Dietary fat and an exogenous emulsifier increase the gastrointestinal absorption of a major soybean allergen, Gly m Bd 30K, in mice

New Perspectives on Food Matrix Modulation of Food Allergies: Immunomodulation and Component Interactions

Food allergy is a multifactorial interplay process influenced not only by the structure and function of the allergen itself but also by other components of the food matrix. For food, before it is thoroughly digested and absorbed, numerous factors make the food matrix constantly change. This will also lead to changes in the chemistry, biochemical composition, and structure of the various components in the matrix, resulting in multifaceted effects on food allergies. In this review, we reveal the relationship between the food matrix and food allergies and outline the immune role of the components in the food matrix, while highlighting the ways and pathways in which the components in the food matrix interact and their impact on food allergies. The in-depth study of the food matrix will essentially explore the mechanism of food allergies and bring about new ideas and breakthroughs for the prevention and treatment of food allergies.

Intestinal protein uptake and IgE-mediated food allergy

Food allergy is affecting 5-8% of young children and 2-4% of adults and seems to be increasing in prevalence. The cause of the increase in food allergy is largely unknown but proposed to be influenced by both environmental and lifestyle factors. Changes in intestinal barrier functions and increased uptake of dietary proteins have been suggested to have a great impact on food allergy. In this review, we aim to give an overview of the gastrointestinal digestion and intestinal barrier function and provide a more detailed description of intestinal protein uptake, including the various routes of epithelial transport, how it may be affected by both intrinsic and extrinsic factors, and the relation to food allergy. Further, we give an overview of in vitro, ex vivo and in vivo techniques available for evaluation of intestinal protein uptake and gut permeability in general. Proteins are digested by gastric, pancreatic and integral brush border enzymes in order to allow for sufficient nutritional uptake. Absorption and transport of dietary proteins across the epithelial layer is known to be dependent on the physicochemical properties of the proteins and their digestion fragments themselves, such as size, solubility and aggregation status. It is believed, that the greater an amount of intact protein or larger peptide fragments that is transported through the epithelial layer, and thus encountered by the mucosal immune system in the gut, the greater is the risk of inducing an adverse allergic response. Proteins may be absorbed across the epithelial barrier by means of various mechanisms, and studies have shown that a transcellular facilitated transport route unique for food allergic individuals are at play for transport of allergens, and that upon mediator release from mast cells an enhanced allergen transport via the paracellular route occurs. This is in contrast to healthy individuals where transcytosis through the enterocytes is the main route of protein uptake. Thus, knowledge on factors affecting intestinal barrier functions and methods for the determination of their impact on protein uptake may be useful in future allergenicity assessments and for development of future preventive and treatment strategies.

Effects of emulsifiers on an in vitro model of intestinal epithelial tight junctions and the transport of food allergens

SCOPE

Certain food emulsifiers may interfere with gut barrier function in ways correlating to increased exposure to allergens. Understanding the consequences of interactions between these food ingredients and the intestinal epithelium is important for evaluating allergen dose exposure characteristics.

METHODS AND RESULTS

Wechallenged Caco-2 cell monolayers, an in vitromodel of human intestinal epithelial tight junctions with synthetic polysorbate-80 or natural lecithin alone, or in combination with known allergens (egg proteins: ovalbumin, ovomucoid, and ovotransferrin; and a synthetic form of galactose-alpha-1,3-galactose (alpha-gal), an allergen of increasing concern). For most doses of individual emulsifiers and allergens, >90% cell viability and <15% cytotoxicity wasobserved; however, toxicity increased at a 0.5% concentration of emulsifiers. At low cytotoxic concentration (0.2%), only polysorbate-80 treatment reduced monolayer integrity (∼20%) with increased lucifer yellow passage. Dose-related differences in expression of tight junction genes and occludin proteins wereobserved with emulsifier treatments. The transport of all tested allergens across the cell monolayers, excluding ovotransferrin, nearly doubled in the presence of 0.2% polysorbate-80 compared to lecithin and untreated control.

CONCLUSION

By modulating paracellular permeability, polysorbate-80 may enhance absorption of allergens in a size-dependent manner. This article is protected by copyright. All rights reserved.

