various systems and for different applications, including nanoparticles, nanofibers, and films with the capacity to retain various active compounds. In food science, gliadin may be encountered as purified wheat gliadin fractions added to food products to modify rheological properties.
Gluten may be one of the first proteins to be studied by scientists. It was isolated in 1728 by Jacopo Beccari, a professor of chemistry at the University of Bologna. He described gluten as a sticky paste that resulted from washing dough made with wheat grain flour with dilute salt solution. About 90 years later, gluten was separated into two fractions that differed in their solubility in alcohol. The proteins in the soluble fraction were referred to as gliadins, while the insoluble fraction was originally named zymon. Zymon was later renamed glutenin (Taddei, 1819).
In the late 1800s and early 1900s, researchers like Osborne and Mendel began fractionating gluten, separating it into the alcohol-soluble gliadin and the alkali-soluble glutenin. Thomas Burr Osborne developed a classification system in the early 1900s based on protein solubility, identifying prolamins like gliadin as alcohol-soluble storage proteins. This system categorized plant proteins into albumins, globulins, prolamins, and glutelins — a framework still used today. Osborne's work laid the groundwork for understanding cereal protein diversity and their roles in nutrition.
Gliadins are well-known wheat grain proteins, particularly important in food science. They were studied as early as the 1700s. As a naturally occurring food constituent rather than a cultivated medicinal herb, gliadin does not have a documented history of intentional therapeutic or folk-medicinal use in the traditional sense. The protein exists as a component of wheat-based foods that have been consumed across cultures for millennia. Gliadin's emergence as a subject of biomedical research — particularly regarding its pathological role — is a modern phenomenon dating primarily to the 20th century. The amino acid glutamine was, notably, first isolated from gliadin, a protein present in wheat, in 1932.
The scientific interest in gliadin as a discrete entity accelerated dramatically with the mid-20th century discovery of its role in celiac disease. The subsequent characterization of its immunotoxic peptides (particularly in the 1990s and 2000s) transformed the field of gastroenterology and mucosal immunology. More recently, gliadin has become a subject of nanotechnology and drug delivery research as a biocompatible scaffold material.
Both gliadins and glutenins consist of numerous, partially closely related protein components characterized by high glutamine and proline contents. The name "prolamins" was derived from the fact that these proteins had lots of proline and amide groups, which we now know derive from a high abundance of glutamine. This unusual amino acid composition — especially the densely proline-rich sequences — has profound biological consequences, because human digestive enzymes are unable to efficiently cleave sequences with multiple adjacent proline residues.
Gliadins are exceptionally resistant to enzymatic hydrolysis during digestion in all individuals, regardless of whether they suffer from celiac disease or not. This resistance generates intact peptide fragments that reach the small intestinal epithelium.
Two broad categories of bioactive gliadin peptides have been extensively characterized:
An unusual feature of α-gliadin epitopes is the presence of multiple proline residues at relative positions within the binding core. These residues may serve to protect from proteolytic cleavage during luminal digestion and/or class II processing.
Celiac disease is a permanent immune-mediated food intolerance triggered by ingestion of wheat gliadins in genetically susceptible individuals. It has been reported that tissue transglutaminase plays an important role in the onset of celiac disease by converting specific glutamine residues within gliadin fragments into glutamic acid residues. This process increases the binding affinity of gliadin peptides to HLA-DQ2/DQ8 molecules, thus enhancing the immune response.
The enzyme converts particular glutamine residues in gluten peptides to glutamic acid during a deamidation reaction. This results in higher affinity of these gliadin peptides for HLA-DQ2 or DQ8, thereby promoting the activation of T cells.
Fasano identified zonulin, a family of paracrine proteins that reversibly modulate the permeability of tight junctions (TJs) upon gliadin exposure. Luminal zonulin release is stimulated upon gliadin exposure, the toxic component of gluten, or microbiome imbalance. On enterocytes and monocytes, gliadin binds to the CXCR3 chemokine receptor and initiates a MyD88-dependent luminal release of zonulin.
