Glycosylation reduces the allergenicity of turbot (Scophthalmus maximus) parvalbumin by regulating digestibility, cellular mediators release and Th1/Th2 immunobalance

Allergenicity Modulation of Casein with the Modifications of Linearization, Cross-Linking, and Glycation via the Regulation of Th1/Th2 Homeostasis

Casein (CN) is the primary allergenic protein in cow's milk, contributing to the worldwide escalating prevalence of food allergies. However, there remains limited knowledge regarding the effect of structural modifications on CN allergenicity. Herein, we prepared three modified CNs (mCN), including sodium dodecyl sulfate and dithiothreitol-induced linear CN (LCN), transglutaminase-cross-linked CN (TCN), and glucose-glycated CN (GCN). The electrophoresis results indicated widespread protein aggregation among mCN, causing variations in their molecular weights. The unique internal and external structural characteristics of mCN were substantiated by disparities in surface microstructure, alterations in the secondary structure, variations in free amino acid contents, and modifications in functional molecular groups. Despite the lower digestibility of TCN and GCN compared to LCN, they significantly suppressed IL-8 production in Caco-2 cells without significantly promoting their proliferation. Moreover, GCN showed the weakest capacity to induce LAD2 cell degranulation. Despite the therapeutic effect of TCN, GCN-treated mice displayed the most prominent attenuation of allergic reactions and a remarkably restored Th1/Th2 imbalance, while LCN administration resulted in severe allergic phenotypes and endotypes in both cellular and murine models. This study highlighted the detrimental effect of linear modifications and underscored the significance of glycation in relation to CN allergenicity.

Insight into the allergenicity and structure changes of parvalbumin from Trachinotus ovatus induced by dense-phase carbon dioxide

Parvalbumin (PV) is a major allergen in fish, and traditional treatments cannot reduce its sensitization. The effects of dense-phase carbon dioxide (DPCD) treatment on the sensitization and spatial structure of PV in Trachinotus ovatus were evaluated in this study. Western blotting and indirect ELISA were used to determine the allergenicity changes and spatial conformations of PV treated by DPCD. Tris-tricine-SDS-PAGE, circular dichroism, surface hydrophobicity, endogenous fluorescence, UV spectrophotometry, free amino group, total sulfhydryl group and SEM analyses were applied to characterize PV structure. The results showed that DPCD treatment (15 MPa, 30 min, 50 °C) could reduce PV-induced allergic reactions by 39-41 %, which destroyed the normal conformational epitopes and reduced the risk of PV-induced allergy. The secondary structure changed from ordered to disordered with a decreased content of α-helical groups, while the internal hydrophobic groups were exposed. The total sulfhydryl group content decreased significantly (P < 0.05). The surface hydrophobicity and ultraviolet absorption spectrum were enhanced, and the endogenous fluorescence peak shifted to a long wavelength. Meanwhile, the content of free amino groups increased significantly (P < 0.05). This study could provide a theoretical basis and a promising technical approach for reduction of PV allergenicities.

A comprehensive review on glycation and its potential application to reduce food allergenicity

Food allergens are a major concern for individuals who are susceptible to food allergies and may experience various health issues due to allergens in their food. Most allergenic foods are subjected to heat treatment before being consumed. However, thermal processing and prolonged storage can cause glycation reactions to occur in food. The glycation reaction is a common processing method requiring no special chemicals or equipment. It may affect the allergenicity of proteins by altering the structure of the epitope, revealing hidden epitopes, concealing linear epitopes, or creating new ones. Changes in food allergenicity following glycation processing depend on several factors, including the allergen's characteristics, processing parameters, and matrix, and are therefore hard to predict. This review examines how glycation reactions affect the allergenicity of different allergen groups in allergenic foods.