Lipophilic Allergens, Different Modes of Allergen-Lipid Interaction and Their Impact on Asthma and Allergy

Molecular allergology research has provided valuable information on the structure and function of single allergenic molecules. There are several allergens in food and inhalant allergen sources that are able to interact with lipid ligands via different structural features: hydrophobic pockets, hydrophobic cavities, or specialized domains. For only a few of these allergens information on their associated ligands is already available. Several of the allergens are clinically relevant, so that it is highly probable that the individual structural features with which they interact with lipids have a direct effect on their allergenic potential, and thus on allergy development. There is some evidence for a protective effect of lipids delaying the enzymatic digestion of the peanut (Arachis hypogaea) allergen Ara h 8 (hydrophobic pocket), probably allowing this molecule to get to the intestinal immune system intact (sensitization). Oleosins from different food allergen sources are part of lipid storage organelles and potential marker allergens for the severity of the allergic reaction. House dust mite (HDM), is more often associated with allergic asthma than other sources of inhalant allergens. In particular, lipid-associated allergens from Dermatophagoides pteronyssinus which are Der p 2, Der p 5, Der p 7, Der p 13, Der p 14, and Der p 21 have been reported to be associated with severe allergic reactions and respiratory symptoms such as asthma. The exact mechanism of interaction of these allergens with lipids still has to be elucidated. Apart from single allergens glycolipids have been shown to directly induce allergic inflammation. Several-in parts conflicting-data exist on the lipid (and allergen) and toll-like receptor interactions. For only few single allergens mechanistic studies were performed on their interaction with the air-liquid interface of the lungs, in particular with the surfactant components SP-A and SP-D. The increasing knowledge on protein-lipid-interaction for lipophilic and hydrophobic food and inhalant allergens on the basis of their particular structure, of their capacity to be integral part of membranes (like the oleosins), and their ability to interact with membranes, surfactant components, and transport lipids (like the lipid transfer proteins) are essential to eventually clarify allergy and asthma development.

The Extract of Soybean Protein Increases Slow-Myosin Heavy Chain Expression in C2C12 Myotubes

Skeletal muscle is composed of four types of fibers in mammals; oxidative slow-twitch type I, oxidative fast-twitch IIA, and glycolytic fast-twitch IIB and IIX/D. In this study using C2C12 myotubes, an extract of soybean protein significantly upregulated mRNA level of myosin heavy chain 7 (Myh7), the predominant isoform expressed in oxidative slow-twitch type I and downregulated mRNA levels of Myh4, the predominant isoform expressed in glycolytic fast-twitch IIB. Similarly, its hydrolysate prepared using digestive enzyme also significantly increased Myh7 expression. In contrast, no significant change was observed in Myh4 mRNA level after the hydrolysate treatment. These findings suggest that dietary intake of the soybean protein extract may increase oxidative slow-twitch fiber in skeletal muscle.

Peanut oleosins associated with severe peanut allergy-importance of lipophilic allergens for comprehensive allergy diagnostics

BACKGROUND

Peanut allergy is one of the most common and most severe food allergies in Western countries and its accurate diagnosis to prevent potential life-threatening allergic reactions is crucial. However, aqueous extracts used for routine diagnostic measurements are devoid of lipophilic allergens such as oleosins. We have recently succeeded in the isolation and purification of these unique proteins, and the present study evaluates their allergenic potential and clinical relevance.

OBJECTIVE

We sought to assess allergenicity and sensitization prevalence of oleosins obtained from both raw and in-shell roasted peanuts. In addition, we tested the utilization of natural and recombinant oleosins for allergy diagnostic purposes.

METHODS

Oleosin sensitization, prevalence, and impact of thermal processing were analyzed by immunoblot with sera from 52 peanut-allergic individuals displaying different clinical phenotypes. The application of natural and recombinant oleosins for allergy diagnostics was investigated by basophil activation test (BAT). IgE-binding epitopes were identified by oligopeptide microarray.

RESULTS

Sensitization to oleosins was observed exclusively in peanut-allergic subjects suffering from severe systemic reactions. IgE-binding capacity of oleosins derived from in-shell roasted peanuts was increased as shown by immunoblot analysis and BAT. Both natural and recombinant molecules can be used to identify oleosin-sensitized patients by BAT. A linear epitope of Ara h 15 was determined that displays high similarity to other seed-derived oleosins.