When exposed to gliadin, zonulin receptor-positive IEC6 and Caco2 cells released zonulin in the cell medium with subsequent zonulin binding to the cell surface, rearrangement of the cell cytoskeleton, loss of occludin-ZO1 protein–protein interaction, and increased monolayer permeability. Pretreatment with the zonulin antagonist FZI/0 blocked these changes without affecting zonulin release.
Gliadin activates zonulin signaling irrespective of the genetic expression of autoimmunity, leading to increased intestinal permeability to macromolecules. Chronic gliadin exposure caused down-regulation of both ZO-1 and occludin gene expression. This indicates that prolonged gliadin exposure causes more sustained barrier dysfunction than acute exposure.
In celiac disease (CD) the prototype of an immune-mediated response dominated by the activation of the adaptive immune system, and in particular of CD4+ HLA class II restricted T cells, has been established. Various seminal studies have established the precise mechanism of how antigen (prolamine)-specific activation of CD4+ mucosal T cells occurs.
Although the structural changes of the celiac mucosa are considered a consequence of sustained mucosal inflammation due to the Th1-TC response, recent data have shown that gliadin peptides, in particular P31–43, induce proliferation of celiac enterocytes. This process is epithelial growth factor (EGF) and IL-15 dependent and has profound upstream effects in inducing the crypt hyperplasia characteristic of the remodeling of the celiac mucosa.
Evidence supports a direct activation of the innate immune system by fragments of prolamins, which are not recognized T cell epitopes. The gliadin-induced activation of the innate immune system might also have a significant role in the induction and persistence of many CD complications, and most definitively for the most aggressive one, namely mucosal T cell lymphomas.
Specific gliadin peptides can bind to DQ2 and DQ8 heterodimers on the surface of antigen-presenting cells (APCs), inducing CD4+ T cell activation in the intestinal lamina propria. A preliminary deamidation step catalyzed by tissue transglutaminase (tTG) appears crucial, as the negative charges introduced in the gliadin molecules by this reaction significantly increase the binding affinity of peptides to DQ2 and DQ8 heterodimers.
Gluten-specific, CD4+ intestinal T cells can be isolated from intestinal biopsies of CD patients but not of controls. These CD4+ cells are TCR-α/β+ and typically of the Th1 phenotype, secreting large amounts of IFN-γ, a cytokine that has been linked to mucosal damage.
Gluten activates innate and adaptive immune responses and induces the secretion of cytokines. The innate and adaptive immune systems may respond synergistically to gliadin peptides. The role of post-translational modifications of gliadin peptides catalyzed by tissue transglutaminase (tTG) is thought to play a crucial role in celiac disease.
Considering bread dough's rheological properties, gliadin contributes to the flow properties, while glutenin contributes to its elasticity and strength. Intrachain disulfide bonds, present in all types except ω-gliadins, stabilize the three-dimensional structure. For ease of understanding, the gluten network represents a two-component glue, in which gliadins can be seen as a "plasticizer" or "solvent" for glutenins. An appropriate ratio of both fractions is essential to impart the viscoelastic dough properties required to achieve a high-quality end product.
Celiac disease, wheat allergy, and non-celiac wheat sensitivity constitute the three main categories of wheat-related disorders. Celiac disease is a well-characterized immune-mediated disease caused by immune reaction against specific gliadin epitopes, the main protein in wheat.
Celiac disease (CD) is an autoimmune disease triggered by the intake of gluten found in wheat, rye, and barley. Around 1% of the population have CD, and most of them express at least one of the two MHC II genes: HLA-DQ2 and HLA-DQ8 haplotypes.
Evidence strength: The mechanistic and pathogenetic role of gliadin in celiac disease is among the best-characterized protein–immune interactions in human medicine. The evidence base is composed of decades of human intestinal biopsy studies, T-cell cloning, molecular epitope mapping, and clinical intervention trials (specifically gluten-free diet). 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. This constitutes robust, well-replicated, mechanistically grounded clinical evidence.