Insights into the Mechanism Underlying the Influence of Glycation with Different Saccharides and Temperatures on the IgG/IgE Binding Ability, Immunodetection, In Vitro Digestibility of Shrimp (Litopenaeus vannamei) Tropomyosin

Tropomyosin (TM) is a heat-stable protein that plays a crucial role as a major pan-allergen in crustacean shellfish. Despite the high thermal stability of the TM structure, its IgG/IgE binding ability, immunodetection, and in vitro digestibility can be negatively influenced by glycation during food processing, and the underlying mechanism remains unclear. In this study, TM was subjected to glycosylation using various sugars and temperatures. The resulting effects on IgG/IgE-binding capacity, immunodetection, and in vitro digestibility were analyzed, meanwhile, the structural alterations and modifications using spectroscopic and LC-MS/MS analysis were determined. Obtained results suggested that the IgG/IgE binding capacity of glycosylated TM, immunodetection recovery, and in vitro digestibility were significantly reduced depending on the degree of glycosylation, with the greatest reduction occurring in Rib-TM. These changes may be attributable to structural alterations and modifications that occur during glycosylation processing, which could mask or shield antigenic epitopes of TM (E3: 61-81, E5b: 142-162, and E5c: 157-183), subsequently reducing the immunodetection recognition and digestive enzyme degradation. Overall, these findings shed light on the detrimental impact of glycation on TMs potential allergenicity and digestibility immunodetection and provide insights into the structural changes and modifications induced by thermal processing.

Reduced Allergenicity of Shrimp (Penaeus vannamei) by Altering the Protein Fold, Digestion Susceptibility, and Allergen Epitopes

The mechanism by which thermal/pressure processing influences the allergenicity of shrimp (Penaeus vannamei) was explored by anaphylaxis in mice, the protein structure, gastrointestinal digestion, and linear epitopes. Roasting induced the unfolding of the structure, which may reduce the allergenicity, but it made more linear epitopes to be exposed, causing mice to exhibit similar systemic anaphylaxis as mice fed with the raw shrimp protein (p > 0.05). However, the roasted + reverse-pressure-sterilized shrimp can significantly reduce specific antibodies, mast cell degranulation, vascular permeability, and histopathological morphology in mice compared with the raw and roasted shrimp (p < 0.05) because reverse-pressure sterilization causes protein to aggregate, hiding the heat/digested stable epitopes of arginine kinase (Glu59-Ser63, Asn112-Lys118, Leu131-Phe136, and Ser158-Glu162) and sarcoplasmic calcium-binding protein (Asn57-Phe67, Ser159-Cys165, and Glu126-Ala130) inside a 3D structure, while gastrointestinal digestion can destroy immunodominant, minor epitopes and the epitopes exposed by roasting. Meanwhile, the low binding frequency of IgE to troponin C was also responsible for maintaining the hypoallergenicity of shrimp.

Assessment of the effect of glycation on the allergenicity of sesame proteins

Sesame allergy is a growing concern worldwide. In this study, sesame proteins was glycated with glucose, galactose, lactose and sucrose respectively, and the allergenicity of different glycated sesame proteins were assessed by a comprehensive strategy, including simulated gastrointestinal digestion in vitro, a BALB/c mice model, a rat basophilic leukemia (RBL)-2H3 cell degranulation model and a serological experiment. Firstly, simulated gastrointestinal digestion in vitro showed that glycated sesame proteins were more easily to digest than raw sesame. Subsequently, the allergenicity of sesame proteins was assessed in vivo by detecting the allergic indexes of mice, and results showed that the levels of total immunoglobulin E (IgE) and histamine were reduced in glycated sesame proteins treated mice. Meanwhile, the Th2 cytokines (IL-4, IL-5, and IL-13) were downregulated significantly, demonstrating that sesame allergy was relieved in glycated sesame treated mice. Thirdly, the RBL-2H3 cell degranulation model results showed that the release of β-hexosaminidase and histamine were decreased to different degrees in glycated sesame proteins treated groups. Notably, the monosaccharide glycated sesame proteins exhibited lower allergenicity both in vivo and in vitro. Furthermore, the study also analyzed the structure alteration of sesame proteins, and the results showed that the secondary structure of glycated sesame proteins were changed (the content of α-helix and β-sheet were reduced), and the tertiary structure of sesame proteins after glycation modification was also changed (microenvironment around aromatic amino acids was altered). Besides, the surface hydrophobicity of glycated sesame proteins was also reduced except sucrose glycated sesame proteins. In conclusion, this study demonstrated that glycation reduced the allergenicity of sesame proteins effectively, especially glycation with monosaccharides, and the allergenicity reduction might be related to structural changes. The results will provide a new reference for developing hypoallergenic sesame products.