CONCLUSIONS

Oleosins are clinically relevant peanut allergens and most likely associated with severe allergic symptoms. In-shell roasting increases their allergenicity, which is consistent with the observation that most allergic reactions are in connection with roasted peanuts.

Do lipids influence the allergic sensitization process?

Allergic sensitization is a multifactorial process that is not only influenced by the allergen and its biological function per se but also by other small molecular compounds, such as lipids, that are directly bound as ligands by the allergen or are present in the allergen source. Several members of major allergen families bind lipid ligands through hydrophobic cavities or electrostatic or hydrophobic interactions. These allergens include certain seed storage proteins, Bet v 1–like and nonspecific lipid transfer proteins from pollens and fruits, certain inhalant allergens from house dust mites and cockroaches, and lipocalins. Lipids from the pollen coat and furry animals and the so-called pollen-associated lipid mediators are codelivered with the allergens and can modulate the immune responses of predisposed subjects by interacting with the innate immune system and invariant natural killer T cells. In addition, lipids originating from bacterial members of the pollen microbiome contribute to the outcome of the sensitization process. Dietary lipids act as adjuvants and might skew the immune response toward a T_H2-dominated phenotype. In addition, the association with lipids protects food allergens from gastrointestinal degradation and facilitates their uptake by intestinal cells. These findings will have a major influence on how allergic sensitization will be viewed and studied in the future.

Development of oral immunotherapy model using B10.A mice and egg white lysozyme

Oral immunotherapy for food allergy has been the focus of a lot of attention recently. The patients have to eat allergenic food instead of eliminating it in this therapy and there is no established standard method yet. To promote clear understanding and improvement of oral immunotherapy, the present study using B10.A mice investigated the effect of multiple oral administration of a model antigen, egg-white lysozyme, on both the antibody response and the anaphylactic reaction induced by subsequent administration of lysozyme. Various doses of egg-white lysozyme (0-100 mg/mouse) were administered to mice intragastrically for 6 d; then additional lysozyme was administered via the intraperitoneal route in all groups. Lysozyme-specific antibody responses were promptly induced by the first oral administration and enhanced by intraperitoneal administration. An anaphylactic reaction was further induced in these sensitized mice by intragastric administration of lysozyme, and the symptoms of shock were compared in order to evaluate the effects of pretreatment. Interestingly, the decrease in rectal temperature which is one of the common anaphylactic symptoms in mice was suppressed in all of the oral pre-administration groups, and the effects were highest in the group that received 20 mg. Consequently, this study using B10.A mice has shown that sensitization can be induced by intragastric administration of lysozyme instead of oral tolerance; however, anaphylactic shock induced by subsequent intragastric administration of lysozyme is suppressed. This mouse model would be useful for assessing the method of oral immunotherapy.

Immunological response in egg-sensitive adults challenged with cheese containing or not containing lysozyme

OBJECTIVE

Lysozyme is an enzyme that hydrolyzes bacterial peptidoglicans. For this reason, it is used in cheese manufacturing in order to prevent a defect of long-ripened hard cheese called "late blowing" due to the outgrowth of spores of Clostridium tyrobutyricum and Clostridium butyricum. Moreover, germination of Listeria monocytogenes spores into vegetative cells is also sensitive to lysozyme. The enzyme can be an allergenic molecule, and for this reason there are concerns about its use in food industry. The immunological and clinical response of consumption of lysozyme-containing cheese has been evaluated in 25 egg-sensitive subjects with or without lysozyme sensitization.

METHODS

A total of 25 egg-sensitive subjects were enrolled in this study. All the subjects were already treated for egg-sensitization and presented a positive skin prick test. All the subjects had a body mass index ≤ 25 kg/m(2) and were in the age range of 20-50 years. Each subject was studied twice and received randomly 30 g of Grana Padano (containing lysozyme) or TrentinGrana cheese (lysozyme-free) of two different aging periods: 16 or 24 months. A washout period of 1 week between each cheese intake was adopted. Blood samples were taken in fasting conditions and 1 hour after cheese intake and IgA, total IgE, and lysozyme-, ovomucoid-, and ovalbumin-specific IgE were measured.

RESULTS

No adverse reactions were observed in both groups of patients after cheese samples were given. Lysozyme did not determine any variation of specific IgE compared with basal level. In lysozyme-sensitive patients a significant relationship between IgA and lysozyme-specific IgE was observed when lysozyme-containing cheese was given, confirming that lysozyme can pass the gut barrier.