Antibodies against native gliadin are not recommended for the detection of celiac disease. The AGA test has a low diagnostic accuracy and is considered outdated. Immunoglobulin A (IgA) anti-tissue transglutaminase (tTG) antibody is the preferred single test for the serologic diagnosis of CD in individuals over the age of 2 years. The IgA anti-tTG test has 95% or higher sensitivity and specificity for CD.
Tests for antibodies against the deamidated peptide of gliadin (DGP) have replaced the classic AGA test. Anti-DGP assays carry a considerably higher diagnostic accuracy than the old AGA assays, especially in the IgG class, and can substitute for anti-tTG tests in patients with selective IgA deficiency.
In a recent review, the pooled sensitivity for IgA deamidated gliadin peptide antibodies was 88%, with specificity of 95%. Testing for IgA and IgG antibodies to unmodified gliadin proteins is no longer recommended because of the low sensitivity and specificity of these tests for celiac disease.
Problematic with AGA is that the typical sensitivity and specificity was about 85%. Gliadin peptides which are synthesized as the deamidated form have much higher sensitivity and specificity, creating two serological tests for CD that approach biopsy diagnostic performance.
Evidence strength: High-quality, well-replicated clinical evidence across multiple systematic reviews and pediatric/adult populations. Diagnostic utility of deamidated gliadin peptide antibodies is well established and endorsed by clinical laboratory authorities.
Non-celiac gluten sensitivity (NCGS) is a clinical entity characterized by the absence of celiac disease and wheat allergy in patients that trigger reproducible symptomatic responses to gluten-containing food consumption. Due to the lack of sensitive and reproducible biomarkers for NCGS diagnosis, placebo-controlled gluten challenges must be carried out for its diagnosis. The gluten challenges can be either double- or single-blind, for research or clinical practice purposes, respectively.
Although approximately 10% of adults worldwide self-report gluten or wheat sensitivity, meta-analyses suggest that, during controlled challenge studies, 16–30% of these individuals have symptoms specifically triggered by gluten. However, methodological variability — including the presence of fermentable carbohydrates in challenge preparations — limits interpretation. Current evidence suggests that fermentable carbohydrates and nocebo effects contribute considerably to symptom generation in many cases.
Non-celiac gluten sensitivity is a syndrome characterized by gastrointestinal and extra-intestinal symptoms occurring a few hours or days after gluten and/or other wheat protein ingestion and rapidly improving after exclusion of potential dietary triggers. There are no established laboratory markers for non-celiac gluten sensitivity, although a high prevalence of first-generation anti-gliadin antibodies of IgG class has been reported in this condition.
In a study of 44 non-celiac gluten sensitivity and 40 celiac disease patients, anti-gliadin antibodies of both IgG and IgA classes were assayed by ELISA after 6 months of gluten-free diet. The majority of non-celiac gluten sensitivity patients (93.2%) showed the disappearance of anti-gliadin antibodies of IgG class after 6 months of gluten-free diet; in contrast, 16/40 (40%) of celiac patients displayed the persistence of these antibodies after gluten withdrawal.
Non-celiac wheat sensitivity, despite being the most recently recognized, has the highest reported prevalence among the three wheat-related entities. It remains, however, particularly poorly characterized due to unclear pathophysiology and lack of diagnostic markers.
Evidence strength: Preliminary to moderate. The existence of NCGS as a distinct clinical entity is acknowledged, but the exact role of gliadin (versus other wheat components such as amylase-trypsin inhibitors or FODMAPs) remains unresolved. Controlled clinical trials are methodologically challenging, and biomarkers are lacking.
Wheat allergy consists of IgE- and non-IgE-mediated reactions, driven by Th2-cells directing eosinophil and basophil responses. Rapid IgE-mediated reactions are characterized by specific IgE antibodies in conjunction with symptoms originating especially from the respiratory and gastrointestinal tracts.