Antioxidant Activity and Cell Protection of Glycosylated Products in Different Reducing Sugar Duck Liver Protein Systems

Duck liver is an important by-product of duck food. In this study, we investigated the effects of glucose, fructose, and xylose on the antioxidant properties of glycosylated products of duck liver protein and their protective effects on HepG2 cells. The results show that the glycosylation products of the three duck liver proteins (DLP-G, DLP-F, and DLP-X) all exhibit strong antioxidant activity; among three groups, DLP-X shows the strongest ability to scavenge DPPH, ·OH free radicals, and ABTS⁺ free radicals. The glycosylated products of duck liver protein are not toxic to HepG2 cells and significantly increase the activity of antioxidant enzymes such as SOD, CAT, and GSH-Px in HepG2 cells at the concentration of 2.0 g/L, reducing oxidative stress damage of cells (p < 0.05). DLP-X has a better effect in reducing oxidative damage and increasing cellular activity in HepG2 cells than DLP-G and DLP-F (p < 0.05). In this study, the duck liver protein glycosylated products by glucose, fructose, and xylose were named as DLP-G, DLP-F, and DLP-X, respectively.

Comparative Analysis of Glycosylation Affecting Sensitization by Regulating the Cross-Reactivity of Parvalbumins in Turbot (Scophthalmus maximus), Conger Eel (Conger myriaster) and Sea Bass (Micropterus salmoides)

Parvalbumin (PV) is the most common allergen in fish. Some patients with fish allergy are allergic to only one species of fish but are tolerant to others; however, the underlying mechanism has not been identified. This study showed that three types of glycated fishes' PV showed a similar decrease in immunoglobulin E (IgE) binding. Glycosylation could improve the simulated gastric fluid (SGF) and simulated intestinal fluid (SIF) digestion resistance of fishes' PV. We also discovered that the cross-reactivity between eel and turbot was weaker than that of bass; glycosylation can reduce cross-reactivity between eel/bass and turbot by downregulating Th2 cytokines and upregulating Th1 cytokines as well as downregulating the expression of G-T PV, G-E PV, G-B PV of IL-4 (94.31 ± 3.16, 73.26 ± 0.91, 94.95 ± 3.03 ng/mL), and IL-13 (38.84 ± 0.75, 33.77 ± 0.71, 36.51 ± 0.50 ng/mL) and upregulating the expression of IFN-γ (318.01 ± 3.46, 387.15 ± 3.30, 318.01 ± 4.21 ng/mL) compared with T PV, respectively. This study showed that glycosylation affected sensitization by regulating the cross-reactivity of parvalbumins.

Fish Allergenicity Modulation Using Tailored Enriched Diets—Where Are We?

Food allergy is an abnormal immune response to specific proteins in a certain food. The chronicity, prevalence, and the potential fatality of food allergy, make it a serious socio-economic problem. Fish is considered the third most allergenic food in the world, affecting part of the world population with a higher incidence in children and adolescents. The main allergen in fish, responsible for the large majority of fish-allergic reactions in sensitized patients, is a small and stable calcium-binding muscle protein named beta-parvalbumin. Targeting the expression or/and the 3D conformation of this protein by adding specific molecules to fish diets has been the innovative strategy of some researchers in the fields of fish allergies and nutrition. This has shown promising results, namely when the apo-form of β-parvalbumin is induced, leading in the case of gilthead seabream to a 50% reduction of IgE-reactivity in fish allergic patients.