CONCLUSIONS

Neither adverse events nor immunological responses were observed after ingestion of cheese containing lysozyme. However, the immunological properties of peptides deriving from cheese protein hydrolysis need to be clarified, as does the effect of lysozyme on bacterial proteolytic activity.

The major soyabean allergen P34 resists proteolysis in vitro and is transported through intestinal epithelial cells by a caveolae-mediated mechanism

Soya is considered to be one of the eight most significant food allergens. Among the allergenic soya proteins determined to date, P34 has been identified as one of the immunodominant soya antigens. Sensitisation to a specific food antigen like P34 generally follows the transit of intact antigens across the intestinal barrier and usually occurs in infants, who are most susceptible to food allergies. In the present study, we used the intestinal epithelial cell line IPEC-J2, which was originally derived from the jejunum of a neonatal piglet, to recapitulate the infant intestinal epithelium and study the binding and uptake of P34 protein. P34 was partially resistant to degradation in an in vitro proteolysis assay. IPEC-J2 cells were able to endocytose intact P34, as shown by immunofluorescence and immunoelectronmicroscopy methods. P34 associated with lipid raft microdomains of IPEC-J2 cells, and disruption of caveolae/lipid raft microdomains using methyl-β-cyclodextrin abolished P34 endocytosis, indicating that the observed endocytosis was mediated by caveolae. Using IPEC-J2 cells grown on Transwell filters, we further demonstrated that P34 is transported through the epithelial monolayer by transcytosis. Piglets frequently show hypersensitivity to soya antigens, and in this study, we show that healthy adult pigs with dietary exposure to soya protein mount an antibody response to soyabean protein P34, suggesting that this protein has entered the body, probably through gastrointestinal uptake. In summary, our data suggest that soya P34 resists proteolysis in the gastrointestinal tract and is transported through the intestinal epithelial barrier, thereby allowing sensitisation of immune cells in the sub-epithelial compartment.

Should digestion assays be used to estimate persistence of potential allergens in tests for safety of novel food proteins?

Food allergies affect an estimated 3 to 4% of adults and up to 8% of children in developed western countries. Results from in vitro simulated gastric digestion studies with purified proteins are routinely used to assess the allergenic potential of novel food proteins. The digestion of purified proteins in simulated gastric fluid typically progresses in an exponential fashion allowing persistence to be quantified using pseudo-first-order rate constants or half lives. However, the persistence of purified proteins in simulated gastric fluid is a poor predictor of the allergenic status of food proteins, potentially due to food matrix effects that can be significant in vivo. The evaluation of the persistence of novel proteins in whole, prepared food exposed to simulated gastric fluid may provide a more correlative result, but such assays should be thoroughly validated to demonstrate a predictive capacity before they are accepted to predict the allergenic potential of novel food proteins.

Safety assessment considerations for food and feed derived from plants with genetic modifications that modulate endogenous gene expression and pathways

The current globally recognized comparative food and feed safety assessment paradigm for biotechnology-derived crops is a robust and comprehensive approach for evaluating the safety of both the inserted gene product and the resulting crop. Incorporating many basic concepts from food safety, toxicology, nutrition, molecular biology, and plant breeding, this approach has been used effectively by scientists and regulatory agencies for 10-15 years. Current and future challenges in agriculture include the need for improved yields, tolerance to biotic and abiotic stresses, and improved nutrition. The next generation of biotechnology-derived crops may utilize regulatory proteins, such as transcription factors that modulate gene expression and/or endogenous plant pathways. In this review, we discuss the applicability of the current safety assessment paradigm to biotechnology-derived crops developed using modifications involving regulatory proteins. The growing literature describing the molecular biology underlying plant domestication and conventional breeding demonstrates the naturally occurring genetic variation found in plants, including significant variation in the classes, expression, and activity of regulatory proteins. Specific examples of plant modifications involving insertion or altered expression of regulatory proteins are discussed as illustrative case studies supporting the conclusion that the current comparative safety assessment process is appropriate for these types of biotechnology-developed crops.