In wheat allergy, a specific sequence of gliadin peptides cross-links two IgE molecules on the surface of mast cells and basophils, triggering the release of mediators such as histamines and leukotrienes. Several studies have shown that sensitization particularly to omega-5 gliadin is associated with challenge-proven wheat allergy. Moreover, recent data imply that gliadin-positive patients have more likely severe reactions after wheat ingestion. A well-characterized severe clinical entity is wheat-dependent, exercise-induced anaphylaxis, in which sensitization to omega-5 gliadin is a prerequisite.
Non-IgE-mediated wheat allergy is a less-well-defined condition, which is often diagnostically challenging due to a longer interval between exposure and symptoms and lack of non-invasive biomarkers. In this condition, wheat as a trigger needs to be established by exclusion followed by dietary challenge.
Evidence strength: The association between omega-5 gliadin and wheat-dependent exercise-induced anaphylaxis (WDEIA) is well established in the allergology literature. IgE-specific testing to gliadin fractions is clinically validated for diagnosing this subset of wheat allergy.
Ex vivo studies using intestinal biopsy specimens showed that intestinal biopsy specimens of CD patients mounted a more pronounced response to gliadin when compared with non-celiac controls, including an increased and persistent release of zonulin and a significant increase in intestinal permeability.
Fasano found that gliadin activates zonulin signaling irrespective of the genetic expression of autoimmunity, leading to increased intestinal permeability to macromolecules. However, the degree and persistence of this effect differs markedly between celiac and non-celiac individuals. Biopsies from non-celiac patients demonstrated a limited, transient zonulin release which was paralleled by an increase in intestinal permeability that never reached the level of permeability seen in celiac disease tissues.
Evidence strength: The mechanistic evidence for gliadin-induced intestinal permeability via zonulin is robust in vitro and ex vivo. Human clinical translation in non-celiac populations remains an active area of research with findings that require further controlled study.
Gliadin is a protein derived from wheat and due to its biodegradable, biocompatible, and natural origin it is used for the synthesis of polymeric nanoformulations. Previous studies have shown the synthesis of gliadin nanoparticles and evaluated them for drug delivery and controlled release applications.
Gliadin nanoparticles are polymers suitable for targeted drug delivery because they show affinity for the upper gastrointestinal tract, but are not well anchored to other gastrointestinal tracts. Gliadin nanoparticles can be used as a controlled-release system suitable for hydrophobic and amphiphilic drugs. The advantage of using water-insoluble proteins is that no additional curing step is required to maintain the integrity in water-based products.
Gliadin nanoparticles are obtained by a desolvation method, also known as drawing-out precipitation. These particles have been shown to be interesting as drug release systems for all-trans-retinoic acid. Comparative work shows that the amount of entrapped Vitamin E and linalool/linalyl acetate is higher than that of cationic benzalkonium chloride, confirming a strong interaction between gliadins and apolar compounds, due to the apolarity of the proteins.
Gliadin nanoparticles (GNPs) have been formulated for their applications in sustained drug release for various drugs including meletin, amoxicillin, polymethoxyflavones, resveratrol, paclitaxel, and carbazole.
Gliadin-based nanoparticles have peculiar bioadhesive properties. Chemical modification of gliadin can enhance its solubility. Gliadin-based films can be employed as biodegradable food-grade packaging materials. Gliadin nanofibers have potential application for tissue engineering.
Phagocytosis and immunogenicity of gliadin nanoparticles are strongly influenced by particle size. The results of this study can provide useful information for rational design of protein-based nanomaterials in drug delivery applications.
Evidence strength: Predominantly preclinical (in vitro and animal model data). Gliadin nanoparticle research is an active and promising field, but as of present, human clinical trials using gliadin as a drug-delivery vector are not established in the published literature surveyed here.
The small intestinal epithelium is the primary site of gliadin's biological effects. Undigested fragments of gliadin cross the brush border via transcellular and paracellular mechanisms, allowing them to stimulate a host of deleterious effects on the small intestine including cytotoxicity, immunomodulation, and gut permeation. In celiac disease, these effects culminate in villous atrophy, crypt hyperplasia, and malabsorption. Initial symptoms of celiac disease are gastrointestinal discomfort as well as increased permeability and inflammation of the small bowel.
Both the innate and adaptive arms of the immune system are activated by gliadin. The pathogenesis of celiac disease involves both innate and adaptive immunity as well as upregulation of IL-15. Macrophage activation is also implicated: gliadin, the most prominent causative agent of celiac disease, has been reported to trigger the production of pro-inflammatory cytokines in macrophages.
Celiac disease is a chronic inflammatory enteropathy caused by gluten in genetically predisposed individuals carrying the HLA-DQ2/HLA-DQ8 genotype. This pathology has a multifactorial etiology in which HLA genes, the microbiome, gluten, and other environmental factors are involved in the development of the disease. Beyond celiac disease itself, gliadin-induced autoimmunity can extend to extraintestinal manifestations including dermatitis herpetiformis (a skin condition) and gluten ataxia (a neurological condition), though detailed discussion of those comorbidities falls outside the primary scope of gliadin biochemistry.
Anti-gliadin antibodies have been detected in patients with certain neurological conditions including gluten ataxia, though this area remains the subject of ongoing research with evidence that is primarily observational in nature.
Because gliadin is not a conventional dietary supplement but a food protein and a subject of biomedical research, "dosage" in the clinical sense refers primarily to experimental concentrations used in laboratory and clinical research settings.
No standardized therapeutic oral dosage of purified gliadin as a dietary supplement has been established in the scientific literature, as gliadin is not used as a supplement for health promotion. Research doses are specific to experimental contexts.
Celiac disease is a well-characterized immune-mediated disease caused by immune reaction against specific gliadin epitopes. In individuals with celiac disease, any exposure to gliadin is pathological. Even small amounts of gliadin trigger the immune cascade leading to intestinal damage. There is no effective treatment other than diet control.
A well-characterized severe clinical entity is wheat-dependent, exercise-induced anaphylaxis, in which sensitization to omega-5 gliadin is a prerequisite. In this condition, gliadin ingestion combined with physical exercise can precipitate systemic anaphylaxis, a potentially life-threatening reaction.
NCGS does not have a strong genetic association and has not been associated with the same nutritional deficiencies, intestinal tissue damage, and autoimmune reactions as celiac disease. However, the symptoms triggered in NCGS are lower in intensity than those triggered in CD and WA, and there is no evidence of long-term complications in comparison to CD.
During the development of gliadin-based particulate systems, understanding the interaction of nanoparticles with blood and immune cells is essential for safety. One of the major limitations of parenterally administered particulates is the recognition by the immune cells of the reticuloendothelial system (RES) and subsequent clearance from the circulation without exerting the intended effect.
All diagnostic serologic testing should be done in patients on a gluten-containing diet. Affected individuals who have been on a gluten-free diet prior to testing may have a negative result. Screening of asymptomatic adults, adolescents, and children is not recommended.
Almost all patients with celiac disease express the MHC class II molecules HLA-DQ2.5, HLA-DQ8, or HLA-DQ2.2, with HLA-DQ2.5 being the major genetic risk factor. The high prevalence of these haplotypes in European populations helps explain the relatively high prevalence of celiac disease in those ancestries.
Research indicates that gliadin induces transient, reversible increases in intestinal permeability even in non-celiac individuals, though the clinical significance of this in healthy persons with intact mucosal immune tolerance remains debated in the scientific literature. The effect is mechanistically distinct from and far less severe than the sustained mucosal damage seen in celiac disease.
Health conditions that Gliadin may help support.
Body systems that Gliadin may help support.
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