Uptake of 2S albumin allergens, Ber e 1 and Ses i 1, across human intestinal epithelial Caco-2 cell monolayers

We have investigated the absorption rates of two purified major allergen 2S albumins, Ber e 1 from Brazil nuts (Bertholletia excelsa Humb. & Bonpl.) and Ses i 1 from white sesame seeds (Sesamum indicum L.), across human intestinal epithelial Caco-2 cell monolayers following gastrointestinal digestion in vitro. The transport from apical to basolateral side in cell monolayers was evaluated by RP-HPLC-UV and indirect competitive ELISA methods, being confirmed by western-blotting analysis. Significant amounts (approximately 15-25 nmol micromol(-1) initial amount/h) of intact Ber e 1 and Ses i 1 were found in the basolateral side. The absorption rates of both plant allergens through the cell monolayer were shown to be constant during the whole incubation period (4 h at 37 degrees C), verifying that the permeability of the membrane was not altered by the allergen digests. Our findings revealed that both purified 2S albumin allergens may be able to survive in immunologically reactive forms to the simulated harsh conditions of the gastrointestinal tract to be transported across the Caco-2 cell monolayers, so that they would be able to sensitize the mucosal immune system and/or elicit an allergic response.

Sodium cromoglycate inhibits absorption of the major soybean allergen, Gly m Bd 30K, in mice and human intestinal Caco-2 cells

Our previous data showed that Gly m Bd 30K was absorbed from the gastrointestinal tract and circulated in blood in mice. This study was conducted to determine the mechanism and identify the inhibitor of such absorption. Using sandwich ELISA and immunoblotting, we found that intact Gly m Bd 30K was absorbed from apical to basolateral solutions and intracellularly accumulated by Caco-2 cells in a dose- and time-dependent manner. The absorption and intracellular accumulation of Gly m Bd 30K were significantly suppressed when Caco-2 cells were treated with sodium cromoglycate (SCG) (0-50 mmol/L) in a dose-dependent manner. In 24-d-old mice orally treated with SCG (10-1000 mg/kg body weight), plasma Gly m Bd 30K concentration decreased significantly 30-120 min after Gly m Bd 30K (2000 mg/kg body weight) administration. Moreover, inhibitors that suppress the clathrin-dependent endocytosis dansylcadaverine, the caveolae-dependent endocytosis nystatin and clathrin, and the caveolae-dependent endocytosis methyl-beta-cyclodextrin had inhibitory effects on the absorption and intracellular accumulation of Gly m Bd 30K by Caco-2 cells. These data indicate that Gly m Bd 30K is absorbed and intracellularly accumulated in Caco-2 cells via clathrin- or caveolae-dependent endocytosis. We propose that the absorption and intracellular accumulation of Gly m Bd 30K are inhibited by SCG via clathrin- or caveolae-dependent endocytosis.

Immunogenic and allergenic potentials of natural and recombinant innocuous proteins

A new aspect of protein immunogenic and allergenic properties has become important recently, when there is a higher chance that our immune system will be exposed to novel protein antigens and/or familiar protein antigens with an unprecedented high frequency and large amount. These proteins are innocuous, nontoxic, and noninvasive by themselves, and include various natural proteins from the environment and recombinant proteins from industry. The technical term allergenic has been used for such proteins and their abilities to induce specific IgE production and to cross-link IgE/Fc epsilonRI on the surface of mast cells and basophiles have been recognized. As for the environmental proteins, some physicochemical properties (solubility, stability, and permeability across a mucosal epithelium) of the proteins indirectly play important roles in their allergenic potential because they do not originate from invasive pathogens as vehicles. Indeed, several lines of experimental evidences have been accumulated indicating that all proteins are absorbed across mucosal epithelia by transcellular transport and/or through interstitial spaces among the epithelial cells but not at equal levels. Some animal models have been established for natural sensitization to some allergenic proteins by feeding or intragastric administration without an adjuvant and, in a few cases, some symptoms resembling human allergy and even anaphylaxis have been induced by oral challenge with the proteins. Sometimes, even to self-proteins, the immunogenic or allergenic potential is given by post-translational modifications and possibly by unknown structural/conformational alterations, when they are exogenous self-proteins, such as recombinant human proteins for drug use. Despite the accumulation of knowledge and the progress in analytical technology on protein allergenicity, it is still crucial to predict the allergenic potential of novel and unused proteins. However, some animal models are applicable for assessing the relative allergenic potential of processed proteins in comparison with that of native proteins in preclinical studies.